Abstracts book
Talk index: [5], [6], [7], [8], [9], [11], [12], [13], [15], [16], [17], [18], [19], [21], [22], [24], [25], [26], [27], [29], [30], [32], [33], [34], [35], [37], [38], [39], [40], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [60], [61], [62], [63], [64], [66], [67], [68], [70], [71], [72], [73], [74], [75], [76], [77], [79], [81], [83], [85], [86], [87], [88], [89], [90], [92], [93], [94], [96], [97], [98], [99], [100], [101], [102], [103], [104], [105], [106], [107], [108], [109], [110], [111], [112], [114], [115], [116], [117], [118], [119], [121], [122], [124], [125], [126], [127], [128], [129], [130], [131], [132], [134], [135], [136], [138], [139], [140], [141], [142], [145], [146], [147], [148], [149], [150], [151], [152], [153], [154], [155], [156], [157], [158], [160], [161], [162], [164], [165], [167], [168], [169], [170], [171], [172], [173], [174], [175], [176], [177], [178], [179], [180], [181], [182], [183], [184], [185], [188], [191], [192], [193], [195], [196], [198], [199], [200], [201], [203], [204], [205], [206], [207], [208], [209], [210], [211], [213], [214], [215], [217], [218], [219], [220], [221], [222], [223], [224], [225], [226], [227], [228], [229], [230], [231], [232], [233], [234], [235], [236], [237], [238], [239], [240], [241], [242], [243], [244], [245], [246], [247], [248], [249], [250], [251], [252], [253], [254], [255], [256], [257], [258], [259], [260], [261], [262], [263], [264], [265], [267], [268], [269], [270], [271], [272], [273], [274], [275], [276], [277], [278], [279], [280], [281], [282], [283], [284], [285], [287], [288], [289], [290], [291], [292], [294], [295], [296], [297], [298], [300], [303], [304], [305], [306], [307], [308], [309], [310], [311], [312], [313], [314], [315], [316], [317], [318], [319], [320], [322], [323], [324], [325], [327], [328], [329], [330], [331], [332], [333], [334], [335], [336], [337], [339], [341], [342], [343], [344], [345], [346], [347], [348], [349], [350], [351], [352], [353], [354], [355], [356], [357], [358], [359], [360], [361], [362], [363], [365], [366], [367], [368], [369], [370], [373], [374], [375], [376], [377], [378], [379], [380], [381], [382], [383], [384], [385], [386], [387], [388], [389], [390], [391], [392], [394], [395], [396], [397], [398], [399], [400], [401], [402], [403], [404], [405], [406], [407], [408], [409], [411], [412], [413], [414], [415], [416], [417], [419], [420], [421], [423], [425], [426], [427], [428], [429], [430], [431], [433], [434], [435], [436], [437], [438], [440], [441], [442], [443], [444], [445], [446], [448], [449], [450], [451], [452], [453], [454], [455], [456], [457], [458], [459], [461], [462], [463], [464], [465], [466], [467], [468], [469], [470], [471], [472], [473], [475], [476], [478], [479], [480], [482], [483], [485], [486], [487], [490], [491], [493], [494], [495], [496], [497], [498], [499], [500], [502], [503], [504], [505], [506], [507], [508], [509], [511], [512], [513], [514], [515], [516], [517], [519], [520], [521], [523], [524], [525], [527], [528], [529], [530], [532], [533], [535], [536], [537], [538], [539], [540], [541], [542], [543], [544], [545], [546], [547], [548], [549], [550], [551], [552], [553], [554], [555], [556], [557], [558], [559], [560], [561], [562], [563], [564], [565], [566], [567], [568], [570], [571], [572], [573], [574], [575], [577], [578], [579], [580], [581], [582], [583], [584], [585], [586], [587], [588], [589], [590], [591], [592], [593], [595], [596], [597], [598], [599]
[5] ID:05-An Efficient and Accurate Asymptotically Correct Equivalent Single Layer Plate Theory (ACESLT) with Variational Asymptotic Approach for Energy-based Analysis
Anup Kumar Pathak (Research Scholar, Department of Mechanical Engineering Indian Institute of Technology, Ropar), Satwinder Jit Singh (Assistant Professor, Department of Mechanical Engineering Indian Institute of Technology, Ropar) and Srikant Sekhar Padhee (Assistant Professor, Department of Mechanical Engineering Indian Institute of Technology, Ropar).
Abstract
This research presents a new development in Equivalent Single Layer (ESL) plate theory, which utilizes the Variational Asymptotic Method (VAM) approach. ESL plate theories are mathematical models used to analyze the behavior of thin or moderately thick plates. They simplify the analysis by assuming that the plate is composed of a single layer, with constant properties throughout its thickness. While previous ESL plate theories exist, the majority of available models are axiomatic-based and assume displacement in the thickness direction. In contrast, VAM-based asymptotically correct plate models do not make assumptions a priori and are more mathematically rigorous. However, these models contain higher-order derivatives of the generalized strains and/or displacements, making the analysis complex and inefficient. Thus, it is necessary to eliminate them.
This paper makes two contributions to the literature. First, it focuses on achieving maximum accuracy to the strains for a particular computational cost, rather than for the displacement field. As a result, the proposed model provides strains that cannot be obtained by considering any assumed form of displacement along the thickness direction. This approach results in a better representation of the energy of deformation of a plate. Second, the paper introduces a novel isoenergetic approach to eliminate the higher-order derivatives of the generalized strains present in the asymptotically correct plate model, while maintaining simplicity and accuracy
[6] ID:06-The Atomistic Origin of Fracture Toughness in Amorphous Silica
Gergely Molnar (CNRS / INSA of Lyon).
Abstract
The talk that delves into the origins of fracture toughness in amorphous silica, focusing on the influence of a rounded crack tip and the limitations of linear elastic fracture mechanics. Griffith's theory states that in the absence of a sharp crack, the energy release rate becomes zero, rendering linear elastic fracture mechanics inadequate for assessing resistance in geometries featuring a rounded crack. To overcome this limitation, the talk employs coupled criterion and phase-field simulations to assess fracture initiation.
Through extensive large-scale atomic-scale simulations, the research identifies damage within the atomic structure. A finite element model update scheme is utilized to pinpoint the critical energy release rate and the regularization length scale during crack propagation.
In conclusion, the talk offers a comprehensive comparison of the identified properties, examining their consistency with the predictions of the homogeneous phase-field solution and the material's tensile strength. Furthermore, the research endeavors to contrast the outcomes of all three methodologies, thereby shedding light on the foundational assumptions that underlie continuum models, including phase-field and finite fracture mechanics. By exploring the interplay between crack geometry and fracture resistance, this study advances our understanding of fracture toughness in amorphous silica and contributes to the ongoing development of more accurate models for predicting fracture initiation and propagation in complex materials.
[7] ID:07-Study of the thermal mechanical coupling effect of a lattice core glass fiber epoxy composite sandwich
Khaled Khalil (ECAM-Rennes), Georgio Rizk (Lebanese University), Samer Alfayad (IBISC - Université Paris-Saclay) and Frédéric Jacquemin (GeM - Université de Nantes).
Abstract
According to the progress in 3D printing, manufacturing of parts with complex patterns became very interesting in the development of specific panels for various industrial applications, from construction to aeronautics. In this work, the effect of elevated temperatures on the mechanical properties of lattice core sandwich panels was studied for better understanding of their thermomechanical behavior. First, mechanical properties of certain cellular topologies were compared to those of the traditional sandwich plates with honeycomb core. Then, an ABAQUS numerical thermal model for a pyramidal lattice core panel was developed. This model was then validated for a composite lattice core panel made of a silicon carbide matrix with carbon fiber reinforcement (C/SiC composites), through comparison between results obtained by numerical simulation versus experimental results. Lastly, the numerical model was then used to optimize the mechanical properties of a pyramidal lattice sandwich panel made of glass fiber epoxy composite when subject to a temperature of 200 °C on a single surface.
[8] ID:08-Higher-order boundary conditions for asymptotic homogenization
Manon Thbaut (Laboratoire de mécanique des solides, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France), Claire Lestringant (Institut Jean Le Rond d'Alembert, Sorbonne Université, CNRS, 75005 Paris, France) and Basile Audoly (Laboratoire de mécanique des solides, CNRS, Institut Polytechnique de Paris, 91120 Palaiseau, France).
Abstract
Architected materials possess two natural scales : the characteristic size of the microstructure and the size of the macroscopic phenomenons. When the ratio of these scales is small, classical homogenization yields an effective behavior that accurately captures the mechanical response of the material. However, when these materials are submitted to strong variations of the macroscopic fields, non-local effects that can be captured by higher gradient models appear. The asymptotic expansion is a systematic method often used to derive such models in the context of periodic media. However, in the classical asymptotic approaches boundary effects are generally neglected, which is likely to ruin the order of approximation of the solution. Besides, in higher-order models, the order of the equilibrium equations is increased and additional boundary conditions are required. The applicable boundary conditions for strain-gradient models have not yet been clearly identified. To overcome these limitations, we combine an asymptotic-energy-based homogenization scheme with a boundary layer analysis. This procedure results in a set of effective boundary conditions whose order of approximation is consistent with that of the solution to the strain-gradient equilibrium equation. To illustrate our approach, we study a 1D periodic chain of springs. We perform a numerical comparison between the predictions of our matched model and predictions from the full discrete system. We show that our model converges towards the discrete solution at an improved rate compared to the classical homogenization framework. Besides, we solve a long-standing issue related to the non-positivity of strain-gradient stiffnesses. This property has been reported in several papers in the context of asymptotic homogenization but its implications remain unclear. In particular, it is known that such property results in the presence of oscillations in the expression of the homogenized solution. We show on this example that our boundary conditions make these oscillating terms negligible.
[9] ID:09-The nonlinear elastic response of bicontinuous rubber blends
Oscar Lopez-Pamies (University of Illinois at Urbana-Champaign) and Fabio Sozio (University of Illinois Urbana-Champaign).
Abstract
Rubber blends are ubiquitous in countless technological applications. More often than not, rubber blends exhibit complex interpenetrating microstructures, which are thought to have a significant impact on their resulting macroscopic mechanical properties. In this talk, as a first step to understand this potential impact, I will present a bottom-up or homogenization study of the nonlinear elastic response of the prominent class of bicontinuous rubber blends, that is, blends made of two immiscible constituents or phases segregated into an interpenetrating network of two separate but fully continuous domains that are perfectly bonded to one another. The focus will be on blends that are isotropic and that contain an equal volume fraction (50/50) of each phase. The microstructures of these blends are idealized as microstructures generated by level cuts of Gaussian random fields that are suitably constrained to be periodic so as to allow for the construction of unit cells over which periodic homogenization can be carried out. The homogenized or macroscopic elastic response of such blends will be determined both numerically via finite elements and analytically via a nonlinear comparison medium method. The numerical approach makes use of a novel meshing scheme that leads to conforming and periodic simplicial meshes starting from a voxelized representation of the microstructures. In will present results for the fundamental case when both rubber phases are Neo-Hookean, as well as when they exhibit non-Gaussian elasticity. Remarkably, irrespective of the elastic behavior of the phases, the results will show that the homogenized response of the blends is largely insensitive to the specific morphologies of the phases.
[11] ID:11-Thermo-electro-mechanical microstructural interdependencies in conductive composites
Javier Crespo Miguel (Department of Continuum Mechanics and Structural Analysis, Universidad Carlos III de Madrid), Sergio Lucarini (Basque Center for Materials, Applications and Nanostructures), Angel Arias (Department of Continuum Mechanics and Structural Analysis, Universidad Carlos III de Madrid) and Daniel Garcia Gonzalez (Department of Continuum Mechanics and Structural Analysis, Universidad Carlos III de Madrid).
Abstract
Additive manufacturing (AM) allows for the design of complex-shape components with multifunctional properties, as conductive polymeric composites. Depending on the nature of the polymeric matrix, such multifunctional materials can be printed via Fused Filament Fabrication (FFF, for thermoplastic polymers) or via Direct Ink Writing (DIW, for elastomeric polymers). The microstructural multi-physical interdependencies that occur at a material level are still an open question. In this work, we conduct a multi-physics characterisation of 3D printed polylactic acid (PLA) and PDMS materials doped with Carbon Black (CB) nanoparticles through combined electrical, thermal and mechanical tests. In addition, a full-field homogenisation approach was employed to model the multi-physical interdependencies that appear at a microstructural level.
From an experimental perspective, we tackle the problematic by performing tests where pairs of physics were isolated. In this regard, three different sets of experiments were performed: i) electro-thermal; ii) thermo-mechanical; and iii) mechano-electrical. Finally, a thermo-electro-mechanical test was performed, considering all the variables simultaneously. For the modelling approach, full-field homogenisation techniques are employed to simulate the interdependencies observed in our experimental campaign. The governing equations of the problem are solved in a Representative Volume Element (RVE) of the composite. The problem domain accounts for three phases: i) polymeric matrix; ii) CB particles; and iii) microscopic voids.
The results obtained in this work show the strong interplays that are highly nonlinear under large deformations. Additionally, we prove that our in-silico methodology has a great potential for conductive filament manufacturers to optimize the multifunctional material properties and scale them to the structural scale. As future work, we finally provide evidence of incorporating hard-magnetic properties within the soft materials to enable self-healing capabilities on top of the electro-mechanical behaviour.
[12] ID:12-A constitutive model of the cell nucleus: chemo-mechanical coupling and negative Poisson's ratio
Marco De Corato (Universidad de Zaragoza) and María Josè Gomez Benito (Universidad de Zaragoza).
Abstract
The mechanical properties of the nucleus in eukaryotic cells are vital for protecting genetic information stored in chromatin. The nucleus experiences various mechanical stimuli that can impact chromatin organization and gene expression. Experiments have demonstrated that nuclear deformation can cause temporary or permanent changes in chromatin condensation and activate genes, affecting protein transcription. These changes in chromatin organization can, in turn, alter the mechanical properties of the nucleus, potentially leading to auxetic behavior and a negative Poisson's ratio. We propose a model that represents the mechanical behavior of the nucleus as a chemically-active polymeric gel. In this model, chromatin can exist in two states: heterochromatin, which is self-attracting, and euchromatin, which is repulsive. The model predicts reversible or irreversible changes in chromatin condensation due to external deformation of the nucleus. The model also indicates an auxetic response across a wide range of parameters for both small and large deformations. These findings align with experimental observations and emphasize the crucial role of chromatin organization in the mechanical behavior of the nucleus.
[13] ID:13-Effect of hydrogen on plasticity of α-Fe: a multi-scale assessment
Pranav Kumar (Department of Applied Mechanics, Indian Institute of Technology, Madras, India), Mohit Ludhwani (Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, India), Sambit Das (Department of Mechanical Engineering, University of Michigan, Ann Arbor, USA), Vikram Gavini (Department of Mechanical Engineering, University of Michigan, Ann Arbor, USA), Anand Kanjarla (Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, India) and Ilaksh Adlakha (Department of Applied Mechanics, Indian Institute of Technology, Madras, India).
Abstract
In this work, the effect of hydrogen on the dislocation-based plastic behavior of α-Fe was examined by carrying out a multi-scale study. The influence of hydrogen concentration on the critical shear stress required for screw dislocation glide was quantified at the atomic length scale. The obtained variation in dislocation glide behavior was utilized to develop an accurate continuum description to examine the dislocation-based plasticity in polycrystalline α-Fe. To enable this study, a new Fe-H interatomic potential was developed that provides an accurate description of various hydrogen - defect configurations, which is essential to accurately study the effect of hydrogen on dislocation glide behavior. The screw dislocation core reconstruction observed due to the presence hydrogen was validated by performing large-scale DFT calculations based on the DFT-FE framework. To comprehensively quantify the effect of varying hydrogen concentration on the dislocation glide mechanics, several atomistic simulations were carried out. Lastly, crystal plasticity simulations were performed to assess the ramifications of the atomistically observed variation in dislocation glide behavior introduced by hydrogen on the meso-scale deformation behavior of polycrystalline α-Fe.
[15] ID:15-Multi-scale simulation of non-linear cellular- and meta-materials with body-force-enhanced second-order homogenisation
Ling Wu (University of Liege), Javier Segurado (IMDEA), Mohib Mustafa (University of Liege) and Ludovic Noels (ULiege).
Abstract
Multi-scale simulation of lattices, cellular materials and meta-materials faces the difficulty of handling the local instabilities which correspond to a change of the micro-structure morphology. On the one hand, first order computational homogenisation, which considers a classical continuum at the macro-scale, cannot capture localisation bands. On the other hand, second-order computational homogenisation, which considers a higher order continuum at the macro-scale, introduces a size effect with respect to the Representative Volume Element (RVE) size.
By reformulating second-order computational homogenisation as an equivalent homogenised volume, non-uniform body forces arise at the micro-scale and act as a supplementary volume term over the RVE. Contrarily to the original uniform body forces resulting from an asymptotic homogenization [1], the devised non-uniform body forces arise from the Hill-Mandel condition and are expressed in terms of the micro-scale strain localization tensor, i.e. the relation between the micro-scale and macro-scale deformation gradients [1].
The consistency and accuracy of the approach are illustrated by simulating non-linear elastic meta-materials and elasto-plastic cellular materials under compressive loading.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 862015.
REFERENCES [1] V. Monchiet, N. Auffray, J. Yvonnet, Strain-gradient homogenization: A bridge between the asymptotic expansion and quadratic boundary condition methods, Mechanics of Materials 143 (2020) 103309. [2] L. Wu, S. M. Mustafa, J. Segurado and L. Noels. Second-order computational homogenisation enhanced with non-uniform body forces for non-linear cellular materials and metamaterials. Computer Methods in Applied Mechanics Engineering, 407: 115931, 2023.
[16] ID:16-A Self-consistent Reinforced minimal Gated Recurrent Unit for surrogate modelling of elasto-plastic multi-scale problems
Ling Wu (University of Liege) and Ludovic Noels (ULiege).
Abstract
Multi-scale simulations can be accelerated by substituting the micro-scale problem resolution by a surrogate trained from off-line simulations. In the context of history-dependent materials, recurrent neural networks have widely been considered to act as such a surrogate, e.g. [1], since their hidden variables allow for a memory effect.
However, defining a training dataset which virtually covers all the possible strain-stress state evolution encountered during the online phase remains a daunting task. This is particularly true in the case in which the strain increment size is expected to vary by several orders of magnitude. Self-Consistent recurrent networks were thus introduced in [2] to reinforce the self-consistency of neural network predictions when small strain increments are expected. This new cell was applied to substitute an elasto-plastic material model.
However when considering a representative volume element response in the context of multi-scale simulations, it was found that the Self-Consistent recurrent networks requires a long training process. In this work, we revisit the Self-Consistent recurrent unit to improve the training performance and reduce the number of trainable variables for the neural network to act as a composite surrogate model in multi-scale simulations.
This project has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101056682.
[1] L. Wu, V. D. Nguyen, N. G. Kilingar, L. Noels, A recurrent neural network-accelerated multi-scale model for elasto-plastic heterogeneous materials subjected to random cyclic and non-proportional loading paths, Computer Methods in Applied Mechanics and Engineering (2020). [2] C. Bonatti, D. Mohr, On the importance of self-consistency in recurrent neural network models representing elasto-plastic solids, Journal of the Mechanics and Physics of Solids (2022). [3] L. Wu, L. Noels, Self-consistent Reinforced minimal Gated Recurrent Unit for surrogate modeling of history-dependent nonlinear problem: application to history-dependent homogenized response of heterogeneous materials. In Preparation.
[17] ID:17-Synchronous Involvement of Topology and Microstructure to Design Additively Manufactured Lattice Structure
Kavan Hazeli (The University of Arizona) and Jason Mayeur (Oak Ridge National Labratory).
Abstract
Most of the natural structures such as bone and tendons, which have been an influential source of inspiration for hierarchical materials design do not have grain structures similar to those that are seen in crystalline metals. Therefore, designing bio-inspired metallic materials with a hierarchical structure such as additively manufactured lattice structures (AMLS) lack from benefiting the property of grain structures. This presentation demonstrates that simultaneously considering the effects of topology and microstructure on the mechanical behavior of AMLS has the potential to substantially improve key performance metrics, e.g., energy dissipation, and to avoid widely reported drastic strength drop of AMLS at the onset of yielding instead, an ever-hardening response is achieved. The distinguishing feature of our approach is that the topological optimization is performed while accounting for the heterogeneous distribution of strut-level microstructural features and concomitant mechanical behavior, which leads to new insights relative to peak AMLS structural performance. A new set of new topologies are designed, built, and validated against experiments. The new topologies demonstrate over 50% improvement on average in energy absorption capacity and flow stress, respectively, of topologies that had been previously optimized using a homogeneous constitutive model throughout the unit cell.
[18] ID:18-Thermomechanobiology: a new concpet for cartilage mechanics
Dominique Pioletti (EPFL).
Abstract
Osteoarthritis is a painful joint disease characterized by progressive degeneration of the osteochondral unit's tissues with no possibility of reversing its progression once its onset. We may have identified one factor favoring this irreversibility: dissipative properties, i.e., the capacity to convert mechanical energy into heat. During our previous study, we made the important observation that degenerated cartilage does not possess high enough dissipative properties to allow its self-heating during mechanical stimulation. The temperature of degenerated cartilage culminates only to a maximum of around 33°C during physiological loadings compared to 37°C for healthy cartilage thanks to its preserved self-heating capability. Therefore, mechanical and thermal stimuli might play an essential role in cartilage homeostasis. Considering the thermomechanobiology aspect in cartilage, we will propose an original approach that may potentially change the therapeutical approach to treating early osteoarthritis.
[19] ID:19-Time effects on the plastic deformation of single crystals
Oana Cazacu (Dept Materials Sciences & Engineering, University of Arizona), Benoit Revil-Baudard (University of Arizona) and Sammy Tin (University of Arizona).
Abstract
A model for description of the multi-axial creep response of single crystals is presented. An over-stress type approach in conjunction with an yield criterion that accounts for the intrinsic crystal symmetries is adopted. The creep stabilization is considered to be governed by the irreversible work per unit volume. The influence of anisotropy, namely crystallographic orientation and loading path history on the creep response is analyzed in detail. We conclude with discussion of possible extensions of the model such as to account for viscoplasticy-damage couplings.
[21] ID:21-The stab resistance of Bombyx mori silk cocoons
Ateeq Ur Rehman (School of Engineering, Institute for Materials and Processes, The University of Edinburgh), Vasileos Koutsos (School of Engineering, Institute for Materials and Processes, The University of Edinburgh) and Parvez Alam (School of Engineering, Institute for Materials and Processes, The University of Edinburgh).
Abstract
We investigated the stab resistance of Bombyx mori silk cocoons to authenticate their purpose as natural material structures with an inherent protective functionality. The cocoon wall is a nonwoven fibroin-sericin composite material architected by strands of continuous silk fibres, which are known to be tough and resilient. Both full ovaloid cocoons, and rectangular flattened specimens of the cocoon wall, were subjected to both static and dynamic stab tests. The blades used for stab testing met HOSDB standards, which using a "Home Office Engineered Knife (01-07164)". Three scenarios were considered: (1) stab tests through the entire ovaloid cocoon, (2) stab tests through only the first wall of the ovaloid cocoon, and (3) stab tests through the flattened rectangular cocoon wall cut from the cocoon. The final test scenario was special as it allowed for direct measurement of the knife penetration depth. Our study examined the structural components of the cocoon in providing stab resistance. We discuss stab resistance from tow perspectives: (a) the micromechanism of stab resistance as a function of silk fibre arrangement and (b) the macromechanisms of stab resistance as a function of cocoon geometry. Our work provides new insights into the inherent hierarchical protective characteristics of silk fibre architectures.
[22] ID:22-A Microstructure-Sensitive Analytical Solution for Short Fatigue Crack Growth Rate in Metallic Materials
Daniel Long (Imperial College London), Yang Liu (Imperial College London) and Fionn Dunne (Imperial College London).
Abstract
Short fatigue crack growth in engineering alloys is among the most prominent challenges in mechanics of materials. Owing to its microstructural sensitivity, advanced and computationally expensive numerical methods are required to solve for crack growth rate. A novel mechanistic analytical model is presented, which adopts a stored energy density fracture criterion. Full-field implementation of the model in polycrystalline materials is achieved using a crystallographic crack-path prediction method based on a local stress intensity factor term. The model is applied to a range of Zircaloy-4 microstructures and demonstrates strong agreement with experimental rates and crack paths. Growth rate fluctuations across individual grains and substantial texture sensitivity are captured using the model. More broadly, this work demonstrates the benefits of mechanistic analytical modelling over conventional fracture mechanics and recent numerical approaches for accurate material performance predictions and design. Additionally, it offers a significant computer processing time reduction compared with state-of-the-art numerical methods.
[24] ID:24-Combining machine learning and in-situ EBSD to assess the influence of microstructure on twinning in polycrystal Mg
Biaobiao Yang (IMDEA Materials Institute; Polytechnic University of Madrid), Valentin Vassilev-Galindo (IMDEA Materials Institute) and Javier Llorca (IMDEA Materials Institute; Polytechnic University of Madrid).
Abstract
Understanding twinning in textured Mg alloys and ascertaining its correlation with microstructure can promote the design of polycrystals with controlled twinning during deformation. Here, twin nucleation in textured Mg alloys was studied using electron back-scattered diffraction (EBSD) in samples deformed in tension along different orientations in more than 3000 grains. In addition, 28 relevant parameters, categorized into different groups (loading condition, grain shape, apparent Schmid factors (SF), and grain boundary features) were recorded for each grain. This dataset was used for training Bayesian Networks models to analyze the influence of microstructural features on the nucleation of extension twins in Mg alloys. It was found that twin nucleation is favored in larger grains and in grains with high twinning SFs, but also that twins may form in grains with very low or even negative twinning SFs if they have at least one smaller neighboring grain and another one (or the same) that is more rigid. Moreover, twinning of small grains with high twinning SFs is also favored if they have low basal slip SFs and have at least one neighboring grain with a high basal slip SF that will deform easily. Finally, via in-situ EBSD, it was confirmed that anomalous non-Schmid extension twins nucleate at the onset of plastic deformation mainly at or near triple point grain boundaries accompanied by the localized compressive stress and due to the severe strain incompatibility between neighbor grains, stemming from the different slip-induced lattice rotations. Moreover, these anomalous twins could grow with the applied strain due to the continuous activation of <a> basal slip in different grains, which enhanced the strain incompatibility. This reveals the role of many-body relationships, including differences in stiffness and size between a given grain and its neighbors, to assess extension twin nucleation and growth in grains unfavorably oriented for twinning.
[25] ID:25-Biomimetic 3D printed poly (glyceryl sebacate)/collagen composite scaffolds for cartilage defect repair
Yuyao Liu (IMDEA Materials Institute, Polytechnic University of Madrid), Claudio Intini (RCSI, University of Medicine and Health Sciences, AMBER Centre), Marko Dobricic (RCSI, University of Medicine and Health Sciences, AMBER Centre), Fergal J. O'Brien (RCSI, University of Medicine and Health Sciences, AMBER Centre), Javier Llorca (IMDEA Materials Institute, Polytechnic University of Madrid) and Monica Echeverry-Rendon (IMDEA Materials Institute).
Abstract
Complete repair of cartilage defects caused by trauma or disease remains a significant clinical challenge due to the limited self-healing ability of cartilage. The development of biomimetic scaffolds that provide sufficient mechanical support and drive efficient mesenchymal stem cell (MSC) chondrogenic differentiation is critical for enhanced cartilage repair efficiency. In this study, we fabricated a 3D printed poly (glyceryl sebacate) (PGS) scaffold with dual porosity by salt fusion method and coated it with porous collagen I/II - hyaluronic acid (CI/II-HyA) framework to obtain a functionalized biomimetic composite scaffold with triple porosity. The PGS scaffold served as the mechanical support reinforcement and exhibited similar mechanical properties to the native cartilage, as well as excellent fatigue resistance similar to the joint tissue under physiological deformations. In in vitro tests, the presence of triple porosity increased cell loading efficiency and improved the metabolic activity of rat-derived MSC cells. More importantly, the combination of CI/II-HyA framework and PGS scaffold sustained an effective rat-derived MSC chondrogenic differentiation with an abundant de-novo cartilage-like matrix deposition by day 35. These results indicate that the biomimetic composite scaffold has the ability to support cartilage tissue growth and stimulate MSC cell proliferation and chondrogenic differentiation, showing great potential in cartilage defect repair.
[26] ID:26-Exploring grain boundary multiplicity by phase field crystal simulations
Håkan Hallberg (Lund University) and Kevin Blixt (Lund University).
Abstract
While ideal minimum-energy grain boundary structures are rarely encountered in actual polycrystalline aggregates, they are usually the only structures considered when characterizing grain boundaries. This limited perspective provides an incomplete view of the structural variability of grain boundaries which has been observed experimentally and which has been indicated by molecular dynamics simulations in several instances. In this study, the possibilities in using phase field crystal (PFC) modeling as a means for exploration of metastable grain boundary states is investigated. For this purpose, PFC is employed in a systematic search of grain boundary variants, based on gamma-surface sampling. Taking a range of symmetric tilt boundaries in FCC bicrystals as a demonstration case, it is shown that PFC indeed provides a useful tool for evaluating the structural multiplicity of grain boundaries. In addition, it is shown that a set of microscopic degrees of freedom (DOF) must be considered in addition to the grain boundaries five macroscopic DOF when identifying variants in structure. This set of microscopic DOF comprises three components of relative crystal translation, plus one DOF describing the atomic density in the grain boundary region. To further illustrate the implications of a multitude of structural variants being possible, grain boundary energy is taken as an example of a key thermodynamic property which is shown to exhibit a considerable spread with variations in the microscopic DOF, at constant macroscopic DOF. The findings underline the need to consider a spectrum of GB energies for each macroscopic GB configuration, rather than just a single value corresponding to an idealized minimum-energy structure, as is usually done. As part of the study, some computationally efficient strategies for setting up the PFC simulation model are also proposed.
[27] ID:27-Phase field crystal modeling of grain boundary structures in diamond cubic systems
Kevin Blixt (Lund University) and Håkan Hallberg (Lund University).
Abstract
The application of Phase Field Crystal (PFC) modeling has proven to be a versatile and effective numerical tool for analyzing crystalline microstructures. However, the predominant focus has been on bulk crystal behavior, with less exploration into crystal defects such as grain boundaries (GBs). This gap is particularly noticeable in crystal structures beyond face- and body-centered cubic crystals, such as diamond cubic (DC) crystal structures. For this reason, a systematic investigation of three different PFC models is performed to gauge the possibility of studying DC systems using PFC. The models employ combinations of two- and three-point correlations. One of the investigated models has been published previously and two are proposed modifications to established models. The findings indicate that the inclusion of a three-point correlation is crucial for stabilizing the expected DC GB structures, including the many multiplicities possible for each macroscopic degree of freedom. Despite inherent limitations in each model concerning the stabilized GB structures and phase stability performance, critical components within the PFC approach are identified as essential for successfully modeling DC structures.
[29] ID:29-A Crystal Plasticity Model to Study Stress Localization and Size-Dependent Tensile Properties of Additively Manufactured Nickle-Base Superalloy: Haynes 214™ at elevated Temperature
Mohammad M. Keleshteri (The University of Arizona), Jason Mayeur (Oak Ridge National Lab) and Kavan Hazeli (The University of Arizona).
Abstract
Additively manufactured (AM) components exhibit distinct microstructures compared to conventionally manufactured ones, primarily due to unique thermal histories at the local level during the build process. Prior studies demonstrated notable variations in the mechanical properties of AM thin-walled structures (TWS) in response to changes in wall thickness, with this variability being temperature-dependent and is more pronounced at elevated temperatures. In this research, the nature of this size effect on tensile properties, including yield strength, strain hardening rate, and ductility, for AM-HAYNES 214 at elevated temperature (250°C and 450°C) is studied. To explore the size effect, TWS were fabricated with four different thicknesses: 1mm, 1.5mm, 2mm, and 2.5mm. To derive the constitutive response, we developed a robust approach using electron backscattered diffraction (EBSD) images of sections to generate distributions of morphological and crystallographic parameters, including grain sizes, texture, and twin fraction. The methodology's effectiveness is validated by comparing simulated microstructure statistics with real EBSD data. Subsequently, we employed the Crystal Plasticity Fast Fourier Transform (CPFFT) based spectral method, relying on a phenomenological hardening law. We successfully established a correlation between the local stress analysis conducted at the grain level and the global mechanical behavior observed in experimental results. This comprehensive examination of stress and strain at the micro level has uncovered variations in mechanical properties that are directly linked to the thickness of the AM-TWS. Additionally, we explored how the local stress state, influenced by grain neighborhood effects, contributes to the observed localization behavior. We explored factors that drive the non-uniform distribution of mechanical responses by addressing how the local stress state, influenced by these grain neighborhood effects, contributes to localization behavior. The study's discovery of manufacturing-induced plastic anisotropy in grain distribution presents research opportunities. It enables the optimization of grain topology and solidification parameters, enhancing the mechanical behavior of AM-TWS.
[30] ID:30-Anisotropic elastic strain-gradient continuum from the macro-scale to the granular micro-scale
Pouriya Pirmoradi (Eindhoven University of Technology), Akke Suiker (Eindhoven University of Technology) and Payam Poorsolhjouy (Eindhoven University of Technology).
Abstract
A multi-scale framework is constructed for the computation of the stiffness tensors of an elastic strain-gradient continuum endowed with an anisotropic microstructure of arbitrarily-shaped particles. The influence of microstructural features on the macroscopic stiffness tensors is demonstrated by comparing the fourth-order, fifth order and sixth-order stiffness tensors obtained from macro-scale symmetry considerations to the stiffness tensors deduced from homogenizing the elastic response of the granular microstructure. Special attention is paid to systematically relating the particle properties to the probability density function describing their directional distribution, which allows to explicitly connect the level of anisotropy of the particle assembly to local variations in particle stiffness and morphology. The applicability of the multi-scale framework is exemplified by computing the stiffness tensors for various anisotropic granular media composed of equal-sized spheres. The number of independent coefficients of the homogenized stiffness tensors appears to be determined by the number of independent microstructural parameters, which are the local particle contact stiffness, the particle size and the fabric parameters, and is equal or less than the number of independent stiffness coefficients following from macro-scale symmetry considerations. Since the modelling framework has a general character, it can be applied to different higher-order granular continua and arbitrary types of material anisotropy.
[32] ID:32-Yin-Yang spiraling transition of a confined buckled elastic sheet
Stéphanie Deboeuf (IJLR d'Alembert (CNRS - Sorbonne Université)), Suzie Protière (IJLR d'Alembert (CNRS - Sorbonne Université)) and Eytan Katzav (HUJI).
Abstract
DNA in viral capsids, plant leaves in buds, and geological folds are examples in nature of tightly packed low-dimensional objects. However, the general equations describing their deformations and stresses are challenging. We report experimental and theoretical results of a model configuration of compression of a confined elastic sheet, which can be conceptualized as a 1D line inside a 2D rectangular box. In this configuration, the two opposite ends of a planar sheet are pushed closer, while being confined in the orthogonal direction by two walls separated by a given gap. Similar compaction of sheets has been previously studied, and was shown to buckle into quasi-periodic motifs. In our experiments, we observed a new phenomenon, namely the spontaneous instability of the sheet, leading to localization into a single Yin-Yang pattern. The linearized Euler Elastica theory of elastic rods, together with global energy considerations, allow us to predict the symmetry breaking of the sheet in terms of the number of motifs, compression distance, and tangential force. Surprisingly, the appearance of the Yin-Yang pattern does not require friction, although it influences the threshold of the instability.
[33] ID:33-Data-driven inverse design of bimaterial strut-based lattice structures
Xiang-Long Peng (Division Mechanics of Functional Materials, Institute of Materials Science, TU Darmstadt) and Bai-Xiang Xu (Division Mechanics of Functional Materials, Institute of Materials Science, TU Darmstadt).
Abstract
By tailoring their microstructural features, microstructured materials can exhibit widely tunable effective properties that are unreachable or even beyond those of the base materials, such as negative Poisson's ratio and negative thermal expansion coefficient. Strut-based lattice structures are typical examples. If more than one base material is introduced in a lattice structure, its effective properties rely on the base material properties as well. To this end, a much wider design space is attained. In practice, the design and application of microstructured materials are two-fold tasks: forward prediction and inverse design. The former tackles the prediction of effective properties of a specified microstructure. The latter is aimed at designing a microstructure with specified target effective properties.
In this contribution, we introduce a few novel bimaterial strut-based lattice structures. They can exhibit negative Poisson's ratios and/or negative thermal expansion coefficients. We consider their inverse design by a data-driven method. We exploit the computational homogenization method to evaluate the effective thermoelastic properties of numerous structure designs with varying structural features, which results in a dataset consisting of structural features paired with the corresponding effective properties. For each type of lattice structure, we construct two artificial neural network (ANN) surrogate models for the forward prediction and inverse design. The ANN models are trained and verified with the dataset. Subsequently, the performance of these data-driven surrogate models is illustrated by typical forward and inverse design tasks. These ANN models will facilitate the application of these novel bimaterial lattice structures in different engineering scenarios for structural and/or functional purposes.
[34] ID:34-Determining the interlaminar fracture toughness of specimens with material or layup asymmetry: the key issues
Panayiotis Tsokanas (KU Leuven) and Yentl Swolfs (KU Leuven).
Abstract
The laboratory specimens used to assess the interlaminar fracture toughness of layered materials can be classified as either standardised or non-standardised. We term standardised a specimen extracted from, for example, a unidirectional composite laminate or an identical-adherend adhesive joint, such as metal-to-metal or composite-to-composite. Assessing fracture toughness using standardised specimens is a common practice guided by international test standards. We term non-standardised a specimen resulting from, for instance, unsymmetric or unbalanced laminates with an elastically coupled behaviour or residual thermal stresses (if cured at elevated temperature), bimaterial or multimaterial joints, or fibre metal laminates. There are certain issues in determining the interlaminar fracture toughness of such non-standardised specimens that inherently feature material or layup asymmetry with respect to the delamination plane. The double cantilever beam test and other well-known delamination tests are used to characterise the interlaminar fracture of these specimens. Nevertheless, a specimen with material or layup asymmetry will experience mixed-mode fracture at its crack front, even if it is remotely loaded in pure mode. Several fracture mode partitioning approaches have been proposed to extract the pure-mode fracture toughnesses, which will be discussed in this presentation. Next, we will elaborate on the critical effects of bending‒extension coupling and residual thermal stresses often appearing in non-standardised specimens by reviewing major data-reduction models that consider those effects. In laminated composites, in particular, the ply orientation angle difference at the delamination interface is another issue that critically affects the interlaminar fracture behaviour. For example, delaminations can migrate when this difference exceeds 15°. Experiments that study the effect of ply orientation at the delamination interface are hence impossible beyond that critical angle. The effects of an elastically coupled behaviour and residual thermal stresses may also appear in these laminated composites, further complicating the fracture toughness analysis.
[35] ID:35-Numerically efficient solution methods in highly nonlinear variational thermomechanics
Hauke Goldbeck (Christian-Albrechts-Universität zu Kiel) and Stephan Wulfinghoff (Christian-Albrechts-Universität zu Kiel).
Abstract
We present a modified Newton scheme applied to a thermomechanical shape memory alloy model, which improves the convergence. Key feature of the model, which is a modified version of the model by Sedlák et al. 2012, is its capability to accurately model the shape memory effect, as well as the superelastic behavior by a thermomechanical potential, compare with Sielenkämper & Wulfinghoff 2022. The variation of this potential yields the energy balance, the linear momentum balance and the evolution equations of the internal variables. Yield and transformation criteria are derived form the corresponding dual dissipation potential. In order to improve the convergence of the thermomechanical model the Newton scheme is adapted using a line search approach. Therefore, the residuum of the convex thermomechanical potential is linearized. The step size of each Newton step is adapted such that the local minimum of each step is approximated as starting point for the following Newton step. This approach improves the numerical robustness of the Newton scheme.
[37] ID:37-The design of lightweight geared mechanical metamaterials optimised for elastic strain energy absorption
Hyeon Lee (The University of Edinburgh), Amer Syed (The University of Edinburgh) and Parvez Alam (The University of Edinburgh).
Abstract
Geared mechanical metamaterials were designed with an aim of maximising elastic strain energy absorption whilst conjointly reducing mass. Modular unit cells were initially designed to contain unmeshed spur gears arranged in parallel, and as using face-centred and body-centred profiles, and these were connected in continuum to loading plates using shafts positioned asymmetrically to generate small-deformation gear rotations. The gears mesh only when the unit cell is loaded and experiences deformation, and the gears thus contribute to load-resistance in the metamaterial unit cell, through tooth interlocking and gear-to-gear contact. Unit cells were parametrically designed using finite element analysis (FEA) methods to ascertain the optimal gear shapes and locations, optimal shaft dimensions and connection angles, and optimal global architectures enabling lightweighting. Care was taken to balance high strain energy storage and low mass to an optimum. Static compression tests were conducted on additively manufactured unit cells to validate the model outputs. Unit cells were subsequently built up into arrays, forming metamaterial structures, and these were tested and validated to ascertain the effects of scaling and modularisation on mechanical properties and behaviour.
[38] ID:38-Image-based finite element method applied to in-situ x-ray tomography compression tests of open cell polymeric foams
Shaoheng Feng (Politecnico di Milano) and Luca Andena (Politecnico di Milano).
Abstract
Polymeric foams are widely used in different industries such as automotive, aviation and military due to their wide density range, high specific strength, strong ability to absorb impact loads, and good thermal insulation properties. In this study, taking advantage of 3D imaging technology based on X-ray computed tomography (CT), in-situ compression tests were carried out to explore the global and local deformation behaviour of open cell polyurethane foams. Different strain levels were recorded, and relevant images were reconstructed from x-ray CT during the in-situ tests. To better understand the deformation behaviour of the interior structure of foams under uniaxial loading, the CT image-based finite element method is widely used which provides a non-destructive and non-invasive way to obtain the real internal structure of the foam for different loading stage. An advanced image-based finite element analysis method was proposed in this study. The finite element models of foam microstructures were generated from images obtained by X-ray CT by applying level set method (LSM) and Delaunay triangulation (DT). Moreover, to improve the mesh quality of the FE models and calculation accuracy, Taubin smoothing was utilized. Then, numerical simulations on the smoothed mesh were implemented to compare with the experimental tests and understand deformation process during compression. Good agreement was observed between the deformations obtained by simulations and in-situ compression experiments at different strain levels. Morphological features of deformed models at different strain level were identified. Three main features were analysed, namely: strut length, strut thickness and strut orientation. The comparison of these features for different deformation stages was carried out. The results suggest that, under uniaxial stress, the open-cell foam deforms by struts bending followed, at sufficiently large loads, by nonlinear deformation within the struts. The deformation behaviour of the interior structure strongly depends on the initial orientation and thickness of struts.
[39] ID:39-Deformation mechanisms of Ti polycrystals from 3D diffraction contrast tomography and high-resolution digital image correlation data: experiments and simulations
Eugenia Nieto Valeiras (IMDEA Materials Institute), Alberto Orozco Caballero (Department of Mechanical Engineering, Chemistry and Industrial Design, Polytechnic University of Madrid), Maral Sarebanzadeh (Department of Materials Science, Polytechnic University of Madrid), Jun Sun (Xnovo Technology) and Javier Llorca (Department of Materials Science, Polytechnic University of Madrid).
Abstract
A combined experimental and simulation strategy is presented to evaluate the impact of slip transfer on the deformation mechanisms in pure Ti. From the experimental viewpoint, the 3D microstructural information was acquired by laboratory diffraction contrast tomography, and thus, all the parameters that characterize grain boundaries were available prior to deformation. Slip transfer across grain boundaries and the strain distribution after deformation were ascertained by means of high-resolution digital image correlation. Despite most of the grains following the usual geometrical slip transfer criteria, some atypical behaviors were observed, such as delayed slip transfer, partial slip transfer, and slip transfer involving poorly oriented slip systems triggered by the local stress state. Simultaneously, a representative volume element of the microstructure was generated from the 3D data, ensuring a direct correspondence between the model and microstructure. The mechanical behavior of the polycrystal was simulated using a dislocation-based crystal plasticity model that accounts for slip transfer/blocking, where the critical resolved shear stress was fitted for each slip system family. The analysis of the experiments alongside the numerical simulations provided a comprehensive understanding of the deformation mechanisms across grain boundaries in pure Ti.
[40] ID:40-Energetics of Mixed-Mode Crack Propagation around Geometric Discontinuities on Thick Composite Structures
Miguel A. Valdivia-Camacho (The University of Edinburgh), Sergio Lopez Dubon (The University of Edinburgh), Conchúr M. Ó Bradaigh (The University of Sheffield) and Parvez Alam (The University of Edinburgh).
Abstract
We introduce a comprehensive mixed-mode stress analysis conducted on a thick composite tidal blade featuring a strategically positioned hole with notches. Tidal blades, crucial components of stream turbines, experience complex loading conditions due to dynamic tidal forces. A mixed-mode analysis approach considering all fundamental modes of crack opening (Mode I, Mode II, and Mode III), is employed to capture the full spectrum of stress states around the notched hole. Here, we revisit existing fracture criteria for 2D and 3D mixed mode loading to evaluate their performance compared to the recorded measurements. A digital image correlation (DIC) method is additionally used to correlate the strain field surrounding the geometric discontinuity. Furthermore, a finite element analysis (FEA) model is validated against the experimental data and various loading scenarios are simulated, including tidal forces, wave-induced vibrations, and fatigue loading. The effects of the hole and the direction of the notches are systematically investigated to assess their impact on stress concentration and crack propagation. This research contributes an understanding of the mechanical behaviour of thick composites under mixed-mode loading, offering valuable insights for the design and modelling stages of composite tidal turbine blades.
[42] ID:42-Recent Advances in Peridynamics
Erkan Oterkus (University of Strathclyde), Selda Oterkus (University of Strathclyde), Yakubu Kasimu Galadima (University of Strathclyde), Wenxuan Xia (University of Strathclyde) and Bingquan Wang (University of Strathclyde).
Abstract
In order to determine the deformation response of materials and structures subjected to external loading conditions, classical continuum mechanics (CCM) was introduced by disregarding the atomistic structure. CCM has been successfully applied to numerous challenging problems. However, its governing equation faced a difficulty when there is any discontinuity in the structure such as a crack, since spatial partial derivatives in its governing equation are not defined for such a condition. In order to overcome this problem, a new continuum mechanics approach, Peridynamics (PD), was recently introduced with the intention that PD equations remain always valid whether there is any discontinuity in the structure or not. This character of PD makes this new approach a powerful tool for predicting crack initiation and propagation. Moreover, PD can be considered as the continuum version of molecular dynamics. Therefore, PD can be a suitable candidate for multi-scale analysis of materials. Furthermore, PD formulation can also be extended to other fields such as thermal diffusion, moisture diffusion, etc., so that it can be used as a single platform for multiphysics analysis of materials and structures with damage prediction capability. Hence, in this presentation, recent advances in peridynamics will be presented such as peridynamic computational homogenization and peridynamic differential operator.
[43] ID:43-Model-Driven Identification Framework for Optimal Constitutive Modelling from Kinematics and Rheological Arrangement
Ernesto González-Saiz (UC3M) and Daniel García-González (UC3M).
Abstract
Soft materials such as biological tissues or magnetorheological elastomers present complex mechanical behaviors that include large deformations, numerous nonlinearities, time- or even external field (magnetic)-dependent responses. The description of their constitutive modelling is challenging and often time-consuming. Numerical algorithms to automatically calibrate model parameters have provided invaluable tools to help this purpose. However, these are mostly limited to the fitting of a set of pre-defined parameters associated with the model used. In this work, we go a step further by developing a machine learning framework capable of automatically identifying not only such model parameters but also the optimal kinematics and rheological model. To this end, we present a multiphysics model-driven framework that optimally selects the most suitable model kinematics, its rheological components and their arrangement for a given set of experimental curves. Subsequently, it calibrates all the material constants belonging to such a model, independent of its complexity. We demonstrate the versatility and capabilities of this framework with examples on hyperelastic, viscohyperelastic and magneto-viscohyperelastic materials. The present work opens new routes to not only fit model parameters but to identify the constitutive ingredients and underlying mechanisms needed to describe nonlinear responses of soft active materials.
[44] ID:44-Modeling of Softening Behavior by Deep Symbolic Regression
Rasul Abdusalamov (RWTH Aachen University) and Mikhail Itskov (RWTH Aachen University).
Abstract
Rubber like materials demonstrate pronounce softening under cyclic loading. This phenomenon known as Mullins effect plays an important role in the stress strain response of these materials. Despite long-term research and numerous modeling approaches proposed in literature an accurate prediction of the Mullins effect especially under complex loading conditions still remains a challenging task. In this work, we propose a novel approach to model the Mullins effect using deep symbolic regression. The goal is to find a strain energy in the form of an algebraic expression fitting the given data as closely as possible. By incorporating deep symbolic regression into the continuum mechanical framework the method combines advantages of known physical relationships with the unbiased optimization approach of symbolic regression. The procedure has already been applied to discover incompressible hyperelastic material models and will be extended here to inelastic effects as well. The proposed approach is validated through benchmark tests using the generalized Mooney Rivlin and the Ogden Roxburgh model. In addition, the proposed framework is tested on an experimental temperature dependent data set. Good agreement between the obtained material models and the experimental data is demonstrated.
[45] ID:45-Continualization of microstructured plates based on a beam-grid lattice for the development of novel continuum models accounting for scale effects
Francisco Gómez Silva (University Carlos III of Madrid) and Ramón Zaera Polo (University Carlos III of Madrid).
Abstract
Formulations based on classical continuum mechanics fail when applied to problems in which scale effects are present due to the discreteness of the matter. In the presented work, different continualization techniques are applied to a 2D beam-grid lattice, thus developing several continuum models that account for the scale effects not captured by the Classic Kirchhoff plate model in dynamic problems. This 2D beam-grid lattice is considered as a reference, and is made up of particles arranged in the x-y plane undergoing displacement in the out-of-plane direction. Adjacent particles are connected by linear rotational springs that are joined to straight segment (bending deformation proportional to their relative rotation). Additionally, each representative unit cell includes springs in the central domain to account for torsion stiffness. Different standard (based on Taylor’s series) and non-standard (employing the pseudo-differential shift operator) continualization procedures are applied to this lattice, the latter leading to new non-classical continuum model with low spatial order, thereby bringing the advantage of not needing extra boundary conditions (unclear physical meaning) to be solved when finite solids are treated. All these models are evaluated via dispersion and natural frequency analyses, comparing their dynamic behaviour with that of the discrete one. Moreover, the intrinsic relationship between wave propagation and vibration of bounded solids is emphasized for both continuum and discrete models. Interestingly, the non-standard models derived in this work are able to accurately capture the scale effects featured by the discrete model through space-time cross derivatives with low spatial order, not presenting any physical inconsistency.
The authors acknowledge support from MCIN/ AEI /10.13039/501100011033 under Grants number PID2021-123294OB-100, from FEDER and ESF. This work has been also supported by the Madrid Government under the Multiannual Agreement with UC3M in the line of Excellence of University Professors (EPUC3M24), and in the context of the V PRICIT.
[46] ID:46-The stab resistance of SLA printed porous Bouligand structured polymer
Praveenkumar Patil (School of Engineering,The University of Edinburgh, Edinburgh, UK), Edward McCarthy (School of Engineering, The University of Edinburgh, Edinburgh, UK) and Parvez Alam (School of Engineering, The University of Edinburgh, Edinburgh, UK).
Abstract
In this study, we subjected polymer slabs with three-dimensional porous Bouligand structures to stab tests, to investigate the influence of the pitch angle and spacing on the stab resistance and fracture of the Bouligand structure. Stab tests were conducted following the HOSDB/P1/B (UK) standard, and the porous Bouligand structured polymer samples were additively manufactured using a Form3 SLA 3D printer. Here, we consider the stab resistance characteristics of porous structures by normalising them against solid (non-porous) polymer material and compared them against the material's relative density. CT microtomography scans were utilised to identify damage profiles, which were then analysed internally through 3D image analysis techniques. Finally, optical methods were employed to analyse the knife penetration depth and damage footprint, aiming to identify critical criteria for stab resistance.
[47] ID:47-Phase-field modelling of grain boundaries for radiation induced segregation predictions
Yanis Calbert (Univ. Lille, CNRS, INRAE, Centrale Lille Institut, UMR 8207, UMET, Unité Matériaux et Transformations) and Ludovic Thuinet (Univ. Lille, CNRS, INRAE, Centrale Lille Institut, UMR 8207, UMET, Unité Matériaux et Transformations).
Abstract
Metallic alloys used in nuclear power plants are under permanent irradiation which causes fast modification of their microstructure through a large variety of defects interacting with each other: interstitials, vacancies, point defect clusters, dislocations, grain boundaries (GBs), etc. In particular, segregation of atoms in these conditions can be observed at GBs, which can alter the structural integrity of the materials. Despite the numerous improvements achieved so far to understand radiation-induced segregation (RIS) at GBs through cutting-edge experimental or modelling tools, several observations remain unexplained. This might be due to the huge diversity of GB structures and the resulting difficulty to correctly describe their interactions with solute and point defect (PD) diffusion.
Recently, phase-field (PF) approaches have been developed to predict RIS behaviour in binary alloys for different conditions. However, in their formalism, the description of GB was still basic since the thermodynamic and elastic properties of the GB and the bulk phase were supposed to be the same, the GB being treated as a simple absorbing plane for PDs (“planar sink” model). As a consequence, these approaches fail to predict thermal segregation, which may interplay with RIS resulting in complex segregation profile at GBs.
To overcome the limitations of this “planar sink” model, we first propose in this work to better describe the thermodynamic heterogeneities between the bulk phase and the GB. For this purpose, a density-based model recently proposed in the literature is adopted, allowing to recover the well documented “W-shape” segregation profile observed experimentally under irradiation. Secondly, the elastic relaxation at the GB is modelled by different approaches, among which the Read and Shockley one for low angle tilt GBs, inducing complex segregation behaviours analysed in detail. Case studies will be presented on Fe Cr and nickel base model alloys for nuclear applications.
[48] ID:48-Cooperative data-driven modeling
Miguel Bessa (Brown University) and Aleksandr Dekhovich (Delft University of Technology).
Abstract
Our scientific community has made great strides in data-driven design and modeling. However, artificial neural networks are currently developed for specific tasks because they suffer from catastrophic forgetting. This is a major impediment to cooperative data-driven modeling. We present a new method addressing this issue in an attempt to open the field to cooperation.
[49] ID:49-Influence of the mineral wool microstrucure on its dynamic macroscopic behaviour
Grégoire Markey (Saint-Gobain Research Paris, Dpt. Sensors, Optics, Datascience and Acoustics), Etienne Barthel (Soft Matter Sciences and Engineering, ESPCI Paris, PSL University, CNRS, Sorbonne Université), Mohamed Rachik (Université de technologie de Compiègne, Roberval (Mechanics, energy and electricity)) and Nicolas Dauchez (Université de technologie de Compiègne, Roberval (Mechanics, energy and electricity)).
Abstract
Fibrous materials, such as mineral wools, can be used for acoustic insulation in different building elements (partition walls, ceilings...). Mineral wools are porous random sparsely linked fibre networks, whose microstructure must be studied to improve their acoustic behaviour. In the past, macroscopic acoustic parameters have been linked to microstructure, based on the hypothesis of rigid fibrous skeleton. This hypothesis appears to be inaccurate to model certain applications, such as floating floor or partition walls, when the structure displacement must be considered. The main goal of this paper is to study the dynamic behaviour of mineral wool, as well as to establish a link between microstructure and macroscopic mechanical properties. Confocal microscope images, and micro-scale observations allowed to identify some characteristics of the material. Preliminary experiments confirmed that it is strongly anisotropic, even at small scales. The through-thickness compression stiffness is relatively low, whereas in the transverse direction fibre naps are identified. Macro-scale measurements of dynamic quantities of interest (stiffness, loss factor) were performed on a batch of samples of different properties. Results showed the influence of the different process/micro-scale parameters on the dynamic behaviour of the material. A Finite Element Method numerical model of a microscale 3D Representative Volume Element (RVE) of a Non-Uniform Rational B-Splines (NURBS) fibres geometrical network is being developed based on the micro-scale observations. The originality of this model lies in description of the three-dimensional small strain dynamic behaviour of a sparsely cross-linked network. Especially, it is necessary to better understand various phenomena, such as contact, friction, or binder influence. A specific modelling strategy is proposed to model the binder links between fibres. Results of the FEM model are compared with macro-scale acoustic measurements. To be able to link model and experiments, a key issue is to identify the scale of the model.
[50] ID:50-Wrinkling of indented sheets on viscous fluid
Ayrton Draux (UMons (Influx)), Pascal Damman (UMons (Influx)) and Fabian Brau (ULB).
Abstract
Indented circular thin sheets floating on water can exhibit wrinkles induced by radial compression at their edge. At low indentation depth, wrinkles cover an annulus but can cover the whole surface for more pronounced indentation. On a highly viscous fluid, the indentation force and the growth of wrinkles are affected by the dynamics. For instance, new wrinkles, much smaller than the static ones, are observed. This wavelength is determined by the viscous force and more classical parameters such as bending modulus. At sufficiently short time, wrinkles are radially uniform and the problem can be solved by considering a linear compression of a rectangular sheet. We discuss the impact of viscous force on the initial wavelength and the time relaxation of those unstable wrinkles by solving the Reynold equation combined with the beam equation.
[51] ID:51-Essential role of papillae flexibility in nectar capture by bees
Pascal Damman (UMons (Influx)), Fabian Brau (ULB) and Ayrton Draux (UMons (Influx)).
Abstract
Many bees possess a tongue resembling a brush composed of a central rod (glossa) covered by elongated papillae which is dipped periodically into nectar to collect this primary source of energy. In vivo measurements show that the amount of nectar collected per lap remains essentially constant for sugar concentrations lower than 50% but drops significantly for a concentration around 70%. To understand this variation of the ingestion rate with the sugar content of nectar, we investigate the dynamics of fluid capture by Bombus terrestris as a model system. During the dipping process, the papillae, which initially adhere to the glossa, unfold when immersed in the nectar. Combining in vivo investigations, macroscopic experiments with flexible rods and an elasto-viscous theoretical model, we show that the capture mechanism is governed by the relaxation dynamics of the bent papillae, driven by their elastic recoil slowed down through viscous dissipation. At low sugar concentrations, the papillae completely open before the tongue retracts out of nectar and thus fully contribute to the fluid capture. In contrast, at larger concentrations corresponding to the drop in ingestion rate, the viscous dissipation strongly hinders the papillae opening, reducing considerably the amount of nectar captured. This study shows the crucial role of flexible papillae, whose aspect ratio determines the optimal nectar concentration, to understand quantitatively the capture of nectar by bees and how physics can shed some light on the degree of adaptation of a specific morphological trait.
[52] ID:52-Modeling of open-porous materials based on their microstructure
Mikhail Itskov (RWTH Aachen University) and Rajesh Chandrasekaran (RWTH Aachen University).
Abstract
Open-porous cellular solids are lightweight structures with ultra-low bulk densities and thermal conductivity, high structural stiffness and energy absorption capacity. In this study, a computational method is developed to model open-porous microstructures and predict their relevant elastic and inelastic mechanical properties, as well as the thermal conductivity. First, the geometry of the microstructure is generated for a given pore size distribution (PSD) and porosity. To this end, the Laguerre-Voronoi tessellation and close sphere packing are applied. This allows us to reproduce highly irregular cell shapes and sizes relevant for biopolymer aerogels considered in this study for a benchmark example. The PSD of the resulting geometry is validated in comparison with the experimental data obtained from nitrogen desorption isotherms and further exported as beam elements to the finite element (FE) model. FE simulations of a representative volume element further allow to evaluate the homogenized mechanical response of the porous structure based on its micromechanics and to study its heat transfer properties. Finally, the influence of PSD and porosity on the mechanical and thermal properties is discussed.
[53] ID:53-When phase field met the coupled criterion
Aurélien Doitrand (MATEIS, INSA LYON), Gergely Molnár (LAMCOS, INSA LYON), Rafael Estevez (SIMAP) and Anthony Gravouil (LAMCOS, INSA LYON).
Abstract
We study the ability of phase field (PF) and the coupled criterion (CC) to predict crack initiation and propagation under opening or shear modes. A confrontation of both approaches reveals that the internal length used in PF is intrinsically correlated to the material tensile strength used in the CC. This correlation also involves the material Poisson’s ratio and the local principal stress state [1,2]. Based on this correlation, a length-free (LF) implementation of the PF approach for fracture is proposed [3]. The inputs of the LF-PF model are similar to the CC inputs, namely the critical energy release rate and tensile strength (or more generally, a strength surface). The proposed approach is tested and compared to the CC on several benchmark examples. The proposed LF-PF approach can be considered as a PF implementation of the CC, both models may be used in a complementary manner since they share the same input parameters and provide similar results regarding crack initiation.
[1] Molnár G, Doitrand A, Estevez R, Gravouil A. 2020. Toughness or strength? Regularization in phase-field fracture explained by the coupled criterion. Theoretical and Applied Fracture Mechanics, Volume 109: 102736. [2] Molnár G, Doitrand A, Jaccon A, Prabel B, Gravouil A. 2022. Toughness or strength? Thermodynamically consistent linear-gradient damage model in Abaqus. Engineering Fracture Mechanics, Volume 266: 108390. [3] Doitrand A, Molnár G, Estevez R, Gravouil A. 2023. Strength-based regularization length in phase field fracture. Theoretical and Applied Fracture Mechanics, Volume 124, 103728
[54] ID:54-Experimental testing of topology optimized structures with hardening material behavior
Miriam Kick (Leibniz University Hannover / Institute of Continuum Mechanics) and Philipp Junker (Leibniz University Hannover / Institute of Continuum Mechanics).
Abstract
In topology optimization it is essential to account for the real-world material behavior in order to result in application-oriented and safe engineering structures. Therefore, we develop the inclusion of hardening material behavior into the thermodynamic topology optimization. Simulation results show the influence of different material behaviors. The optimized structures are experimentally validated to ensure the usage of our method for real-world applications.
We present the method of thermodynamic topology optimization including hardening material behavior. Parameters for the material model are determined by tensile tests. An experimentally testable boundary value problem is optimized due to the hardening material behavior. In addition, a reference structure with linear elastic material behavior is optimized. Both structure specimens are additively manufactured and experimentally tested. The test results verify the influence of the material behavior on optimized structures. Therefore, we demonstrate that it is beneficial for designing real-world engineering structures to include a precise material behavior in the topology optimization.
[55] ID:55-Deploying Complex shapes using Kirigami
Joo-Won Hong (PMMH), Marie Tani (Tokyo Metropolitan University), José Bico (PMMH), Étienne Reyssat (PMMH), Alejandro Ibarra (PMMH) and Benoît Roman (PMMH).
Abstract
A sheet of paper or plastic is difficult to stretch. However, by alternately cutting the sheet, it can be made macroscopically stretchable. What's the secret of this flexibility? Locally, the structure unfolds by bending, a low-energy deformation for a thin sheet. This kirigami technique is not limited to linear "garlands", it can be developed in both planar directions, resulting in three-dimensional structures. The final state depends on the geometry of the cuts. Can these cuts be programmed into the sheet to achieve the desired expanded shape? We've partially solved the problem for axisymmetric shapes, but what about an arbitrary target shape?
[56] ID:56-Predicting the intrinsic tensile strength of etched glass using the coupled criterion
Dominique Leguillon (CNRS - Sorbonne University), Isabell Ayvaz (ISMD - Technical University of Darmstadt), Sebastian Schula (SGS - Engineering Services in Civil Engineering GmbH - Heusenstamm) and Philipp Rosendahl (ISMD - Technical University of Darmstadt).
Abstract
Etching is used to improve the tensile strength of glass by blunting or even eliminating surface defects. It involves immersing test specimens in a hydrofluoric acid bath at varying concentrations and for varying durations. So, an initial surface crack is gradually transformed into a U-notch, the radius of which increases with immersion time. Under these conditions, Griffith’s criterion traditionally used for crack-like defects becomes ineffective for predicting the critical failure stress. The Coupled Criterion (CC) based on a twofold condition in stress and energy can take over. It requires the knowledge of the tensile strength of the material together with its toughness and can predict crack initiation at stress concentration points, e.g. V- or U-notch tips, holes, inclusions. Experiments have been carried out on specimens made of soda lime glass for construction industry. In a first step, a scratch is produced with a conical 120° diamond indenter, leading to a crack of controlled depth. The specimens are then immersed in fluoric acid baths of varying concentrations for varying durations, cracks are therefore transformed into U-notches. Some specimens are reserved for measuring the notches depth and radius, while others are subjected to double ring bending tests until failure. The CC is then used in a reverse manner to identify the intrinsic strength of the soda lime glass, i.e. its resistance when all surface defects (extrinsic defects) have been eliminated. It relies on the inner structure of the material and, even though glass is classified as an amorphous material, it is a rather hasty assumption to suppose that it has no micro-structure at all, crystallites may be present for instance, not forgetting impurities, bubbles, among others. A value around 1000 MPa is derived, far below the molecular strength which is at least one order of magnitude higher.
[57] ID:57-Mechanism of thermally-activated prismatic slip in Mg
Xin Liu (École Polytechnique Fédérale de Lausanne) and William Curtin (Brown University).
Abstract
Prismatic slip of the screw <a> dislocation in magnesium at temperatures ≳ 150 K is understood to be governed by double-cross-slip of the stable basal screw through the unstable prism screw and back to the basal screw, with the activation energy controlled by the formation energy of two basal-basal kinks. However, atomistic studies of the double-kink process predict activation energies roughly twice those derived experimentally. Here, a new mechanism of prism glide is proposed, analysed theoretically, and demonstrated qualitatively and quantitatively via direct molecular dynamics (MD) simulations. The new mechanism is intrinsically 3d, and involves the nucleation of a single kink at the junction where a 3d prismatic dislocation loop transitions from the basal screw segment to non-screw prismatic character. The relevant kink energies are calculated using recently-developed Neural-Network Potentials (NNPs) for Mg that show good agreement versus DFT for basal and prism <a> dislocations, enabling a parameter-free analytic model for the activation barrier. Direct MD simulations show both operation of the precise proposed mechanism and a stress-dependent activation barrier that agrees reasonably with the analytic model. Predictions of dislocation velocity compare very well with in-situ TEM data, and macroscopic strength versus temperature can also be understood. Overall, the new intrinsically 3d mechanism for dislocation glide due to single kink nucleation rather than double-kink nucleation explains key features of the prismatic slip in Mg and may have broader applicability in other metals where kink nucleation processes control thermally-activated flow.
[60] ID:60-Efficient variational three-field reduced order modeling for nearly incompressible materials
Muhammad Babar Shamim (Kiel university) and Stephan Wulfinghoff (Kiel university).
Abstract
This study presents an innovative approach for developing a reduced-order model (ROM) tailored specifically for nearly incompressible materials at large deformations. The formulation relies on a three-field variational approach to capture the behavior of these materials. To construct the ROM, the full-scale model is initially solved using the finite element method (FEM), with snapshots of the displacement field being recorded and organized into a snapshot matrix. Subsequently, Proper Orthogonal Decomposition (POD) is employed to extract dominant modes, forming a reduced basis for the ROM. Furthermore, we efficiently address the pressure and volumetric deformation fields by employing the k-means algorithm for clustering. A well-known three-field variational principle allows us to incorporate the clustered field variables into the ROM.
To assess the performance of our proposed ROM, we conduct a comprehensive comparison of the ROM with and without clustering with the FEM solution. The results highlight the superiority of the ROM with pressure clustering, particularly when considering a limited number of modes, typically fewer than 10 displacement modes. Our findings are validated through two standard examples: one involving a block under compression and another featuring Cook's membrane. In both cases, we achieve substantial improvements based on the three-field mixed approach. These compelling results underscore the effectiveness of our ROM approach, which accurately captures nearly incompressible material behavior while significantly reducing computational expenses.
[61] ID:61-Bistable Anisotropic Conjugate Minimal Surfaces
Marcelo Dias (The University of Edinburgh) and Evripides Loukaides (University of Bath).
Abstract
Multistability in shell structures is common both in nature and - sometimes unintentionally - in manmade structures. It can be induced in diverse geometries by material anisotropy, residual stresses, surface texturing and creasing. Modelling of such structures is challenging due to the need to account for both bending and stretching energy when exploring the available stable geometries and the transition between states. Here, we focus on minimal surfaces and their isometric transformations thus allowing us to focus our mathematical treatment on the bending energy variation. At the same time, we employ anisotropy to tune multistability for this category of geometries. We confirm our results through physical demonstrators.
[62] ID:62-Internally-pressurized plastic pipes mimicked by plane strain grooved tensile (PSGT) specimens
Cristian Ovalle (Mines Paris, PSL University, Centre for Material Sciences (MAT)), Morgane Broudin (EDF-R&D Lab Les Renardières) and Lucien Laiarinandrasana (Mines Paris, PSL University, Centre for Material Sciences (MAT)).
Abstract
ISO 23228:2011[1] proposed a testing method in which the plastic material, experimental resins or compounds for pipes and fittings, can be exposed to stress conditions that mimic internally pressurized end-capped pipes. The stress conditions are mimicked by the use of a plaque specimen having a grooved reduced section called plane strain grooved tensile (PSGT) specimens producing a bi-axial state of stress under uni-axial loading.
In this study, PSGT specimens were cut-out from HDPE pipes. Two shape ratios, ratio between the width and the groove thickness, equal to 20 and 25, were used. Both the axial and transverse displacements and strain fields were followed by a Digital Image Correlation (DIC) camera during tensile and creep loading, both at room and high temperature.
The increasing effect of the temperature in both the axial and transverse displacement and strain was noticed; conversely, no significant effect of the width was highlighted. The results have evidenced that, as the plane-strain condition in the width is assured during the tests, PSGT specimens can be used to mimic internally pressurized pipes under monotonic increasing or constant-in-time loading at both room and high temperature, but it must be better to use specimens with a higher shape ratio, i.e. higher width[2]. The results, which will be discussed during the presentation, contribute to the 9th Sustainable Development Goal: Industry, Innovation and Infrastructure, by promoting a sustainable industrialization and fostering innovation.
REFERENCES [1] ISO/TC 138, Thermoplastics pipes for the conveyance of fluids – Determination of the stress-rupture resistance of moulding materials using plain strain grooved tensile (PSGT) specimens, 23228:2011(E), 2011. [2] C. Ovalle, M. Broudin, L. Laiarinandrasana, Plane–strain condition in plane–strain grooved tensile (PSGT) specimens during traction and creep loading at room and high temperature, Strain 2023, e12467.
[63] ID:63-Geometrical and Crystal Plasticity Modelling of Effects of Microstructure on Mechanical Properties of Additively Manufactured 316L Parts
Majid Kavousi (University of Galway), Peter McHugh (University of Galway), Patrick McGarry (University of Galway) and Seán Leen (University of Galway).
Abstract
Laser powder bed fusion (LPBF) additive manufacturing (AM) is gaining popularity as a versatile, pioneering and time-efficient method for manufacturing intricate parts directly from CAD designs, especially for biomedical applications such as stents or patient-specific orthopaedic implants [1]. However, given the wide range of AM process variables and complex melting/solidification histories, defects and porosity are almost inevitable, which in turn affect the integrity and mechanical performance of produced parts [2]. This modelling study establishes a process-structure-property (PSP) relationship for additive manufacturing of AISI 316L specimens. The methodology is based on a new geometrically-based rationale for the selection of AM process variables (hatch spacing, layer thickness and laser energy density), combined with crystal plasticity finite element (CPFE) micromechanical models that include melt pool microstructural morphology, texture and porosity. The effects of AM process variables and porosity on ductility, yield strength and UTS are analysed. The new methodology has allowed identification of optimal hatch spacing and layer thickness for a given laser spot size, power and scanning speed. Moreover, CPFE modelling reveals the detrimental effect of porosity on the ductility and strength of the struts.
[64] ID:64-Numerical study and analytical characterization of soft magnetorheological foams
Zahra Hooshmand Ahoor (Ecole Polytechnique), Laurence Bodelot (Ecole Polytechnique) and Kostas Danas (Ecole Polytechnique).
Abstract
Particle-filled magnetorheological elastomers (MREs) represent a sophisticated class of two-phase composites, where metallic magnetic micron-sized particles are randomly dispersed within a non-magnetic and mechanically soft elastomer matrix. Recently, magnetoactive polymer foams have been produced, resulting in a lightweight three-phase porous material characterized by millimeter-sized voids. The magnetic and mechanical properties of the resulting active foam can be tuned to meet specific performance requirements. This can be done through the control of the manufacturing process parameters and by adjusting the quantity of magnetic particles. Motivated by these advancements, this study employs numerical simulations to investigate the response of MRE foams under finite deformations and in the presence of magnetic fields. In addition, we propose analytical models that capture the effective responses of these materials.
[66] ID:66-Hard-Magnetic Soft Metamaterials for Remote Tunability of Elastic Waves
Quan Zhang (University of Galway) and Stephan Rudykh (University of Galway).
Abstract
Hard-magnetic active elastomers consist of hard-magnetic particles embedded in a soft matrix. Their ability to rapidly and reversibly change the shape and properties under remote magnetic stimuli, makes them an attractive material platform for soft robotics, actuators and sensors, and biomedical devices. The research area has been witnessing explosive growth, driven by the development of material fabrication enabling the programming of intricate magnetization patterns in soft active materials. Recent studies include the exploration of shape-morphing, instability phenomenon, and achieving untethered actuation. However, despite these recent advances, a systematic understanding of their dynamic behaviors remains elusive, limiting their tremendous potential in nondestructive testing, energy harvesting, and smart soft wave devices.
Here, we put forward a novel design of Hard-magnetic Soft Metamaterials (HSMs) capable of active and remote manipulation of elastic waves, including the highly desirable broadband low-frequency wave attenuation, invisible cloaking, and solitary propagation. The metamaterial properties originate in their highly ordered microstructures that are fixed once designed and manufactured. Therefore, the active tunability of current metamaterials is limited. We utilize the complex magneto-mechanical coupling in highly ordered HSMs to break through the limitation in the metamaterial functions. The developed HSMs will open new levels of performance in applications ranging from broadband vibration isolation at challenging low-frequency ranges to robust energy harvesting with ultra-high transmission rates.
[67] ID:67-Stretching the endothelium: characterization and modeling of mechanical damage in young and aged endothelial cells.
Young Choi (ETH Zurich), Raphael Jakob (ETH Zurich), Alexander Ehret (Empa Dübendorf, ETH Zurich), Costanza Giampietro (Empa Dübendorf, ETH Zurich) and Edoardo Mazza (ETH Zurich).
Abstract
The endothelium is the biomaterial lining the luminal surface of blood vessels and is undergoing significant stretch in cardiovascular physiology and pathology. Using custom stretch devices and protocols, we challenged young and aged/senescent endothelial monolayers with a range of physiological and supraphysiological deformations in vitro. The results show that upon acute high-rate stretch endothelial monolayers developed prominent damage, visible as intercellular and intracellular void formation. For all cells, damage increased proportionally to level of stretch applied, but damage extent depended on cell phenotypes. The subsequent response to after acute stretch determined the partial death and detachment of senescent and aged endothelial cells from the substrate, while the young counterpart rapidly restored the monolayer integrity. Similarly, we observed higher fragility of senescent cells when subjected to physiological levels of cyclic stretch stimulation. In order to rationalize the experimental observations we developed a computational model representing endothelial cells as discrete networks of cytoskeletal components. Adapted to the different cell populations, the model predicted differences in stretch induced mechanical loading of stress fibers and cell-cell junctions, pointing at the more affine deformation of the senescent monolayer as the main factor causing the observed damage. Based on the results of the model, we biochemically decreased the adhesion to the substrate of the senescent monolayers, in order to reduce their affine deformation. This was sufficient to dampen the stretch-induced damage, thus confirming model predictions. Overall, our results show that young endothelia are more resilient to stretch, and that the fragility of senescent monolayers is associated with their stronger adhesion to the substrate. This result is intriguing and may open new avenues for reducing the risk of barrier impairment in aged blood vessels.
[68] ID:68-Patient Characteristics and Biomechanics of Thoracic Aortic Aneurysms
Richard Leask (McGill).
Abstract
The management of thoracic aortic aneurysm patients involves stratifying the risk of dissection and rupture using diameter measurements. Traditional guidelines group patients into categories based on known syndromic pathologies (Marfan, Turners, Ehlers-Danlos) and sporadic (acquired) groups based on aortic valve type (tricuspid or bicuspid). Aortic diameter alone is a poor predictor of aortic tissue integrity.
I will present the results of machine learning models of the patient characteristics from the McGill University Health Centre Aortic Clinic. Patient information was collected from the clinic cohort (146 patients) along with ex vivo planar biaxial tensile properties of resected tissue, genetic screening, in vivo strain imaging to better understand our patient population profiles and ability to predict biomechanical function. Supervised machine learning algorithms provided good estimates of ex vivo biomechanics based on clinically based metrics. Moreover, an unsupervised model demonstrated TAA patients cluster into unique and reproducible clinical subgroups with distinct biomechanical profiles and aneurysm geometry.
[70] ID:70-Solute effects on softening/strengthening of prismatic slip in Mg
Masoud Rahbarniazi (epfl) and William Curtin (EPFL).
Abstract
The activation of prismatic slip in Mg and its alloys can improve the ductility. Experimental results demonstrate the softening effect of dilute addition of Zn and Al at/below room temperature and their strengthening effect at higher temperatures. This work aims at unraveling the mechanisms responsible for the effects of solutes on the ease of prismatic slip using atomistic simulations and theory. Based on first-principles Zn-solute/dislocation interaction energies, prism edge dislocation strengthening is investigated considering solute strengthening and dynamic strain aging via cross-core diffusion. Cross-core diffusion leads to a significant increase in the critical resolved shear stress for edge dislocation motion at high temperatures. But this stress is 60% below experiments. Turning to screw dislocations, we discuss mechanisms of solutes softening and strengthening, as revealed by first-principles results and a new neural network interatomic potential for Mg-Zn.
[71] ID:71-Harnessing Gradients for Self-Assembly of Peptide-Based Nanocapsules: A Pathway to Advanced Drug Delivery Systems
Xuliang Qian (Nanyang Technological University), Haopeng Li (Nanyang Technological University), Harini Mohanram (Nanyang Technological University), Xiao Han (Nanyang Technological University), Huitang Qi (Dalian University of Technology), Guijin Zou (Institute of High Performance Computing, A*STAR), Fenghou Yuan (Dalian University of Technology), Ali Miserez (Nanyang Technological University), Qing Yang (Chinese Academy of Agricultural Sciences), Tian Liu (Dalian University of Technology), Huajian Gao (Nanyang Technological University) and Jing Yu (Nanyang Technological University).
Abstract
Biological systems often create materials with intricate structures to achieve specialized functions. In comparison, precise control of structures in man-made materials has been challenging. Here, we report a serendipitous discovery of insect cuticle peptides (ICPs) spontaneously forming nanocapsules through a single-step solvent exchange process, where the concentration gradient resulting from mixing of water and acetone drives the localization and self-assembly of the peptides into hollow nanocapsules. The underlying driving force is the intrinsic affinity of the peptides for a particular solvent concentration, while the diffusion of water and acetone creates a gradient interface that triggers peptide localization and self-assembly. This gradient-mediated self-assembly offers a transformative pathway towards next-generation drug delivery systems based on peptide nanocapsules.
[72] ID:72-Microstructure characterization of unsaturated wet granular materials using x-ray microtomography
Ahmad Awdi (Navier, Ecole des Ponts, University Gustave Eiffel, Marne La Vallée), Jean-Noël Roux (Navier, Ecole des Ponts, University Gustave Eiffel, Marne La Vallée), Abdoulaye Fall (Navier, Ecole des Ponts, University Gustave Eiffel, Marne La Vallée) and Camille Chateau (Navier, Ecole des Ponts, University Gustave Eiffel, Marne La Vallée).
Abstract
Unsaturated wet granular materials exhibit intricate microstructures composed of solid particles, liquid phases, and void spaces. Understanding the morphological and rheological characteristics of these materials is essential for various applications, from geotechnical engineering to environmental science. By employing X-ray tomography, we aim to understand the relationship between the microstructural features and rheological properties of these materials, shedding light on their behavior and interactions in various conditions. Our focus is on slightly polydisperse polystyrene beads mixed with a minimal amount of liquid, specifically in the pendular regime (the ratio between the liquid volume and the volume of polystyrene beads is less than 0.075), where capillary bridges are the primary liquid morphology, although other morphologies also exist in smaller proportions. A custom shear device, compatible with an X-ray microtomography imager, has been designed to observe microstructural evolution under imposed confining stress and shear rate. Through these X-ray microtomography experiments, we capture detailed 3D images at different deformation stages. Employing advanced image segmentation techniques, which integrate machine learning and deep learning, we can analyze these complex microstructures accurately and comprehensively. Our segmented images offer a deeper understanding of grains and liquid distribution, as well as the different liquid morphologies. In particular, we have developed an automatic tool for classifying the different liquid morphologies within the sample. This method enables us to analyze the 3D spatial distribution of the grains and liquid fractions, in addition to the changes in the liquid morphologies, providing insights into their responses under shear conditions.
[73] ID:73-Coalescence of slender structures removed from a liquid bath
Fabian Brau (Université libre de Bruxelles (ULB)), Emmanuel Siéfert (Université libre de Bruxelles (ULB)), Hadrien Bense (Université libre de Bruxelles (ULB)), Basile Radisson (Université libre de Bruxelles (ULB)), Hoa-Ai Béatrice Hua (Université libre de Bruxelles (ULB)) and Lucie Domino (Université libre de Bruxelles (ULB)).
Abstract
We study the coalescence between two slender structures withdrawn quasi-statically or at finite velocity from a liquid bath. When partially immersed, the structures interact with each other through the capillary force induced by their menisci whose shape changes with the retraction speed. As the structures are removed from the bath, their dry length increases, and they become easier to bend until the capillary force is strong enough to trigger contact. Surprisingly, the structures snap to contact from a finite distance at a critical dry length. The transition to coalescence is thus subcritical and exhibits a large hysteresis loop between two stable states.
An analytical coalescence criterion is derived when the structures are withdrawn quasi-statically from the bath with a good agreement with experimental data for rods and lamellae.
In the case of two rods removed at finite velocity, the size of the menisci around them grows with the retraction speed and the capillary interaction increases. The rods coalesce then at a shorter dry length. We characterize the menisci growth as a function of the capillary number and show that the interaction between the structures is given by the static interaction with an effective surface tension increasing with the capillary number.
In the case of two lamellae, the flow created between them during their removal from a bath generates a positive pressure pushing them away before the capillary interaction can, in some cases, bring them into contact. To study this overpressure, rigid lamellae are used and the variation in height of the liquid column between them during the removal is characterized as a function of the system parameters. This ingredient can then be used to describe the complex motion of flexible lamellae during their withdrawal from a bath.
[74] ID:74-Elastic-plastic lattice materials - machine learning based constitutive modeling
Clemens D. Fricke (Institute of Lightweight Design and Structural Biomechanics, TU Wien), Luka Mitrovic (Institute of Lightweight Design and Structural Biomechanics, TU Wien) and Heinz E. Pettermann (Institute of Lightweight Design and Structural Biomechanics, TU Wien).
Abstract
The prediction of the structural response requires the constitutive description of the material from which the structure is built. For complex elastic-plastic anisotropic materials, analytical closed form constitutive models with sufficient accuracy may not exist. Concurrent modeling (i.e. FE^2) is extremely costly, in particular for larger three-dimensional structures.
Alternatively, data driven approaches based on machine learning gains increasing attention. In this contribution such an approach will be presented for a periodic lattice material with cubic material symmetry and elastic-plastic parent material. Not only the elastic anisotropy is very pronounced, but also the initial yield surface and the hardening response is highly direction dependent.
A periodic unit cell model is set up in the framework of the Finite Element Method to predict the non-linear stress response to strain controlled monotonic proportional loading. The resulting data base is used for training, testing, and validation of an artificial neural network. Additionally, energy considerations are included in terms of elastic recoverable and plastic dissipative contributions to distinguish between loading and unloading. Moreover, the predictive capabilities for (mildly) non-proportional strain histories is assessed.
The AI-based constitutive model is implemented as VUMAT into ABAQUS/Explicit to run structural analyses. As example a cantilever beam formed by ten times hundred unit cells is studied under various loading conditions and the performance of the developed constitutive model is evaluated. Since the example beam is small enough to fully discretize the all lattice members, detailed comparison to the reference model is possible.
[75] ID:75-Heterogeneities in solid-state MLFS additively manufactured 7075 aluminium alloy
Matthieu Jadot (Institute of Mechanics, Materials and Civil Engineering, UCLouvain & WEL Research Institute), Jishuai Li (Institute of Mechanics, Materials and Civil Engineering & CRRC Technology Innovation (Beijing) Co., Ltd), Romain Gautier (Institute of Mechanics, Materials and Civil Engineering, UCLouvain), Jichang Xie (Laboratoire Roberval, UTC, Sorbonne Universités), Matthieu B. Lezaack (Institute of Mechanics, Materials and Civil Engineering, UCLouvain), Thaneshan Sapanathan (Institute of Mechanics, Materials and Civil Engineering & Curtin Corrosion Centre, WA School of Mines), Mohamed Rachik (Laboratoire Roberval, UTC, Sorbonne Universités) and Aude Simar (Institute of Mechanics, Materials and Civil Engineering, UCLouvain & WEL Research Institute).
Abstract
The solid-state additive manufacturing (AM) process of Multi-Layer Friction Surfacing (MLFS) is ideal for building 3-dimensional parts made of precipitation hardened high-strength 7075 aluminium alloy. 7xxx aluminium alloys have the advantage of high performances to weight ratio but 7xxx series are still a challenge to process using fusion-based AM processes. That is why, MLFS is a good candidate for high quality part building by avoiding solidification defects. This process leads to produce microstructural (grain size and precipitate size and distribution) and mechanical (hardness) heterogeneities.
The thermal history is studied using a multilayer thermal model, including temperature, cooling rate and heat accumulation simulations, that provides a better understanding of the effect of multiple thermal cycles on microstructural heterogeneities. The grain size evolution in a layer shows small grains in the layer centre with even finer grains at the bottom and top of the layer. Indeed, feedstock material grains are fully recrystallized and refined. The grain size profile also varies along the deposition height of the multi-layer structure. These variations with height result from a combination of mechanical and thermal effects during MLFS. The strengthening precipitates are significantly affected in the layered structure due to the complex thermal field. The size and density gradients of the precipitates along the height of the structure is responsible for the significantly higher microhardness of the top layer.
For some applications homogeneous parts are required. Using post-MLFS T6 heat treatment, the hardening precipitation is restored, improving significantly the microhardness. The microhardness profile is uniform and reaches the peak-aged T6 state stage. Abnormal grain growth occurs during the T6 heat treatment. However, tensile properties are restored to 7075 classical T6 values, as tensile specimens show strength exceeding 500MPa and a typical elongation of 10%.
[76] ID:76-Storing Driving History within Beam Counter Metamaterials
Lennard Kwakernaak (LION, Universiteit Leiden) and Martin van Hecke (AMOLF).
Abstract
Irreversible responses in materials encode information about past driving; however, this information is often challenging to recover. In this study, we introduce a beam counter metamaterial designed to track applied driving cycles by elastically deforming into easily interpretable internal states. We further demonstrate how combining multiple of these counters together allows us to extract rich information from applied driving, considering both the magnitude and order of driving events. Finally, we realize a 'lock and key' metamaterial with a unique internal state reachable only through the application of a specific 'key' driving input. This design strategy is robust and scalable, laying the foundation for the development of 'memory materials' that maximize the recoverable information stored about past driving.
[77] ID:77-Simulation of size effects in cracked ductile specimens using a GTN nonlocal model
Daniella Lopes Pinto (Mines Paris / Transvalor S.A.), Luciano Meirelles Santana (Mines Paris), Yazid Madi (Mines Paris), Nikolay Osipov (Transvalor S.A.) and Jacques Besson (CNRS).
Abstract
Industrial power generation and transport structures, designed for a typical service life of up to 40 years, require a profound understanding of the long-term evolution of material behavior to ensure the safety and reliability of these installations. Small coupons (2–3 mm thickness) extracted from these structures may provide material for machining sub-size test specimens, enabling the characterization of aged materials. Conducting tests on these mini-specimens allows quasi-non-destructive sampling, avoiding disruptions to transit or subsequent repairs.
The test campaign comprises small tensile and fracture mechanics specimens, including Compact Tensile (CT) specimens. However, due to their reduced size, mini-CT specimens do not meet the validity criteria of the ASTM E1820 standard. Therefore, this study proposes to use the finite element method to simulate valid CT specimens using a nonlocal Gurson-Tvergaard-Needleman (GTN) model with parameters tuned for sub-size specimens.
Focusing on two ferrite-pearlite steels - a vintage steel used for pipe manufacturing and a modern steel for tube production - this study covers tests conducted on both standard and sub-size CT specimens with thicknesses of 2, 3, and 5 mm. The study involves the derivation of J-R curves for crack propagation resistance using the load/unload compliance technique, yielding highly reproducible results. Particularly for the vintage steel, toughness decreases with thickness, whereas for the modern steel it increases.
The mechanical tests are additionally and comprehensively simulated using the finite element method and a nonlocal GTN model, which captures both plasticity and ductile damage. Model parameters, including hardening, damage (void nucleation and growth), and internal lengths, are fitted for both materials. The choice of employing a nonlocal formulation specifically ensures mesh independence. The model can be effectively used to simulate specimens large enough to meet the validity criteria of the ASTM E1820 standard, and the resulting J-R curve can be used for safety evaluation.
[79] ID:79-Compressed earth blocks for masonry buildings in seismic zone
Noura Zarzour (Universite Cote d Azur), Maria Paola Santisi D Avila (Universite Cote d Azur), Diego Mercerat (CEREMA), Luca Lenti (CEREMA) and Michel Oggero (FILIATER).
Abstract
The Compressed Earth Block (CEB) represents a low-carbon construction material for masonry buildings, permitting the reuse of local soil, removed after leveling and other earthworks, and then reducing the energy consumption related to its collection, transport, recovery, and disposal. The CEB masonry buildings can be constructed if fine-grained soil is available at the construction site. The soil is mixed with water, cement-stabilized, and then compressed in-situ by a machine to achieve a target compressive strength. A pilot project of a CEB masonry building is analyzed. It is built in Southern France in 2023, in a medium-high seismic hazard zone. The mechanical parameters of CEB and mortar are obtained by experimental tests. Whereas, the mechanical parameters of CEB masonry are obtained using homogenization formulas according to the Eurocode, considering the regularity of masonry. Even if the CEB is a promising construction material, contributing to a more sustainable building industry, the assessment of structural performance in seismic zones can limit their use. The unreinforced masonry building is modeled according to the equivalent frame (EF) approach, accepted by the Eurocode for earthquake design of buildings. Deformable macro-elements representing the wall panels are connected by rigid nodes (modeling the stiffer zones between them). The wall element response to shear, bending, and axial force is coupled according to strength domains. The intersection of strength domains gives information about the expected in-plane failure mode of the masonry panel (bending-rocking or shear mechanisms). The modal characteristics, ductility, and expected seismic performance of the CEB masonry building are investigated. An ambient vibration recording campaign is conducted in the building and the elastic building behavior, simulated using the EF model, is validated by comparing the dynamic properties obtained by numerical and operational modal analysis. Consequently, the elastic mechanical parameters of CEB masonry used in the model are validated.
[81] ID:81-Effect of Contamination Morphology on Stress Corrosion Cracking and Fatigue Life
Mustafa Elsherkisi (Cranfield Universtity), Fabian Duarte Martinez (Cranfield University), Simon Gray (Cranfield Universtity) and Gustavo Castelluccio (Cranfield University).
Abstract
Although it is well known that local contamination can accelerate the initiation and propagation of cracks, it is not well understood the role of the morphology of the contamination pattern. Indeed, most experimental approaches deposit layers of contaminants without understanding the experimental epistemic uncertainty of this approach. This work integrates models and experiments to explor the cracking of Ni base single crystal superalloys induced by salt under sulphur environments at moderate temperatures. A phase field model is implemented to understand the interaction of multiple cracks arising from the contaminant while C-ring and fatigue tests were employed to validate the analysis. The results demonstrate that multiple nucleation of cracks can be avoided by reducing the size of the contaminant. As a result, crack shielding and coalescence can be prevented, which has a significant impact on damage, including ten times longer cracks and half the fatigue life.
[83] ID:83-Viscoelastic characterization of ultrasoft material by unifying different time and length scales
Laura Ruhland (Friedrich-Alexander Universität Erlangen- Nürnberg) and Kai Willner (Friedrich-Alexander Universität Erlangen-Nürnberg).
Abstract
Contradictory mechanical responses are a persistent problem concerning experimental studies of ultrasoft materials such as brain tissue when using different testing techniques. These inconsistencies are mainly attributed to the varying testing conditions of the different techniques. Particularly challenging is the use of multiple time and length scales across the experiments. Consequently, a robust identification strategy over a wide strain and frequency range is crucial to achieve reliable mechanical, in particular viscoelastic, parameters of the ultrasoft material. The aim of this contribution is to reconcile the material parameters obtained from experiments that differ in their time and length scales. A phantom material based on oxidized hyaluronic acid (OHA) and gelatin (GEL), showing promising results to mimic the viscoelastic behavior of brain tissue, was used for the measurements. The mechanical behavior of the hydrogel was examined via two testing techniques. At a rheometer quasi-static experiments in the time domain were conducted. The measurements investigated the material behavior in compression, tension and shear. With magnetic resonance elastography the material responses in the frequency domain were obtained. A 0.5T magnet measured the vibrations induced in the material by a piezoelectric actuator. This measurement technique enables to acquire vibration data from a few 100Hz up to several kHz. Aiming at the unification of the mechanical tests in one continuum-based model, the experimental results of both testing techniques are compared by their viscoelastic parameters. The storage and loss modulus are calculated for the experimental data in the time and the frequency domain by viscoelastic standard models resulting from a combination of spring and dashpot elements.
[85] ID:85-Mechanics of architected interpenetrating phase composites: experimental, numerical and machine learning analysis results
Nikolaos Karathanasopoulos (New York University) and Agyapal Singh (New York University Abu Dhabi).
Abstract
Interpenetrating phase composites (IPCs) based on architected media allow for mechanical properties well beyond the bounds of their constituent phases. The arising mechanical response depends on a series of underlying influential design features, which include the material properties of the phases involved, their architectural design, their volume fraction, as well as loading-related parameters, such as the strain-rate of the loading. In the current contribution, extensive numerical and experimental insights on the dependence of the effective composite material performance on the aforementioned design parameters are provided, for different IPC materials that include polymer and soft matrix phase composites. The data are used as a reference for the development of dedicated tree and deep learning modelling architectures that can, not only accurately capture the effective composite performance, but also be used as surrogate models for subsequent explainability analysis tasks. In particular, dedicated high-accuracy and low computational cost machine learning models are elaborated and employed to assess the significance of the underlying influential design parameters, as well as their interaction, classifying their importance for different base material combinations and loading scenarios.
[86] ID:86-Experimental and computational analysis of magneto-mechanically induced diffusion processes in ultra-soft hydrogels
Jorge González-Rico Iriarte (Continuum Mechanics and Structural Analysis Department, Universidad Carlos III de Madrid), Sara Garzón Hernández (Continuum Mechanics and Structural Analysis Department, Universidad Carlos III de Madrid), Chad Landis (The University of Texas at Austin, Aerospace Engineering and Engineering Mechanics) and Daniel García-González (Continuum Mechanics and Structural Analysis Department, Universidad Carlos III de Madrid).
Abstract
Magneto-active hydrogels (MAHs) consist of a soft polymeric network doped with magnetic particles that confer the ability to mechanically respond to external magnetic actuation. These multifunctional properties allow to control the material's state of deformation and its properties in a remote, dynamic and non-invasive manner. Taking advantage of this high degree of control of the mechanical properties of the hydrogel, the solvent diffusion dynamics between the MAH and the aqueous medium it is embedded within can be heavily affected and controlled. These characteristics, along with the low magnetic permeability of biological tissues and the good biocompatibility of hydrogels, make MAHs excellent for their application in the biomedical field as drug delivery vessels or for the collection of liquid samples from a localized region within the human body. However, the underlying physics of the magneto-mechanical-diffusion coupled problem are highly complex [1]. This work conceptualises new biocompatible MAHs from human blood plasma, with strong magneto-mechanical actuation. The material is experimentally tested using a technological in-house device to control different states of magnetic actuation [2]: controls with null actuating fields, sustained actuations under constant fields, and several modes of dynamic actuation at different modes and frequencies. This methodology enables an efficient and deep analysis of the diffusion process under magneto-mechanical actuation. In addition, we provide a new constitutive formulation and its implementation to model the diffusion process of two different species within a magneto-responsive material. The application of this mathematical model helps in understanding the underlying physical phenomena affecting diffusion dynamics. Taking together, the experimental and computational open new exciting opportunities for the use of ultra-soft (~100 Pa) MAHs in bioengineering applications.
1- D. Garcia-Gonzalez, C.M. Landis. Journal of the Mechanics and Physics of Solids, 139:103934, 2020.
2- M.A. Moreno-Mateos, J. Gonzalez-Rico, et al. Applied Materials Today, 27:101437, 2022.
[87] ID:87-Magneto-mechanical system to evaluate mechanical and functional responses in astrocytes under alternating substrate deformation modes
Clara Gomez-Cruz (Universidad Carlos III de Madrid), Miguel Fernandez-de la Torre (Universidad Carlos III de Madrid), Dariusz Lachowski (Universidad Carlos III de Madrid), Armando del Rio Hernandez (Universidad Carlos III de Madrid), Gertrudis Perea (Instituto Cajal), Arrate Muñoz-Barrutia (Universidad Carlos III de Madrid) and Daniel Garcia-Gonzalez (Universidad Carlos III de Madrid).
Abstract
This work introduces NeoMag, a system designed to enhance cell mechanics assays in substrate deformation studies. NeoMag uses multidomain magneto-active materials and external magnetic fields to mechanically actuate the substrate, transmitting reversible mechanical cues to cells. The system boasts full flexibility in alternating loading substrate deformation modes, seamlessly adapting to both upright and inverted microscopes. The multidomain substrates facilitate mechanobiology assays on 2D and 3D cultures. In addition, the integration of the system with nanoindenters allows for precise evaluation of cellular mechanical properties under varying substrate deformation modes. The system's efficacy is demonstrated by studying the impact of substrate deformation on astrocytes, simulating mechanical conditions akin to traumatic brain injury and ischaemic stroke. The results reveal local heterogeneous changes in astrocyte stiffness, strongly influenced by the orientation of subcellular regions relative to substrate strain. These stiffness variations, exceeding 50% in both stiffening and softening, and local deformations significantly alter calcium dynamics. Furthermore, sustained deformations induce actin network reorganization and activate Piezo1 channels, leading to sustained calcium influx that inhibits calcium events. Conversely, fast and dynamic deformations transiently activate Piezo1 channels and disrupt the actin network, causing cell softening over 24 hours. These findings unveil mechanical and functional alterations in astrocytes during substrate deformation, illustrating the multiple opportunities this technology offers.
[88] ID:88-The problem of out-of-plane perturbation of a semi-infinite crack in an infinite 3D body revisited
Jean-Baptiste Leblond (Sorbonne Universite).
Abstract
The 3D problem of out-of-plane perturbation of a semi-infinite plane crack, loaded arbitrarily in an infinite elastic body, was solved by Movchan et al. His method used analytical tools specifically adapted to the infinite geometry. In contrast, the same problem is solved here using a more general approach, relying on a recent extension of the author’s of Buekner-Rice’s theory. In its original form, this theory provided the first-order expression of the variation of displacement anywhere in the body, induced by a small tangential perturbation of the crack front (lying within the local tangent plane); in its extended form, it provides the same result but for a general perturbation of the crack front and surface, involving tangential and normal components. The variation of displacement is expressed as a sum of two integrals over the crack front and surface, respectively.
The extended theory is applied to Movchan’s problem in three steps :
(1) Letting the point of observation of the variation of displacement go to the crack surface, we first get the variation of the displacement discontinuity across this surface, anywhere on it. (2) We then use Bueckner-Rice’s original theory to get the displacement discontinuity anywhere on the unperturbed surface, induced by certain point loads – whose expression is required to apply the extended theory. (3) Applying the extended theory, we finally let the point of observation of the variation of the displacement discontinuity go to the crack front, to get the perturbed stress intensity factors there.
Although the derivation involves non-trivial evaluations of certain limits of integrals, it reduces the treatment to this purely mathematical task, circumventing the search of a method of solution of the full elasticity problem implied. This makes the method versatile and potentially applicable to other cracked geometries, closer to those of actual fracture experiments.
[89] ID:89-Modulating Grain Boundary-Mediated Plasticity of High-entropy Alloys via Chemo-Mechanical Coupling
Xiao-Tong Li (Department of Mechanics, Beijing Jiaotong University, Beijing, Beijing, China), Xiao-Zhi Tang (Department of Mechanics, Beijing Jiaotong University, Beijing, Beijing, China), Ya-Fang Guo (Department of Mechanics, Beijing Jiaotong University, Beijing, Beijing, China), Haoyu Li (Department of Mechanical Engineering, University of Michigan, Ann Arbor, Ann Arbor, MI, United States) and Yue Fan (Department of Mechanical Engineering, University of Michigan, Ann Arbor, Ann Arbor, MI, United States).
Abstract
High-entropy alloys (HEAs) exhibit great promise for engineering application due to their superior mechanical property combinations. Intrinsic chemical disorder and the subsequent interfacial roughening have posed formidable challenges in elucidating the grain boundary (GB)-mediated plasticity in HEAs. Here using a self-propelling atomistic algorithm – activation relaxation technique (ART) – to probe the complex energy landscape of the CoCrFeMnNi HEAs, in conjunction with location-specific perturbations across GBs exposed to different environments, we investigate atomic-reconfiguration ensembles near GBs and their sensitivities to various chemo-mechanical conditions. Two distinct modes, collective and random, are discovered and decomposed. Their partitions are dictated by multiple factors, including the activation energy window, external mechanical loading, and local compositions at GBs. Remarkably, Fe has a disproportionately promoting effect on collective events which is immediately related to slip activities, and Fe enrichment at GB amplifies such positive effect. In stark contrast, Cr atoms suppress the emission of partial dislocations from GBs. These findings imply promising solutions – via synergistic combination of microalloying, heat treatment, and mechanical loading – to selectively trigger desired plasticity modes at needed deformation stage, and hence to achieve an enhanced tunability of HEAs' mechanical behaviors.
[90] ID:90-Development of adaptative printing parameters for enhanced productivity of L-PBF printed AlSi10Mg
Sergi Bafaluy Ojea (Leitat Technological Center), Isidre Rivero Pérez (Leitat Technological Center), Pilar Castejón Galan (Leitat Technological Center), Oscar Alonso Almirall (Leitat Technological Center), Charbell de Soto (Leitat Technological Center) and Iban Gonzàlez (Leitat Technological Center).
Abstract
Current state of the art in L-PBF printing has demonstrated a dependance of the parts density to the layer thickness being employed. This fact limits the achievable productivity of the technology due to very thin layers being needed for consolidation. In addition, the variability sources of the printing equipment, including sub-systems proximity, part region or thermal history can lead to a heterogeneous defect distribution within the parts, which are more prominent in the case of thicker layers. The objective of the present work is to develop novel adaptative printing strategies that are able to increase the quality of AlSi10Mg parts printed with 90 µm layer thickness. For this purpose, a quantification of the defects encountered through conventional printing strategies is made through microstructure and porosity characterization. In addition, process monitoring tools are employed to understand the energy being deposited. As a result, a correlation between printing parameters and part’s defects is made. Finally, and based on the observed results, an alternative 3D printing strategy consisting of variable printing parameters across the part is proposed and assessed.
[92] ID:92-Crystallographic effects on strain heterogeneity and fracture revealed by X-ray lab tomography and crystal plasticity simulations for a 6016 aluminium alloy under plane strain tension
Maryse Gille (MINES Paris, PSL University, Centre des Matériaux, CNRS UMR 7633), Henry Proudhon (MINES Paris, PSL University, Centre des Matériaux, CNRS UMR 7633), Jette Oddershede (Xnovo Technology ApS) and Thilo F. Morgeneyer (MINES Paris, PSL University, Centre des Matériaux, CNRS UMR 7633).
Abstract
Aluminium alloys are widely considered by automakers to replace steel and meet the lightweighting demand to reduce CO2 emissions. New challenges remain to optimize their formability. This work focuses on a 6016 T4 aluminium alloy and to study strain heterogeneity leading to localization and final fracture under plane strain tension as this is the most critical strain state in stamping processes. Polycrystalline effects on the strain heterogeneity are investigated thanks to correlative 3D tomography, Digital Image Correlation (DIC) techniques within the material bulk and a digital twin finite element model of the tested specimen with grain information in the 3D volume. A miniaturized plane strain tensile specimen inspired by Park et al. [1] was developed and validated using 2D DIC on the specimen surface to verify the plane strain condition. The designed specimen was then tested in situ in a lab tomograph. Initially, a non-destructive acquisition of the three-dimensional grain map in the central region was performed using Diffraction Contrast Tomography (DCT) [2]. An in situ tensile test with Absorption Contrast Tomography (ACT) was then carried out in 12 increments up to fracture. The projection-DIC technique, based on projected 3D image contrast onto a 2D plane, was used to compute the real internal strain field in the specimen bulk, revealing a heterogeneous strain field with localization bands matching the fracture location. Subsequently, 2D generalized plane strain and 3D crystal plasticity simulations were performed using the measured grain map of the specimen. Simulated and experimental results are compared to investigate crystallographic effects on strain heterogeneity. [1] N. Park et al, “A new approach for fracture prediction considering general anisotropy of metal sheets,” Int. J. Plast., vol. 124, pp. 199–225, 2020 [2] F. Bachmann et al, “3D grain reconstruction from laboratory diffraction contrast tomography,” J. Appl. Crystallogr., vol. 52, Jun. 2019
[93] ID:93-Structure-Property Relations for Semi-Crystalline iPP Polymorphs
Hans van Dommelen (Eindhoven University of Technology), Hernán Chávez Thielemann (Eindhoven University of Technology) and Leon Govaert (Eindhoven University of Technology).
Abstract
The mechanical properties of thermoplastic polymers strongly depend on processing conditions, which mainly affect molecular orientation, in the case of amorphous as well as semi-crystalline polymers. The use of orientation induced by processing is a current manufacturing trend to make products with outstanding properties. Therefore, it is of key importance to understand the relationship between microstructure, isotropic or oriented, and mechanical properties.
This work focuses on modeling concepts that capture the effects of molecular arrangements and orientation on the elasto-viscoplastic response of semi-crystalline isotactic polypropylene (iPP). The complexity of this problem lies in the polymorphic nature of iPP and the contribution of isotropic or oriented phases, both crystalline and amorphous, to the final material response. To investigate the different contributions to the total anisotropic response, a mean-field micromechanical model is used to link the structure to properties, accounting for the elasto-viscoplastic deformation of each constitutive phase and the texture evolution of the crystals. The crystalline phase is modeled with crystal viscoplasticity, and the so-called EGP model is used for the amorphous phase. The effect of anisotropy in the crystalline layer is naturally captured with the orientation distribution. The amorphous phase model was extended by combining modeling concepts developed for isotropic and oriented polymers, ending up with an anisotropic relaxation spectrum and a flow rule based on Hill’s stress.
The method is used to characterize the macroscopic response of semi-crystalline isotropic α-iPP. The response to tensile and compressive loading and the time-to-failure are well captured. The micromechanical model approach is also used to unravel the slip kinetics of β-iPP. Finally, the anisotropic version of the model is used to describe the elasto-viscoplastic behavior of an oriented film, containing mainly α crystals. The results capture the effect of loading angle and the strain rate dependence of the elastic and yield response.
[94] ID:94-Multiply scattered sound and strain in a granular suspension
Ibrahim Awada (Université Gustave Eiffel), Julien Leopoldes (Université Gustave Eiffel) and Vincent Langlois (Université Gustave Eiffel).
Abstract
Granular materials are systems for which describing mechanical properties poses a major challenge due to the complexity of their amorphous structure. The lack of knowledge on the nature of the elementary mechanisms responsible for plasticity makes the understanding of how they deform a daunting task. It is nevertheless essential to better predict landslides and earthquakes. Advanced characterization approaches, such as optics and X-ray tomography, offer the possibility to study deformation at the scale of the particle but are hampered by their complexity and long acquisition times. Characterizing the deformation of granular materials is challenging, particularly in sudden phenomena such as avalanches. In this context, scattering methods may provide complementary information to scanning methods. Namely, acoustic waves benefit from long propagation distances and are able to effectively probe in the bulk systems such as granular suspensions. Here, we study a dense granular suspension in the elastoplastic regime, inserted in a rotating drum oscillating at angles inferior to the angle of repose. To probe the structure of the suspension, some ultrasound pulses are emitted from one side of the drum and the transmitted signal is collected at the other side. Experimentally, the granular suspension compacts, leading to rearrangements of grains and modifications of transmitted ultrasound signals. In order to measure strain, we propose a new method based on the correlation of transmitted multiply scattered ultrasound waves, sensitive to volumetric deformation of 10^-5. The method can detect local strain at the scale of a few grains and can therefore be applied in systems with heterogeneous deformations.
[96] ID:96-Phase field model of chemo-electro-mechanical processes during corrosion of bioabsorbable Mg alloys for biomedical applications
Sasa Kovacevic (University of Oxford), Wahaaj Ali (IMDEA Mateirals Institute), Emilio Martínez-Pañeda (University of Oxford) and Javier Llorca (Polytechnic University of Madrid & IMDEA Materials Institute).
Abstract
Bioabsorbable Mg alloys are currently being considered for biomedical devices that gradually disappear with time and neither hinder the growth of natural tissue nor require a second surgery for removal. Degradation of bioabsorbable materials should take place at a speed compatible with the growth of natural tissue and is important to develop simulation tools to assess the evo-lution of the corrosion over time and the corresponding degradation in mechanical properties. Mg corrosion in a chlorine solution was simulated using a phase-field model that incorporates both the anodic and cathodic reactions as well as the formation and dissolution of a Mg(OH)2 passivation layer, together with the role of mechanical stresses in accelerating corrosion kinetics. To this end, the free energy functional includes the chemical, electrical, gradient and mechanical energy contributions and the motion of the solid/liquid interface is governed by the electrochem-ical reaction at the interface, following the Allen-Cahn equation. Moreover, the transport of ionic species in the electrolyte and within the passivation film follows the mass balance law, while the formation and passivation of the passivation film is also considered. The model is validated against experimental results of corrosion Mg wires in fluids with different pH and chlorine ion contents, showing the potential of this strategy to assess the degradation of Mg devices in bio-logical fluids.
[97] ID:97-Modeling the Statistical Distribution of Fatigue Crack Formation Lifetime in Large Volumes of Polycrystalline Microstructures
Tang Gu (Institute of Polytechnic Science and Aeronautics (IPSA)) and Chuan Xu (INRIA Sophia Antipolis).
Abstract
Microstructure-scale interactions involving crystallographic texture (orientation and disorientation distributions), distributions of grain shape and size, nearest neighbor grains/phases, etc. in polycrystals can be simulated using the Crystal Plasticity Finite Element Method (CPFEM). Digital statistical volume element (SVE) instantiations that comprise a significant number of grains are analyzed by CPFEM to compute fatigue indicator parameters (FIPs) which are used as surrogate measures of the driving force for fatigue crack formation within the first grain or nucleant phase. The computed maximum FIPs usually increase in magnitude with larger numbers of realistic microstructure instantiations or SVEs analyzed. This work predicts the extreme value distribution (EVD) of the maximum FIPs associated with large engineering components comprised of up to 10^8 SVEs using a recent-developed upscaling scheme, based on statistical information identified from simulations involving only hundreds of SVEs, with each SVE containing nominally 264 grains. This scheme is numerically validated by extensive simulations for samples of duplex Ti-6Al-4V microstructure models with sharp transverse texture strained in two characteristic directions. The size of the training dataset for a reliable prediction is determined for different textures and loading directions based on uncertainty analysis. Finally, the statistical distribution of fatigue crack formation lifetime (FCFL) is correlated with the EVD of the maximum FIPs, facilitating quantitative exploration of the effect of crystallographic texture and sample size on the FCFL.
[98] ID:98-Bayesian calibration of a nucleation model for ductile spalling failure
Clement Cadet (CEA DIF) and Yann Coget (CEA DIF).
Abstract
Under high strain-rate loading conditions like in plate impact experiments, material failure may happen by spallation, i.e. a damage process due to localized tensile stress states generated by interacting release waves. For ductile materials, the failure process is commonly divided in nucleation, growth and coalescence stages. A key component of the modeling of spallation is the representation of the growth stage with a Gurson-like model. Adding a description of nucleation requires determining void nucleation statistics, for instance through post-mortem microscopic observations; yet such analyses are difficult and require careful recovery of specimens. Another approach would be to directly estimate nucleation statistics from more easily available macrocopic measurements such as the evolution of free surface velocity (FSV).
We propose to calibrate three ductile failure models from plate impact experiments on tantalum using only FSV data. The first model only describes growth (with an initial porosity free parameter), whereas the two other models add nucleation, through a Weibull density describing critical nucleation stress dispersion (either with all Weibull parameters kept free for identification, or through a simplified version with some fixed parameters). A Bayesian calibration approach is used (with Openturns software), so as to quantify uncertainties for the identified model parameter values.
More precisely, for each reference experiment, a limited number of simulations with different parameters are performed using a hydrodynamical code. From the simulations, characteristic points (the first minima and maxima of the free surface velocity) are extracted, so as to train Gaussian Process metamodels. A Bayesian calibration comparing the metamodels to the experimental results, using Markov Chain Monte Carlo sampling, finally provides posterior distributions for each model parameter. The calibration results are used to assess to what extent the nucleation models can be reliably identified from pure macroscopic data.
[99] ID:99-Deformation modes and damage mechanisms of a basal-textured ZnAlMg coating under multiaxial loading
Mikel Bengoetxea Aristondo (Mines Paris-PSL University), Ahmed Zouari (Mines Paris-PSL University), Fabrice Gaslain (Mines Paris-PSL University), Kais Ammar (Mines Paris-PSL University), Samuel Forest (Mines Paris-PSL University), Vincent Maurel (Mines Paris-PSL University), Houssem Eddine Chaieb (OCAS NV), Joost De Strycker (OCAS NV) and Jean-Michel Mataigne (ArcelorMittal Global R&D).
Abstract
In this study, uniaxial tensile tests and equi-biaxial Marciniak tests were carried out to identify the deformation modes and damage mechanisms of a ZnAlMg coating (5 wt%Al and < 1 wt%Mg) deposited on a sheet of S250GD grade structural steel. The microstructure of the coating consists of dendrites surrounded by binary and ternary eutectics. As with most ZnAlMg coatings, the formability and subsequent corrosion resistance of the coating is affected by the differences in mechanical properties of these microconstituents and the different crystal orientations of the grains. Mechanical testing was executed for monotonical loading and tests were interrupted at different levels of deformation. Local strain fields were calculated by digital image correlation and related to ex-situ crack distributions at the mesoscopic scale obtained by scanning electron microscope (SEM) imaging. SEM imaging and electron backscatter diffraction (EBSD) analyses showed that strain was mainly accommodated by twinning and slip in the zinc phase, leading to dynamic recrystallisation in some locations. Three main damage mechanisms were observed: cleavage in the zinc phase, decohesion at the interface of Al-Zn eutectoid globules and cracking in MgZn2 lamellae. These tests and observations were complemented by an in-situ SEM tensile test, to understand crack propagation and activation of plasticity better. Crystal plasticity finite element simulations were carried out for a coating/substrate system, where the coating was modelled as a polycristal with a single grain in the thickness direction. Three material behaviours were considered: one for the zinc dendrites, another for the mixture of eutectics and a macroscopic elastoviscoplastic behaviour for steel. Several features of the coating microstructure, such as dendrite/eutectic ratio, grain size and basal texture, were experimentally characterised by SEM analysis. Finally, calculated twinning and slip activities, and local strain and stress fields were compared with orientation maps and crack patterns observed in the experimental tests.
[100] ID:100-Inhibition Effect of Segregation and Chemical Order on Grain Boundary Migration in NbMoTaW Multiprincipal Element Alloy
Xiao-Zhi Tang (Department of Mechanics, Beijing Jiaotong University, Beijing, Beijing, China).
Abstract
Wide-range applications of high entropy materials (HEA) requires their superior mechanical properties, which essentially relies on grain boundary (GB) stability for sustaining plastic deformation. While the fundamental mechanisms of GB migration in HEA differ from the ones in conventional materials due to lattice distortion and local chemical environments. Particularly the GB segregation in HEA always accompanies local chemical order (LCO) change. To quantificationally and efficiently investigate the impacts of solute segregation and chemical order on GB migration, we applied atomistic simulations for the NbMoTaW multiprincipal element alloy. Assisted by a contrived Nb-rich model, it is found that solute segregation and chemical order synergistically inhibit GB migration. Nb segregation increase the critical stress for GB migration, and the presence of chemical order further enhances the resistance of GB to plastic deformation. The destruction of local ordering structures is responsible for the difficult GB migration. Transition pathway analyses show that GB modified with both Nb segregation and chemical order requires high migration barrier, and the prior migration of GB sites tends to avoid regions with heavier chemical order. These results provide new insight into how chemical complexity affects elementary GB motion and contribute to manipulating the stability of MPEAs.
[101] ID:101-Surrogate modeling for computational homogenization of viscoplastic composites
Yosuke Yamanaka (Tohoku University), Shuji Moriguchi (Tohoku University) and Kenjiro Terada (Tohoku University).
Abstract
This study presents an RBF-based surrogate computational homogenization for viscoplastic composites. Recently, several surrogate models and data-driven methods have been developed to replace the classical constitutive model for history-dependent materials, such as elastoplastic and viscoplastic materials, with the help of mechanistic machine learning techniques (MMLT). Meanwhile, the application of MMLT to multi-scale problems has also been studied in order to reduce computational costs for micro-macro coupled two-scale analyses. However, to the best of our knowledge, most of those studies employ neural networks, in which the regression processes are black box-like in terms of mechanism. Against this issue, we proposed to extensively utilize radial basis function (RBF) interpolation to create a surrogate model that can be a substitute for the microscopic simulation in the two-scale analysis of viscoplastic composites. The macroscopic stress is represented by the surrogate model in consideration of the dependencies on strain rate and temperature. Also, thanks to the simplicity of RBF interpolation, we can easily understand how the macroscopic stress is regressed. The capability of the present method is demonstrated through numerical examples. First, by conducting numerical material tests (NMTs) on a representative volume element (RVE) consisting of multiple viscoplastic materials, we obtain a data set representing the macroscopic constitutive relationships for various deformation patterns. Second, a surrogate model is created by applying RBF interpolation with the data set. Third, for validation purposes, the responses of the surrogate model are compared with the results of NMT that has been performed with unseen loading and temperature histories. Finally, a macroscopic analysis is performed as online computation, followed by the localization analysis. The resulting macroscopic and microscopic responses are compared with the results of direct numerical simulations to demonstrate the validity of the present methodology.
[102] ID:102-Data-driven simulation of the inelastic behavior of open-cell foam structures
Martin Abendroth (TU Bergakademie Freiberg), Alexander Malik (TU Bergakademie Freiberg) and Bjoern Kiefer (TU Bergakademie Freiberg).
Abstract
The presentation compares two approaches for modeling the inelastic behavior of foam structures. The first approach is classical in nature, where analytical representations for the yield surface and the yield potential are used in a thermodynamically consistent modeling concept. The difficulty here is to formulate the analytical approaches. By adapting the formulation for a yield surface by Ehlers, which was originally developed for geomaterials, a very good agreement with numerically determined yield surfaces could be achieved. The parameters of the analytical yield surface can be represented as functions depending on a hardening variable. The second approach is purely data-driven and uses approximations such as bivariate splines or neural networks for the representation of yield surface and yield potential. The neural networks used are so-called feed forward networks and are used as universal approximators or regressors. The data required for the training of the neural network or the calibration of the analytical model are obtained from finite element simulations of representative volume elements of generic foam structures, whereby the stress-controlled load paths are systematically varied. The approaches used are compared in terms of their suitability, flexibility and accuracy for describing the inelastic behavior of foam structures.
[103] ID:103-Ductility limit predictions for porous materials using a damage coupled CPFEM approach
Shuai Zhou (Université de Lorraine, CNRS, Arts et Métiers Institute of Technology, LEM3, F-57070 Metz, France), Mohamed Ben Bettaieb (Université de Lorraine, CNRS, Arts et Métiers Institute of Technology, LEM3, F-57070 Metz, France) and Farid Abed-Meraim (Université de Lorraine, CNRS, Arts et Métiers Institute of Technology, LEM3, F-57070 Metz, France).
Abstract
Accurate predictions of ductility limits play a crucial role in product design and manufacturing, offering substantial cost reductions in development. In this investigation, attention is focused on the prediction of ductility limits for porous materials. Unlike previous contributions [1,2], we integrate a microscopic damage model based on thermodynamics into the crystal plasticity finite element method (CPFEM) framework in the current study. In this regard, Representative Volume Elements (RVEs) are selected to represent the porous materials at the macroscopic level and an ABAQUS Voronoi Toolbox is developed to generate these RVEs. The macroscopic behavior of these RVEs is determined from that of the constituent single crystals using the periodic homogenization multiscale scheme [1,2,3]. At the single crystal scale, the constitutive equations follow a finite strain rate-independent framework, where the damage variables are defined for each individual slip system. The plastic flow rule is governed by the classical Schmid law. The proposed model is applied to predict the ductility limits for porous materials using the Rice bifurcation criterion. The results show that the damage coupled CPFEM approach accurately predicts the ductility limits, offering valuable tools for optimizing the mechanical properties of advanced materials. REFERENCES [1] Zhu JC, Ben Bettaieb M, Zhou S, Abed-Meraim F. Ductility limit prediction for polycrystalline aggregates using a CPFEM-based multiscale framework. Int J Plast 2023;167:103671. [2] Zhu JC, Ben Bettaieb M, Abed-Meraim F, Huang MS, Li ZH. Coupled effects of crystallographic orientation and void shape on ductile failure initiation using a CPFE framework. Eng Fract Mech 2023;280:1–21. [3] Miehe C, Schröder J, Schotte J. Computational homogenization analysis in finite plasticity simulation of texture development in polycrystalline materials. Comput Methods Appl Mech Eng 1999;171:387–418.
[104] ID:104-Negative refraction in a single-phase flexural metamaterial with hyperbolic dispersion
Kim Pham (ENSTA Paris), Agnès Maurel (Institut Langevin ESPCI) and Jean-Jacques Marigo (Ecole Polytechnique).
Abstract
We analyze the band structure of a single-phase metamaterial involving low-frequency flexural resonances by combining asymptotic homogenization and Bloch–Floquet analysis. We provide the closed-form expression of the dispersion relation in the whole Brillouin zone. The dispersion relation involves two effective, frequency-dependent, mass densities associated with symmetric and antisymmetric flexural resonances of the beams at the microscopic scale. We demonstrate that our simple locally-resonant structure produces at low-frequency band-gaps and, in the hyperbolic regions of the dispersion diagram, negative refraction. Our findings are validated by direct numerical calculations.
[105] ID:105-A continuum consistent discrete particle method: phase changes and scratching of silicon
Marc Geers (Eindhoven University of Technology), Sven Sperling (Eindhoven University of Technology), Johan Hoefnagels (Eindhoven University of Technology) and Kasper van den Broek (VDL ETG Technology and Development).
Abstract
Complex deformation and fracture events are of great importance for predictive modelling of materials in various applications. Among the existing approaches, discrete particle methods are versatile tools for tracking complex and arbitrary discontinuities. Yet, the continuum consistency of existing particle methods such as the Discrete Element Method (DEM), Smoothed Particle Hydrodynamics (SPH) and Peridynamics remains problematic. To resolve this, an innovative discrete particle method is here proposed that extracts the deformation gradient tensor at each particle from the kinematics of the particle's nearest neighbours. The resulting Continuum Bond Method (CBM), fully preserves the constitutive properties of conventional continuum models. Moreover, its discreteness preserves the powerful fracture characteristics of discrete particle methods. To demonstrate the capabilities of the CBM method, two examples are analysed. The first example is an elasto-plastic tensile bar subjected to large deformations. The results are assessed in direct comparison with a FEM reference solution, confirming the achieved discrete-continuum consistency. Further comparisons are made with typical SPH results, highlighting the violations in terms of continuum consistency for the latter. The second example focuses on complex fracture capabilities, for which a dynamic crack branching problem is considered.
The methodology is next applied to the micro-scale scratching of mono-crystalline silicon, whereby pressure-induced phase transformations are taken into account. The resulting model consists of a three-dimensional LAMMPS implementation of CBM combined with a phase transformation constitutive law for silicon. Cross-sectional TEM micrographs of silicon scratched with a sharp indenter, extracted from the literature, reveal a qualitative agreement with the simulated spatial phase distribution. Next, scratch experiments with a blunt indenter are executed and the surface profiles obtained with AFM are compared to the simulated ones for varying normal scratching forces. A qualitative agreement between the experimental and numerical post-scratch surfaces in the steady-state scratching regime is thereby achieved.
[106] ID:106-Fluid-structure interaction model for hydrocephalus shunt systems
Elizabeth Hayman (Univeristy of Oxford), Pablo Sanchez Naharro (Lurtis Ltd.), Jayaratnam Jayamohan (John Radcliffe Hospital), José Maria Peña (Lurtis Ltd.), Antoine Jerusalem (University of Oxford) and Sarah Waters (University of Oxford).
Abstract
Paediatric hydrocephalus is a serious medical condition characterised by an excess of cerebrospinal fluid (CSF) in the lateral ventricles of the brain. CSF is produced by the Choroid Plexus (CP) tissue, a vascularised fin-like structure rooted to the bottom of the ventricles. A common treatment for congenital paediatric hydrocephalus is the insertion of a shunt system containing a ventricular catheter, a hollow tube with inlet holes arranged in the tube wall close to the closed tip. Shunt systems run the risk of the CP occluding the catheter holes during drainage, causing it to block and require replacement. Replacement surgery has the added risk of haemorrhage if the entwined CP tears when the blocked catheter is removed. While various catheter geometries have been proposed over the last 50 years to minimise blockage risk, there is no clear evidence of the relative efficacy of different designs. We present a computational fluid-structure interaction (FSI) model combining open-source OpenFOAM with in-house software MuPhiSim, which simulates the deformation of the CP in an idealised ventricle-catheter environment. The resulting FSI model provides a framework to test the efficacy of different catheter designs, with two catheters currently in use in clinical settings being compared. A reduction of the model to 2D – computationally far more efficient – is used for parameter sweeps over hole size and position. The results are then used to motivate candidates for new 3D designs. These geometries are simulated in the full FSI environment and shown to be an improvement on existing designs.
[107] ID:107-Mechanical metamaterials: frequency-independent enriched continua from frequency-dependent models
Gianluca Rizzi (TU Dortmund), Jendrik Voss (TU Dortmund), Svenja Hermann (TU Dortmund), Leonardo A. Perez R. (TU Dortmund), Plastiras Demetriou (TU Dortmund) and Angela Madeo (TU Dortmund).
Abstract
Mechanical metamaterials are gaining attention for their unique responses, offering novel possibilities in elastic wave control. Researchers focus on developing new unit cells that produce unconventional macroscopic responses, such as band-gaps, cloaking, and negative refraction, etc [2, 3, 4]. To model large samples, homogenisation techniques establish equivalent continuum models for macroscopic metamaterials. A common approach assumes a classical linear Cauchy continuum, considering frequency-dependent parameters to capture complex responses in the frequency domain. However, these models may exhibit negative effective masses or effective elastic coefficients near resonance frequencies, making the Cauchy continuum non-positive-definite. We propose a procedure to convert frequency-dependent models into enriched continuum models of the micromorphic type [1]. The enriched model’s parameters are constant, and the well posedness of the model is ensured across all frequencies. The work bridges upscaling techniques with the idea that micromorphic continua are suitable for modelling metamaterial responses at the macroscopic scale.
References [1] G. Rizzi, M.V. d’Agostino, J. Voss, D. Bernardini, P. Neff, & A. Madeo. From frequency-dependent models to frequency-independent enriched continua for mechanical metamaterials. To appear in European Journal of Mechanics - A/Solids (2024) [2] C. Bellis, & B. Lombard. Simulating transient wave phenomena in acoustic metamaterials using auxiliary fields. Wave Motion, 86, 175-194. (2019) [3] L. Liu, A. Sridhar, M. G. D. Geers, & V. G. Kouznetsova. Computational homogenization of locally resonant acoustic metamaterial panels towards enriched continuum beam/shell structures. Computer Methods in Applied Mechanics and Engineering, 387, 114161. (2021) [4] A. Sridhar, V. G. Kouznetsova, & M. G. Geers. Homogenization of locally resonant acoustic metamaterials towards an emergent enriched continuum. Computational mechanics, 57, 423-435 (2016)
[108] ID:108-Phase field modeling of crack propgation in heterogeneous materials: effect of the nature of the disorder.
Hervé Henry (PMC, CNRS, Ecole Polytechnique, IP Paris).
Abstract
The fracture behaviour of a material composed of spherical soft inclusions in a matrix is studied numerically. To this purpose a phase field model of dynamic crack propagation is used and the statistical nature of the disorder is varied (from a random distribution with simple hard sphere exclusion to a more uniform distribution of inclusions).
While for high speed crack propagation, effects of the nature of disorder is small, it is seen that close to propagation threshold the nature of the disorder can have significant effects: The more uniform the inclusion distribution the lower the apparent fracture energy is.
[109] ID:109-Phase-field modelling of interactions between extended defects in metals placed under extreme conditions
Antoine Ruffini (LEM (ONERA/CNRS)), Benoît Dabas (ONERA/CEA), Alphonse Finel (LEM (ONERA/CNRS)), Yann Le Bouar (LEM (CNRS/ONERA)) and Thomas Jourdan (CEA (SRMP)).
Abstract
Metals under extreme conditions (high stress, high temperature, high flux of radiations, etc.) exhibit extended defects such as dislocations and cavities whose interactions and evolution dictate the macroscopic response of the whole material. However, because of their multi-physics aspects, the underlying phenomena are difficult to characterize, either by numerical simulations or by experimental approaches. Therefore, there is a need to develop efficient and physically justified numerical tools that are able to tackle such problems.
In this work, we propose a phase-field model that couples vacancy diffusion, dislocation climb and pore evolution [1]. This model naturally accounts for the elastic interactions between the objects and guarantees through variational constraints that matter is conserved when vacancies are exchanged [2].
In a first part, we will present the model and provide some details about its numerical implementation that include an improved solver for the equation controlling the vacancy field evolution. We will show that the use of this solver drastically increases the accessible diffusion time scale, allowing us to perform efficient mesoscopic simulations. In a second part, we will validate the phase-field model by comparing numerical results of elementary systems with known analytical results. In a third and last part, we will present results from 2D-simulations of climbing dislocations interacting with an assembly of cavities, highlighting a significant role of elastic interactions on the microstructural evolution of irradiated materials.
References [1] B. Dabas. PhD Thesis of Sorbonne University, 2022. [2] P. A. Geslin, B. Appolaire, A. Finel. Applied Physics Letters, 2014, 104(1), 011903.
[110] ID:110-Stereo X Ray tomography for high temporal resolution experiments
Eric Maire (Laboratory MateIS, CNRS, INSA-LYON), Joel Lachambre (Laboratory MateIS and laMCoS, CNRS, INSA-LYON), Jerome Adrien (Laboratory MateIS, CNRS, INSA-LYON) and Gustavo Pinzon (Laboratory MateIS, CNRS, INSA-LYON).
Abstract
MATEIS Laboratory has developed the concept of a new microCT platform designed, developed and manufactured by RX Solutions. The DTHE, stating for Double Tomograph for High Energy, covers some of the lab scale current challenges. This “out of catalogue” unique piece of equipment is designed around one rotation axis and two strictly identical 300 kV Xray lines. The platform is dedicated to large samples and/or highly absorbent materials. It allows microCT scans using a spot size ranging from 4 μm to few hundreds of microns, with simultaneous or sequential acquisition, with identical or distinct resolution, with identical or distinct energy, with or without external sollicitation, etc... This presentation will first quickly describe the equipment and then show some examples of first results of in situ experiments in different scientific domains where the capabilities of the equipement is used to improve acquisition speed or image quality.
[111] ID:111-Competition between epithelial tissue elasticity and surface tension in cancer morphogenesis
Filippo Recrosi (Department of Engineering and Geology (INGEO), University of Chieti-Pescara), Antonino Favata (Department of Structural Engineering and Geotechnics (DISG), La Sapienza University, Rome), Roberto Paroni (Department of Civil and Industrial Engineering, University of Pisa) and Giuseppe Tomassetti (Department of Industrial, Electronic and Mechanical Engineering, University of Roma Tre).
Abstract
The purely-mechanical model proposed is devoted to explore the interplay between the overall elasticity of the epithelium and the surface tensions associated with its apical/basal sides (for an epithelial sheet/tube). We describe an epithelial monolayer as a thin two-dimensional entity endowed with bulk and surface energy on its apical/basal sides. The interplay between these energetic components characterizes the model: the former favors an undeformed state, while the latter induces bending when there is an imbalance in apical/basal energies. Employing dimension reduction, based on kinematic Ansatz, we simplify the model to a one-dimensional representation of a nonlinear elastic rod. The equilibria of this rod are determined by the competition among the aforementioned energetic contributions. Once the apico-basal tension imbalance overcomes a critical threshold, a subcritical bifurcation appears, leading the epithelium to assume its characteristic folded configuration which is observed in normal conditions. More in details, two dimensionless key parameters, γ and σ (the critical load), are introduced: γ gauges the relative importance of surface energy compared to bulk energy, while σ measures the imbalance between apical and basal tensions. As γ increases, surface energy becomes more influential, causing the shortening of the apical and basal sides and an increase in thickness. A rise in σ promotes curved configurations. Through an asymptotic analysis employing the Lyapunov–Schmidt decomposition method, we discover that the bifurcation is subcritical, a finding corroborated by our branches numerical continuation [1]. Moreover, our model predicts a distinctive mechanical behavior for pre-cancerous cells: cells in the pre-tumoral state exhibit reduced stiffness compared to their healthy counterparts [2]. By using data from Messal et al. (2019), we estimate softening in pre-tumoral pancreatic Neoplasia. These findings are also in accordance with elastographic measures.
References [1] Favata,A., Paroni,R., Recrosi,F. & Tomassetti,G. (2022), IJES, 176, 103677 [2] Favata,A.,Paroni,R.,Recrosi,F. & Tomassetti,G. (2022), Mech.Res.Commun., 124, 103952
[112] ID:112-Experimental screening of mechanical and corrosion behavior as well as biocompatibility of Zn alloys for biomedical applications
Guillermo Domínguez López (IMDEA Materials Institute, Polythechnic University of Madrid), Paul Luis Williams (IMDEA Materials Institute), Javier Llorca (IMDEA Materials Institute, Polythechnic University of Madrid) and Mónica Echeverry-Rendón (IMDEA Materials Institute).
Abstract
This study explores the potential of biodegradable zinc (Zn) alloys to minimize the need for second surgeries in cardiovascular and bone implants. With a degradation rate in between the ones of magnesium and iron, our research aims to enhance Zn’s biological and mechanical properties through alloying. Twenty-one Zn alloys, manufactured using casting methodology, underwent thorough scientific screening. Six were binary alloys with a 0.8% wt of alloying element, Mg, Fe, Mn, Ca, Cu and Sr. The remaining materials were ternary alloys with 0.8% wt for the first alloying element and 0.5% wt for the second. Microstructural analysis employed scanning electron microscopy (SEM), energy dispersed X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Results revealed a homogenized structure for the alloys with Mg, Mn and Cu, supported by superior mechanical performance. ZnMg alloy increased hardness by 53.7%, ZnMn by 78.7%, and ZnCu by 49.7%. Ternary alloys, such as ZnMgFe (168.2 %), ZnMgMn (143.3%), and ZnMgCu (141.2%), also exhibited improved mechanical properties over c.p. Zn. Electrochemical tests demonstrated reduced corrosion rates for the alloys compared to c.p. Zn, with values around 0.05 mm/year versus 0.15 mm/year for pure Zn. In the final screening stage, selected materials underwent biological characterization through cell viability assays with osteoblasts and endothelial cells. ZnMgFe, ZnMgMn and ZnMnFe emerged as promising for cardiovascular applications, showing no cytotoxicity with endothelial cells. For osteoblasts, ZnMn, ZnMgMn and ZnMnFe reduced the cytotoxicity of c.p. Zn. In summary, the alloyed Zn materials presented in this study demonstrate enhanced mechanical properties, reduced corrosion rates, and promising biocompatibility, suggesting their potential for advanced cardiovascular and bone implant applications.
[114] ID:114-Experimental and numerical investigations of structural inhomogeneity of pharmaceutical compacts
Gweni Alonso Aruffo (Institut Clément Ader, IMT Mines Albi), Driss Oulahna (RAPSODEE, IMT ines Albi) and Abderrahim Michrafy (CNRS, IMT Mines Albi).
Abstract
Powder compaction is widely used in several industrial fields. This forming process is particularly useful to produce complex net shaped compacts. However, the final structural homogeneity of the compact is, among others, dependent on the material behavior, the complex geometry of the punches used, and the wall friction. Understanding of the development of stress and relative density fields in compaction process is thus a crucial step for improving product quality. The aim of this study was to develop a continuum modelling of pharmaceutical powder compaction process to predict structural inhomogeneity of the compact not only due to wall friction but also to the non-uniform applied pressure linked to the embossed punch surface. The development was applied to special configurations in which the upper and lower punch are identically designed with two or multiple deep trapezoidal grooves. The modelling ambition was to capture the density gradient in between opposite grooves, which was suspected as responsible of the compact damage during the unloading. The powder behaviour was described in the framework of porous mechanics using the phenomenological model of Drucker Prager Cap (DPC) in which material parameters are density dependent and have been determined by means of diametral and uniaxial failure tests and compaction trials in instrumented die. Simulations of the loading and unloading were performed in 2D plane strain using a finite element method and an explicit integration incorporated in the Abaqus software. Predictions of the density gradient between the opposite grooves were validated using X-ray tomography analyses. Results showed a good agreement between predictions and X-ray tomography measurements. They showed also that the multiple grooves promoted more the structural homogeneity of the compact.
[115] ID:115-3D printed polymers by photopolymerization: link between resin chemistry, printing parameters and mechanical properties
Laura Schittecatte (Université Paris‑Saclay, CEA, CNRS, NIMBE, LIONS), Valérie Geertsen (Université Paris‑Saclay, CEA, CNRS, NIMBE, LIONS), Daniel Bonamy (Université Paris-Saclay, CEA, CNRS, SPEC, SPHYNX), Patrick Guenoun (Université Paris‑Saclay, CEA, CNRS, NIMBE, LIONS) and Thuy Nguyen (Léonard de Vinci Pôle Universitaire).
Abstract
3D printed polymer materials present a growing interest in a number of fields including aerospace, energy, construction industries, as well as bioengineering applications [1]–[3]. While conventional molded or extruded polymer materials are well known and characterized via standardized procedures, this is not the case for 3D printed polymers. More precisely, it is of prime importance to better understand the influence of the 3D photopolymerization process and resin chemistry on the final mechanical properties of the object [4]. In our work, we formulated in-house acrylate resins with controlled resin chemistry. The resin physico-chemical properties and their printability were fully characterized. In particular, we investigated the influence of the nature of the acrylate monomer on the resin properties. Besides, after successful printing, the resin mechanical properties were investigated via Dynamic Mechanical Analysis (DMA) in flexion to determine the elastic modulus of the final materials. The results were compared to a molded analog acrylic polymethyl methacrylate (PMMA) and to commercial resins. We observed that by tuning the resin formulation and optimizing the printing process, it is possible to achieve PMMA-like stiffnesses with 3D printed pure acrylate resins. A statistical analysis was also performed, revealing a greater dispersion of the results in terms of reproducibility for 3D printed materials (both commercial and formulated resins) with respect to that in molded PMMA. However, our homemade resins have a lower dispersion than commercial resins, which underlines the importance of controlling both resin chemistry and printing parameters.
References: 1. Zhang, F. Addit. Manuf. 48, (2021). 2. Zhang, J., Int. J. Bioprinting 6, 12–27 (2020). 3. Al Rashid, A., Processes and applications. Addit. Manuf. 47, 102279 (2021). 4. Schittecatte, L., MRS Commun. 13, 357–377 (2023).
[116] ID:116-FFT-based methods for data reduction and modelling of micromechanical experiments for advanced characterization of metals
Ricardo Lebensohn (Los Alamos National Laboratory).
Abstract
Crystal plasticity (CP) is extensively used to model microstructure-sensitive mechanical response of polycrystalline metals. Fast Fourier Transform (FFT)-based methods are attractive due their higher efficiency compared with CP-Finite Elements, and their direct use of voxelized microstructural images. In this presentation, we will report recent advances in the integration of FFT-based formulations with advanced characterization techniques, both for micromechanical modelling and for improved data reduction. Specifically, we will show: a) applications of the large-strain elasto-viscoplastic FFT-based (LS-EVPFFT) model [1] to interpret micromechanical characterization in nano-metallic laminates, including the formation of localization bands observed in nano-pillar experiments, and b) a novel FFT-based methodology to impose micromechanical constraints to arbitrary voxelized stress fields obtained by x-ray diffraction [2]. The proposed stress filtering method consists in finding the equilibrated stress field closest to a non-equilibrated field, posed as an optimization problem. References: [1] M. Zecevic., R.A, Lebensohn R.A., L. Capolungo, Non-local large-strain FFT-based formulation and its application to interface-dominated plasticity of nano-metallic laminates. JMPS 173, 105187 (2023). [2] H. Zhou, R.A. Lebensohn, P. Reischig, W. Ludwig, K. Bhattacharya, Imposing equilibrium on measured 3-D stress fields using Hodge decomposition and FFT-based optimization. Mechanics of Materials 164, 104109 (2022).
[117] ID:117-Hydrogen-assisted fatigue damage modeling using phase field method
Shaymaa Merheb (IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Materials and Processes, F-59000 Lille, France), Dmytro Vasiukov (IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Materials and Processes, F-59000 Lille, France), Modesar Shakoor (IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Materials and Processes, F-59000 Lille, France), Salim Chaki (IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Materials and Processes, F-59000 Lille, France), Daniella Guedes Sales (CETIM, Centre Technique des Industries Mécaniques, 44308 Nantes, France), Philippe Rohart (CETIM, Centre Technique des Industries Mécaniques, 60300 Senlis, France) and Samir Assaf (CETIM, Centre Technique des Industries Mécaniques, 60300 Senlis, France).
Abstract
It is impossible to underestimate the importance of hydrogen, especially renewable hydrogen, in the energy transition. Despite the huge potential and rising demand for renewable hydrogen, there are significant challenges that need to be overcome. One specific problem is the use of metallic equipment for high-pressure hydrogen gas applications (pressure vessels, transport networks...). These components are susceptible to hydrogen embrittlement, a phenomenon that can lead to structural degradation and severe damage. The effects of hydrogen embrittlement present a significant risk since they may shorten the life of these structures and affect their reliability and security. Therefore, the development of a numerical model to validate the design of hydrogen related systems is critical for addressing the massive industrial challenge and scientific obstacle. In this context, this study consists in developing a finite element (FE) model based on the phase field theory for hydrogen assisted fatigue. The phase field theory has recently gained a big popularity in the scientific community due to its ability to model initiation and propagation of cracks and to facilitate the integration of complex physics. In this work, the phase field theory was extended to model hydrogen embrittlement and fatigue. The FE tool thus developed integrates both mechanical modeling of the stress and strain fields, phase field modeling of damage and cracking, and modeling of the local hydrogen concentration and its evolution. Knowing that the mechanical response of the structure is sensitive to the hydrogen pressure and the loading frequency applied, different cases of applications were investigated by varying these two parameters at room temperature. Moreover, the model was employed to capture crack interaction with other defects. In this presentation, these different aspects of the FE model will be detailed as well as the different case studies that will demonstrate the capabilities of the FE simulation tool.
[118] ID:118-On the connection between cellular design, defects, and fatigue performance in additively manufactured metamaterials
Daniel Barba (Universidad Politécnica de Madrid), Antonio Vázquez-Prudencio (Universidad Politécnica de Madrid), Sergio Perosanz (Escuela Técnica Superior de Ingeniería Aeronaútica y del Espacio (ETSIAE)) and Conrado Garrido (Universidad Politécnica de Madrid).
Abstract
The development of architected metallic metamaterials produced through additive manufacturing has introduced a vast array of properties beyond those observed in traditional bulk alloys called to revolutionise multiple critical sectors like the aerospace or biomedical. However, the intricate geometries and high surface-to-volume ratio inherent in these architected metamaterials, coupled with the surface characteristics derived from the additive manufacturing (AM) process, give rise to a more complex fatigue behavior when compared to conventional bulk alloys. This complexity poses a significant challenge in the technological application of architected AM materials.
This research addresses this issue through a systematic multiscale study that investigates the interconnection between metamaterial design, defects, and fatigue behavior through the combination of experimentation and modelling. The base material used is a commercial aluminum alloy, AlSi10Mg, processed through selective laser melting. The study employs a combination of fatigue experimentation, computational modeling, and defect identification to analyze the impact of processing conditions and design geometry on microstructural defects and surface quality. By systematically connecting these factors with the fatigue life of the metamaterials, the research aims to provide insights that can help mitigate the challenges associated with the fatigue behavior of metamaterials. The results show the importance of neglecting at the design stage the strut geometrical deviations, broken struts, and porosity in the overestimation of the fatigue performance and how these defects are produced by large unsupported elements and small feature sizes. Ultimately, this work seeks to set the path to enhance the reliability and performance of architected metallic metamaterials, addressing concerns and advancing their potential for use in various technological applications.
This work has received funding from Proyecto PID2020-116440RA-I00 financed by MCIN/AEI/10.13039/501100011033.
[119] ID:119-Multiphysics and Multiscale Simulation of Cold Spray Additive Manufacturing
Jiashuo Qi (Alliance Sorbonne Université, Université de Technologie de Compiègne), Rija Nirina Raoelison (Université de Technologie de Belfort-Montbéliard) and Mohamed Rachik (Alliance Sorbonne Université, Université de Technologie de Compiègne).
Abstract
The field of additive manufacturing (AM) has evolved significantly over the past decades, notably through systematic numerical modeling efforts, with the aim of manufacturing complex structural parts with good control precision, virtually unlimited design freedom, improved and even locally variable properties. Numerical modelling has become a decision-making tool for revealing the complex process-structure-property-performance relationships in cold spray (CS) process. It is used to speed up the development and qualification of CS coating, CSAM and CS repair techniques. The objective of this work is to investigate high-fidelity modelling and simulation of multiple physical phenomena (fluid dynamics, heat transfer, particle dynamics, non-equilibrium transformations and material behavior) involved in CSAM process. A good understanding of these phenomena is a key factor for predicting the optimal process parameters, the suitable microstructure and improving mechanical properties under different impact conditions. The adopted strategy consists in integrated Multiphysics, multiscale computational model (IMMCM) with four main ingredients: 1. Computational fluid dynamics (CFD) simulation for a high-pressure nozzle with axial powder injection including supersonic gas flow, particle acceleration, particle trajectory and heat transfer 2. Meso-scale finite element method (FEM) and atomic-scale molecular dynamics simulation for single particle impact behavior and interfacial bonding characteristics 3. Meso-scale FEM simulation of multi particle-substrate impact behavior and part build-up using coupled eulerian-lagrangian technique to predict surface morphology and porosity 4. A quantitative understanding of the microstructural evolution, damage initiation of cold sprayed deposit materials using physically dislocation density-based computational microstructural modelling, combining experimental investigations and validation efforts, taking into account topological effects on phase distribution for CSAM optimization. The developed model is combined with experimental investigations to contribute to a good understanding of the mechanisms that take place during the process. The obtained results pave the way to establishing a correlation between the process parameters and the state of the material
[121] ID:121-Testing and phase-field modeling of fracture in Al2O3/Cr and Al2O3/AlSi12 metal-matrix composites under quasi-static and dynamic loads
Hossein Darban (Institute of Fundamental Technological Research, Polish Academy of Sciences), Kamil Bochenek (Institute of Fundamental Technological Research, Polish Academy of Sciences), Witold Węglewski (Institute of Fundamental Technological Research, Polish Academy of Sciences), Ivo Dlouhý (Institute of Physics of Materials, Czech Academy of Sciences) and Michał Basista (Institute of Fundamental Technological Research, Polish Academy of Sciences).
Abstract
Metal-ceramic composites represent advanced materials that combine the hardness of ceramics with the strength and toughness of metals, resulting in high stiffness, wear resistance, and thermal properties. They find applications as structural materials in the aerospace, automotive, and energy sectors, where they are often subjected to severe quasi-static and dynamic loads. Employing phase-field modeling to homogenized domains characterized by effective mechanical properties serves as a solution to avoid the computational costs and limitations associated with modeling real microstructures in metal-ceramic composites. However, determining the appropriate length scale parameter is crucial for successful implementation.
Following [1], this study aims to propose an experimental approach for establishing a physically meaningful length scale parameter in the phase-field modeling of quasi-static and dynamic fracture in metal-ceramic composites with brittle or ductile matrices. To accomplish this objective, a series of quasi-static and dynamic fracture tests are performed at room temperature using a 50J instrumented impact pendulum. The tests involve three-point bending on mode I and mixed-mode I/II V-notched specimens made of Al2O3/Cr and Al2O3/AlSi12 composites. The Al2O3/Cr samples exhibit brittle fracture behavior, while the Al2O3/AlSi12 samples show ductile fracture behavior. Detailed studies of the fracture surfaces are conducted to identify fracture micromechanisms in the investigated composites and measure the length of the fracture process zone or the stretching zone ahead of the initial crack tip. The length scale parameter in the phase-field modeling is then set equal to the measured length.
The fracture toughness is determined from the phase-field simulations by fitting the numerical load-displacement curves to the experimental data. The numerically and experimentally determined fracture toughness values are compared to validate the proposed method for the experimental determination of the phase-field length scale parameter.
[1] Darban H., Bochenek K., Węglewski W., Basista M., Metallurgical And Materials Transactions A, Vol. 53, p. 2300–2322, 2022.
[122] ID:122-Collapse of hierarchical honeycombs with sandwich-structured cell walls
Omar El Khatib (Khalifa University) and Andreas Schiffer (Khalifa University).
Abstract
Structural hierarchy in honeycombs is a design scheme that introduces geometrical complexities at different length scales, which in turn influence the mechanical behaviour by altering the unit cell mechanics. One way to realize a hierarchical honeycomb is to replace the monolithic cell walls with sandwich-structured walls with enhanced mass-specific properties. The effective elastic properties of such type of honeycombs, also known as sandwich-structured honeycombs (SSHC), were recently investigated [1], revealing great enhancements in the in-plane stiffness as compared to monolithic honeycombs of equal weight. Building on that knowledge, we present an analytical model of the in-plane compressive strength of SSHCs considering four distinct collapse modes: face yielding, core shear, elastic buckling and face wrinkling. Closed-form expressions of the collapse stress were derived in uniaxial, biaxial and shear loading cases, and collapse mechanism maps were constructed for a wide range of architectural parameters. The latter maps showed dominance of the core shear mode followed by face yielding over a practical design space encompassing a broad range of core and face sheet thickness ratios. Numerical simulations and experimental findings were compared to the results predicted by the analytical model, showing good agreement in terms of collapse load and mechanism. The results also showed that the incorporation of sandwich-structured cell walls is an effective strategy for enhancing the compressive strength of honeycomb structures, reporting enhancements in the collapse stress by factors of 4-20 when compared to conventional honeycombs with monolithic cell walls of equal weight. REFERENCES [1] El Khatib, O., Kumar, S., Cantwell, W.J. and Schiffer, A., 2023. Effective Elastic Properties of Sandwich-Structured Hierarchical Honeycombs: An Analytical Solution. International Journal of Mechanical Sciences, p.108883.
[124] ID:124-Multiscale analysis of the dynamic behavior of additively manufactured Ti6Al4V architected metamaterials
Andrea Cardeña Díaz (Universidad Politécnica de Madrid), Rafael Sancho Cadenas (Universidad Politécnica de Madrid), Francisco Gálvez Díaz-Rubio (Universidad Politecnica de Madrid) and Daniel Barba (Universidad Politécnica de Madrid).
Abstract
Additive manufacturing (AM) enables the creation of intricate, customizable geometries such as cellular lattices with customizable mechanical behavior. This method results in materials with unprecedent properties, reduced waste, minimized economic impact and shorter manufacturing durations. This is particularly the case for new high-energy absorption metamaterials for dynamic applications.
However, there are still gaps in knowledge around the effect of cell design, processing defects and dynamic behavior of cellular lattice materials. Understanding the effects of lattice architecture and processing on the mechanical behavior under high strain rates is crucial for enhancing the energy absorption of these cellular materials under extreme conditions.
This study investigates the dynamic behavior of Ti6Al4V cellular lattice structures manufactured through Laser Powder Bed Fusion (LPBF) from a multiscale approach: from the high strain rate behavior of their individual strut elements to the overall macroscopic dynamic behavior of the architected lattice. The technique used is the Split Hopkinson Pressure Bar technique. Design and processing variables like strut diameter and printing orientation are accounted for.
The research highlights a strong correlation between strut diameter, printing orientation, dynamic strength, toughness, and failure mode both within the lattice structures and the elemental struts. For single elemental struts, observations indicate that smaller strut diameters lead to increased strength but reduced ductility and energy absorption. Regarding the printing orientation, the study shows a general drop in mechanical properties as the printing angle tilts. For the case of the macroscopic behavior of lattices, dynamic tests reveal an enhanced energy absorption in lattices with larger strut diameters but a more ductile fracture mode with increased homogeneous deformation across all the struts for smaller diameters.
Grant PID2020-116440RA-I00 funded by MICIU/AEI/10.13039/501100011033. Grant EQC2019-006491-P funded by MICIU/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”. Grant PRE2021-097388 funded by MICIU/AEI/10.13039/501100011033 and by “ESF+”.
[125] ID:125-Ductile fracture of materials with randomly distributed defects
Clément Cadet (Mines Paris PSL CNRS) and Samuel Forest (Mines Paris PSL CNRS).
Abstract
The determination of the onset of void coalescence is critical to the modelling of ductile fracture in metallic alloys. Most numerical models rely on analyses of single defect cells, and therefore underestimate the void interactions. This study provides an analysis of the response of microstructures with random distributions of voids to various loading conditions.Cells embedding a random distribution of identical spherical voids are generated within an elastoplastic matrix and subjected to a macroscopic loading with constant stress triaxiality and Lode parameter under periodic boundary conditions in finite element simulations. The strain field developing in random microstructures and the one in unit cells are shown to feature distinct dependencies on the Lode parameter L owing to different failure modes. The cell may fail in extension (coalescence) or in shear. Moreover the random void populations lead to a significant dispersion of failure strain, which is present even in simulations with high numbers of voids. Strain localization is detected in the simulations using Rice’s criterion computed at the cell level. This criterion is shown to capture the onset of localization and the type of failure mode, either extension or shear banding. Moreover, the influence of the loading orientation, i.e. the orientation of the principal axes of the applied stress tensor with respect to the microstructure cube, is systematically studied. Significant anisotropy of failure behavior is observed, especially in the case of single void unit cells, which can be attributed to the intrinsic anisotropy of the simulation cells. Finally minimal failure strain values at localization with respect to all loading orientations are found. A zone of reduced ductility is observed under generalized shear loading conditions [1]. [1] C. Cadet, J. Besson, S. Flouriot, S. Forest, P. Kerfriden, L. Lacourt, V. de Rancourt, Journal of the Mechanics and Physics of Solids 166, 104933, 2022. doi:10.1016/j.jmps.2022.104933
[126] ID:126-Experimental characterisation and modelling of electrospun biomedical fibres
Thales Zanetti Ferreira (Oxford University), Pierre-Alexis Mouthuy (Oxford University) and Laurence Brassart (Oxford University).
Abstract
Electrospinning is a simple yet robust method for fabricating biomedical fibres by stretching a charged viscoelastic polymer solution using an electric field. During electrospinning, fibres in the micro- to nano-scale range are continuously deposited onto a collecting device leading to an interconnected non-woven mesh. Traditionally, meshes are generated by collecting fibres using plates, drums, bars, discs, and funnels, however these are limited in their ability to scale-up production for commercial applications. In recent years, Mouthuy and collaborators have developed a new automated technique in which fibres are deposited onto a continuous guiding wire to produce electrospun filaments. The filaments can further be processed into braided structures with tailorable mechanical properties, which can be used as scaffold for tissue engineering applications such as tendons and ligaments repair. However, the mechanical and degradation behaviour of this novel biomaterial scaffold has not been characterised.
In this work, we characterise the mechanical properties of electrospun polycaprolactone (PCL) filaments through experimental tests and constitutive modelling. Uniaxial monotonic, cyclic, and stress relaxation tests were conducted, along with (in-situ) SEM characterisation of the porous microstructure. Experimental results reveal that filaments exhibit viscoelastic-viscoplastic behaviour with pronounced post-yield hardening at large deformations, which correlates with the straightening of the fibres at the microscale. Our study also emphasises the role of the testing grips (screw-side or bollard grips) on the apparent material response. A large-deformation viscoelastic-viscoplastic phenomenological model was developed, which can successfully capture the material response up to large strains. Micromechanisms underpinning the macroscopic response are discussed.
[127] ID:127-Ultra-miniaturised fracture toughness testing of nanostructured tungsten films in the context of nuclear fusion
Salah Eddine Naceri (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium), Sahar Jaddi (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium), Michaël Coulombier (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium), Morgan Rusinowicz (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium), Laurent Delannay (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium), Nicolay Tumanov (Chemistry department, Université de Namur, Rue de bruxelles 61-5000 Namur, Belgique) and Thomas Pardoen (WEL Research Institute, avenue Pasteur, 6, 1300 Wavre/IMMC, UCLouvain, 1348 Ottignies-Louvain-la-Neuve, Belgium).
Abstract
In the context of Euro fusion structural integrity assessment of the fusion materials, the mode I fracture toughness of nanostructured freestanding tungsten thin films is investigated using the ultra-miniaturized crack-on-chip (COC) method. A MEMS-based process has followed to create on-chip test structures involving an actuator undergoing large tensile stresses and a notched specimen beam. Upon release from the substrate, the actuator applies a pulling force to the specimen. A crack initiates, propagates and arrests. Tungsten films with a 370 nm thickness were deposited using the DC magnetron sputtering under different deposition conditions. The films were characterised using grazing Incidence X-ray diffraction (GIXRD), surface curvature measurements, scanning electron microscope (SEM), and nano-indentation. The microstructure evolution, phase development, residual stress, and mechanical properties were explored to confirm the BCC α-phase similar to the bulk tungsten. Subsequent annealing was also applied to reduce the internal stresses of the selected W films in order to enhance the mechanical stability with respect to the cracking test method. The fracture toughness of the W thin films was assessed on-chip using a combination of scanning electron microscope (SEM) observations to measure the arrest crack length and finite element modelling (FEM) to extract the critical stress intensity factor KIc. The analysis was conducted on 90 successful test structures, resulting in an average fracture toughness value of 3.03 ± 0.64 MPa √m. This value is about 50 % of the fracture toughness of bulk tungsten recorded at room temperature, despite the film having a submicron thickness. This indicates the potential of this approach to provide valuable information about the fracture toughness of tungsten under irradiation.
[128] ID:128-Flexible strain-gradient crystal plasticity models : towards comprehensive modeling of size effects.
Yaovi Armand Amouzou-Adoun (Arts et Metiers Institute of Technology, CNRS, Université de Lorraine, LEM3, F-57000 Metz, France), Mohamed Jebahi (Arts et Metiers Institute of Technology, CNRS, Université de Lorraine, LEM3, F-57000 Metz, France), Samuel Forest (Mines Paris, PSL University, Centre des matériaux (CMAT), CNRS UMR 7633, BP 87, 91003 Evry, France) and Marc Fivel (Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMaP, F-38000 Grenoble, France).
Abstract
Recognizing the significance of Geometrically Necessary Dislocations in modeling size effects, kinematic hardening has been incorporated into higher-order Strain Gradient Crystal Plasticity (SGCP) through two separate approaches. The proposed models are based on the decomposition in series of the gradient of the plastic slip which helps modeling higher-order dissipation while avoiding the production of elastic gaps [1] as found with the original Gurtin approach. The first model involves multiple decomposition of the gradient of the plastic slip into reversible and dissipative parts resulting in a kinematic stress that equals the sum of various stresses. This theory is linked to the kinematic hardening modeling approach of Chaboche. The second model employs only one serial decomposition but includes a higher-order Prager kinematic hardening, which depends on the dissipative part. A shared characteristic of these models is the use of less-than-quadratic defect energy as there is no experimental evidence to support the classical quadratic form. In this study, the SGCP formulations introduced, aim to replicate size effects observed with Discrete Dislocation Dynamics under 2D shear loading. More specifically the focus is put on strengthening and the uncommon Asaro’s type III kinematic hardening. In the continuum formalism, the later observation is purely the outcome of a non-quadratic form of the defect energy. The proposed models are then used to investigate size effects experimentally observed by Zhang et al. [2] in combined bending-torsion of a FCC single crystal.
[1] Y. A. Amouzou-Adoun, M. Jebahi, M. Fivel, S. Forest, J. S. Lecomte, C. Schuman, and F. Abed-Meraim. On elastic gaps in strain gradient plasticity: 3D discrete dislocation dynamics investigation. Acta Materialia, 252:118920, 2023. [2] B. Zhang, K. L. Nielsen, J. W. Hutchinson, and W. J. Meng. Toward the development of plasticity theories for application to small-scale metal structures. Proceedings of the National Academy of Sciences, 120(44):2017,2023.
[129] ID:129-Particular risk assessment and subsequent shielding: Numerical validation of promising concepts
Roland Ortiz (ONERA), Jeremy Germain (ONERA) and Gerald Portemeont (ONERA).
Abstract
Objective of this work is to identify potential safety issues related to uncontained engine installation and to evaluate the impact on aircraft design. A careful assessment of the certification specifications relating to propeller installation is therefore carried out. To identify the safety issues, it is required to do an analysis to evaluate the area and danger of propeller debris impact.
The results of this analysis will be used to identify modifications to the aircraft design and to evaluate the weight increase due to debris shielding addition. New materials (composite, hybrid) are considered in shielding application vs a fuselage made out of aluminium. A summary presentation of the most promising material is presented to see/conclude on the utility of them for the reinforcement of structures submitted to high impact as blade release with high energy. Each material is regarding: potential for the shielding function, the manufacturability, the expected development effort regarding design, the simulation possibilities and the feasibility/viability of the concept. Thus, an approach with added patches on conventional structure seems to be the best compromise regarding mass, cost, manufacturing and integration aspect. Numerical simulations [10] based on a mesoscopic approach (modelling of plies and potentially delaminating interfaces) provide a detailed analysis of the consequences of a high-speed impact on a shielding-type material. However, they remain too costly for a shielding evaluation study.
This is why ONERA has decided to develop the following computational strategy: - A numerical homogenization approach is used to represent any type of potential shielding material, and more particularly shielding with laminates or woven architectures that could be found in patch form. - An optimization strategy to determine the required mechanical properties and orientation of plies and woven to absorb the impact energy providing from a blade release. A strategy of optimization is presented for shielding evaluation.
[130] ID:130-Influence of processing defects on the mechanical performance of additively manufactured titanium cellular materials
Conrado Garrido (E.T.S de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid), John Orbell (Department of Engineering Science, University of Oxford), Roger C Reed (Department of Engineering Science, University of Oxford), Enrique Alabort (Alloyed Ltd.) and Daniel Barba (E.T.S de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid).
Abstract
The integration of additive manufacturing (AM) and architected lattice structures has sparked significant scientific interest and excitement in the materials field. This innovative approach allows for the creation of custom cellular metamaterial components, introducing a new realm of lightweight, functional, and efficient structures that hold the potential to revolutionize various industries, including biomedicine, aerospace, and energy production.
Despite remarkable progress in metal AM technology, there are still challenges related to the processing and manufacturability of lattice structures. Processing defects that emerge during manufacturing can have a profound impact on the mechanical behavior of cellular materials, and these effects are not yet fully understood. The dependencies of these defects on unit cell design and printing size remain unclear and usually overlooked during the component design phase.
This work aims to address these challenges by employing a comprehensive approach that combines mechanical experimentation, material characterization, and computational modeling across various scales relevant to the problem. The study uses Ti6Al4V as the base material and selective laser melting as the AM technology. Three different cellular designs and three distinct strut thicknesses are employed to investigate the influence of both cell geometry and strut thickness on the manufacturing accuracy and mechanical performance of cellular materials.
The assessment of manufacturing accuracy begins with 3D surface comparison using X-ray tomography. Subsequently, mechanical performance experiments are conducted on the cellular materials. Computational models are then employed to establish connections between cellular design, relative density, the occurrence of defects, geometrical deviations, and mechanical performance of the lattice structures.
The findings of this research underscore the critical importance of incorporating defects and manufacturing deviations into the metamaterial design process. By doing so, a more reliable mechanical framework for the design of metamaterial components has been achieved.
This work has received funding from Proyecto PID2020-116440RA-I00 financed by MCIN/AEI/10.13039/501100011033.
[131] ID:131-Investigation of mechanical dissipation effects during cyclic nanoindentation of thermally aged filled elastomer networks
Florian Feyne (Institut PPrime), Eric Le Bourhis (Institut PPrime), Florian Lacroix (Université de Tours), Laurence Autissier (CEA, DAM, Le Ripault) and Olga Smerdova (Institut PPrime).
Abstract
Filled elastomer networks are reported to dissipate energy when subjected to cyclic tension or compression tests. Mullins effect is considered the main contributor to this dissipation during the first loading-unloading cycle. At the same time, other mechanisms, such as damage, viscosity, and strain-induced crystallisation, contribute to the long-term energy dissipation. A recent study attributed the Mullins effect to the covalent bond scission in filled silica polydimethylsiloxane (PDMS) using mechanoluminescent cross-linkers during cyclic uniaxial tests. In contrast, little work has been reported on the cyclic response at the micrometre scale, particularly in silica-filled PDMS. In this presentation, we use cyclic nanoindentation tests to study the mechanical behaviour of room-temperature vulcanised (RTV) PDMS at a small scale. Its mechanical behaviour under cyclic uniaxial tensile tests is also investigated. The considered RTV PDMS is filled with SiO2 (50phr) and CaCO3 (10phr). Moreover, the samples are thermally aged between 30°C and 70°C from 10 to 300 days. The dissipative work is quantified as the hysteresis between loading and unloading cycles. Additional stress relaxation tensile tests have been performed to discriminate viscoelastic relaxation and Mullins behaviours during unloading phases, as they are likely to simultaneously contribute to this energy dissipation. The results of tensile tests show negligible viscoelastic relaxation while the Mullins effect is dominant. The above result is used to analyse the local mechanical behaviour of the virgin material surface. Numerous indentation tests are carried out to study the hysteresis area. Hysteretic dissipation is compared at both scales. Thermal ageing influences the evolution of the hysteresis area characterised in both tests.
[132] ID:132-Mechanical response of a hydrogel: from small deformations to the dehydration-induced glass transition
Caroline Kopecz-Muller (LOMA - University of Bordeaux), Vincent Bertin (Physics of Fluids group, Departement of Science and Technology, University of Twente), Yvette Tran (SIMM, ESPCI, Paris PSL University), Elie Raphaël (Gulliver, ESPCI, Paris PSL University), Laurent Duchemin (PMMH, ESPCI, Paris PSL University), Thomas Salez (LOMA, University of Bordeaux) and Joshua D. McGraw (Gulliver, ESPCI, Paris PSL University).
Abstract
When a rigid object approaches a soft material in a viscous fluid, hydrodynamic stresses arise in the lubricated contact region and deform the soft material. The elastic deformation modifies in turn the flow, hence generating a soft-lubrication coupling. Moreover, soft elastomers and polymer gels are often porous, and can be permeable to the surrounding fluid. In particular, poly-N-isopropylacrylamide (PNIPAM) hydrogels swell by a few hundred percents in thickness when brought into contact with a solvent. Here, we present Surface Forces Apparatus (SFA) experiments, in sphere-on-flat mode, performed on initially fully swollen PNIPAM nanometric films. Together with modelling efforts, the progressive approach and indentation of the gel enables to highlight a succession of several different mechanical responses. From a regime with no gel-probe interaction, the hydrogel first undergoes a gentle deformation of its surface in a lubricated regime. Then, the indentation of the probe in a contact regime forces the expulsion of the solvent from the polymer matrix. We finally show that, at room temperature, the imposed mechanical load triggers the dehydration-induced glass transition of the PNIPAM. Our results are relevant in the context of biomimetic systems and/or living systems, that exhibit complex and different responses depending on the stimulation conditions, such as cartilages or biological membranes.
[134] ID:134-Experimental and numerical insights into filament coalescence during printing
Vincent Guillaume (École polytechnique), Maria Luisa Lopez-Donaire (Department of Continuum Mechanics and Structural Analysis, University Carlos III of Madrid), Daniel Garcia-Gonzalez (Department of Continuum Mechanics and Structural Analysis, University Carlos III of Madrid) and Sara Garzon-Hernandez (Department of Continuum Mechanics and Structural Analysis, University Carlos III of Madrid).
Abstract
Extrusion-based additive manufacturing (EB-AM) technologies are one of the most widely used 3D printing technologies. In recent years, this technique has moved a step further towards the so-called 4D printing. This new term allows not only the control of structural characteristics of the components but including other functionalities with properties that vary in space and/or time. To obtain this extra performance, the polymeric matrices are reinforced with particles. This idea is enabled by different EB-AM technologies that use a starting material in a semi-liquid state, e.g.: FFF that melts polymeric filaments during the extrusion; or DIW that uses a pre-cured polymeric “ink”. All these techniques involve extrusion through a nozzle and, therefore, the material viscosity and its temporal evolution during printing is crucial. This needs to be sufficiently low to facilitate extrusion and the coalescence with other filaments but, at the same time, high enough to ensure shape fidelity. With the aim to understand the mechanics of the coalescence between printed filaments and the role that viscosity and surface tension play in the process, we propose a hybrid experimental-computational methodology. We first develop an experimental campaign to record the filament coalescence depending on the material used, and with a special focus on those whose rheological properties evolve over printing time [Lopez-Donaire et al., Adv. Mat. Tech. 2023]. Then, we propose a phase-field model with time-dependent properties that describes the dynamics of two non-miscible phases (material printed and surrounding medium). This methodology allows for identifying the optimal parameters of the printing process. Acknowledgment: The authors acknowledge support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 947723, project: 4D-BIOMAP). S. Garzon-Hernandez acknowledges support from the Talent Attraction grant (CM 2022 - 2022-T1/IND-23971) from the Comunidad de Madrid.
[135] ID:135-Profilometry-based Indentation Plastometry (PIP), a Technique to Measure Stress-Strain Curves from Indentation
Thomas Southern (Plastometrex) and Jimmy Campbell (Plastometrex).
Abstract
Profilometry-based indentation plastometry (PIP) can be used to determine the stress-strain characteristics of metallic materials from indentation testing of a small, localised area. It is currently very well suited for testing on isotropic, fully dense and homogeneous metals. The procedure uses the residual indent profile and an (accelerated) iterative finite element simulation of the indentation process. The plasticity parameters in a constitutive law (within an indentation finite element model) are iteratively changed until optimum agreement between measured and predicted residual profile shapes is obtained. The technique characterises the full uniaxial stress-strain relationship, including the yield stress and up to the ultimate tensile strength. Comparisons are drawn with results from tensile coupons and hardness testing to demonstrate the equivalency with tensile and improvements over hardness testing. One of the attractions of PIP is that it allows stress-strain curves to be obtained for relatively small volumes of material, such that local properties can be mapped in regions where they are changing over short distances. This makes it uniquely well-suited for measuring local variations in properties in, for example, the vicinity of welds or in functionally graded materials. This can be further expanded to include testing different regions of a single part that have undergone different processing conditions. The additional information provided by PIP can then enhance design optimization by offering insights beyond those obtained solely from witness coupons, highlighting the importance of considering alternative approaches for comprehensive part characterization.
[136] ID:136-Capillarity-induced Wrinkling in Fibrous Liquid-Infused Membranes
Jiayu Wang (Institut Jean-Le-Rond ∂'Alembert, Sorbone Université), Arnaud Antkowiak (Institut Jean le Rond ∂’Alembert, Sorbonne Université) and Sébastien Neukirch (Institut Jean le Rond ∂’Alembert, CNRS).
Abstract
Slender structures or those composed of soft materials typically exhibit low rigidity, responding to small external loads. Capillary forces, often overlooked at larger scales due to their perceived weakness compared to other effects, can play a crucial role in shaping slender structures and soft materials. Recent studies have highlighted diverse deformations induced by capillary forces, such as softening the sharp geometry of a soft substrate, bending and buckling of flexible fibers, and folding, wrapping, and wrinkling of thin sheets. Our study builds upon experimental observations of a nano-fibrous liquid-infused tissue. Under slight compression, it spontaneously develops wrinkles through elasto-capillarity effects. Upon further contraction, specific regions undergo substantial collapse, forming surface reservoirs that enhance the membrane's deformability. The remarkable deformability of this synthetic system closely resembles that of cell membranes, making it suitable for applications in stretchable electronics, smart textiles, and soft biomedical devices. To elucidate the underlying mechanism, we employ theoretical and numerical modeling. The system is simplified to a 2D scenario, featuring a thickness-neglected, inextensible membrane confined within a liquid layer of constant volume. The configuration of the membrane-liquid system under certain compression is framed as an optimization problem. After discretization, the nonlinear problem is solved using an open-source tool CasADi for nonlinear optimization. Numerical continuation aids in identifying solutions under greater compression, where analytical solutions become impractical due to nonlinearity. The model reveals homogeneous wrinkles with slight compression, aligning with experimental findings. As compression increases beyond a certain threshold, wrinkles localize at one specific spot on the membrane. This transition provides insights into experimental observations, prompting further investigations into the behavior of liquid-infused membranes.
[138] ID:138-Multi-scale modelling of material with heterogeneous random micro-structure
Inna Gitman (University of Twente).
Abstract
In order to describe the mechanical behaviour of solid, microstructurally complex, materials multi-scale modelling techniques can be used. There exist a large number of conceptually different multi-scale strategies, ranging from phenomenological models, to continualisation or homogenisation approaches, etc. In this talk two classes of different approaches will be presented. First, the conventional homogenisation methodology will be discussed, through either analytical homogenisation, e.g. so called gradient enriched models, or numerical homogenisation. The main difference between these methodologies is the existence (or lack of) an explicitly given constitutive equation on the macro-level. In both methodologies, by means of hierarchical multi-scale procedures, homogenised information of the detailed (heterogeneous, random) micro-structural description is brought to the macro-level in the form of effective properties. Thus, the homogeneous macro-structural behaviour is driven by the heterogeneous micro-structure.
A second, alternative methodology that will be discussed, is more data driven approach. It is based on an analysis of existing (experimental) data, such as, for example, digital images of material micro-sections, it uses fuzzy sets theory to estimate effective macroscopic properties of a material.
We will discuss advantages and potential limitations of aforementioned approaches, new findings and open-ended questions.
[139] ID:139-Modelling hydrolytic degradation in rubber networks: discrete stochastic and continuum approaches
Lucas Mangas Araujo (University Of Oxford) and Laurence Brassart (University of Oxford).
Abstract
Hydrolytic degradation is a common degradation mechanism in biodegradable hydrogels used in biomedical applications such as tissue engineering and drug delivery. Hydrolysis causes the cleavage of chains in the polymer network, leading to a reduction in elasticity and swelling, as well as to mass loss. Recently, hydrolysis-assisted cracking has also been identified as a possible reason why cracks can propagate in rubber networks under small loads. The reaction kinetics is enhanced by the force experienced by the chains, and since the stress field is amplified around the crack tip, chains in that region are more prone to cleave than in the bulk. However, there have been limited attempts at developing comprehensive constitutive models that couple the effects of stress and hydrolytic degradation in rubbery networks. Specific challenges include capturing the effect of degradation on the elastic properties, and the force-dependent kinetics of chain scission. Ideally, models should also account for the architecture of the underlying polymer network, which ultimately dictates the macroscopic properties. In this work, we combine a Discrete Network (DN) model of rubbery elasticity with a stochastic degradation model based on the Kinetic Monte Carlo method to explicitly account for the evolving network structure and force-dependent hydrolysis. We illustrate the capability of the model by simulating degradation under free and constrained conditions. Our results show that force-dependent kinetics significantly impacts the degradation response, and that it can induce anisotropy. Using the results of the DN model as reference, we also develop a simplified mean-field continuum model able to reproduce the key trends of the DN model. The continuum model is suited for large-scale finite-element simulations coupling large deformations and the transport of water and reaction products.
[140] ID:140-The contribution of infrared thermography to impact testing at low and high velocities
Julien Berthe (ONERA), Gérald Portemont (ONERA) and Peroche Alexandre (ONERA).
Abstract
Measuring the appearance and propagation of damage during impact testing remains a difficult task. A recent study (by the authors) using high-speed infrared thermography has shown that this measurement technique gives access to in-situ damage measurement during low velocity impact tests. In particular, matrix cracking in the surface ply and delamination of the first interface below the non-impacted surface can be monitored. The aim of this study is to evaluate the possible extension of this methodology to high velocity impacts. For that purpose, ballistic impact tests were carried out using a gas gun and a rigid 16 mm diameter ball. Various impact velocities were tested between 40 m.s-1 and 75 m.s-1, preferably below the ballistic limit. An infrared mirror was used to monitor the opposite surface using an infrared camera. A metrological investigation with an extended blackbody was performed to ensure that temperature measurement is not disturbed by this specific configuration. The stacking sequence used for this experimental investigation is a [0/+60/-60]ns made from T700/M21 UD ply leading to a total thickness of approximately 3.25 mm. This may allow direct comparison with the results available in the literature on a triaxially braided composite material with the same fibre orientations. Although the number of images captured for these high-speed impact configurations is limited, they nevertheless provide some information about the damage scenario during these tests.
[141] ID:141-Room temperature electron beam sensitive viscoplastic response of ultra-ductile Al/a-Al2O3 model system
Ankush Kashiwar (Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Andrey Orekhov (Electron Microscopy for Materials Science, University of Antwerp, Belgium), Ihtasham Ul Haq (Electron Microscopy for Materials Science, University of Antwerp, Belgium), Michaël Coulombier (Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Jean-Pierre Raskin (ICTEAM, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Dominique Schryvers (Electron Microscopy for Materials Science, University of Antwerp, Belgium), Thomas Pardoen (Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium) and Hosni Idrissi (Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium).
Abstract
Hybrid nanolaminates (NLs) consisting of alternating layers of metal and metal oxide exhibit excellent mechanical properties and resistance to irradiation damage, which are critical for various structural and functional applications. The strength and ductility of NLs very much depend on layer thicknesses and interfacial characteristics. Investigations by in situ nanomechanical testing in a transmission electron microscope (TEM) are extremely valuable in relating the mechanisms of deformation and failure to microstructural evolutions within individual layers as well as at the interfaces. In addition, the influence of the electron beam irradiation (EBI) must be assessed to evaluate possible artifacts but also to enlarge the range of test conditions.
Here, we address Al/Al2O3/Al tri-layer model systems involving two amorphous/crystal interfaces that exhibit enhanced ductility over 50% with a high ultimate tensile strength above 1550 MPa under uniaxial tension. The extreme plasticity results from the time-dependent viscoplastic response under low-strain rate (10-6 s-1) deformation which is very much controlled by EBI. The influence of EBI on the stress-strain behavior was systematically confirmed by switching on and off the electron beam which led to drastic changes in the mechanical response. The microstructure of the NL deformed under beam-on was characterized by significant delocalization of the plasticity. Intriguingly, both Al-layers exhibited localized necking at the majority of grain boundaries (GBs). This suggests that GB diffusion creep is the dominant mechanism operating at low-strain rates and this feature did not manifest itself in samples deformed at higher strain rates or in the absence of EBI. Furthermore, the localized plasticity at GBs is associated with GB migration which we have analyzed in our study based on the novel combination of nanoscale digital image correlation (DIC) with nanomechanical testing inside TEM. The role of the crystal/amorphous interface and the transmission of plasticity at this interface is also discussed.
[142] ID:142- 3D numerical analysis of instability patterns formed at the surface of magnetorheological elastomer film/substrate systems under magneto-mechanical loading.
Vignesh Selvam (École Polytechnique), Laurence Bodelot (École Polytechnique) and Konstantinos Danas (École Polytechnique).
Abstract
This work investigates macroscopic magneto-mechanical instabilities formed at the surface of stiff magnetorheological elastomer (MRE) films bonded to a soft passive substrate undergoing finite strains and large magnetic fields, using full-field 3D numerical simulations. We exploit a recently proposed microstructure-guided explicit analytical model based on a simple F-B variational energy formulation with few calibration parameters. This allows for an effective numerical implementation of the model to solve macroscopic boundary value problems for a wide range of parameters, such as the magnetic particle volume fraction and the material properties of the individual constituents. The model can thus be used to study numerically the dependence of instabilities on both the magnetic and mechanical properties of film/substrate system in a three-dimensional finite element setting. We first discuss some of the numerical limitations and assumptions used in this work, and then establish a 3D boundary value domain based on mesh sensitivity analysis. A parametric study is also performed to analyze the influence of different material parameters on the arising 3D patterns. Finally, we investigate both experimentally and numerically the instability patterns formed in a heterogeneous MRE layer comprising four magnetoactive discs embedded in a soft silicone square substrate as a function of the applied magnetic field.
[145] ID:145-Development of HCF testing for small cracks propagation study
Marie Bouyx (ONERA), Vincent Bonnand (ONERA) and Grégoire Wisdorff (ONERA).
Abstract
This work focuses on damage tolerance study and fatigue life prediction of aeronautical parts. The goals are to understand fatigue small crack growth initiated from an artificially generated surface defect and to analyze the effects of the surrounding microstructure on the characteristics of the crack (path and velocity) and on the propagation mechanisms. The material of the study is a nickel-based superalloy used for the manufacturing of turbine disks in aircraft turbojets. It has been chosen to introduce an artificial defect on the surface of the specimen by electro-erosion. This approach is favored to fulfill dimensional constraints: obtaining the smallest experimentally feasible defect with dimensions greater than those of natural flaws and this without pronounced residual stress. Three grain sizes - ranging from conventional material (8µm) to hundreds of microns - are considered in order to better understand the influence of grain boundaries on crack growth and on dislocation mechanics. This is achieved with specific heat treatments (main phase grain growth control). Conventional propagation test methodology is extended to the small crack regime. We need to detect the crack initiation from the surface defect (20µm) and carry out the fatigue test up to the “long crack” regime. This requires the adaptation of the monitoring methods (electric potential, optical microscopy and images correlation, replica techniques) and of the cracking test protocols since we want to investigate incubation time and microstructural propagation threshold at given length (replacing respectively the pre-cracking and the decay research approaches). Those considerations lead to the utilization of a high frequency fatigue machine associated with high-speed camera. We will present results of the impact of the tests frequency (2 - 200Hz) on Paris law parameters and threshold values. Ultimately, the goal is to understand the role of the microstructural barriers and crystallographic orientations on the short crack regime.
[146] ID:146-Fabrication and characterization of soft magnetorheological foams
Zehui Lin (Ecole polytechnique), Konstantinos Danas (Ecole polytechnique) and Laurence Bodelot (Ecole polytechnique).
Abstract
Magnetorheological elastomers (MREs) are two-phase composite materials obtained by dispersing metallic magnetic particles in a soft elastomer matrix. The elastomer matrix can be further modified to be a foam, thereby yielding a three-phase porous material exhibiting millimeter-sized voids. Such magnetorheological foams, akin to MREs, show variable stiffness and can be deformed upon application of a magnetic field, but they have the additional advantage to be even more lightweight than MREs. This study investigates the fabrication of magnetorheological foams and addresses their characterization. In particular, their characterization involves the analysis of pore structure and distribution, alongside with the calculation of porosity and particle filling factor, as a function of fabrication parameters. Finally, the magneto-mechanical behavior of the obtained magnetorheological foams is assessed via a dedicated experimental setup.
[147] ID:147-Analytic insights on isotropic energy forms based on experiments of finite torsion
Federico Oyedeji Falope (University of Modena and Reggio Emilia), Luca Lanzoni (University of Modena and Reggio Emilia, Department of Engineering Enzo Ferrari) and Angelo Marcello Tarantino (University of Modena and Reggio Emilia, Department of Engineering Enzo Ferrari).
Abstract
In finite torsion of cylinder a huge number of non-linear complex effects occur: contraction of the radius, elongation of the cylinder, arising of axial force, and the onset of instability are fascinating effects induced by the fully non-linear context. However, there is no trace in the literature of an exhaustive and complete work which fully investigates each case of torsion from a theoretical and experimental standpoint. Different cases of torsion are accounted for in the framework of non-linear elasticity: free torsion and restrained torsion. For these cases of torsion, experiments are very rare in the literature for soft materials as they require extremely sophisticated devices for the measurement of displacement fields and forces. Moreover, the case of pure torsion, which leads to a fundamental universal relation of solid mechanics, was never investigated in terms of the reliability of its fundamental assumptions. We present a new set of experiments on the free torsion and restrained torsion of polyurethanes and silicon rubbers. Along with the torsion tests, uniaxial tests of the rubber are presented. Based on the experiments and universal relation of pure torsion, we experimentally proof the relevance of the second invariant of deformation. We point out that the relevance of the second deformation invariant decreases as the deformation increases. Characterization of the materials, by means of the best fit procedure of the experiments, shows how much the simultaneous fitting of multiple states of stress can reduce the quality of the fitting. Among the energy forms here considered, both incompressible and compressible, we show that only the compressible energy law can grasp the experimental Poynting elongation of the rubbers. In addition to the above, we propose a new formulation in non-linear elasticity to predict the onset of instability in the case of restrained torsion.
[148] ID:148-Accelerated modelling of ratchetting and shear strain induced plastic damage accumulation in rail steels using GPU based parallel computing.
Philomenah Holladay (University of Sheffield), David Fletcher (University of Sheffield) and Francis Franklin (University of Newcastle).
Abstract
It is well established that the failure of rail steels originates in plastic strain accumulation, however the cyclic nature of simulating the phenomena is inherently slow. Recent advances in parallel computing for simulations have facilitated the remapping of a previously computationally limited model of the material response of rail steels under repeated rolling contact. A parallel computing framework using Nvidia graphics processing units (GPUs) has allowed for the introduction of new materials behaviour and expanded the scope for future work.
The dynamic ratchetting (Dynarat) model, developed in 2001, discretises a section of rail into a grid of elements called ‘bricks’, each of which are characterised by material properties such as shear yield and critical shear strain. Bricks accumulate strain in a ratcheting process with varying rates according to the maximum shear stress they experience, and the work hardening behaviour of the material. A brick is considered to have failed once the limit of critical shear strain is exceeded, which represents the formation of voids or cracks in the material. Originally used to model wear and microcrack behaviour in rail steels, lack of strain continuity between bricks and limited scale were deficiencies of the model that could not be addressed previously. However, the FLAME GPU framework, Flexible Large-scale Agent Modelling Environment for Graphics Processing Units, has allowed for the expansion of the model dimensionally, and for the addition of bonds between bricks to address continuity issues.
The paper documents the translation of the existing mechanics of materials model to an agent-based parallel simulation, facilitated by the GPU accelerated framework FLAME GPU. A study is reported here on how modelling speed is determined by factors including agent communication strategy. Enabled by the accelerated model, this also includes the addition of material bonds to improve the continuity and behaviour of the model.
[149] ID:149-Formulation of mean-field model for the accurate prediction of creep deformation of alloy 800H under very-high temperature and low-stress loadings
Carlos Rojas-Ulloa (ArGEnCo department, University of Liège), Fan Chen (ArGEnCo department, University of Liège), Víctor Tuninetti (Mechanical engineering department, University of La Frontera), Amedeo Di Giovanni (R&D department, Drever International), Olivier Pensis (R&D Department, Drever International), Laurent Duchêne (ArGEnCo department, University of Liège) and Anne Marie Habraken (ArGEnCo department, University of Liège; Fonds de la Recherche Scientifique -F.R.S.-F.N.R.S.).
Abstract
Incoloy 800H is an austenitic Fe-Ni-Cr alloy whose creep behaviour is characterized by the onset of two minima within the creep strain rate-time curve. The underlaying physical phenomena inducing this mechanical response are still unclear. (Guttmann and Bürgel, 1983) attribute the first creep rate minimum to a creep mechanism transition induced by dislocation-pinning, whereas the second one is said to be consequence of internal nitridation. The creep hardening effect of nitridation in 800H is evidenced in (Young et al., 2023). Meanwhile, studies on austenitic steels exhibiting similar creep responses attribute both creep rate minima to two separate precipitate strengthening phenomena (Hatakeyama et al., 2022). it is thereby clear that the accurate prediction of the creep behaviour in 800H alloy requires the assessment of creep micromechanics and microstructure evolution. In this work, we provide a numerical framework for the implementation of a mean-field creep model adapted to predict the high-temperature creep deformation response of Incoloy 800H. As a semi-physical model, microstructure evolution is considered in the form of dislocation density distributions, average grain and sub-grain size, and primary precipitate kinetics. The latter is calculated separately via thermodynamic simulations. This approach has proved high accuracy for the prediction of dislocation-based creep deformation of P91 steel (Riedlsperger et al., 2020), and diffusion + dislocation creep deformation observed in A617 Ni-alloy (Riedlsperger et al., 2023). To predict the creep deformation response of 800H alloy, we adapt the model to consider all primary precipitates known to play a role in its creep behaviour (namely MC, M23C6 and TiN). On the basis of the work of (Young et al., 2023), further discussion is given on the possibility of the extension of the model to account for the internal nitridation of the alloy by including the precipitate kinetics of chromium (CrN, Cr2N) and aluminium (AlN) nitrides.
[150] ID:150-Delamination from an adhesive sphere: Curvature-induced dewetting versus buckling
Finn Box (University of Manchester), Lucie Domino (Institute of Physics, Universiteit van Amsterdam, Amsterdam 1098 XH, The Netherlands), Mokhtar Adda-Bedia (Laboratoire de Physique, Univ Lyon, École Normale Supérieure de Lyon, CNRS, Lyon 69342, France), Vincent Démery (Gulliver, CNRS, ESPCI, Paris Science et Lettres, Paris 75005, France), Dominic Vella (Mathematical Institute, University of Oxford, Oxford OX2 6GG, UK) and Benny Davidovitch (Department of Physics, University of Massachusetts, Amherst, MA 01003).
Abstract
Everyday experience confirms the tendency of adhesive films to detach from spheroidal regions of rigid substrates—what is a petty frustration when placing a sticky band aid onto a knee is a more serious matter in the coating and painting industries. The geometry of curved surfaces and the mechanics of thin materials make this, apparently simple, procedure difficult: adhering two materials of different Gaussian curvature requires incompatible deformations. Nevertheless, sufficiently small sheets smoothly adhere to, for example, a sphere. We study in detail the threshold size below which smooth adhesion is possible and show that for very thin materials its failure occurs significantly sooner than expected from previous theoretical work. This earlier onset is the signature of buckling-induced delamination and not the dewetting-like transition previously assumed. Combining mechanical and geometrical considerations, we introduce a minimal model for curvature-induced delamination accounting for the two buckling motifs that underlie partial delamination: shallow “rucks” and localized “folds”. We predict nontrivial scaling rules for the onset of curvature-induced delamination and various features of the emerging patterns, which compare well with experiments.
[151] ID:151-Icosahedral short-range order mediated twin formation in laser direct energy deposited 316L stainless steel with silicon
K. Chen (Ecole Polytechnique), J.G. Santos Macías (Ecole Polytechnique), N. Isac (Ecole Polytechnique), M. Vallet (Université Paris-Saclay), L. Cornet (Université Paris-Saclay) and M.V. Upadhyay (Ecole Polytechnique).
Abstract
316L stainless steel (316L) with 0.5wt% Si and 2.3wt% Si were fabricated using laser direct energy deposition (LDED). A stark difference is found in the density of ∑3 twins and fine grains in the microstructures of the two materials. 316L with 2.3wt% Si exhibits a remarkably high percentage (23%) of ∑3 twin boundaries whereas 316L with 0.5wt% Si exhibits very low (less than 3%) of these boundaries. In this work, we aim to understand the origin of this difference. EBSD analysis of 316L with 2.3wt% Si reveals that clusters of twins exhibiting shared <110> five-fold symmetry axes are present in the microstructure, which suggests that they formed via the icosahedral short-range order (ISRO)-mediated nucleation during solidification [1]. Additionally, twins form during grain growth due to an ISRO-induced stacking fault mechanism, as evidenced by twin variant analysis showing more than 3 variants, which cannot occur during nucleation from one ISRO motif. This result is surprising because ISRO-based mechanisms have been mainly reported in face-centered cubic alloys printed via laser-powder bed fusion. In this talk, we will demonstrate why and how these mechanisms can occur in LDED 316L. [1] M. Rappaz, Ph. Jarry, G. Kurtuldu, J. Zollinger, Metall. Mater. Trans. A 51 (2020) 2651–2664.
[152] ID:152-Soft active magnetorheological elastomers: from material characterization to instability harnessing
Laurence Bodelot (Ecole Polytechnique) and Konstantinos Danas (Ecole Polytechnique / CNRS).
Abstract
Magnetorheological elastomers (MREs) are composite materials made of magnetizable particles embedded in a soft elastomer matrix. They belong to the class of smart materials since some of their properties, such as their stiffness, can be modified by the application of an external stimulus, a magnetic field in their case. In the presence of a magnetic field, they can also exhibit large deformations and/or displacements. Hence, they stand as promising candidates for numerous engineering applications linked to tunable damping, non-contact actuation, morphing surfaces or artificial muscles. The simplest form of MRE samples is isotropic due to a homogeneous dispersion of magnetizable spherical particles in their matrix but curing these composites under magnetic fields can impart them with anisotropic properties through the creation of particle chains in the direction of the curing field. In this work, the coupled magneto-mechanical behavior of both isotropic and anisotropic soft MREs is characterized experimentally and reveals that structural instabilities are ubiquitous in the samples. Such instabilities are further harnessed in model structures including an MRE thin film deposited on a soft non-magnetic substrate that can display reversible 2.5D wrinkles at its surface under coupled magneto-mechanical loading. The influence of the magneto-mechanical loading parameters on the morphology of the obtained wrinkles is analyzed and the prospect for transitioning from 2.5D patterns to 3D patterns is discussed.
[153] ID:153-Mechanistic origin of screw dislocation strengthening by interstitials in advanced high-strength steels
Predrag Andric (SKF), Sebastian Echeverri Restrepo (SKF) and Francesco Maresca (University of Groningen).
Abstract
Screw dislocations are known to control strength of body-centered-cubic alloys. Interstitials such as C and N play a key role in the strengthening mechanisms. Yet, a mechanistic theory that enables the prediction of strength of alloys over a broad range of compositions and interstitial contents is not available. Here, we provide such a theory and apply it to screw dislocations with C and N in iron, from dilute to larger concentration. The theory, which accounts for interstitial solute segregation by Cottrell atmospheres, is validated with respect to atomistic simulations and used to predict the yield strength of a broad range of alloys, showing fully ferritic, martensitic and precipitation-strengthened microstructures. By using a recent model developed by the authors to predict the dislocation density of martensite as a function of the interstitials content, we find a new scaling of the yield strength with the dislocation density, which matches experiments and differs from the commonly used Taylor equation.
[154] ID:154-Creep behavior of SAC305 quasi-single crystal at 185°C
Alexandre Bleuset (SLB) and Eric Charkaluk (CNRS, École polytechnique).
Abstract
Tin alloy SAC305 is a popular lead-free solder since the phase out of Lead from consumer electronics about twenty years ago. Electronic cards are generally submitted to complex thermomechanical loadings inducing fatigue and/or creep damage. Numerous publications cover its mechanical behavior for a large range of testing conditions but results vary significantly from one author to another. SAC305 solder joints are typically constituted of 1-3 crystal orientations and failure has been found to be related to specific orientations. However, generally, only macroscopic polycrystalline characterization have been done on such Tin alloy. Rare characterizations have been conducted on SAC305 quasi-single crystals and with only very limited crystal orientations variations. In the same way, isotropic models are generally used for lifetime estimations, which limits the predictions done. In this study, SAC305 quasi-single crystal specimens have been obtained with a large variety of crystal orientations. Creep tests were conducted at 185°C on these specimens and the measured creep lives spread on almost 3 orders of magnitude depending on crystal orientations. From slip line analysis and digital image correlation during tests the activation of two slip system families was pointed out. Complementary, a crystal plasticity model implementing the identified slip systems reproduced well the deformation of the samples, the strain localization and the local rotation of the Tin crystal.
[155] ID:155-Numerical simulation of additive manufacturing based on fused deposition modeling: Application to the prediction of geometric deviations and mechanical performances of 3D printed prosthetic devices
Mohamed Yousfi (Université de Lyon, CNRS, UMR 5223, Ingénierie des Matériaux Polymères, INSA Lyon, 69621 Villeurbanne, France), Stephane Raynaud (Mechanical Engineering Department, INSA Lyon, 69100, Villeurbanne, France), Nicolas Tardif (Univ. Lyon, INSA Lyon, CNRS, LAMCOS, UMR 5259, 69100, Villeurbanne, France), Thomas Elguedj (Univ. Lyon, INSA Lyon, CNRS, LAMCOS, UMR 5259, 69100, Villeurbanne, France), Christine Billon-Lanfray (Mechanical Engineering Department, INSA Lyon, 69100, Villeurbanne, France), Maxime Belfort (Mechanical Engineering Department, INSA Lyon, 69100, Villeurbanne, France), Jérôme Chevalier (Université de Lyon, INSA de Lyon, MATEIS, UMR CNRS 5510, 69100, Villeurbanne, France), Abder Banoune (Rehabilitation Division, HI-Humanity and Inclusion, 69371, Lyon, France), Valentine Delbruel (Université de Lyon, CNRS, UMR 5223, Ingénierie des Matériaux Polymères, INSA Lyon, 69621 Villeurbanne, France) and Jannick Duchet-Rumeau (Université de Lyon, CNRS, UMR 5223, Ingénierie des Matériaux Polymères, INSA Lyon, 69621 Villeurbanne, France).
Abstract
Nowadays, about 15% of people living in post-war countries needing prosthetic and orthotic equipment they have access due to their long, high costs and complex manufacturing processes. In recent years, additive manufacturing (AM) is increasingly popular in the rehabilitation centers as an alternative since prototypes can be manufactured without resorting to the manufacture of expensive molds. However, 3d printing of orthopedic devices is still primarily based on a trial-and-error experiments, leading to waste and a high material and time-consuming. Therefore, we investigated the possibility of utilizing virtual AM environment to identify the critical points of lower limb prostheses, which are otherwise difficult to obtain with physical tests, and thus avoid errors while making adjustments upstream during their design. The present work aims to explore and evaluate the fused deposition modeling (FDM) process as an affordable technology to build high performance transtibial prosthesis devices based on Acrylonitrile butadiene styrene (ABS) using a combined numerical and experimental approaches. To do that, a numerical workflow was implemented starting from a 3D scan of the patient stump. Then, through reverse engineering, we created a 3D model necessary to manufacture the socket and the junction base of the equipment. The topological optimization was then performed by taking into account the mechanical properties of the ABS material and the stresses generated during gait cycle phases. The FDM process was then simulated through the Digimat® AM software to measure the impacts of material and printing parameters on the warpage of the as-printed parts. Thereafter, structural analysis was carried out, taking into account the FDM process history which allows the prediction of mechanical strength and deformations of prostheses under different gait loading efforts. Finally, a metrological control was deployed on the optimized geometrical 3D printed parts by comparing the numerical results with the experimental 3D scan data.
[156] ID:156-Estimating the bounds on anisotropic elastic moduli in two-dimensional structured materials
Jagannadh Boddapati (California Institute of Technology) and Chiara Daraio (California Institute of Technology).
Abstract
When the elastic properties of structured materials become direction-dependent, the number of descriptors of their elastic properties (e.g., the elasticity tensor moduli) increases. In two dimensions (2D), for example, an anisotropic material can be described by up to 6 independent elasticity tensor moduli, as opposed to 2, when the properties are direction-independent. Such a high number of independent elastic moduli expands the design space of structured materials, and leads to unusual phenomena, such as materials that can shear under uniaxial compression, or materials presenting shear-normal coupled deformations. These coupled deformations have applications ranging from shape-morphing to wave mode-conversion of longitudinal and shear waves. However, this increased design space makes it challenging to understand structure-property relations. There are no clear design rules, to understand how the architectural symmetries directly correlate to the observed structural properties and their moduli. There are also no well-defined upper and lower bounds on these moduli equivalent to the well-known Hashin-Shtrikman bounds on isotropic elasticity. This range is known as G-closure and provides limits for achievable tensors. In our work, we construct a database of two-phase periodic anisotropic unit-cell geometries, using a method inspired by the modeling of phase separation in spinodal decomposition. We utilize the database to visualize regions in the high dimensional design and property space and identify extremal properties that are yet to be explored. The constructed database is compared against properties achieved by hierarchical laminates, which are known to cover a vast design space. We further validate the elastic moduli of representative geometries from the database using mechanical testing on additively manufactured samples. We discuss the role of invariants of the elasticity tensors and how they can be related to the bounds on anisotropic elastic moduli.
[157] ID:157-A Discontinuous Galerkin Finite Element Scheme for A Dislocation Density Transport Based Crystal Plasticity Formulation
Zhangchen Fan (Harbin Institute of Technology, Shenzhen), Qichao Ruan (Harbin Institute of Technology, Shenzhen), Chao Ling (Harbin Institute of Technology, Shenzhen), Esteban Busso (Harbin Institute of Technology, Shenzhen) and Dongfeng Li (Harbin Institute of Technology, Shenzhen).
Abstract
Crystal Plasticity formulations based on dislocation density field concepts incorporate a transport term in the evolutionary behavior of the dislocation densities. They consist of coupled, nonlinear differential equations that describe diffusive and convective transport mechanisms. Due to the hyperbolic nature of the dislocation density transport equations, the standard Galerkin finite element method results in spurious numerical oscillations and thus is unsuitable for achieving a stable numerical. Amongst the numerical problems used to address such dislocation density transport phenomena is the so-called upwind method. However, its use in solving highly nonlinear hyperbolic equations typical of those of interest in dislocation density field-based crystal plasticity formulations can result in slow convergence of the numerical solutions. In this work, it will be shown that it is possible to achieve higher numerical stability and efficiency by implementing the discontinuous Galerkin method. Several classical boundary value problems involving dislocation pile-up and the simple shear deformation of a constrained single crystal strip are carried out. A comparison of the computational efficiency of the upwind and discontinuous Galerkin methods is also discussed.
[158] ID:158-Elongated Grains in Silos: A 3D Odyssey through Non-linear Flow Variations
Agathe Bignon (LMGC, Univ. Montpellier, CNRS, Montpellier, France | Thess Corporate, Montpellier, France), Mathieu Renouf (LMGC, Univ. Montpellier, CNRS, Montpellier, France) and Emilien Azéma (LMGC, Univ. Montpellier, CNRS, Montpellier, France | Institut Universitaire de France (IUF), Paris, France).
Abstract
Three-dimensional contact dynamics simulations are used to study the flow properties of elongated grains in a silo. The grains have a sphero-cylinder shape described by their aspect ratio, which varies from 1 (sphere) to 5 for a thin elongated grain. To ensure accurate statistics, a "perpetual" discharge is simulated for different orifice sizes by 1) reintroducing the exiting grains at the top of the silo and 2) implementing a procedure to break arches when the flow comes to rest, especially for small orifice sizes. As a general observation, when the flow rate Q is plotted as a function of orifice size, it follows a Beverloo-like curve for all shapes. In contrast, for a given orifice size, the flow rate Q is found to vary non-linearly with grain elongation: It first increases to a maximum and then decreases with increasing elongation. Both the packing fraction and velocity profiles are found to be self-similar near the orifice when normalised to the maximum packing fraction and velocity measured at the center of the orifice, respectively. From these profiles, a 3D theoretical expression, inspired by the work of Janda et al [Phys. Rev. Lett. 108, 248001], for the evolution of the flow rate with grain shape is derived, proving that the non-linear variation of Q has its origin in the non-linear variation of the packing fraction with grain shape measured at the centre of the orifice.
[160] ID:160-A novel statistically compatible hyper-reduction method for computational homogenization
Stephan Wulfinghoff (Kiel University).
Abstract
The computational bottleneck of reduced order models (ROMs) in nonlinear homogenization is usually given by the local material laws, which need to be evaluated in a large number of microscopic integration points. Hyper-reduction methods use only a small subset of the integration points and reach tremendous speed-ups at high accuracy. However, the underintegration breaks the overall compatibility of the microscopic strain field and is in this sense disrespecting the microscopic boundary value problem. Here, a new type of generalized integration points is introduced in strain space in order to remedy this shortcoming. Being inspired by results from nonlinear homogenization theory, the concept of statistical compatibility is developed and forms the theoretical basis for the new integration points, which respect the compatibility of the microscopic strain field in a statistical sense. The statistically compatible integration points can be derived offline and replace the conventional ones in a Galerkin-projection based setting with global modes identified via proper orthogonal decomposition (POD). The method is tested for various reinforced composites, indicating that 10-20 integration points are often sufficient to reach errors smaller than 3%, with CPU-times in the μs-range (per time step). A possible extension of the method for problems with higher nonlinearity and stronger field fluctuations is discussed within the context of a porous microstructure.
[161] ID:161-An investigation of the role of defects on the mechanical response of LPBF-manufactured architected cellular materials with random pores features
Selma Leonardi (Université Paris-Saclay, CNRS UMR8182, Institut de chimie moléculaire et des matériaux d’Orsay,), Anne-Laure Helbert (Université Paris-Saclay, CNRS UMR8182, Institut de chimie moléculaire et des matériaux d’Orsay,) and Maria Gabriella Tarantino (Universié Paris-Saclay, CNRS UMR9026, Laboratoire de Mécanique Paris-Saclay).
Abstract
Porous materials with heterogeneous pore features are used in many branches of technology, from lightweight structures to biomedical implants and electrodes. These materials derive their properties from their internal architecture, which is often poorly controlled via conventional manufacturing routes (e.g. foaming, templating). Here, we combine laser powder bed fusion (LPBF) additive manufacturing technology with computer design to fabricate metallic cellular architectures with heterogeneous, yet precisely-controlled, pore features. The materials of this study contain through-thickness pores - of micrometric circular size - randomly dispersed into a dense metallic matrix. Their porous architecture is generated numerically using a random sequential absorption algorithm [1, 2], and is 3D-printed out of AlSi10Mg powders. In this work, we focus specifically on elucidating the impact of a wide set of LPBF parameters on the topological features of random architected materials with through-thickness voids. In addition to the analysis of the pore topological imperfections, our work also examines the role of the metallurgical defects inside the matrix. These too are greatly impacted by the LPBF parameters. To assess their influence on the mechanical response of the cellular materials, modelling tools were developed to incorporate those defects in finite element models of the porous structures. The results of simulations were found to be in good agreement with the results of compression experiments. Collectively they showed that the mechanical response of metallic cellular materials is less sensitive to topological imperfections, whereas metallurgical defects within the matrix are the main precursor of damage.
[1] M.G. Tarantino, O. Zerhouni, K. Danas, Random 3D-printed isotropic composites with high volume fraction of pore-like polydisperse inclusions and near-optimal elastic stiffness, Acta Materialia 175 (2019) 331–340. [2] Z. Hooshmand-Ahoor, M.G. Tarantino, K. Danas, Mechanically-grown morphogenesis of Voronoi-type materials: Computer design, 3D-printing and experiments, Mechanical of Materials 173 (2019) 104432.
[162] ID:162-Systematic design of spatially graded metamaterials for wave guidance
Charles Dorn (ETH Zurich) and Dennis Kochmann (ETH Zurich).
Abstract
Periodic metamaterials and architected materials have emerged as a powerful tool for, among others, controlling or suppressing elastic waves by bandgap engineering. However, the manufacturable design space extends far beyond periodic structures. Spatially graded architectures with smoothly varying unit cell designs have hardly been explored for wave manipulation but offer a rich playground for wave manipulation. We here present a combined experimental-computational study into this rich design space at the example of spatially graded truss lattices. We confirm experimentally that Bloch-Floquet theory is an accurate approximation, as long as the grading in unit cell design is smooth. We further introduce ray tracing for dispersive elastic media as a convenient numerical approach to predict and design wave motion in graded, elastic and dispersive media (by separating the small-scale unit cell design from the large-scale spatial variations in a homogenization step). Using an adjoint-based optimization scheme, we present examples of how design optimization can lead to interesting and peculiar wave motion in graded truss lattices, including wave focusing, frequency splitting, and the realization of complex wave trajectories.
[164] ID:164-Exploring thickness effect on fracture toughness of thin metal sheets: a parametric analysis with advanced Gurson model
Antonio Kaniadakis (UCLouvain), Van-Dung Nguyen (University of Liège), Ludovic Noels (University of Liège) and Thomas Pardoen (UCLouvain - WEL Research Institute, Wavre).
Abstract
Thin-walled structures find widespread applications across various fields, such as in automotive and aerospace. Achieving optimal weight reduction is crucial, requiring thin structures while preserving the best combination of ductility, strength, and resistance to crack propagation through a high fracture toughness (FT), e.g. [1]. The literature shows that there exists an optimum thickness, typically in the mm range at which FT exhibits a maximum. Although this has been known for five decades, very few studies attempted at understanding and predicting this optimum FT. In this context, 3D finite element simulations are performed using a so-called small-scale yielding (SSY) model. A SSY model considers a cylindrical region with a very large external radius with a through-thickness crack with the tip located at the center region. Monotonically increasing displacements are applied at the outer periphery following the elastic mode I solution, corresponding to a well-defined applied K_I value. In this work, we present the results of a parameter study, relying on the nonlocal advanced Gurson model by Nguyen et al. [2]. This model has been validated against direct experimental data, recently demonstrating its capacity to, among others, capture thickness effects in the case of a flat crack propagation mode. The goal is to explore the effects of plate thickness, hardening law, and damage parameters on FT and in particular, on the FT thickness dependence. In particular, the focus is on the peak FT and the corresponding thickness, and how these are affected by the material parameters.
REFERENCES [1] 10.1016/j.actamat.2023.119280 [2] 10.1016/j.jmps.2020.103891
[165] ID:165-Thermodynamic topology optimization for hyperelasticity with varying time integration schemes and arc-length control
Max von Zabiensky (Leibnitz Universität Hannover, Institut für Kontinuumsmechanik), Dustin Roman Jantos (Leibnitz Universität Hannover, Institut für Kontinuumsmechanik) and Philipp Junker (Leibnitz Universität Hannover, Institut für Kontinuumsmechanik).
Abstract
Previous studies have shown that thermodynamic topology optimization (TTO) is an variational optimization approach that can also be used for hyperelastic components. Large deformations offer the opportunity, for example, to integrate the function of a hinge or a joint in just a single component. Accordingly, the TTO provides promising potential in terms of sustainability. However, the severe non-linearities due to the large deformations setting are the source of manifold numerical challenges that need efficiently to be counteracted to enable TTO applicable for industrially relevant optimization problems.
In the current contribution, we investigate the update of the TTO in connection with the update of the displacement field in large detail to discover an ideal update procedure for the staggered solving of the two coupled partial differential equations (displacements and density variable). For this purpose, the optimization is carried out at different stages of the numerical solution process (time steps) leading to different time integration schemes. The effect of these variants is examined in terms of their achieved optimization and computational performance. Along with theoretical basis we present various numerical results.
[167] ID:167-Study of crack-tip damage initiation in anisotropic aneurysmatic tissues
Jaynandan Kumar (Indian Institute of Technology Bhilai) and Anshul Faye (Indian Institute of Technology Bhilai).
Abstract
The biomedical community faces significant challenges regarding aneurysm rupture. Aneurysm growth is linked to the degeneration of the aortic wall and collagen, where, over time, certain collagen fibres may rupture. Consequently, the orientation of micro-cracks resulting from collagen rupture can influence the progression of the damage. This study investigates the damage initiation at the crack tip under uniaxial loading perpendicular to the crack. The analysis is done with numerical simulations using a user subroutine in ABAQUS, based on the Gasser–Ogden–Holzapfel (GOH) model for anisotropic tissue. This study will help to predict the critical crack orientation for the aneurysm rupture.
[168] ID:168-Mechanical heterogeneities in spherulitic microstructures of semi-crystalline polymers: quantitative characterization from micrometric to nanometric scales using nanoindentation and atomic force microscopy
Jérémy Grondin (Institut Pprime - CNRS), Olga Smerdova (Institut Pprime - CNRS), Sylvie Castagnet (Institut Pprime - CNRS) and Christophe Tromas (Institut Pprime - CNRS).
Abstract
Semi-crystalline polymers are heterogeneous materials with different structural scales. At the nanoscale, they are characterized by crystalline and amorphous phases arranged in a complex stacking of crystalline lamellae separated by the amorphous phase. These lamellae form a superstructure known as spherulite at the micrometer scale, significantly influencing the material's mechanical properties at all scales. However, the impact of each structural scale on macroscopic mechanical behavior remains unclear. This is primarily due to insufficient experimental testing and mechanical models, which capture the microstructure's mechanical properties and morphology at these scales.
This study investigates the quantitative elastic mechanical behavior of the spherulitic microstructure of semi-crystalline polymers at the nanometric and micrometric scales. Experimental methods utilizing indentation techniques with tips ranging from nanometers to micrometers were used. The novelty of this research lies in the similar experimental tests across the nanometric and micrometric scales, enabling comparisons between them.
A bulk sample of isotactic polypropylene (i-PP) was prepared to exhibit a spherulitic morphology, including on the surface, with spherulites having a mean diameter of ~120 µm. At the intra-spherulitic scale, nanoindentation (equivalent contact diameter ~1.4 µm) provided modulus mappings within several spherulites. The results reveal a modulus gradient between the stiffer center of the spherulites and their edges —attributed to spherulitic growth resulting in varying lamellae density across the branches of the spherulites. At the lamellar scale, elastic modulus maps obtained by AFM in mechanical mode (equivalent contact diameter ~20-40 nm) revealed heterogeneous moduli within branches of the spherulites, reflecting different local lamellar orientations. Across larger scales, from intra-spherulitic to spherulitic scales, nanoindentation tests demonstrated a decreasing modulus with increasing tested volume, eventually converging to a uniform value for indentation sizes in the tens of microns. This suggests that understanding the material's macroscopic mechanical behavior requires consideration of scales below this tested volume.
[169] ID:169-Crystal Plasticity Modelling of Zirconium Welds under Cyclic Irradiation-Temperature Synergy
Yang Liu (Imperial College London), Daniel Long (Imperial College London), Yilun Xu (Imperial College London) and Fionn P.E. Dunne (Imperial College London).
Abstract
Understanding the impact of reactor load and environment on the Zr weld joint is one of the key factors to the structural integrity of light water reactors. New mechanistic modelling has been established by incorporating thermal recovery of loop dislocations and temperature-dependent loop-dislocation interactions to capturing the tensile behaviours of pre-irradiated Zr samples under thermal conditions. A critical bending test is set up for welded microstructure with notch embedded under thermo-mechanical cycles within reactor conditions. Accordingly, multi-scale modelling of high-fidelity weld is performed by incorporating real-time bending stresses (normal and shear) onto the local welded microstructure from EBSD scan, which captures the post-cycle and post-thermal material strengths. At potential crack nucleation sites identified by stored energy density, non- and pre-irradiated cases show completely different historical change. The synergy between thermal recovery and channel clearing is argued to be the main driver for creep fatigue initiation.
[170] ID:170-An anisotropic damage model for strain-softening in rubber-like materials
Gordon Kumar (University of Oxford) and Laurence Brassart (University of Oxford).
Abstract
Rubber-like materials make up key components in a wide variety of engineering applications, ranging from replacement heart valves and soft robotics to O-rings in rocket stages. In many applications, rubbers are subjected to complex, non-proportional loading histories and exhibit the Mullins effect, a stress softening phenomenon where the apparent material stiffness in a given direction drops with stretching in the same direction. The Mullins effect is highly anisotropic - softening in one direction under uniaxial tension causes negligible softening in the orthogonal directions. Computationally efficient models for this effect are essential for the design of rubber components.
To this end, we present a model for the Mullins effect with a particular focus on the development of mechanical anisotropy. We maintain the micromechanical picture of rubber elasticity (where the rubber network is broken down into the behaviour of its constituent chains) and incorporate damage at the level of the individual chain. A tensorial description of the damage distribution is introduced from which the driving force for damage is identified. Anisotropic evolution laws for the damage distribution reminiscent of kinematic hardening in the theory of plasticity are then presented in both a damage function formulation and a variational formulation, ensuring thermodynamic consistency and enabling calculation of the consistent material tangent for finite element implementation. The model is verified against experimental data for homogenous deformations with changes in stretching direction. The model is implemented in the commercial finite element software ABAQUS as a user subroutine and simulations of complex loading are presented.
[171] ID:171-Design and control of shape-changing elastic robotic structures
Valentina Soana (Department of Mechanical Engineering, University College London), Shahram Sabery (Bartlett School of Architecture, University College London), Federico Bosi (Department of Mechanical Engineering, University College London) and Helge Wurdermann (Department of Mechanical Engineering, University College London).
Abstract
This research proposes a novel multidisciplinary framework for designing and controlling robotically actuated elastic shape-changing material systems, defined as Elastic Robotic Structures (ERS). ERS encompass a wide range of hybrid structures combining bending, tensile and inflatable elements that are mechanically and pneumatically actuated. ERS are designed to operate at human scale for various design applications, including adaptive building systems, creative robotics and interactive objects. The goal is to develop everyday intelligent systems capable of interacting with humans and responding to different parameters.
Elastic materials’ capacity to undertake large deformations under different load conditions makes them inherently adaptive. However, their non-linear behaviour makes these systems challenging to predict. Given the complexity of designing continuously operating elastic systems at human scale, ERS research sits at the intersection of architecture, engineering and robotics. Recent advancements in computational and numerical methods have enhanced the design process, facilitating the creation of complex, structurally efficient elastic structures with significant design potential. However, the lack of methods for controlling continuously operating systems means that most of these structures remain static or display limited changes.
Shape-changing elastic systems, explored in various engineering fields like soft robotics, human-computer interaction and structural mechanics, often face limitations in terms of scale and shape diversity, driven by the specialised approach of engineering applications. Soft robotics offers solutions that can be implemented for the control of elastic shape changing systems with complex shapes and continuously operating systems. The ERS framework integrates methods used to design, characterise and control soft robots with simulation and design approaches used in architectural design and structural engineering. The work offers an overview of these approaches, illustrating how they were used to design different ERS. It also aims to be a guide for the design of similar systems.
[172] ID:172-Emergence of crack patterns in thin films as a collective phenomenon
Matthieu Degeiter (DMAS / ONERA, LSPM / Université Sorbonne Paris Nord-CNRS), Umut Salman (LSPM / Université Sorbonne Paris Nord-CNRS), Damien Faurie (LSPM / Université Sorbonne Paris Nord-CNRS), Yann Le Bouar (LEM / ONERA-CNRS) and Alphonse Finel (LEM / ONERA-CNRS).
Abstract
We are concerned with nanometric magnetic films deposited on polymer-based flexible substrates, whose main applications concern the field of flexible electronics. The main issue is to understand the effects of deformations on the system functional properties. The system stretching or curvature induce high mechanical stresses in the metallic film and at the film-substrate interface. Though polymer substrates are suited to large strains, the brittle thin film carrying the functionality is usually responsible for the system weak durability. It is therefore crucial to optimize the film adhesion on the substrate, and to predict or even limit the cracking and decohesion phenomena.
In this context, we study the formation of crack patterns in thin films and the various factors which influence this process, including the film thickness, the substrate properties and the loading conditions. Using a minimal phase field model consisting of a breakable metallic thin film bonded with a deformable elastic substrate, we use linear stability analyses and numerical calculations to explore how multiple cracks form simultaneously in an initially crack-free thin film.
[173] ID:173-Simulations of the postbuckling response of lattice beams using micropolar continuum theory
Marius Schasching (TU Wien) and Melanie Todt (TU Wien).
Abstract
Lattice materials are becoming increasingly important in lightweight design as they can now be manufactured to meet desired properties using advancing additive manufacturing techniques. Among the numerous failure mechanisms that may occur in lattice materials, buckling caused by global compressive loading is of special interest, especially for lattice materials with slender lattice members. Micropolar continuum theory in conjunction with the finite element method is a promising and efficient approach to predict the buckling deformations based on the internal length scale of lattice materials.
Buckling predictions require a geometrically nonlinear model, which is not readily available for micropolar continua.
Therefore, a geometrically nonlinear micropolar continuum model proposed in the literature is implemented in ABAQUS 2019/Standard (Dassault Syst\`emes Simulia Corp., Providence, RI, USA) as a user element, which is verified against benchmark problems. The model is employed for predicting the critical load and the post-buckling behavior of finite-sized lattice beams showing body-centered cubic or primitive cubic base cells. The micropolar elastic constants of the lattice materials required for the constitutive relations are derived using an energy-based homogenization approach commonly used in the literature. The predictions are compared with results obtained using discrete models.
The comparison shows that although the initial stiffnesses of the continuum and discrete models are in good agreement, the buckling loads are overestimated by the micropolar model. However, the postbuckling response is captured well in a qualitative manner even for unstable behavior. This holds true as long as the localized deformations remain small.
[174] ID:174-Constructing a database of Fully-Uncoupled Multi-Directional (FUMD) specimens for delamination testing
Torquato Garulli (University of Girona), Albertino Arteiro (University of Porto), Norbert Blanco Villaverde (University of Girona) and Jordi Renart Canalias (University of Girona).
Abstract
Fibre Reinforced Polymers (FRPs) are extensively used in structural applications, due to their outstanding specific mechanical properties. To guarantee safety, knowledge of their damage mechanisms is essential.
Interlaminar fracture, or delamination, is a critical damage mechanism for laminated FRPs. Characterization of interlaminar fracture toughness (IFT) follows international standards, which recommend using unidirectional (UD) specimens, where delamination is propagated along the fibre direction. In real applications, however, multidirectional (MD) laminates are used, and delamination may initiate at any interface and grow in any direction, with a different IFT.
Due to several problems (three-dimensional effects, thermal residual stresses, undesired energy dissipation mechanisms, delamination migration) there is no agreement on how to characterize IFT using MD specimens. Researchers have been trying to design optimal MD specimens for decades. A major recent development was the introduction of Fully-Uncoupled Multi-Directional (FUMD) specimens, featuring unprecedented thermoelastic uncoupling properties and enabling testing of any desired interface. Preliminary studies demonstrated the potential of FUMD specimens, making them interesting candidates for standardisation purposes.
The number of feasible FUMD specimens increases with the specimen ply number, and it can become large. Wide adoption and standardisation require knowledge of all feasible designs, their evaluation and selection. In this study, we derive the full set of layups for FUMD specimens design, up to current computational limitations. Specifically, since FUMD layups are obtained from quasi-trivial (QT) quasi-homogeneous layups, we formalise the process to select, from a complete database, those QT layups usable for FUMD specimens, and implement a code to perform the selection at scale. We classify and analyse the sequences obtained to glean insight on aspects of practical interest to specimen design, such as number of usable orientations, possibility to include 0º layers and their number, feasible delamination interfaces as a function of the ply number.
[175] ID:175-Modelling of Recycled Fibre-Reinforced Polymer Composites
Nogol Nazemzadeh (University of Twente), Inna Gitman (University of Twente), Fengxian Liu (University of Twente) and Remko Akkerman (University of Twente).
Abstract
Fiber-reinforced polymer composites have gained popularity due to their high specific mechanical properties and lightweight construction, leading to greater industrial scrap production. The recycling of CFRPs is encouraged by the European Parliament's Directive 2008/98/EC. The recycling process begins with the shredding of scraps, followed by the compression molding of the resulting small flakes. Predicting the mechanical properties of recycled composites accurately is challenging due to their heterogeneous structure, which includes flakes and resin with different mechanical properties. This complexity makes modeling with mono-scale numerical methods difficult. This study employs a multiscale technique to investigate the complex mechanical properties of recycled composites. The numerical model includes micro-level interactions (fibers in thermoplastic matrices), meso-level components (loaded chips and resin), and macro-level analyses, providing a comprehensive understanding of material behavior. At the meso-level, the detailed geometric model in finite element analysis is critical for accurately predicting the mechanical properties of recycled composites. This includes in-plane and out-of-plane orientations, resin-rich areas, and interactions among flakes. The primary objective is to establish a predictive model for the mechanical properties of recycled fiber-reinforced composites using voxel-based approach. Flake generation through the random sequential adsorption (RSA) algorithm, subdivision into sub-cubes, and a sinking process based on finding neighbor process ensures essential geometrical features such as out-of-plane orientation and resin-rich areas. Cohesive zone modeling defines interactions between flakes, with assigned material properties for Carbon/ Poly-ether-ether-ketone (C/PEEK) and PEEK in flakes and resin-rich areas, respectively. Validation, based on microscopic images, confirms the accuracy of the geometrical model. The consistent alignment between mechanical test results and simulation outcomes reinforces the reliability of our predictive model. This study provides a big step forward in our understanding and prediction abilities in recycling composite materials.
[176] ID:176-Coupling a continuous wave laser with a scanning electron microscope to achieve characterisation and improvement of additively manufactured materials microstructure
Juan Guillermo Santos Macías (IMDEA Materiales), Kewei Chen (Ecole Polytechnique), Alexandre Tanguy (Ecole Polytechnique), Maxime Vallet (CentraleSupélec), Louis Cornet (CentraleSupélec), Vincent Michel (Arts et Metiers Institute of Technology) and Manas Upadhyay (Ecole Polytechnique).
Abstract
It is widely agreed that additive manufacturing is currently at a stage where a comprehensive knowledge of its processing parameters, microstructure and mechanical behaviour relationship is needed to advance into a more general implementation. However, this task is particularly complex for this technology due mainly to the extreme process conditions. A novel coupling between a continuous wave laser and an environmental scanning electron microscope can turn out to be a very valuable tool to help accomplish the aforementioned task. In fact, it allows process characterisation and parameter control, enabling the development of the technology. Furthermore, post processing and surface treatment can also be developed with this device. A practical example of the potential of the laser SEM coupling is the mechanical behaviour enhancement of laser metal deposition 316L steel. The device was used to post process and characterise this material. Microstructural refinement and surface roughness reduction were achieved. In consequence, a very significant strengthening, without ductility loss, and fatigue resistance improvement were obtained. These results convey in an unprecedented manner the potential of lasering for microstructure enhancement.
[177] ID:177-Softening and stiffening of pressurized cellular solids: Experiments and modelling
Louison Fiore (Aix Marseille Univ, CNRS, ISM, Marseille, France), Paul Lacorre (Aix Marseille Univ, CNRS, ISM, Marseille, France) and Loïc Tadrist (Aix Marseille Univ, CNRS, ISM, Marseille, France).
Abstract
Turgor pressure (pressure inside cells) changes the rigidity of soft living tissues. For instance, the basil wilts when dehydrated or carrots soften when forgotten in the fridge. How does the stiffness of pressurized solids vary with turgor pressure and cell geometry? Current models of pressurized cellular solids show pressure-induced stiffening, regardless of the internal fluid behaviour. For a fixed volume, Nilsson (1958) showed that apparent Young modulus increases with turgor pressure. For a fixed pressure in shells, Vella et al. (2012) and more recently Couturier et al. (2022) also showed pressure-induced stiffening. Surprisingly, preliminary experiments on cubic cells showed pressure-induced softening of the cellular material. Both geometry and fluid behaviour seem to be key ingredients for mechanics of pressurized cellular solids. We tackle this problem experimentally considering a pressurized spherical membrane model enclosed between two parallel planes. Fluid behaviours considered experimentally are (1) isobar, (2) adiabatic and (3) isothermal. A finite element modelling is used to complement the experimental data with (4) isochoric behaviour. This finite element modelling also allows testing cubic cell mechanical response with well defined boundary conditions. Results show global stiffening following the Laplace coefficient of the thermodynamic transformation. Systematic tests are automatically performed on polymeric commercial membranes of radius R and Young modulus E (sport balls/Yoga balls). Dimensionless thickness, t/R, baro-elastic number P/E, and dimensionless indentation δ/R are considered to output the dimensionless force F/PR2. This work aims to understand the link between complex tissue architecture and tissue stiffness. Further steps are (1) mimicking living tissues to create mechanically tunable materials, (2) mimicking turgor induced motions and (3) the creation of resilient actuators.
[178] ID:178-The Effect of Calcification on the Mechanical Behavior of Clot Analogs for Acute Ischemic Stroke
Jose Monclova (The Pennsylvania State University), Daniel Walsh (The Pennsylvania State University), Vikas Kannojiya (The Pennsylvania State University), Francesco Costanzo (The Pennsylvania State University), Scott Simon (Penn State College of Medicine) and Keefe Manning (The Pennsylvania State University).
Abstract
Stroke is a leading cause of death worldwide, with approximately 3 million deaths in 2022. This study investigates the effect of calcium content on embolus analog (EA) mechanical properties as an indication of EA behavior in time dependent, high strain load states such as mechanical and aspiration thrombectomy.
Human blood was collected from healthy donors, anticoagulated, separated via centrifugation, and controlled for platelet count and hematocrit. Blood was recalcified in a Chandler loop and allowed to coagulate at 37C for 1 hour. EAs were then placed in 0 (Dulbecco’s Modified Eagle Media), 0.2 M calcium chloride, and 2 M calcium chloride baths for 1 and 10 days with control clots tested on day 0. Cylindrical specimens were loaded onto an Instron (Natick, MA, USA) uniaxial load frame to perform a high-strain relaxation test. Tangent stiffnesses at 10 and 75% strain, percent relaxation, and clot area were recorded, and a histological analysis was used to visualize clot structure. Statistical analyses were performed in MATLAB.
Peak stress and tangent moduli were significantly higher, and percent relaxation was lower for days 1 and 10, 2 M calcium EAs, while clot diameter did not change significantly over the aging and calcification period. Preliminary histological analysis reveals a decrease in red blood cell percentage for all aged clots. Significant changes in aged and calcified clot properties and decrease in clot viscous relaxation behavior suggests that calcification may increase the risk of thrombectomy complications because of increased clot stiffness, a factor directly affecting surgical outcomes.
[179] ID:179-Experimental characterisation of the hardening mechanisms of an aluminium alloy produced by the L-PBF process
Louise Toualbi (ONERA/DMAS), Yann Le Bouar (ONERA/CNRS/LEM), Frédéric Fossard (ONERA/CNRS/LEM), Jean-Sébastien Mérot (ONERA/CNRS/LEM), Pauline Stricot (ONERA/DMAS), Simon Fritz (INSA/MATEIS), Agnès Bachelier-Locq (ONERA/DMAS), Nicolas Horezan (ONERA/DMAS), Quentin Barres (ONERA/DMAS), Maria Tsoutsouva (ONERA/DMAS) and Mathieu Fèvre (ONERA/CNRS/LEM).
Abstract
The Laser Powder Bed Fusion process is of particular interest to the aerospace industry because of its ability to produce metal parts with complex geometries. Structurally hardened aluminum alloys produced by L-PBF exhibit specific metallurgical characteristics due to non-equilibrium solidification. These include the formation of metastable phases and of thermally induced dislocations pinned to nanometric precipitates. As a result, the as-built material exhibits remarkable properties that make it possible to avoid a post-fabrication heat treatment. This opens the route for the development of specific alloy grades that fully take advantage the unique features of the L-PBF process. This work focuses on a model binary Al-Fe alloy produced by L-PBF. The objective is to better understand the metallurgical and thermal mechanisms associated with the rapid solidification and cooling rates that characterize L-PBF manufacturing route and lead to the structural hardening of the alloy in the as-built condition. To this end, detailed characterization by scanning and transmission electron microscopy and X-ray diffraction has been carried out on samples obtained using different processing parameters. Nano- and micro-indentation measurements and macroscopic tensile tests have also been performed. Our results reveal the heterogeneity of the mechanical behavior and show that the macroscopic behavior is largely controlled by the size of the solidification cells. We have also performed a transmission electron microscopy study of the hardening mechanisms such as the pinning of dislocations to nanometric precipitates. Finally, the contributions of all the hardening mechanisms have been considered to develop a macroscopic hardening model for Al-Fe alloys produced by L-PBF. The parameters of the phenomenological model have been carefully selected using dedicated measurements and literature data. The aim is now to use this model to link the processing parameter to the mechanical behavior and to use this link to optimize these alloys in the as-built state.
[180] ID:180-Aero-thermo-chemo-mechanical couplings and aging occurring during exposure of polymer materials under high-speed airflow at high temperature.
Aurélien Doriat (Institut Pprime, Chasseneuil Futuroscope, France), Marco Gigliotti (Institut Pprime, Chasseneuil Futuroscope, France), Marianne Beringhier (Institut Pprime, Chasseneuil Futuroscope, France), Gildas Lalizel (Institut Pprime, Chasseneuil Futuroscope, France), Eva Dorignac (Institut Pprime, Chasseneuil Futuroscope, France), Patrick Berterretche (Institut Pprime, Chasseneuil Futuroscope, France) and Matteo Minervino (Safran Aircraft Engine, France).
Abstract
Carbon-fibre reinforced epoxy polymer (CFRP) composite materials are widely used in aeronautical cold structures, such as wings, empennages, fuselages: in aero-engine applications, fan blades CFRP may be subjected to particularly harsh environmental conditions, since temperatures can be as high as 150°C, and the flow speed can be in the range of Mach 1.
It is widely known (see for instance [1]) that epoxy polymers are subjected to thermo-oxidation phenomena when exposed to high temperatures, that is, a coupled diffusion-reaction of oxygen within the macromolecular polymer leading to color change, material antiplasticization and embrittlement, development of shrinkage strain due to the departure of reaction volatile products. So far, aging tests have only been conducted in oven settings under static air, which provides a detailed understanding of the phenomenon. The present study aims to improve the understanding of the coupling between airflow and material degradation, by exploring the effect of airflow temperature and speed on thermo-oxidation phenomena. The hot airflow at high speed may lead to energy exchanges with the polymer sample, leading to heating and thermo-oxidation diffusion-reaction phenomena, ultimately affecting color and material property changes, polymer shrinkage and degradation. Samples were aged in oven and in specific BATH setup able to simulate an air flow at high temperature and high speed. Several experimental techniques (color change measurement by optical measurements under microscope, material property change measurement by nanoindentation, and roughness measurement by optical profilometry) were used to analyze material degradation, and to explore the impact of airflow. Aero-thermo-chemo-mechanical coupled models were employed to enhance the understanding of the complex experimental scenario.
[1] Celina, Mathew C., Review of polymer oxidation and its relationship with materials performance and lifetime prediction (2013), Polymer Degradation and Stability, Vol.98, No.12, p.2419-2429
[181] ID:181-A comparison of Single- and Double-generator formulations for Thermodynamics-Informed Neural Networks
Pau Urdeitx (ESI Group Chair, Aragon Institute in Engineering Research (I3A), Universidad de Zaragoza. Zaragoza, Spain.), Francisco Chinesta (ESI Group Chair. PIMM Lab, Arts et Métiers Institute of Technology, Paris. France) and Elías Cueto (ESI Group Chair, Aragon Institute in Engineering Research (I3A), Universidad de Zaragoza. Zaragoza, Spain).
Abstract
We compare two different formulations for the construction of inductive biases in the framework of scientific machine learning. The objective is to ensure that a neural network's prediction of a mechanical system's behavior inherently satisfies thermodynamic principles (energy conservation, non-negative entropy production). At least two different approaches can be considered either by using a single generator (the generalized free energy of the system, F), giving rise to the so-called single bracket formalism. This generalized free energy potential is a combination of the internal energy and the generalized entropy of the system, i.e., F=E+S. This opens the possibility to separate into two generators, giving rise to the so-called GENERIC or metriplectic formalism, where an energy potential associated with conservative energy (E) and the non-conservative effects (S) are defined (1). Through developed neural networks, the dynamics of different non-conservative systems has been learned by reconstructing the two described formalisms: Single Bracket (SB) and double bracket or GENERIC (G) (2). The impacts of different hyperparameters and their computational costs were analyzed in data reconstruction, revealing the advantages, and limitations of each formulation. Both methods effectively reconstruct the dynamics of various studied problems, although the SB formalism does not impose energy conservation explicitly (3). Despite formalism similarities, results exhibit significant variations under diverse network conditions. The SB formalism improves precision with increasing data but relies heavily on network capacity. Conversely, the G formalism takes advantage of the separation of energy terms to directly impose the first and second laws of thermodynamics. This effect enhances system robustness, enabling valid reconstruction with less data, improving generalization, and limiting overfitting. 1. C. Eldred, F. Gay-Balmaz, J. Phys. A Math. Theor. 53, 395701 (2020). 2. Q. Hernández, et al., J. Comput. Phys. 426, 109950 (2021). 3. H. Yu, et al., Phys. Rev. Fluids. 6 (2021).
[182] ID:182-A fuzzy inference model for prediction of delay risk associated with low rail-wheel adhesion
Iwo Slodczyk (University of Sheffield), David Fletcher (University of Sheffield), Inna Gitman (University of Twente), Roger Lewis (University of Sheffield), Louis Schmandt (Chiltern Railways) and Thomas Butcher (University of Sheffield).
Abstract
Low adhesion zones resulting from rail-wheel contamination, often associated with leaves, pose significant danger to train operation during autumn months, extending braking distances and leading to potential station overruns. While a range of mitigations exist, they often come with significant drawbacks. Due to this, there is appreciable motivation to predict problematic areas of low adhesion before they form, based on the location characteristics such as tree species and density near the track. Accurate predictions would help to direct mitigation work and address underlying conditions, reducing the number of affected areas, and so improving passenger safety. A new technique has been employed, allowing consideration of multiple complex parameters. Field data was applied to a novel fuzzy inference model, which been shown to be successful at generating adhesion delay predictions. The model was trained and validated, demonstrating excellent performance of the fuzzy method (less than 8% error). Through conducting a sensitivity analysis, it has been found that the density of trees and their distance from the track as well as the presence of problematic species play a significant role in producing low adhesion zones. Meanwhile, factors such as the overhang of trees or if the track is in a rural or urban area have been shown to have small influence on leaf layer buildup. The effectiveness of the model has been demonstrated for prediction of low adhesion zones and the methodology is ready to be further validated, moving towards operational application.
[183] ID:183-Fatigue crack nucleation mechanisms in Ni-based superalloys subjected to strain-controlled cyclic deformation
Ignacio Escobar (Universidad Politécnica de Madrid) and Javier Llorca (IMDEA Materials Institute).
Abstract
Ni-based superalloys are widely used in gas turbines. Nevertheless, the influence of the microstructure on the fatigue crack initiation mechanisms is not fully understood yet. This investigation analyzes the relationship between slip transfer and fatigue crack initiation in two solution-hardened alloys (Inconel 600 and Hastelloy C276) tested under fully-reversed cyclic deformation under strain control in the low-cycle fatigue regime. EBSD-based slip trace analysis was utilized to identify the active slip systems across after interrupted fatigue tests. Furthermore, the strain fields in the microstructure and the slip activity were captured by means of high-resolution digital image correlation after interrupted fatigue tests. This information was employed to analyze slip transfer and crack initiation at regular grain and twin boundaries. It was found that fatigue cracks were nucleated at grain and twin boundaries when the slip transfer across was blocked. This behavior was associated with stress concentrations at grain and twin boundaries as well as triple junctions that are enhanced under strain-controlled deformation while fatigue crack nucleation along slip bands parallel to twin boundaries was observed in other investigations carried out under stress-controlled loading.
[184] ID:184-Upscaling transformation plasticity in steel based on full field FFT simulations of polycrystals undergoing phase transformations under applied loads
Shahul Hameed Nambiyankulam (Institut Jean Lamour, CNRS, Université de Lorraine, Nancy, France), Daniel Weisz-Patrault (LMS, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, Palaiseau, France), Benoit Appolaire (Institut Jean Lamour, CNRS, Université de Lorraine, Nancy, France) and Sabine Denis (Institut Jean Lamour, CNRS, Université de Lorraine, Nancy, France).
Abstract
Transformation plasticity refers to the anomalous average strain observed when steels undergo solid-state phase transformations under applied loads. This phenomenon has gained widespread attention due to its significant impact on various industrial fabrication and forming processes, including heat treatment, welding, run-out table processes, and coiling. Several analytical macroscopic models, based on idealized microstructures and strong assumptions, have been proposed. However, a common limitation of these models is their linearity (or weak non-linearity) concerning applied stress, making them suitable only for small loadings. Experimental evidence suggests that the transformation plastic strain becomes highly non-linear with increasing applied stress. Additionally, analytical models often exhibit a logarithmic behavior as a function of product phase proportion, a trend not consistently confirmed by experiments, especially in cases of diffusion-controlled transformations.
As a result, comprehensive full-field simulations of polycrystals have been conducted to enhance our understanding of transformation plasticity. These simulations typically use fast Fourier transform (FFT) algorithms on periodic microstructures, focusing solely on volume expansion due to phase transformation. In this contribution, full-field FFT simulations incorporating visco-plasticity (Chaboche law) and the complete eigenstrain associated with the austenite-to-ferrite phase transformation (e.g., Bain strain) at high-temperature conditions (750°C) are performed with variations in grain distributions, grain orientations, precipitate locations, and applied stresses. The dual objective is to gain deeper insights into the detailed mechanisms responsible for non-linearity with respect to applied stress and the evolution of average plastic strain concerning product phase proportion and to establish a computation database to develop a statistical macroscopic model. This model would incorporate, as input parameters, not only applied stress and product phase proportion but also the average strain rate governed by viscoplastic effects.
[185] ID:185- A reappraisal of the essential work of fracture method based on full three-dimensional advanced Gurson-based finite element simulations
Van-Dung Nguyen (Université catholique de Louvain), Antoine Hilhorst (Université catholique de Louvain), Antonio Kaniadakis (Université catholique de Louvain), Ludovic Noels (Université de Liège) and Thomas Pardoen (Université catholique de Louvain, WEL Research Institute).
Abstract
The essential work of fracture (EWF) has been used for long to characterise the cracking resistance of thin ductile sheet metals. The EWF corresponds to the plastic and fracture dissipation per unit crack surface spent in the fracture process zone (FPZ), where necking and damage occur. To experimentally extract EWF, pre-cracked thin specimens with different ligament lengths are loaded until full fracture. The energy expenditure can be separated into a diffused plastic zone (DPZ) and a localised FPZ. Because the plastic dissipations in these zones scale differently, they can be separated using geometrically similar specimens with different ligament lengths, e.g. double edge notched tension (DENT) specimens. As a result, the EWF is extracted as the dissipation per surface area spent in FPZ, averaged over the entire crack propagation. The main drawback of the EWF method is with the need for using many geometrically similar specimens of different sizes.
The objective of this study is to perform full 3D finite element simulations of DENT specimens with a micromechanics-based ductile fracture model to determine the EWF and to explore the major factors affecting the EWF. A recently developed nonlocal advanced Gurson-based model [1] is used for this purpose and applied to several materials. For each material, the parameters are first identified and then validated with the corresponding experimental data. Next, geometrically similar DENT specimens with a wide range of ligaments as well as thicknesses are simulated to extract EWF as a function of the material parameters and thickness. The results, among others, essentially confirm the empirical rules of validity for the EWF, now rooted on a fundamental micromechanics-based analysis.
References: [1] https://doi.org/10.1016/j.jmps.2020.103891
[188] ID:188-Lipid Peroxidation-induced Membrane Mechanics Modulation and Nanovesicle Shape Transformation
Changjin Huang (Nanyang Technological University) and Choon-Peng Chng (Nanyang Technological University).
Abstract
Plasma membranes form the physical barrier that separates the intracellular contents from the extracellular environments and are essential to the homeostasis of the cell. It has been identified that lipid peroxidation is associated with multiple pathological conditions, including neurodegenerative diseases, atherosclerosis, diabetes, preeclampsia, aging, cancer, etc. However, how exactly lipid peroxidation contributes to those pathological conditions remains largely elusive. Especially, contradictory results regarding its regulation of membrane properties have been reported in experiments. In this study, we first performed molecular dynamics simulations to systematically investigate how lipid peroxidation modulates the structural and mechanical properties of planar lipid membranes. We then extended our simulation systems to nanosized lipid vesicles to interrogate how the change in membrane mechanics caused by lipid peroxidation might alter the vesicle shape. Our results reveal that lipid peroxidation modulates lipid bilayer mechanics in a peroxidation site-specific manner: peroxidation at sites in the bilayer interior disturbs and softens the membrane, whereas peroxidation at sites near the membrane-water interface results in a more ordered and stiffer membrane. Interestingly, we find that the increase in the area per lipid as a result of lipid peroxidation at sites in the bilayer interior leads to a dramatic shape transformation of nanosized vesicles from spherical to prolate. Our finding is essential to a more accurate understanding of the initiation of lipid peroxidation-induced downstream biochemical events in various pathological conditions. In addition, the lipid peroxidation-induced vesicle shape transformation suggests a novel way to fabricate non-spherical nanoliposomes that may serve as a more efficient drug delivery system.
[191] ID:191-Nanoindentation of strong and ductile Al2O3/Al hybrid nanolaminates
Morgan Rusinowicz (Mines Saint-Etienne, CNRS, UMR5307 LGF, Centre SMS, 42023 Saint Etienne, France), Paul Baral (Mines Saint-Etienne, CNRS, UMR5307 LGF, Centre SMS, 42023 Saint Etienne, France), Sahar Jaddi (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Andrey Orekhov (EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium), Hui Wang (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Audrey Favache (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Frederik Van Loock (Department of Mechanical Engineering, Eindhoven University of Technology, 5600, Eindhoven, MB, The Netherlands), Michaël Coulombier (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Hosni Idrissi (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium) and Thomas Pardoen (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium).
Abstract
Protective coatings are required to endure severe mechanical stresses, with their durability directly affecting that of the underlying device or system. These layers must therefore exhibit high mechanical performance, ideally maximizing all the components of the well-known strength-ductility-toughness triptych. In this work, we employed a “nanolamination” strategy to design a coating system that meets this complex portfolio of properties. It consists of a multilayered stack alternating amorphous Al2O3 thin films as hard brittle constituents and crystalline Al thin films as softer “gluing” and/or “crack arrestor” constituents, with individual thicknesses below 100 nm. Thanks to an in-depth study combining micro- nanomechanical tests (nanoindentation, lab-on-chip, microscratch, push-to-pull), electron microscopy (SEM, TEM) and numerical simulations (FEM), an optimal nanolaminate system was identified. This optimization methodology will be presented through the eye of the nanoindentation investigations.
[192] ID:192-On the characterization of the plane stress fracture toughness of high-entropy alloys at room and cryogenic temperatures
Antoine Hilhorst (IMAP iMMC UCLouvain), Pascal J. Jacques (IMAP iMMC UCLouvain) and Thomas Pardoen (IMAP iMMC UCLouvain; WEL Research Institute).
Abstract
Remarkable mechanical properties have been reported in recent literature [1] for CoCrFeMnNi-based high entropy alloys (HEAs), making these HEAs potentially attractive candidates for future cryogenic applications. However, the damage and fracture behavior of HEAs has not yet been fully explored, especially at low temperature.
The present study evaluates the plane-stress fracture resistance of CrMnFeCoNi and CrCoNi alloys at room and cryogenic temperatures using the essential work of fracture (EWF) method. The EWF approach is a well-adapted method for simple and efficient characterization of the fracture resistance of thin sheets made of ductile materials
Stainless steels are found to exhibit an outstanding low-temperature fracture energy, reaching up to 2500 kJ/m^2, surpassing the 700 kJ/m^2 determined for HEAs. A predictive model was developed and validated experimentally in order to connect the thin sheet fracture toughness to the strain hardening capacity through separating the necking and damage work spent in the fracture process zone [2]. The insights gained from this study offer valuable guidelines for refining and optimizing metallic alloys further.
[1] Laplanche, G., et al. "Reasons for the superior mechanical properties of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi." Acta Materialia 128 (2017): 292-303. [2] Hilhorst, Antoine, Pascal J. Jacques, and Thomas Pardoen. "Towards the best strength, ductility, and toughness combination: High entropy alloys are excellent, stainless steels are exceptional." Acta Materialia 260 (2023): 119280.
[193] ID:193-Identification of crystal plasticity using microstructures digital twins and machine learning
Daria Mesbah (CEA Saclay / Mines Paris), David Ryckelynck (Mines Paris), Henry Proudhon (Mines Paris) and Lionel Gélébart (CEA Saclay).
Abstract
The observation of deformation heterogeneities within polycrystalline materials has encouraged the development of mechanical models of crystal plasticity (CP), taking into account the local characteristics of the microstructure [1]. Usually, the comparison between simulations run with CP models and experimental results are carried out by focusing on effective responses. However, more local data can enrich the experimental database, using electron diffraction for surface data [2] or X-Ray diffraction for volume data [3]. Obtaining highly resolved experimental fields, witnessing the deformation of polycrystalline materials, opens the way to a fullfield confrontation, with CP simulations.
Diffraction Contrast Tomography allows the mapping of the microstructure, in terms of grains morphology and orientation at resolutions (few hundreds of nanometres) and over thicknesses (few hundreds of micrometres) unachievable by more conventional techniques. This way, a 3D description of the microstructure can be used as input for CP simulations with FFT-based methods, for computational efficiency purposes.
The implemented methodology offers the opportunity to perform identification for CP laws, using a Machine Learning-based approach and a multiscale and multimodal experimental database.
REFERENCES [1] Meric, L., Poubanne, P., and Cailletaud, G.. Single Crystal Modeling for Structural Calculations : Part 1—Model Presentation, Journal of Engineering Materials and Technology, 113(1): 162–170. 1991. [2] Chen, Z., Lenthe, W., Stinville, J.C. et al. High-Resolution Deformation Mapping Across Large Fields of View Using Scanning Electron Microscopy and Digital Image Correlation. Exp Mech 58, 1407–1421 (2018). https://doi.org/10.1007/s11340-018-0419-y [3] Reischig, P. and Ludwig, W. Three-dimensional reconstruction of intragranular strain and orientation in polycrystals by near-field X-ray diffraction, Current Opinion in Solid State and Materials Science, 24(5): 100851. 2020.
[195] ID:195-A local definition of multiaxiality in elastomers and its application to fatigue testing
Benjamin Martin (Elanova ; GeM - École Centrale de Nantes), Michel Coret (GeM - École Centrale de Nantes), Nathan Selles (Elanova) and Erwan Verron (Gem - École Centrale de Nantes).
Abstract
Recent work on elastomer fatigue shows that it is still difficult to establish the link between lifetimes measured on laboratory specimens and the lifetimes of real parts. In particular, it is difficult to predict the effect of complex loadings on a part whose geometry is itself complex. We propose to present recently developed tools to help make this transition from laboratory to in-service behavior.
Based on theoretical work that defines locally the multiaxiality of a deformation state, and on finite element simulations, we propose a method for constructing fatigue test campaigns that are representative of real-life stresses. This method uses finite elements to explore distortion modes within the material and their intensity, in order to reproduce them in the laboratory. Through this method, we propose to link the local state in the sense of continuum mechanics to the control of a tension-torsion machine.
[196] ID:196-Multiscale geometric design of friction-based interleaved membranes
Lorenzo Guiducci (Technische Universität Dresden), Maxie Schneider (Max Planck Institute of Colloids and Interfaces), Christiane Sauer (weißensee kunsthochschule berlin) and Peter Fratzl (Max Planck Institute of Colloids and Interfaces).
Abstract
The extraordinary large traction force needed to separate two stacks of interleaved paper sheets (popularly known as the phonebook enigma) is caused by a geometric amplification of friction. Although its origin is well described in the literature (Alarcon et al. 2016), this remarkable interfacial effect has not been further explored in terms of possible applications. We consequently create higher level assemblies of paper sheets’ stacks connected together solely by interleaving and evaluate their tensile behavior. In particular, we compare manually assembled macroscopic membranes with different types of woven structure. Through mechanical tests, FE simulations and analytical modelling we demonstrate superior traction force for a double-weave assembly due to an increase in self-induced compression at the stack level which is orders of magnitude larger than what is reported in the literature. Moreover, via nanoindentation measurements we are able to characterize the effect of increased compression force at the paper sheet surface, thus highlighting how macroscopic loading conditions (membrane tension) translate at the microscopic level (inter-sheet friction) and contribute to the overall friction amplification effect of the entire assembly. Finally, we demonstrate a possible usage of such structures by building a structurally stable 5 meters span hanging bridge. Our work thus shows how to program the overall mechanical behavior of a structure via geometric design at multiple hierarchical levels, which is held together by interfacial friction forces alone.
[198] ID:198-The loading of the fetal brain during the second stage of labour
Alice Collier (University of Oxford), Erin Louwagie (Columbia University), Ghaidaa Khalid (Middle Technical University), Mike Jones (Cardiff University), Kristin Myers (Columbia University) and Antoine Jerusalem (University of Oxford).
Abstract
The fetal head is comprised of bony plates joined together by soft connective tissue, known as sutures. During the second stage of labour, the fetus is expelled from the uterus through the birth canal. Sutures allow the fetal head to mould whilst in the birth canal, which, due to the constraints of the maternal anatomy, significantly aides the descent of the fetus. However, moulding of the fetal cranium also causes moulding of the fetal brain. Excessive moulding can result in brain trauma and other long-term sequelae for the fetus. Therefore, understanding the loading experienced by the fetus during labour could help elucidate the risk and mechanism of injuries, and conversely helping predict the safety of the newborn during vaginal delivery. This study proposes a computational model comprised of the fetal head and maternal labour environment capable of predicting the stresses and deformations experienced by the fetal brain during the second stage of labour. The finite element model was adapted from existing studies to represent the geometry of full-term pregnancy. Different model metrics were varied and then compared based on their effect on labour, the results of which will be discussed in this presentation.
[199] ID:199-Prediction of admissible residual stress using fatigue criteria
Akrache Radouane (Université de Versailles saint quentin) and Ghorbel Halima (Université de Versailles saint quentin).
Abstract
The investigated study proposes a mechanical design tool that it can be used for fatigue life prediction. The fatigue life estimation of structures under multiaxial cycle’s loadings on FGS cast iron was simulated using the 3D finite element method. A CAD Modeler, which predicts the admissible residual stress using fatigue criteria, was used to assure the mechanism security in the integrated design phase. A new approach to simultaneous engineering was applied using the components mechanical design with considerate the residual stress. The admissible residual stress calculate after one both a loading and a cycles number is conducted on FGS cast iron specimens, and the fatigue cracks initiation zones as well as the proposed models shall be compared with those obtained from experimental fatigue tests, where satisfactory prediction capabilities on both the fatigue crack initiation locations, which it needs to be introduced by different treatments. The fatigue life of the model is demonstrated
[200] ID:200-Localizing gradient damage model integrated with smoothed finite element method for simulating quasi-brittle fracture
Sachin Kumar (Indian Institute of Technology Ropar), Rajeev Kumar (Indian Institute of Technology Ropar), Anshul Pandey (Indian Institute of Technology Ropar) and Umed Singh (Indian Institute of Technology Ropar).
Abstract
In this work, localizing gradient damage model is combined with smoothed finite element method (SFEM) to investigate the fracture behavior of quasi-brittle materials. The cell-based strain smoothing approach is considered over the domain to convert the classical domain integration to line integration along the each boundary of the smoothing cell, which eliminates the requirement of derivatives of shape functions in the computation of field gradients. The gradient damage framework uses the stress-based evolving anisotropic nonlocal interaction domain, which helps to maintain the localized damage bandwidth during later stages of loading and overcomes the limitations associated with conventional gradient damage models. The anisotropy in nonlocal interactions is modelled using an anisotropic gradient tensor, which governs the orientation of the nonlocal interaction domain based on the principal stress state at a given material point. The stress tensor obtained through SFEM is utilized for determining the principal stress state, to enforce a properly oriented interaction across the bandwidth of the damage process zone throughout the loading process. The proposed framework is extended to simulate the standard fracture mechanics problems of mode-I, mode-II and mixed mode. The obtained results are compared with the traditional FEM counterpart and literature. The comparison of results clearly shows improvement in the computational efficacy over the traditional FEM, and also shows a great potential of it for simulating large deformation problems where element distortion is a critical issue.
[201] ID:201-Multi-scale modelling of irradiated metallic materials for fusion reactors
Luca Reali (UK Atomic Energy Authority), Max Boleininger (UK Atomic Energy Authority), Mark R Gilbert (UK Atomic Energy Authority) and Sergei L Dudarev (UK Atomic Energy Authority).
Abstract
Steels, tungsten and copper alloys are important in fusion engineering for structural, plasma-facing and cooling applications. They must withstand intense radiations that cause both volume swelling and irradiation-creep even at low temperature. Hence neutron transport calculations and materials modelling are two key ingredients of tokamak-scale structural simulations. The first provide the neutron fluxes and the second quantify their consequences. Irradiation produces microscopic defects in the metallic lattice, where the mismatch between the relaxation volumes of self-interstitials and vacancies gives rise to high stress concentrations in reactor components. Macroscopic swelling and dimensional changes stem also from the accumulation of nano-scale defects that gradually evolve into mesoscopic defect structures such as extended dislocation networks and vacancy clusters. This complex low-temperature evolution was simulated using molecular dynamics. Starting from the concept of the dipole tensor for an individual defect and introducing the density of relaxation volumes–which in the framework of elasticity is related to the general notion of eigenstrain– we outline and illustrate applications of a multi-scale approach to the evaluation of macroscopic stress and deformations arising due to irradiation at the component scale in a fusion power plant. The element- and alloy-specific density of relaxation volumes is derived from atomistic simulations or experiments, and it is directly implemented as a source of stress and strain in a finite element model, closing the length-scale gap. Alongside swelling, another technologically relevant radiation effect is the degradation of thermal conductivity of the metals, which is also directly taken from experiments in literature. We exemplify the two effects using fusion reactor components such as a breeding blanket module and an ITER divertor monoblock. We highlight how radiation-induced stresses arise primarily from the spatial variation of swelling, which can be caused by neutron exposure and/or temperature gradients. This is then up-scaled to full tokamak reactor simulations.
[203] ID:203-Mechanics in Forensic Science: predicting Traumatic Brain Injury via mechanics enhanced machine learning
Yuyang Wei (Oxford), Jeremy Oldroyd (Thames Valley Police), Jayaratnam Jayamohan (University of Oxford John Radcliffe Hospital), Michael Jones (Cardiff University), Nicholas Casey (National Crime Agency), Jose-Maria Pena (Lurtis Ltd.), Sonya Baylis (National Crime Agency), Stan Gilmour (Thames Valley Violence Reduction Unit) and Antoine Jerusalem (University of Oxford).
Abstract
In the last decade, clinical research has made important progress on the use of machine learning for Traumatic Brain Injury (TBI) outcome predictions in large cohorts of patients. While these efforts mainly focus on the identification of biomarkers for injury identification and evolution, the question asked by forensic investigators in the context of law enforcement is different. Instead, police forces tend to focus on the likelihood that a given impact scenario leads or not to an observed injury. Traditional methods in forensic analysis, combining biomechanics and neuro-clinical knowledge, often do not provide an objective probabilistic assessment. Here, we propose to bridge this gap by introducing a comprehensive numerical framework coupling biomechanical simulations of various injurious impacts with machine learning algorithms. The model was trained against 200 finite element simulations representing various impact scenarios, alongside 53 detailed criminal assault reports provided by UK’s Thames Valley Police and the National Crime Agency's National Injury Database. Once trained, the proposed framework takes, as input, police reports data and predicts the risk of TBI for three specific symptoms: skull fracture, loss of consciousness and intracranial haemorrhage. The model demonstrates exceptional predictive accuracy, with rates exceeding 92% for skull fractures, 74% for loss of consciousness, and 87% for intracranial hemorrhages, with very high sensitivity and specificity. A notable feature of this research is its ability to identify which inputs, including specific mechanical properties and regions of the human head, are most influential in predicting targeted injuries. This insight underscores the critical role of the mechanics perspective in enhancing the model's accuracy. Despite its current limitation due to the available data on head injury cases, the framework shows remarkable predictive power and potential for future expansion and refinement.
[204] ID:204-Pin-ended buckling test on plain and open hole composites to evaluate the strain gradient effect on compressive failure
Tobias Bianchi (ISAE-SUPAERO 10 av. E. Belin, CEDEX 4, 31055 Toulouse, France/Segula technologies), Jawad Naciri (ISAE-SUPAERO 10 av. E. Belin, CEDEX 4, 31055 Toulouse, France/Segula technologies), Christophe Bouvet (ISAE-SUPAERO 10 av. E. Belin, CEDEX 4, 31055 Toulouse, France), Joël Serra (ISAE-SUPAERO 10 av. E. Belin, CEDEX 4, 31055 Toulouse, France) and Léon Ratsifandrihana (SEGULA Technologies 24 boulevard Déodat de Séverac, 31770 Colomiers, France.).
Abstract
A pin-ended buckling test inspired by Wisnom's [1] has been developed to evaluate the effect of the strain gradient on the compressive failure strain for composite laminates. Tests were carried out on UD carbon/epoxy AS4/8552 composite on open hole and plain specimens. Strains were measured using digital image correlation. Besides, an infrared camera was used to follow visible material damages and kink-band propagation. Different cross ply stacking sequences [(0/90)4]S, [02/(90/0)3]S, [04/(90/0)2]S and [(0/90)8]S, [(0/90)4]S, [(0/90)2]S were tested to investigate both the effect of the thickness of the outer 0° ply and of the thickness specimen on the compressive failure strain. Initial results on plain specimens show a non-linear behaviour in the increase of the compressive strain failure as a function of the strain gradient for the material studied, which does not accord with Wisnom’s results which showed a linear trend. Secondly, most of the plain specimen failed in the tension side, due to the high compressive strenght helped by the strain gradient, and at the same time the tension failure strain remains unaffected by the strain gradient. Open hole specimens add the presence of an in-plane strain gradient due the stress concentration at the hole edge. The results of the open hole specimens show that the presence of the hole helps compressive failure, since all the specimens failed in compressive side whereas the same plain specimens failed in tension. Despite the second plane gradient, the open holes specimens seem to have less of a gradient effect than the plain ones. [1] Wisnom, M. R., J. W. Atkinson, et M. I. Jones. 1997. « Reduction in Compressive Strain to Failure with Increasing Specimen Size in Pin-Ended Buckling Tests ». Composites Science and Technology 57(9 10):1303 8. doi: 10.1016/S0266-3538(97)00057-2
[205] ID:205-Simulation framework for the chemical degradation in polymeric solids
Konstantinos Steiakakis (Eindhoven University of Technology, and DPI, P.O. Box 902, 5600 AX Eindhoven, the Netherlands), Georgios G. Vogiatzis (National Technical University of Athens, and DPI, P.O. Box 902, 5600 AX Eindhoven, the Netherlands), Lambèrt C. A. van Breemen (Eindhoven University of Technology) and Markus Hütter (Eindhoven University of Technology).
Abstract
Chemical degradation of polymeric materials results in a deterioration of mechanical properties, which limits the serviceability of polymer products. To unravel the molecular processes at the origin of this degradation, molecular simulation can be employed. However, the timescales of chemical reactions leading to polymer degradation are typically beyond what can be reached with conventional molecular dynamics (MD) simulations. To retain molecular detail in combination with the ability to reach long timescales, so-called network dynamics has been developed [1-4]. This approach focusses exclusively on local minima in the free-energy landscape and transitions between them via saddle points – with corresponding energy barriers – to describe the long-time dynamics, including chemical reactions. At the core of the network-dynamics approach is an efficient numerical procedure to – departing from local minima – establish nearby saddle-points and then in turn find other connected local minima, without the need for the full dynamics. After discussing the main principles of this simulation strategy, initial results for the chemical degradation of polystyrene in the glassy state will be presented. For the latter, we use both reactive force-fields (ReaxFF) [5] as well as density-functional theory (DFT) simulations to study the reaction pathways and energy barriers, which will eventually be used in the network dynamics.
Acknowledgment: Part of this research forms part of the research program of DPI, projects #745ft14, #820, and #829.
[1] GC Boulougouris, DN Theodorou, J. Chem. Phys., 2007, 127, 084903. https://doi.org/10.1063/1.2753153 [2] GG Vogiatzis, LCA van Breemen, M Hütter, DN Theodorou, Mol. Syst. Des. Eng., 2023, 8, 1013. https://doi.org/10.1039/D2ME00256F [3] GG Vogiatzis, LCA van Breemen, M Hütter, J. Phys. Chem. B 2021, 125, 7273. https://doi.org/10.1021/acs.jpcb.1c02618 [4] GG Vogiatzis, LCA van Breemen, M Hütter, J. Phys. Chem. B 2022, 126, 7731. https://doi.org/10.1021/acs.jpcb.2c04199 [5] W Zhang, ACT van Duin, J. Phys. Chem. B 2018, 122, 4083. https://doi.org/10.1021/acs.jpcb.8b01127
[206] ID:206-Mechanics of liquid crystal inclusion reinforced composites
Yifei Bai (Department of Engineering Science, University of Oxford) and Laurence Brassart (Department of Engineering Science, University of Oxford).
Abstract
Composites made of liquid crystal (LC) inclusions embedded into a stiff polymer matrix have long been developed for engineering applications, such as switchable windows and smart screens for light shuttering and energy preserving purposes. Recently, LC inclusions have also been incorporated into soft matrices, such as hydrogels, for applications like artificial tissues and biosensors. For example, ultrasensitive flexible sensors are designed to detect weak mechanical stimulus. Loadings on such sensors can trigger the reorientation of the LC molecules and alters the electronic characteristics of the composite, which accurately measures the load. Understanding the behaviour of such systems requires an accurate description of the various physics involved, including the elasticity of the LC inclusions and the soft matrix, and surface tension.
In this work, we have developed a continuum mechanics formulation for a hyperelastic matrix reinforced with (nematic) LC inclusions. The elastic energy of the inclusions, attributed to the distortion of the director field, is described using Landau-de Gennes theory. Anchoring effects at the inclusion-matrix interface are described through anisotropic surface tension. We have implemented our continuum theory in the finite element code FEniCSx to investigate the role of various material parameters (anchoring strength, distortion elastic constants, volume fraction) on the effective properties of the composite. We show that the LC inclusions can stiffen the composite, and further that the stiffening depends on the loading direction relative to the LC director field. This is attributed to interfacial effects, which mediate the interactions between matrix deformation and reorientation of the LC molecules. The theory is further generalised to describe the effect of applied electro-magnetic fields. Our results contribute to a better understanding of the stimuli-responsive properties of polymer dispersed liquid crystals and provide useful insights for material design.
[207] ID:207-Finite-size metamaterials and non-coherent reduced relaxed micromorphic interfaces
Leonardo A. Perez R. (TU Dortmund), Angela Madeo (TU Dortmund), Jendrik Voss (TU Dortmund), Gianluca Rizzi (TU Dortmund), Svenja Hermann (TU Dortmund) and Plastiras Demetriou (TU Dortmund).
Abstract
Metamaterials can present special properties, e.g., negative constitutive parameters and exotic interactions with elastic waves (band gaps, cloaking, focusing, among others), that derive from their underlying microstructures. Thanks to their potential engineering applications, there has been increasing interest in making accurate and computationally cost-effective simulations for metamaterials' design. One approach to account for the complexities of these systems, while remaining less computationally expensive, has been the use of enriched models of the micromorphic type. Although micromorphic-type models have extensively been proven to accurately capture the behavior of infinite-size metamaterials (bulk’s response), their accuracy in capturing the behavior of finite-size metamaterials has been proven to be effective only for sufficiently large metamaterials' specimens.
Working with finite-size metamaterials introduces the need for consistent and appropriate boundary conditions. For example, if we take two bulk samples of an arbitrary metamaterial, they will have the same bulk. However, their boundaries most likely won’t match because the same metamaterial can be cut in different ways. This suggests possible differentiated local boundary effects, which need to be considered when setting the boundary conditions in the homogenized (micromorphic) framework. In this work, we simulate finite-size metamaterials using the reduced relaxed micromorphic model. In order to account for the differentiated response of distinct metamaterial boundaries, we implement a non-coherent interface model with microstructure-driven interface forces. The results of our simulations show that this approach allows for retrieving the differentiated response of finite-size metamaterials that have the same bulk, but distinct boundaries. They also show a possible way to enhance the precision of micromorphic-type metamaterials' simulations when local boundary effects have a significant weight on their response.
[208] ID:208-Modeling and simulation of pyropiezoelectric energy harvesting
Michael S. Schwarz (FAU Erlangen-Nürnberg), Ryota Yamamoto (Nagoya Institute of Technology), Ken-Ichi Kakimoto (Nagoya Institute of Technology) and Julia Mergheim (FAU Erlangen-Nürnberg).
Abstract
Energy harvesters are an evolving technology for the Internet of Things as well as for all areas in which devices and sensors are operated with low power consumption. In general, they offer the possibility to harvest electrical energy from ambient energy sources. One way of harvesting is thereby to use the piezoelectric effect to convert ambient vibrations into electrical energy. To also utilize occurring thermal fluctuations, the pyroelectric effect can be used. Since both effects occur simultaneously in some materials, the combination of both effects offers the possibility of increasing the harvested energy. However, since the energy harvested is typically too low to continuously power devices, the base structure has to be attached to an electric circuit that fulfills the purpose of rectifying, accumulating and storing the electric signal of the base structure. The simulation of such a pyropiezoelectric energy harvesting structure together with its attached electric circuit is the main topic of the presentation. The base structure is modeled via linear thermopiezoelectricity and solved with the finite element method, taking into account the connected circuit by means of appropriate boundary conditions. All three fields (mechanical, electrical and thermal) are fully coupled and solved simultaneously so that all coupling phenomena can be considered. Since dynamic contributions for the mechanical and thermal field have to be taken into account, details on the time integration methods used to ensure convergence are given. To illustrate the practical applicability of the simulation approach, results for numerical examples are given and discussed.
[209] ID:209-Improving mechanical properties in Wire Arc Additive Manufacturing of Aluminium Alloys - exploring laser cleaning
Rafael Nunes (Université Catholique de Louvain, Ghent University, Belgian Welding Institute), Wim Verlinde (Belgian Welding Institute), Matthieu Lezaack (Université Catholique de Louvain), Wim De Waele (Ghent University) and Aude Simar (Université Catholique de Louvain).
Abstract
Wire arc additive manufacturing (WAAM) is a widely studied technology known for its high deposition rate and capacity to fabricate large components. Despite the advantages of additively manufacturing aluminium alloy components, challenges such as porosity, surface oxidation, cracking, warping, residual stresses, and geometric accuracy limit its widespread application. Among these challenges, porosity is considered a factor that will affect the mechanical properties of WAAM-manufactured aluminium alloys. Numerous strategies to address these challenges have been explored in scientific literature, focusing on optimizing parameters such as heat input, wire feed rate, metal transfer mode, wire batch, shielding gas flow, and shielding gas preheating. While these techniques show potential improvements in mechanical properties, further development is still needed. This study investigates the potential of automatic interlayer Laser Cleaning (LC) in the WAAM process. LC is an environmentally friendly method that is commonly used to remove rust, paint, oxide, and other contaminants from metal surfaces. The benefits of LC have been successfully demonstrated for conventional joining applications using arc and laser beam welding since 2014. Its application in WAAM of aluminium alloys has not yet been explored. To assess the benefits of LC in WAAM production of aluminium alloys, parts were produced using ER 5183 and ER 2219 aluminium alloys with and without laser cleaning between deposited layers. The removal of the oxide layer is expected to reduce the percentage, size, and distribution of porosities, directly influencing mechanical properties. The samples underwent characterization using computed tomography, tensile testing, and SEM/EDX analysis to provide a comprehensive comparison and evaluation of the impact of laser cleaning on WAAM-produced aluminium alloys. The study aims to numerically quantify the influence of interlayer laser cleaning on the mechanical properties of WAAM-manufactured aluminium alloy components.
[210] ID:210-The elastic Leidenfrost effect: An interplay between vaporization rate, gas flow rate, and shape.
Vicente Luis Diaz Melian (Institute of Science and Technology Austria ISTA), Isaac Lenton (Institute of Science and Technology Austria ISTA), Jack Binysh (University of Amsterdam), Anton Souslov (University of CAmbridge) and Scott Waitukaitis (Institute of Science and Technology Austria ISTA).
Abstract
When a liquid droplet comes near a hot surface, vaporization can become sufficient to cause the drop to levitate—this is the Leidenfrost effect. Vaporizable soft solids, e.g., hydrogels, can also exhibit levitation or, additionally, a sustained bouncing effect. In the floating liquid case, vapor pressure and surface tension balance create an inversion of curvature on the droplet underbelly. Naively, one might expect that in the case of a floating soft solid, vapor pressure and elasticity would create a similar equilibrium with a similar curvature inversion, and indeed theoretical work predicts this is the case. We use high-speed interferometric imaging to measure the 2D height profile underneath a floating hydrogel sphere, and to our surprise, we find that there is no curvature inversion. Instead, a downward-facing conical shape is created underneath the sphere. We speculate that the interplay between vaporization rate, gas flow rate, and shape is essential for this behavior.
[211] ID:211-Micro-mechanical modeling of semi-crystalline PEEK
Rosa A. M. Geveling (Department of Mechanical Engineering, Eindhoven University of Technology), Leon E. Govaert (Department of Mechanical Engineering, Eindhoven University of Technology) and Johannes A. W. van Dommelen (Department of Mechanical Engineering, Eindhoven University of Technology).
Abstract
PEEK is a high-performance thermoplastic for demanding load-bearing applications, where reliable prediction of mechanical behavior is essential. As a semi-crystalline polymer, the mechanical performance of PEEK depends on the crystallinity and morphology (including preferential orientation) which depend strongly on cooling and flow conditions during moulding. In injection moulding, variations in processing conditions over the mold induce variations of crystalline morphology and resulting mechanical properties throughout the component. Accurate prediction of the resulting mechanical response requires: 1) prediction of structure development during processing, and 2) an adequate structure-property relation. This study focuses on the latter and aims to develop a micromechanical model that links morphological details such as crystallinity and crystalline orientation distribution directly to mechanical performance.
In the micromechanical approach, the amorphous and crystalline phases are considered separately and connected in aggregates of two-phase layered domains. The response of these domains is coupled via a hybrid interaction law. This model, called the composite inclusion model, has described micro-mechanical relationships in other semi-crystalline materials [1] and is now applied to PEEK. The crystalline phase is modeled with crystal plasticity, governed by crystallographic slip. The amorphous phase is modeled with a phenomenological model, the Eindhoven Glassy Polymer (EGP) model.
To isolate the model parameters for the amorphous phase, PEEK is quenched to a fully amorphous state. Uniaxial compression tests are performed on the amorphous PEEK and modeled using the EGP model. The amorphous phase of the model includes physical aging, for which the effect of temperature- and stress-induced aging is measured in uniaxial tensile tests. The crystalline parameters are then identified by uniaxial compression tests on semi-crystalline material. The model's versatility can be demonstrated by comparing experiments and simulations at different levels of crystallinity and for different thermal histories.
[1] J.A.W. van Dommelen et al., Mechanics Research Communications, 80, 4, 2017
[213] ID:213-Data-driven methodologies to estimate process parameters, design parameters and mechanical properties of fused deposition modelling polylactide components
Ruixuan Tu (Department of Mechanical Engineering, University of Sheffield), Inna Gitman (Computational Design of Structural Materials, University of Twente) and Luca Susmel (Department of Civil and Structural Engineering, University of Sheffield).
Abstract
According to the current understanding of fused deposition modelling (FDM), a typical extrusion-based 3D printing technology, it is expected that the stronger component can be achieved with the higher infill density. However, due to the complexity of the cross-correlations between multiple processing parameters, the prediction of mechanical strength of printed parts can be highly inaccurate. Therefore, considering the large variety of possible combinations of these parameters, the evident level of non-linearity between them and the mechanical strength has become the main problem to be solved.
The present research includes the application and evaluation of alternative data-driven methodologies, with development of prediction frameworks: dependent on the user needs, “direct” and “inverse” schemes. The former can be used to estimate mechanical strength with known processing parameters, whereas the latter can help identify the optimal combination of processing parameters that ensures the required mechanical strength. Note that the estimated processing parameters from the inverse framework must be adjusted with respect to specifications of the printer and the software.
In this investigation, three various data-driven methodologies were adopted and evaluated regarding their accuracy and efficiency, including the fuzzy inference system (FIS), artificial neural network (NN) and adaptive neural fuzzy inference system (ANFIS). The research has confirmed that with the priority being accuracy, the ANFIS is seen to be the most accurate approach, which requires particular computing power; however, FIS is reported to be the most efficient approach.
The intrinsic versatility of the analysed data-driven methodologies has proven that these approaches can be adopted not only for process and geometrical design parameters, but also for cost-relevant parameters such as printing time and material consumption. It is shown that data-driven methodologies can be an effective and robust decision-making tool in design and cost management problems.
[214] ID:214-Semi-Analytical Model of Grain Boundary Stresses in Elastic Polycrystals
Samir El Shawish (Jozef Stefan Institute) and Timon Mede (Jozef Stefan Institute).
Abstract
We derive a semi-analytical model of intergranular normal stresses for a general elastic polycrystalline material with arbitrary shaped and randomly oriented grains under uniform loading. The model provides algebraic expressions for the local grain-boundary-normal stress and the corresponding uncertainties, as a function of the grain-boundary type, its inclination with respect to the direction of external loading and material-elasticity parameters. The knowledge of intergranular normal stresses is a necessary prerequisite in any local damage modeling approach, for example, to predict the initiation of intergranular stress-corrosion cracking, grain-boundary sliding or fatigue-crack-initiation sites in structural materials.
The model is derived in a perturbative manner, starting with the exact solution of a simple setup and later successively refining it to account for higher order complexities of realistic polycrystalline materials. In the simplest scenario, a bicrystal model is embedded in an isotropic elastic medium and solved for uniaxial loading conditions, assuming 1D Reuss and Voigt approximations on different length scales. In the final iteration, the grain boundary becomes a part of a 3D structure consisting of five 1D chains with arbitrary number of grains and surrounded by an anisotropic elastic medium. Constitutive equations can be solved for arbitrary uniform loading, for any grain-boundary type and choice of elastic polycrystalline material. At each iteration, the algebraic expressions for the local grain-boundary-normal stress, along with the corresponding statistical distributions, are derived and their accuracy systematically verified and validated against the finite element simulation results of different Voronoi microstructures.
[215] ID:215-In situ EBSD/HRDIC-based investigation of twin-twin interaction at grain boundaries in Mg
Maral Sarebanzadeh (IMDEA Materials, Universidad Politécnica De Madrid), Alberto Orozco Caballero (Universidad Politécnica De Madrid), Eugenia Nieto (IMDEA Materials, Universidad Politécnica De Madrid) and Javier Llorca (IMDEA Materials, Universidad Politécnica De Madrid).
Abstract
This investigation employs an innovative in-situ EBSD/HRDIC technique for a thorough exploration of the complex twinning process in magnesium alloys. Utilizing multi-step in-situ deformation experiments, the study investigates grain orientation through in-situ electron backscatter diffraction (EBSD) and strain maps through high-resolution digital image correlation (HRDIC). The research delves into the intricate role of twin-twin interaction, addressing key questions regarding the twin ability of a grain, twin nucleation at grain boundaries, and twin variants selection among the six possible tension twins. In the course of in-situ tensile tests, it is revealed that grain boundaries exhibit more twin pairs than single twins, and contrary to conventional understanding, not all twin pairs result from twin transfer events. Instead, a predominant number of twin pairs at grain boundaries form through the co-nucleation of two twins in neighboring grains. A comprehensive statistical analysis, considering Schmid factors, geometric alignment of twin plane normal and shear directions, and the activity of basal slip in the parent grain, sheds light on twin transmission and co-nucleation across grain boundaries. This detailed investigation contributes significantly to advancing our understanding of deformation processes in magnesium alloys.
[217] ID:217-Effect of elastic strains on the catalytic activity of gold thin films for HER and ORR
Jorge Redondo (IMDEA Materiales), Jayachandran Subbian (IMDEA Materiales), Miguel A. Monclús (IMDEA Materiales), Afshin Pendashteh (IMDEA Materiales), Daniel Pérez (Department of Materials Science: Universidad Politécnica de Madrid), Jesús Ruiz-Hervías (Department of Materials Science: Universidad Politécnica de Madrid), Carmen Martínez-Alonso (IMDEA Materiales; Department of Inorganic Chemistry: Universidad Complutense de Madrid), Valentín Vassilev (IMDEA Materiales), Jon Molina (IMDEA Materiales; Mechanical Engineering Department, Universidad Politécnica de Madrid) and Javier Llorca (IMDEA Materiales; Department of Materials Science: Universidad Politécnica de Madrid).
Abstract
Elastic strains can be used to modify adsorption energy barriers (and, thus, the catalytic activity) of surfaces. This strategy is used here to modify the catalytic activity of Au thin films for the Hydrogen Evolution Reaction (HER) and the Oxygen Reduction Reaction (ORR), that are key processes to produce hydrogen by water splitting and the generation of energy from hydrogen in fuel cells.
Au thin films of 100 nm thick and a strong <111> texture were manufactured by DC magnetron sputtering on Si, polyamide, and NiTi substrates. Prior to deposition, the shape memory NiTi substrates with martensitic microstructure were loaded in four-point bending at ambient temperature. The Au thin films were deposited on the surfaces deformed in tension or compression, and the substrate/thin film was then heated above the phase transition temperature. The NiTi substrate was transformed to the austenitic phase, recovering the initial shape (before four-point bending loading), and transferring the elastic strains to the Au film.
The microstructure of the Au thin films was analyzed by means of atomic force and transmission electron microscopy and the residual strains induced in the film were assessed using X-ray diffraction. The electrocatalytic activity of the thin films with different residual strains was determined in acidic media towards the HER and ORR using linear sweep voltammetry and cyclic voltammetry. Accordingly, improved electrocatalytic performance (i.e., smaller reaction overpotential and smaller Tafel slopes) was observed in the presence of tensile strains, while compressive strains led to opposite behavior (particularly for HER). This is in full agreement with theoretical predictions based on density functional theory. Furthermore, the impact of the surface morphology on the catalytic activity is studied.
[218] ID:218-Simulation of packing kinetic and diffusive properties of fragment beds using the DEM-FFT method
Jean-Mathieu Vanson (CEA, DES, IRESNE, DEC, SESC, Cadarache, 13108 Saint-Paul-lez-Durance), Fabien Bernachy-Barbe (CEA, DES, IRESNE, DEC, SESC, Cadarache, 13108 Saint-Paul-lez-Durance) and Marc Josien (CEA, DES, IRESNE, DEC, SESC, Cadarache, 13108 Saint-Paul-lez-Durance).
Abstract
The simulation of the effective properties of granular media such as diffusion or thermal conductivity is of a great interest for many applications especially for those where experimental measurements are either complex, impossible or expensive to handle.
We developped a simulation tool[1] chaining Discrete Element Method (DEM)[2, 4] and Fast Fourier Transform (FFT)[3] to compute the effective diffusive properties of granular media. The mechanical behaviour and the kinetic of the grains are computed using the Discrete Element Method (DEM). The effective diffusive properties are then computed using the Fast Fourier Transform Method. To make the link between the DEM and the FFT we developped a procedure to voxelize the DEM grains thanks to Merope code[5]. The case of ill defined interface (solid/gas), called fuzzy voxels, is considered carefully and specific treatment is set up. Several treatments are tested and compared and we show that applying a Reuss/Serie model to the fuzzy voxels.
This method is applied to the behaviour of fragmented nuclear fragments to compute its equivalent thermal conductivity. Starting from granulometries characterized experimentally, we set up a two scale procedure to take into account the huge polydispersity characteristic of the fragments. Several thermal effects such as Knudsen and radiation are taken into account and the resulting conductivities are compared with analytical models from the litterature. We evaluate the sensitivity of the two scale scheme and provide experimental validation of the single scale scheme.
REFERENCES [1] T. Calvet, J-M. Vanson and R. Masson, International Journal of Thermal Sciences, 172, 107339, 2022. [2] M. Stasiak, G. Combe, V. Richefeu, G. Armand, J. Zghondi, Computational Particle Mechanics, 9, 825-842, 2022. [3] J-C. Michel, H. Moulinec and P. Suquet, Computer Methods in Applied Mechanics and Engineering, 172, 109-143, 1999. [4] https://richefeu.github.io/rockable/ [5] https://github.com/MarcJos/Merope
[219] ID:219- Characterization of the creep behavior of the nickel-based superalloy 2.4842 utilizing miniature testing techniques and numerical investigations
Richard Wolfgang Schirmer (Technische Universität Bergakademie Freiberg), Martin Abendroth (Technische Universität Bergakademie Freiberg) and Bjoern Kiefer (Technische Universität Bergakademie Freiberg).
Abstract
The small punch test (SPT) is a miniaturized testing method used for determining thermo-mechanical material properties. In this method, a flat cylindrical sample (D8 x 0.5 mm) is centrally loaded by a punch featuring a spherical tip (R1.25 mm). The attractiveness of this approach, developed in the 1980s, lies in its simplicity and the minimal amount of material required. However, challenges arise due to the inhomogeneous stress and deformation state, complicating the determination of constitutive material parameters. To address this issue, an inverse approach is employed, utilizing finite element simulations of the SPT and nonlinear optimization methods to identify a parameter set that aligns the simulation results most closely with experimental findings. In the context of high-temperature small-punch creep tests conducted on the nickel-based superalloy 2.4842 (Alloy 699 XA), two strategies are employed to reduce test duration while preserving information quality. These include elevating test temperatures based on Larson and Miller's work, to achieve shorter failure times under equal forces. Additionally, the testing duration is limited to t=100h. Among the three applied loads, one is defined to induce specimen failure within 100 hours, while the others do not lead to specimen failure. The material model aims to predict the structural behavior of the nickel-based superalloy at high temperatures and is comprised of three components: linear isotropic elasticity, non-linear isotropic plasticity, and creep. The creep model represents a novel approach enabling the prediction of creep behavior across wide stress and temperature ranges. The identified creep parameters are largely independent of temperature and are suitable for extrapolation in terms of time and temperature, resulting in a much more realistic behavior compared to the commonly used Norton creep model.
[220] ID:220- Twinning hierarchy in NiTi revealed by atomistic modelling of twin interfaces.
Lorenzo La Rosa (University of Groningen) and Francesco Maresca (University of Groningen).
Abstract
Twinning is a crucial process in many crystalline materials that undergo martensitic transformation, particularly in Shape Memory Alloys (SMAs) [1]. These unique materials can recover large strains under stress or thermal cycles due to the athermal nucleation and migration of twin interfaces [1]. While well-established theories [2] have successfully described twinning systems in SMAs, some twin systems are more commonly observed than others [3], and existing theories still need to understand this phenomenon completely. This knowledge gap limits the design of SMAs.
This study [4] focuses on the NiTi SMA, a prototypical example demonstrating the significant impact of twin interface mobility on twinning emergence. We provide an integrated approach by combining crystallographic theory, state-of-the-art atomistic modelling [5], topological model [6], and validation through high-resolution transmission electron micrographs [7]. Our atomistic simulations reveal a surprising trend where twinning is influenced by twinning stress rather than interfacial energy. These findings answer longstanding questions and illuminate the propagation mechanisms of twin interfaces beyond established theories of martensite crystallography. By discovering the critical role of interface mobility in twin formation, we can inform variant selection and guide the design of SMAs with enhanced functional performance.
[1] Otsuka, K. & Wayman, C. M. Shape memory materials (Cambridge University Press, 1999). [2] Ball, J. M. & James, R. D. Arch. for Ration. Mech. Analysis 100, 13–52, (1987). [3] Nishida, M., Ohgi, H., et al. Acta Metall. et Mater. 43, 1219–1227, (1995). [4] La Rosa, L. & Maresca, F. under review, (2023). [5] Ko, W.-S., Grabowski, B., et al. Phys. Rev. B 92, 134107, (2015). [6] Pond, R. C. & Hirth, J. P. Acta Mater. 151, 229–242, (2018). [7] Nishida, M., Yamauchi, K., et al. Acta Metall. et Mater. 43, 1229–1234, (1995).
[221] ID:221-Development of repair of large stainless steel parts by direct metal deposition for the energy sector
Cédric Georges (CRM), Norberto Jimenez (CRM), Marine Jean-Baptiste (CRM), Yves Derrienic (Westinghouse Electrical Belgium), Rami El Dakdouki (Westinghouse Electrical Belgium) and Xavier Pitoiset (Westinghouse Electrical Belgium).
Abstract
The energy sector uses a large amount of moving metallic parts, for example stainless steel pumps or collectors. Such kind of parts can be damaged during the use life and small cracks can appear after some years. Classically, the cracks are manually repaired with welding techniques leading to large internal stresses. In this study, we have developed repairs by using direct metal deposition. The impact on the substrate has been studied and a robust process window has been defined. The quality of the repair is excellent in terms of level of porosity, chemistry and mechanical properties. Moreover, the automation of this process will be presented.
[222] ID:222-General grain boundary K-test framework for the assessment of liquid metal embrittlement at the atomic scale
Florian Brunner (University of Groningen) and Francesco Maresca (University of Groningen).
Abstract
Liquid metal embrittlement (LME) refers to the reduction in ductility and toughness of a solid metal when in contact with liquid metals. This kind of material property degeneration poses a serious challenge for several industrial sectors, including the automotive industry, in which the embrittlement of advanced high-strength steels by their liquified Zn coating during welding is of major concern. This makes Fe in contact with liquid Zn a highly relevant example of an LME-susceptible metal couple.
To aid the elucidation of the atomic-scale origins of LME, we established an atomistic simulation framework, which offers sufficient versatility for the assessment of general grain and phase boundaries. This framework takes the form of a K-controlled molecular dynamics (K-test) setup for interfacial cracks. The simulation domain is confined to the area of interest regarding LME, i.e. the near-crack tip region, and can be constructed using anisotropic linear elasticity theory. Thereby, the employment of the Stroh formalism allows accounting for cracks along the boundaries of arbitrarily oriented dissimilar anisotropic materials.
The second crucial ingredient for accurate and reliable predictions of material properties using molecular dynamics approaches is the choice of a suitable interatomic potential (IAP) that describes the interaction between the system’s atoms. Since there is no such potential for the Fe-Zn system yet, we are developing a new machine-learning IAP to this end. Therefore, atomic cluster expansion (ACE) potentials are employed, since they feature a superior combination of accuracy and evaluation speed. The three main stages of the development process are the establishment of a suitable database, containing all relevant atomic configurations, the training procedure and the testing and validation of the obtained IAP. These stages are discussed, as well as obtained results. Finally, the application of the overall framework for the investigation of LME at the atomic scale is discussed.
[223] ID:223-Valorization of titanium Ti-6Al-4V scrap into high added value powders for manufacturing technologies
Marine Jean-Baptiste (CRM), Cédric Georges (CRM), Salvatore Pillitteri (Granutools) and Anders Bæk Hjermitslev (DTI).
Abstract
Currently most of the titanium scraps are collected, sent out of Europe and re-melted into ingots for further use. In the present study, we have demonstrated that it is possible to valorize titanium Ti-6Al-4V scrap into high added value powders for various manufacturing technologies (SLM and DED). The different steps needed to get the final product (cleaning, hydrogenation-dehydrogenation (HDH) process, grinding and sieving) will be described. The obtained powder has been characterized. Both physical (morphology, particle size, chemistry) and processability (flowability, compaction) characteristics have been determined and compared to commercial titanium TA6V powder. Then, some preliminaries trials of additive manufacturing have been performed with laser powder bed fusion (SLM) and laser metal deposition (DED) technics. Material health and mechanical properties have been assessed and also compared to commercial titanium TA6V powder. Regarding the recycling of the titanium chips, a lot of issues have been tackled to successfully manage to produce the right titanium powder.
[224] ID:224-Investigating the role of microstructural features in plastic deformation of friction-stir deposited aluminum
Florian Girault (ONERA), Louise Toualbi (ONERA), Matthieu Lezaack (IMMC - Université Catholique de Louvain), Alexandre Tanguy (LMS - Ecole polytechnique, CNRS), Thibaut Bouilly (CNES - Space Transportation Directorate) and Eric Charkaluk (LMS - Ecole polytechnique, CNRS).
Abstract
Repairing damaged industrial parts poses a significant industrial challenge: cost reduction, increased lifetime and wastes avoidance are some of the pursued objectives. Applying conventional Additive Manufacturing repair processes, which feature transformation under liquid state, on structurally hardened aluminum-based alloys, is complicated by their metallurgical characteristics and the difficulty of subsequent heat treatment in the case of massive parts. This study focuses on Additive Friction Stir Deposition, with the aim of validating this repair route in the context of a reusable launch vehicle application. The behavior of the interface between the damaged part to be repaired and the material deposited on the surface will be particularly investigated. The methodology is the following. First, optical and scanning electronic microscopies are used to analyze the microstructure of repaired samples, particularly the local crystallography. Then an experimental study is conducted in order to characterize the mechanical behavior of the repaired parts. In-situ SEM tensile tests are performed, coupled with digital image correlation analysis based on lithography and speckle patterns to access the local microstructural strain fields. Various areas were explored, considering the microstructure variations in the repaired parts : the original material, the bulk deposited material and the interface between them. The impact of several microstructural features in plastic deformation localization is investigated. Coarsest intermetallic compounds are demonstrated to be fragile, cracking at high loads as well as triggering high strain concentration in their vicinity. Crystallography parameters and deformation fields were also correlated, with results dependent on the analyzed area's location. Grain boundaries are also identified as sites of high plastic strain. However, because of the interdependence of the contributions to plastic deformation of each feature type, they cannot be analyzed separately. Consequently, a scenario for explaining plastic deformation as a function of local microstructure is proposed, taking these interconnections into account.
[225] ID:225-Analytical and numerical comparisons of incremental mean-field homogenization schemes.
Eléonore Bourdier (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert), Sophie Dartois (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert), Rémi Cornaggia (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert) and Renald Brenner (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert).
Abstract
Mean-field homogenization schemes, widely used to characterize the macroscopic behavior of composite materials, can be based on incremental processes. These methods are particularly relevant to estimate the effective characteristics of highly inclusionary media. Our study focuses on two incremental homogenization approaches: the so-called differential scheme [1,2] and iterative homogenization method [3]. These schemes gradually introduce different families of inclusions into an updated embedding medium. Our aim is to pursue a thorough comparison of these two models in various contexts, including anisotropic, multiphase media and different inclusion geometries (spherical, spheroidal, ellipsoidal).
On the one hand, the limit behavior of these two schemes for an infinite number of iterations is investigated analytically. In the case of isotropic two-phase media and spherical inclusion, Zimmerman estimates [2] are retrieved for both schemes. For more general cases, a criterion is proposed to determine a fittest number of intermediate media required to remain in the validity domain of the dilute distribution scheme used at each homogenization step. On the other hand, numerical simulations are performed to investigate the influence of the order of introduction of several inclusion families. These results are validated by comparisons with classical mean-field models and full-field FFT-based simulations.
[1] A. N. Norris, «A differential scheme for the effective moduli of composites», Mechanics of Materials, vol. 4, nᵒ 1, p. 1‑16, 1985. [2] R. W. Zimmerman, «Elastic moduli of a solid containing spherical inclusions», Mechanics of Materials, vol. 12, nᵒ 1, p. 17‑24, 1991. [3] R. Zouari, A. Benhamida and H. Dumontet, «A micromechanical iterative approach for the behavior of polydispersed composites», International Journal of Solids and Structures, vol. 45, nᵒ 11‑12, p. 3139‑3152, 2008.
[226] ID:226-The Stability of Hollow Multiply Twinned Particles within the Principles of the Irreversible Thermodynamics
Kracnitckii Stanislav (St. Petersburg State University, St. Petersburg, Russia, 199034), Smirnov Andrey (ITMO University, St. Petersburg, Russia, 197101) and Gutkin Mikhail (Institute for Problems of Mechanical Engineering RAS, St. Petersburg, Russia, 199178).
Abstract
The issue of void stability in multiply twinned particles is reconsidered in terms of thermodynamics of irreversible processes. The evolution equation of the particles is derived according to the principle of maximum dissipation of non-equilibrium thermodynamics [1] to provide the kinetic model of the strain-induced void evolution. It is demonstrated that the relaxation of the surface and strain energies aroused by either void growth or shrinkage strongly determines the stability of hollow multiply twinned particles. Particularly, the void tends either to reach equilibrium state or shrink with subsequent collapse in dependence to initial conditions and material moduli. Analysis of void evolution modes are performed to reveal the critical and optimal parameters of this process. The latter ones are in good agreement with available data on the experimental investigations of the hollow multiply twinned particles synthesized by different methods [2]. Acknowledgements. This work was supported by the Russian Science Foundation (grant No. 22-11-00087, https://rscf.ru/en/project/22-11-00087/). Reference [1] Fischer F.D., Svoboda J. High temperature instability of hollow nanoparticles. J Nanopart Res, 2008, 10, 255-261. [2] Yasnikov I.S., Vikarchuk A.A. Voids in icosahedral small particles of an electrolytic metal. JETP letters, 2006, 83, 42-45.
[227] ID:227- Quasi-brittle Fracture Mechanics and Human Cortical Bone
Glynn Gallaway (Purdue University) and Thomas Siegmund (Purdue University).
Abstract
Human cortical bone undergoes remodeling processes resulting in a hierarchical, heterogeneous, anisotropic microstructure. Osteons (~200-micrometer diameter) are a key feature, introducing a microstructure length scale. The cortical wall thickness (~5 millimeters) is the structural dimension. Crack tip fields are therefore disturbed by the microstructure. Currently, measurements of fracture toughness of bone use either linear elastic fracture mechanics or the J-integral. This neglects the length scale dependence of fracture properties emerging from the competing length scales. Here, quasi-brittle fracture mechanics is used which introduces a length scale.
Human cadaveric femur tissue is sectioned into nominal 4 x 4 x 24 mm3 beams and notched endostally at half height. Low-rate, in-situ 4-point bending experiments are undertaken in a 3D X-ray microscope with a bath of saline to maintain tissue hydration. At peak load, the specimen is held in the deformed configuration while a 3D image of the sample is obtained (voxel size ~4.2 microns). The size of the fracture process zone (FPZ) is then measured directly from 3D images. The effective crack length (sum of initial notch and FPZ size) is used to compute the quasi-brittle fracture toughness. Experiments reveal the FPZ size in human cortical bone in the transverse direction is 600 to 1000 micrometers, i.e. extending across 3-5 osteons. Using standard ASTM configuration factors and accounting for the FPZ size results in quasi-brittle fracture toughness in the range of Gc=1-2 N/mm, which is approximately 70% larger than that determined from LEFM. When microstructure heterogeneity and anisotropy are considered and evaluated computationally for specimen-specific configurations, Gc is double that obtained with the ASTM configuration. We conclude by discussing the potential implications of using quasi-brittle fracture mechanics to interpret the effects of aging and therapeutics on osteoporosis.
This work is supported by NSF (CMMI) award 1952993. G.G. is supported by NSF-GRF DGE-1842166.
[228] ID:228-Design and numerical analysis of bionic – inspired ceiling panels in terms of the air flow
Artur Wirowski (Lodz University of Technology, Department of Structural Mechanics), Weronika Walisiak (Lodz University of Technology, Department of Structural Mechanics), Paulina Kaszubska (Lodz University of Technology, Department of Structural Mechanics) and Ewelina Kubacka (Lodz University of Technology, Department of Structural Mechanics).
Abstract
With the development of modern technology and materials, the expectations of customers and users regarding the broadly defined comfort of office and residential spaces are increasing. One of the more innovative solutions to provide better thermal comfort for users is diffuse ceiling ventilation. Due to its numerous advantages mainly associated with the elimination of local draughts and high cooling capacity, it is gradually gaining popularity, replacing traditional systems based on a series of pipes and point air outlets.
Therefore, interior architects are faced with the challenge of designing raster ceilings in such a way that profits from the use of diffuse ventilation can be maximised, while maintaining an aesthetically pleasing appearance. Increasingly, bionic inspiration is being used for this purpose, so that people in rooms designed with reference to natural patterns can work and live in a friendlier atmosphere.
The aim of this study is to model bionic-inspired raster ceiling tiles and analyse the airflow through various geometries of these tiles, differing in size, shape, and distribution of openings. Thanks to extensive numerical analyses, it was possible to draw general conclusions, determine certain geometrical parameters of the analysed tiles and their influence on pressure distribution and airflow velocity. The entire work is illustrated by graphs, histograms, and maps of distribution of the airflow parameters, which will make it possible in the future to design optimised bionic-inspired raster ceilings over entire rooms, thus enabling the most profitable use of diffuse ceiling ventilation, better thermal comfort of users and unique aesthetic experience.
[229] ID:229-Optimization and analysis of plates with a variable mass distribution in terms of dynamic properties
Izabela Kowalczyk (Lodz University of Technology, Department of Structural Mechanics) and Łukasz Domagalski (Lodz University of Technology, Department of Structural Mechanics).
Abstract
The aim of the research is to investigate an impact of mass distribution on the plate surface to the dynamic properties and natural frequencies of the simple structural elements (plates). In the optimization process, a genetic algorithm was used. The authors attempt to optimize the arrangement of mass on the plate's surface to maximize the gaps between adjacent natural vibration frequencies. Problems related to structural dynamics were solved by FEM implementation into the algorithm. The research provides data on the correlation between the occurrence of bandgaps in frequencies and the mass distribution. The obtained results were analyzed and described in terms of plate’s dynamics properties after optimization process. The authors also demonstrate the validity of applying the described optimization tool to the presented problems.
[230] ID:230-Experimental measurements of forced vibrations of bionic-inspired ceiling tiles
Weronika Walisiak (Lodz University of Technology, Department of Structural Mechanics), Artur Wirowski (Lodz University of Technology, Department of Structural Mechanics), Ewelina Kubacka (Lodz University of Technology, Department of Structural Mechanics) and Wiktoria Sadok (Lodz University of Technology, Department of Structural Mechanics).
Abstract
With the development of modern technology and materials, the expectations of customers and users regarding the broadly defined comfort of office and residential spaces are increasing. One of the more innovative solutions to provide better thermal comfort for users is diffuse ceiling ventilation. Due to its numerous advantages mainly associated with the elimination of local draughts and high cooling capacity, it is gradually gaining popularity, replacing traditional systems based on a series of pipes and point air outlets.
Therefore, interior architects are faced with the challenge of designing raster ceilings in such a way that profits from the use of diffuse ventilation can be maximised, while maintaining an aesthetically pleasing appearance. Increasingly, bionic inspiration is being used for this purpose, so that people in rooms designed with reference to natural patterns can work and live in a friendlier atmosphere. The aim of this study is to model bionic-inspired raster ceiling tiles and analyse the vibration induced various sources: fans, ventilator and impact hammer . Openings in raster ceiling tiles have different size, shape, and distribution of openings. Also raster ceiling tiles are composed from different materials steel, aluminium, mycelium base composite (MBC) and bamboo base composite. Obtained experimental results have been compared with numerical results from ABAQUS programme.
The entire work is illustrated by graphs, which will make it possible in the future to design optimised bionic-inspired raster ceilings over entire rooms, thus enabling the most profitable use of diffuse ceiling ventilation without problems with unwanted vibrations for better thermal comfort of users and unique aesthetic experience.
[231] ID:231-Design and numerical analysis of bionic – inspired ceiling panels in terms of their dynamic properties.
Weronika Walisiak (Lodz University of Technology, Department of Structural Mechanics), Paulina Kaszubska (Lodz University of Technology, Department of Structural Mechanics), Artur Wirowski (Lodz University of Technology, Department of Structural Mechanics) and Ewelina Kubacka (Lodz University of Technology, Department of Structural Mechanics).
Abstract
Raster ceilings are widely used in office spaces and residential buildings. Their application may involve the use of ventilation – both distributed and traditional – located in the space above the suspended ceiling. Both types of ventilation generate vibrations that are oppressive to users, which in case of inappropriate use of the ceiling tiles materials, may be additionally amplified by the phenomenon of resonance. Therefore, the issue of awareness of the dynamic properties of ceiling panels becomes extremely important. Due to this knowledge, it will be possible to avoid the occurrence of unfavourable acoustic phenomena. The inspiration from bionics influences users’ perception of space, increases their feeling of comfort and makes the room more friendly. Inspiration from nature is therefore becoming an increasingly popular trend in the design of materials used to finish spaces intended for people. The aim of the study is to analyse the dynamic properties of raster plates - in particular their natural and forced vibration frequencies, as well as deformations under the influence of air flow from distributed air conditioning. As part of the work, the Ansys program was used to model a number of different slot geometries in simply supported square coffers slabs. Based on the created slab models, an analysis was made and general conclusions were drawn, so that in the near future it will be possible to design raster ceilings that suppress vibrations coming from air conditioning instead of propagating them additionally.
[232] ID:232-Static and Dynamic Analysis of Bidirectionally Sinusoidal Corrugated Steel Shells: A Comparative FEA Study
Damian Kozanecki (Lodz University of Technology, Department of Structural Mechanics), Artur Wirowski (Lodz University of Technology, Department of Structural Mechanics) and Martyna Rabenda (Lodz University of Technology, Department of Concrete Structures).
Abstract
This study presents a comprehensive investigation of bidirectionally sinusoidal corrugated steel shells using advanced finite element analysis (FEA) software, primarily ABAQUS, supplemented by RFEM for initial result comparison. The research aims to establish a robust numerical solution, unravelling the intricate structural behaviour of these shells under static and dynamic loading conditions.
This study initiates with the execution of meticulous calculations for a carefully selected structural element, providing a comprehensive foundation for subsequent analyses. The paper places emphasis on a comparative analysis between ABAQUS and RFEM, offering valuable insights into their respective roles in simulating the response of bidirectionally sinusoidal corrugated steel shells.
Moreover, the investigation systematically explores an array of model parameters, including variations in geometrical and mechanical properties. Through detailed analyses and rigorous comparisons, the research elucidates the nuanced influence of these parameters on critical aspects such as deformation, stress distribution, and dynamic behaviour exhibited by the corrugated steel shells.
A distinctive feature of this research involves the development and utilization of a coded script. This script enables the systematic generation of a diverse array of numerical models, allowing for a thorough exploration of the structural system's response.
In conclusion, this study significantly contributes to advancing the understanding of bidirectionally sinusoidal corrugated steel shells' structural behaviour. By leveraging the capabilities of ABAQUS and thoughtfully integrating RFEM for preliminary comparisons, the research provides valuable insights into the simulation of complex structural systems. These findings are poised to elevate current structural analysis and design practices, particularly by optimizing geometrical and mechanical parameters for the enhanced performance of these innovative structural elements across a spectrum of engineering applications.
[233] ID:233-Mechanisms of deformation and voiding using tomography on neat and glass syntactic polypropylene : Finite Element simulations on flat notched specimens
Lucien Laiarinandrasana (Centre des Matériaux - Mines ParisTech - PSL University), Sébastien Blassiau (SAIPEM S.A., Subsea Engineering (SUB) Department) and Cristian Ovalle (Centre des Matériaux - Mines ParisTech - PSL University).
Abstract
Glass syntactic polypropylene (GSPP) is used for thermal insulation of subsea pipelines. Flat notched specimens, with two notch root radii, were used to study the mechanisms of deformation and voiding thanks to in-situ tensile tests conducted at Psiché beamline of Soleil Synchrotron Radiation Facility. High resolution data sets (1 px = 1.3 µm) were obtained all along the applied deformation. The interaction between the glass hollow microspheres and the matrix was highlighted using gradually the images of : i) the neat PP matrix; ii) embedded unique microsphere within this matrix; iii) the GSPP composite with the real distribution of microspheres. In the PP-matrix void nucleation, growth and coalescence resulted in crazes like microstructures under the deformed states. For GSPP, voids nucleated at the polar zones, by the decohesion of the matrix, leading to two caps above and below each microsphere. During the deformation of GSPP these voiding mechanisms resulted in a significant irreversible volume change (plastic dilation). This latter was measured: i) at the macroscopic scale, by using the reduction of the width and the thickness; ii) at the microscopic scale, by determining a volume of interest allowing the spatial and time distributions of the void volume fraction to be plotted. Using the mechanics of porous media concepts, Finite Element simulations of the in-situ tests were attempted. The simulated and experimental plastic dilation observed at both macroscopic and microscopic scales were in good agreement.
[234] ID:234-Experimental investigation of early strain localizations of ferrite-pearlite steel with microstructure gradient under cyclic loading.
Nagesh Narasimha Prasad (Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LaMcube - Laboratoire de Mécanique, Multiphysique, Multiéchelle), Ahmed El Bartali (Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LaMcube - Laboratoire de Mécanique, Multiphysique, Multiéchelle), Jean-François Witz (Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LaMcube - Laboratoire de Mécanique, Multiphysique, Multiéchelle), Nathalie Limodin (Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LaMcube - Laboratoire de Mécanique, Multiphysique, Multiéchelle) and Denis Najjar (Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LaMcube - Laboratoire de Mécanique, Multiphysique, Multiéchelle).
Abstract
The use of fatigue-resistant steel grades is critical in advancing the durability and reliability of railway components. Ferrite-pearlite steels are frequently employed due to their balance of strength and toughness. The existence of multiple grains with distinct orientations and sizes within such a polycrystalline material can result in non-uniform strain distributions, commonly referred to as strain heterogeneities. These heterogeneities have the potential to induce premature failure and limit material performance. Furthermore, the incorporation of heat treatments during the manufacturing process and plastic deformation during operation generates micro-structural gradients, modifying the material's mechanical properties. Nevertheless, the effect of these microstructure gradients on fatigue characteristics remains ambiguous.
In response, we devised an experimental approach incorporating in-situ optical-based Digital Image Correlation (DIC) to quantify local strain during Low Cycle Fatigue (LCF) loading. Flat specimens were extracted at various depths from a railway wheel composed of ER7 steel, with a microstructure featuring ferrite and pearlite. These specimens were designed with a semi-circular notch. A Region of Interest (ROI) was marked, and a speckle pattern was applied to the surface. LCF tests were performed, wherein images were captured of the speckle pattern at cyclic load peaks. Subsequently, the DIC technique was employed to compute displacement fields. These fields were spatially correlated onto the surface microstructure and Electron Back-scatter Diffraction (EBSD) data of the ROI, captured before the test. This methodology allowed for the identification of strain localization and potential sites for the initiation of cracks.
A prior study in monotonic tension on ER7 steel reveals varied deformation behaviours, such as early plasticity and stress plateau, influenced by microstructural differences. Statistical analysis identified correlations between pro-eutectoid ferrite grains prone to deformation and adjacent pearlite nodules. Our study aims to understand the early strain localization patterns in ferrite-pearlite steel with a microstructure gradient under cyclic loading.
[235] ID:235-Dynamic Actuation Modes in Magneto-Responsive Bistable Structures: A Rate-Dependent Approach
Carlos Pérez García (University Carlos III of Madrid), Josué Aranda Ruiz (University Carlos III of Madrid), Maria Luisa Lopez Donaire (University Carlos III of Madrid), Ramón Zaera (University Carlos III of Madrid) and Daniel Garcia Gonzalez (University Carlos III of Madrid).
Abstract
The use of structural instabilities allows for swift responses triggered by mechanical force or specific displacement thresholds. The advent of responsive materials has facilitated the adaptation of such structural instabilities into actuators that promptly deform under external stimuli. Nevertheless, the rapid transitions between equilibrium states entail significant viscoelastic roles at the material level, influencing the structural behavior on a larger scale. Our study offers a comprehensive understanding of the impact of viscoelastic effects on bistable structural transitions, incorporating both a novel experimental perspective and a thorough modeling analysis. These findings are applied to magneto-responsive bistable structures, presenting a roadmap for designing effective actuation conditions. The bistable transition's functionality relies on the interplay between the magnetic field amplitude and application rate. The comprehension of viscoelastic and magneto-mechanical coupling enables efficient actuation through temporal magnetic pulses, eliminating the need for sustained magnetic fields. Ultimately, we integrate these insights to create a responsive structural component, enabling modulation of transient and steady bistable transitions based on the application rate of external magnetic stimuli.
[236] ID:236-Cubic symmetry preservation and homogeneity in elastic properties of β+ω and β+α Ti-alloys. An ultrasound-based study
Michaela Janovska (Institute of Thermomechanics of the Czech Academy of Sciences), Juraj Olejnak (Institute of Thermomechanics, Czech Academy of Sciences, Prague), Petr Sedlak (Institute of Thermomechanics, Czech Academy of Sciences, Prague), Kristyna Repcek (Institute of Thermomechanics, Czech Academy of Sciences, Prague), Pavla Stoklasova (Institute of Thermomechanics, Czech Academy of Sciences, Prague), Tomas Grabec (Institute of Thermomechanics, Czech Academy of Sciences, Prague), Jana Smilauerova (Faculty of Mathematics and Physics, Charles University, Prague), Petr Harcuba (Faculty of Mathematics and Physics, Charles University, Prague) and Hanus Seiner (Institute of Thermomechanics, Czech Academy of Sciences, Prague).
Abstract
Relationship between the microstructure of secondary phases and the mechanical performance of metastable β −Ti - alloys is currently an intensively studied topic. Even very small changes in volume fractions of secondary phase particles have a measurable effect on the elastic constants of the dual-phase material. This effect is particularly pronounced for the softest shear elastic constant C´, that stiffens two times between the solution-treated material and a material with approximately 60% of ω particles for Ti15Mo. We present the capability of ultrasonic methods to assess the effective crystal symmetry (and the deviations therefrom) in the dual-phase Ti alloys and the homogeneity in their elastic properties. In addition, the results illustrate the different nature of elasticity relationships between the matrix and the secondary phase particles in the β + α and β+ ω alloys and explain the different mechanisms of elastic stiffening of the matrix by these particles. Single crystals of two different metastable (LCB and Ti15Mo) dual-phase β-titanium alloys with different phase compositions and different volume fractions of individual phases were investigated using resonant ultrasound spectroscopy (RUS) and transient grating spectroscopy (TGS). The combination of these two methods enables us also to discuss the homogeneity of the observed changes in the elastic constants by comparing the local data from TGS with the results from RUS representing the effective response of the whole crystal.
[237] ID:237-An imaging technique for the strain-engineering of deformable electrodes
Christophe Rousselot (UFC- FEMTO-ST), Yves Gaillard (UFC- FEMTO-ST), Marina Raschetti (UFC- FEMTO-ST), Marion Vieira (UFC - FEMTO-ST), Frédéric Kanoufi (CNRS - ITODYS) and Fabien Amiot (CNRS- FEMTO-ST).
Abstract
Hydrogen is today mainly obtained by hydrocarbon steam reforming, which produces large CO2 quantities. Because of the rising concern about greenhouse gas emissions, the widespread use of hydrogen as an energy carrier requires the development of a carbon-free production chain. In case it makes use of renewable electricity sources, hydrogen production by electrolysis may be the key to trigger the expansion of this promising sector. However, only a few percent of the total hydrogen production comes today from water electrolysis, mainly because of its cost, which is about four times higher than the cost of hydrogen obtained by steam reforming. Electrolysis requires an electrocatalyst, typically platinum, which is rare and expensive. Electrolytic production of H2 is thus handicapped by its dependence on platinum and by the adverse role played by the hydrogen bubbles produced at the electrode surface in the hydrogen production itself. It is therefore crucial, in order to minimize the cost and energy losses, to avoid materials like platinum as much as possible, and to limit the adverse effects of bubbles production. It has already been demonstrated that elastic strains can modulate the electrocatalytic activity of metals [1-3], so that more abundant materials could be strained in order to compare with platinum in terms of electrocatalytic activity. The question of the optimal position in the 6-dimensional strain space is however open, and we propose an experimental approach based on an original imaging technique to address this issue. [1] Mavrikakis et al. Phys. Rev. Lett. 81 (13), 1998. [2] Kibler et al. Angew. Chem. Int. Ed. 44, 2005. [3] Martinez-Alonso et al. PCCP 24, 2022.
[238] ID:238-Waltzing with Instabilities to Morph Rotating Structures
Eduardo Gutierrez-Prieto (EPFL, fleXLab), Gilad Yakir (EPFL, fleXLab), Michael Gomez (King's College London) and Pedro M. Reis (EPFL, fleXLab).
Abstract
Nearly every machine built since the Industrial Revolution involves rotating elements (e.g., wheels, gears, fans, pumps, and turbines), which are so ubiquitous that they often go unnoticed. These rotating systems are affected by three fictitious forces: the (i) Centrifugal, (ii) Euler, and (iii) Coriolis forces (this latter can typically be neglected in many engineering systems). Despite rotodynamics being a mature field studying the mechanics of rotating systems, the effects of Euler forces, produced by changes in angular velocity, remain surprisingly understudied. Predictive rotodynamics models are developed to optimize performance and predict the onset of instabilities to avoid failure. We introduce "Gyrophilia'' as an alternative approach to harness the combination of Centrifugal and Euler forces for novel functional mechanisms in rotating systems with tunable, switchable, and programmable characteristics. We have built a fully automated experimental setup to study slender elastic beams in a rotating frame, allowing accurate control of the angular velocity and acceleration. With our apparatus, accompanied by a simplified elastica model, we investigate the (in)stability of slender elastic beams with different boundary conditions. Our results demonstrate large and tunable structural deformation, buckling, and snap-through of pre-arched beams. We envision utilizing bistable beams as mechanical switches actuated through the angular acceleration, whose response to the rotational loading can be tuned by imposing non-trivial boundary conditions (e.g., angled clamps, contact, etc). We can engineer mechanical systems comprising multiple bistable beams subject to differing boundary conditions such that each component responds differently to a given loading condition. We can then apply principles of mechanical logic to build mechanical circuits that can be programmed through an accurate control of the angular velocity. We demonstrate how such principles could be exploited to sequentially actuate three rotating bistable beams, which could act as a peristaltic pump in a centrifugal microfluidics cartridge.
[239] ID:239-Mechanic-Based Therapies in Osteoporosis: A Multimodal approach
Juan José Toscano-Angulo (University of Seville), Juan Mora-Macías (University of Huelva), Pablo Blázquez (University of Seville), Juan Morgaz (University of Córdoba), Jaime Domínguez (University of Seville) and Esther Reina-Romo (University of Seville).
Abstract
Osteoporosis (OP) is a skeletal disorder characterized by a decrease in bone mineral density (BMD) and a microarchitectural deterioration of the bone tissue, leading to increased bone fragility and risk of sudden fractures. One of the main problems of osteoporotic patients is their poor osteogenesis capability during bone regeneration processes, such as those occurring after fractures. The effects of mechanics on the newly formed bone, occur at the tissue, cellular, and even molecular scale. However, at all these scales, the identification of the mechanical parameters and their mechanisms of action are still unknown and continue to be investigated. This mechanical regulation of biological processes is the basis of mechanobiology and is used in this study to understand the multimodal response of the osteoporotic bone callus to external mechanical stimulation. An in vivo bone transport (BT) treatment was performed in the right-back metatarsus of three female merino sheep after a 30-week OP induction protocol to reach a 10% reduction in BMD. After the implantation of an instrumented external fixator, a 15-mm metatarsal defect was surgically induced. The BT process considers a latency period of 7 days, after which an electrical stimulation treatment was applied (5 h/day, 5 days/week) during the distraction and the consolidation phases till sacrifice, 40 days after surgery. In the distraction phase, a bone segment was gradually transported (1 mm/day) toward the position of the original bone defect for 15 days. Different monitoring techniques at the tissue and fibril scales (distraction forces measurement, gait analysis, ex vivo techniques) have been applied to simultaneously characterize the main biological and mechanical events in bone regeneration during osteoporosis. This work points out the unquestionable role mechanical and structural parameters play in the biological regulation of bone regeneration during osteoporosis.
[240] ID:240-Multiscale Analysis of Elastomer-Based Composite Materials Using Strain Energy Homogenisation
Elizaveta Karaseva (University of Twente, Production Technology), Inna Gitman (University of Twente, Computational Design of Structural Materials), Ton Bor (University of Twente, Production Technology), Anke Blume (University of Twente, Elastomer Technology and Engineering) and Dengpeng Huang (University of Twente, Elastomer Technology and Engineering).
Abstract
In response to the growing demand for efficient materials in modern technology, elastomer-based composites have emerged as high-performance engineering materials. The description of the finite deformations in elastomers typically involves formulations based on strain rates and the application of the finite element method (FEM) and homogenisation for elastomer-based composites with the assumption of effective material properties. However, using FEM, especially in composite materials, usually is a trade-off between accuracy and computational speed. Therefore, developing novel approaches is essential for predicting elastomer composites’ mechanical behaviour without extensive experimental trials. In this context, the comprehensive homogenisation approach for elastomer-based composite materials explores the interaction between a hyperelastic matrix and a linear elastic filler in a carbon black-reinforced S-SBR composite. The framework helps to optimise the manufacturing process for nano-filler-reinforced elastomer-based composites, allowing a quantitative assessment of the impact of both the matrix and the filler on the final material properties and applying strain energy functions for describing the mechanical behaviour of the composite components. On the mesoscale, a unit cell of the material is proposed for the first iteration that considers the fractal dimension of the filler structure, defining volume fractions for the filler, matrix, and interphase. This enables the use of the rule of mixture, summing the strain energy required to predict the deformation in the composite. The work provides a comprehensive perspective on the suggested homogenisation and demonstrates the potential of the strain-energy-based homogenisation approach for elastomer-based composites.
[241] ID:241- Influences of mechanical and water aging on changes in mechanical behavior and damage mechanisms on sandwich structures used as windturbine blades in marine environment (EMR)
El Hadji Amadou Ba (CIMAP UMR 6252 CNRS Université Caen Normandie), Khalid Aoujdad (LOMC Université Le Havre Normandie), Florian Gehring (CIMAP UMR 6252 CNRS Université Caen Normandie), Damien Leduc (LOMC Université Le Havre Normandie), Pierre Marechal (LOMC Université Le Havre Normandie), Mounsif Ech-Cherif El-Kettani (LOMC Université Le Havre Normandie) and Alexandre Vivet (CIMAP UMR 6252 CNRS Université Caen Normandie).
Abstract
The French law relating to the energy transition, passed on August 2015, aimed to promote the proportion of green energy in the energy mix in France, with a proportion of land and marine wind energy production by 20% in 2028, corresponding to a production of electricity of 10 GW. Marine windturbine blades, in service, are subjected to combined mechanical stresses (torsion, bending, centrifugal force, impact) and environmental ageing (humidity, temperature). To minimize maintenance operations and optimize their service life, it is necessary to be able to estimate as accurately as possible the material and structure integrity. The majority of blades has a sandwich structure. Skins are in thermosetting resin/fiberglass laminates and core is made of polymer foam with localized reinforcements of resin/carbon fibers laminates. The understanding of the internal damage mechanisms is then an essential step of the knowledge of the structure integrity evolution. For this, sandwich samples are submitted to hygro-thermal ageing and low energy impact. These two kinds of ageing are representative of the life service of marine windturbine blades. Mechanical tests, at different ageing levels, show the influence of intern damages on the macroscopic behaviour of sandwich materials. In-situ, by acoustic emission monitoring, et post-mortem observations allow to have a better understanding of the kinetics of the damage mechanisms identified at different scales especially, the phenomena identified at the level of interval interfaces (skins/core and fibers/matrix).
[242] ID:242_Stress field estimation for a 316L stainless steel through full-field measurement
Qi Hu (Laboratoire de Mécanique Multiphysique Multiéchelle (LaMcube) UMR CNRS 9013), Arnaud Beaurain (Laboratoire de Mécanique Multiphysique Multiéchelle (LaMcube) UMR CNRS 9013), Jean-François Witz (Laboratoire de Mécanique Multiphysique Multiéchelle (LaMcube) UMR CNRS 9013), Ahmed El Bartali (Laboratoire de Mécanique Multiphysique Multiéchelle (LaMcube) UMR CNRS 9013) and Denis Najjar (Laboratoire de Mécanique Multiphysique Multiéchelle (LaMcube) UMR CNRS 9013).
Abstract
Composed of an aggregate of grains with different sizes and local orientations, the deformation of polycrystalline metals exhibits heterogeneity at the microstructure scale under loading. The investigation of this heterogeneous localization has been greatly facilitated by the development of full-field measurement techniques such as Digital Image Correlation (DIC). However, the measurement of stress fields still remains an open problem. To access the local stress, some methods have been reported, such as inverse methods or data-driven identification based on DIC measurements, which require extensive simulation work or mathematical calculations or thermomechanical coupling measurements. In this study, a more straightforward method is proposed to estimate the local stress distribution in 316L austenitic polycrystalline stainless steel using the Ludwik hardening model. This approach requires the identification of local elastic limits and hardening strength coefficients. For this purpose, we first develop a strategy to identify the moments of plasticity onset based on strain evolution measured by DIC at the grain-scale, where all quantities are averaged within each grain. Assuming isotropic material properties, the grain-scale elastic limits are then identified using Hooke's law with the strain information at plasticity onset. Moreover, based on the qualitative relationship between the hardening strength coefficient and the plastic strain rate, another strategy is proposed to identify the grain-scale strength coefficients. A correlation between grain-scale von Mises strain and strength coefficients has been established. With the identified elastic limits and strength coefficients, the grain-scale stress fields are estimated, and their averaged values align well with the engineering ones, validating the reliability of the proposed approach. The strategies for elastic limits and hardening strength coefficients can be further extended to each measurement point, allowing the estimation of microscale stresses that highlight intragranular heterogeneities in the stress distribution.
[243] ID:243-Efficient prediction of strain localisation and limit load in heterogeneous solids via upper bound limit analysis
Jonas Hund (Aarhus University), Varvara Kouznetsova (Eindhoven University of Technology), Laura Alessandretti (Technical University of Denmark) and Tito Andriollo (Aarhus University).
Abstract
To predict the limit load and onset of failure of a part under a given load, knowledge of the points of stress and strain localisation is crucial. Reasons for strain localisation can be macroscopic, such as the part's geometry. However, strain localisation can also be a result of microscopic features like material morphology. Considering heterogeneous solids with voids, strain localisation occurs in the form of shear bands that depend on the potentially non-uniform void distribution. Hence, predicting the onset of damage and failure in parts featuring a non-uniform void distribution may require resolving their microstructure. However, high-resolution micromechanical methods capable of doing that are restricted to the microscale due to high computational costs. In this contribution, the aim is to assess the strain localisation due to shear banding in representations of 2D random microstructures with a given porosity through an upper bound limit analysis method at reduced computational cost compared to other micromechanical approaches. The model domain is discretised using rigid elements. Deformation and energy dissipation are restrained to discontinuities of the velocity field introduced at element boundaries. Previous work of the authors established that the Delaunay triangulation of the considered microstructures features edges that coincide with the locations of shear bands when the void centroids serve as the nodal grid. Based on this finding, the model domain is discretised via Delaunay triangulation with the discontinuities introduced along element boundaries representing potential locations of shear bands as narrow zones of strain localisation and plastic dissipation. This discretisation approach efficiently and effectively reduces the number of potential discontinuities, thus further lowering the computational cost of the analysis method. To demonstrate the approach's capabilities, predicted limit loads under uniaxial tension and deformation patterns in representations of random periodic microstructures are compared to results from a finite element study.
[244] ID:244- Inverse Analysis of Defects in CFRP Specimen with Multiple Microscopic Structures by Graph Neural Network Using Stress Distribution of FEM
Yuta Kojima (Keio University), Kenta Hirayama (Keio University), Yoshihisa Harada (National Institute of Advanced Industrial Science and Technology) and Mayu Muramatsu (Keio University).
Abstract
In this study, for a complex-shaped carbon-fiber-reinforced plastic (CFRP), machine learning model is used to predict the three-dimensional information of defects from the sum of principal stresses at the surface (DSPSS) calculated from the finite element method (FEM). The reason for using DSPSS in this study is that it is intended to perform inverse estimation of defects using infrared stress measurements. CFRP specimens are made in different microstructure and the way of lamination. Here, a prosthetic leg with a curved surface is used as the analysis model. A CFRP prosthetic leg is characterized by the lamination of prepregs with multiple microstructures, such as plain weave, twill weave, and unidirectional in practical use. CFRP prosthetic leg models which have different microstructures and the way of lamination are created in FEM, and homogenized finite element analysis is conducted to obtain DSPSS. In the process of prediction, the predictabilities of internal defects for each model are compared, and differences among microstructures are discussed using microstructural features and stress distributions. A graph neural network is used to predict the three-dimensional structure of the defects inside the prosthetic leg based on DSPSS of the prosthetic leg analyzed by FEM. As an adaptation, this machine learning model can be used in the experimental data.
[245] ID:245-Numerical Implementation of Strain Gradient Crystal Plasticity in Irradiated Polycrystalline Aggregates Using FFT-Homogenization Method
Amirhossein Lame Jouybari (Jožef Stefan Institute), Samir El Shawish (Jožef Stefan Institute) and Leon Cizelj (Jožef Stefan Institute).
Abstract
This study investigates the numerical implementation of strain gradient crystal plasticity theory using the Fast Fourier Transform (FFT)-homogenization method for irradiated polycrystalline aggregates subjected to tensile loading. The formulation of strain gradient crystal plasticity is established to enhance the accuracy of the results compared to classical crystal plasticity, especially in cases where strain localization bands emerge. In particular, various nonlocal parameters are introduced and types of generalized boundary conditions applied to grain boundaries when solving the generalized balance equation, which is derived by the principle of virtual power together with linear momentum balance equation (Cauchy’s equation of motion). These boundary conditions, commonly known as micro-free, micro-continuity, and micro-hard, improve the control of dislocation transmission between the neighboring grains. The study also explores the influence of irradiation on the realistic type of microstructure, such as Voronoi polycrystalline aggregate, by analyzing the formation of localization bands, commonly referred to as “clear channels”. The simulations reveal two distinct types of localization bands: slip bands (aligned with the active slip system) and kink bands (rotated with respect to the active slip system). Computationally, to obtain the results, a fixed-point algorithm (basic scheme) is employed to address the proposed micromechanical model of classical crystal plasticity within the FFT-homogenization framework. However, a pseudo-explicit algorithm is utilized for strain gradient crystal plasticity. To enhance the performance, the algorithm is enriched by the rotated scheme for the Green operator and a specific variant of the Anderson acceleration known as the alternate 2-δ method. Both enrichments accelerate the convergence and refine the results. Furthermore, going beyond the linear momentum balance equation, the resolution of the generalized balance equation in the context of strain gradient crystal plasticity theory incorporates a 21-voxel finite difference scheme due to its superior performance in regions characterized by strong discontinuities such as grain boundaries.
[246] ID:246-Modeling Thermo-Mechanical Behavior in Filled Elastomers: Applications to Finite-Element Numerical Simulation
Rebeca Cedeno (Laboratoire de Mécanique et d'Acoustique) and Stéphane Lejeunes (Laboratoire de Mécanique et d'Acoustique).
Abstract
The thermomechanical behavior of natural rubber (NR) and butadiene rubber (BR) blends is explored in this study, focusing on an in-depth examination of nonlinear viscoelasticity, in particular the Payne and preload effects, and the integration of finite element analysis. A comprehensive theoretical framework is developed to capture the intricate interplay of these factors, providing a description of the mechanical responses of NR-BR blends under varying thermomechanical conditions. Experimental investigations complement the theoretical modeling with dynamic mechanical analysis (DMA) and uniaxial tensile testing to unveil the material properties of NR-BR blends. The experimental data help to validate and improve the theoretical model, reinforcing the correlation between the theoretical predictions and observed behavior. The model is implemented in a user material subroutine (UMAT) to employ finite element analysis (FEA) in ABAQUS to simulate and predict the macroscopic behavior of NR-BR blends, offering insights into the material performance under diverse loading scenarios and geometric configurations. By incorporating FEA with both experimental and theoretical results, our study improves the current state-of-the-art in terms of integrality and accuracy. The insights gained from this research are a first step in guiding the design and engineering of new self-healing rubber formulations with targeted applications in the automotive and aerospace industries.
[247] ID:247-Controlling damage localization through hierarchical microstructure
Christian Greff (Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)), Paolo Moretti (Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)) and Michael Zaiser (Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)).
Abstract
Hierarchical materials are complex, multi-scale systems where structural patterns are repeated across scales in a self-similar fashion. Hierarchical microstructural patterns are often credited as a determinant factor in the high fault tolerance of biological and bio-inspired architected materials. For the effective modelling of such meso-scale systems, discrete hierarchical lattice/network models have been used in recent years, where the network constituents are elastic load-carrying elements, subject to a failure criterion. They capture how hierarchical structures redistribute stress over multiple microstructural levels, leading to arrest of crack propagation, the emergence of diffuse damage, and the increase of fault tolerance. In this work, we specifically address the case of interface adhesion and failure/detachment of hierarchically structured thin films in contact with heterogeneous substrates under quasi-static tension. To this end, we introduce a three-dimensional hierarchical network model, where discrete links/elements fail based on a maximum distortion energy (von Mises) criterion with Weibull distributed thresholds, modeling inhomogeneities in local cohesive and adhesive strengths. Element elasticity is modeled in terms of the scalar Random Fuse Model. Our statistical analysis of fracture surfaces indicates that the hierarchical organization is responsible for a substantial enhancement in the localization of damage near the interface. We discuss the origin of this localization phenomenon using concepts of spectral graph theory and multiscaling analysis techniques as well as the influence of hierarchical structuring on performance in terms of peak stress and work of fracture. Further insights into stress redistribution are gained by means of Green functions, an approach that extends beyond these scalar models. While our study of hierarchical fracture and failure is motivated by examples of fibrous materials of biological interest, our results indicate that hierarchical patterns can be useful in engineering scenarios where the focus is on tuning and optimizing adhesion properties or on predetermining locations of failure.
[248] ID:248-Influence of yield surface on stress redistribution and strain localization in a flat notched sample for turbine disk application
Elodie Barrot (Mines ParisTech, PSL University / DMAS, ONERA, Paris Saclay University / SafranTech), Sylvia Feld-Payet (DMAS, ONERA, Paris Saclay University F-92322 Châtillon), Samuel Forest (Mines ParisTech, PSL University CNRS UMR7633), Tonya Rose (Safran Tech Paris Saclay, Rue des jeunes bois, Chateaufort CS80112 78114 Magny les Hameaux), Moubine Al Kotob (Safran Aircraft Engines Villaroche, Rond Point René Ravaud - Réau , 77550 Moissy-Cramayel) and Sylvain Zambelli (Safran Aircraft Engines Villaroche, Rond Point René Ravaud - Réau , 77550 Moissy-Cramayel).
Abstract
The plasticity criterion has been shown to strongly influence the global behavior of a rotating aeronautical turbine disk and its expected burst speed. Moreover, yield surfaces can evolve very rapidly with plastic strain. Their accurate knowledge is thus essential to precisely predict the behavior of a part subjected to multiaxial and non-proportional loadings such as the turbine disk. The use of polycrystalline plasticity models allows the numerical reproduction of yield surface distortion effects observed experimentally for all loading paths thanks to the model's proximity to the physical mechanisms at the origin of the plasticity.
In this study, experiments were conducted on a flat notched sample loaded in tension designed to enhance the effects of chosen plasticity parameters on the stress redistribution and strain development in the sample. Field measurement techniques were then used to compute the experimental fields throughout the loading and measure the boundary conditions to use in the simulations to better suit the experiment. This allowed the experimental fields to be compared to those predicted by finite element simulations of the sample carried out using Zset software. Two material behavior laws were identified on previous test results and used in this study : one model uses Hosford’s macroscopic phenomenological plasticity criterion whereas the second model is a simple polycrystalline model. Then, finite element model updating is performed to enhance the identification of material parameters. Finally, the strain localization during finite element simulations of the sample is studied in order to investigate the influence of numerical and material parameters on the global stress/strain curve and on the geometric properties of localization.
[249] ID:249-Hybrid manufacturing of metallic metamaterials: Process, microstructure and mechanical response
Agyapal Singh (New York University Abu Dhabi), Nikolaos Karathanasopoulos (New York University) and Agyapal Singh (New York University Abu Dhabi).
Abstract
Metallic metamaterials are engineered materials that exhibit unconventional desirable physical and mechanical properties such as low density, high specific strength, and stiffness, making them attractive materials in structural engineering applications. Their fabrication techniques have evolved over time with additive manufacturing (AM), specifically powder bed fusion techniques, facilitating their manufacturing with complex geometries and high accuracy. However, major challenges of these laser-based techniques include the high initial and running costs, limited to few specific alloys, and low building efficiency. The hybrid manufacturing approach combining additive manufacturing and casting, also known as AM-assisted casting or hybrid casting, can be an alternative for the production of metallic lattices and has great potential in reducing the cost associated with the manufacturing. In the current work, we investigate the microstructural attributes and effective mechanical response of architected materials manufactured through hybrid casting in a combined manner for the first time [1], [2]. Different metamaterial topologies are engineered, and their microstructural properties arising from the hybrid casting process are thoroughly assessed using Scanning Electron Microscopy and Computer Tomography methods. To provide quantitative insights into their effective mechanical performance, their static and impact responses are also investigated and compared thoroughly with PBF effective metamaterial attributes. Distinct elastic and post-elastic characteristics, along with failure modes, are identified and comprehensively evaluated. The present work provides benchmark results regarding the process-structure-property attributes of hybrid-manufacturing AlSi10Mg-based metamaterials. Overall, the current study has demonstrated an alternative approach to producing complex metallic lattice materials with the capability of scaling directly to other alloys beyond the ones investigated here.
[250] ID:250-Mechanical identification and modelling of impregnated Nb3Sn Rutherford cable stacks under compressive loading
Xiang Kong (ETH Zurich), André Brem (Paul Scherrer Institution (PSI), Villigen), Douglas Martin Araujo (Paul Scherrer Institution (PSI), Villigen), Michael Daly (Paul Scherrer Institution (PSI), Villigen), Bernhard Auchmann (Paul Scherrer Institution (PSI), Villigen) and Theo A. Tervoort (ETH Zurich).
Abstract
Superconducting accelerator magnets are being developed for enhanced magnetic fields in the Future Circular Collider (FCC) at CERN, which means that, during operation, the superconductive coils will be exposed to even higher electromagnetic (Lorentz) forces. To ensure the mechanical stability and quench protection during normal operation, in this study, the epoxy-impregnated 10-stack made from Nb3Sn Rutherford cables, which can be regarded as a unit cell of superconductive coils, is investigated under compression for its anisotropic mechanical characterization at room and cryogenic temperatures.
In addition, detailed constitutive relations for each Rutherford-cable component (epoxy resin, annealed copper, Nb3Sn superconductor and insulation mica/glass layer) will be determined, in order to build a 2D representative finite element (FE) model at the 10-stack level. This will enable us to predict thermo-mechanical behavior of 10-stack Rutherford cables under cyclic loadings. The homogenized constitutive response of these 10-stack cubes is of significance for the feasibility of coil design and construction.
An in situ full-field deformation measurement is performed at the level of cable stacks via image-based analyses. Rather than the stress-strain curve fit, the image analysis will provide strain measurements at the local strand level, which will be used to validate the FE simulations and, ultimately, explain the failure from knowledge of the detailed mechanical loading.
[251] ID:251-Local Strain Prediction of single phase polycrystalline materials with low-Rank Approximation.
Prabhat Karmakar (Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, 600036, , India), Ilaksh Adlakha (Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, 600036, , India) and Sayan Gupta (Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, 600036, , India).
Abstract
This research introduces a computationally efficient mathematical framework designed to predict the mesoscale (local) strain field in single-phase polycrystalline materials under mechanical loading. The framework utilizes low-rank approximations to estimate the intricate meso-scale strain field precisely, considering the underlying microstructure of single-phase polycrystalline materials. The effectiveness of this framework is evaluated across a broad design space, encompassing various microstructures of single-phase polycrystalline materials and diverse mechanical properties for the constituent phases. Comparative assessments against finite element predictions highlight the predictive capability of the proposed framework. A crucial aspect of this approach involves calibration using data, and the impact of dataset size on accuracy is systematically examined through different statistical measures. Results indicate that the proposed method performs accurately and requires a substantially smaller dataset compared to existing deep learning techniques.
[252] ID:252-Emerging anisotropy and tethering with memory effects in fibrous materials
Antonino Favata (Sapienza University of Rome), Andrea Rodella (Sapienza University of Rome) and Stefano Vidoli (Sapienza University of Rome).
Abstract
Fibrous materials may undergo an internal reorganization, which turns out in the emergence of preferential directions. This is a peculiar behavior of many biological tissues, which drive reorientation by external stimuli at chemo-mechanical levels. In particular, it is detected that contractile cells can reorganize fibrous extracellular matrices and form dense tracts of aligned fibers (tethers), that guide the development of tubular tissue structures and may provide paths for the invasion of cancer cells. Tether formation is caused by buckling instability of network fibres under cell-induced compression. We present a simple mechanical model within a variational framework that captures the essential aspects of these phenomena. The model qualitatively describes: (i) the emergence, induced by local compressive strain, of anisotropy, where fibrous materials exhibit directional preferences; (ii) the occurrence of micro-buckling, which leaves a lasting plastic deformation in the material; and (iii) the formation of localized field patterns, which contribute to the overall behavior of the material. By considering these fundamental aspects, our model provides insights into the mechanical response of fibrous materials and sheds light on the underlying mechanisms driving their behavior.
[253] ID:253-Wear behaviour of as-built and heat treated AISI S2 Tool Steel processed by Laser Powder Bed Fusion
Enrico Saggionetto (Metallic Materials for Additive Manufacturing Unit, Aerospace & Mechanical Engineering Dpt., University of Liège), Alessandra Segatto (Metallic Materials for Additive Manufacturing Unit, Aerospace & Mechanical Engineering Dpt., University of Liège), Olivier Dedry (Metallic Materials for Additive Manufacturing Unit, Aerospace & Mechanical Engineering Dpt., University of Liège), Jérôme Tchoufang Tchuindjang (Metallic Materials for Additive Manufacturing Unit, Aerospace & Mechanical Engineering Dpt., University of Liège) and Anne Mertens (Metallic Materials for Additive Manufacturing Unit, Aerospace & Mechanical Engineering Dpt., University of Liège).
Abstract
Over recent years, manufacturing of tool steels by Laser Powder Bed Fusion (LPBF) has been the object of increasing attention for the possibility of producing parts, with complex shape difficult to obtain through conventional methods. Moreover, the ultra-fast heating and cooling rates pertaining to the LPBF process are responsible for the formation of strongly out-of-equilibrium microstructures, involving supersaturated solid solution and new metastable phases, thus offering new possibilities in terms of usage properties. Therefore, research is now focusing on the development of tool steels with complex chemical composition and higher carbon contents. Under the conditions achieved during the LPBF process, such tool steels composition may lead to the presence of residual stresses within the part promoting cracks nucleation and propagation, thus making the part unusable. In this work, a low alloy tool steel AISI S2 with a medium carbon content (0.5 wt. %) was successfully processed by LPBF. As-built microstructure revealed fresh martensite, bainite and tempered martensite in a supersaturated condition, with the presence of residual stresses. In addition, phase transformations can occur in service at high temperature, affecting the mechanical properties of the part. Therefore, Differential Scanning Calorimetry (DSC) was performed on as-built samples to investigate the thermal behaviour of the material within the range 200 – 400 °C, with the aim to design a post-thermal treatment to stabilize the microstructure. Microstructural characterization was carried out on as-built and heat treated samples, in combination with macro- and nano-hardness analysis. Tribological tests were also carried out on as-built and heat treated samples. Wear properties were further assessed through observations of the worn track and counter-body surfaces and of transversal sections underneath the worn track.
[254] ID:254-A Discrete Slip Plane Approach to Simulate the Deformation of Tungsten Nanostructures
Carlos Ruestes (IMDEA Materials Institute) and Javier Segurado (IMDEA Materials Institute).
Abstract
The mechanical response of nanostructured metals is influenced by microstructure, characteristic timescales, and lengthscales. Notable examples include single crystalline pillars and nanoporous foams. Computational homogenization tools are useful for linking macroscopic response with microstructural behavior by means of representative volume elements of the system. FFT spectral methods offer improved numerical performance over standard Finite Element based homogenization, thus allowing for detailed RVE models. FFT homogenization for metals relies on the crystal plasticity model, which assumes the homogenization of dislocation ensembles at the nano-scale to define a flow-rule for each slip system. However, at sub-micron scales, the plastic behavior of metals is dominated by few discrete slip events of stochastic nature producing discontinuities along the slip planes involved. Therefore, standard crystal plasticity is not adequate for these sizes. This study introduces a stochastic approach, considering the slip of individual planes, implemented in an FFT-based homogenization software by incorporating each slip event as a shear eigenstrain field. The implementation is initially applied to predict the behavior of tungsten micropillars and then extended to simulate nanoporous tungsten with random bicontinuous open-cell representative volume elements obtained using levelled-wave methods. The model results are compared against experimental observations. It is shown that both macroscopic stress-strain curves and deformation patterns agree with experimental results.
[255] ID:255-Modeling of Short Crack Propagation: Coupling Phase Field Method with Discrete Dislocation Dynamics
Luis Eon (Laboratoire d'Etude des Microstructures (CNRS/ONERA)), Benoît Appolaire (Institut Jean Lamour (CNRS/Université de Lorraine)) and Riccardo Gatti (Laboratoire d'Etude des Microstructures (CNRS/ONERA)).
Abstract
The propagation of short cracks in FCC metals is strongly influenced by microstructures, in particular associated with the linear defects of the crystals, i.e. dislocations.
In this work, a new coupling between two methods at the mesoscale is proposed to investigate the interaction of moving cracks with three-dimensional dislocation microstructures. First, crack propagation is predicted by a phase field model. In this approach, cracks are described by some continuous damage field that evolves so as to minimize the total free energy, including stored elastic energy and surface energy associated with the crack. Second, dislocation microstructures are handled by a Discrete Dislocation Dynamics (DDD) model that describes plastic deformation by the movement of dislocations under external loading.
To couple both models, the DCM (Discrete-Continuous Model) approach is used, where dislocations are described by continuous fields (eigenstrain or Nye tensor) in an elastic solver. Fast Fourier Transform (FFT) based solvers are used for their computational efficiency. Particular discretization schemes have been adopted to minimize the smoothing of dislocation cores, usually performed in DCM approaches. The different schemes are carefully analyzed with respect to the quality of the predicted fields. In addition, the resulting model is implemented using efficient parallelization solutions.
Thanks to this new coupling, we have been able to study the elastic shielding on crack propagation according to the nature of the slip systems and the dislocations density. We have also been able to investigate phenomena and ingredients rarely accounted for, such as dislocation cross slips close to the crack front or the influence of the number of sources. This mesoscale method constitutes a breakthrough for the thorough analysis of physical mechanisms controlling the early stages of fracture in metallic materials.
[256] ID:256-Constitutive modelling of damage-induced stress softening of biological soft materials
Sarah Iaquinta (LMGC, IMT Mines Ales, Univ Montpellier, CNRS, Ales, France), Grégory Chagnon (Univ. Grenoble Alpes, CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, 38000 Grenoble, France) and Anne-Sophie Caro (LMGC, IMT Mines Ales, Univ Montpellier, CNRS, Ales, France).
Abstract
Dysfunctions and anomalies in pelvic tissues cause numerous consultations and surgical interventions in women throughout their lives and during pregnancy. These issues are primarily attributed to the degradation or alteration of the biomechanical properties. For clinicians, understanding the mechanical behavior of this tissue is crucial for anticipating its degradation. This study aims to introduce an animal model using pig perineal tissues. To simplify the modelling process, the tissue is conceptualized as a multilayered tissue as it is mainly composed by three layers of skin, connective tissue, and anal sphincter muscles. The model relies on instrumented tensile tests, cyclic stress-relaxation, and unloading tests to effectively separate the influences of viscosity and damage effects on samples from the three layers as much as possible. Initial findings suggest a strong correlation between applied stretches, relaxation stress loss, and stress softening (Mullins effect), which is clearly observable during unloading sequences. A macroscopic modelling is employed to propose a 3D formulation including hyperviscoelasticity and stress softening. A set of parameters is identified to describe the mechanical behavior of the skin, connective tissue, and anal sphincter muscles during the loading, relaxation and unloading cyclic phases.
[257] ID:257-Characterization of the deformed state before the onset of recrystallization in pure aluminium by in situ SEM tensile tests and CPFEM simulations
Pauline Stricot (ONERA, the french aerospace lab), Anna Ask (ONERA, the french aerospace lab), Louise Toualbi (ONERA, the french aerospace lab), Yves Renollet (ONERA, the french aerospace lab), Quentin Barres (ONERA, the french aerospace lab), Henry Proudhon (MINES Paris, PSL Research University, MAT - Centre des matériaux, CNRS UMR 7633) and Samuel Forest (MINES Paris, PSL Research University, MAT - Centre des matériaux, CNRS UMR 7633).
Abstract
Conventional metallurgy is based on thermomechanical processes. The coupling between strain and temperature during these processes leads to grain boundary migration, recovery and recrystallization mechanisms. Although these mechanisms have been observed and studied for a long time, they are yet to be fully understood. Therefore, it is of particular interest to have a numerical model that can predict the final microstructure of a given material under specific stress and temperature conditions. To achieve this, it is necessary to couple two models: one that predicts microstructure evolution caused by deformation and the other for that predicts evolution caused by temperature. This was accomplished using a coupled phase-field-Cosserat model. However, to quantitatively predict microstructure evolution, the model needs to be calibrated against experimental observations. This study focuses on the microstructural evolution of pure aluminium (99.999 %) during deformation, both at room and high temperatures. First, in situ SEM tensile tests coupled with EBSD analysis are conducted at room temperature to assess the modification of crystallographic orientation. The results, including strain and crystal lattice reorientation, are compared to those obtained from crystal plasticity finite element method (CPFEM) simulations. To obtain an accurate description of the initial microstructure, the sample is characterized using diffraction contrast tomography. This provides a 3D orientation map, which is used to construct the synthetic microstructure. The comparison between the numerical and experimental microstructural evolutions enables fine calibration of the CPFEM simulations and verification of the model’s ability to accurately reproduce lattice reorientation and energy accumulation resulting from plastic deformation. The calibration procedure will then be carried out similarly using hot temperature SEM tensile tests coupled with EBSD analysis. This will allow us to proceed with the calibration of our coupled phase-field-Cosserat model for predicting dynamic recrystallization in polycrystalline metals.
[258] ID:258-Elasto-granular coupling : how a granular heap deforms a soft substrate
Sophie Monnery (Institut Jean le Rond d'Alembert, Sorbonne Université), Anaïs Abramian (Institut Jean le Rond d'Alembert, Sorbonne Université), Suzie Protière (Institut Jean le Rond d'Alembert, Sorbonne Université) and Arnaud Lazarus (Institut Jean le Rond d'Alembert, Sorbonne Université).
Abstract
Many problems involve an interplay between granular matter and elastic structures, including food packaging (e.g. coffee beads in plastic bags), cell membrane deformations in plants, or soil-root interactions. Here, we explore this coupling in a simplified system, investigating how an elastic structure deforms under the weight of grains. We set up a two-dimensional experiment consisting of an extensible ribbon, placed between two walls, onto which grains are deposited to form a heap. We show that the ribbon, as it deforms, acts as a reservoir of grains, altering the shape of the grain pile, including the angle of repose and the spreading of the heap, depending on the initial tension and rigidity of the ribbon. By increasing then significantly the volume of grains, the ribbon elongation and the spreading of the heap eventually saturate above a threshold related to the nonlinear behavior of the ribbon.
[259] ID:259-Harnessing stiffness asymmetry in thin sheets inflatables for high deformation shape morphing
Nathan Vani (ESPCI-PSL), Alejandro Ibarra (ESPCI-PSL), Étienne Reyssat (CNRS, ESPCI-PSL), José Bico (ESPCI-PSL) and Benoît Roman (ESPCI-PSL).
Abstract
Inflatables are particularly popular in the field of shape morphing materials. Their simple, purely mechanical actuation allows for fast deployment and high reusability. Moreover, just as the overall shape and stiffness of a party balloon are directly linked to its internal pressure, inflatable objects offer an elegant example of the coupling of elasticity and geometry.
We study networks of parallel inflatable tubes obtained through the planar welding of two plastic sheets. Composite tubes presenting two sides of distinct stiffness can be made by using two sheets of different thicknesses. Upon inflation of such tubes, a mismatch of curvature between the two walls rotates the seam line connecting them. Those local displacements allow for enormous deformations when integrated across large networks. We present experimental results on the mechanics of inflation of either one or several connected tubes.
The shapes of the tubes can be predicted throughout inflation using a simple Kirchhoff beam model, for which analytical solutions are determined for the limit cases of low and high pressures. In the latter case, a boundary layer at the edge of the seam line fully determines the rotation between two connected tubes. We highlight as well how contact between neighboring tubes limits in practice the overall motion of our inflatables.
Afterwards we formulate and solve an inverse problem to design a wide variety of objects that can be described as a two-dimensional curve perpendicularly to the direction of the tubes. The question of the stiffness of such structures is discussed as well. We finally present several applications of asymmetric tubular inflatables to more complex geometries: axisymmetric surfaces, kirigami, and curved folding.
[260] ID:260-Effect of processing on morphological features and mechanical properties of extruded pea starch-protein composites
Imen Jebalia (INRAE-BIA), Magdalena Kristiawan (INRAE-BIA), Sofiane Guessasma (INRAE-BIA) and Guy Della Valle (INRAE-BIA).
Abstract
Extruded foods from pulses can be envisaged as solid foams with cell walls, considered as a dense starch-protein composites. Pea flour (PF) and blends of pea starch and pea protein isolate (PPI) with different protein contents (0.5-88% dry basis) were extruded under various thermomechanical conditions (Specific Mechanical Energy=102-103kJ/kg) to obtain models of dense starch-protein composites with different morphology. Their morphology was revealed by CLSM microscopy, and their mechanical properties were investigated using a three-point bending test, complemented by Finite Element Method (FEM) modelling. Composite morphology revealed protein aggregates dispersed in the starch matrix. It was described by a starch-protein interface index Ii computed from the measured total area and perimeter of protein aggregates. The mechanical test showed that the extruded PF and PPI ruptured in the elastic domain, while the extruded starch-PPI (SP) blends ruptured in the plasticity domain. The mechanical properties of pea composites were weakened by increasing the particle volume fractions, including proteins and fibres, probably due to the poor adhesion between starch and the other constituents. The mechanical behaviour of pea composites did not accurately follow simple mixing laws because of their morphological heterogeneity. Modelling results show that the elastoplastic constitutive model using the Voce plasticity model satisfactorily described the hardening behaviour of SP blend composites. Reasonable agreement (2-10%) was found between the experimental and modelling approaches for most materials. The computed Young's modulus (1.3-2.5 GPa) and saturation flow stress (20-45 MPa) increased with increasing Ii (0.7-3.1), reflecting the increase of interfacial stiffening with the increase of contact area between starch and proteins. FEM modelling was shown to be a relevant approach to consider the microstructure heterogeneity of starch-protein composites, and to contribute to the design of extruded pea products with desired properties.
[261] ID:261-Experimental study and modeling of bending behavior in temperature of a SMAT-treated Ni-based superalloy
Anna Garambois (ONERA), Pascale Kanouté (ONERA), Louise Toualbi (ONERA), Yves Renollet (ONERA), Quentin Barrès (ONERA) and Delphine Retraint (LASMIS - Université de Technologie de Troyes).
Abstract
Mechanical surface treatments are commonly used in the aerospace industry to improve the surface properties and delay fatigue crack initiation of critical parts, such as turbine disks. SMAT (Surface Mechanical Attrition Treatment) is a process that creates a nanocrystalline layer on the surface of treated mechanical parts in addition to superficial compressive residual stress and strain hardening. Previous studies have shown that SMAT treatment can increase the yield strength, stress at failure, and fatigue life of metal parts by inducing severe plastic deformations at the material's surface without altering its chemical composition or core microstructure.
This study aims to investigate the effect of SMAT on the fatigue resistance of nickel-based superalloys in order to build a physically-based fatigue life model. The first stage focuses on precisely characterizing the impact of SMAT on the mechanical behavior of the material and its work-hardening mechanisms. To achieve this, an experimental study was conducted on Inconel 718 SMAT-treated specimens. In situ SEM 4-point bending tests were performed at 20°C and 450°C, combined with digital image correlation (DIC) based on a speckle pattern in order to access the local strain fields of the specimen. The resulting information was used to analyze the constitutive behavior along the SMAT-affected zone, up to a few hundred microns from the surface, in both tensile and compressive stress zones of the specimen.
In addition to the mechanical characterization, we investigated the gradient of material properties and their evolution under thermomechanical stress through microhardness measurements, crystal disorientation measurements using EBSD, and residual stress measurements using XRD. These complementary results allow the monitoring of the evolution of the SMAT induced properties under load cases representative of part service conditions.
Later on, fatigue tests will be conducted to study crack initiation mechanisms on SMAT-treated material, with particular attention given to the extrusion/intrusion phenomenon
[262] ID:262-X-ray CT of AM Defects and their Role in Fatigue
Philip Withers (Royce Institute, University of Manchester).
Abstract
Additive Manufacturing (AM), has the potential to revolutionize manufacturing processes for complex 3D, low production number components, to reduce part numbers, as well as to repair retired components. However the wider application of AM for high structural integrity components is in many cases limited by their unacceptable fatigue performance. This arises in large part from the entrainment of a variety of defects including loss of fusion defects and gas porosity. Here X-ray CT is applied to study the nature and location of AM defects according to the manufacturing process. Further it is used relate the fatigue life to the presence and location of critical defects, their potency and their behaviour. In particular, time resolved X-ray CT is used to track the behaviour of cracks initiated from different types of defects and used to assess and validate various models for fatigue crack growth and lifetime prediction.
[263] ID:263-Investigation of free vibrations of porous functionally graded plates using the R-functions theory
Tetyana Shmatko (NTU "KhPI") and Lidiya Kurpa (NTU "KhPI").
Abstract
Research of free vibrations of porous functionally graded material (FGM) plates with complex shape is carried out. It is supposed that thickness of the plate changes in direction of one of the axes. Two types of porosity distributions through the thickness even and uneven are considered. To obtain the mathematical model of the given problem the first order shear deformation theory of the plate (FSDT) is used. The effective material properties in the thickness direction is modelled by the power law. Variational Ritz’s method joined with the R-functions theory is used for solution of the formulated problem. The developed approach is tested on a lot of problems. Comparative analysis of the obtained results for rectangular plates confirms their verification. Demonstration of the efficiency of the proposed approach is fulfilled for FGM plate with complex shape and various boundary conditions. Effect of the different parameters on vibration characteristics such as porosity, volume exponent, types of FGM, boundary conditions is studied.
Nathan Vani (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université de Paris), Alejandro Ibarra (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université de Paris), Etienne Reyssat (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université de Paris), José Bico (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université de Paris) and Benoît Roman (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université de Paris).
Abstract
We study the mechanical and geometrical behavior of two ribbons that are joined together at one extremity in the form of a dowsing Y-rod. The ribbons are pulled apart at their free ends in opposite directions. We consider the angle $\theta$ made by the connected end with the normal to the direction of the pulling forces.
If both ribbons are identical, the connected end is oriented normal to the pulling direction, $theta=0$. Breaking the symmetry of the system with different bending stiffnesses modifies that angle, with the joined end pointing towards the pulling force on the weaker ribbon. Surprisingly, over a wide range of forces, this angle is independent of the load and is a function of the stiffness asymmetry alone.
We rationalize this observation with a boundary layer analysis in the framework of two coupled Kirchhoff beams. The analytical solution found for the shape of the boundary layer allows us to use this simple test as a quite accurate measurement of relative bending stiffness. We present this model, as well as its limits for forces large enough to violate hypotheses, introducing either plasticity or three-dimensional effects in the boundary layer.
Finally, by allowing an inhomogeneous cross-section of one of the ribbons along its length, and thus a curvilinear variation of its bending stiffness, we prevent the angle from being load-independent. The dependence of the angle $\theta$ with the applied force can be chosen by figuring out the corresponding spatial evolution of the beam’s cross-section. We formulate this inverse problem in the framework of the tapered Elastica, and present a direct application to a visual linear force sensor made with two thin pieces of Mylar and one piece of double-sided tape.
[265] ID:265-Nonlinear plate theory for inflatable panels: theoretical, numerical and experimental investigations
Paul Lacorre (Aix-Marseille Université, CNRS, ISM, Marseille, France), Jean-Christophe Thomas (Nantes Université, École Centrale Nantes, CNRS, GeM, UMR 6183, F-44000 Nantes, France), Rabah Bouzidi (Nantes Université, École Centrale Nantes, CNRS, GeM, UMR 6183, F-44000 Nantes, France) and Anh Le Van (Nantes Université, École Centrale Nantes, CNRS, GeM, UMR 6183, F-44000 Nantes, France).
Abstract
Structures made of pressurized membrane elements are gaining in popularity due to their numerous ecological qualities, including reusability, ease of repair, and minimal material usage. Such components are made from airtight coated fabric that acquire load-bearing capacity when filled with a pressurized gas. Although the majority of inflatable components exhibit curvature, such as inflatable cushions and beams, inflatable panels remain flat after inflation due to a large number of threads (known as "drop-stitch") that connect the two parallel flat sides. However, standard plate theories cannot capture their pressure-dependent behavior. In this work, inflatable panels are investigated analytically, numerically and experimentally. Nonlinear equations of motion are obtained from the principle of virtual power in coordinate-free notations. These equations take into account the shear effects through the Mindlin-Reissner kinematics as well as the inflation pressure dependency which tends to increase the overall stiffness. Solutions to the linearized equations are given for a circular panel with uniform vertical load. The analytical solutions are successfully compared to experimental results and to fully nonlinear simulations of the three-dimensional structure of the panel. Furthermore, the linearized eigenvalue problem is solved to obtain the natural frequencies and shapes for clamped, simply-supported and free edges. The successful derivation of the equations of motion now enables the study of buckling of inflatable panels, and the creation of a dedicated plate finite element. We anticipate that this work will facilitate the design and reliability analysis of inflatable buildings.
[267] ID:267-Numerical and experimental study of the effects of initial defects on the compressive and buckling behaviour of composites stiffened panels
Juan Manuel García (DMAS, ONERA, Université Paris Saclay, F-92322 Châtillon - France), Christian Fagiano (DMAS, ONERA, Université Paris Saclay, F-92322 Châtillon - France) and Frédéric Laurin (DMAS, ONERA, Université Paris Saclay, F-92322 Châtillon - France).
Abstract
The effect of initial defects on the compression and buckling behaviour of thermoplastic composites stiffened panels is assessed via an experimental and numerical approach. In the aerospace industry, there is a constant need for increasing the production rates. The manufacturing process of composite entails defects that could impact the mechanical behaviour. The exemption for the acceptability for defects becomes a major industrial issue. Whilst a certain wealth of knowledge is available, the effect of defects on the compressive behaviour of composites structures requires further study. Two composites panels featuring Z-shaped stiffeners are manufactured using a carbon fibre reinforced thermoplastic matrix. Ultrasonic scans and X-ray computed tomography are used to characterize defects. During the compressions tests, the displacement fields are monitored using optical cameras and the damage evolution using thermography and acoustic emission sensors. Numerical simulations are performed using two approaches: one based on the use of shell element, while the other incorporates a combination of shell and continuous elements. The strategies proposed for representing defects involve explicitly meshing delamination and penalizing the material elastic properties at the locations in which voids are detected. With respect to the first panel, the second panel exhibits higher levels of porosity at its skin and lower levels of initial delamination at the stringer’s webs. The buckling modes are detected using the out-of-plane displacement fields. Surprisingly, the panel featuring less defects collapsed at a lower load. Since the panels are free to rotate around the loading axis at the bottom clamp, the dissymmetry given by both the panel geometry and the defects induced an additional torsional deformation leading to an angle of twist. The angle of twist and the buckling mode are properly captured by the numerical simulations. The effects of defects are discussed based on both the experimental tests and the numerical simulations.
[268] ID:268-Mechanical characterization of repaired 7xxx aluminum components via Direct Energy Deposition using novel Al-Mg-Zn alloys
Norberto Jimenez Mena (CRM group) and Nicolas Nutal (CRM group).
Abstract
Aluminum alloys are gaining significant attention in additive manufacturing. However, most of available alloys primarily target Laser Powder Bed Fusion (L-PBF) applications i.e., they are optimized to perform exceptionally well under the high solidification and cooling rates characteristic of this additive manufacturing technique. When these alloys are employed in Direct Energy Deposition (DED) applications, such as LMD, WAAM and WLAM, they often fall short in terms of mechanical performance due to the relatively lower cooling rates compared to L-PBF. In this study, we present the development of novel Al-Mg-Zn alloys specifically designed for DED applications, both for additive printing and repair purposes. The compatibility of these candidate alloys with DED was rapid remelting on cast ingots without the need to atomize all of them. The selected alloy, which exhibits resistance to solidification cracking and a refined microstructure, underwent testing within the LMD process. Initially, a parameterization study was carried out, revealing that the development of porosity was largely due to the hydrogen content in the initial powder. The use of a dry powder yielded densities exceeding 99.9%. This new material was subsequently characterized for both bulk printing and repair applications. Despite the loss of Zn, the printed coupons exhibited low anisotropy, a yield strength of 400 MPa, and a total elongation exceeding 4%. Even in the as-built state, the achieved yield strength surpassed that of LMDed Scalmalloy after the corresponding heat treatment. The research on repairing pre-existing 7075 alloy structures focused on (i) the deposition parameters, (ii) parameters to avoid liquation cracking at the interface, and (iii) the development of an in-situ laser heat treatment to increase the strength in the refurbished zone without the need to fully re-heat treat the entire component. Tensile testing across the interface was used to assess the mechanical properties of the various repair approaches.
[269] ID:269- Influence of crystallization conditions on local matrix mechanical properties and fracture behavior of carbon fiber-reinforced PEEK composite
Sophie Vanpee (Institute of Mechanics, Materials & Civil Engineering, UCLouvain), Jérémy Chevalier (Material Science Application Center, Syensqo), Bernard Nysten (Institute of Condensed Matter & Nanosciences, UCLouvain) and Thomas Pardoen (Institute of Mechanics, Materials & Civil Engineering, UCLouvain).
Abstract
In the context of the energy transition, the transportation sector faces the double challenge of producing light but high-performance structural parts while improving their recyclability. Thermoset-based composite materials allow the manufacturing of light structures with excellent mechanical properties, but are hardly recyclable and can only be processed via liquid molding techniques or prepreg consolidation. Moreover, high-rate composite processing is impossible with such matrices, as the necessary curing step often lasts few hours at a high temperature. Transitioning from thermoset to thermoplastic polymer matrix composites overcomes these shortcomings. However, the successful transition requires an understanding of the influence of processing conditions on the microstructure of the thermoplastic matrix and the mechanical performances of the composite.
Among thermoplastic polymers, semi-crystalline polymers like polyetheretherketone (PEEK) offer superior mechanical properties. However, their mechanical behavior is related to the amount and characteristics of the crystalline phase, which depend on the processing conditions. In this work, the effects of crystallization conditions (processing conditions and fiber proximity) on the microstructure and mechanical properties of ‘model’ carbon fiber-reinforced PEEK samples and of UD composite samples are investigated. The degree of crystallinity and crystalline phase morphology are first assessed. The mechanical properties of the PEEK matrix processed in different conditions and its resulting phases (inter-/intra-spherulitic and transcrystalline zones) are then evaluated via nanoindentation (NI) and atomic force microscopy (AFM). The local mechanical properties assessed by NI are later compared to the macroscopic mechanical ones obtained from transverse compression tests of thin composite specimens processed in the same conditions. In addition, the deformation and damage mechanisms occurring in the matrix at the micro-scale during transverse compression are studied using nano-digital image correlation (nano-DIC).
[270] ID:270-Accounting for spatial distribution in mean-field homogenization of particulate composites
Oscar Luis Cruz-González (Aix Marseille Univ, IRPHE UMR 7342 and AMSE UMR 7316), Rémi Cornaggia (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert), Sophie Dartois (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert) and Renald Brenner (Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond ∂’Alembert).
Abstract
Several mean-fields homogenization methods are readily available to estimate the effective properties of particulate composites, which account for the particles volume fraction, shapes and orientations. To also account for their spatial distribution, the Ponte-Castañeda and Willis (PCW) model [1] embeds a parametrization of the statistical distribution law, while the Interaction Direct Derivative (IDD) model [2] associates a matrix cell to each inclusion, representative of close interactions.
To calibrate and exploit these models, we propose a novel approach in the context of 2D linear conductivity when representative images of the microstructure are available. We discuss the links between the models [3] and the range of validity of the IDD model. When the IDD estimate lacks the necessary symmetry, both an IDD-based PCW model and a two-step scheme are proposed. Finally, an image analysis method using Voronoı̈ diagrams, inspired by a proposition of [2], is implemented to define the cells associated to each inclusion and supply the models.
The method is validated by comparisons between the obtained IDD and PCW estimates, the Mori-Tanaka (MT) model and benchmark full-field numerical simulations. Accounting for the inclusion distribution is seen to lead to better estimates, both qualitatively (by capturing anisotropic behaviors due to the sole distribution) and quantitatively.
[1] Ponte-Castañeda, P. & Willis, J. R. The effect of spatial distribution on the effective behavior of composite materials and cracked media JMPS, 1995
[2] Du, D. X. & Zheng, Q. S. A further exploration of the interaction direct derivative (IDD) estimate for the effective properties of multiphase composites taking into account inclusion distribution Acta Mechanica, 2002
[3] Hessman, P. A.; Welschinger, F.; Hornberger, K. & Böhlke, T. On mean field homogenization schemes for short fiber reinforced composites: Unified formulation, application and benchmark IJSS, 2021
[271] ID:271-Study of the compressive behavior of polymer cable in a rubber matrix
Kablan Agniman (a. Université Paris-Saclay, CentraleSupelec, CNRS, Laboratoire de Mécanique Paris-Saclay, Gif-sur-Yvette, France), Jan Neggers (a. Université Paris-Saclay, CentraleSupelec, CNRS, Laboratoire de Mécanique Paris-Saclay, Gif-sur-Yvette, France), Damien Durville (a. Université Paris-Saclay, CentraleSupelec, CNRS, Laboratoire de Mécanique Paris-Saclay, Gif-sur-Yvette, France), Damien Charleux (b. Manufacture Française de Pneumatique Michelin, Clermont-Ferrand, France), Sophie Charpin (b. Manufacture Française de Pneumatique Michelin, Clermont-Ferrand, France) and Véronique Aubin (a. Université Paris-Saclay, CentraleSupelec, CNRS, Laboratoire de Mécanique Paris-Saclay, Gif-sur-Yvette, France).
Abstract
The tire's structure architecture incorporates several composite plies of polymer cables within an elastomer matrix. The manufacturing process of these textile cables makes them complex mechanical objects. Hundreds of textile filaments of 10 to 30 µm diameter are assembled to form one or more filament bundles yarns. Then the filament bundles are twisted together to form a twisted cable. The resulting twisted cables undergo several chemical and thermal treatments to reach the final state. Textile cables are designed to support tensile stress in the rubber matrix to perform this function. Yet, due to the relatively specific arrangement of the plies, combined with certain conditions of tire use, the cables are also subjected to axial compression. Therefore, there is a need to quantify and understand the effect of this stress on cables in tires.
This study consists in evaluating the contribution of textile cables to the overall stiffness of the rubber/textile cable composite in compression, determining the critical points of damage to cables in compression by analysis of deformation mechanisms and finally, providing elements to feed numerical models for finite element simulation.
To assess the contribution of textile cable to the overall compressive stiffness of the elastomer/textile cable composite, an experimental protocol for compression testing on elastomer/textile cable composite has been set up. It considers the sample geometry, sample fabrication and test parameters required to achieve the conditions for a compression test. Initial test results show that the contribution of textile cables to the overall compressive stiffness of the composite depends on the stiffness of the elastomer in which the cable is immersed. The stiffer the elastomer, the greater the cable's contribution to the composite's overall compressive stiffness. Additionally, compression tests were carried out in-situ in a laboratory tomograph to study cable deformation mechanisms.
[272] ID:272-Machine learning-based prediction of brain mechanics in sports-like head-to-head collisions
Phoebe Haste (University of Oxford), Yuyang Wei (University of Oxford), Jeroen Bergmann (University of Oxford) and Antoine Jerusalem (University of Oxford).
Abstract
Sports-related traumatic brain injury (SR-TBI) is a serious condition which can result in fatal secondary injuries. Finite Element (FE) models have often been used in the context of TBI as an approach to investigate quantities such as stress, strain or energy inside the brain during impact. In sports, however, these efforts are hindered by the fact that accurate kinematic information is difficult to obtain during collisions. Here, we focus on head-to-head collision in sports-like conditions and propose the use of a head and neck model to identify the sporting scenarios from the range modelled with the highest likelihood of inducing SR-TBI. To allow for large scalability and circumvent the computational cost of such large simulations, the FE models are used to train a machine learning layer able to accurately predict the mechanical quantities in the different brain regions of interest. Analysis of these quantities could provide further insight into the mechanisms of SR-TBI itself. We present here the model, the kinematic assumptions and the preliminary results of our approach.
[273] ID:273-Ratcheting behaviour of SS316L at room and low temperatures
Hitarth Maharaja (Indian Institute of Technology Bombay), Bimal Das (School of Engineering and Applied Science, Ahmedabad University), Sushil Mishra (Indian Institute of Technology Bombay) and Amit Singh (Indian Institute of Technology Bombay).
Abstract
In the present study, stress-controlled fatigue is carried out on SS316L at room temperature and -80 ℃ to understand its ratcheting behaviour. Two sets of tests were conducted, i.e. keeping stress amplitude constant and keeping mean stress constant. Plastic strain accumulation was observed in all the tests. However, there was a steady increase in plastic strain accumulation at room temperature, but an increase followed by a saturation of plastic strain was observed at -80 ℃. This saturation can be attributed to strain-induced martensitic transformation (SIMT) which was confirmed with the help of X-ray diffraction methodology. At maximum mean stress as well as maximum stress amplitude, the damage initiation started too early for any SIMT to take place, hence the saturation in plastic strain is not observed at those stress levels.
[274] ID:274-Low cycle fatigue of 22MnB5 cold rolled steel: Insights on Microstructure and Crystallographic Bulk Texture
Peeyush Mahajan (IIT Bombay), Hitarth Maharaja (IIT Bombay) and Sushil Mishra (IIT Bombay).
Abstract
In the present study, uniaxial low cycle fatigue (LCF) tests were conducted on cold rolled 22MnB5 steel at two different strain amplitudes of 0.4% and 0.6%. Specimen tested at 0.4% strain amplitude shows initial cyclic softening followed by hardening, whereas 0.6% strain amplitude specimen shows initial hardening in continuation with softening and then secondary hardening. Interrupted tests were done when the material showed change in hardening behaviour. At the interrupted points, a detailed microstructure and bulk texture evolution was investigated using the electron backscattered diffraction (EBSD) and x-ray diffraction (XRD) techniques. From the microstructure evolution it is evident that the grain average misorientation (GAM) is more in the 0.6% strain amplitude compared to 0.4%. From 2-theta measurement the evolution of dislocation density was determined which aligned with the softening and hardening behaviour. i.e increases with the hardening and decreases with the softening. From the quantification of the texture components, it was observed that the fraction of the cube (100)<001> and the copper (112)<111> texture orientation is increased with the increase in the number of cycles for both the strain amplitudes.
[275] ID:275-The energy-stepping Monte Carlo method: a highly efficient sampling algorithm for data-driven and statistical mechanics
Ignacio Romero (Universidad Politécnica de Madrid) and Michael Ortiz (California Institute of Technology).
Abstract
Often, data-driven models require sampling complex, high-dimensional probability distributions. For that, Markov chain Monte Carlo (MCMC) methods are the standard tools. Naïve implementations of these algorithms have a huge cost and thus, many optimized methods have been proposed. One of the most popular ones, the Hamiltonian Monte Carlo (HMC) method, transforms the sampling process into a surrogate dynamical problem that needs to be integrated in time. The discrete solution of these trajectories is then interpreted as proposal samples that are later accepted or discarded depending on detailed rules that achieve the desired distribution.
In this talk, we will present the energy-stepping Monte Carlo (ESMC) method. It is an HMC method where the time-integration phase of the algorithm is performed using the energy-stepping scheme. As a result, the new method possesses remarkable properties: in particular, no proposed sample is ever discarded irrespective of the dimensional and complexity of the sampled distribution, hence being more efficient than other HMCs.
The talk will describe the theory behind the method, numerical examples showcasing its favorable properties as compared with other MCMC methods, and how the latter can impact data-driven simulations.
[276] ID:276-Theoretical Investigation of Fast Low-Temperature Irradiation Creep - Development of a parameter-free digital shadow for quantitative predictions
Max Boleininger (United Kingdom Atomic Energy Authority), Alexander Feichtmayer (Max Planck Institute for Plasma Physics, Technical University Munich), Daniel Mason (United Kingdom Atomic Energy Authority), Luca Reali (United Kingdom Atomic Energy Authority), Johann Riesch (Max Planck Institute for Plasma Physics), Rudolf Neu (Max Planck Institute for Plasma Physics, Technical University Munich) and Sergei Dudarev (United Kingdom Atomic Energy Authority).
Abstract
The realisation of economically viable fusion reactors requires developing a full-scale “virtual reactor” representation of an operating tokamak device, informed by predictive materials models spanning the parameter space of simultaneous thermal, mechanical, and radiation loads. This work describes a combined in silico and in vivo study focused on quantifying deformation under stress and irradiation at low temperature.
While it is well known that irradiation accelerates creep deformation in metals, the phenomenon of irradiation creep becoming more pronounced at low temperature defies conventional understanding. In this talk, we will discuss the development of a virtual representation, or “digital shadow”, of the custom-designed “GIRAFFE” experiment for measuring stress-relaxation in a tensioned tungsten wire under irradiation. We show how atomic simulations can be used to generate a multiscale model capable of quantitatively predicting the elastoplastic response of a material under conditions of both stress and irradiation — ahead of the actual observation, without use of any adjustable parameters.
We discover that, under irradiation at room temperature, internal stresses of up to 2 GPa relax within minutes. As opposed to conventional notions of radiation creep, the effect arises from the self-organisation of nano-scale crystal defects, athermally coalescing into extended polarized dislocation networks that compensate and alleviate the external stress. The actively cooled materials, in which the stress concentrations critical to structural integrity are expected to form, would relax through the favourable low temperature creep mechanism explored in this study.
[277] ID:277-Chemo-mechanical Damage Modeling of the Impact of Microstructure on Performance and Cracking in Polycrystalline Lithium-ion Battery Cathode Active Material
Armin Asheri (Volkswagen AG, Technische Universität Darmstadt), Shahed Rezaei (Access e.V.), Vedran Glavas (Volkswagen AG) and Bai-Xiang Xu (Technische Universität Darmstadt).
Abstract
Structural instability is one of the major causes of degradation in layered structures such as nickel-manganese-cobalt-oxide (NMC) and it mainly happens due to the anisotropic volume change in these high-capacity cathode active material for lithium-ion batteries during cycling and limits their widespread application despite high energy density. Here an anisotropic chemo-mechanically coupled model is implemented in 3-dimensions to simulate the electrochemical performance and fracture in polycrystalline cathode active material, where a two-way coupling between the mechanics and diffusion is employed and the damage at the grain boundaries is modeled using a cohesive zone model. Furthermore the wetting of the freshly cracked surfaces by the electrolyte is also considered in the model and we studied the impact of electrolyte penetration into the cracks. Due to the anisotropic material properties of layered structures such as NMC, the effect of crystallographic orientation of grains on electrochemical performance and cracking of active material is investigated, where orientations based on electron backscatter diffraction measurements are employed. Furthermore, the impact of primary and secondary particle's size, and grain morphology are studied. Results suggests that the electrolyte penetration into the cracks enhances the Li transport and electrochemical performance. Moreover, secondary active material particles with smaller and radially elongated grains alleviate the mechanical damage better.
[278] ID:278-Experimental Investigation of Fast Low-Temperature Irradiation Creep – A Novel Experiment for Materials Testing under Extreme Conditions
Alexander Feichtmayer (Max Planck Institute for Plasma Physics, Technical University Munich), Max Boleininger (United Kingdom Atomic Energy Authority), Till Höschen (Max Planck Institute for Plasma Physics), Johann Riesch (Max Planck Institute for Plasma Physics), Thomas Schwarz-Selinger (Max Planck Institute for Plasma Physics), Sergei Dudarev (United Kingdom Atomic Energy Authority) and Rudolf Neu (Max Planck Institute for Plasma Physics, Technical University Munich).
Abstract
On the path towards nuclear fusion as a future energy source, the degradation of materials in structures and plasma-facing components represent a central challenge. These materials must withstand the harsh conditions of the fusion environment, such as high heat and particle fluxes of hydrogen and helium as well as intense irradiation by high-energy neutrons. It is known that the irradiation of metals using high-energy ions leads to accelerated creep, resulting in significant deformations. A detailed description of this effect has not yet been feasible due to the complexity of simulating such conditions in the laboratory.
For the experimental investigation of materials under such conditions, the General-Purpose Irradiated Fiber and Foil Experiment (GIRAFFE) was developed. A dedicated tensile testing machine that can perform mechanical testing under simultaneous irradiation with high-energy ions. Cold-drawn tungsten wire with a diameter of 16 µm was used as sample material to investigate the mechanical properties of tungsten under irradiation. This wire has a nano-scale microstructure, resulting in a large number of grains and grain boundaries in the irradiated volume, even at the low penetration depth of around 2 µm of 20.3 MeV W6+ ions. This makes the wire a suitable model system for describing polycrystalline tungsten.
Comprehensive irradiation induced stress relaxation experiments were performed by loading single 16 µm tungsten wires with an elastic tensile stress between 0.5 and 2.0 GPa while damaging them simultaneously up to a displacement damage of 5 dpa. During the experiment, the elongation of the sample is kept constant while the load drop is measured. Measurement of this load drop, caused by irradiation-induced stress relaxation, was enabled through a novel approach to in-situ investigations of the mechanical properties of materials during irradiation. The obtained data is thereby used for the validation of material models and for the engineering of fiber-reinforced composites.
[279] ID:279-The effects of network structure on percolation and elastic moduli of fibrous networks
Amir Hossein Namdar (Department of Mathematics, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester), Tom Shearer (Department of Mathematics, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester) and Alberto Saiani (Division of Pharmacy and Optometry, Faculty of Biology Medicine and Health, The University of Manchester).
Abstract
Fibrous networks are prevalent in both natural materials, ranging from body tissues to plants, and synthetic materials such as textiles, polymers and hydogels. Various properties of such materials, such as percolation and elastic moduli, can be studied by modelling them as stochastic networks. In stochastic networks, a given number of fibres are placed in a study domain and their intersection points are defined to act as cross links between the fibres. There is a large body of work dedicated to investigating the behaviour of random networks (a type of stochastic network where individual fibres are placed independently of each other), but local interaction of fibres, which results in departures from randomness, and are seen in materials such as polypeptide hydrogels, affect the structure of the network and are poorly studied and understood. In this talk, to investigate the effects of departures from randomness, we modify the process of generating the random network by allowing the probability of a fibre appearing and its orientation to depend on its proximity to existing fibres. Our results show that in more homogeneous networks, percolation occurs at a lower fibre density. Moreover, the rate of change of elastic moduli with respect to fibre density is lower for more homogeneous networks. In contrast, at densities much higher than the percolation threshold, various properties of these modified networks converge to those of unmodified stochastic fibre networks, which shows that the effects of departure from randomness are not considerable at high densities.
[280] ID:280-Development of a simulation model of the thermoforming process of polymer matrix composite materials and definition of a Forming Limit Curve to identify defects and optimize their manufacture
Adrian Pedrosa Valbuena (CIDAUT), Alberto Blanco Rodríguez (CIDAUT), Esteban Cañibano Álvarez (CIDAUT), María Teresa Fernández Peña (CIDAUT) and Rubén Perez Torices (CIDAUT).
Abstract
The current trend in transportation industries such as aerospace, automotive, or railway towards the use of recyclable materials has increased the manufacturing of composite parts made of thermoplastic materials through thermoforming processes. Considering the limitations in shaping these types of materials, the development of a simulation-based methodology is necessary to study the manufacturing process and make informed decisions to ensure the quality of the parts. In this scenario, numerical analysis emerges as a fundamental resource in reducing time and costs compared to a purely experimental procedure. Simulation provides a new approach, allowing for faster iterations and the prediction of defects such as wrinkles, delaminations, or distortions, enabling corrective actions to enhance process efficiency. This article focuses on constructing a virtual model to study and optimize the manufacturing of a structural component through a thermoforming process using PAEK thermoplastic material reinforced with unidirectional carbon fiber, employing the PAM-COMPOSITES software from ESI Group. The development of Forming Limit Curve based on shearing and tensile deformation is also explored to assess anomalies in the manufacturing process of composite components through thermoforming. The obtained results are compared with the experimentally manufactured part, analyzing the presence of defects and distortion phenomena, thereby validating the model and establishing a methodology to optimize various phases of the process.
[281] ID:281-Macroscopic mechanical properties of pressurized cellular solids
Loïc Tadrist (Aix-Marseille Université), Paul Lacorre (Aix-Marseille Université) and Louison Fiore (Aix-Marseille Université).
Abstract
Most soft biological tissues are pressurized cellular solids. In plants, motion is performed by controlling pressure at the cellular level. An increase of the fluid pressure inside the elastic cell, that is called turgor pressure, creates cell expansion and deforms the tissue. This motion-by-deformation strategy occurs in almost all growing shoots but also in some mature plant actuators. For instance, Mimosa Pudica moves its leaves on demand by playing on turgor pressure gradients in pulvini.
Turgor pressure creates motion but it also changes the mechanical properties of pressurized cellular solids. We investigate the macroscopic (or apparent) mechanical properties of pressurized cellular solids considering a cell enclosing fluid. Several fluid behaviours (isobar, isochoric, adiabatic, isotherm and osmotic) and cell geometries (spheres or cubes) are considered as these play on apparent stiffness. This problem is written in terms of elastic and fluid energies. The second derivative of the total energy in a direction gives the elastic constant of the cell. This elastic constant is scaled by the volume of the cell after pressurization to obtain the apparent Young modulus.
The model shows that considering linear behaviour for solids, the effect of pressure on the apparent Young modulus is complex, and dependent on both cell relative thickness t/R and Poisson ratio. Considering mechanical properties of plant cells, the current model does not reproduce the pressure-induced stiffening of plant tissues observed in nature. We conclude that non-linear effects must be key in the observed stiffening in living tissues.
[282] ID:282-The influence of matrix and fibers on the mechanical response of recycled fiber-reinforced polymer composites from aeronautic sector
Mercedes Santiago-Calvo (FUNDACIÓN CIDAUT), Antonio Velasco GonzÁlez (FUNDACIÓN CIDAUT), MarÍa Asensio-ValentÍn (FUNDACIÓN CIDAUT), Carlos Alonso (FUNDACIÓN CIDAUT), Maite FernÁndez (FUNDACIÓN CIDAUT) and Esteban CaÑibano (FUNDACIÓN CIDAUT, UNIVERSIDAD DE VALLADOLID).
Abstract
Polymer composites containing glass or carbon fibers (GFs o CFs) are extensively used in industries such as automotive, aeronautic, and civil engineering where there is a need for lightweight high-strength parts. These sectors often employ engineering polymers like polyetherimide (PEI), polyphenylene sulphide (PPS), and polyetheretheretheretherketone (PEEK) due to their excellent performance characteristics. However, with the increasing demand and economic value of these polymer composites, there is a growing interest in their recycling and revaluation [1,2]. Compared to the recycling of thermoset composites, the recycling of these polymer composites is relatively new and less developed [3]. Most research efforts have concentrated on mechanical recycling, neglecting chemical or thermal methods that require more energy and produce chemical waste [3]. Unfortunately, mechanical recycling technology faces challenges in preserving the fiber length, which in turn adversely affects the mechanical properties of the recycled materials and often results in downcycling. Thus, the present investigation is focused on evaluating the quality of recycled material obtained in the first cycle of mechanical recycling of short-GF reinforced PEI waste from injected parts designed to replace the metal parts of the aeronautical sector. Injected samples are prepared using recycled material (PEI and PEI reinforced with short GFs) to assess the effect of matrix and fibers on their mechanical properties (tensile, flexible and impact properties). Moreover, the content and length fibers are characterized to observe if there are changes after the recycling process.
[283] ID:283-Finite element simulations of jerky flow in nickel-based superalloy IN718
Florian Billon (Mines Paris, PSL University, MAT-Centre des matériaux, CNRS UMR 7633, BP 87, 91003 Evry, France.), Samuel Forest (Mines Paris, PSL University, MAT-Centre des matériaux, CNRS UMR 7633, BP 87, 91003 Evry, France), Matthieu Mazière (Mines Paris, PSL University, MAT-Centre des matériaux, CNRS UMR 7633, BP 87, 91003 Evry, France), Aurélien Vattré (Onera, Université Paris-Saclay, Materials and Structures Department, 29 av. Division Leclerc, 92320 Châtillon, France), Moubine Al Kotob (Safran Aircraft Engines Villaroche, Rond Point René Ravaud-Réau, 77550 Moissy-Cramayel, France) and Sylvain Zambelli (Safran Aircraft Engines Villaroche, Rond Point René Ravaud-Réau, 77550 Moissy-Cramayel, France).
Abstract
The Portevin-Le Chatelier effect is a localization phenomenon resulting in the heterogeneity of the plastic deformation. Its accurate characterization is of primary interest for the sizing of industrial structures via finite element simulations. The present study seeks to ascertain the fidelity of our current models to describe correctly the heterogeneity of the PLC effect. Finite element simulations, utilizing the KEMC model [1], were used to simulate the PLC observed in our experiments.
In order to compare both simulations and experiments, tools were developed for the quantitative analysis of the PLC. Direct measurements of serrations amplitudes and periods enables the identification of trends in their dynamics. Subsequently, the use of tools derived from chaos theory, such as power spectrums and multifractal analysis, allows the quantification of the heterogeneity inherent in the Portevin-Le Chatelier signal. Our findings demonstrate that the simulations successfully re- produce the observed trends in our experiments. These outcomes not only provide insights into the potential application of these indicators in identification strategies but also offer avenues for refining pre-existing models.
References [1] N. Guillermin, J. Besson, A. K¨oster, et al.,“Experimental and numerical analysis of the Portevin–Le Chatelier effect in a nickel-base superalloy for turbine disks application,” International Journalof Solids and Structures, vol. 264, p. 112 076, 2023, issn: 0020-7683. doi: 10.1016/j.ijsolstr.2022.112076.1
[284] ID:284-Post-processing of displacement fields from digital image correlation for non-local variables and crack initiation criteria identification in fretting-fatigue
Naansonou Patrick Lare (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS - Laboratoire de Mécanique Paris-Saclay), Yoann Guilhem (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS - Laboratoire de Mécanique Paris-Saclay), Florian Meray (Safran Aircraft Engines), Kevin Cosseron (Safran Aircraft Engines) and Sylvie Pommier (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS - Laboratoire de Mécanique Paris-Saclay).
Abstract
In aeronautical industry, blade/disk root attachments are subjected to fretting-fatigue conditions that can lead to cracking damage and reduce significantly the service fatigue life. To characterize the crack initiation risk in fretting-fatigue, a non-local approach was proposed. The approach consists of partitioning in a reference frame attached to the contact front, the velocity field as the product between non-local variables and spatial shape functions. Based on non-local variables, non-local fretting-fatigue crack initiation criteria are formulated. Thanks to the non-intrusive nature of the partitioning technique, the non-local approach can be applied to any displacement field derived from an independent calculation. In this paper, the approach is applied to a displacement field computed by Digital Image Correlation technique from images captured during fretting-fatigue experiment under variable normal loading condition. The time variability of the normal load implies a variability in time and space of the contact front position, leading to a spatial dispersion of contact damage. One of the main challenge in this study is the detection of contact front position for each time increment. An incorrect choice of contact front position leads to an incorrect identification of non-local variables. A physics-based methodology for the detection of contact front position was therefore developed to track the contact front position during image analysis. The validity of the methodology was first tested and proven on displacement fields obtained by numerical simulation for configurations where the position of the contact front is known analytically. By adding random noise to the displacement fields derived from numerical simulation, the contact front search algorithm detect the same positions as when there is no noise, demonstrating the robustness of the methodology. With this methodology, the evolution of contact front position is tracked during image analysis and for each position, the non-local variables are extracted.
[285] ID:285-Characterization of cleavage initiation sites in relation to the microstructure and tempering conditions of a Reactor Pressure Vessel steel
Romain Weisbecker (Mines Paris – PSL, Centre des Matériaux, UMR CNRS 7633), Anne-Françoise Gourgues-Lorenzon (Mines Paris – PSL, Centre des Matériaux, UMR CNRS 7633), Sylvain Dépinoy (Mines Paris – PSL, Centre des Matériaux, UMR CNRS 7633), Frank Tioguem-Teagho (Framatome Le Creusot) and Maxi Cadet (Framatome Le Creusot).
Abstract
Low alloy bainitic steels are used for Reactor Pressure Vessels in nuclear power plants. Certification of these components requires strict compliance with minimum impact toughness values in the Ductile to Brittle Transition Temperature (DBTT) domain. As a result of the slow solidification of massive ingots, pressure vessel steels exhibit post-forging chemical segregation at a millimetric scale, and therefore local heterogeneities in composition and hardenability (upper vs lower bainite). In addition, the large wall thickness of such parts implies heterogeneous thermal histories during heat treatments, e.g. during water quenching. Lower bainite, with fine grains and/or small precipitates, is known to be tougher than coarser upper bainite. Moreover, recent work suggested that brittle fracture may initiate from molybdenum-rich carbides [1]. Until now, investigations, including [1] focused on lab-scale specimens.
The present study addressed the transposition of known laboratory results to the industrial reality by considering a full-scale part after monitored quenching. It focused on two regions with average cooling rates of 1000°C/h and 4000°C/h. These materials were slowly reheated and tempered at 645°C for 2h to 20h. The bainitic matrix and carbide size distributions were quantified in both segregated and non-segregated regions.
An increase/decrease of 30°C in the Charpy DBTT was observed after a 20h tempering compared to a 2h tempering. For each tempering condition, the nature of the brittle fracture initiation sites was investigated for specimens broken between -100°C and -20°C. Initiation sites were identified as inclusions, Mn/Mo-rich carbides, ductile ridges, and micrometric inter-granular areas. Mo-rich particles seemed to be present in most sites for particular tempering conditions. The effect of the cooling rate and tempering time on the nature of the initiation sites, in relation to the microstructure, is then discussed.
[1] P. Chekhonin, A. Das, F. Bergner, et E. Altstadt, Nuclear Materials and Energy 37 (2023). 101511
[287] ID:287-Parallel versus series decomposition in modeling higher-order effects in gradient-enhanced plasticity theories
Mohamed Jebahi (Arts et Metiers Institute of Technology, CNRS, Université de Lorraine, LEM3, F-57000 Metz, France), Yaovi Armand Amouzou-Adoun (Arts et Metiers Institute of Technology, CNRS, Université de Lorraine, LEM3, F-57000 Metz, France), Samuel Forest (Mines Paris, PSL University, Centre des matériaux (CMAT), CNRS UMR 7633, BP 87, 91003 Evry, France) and Marc Fivel (Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMaP, F-38000 Grenoble, France).
Abstract
In the realm of material science, the development of gradient-enhanced plasticity theories has marked a significant advance in modeling small-scale phenomena. These theories can effectively capture the size-dependent behavior of materials at small scales, where traditional plasticity approaches are often inadequate. A key focus of recent research is the accurate modeling of higher-order effects using such advanced theories. Despite ongoing debates, there is a consensus among researchers about the necessity of considering both energetic and dissipative higher-order effects to enhance the accuracy of these theories. To this end, two main decomposition methodologies have been proposed: higher-order stress decomposition (parallel approach) and higher-order kinematic decomposition (series approach) into recoverable (energetic) and unrecoverable (dissipative) parts. The present contribution aims at providing a comparative study of these two methodologies, within strain gradient crystal plasticity (SGCP) framework. Their capabilities to deal with elastic gaps under non-proportional loading conditions are also investigated. Findings of this work highlight the effectiveness of the higher-order kinematic decomposition approach. This approach has shown promise in avoiding elastic gaps, and the associated results are qualitatively in good agreement with those obtained using discrete dislocation dynamics (DDD). This suggests that this decomposition approach may be more accurate and reliable for modeling small-scale material behaviors by gradient-enhanced continuum theories.
[288] ID:288-A quantitative phase-field study of hydrogen embrittlement in metals
Gabriel Frank Bouobda Moladje (ONERA/CNRS), Antoine Ruffini (ONERA/CNRS), Yann Le Bouar (ONERA/CNRS) and Alphonse Finel (ONERA/CNRS).
Abstract
Hydrogen-enhanced decohesion (HEDE) is one of the Hydrogen Embrittlement (HE) mechanisms and consists in the lowering of the atomic bond strength due to the trapping of dissolved hydrogen atoms at the crack surface of a material. In the last few years, phase-field methods have emerged as a powerful tool to describe such a phenomenon at the continuous scale. Usually, the reduction in the cohesion properties is modeled by explicitly decreasing the critical energy release rate, as a function of the hydrogen coverage.
In this work, to simulate the HEDE mechanism, we propose a new phase-field approach, based on the Kim-Kim-Suzuki (KKS) formalism, which is more rigorously connected to the segregation physics of the hydrogen atoms at the crack surface. This variational formulation accounts naturally for the decrease of the surface energy, in conjunction with the hydrogen atoms trapping, by minimization of the total free energy of the system. The present model and some validation tests are first presented, followed by a systematic study of the HEDE mechanism in Ni-based alloy. We investigate in particular the role on HE of pre-existing microstructural features like dislocations, grain boundaries, etc.
[289] ID:289-Advanced characterization of Additively Manufactured Functionally Grade Materials (FGMs) coupled with Thermodynamic Simulations.
Jorge Valilla (IMDEA Materials), Damien Tourret (IMDEA Materials) and Ilchat Sabirov (IMDEA Materials).
Abstract
Additive manufacturing of metallic materials enables the design of functionally graded materials (FGMs) that exhibit a gradual change of chemical composition within the same part. This comes as a great option for dealing with dissimilar joints or for creating location-specific properties (and/or functionality). Here, we investigate material compatibility and explore processing parameters for parts graded from a stainless steel 316L and a Ni-based superalloy IN718. We combine (1) advanced characterization (SEM, EDX, EBSD, micro & macro hardness, X-ray tomography and diffraction) of print quality, microstructure and properties of graded samples manufactured by direct energy deposition (DED) technique and (2) computational thermodynamics (CalPhaD) exploration of phase diagrams and assessment of thermal properties along the material gradient. We explore the fundamental mechanisms of microstructure selection and properties in metallic FGMs and investigate the appearance of defects, e.g. (micro-)cracks, and phases/constituents in specific regions of the compositional gradient. By doing so, we look to establish a robust pathway for the design, manufacture, and characterization of metallic graded materials for several industrial applications – here, specifically oriented toward enhancing the local resistance to thermal cycling in steelmaking components.
[290] ID:290-Mechanical behavior of elastomeric bistable dome shell with tunable energy barrier asymmetry
Frédéric Albertini (LISV, UVSQ, Université Paris-Saclay, 78140 Vélizy-Villacoublay, France), Gabriella Tarantino (LMPS, ENS Paris-Saclay, CentraleSupélec, Université Paris-Saclay, CNRS, 91190 Gif-sur-Yvette, France) and Laurent Daniel (GeePs, CentraleSupélec, Université Paris-Saclay, CNRS, 91192, Gif-sur-Yvette, France).
Abstract
For decades, numerous efforts have been made to design structures against buckling and instabilities, which often lead to their catastrophic failure. By contrast, recent studies have shown that harnessing mechanical instabilities can provide structures with new features as negative stiffness and energy dissipation [1]. Domes are shell structures that can exhibit up to two stable states, mostly depending on geometric and material parameters [2]. Apart from its basis state, a dome can be subjected to snap-through buckling and remain stable in this state indefinitely over time in absence of external loadings, being then considered as bistable. Recently, studies showed that bistability of domes may be used for shape morphing of soft sheets [3] and mechanical programmability [4]. However, to design such structures based on multiple bistable units, the knowledge of the mechanical behavior of individual dome shells is required. Furthermore, the strain energy required to switch between both stability states (often referred to as the energy barrier) varies upon loading (i.e. snap-through instability) and unloading (i.e. snap-back instability), and is needed to determine an actuation strategy.
The present work exploits non-linear FEA and experimental measurements to explore the mechanical behavior of elastomeric dome shells. The mechanisms behind dome shell asymmetrical energy barrier are investigated. Single element snapping and bistability are computationally analyzed and results are compared with experiments. The strain energy required to switch between stable states is computed, and an asymmetry index is proposed. These results are expected to be used as a guideline to design morphing structures based on bistable dome shells.
[1] Zhang et al., Scientific Reports, 2019. [2] Brodland et al., International Journal of Solids and Structures, 1987. [3] Faber et al., Advanced Science, 2020. [4] Udani et al., Extreme Mechanics Letters, 2021.
[291] ID:291-Asymptotic higher order homogenization of discrete microstructures
Yang Ye (Laboratoire de Mécanique des Solides, Ecole Polytechnique), Basile Audoly (Laboratoire de Mécanique des Solides, Ecole Polytechnique) and Claire Lestringant (Institut Jean Le Rond d'Alembert, Sorbonne Université).
Abstract
Periodic lattice structures are increasingly used to achieve functions such as shock absorption, wave propagation, wave guiding, and/or programmable materials. The design of such systems calls for effective continuous homogenized models capable of precisely capturing the mechanical behavior of these complex periodic or quasi-periodic microstructures [VP12]. We propose a versatile and systematic method for deriving higher-order asymptotic continuum models for periodic beam networks. It yields a homogenized energy that is asymptotically exact two orders beyond that obtained by classical homogenization [AL23]. Our homogenization method is applicable to various types of networks, in 2D or 3D and we validate it by comparing the predictions of the microscopic displacement to that obtained by full discrete simulations. When used incrementally, the method extends to lattices subject to finite deformation. We take the 'triangular–hexagonal'-Kagome lattice as an example. It features zero-energy modes [NCH20] and under finite deformation, the solutions are close to a mechanism with small deviations that are sensitive to the gradient effect, which motivates us to model this microstructure with our gradient theory. In the presentation, we present the effective nonlinear energy for the Kagome lattice and we investigate how it captures gradient effect for a given boundary value problem. Bibliography [VP12] Andrea Vigliotti and Damiano Pasini. Linear multiscale analysis and finite element validation of stretching and bending dominated lattice materials. Mechanics of Materials, 46:57–68, 2012. [AL23] B. Audoly and C. Lestringant. An energy approach to asymptotic, higher-order, linear homogenization. Journal of Theoretical, Computational and Applied Mechanics, 2023. [NCH20] Hussein Nassar, Hui Chen, and Guoliang Huang. Microtwist elasticity: a continuum approach to zero modes and topological polarization in kagome lattices. Journal of the Mechanics and Physics of Solids, 144:104107, 2020.
[292] ID:292-Room temperature electron beam sensitive viscoplastic response of ultra-ductile amorphous olivine films
Patrick Cordier (Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 - UMET - Unité Matériaux et Transformations, F-59000 Lille, France), Andrey Orekhov (EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium), Nicolas Gauquelin (EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium), Guillaume Kermouche (Mines Saint-Etienne, Univ Lyon, CNRS UMR 5307LGF, Centre SMS, 158 Cours Fauriel, 42023 Saint-Etienne, France), Paul Baral (Mines Saint-Etienne, Univ Lyon, CNRS UMR 5307LGF, Centre SMS, 158 Cours Fauriel, 42023 Saint-Etienne, France), Ralf Dohmen (Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44801 Bochum, Germany), Michaël Coulombier (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium.), Johan Verbeeck (EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium), Jean Pierre Raskin (ICTEAM, UCLouvain, B-1348, Louvain-la-Neuve, Belgium), Thomas Pardoen (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Dominique Schryvers (EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium) and Hosni Idrissi (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium).
Abstract
Recent studies demonstrating amorphization of olivine under high-stress have raised interest in the mechanical properties of amorphous olivine (a-olivine) [1, 2]. In this study we investigate the mechanical properties of amorphous olivine deformed at room temperature either ex situ by nanoindentation, or in situ in a TEM under uniaxial tension using a Push-to-Pull (PTP) device. Thin films of a-olivine were deposited by pulsed laser deposition (PLD). In nanoindentation, a-olivine a-olivine exhibit a viscoelastic-viscoplastic behavior without fracture. Long-term relaxation tests show a strain-rate sensitivity m∼0. 05 [3]. Under uniaxial tension in situ in the TEM, a-olivine deforms plastically but with a gradual transition that makes impossible the determination of a precise threshold. The strength attains values up to 2.5 GPa. The fracture strain reaches values close to 30 % without e-beam irradiation. Under electron illumination at 200 kV, the strength is lower, around 1.7 GPa while higher elongations close to 36 % are obtained. Alternating beam-off and beam-on sequences lead to exceptionally large fracture strains equal to 68 % at 200 kV and 139 % at 80 kV. EELS measurements were performed to characterize the interaction between the electron beam and a-olivine. At a voltage of 80 kV, radiolysis accompanied by oxygen release dominates whereas at high voltage the interaction is dominated by knock-on type defects. Radiolysis is also the dominant interaction mechanism at 200 kV with low exposition which corresponds to most of our deformation experiments.
[1] K. Kranjc et al. (2020). Amorphization and plasticity of olivine during low‐temperature micropillar deformation experiments. Journal of Geophysical Research: Solid Earth, 125, e2019JB019242.
[2] V. Samae et al. (2021) Stress-induced amorphization triggers deformation in the lithospheric mantle. Nature 591, 82–86.
[3] P. Baral et al. (2021) Rheology of amorphous olivine thin films characterized by nanoindentation. Acta Materialia, 219, 117257.
[294] ID:294-Effect of Stress and Viscoplastic Behavior on the Electrochemical Response of Amorphous Silicon Electrodes
Xavier Bruant (Ecole polytechnique/LMS), Anh Tuan Le (Ecole polytechnique/LMS), Michel Rosso (Ecole polytechnique/PMC), François Ozanam (Ecole polytechnique/PMC), Michel Jabbour (Ecole polytechnique/LMS) and Laurent Guin (Ecole polytechnique/LMS).
Abstract
Silicon electrodes for lithium-ion batteries exhibit a theoretical capacity ten times higher than that of graphite electrodes currently used in commercial systems. When lithiated/delithiated, silicon experiences stresses on the order of one GPa, thus inducing damage in the material which results in poor cyclability. Irreversible continuum thermodynamics predicts that these stresses affect the lithiation itself in different ways for monophasic and biphasic lithiation (progressive invasion of the electrode by a lithiated phase of given composition) [1]. When lithiation takes place homogeneously (without phase transformation), mechanical stresses affect lithiation through their effect on the chemical potential of diffusing lithium (Larché-Cahn theory). This coupling has first been probed experimentally in homogeneous lithiation using a method where the stress state of silicon is modified indirectly through incremental delithiation [2].
On the other hand, we investigate here the coupling through a converse experiment by imposing mechanical loading at various lithiation rates and measuring the effect on the electrochemical response of an amorphous silicon thin film, deposited on a stainless-steel substrate. This mechanical loading is applied by deforming elastically the steel substrate of the silicon thin film, which allows to directly probe the contribution of mechanics to the lithiation/delithiation processes. Under galvanostatic conditions, incremental changes in stress lead to instantaneous change in the electrode potential, followed by its relaxation. Experimental results from uniaxial tensile tests show that an applied strain of 0.3%, resulting in changes in stress in silicon of ~200-300 MPa, induces a potential variation of about 2.5 mV. These experimental results have more recently been modeled through the use of a viscoplastic flow rule for the amorphous material, which captures both this instantaneous change in the electrochemical potential and its subsequent relaxatios, confirming previous modeling choices.
[1] Bower, Chason, Guduru, Sheldon, Acta Mater. (2015) [2] Sethuraman, Srinivasan, Bower, Guduru, J. Electrochem. Soc. (2010)
[295] ID:295-Anisotropic elasticity of strongly textured Ti studied by resonant ultrasound spectroscopy
Martin Koller (Institute of Thermomechanics of the Czech Academy of Sciences), Karel Tesar (Institute of Physics of the Czech Academy of Sciences), David Vokoun (Institute of Physics of the Czech Academy of Sciences) and Petr Sedlak (Institute of Thermomechanics of the Czech Academy of Sciences).
Abstract
Laser-based resonant ultrasound spectroscopy (RUS) is an experimental technique where elastic properties of millimeter-sized samples are determined from their free vibrations. By using a laser vibrometer, resonant frequencies and modal shapes of vibrations are detected by scanning one side of the elastically vibrating sample. The precise determination of resonant spectra by the laser-based RUS technique allows measurements of the full set of elastic coefficients even for highly anisotropic materials, when several dozens of resonant modes are detected. The presented study focuses on polycrystalline pure alpha-titanium processed by equal channel angular pressing (ECAP). After four repetitions of the ECAP process, the grain size was reduced to sub-micrometer size with a strong (0001) texture, which was preserved even after annealing at various temperatures. Due to the hexagonal structure of pure Ti, the strong texture in the polycrystalline material results in its significant elastic anisotropy. This is evident in the distribution of Young’s modulus, as determined through RUS measurements, where the maxima of Young's modulus align with the direction of the (0001) texture maxima. Additionally, as the laser-based RUS is fully contactless, the ECAPed Ti samples were placed into the chamber with precise temperature control, where resonant spectra were detected along temperature cycles up to 590 °C. This allowed us to observe several internal processes affecting elastic moduli (related to the resonant frequencies) or internal friction (related to the width of the resonant peaks).
[296] ID:296-Size-dependent large-deformation elastoplasticity relying on Eulerian rates of elastic incompatibilities
Lorenzo Bardella (University of Brescia) and M.B. Rubin (Technion-Israel Institute of Technology).
Abstract
The notion of elastic incompatibilities considers elastic deformations from one configuration to another. In this contribution, elastically anisotropic materials are discussed within the context of a large-deformation Eulerian formulation that is free from arbitrary choices of reference and intermediate configurations as well as definitions of total and plastic deformations. Specifically, the assumed formulation holds for elastically anisotropic materials, as it relies on evolution equations for a right-handed triad of linearly independent microstructural vectors. In particular, these evolution equations involve the plastic rate second-order tensor, which requires a constitutive prescription. The microstructural vectors are internal state variables since they are assumed to be measurable in the current state. They describe elastic deformations and orientation changes of material directions relative to a zero-stress state, so that they also determine the Cauchy stress in the current configuration. Hence, an elastic deformation is defined from an arbitrary initial configuration that can have a state with elastic incompatibilities. Necessary and sufficient conditions are obtained for additional elastic incompatibilities developing from this initial configuration. Moreover, a second-order Eulerian tensor is proposed, based on the current curl of the plastic rate tensor, which measures the current rate of incompatibility. If restricted to small strains and rotations, this incompatbility tensor is the opposite of the rate of the Nye-Kroner dislocation density tensor; therefore, the diagonal and off-diagonal components of the proposed incompatibility tensor correspond to screw and edge dislocation density rates, respectively. A hardening law dependent on the this incompatbility tensor is developed to study size-effects in small-scale metal plasticity. In order to unveil the features of the proposed theory, the large-deformation torsion of a cylinder is analyzed for both monotonic and cyclic loadings.
[297] ID:297-Experimental and numerical investigation of micro-textured tools fabricated using RµEDM in sustainable machining of Ti6Al4V
Chandrakant Kumar Nirala (Indian Institute of Technology Ropar), Gaurav Saraf (Indian Institute of Technology Ropar) and Sharib Imam (Indian Institute of Technology Ropar).
Abstract
Machining titanium alloys presents formidable challenges due to their high thermal strength, low thermal conductivity, low modulus of elasticity, and heightened chemical reactivity [1]. Micro-pillar textured tools have emerged as a proven method for enhancing the machinability of titanium alloys. These tools demonstrate the ability to reduce tool-chip contact length through improved chip curling and enhanced heat dissipation from the interface to the surroundings [2,3]. Despite their effectiveness, the exploration of texture shapes and dimensions on performance remains limited due to constraints imposed by fabrication techniques.
To address this gap, finite element analysis serves as an efficient alternative to experimental studies, overcoming fabrication challenges and minimizing practical costs and resource requirements. The accuracy of the numerical model relies on the material behaviour model, leading to the experimental validation of cutting forces with ten different Johnson-Cook parameter sets. Parameters with minimal deviation from experimental results are selected for further investigation.
To ensure the study's simplicity and comprehensiveness, this research presents a numerical analysis of 3D orthogonal machining of Ti6Al4V using plain and micro-pillar textured tools of various shapes (circular, rectangular, elliptical, etc.). The reverse micro electrical discharge machining (RµEDM) is employed for fabricating micro-pillar-shaped textures on tungsten carbide (WC) cutting tools. The challenges and critical aspects of micro-texture fabrication are extensively covered. All these shapes are explored under varying texture dimensions. The micro-pillar textures are specifically designed to address challenges associated with other patterns like micro-dimples and micro-grooves [3]. Consequently, a comparative study is conducted among these three texture patterns to elucidate the pros and cons of each.
References
[1] https://doi.org/10.1016/j.jmatprotec.2008.06.020 [2] https://doi.org/10.1016/j.jmatprotec.2018.05.032 [3] https://doi.org/10.1016/j.mfglet.2023.04.001
[298] ID:298-Pre-contour scans as a new design tool for PBF-LB/M thin-wall structures
Ignacio Rodriguez Barber (IMDEA Materials Institute and Universidad Carlos III Madrid), Srdjan Milenkovic (IMDEA Materials Institute and Universidad Carlos III Madrid) and María Teresa Pérez Prado (IMDEA Materials Institute).
Abstract
Laser powder bed fusion (PBF-LB/M) has long been a subject of interest due to the possibilities it offers in terms of design flexibility, enabling the fabrication of geometries not achievable otherwise. This is of special interest regarding the manufacture of thin-wall sections (<1 mm) for cooling channels, heat exchangers, or lattice structures, amongst other applications. Additive manufacturing of thin sections can be particularly challenging due to different phenomena such as heat accumulation, geometrical accuracy, or residual stress distribution. Therefore, further efforts are needed to gain a deep understanding of the relationship between the processing parameters and, more specifically, the scanning strategy, and the resulting microstructure, as this would contribute to enhance thin wall performance. This study investigates the influence of pre- and post-contour scanning on the microstructure of thin-wall Inconel 939 (IN939) structures produced by laser powder bed fusion (PBF-LB/M) [1]. Optical and scanning electron microscopy techniques, including electron backscattered diffraction (EBSD), are used to characterize the microstructure of the manufactured thin sections at different length scales. The influence of the scanning order and of the wall thickness on different microstructural features is discussed in depth. Our findings reveal that pre-contouring mitigates heat accumulation issues, reducing grain and melt pool size and the density of geometrically necessary dislocations (GNDs). This strategy effectively shifts normalized enthalpy towards lower values, thereby enhancing processability for thin sections. Overall, this study demonstrates the potential of pre-contouring as an effective method to improve printability of thin-wall sections. [1] I. Rodríguez-Barber, A. M. Fernández-Blanco, I. Unanue-Arruti, I. Madariaga-Rodríguez, S. Milenkovic, and M. T. Pérez-Prado, “Laser powder bed fusion of the Ni superalloy Inconel 939 using pulsed wave emission,” Mater. Sci. Eng. A, vol. 870, no. February, 2023, doi: 10.1016/j.msea.2023.144864.
[300] ID:300-A nonlinear anisotropic viscoelastic model of the macaque rhesus cervix to quantify cervical remodeling
Camilo Duarte-Cordon (Columbia University), Shuyang Fang (Columbia University), Ivan Rosado-Mendez (University of Wisconsin-Madison), Timothy J. Hall (Unversity of Wisconsin-Madison), Helen Feltovich (Mount Sinai) and Kristin Myers (Columbia University).
Abstract
Through pregnancy, the cervix, a collagenous and hydrated tissue, undergoes a remarkable transformation from a rigid/closed structure that keeps the fetus inside the uterus to a more compliant/extensible one that opens to facilitate delivery at parturition. This process, known as cervical remodeling, involves complex changes in the cervix's equilibrium and dynamic mechanical properties, such as stiffness, viscoelasticity, and permeability. Constitutive models of the cervix extracellular matrix (ECM) calibrated with experimental data at equilibrium and obtained from animal cervical tissue, mostly rodents, have proven helpful in studying how the cervix softens through gestation. Recently, a poro-viscoelastic model of the human cervix was used to describe the human cervix's time-dependent behavior but limited to compressive strains and two gestational points (pregnant and nonpregnant). Building upon these previous constitutive models, we implemented a nonlinear anisotropic viscoelastic model of the cervix ECM, which captures the poro-visco-elastic behavior of the cervix under both compressive and tensile deformation. To calibrate our model, we used force-displacement experimental data from spherical indentation and uniaxial tension tests in cervix samples from Rhesus macaques, chosen because of their homology to humans, and collected at four relevant gestational time points. We observed that different mechanisms dominate the viscoelastic response of the cervix depending on the state of stresses and gestational time point. Under compressive load, as it occurs in indentation tests, the cervix's dynamic behavior is dominated by interstitial fluid flow through the porous cervix ECM. In contrast, in the case of uniaxial tension, the arrangement of the collagen network and interactions with other ECM components, such as proteoglycans, play a more critical role. This work gives insights into normal cervical remodeling, which is crucial to developing diagnostic methods and treatments for conditions such as cervical insufficiency, which is known to lead to preterm birth (birth before 37 weeks).
[303] ID:303-Quantifying stress intensity factors in fretting tests via digital image correlation
Filipe R. Chaves (Ecole Normale Supérieure Paris-Saclay), Sylvie Pommier (Ecole Normale Supérieure Paris-Saclay), Yoann Guilhem (Ecole Normale Supérieure Paris-Saclay), Nathalie Serres (Safran Aircraft Engines) and Jean Balmon (Safran Aircraft Engines).
Abstract
Fretting is a phenomenon occurring between two contacting bodies in a mechanical system, potentially leading to crack initiation and consequential damage to the components. As shown by C. Montebello [1] and G. Rousseau [2], in partial slip conditions, stress intensity factors (SIFs) can be used to characterize the stress field around the contact edge independently of the geometries of the parts in contact. Experimental fretting tests conducted at different tangential load levels provided access to stress intensity factors through an integrated approach of digital image correlation (DIC). A sensitivity study was carried out to evaluate the impact on the measured stress intensity factors of a series of experimental parameters (zoom scale factor, outer radius of the ROI, inner radius of the ROI, size of the ROI mesh element, position of the ROI mesh, plane stress/strain state, first term of the Williams series and last term of the Williams series). The reference case study demonstrated, under different tangential loads, minimal impact of the zoom level on ΔK2 values. Among the analyzed parameters, the mesh size of the region of interest has the least influence on the ΔK2 result. Conversely, varying the remaining parameters by approximately 20% has an impact of around 5% on ΔK2 results. This observation underscores the remarkable robustness of the chosen approach for addressing the problem at hand.
[304] ID:304-New Mechanics in Cell-Nanomaterial Interactions: Boron Nitride Nanosheets Inducing Water Channels Across Lipid Bilayers
Xuliang Qian (School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore), Matteo Andrea Lucherelli (CNRS, Immunology, Immunopathology and Therapeutic Chemistry, Strasbourg), Paula Weston (Department of Pathology and Laboratory Medicine, Brown University, Providence, RI), Matilde Eredia (CNRS, ISIS, University of Strasbourg, Strasbourg), Wenpeng Zhu (School of Physics, Sun Yat-sen University, Guangzhou), Paolo Samorì (CNRS, ISIS, University of Strasbourg, Strasbourg), Huajian Gao (School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore), Alberto Bianco (CNRS, Immunology, Immunopathology and Therapeutic Chemistry, Strasbourg) and Annette von Dem Bussche (Department of Pathology and Laboratory Medicine, Brown University, Providence, RI).
Abstract
While the interaction between 2D materials and cells is of key importance to the development of nanomedicines and safe applications of nanotechnology, still little is known about the biological interactions of many emerging 2D materials. Here, an investigation of how hexagonal boron nitride (hBN) interacts with the cell membrane is carried out by combining molecular dynamics (MD), liquid-phase exfoliation, and in vitro imaging methods. MD simulations reveal that a sharp hBN wedge can penetrate a lipid bilayer and form a cross-membrane water channel along its exposed polar edges, while a round hBN sheet does not exhibit this behavior. It is hypothesized that such water channels can facilitate cross-membrane transport, with important consequences including lysosomal membrane permeabilization, an emerging mechanism of cellular toxicity that involves the release of cathepsin B and generation of radical oxygen species leading to cell apoptosis. To test this hypothesis, two types of hBN nanosheets, one with a rhomboidal, cornered morphology and one with a round morphology, are prepared, and human lung epithelial cells are exposed to both materials. The cornered hBN with lateral polar edges results in a dose-dependent cytotoxic effect, whereas round hBN does not cause significant toxicity, thus confirming our premise.
[305] ID:305-Stress intensity factors and energy release rates of both deflected and branched cracks
Yujie Wei (Institute of Mechanics, Chinese Academy of Sciences).
Abstract
When cracks propagate, either quasi-statically or dynamically, they may deflect from its original plane or bifurcate into several branches. Both deflected and branched cracks are of engineering significance, as epitomized by hydraulic fracture or crack extension in heterogeneous media. In this talk, we may cover several aspects pertinent with deflected or bifurcated cracks. 1, A close-form crack deflection criterion: when G_w/G_0≤cos^4 (α/2), the crack deflects into the weak plane with the critical energy release rate G_w, and that for straight crack propagation is G_0, α is the deflecting angle. This equation supplies a simple yet elegant criterion for the transition of a straight crack deflecting into a weak plane. 2, The elastic field of kinked cracks of arbitrary size. By adopting the Schwartz-Christoffel conformal mapping and the Muskhelishvili theory, we supplied a general way to solve the elasticity problem of cracks with complicated geometries, for both kinked and branched cracks. 3, The elasticity of a cracked half-plane with two typical scenarios: a double branched crack with two rays emanating from one point on the edge and two edge cracks spaced by a certain distance. Typical loading conditions are considered, including far-field uniform tensile stress and concentrated loads along either the tangential or the normal direction of the free surface. The talk includes a semi-analytic solution to those boundary-value problems in the cracked half-plane.
[306] ID:306-Alternating ductile and brittle cracking mode in medium manganese steel sheets
Thibaut Heremans (UCLouvain), Astrid Perlade (ArcelorMittal Maizières Research SA), Pascal J. Jacques (UCLouvain) and Thomas Pardoen (UCLouvain).
Abstract
Steel sheets are extensively used in the automotive industry for an excellent combination of strength-ductility-cost performances. However, the ongoing optimization of this set of usually conflicting properties has brought forward cracking resistance issues in new advanced high strength steel products, leading to fracture toughness concerns.
This study investigates an unusual alternating failure mode transition from ductile damage to brittle (quasi-)cleavage, leading to arrowhead marking (AHM) patterns pointing towards the crack propagation direction. The sheet materials are 1.5 mm thick medium-manganese and quenching & partitioning steel grades. Arcan cracking tests have been carried out, involving the propagation of cracks into modified single edge notched tensile specimens where the initial notch can be tilted with respect to the tensile direction. One of the goals is to discriminate the influence of shear stress at fixed stress triaxiality on crack initiation and propagation. Two loading angles, 0° (pure mode I) and 45° (mixed mode I & II) were imposed, as well as three loading speeds, 0.1, 1.0 and 10 mm/min.
All materials and loading conditions lead to a slant mode exhibiting well-defined arrowhead markings on the fracture surfaces. The phenomenon is strain rate sensitive as the number of AHMs directly increases with loading rate while the AHMs size and spacing both decrease. Further geometrical characterization of these arrowhead markings suggests a strong connection between the intrinsic energies of both ductile and brittle failure modes. The mechanism presumably involves a crack arrest and re-blunting process. The understanding and mitigation of this singular failure mechanism is of prime importance in the context of the development of high performance steel sheets.
[307] ID:307-Thermal management from the build platform for laser powder bed fusion of Fe-Si alloys
Simon Van Roy (UCLouvain), Bruno Dehez (UCLouvain), Olivier Poncelet (UCLouvain), Thomas Kairet (Sirris), Erin Kuci (Cenaero) and Aude Simar (UCLouvain).
Abstract
In the process of actuator design, the limitations imposed by conventional manufacturing processes can be very restrictive. This is particularly true for certain types of actuators such as axial flux machines, where the lamination of the magnetic circuit, necessary to limit the occurrence of induced currents, is very complex. Additive manufacturing techniques, and in particular laser powder bed fusion (LPBF) of soft magnetic Fe-Si alloys, are likely to provide an answer to these limitations. To reach good magnetic properties, both in terms of magnetic permeability and iron losses, high silicon content Fe-based alloys have potential. However, at the desired contents, these alloys become very brittle, leading to numerous defects when used with LPBF, in particular the appearance of cracks and porosities. Babuska et al [1] showed that it is possible to enhance the ductility of Fe-50Co, and thus reduce the appearance of defects on brittle magnetic alloys, by regulating heat flows during the print. Inspired by their work, the present study aims to investigate how heat fluxes towards the building platform influence the formation of defect in the printed component. The effect of various support topologies is investigated by studying thermal dynamics using print-specific thermal curves. Dynamic finite element method (FEM) simulations are used to understand and manage heat fluxes. Finally, the validity of the thermal simulations is assessed by comparison with thermal measurements, and an evaluation is carried out on a complete print to reinforce the impact of heat flow management.
[1] Tomas F. Babuska et al., An additive manufacturing design approach to achieving high strength and ductility in traditionally brittle alloys via laser powder bed fusion, Additive Manufacturing, Volume 34, 2020, 101187, ISSN 2214-8604, https://doi.org/10.1016/j.addma.2020.101187
[308] ID:308-Mechanics of interfacial fracture of co-consolidated thermoplastic joints with and without crack stoppers
Ioannis Sioutis (University of Patras) and Konstantinos Tserpes (University of Patras).
Abstract
In this work, we have studied the mechanics of interfacial fracture in co-consolidated thermoplastic joints with and without crack stoppers subjected to quasi-static and fatigue loading by experiments and numerical models. We have performed quasi-static and fatigue tests on double-cantilever beam (DCB), end-notch flexure (ENF), single-lap shear (SLS) and crack-lap shear (CLS) coupons and on a mono-stringer sub-element. Also, we have developed two numerical models based on the cohesive zone modeling (CZM) method. The first model utilizes a modified tri-linear traction separation law, which is built by superimposing the bi-linear behaviors of the matrix and fibers, to simulate the mixed-mode fracture of co-consolidated thermoplastic joints by considering fiber bridging and the second model utilizes a modified bi-linear traction separation law to simulate fatigue interfacial crack growth of co-consolidated thermoplastic joints for any I+II mode-mixity ratio, requiring only pure mode I and II loading data as input. The models were fed and successfully validated by experimental data and then used to numerically design two crack stoppers, namely the Friction Stir Spot Welding (RFSSW) and the Induction Low Stir Friction Riveting (ILSFSR) crack stoppers, which were applied on the CLS coupons and the sub-element. It was found that both crack stoppers are capable of delaying the interfacial crack growth for the fatigue loading. The methods and findings of the present work show a great potential for use in the design of thermoplastic aerostructures assembled by co-consolidation or welding and can be proved very useful in the development of digital twins and in the digital certification process.
[309] ID:309-Understanding Graphene Mechanics: From Molecular to Continuum Modeling
Matteo Pelliciari (University of Modena and Reggio Emilia).
Abstract
Thanks to its exceptional mechanical and physical properties, graphene has attracted researchers from various engineering fields. A thorough understanding of its mechanical behavior is essential to fully exploit its potential. However, due to the small scale of this material, only a limited number of experimental tests have been conducted. Therefore, the development of accurate mechanical models for graphene mechanics is crucial. In this study, a molecular mechanics model in nonlinear elasticity is introduced to investigate the size effect in graphene membranes. It is observed that the response of graphene remains unchanged beyond a certain threshold size. This threshold size marks the transition to the continuum theory, which is developed as a hyperelastic membrane model. Explicit relations between stretches and stresses of the membrane under large strains are derived for both uniaxial and equibiaxial loads. Unlike other continuum models in the literature, the approach proposed in this work is entirely developed in nonlinear elasticity, serving as a foundation for accurate predictions of graphene mechanics under stress states of practical interest.
[310] ID:310-Domain switching mechanisms dictating the bulk ferroelectric response
Claire Griesbach (ETH Zurich), Vignesh Kannan (ETH Zurich, Ecole Polytechnique), Mathieu Brodmann (ETH Zurich) and Dennis Kochmann (ETH Zurich).
Abstract
Despite their widespread use, the ferroelectric switching mechanisms within lead zirconium titanate (PZT) ceramics are not well understood due to the complexities in characterizing a polycrystalline microstructure containing intragranular nanodomains and defects such as pores and precipitates. The grain orientation, misorientation to neighboring grains, proximity to defects, and initial domain structure can all influence the domain evolution during the application of an electric field. Furthermore, the domain evolution is influenced by couped thermo-electro-mechanical loading conditions. Here, we investigate the influences of the loading conditions and the initial microstructure on the domain evolution and resultant bulk ferroelectric response in PZT ceramics. We have developed an in-house electrical testing setup capable of capturing the time-resolved ferroelectric strain and bulk polarization as a function of the applied electric field. To connect the bulk ferroelectric response to the microstructural evolution, we use electron microscopy to characterize the microstructure before and after applying the electric field. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analysis are powerful tools to resolve nanodomain structures in polycrystalline ferroelectrics but have been underutilized due to a few technical challenges—including the possibility of locally switching domains and difficulties in identifying the unit cell inversion of 180-degree domains. We demonstrate techniques to overcome both challenges and obtain high resolution microstructural information about the grain orientations, domain structure, and defect distributions from EBSD scans and SEM images optimized for high domain contrast. These techniques are extended to the third dimension through FIB-SEM tomography, providing full three-dimensional microstructural data. The wealth of microstructural data obtained before and after different electrical load histories provides insight into the condition-specific ferroelectric switching mechanisms, which will guide materials-based design strategies at the microstructural level for better control of the bulk ferroelectric response.
[311] ID:311-Swelling-related mechanical propeties of hydrogels
Roberto Brighenti (University of Florence), Noy Cohen (Technion - Israel Institute of Technology) and Silvia Monchetti (University of Florence).
Abstract
Hydrogels are hydrophilic polymers keen to uptake a large amount of water within their molecular network. Thanks to their physical, chemical, and mechanical properties close to those of biological matters and tunable in a wide range of values, hydrogels can be conveniently employed in a variety of fields, ranging from soft robots to biomedical applications [1]. Mechanical properties of gels are strictly related to the amount of water present in their network, and it has been recognized that – among others – the gel’s elastic modulus usually decreases with the degree of swelling. In the present paper, we experimentally investigate the swelling degree-hydrogel stiffness relationship. It is experimentally observed the unexpected swelling-induced stiffening for extremely high water contents. A physics-based theoretical model considering: (1) the dissociation of intermolecular hydrogen bonds (which results in a decrease in chain density and an increase in the contour length of the chains) [2], and (2) swelling leading to the stretching of the chains [3] to accommodate additional water molecules, is proposed to justify the observed behavior. This finding opens new perspectives in obtaining gels whose stiffness can be made to vary by tuning the water content. This can be achieved, for example, by varying the temperature in temperature-sensitive hydrogels.
References [1] Flory, P. J. (1942) Thermodynamics of high polymer solutions. The Journal of chemical [2] Cohen, N., and Eisenbach, C. D. (2019) A microscopically motivated model for the swelling-induced drastic softening of hydrogen-bond dominated biopolymer networks. Acta Biomaterialia 96, 303 – 309. [3] Kuhn, W., and Grun, F. (1942) Beziehungen zwischen elastischen Konstanten und Dehnungsdoppelbrechung hochelastischer Stoffe. Kolloid-Zeitschrift 101, 248–271.
[312] ID:312-Towards 3D architected materials in Laser Powder Bed Fusion via local microstructure control, in situ alloying and multi-material printing
Roland Logé (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Reza Esmaeilzadeh (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Vigneashwara Pandiyan (Swiss Federal Laboratories for Materials Science and Technology (Empa)), Lucas Schlenger (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Amir Jamili (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Claire Navarre (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Jamasp Jhabvala (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Eric Boillat (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Giulio Masinelli (Swiss Federal Laboratories for Materials Science and Technology (Empa)), Patrik Hoffmann (Swiss Federal Laboratories for Materials Science and Technology (Empa)), Cyril Cayron (Ecole Polytechnique Fédérale de Lausanne (EPFL)), Nicola Casati (Paul Scherrer Institute (PSI)), Daniel Grolimund (Paul Scherrer Institute (PSI)), Federica Marone (Paul Scherrer Institute (PSI)) and Steven Van Petegem (Paul Scherrer Institute (PSI)).
Abstract
Laser Powder Bed Fusion (LPBF, also known as SLM, Selective Laser Melting) is a well-known Additive Manufacturing technology, among the most studied in literature for metals and alloys. Advanced LPBF now includes the ability to vary the laser parameters during fabrication, to perform in situ laser heat treatments, and to mix different powders. These recent developments open the possibility of printing architected materials, for which properties vary in space.
In the present work, we demonstrate how microstructures in LPBF can be modulated by proper control of laser parameters and/or associated selective laser heat treatments, operating in the solid state. One example refers to phase transformations in Ti-6Al-4V, and to the effect of Fe addition through in situ alloying. Microstructure changes are shown to be accurately monitored through operando high energy X-Ray diffraction, and acoustic emission. A second example illustrates how multi-material printing can benefit from the combination of powders and metallic foils, when dealing with “non-weldable” materials. The related hybrid LPBF process shows clear advantages over the combination of different powders, due to reduced residual stresses and better control of the formation of brittle intermetallics.
[313] ID:313-Scale Bridging via Peierls-Nabarro Modeling of Dislocations in Complex Alloys
T Moran (EPFL), B Aymon (EPFL), Xin Liu (EPFL) and William Curtin (Brown University).
Abstract
Dislocations in alloys with random solute distributions, short-range order, or clustering have a range of competing length and energy scales that establish overall energy barriers to dislocation motion. The flow stress then depends on many different underlying atomistic material parameters and emergent length scales. To gain understanding and to guide theory development, we show how a Peierls-Nabarro (PN) model can enable highly efficient scale bridging along with accurate parametric exploration of dislocation behavior as a function of (controllable) material parameters. First applications of the PN/ model to (i) understanding dislocation line tension in both fcc and bcc metals, (ii) the emergence of characteristic dislocation length scales in high entropy alloys (HEAs), and (iii) zero-temperature strength in HEAs, are then presented and discussed in the context of current theories.
[314] ID:314-Coarse approximation of heterogeneous elasticity problems
Frederic Legoll (ENPC and Inria), Claude Le Bris (ENPC and Inria) and Simon Ruget (Inria).
Abstract
We consider a heterogeneous elasticity problem and we show how to approximate it using a problem of the same type, but with effective constant coefficients that are defined by an optimization procedure. Our approach is based on the sole knowledge of the average displacement and stress at the boundary of the system, which are quantities that experimental measurements can provide. In the limit of infinitely small oscillations of the coefficients, we illustrate the links between this approach and the classical theory of homogenization. We also discuss comprehensive numerical tests and comparisons that show the practical interest of the approach.
This is joint work with Claude Le Bris and Simon Ruget (Ecole des Ponts and Inria).
[315] ID:315-Geometrically Informed Material Clustering for Data-Driven Multi-scale Modelling of Complex Material Architectures
Bassam El Said (University of Bristol), Jagan Selvaraj (University of Bristol) and Yi Wang (University of Bristol).
Abstract
Multi-scale modelling is the method of choice for modelling materials with complex internal architectures. One of the main assumptions often used in such models is material periodicity. However, in some categories of materials, such as 3D woven composites, the material loses periodicity during manufacturing. The interaction between the weave architecture and structural geometry leads to a non-periodic internal architecture which is unique to each structure. A novel approach based on geometric informed material clustering is introduced to address the challenges arising from material non-periodicity. The proposed approaches identifies repeatable patterns that appear in the material architecture on the sub-meso-scale. These patterns called “Material Clusters” are grouped using data clustering and 3D image registration algorithm. Here, an objective metric for the cluster similarity is used to categorise the cluster based on their morphology and local material properties. The material response is sampled using meso-scale models of a number of structural features and under different loading conditions. The output from these models is used to populate database of material clusters, consisting of the clusters geometric information, their elastic response, and their history-dependent damage response. On the macro-scale, structural scale simulations are carried out by querying the cluster database for previously stored responses, instead of solving the complete structure in real-time. The proposed approach benefits is twofold. First, is a significant reduction in the computational cost of structural scale models while still representing the material architecture, with no periodicity assumption. Second, the proposed framework continually accumulates knowledge about the material response as the number of simulations carried out increases. The framework can identify previously unseen material clusters / loading conditions which are then simulated and added to the database for future use. In this work, the details of the framework development, application to 2D and 3D woven composites and benchmarks will be presented.
[316] ID:316-Unraveling the Dynamics of Supershear Mode I Crack Growth
David Kammer (ETH Zurich), Mohit Pundir (ETH Zurich) and Mokhtar Adda-Bedia (CNRS - ENS Lyon).
Abstract
Linear elastic fracture mechanics (LEFM) theory has long postulated that the speed of crack growth is constrained by the Rayleigh wave speed. While numerous experimental and numerical studies have generally supported this prediction, some exceptions have raised questions about its validity and the underlying factors influencing dynamic crack behavior. In this work, we present new numerical results showing that tensile (mode I) cracks can surpass the Rayleigh wave speed and exhibit propagation at supershear velocities. The key to this finding lies in incorporating geometric non-linearities into the material model. While such non-linearities are inherent in most materials, their effects on dynamic fracture growth have been largely overlooked in previous work. Our results reveal that accounting for geometric non-linearities is sufficient to enable supershear crack propagation. In addition, we show that these non-linearities induce modifications in the crack-tip singularity, leading to unconventional crack-tip opening displacements, cohesive zone behavior, and altered energy flow dynamics toward the crack tip. These observations suggest that the elastic fields and energy budgeting in the vicinity of the crack tip of geometrically non-linear materials have a completely different behavior than that of linear elastic materials, which is commonly assumed in LEFM theory. Consequently, this provides a novel perspective on dynamic crack growth that challenges existing theoretical frameworks.
[317] ID:317-Compression of dewetted nickel microparticles at ultra-high strain rates
Bárbara Bellón (Max-Planck-Institute for Iron Research), Lalith Kumar Bhaskar (Max-Planck-Institute for Iron Research), Tobias Brink (Max-Planck-Institute for Iron Research), Raquel Aymeirich-Armengol (Max-Planck-Institute for Iron Research), Dipali Sonawane (Max-Planck-Institute for Iron Research), Gerhard Dehm (Max-Planck-Institute for Iron Research) and Rajaprakash Ramachandramoorthy (Max-Planck-Institute for Iron Research).
Abstract
Small-scale metals have been extensively studied under quasistatic conditions. In recent years, there has been an effort to increase strain rates in micro/nanomechanical tests, but they are mostly limited to impact experiments. The acquisition of quantitative stress-strain signatures of micro/nanoscale metals under extreme mechanical loading conditions, e.g., strain rates beyond 10^3/s, remains unexplored. Moreover, simulation tools such as molecular dynamics (MD), which allow the visualization of internal features in materials and their evolution in silico can only be performed at very high strain rates: 10^6/s-10^9/s. Advanced experiments closer to these extreme strain rates could validate computational findings and further enhance the understanding of how size, defect density, temperature, and strain rate influence the deformation mechanisms. We report for the first time in situ mechanical testing performed on nickel microparticles at strain rates up to 10^4/s, coupled with MD simulations on particles with corresponding shapes, closing the strain rate gap to two orders of magnitude. Well-defined, defect-free microparticles with the expected equilibrated Wulff shape were obtained by annealing nickel thin films via solid-state dewetting. The microparticles were compressed at strain rates ranging from 10^-3 to 10^4/s at room temperature and between 10^-3 and 10/s at cryogenic temperatures. Based on the stress-strain signatures, thermal activation analysis, and pre-and post-test microstructural characterization, together with near-direct comparison to MD simulations, an extensive deformation map of pristine microscale nickel as a function of temperature and strain rate has been obtained. The properties of the microparticles reveal a convolution between size effect, strain rate effect and temperature. We have a transition in strain rate sensitivity that increases 10-fold beyond 10/s, and this transition is even stronger in smaller particles. Finally, based on the low activation volumes ascertained ~10b^3 from experiments and the MD results, surface nucleation of defects is suggested as the dominating main deformation mechanism.
[318] ID:318-Thin-film stripe-shaped magnetic domain continuum theory
Stephan Wulfinghoff (Kiel University) and Christian Dorn (Kiel University).
Abstract
Micromagnetic simulations are computationally demanding and hence usually restricted to systems of strongly limited size. In practice, we typically either choose to investigate microscopic systems or we use phenomenological magnetic material models on the macroscale, which are often linearized around the working point. Continuum models on an intermediate scale (mesoscale) are mostly missing. On this scale, there are too many domains for economic micromagnetic simulations but the domain structure has a distinct effect on the overall system behavior. To address the problem, we devised a continuum theory for magnetic materials being dominated by stripe-shaped domains (the term 'stripe-shaped domains' is used to distinguish the considered domain structure from the established term 'stripe domains'). We derive a mesoscopic potential starting from a potential-based kinematical description of continuously distributed stripe-shaped domain walls. Our formulation of the mesoscopic theory is based on a few fields with physically meaningful microscopic interpretation. A phenomenological closure-domain extension completes the picture and allows us to introduce a constrained energy minimization principle. We propose a monolithic finite-element based numerical solution algorithm and, based on a consistent linearization of the numerical algorithm, we obtain quadratic convergence for the nonlinear solution procedure. A first simple examination of the theory is preformed by simulating a thin film with spatially and temporally non-constant effective anisotropy. We find the results to be consistent with analytical predictions.
[319] ID:319-Stress-induced amorphization and grain boundary sliding in olivine
Hosni Idrissi (Institute of Mechanics, Materials and Civil Engineering / Université catholique de Louvain), Ihtasham Ul Haq (EMAT - University of Antwerp), Ankush Kashiwar (IMMC - Université catholique de Louvain (UCLouvain) / EMAT - University of Antwerp), Dominique Schryvers (EMAT - University of Antwerp) and Patrick Cordier (University of Lille).
Abstract
Olivine is the most volumetric abundant mineral phase in the upper mantle and also the one which deforms the most and controls the rheology of the upper mantle. Deformation mechanisms in olivine have attracted considerable attention since several decades. One of the problems with this orthorhombic mineral is that there are not enough slip systems to produce a general deformation. The observation of a non-linear deformation regime depending on the grain size has led to the suggestion of the possibility of slip at the grain boundary [1], which has only recently been demonstrated microstructurally [2]. In this work we show that under high stresses, this grain boundary sliding can be due to the amorphization of the grain boundary and to the flow of this amorphous intergranular phase [3]. We show how nanomechanical testing in situ in the TEM allows to characterize this individual mechanism as well as the rheology of amorphous olivine. We finally propose that this mechanism of stress-induced amorphization is an important deformation mechanism in its own right under conditions of high stress [4].
[1] Hirth, G., & Kohlstedt, D. (1995) Experimental constraints on the dynamics of the partially molten upper mantle: 2. Deformation in the dislocation creep regime, J. Geophys. Res., 100, 15,441–449. [2] Bollinger, C., Marquardt, K. & Ferreira, F. (2019) Intragranular plasticity vs. grain boundary sliding (GBS) in forsterite: microstructural evidence at high pressures (3.5–5.0 GPa). American Mineralogist 104, 220–231. [3] V. Samae, P. Cordier, S. Demouchy, C. Bollinger, J. Gasc, S. Koizumi, A. Mussi, D. Schryvers & H. Idrissi. Stress-induced amorphization triggers deformation in the lithospheric mantle. Nature, 2021, 591, 82 [4] Idrissi, H., Carrez & P.Cordier, P. (2022) On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State & Materials Science. 26(1), 100976
[320] ID:320-Wave propagation in graphene-based functional architectures: Dynamics captured by homogenization
Mahmoud Mousavi (Uppsala University) and Bo Yang (Uppsala University).
Abstract
Graphene-based architectures has attracted attention in diverse applications ranging from guiding wave and energy materials, to water desalination. Understanding the wave propagation in such materials is paramount for applications with exposure to dynamic loading. In this presentation, we address perfect architectures including single- as well as multi-layer graphene and (armchair and zigzag) carbon nanotube. Employing the wave finite element method and considering geometric nonlinearity, the corresponding unit cells are homogenized to study the wave propagation, dispersion relations and band structures. The generalized continuum theory of second-strain gradient elasticity will be used to capture the nonclassical features and comparatively look into the classical, first-strain and second-strain gradient elasticity theories.
Acknowledgements. This work is funded by the European Union’s Horizon Europe Programme (NANOWAVE) under the Marie Skłodowska-Curie Action grant agreement No. 101105373.
References: [1] Yang B., Mousavi M., 2024, Nonlinear dynamic behavior of carbon nanotubes incorporating size effects. International Journal of Mechanical Sciences. Accepted. [2] Yang B., Fantuzzi N., Bacciocchi M., Fabbrocino F., Mousavi M., 2024, Nonlinear wave propagation in graphene incorporating second strain gradient theory. Under review.
[322] ID:322-Shape Optimization of Auxetic Sandwich Panel for Enhanced Underbelly Blast Protection of Armoured Vehicle
Mayank Rai (Indian Institute of Technology Delhi), Anoop Chawla (Indian Institute of Technology Delhi) and Sudipto Mukherjee (Indian Institute of Technology Delhi).
Abstract
Near-field detonation of high explosives liberates a large amount of energy in a short time and exerts high localized forces on the interacting structure. Sandwich panels with energy-absorbing cellular materials in the core, that dissipate the blast energy by undergoing progressive plastic deformation, have been widely used as sacrificial cladding. Conventional core materials with positive Poisson’s ratio exhibit localized resistance against localized loading allowing only a small volume of core to participate in energy dissipation. However, auxetic materials possess a Negative Poisson’s Ratio (NPR), allowing them to undergo lateral contraction during a longitudinal compression, engaging more volume of the core that can participate in the dissipation of blast energy. This research investigates the application of a Re-entrant Honeycomb Sandwich Panel (RHSP) as protective cladding beneath an armoured vehicle to counter an underbelly blast. It also examines the influence of shape variables of a re-entrant unit cell: the re-entrant angle (θ), the horizontal length (L), and the slant length (D) on the blast response. Besides shape variables, the effect of variation in the number of core layers was also analyzed. TCL scripting was used to generate automated Finite Element (FE) models based on different values of shape variables. It was observed that the collapse kinematics of the auxetic core varies for different values of shape variables. This contributes significantly to the amount of material being recruited in the impact zone and consequently the energy absorbed by the auxetic sandwich panel and the force transmitted to the armoured vehicle.
[323] ID:323-Understanding the impact of the texture on the bendability of aluminium sheets
Alain Twisungemariya (Constellium CTEC, Voreppe, France), Dominique Saletti (Constellium CTEC, Voreppe, France), Fanny Mas (Constellium CTEC, Voreppe, France), Dominique Daniel (Constellium CTEC, Voreppe, France) and Laurent Laszczyk (Constellium CTEC, Voreppe, France).
Abstract
Bending performances for automotive body sheet is a key feature for validating the use of an aluminum alloy in an industrial application. Understanding the impact of the texture on the bendability of the material is then of interest to help industrials tuning composition and milling process parameters in order to match the bending performances with the application expectations. The first part of the paper presents the methodology adopted to evaluate the bending performances of a virtual texture before doing any experimental test. It lies on the use of a two-scale model approach: a macro-scale with a FEM modeling of a VDA bending test and a micro scale, representative of the volume element, with a crystal plasticity simulation thanks to the open-source DAMASK software. By coupling these two scales, it is possible to study the response of the virtual texture at the grain size. By using different type of textures, it is then possible to rank them according to their bending performances. The main assumptions, constitutive laws and model’s preparation will be detailed to understand the whole frame of the methodology. The first results on ideal textures (i.e. with a high proportion of a unique component such as Goss or Copper) give bending performances and ranking in accordance with the existing literature. The application of this methodology on three real industrial and significantly different textures for which experimental campaigns have been done shows as well a good correlation between virtual and experimental ranking. The paper will be concluded with a proposition of criterion to evaluate the bending performance of a texture. Finally, the role of iron particles will be discussed as an opportunity for further studies.
[324] ID:324-Micromechanics-informed parametric deep material network for physics behavior prediction of heterogeneous materials with a varying morphology
Tianyi Li (Dassault Systèmes).
Abstract
Deep Material Network (DMN) has recently emerged as a data-driven surrogate model for heterogeneous materials. Compared to other neural networks, DMN distinguishes itself by the capability to encode directly the morphology of a particular microstructure through its fitting parameters. After an offline training solely based on linear elastic data generated by computational homogenization, the trained model is able to accurately extrapolate to history-dependent complex inelastic behaviors such as plasticity.
In this work, a novel micromechanics-informed parametric DMN (MIpDMN) architecture is proposed for multiscale materials with a varying microstructure described by several parameters. A single-layer feedforward neural network is used to account for the dependence of DMN parameters on the microstructural ones. Micromechanical constraints are prescribed both on the architecture and the outputs of this new neural network. Offline training is performed by minimizing a loss function aggregating the data generated at various morphologies. The proposed MIpDMN has been tested numerically with success for different parameterized microstructures. The trained MIpDMN is able to predict accurately the structure-property relationships for linear and nonlinear behaviors and demonstrates satisfying generalization capabilities when morphology varies. In addition, significant speed-up can be obtained in terms of computational time compared to full scale finite element simulations.
The proposed MIpDMN is also recast in a multiple physics setting, through an adequate redefinition of the DMN laminate homogenization function (building block of the neural network). Numerical simulations indicate that physical properties other than the mechanical ones such as thermal conductivity and coefficient of thermal expansion can also be predicted using the same model trained previously on isothermal data. This shows that MIpDMN learns the parameterized microstructure per se, and not a physical property in particular.
[325] ID:325-Multiscale modelling using recurrent neural network for microscale surrogation to achieve acceleration in simulation of rate-dependent dissipative lattice based and cellular (meta) materials
Mohib Mustafa (University of Liege), Ling Wu (University of Liege), Ludovic Noels (University of Liege) and Javier Segurado (Universidad Politécnica de Madrid, IMDEA Materials Institute).
Abstract
FE2 complexity renders multiscale cellular meta material simulations impractical on account of excessive time and (computational) resource requirements. Especially the rate dependent, dissipative material nature of the base material alongside the fine discretization of the underlying repeated lattices necessitates acceleration of the numerical scheme. Resolution of the micro scale boundary value problem by a surrogate is investigated and its applicability is demonstrated using lattice based meta materials.
An effective surrogate model sensitive to (strain) rate and (microscale) geometrical parameters using a recurrent neural network (RNN) is trained (offline) on a dataset populated by performing full-field simulations. Populating the dataset, including identification of generation parameters, establishing bounds for spanning a functional space, designing of the surrogate model and tuning of the training parameters is presented.
The quality of the trained surrogate is evaluated by means of testing data and FE2 counterparts by substitution in equivalent multiscale simulations. Comparisons are made on the predictions demonstrating the sensitivity on (strain) rate, local constitutive behaviour, local (lattice) geometrical parameters using various loading scenarios. Performance gains in (simulation) time are reported alongside the modalities for population of a useful dataset and training of a reliable surrogate.
One potential area of application for surrogated multiscale modelling is microscale level optimization to maximize / minimize an objective function defined on macroscale level. This is achieved by the reduction in computational resources enabling fast and cheap evaluation of the objective function (multiscale FE simulation).
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 862015
[327] ID:327-Mesoscale modelling of complex textile-reinforced composite materials using the finite cell method
Elias Börjesson (Dept. Industrial and Materials Science, Chalmers University of Technology), Clemens V. Verhoosel (Dept. Mechanical Engineering, Eindhoven University of Technology), Joris J.C. Remmers (Dept. Mechanical Engineering, Eindhoven University of Technology), Fredrik Larsson (Dept. Industrial and Materials Science, Chalmers University of Technology) and Martin Fagerström (Dept. Industrial and Materials Science, Chalmers University of Technology).
Abstract
Modelling the mechanical behaviour of heterogeneous materials, such as textile-reinforced polymer composites, requires consideration of the underlying material heterogeneity. For textile composites, this means accounting for the weave architecture in a representative yet computationally efficient manner. Doing this on the mesoscale means including a discrete representation of the weaving pattern of the impregnated textile, along with pure matrix regions as separate entities. A significant challenge is generating high quality finite element discretisations. Traditional meshing techniques often fall short, particularly for proper discretisation of pure matrix regions. The close proximity of complex shaped fibre bundles often creates narrow regions where a high density of elements is required. This poses significant difficulties in generating finite element meshes with an acceptable balance between mesh quality and computational cost.
An attractive alternative is therefore to decouple the geometrical representation from the numerical discretisation, resorting to embedded or immersed methods. In this contribution, we explore the use of the Finite Cell Method [1] to achieve the necessary decoupling. FCM is a popular approach within a class of immersed methods for which straightforward, un-fitted meshes (resembling voxel structures) are used to discretise the unknown fields, while capturing the geometry through specially designed quadrature rules. Thereby, the approach allows the discretisation process to be automated, making it flexible and effective for complex weave architectures. The proposed methodology is demonstrated on several mesoscale structures common to textile-reinforced composites, including both 2D-woven and 3D-woven architectures. In addition, the importance of numerical stabilisation, achievable e.g. through the ghost penalty method, is highlighted and explained. In summary, this contribution shows the benefit and flexibility of FCM in developing mesoscale models of textile composites, to be adopted e.g. in multiscale analyses of larger structures.
[1] E. Rank et al., Computer Methods in Applied Mechanics and Engineering, Vol: 249–252, 2012, pp: 104-115.
[328] ID:328-Failure of thin incompressible membranes at finite deformations
Mahmood Jabareen (Faculty of Civil and Environmental Engineering; Technion - Israel Institute of Technology).
Abstract
In the present study, a finite element formulation for modeling crack propagation in hyperelastic thin membranes is developed. The crack formation and propagation is modeled by means of the material-sink approach stemming from the physical observation of the diffused bond breakage. Keeping in mind that loss of local bonds leads to localized material loss, the mass density can be considered as a variable, which numerically decreases in the area where damage localizes into a crack. This notion requires mathematical consideration of mass balance as an additional and active law, which regularizes the computational model. From the numerical point of view, the developed computational model has displacement and density degrees of freedom. Also, a monolithic approach was applied that ensures stable incrimination of the nonlinear problem. Numerical examples of the fracture of different geometries demonstrate the high robustness of the proposed approach in modeling crack propagation in membrane structures.
[329] ID:329-Pore morphology development in viscoelastic foods during drying
Ruud van der Sman (Wageningen University & Research), Luciano Teresi (Univ. Rome Tre) and Michele Curatolo (Univ. Rome Tre).
Abstract
In this contribution we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during dry- ing. The food material has been idealized as a spherical object, with core/shell structure and a central gas-filled cavity. The shell represents a skin as present in fruits/vegetables, having a higher elastic modulus than the tissue, which we approximate as a hydrogel. The gas-filled pore is in equilibrium with the core hydrogel material, and it represents pores in food tissue as present in intercellular junctions. The presence of a rigid skin is a known prerequisite for cavitation (inflation of the pore) during drying.
For the modelling we follow the framework of Suo and coworkers, describing the inhomogeneous large deformation of soft materials like hydrogel - where stresses couple back to moisture transport. In this paper we have extended such models with energy transport, and viscoelasticity - as foods are viscoelastic materials, which are commonly heated during their drying.
To approach the realistic properties of food materials we have made viscoelastic relaxation times a function of Tg/T , the ratio of (moisture dependent) glass transition temperature (Tg) and actual product temperature (T). We clearly show that pore inflation only occurs if the skin gets into the glassy state, as has been observed during the (spray) drying of droplets of soft materials like foods.
[330] ID:330-Dialogue between brittle fracture mechanics and experiments using additive manufacturing to study crack propagation in anisotropic materials
Veronique Lazarus (Institut Polytechnique de Paris, ENSTA, IMSIA, UMR), Thomas Corre (Nantes University, Ecole Centrale Nantes, CNRS, GeM, UMR), Xinyuan Zhai (Institut Polytechnique de Paris, ENSTA, IMSIA, UMR), Stella Brach (IBM Research Zurich) and Andrès Léon Baldelli (Institut Polytechnique de Paris, CNRS, IMSIA, UMR).
Abstract
To extend the use of single crystals or additively manufactured materials to sensitive components, for instance in aerospace industry where catastrophic failure must be avoided at all costs, it is crucial to have models capable of reliably determining how and when a crack propagates for anisotropic materials. While Linear Elastic Fracture Mechanics (LEFM) has been certified experimentally for isotropic materials, its extension to the anisotropic case lacks close comparison with experiments.
To fill this gap, we have developed experiments designed to precisely test and identify the material parameters of the generalized energy release rate criterion, based on Griffith's energy balance, and an associated phase field variational approach (Li and Maurini, 2019).
The reference material used is Polycarbonate printed by Fused Deposit Modeling to fit within the framework of LEFM. As an initial study, the printing strategy has been tuned to get some 2D isotropic elasticity, that permits the use of standard tools (Stress Intensity Factors and Digital Image Correlation) while exhibiting some strong fracture anisotropy (Corre and Lazarus, 2021).
References:
Corre, T., Lazarus, V., 2021. Kinked crack paths in polycarbonate samples printed by fused deposition modelling using criss-cross patterns. Int. J. Fract. 230, 19–31. https://doi.org/10.1007/s10704-021-00518-x
Li, B., Maurini, C., 2019. Crack kinking in a variational phase-field model of brittle fracture with strongly anisotropic surface energy. J. Mech. Phys. Solids 125, 502–522. https://doi.org/10.1016/j.jmps.2019.01.010
[331] ID:331-Verification of a Data driven inverse stochastic models for fiber reinforced concrete
Ivica Kožar (University of Rijeka Faculty of Civil Engineering).
Abstract
Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. In order to accommodate variations in experimental results we have adopted stochastic model that is based on the 'fiber bundle representation'. The initial stochastic model formulation has been generalized into a two-parameter exponential material model that has been used as a basis for a simple three-point beam-bending model. In addition, laboratory experiments of three-point beam bending have been performed with an intention of using experimental data for determination of material parameters. It is not possible to use 'forward' beam model for extraction of material parameters so an inverse model has been devised. The inverse model is an iterative procedure based on derivative of experimental data and has successfully recovered the initial material parameters.
[332] ID:332-A combined experimental and numerical study to assess austenitic stainless steels oxidized grain boundaries fracture properties
Jérémy Hure (CEA), Rachma Azihari (CEA & CEMES-CNRS), Marc Legros (CEMES-CNRS) and Benoît Tanguy (CEA).
Abstract
Austenitic stainless steels are commonly used in industry due to their exceptional mechanical properties and corrosion resistance. However, intergranular fracture can occur in high-temperature aqueous environments, such as in Pressurized Water Nuclear Reactors (PWR). To model and predict stress corrosion cracking, it is necessary to estimate the fracture properties of oxidized grain boundaries, but experimental data is limited. This study assesses the fracture properties of a FeCr12Ni26Si3 austenitic stainless steel grain boundaries through a combined experimental and numerical approach. Micro-cantilever beams are milled at grain boundaries using Focused Ion Beam on samples oxidized in PWR environment up to 7470h. In-situ Scanning Electron Microscope bending tests are performed at room temperature, leading to brittle fracture either inside the intergranular oxide or at the metal/oxide interface. Preliminary estimates of critical stress and fracture energy can be obtained from experiments. However, for more accurate estimations, numerical modelling is required. Finite element numerical simulations, including cohesive zone modelling, are performed to predict micro-cantilever deformation and fracture. The critical stress (σc) and fracture energy (γc) are adjusted to reproduce the experimental data, resulting in σc = 1000 ± 250 MPa and γc = 11 ± 3 J.m-2. These values are in agreement with available experimental data for similar materials. Finite element simulations are finally used to assess the dependence of fracture properties and locations on experimental parameters, providing guidance for refined experimental assessment of grain boundary fracture properties.
[333] ID:333-FFT implementation of a microscopic chemo-mechanical model for damage in lithium batteries
Gabriel Zarzoso (IMDEA Materials Institute, Universidad Politécncia de Madrid,Department of material science,E.T.S.I.Caminos), Eduardo Roque (Universidad Loyola Andalucía,Materials and Sustainability,Department of Engineering), Francisco Montero-Chacón (Universidad Loyola Andalucía,Materials and Sustainability,Department of Engineering) and Javier Segurado (IMDEA Materials Institute, Universidad Politécncia de Madrid,Department of material science,E.T.S.I.Caminos).
Abstract
A novel numerical framework based on FFT solvers is proposed to simulate fracture at themesoscale in chemo-mechanical processes. The modeling approach is based on the phase-field fracture model integrated into a chemo-mechanical solver in finite strain. The simulations rely on an implicit staggered approach in which the three coupled problems are solved sequentially until reaching convergence. This FFT framework has been validated against finite element solutions in different cases and the computational cost has also been studied. The resulting framework has excellent performance and allows to resolve problems on representative volume elements of realistic three-dimensional microstructures.
The method has been parameterized to simulate the chemo-mechanical damage occurring in the active particles of ion-lithium batteries. In these particles, the intercalation and deintercalation cycles in the electrode particles lead to the initiation and propagation of cracks which degrades their behavior. The method proposed was able to simulate the response until the failure of irregular shape particles in three dimensions showing degradation and cracking patterns similar to the ones obtained in experiments.
[334] ID:334-Exploring the evolution of mechanical deformation of intact and degraded SLM WE43 scaffolds: An In Situ X-ray Characterization
M. Dolores Martin-Alonso (IMDEA Materials), Felix Benn (Queen's University Belfast), Alexander Kopp (Meotec GmbH), Jon M. Molina-Aldareguia (IMDEA Materials & Polytechnic University of Madrid), Federico Sket (IMDEA Materials) and Marta Majkut (ESRF).
Abstract
Porous Mg scaffolds, manufactured through laser powder bed fusion (LPBF), hold potential for bone regeneration as they support tissue ingrowth and enable fluid transportation. Additionally, Mg implants can be fully re-absorbed by the human body, and they share mechanical properties with bone, which prevents stress shielding effects. Applying Mg scaffolds as a bone regeneration system requires detailed knowledge of the load-bearing capability during degradation. This property is investigated to obtain suitable mechanical strength and uniform stress distribution, the latter to ensure a smooth breaking mode.
LPBF-manufactured open porous cubic scaffolds of 10x10x10 mm3 of WE43 alloy with different lattice structures (BCC, FCC, TPMS), and an average strut diameter of 500 μm were surface modified by plasma electrolytic oxidation (PEO) to improve corrosion resistance and biocompatibility. The mechanical properties and fracture mechanisms are explored through in situ synchrotron X-ray microtomography compression tests conducted on both as-built scaffolds and those immersed in simulated body fluid for varied durations (7, 14, 21 days).
This study employs Digital Image Correlation (DIC) and Volume Correlation (DVC) techniques to delve deeper into the material mechanical behaviour. DIC and DVC provide a detailed analysis of localized deformations and strain fields across the scaffold structure. By scrutinizing the evolution of these parameters, we gain insights into the influence of corrosion on mechanical failure. This comprehensive approach enhances our understanding of the intricate interplay between material degradation and mechanical performance in the context of Mg scaffolds for bone regeneration.
[335] ID:335-Data-driven inelasticity enhanced by neural networks: Opportunities in computational mechanics
Marius Harnisch (Institute of Mechanics, TU Dortmund University), Thorsten Bartel (Institute of Mechanics, TU Dortmund University), Ben Schweizer (Chair I (Analysis), TU Dortmund University) and Andreas Menzel (Institute of Mechanics, TU Dortmund University,Germany and Division of Solid Mechanics, Lund University, Sweden).
Abstract
In recent years, various data-driven methods have been developed in the field of computational mechanics. Data-driven mechanics, introduced by Kirchdoerfer and Ortiz [1], replaces conventional material modeling with data-sets containing snapshots of stress and strain assumed to be sufficiently accurate representations of the underlying material behavior. Build on these snapshots, termed material states, and on states fulfilling equilibrium and kinematic compatibility, denoted mechanical states, is a distance function, the minimization of which with respect to both of these states yields the boundary value problems’ solution.
Originally introduced for elasticity, the extension to inelasticity poses a significant challenge and different approaches have been proposed in literature. Our extension allows to preserve the spirit of the original method so that no real-time adjustments of the data-set are required. We achieve this by storing essential information of the history in a history surrogate and update this quantity at the end of each time step using a propagator. Finding suitable choices of these quantities can be challenging. By utilizing a Neural Network as propagator, we can let the Network tackle this task autonomously without resorting to a material model.
In this contribution, we present simulations for both a neural network and an intuitive propagator. We highlight the capabilities of our extension and provide a discussion of the obtained results. The neural network enhancement allows for an automated framework for which we show the necessary training routines and the results of which we compare to those of an intuitive choice of history surrogate an propagator.
[1] T. Kirchdoerfer, M. Ortiz, Data-driven computational mechanics, Comput. Methods Appl. Mech. Engrg. 304 (2016) 81-101 [2] T. Bartel, M. Harnisch, B. Schweizer, A. Menzel, A data-driven approach for plasticity using history surrogates: Theory and application in the context of truss structures, Comput. Methods Appl. Mech. Engrg. 414 (2023), 116-138
[336] ID:336-An uncoupled two-scale finite element model to investigate air entrapment during PET polymer thin film lamination
Vahid Rezazadeh (Eindhovne University of Technology), Hans van Dommelen (Eindhoven University of Technology) and Marc Geers (Eindhoven University of Technology).
Abstract
Packaging steels are coated with the polymer PET for preserving content quality, preventing corrosion, and enabling printability on the surface. The industrial lamination process must handle large volumes at high speeds, imposing a critical challenge. At elevated production speeds, air bubbles are entrapped between the polymer coating and the steel substrate, significantly impacting the final product's quality. The physics governing this air entrapment process are poorly understood, and establishing the relationship with overall process parameters is crucial.
In this presentation, we will address the air entrapment problem using a two-scale finite element modeling strategy, complemented by experiments. The coarse-scale model is developed to establish the connection between processing parameters (line speed, roll pressure, temperature, etc.) and the actual loading conditions in the lamination nip where the polymer film bonds. The fine-scale model delves into the roughness asperities of the steel sheet, explicitly studying the plastic flow of the film at high temperatures and strain rates into the roughness valleys.
The Eindhoven Glassy Polymer (EGP) is employed to model the behavior of PET under extreme rate/temperature conditions, where thermo-mechanical parameters are taken from literature or calibrated through experiments. The results from the two-scale finite element model reveal that air bubble formation is highest when the temperature of the substrate steel is low or the lamination speed is high. The model allows us to establish a quantitative link between macro-scale process parameters and incomplete filling or bonding of PET at the micro-scale. This paves the way for controlling the air entrapment, thereby enhancing the quality of the coated steels.
[337] ID:337-X-ray in-situ testing and numerical analysis of SLS manufactured lattice structures
Lucia Cobian Gonzalez (Universidad Politécnica de Madrid and Instituto IMDEA Materiales), Javier Garcia (Instituto IMDEA Materiales), Eric Maire (INSA Lyon, University of Lyon, MATEIS), Maria Dolores Martin (Instituto IMDEA Materiales), Miguel Alberto Monclus (Instituto IMDEA Materiales), Mohib Mustafa (University of Liege) and Javier Segurado (Universidad Politécnica de Madrid and Instituto IMDEA Materiales).
Abstract
Selective laser sintering (SLS) has made possible the fabrication of lattice metamaterials, consisting of periodical structures with interconnected struts. However, SLS manufacturing originates porosity and surface roughness that critically affect the mechanical behavior of these structures due to their small diameters and high specific surface.
An experimental fracture analysis of unit cells and single struts of Polyamide12 has been made to analyze how the defects influence mechanical behavior and fracture of these materials.
In-situ compressive and tensile tests of unit cells and single struts of different diameters have been performed using X-ray tomography. Observations show that the behavior of both unit cell and strut material is less stiff than the one found in bulk samples. In the struts, the fracture occurs by crack nucleation in surface defects and its propagation, which depends mainly on the printing direction. In unit cells, on the other hand, crack nucleation and propagation is observed on the nodes that join at least a strut parallel to the applied force, which depends on geometry rather than defects.
This analysis is be complemented with a numerical analysis. The tomographies are used to generate voxelized geometries that include the actual strut shape, including the defects that originated during the printing process. These geometries are simulated using an FFT-based method, considering a phase-field fracture model.
[339] ID:339-An Incompatible Finite Element formulation for enhanced representation of solutions in Phase-Field problems: Application to Regularized Fracture
Miguel Castillón (Instituto IMDEA Materiales, Eric Kandel 2, Tecnogetafe, 28906 Madrid), Javier Segurado (Instituto IMDEA Materiales, Eric Kandel 2, Tecnogetafe, 28906 Madrid) and Ignacio Romero (Instituto IMDEA Materiales, Eric Kandel 2, Tecnogetafe, 28906 Madrid).
Abstract
One of the main limitations of phase field-based models is their high computational cost. Within the framework of finite elements, the size of the finite elements must be orders of magnitude smaller than the scale factor responsible for regularizing the diffuse field. This requirement necessitates many elements to capture the interface or discontinuity. Additionally, the solution exhibits a strong dependence on the orientation of the elements. In order to reduce the computational cost and improve the convergence rate of the solution, a non-conforming finite elements formulation is presented. This formulation enriches the Galerkin solution space with non-conforming functions, including incompatible bubbles. All of this is carried out within a consistent variational formulation. The developed formulation demonstrates better convergence errors than the standard formulation and reduces the influence of the element's orientation. The application of this formulation is proposed for phase-field fracture models.
[341] ID:341- Influence of the irreversibility strategy in phase-field fracture models
Maurice Rohracker (Institute of Applied Mechanics, Friedrich-Alexander-Universität Erlangen-Nürnberg), Paras Kumar (Institute of Applied Mechanics, Friedrich-Alexander-Universität Erlangen-Nürnberg) and Julia Mergheim (Institute of Applied Mechanics, Friedrich-Alexander-Universität Erlangen-Nürnberg).
Abstract
Fracture is an irreversible process in brittle materials, and one modeling method that has become increasingly popular in science in recent years is the phase-field fracture method. Here, a discrete crack is approximated by a smeared field variable, the phase-field. Several strategies have been proposed to maintain the irreversibility condition. Bourdin et al. used a direct method to handle the irreversibility by introducing a threshold value to fix the fully damaged degrees of freedom. A penalization method was proposed by Gerasimov and De Lorenzis, which includes an additional penalty term in the phase-field evolution equations. Miehe et al. introduced a history field as the crack driving force related quantity, which is the maximum of all tensile strain energies over the simulation time. Based on the definition of the history field, there are two possible options. If the history field is defined only as the maximum of all previous load steps, the coupling of the displacement and phase-field equations is only one way and allows solving a load step in a single staggered iteration. However, small pseudo time-step sizes are essential for proper fracture detection. On the other hand, multiple staggered iterations are required when the history variable depends on the tensile strain energies of the current load step, but this allows the number of load steps to be significantly reduced. From a performance perspective, the multiple staggered iterations lead to computationally expensive simulations. We have combined different methods to reduce the computational cost while still achieving physically correct results. In addition to adaptivity in space, an improved energy-based convergence criterion is introduced for the combined convergence control in the staggered iterations, and adaptivity in time is integrated. We determine appropriate modeling parameters in typical benchmark simulations and apply them to more complex and realistic simulations of a pre-cracked particle-reinforced microstructure.
[342] ID:342-Macroscopic intermittent plasticity model by avalanches
Mathias Lamari (Mines Paris PSL), Pierre Kerfriden (Mines Paris PSL), Vladislav Yastrebov (Mines Paris PSL), Kais Ammar (Mines Paris PSL) and Samuel Forest (Mines Paris PSL).
Abstract
Plastic flow is conventionally treated as continuous in finite element (FE) codes, whether in isotropic or crystal plasticity. This approach, derived from continuum mechanics, contradicts the intermittent nature of plasticity at the elementary scale. During micropillar compression, the stress-strain curve exhibits strong serrations, linked to the abrupt activation of a very small number of slip planes. Acoustic emission on centimeter-sized single-crystal samples also demonstrate the non-chaotic but organized nature of plastic flow linked to dislocation avalanche interactions.
Understanding crystal plasticity at nanoscopic scale opens the door to new engineering applications, such as nanoscale machining and the design of radical new materials.
Various models in the literature also demonstrate the intermittence of plasticity, such as the mesoscopic tensorial model, molecular dynamics and discrete dislocation dynamics models. These models replicate the correlated nature of dislocation avalanches.
In this work, we propose a new approach to account for the intermittence of plastic deformation while remaining within the framework of continuum mechanics. We introduce a constant, the plastic deformation quantum, denoted as Δpmin, corresponding to the plastic deformation carried by the minimal dislocation avalanche within the material. The incremental model is based on the traditional predictor-corrector algorithm to calculate the elastoplastic behavior of a material subjected to any external deformation. The model is presented within the framework of small deformations for von Mises plasticity. The plastic strain increment Δp is calculated using normality rules and is accounted for only if it is higher than Δpmin. The simulations show that the introduction of the plastic quantum allows for the reproduction of the spatiotemporal intermittence of plastic flow, capturing the self-organization of plastic flow in complex loading scenarios within an FE model. Localized deformation bands spontaneously emerge in complex geometries, exhibiting correlation with stress drops observed in the tensile curves. The model is rate-independent.
[343] ID:343-Fracture initiation in a cohesive granular layer
Thomas Chau (Institut d'Alembert, Sorbonne Université, CNRS), Claire Lestringant (Institut d'Alembert, Sorbonne Université, CNRS) and Anaïs Abramian (Institut d'Alembert, Sorbonne Université, CNRS).
Abstract
Among different types of avalanches, the "slab avalanches" initiate by a long crack perpendicular to the slope, and rapidly propagate downhill during the flow. Modeling these avalanches presents challenges, including predicting the threshold for crack initiation in such a cohesive granular material, and understanding the impact of snow properties on fracture propagation.
To address these questions, we conducted experiments using a cohesion-controlled granular material encompassing a wide range of cohesion. We established an experimental setup specifically designed to explore the formation of fractures in a quasi static regime. In our setup, a layer of the cohesion-controlled material undergoes flexural deformation. Upon reaching a threshold in tensile stress, cracks emerge with a distinct wavelength that increases with cohesion. We compare these measurements to phase-field model used in damage mechanics.
[344] ID:344-Plastic chip formation in Swiss cheese the "tête de moine"
Jishen Zhang (PMMH, ESPCI, Paris 6), Alejandro Ibarra (PMMH, ESPCI, Paris 6), Matteo Cicotti (SIMM, ESPCI), Marc Rabaud (Université Paris-Saclay, CNRS, FAST) and Benoît Roman (PMMH, ESPCI, Paris 6).
Abstract
The cheese of Swiss origin “Tete de moine” is generally cut by scraping its surface with a sharp tool attached to a shaft. Scraping the cheese produces thin sheets of cheese that are strongly wrinkled at the edge. In this work we experimentally demonstrate that these wrinkles are produced by the change of mechanical properties in the radial direction of the cheese and the scraping process itself, establishing an analog between our cheese scraping process and mechanical machining widely used in the industry. To do this, we built an experimental system that allows us to carry out the scraping process systematically, for controlled load levels on the cutting tool. We found that the wrinkle formation process is strictly plastic and that due to the change in mechanical properties in the radial direction, it is reflected in a change in the compression ratio in the radial direction of the cut cheese sheet. Additionally, we independently measure the surface friction and the elastic limit of the material, to explain from mechanical parameters the change in compression ratio found when producing the cheese sheets and show that the process is strictly plastic.
[345] ID:345-High-Throughput MD Simulations and multi-model Molecular Representations for Copolymer Property Assessmen
Elaheh Kazemi Khasragh (Universidad Politécnica de Madrid, E.T.S. de Ingenieros de Caminos, 28040 Madrid, Spain), Carlos Gonzalez (IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid, Spain) and Maciej Haranczyk (IMDEA Materials Institute, C/Eric Kandel 2, 28906 Getafe, Madrid, Spain).
Abstract
Copolymers play an integral role across diverse industries, driven by their abundant availability and adaptable properties. To leverage the vast usage of polymers in industry, there is a crucial need to precisely control the properties of these materials according to specific applications. Polymer characterization has evolved from traditional empirical methods, relying on trial-and-error experimentation, to more advanced strategies. Computational methods, including computer-aided design and simulation, have enabled a systematic exploration of the polymer chemical space, allowing for more precise predictions of properties. In this research endeavor, the primary focus is on comprehensively exploring the properties of copolymer materials, specifically random, block, and alternative copolymers. For reach to this goal, we harness the power of molecular dynamics (MD) sim- ulations. This tool contributed to the calculation of 14 key properties, providing valuable support in our efforts to generate the dataset for 130 copolymer systems with high accuracy. Our study is driven by the overarching goal of addressing a significant gap in reference data for sepcial type of copolymers. These data serve as a valuable foundation for data-driven approach. By combining MD simulations with machine learning (ML) techniques, we aim to develop predictive models for optimizing copolymer performance based on the calculated properties. In addressing this challenge, we aim to provide an in-depth understanding of the molecular composition, configuration, and sequence distribution of copolymers. Our methodology involves utilizing a diverse set of representations, notably a graph-based representation, to achieve this comprehensive understanding. This approach excels in capturing crucial aspects of polymeric materials, encompassing chain architecture, monomer stoichiometry, possible monomer sequences, degree of polymerization, diverse chain topologies, and varying monomer compositions.
[346] ID:346-A discrete-continuum model for hydrolytic degradation in polymers
Zhouzhou Pan (University of Oxford) and Laurence Brassart (University of Oxford).
Abstract
Biodegradable polymers are materials designed to break down, and eventually disappear, after having fulfilled their structural function. They are widely used in healthcare applications such as sutures, stents, and tissue engineering scaffolds, where they eliminate the need for retrieval surgery. In this context, accurate predictions of the polymer service life and evolving mechanical properties is of fundamental importance. This study focuses on hydrolytic degradation, which involves the scission of polymer chains by reaction of susceptible backbone bones with water. We develop a reaction-diffusion continuum framework incorporating a discrete chain scission model able to describe various degradation mechanisms (random scission, chain-end scission, or any combination of these). Hydrolysis kinetics (including autocatalysis) is described independently of the chain scission model. This decoupling enables the identification of the chain scission mechanism from molecular weight reduction and mass loss curves commonly reported in experimental degradation studies. We further propose a reduced continuum model which is better suited for large-scale simulations of heterogeneous degradation, while retaining the predictive capability of the full discrete-continuum model. The model capability is illustrated in representative case studies based on experimental data from the literature for different materials and geometries. Generalisation of the continuum model to describe coupled degradation and mechanics will also be discussed, including the effect of degradation (decreasing molecular weight) on mechanical properties and the effect of stress on degradation rate.
[347] ID:347-Influence of the Loading Type on the Very High Cycle Fatigue Behaviour of Composite Materials
Martin Bartelt (TU Braunschweig, Institute of Aircraft Design and Lightweight Structures), Peter Horst (TU Braunschweig, Institute of Aircraft Design and Lightweight Structures), Sebastian Heimbs (TU Braunschweig, Institute of Aircraft Design and Lightweight Structures) and Tim Luplow (TU Braunschweig, Institute of Aircraft Design and Lightweight Structures).
Abstract
Testing in the Very High Cycle Fatigue (VHCF) regime comes with a number of difficulties that lead to a lack of research, resulting in conservative designs of wind turbine and helicopter rotor blades. With low loads and up to 108 load cycles, small variations of test parameters can have a huge impact. This study investigates the effect of pure tensile loading compared to four-point bending fatigue, both with a stress ratio of R = 0.1. Two test series with a (902/02)s and a (90/0)2s cross-ply lay-up made of glass fibres and epoxy resin are tested at four load levels. The bending tests are conducted on a special VHCF test rig, to overcome typical problems such as long testing times, specimen heating and self-fatigue of the test equipment. In addition to the in-situ flexural modulus recorded by the test system, the crack density and the delamination area ratio are determined from transmitted light photographs automatically taken throughout the test. The tensile tests are performed on a hydraulic testing machine, to archive the high loads required. To avoid fatigue damage to the hydraulic test machine, the majority of the tests are stopped after the first cracks appear. Only two specimens per test series are tested up to 108 load cycles. Therefore, this study focuses on the comparison of first damage, such as crack initiation, on the experimental side. Further investigations of the crack growth and delamination growth tendencies are conducted with numerical simulations using a parametric FE model. The evaluation of the experimental data shows higher fatigue limits under four-point bending fatigue. The numerical simulations indicate a higher tendency for delamination growth under pure tensile loading. This is supported by the stronger delamination growth on tensile specimens observed in the experimental data.
[348] ID:348-Ageing of a PBSAT fishing net: a multiscale study
Louis Le Gué (Research and Technological Development, Ifremer), Esther Savina (DTU Aqua, Section for Fisheries Technology), Mael Arhant (Research and Technological Development, Ifremer), Peter Davies (Research and Technological Development, Ifremer) and Benoît Vincent (DECOD (Ecosystem Dynamics and Sustainability), Ifremer, INRAE, Institut Agro).
Abstract
Ghost fishing refers to a gear’s capability to continue capturing marine life even after being lost. When an animal becomes entangled in a fishing net, the consequences are severe, including restricted movement, suffocation, injuries, and potential death due to starvation or predator attacks. To address this issue, biodegradable polymers such as poly(butylene succinate-co-adipate-co-terephthalate) (PBSAT) have been developed to reduce the mechanical impact of lost gear. While various studies have examined fishing nets made of biodegradable polymers, most have focused on gear selectivity, with limited attention given to the net structure’s mechanical properties and degradation. This study aims to characterize a PBSAT net as a multiscale structure, and to study its ageing in seawater using the same approach. Tensile tests on pristine samples showed that the PBSAT monofilament was more affected by the knotting than the commercial PA6 monofilament. X-ray tomography-derived curvature calculations demonstrated that breakage occurred mainly in high curvature zones for both materials. For ageing experiments, samples were immersed in natural seawater at different temperatures (15°C, 25°C, 40°C) for up to 8 months. Mechanical property degradation was observed across all temperatures and scales for PBSAT, while no changes were noted for PA6. High curvature zones induced high surface erosion after 240 days of immersion at 25°C. The alternative PBSAT nets tested in this study exhibited inadequate mechanical properties to replace conventional PA6 nets in commercial fisheries, primarily due to the material’s poor resistance within the knots. Moreover, the mechanical properties of the PBSAT net were highly sensitive to seawater ageing, showing accelerated degradation within the knots. The development of new biodegradable filaments will then need to be accompanied by testing and modelling.
[349] ID:349-A finite element model of TiAl/TiAlN nano-multilayered coatings
Sylvain Giljean (Université de Haute-Alsace, LPMT UR 4365), Yves Gaillard (Université de Franche-Comté, CNRS, institut FEMTO-ST), Christophe Rousselot (Université de Franche-Comté, CNRS, institut FEMTO-ST), Corinne Bouillet (Plateforme MACLE-CVL UAR2590), Fabrice Richard (Université de Franche-Comté, CNRS, institut FEMTO-ST) and Marie-José Pac (Université de Haute-Alsace, LPMT UR 4365).
Abstract
Although nanocrystalline metal nitride coatings are currently used for their outstanding properties such as hardness and wear resistance, improving these properties remains a challenge in metalworking industries, to lengthen tool life and increase cutting performance. Metal nitrides like TiN, (Ti,Al)N and metal carbides such as TiC, WC are commonly used. To move towards better performing coatings, one solution consists in depositing TiAl/TiAlN metal/nitride multilayered coatings using a recent sputtering technique (Reactive Gas Pulsing Process RGPP). This process allows to easily modulate the stacking of the coating at the nanometer scale to take advantage of the properties of the nitride, the metal and the interfaces to improve the fracture toughness of the coating while maintaining very high hardness. Ti0.67Al0.33 and Ti0.54Al0.46N (labelled TiAl and TiAlN) monolithic coatings and (TiAl/TiAl)n multilayered coatings were deposited by radio-frequency magnetron sputtering from a single sintered titanium/aluminium target using conventional and RGPP processes with two different periods (10 and 50 nm) respectively. A finite element model reproducing the mechanical behaviour during nanoindentation tests of those as-deposited coatings was developed. Identification of the material’s elasto-platic behaviour of the metal and nitride compounds in the nano-stacking was performed using experimental indentation of TiAl and TiAlN monolithic coatings for the elastic part. The plastic part was determined by finite element model updating of dual Berkovich and cube corner indentations with an experiment design guided by an identifiability index. The stacking of the multilayered coatings was specified by N-K-edge Electron Energy-Loss Spectroscopy to introduce in the numerical model an interface between each metal and nitride layers. The elasto-plastic properties of these interface layers were considered as a rule of mixtures of the metal and nitride properties using two hypotheses: parallel or serial. We proved that the properties of the interface layers are intermediate between the two hypotheses.
[350] ID:350-Residual stress level of fiber-reinforced composite laminates : influence of manufacturing conditions
Aboubakar Sédick Ibrahim Mamane (Université de Haute Alsace, Laboratoire de Physique et Mécanique Textiles), Sylvain Giljean (Université de Haute Alsace, Laboratoire de Physique et Mécanique Textiles), Gildas L'Hostis (Université de Haute Alsace, Laboratoire de Physique et Mécanique Textiles) and Marie-José Pac (Université de Haute Alsace, Laboratoire de Physique et Mécanique Textiles).
Abstract
The level of residual stresses in a part is an important data to consider when sizing it. Residual stresses can have detrimental effects on the properties and durability of parts. These are stresses trapped in the material without any external load being applied. They build-up during the manufacture and/or life of the piece. In this work, residual stresses are determined in different fiber-reinforced composite laminates. This type of material is particularly subject to residual stresses due to the mismatch in coefficient of thermal expansion between fibers and matrix. The incremental hole drilling is one of the most widely used methods for determining residual stresses. It consists of drilling a hole increment by increment through the thickness of the material and measuring for each increment the strains induced by the local redistribution of the residual stresses. These strains are then converted into stresses using coefficients called calibration coefficients, which are calculated by finite element simulations. The objective of this study is to better understand the influence of manufacturing conditions and the structure of the composites (reinforcement type and stacking) on the residual stress state in the materials. For this, the residual stresses are calculated by the incremental hole method in samples with different cure cycles, different stackings and different reinforcements. The experimental and numerical aspects of the method as well as the coupling of the two are presented.
[351] ID:351-Local to global fracture behavior of 2D lattices
Alessandra Lingua (ETH Zürich) and David Kammer (ETH Zürich).
Abstract
Mechanical metamaterials deliver unconventional properties arising from their periodic architecture. Their functionalization offers opportunities for lightweight components in a wide range of applications where local toughening is of interest. While the advances in digital manufacturing unlock extraordinary design space, the poor understanding of the failure of metamaterials hinders their application to structural components. Moreover, a robust criterium for numerically predicting strut failure through architected materials with arbitrary cell geometry is currently lacking. Therefore, it is necessary to uncover the local failure mechanisms by in-situ characterization. In the presented work, we characterize the fracture behavior of 3D-printed polymer lattices under Mode I loading. We focus on unraveling the link between the local failure behavior of single struts and the work to fracture. We observe that, despite the brittle nature of the base resin, the cell tessellation introduces local non-linear effects, enabling higher work before catastrophic failure. In-situ imaging reveals distinct failure mechanisms, such as strut buckling or stress concentration at the lattice joints. Moreover, we quantitatively characterize the impact of the relative density on the failure energy of single-edge notched bend specimens. The direct monitoring of the breaking of individual struts will foster the development of robust failure criteria for 2D lattices. Overall, the outcomes of this work will guide the design of mechanical metamaterials with tunable crack propagation.
[352] ID:352-Mass transport in nanoparticle sintering stage of additive manufacturing: Macro- and meso-scale computational models.
Sasa Kovacevic (University of Oxford), Sandra Ritchie (Carnegie Mellon University), Prithviraj Deshmukh (Carnegie Mellon University), Rahul Panat (Carnegie Mellon University) and Sinisa Mesarovic (Washington State University).
Abstract
Sintering is the key stage of additive manufacturing of micro-scale metal components. For the case of free form (statically determinate) structures, the existing sintering theories predicts no long-range mass transport or distortion for uniformly heated particles. However, in sintering-based advanced additive manufacturing processes, permanent part distortion is observed [1]. Sintered needles and walls first develop large transient curvature and then smaller permanent curvature, features not predicted by standard sintering models. We conclusively demonstrate that part distortion during sintering is a result of a long-range mass transport. Two possible mass transport mechanisms are defined and the macro-scale continuum model applicable to both formulated. The macro-scale model accurately predicts the transient and permanent distortion observed during our experiments, including their size dependence, irrespective of the actual mass transport mechanism.
To distinguish between the possible mass transport mechanisms, the meso-scale computational model is formulated based on the phase filed framework and encompassing: diffusion through the grains and interfaces, particle motion and elasticity of the grains. The meso-scale model represents significant mathematical challenges, since it connects two heterologous continua: lattice continuum for the solids with diffusion [2], and mass continuum for the gas, which flows out in the initial phases of sintering and is trapped and compressed in the later stages. Preliminary meso-scale computational results are presented.
References [1] Ritchie, S., Kovacevic, S., Deshmukh, P., Mesarovic, S.Dj., Panat, R. 2023 Shape distortion in sintering results from nonhomogeneous temperature activating a long-range mass transport. Nature Communications 14, 2667. https://doi.org/10.1038/s41467-023-38142-z [2] Mesarovic, S.Dj. 2016 Lattice continuum and diffusional creep. Proc. R. Soc. A 472, 20160039. http://dx.doi.org/10.1098/rspa.2016.0039
[353] ID:353-A Contactless Approach to Quantify Fracture Resistance and Crack Size in Thick Metallic Specimens
Xudong Qian (National University of Singapore).
Abstract
Digital image correlation has emerged as a convenient approach in characterizing and measuring the fracture parameters mostly for thin specimens. This presentation presents an approach to extend the digital image correlation to determine the energy release rate and to quantify the evolution of the through-thick crack size under increasing load in thick metallic specimens. This presentation first introduces the theoretical basis, which allows the characterization of the through-thickness average energy release rate through the displacement, strain and stress fields determined from the specimen surface, followed by experimental validations. Following that, this presentation proposes a normalization method, directly measurable by digital image correlation, to quantify the evolution of through-thickness crack size, based on optimal correlations. The proposed approach enables sizing of cracks in specimens with two crack fronts, e.g., the middle tension crack specimen. Comparison against the experimental results demonstrates the promising potential of the contactless method in quantifying the fracture resistance curves for various types of thick specimens.
[354] ID:354-A monolithic hyperintegrated ROM FE² method with clustered training strategy
Nils Lange (TU Bergakademie Freiberg), Geralf Hütter (Brandenburg University of Technology Cottbus-Senftenberg) and Bjoern Kiefer (TU Bergakademie Freiberg).
Abstract
Numerical homogenization methods are widely used in science and industrial applications to predict the effective behavior of engineering materials in structural components based on their microstructure. For nonlinear material behavior, this requires solving coupled boundary value problems for the microscale and macroscopic scale in a concurrent way. The most flexible approach for this purpose is the utilization of the finite element method on both scales, known as the FE² method. The high flexibility and generality comes along with high computational costs, which motivated numerous techniques to reduce these costs. In particular, neural network (NN)-based surrogate models or reduced-order models (ROM) have attracted a lot a research effort. Both types of models are driven by training data from expensive fully-resolved microscale simulations as their input. But while NN-based models need to be augmented to capture physical constraints, ROM-FE models form variational approximations to the microscale problem and thus inherit their fundamental physical behavior, though still at higher computational costs than surrogate models. The costs do not only comprise the online computational time during the actual structural simulation, but also the so-called offline costs for generating the training data. The present contribution shows how a hyperintegrated ROM method can be combined with a monolithic solution strategy to reduce the online costs, in conjunction with a clustered training strategy to lower offline costs.
[355] ID:355-Crack tip kinematics reveal the process zone structure in brittle hydrogel fracture
Chenzhuo Li (Engineering Mechanics of Soft Interfaces, School of Engineering, Ecole Polytechnique Fédérale de Lausanne), Xinyue Wei (Engineering Mechanics of Soft Interfaces, School of Engineering, Ecole Polytechnique Fédérale de Lausanne), Meng Wang (The Racah Institute of Physics, The Hebrew University of Jerusalem), Mokhtar Adda-Bedia (Laboratoire de Physique, CNRS, ENS de Lyon, Université de Lyon) and John Kolinski (Engineering Mechanics of Soft Interfaces, School of Engineering, Ecole Polytechnique Fédérale de Lausanne).
Abstract
When brittle hydrogels fail, several mechanisms conspire to alter the state of stress near the tip of a crack, and it is challenging to identify which mechanism is dominant. In the fracture of brittle solids, a sufficient far-field stress results in the complete loss of structural strength as the material ‘unzips’ at the tip of a crack, where stresses are concentrated. Direct studies of the so-called small-scale yielding zone, where deformation is large, are sparing. Using hydrogels as a model brittle solid, we probe the small-scale yielding region with a combination of microscopy methods that resolve the kinematics of the deformation. A zone over which most of the energy is dissipated through the loss of cohesion is identified in the immediate surroundings of the crack tip. With direct measurements, we determine the scale and structure of the process zone, and identify how the specific loss mechanisms in this hydrogel material might generalize for brittle material failure.
[356] ID:356-Advanced characterization techniques to inform digital twins of deformed Inconel 718 and predict plastic localization using FFT-based simulations
Sylvain Vallot (Clement Ader Institute), Julien Genée (Clement Ader Institute), Damien Texier (Clement Ader Institute) and Denis Delagnes (Clement Ader Institute).
Abstract
This work’s long-term objective is to assess the continuity of material deformation at the grain- and mesoscopic scale from processing to subsequent mechanical loading using crystal plasticity strain gradient models. To that end, advanced digital image correlation (HR-DIC) is performed on a pre-deformed microstructure of an Inconel 718, in order to provide plastic localization and discrete slip events necessary to instantiate simulation volumes. A numerical non-local crystal plasticity model has been developed, and implemented using FFT spectral method, to take into account initial deformation gradients and to describe their evolution under different loading conditions. Advanced experiment/simulation dialogue is expected to predict both localization of plastic strain at the sub-grain level and the macroscopic stress-strain behavior in recrystallized and pre-deformed microstructures. The process history of this latter microstructure will be purposely generated using stress-path change strategies on bi-axial specimens.
[357] ID:357-Combining nano-DIC and ACOM TEM to study the ductility enhancement of aluminium films by grain boundary sliding
Paul Baral (Mines Saint Etienne, Univ. Lyon, CNRS, UMR 5307 LGF, 158 Cours Fauriel 42023, Saint Etienne), Ankush Kashiwar (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Michael Coulombier (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Laurent Delannay (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium), Khalid Hoummada (IM2NP, Aix Marseille Univ/CNRS, UMR 7334, 13397 Marseille, France), Jean Pierre Raskin (ICTEAM, UCLouvain, B-1348, Louvain-la-Neuve, Belgium), Hosni Idrissi (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium) and Thomas Pardoen (Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium).
Abstract
The viscoplastic response of metallic nano-crystalline films has been widely studied in the literature by means of nanomechanical testing, such as with in situ TEM experiments [1], [2] or dedicated on chip test methods [3]. The enhancement of ductility (as compared to large grain samples) has been attributed to different mechanisms, including grain boundary sliding, grain growth or kinematic hardening due to dislocation pile up [2], [4]. However, observations of the polycrystal deformation are challenging due to highly refined grain sizes. The correlative methodology developed in this work allows probing the relationships between the microstructural changes and the total strain field, at a scale never resolved before – i.e. sample size of 2.5 x 25 µm and strain field resolution of 50 nm. The aluminium films deposited by sputtering (210 nm thickness) are mechanically loaded with an on chip method [3] and then observed after deformation in the transmission electron microscope (TEM). Nanoscale digital image correlation (nano-DIC) reveals multiple necking regions appearing at low plastic strains and further spreading along the sample gauge without leading to critical failure. Automated crystal orientation mapping (ACOM TEM) indicates that strain localization bands correspond to grain boundaries (GB) and that the global texture remains unchanged. The local shear amplitude achieved by such GB sliding correlates, to some extent, with the GB character. The complementary results obtained by both techniques shed some new light on the link between GB mediated plasticity and enhanced macroscopic ductility.
REFERENCES [1] H. Idrissi et al., Applied Physics Letters, vol. 104, no. 10, p. 101903, 2014. [2] J. P. Liebig et al., Acta Materialia, vol. 215, p. 117079, 2021. [3] S. Gravier et al., J. Microelectromech. Syst., vol. 18, no. 3, pp. 555–569, 2009. [4] F. Mompiou et al., Acta Materialia, vol. 61, no. 1, pp. 205–216, 2013.
[358] ID:358-Mechanics and damage tolerance of nanowire network materials
Felipe Lozano-Steinmetz (IMDEA Materials Institute), Anastasiia Mikhalchan (IMDEA Materials Institute) and Juan J. Vilatela (IMDEA Materials Institute).
Abstract
A nanowire is an extremely thin wire-like 1D structure, with a diameter on the nanometer scale, typically ranging from a few to hundreds of nanometres, and high aspect ratio (length-to-diameter ratio). A nanowire network refers to a three-dimensional interconnected mesh or network of nanowires, typically with a complex porous microstructure. Recently, we demonstrated lab-scale synthesis of networks by gas-phase reaction of Floating Catalyst CVD, where grown 1D nanowires of SiC, Si, or carbon nanotubes form a macroscopic material with an interesting combination of mechanical, thermal, and electrical properties. Models for predicting the elastic properties and ductile fracture of nanostructured network materials are essential for understanding their mechanical properties at the nanoscale. A combination of experimental characterization and computational modeling can be used to accurately describe and predict their properties. Specifically, damage propagation in nanonetworks is a complex phenomenon, involving multiple types of damage, such as point defects, localized bundle separation, nanowires or bundles sliding and shear, resulting in ductile behaviour and superior toughness. Experimental microscopy and spectroscopy techniques can be used to detect changes in the network structure in situ as a crack grows and propagates. The goal of this work is to combine experimental methods with analytical models to describe the tensile mechanical properties, stress transfer and inherent structural toughness of the nanoscale network systems that results in their high damage tolerance. We use WAXS/SAXS methods to determine nanowire alignment and track its evolution during network stretching, in order to identify and separate the contributions of nanowire orientation and chemical composition to the global mechanical properties. The micromechanical models emerging from this work will be also applied to study damage-tolerance of nanowire network electrodes used for energy-storage devices and batteries.
[359] ID:359-Strain gradient plasticity of constrained thin lithium layers subjected to compression and shear
Alessandro Leronni (University of Bath), Vikram Deshpande (University of Cambridge) and Norman Fleck (University of Cambridge).
Abstract
The commercialisation of solid-state lithium-ion batteries is currently hampered by the phenomenon of lithium dendrite growth across the ceramic electrolyte upon battery charging. In order to mimic the mechanical environment experienced by lithium dendrites, compression experiments have been performed on thin lithium layers sandwiched between ceramic substrates. These experiments reveal that the average pressure on the lithium layer increases with decreasing layer thickness, due to a combination of plastic constraint and size effect. Shear experiments have also been conducted and they reveal a moderate size effect. Strain gradient plasticity is used to explain and predict size effects in both compression and shear. It is assumed that lithium behaves as a rigid, plastically incompressible, power law creeping solid, and that the effective plastic strain rate depends on the plastic strain rate gradient through a single plastic length scale. Approximate analytical solutions are obtained for an assumed velocity field by energy minimisation. Full numerical solutions are also obtained to verify analytical solutions. For compression of specimens of high aspect ratio, the analytical solution shows that the enhancement in average pressure due to plastic constraint and size effect can be decoupled in a multiplicative manner. The best match between theory and experiments is obtained by assuming fully constrained higher-order boundary conditions and for a plastic length scale on the order of a few microns.
[360] ID:360-Evaluation of elasticity in binary ordered systems by phase-field crystal simulations
Jacob Holmberg-Kasa (Division of Solid Mechanics, Lund university), Pär Olsson (Department of Materials Science and Applied Mathematics, Malmö University) and Martin Fisk (Department of Materials Science and Applied Mathematics, Malmö University).
Abstract
During the heat treatment of alloys containing ordered precipitates, intergranular cracking can occur due to lattice misfits between the matrix and precipitates. The initiation and propagation of these cracks have been found to be linked to the location and growth of the precipitates. In order to enhance the understanding of intergranular cracking behavior, numerical models that are capable to accurately capture precipitation and growth over diffusive time scales need to be developed. The phase-field crystal (PFC) method presents a promising approach for modeling the behavior of ordered precipitates. This method allows for the creation of numerical models that can track the evolution of lattice structure on diffusive time scales, providing a comprehensive description of the behavior of ordered precipitates. In this contribution, different aspects of the implementation of a PFC model for disorderd to ordered phase transitions is presented. This includes a simple two point correlation function to stabilize a ordered square structure in two dimensions with predetermined elastic properties. The strain state is evaluated for the developed model for single- and multi-precipitate systems.
[361] ID:361-A strain based Lipschitz regularization in Data Driven Computational Mechanics
Vasudevan Kamasamudram (Centrale nantes) and Laurent Stainier (Centrale Nantes).
Abstract
The notion of Data Driven Computational Mechanics (DDCM) has been introduced in Kirchdoerfer and Ortiz, CMAME 2016, where the behavior of the material is described by the stress-strain database obtained from the experiments or through the simulations performed at a lower scale. This database is directly used in Finite Element simulations, for instance, rather than using a constitutive model to describe the material behavior. The DDCM methodology has been applied for linear, non-linear elasticity, and inelasticity in multiple references. However, its application to scenarios involving softening remains relatively open. In applications that involve softening, a characteristic length is necessary to render the results of the Finite Element simulations independent of the mesh size. In the case of granular materials, the length scale has been introduced in DDCM by treating the material as a Cosserat medium. However, this technique is effective only when the body is subjected to a shear loading. To introduce a length scale in a general scenario, a strain-based Lipschitz regularization has been introduced in an earlier study. The contribution of the current work is to include the Lipschitz regularization technique in the DDCM methodology for applications that involve damage. This work first presents the regularization technique followed by its application to some test cases. Some challenges encountered and future perspectives will be presented.
[362] ID:362-How GBS and diffusion-aided redundant displacements of adjacent grains contribute to the overall viscosity of a porous polycrystal
Laurent Delannay (UCLouvain) and Francis Delannay (UCLouvain).
Abstract
Under conditions favoring grain boundary sliding (GBS), metallic polycrystalline aggregates tend to preserve equiaxed grain shapes. The motion of the grain centroids then differs significantly from the affine displacement field that could be deduced from the macroscopic strain. Instead, if GBS operates, grains tend to switch neighbours and this involves cooperative displacements of the surrounding grains. The present work assumes that the overall viscosity of a polycrystal subjected to GBS is dictated by such redundant motion of the grains, i.e. by accommodating displacements which do not contribute to the macroscopic strain. Based on a simplified numerical modeling of diffusion-aided GBS (Rachinger creep) inside a 2D polycrystal, we estimate the energy that is dissipated when prescribing the motion of a single grain and allowing accommodation only in the close neighbourhood. The focus of the analysis is set on the influence of the presence porosity at triple junctions, which is characteristic of the final densification stage during the sintering of metallic alloys. The ratio of the macroscopic bulk viscosity and the macroscopic shear viscosity is shown to evolve as a function of porosity.
[363] ID:363-Toughening of brittle solids via crack front complexity
Xinyue Wei (EPFL), Chenzhuo Li (EPFL), Cían McCarthy (Williams College) and John Kolinski (EPFL).
Abstract
Crack growth and propagation typically lead to the failure of brittle solids. Linear elastic fracture mechanics (LEFM) is commonly employed to model this process, quantifying a material's toughness through the critical stress intensity factor or the pre-factor of the singular stress field. Although widely accepted, this theory is designed for planar cracks, which contrasts with the geometrically complex nature of actual cracks. In this work, we examine the 3D kinematics of complex crack fronts using confocal microscopy on various transparent, brittle materials, including hydrogels with different chemistries and an elastomer. Our findings reveal a direct proportionality between the critical strain energy needed to drive the crack and the geodesic length of the crack, which makes the sample effectively tougher. The correlation between crack front geometry and toughness holds implications for the theoretical modeling of 3D cracks, and highlights an important gap in the current theory for 3D cracks.
[365] ID:365-Manufacture of Inserts for High Pressure Aluminum Injection Molds by Additive Manufacturing
Carlos Sacchelli (UFSC), Carlos Alberto Costa (Design and Manufacturing Engineering Research Group), Alexandre Michels (PPGMAT - UCS), Adriano C. Batista (Centro de Inovação e Tecnologia - CIT), Tiago M. Oliveira Santos (Centro de Inovação e Tecnologia - CIT) and Natanael C. Q. Campos (UFSC).
Abstract
High Pressure Die Casting (HPDC) using Aluminum (Al) has emerged as an option for producing parts with high mechanical strength, high geometric precision and low weight for the automotive industry. In this type of process, injection molds are subjected to pressure and temperature cycles, suffering high thermal fatigue in their structure, especially in inserts exposed to the Al flow. In this sense, many scenarios require the definition of a minimum number of cycles to shape cavity components. Some traditional materials are used in injection molds for this process and the use of processes such as Additive Manufacturing (AM) to manufacture components for this type of mold, although it is an interesting option, presents some issues that must be considered. This work presents a study of the application of the additive manufacturing process in the manufacture of mold inserts for Aluminum HPDC in the automotive industry. To analyze the performance of the insert produced by AM, a set of inserts was also produced using the conventional manufacturing process, that is, machining and using traditional steel. These inserts were tested in an HPDC production mold and were periodically replaced after each number of cycles defined by the company. The inserts manufactured by the AM process were produced in DIN 1.2709 steel (Maraging 300) and underwent subsequent machining, heat treatment and surface coating processes. The costs involved in AM and conventional manufacturing were compared and field tests are being carried out at the partner company with the aim of validating the option of applying AM in aluminum injection molds. AM inserts have so far been used in up to ten thousand cycles, this number is the average use of inserts produced with traditional materials, which validates the use of AM in this condition without identifying apparent thermal cracks.
[366] ID:366-Multi-scale computational homogenization for interfaces with serrated deformation towards an enriched cohesive interface model
Varvara Kouznetsova (Eindhoven University of Technology), Lei Liu (Eindhoven University of Technology), Francesco Maresca (University of Groningen), Johan Hoefnagels (Eindhoven University of Technology) and Marc Geers (Eindhoven University of Technology).
Abstract
This work presents a comprehensive exploration of interface damage in engineering materials characterized by an anisotropic/isotropic phase combination. Examples include twins impinging on a grain boundary, crystalline-amorphous interface or martensite-ferrite interface in advanced multi-phase steels, where martensite islands typically deform by sliding on the retained austenite films. In these cases the anisotropic deformation of one phase, when favourably oriented, induces interface damage through a jagged deformation mechanism, complementing the classical cohesive interface deformation mechanism. To capture these two microscopic mechanisms, i.e. jagged damage and cohesive opening, at the mesoscale, a novel computational homogenization framework is developed. The mesostructure, comprising multiple anisotropic particles in an isotropic matrix, is modelled with interfaces represented by enriched cohesive zones. The microscopic interfacial zone unit cell resolves the laminated structure of the anisotropic phase, defining effective interface separation and internal kinematic quantities associated with jagged and cohesive deformation mechanisms. The generalized Hill-Mandel condition yields tractions work-conjugated to these internal kinematic quantities, leading to a mesoscale enriched cohesive law identified through representative microscopic unit cell simulations. Comparison to a fully resolved model of mesoscopic interfacial zones demonstrates the efficacy of the developed enriched cohesive interface model, emphasizing the importance of considering both microscopic mechanisms in predicting anisotropic/isotropic interface separation and overall material failure. The model is applied to a dual-phase steel microstructure, where the model performance is validated against microscale experimental results. The proposed microphysics-based effective interface model provides a valuable tool for understanding and predicting interface damage in complex materials.
[367] ID:367-A strain energy function for large volumetric deformations of elastomers
Stefano Sirotti (University of Modena and Reggio Emilia), Matteo Pelliciari (University of Modena and Reggio Emilia) and Angelo Marcello Tarantino (University of Modena and Reggio Emilia).
Abstract
Elastomers are typically modelled under the assumption of material incompressibility. Performing simple tension and bulk tests, we show that some class of elastomers can experience significant volume changes when large deformations are involved. The volumetric strain energy density (SED) functions available in literature exhibit limitations in modeling the large volumetric deformations of elastomers. Therefore, we propose a new volumetric SED which is capable of: (1) accurately describe the response of rubbers for both small and large volumetric deformations; (2) reproduce different behaviors for volume shrinkage and volume expansion; (3) adapt to other compressible materials, such as soft tissues, foams and gels. Following the deviatoric–volumetric split of the strain energy function, the Yeoh-Fleming hyperelastic model is chosen as deviatoric part for the proposed SED. An overall fitting to the experimental data from simple tension and bulk tests is carried out to calibrate the parameters of the combined SED. The results prove the effectiveness of the combined SED in modeling the response of elastomers under both shape and volume deformations. The proposed SED can be implemented in numerical codes to solve more complex problems involving compressible materials.
[368] ID:368-A Gurson-type model unifying hydrogen enhanced plasticity and decohesion
Haiyang Yu (Department of Materials Science and Engineering, Uppsala University), Meichao Lin (Department of Structural Engineering, Norwegian University of Science and Technology), Jianying He (Department of Structural Engineering, Norwegian University of Science and Technology) and Zhiliang Zhang (Department of Structural Engineering, Norwegian University of Science and Technology).
Abstract
The detrimental effect of hydrogen on metals which manifests itself as a transition from a ductile to a brittle failure mode is simulated via a unified continuum-scale predictive framework. The so-called complete Gurson model, originally formulated for predicting ductile failure via voiding, is now enhanced to include failure due to decohesion. Hydrogen enhanced localized plasticity (HELP) is represented by the accelerated voiding process, while hydrogen enhanced decohesion (HEDE) manifests through a reduction in the decohesion threshold. This ductile-to-brittle transition, driven by local hydrogen concentration, is effectively captured by the model. It enables predictions of realistic embrittlement levels and the suppression of dimples on hydrogen-induced fracture surfaces. Being generic, versatile, and easy to implement, the model may serve as a basis for interpretation of laboratory experiments and enable the transferability of the laboratory results to engineering structural assessment in hydrogen environment. Additionally, this talk introduces recent advances in incorporating the hydrogen enhanced strain induced vacancy (HESIV) mechanism into this modeling framework.
[369] ID:369-Characterization of High-Strength Aluminum Alloys Lattice Structures produced using Laser Powder Bed Fusion
Mohammed Farag (IMMC, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Nicolas Nothomb (IMMC, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Grzegorz Pyka (IMMC, Université catholique de Louvain, Louvain-la-Neuve, Belgium), Jean-François Remacle (IMMC, Université catholique de Louvain, Louvain-la-Neuve, Belgium) and Aude Simar (IMMC, Université catholique de Louvain, Louvain-la-Neuve, Belgium).
Abstract
The manufacturing of lattice structures using laser powder bed fusion (L-PBF) technology has not yet been explored for high-strength aluminum alloy 7075. The present study is part of a project aiming at additive manufacturing components combining high strength with reduced weight and exploring the possibility to combine with self-healing capabilities.
The possibility to build lattice structures has been demonstrated for two distinct design categories: triple periodic minimal surfaces (TPMS) and strut-based lattices. The strut size is varied. These intricate geometries, manufactured in aluminum 7075, represent a significant advancement in the additive manufacturing domain, particularly for applications requiring a balance of strength and lightness.
The specific process parameters and powder composition are optimized for L-PBF to produce these high strength lattice structures. The porosity level, mechanical properties of the new lattices are characterized microstructurally and mechanically. In particular, in-situ X-ray tomography compression testing with Digital Volume Correlation to track local strains is performed on the manufactured lattice structures.
The initial outcomes indicate a promising potential for the use of these lattice structures in high-performance applications. The novelty of the work lies not only in the material used but also in the potential for these structures to exhibit self-healing properties, a feature that could redefine durability and longevity in critical applications.
[370] ID:370-Data-adaptive modeling of hyperelastic constitutive laws: application to extremely soft materials
Simon Wiesheier (Friedrich-Alexander-Universität Erlangen-Nürnberg), Miguel Angel Moreno Mateos (Friedrich-Alexander-Universität Erlangen-Nürnberg) and Paul Steinmann (Friedrich-Alexander-Universität Erlangen-Nürnberg).
Abstract
The traditional approach to modeling the non-linear constitutive behavior of soft materials at finite strains relies on hyperelasticity, a paradigm that inherently involves uncertainties in phenomenological constitutive modeling. This method often results in information loss since experimental data is not directly integrated into calculations, and the engineer's selection of a suitable strain energy function heavily depends on experience.
In contrast, data-driven approaches present a promising alternative. We recently introduced an innovative data-adaptive approach for modeling hyperelastic materials at finite strains allowing for more efficient inclusion of experimental data. The proposed modeling procedure ensures adherence to crucial constraints such as thermodynamic consistency, material objectivity, frame indifference, and material symmetry a priori. The fundamental concept involves formulating an approximation of the strain energy function using a sum of basis functions multiplied by parameters. The basis functions are expanded over the space of invariants, and support points, where the parameters are defined, are distributed in the invariant space. These parameters are determined through a nonlinear optimization problem, minimizing the 2-norm of the residual vector, representing the difference between measured and computed displacements and reaction forces. Importantly, our approach does not depend on measured stresses, setting it apart from many existing data-driven and model-free methods.
In our initial investigation, we demonstrated the efficiency and flexibility of our method based on numerical experiments and linear finite-element-like basis functions. The focus of this contribution is on the applicability to real experimental data obtained from Digital-Image-Correlation and basis functions with higher continuity. Specifically, we concentrate on a substantial experimental database encompassing various soft materials, particularly ELASTOSIL, VHB, and DOWSIL, with the aim of identifying a set of strain energy functions characterizing these materials in a fully automated and reliable manner.
[373] ID:373-Effect of post-processing heat treatments on mechanical anisotropy of Ti-6Al-4V alloy fabricated by L-PBF
Quentin Gaillard (Mines Saint-Étienne, Univ. Lyon, CNRS UMR 5307 LGF), Sophie Cazottes (Univ. Lyon, INSA Lyon, MATEIS, UMR CNRS 5510), Xavier Boulnat (Univ. Lyon, INSA Lyon, MATEIS, UMR CNRS 5510), Sylvain Dancette (Univ. Lyon, INSA Lyon, MATEIS, UMR CNRS 5510) and Christophe Desrayaud (Mines Saint-Étienne, Univ. Lyon, CNRS UMR 5307 LGF).
Abstract
In recent years, additive manufacturing of Ti-6Al-4V (Ti64) alloy by Laser Powder Bed Fusion (L-PBF) became mature enough to consider manufacturing structural components for specific applications. Nevertheless, post-processing operations seem to be unavoidable to meet the product requirements in term of static and dynamic mechanical behavior.
As a consequence of high cooling rates involved during L-PBF, as-printed Ti64 parts present an α’ martensitic microstructure consisting of fine, hierarchical and entangled needles. The α’ phase grows upon cooling in columnar parent β grains whose morphological and crystallographic texture is oriented parallel to the building direction. This microstructural anisotropy affects the tensile properties and in particular the ductility of the samples built with different orientation.
In order to relieve the residual stresses formed during the process and to decompose the martensitic phase into an equilibrium α+β mixture, post-processing heat treatments (HT) are performed on Ti64 as-built parts in the sub-transus range. The induced phase transformation helps to balance the strength / ductility compromise that mainly depends on α laths width and β phase fraction.
In this study, 5 post-processing HT ranging from 720°C to 980°C were performed on Ti64 bars, built with vertical and horizontal orientations, that are then machined into tensile specimens. The microstructure and tensile properties in the as-built condition and after HT are presented extensively. In particular, the embrittlement mechanisms that possibly affect the elongation anisotropy are investigated through interrupted tensile tests coupled with EBSD characterization. Finally, one discusses the effect of HT on the mechanical anisotropy evolution.
[374] ID:374-Critical state seen as an emerging property in granular materials
Antoine Wautier (INRAE, Aix-Marseille University, UMR RECOVER), Na Deng (Université Grenoble-Alpes, Laboratoire Sols Solides Structures), Zeyong Liu (Université Savoie Mont Blanc, ISTerre) and François Nicot (Université Savoie Mont Blanc, ISTerre).
Abstract
Granular materials is a particular example of a porous material seen as a complex system. While individual grains can be modeled as solid bodies in interaction through contact forces, the large number of grains involved at the engineering scale result in a collective complex behavior that needs to be modeled within the framework of continuum mechanics. In the change of scale, some properties emerge fundamentally different from those at lower scales. With respect to constitutive modeling of granular plasticity, the concept of critical state emerge from the detailed balance of conformational transitions. Reorganizations in the microstructure makes it possible for granular materials at critical state to be sheared with no volume change under a constant stress state. As such, critical state stands as a cornerstone of constitutive theory for granular materials. To better understand the microscale origin of critical state, we analyze the rates of mesostructural transformations in simulations based on the discrete element method (DEM). Then, a deactivation/reactivation procedure acting on the local mesoscale is proposed to enrich a specific multiscale constitutive model for granular materials (the H-model). This procedure mimics the microstructure changes resulting from contact grain and loss that modifies the contact network with no volume change. We show how this procedure enable to make stationary regimes emerge naturally in multi-scale constitutive modeling without drawing from any empirical law at the macroscopic scale.
[375] ID:375-Thermo-mechanical attributes and strain gradient field of materials with uniform and graded inner architectures
Dimitrios Rodopoulos (New York University Abu Dhabi, Department of Mechanical Engineering, Abu Dhabi, UAE) and Nikolaos Karathanasopoulos (New York University, Tandon School of Engineering, NY, USA).
Abstract
Recently, the progress in additive manufacturing led to the design of a new class of artificial materials with complex inner architectures that characterized by mechanical attributes that are commonly cannot be found in natural engineering materials. The present work focuses on a numerical study of thermomechanical effective properties as well as the strain gradient field of materials with uniform and graded inner architectures. The effective property calculation is based on numerical implementation for the solution of thermoelasticity equations on a predefined Representative Volume Element (RVE), employing the appropriate periodic boundary conditions. Using the field (temperature, displacement) and flux field (heat flux, traction) calculations, the effective values of Young modulus, shear modulus, thermal conductivity, thermal expansion and Poisson ratio are estimated by computing the corresponding average quantities. A parametric study is conducted considering inner architecture designs based on Gielis' formula and different combinations of base materials and Volume fractions. Then, a Neural Network (NN) model capable of predicting the effective properties for several combinations of inner architecture designs, base material properties and volume fraction is constructed and trained with the obtained numerical results. Finally, the developed numerical formulation is employed for the thermoelastic strain gradient field calculation on architected materials occurring from thermal and mechanical loads.
[376] ID:376- In-vivo estimation of white matter tract-related deformation under mild head impacts
Zhou Zhou (KTH Royal Institute of Technology), Christoffer Olsson (KTH Royal Institute of Technology) and Svein Kleiven (KTH Royal Institute of Technology).
Abstract
White matter (WM) tract-related strains have been increasingly used to quantify brain responses, but its dynamics under the live, human brain during non-injurious impact conditions remain largely unknown. Recently, one in-vivo study measured the normal strain along the WM fiber tracts (i.e., tract-oriented strain), but it only represents a partial description of the fiber deformation. We aim to extend the measurement of WM deformation by quantifying the normal strain perpendicular to the fiber tracts (i.e., tract-perpendicular strain) and the shear strain along and perpendicular to the fiber tracts (i.e., axial shear strain and lateral shear strain, respectively) under voluntary neck rotation and neck extension. To achieve this, we combined the three-dimensional strain tensor from the tagged magnetic resonance imaging with the diffuse tensor imaging (DTI) from an open-access dataset, including 41 subjects under neck rotation (n = 27) and neck extension (n = 14). The strain tensor was rotated to the coordinate system with one axis aligned with the DTI-revealed fiber orientation, through which three tract-related strains were extracted. The results showed that the strain peak is dependent on the loading mode (p<0.05, Mann-Whitney U test). Under neck rotation, the peak values ranged from 0.012 ~ 0.042 for tract-perpendicular strain, 0.010 ~ 0.035 for axial-shear strain, and 0.010 ~ 0.035 for lateral-shear strain. Under neck extension, the maximum values varied from 0.012 ~ 0.024 for tract-perpendicular strain, 0.010 ~ 0.020 for axial-shear strain, and 0.011 ~ 0.022 for lateral-shear strain. The strain distribution is dependent on both the strain modality and loading mode. Our study presented the first in-vivo analysis of tract-perpendicular strain, axial-shear strain, and lateral-shear strain towards an improved understanding of WM dynamics. The reported strain results can be used to evaluate the reliability of computational head models, especially those intended to predict brain strains under non-injurious conditions.
[377] ID:377- Testing and Modelling of Welded Aluminium Joints
Sigurd Aune (Structural Impact Laboratory (SIMLab), Norwegian University of Science and Technology (NTNU)), David Morin (Structural Impact Laboratory (SIMLab), Norwegian University of Science and Technology (NTNU)), Magnus Langseth (Structural Impact Laboratory (SIMLab), Norwegian University of Science and Technology (NTNU)), Ole Runar Myhr (Hydro Aluminium, Research and Technology Development (RTD)) and Arild Clausen (Structural Impact Laboratory (SIMLab), Norwegian University of Science and Technology (NTNU)).
Abstract
In the case of aluminium structures, welding may introduce weak zones, so-called heat-affected zones (HAZ), close to the weld. Such zones should be accounted for when predicting the overall behaviour of the structure since the deformation tends to localise within such weak zones, leading to failure initiation. In an early design stage, the structural capacity is usually assessed based on numerical simulations using the finite-element (FE) method and shell elements rather than carrying out extensive test campaigns. A literature review reveals that numerical tools could predict the spatial variation of material properties within a HAZ when using a fine discretisation of solid elements. No unified approach, however, exists for large-scale analyses of thin-walled structures where only a few shell elements represent the HAZ behaviour until fracture.
To address this challenge, this work presents a virtual calibration procedure establishing the mechanical behaviour of a welded aluminium connection relevant to an early design stage. A modelling framework that captures the overall weld and HAZ behaviour until fracture in large-scale analyses is calibrated using a multi-scale approach. The input is the chemical composition and the through-process history of the material, where welding simulations are used to account for the welding process. A nanostructure model predicts the material flow stress by considering the intrinsic resistance to dislocation motion and classical dislocation theory. The spatial variation of flow stress is introduced into a detailed FE model of an idealised HAZ, and the plasticity and fracture parameters for the shell elements are based on this HAZ. To this end, numerical simulations using the proposed calibration procedure are compared against experiments.
[378] ID:378-Simulation methodology for predicting initiation of surface cracks in railway rails
Nasrin Talebi (Department of Industrial and Materials Science, Chalmers University of Technology, Sweden), Magnus Ekh (Department of Industrial and Materials Science, Chalmers University of Technology, Sweden) and Knut Andreas Meyer (Institute of Applied Mechanics, TU Braunschweig, Germany).
Abstract
Rolling Contact Fatigue (RCF) cracks in rails cause high maintenance costs and can reduce traffic safety. Hence, accurate predictions of RCF crack initiation are highly needed. Such predictions require reliable fatigue crack initiation criteria, depending on stress and strain histories. Thus, it is essential to use plasticity models that can accurately estimate the stress and strain states in rails, whose material properties evolve during rolling contact loading. In this contribution, a plasticity model with an anisotropic yield surface (based on Meyer and Menzel [1]) is calibrated against the previously conducted experiments with railway-like cyclic loading (compression and shear) on pearlitic R260 steel specimens. In these experiments, solid test bars were first predeformed in an axial-torsion machine to obtain different degrees of anisotropy. They were then re-machined into thin-walled tubular test bars and subjected to multiaxial cyclic loading. Based on the test results, material parameters are identified to describe the material behavior at different depths from the surface layer. The calibrated plasticity model is then used in the finite element simulations of realistic traffic situations to obtain accurate stress and strain histories. These are used to predict the number of cycles to macroscopic crack initiation in the rail surface layer using a newly developed RCF crack initiation criterion. This criterion accounts for the inhomogeneous stress-strain field in the surface layer and has been calibrated against three types of experiments: Large shear increments under different amounts of axial stresses (predeformation), strain-controlled low cycle fatigue tests after some levels of predeformation, and stress-controlled axial high cycle fatigue experiments. [1] K.A. Meyer and A. Menzel, “A distortional hardening model for finite plasticity,” Int. J. Solids and Struct., vol. 232, p. 111055, 2021
[379] ID:379-Multiaxial characterization of 3D printed polymers for patient-specific surgical simulators
Margot Leclercq (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS), Elsa Vennat (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS) and Jan Neggers (Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LMPS).
Abstract
Additive manufacturing processes are taking hold in the medical sector, enabling the production of patient-specific devices that improve patient care while reducing associated costs. In the case of Endovascular Aneurysm Repair (EVAR) procedures, 3D printing is used to provide patient-specific 3D models of anatomies, enhancing surgical training, enabling rehearsal of complex cases, and improving intra-operative procedures. Thanks to the PolyJet additive manufacturing process, these physical models can be printed by combining different soft and rigid photopolymer materials to reproduce the haptic feedback of the human aorta. While 3D printing has proven valuable in reproducing anatomical structures, accurately simulating stress and strain states in these printed models remains a significant challenge. This challenge stems from the need to understand the mechanical behavior of printed materials, especially in the PolyJet technology, which exhibits complex structure-process-properties relationships [1][2][3]. Existing studies primarily focus on the response of materials to uniaxial loading, not considering the materials' response to multiaxial loading experienced by the 3D-printed anatomical models during surgical procedures. This study enriches our understanding of the mechanical response via biaxial loading tests while considering the anisotropy of the printed materials. Due to the complex characterization of these multiaxial tests, the material properties are identified using an integrated digital image correlation method [4].
[380] ID:380-Dynamic fractures in brittle isotropic materials analysed by high-speed photography and a dynamic phase-field finite element model
Parnian Hesammokri (Uppsala University) and Per Isaksson (Uppsala University).
Abstract
A pivotal aspect in the application of phase-field theories is the decomposition (or, split) of the strain energy density into tensile and compressive components, crucial for preventing the interpenetration of crack surfaces and ensuring the physical fidelity of predicted crack paths. While popular methods such as spectral decompositions and hydrostatic-deviatoric decompositions are employed for this purpose, challenges arise in effectively handling crack growth in compression, prompting the exploration of alternative decomposition schemes.
A recently suggested model [1], inspired by the classical Mohr-Coulomb fracture criterion, combines the spectral and the hydrostatic-deviatoric splits to address the shortcomings of existing methods. To assess its efficacy, a series of global compression tests induced by impacts were conducted on brittle gypsum plaster specimens with embedded flaws and holes. Crack developments in these impact experiments were meticulously monitored using a high-speed camera. Dynamic phase-field finite element simulations were conducted using the aforementioned model and compared to the experimental results. The outcome dictates a commendable agreement between the model and the experiments, implying that the model is capable of capturing rapid transient effects in isotropic brittle materials subject to global compression induced by impacts emphasizing the model's potential to offer mechanistic insights into the dynamic mixed-mode fracture in brittle materials.
[1] Hesammokri P, Yu H, Isaksson P (2023). An extended hydrostatic–deviatoric strain energy density decomposition for phase-field fracture theories. Int J Solids Structures 262-263: 112080. https://doi.org/10.1016/j.ijsolstr.2022.112080
[381] ID:381-Modelling band-gaps using nonlocal elasticity of Klein-Gordon type with internal length and time scales
Eleni Agiasofitou (Karlsruhe Institute of Technology (KIT)) and Markus Lazar (Karlsruhe Institute of Technology (KIT)).
Abstract
In this work, a nonlocal elasticity model of Klein-Gordon type, characterized by nonlocality in space and time, is developed for the investigation of wave propagation in isotropic elastic media [1]. Nonlocal elasticity theory having a close link to the underlying microstructure has the advantage to capture effects at small scales [2]. Specifically, nonlocal elasticity is valid down to the Ångström-scale and it can be considered as a generalized continuum theory of Ångström-mechanics as it has been shown in [3]. For the first time in the framework of nonlocal elasticity theory, the proposed nonlocal elasticity model of Klein-Gordon type possessing one characteristic internal time scale parameter in addition to the characteristic internal length scale parameter describes spatial and temporal nonlocal effects at small scales. The dispersion relations of the considered isotropic nonlocal model of Klein-Gordon type are analytically determined predicting in addition to the acoustic modes (low-frequency modes), optic modes (high-frequency modes) as well as frequency band-gaps between the acoustic and optic modes. The ranges of the frequency band-gaps for longitudinal and transverse waves are determined. Moreover, the phase and group velocities are calculated for the acoustic and optic branches of longitudinal and transverse waves showing that all four modes exhibit normal dispersion with positive group velocity. The proposed nonlocal model of Klein-Gordon type possessing only 4 constitutive parameters (2 elastic constants, 1 length scale and 1 time scale) provides an appropriate framework for the modelling of accurate frequency band-gaps and overall physically realistic dispersive wave propagation.
References [1] M. Lazar, E. Agiasofitou. Nonlocal elasticity of Klein-Gordon type: fundamentals and wave propagation. Wave Motion 114: 103038, 2022. [2] A.C. Eringen. Nonlocal Continuum Field Theories. Springer, New York, 2002. [3] M. Lazar, E. Agiasofitou, G. Po. Three-dimensional nonlocal anisotropic elasticity: a generalized continuum theory of Ångström-mechanics. Acta Mechanica 231: 743-781, 2020.
[382] ID:382-A Molecular Dynamics Study of Nanoporous Aluminum Structures with Predefined Topology
Sergei Zorkaltsev (IMDEA Materials Institute) and Maciej Haranczyk (IMDEA Materials Institute).
Abstract
Nanoporous metal structures are of high interest in both academic research and industry due to their tunable mechanical properties and light weight. However, understanding the mechanical properties of these materials is still a challenge. Existing research has demonstrated that among many other parameters (relative density, ligament diameter, specific surface area, etc.), topology plays a key role in determining the structural properties. Despite the nearly countless ways to define the topology of a porous structure, current works have focused mostly on random Al or Au structures and on several common topologies such as FCC, BCC, gyroid, and others. This study focuses on an alternative set of topologies reported in the context of the reticular chemistry of nanoporous (non-metallic) crystalline materials. Specifically, by performing a series of Molecular Dynamics (MD) simulations, we examined 22 topologies in terms of yield stress and Young's modulus, while comparing them to stochastic nanoporous aluminum structures. The results show that structures constructed with predefined topologies have superior Young's modulus and yield strength. Moreover, distinct scaling laws of mechanical properties are observed for different topologies, revealing the relationship between topology and mechanical behavior in nanoporous materials. Additionally, Machine learning models were implemented to connect numerical descriptors of studied structures with their mechanical properties.
[383] ID:383-Dynamics of a multi-supported beam: homogenized models and relevant boundary conditions
Antoine Rallu (ENTPE / LTDS / CNRS) and Claude Boutin (ENTPE / LTDS / CNRS).
Abstract
This paper describes the long wavelength dynamic behaviour of a periodic structure whose irreducible period consists of an Euler beam supported by two co-located springs (one rotational and one compressive).
The homogenisation method for discrete periodic media is used to obtain the macroscopic behaviour of the equivalent continuous multi-supported beam, provided that the wavelength is much larger than the period size. Under this assumption, each elementary beam remains in the quasi-static regime. Depending on the orders of magnitude of the stiffnesses of the springs relative to the bending stiffness of the elementary beam, the equivalent continuous structure exhibits different dominant order behaviours, governed either by shear, by bending, or by both. In an infinite medium, the long-wavelength dispersion relations obtained for each model agree with those obtained by Bloch waves.
In a finite domain, it remains to be specified how the boundary conditions actually applied to the structure can be transferred to the homogenised models. This is necessary in order to perform the modal analysis of the real system using the homogenised model. To overcome this issue, which is still open for beam systems, we propose the following method: local kinematic conditions are directly transferred to the macroscopic kinematic variables. However, local force-type conditions cannot be directly related to macroscopic forces. It is therefore necessary to express the exact local equilibrium conditions in function of the macroscopic kinematic variables. This yields the conditions on the macroscopic kinematic variables that effectively express the real force conditions. This procedure makes it possible to recover the modal analysis results obtained from numerical calculation, both in terms of frequency and deformation. It is also observed that the boundary conditions only alter the modal kinematics on a boundary layer of the order of the period and located at both ends.
[384] ID:384-Micro-scale Characterisation of Residual Stresses Generated during Face Turning using Focused Ion Beam Milling and Digital Image Correlation
Aritz Dorronsoro (CEIT-BRTA), Daniel Perez-Gallego (CIME, UPM), Jesús Ruiz-Hervías (CIME, UPM), Mikel Arizmendi-Jaca (Tecnun), Jose Manuel Martínez-Esnaola (CEIT-BRTA) and Jon Alkorta (CEIT-BRTA).
Abstract
A technique for the highly localised measurement of residual stresses at the surface of metallic samples is presented in this paper. Residual stresses are relaxed by removing a small volume of material via focused ion beam (FIB) milling. The new free surfaces of the milled geometry produce displacements in the neighbouring material, which generates micro-strains. These strains are detected by applying digital image correlation (DIC) algorithms to images captured using a scanning electron microscope and related to residual stresses via finite element simulations. Owing to the material removal and strain detection methods it uses, this technique is named FIB-DIC. The spatial resolution of the technique is of the order of tens of microns, and the sensitivity of the displacement measurement of the order of tens of nanometres. Previous measurements using this technique have been focused on validating the technique, by comparing its results satisfactorily to X-ray diffraction measurements. In this work, the residual stress distribution generated at the surface of an aluminium sample during face turning is characterised. Process parameters are related to microscale residual stress patterns, and local measurements using FIB-DIC are compared with the standard X-ray diffraction residual stress measurements.
[385] ID:385-Determination of Fracture Parameters in Structural Composites using AI
Davide Mocerino (IMDEA Materials Institute) and Carlos González (IMDEA Materials Institute).
Abstract
This research explores the fracture properties of thermoset IM7/8552 composite materials, focusing on translaminar behaviour. Cross-ply laminates with a [0°/90°]6s configuration were crafted via autoclave consolidation, resulting in a 5.9 mm thickness and a 57.4% nominal fiber volume fraction. Four Compact Tension specimens, featuring well-defined pre-crack tips, were extracted for fracture tests under displacement control. A compliance calibration (CC) method established crack resistance curves using instantaneous critical load values to track fracture propagation and calculate energy release rates. The compact tension specimen's 2D geometry underwent finite element discretisation, modelling fracture behaviour with a 0.1 thickness layer of cohesive elements. Constitutive behaviour of cohesive elements followed linear (LCL) and bilinear (BCL) softening laws. The material behaviour included parameters like elastic modulus (E) and specific softening curve parameters. For the linear case (LCL), the parameter set was ΘLCL = [E, XT, GIC]. A superposition technique was used in the bilinear softening curve (BCL), obtaining ΘBCL = [E, XT, GIC, n, m]. 200 cases, each with distinct parameters drawn from uniform random distributions, were generated for virtual fracture tests in Abaqus Standard, collecting displacement (δ), load (P), crack growth (∆a), and computed GI. An artificial neural network (ANN) connected the input fracture parameter dataset with FEM-obtained load-displacement, crack-displacement, and dissipated energy-displacement. Normalising both datasets to a non-dimensional scale (0, 1) enhanced ANN accuracy. Discrepancies between actual and predicted load-displacement and crack-displacement curves for unseen test data consistently stayed below 1.5%, affirming a strong agreement between ground truth and surrogate model predictions. This underscores the surrogate's efficacy in providing a rapid and dependable response.
[386] ID:386-Phase-field modeling of deformation twinning and its interaction with plastic slip during nano-indentation
Mohsen Rezaee-Hajidehi (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences), Przemysław Sadowski (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences) and Stanisław Stupkiewicz (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences).
Abstract
Deformation twinning is a prevalent inelastic deformation mechanism in certain metals and alloys. Modeling twinning poses additional challenges in comparison to plastic slip due to the critical dissimilarities in the underlying mechanisms and characteristics. In this study, a finite-strain model of coupled twinning and plastic slip is formulated by combining the phase-field method and crystal plasticity. A distinctive aspect of the model lies in its treatment of deformation twinning as a displacive transformation (as in martensitic phase transformation), and thus the related kinematics is characterized by a volume-preserving stretch and a rigid-body rotation, rather than a simple shear as in the classical approach. The stretch-based kinematics is particularly relevant when conjugate twinning systems are crystallographically equivalent.
Spatially-resolved evolution of twin microstructure under nano-indentation is studied for an Mg alloy with an HCP crystal structure. To this end, a two-dimensional finite-element-based computational model is developed that includes one twin deformation variant, i.e., two conjugate twinning systems, and three effective slip systems (one basal and two pyramidal slip systems). The simulation results reveal several interesting effects, including an intriguing branched microstructure and pop-in events. A detailed analysis is conducted regarding the sensitivity of the twin microstructure and load-indentation depth on the lattice orientation and indenter radius (size effects).
[387] ID:387-Experimental study of polymer-based 3D auxetic structures manufactured by SLA.
Jordi Martin-Montal (Carlos III University), Jesus Pernas-Sanchez (University Carlos III of Madrid) and David Varas (Universidad Carlos III de Madrid).
Abstract
In recent decades, the engineering field has been focused on finding novel materials and structural configurations that can enhance mechanical performance while reducing costs. The goal is to develop structures that are stronger, lighter, and more resilient to meet specific load conditions and boundary requirements. Additive manufacturing has opened up new possibilities, enabling the investigation of novel geometric configurations and leading to the emerging field of metamaterials. One kind of those metamaterials are the auxetic structures, which are characterized by a negative Poisson's ratio. They exhibit exceptional shear strength, indentation resistance, high fracture toughness, and significant energy dissipation capacity. These properties make them suitable for various purposes, including shock absorbers, filters, biomedical implants, and protective elements. Understanding the behaviour of auxetic structures under different types of loading is crucial for their development and the design of different applications. This understanding relies on the fundamental 'unit cell' of auxetic structures, which determines their mechanical characteristics. The objective of this study is to investigate the effect of varying unit cell parameters on the mechanical behaviour of polymer-based auxetic structures, manufactured using a stereolithography (SLA) 3D printer. To that end, quasi-static compression tests were performed on auxetic structures with different beam lengths, cross-sectional thicknesses and re-entrant angles of the unit cell. Furthermore, the effect of the number of cells within the structure was examined. The data and images obtained during the tests allowed to analyse the maximum crushing force, the energy absorption capacity, the auxetic behaviour or the failure mode of the structures and hence to compare the effectiveness of studied structures. The conclusions reached contribute to the comprehension of the behavior of auxetic structures and their potential for energy absorption across diverse structural designs.
[388] ID:388- Influence of Lattice Architecture Mixing Strategy for Improved Mechanical Properties in Additively Manufactured Inconel718 Lattices
Souvik Sahoo (Postdoctoral Research Associate), Isaac Toda Caraballo (Tenured Scientist), Maciej Haranczyk (Senior Researcher) and Maria Teresa Pérez Prado (Senior Scientist).
Abstract
The present study explores the effect of mixing various lattice architectures on the mechanical behavior of selective laser melted (SLM) Inconel 718 strut-based lattices. As a first approximation, we have selected several lattice architectures (BCC, FCC, OT, and SC) to analyze how a meta-lattice with a mixture of them respond from the mechanical behavior point of view. We have employed two mixing strategies: one where the lattice architectures are randomly distributed in the meta-lattice, and other, by using special quasi-random structures (SQS) to maximize the mixing and homogeneity. The mixing was carried out considering binary, ternary and quaternary meta-lattices, corresponding to using two, three or four lattice architectures respectively. Pure bending and stretching dominated behavior are noticed in pure BCC and SC lattice respectively, whereas a peak after elastic region followed by bending dominated behavior is noticed in pure FCC and OT lattices. In all the mixed lattices, either pure bending or very small peak after elastic region followed by pure bending dominated behavior is noticed. The specific yield strength (normalized by relative lattice density) is high for OT (220 MPa) and low for BCC (63 MPa), whereas it is similar for FCC (158 MPa) and SC (160 MPa) lattices. The results indicate that the mixing of architectures offers generally better mechanical properties than the rule of mixture using the results of the pure individuals. Also, the SQS lattices show in general better mechanical properties than the random lattices. Importantly, some of the combined architecture lattices show improved yield strength and strength at 30% engineering strain compared to the original lattices. It is noticeable the effect of adding SC to other lattices, where a systematic improvement of mechanical properties is observed.
[389] ID:389-Relating laser powder bed fusion process parameters to (micro)structure and to soft magnetic behaviour in a Fe-based bulk metallic glass
Marcos Rodríguez Sánchez (IMDEA Materials Institute, Madrid), Saumya Sadanand (IMDEA Materials Institute, Madrid), Amir Hossein Ghavimi (Saarland University, Chair of Metallic Materials), Ralf Busch (Saarland University, Chair of Metallic Materials), Paola Maria Tiberto (Istituto Nazionale di Ricerca Metrologica), Enzo Ferrara (Istituto Nazionale di Ricerca Metrologica), Gabriele Barrera (Istituto Nazionale di Ricerca Metrologica), Lena Thorsson (Hereaus AMLOY Technologies GmbH), Hans-Juergen Wachter (Hereaus AMLOY Technologies GmbH), Isabella Gallino (Saarland University, Chair of Metallic Materials) and María Teresa Pérez-Prado (IMDEA Materials Institute, Madrid).
Abstract
Fe-based soft magnetic bulk metallic glasses (BMGs) have shown unprecedented magnetization saturation and coercivity values and are thus envisioned as potential candidates to increase the efficiency of electromagnetic components. Laser powder bed fusion (LBPF) allows to manufacture relatively large BMG parts while retaining an amorphous microstructure due to high local cooling rates. However, in practice, the thermal cycles generated in the layer-wise LBPF process tend to cause undesired crystallization, which hinders the magnetic properties of printed parts. In general, the processing parameters that yield the densest prints also cause severe crystallization upon solidification. On the other hand, the parameters that allow the material to retain the amorphous microstructure tend to leave structural defects, mainly due to lack of fusion. To date, complex LPBF scanning strategies, which are difficult to replicate, have been the most successful avenue to avoid crystallization of BMG’s during fabrication. However, the fundamental relationship between processing parameters, defects, (micro)structure and properties, still remains unclear for many BMG compositions.
This work aims to provide a thorough study of the individual effect of the main LPBF processing parameters (laser power, scaning speed, and hatch distance) on the resulting (micro)structure and mechanical and magnetic properties of a commercial Fe-based BMG alloy. The feedstock amorphous powder is processed using a pulsed-wave laser system and a simple scanning strategy. Complementary experimental techniques such as image analysis, X-ray diffraction (XRD), differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD) and mechanical and magnetic testing were used to characterize the evolution of (micro)structure and magnetic properties. This study defines guidelines for the successful additive manufacturing of Fe-based BMGs by pulsed laser powder bed fusion.
[390] ID:390-A length scale insensitive cohesive phase-field model for inter-/trans- granular fractures: application to image-based reconstructed NMC cathode particles
Wanxin Chen (The Technical University of Darmstadt) and Bai-Xiang Xu (The Technical University of Darmstadt).
Abstract
The pursuit of high-performance energy storage devices demands a comprehensive understanding of the intricate interplay between chemical and mechanical phenomena, and the damage and failure mechanisms within electrode materials. In this work we proposed a length-scale insensitive cohesive chemo-mechanical phase-field model for simulating and elucidating fracture-induced damage and degradation phenomena in the polycrystalline LixNi0.5Mn0.3Co0.2O2 (NMC532) cathode. One significant challenge thereby is how a diffusive interface-based phase-field fracture model can reproduce the sharp interfacial damage at grain boundary/interface, while preserving the energy-based fracture criterion (global dissipation equivalence). In particular, the length scale insensitivity of the proposed phase-field model in the context of inter- and trans-(intra-) granular fractures is validated with several representative benchmark examples. As application examples, the (de-)lithiation induced fracture and degradation in the polycrystalline NMC532 cathode materials was simulated. Thereby image-based reconstructed 3D polycrystalline geometry was employed for finite element (FE) mesh. Simulation results show that the model can capture various crack evolution features (e.g., nucleation, propagation, branching and diverse modes including inter-/trans-(intra-) granular patterns. Specifically, we reveal the impact of various microstructure aspects, including grain boundary fracture energy, charging rates, grain size. This comprehensive analysis provides valuable insights into the chemo-mechanical fracture and degradation within polycrystalline NMC cathodes.
[391] ID:391-Understanding serrated flow in Inconel 718 architected lattices
Souvik Sahoo (IMDEA Materials Institute), Zhi Chen (Technion-Israel Institute of Technology), Shruti Banait (IMDEA Materials Institute), Dan Mordehai (Technion-Israel Institute of Technology), Maciej Haranczyk (IMDEA Materials Institute) and María Teresa Pérez-Prado (IMDEA Materials Institute (CIF: G 84908953)).
Abstract
Lightweighting of components in transport systems by the substitution of traditional bulk parts by architected structures has been lately facilitated by the advent of metal additive manufacturing methods. Numerous studies in the literature have reported the relationship between the architecture, the material microstructure, and the mechanical behavior of lattice structures. However, these studies have mostly been conducted at room temperature, and the high temperature behavior of architected materials remains largely underexplored.
In a recent study the current authors reported for the first time the occurrence of serrated flow at moderate temperatures in strut-based Inconel 718 lattices produced by laser powder bed fusion (LPBF) [1]. It was shown that the testing conditions (temperature, strain rate) under which serrated flow appears are topology-dependent. The origin of such dependence is unknown. Moreover, the fundamentals of serrated flow in bulk samples of Ni-based superalloys have still not been well established. While in steels and Al alloys flow instabilities have been linked to the occurrence of dynamic strain aging (DSA), the origin of serrated flow in Ni-based superalloys remains elusive.
In this work we investigate the occurrence of serrated flow in Inconel 718 strut-based lattices with different geometries manufactured by LPBF. Flow instabilities are investigated at temperatures ranging from 300 to 600°C. It will be shown how the combination of experiments and finite elements modeling (FEM) sheds new light on the origin of the critical strain at which the first serrations appear.
[1] S. Banait, M. Campos, M.T. Pérez-Prado, Mat. Lett. 353 (2023) 135314.
[392] ID:392-Effect of fibre rotation on the coupling between matrix cracking and delamination.
Radouan Bouallala (Universidad Politécnica de Madrid and IMDEA materials Institute), Carlos González (Universidad Politécnica de Madrid and IMDEA Materials Institute) and Ignacio Romero (Universidad Politécnica de Madrid and IMDEA Materials Institute).
Abstract
Coupon testing is pivotal in aeronautical design, offering a great understanding of material behaviour under varied stress conditions. Integrating simulation at this stage could significantly reduce the need for extensive physical tests. This approach reduces costs and time associated with traditional testing, enhancing design optimisation and safety. However, creating any realistic model requires a lot of care and knowledge.
Previous models have demonstrated the ability to predict coupon laminates' strength and damage behaviour, effectively reproducing experimental tests using techniques such as aligned mesh to mitigate mesh-induced direction bias. However, a significant challenge arises with the replication of aligned mesh in complex geometries. While regular mesh is a potential alternative, it could not accurately predict crack propagation. In the case of (±45⁰) plies, the crack prediction in the final failure is captured mainly in only one direction when using regular mesh, whereas, in experimental results, the crack in the specimens appeared in both directions.
A possible method to mitigate this rising issue is defining and using an objective derivative and a rotated frame from the rotation of the fibre rather than using the Abaqus built-in approach (Green-Naghdi stress objectives derivatives).
An initial test of this new method applied to a two-ply laminate, has presented promising results. The preliminary findings suggest that this technique could more accurately predict crack propagation and damage patterns in coupon laminates.
[394] ID:394-Pneumatic surface morphing plates fabricated through a direct ink writing
Alejandro Ibarra (ESPCI), Jose Bico (ESPCI), Etienne Reyssat (ESPCI) and Benoit Roman (ESPCI).
Abstract
Achieving the transformation from a two-dimensional surface to a three-dimensional structure requires locally changing the curvature of the flat surface and therefore locally changing the metric of the surface, according to Egregium theorem. To build this type of flat structure, we manufacture channels within a silicone plate, using the direct ink writing (DIW) technique. This technique allows us to build channels of various diameters and different heights of the cross-section. By pressurizing the channels the plate deforms locally in the direction perpendicular to them.
We have found that by printing channels centered on the neutral plane of the plate, they allow us to change the metric depending on the applied pressure, and on the other hand, if the channels are outside the neutral plane, they allow us to change the local curvature. The flexibility of this manufacturing technique allows us to build plates with multiple channels in the same section, therefore we can locally change the curvature and metric depending on the pressures applied to the different channels.
Additionally, we explore the interaction of different sets of channels that are pressurized independently, exhibiting, in the same structure, different shapes and mechanical behaviors for different combinations of applied pressures. Finding that when the control of local curvature dominates the structures are stable and when the control of the metric dominates the structures can be multi-stable.
[395] ID:395-Control and instabilities of fracture paths when tearing brittle sheets
Benoit Roman (PMMH (CNRS/ESPCI/SorbonneUniv/ParisUniv)), Alejandro Ibarra (PMMH (CNRS/ESPCI/SorbonneUniv/ParisUniv)), Jose Bico (ESPCI), Juan Francisco Fuentealba (Facultad de Ingeniería y Arquitectura, Universidad Central de Chile) and Francisco Melo (Departamento de Física Universidad de Santiago de Chile and Center for Soft Matter Research, SMAT-C).
Abstract
Fracture propagation in brittle thin sheet often follows very reproducible fracture paths. Since our schoolyear we all intuitively know how to cut of a sheet of paper laid on a table with a ruler A description of this mundane situation is however difficult because of the incompatibility in fundamental assumptions for thin plate mechanics (averaging stress field along the thickness) and Fracture mechanics (requiring a detailed description of the divergent stress field close the crack tip). I will show how a variational approach can help explain the robustness and the geometry of torn fracture trajectories, and rationalise the controlled cutting of a paper sheet so that the cut follows the clamping ruler.
[396] ID:396-Modelling the elastic-viscoplastic behaviour during presureless sintering of 17/4PH steel parts obtained by Binder Jetting
Jorge Rodríguez Páez (CEIT) and Jon Alkorta (CEIT).
Abstract
Binder Jetting (BJ) is an advanced additive manufacturing technology which allows the production of intricate metal components. The resulting part consists of a mixture of thermoplastic binder and metal powder, requiring further steps of debinding and presureless sintering of the green part. In the sintering stage, part densification involves both shrinkage and distortion. This paper introduces an elastic-viscoplastic model that accounts for the macroscopic deformation behaviour in the sintering process of 17/4PH steel parts produced through BJ. The model addresses the problem by considering a viscoplasticity model that depends on the first and second invariants of the stress tensor and an effective sintering stress that mimics the shrinkage due to diffusional mechanisms involved in the sintering process. The parameters arising in the formulation were identified through a calibration procedure involving an experimental campaign including dilatometry tests. The model, implemented in finite element software, has demonstrated its capability to reproduce the macroscopic deformation behaviour of 17/4PH steel parts obtained through BJ, encompassing different geometries.
[397] ID:397-From thermal activity in DED process to microstructure prediction
Quentin Dollé (Univ. Lille, CNRS, Centrale Lille, UMR 9013, LAMCUBE , F-59000 Lille, France), Jean-François Witz (Univ. Lille, CNRS, Centrale Lille, UMR 9013, LAMCUBE , F-59000 Lille, France), Daniel Weisz-Patrault (LMS, CNRS, École Polytechnique, Institut Polytechnique de Paris, F-91128 Palaiseau, France) and Ahmed El Bartali (Univ. Lille, CNRS, Centrale Lille, UMR 9013, LAMCUBE , F-59000 Lille, France).
Abstract
Additive manufacturing parts process specific microstructures related to the specific thermal conditions undergone during the process. Process parameters have substantial impact on the resulting microstructure which partly influence the mechanical behavior of the final part. Targeting microstructures could be expected in a matter of optimization. To achieve, thermal activity is a suitable gateway bridging process parameters and microstructure while monitoring it in-situ.
Cellular Automaton models are widely used to simulate solidification process during additive manufacturing, often coupled with finite element methods to compute thermal activity within the melt pool. However the computational cost remains significant particulary for large simulations limiting their practical use in experimental design.
In this study, a two-color pyrometer and a monochromatic infrared camera are coupled together and setup during Direct Energy Desposition (DED) process. Temperature field near the melt pool is observed, providing appropriate insights for microstucture prediction such as cooling rates, thermal gradients and melt pool shape.
Recently, we have developed a new fast model for microstructure prediction based on upscaling complexe phenomena taking place at the scale of the solidification process into simpler evolution laws. This new approach reduces the degree of freedom from O(n^3) to O(3n) in 3D. As the resulting microstructure is strongly correlated to the unknown microstructure of the subratre upon which the epitaxial growth takes place, the proposed approach leads to a statistical analysis of the microstructure resulting from the solidification process.
Understanding the relationship between thermal activity and microstrcuture, the previous infrared sensors become suitable tools for in-situ monitoring of the process and control it.
[398] ID:398-Doping-regulated room-temperature dislocation plasticity in SrTiO3: a nanoindentation approach
Chukwudalu Okafor (Technical University of Darmstadt, Germany), Ahmad Sayyadishahraki (Technical University of Darmstadt, Germany), Sebastian Bruns (Technical University of Darmstadt, Germany), Karsten Durst (Technical University of Darmstadt, Germany) and Xufei Fang (Technical University of Darmstadt, Germany).
Abstract
Modern functional oxides are mainly tailored by doping, namely, by changing the defect chemistry, which is essentially the studies of point defects and their interactions in solid state. On the other hand, in recent years, dislocations as line defects have been shown to improve the mechanical and functional properties of a fraction of advanced oxides for promising applications such as actuators and sensors. This poses an increasing demand to understand the interaction of dislocations and point defects in functional oxides. Here, we report the influence of doping on the mechanical response of single-crystal strontium titanate using nanoindentation tests. By using the Berkovich and 2 µm spherical indenter tips, we observe the changes in the pop-in event which is reflected in the maximum shear stresses for dislocation nucleation, as well as the nanoindentation creep rate. The possible contributing factors: cation (Sr,Ti/Nb) and anion (O) vacancies, doping elements and lattice distortion induced by dopant elements are discussed, and the lattice frictional stress is estimated based on the dislocation etch pits. The nanoindentation results are further linked with the bulk plastic deformation behavior of the doped and undoped samples. The current results shed new light on the interaction between dislocations and point defects, which appear to strongly impact the dislocation nucleation, multiplication and mobility, hence the room-temperature plasticity of strontium titanate.
[399] ID:399-High temperature nanoindentation of different metals: evaluating thermal drift, frame stiffness and composition effects on the mechanical properties
Velislava Yonkova (Forschungszentrum Jülich), Steffen Brinckmann (Forschungszentrum Jülich) and Ruth Schwaiger (Forschungszentrum Jülich).
Abstract
High-temperature nanoindentation analysis is challenging due to instrument-related artifacts such as thermal drift and frame stiffness. Here, we investigated the impact of frame stiffness and thermal drift on the apparent mechanical properties by comparing the results of static nanoindentation experiments at different temperatures. The indents were analyzed using the Oliver-Pharr method, while two different load profiles were applied. Additionally, automatic image recognition (AIR) of the micrographs of the indents as well as statistical methods, i.e., correlation heatmap and p-value evaluation, were employed to understand the instrument-related artifacts. The tested materials include ferritic, martensitic, and austenitic steels as well as a Ni-based alloy for high-temperature applications.
The thermal drift analysis showed significant drift at 400 °C, which then decreased at 600 °C. Frame stiffness varied considerably for different temperatures, showing an inverse correlation with thermal drift. Both the Oliver-Pharr method and AIR revealed a hardness decrease of the materials with increasing temperature. As expected, AIR demonstrated less susceptibility to thermal drift. The heatmap correlation and p-value evaluation of the hardness with respect to the materials’ chemical compositions indicated that Cr and Ni positively influence the hardness resulting in improved hardness with increasing temperatures. The combination of the two analysis methods yields reliable mechanical properties despite the significant fluctuations in thermal drift and frame stiffness for different temperatures.
[400] ID:400-Mechanical behavior of grain boundaries containing precipitates in a refractory compositionally complex alloy
Jin Wang (Institute of Energy and Climate Research, Forschungszentrum Juelich GmbH), Silva Basu (Institute of Energy and Climate Research, Forschungszentrum Juelich GmbH) and Ruth Schwaiger (Institute of Energy and Climate Research, Forschungszentrum Juelich GmbH).
Abstract
Refractory compositionally complex alloys (RCCAs) may exhibit improved high-temperature resistance compared to face-centered-cubic (FCC) CCAs and superalloys. However, the brittleness of most CCAs at room temperature limits their applicability, while the role of the individual microstructural components has not yet been studied in detail. To understand the influence of microstructure on the deformation behaviors of these alloys, we conducted micro-mechanical experiments, including nanoindentation and micro-pillar compression tests, on a representative NbMoCrTiAl alloy at room temperature. The indentation at the grain boundaries showed increased shear stress and hardness compared to the matrix (ordered B2 crystal structure) due to the presence of intermetallic precipitates (C14 and A15 phases). Although the NbMoCrTiAl alloy exhibited no ductility at the millimeter scale in previous compression experiments, the micro-pillars containing a grain boundary with precipitates demonstrated higher yield strength and significant plastic strain >30% at room temperature. Numerous slip lines were observed inside grains, while cracks and sometime fracture occurred at higher levels of deformation. The grain boundaries containing precipitates appear more likely to exhibit crack initiation and propagation, while only in few cases catastrophic failure of the pillars was observed.
[401] ID:401-Strain engineering of thin semiconductor films investigated using the residual-stress-actuated on-chip testing method
Marie-Stephane Colla (University of Louvain - Institute of Mechanics, Materials and Civil Engineering), Nicolas Roisin (University of Louvain - Institute of Information and Communication Technologies, Electronics and Applied Mathematics), Denis Flandre (University of Louvain - Institute of Information and Communication Technologies, Electronics and Applied Mathematics), Jean-Pierre Raskin (University of Louvain - Institute of Information and Communication Technologies, Electronics and Applied Mathematics) and Thomas Pardoen (University of Louvain - Institute of Mechanics, Materials and Civil Engineering, WEL Research Institute).
Abstract
The versatile residual-stress-actuated on-chip tensile testing method has proven over the last years its potential for the characterization of the link between the mechanical behaviour and microstructure at the micro- and nanoscale. Recently, the on-chip method has appeared promising to tackle challenges related to strain engineering studies. Strain engineering studies refer essentially to the exploration of the evolution of functional properties under elastic distortions. Nano- and micro-scale specimens are particularly suited as they usually are stronger than macroscopic specimens and thus allow larger elastic strain without fracture. The difficulty is to impose well-defined mechanical conditions at small scale. Two practical examples are presented in this work.
First, experimental validation of theoretical band gap calculations (first-principles calculations based on density functional theory) is provided through photoluminescence spectroscopy measurements performed on on-chip microfabricated monocrystalline Si specimens deformed up to ∼1% under uniaxial tensile stress.
Second, while uniaxial tension is highly relevant to determine several mechanical properties, the first-principles calculations have highlighted the interest of biaxial and shear loading configurations to improve more efficiently the band structure of silicon. On-chip shear and biaxial configurations have thus been designed. Experimental proof of concept of these new structures is provided on monocrystalline silicon.
[402] ID:402-Full-field strain measurements in homogeneous solids enabling discovery of new material physics
Zifan Wang (University of Cambridge), Angkur Shaikeea (University of Cambridge), Akshay Joshi (University of Cambridge), Shuvrangsu Das (University of Cambridge) and Vikram Deshpande (University of Cambridge).
Abstract
X-ray computed tomography (XCT) is a reliable tool for measuring internal flaws and microstructural features in engineering materials. As an extension to XCT, Digital Volume Correlation (DVC) methodology enables tracking 3D deformation field based on local grayscale contrast. Nevertheless, its applicability and spatial resolution have been limited by the need for tracer particles or inherent microstructural features that are distributed in the material volume. To address these limitations, we developed a Flux Enhanced Tomography for Correlation (FETC) technique that leverages inherent inhomogeneities in engineering materials (polymers to metals) to measure all nine components of the deformation gradient without relying on artificial X-ray tracers. Via this unprecedented full-filed measurement technique, the mechanical behaviour of various engineering polymers was examined, and new observations was made on the well-established rubber elasticity. It was found that many polymers undergo significant local volume changes but the overall volume remains constant during mechanical loading. The presence of a mobile phase within the material volume has been proved which gives rise to negative local bulk moduli. By extending its application on other materials, FETC is expected to bring more electrifying discoveries of new material physics.
[403] ID:403-Automatic voxel-based generation of 3D mesostructures of stochastic tow-based discontinuous composites for the prediction of elastic properties
Luis Gulfo (Chalmers University of Technology), Ioannis Katsivalis (Chalmers University of Technology), Leif E. Asp (Chalmers University of Technology) and Martin Fagerström (Chalmers University of Technology).
Abstract
High-performance discontinuous composites manufactured with randomly oriented prepreg tapes have been developed to obtain an in-plane isotropic response combined with high stiffness and strength. Compared to composite laminates requiring a controlled lay-up, stochastic tow-based discontinuous composites also benefit from high manufacturability due to the random deposition of chopped tapes. Moreover, the use of thick, thin, and ultra-thin tapes has opened a design space with new structural applications. However, the high variability in terms of their 3D microstructures and mechanical properties imposes numerous challenges for numerical modelling. In particular, stochastic tow-based discontinuous composites show variations in tape waviness, tape draping, size of resin pockets, local fibre volume fractions, and thickness, which strongly affect the mechanical properties and therefore must be captured by any predictive modelling. One way to account for such effects is through detailed mesoscale modelling.
This study proposes a new 3D voxel-based mesostructure generator using a 3D random sequential absorption technique that incorporates bin-guided tape deposition, a tape draping method to produce waviness and resin pockets, and a control strategy for plate thickness variations. The numerical framework is fully integrated with finite element simulations to predict the elastic properties of thick, thin, and ultra-thin discontinuous composites via 3D computational homogenisation. A detailed statistical analysis is conducted to investigate the size of the statistical volume elements and the convergence of the elastic properties. In addition, microscopy analysis and nitric acid tests have been used to extract key modelling parameters for an ultra-thin discontinuous composite. Despite the uncertainties in the input properties of the tapes, the predicted results are in good agreement with the experimental values found in the literature. Finally, a comparison with equivalent laminate models is also provided. This illustrates the capabilities of the framework for potential applications requiring detailed 3D models such as material optimisation and damage studies.
[404] ID:404-Exploring magnetorheological elastomer fracture via phase-field modeling
Sergio Lucarini (BCMaterials / Ikerbasque Fundation), Josu Fernández Maestu (BCMaterials), Ane García García (BCMaterials), Ander García Díez (BCMaterials) and Senentxu Lanceros-Méndez (BCMaterials / Ikerbasque Fundation / UMinho).
Abstract
Magnetorheological elastomers (MRE) are composed of elastic matrices infused with magnetic particles, which exhibit adaptive reactions to external magnetic fields. These responses result in mechanical deformations and modifications of the magnetorheological characteristics. Recently, there has been growing interest in soft MREs, characterized by polymeric matrices and malleable magnetic fillers, due to their potential applications in soft robotics, biomedicine and industrial components [1]. In particular, these materials show increased toughness during the fracture process when subjected to magnetic field actuation, a phenomenon attributed to the intricate interactions between magnetic particles [2].
This study delves into a comprehensive examination of the inherent fracture behavior of soft MREs under the influence of magnetic fields. Taking advantage of phase-field fracture modeling [3], a powerful approach known for its fracture regularization and the absence of predefined fracture trajectories, we present a pioneering magnetomechanical fracture modeling framework. This framework allows us to examine the complex interactions between magnetism and mechanics, with particular focus on understanding fracture behavior. The results of this research promise to reveal new insights into the post-fracture magnetic characteristics of soft MREs, paving the way for advanced applications and breakthrough innovations in multifunctional materials.
[1] A.K. Bastola, M. Hossain, A review on magneto-mechanical characterizations of magnetorheological elastomers, Composites Part B: Engineering, 200:108348, 2020.
[2] M.A. Moreno-Mateos, M. Hossain, P. Steinmann, D. Garcia-Gonzalez, Hard magnetics in ultra-soft magnetorheological elastomers enhance fracture toughness and delay crack propagation, Journal of the Mechanics and Physics of Solids, 173:105232, 2023.
[3] C. Miehe, L.M. Schänzel, Phase field modeling of fracture in rubbery polymers. Part I: Finite elasticity coupled with brittle failure, Journal of the Mechanics and Physics of Solids, 65: 93-113, 2014.
[405] ID:405-Development of a polyhedral DEM method for simulating the relocation of nuclear fuel during a LOCA.
Thibault Bessiere (EDF Lab Les Renardières, Laboratoire de Mécanique et Génie Civil, Université Montpellier 2), Serguei Potapov (EDF Lab Paris-Saclay) and Philippe Lafon (EDF Lab Paris-Saclay).
Abstract
During a Loss of Coolant Accident (LOCA), fuel rods are heated by the residual power. The resulting increase of internal pressure leads to a ballooning of the cladding which allows the fuel to relocate and, if there is a rupture, to disperse into the primary circuit.
Here, we propose to assimilate the fragmented fuel to a granular medium and implement a Discrete Element Method (DEM) to model the behavior of fragments within the rod. The aim is to describe their relocation through the analysis of packing fraction along the rod. This model echoes previous DEM-focused numerical simulation works on fragment relocation. Some of these models have limitations in terms of representation which we aim to overcome by creating a realistic 3D model to describe the main features of the fuel rod during a LOCA: • The complex shape of the fragments; • The deformation of the cladding and the interaction of fragments with the inner wall; • The interaction of fuel fragments with fission gases and the confinement gas;
The initial developments aimed to adapt the discrete element method and extend it to arbitrary polyhedral geometries, adopting a method based on sphero-polyhedra. This method allows to facilitate the contact detection stage, which is challenging to implement for complex geometries.
Verification and validation test cases of the polyhedral DEM method have been conducted. They serve as benchmarks for applied simulations aimed at studying the effect of size and shape distribution of fragments on relocation in the case of a dry granular medium.
Further developments are in progress to address the effects of fragment interaction with cladding walls and fission gases. Various coupling methods with DEM are being explored, and their selection is the subject of current research efforts.
[406] ID:406-Quantification of internal damage during tensile straining of LPBF-manufactured cellular materials with random voids
Laura Salvi (Uni. Paris-Saclay, CentraleSupélec, ENS Paris Saclay, CNRS Laboratoire de Mécanique Paris-Saclay, France), Benjamin Smaniotto (Uni. Paris-Saclay, CentraleSupélec, ENS Paris Saclay, CNRS Laboratoire de Mécanique Paris-Saclay, France), François Hild (Uni. Paris-Saclay, CentraleSupélec, ENS Paris Saclay, CNRS Laboratoire de Mécanique Paris-Saclay, France) and Gabriella Tarantino (Uni. Paris-Saclay, CentraleSupélec, ENS Paris Saclay, CNRS Laboratoire de Mécanique Paris-Saclay, France).
Abstract
Metallic cellular materials are of interest in numerous engineering applications as they combine low density with attractive features of metals (e.g., ductility and strength). Today, these materials are routinely used (e.g., in structures that absorb mechanical energy, or as biomedical scaffolds and heat exchangers). To reveal their potential in novel emerging applications (e.g., as battery electrodes), a fine understanding of their mechanical deformation and failure is instrumental.
In this work, the tensile response is investigated experimentally for AlSi10Mg cellular materials produced by laser powder-bed fusion (LPBF). Specifically, the metamaterials of this study have a porous architecture in which pores, of arbitrary elliptical shape, are randomly-dispersed in the Al-alloy matrix. Their porous mesostructure is first generated numerically by means of a random sequential absorption algorithm [1], and then fabricated by LPBF additive manufacturing. Using FE-based Digital Image Correlation (DIC) [2] with mesoscale meshes consistent with the pore distribution combined with X-Ray tomography, the mesoscale damage mechanisms underlying tensile deformation is quantified for this class of cellular solids. It is shown that the latter combine features of ductile fracture of metals with the defect-sensitivity typical of cellular metals produced by additive manufacturing.
[1] Hoosmand-Ahoor et al. Mechanics of Materials 173 (2022): 104432. [2] Hild et al. Experimental Mechanics 61.2 (2021): 431-443.
[407] ID:407-Poro acosutics with evaporation/condensation
Claude Boutin (Université de Lyon - ENTPE - CNRS5513) and Rodolfo Venegas (Universidad Austral - Instituto de acoustica).
Abstract
This article deals with moist rigid porous media and studies the propagation of long acoustic waves in presence of evaporation/condensation. At equilibrium, the solid walls are covered by a thin water film and water vapour in the air is at its equilibrium-temperature-dependent saturation pressure. Under acoustic excitation, water vaporises or condenses. The reversibility of this phase change and the assumed small acoustic harmonic perturbation leads to a linear problem where the usual local poro-acoustics physics (Fourier-Stokes system) is enriched with the (i) Clapeyron relation (CR) which links the liquid-wall temperature, the vapour pressure, and the latent heat of vaporisation, (ii) heat transfer of the latent heat in the solid, (iii)diffusion equation for water vapour in air, (iv) water vapour’s equation of state.
Using the two-scale homogenisation method, it is first shown that the gas pressure is locally constant. Then, the method yields the usual visco-inertial Darcy’s law and the mass and heat fluxes associated with the phase change. The latter are obtained from a coupled thermo-diffusion problem with specific boundary conditions at the gas/liquid interface : (i) liquid-wall temperature imposed by CR and (ii) discontinuity in heat flux due to water phase change induced heat flux. Finally, the gas effective compressibility is derived from the overall mass conservation of dry air and water vapour in the pores. The role of dimensionless parameters and characteristic frequencies on the speed of sound and attenuation is also discussed with respect to the equilibrium temperature.
[408] ID:408- O-embrittlement and microstructure effects on fatigue life of quasi-alpha Ti alloys
Lucille Bornowsky (ONERA Châtillon, LaSIE La Rochelle University), Pascale Kanouté (ONERA Châtillon), Aldo Marano (ONERA Châtillon) and Xavier Feaugas (LaSIE La Rochelle University).
Abstract
Titanium alloys are increasingly used in aircraft engines. Ti components experience elevated temperatures of up to 550°C in oxygen-containing environments. Quasi-alpha Ti alloys are particularly prone to oxygen ingress, exhibiting up to 33% at. O, making oxygen-induced embrittlement a major concern for its deployment to higher temperatures. This work aims to improve the understanding of the interplay between oxidation induced embrittlement, aging and microstructural effects on fatigue life of quasi-alpha titanium alloys. We focus on a forged Ti6242S commercial alloy commonly used in aircraft engines. Two bimodal microstructures of high/low lamellar colonies surface fraction are studied in their reference state as well as after oxidation at 600°C for 3000 hours. Pre-oxidation led to the formation of an ~80 µm oxygen-enriched layer, characterized by SEM-WDS. Tensile properties and fatigue life were investigated through mechanical testing at room temperature and 550°C, SEM-fractography and TEM-FIB dislocation networks analysis. Tensile tests did not show any detrimental effect of oxygen-ingress on fracture strain at 550°C. Fatigue life was found to be mainly driven by crack initiation. At both ambient temperature and 550°C, both the pre-oxidation and the fraction of lamellar colonies exhibited a significant influence on fatigue life. At room temperature, pre-oxidized samples exhibited a stress threshold phenomenon, with no observable O-induced embrittlement on fatigue life below approximately 650 MPa and a drastic decrease in fatigue life at higher stress amplitudes.
[409] ID:409-A gradient-enhanced phase-field crystal plasticity model for ductile failure predictions
Kim Louisa Auth (Chalmers University of Technology), Jim Brouzoulis (Chalmers University of Technology) and Magnus Ekh (Chalmers University of Technology).
Abstract
Failure of engineering components made from metals is often preceded by the development of significant plastic strains. For the life span prediction of such components, it is important to understand the details of the fracture process. This particularly includes the interaction between the development of plastic deformation and damage on a microstructural level, leading to microscopic cracks which ultimately evolve into macroscopic cracks and then cause structural failure.
This study addresses ductile fracture of single grains in metals by modeling the nucleation and propagation of transgranular cracks. We present a model that integrates gradient-enhanced hardening, phase-field modeling for fracture, and crystal plasticity, presented in a thermodynamic framework within large deformation kinematics. The phase-field model employs a micromorphic formulation that is used for assuring irreversibility upon unloading.
We present ability of the model to predict the influence that grain boundaries and other obstacles have on transgranular crack growth. Therefore, we study the size effects introduced by the length-scale parameters in the gradient-enhanced hardening and phase-field models. Furthermore, it is demonstrated that the model is able to handle loading-unloading situations. Finally, we provide an example of how the presented model handles material inhomogeneities, such as inclusions arising during casting. Numerical examples are provided both in 2D and 3D.
[411] ID:411-Characterization of keyhole regime for Laser Powder Bed Fusion: from single track formation to multi layers volume, the change in laser and matter interaction
Maxence Guillon (Mines Saint Etienne), Pauline Chanin Lambert (Mines Saint Etienne), Christophe Desrayaud (Mines Saint Etienne), Xavier Boulnat (Mateis) and Thomas Elguedj (Lamcos).
Abstract
Metallic additive manufacturing by Laser Powder bed Fusion enables the on-demand production of components with complex geometry and high added value. Despite its strengths, there are still challenges in fully understanding the interaction between laser and material. Energy density and normalized enthalpy are crucial factors to predict and control the overall process. When the energy density reaches a sufficient level, a specific state is attained: the keyhole regime. In this scenario, the melt pool forms a deep and narrow cavity, and intense competition occurs within it. This regime is inherently unstable and prone to collapse, often resulting in the formation of characteristic pores. In this study, the 316L powder is used. Single tracks were generated to explore the boundaries of the keyhole domain. A process window was defined by adjusting power, scanning speed, and spot size parameters. However, the interaction between laser and material differs significantly between single tracks and multiple tracks due to the changes in interaction dynamics. In a single track, the laser only interacts with the powder on the both sides of the edificated seal. In contrast, for multiple tracks, the laser also interacts with the previously laid tracks. This underscores the inadequacy of characterizing only a single track for a comprehensive understanding of the interactions. Hence, this works aims at characterizing the melt pool during the formation of different sample construction: single tracks, multiple tracks on the same layer, and tracks between several layers. The purpose is to understand how the interaction between laser and material evolves on different successive tracks and layers. Various sets of keyhole processing parameters were chosen to fully understand the range of keyhole process windows. The assessments involve dimensions of the melt pools through metallographic measurement, characterization of pores formation through micro-tomography and the evolution of microstructures through EBSD measurement.
[412] ID:412-Towards efficient modeling for quantum-informed mechanics of polymers: a DFTB+MBD framework
Zhaoxiang Shen (Department of Engineering, Faculty of Science, Technology and Medicine, Universtiy of Luxembourg), Raul Ian Sosa (Department of Physics and Materials Science, Faculty of Science, Technology and Medicine, University of Luxembourg), Alexandre Tkatchenko (Department of Physics and Materials Science, Faculty of Science, Technology and Medicine, University of Luxembourg), Stéphane Bordas (Department of Engineering, Faculty of Science, Technology and Medicine, Universtiy of Luxembourg) and Jakub Lengiewicz (Department of Engineering, Faculty of Science, Technology and Medicine, Universtiy of Luxembourg).
Abstract
The macroscopic behaviors of materials are determined by phenomena that occur at different lengths and time scales. We show in this presentation that describing, predicting and understanding these behaviors may require models that rely on insights from electronic and atomic scales. Depending on the application, classical simplified approximations at those scales are insufficient, and quantum-based modeling is inevitable. This presentation explores how quantum effects can modify mechanical properties of certain molecular systems, from one-dimensional carbon structure to Ultra High Molecular Weight Polyethylene (UHMWE). Our study employs a high-fidelity modeling framework that combines two computationally efficient models rooted in first principles of quantum mechanics: Density Functional Tight Binding (DFTB) and many-body dispersion (MBD). DFTB is a semi-empirical method rooted in Density Functional Theory (DFT), and the MBD model is applied to accurately describe van der Waals dispersion interactions. Through various benchmark applications, we demonstrate the capabilities of this framework and the limitations of simplified modeling, like classical force fields. This framework serves as a practical tool that we hope will support the development of future research in effective ab-initio large-scale and multi-scale modeling.
[1] A. Tkatchenko, R. A. DiStasio, R. Car, and M. Scheffler. Accurate and efficient method for many-body van der Waals interactions. Phys. Rev. Lett., 108:236402, Jun 2012. [2] P. Hauseux, T.-T. Nguyen, A. Ambrosetti, K. Saleme Ruiz, S.P.A. Bordas, and A. Tkatchenko. From quantum to continuum mechanics in the delamination of atomically-thin layers from substrates. Nature Communications, 11(1):1651, 2020.
[413] ID:413-Plasticity during ductile tearing : crystallographic and dynamic strain aging effects
Thilo Morgeneyer (Centre des Matériaux, Mines Paris - PSL).
Abstract
During ductile tearing of ductile thin sheets, large plastic strains develop before failure. Numerically, plasticity is generally treated with macroscopic von Mises type plasticity but more complex plasticity effects may be at play affecting the tearing behavior. In this study, the effect of crystallographic texture and grain shape and size on the strain development during ductile tearing is assessed both experimentally and numerically for five different Al alloys sheets of one mm thickness [1,2,3]. Experimentally, in situ synchrotron imaging experiments are carried out to study the strain fields and damage development in the material ahead of the notch. Synchrotron laminography is used to image regions of interest in the aluminium sheets at micrometer resolution. Image correlation of projected 3D image contrast in the material bulk is used to identify the strain fields. For textured materials, strongly heterogeneous strain fields differing from the von Mises type model predictions are found whereas fine grained materials with little texture lead to strain field similar to those obtained by simulations using von Mises plasticity. Plane strain crystal-plasticity simulations are carried out to understand the experimentally found strain heterogeneity and allow the experimental trends to be reproduced [3]. Another phenomenon, leading to strain localization and instabilities during ductile tearing is the Portevin-le Chatelier (PLC) effect. The influence of the PLC effect on strain development for a 2XXX alloy and a C-Mn steel is studied using incremental surface image correlation thereby studying the experimental equivalent to strain rate [4].
[1] T.F. Morgeneyer, et al. Acta Materialia, 69 (2014) 78-91 [2] A. Buljacet al. Acta Materialia, 149 (2018) 29-45 [3] T. F. Morgeneyeret al. International Journal of Plasticity144 (2021) 103028 [4] S. Ren et al. International journal of plasticity 136 (2021) 102880
[414] ID:414-Viscoelastic Properties of Magnetorheological Elastomers for Multilayered Semi-Active Damper Applications
Matteo Ruggieri (Università degli Studi Roma Tre), Jacopo Ciambella (Università degli Studi di Roma, La Sapienza), Stephan Rudykh (University of Wisconsin-Madison) and Giuseppe Tomassetti (Università degli Studi Roma Tre).
Abstract
Magnetorheological elastomers (MREs) are smart materials characterized by their modifiable mechanical and viscoelastic properties when subjected to a magnetic field. These materials are composed by magnetizable particles disperse within solid elastomer bases, aligning into chain-like structures during the curing phase.
Owing to their unique characteristics, MREs can be widely used in several aplication including the effective development of isolation and vibration reduction systems with tunable mechanical properties.
In this contribution, we will present an analytical formulation to describe a laminate structure comprising alternating layers of MREs and a passive yet stiffer material, such as an aluminum. The constitutive equation of the MRE is derived in the context of finite strain regimes, where an additional internal variable representing the elastic deformation of the matrix is used to account for the dissipative effects and is constitutively coupled with the external magnetic field. As a result, the elastic moduli and relaxation times are influenced by the external magnetic field. The response of the laminate structure is explored under forced oscillations.
The analytical framework provided in this context establishes a basis for comprehending and enhancing the performance of laminates based on MREs, providing valuable insights for their utilization in creating controllable semi-active damping systems.
[415] ID:415- Identification of inelastic interphase properties in polymer nanocomposites based on molecular dynamics
Maximilian Ries (Friedrich-Alexander-Universität Erlangen-Nürnberg), Gunnar Possart (Friedrich-Alexander-Universität Erlangen-Nürnberg), Paul Steinmann (Friedrich-Alexander-Universität Erlangen-Nürnberg) and Sebastian Pfaller (Friedrich-Alexander-Universität Erlangen-Nürnberg).
Abstract
Polymers are used in many engineering applications due to their high versatility and low-cost production. Adding nano-sized fillers significantly enhances their mechanical performance, yielding polymer nanocomposites suitable for highly demanding applications. These beneficial properties are mainly attributed to the formation of a polymer-filler interphase surrounding the nanoparticles. Within this interphase, the properties of the polymer are altered due to the proximity of the filler particles. Due to the high surface-to-volume ratio of nanofillers, polymer nanocomposites feature a considerable interphase volume fraction. Therefore, precise knowledge of the interphase's mechanical properties is crucial for understanding and modeling the macroscopic material behavior. The small scale makes the interphase region's experimental investigation extremely challenging. Therefore, we rely on molecular dynamics to resolve the microscale and translate the obtained results into constitutive laws. This multiscale approach enables us to identify the inelastic property gradients within the interphase layer and their effect on the macroscopic behavior employing suitable representative volume elements. With these insights, we gain a better mechanical understanding of polymer nanocomposites, a prerequisite to exploiting their full potential.
[416] ID:416-AI-based design of optimal architectures for ultra-light isotropic microtruss-based metamaterials
Thibaud Derieux (CEA ParisSaclay), Daniel Bonamy (CEA ParisSaclay) and Patrick Guenoun (CEA ParisSaclay).
Abstract
Microtruss-based architectured materials offers an unprecedented range of mechanical properties, expanding their potential applications. Their remarkable stiffness-to-weight ratio has attracted significant attention in transportation research. However, in most cases, the proposed architectures are anisotropic on a large scale, making it difficult to characterize their response to fracture, in particular [1]. In our work, we designed a new class of microtruss-based metamaterials, characterized by isotropy at small scales. This led us to develop a new set of numerical tools to create such structures and their digital twins to predict each of their mechanical properties [2]. We will see that these novel microtruss-based materials of locally isotropic structures can reach an unprecedented stiffness-to-density ratio, closely approaching the theoretical upper bounds established by Hashin-Shtrikman for isotropic porous solids [3]. Conversely, they exhibit rather weak compression strength and we will discuss an on-going AI-based approach to increase this strength by introducing a complex spatial modulation of the local microbeam features (diameter, shape, constituent material…) in an appropriate manner.
References: [1] Shaikeea, A. J. D., Cui, H., O’Masta, M., Zheng, X. R., & Deshpande, V. S. (2022). The toughness of mechanical metamaterials. Nature materials, 21(3), 297-304. [2] A. Montiel, T. Nguyen, C. L. Rountree, V. Geertsen, P. Guenoun, and D. Bonamy Effect of architecture disorder on the elastic response of two-dimensional lattice materials (2022), Phys. Rev. E 106, 015004 [3] Z. Hashin, Shtrikman A variational approach to the theory of the elastic behaviour of multiphasematerials, S. J Mech Phys Solid (1963) 127e140.
[417] ID:417-Mechanochemical inhibition of growth in avascular tumours
E. Javierre (Universidad de Zaragoza), M.T. Sánchez Rua (Universidad de Vigo), F.J. Gaspar (Universidad de Zaragoza) and C. Rodrigo (Universidad de Zaragoza).
Abstract
Cancer progression is characterised by uncontrolled cell growth and changes in the mechanical properties of the extracellular matrix (ECM) of affected tissues [1]. In its avascular stage, tumour growth is strongly influenced by nutrient availability and the physical forces and stresses generated during tissue development. The role of the latter is not yet fully understood and is the subject of intense research, where the development of theoretical and computational models may help to reveal complex cues in growth dynamics [2].
In this work, we consider the tumour (and host) tissue as a porous material and address the interaction between cells, interstitial fluid and ECM through the mechanochemical coupling of cell function. We discuss the numerical solution of the resulting coupled problem and present numerical results illustrating tumour growth under free and constrained conditions.
[1] J.M. Northcott, I.S. Dean, J.K. Mouw, V.M. Weaver (2018). Feeling Stress: The Mechanics of Cancer Progression and Aggresion. Frontiers in Cell and Developmental Biology, Vol. 6:17.
[2] J.A. Bull, H.M. Byrne (2022). The Hallmarks of Mathematical Oncology. Proceedings of the IEEE, Vol. 110, pp. 523-540.
[419] ID:419-Comprehensive investigation of a sphere on plane contact using In Situ X-Ray Computed Tomography
Davy Dalmas (Laboratoire de Tribologie et Dynamique des Systèmes (LTDS)), Vito Acito (Laboratoire de Tribologie et Dynamique des Systèmes (LTDS)), Jérome Adrien (Laboratoire MATEIS) and Sylvain Dancette (Laboratoire MATEIS).
Abstract
Nowadays, to study in-situ or in operando the contact and friction behavior of an interface, measurements are mostly made through optical devices which requires the use of at least one optically transparent material and limit the analysis to only the evolution of the interface and more specially to the real contact area. Thus information outside this confined zone are most of time inaccessible. In this study, we overcame these two limits by using an X-ray Computed Tomography (XRCT). Starting from the very few pioneering studies, we adopted a more model approach to investigate by XRCT the classical laws of contact mechanics in a model sphere on plane contact. Our main objective was to examine the relationship between loading conditions, material properties, contact area and bulk deformation in 3D.
Thanks to an experimental loading device installed in a laboratory tomograph, we were able to obtain 3D images of a contact between a smooth PDMS sphere against a smooth PMMA plane for different loading conditions: pure normal loading/unloading (indentation) and shear loading under constant normal force (friction test). First, after segmentation of the 3D volumes, we extracted the evolution of real contact area and the surface displacement field of the PDMS specimen as function of the loading conditions (for indentation and friction tests). We then compared these evolutions to established experimental results and to the classical theoretical models of contact mechanics. Finally, we performed Digital Volume Correlation analysis by analyzing the displacement of dispersed particles that were inserted inside the PDMS sphere. We, thus, measured the 3D bulk displacement, strain and stress fields and compared them again with the prediction of theoretical models.
[420] ID:420-Multiphysics behaviour of photo-activated polymers for tissue bioprinting
Lorenzo Zoboli (Università Campus Bio-Medico di Roma), Daniele Bianchi (Università Campus Bio-Medico di Roma), Michele Marino (University of Rome Tor Vergata) and Alessio Gizzi (Università Campus Bio-Medico di Roma).
Abstract
Bioprinting is an advanced engineering procedure aiming at recreating a selected tissue by extruding a mixture of stem cells encapsulated in an external gel, named bio-ink, into a desired pattern. The transfer of the printed construct to a culture bath triggers cell differentiation and growth. However, prior to activating cellular processes, the gel must first be cured into a stiffer polymer construct to provide proper structural support for the cells. One of the most used techniques to achieve this is UV-induced polymerisation, whereby light interacts with the dispersed monomers in the construct and gradually transforms them into long, developed polymer chains. Many parameters regulate the interaction of the forming polymer with light: direction of incident light, exposure time, target value of the degree of conversion, the concentration of chemical species such as photo-initiators, monomers and oxygen to name a few. Since in many application fields the suitable choice of these parameters follows no standard protocols, this work intends to help in grounding their choice to a rational basis. To achieve this, the relevant Physics of what happens during the curing process is deposited has been represented through customized multiphysics Finite Element simulations, where the kinetics of polymer cross-linking has been coupled with finite deformation formulations.
[421] ID:421- Instability analysis of layered magnetoactive elastomers
Chen Xie (University of Galway), Andrei Cherkasov (University of Galway), Quan Zhang (University of Galway), Parag Pathak (University of Wisconsin – Madison) and Stephan Rudykh (University of Galway).
Abstract
Magnetoactive elastomers (MAEs) are composite materials whose mechanical behavior can be tuned by an external magnetic field. This characteristic leads to numerous applications such as soft robots, sensors, and noise barriers. This work aims to provide a guideline to actively and remotely control microstructure transformations and mechanical properties in magnetoactive soft composites by triggering magnetic-induced instabilities. For this purpose, a framework to perform instability analysis of MAEs is proposed. Specifically, take the laminates as an example, numerical and analytical models of layered MAEs with soft/hard magnetic inclusions are developed based on the finite element method and classical magneto-elasticity theory. Buckling and post-buckling analysis are performed to predict the onsets of instabilities at the microscopic and macroscopic length scales. Based on the established models, we obtained the relationships between critical stretch (critical wavelength) and magnetic field level. Further, we have studied the effect of volume fraction, additional invariants, and initial susceptibility on the onset of magneto-mechanical instabilities.
[423] ID:423-Characterising and Modelling the Rate Dependent Mechanical Response of 3D-Fabric Reinforced Composites
Carolyn Oddy (Chalmers University of Technology), Filippo Panteri (KTH Royal Institute of Technology), Adeline Kullerstedt (GKN Aerospace) and Sibin Saseendran (GKN Aerospace).
Abstract
As their name suggests, 3D-fabric reinforced composites, are manufactured by intertangling yarns together in three-dimensional space to create a near-net-shape dry fabric preform. After infusing this preform with a resin matrix system, a light-weight component is created which demonstrates both high in- and out-of-plane stiffness and strength. The through-thickness reinforcements present in this material class, prevent delamination and allow for stable and progressive damage growth in a quasi-ductile manner.
Composites with 3D-fabric reinforcement present several advantages, both in terms of their manufacturing and mechanical performance. However, the woven yarn structure creates a material with a number of interesting behaviours and features which need to be accounted for when developing a model to predict how the material will deform and eventually fail. To begin with, these materials are highly anisotropic and show varying levels of non-linearity depending on loading mode. This non-linearity can be due to a variety of subscale behaviours: microcracking in the matrix or fibre-bundles, yarns straightening and fibres breaking and viscous effects from the polymer matrix.
One of the big questions when working with this class of materials is then; what is causing the non-linear behaviours and how can they be modelled in a physically meaningful way. For this reason, a testing campaign initially proposed by Zscheyge et al. (2020) for laminated composites is carried out in this work. It involves cyclically loading and unloading test samples at different orientations with creep and relaxation period in between. From a single test, it is then possible to determine how permanent strains, stiffness degradation and rate dependence develop as the deformation increases. A phenomenologically based macroscale model is then developed and presented. It considers the material as a homogenous and anisotropic solid. The experimental tests results are used to formulate and calibrate an anisotropic viscoplastic-damage model for 3D-fabric reinforced composites
[425] ID:425-Laser powder bed fusion of NiTi alloy parts for cardiovascular applications
Oscar Contreras-Almengor (IMDEA Materials Institute), Carlos Aguilar (Universidad Politécnica de Madrid), Rodrigo Zapata (Universidad Politécnica de Madrid), Muzi Li (IMDEA Materials Institute), Andrés Díaz Lantada (Universidad Politécnica de Madrid) and Jon Molina-Aldareguia (Universidad Politécnica de Madrid).
Abstract
Shape memory alloys (SMA) offer unique shape memory (SME) or superelastic (SE) effects that have attracted the interest of different industrial sectors, such as aerospace, automotive, robotics, and biomedical devices. NiTi, also called nitinol, is the most extensively used SMA in the biomedical field due to its excellent biocompatibility, corrosion resistance and mechanical properties, especially in manufacturing self-expandable cardiovascular devices. However, current methods for manufacturing NiTi-based cardiovascular devices only allow for simple geometries and prevent the manufacturing of patient-specific personalized devices. In recent years, laser powder bed fusion (LPBF) has emerged as an additive manufacturing technique that should allow both the production of complex-shaped and custom-made NiTi devices. In order to manufacture different devices for cardiovascular applications, two types of NiTi composition have been used to achieve the two properties of superelasticity and shape memory. To do this, the process parameters were optimized to obtain the maximum density of the part and draw a graph where the optimal printing area can be observed. These process parameters were employed for the manufacture of cardiovascular devices. The design of different stent models has been tested in axial and radial compression to evaluate how it influences their mechanical properties.
[426] ID:426-Data-driven games in elastic materials
Kerstin Weinberg (Universität Siegen), Laurent Stainier (EC Nantes) and Michael Ortiz (California Institute of Technology).
Abstract
In the data-driven mechanics, the constitutive material modeling is eluded, and data are directly employed as an input for finite-element analysis instead. Here we resort to game theory in order to formulate Data-Driven methods for solid mechanics in which stress and strain players pursue different objectives [1]. The objective of the stress player is to minimize the discrepancy to a material data set, whereas the objective of the strain player is to ensure the admissibility of the mechanical state, in the sense of compatibility and equilibrium.
Unlike the cooperative Data-Driven games proposed in the past, the new non-cooperative Data-Driven games identify an effective material law from the data and reduce to conventional displacement boundary-value problems, which facilitates their practical implementation. In particular, the effective material law is directly learned from the data, without recourse to regression to a parameterized class of functions such as neural networks. We present selected examples of implementation and application that demonstrate the versatility of the approach.
[1] K. Weinberg, L. Stainier, S. Conti, M. Ortiz: Data-Driven games in computational mechanics, Computer Methods in Applied Mechanics and Engineering, Volume 417, 2023, 116399, doi.org/10.1016/j.cma.2023.116399
[427] ID:427-Characterising the effect of void morphology on composites strength using deep learning
Iryna Tretiak (Bristol Composites Institute) and Bassam El Said (Bristol Composites Institute).
Abstract
Voids are one of the most common, and arguably most critical, manufacturing defects in composites. They are difficult to avoid and detrimental to composite performance. Research has indicated that void morphology significantly influences failure, but difficulties in understanding these influences has resulted in industry implementing conservative part rejection criteria based on average void content. To maximise material utilisation, and reduce material waste, it is crucial to adopt an approach that takes these factors into account when assessing the impact of voids on composite strength. Currently, finite element (FE) methods are widely employed to predict the performance of laminates with voids. FE modelling of samples with voids can be at the micro-scale or meso-scale, and is generally computationally expensive due to the need for refined meshes around voids. In this study, deep learning, specifically convolutional neural networks (CNN), was applied to experimental data in order to predict the short beam shear strength of the composite materials with voids. A total of 230 samples were manufactured using two commonly used material systems (Hexcel’s IM7/8552 and IMA/M21). All samples were CT-scanned prior to testing. Two CNN approaches were investigated: the first approach involved deep CNN networks with varying architectures and complexities, the second approach involved CT-Scan parametrisation using autoencoders that are subsequently coupled with a Gaussian Process surrogate to predict material strength. Several parameters were analysed to optimise the performance of the CNN, including learning rate, mini-batch size and CT-Scan resolution. A 5-Fold cross-validation approach was used to evaluate the network performance, and the results demonstrated that deep learning holds significant potential in strength prediction of composites with voids.
[428] ID:428-Elastic Instability in Soft Particulate Composites with Stiffening Behavior
Janhavi Anilkumar Tarale (School of Mathematical and Statistical Sciences, University of Galway, Ireland), Dean Chen (Department of Mechanical and Aerospace Engineering, University of California-Los Angeles, United States.) and Stephan Rudykh (School of Mathematical and Statistical Sciences, University of Galway, Ireland).
Abstract
We investigate instability-induced patterns in soft particulate composites under finite strains. Soft material can exhibit stiffening at finite deformations. In turn, this material nonlinearity influences the elastic instabilities and the subsequent development of buckling patterns. In our study, we employ the Gent model to analyze and illustrate the behaviour of soft particulate composites. This model uses a single locking parameter (Jm) to adjust the stiffness of the soft material. We illustrate how the inhomogeneous deformation, together with the deformation-induced stiffening of the matrix, influences the instability characteristics, such as critical wavelength and critical strain. The inhomogeneous deformation gives rise to two particulate systems, resulting in stabilization at lower aspect ratios. Notably, we observe that this stabilization becomes more significant with variation in stiffness.
With higher Jm values, the composite’s behaviour closely aligns with the neo-Hookean model. Conversely, a decrease in Jm leads to earlier buckling, especially at larger aspect ratios, while interestingly, for lower aspect ratios, this buckling occurs later than in the case of larger aspect ratios. Furthermore, we find that the stabilization effect for lower aspect ratios becomes more prominent with lower values of Jm. Finally, our results reveal that the material stiffening, associated with decreasing Jm, does not consistently lead to earlier buckling due to the influence of nonlinearity in the strain field.
[429] ID:429-Agglomerate crack propagation under micro-compression as seen by phase-contrast tomography
Jean-Philippe Bayle (CEA), Antoine Egèle (Institut Charles Sadron, Université de Strasbourg, C.N.R.S., UPR22, 23 rue du Loess 67034 Strasbourg, France), Damien Favier (Institut Charles Sadron, Université de Strasbourg, C.N.R.S., UPR22, 23 rue du Loess 67034 Strasbourg, France), Timm Weitkamp (Synchrotron SOLEIL, Saint-Aubin, L’Orme des Merisiers, 91190 Saint-Aubin, France), Laure Ramond (CEA) and Patrick Kekicheff (Institut Charles Sadron, Université de Strasbourg, C.N.R.S., UPR22, 23 rue du Loess 67034 Strasbourg, France).
Abstract
The context of this study is an investigation for understand agglomerates breakage mechanisms. To do that, experimentations based on agglomerate micro-compressions on tomograph in Anatomix X ray beam line synchrotron Soleil has been carry out. This study is the result of a collaboration between Strasbourg University (Unistra), Anatomix beam line (Soleil synchrotron) and atomic energy office (CEA) teams. These teams pooled their skills for these investigations. The results are in agreement to Kendall’s theory, which argued that the fracture of granule is a consequence of crack nucleation at flaws leading to subsequent crack propagation through the granular structure. The 340µm agglomerate diameter was investigated by one-way cyclic micro-compression test and other agglomerates with a simple load and unload cycle until breakage have been tested. The tomographic post-treatments have enabled the porosities volumes and surfaces created after breakage, the origin of the main crack and its propagation,
[430] ID:430-Understanding the grain boundary sliding in Ni bicrystal via micromechanical testing
Divya Sri Bandla (Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany), Subin Lee (Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany) and Christoph Kirchlechner (Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany).
Abstract
It has been widely accepted that in polycrystalline materials at high temperatures, low strain rates, and small grain sizes, grain boundary sliding dominates other deformation mechanisms. The grain boundary sliding often leads to stress concentration at grain boundary triple junction points which should be relieved to promote the sliding further. Because grain boundary sliding is a complex phenomenon which depends on material, grain boundary type, testing temperature, and likely, defects at the grain boundary, a quantitative understanding of grain boundary sliding is still missing. In this talk, we present temperature-dependent grain boundary sliding behavior in Ni bicrystal quantified by using in situ SEM micropillar compression. The orientation of crystals is close to <344> and <324> with a high angle grain boundary in between with a misorientation of ~ 20°. Micropillar compression tests performed on the pillars of diameter from 0.5 µm to 6 µm showed a mechanical size effect in both the crystals with a size exponent of ~ -0.5. Bicrystal micropillars are also tested which contain a 45° inclined grain boundary at the elevated temperature. In the talk, details on the experimental protocol as well as first insights into the size- and temperature-dependency of grain boundary sliding will be presented and discussed.
[431] ID:431-The inclusion of the epithelium in numerical models of the human cornea
Anna Pandolfi (Politecnico di Milano) and Andrea Montanino (Universita' di Napoli Federico II).
Abstract
We present a patient-specific finite element model of the human cornea that accounts for the presence of the epithelium. The thin anterior layer that protects the cornea from the external actions has a scant relevance from the mechanical point of view and it has been neglected in most numerical models of the cornea, which assign to the entire cornea the mechanical properties of the stroma. Yet, modern corneal topographers capture the geometry of the epithelium, which can be naturally included into a patient-specific solid model of the cornea, treated as a multi-layer solid. For numerical applications, the presence of a thin layer on the anterior cornea requires a finer discretization and the definition of two constitutive models (including the corresponding properties) for stroma and epithelium. In this study we want to assess the relevance of the inclusion of the epithelium in the model of the cornea, by analyzing the effects in terms of uncertainties of the mechanical properties, stress distribution across the thickness, and numerical discretization. We conclude that if the epithelium is modelled as stroma, the material properties should be reduced by 10\%. While this choice represents a sufficiently good approximation for the simulation of in-vivo mechanical tests, it might result into an underestimation of the postoperative stress in the simulation of refractive surgery.
[433] ID:433-Developing Hydrogen-Assisted Fracture Testing of Alloys
Livia Cupertino Malheiros (Imperial College London).
Abstract
A wide range of commonly used metals and alloys are susceptible to hydrogen embrittlement (HE), which currently limits the design of structures in many industrial sectors, notably energy and transportation. HE is strongly related to hydrogen interactions with the metal lattice structure and its crystallographic defects, such as interfaces, dislocations, second-phase particles and vacancies, as well as local mechanical states (hydrostatic stress and/or plastic strain). Therefore, understanding the underlying mechanisms of hydrogen-assisted fracture requires fit-for-purpose testing methodologies capable of capturing the specificities of the fracture mechanisms of each alloy-hydrogen system. This work shows recent developments in fracture testing for hydrogen-assisted intergranular cracking in nickel and hydrogen-assisted fracture of pipeline steels. The results provide new insights into the threshold conditions that determine the HE fracture mode and the preferred cracking path as a function of hydrogen concentration, depending on the hydrogen-containing environment to which the alloys are exposed to.
[434] ID:434-Capturing fatigue crack propagation of isotactic polypropylene: effects of temperature and molecular weight
Sten van den Broek (Eindhoven University of Technology), Tom Engels (Eindhoven University of Technology) and Leon Govaert (Eindhoven University of Technology).
Abstract
Isotactic polypropylene is one of the most used semi-crystalline polymers due to its low cost, ease of processing and versatile mechanical properties. In long-term applications, one of the key properties is the resistance against fatigue crack propagation (FCP), i.e. the resistance to the growth of small initial flaws that ultimately trigger failure. The resistance against FCP in polypropylene is, however, not systematically studied in literature or well understood. Therefore, in this study, we present an overview of the FCP in polypropylene as a function of both temperature and molecular weight and relate the observed performance to the local fibril deformation mechanisms active at the crack tip. To measure the FCP, Compact Tension samples were combined with an image acquisition setup to measure the crack length in-situ over time. From the measured crack length a, the stress intensity factor K_I and the crack growth rate da/dt are determined. Combined these give the crack growth kinetics described by a Paris law; and are defined by a pre-factor A and slope m according to: da/dt=A⋅(K_I⋅(a))^m. Experiments conducted over a range of temperatures reveal that the slope m varies with temperature which has not been observed for, e.g., polyethylene. Additional experiments conducted at different frequencies and load ratios show that at high temperatures the FCP is insensitive to frequency and decelerates with decreasing load ratio, suggesting a fibril disentanglement mechanism is dominant, whereas at low temperatures the FCP becomes frequency dependent and accelerates with decreasing load ratio, suggesting a fibril buckling mechanism becoming dominant. The transition between these two mechanisms depends on the molecular weight of the material. Remarkably, temperature superposition can be successfully applied to the range of molecular weights. These observations enable us to uniquely model the FCP behaviour in polypropylene as a function of molecular weight, temperature, load ratio and frequency.
[435] ID:435-Fracture toughness of hierarchical lattices
Akseli Leraillez (Aalto university) and Luc St-Pierre (Aalto University).
Abstract
Previous studies have consistently demonstrated that incorporating hierarchy into lattices can significantly enhance their mechanical properties. Many biological materials, known for their exceptional fracture toughness possess a hierarchical architecture. This work introduces hierarchy to three topologies (hexagonal, Kagome, and triangular) by incorporating a finer length scale triangular lattice. Our study quantifies the mode I fracture toughness through finite element simulations employing the boundary layer method. Additionally, analytical predictions are provided to explain the effect of hierarchy on fracture toughness. The findings indicate that hierarchy significantly improves the fracture toughness of bending-dominated lattices. The hierarchical hexagonal lattice exhibits superior fracture toughness compared to the simple hexagonal lattice. Notably, the fracture toughness of the hierarchical hexagonal lattice scales linearly with the relative density, while the fracture toughness of the simple hexagonal lattice scales as relative density squared. Stretching-dominated lattices did not benefit from introducing hierarchy. The numerical and analytical predictions were in good agreement, offering a comprehensive explanation of the advantages offered by a hierarchical design.
[436] ID:436-Phase Field Fracture in 3D Printed Fibre Reinforced Composites Using Virtual Elements
George Pissas (National Technical University of Athens) and Savvas Triantafyllou (National Technical University of Athens).
Abstract
Additively manufactured fiber-reinforced components (FRC) rapidly gain traction in the European aerospace and transport industry. This is attributed to their well-established benefits, including reduced machine, material, and labor costs, minimized manufacturing waste, and the utilization of more efficient materials. Despite these advantages, a notable drawback of additively manufactured components lies in their intricate and often tessellated geometry. This complexity gives rise to combined damage mechanisms, such as fiber pull-outs and matrix cracking, deviating from the conventional paradigm of "high strength and ductile metal". To address this challenge, the phase-field method emerges as a robust approach for damage modeling, offering capabilities to accurately resolve the initiation, propagation, branching, and merging of complex curvilinear crack topologies.
In this work, we revisit the cohesive phase-field model introduced in [Geelen, 2019] for isotropic domains and extend it to resolve intra-laminar damage response in 3D printed FRCs. The damage model incorporates a linear crack-surface density functional, exhibiting pure-elastic behavior until damage onset, and a quasi-quadratic degradation function which can be used to calibrate experimental strain softening curves, thereby accurately predicting quasi-brittle damage response in FRC.
The resulting coupled governing equations are discretized using the Virtual Element Method (VEM). It has been shown that the use of polygonal virtual elements achieves higher order FEM convergence [Aldakheel, 2018] in reduced computational costs. Furthermore, with its ability to handle irregular and complex geometries, the VEM addresses the challenges posed by the intricate and tessellated structures inherent in additively manufactured components. This integration holds the potential to optimize the discretization process, overcoming limitations associated with finer mesh requirements and mitigating the computational costs associated with conventional methods. The effectiveness and robustness of the combined methodology is explored within the context of 2D deformable domains and comparison is conducted between numerical models employing either quadrilateral/triangular meshes or polygonal meshes.
The research work was supported by the funding received in the framework of H.F.R.I call “Basic research Financing (Horizontal support of all Sciences)” under the National Recovery and Resilience Plan “Greece 2.0” funded by the European Union –NextGenerationEU (H.F.R.I. Project Number: 15097).
[437] ID:437-Neural Operator-Driven Analysis of Heterogeneous Microstructures: Mechanical and Thermal Behaviors
Ali Harandi (RWTH Aachen University), Shahed Rezaei (Access e.V.), Yusuke Yamazaki (Graduate School of Science and Technology, Keio University), Pranav Shettigar (RWTH Aachen University), Tim Brepols (RWTH Aachen University) and Stefanie Reese (RWTH Aachen University).
Abstract
This study presents an innovative approach using physics-informed neural operators to create a universal surrogate model. Our focus is on accurately predicting the mechanical behavior of heterogeneous microstructures under a given set of boundary conditions, considering different heterogeneity patterns and phase contrast ratios. We explore different architectures of neural operators and evaluate their effectiveness both with and without the presence of labeled data. A significant achievement of our work is the ability of the network to reliably predict unseen cases, especially in the context of periodic boundary conditions. The model efficiently computes the homogeneous stress tensor, essential for two-scale calculations. We extend our methodology to solve the steady-state heat equation in microstructures with varying conductivity ratios, demonstrating the versatility of our approach. On the one hand, deep neural operators are used, which condense the information of the microstructures through a branch network and evaluate the solution at a given point to the trunk network. On the other hand, a novel integration of operator learning with finite elements is presented. This method solves boundary value problems by minimizing the discretized weak form, exploiting the strengths of the finite element method. We show that the trained neural operator significantly reduces the solution evaluation time compared to traditional methods such as finite element analysis, without compromising accuracy for any arbitrary shape of microstructures. This work opens new avenues for efficient microstructural analysis in materials science.
[438] ID:438-Modeling Self-oscillation in Immersed Liquid Crystal Elastomer Beams under Constant Light: A Multi-physics Approach
Reza Norouzikudiani (The BioRobotics Institute, Scuola Superiore Sant’Anna, Pontedera, Italy), Luciano Teresi (Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Roma, Italy) and Antonio DeSimone (The BioRobotics Institute, Scuola Superiore Sant’Anna, Pontedera, Italy).
Abstract
Liquid crystal elastomers (LCEs) represent a class of responsive materials capable of substantial and reversible deformations when subjected to external stimuli, such as light. These materials hold promise for advancing propulsion systems, particularly in emulating cilia-like motions. Hence, understanding the fundamental physics governing their dynamic response within a fluid medium under light exposure is crucial for optimizing their shape and augmenting their performance. In this study, we've developed a multi-physics fluid-structure interaction model in COMSOL software to explore the self-oscillation phenomenon of an LCE beam immersed in a fluid and subjected to illumination. The beam is clamped at one end and exposed locally to constant-intensity light near the fixed edge. Upon illumination, the LCE beam bends towards the light source due to temperature gradient along its thickness. As it surpasses the vertical position due to inertia, a self-shadowing effect is triggered, leading to cooling of the system. Despite energy dissipation from drag forces, the negative feedback resulting from self-shadowing injects energy into the system, initiating the self-oscillation phenomenon. Our investigation involves parametric studies exploring the impact of beam length, Young’s modulus, and light intensity on the oscillation's amplitude and frequency under illumination. Our findings indicate that shorter lengths or higher stiffness induce oscillations in the beam with the first mode of vibration. Conversely, longer lengths or reduced stiffness trigger the second mode of vibration. Additionally, applying higher light intensity increases the frequency of oscillation.
[440] ID:440-Multi-objective shape optimisation of periodic lattices
Farooq I Azam (University College London), Pj Tan (University College London) and Federico Bosi (University College London).
Abstract
The advancement of lattice materials has recently gained significant traction through the application of reduced-scale additive manufacturing techniques. These fabrication methods enable precise manipulation of geometrical features at both the micro and nanoscales, offering control over macroscopic properties and facilitating the production of lattices with exceptional mechanical characteristics. Architected materials, characterized by heightened stiffness and an impressive strength-to-weight ratio, have found widespread utility in high-strength lightweight materials, energy storage applications, and various other fields. While conventional periodic lattices typically rely on unit cells featuring struts with uniform cross-sections, a strategic redistribution of material along the strut length holds promise for enhancing the material's mechanical response, particularly in bending-dominated topologies [1].
In this investigation, we scrutinize 2D periodic lattices, bending and stretch dominated, aiming to quantify the impact of solid distribution on their mechanical properties. Employing a combination of analytical calculations, finite element modelling, and Genetic Algorithm techniques, we conduct multi-objective optimization of the strut shape to maximize stiffness, yield, and buckling strength. Multiple strategies of redistributing the material along the strut are assessed while benchmarking against the regular-shaped lattices. The unit cell is subjected to diverse loading conditions, and we assess how relative density and material redistribution influence the location of plastic hinge formation and the transition between plastic failure and buckling. Periodic lattices with optimized topologies are fabricated at finite sizes and subjected to experimental testing to validate the predictions of the theoretical models.
REFERENCES [1] Simone AE, Gibson LJ. Effects of solid distribution on the stiffness and strength of metallic foams. Acta Materialia 1998; 46: 2139-50.
[441] ID:441-Atomistic-to-continuum coupled simulations for fracture of glassy polymers with non-uniform deformations
Wuyang Zhao (Friedrich-Alexander-Universität Erlangen-Nürnberg) and Sebastian Pfaller (Friedrich-Alexander-Universität Erlangen-Nürnberg).
Abstract
Fracture in glassy polymers involves the rearrangement of atoms or the breakdown of covalent bonds, which cannot be accessed by experiments. At atomistic scales, molecular dynamics (MD) simulations are appropriate tools to reveal the physical mechanisms of fracture behavior. Various studies have been conducted on the fracture of polymers using MD simulations. However, most of them consider MD systems with uniform deformations at the boundaries, resulting in a limited size for the process zone during fracture. Due to the limitation of the total system size constrained by prohibitive computational costs, these studies neglect the effects of non-uniform deformations, which are, however, crucial in determining the fracture behavior of glassy polymers.
To overcome this, we consider an atomistic-to-continuum coupled system with an MD domain with non-periodic boundary conditions surrounded by a continuum domain solved by the Finite Element method. The continuum domain interacts with the MD domain in their overlapping region to provide appropriate boundary deformation conditions. The coupling is implemented through energy blending and the constraint of deformation consistency in the overlapping region. The constitutive model in the continuum domain is predefined to reproduce the bulk behavior in MD simulations. With this coupling method, we conducted fracture simulations for a sample of coarse-grained polystyrene with pre-cracks and aimed to extract the relation between the microscopic structure and the macroscopic behavior.
[442] ID:442- In-process alteration of Ti6Al4V microstructure during additive manufacturing
K.Abdellah Abdesselam (Laboratoire de Mécanique des Solides, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France), Steve Gaudez (PEM, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland), Steven Van Petegem (PEM, Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland), Veijo Honkimaki (European Synchrotron Radiation Facility, 71 Avenue des Martyrs, CS40220, F-38043 Grenoble Cedex 9, France) and Manas Upadhyay (Laboratoire de Mécanique des Solides, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France).
Abstract
The aim of this study is to investigate the potential of in-process laser heat treatment during additive manufacturing of Ti-6Al-4V in order to control the quantities of α'/α and β phases during building. The eventual goal is to study the potential of such in process laser treatments to replace costly and time-consuming post building heat treatments.
Operando synchrotron X-ray diffraction was carried out at the ID31 beamline of the European Synchrotron Radiation Facility (ESRF, France) during laser metal deposition (LMD) of Ti6Al4V using a miniature LMD machine [1]; in order to monitor the evolution of phases and their quantities during the printing process and during laser heat treatments steps.
Scanning electron microscopy was used to analyse the microstructures of non-heat-treated and heat-treated samples in order to obtain information on the different effects of such heat treatments i.e. phase morphologies and to differentiate between the α’ and α phase content.
This study aims to provide insight into the phase transformations that occur during printing, as well as the evolution of phase fractions as a function of time and the number of added layers. Additionally, the study aims to give understanding into the effect of such in process heat treatments on the quantity and morphology of the phases.
[1] S. Gaudez, K. A. Abdesselam, H. Gharbi, Z. Hegedüs, U. Lienert, W. Pantleon and M. V. Upadhyay, High-resolution reciprocal space mapping reveals dislocation structure evolution during 3D printing, Additive Manufacturing, Volume 71, 2023. DOI: https://doi.org/10.1016/j.addma.2023.103602
[443] ID:443- Homogenization of composite materials with fractional viscoelastic constituents
Patricia Vernier (Sorbonne Université, CNRS, Institut Jean-Le-Rond d'Alembert, 75005 Paris, France) and Renald Brenner (Sorbonne Université, CNRS, Institut Jean-Le-Rond d'Alembert, 75005 Paris, France).
Abstract
Fractional viscoelastic constitutive laws are expressed by differential equations involving derivative operators of non-integer order. This formalism allows to take into account long-memory effects that are experimentally observed in materials like polymers, ice or foams. In this talk, we address the homogenization of composite materials with such phases by means of an incremental variational approach. Specifically, we make use of the Effective Internal Variable (EIV) method, developed by Lahellec and Suquet, 2007. The EIV method was successfully applied to classical viscoelastic constituents (Tressou et. al., 2018), and is particularly attractive compared to the commonly used correspondence principle as it provides the fluctuations of the fields. This homogenization method relies on the Generalized Standard Materials framework in which the dissipative materials are entirely described by means of two convex thermodynamic potentials. Contrary to classical viscoelasticity, these thermodynamic potentials are not straigtforwardly expressed, but are obtained through the rheological interpretation of any fractional viscoelastic constituent as a generalized Maxwell model. We thus take advantage of the extension of the EIV method for several internal variables developed by Tressou et. al, 2023. Regarding the individual constituents, the distribution of the characteristic times is explicitely given by the expression of the fractional viscoelastic spectrum, thus they can be appropriately chosen by following the discretization procedure developed by Papoulia et. al, 2010. In order to consider fractional Zener constituents, we extend this discretization method to the Mittag-Leffler function. In this work, we consider a fractional Zener matrix reinfoced with elastic inclusions subject to a harmonic loading and compare our results with FFT-based computations.
[444] ID:444-Micromechanically-based computational modelling of ductile solids incorporating non-uniform void size distributions
Lars Edvard Blystad Dæhli (Norwegian University of Science and Technology (NTNU)), David Didier Morin (Norwegian University of Science and Technology (NTNU)) and Odd Sture Hopperstad (Norwegian University of Science and Technology (NTNU)).
Abstract
Ductile fracture of structural metal alloys is commonly associated with the nucleation, growth, and coalescence of microscopic voids. In high-strength 6000-series aluminium alloys, the iron-rich constituent particles formed during solidification are often responsible for failure initiation. The constituent particles have various shapes and sizes, ranging from less than one to several micrometres. Micromechanics-based numerical studies are usually based on unit cell simulations where the microstructure is idealized as a spatially uniform distribution of equal-sized voids. However, unit cell models cannot account for effects emerging due to varying particle sizes that could be significant for strain localization and ductile failure. The current work is devoted to examining how the heterogeneity due to realistic particle size distributions influences the failure strains predicted using micromechanics-based models. To this end, we conduct finite element simulations using models containing many voids sampled from a log-normal size distribution. Statistically representative void samples cannot be resolved in 3D finite element models. Assuming that the voids are regularly spaced, a cost-effective modelling alternative is to describe each by a porous plasticity model. The validity of this approximation is assessed by comparison with simulations of models where the voids are spatially resolved. Consequently, simulations of 2D plane strain models containing many voids are conducted using both modelling approaches. The simulations exhibit a large variation in the macroscopic response after peak stress due to the void size-induced heterogeneity. Failure is expedited and there is less variation in failure strain when more voids are included. A key result is that the models using a homogenized void description give similar results as simulations using spatially resolved voids while reducing the computational runtimes by several orders of magnitude. This opens for 3D simulations of microstructures with statistically representative particle size distributions.
[445] ID:445-Dynamic phase-field fracture with a first-order discontinuous Galerkin method for elastic waves
Christian Wieners (Karlsruhe Institute of Technology).
Abstract
We present a new numerical method for dynamic fracture at small strains which is based on a discontinuous Galerkin approximation of a first-order formulation for elastic waves and where the fracture is approximated by a phase field driven by a stress based fracture criterion. The staggered algorithm in time combines the implicit midpoint rule for the wave propagation followed by an implicit Euler step for the phase field evolution. Then, driven by the fracture criterion, the material is degradated, and the waves are reflected at the diffusive interface. We demonstrate in 2D and 3D applications the dynamic fracture evolution with multiple fractures initiated by reflections.
Then we discuss the extension to visco-elastic materials and different energy based elastic driving forces. Here we show that the first-order approach extends to visco-elastic materials and remains stable also in the limit of very small viscosity.
Finally, the phase field approximation of wave-induced fracture phenomena is compared with results obtained by continuum-kinematics-based peridynamics.
Weinberg, K. and Wieners, C. (2022): Dynamic phase-field fracture with a first-order discontinuous Galerkin method for elastic waves. Computer Methods in Applied Mechanics and Engineering, 389, 114330.
Partmann, K., Wieners, C. and Weinberg, K. (2023): Continuum-kinematics-based peridynamics and phase-field approximation of non-local dynamic fracture. International Journal of Fracture, 244(1), 187-200.
[446] ID:446-Understanding stress-plastic strain evolution of AM 316L steel microstructures due to post process laser scanning: experiment-driven thermomechanical study
Nikhil Mohanan (Laboratoire de Mécanique des Solides, CNRS UMR 7649, Ecole Polytechnique, IPP, Route de Saclay, 91128 Palaiseau Cedex), Juan Guillermo Santos Macías (IMDEA Materials Institute, Eric Kandel 2, Tecnogetafe - Getafe 28906), Jeremy Bleyer (Laboratoire Navier, CNRS UMR 8205, Ecole des Ponts ParisTech, Université Gustave Eiffel, 77455 Marne-la-Vallée Cedex 2), Thomas Helfer (CEA, DEN/DEC/SESC, Cadarache, Saint-Paul-lez-Durance) and Manas V. Upadhyay (Laboratoire de Mécanique des Solides, CNRS UMR 7649, Ecole Polytechnique, IPP, Route de Saclay, 91128 Palaiseau Cedex).
Abstract
In recent years, additive manufacturing (AM) has shown immense potential towards applications in the field of automotive, aerospace, biomedical, energy, etc., owing to its efficient material usage and ability to rapidly prototype metallic parts of any shape. However, the action of extreme thermal loads generates significant residual stresses that impact the mechanical response and failure of these parts.
This study proposes an experiment-driven modelling and simulation approach to understand the origin and formation of intergranular residual stresses and localization of plastic strain during post-process laser scanning of an AMed stainless steel.
Using a novel coupling between a continuous-wave laser and a scanning electron microscope, a series of single-scan laser scanning experiments were performed on AM 316L stainless steel microstructures. Detailed analysis revealed refinement of cellular microstructure, formation of misorientation bands, and hence, geometrically necessary dislocations (GNDs) within the lasered zone.
This information was used to guide the development of a polycrystalline thermo-elasto-viscoplastic finite element (TEVP-FE) model in small-strain framework to understand the evolution of intergranular stresses and plastic strains. The model predicted polar dislocation density distribution was compared with the experimentally measured one. The role of laser scanning induced microstructure refinement, elastic anisotropy and plastic heterogeneity on the formation of local residual stresses and plastic strains was then analysed. These results will be presented in this talk.
[448] ID:448-Machine Learning for Structure-from-Property Guided Microstructures Optimization and Process Design
Tarek Iraki (Forschungszentrum Juelich GmbH, Institute for Advanced Simulations (IAS-9)), Lukas Morand (Fraunhofer-Institut für Werkstoffmechanik IWM), Stefan Sandfeld (Forschungszentrum Juelich GmbH, Institute for Advanced Simulations (IAS-9)), Norbert Link (Hochschule Karlsruhe – University of Applied Sciences (HKA)) and Dirk Helm (Fraunhofer-Institut für Werkstoffmechanik IWM).
Abstract
In the sense of the process-structure-property chain, to add value to the development of new advanced materials, materials design approaches must be tailored to support downstream optimal processing approaches. In this contribution, we combine recently developed data-driven machine learning-based approaches to address two critical identification problems: (1) a materials design problem, which identifies near-optimal material microstructures for desired properties, and (2) a process design problem, that aims to guide manufacturing processes to produce identified microstructures. Both identification problems are ill-posed inverse problems and are therefore, typically non-unique (i.e., more than one solution exists). This offers an advantage which is leveraged in the machine learning-based approaches to guide the underlying manufacturing process efficiently to produce the best reachable microstructures. The approaches presented are demonstrated at the example of a simulated metal forming process, aiming to optimize crystallographic texture.
[449] ID:449-A nonlinear variational model of cracks and dislocations
Godefroy Engrand (1 : Université Paris-Saclay, ONERA, CNRS, Laboratoire d’Etude des Microstructures, 92320 Châtillon, France.), Antoine Ruffini (1 : Université Paris-Saclay, ONERA, CNRS, Laboratoire d’Etude des Microstructures, 92320 Châtillon, France.), Yann Le Bouar (1 : Université Paris-Saclay, ONERA, CNRS, Laboratoire d’Etude des Microstructures, 92320 Châtillon, France.) and Alphonse Finel (1 : Université Paris-Saclay, ONERA, CNRS, Laboratoire d’Etude des Microstructures, 92320 Châtillon, France.).
Abstract
In crystalline materials, fracture is often coupled with plastic activity. A comprehensive mesoscale modeling of fracture should therefore incorporate crack propagation and its interplay with dislocation multiplication and glide.
Both cracks and dislocations are associated with discontinuities in the displacement field. Therefore, it should be possible to construct a model based only on the displacement field. This requires the identification of a nonlinear elastic energy functional that is invariant with respect to the point group of the lattice, but also with respect to any shear deformation that leaves the lattice invariant.
In this talk, we show how to construct this infinitely degenerate potential energy and discuss the numerical implementation of the model. Finally, we present simulation results that reproduce the nucleation and propagation of dislocations in a potentially cracked crystalline system.
[450] ID:450-Geometric and Constitutive Modeling of MgO-C Refractories Based on Recyclates for Thermo-Mechanical Simulations: Influence of Graphite Flakes
Jishnu Vinayak Gopi (TU Bergakademie Freiberg), Stephan Roth (TU Bergakademie Freiberg) and Bjoern Kiefer (TU Bergakademie Freiberg).
Abstract
Refractories are polycrystalline, porous, heterogeneous, non-metallic materials utilized as protective liners in high-temperature manufacturing processes. Microscopic and mechanical characterization studies of MgO-C refractories in the literature show a strong correlation between the underlying microstructure and the thermo-mechanical response of these materials. The present study focuses on developing a simulation tool that assesses the behavior of recycled refractory composites, specifically the influence of microstructural features on their thermal shock resistance. Experimental findings show that the anisotropic behavior of graphite flakes and their preferred orientation significantly influence the mechanical properties of MgO-C refractories. In contrast to prior modeling methodologies, the heterogeneous microstructure of MgO-C in this approach is conceptualized as a three-phase composite by explicitly modeling the graphite phase along with coarse magnesia aggregates and a homogenized matrix. A pre-processing tool is developed to synthetically generate this idealized 2D microstructure representation from statistical data, utilizing open-access Python packages [1]. According to the current hypothesis and experimental findings, the principal mechanism of damage in these materials involves the debonding of phase interfaces due to thermally-induced stresses. Consequently, this interface damage is modeled using the cohesive zone approach [2]. Basic thermal shock simulations are performed employing the synthetic microstructures to investigate the influences of thermal expansion coefficient mismatches and thermal gradients on the local interface damage. Furthermore, a sensitivity study is presented to analyze the influence of the graphite flake orientation and volume fraction on the thermal shock resistance of these refractory composite materials.
[1] K. A. Hart and J. J. Rimoli. Generation of statistically representative microstructures with direct grain geometry control. Computer Methods in Applied Mechanics and Engineering, 370, 2020.
[2] M. Kuna and S. Roth. General remarks on cyclic cohesive zone models. International Journal of Fracture, 196, 11 2015.
[451] ID:451-Numerical simulation and R-curves computation of CFRP Compact Tension tests using the Discrete Ply Model
Romain Rutar (ISAE-SUPAERO), Christophe Bouvet (ISAE-SUPAERO) and Joel Serra (ISAE-SUPAERO).
Abstract
Efficient and accurate failure modelling of composite materials is crucial due to their extensive use in the industry. Specifically, simulating translaminar failure, such as Compact Tension (CT) tests using Finite Element analysis has proven to be particularly challenging. This study applies the mesoscale Finite Element Discrete Ply Model (DPM) to the case of unidirectional carbon fibers CT tests. The stacking sequence employed is [45/-45/[0/90]4]s. This configuration has been shown to have significant experimental advantages, such as no specimen buckling and low matrix plasticity. However, it also exhibits a more complex combination of failure modes, including extensive delamination during crack propagation. This leads to inaccurate computation of the strain energy release rate, hence new analysis methods are needed. In the DPM, matrix cracking and delamination are explicitly represented. Failure modes such as fiber failure in tension/compression, shear damage and crushing are modelled within the behavior volume elements. A new law that accounts for the increase in compressive failure strain when planar or out-of-plane strain gradients are present, is proposed and shown to be essential to the correct complete computation of the failure scenario. This approach shows relevant numerical and experimental correlation, both for the force-displacement curves and for the strain energy release rate GIC computed with the compliance method. To address the issue of the complex CT failure scenario, the model estimates the energy dissipated by each failure mode (namely delamination, matrix cracking and fiber failure). A numerical R-curve is also computed directly from these energies, allowing the discussion of the different ways of computing R-curves, numerically and experimentally. Eventually, the R-curve effect (i.e. an increase in GIC with the crack length) is shown to be related to the damage zone height, demonstrating that this effect is indeed not material but structural.
[452] ID:452-An examination of distortion and residual stresses in thermo-mechanical FE simulations of AM components via the EMMI ISV model
Matthew Priddy (Mississippi State University) and Matthew Dantin (Naval Surface Warfare Center | Carderock Division).
Abstract
The prediction of part distortion and component-level residual stresses in additive manufacturing (AM) is of high priority as the community seeks to increase part complexity and size. As-built stress-state predictions are particularly challenging for metal-based AM because many of the material models previously developed were not intended for the cyclic and heterogeneous heating present during the AM process. Additionally, accurate representation of the thermal history requires the use of a moving heat source and material deposition, both of which add significant computational expense. This work examines the influence of material model choice in thermo-mechanical finite element (FE) simulations of the directed energy deposition (DED) process of Ti-6Al-4V components. Specific emphasis will be placed on distortion and as-built residual stress predictions from the various material models. The Evolving Microstructural Model of Inelasticity (EMMI) internal state variable (ISV) model and an elastic-perfectly plastic (EPP) model were selected for comparison. EMMI is a physically-based strain rate- and temperature-dependent dislocation mechanics-based ISV plasticity model that was previously developed for FE simulations of welding; it has been adopted in this work for use with the metal-based DED process. The thermal model calibration procedure will also be examined to determine its effect on mechanical response. Results show significant differences predicted in the stress evolution and overall stress contour across the part despite similar maximum von Mises stress.
[453] ID:453-Curvature-guided design of shell-based spinodal metamaterials
Somayajulu Dhuilipala (MIT) and Carlos Portela (MIT).
Abstract
Research in the field of architected materials has enabled engineered materials with mechanical properties that were previously thought unattainable. For instance, hollow truss-based lattices demonstrate high stiffness- and strength-to-weight ratios. However, these structures suffer from a bending-dominated response and stress concentrations at the sharp joints, the latter of which result in failure. Shell-based spinodal metamaterials have been proposed as an alternative to combat these stress concentrations due to their finite (low) curvature and bicontinuous morphologies. In particular, the mechanical properties of spinodal metamaterials can be tuned by introducing preferential interface directions which results in tailorable anisotropy.
In this study, we explore the effect of curvature and its anisotropic distribution on the stiffness and strength of spinodal metamaterials. The spinodal morphologies are generated using a computational spinodal decomposition framework where tunable anisotropy is introduced by energetically penalizing preferential directions for interface formation, resulting in a mean- and Gaussian-curvature distribution that is dependent on the direction of the surface normal. We propose a shell theory-based analytical framework to calculate the bending and stretching energies of these anisotropic shell-based spinodal morphologies and use this as a predictive metric for their direction-dependent relative stiffening and strengthening. Complemented by finite element models of the as-generated morphologies, we demonstrate a relation between curvature distributions and the stress distribution of these metamaterials. Furthermore, using a two-photon lithography process we fabricate prototypes of these anisotropic spinodal morphologies and perform in-situ nanomechanical uniaxial compression to determine their curvature-dependent stiffness and strength to further validate our analytical approach. Lastly, we extend the applicability of our analytical framework to other shell-based metamaterials such as triply periodic minimal surfaces (TMPS). Our findings present the potential of our analytical framework as an efficient tool for characterizing shell-based metamaterials to guide their curvature-dependent design.
[454] ID:454-Magneto-mechanical instabilities in soft magnetoactive particulate composites
Andrei Cherkasov (University of Galway), Dean Chen (University of California), Nitesh Arora (Georgia Institute of Technology), Quan Zhang (University of Galway) and Stephan Rudykh (University of Galway).
Abstract
In our research, we explore microscopic and macroscopic instabilities in periodic soft magnetoactive composites. Our focus is on particulate composites comprising a non-magnetic hyperelastic matrix and hard-magnetic active inclusions, undergoing uniaxial compression in the presence or absence of an external magnetic field. Employing coupled magneto-mechanical simulations through the Bloch-Floquet method, we determine critical loads and corresponding eigenmodes. Through our comprehensive numerical analysis, we find distinct instability modes developing in the composites upon the critical deformation level. In particular, the microstructure exhibits transformations into strictly alternating periodic patterns, seemingly non-periodic states, or longwave patterns. We analyze the underlying mechanisms driving the development of these diverse instability modes and compare various magnetic configurations with a non-magnetic model. Moreover, we illustrate the distinctive features of magnetic influences on pattern formation, providing insights into the role of magnetization in shaping the composite's response. Finally, we discuss the tunability of magnetoactive composites through the manipulation of external magnetic fields.
[455] ID:455-Adaptive grids for FFT based field dislocation mechanics
Rodrigo Santos-Güemes (Universidad Rey Juan Carlos), Gonzalo Álvarez (Universidad Politécnica de Madrid) and Javier Segurado (IMDEA Materials).
Abstract
Methods based on the Fast Fourier Transform are of high interest in micromechanics due to their computational efficiency in applications such as computational homogenization or Field Dislocation Mechanics (FDM). However, one of the main limitations of FFT calculations is the use of regular grids which prevents using different level of discretization in the domain, contrary to the Finite Element methods. To overcome this limitation, an adaptive FFT approach is proposed which allows to have finer grids in the area of interest and coarser grids elsewhere. The method relies on defining a map which deforms the structured grid, concentrating more discretization points in some target areas. Then, the differential operators involved in the governing partial differential equations are redefined based on the standard Fourier differentiation multiplied by the gradient of the mapping function. The result for a linear PDE is a system of equations that is solved using a Krylov solver.
This adaptive method is applied to the FDM problem, where strong gradients of the mechanical fields are found in very small areas around the dislocation lines. A finer grid was concentrated within the dislocation core in order to accurately represent the stress and strain resulting from a non-singular approach, while maintaining a coarser grid where the gradients were smaller. This method opens up the possibility of considering large Representative Volume Elements (RVE) of the microstructure maintaining an accurate description of the mechanical fields efficiently in terms of computational time and memory use.
The previous approach was used to study the elastic interaction of dislocations with other defects. The high accuracy of the mechanical fields computed around the dislocation allowed reliable calculations of the energy of the system which can be directly applied to Kinetic Monte Carlo models of defect evolution.
[456] ID:456-Multi-scale strain localization in Magnesium via in situ full-field digital image correlation
C. Can Aydıner (Bogazici Universitesi).
Abstract
As the lightest structural metals, there is strong motivation to study Magnesium alloys and expand their structural applications. A strong impediment is their complicated mechanical behavior with multiple twin and slip mechanisms. To develop predictive capability for these complex materials, fundamental scale modeling approaches are key. Recent full-field crystal plasticity models seek fidelity not only for the aggregate-averages but for the local fields with intragranular resolution. This in turn requires extensive experimental data at equivalent length scales for validation. We use an area-scanning version of the digital image correlation technique with optical microscopy to produce such data sets. By developing automated corrective measures in a custom setup, high resolution (numerical aperture) objectives are employed for maximal intragranular resolution while area-scanning allows data over a gross number of grains. The method has been applied in situ over finely spaced data points under monotonic and reversed load paths [1] for different textures of wrought Magnesium. Two phenomena are related to heavy microstructural strain localization observed in these materials. The more straightforward one is microstructural: Micro-texture bands, inherited from the previous forming processes have a considerable effect due to the extreme plastic anisotropy of Magnesium. The more sophisticated phenomenon is the coordinated propagation of twinning. This event is decisively texture dependent: rolled and extruded samples that show equivalent stress strain curves, in fact, deform with vastly different localization fields. The much sharper twin bands in rolled Magnesium are also intensely anisotropic. Recently, we have further guided these twinning bands with stress raisers and studied their enforced interaction [2]. Accordingly here, we cover multi-scale strain localization in wrought Magnesium with its dependencies on microstructure, load-path, and local deformation. [1] N. Shafaghi, E. Kapan, C.C. Aydıner, Exp Mech 60 (2020) 735–751. [2] S.C. Erman, L. Stainier, C.C. Aydıner, Mater Today Commun 35 (2023) 106203.
[457] ID:457-Rate-dependent instabilities in soft visco-hyperelastic composites
Tatiana Lapina (University of Galway), Yuhai Xiang (University of Wisconsin–Madison), Qi Yao (University of Wisconsin–Madison), Dean Chen (University of Wisconsin–Madison), Jian Li (Central South University) and Stephan Rudykh (University of Galway).
Abstract
In this work, we explore rate-dependent instabilities in visco-hyperelastic periodic composites through post-buckling analysis. Our investigation into the influence of loading strain rate on critical strain and wavenumber integrates numerical simulations and analytical predictions. Analytical estimates for critical strain in visco-hyperelastic laminates are developed, considering the interplay between fiber-to-matrix stress contrast. These analytical results align well with numerical simulations, validating the reliability of our proposed estimates. Our findings demonstrate a relationship between critical strain and strain rate, indicating a consistent decrease in critical strain with increasing strain rate. This rate-dependent behavior is characterized by distinct bounds for fast and slow loading rates. Furthermore, we observe that the critical wavenumber of laminates with lower fiber volume fractions decreases from a finite value to almost zero as the strain rate increases. In contrast, laminates with higher fiber volume fractions maintain a nearly zero critical wavenumber, irrespective of the strain rate.
[458] ID:458-Crystal plasticity modeling of nanoindentation in ITER-relevant W/Cu joints
Raul Ruiz (Institute of Mechanics, Materials, and Civil Engineering; UCLouvain), Laurent Delannay (Institute of Mechanics, Materials, and Civil Engineering; UCLouvain) and Thomas Pardoen (Institute of Mechanics, Materials, and Civil Engineering; UCLouvain).
Abstract
The divertor, one of the main parts of the International Thermonuclear Experimental Reactor (ITER), extracts the heat and radiating species generated by the fusion reaction. The divertor contains various sub-assemblies, each comprising numerous components made of copper-chromium-zirconium (CuCrZr) cooling ducts which are joined to tungsten (W) monoblocks using a copper (Cu) interlayer. The W/Cu joint is paramount not only for efficient heat exhaustion but also for maintaining the structural integrity of the divertor under the extreme environmental conditions expected at ITER; thereby its assessment is crucial. It is in this regard that the present work aims to understand the mechanical behavior across W/Cu joints through FEM modeling of nanoindentation. A crystal plasticity model implemented a user-defined material law that allowed grain-scale FE modeling of the plastic strain field and lattice distortions expected after nanoindentation in the close vicinity of a W-Cu joint. The influence of the local lattice orientation and the proximity of the joint was investigated by comparing numerical predictions to experimental observations. The further simulation of heat cycles provides insights that could be useful for further assessment of ITER monoblocks.
[459] ID:459-Retained Austenite in Advanced Steels: An experimentally-informed DAMASK Crystal plasticity analysis
Erick Córdova-Tapia (CENIM-CSIC), Martin Diehl (KU Leuven), Germán Alcalá (Universidad Complutense de Madrid) and Lucia Morales-Rivas (CENIM-CSIC).
Abstract
The development of new advanced steels, with a proper combination of mechanical properties, is supported to a wide extent by the design of microstructures consisting of a mixture of retained austenite and martensite/bainitic ferrite/proeutectoid ferrite. In this scenario, the exploitation of the transformation-induced plasticity (TRIP) phenomenon is key, which can be achieved by controlling the stability of retained austenite. Crystal plasticity has proven to be a useful tool for the identification of critical stress/strain conditions in complex polycrystalline microstructures. In the case of islands or blocks of retained austenite embedded in a matrix of either proeutectoid ferrite, dual-phase models based on crystal plasticity are well established. For more complex cases, such as microstructures where austenite islands are surrounded by bainitic blocks containing both film-like retained austenite and bainitic ferrite, simplified crystal-plasticity approaches might be wished. For that purpose, morphological, crystallographic and chemical factors, contributing to the strength of the bainitic microconstituent and constraining the deformation, need to be considered. In this work, DAMASK, a unified multi-physics crystal plasticity simulation package [1], is used to simulate the stress/strain response preceding mechanically-induced martensitic transformation in complex advanced steels containing retained austenite embedded in ferritic matrix. The microstructural models and simulations are experimentally informed with data from X-Ray Diffraction, nanoindentation and scanning electron microscopy. Acknowledgments: We express our gratitude to Carlos Garcia-Mateo and José Antonio Jiménez for the fruitful discussions. Special thanks to Radhakanta Rana (Tata Steel) for providing the material and engaging in insightful dialogues. Erick Cordova-Tapia and Lucia Morales-Rivas acknowledge CSIC for an iMOVE grant (Ref. IMOVE23203).
1.Roters, F. et al. DAMASK – The Düsseldorf Advanced Material Simulation Kit for modeling multi-physics crystal plasticity, thermal, and damage phenomena from the single crystal up to the component scale. Computational Materials Science 158, 420–478 (2019).
[461] ID.461-On the local stress information from a partial unload with in situ microscopic digital image correlation
Olcay Türkoğlu (Bogazici University) and C. Can Aydıner (Bogazici Universitesi).
Abstract
In experimental solid mechanics, measurement of stress is rather associated with diffraction techniques that inherently measure lattice (elastic) strain. Recently, with the microscopic applications of techniques like digital image correlation (DIC), however, extensive information is gathered on a polycrystal with inherently higher spatial resolution and continuous material coverage with strain mapping. As real space techniques, these inherently measure total strain, which is quickly dominated by plastic strain after loading. Nevertheless further, DIC rarely has the sensitivity to explore elastic strains in common metals. With DIC over a polycrystal with intragranular resolution, the sensitivity can be increased by local averaging, with the averaging domains functionally chosen as grains. Thus, grain-averaged strain sensitivity can, in principal, reach the elastic strain orders. DIC, however, can only elaborate elastic strains if they are equal to total strains. Once a polycrystal is plastically strained, this state is uniquely realized over unloads. Hence, here, we will employ a functional unload over such a polycrystal, measuring the in-plane components of elastic strain release with an area-scanning in situ variant of microscopic DIC [1]. For the stress interpretation of these values (after grain-averaging) for each grain, their orientations are predetermined by electron backscatter diffraction. Pure FCC Nickel (with anisotropy ratio 2.5) is selected for this fundamental study. Crucially, the in situ measurement capability is utilized to conduct DIC imaging at multiple points over the unload to evaluate the linearity of the response. A formalism is presented that elaborates the nature of local stress information that is available through a macroscopic unload. [1] N.A. Özdür, I.B. Üçel, J. Yang, C.C. Aydıner, Exp Mech 61 (2021) 499–514.
[462] ID:462-Microstructure - defect competition in high cycle fatigue of a duplex stainless steel obtained by laser powder bed fusion
Maxime Piras (Institut Clément Ader), Anis Hor (Institut Clément Ader) and Eric Charkaluk (Laboratoire de Mécanique des Solides).
Abstract
Duplex stainless steels (DSS) are used in corrosive environments thanks to their mechanical and chemical properties. Their static and cyclic behavior are well known within the conventional process framework. Since few years, these dual-phase materials are used in additive manufacturing (AM). However, DSS elaborated by laser powder bed fusion (LPBF) are fully ferritic in the as-built state. Heat treatments (HTs) are therefore mandatory to obtain the dual-phase material. Several HTs are possible and giving rise to different microstructures (phases ratio, grain morphology, texture). The influence of these HTs on static behavior of AM DSS was studied by many authors. But the effect on high cycle fatigue (HCF) behavior still lacks some investigation. This work aims to understand the influence of the microstructure and its competition with LPBF process induced defects on the HCF behavior of additively manufactured DSS SAF2507. Firstly, four microstructures were selected : (i) the as-built state which is fully ferritic, (ii) the 50-50 austenite-ferrite ratio with fine grain microstructure reminding the LPBF thermal history, (iii) the 50-50 austenite-ferrite ratio with coarser grains, and (iv) the hot isostatic pressure (HIP) microstructure. Secondly, tensile and torsional HCF strength were determined for each microstructure. Then, the fatigue fracture mechanisms were investigated by fractographic analysis. Finally, these microstructures were explicitly modeled using Neper software. CPFE simulations were performed to determine the microstructure sensitivity of the HCF strength. The experimental results show that there is a microstructure-defects competition for tensile HCF since both fine grains microstructure with defect and defect free coarser grains microstructure (HIP) improved fatigue life to the same extent. In contrary, torsional HCF is less sensitive to defects and defect free crack initiations were observed for microstructure having process induced defects. The CPFE analysis illustrates a preponderant effect of LPBF induced defects compared to the microstructure.
[463] ID:463-Surface evolution in a stainless steel induced by electrochemical hydrogen charging
Huichao Wu (Forschungszentrum Jülich - Structure and Function of Materials (IEK-2)), Steffen Brinckmann (Forschungszentrum Jülich - Structure and Function of Materials (IEK-2)) and Ruth Schwaiger (Forschungszentrum Jülich - Structure and Function of Materials (IEK-2)).
Abstract
Hydrogen embrittlement in engineering materials poses significant practical and economic hazards and involves a number of different mechanisms, which depend on the specific microstructures of a material. In this study, we investigated the evolution of an initially smooth surface of a stable austenitic stainless steel under hydrogen exposure and the effect on the mechanical properties. The material was electrochemically charged for 120 h to achieve a significant hydrogen content. The effect of hydrogen was studied regarding lattice defects and the plastic deformation that prevails at the free surface. Based on Vegard’s law, an analytical model for hydrogen-induced resolved shear stresses on the different crystallographic planes was developed. This model explains the formation of slip lines and the occurrence of plastic deformation in the surface region. Nanoindentation was used to evaluate the effect of hydrogen charging and the related microstructural changes on the hardness and elastic modulus.
[464] ID:464-Phase field modelling of fractures in ice sheets and glaciers
Emilio Martinez-Paneda (University of Oxford).
Abstract
Sea-level rise is one of the most critical issues the world faces under global warming. However, the accuracy of sea-level rise projections is compromised by the crude, empirical laws used to characterise mass loss from glaciers and ice sheets, the phenomenon that constitutes the largest contributor to sea-level rise. There is a need for physically-based computational models capable of predicting iceberg calving due to hydrofracture, one of the most prominent yet less understood glacial mass processes. In this work, we have developed a phase field fracture formulation capable of predicting the growth of crevasses (deep crack-like defects) and subsequent iceberg calving, as well as the role that increasing meltwater plays in accelerating these phenomena. The potential of the computational framework presented is demonstrated by addressing a number of 2D and 3D case studies, involving single and multiple crevasses, and considering both grounded and floating conditions. The model results show a good agreement with analytical approaches when particularised to the idealised scenarios where these are relevant. More importantly, we demonstrate how the model can be used to provide the first computational predictions of crevasse interactions in floating ice shelves and 3D ice sheets, shedding new light on these phenomena. Also, the creep-assisted nucleation and growth of crevasses is simulated in a realistic geometry, corresponding to the Helheim glacier. The computational framework presented opens new horizons in the modelling of iceberg calving and can be readily incorporated into numerical ice sheet models for projecting sea-level rise.
[465] ID:465-Phase field modelling of fatigue in inert and hydrogen-containing environments
Emilio Martinez-Paneda (University of Oxford).
Abstract
Predicting fatigue failures remains one of the most elusive challenges for scientists and engineers. In this work, we develop a comprehensive phase field model capable of predicting fatigue failures of arbitrary complexity. Through comparison with experiments, the model is shown to accurately predict the fatigue behaviour of materials, including S-N curves, Paris law crack growth, the influence of the load ratio, mean stress effects, stress concentrator factors and the endurance limit. In brittle and quasi-brittle solids, the model is able to predict fatigue crack growth rates from S-N curves, and vice-versa. Moreover, the framework is extended to account for the presence of hydrogen, which is known to significantly impact the fatigue resistance of metals. The resulting coupled deformation-diffusion-damage model is shown to be able to qualitatively and quantitatively capture the role of hydrogen in increasing fatigue crack growth rates and decreasing the number of cycles to failure. Our numerical experiments enable mapping the three loading frequency regimes and naturally recover Paris law behavior for various hydrogen concentrations. In addition, Virtual S–N curves are obtained for both notched and smooth samples, exhibiting a good agreement with experiments. Aspects of the numerical implementation will also be discussed, showing how complex fatigue cracking phenomena in 2D and 3D can be captured, over millions of cycles, through the development and use of new acceleration schemes.
[466] ID:466-Crystal plasticity and misorientation dependent homogenisation in the APL programming language
Jesús Galán López (Dyalog Ltd / Ghent University).
Abstract
When designing a crystal plasticity model, a choice must be made between using either a full-field approach that offers a detailed solution in a small region of the material or a more statistically-sound solution found using a homogenisation (mean-field) method. Unfortunately, when using a mean-field approach, important information about the microstructure, such as the topology of its different elements and the relationships between them, is missed. Therefore, when different materials are differentiated only by their topology, mean-field models cannot capture these differences, and full-field simulations with large representative volume elements have to be used.
In this work, a new crystal plasticity framework, completely written in APL, is presented. APL is both an alternative to mathematical notation and a full-featured programming language. The language is particularly well suited for the solution of complex computational problems by domain experts.
The presented model allows the usage of different homogenisation schemes. In addition to classical options, such as the full-constrained and relaxed-constraints approaches of Taylor and Sachs, new homogenisation schemes that take into account the topology of the microstructure are introduced. This information is added into the model by considering a different environment for each crystallographic orientation based on the misorientation distribution, or even on different distributions for each direction.
The model is, first introduced, and then used for the solution of several example problems, using as input different syntectic microstructures.
[467] ID:467-Swelling theory for multidomain materials
Michele Curatolo (Roma Tre University), Ruud van der Sman (Wageningen University & Research) and Luciano Teresi (Roma Tre University).
Abstract
The so-called mechano-diffusion theory can describe many different phenomena dealing with a solid matrix swollen with a liquid; in particular, it describes the effects of liquid uptake or release, called swelling and drying, respectively.
We present a unified approach to set and solve mechano-diffusion problems where the solid matrix is made of two or more materials having different elastic and chemical properties. The amount of liquid that can be absorbed by the solid matrix depends on the chemo-mehanical properties of the material, and there are uncountable examples of swollen solids made of very different materials, having an almost steady and stress-free configuration; however, these free-swollen configurations will become stressed and distorted upon any change of liquid content because of swelling incompatibility.
The approach presented here is based on the theory of nonlinear mechanics with large distortions, coupled with that of swelling, describing the effects of solvent uptake in a solid matrix. Basing on the hypotheses underlying the two theories, and using some key principles of continuum mechanics, we present a chemo-mechanical model which describes the effects of swelling for materials made of domains having different properties
We presents some examples of gels having a hard skin surroundig a soft core; the geometry and the materials properties might yield noticeable shape changes during wetting or drying.
[468] ID:468-Characterizing the Onset of Cold Welding of CuSn6 Using a Custom Milli-Ohm Meter
Theeba Shafeeg (South East Technological University, Carlow) and Mark Wylie (South East Technological University, Carlow).
Abstract
In the near vacuum of space, metal-to-metal fusion in mechanisms that have undergone wear has been attributed to a number of mission failures. This phenomenon is otherwise known as cold-welding and occurs when the base metals are exposed after the oxidation or lubrication layer has been removed. This research is concerned with the potential application of cold welding as a repair method for spacecraft hull post-debris/micrometeoroid impact. Specifically, this paper details a cold-welding onset measuring technique using electrical contact resistance of cold welding CuSn6 rods and is verified first in atmospheric conditions. Factors that allow for cold welding at reduced forces will also be investigated. Since the 1930s, research has been carried out into cold welding adhesion mitigation using advanced coating and lubricant development. This research also shows cold welding occurring at low forces when in the near vacuum. It is possible however, to cold weld certain metals in terrestrial environment by the yielding metals into one another. Other factors that may reduce these forces include material ductility, surface cleanliness and roughness. Metal fusion (and the forces required for this) is difficult to detect in real-time, however, the Kelvin Double Bridge can be used to detect this by monitoring the electrical resistance and identifying markers. A milliohm meter (1-100mΩ) is currently under development for measuring the onset of cold welding in 3mm CuSn6 rods as a function of applied force using a custom test rig. The electronic circuit incorporates a MAX680 voltage monitor and an LT3092 precision current reference that allows resistance measurements through the application of Ohm's Law. The test rig is under development for the application of forces between 10–500N. Successful detection of cold-welding joints allows for further studies into surface preparation methods to minimize the applied forces for the fusion mechanism.
[469] ID:469-Mechanics of Anisotropic PVA Hydrogel Fibers as Biomimetic Soft Tissue Substitutes
Andrea Diaz Colina (Mines Paris, PSL University. ESPCI Paris, PSL University.), Laurent Corte (Mines Paris, PSL University. ESPCI Paris, PSL University.) and Yannick Tillier (Mines Paris, PSL University).
Abstract
Synthetic polyvinyl alcohol (PVA) hydrogels are interesting materials as substitutes for the reconstruction of soft tissues due to their biocompatibility and adjustable mechanical properties. In particular, their tensile response can be enhanced by orienting their semi-crystalline network. Assemblies of such anisotropic PVA hydrogel fibers were shown to reproduce the water content, dimensions, and tensile response of the human ligament. Here, we investigate the role of the network anisotropy in the mechanical response of PVA hydrogels. For that, we compare anisotropic PVA hydrogel fibers to isotropic PVA hydrogel films having similar crystallinity (50 ± 2%) and swelling ratio (2.5 ± 0.2). Uniaxial tensile tests were performed on single fibers and films in water at 20°C and 37°C. Both systems exhibited very different non-linear viscoelastic behaviors. For low tensile strains (0-20%), anisotropic hydrogel fibers were significantly stiffer than isotropic hydrogel films, with Young’s moduli of 13.5 ± 2.5 MPa and 2.7 ± 0.3 MPa, respectively. For large strains, the tensile responses differed even more. The isotropic hydrogel films softened considerably above 50% strain with a high elongation at break of 300% and tensile strength of 2.8 ± 0.4 MPa. On the contrary, the anisotropic hydrogel fibers exhibited a marked non-linear stiffening similar to that of biological tissues with a tensile modulus increasing up to 40 MPa and tensile strength values (20-30 MPa) close to those of human ligaments (20-40 MPa). Moreover, cyclic loading tests show that individual fibers undergo a softening after the first cycle but fully recover their pristine behavior after a few hours rest. These softening and self-recovery are well explained by the dissociation and reformation of reversible hydrogen-bonds in the swollen phase of the hydrogel. Such fibers constitute promising building blocks to design durable tissue substitutes able to sustain physiological fatigue loadings representative of ligament biomechanics.
[470] ID:470-Cellular automaton modeling of bainite in steels
Hugo Guichard (CEA), Benoît Appolaire (Université de Lorraine), Sabine Denis (Université de Lorraine), Victor de Rancourt (CEA) and Jacques Bellus (Aubert & Duval).
Abstract
Bainitic steels have been studied for nearly a century. They are of high interest in the industry due to their unique combination of toughness and mechanical strength. Despite the current extensive knowledge on bainitic steels, many questions still remain. In particular, many observations and measurements suggest that local mechanical stresses are likely to play an important role on the final microstructure, which cannot be taken into account precisely within the classical mean-field models. An enhanced modelling approach, that takes into account the stress fields at the scale of the polycrystal, must therefore be implemented to gain understanding of the final microstructure. The present work focuses on the modeling of bainite formation at the scale of the initial austenite polycrystal using a cellular automaton coupled with an FFT-based elastic solver. The solver is optimized to efficiently handle 3D polycrystals with a significant number of prior austenite grains. The morphology of the bainite sheaves is simplified by considering ellipsoids adapted to plate/lath structures. The sheaves are assumed to grow along theoretical directions based on the phenomenological theory of martensite crystallography. Growth velocity in the main direction and carbon partitioning are calculated following a thermodynamical model. Furthermore, in a first step, the local stress field is considered only in the selection of the orientation of a new bainite sheaf. In a second step, it is also considered in the growth laws of bainite sheaves. The present work discusses the different sets of parameters that best predict the kinetics, microstructure and microtexture of bainite with respect to experimental characterization.
[471] ID:471-On the identification of stretching-dominated topologies based on Triply Periodic Minimal Surfaces
Lucia Doyle (IMDEA Materials), Humberto Terrones (Rensselaer Polytechnic Institute) and Carlos Gonzalez (IMDEA Materials).
Abstract
With the advancements in additive manufacturing, the fabrication of complex lattice structures has become possible. This has led to increased interest in architected materials featuring topologies based on Triply Periodic Minimal Surfaces (TPMS) due to their mathematically controlled geometries and excellent mechanical properties. Triplic Periodic Minimal Surfaces (TPMS) refer to a type of periodic implicit surface characterized by having zero mean curvature. In essence, these surfaces are locally minimizing the surface area for a specified boundary. A great number of TPMS have been identified. While ongoing efforts focus on characterizing individual TPMS topologies, the successful selection of these topologies for specific functions necessitates a general understanding of how geometric features influence mechanical behaviour. While most cellular structures are bending-dominated, stretching-dominated cellular structures present greater stiffness and strength than bending-dominated structures of the same relative density. Thus, it is of interest to identify stretching-dominated microstructures for lightweight structural applications. Currently, the Schwarz P topology stands out as the only identified stretching-dominated TPMS topology. This study explores the correlation between the crystallographic space group of the lattice and its deformation mode. The elastic properties of the Schwarz P, Neovious, P+C(P), OCTO, PJx and PPJPxxx-J, all belonging to the Pm3 ̅m space group, were obtained through finite element analysis with periodic boundary conditions. A linear correlation between the E modulus and the relative density has been found, suggesting stretching-dominated deformation. Simulations are complemented with experimental uniaxial compression tests.
[472] ID:472-Bioinspired Soft-Hard Interfaces Fabricated by Multi-material Additive Manufacturing: A Fracture Mechanics Investigation using Essential Work of Fracture
Umut Altuntas (Middle East Technical University), Demirkan Coker (Middle East Technical University) and Denizhan Yavas (Rice University).
Abstract
This study employs the Essential Work of Fracture (EWF) concept to evaluate the interfacial fracture toughness of bioinspired interfaces between soft-hard polymer phases. The experimental framework utilizes a model material system with Polylactic Acid (PLA) as the hard phase and Thermoplastic Polyurethane (TPU) as the soft phase. Employing the Fused Filament Fabrication (FFF) technique, bioinspired sutural interfaces are created, characterized by interpenetrating soft and hard protrusions. The modulation of a critical parameter in the FFF process enables the variation of interpenetration length of protrusions, thereby achieving a spectrum of interfacial strength and toughness. The determination of essential work of fracture from double edge notch tension samples, with varied ligament sizes, allows for the specific EWF measurement. This specific EWF is found to align with the initiation value of plane strain interfacial fracture toughness obtained through the double cantilever beam test. Therefore, the proposed approach asserts the elimination of the need for complex interfacial fracture tests, such as the double cantilever beam test. A noteworthy discovery is the establishment of a correlation between specific plastic energy dissipation and protrusion length. This correlation suggests an increased plastic dissipation with longer protrusions within the investigated bioinspired interface. Due to this heightened plastic energy dissipation, the shape of the interfacial nominal stress-displacement curves demonstrates substantial dependence on interface morphology, shifting from a triangular shape to a trapezoidal shape as protrusion length increases. These findings offer valuable insights into the mechanics of bioinspired interfaces, presenting a more efficient and nuanced approach to characterizing their fracture properties.
[473] ID:473-Coupled problems of chemo-mechanics: localized and volume reactions within a chemical affinity tensor framework
Alexander Freidin (Institute for Problems in Mechanical Engineering of the Russian Academy of Sciences, St. Petersburg, Russia), Aleksandr Morozov (Institute of Mechanics, Berlin Institute of Technology, Berlin, Germany) and Mikhail Poluektov (Department of Mathematics, School of Science and Engineering, University of Dundee, Dundee, UK).
Abstract
Coupled problems of chemo-mechanics are discussed for chemical reactions between diffusing and solid reactants. Reactions such as silicon oxidation or silicon lithiation are implied. The reaction is accompanied by the transformation strain, which generates stresses which, in turn, affect the reaction rate. First, a reaction localized at the reaction front – a sharp interface is considered. As it was derived earlier, the configurational force driving the chemical reaction front is determined by a chemical affinity tensor which is a combination of chemical potential tensors of solid constituents and a chemical potential of a diffusing constituent. Examples of solving coupled problems “diffusion–chemistry–mechanics” are given which demonstrate how the mechanical stresses can retard and block the reaction front propagation. Two types of reactions are highlighted: stress-affected reactions which can go without stresses, and stress-induced reactions which can go only under a proper loading. Then the stability of the reaction front is examined on the basis of the developed procedures of the analytical stability analysis and numerical simulations of the front propagation. The competition between the global macro-kinetics of the reaction front propagation and the local kinetics of the front perturbations far and near the blocking position of the front is discussed. Finally, modelling a volume chemical reaction with a reaction extent related with a phase field parameter is considered. Dissipation inequality is written down for a solid undergoing a volume chemical reaction and a configurational force driving the reaction is derived. It is shown how the configurational force is related with the chemical affinity tensor. The simplest problem is solved and the profiles of the reaction extent and the concentration of the diffusing constituent are constructed.
[475] ID:475-Additively Manufactured Jammable Structured Fabrics for Deployable Structures
Tracy Lu (California Institute of Technology), Punnathat Bordeenithikasem (NASA Jet Propulsion Laboratory), Connor McMahan (California Institute of Technology) and Chiara Daraio (California Institute of Technology).
Abstract
The 2017-2027 Decadal Survey outlines the need for high-frequency antenna capabilities in CubeSat constellations, to aid Earth science objectives. Due to launch volume constraints, deployable structures become essential for antennas. Current solutions, like metallic mesh reflectors or reflect arrays, face limitations in lacking the stiffness to maintain surface accuracy for higher frequencies, prompting exploration of alternative technologies which have a deployable solid active surface. Structured fabrics, with compliant and jammed (stiff) modes, offer an alternative avenue. Leveraging this, we are developing a different deployable antenna architecture featuring a solid active surface with a pre-stretched elastic membrane as the multidirectional transformation mechanism. We explore a type of structured fabric that starts from a flat and foldable initial configuration, but upon release of the pretension, has a static equilibrium that achieves a desired three-dimensional shape. The computational design of the rigid tiles attached to these elastic sheets and their spatial distribution are optimized for specific fold lines and allows for a solid surface upon actuation. Upon releasing the pre-tensioned membrane, contracting forces on the tiles control the global structure shape through predetermined collisions at angles with neighboring tiles. The resulting local curvatures thereby control the global structure shape. This computational design approach was used to fabricate and demonstrate a paraboloid (resembling an antennae) of a desired focus, using a specific fold pattern that was previously designed to stowage an optical shield into a compact volume. The structured fabric design methods could be extended to designing deployments for other global target shapes and stowage volumes. Future exploration includes internal latticing for reduced structure density, kinematic mounts for deployment accuracy, and latching mechanisms for post-deployment stabilization.
[476] ID:476-Energy absorption capability of novel composite materials employed in mechanicallyfastened joints
Pedro Campos (FEUP), Denis Dalli (INEGI), Igor Lopes (INEGI), Federico Danzi (INEGI), Teresa Duarte (FEUP) and Albertino Arteiro (FEUP).
Abstract
Mechanical fasteners are still a fast and effective way of joining composite components and subcomponents. The mechanical properties and associated failure modes for such joints can be characterised following the ASTM D5961 standard. More recently some mechanical joint designs have included an additional design case catering for controlled energy absorption, such as the tension-absorbers deployed in aeronautical applications. These joints offer a sustained level of energy absorption through an extended bearing failure mode, leading to controlled crushing, while avoiding the undesired fastener pull-out through the composite thickness. To date these fastened joints have been designed using more conventional thermoset resin carbon-fibre composites. A number of new material systems have recently been introduced in the transportation sector, including thin-ply CFRPs, as well as more environmentally sustainable alternatives, such as thermoplastics and natural fibre composites (NFCs). This work aims to study the energy absorption performance of an advanced thermoplastic system employed in fastened joints. A quasi-static experimental study was conducted, including bearing and extended bearing tests. This study also investigates the influence of the tightened fastener, through independent coupon testing of both pinned and fastened joints. A stable crushing stress corresponding to approximately 50% of the peak bearing stress for pinned joints is observed, in line with the observed results in the literature for thermoset matrix composites. The employment of a bolted joint leads to an increase in peak and crushing bearing stresses of approximately 100% with respect to the pinned joint, caused by the confinement of the crash front and suppression of delamination. In addition, different specimen geometries were studied, focusing on the variation of the overall w/D (width/hole diameter) ratio, showing its effect on the failure mode transition from the desired bearing to net tension failure by split cracking, net-section delamination, and fibre tensile failure.
[478] ID:478-Understanding twinning mechanisms and measuring twinning stress of CoCrFeNiMn high entropy alloy using micro-mechanical testing
Camila Aguiar Teixeira (Karlsruher Institute of Technology (KIT)), Ujjval Bansal (Karlsruher Institute of Technology (KIT)), Subin Lee (Karlsruher Institute of Technology (KIT)) and Christoph Kirchlechner (Karlsruher Institute of Technology (KIT)).
Abstract
The equiatomic CoCrFeMnNi high entropy alloy (HEA) have shown an outstanding combination of mechanical properties not only at room temperature but also at cryogenic conditions. At room temperature, dislocation slip is the predominant deformation mechanism, however, under cryogenic conditions their mechanical response is dominated by extensive deformation twinning, which results in a significant increase in ductility, tensile strength and fracture toughness. This extensive mechanical twinning is attributed to their low stacking fault energy. Given the importance of twinning as a deformation mechanism for FCC HEAs, in-depth understanding and quantitative insights of the stresses required for its activation are crucial for advanced HEAs design. In this work, we aim to develop protocols to assess the critical resolved shear stress (CRSS) required for twinning to occur by applying in situ micromechanical testing. Therefore, three micromechanical geometries (micropillar, microcantilever and microshear) were chosen to activate deformation twinning in different stress conditions. Specific orientations to favor deformation twinning were carefully selected through electron backscatter diffraction (EBSD) analyses. Post-mortem analysis included scanning electron microscopy (SEM) imaging, EBSD and transmission electron microscopy (TEM) to verify if twin microstructure could be observed. It is found that deformation twinning was visible only in the pillars with CRSS exceeding 200 MPa, suggesting that the twinning stress for this HEA is close to 200 MPa at room temperature. A detailed analysis of the twinning stress and a comparison between three different micromechanical geometries will be discussed in the presentation.
[479] ID:479-Large deformations in strain-gradient special Cosserat rods
Vipin Kumar Yadav (Indian Institute of Technology Hyderabad, India) and Prakhar Gupta (IIT Hyderabad).
Abstract
In this talk, we will discuss one-dimensional strain-gradient theory for special Cosserat rods. A general framework for micro- and nano-scale rods that accounts for large deformations, chirality, and size effects has been developed. Firstly, the linear momentum and angular momentum balance equations for rods have been derived using the three-dimensional strain-gradient elasticity theory. Additionally, the constitutive relations for the strain-gradient elastic rods have been derived using the principle of material objectivity. Subsequently, these constitutive relations have been used to show the applicability of the current theory by deducing the various closed-form solutions for geometrically nonlinear thin strain-gradient rods subjected to extension and bending deformations (like Elastica). Finally, we discuss the role of the length scale parameter on all these deformations of the strain-gradient elastic special Cosserat rod.
[480] ID:480-Finite size effect on soft granular materials under compaction
Kamilia Ayed (LMGC, UNIV. MONTPELLIER, CNRS), Serge Mora (LMGC, UNIV. MONTPELLIER, CNRS), Jean-Yves Delenne (IATE, UNIV. MONTPELLIER,INRAE) and Saeid Nezamabadi (LMGC, UNIV. MONTPELLIER, CNRS & IATE, UNIV. MONTPELLIER,INRAE).
Abstract
Soft granular materials, consisting of highly deformable disordered particles, find applications in various industrial sectors such as pharmaceuticals, cosmetics, food, and powder metallurgy. These materials are often shaped under confinement stresses in processes like extrusion or compaction, resulting in tablets or compacts with a microstructure resembling that of porous media. The compaction stage remains challenging to describe, marked by changes in particle shape, volume, and rearrangements within the grain bed. In this context, suitable numerical models are necessary to capture the significant deformations of particles at the contact level. An important challenge lies in ensuring the representativity of simulated systems for industrial applications. The number of simulated particles relative to the system size is a key parameter. In tis presentation we will focus specifically on the finite size effects of systems composed of slightly polydisperse elastic spherical particles confined within rigid cylinders of varying diameters. These particles will undergo quasi-static uniaxial compression with a home-made code relying on couple approaches based both on material point method for bulk particle deformations and contact dynamics method to address particle-particle interactions. The diameter and height of the cylinders will be vary based on the number of particles, allowing us to elucidate how the number of particle influences important packing parameters such as stress transmission, solid fraction, or connectivity.
[482] ID:482-Micromechanical study of synthetic rock salt by X-ray µCT in situ triaxial tests
Nina Du (Ecole Polytechnique, CNRS UMR 7649, Laboratoire de Mécanique des Solides, Palaiseau), Michel Bornert (Ecole des Ponts, Université Gustave Eiffel, CNRS UMR 8205, Laboratoire Navier, Marne-la-Vallée), Patrick Aimedieu (Ecole des Ponts, Université Gustave Eiffel, CNRS UMR 8205, Laboratoire Navier, Marne-la-Vallée) and Alexandre Dimanov (Ecole Polytechnique, CNRS UMR 7649, Laboratoire de Mécanique des Solides, Palaiseau).
Abstract
Energy transition towards low-carbon energy sources, like renewable energies, has increased the interest of hydrogen as an energy carrier. However, its massive storage still remains a challenge. Underground seasonal storage of hydrocarbons in salt caverns, in use for decades, could be adapted to shorter term storage of hydrogen. However, cycles, adapted to the intermittency of renewable energies, represent short term thermomechanical cycling, which deserves a better understanding of the behaviour of rock salt, with specific focus on micro-damage development. Studies have focused on the mechanical behaviour of halite and have highlighted different deformation mechanisms, such as crystal plasticity, grain boundary sliding, micro-damage, grain boundary migration and diffusional mass. The constitutive relations inherently depend on their respective contributions to the overall strain, which depends on the stress state, the temperature and the mechanical loading rate, but also on the presence of brine. In this work we specifically focus on the development of micro-damage during compression tests, considering the effects of confining pressure and brine. Synthetic samples have been prepared in both dry and humid conditions. Compression tests at constant displacement rate at uniaxial and triaxial conditions were conducted, using a specifically designed triaxial cell transparent to X-rays. X-ray microcomputed tomography (XR-µCT) allowed us to perform time-resolved observations of the damage development during deformation. The 3D in situ observations are complemented with post mortem 2D microstructural investigations by SEM (scanning electron microscopy) and EBSD (electron back-scatter diffraction) analysis. The results suggest that dry material is prone to develop substantial micro-damage irrespective of confining pressure. The anisotropic crystal plasticity of NaCl generates plastic incompatibilities at grain boundaries, resulting in stress concentration and inter-granular micro-cracks, followed by interfacial shear sliding and further wing cracks damage. Conversely, the presence of brine appears to strongly reduce micro-damage development, most likely due to dissolution-precipitation related healing mechanisms.
[483] ID:483-Toward realistic simulation of transient events within an efficient workflow using implicit and explicit solver: Application on laminated composite materials
Jeremy Germain (ONERA / DMAS, Université Paris Saclay, F-59014 Lille - France).
Abstract
Numerical simulation is a promising method to evaluate risk associated to an accidental loading on a structure in service, but a numerically efficient evaluation remains difficult due to the nature of the loadings to be accounted for. Accidental events are usually transient dynamic events modelled with explicit finite element code. To accurately predict damage and strength, this loading must be added up to the current structure loads. Indeed, structures are generally stressed when an accidental event occurs, initial loads are usually quasi-static and are efficiently solved using implicit-based finite element code. An existing strategy in commercial finite element code to introduce an initial loading consists in using a viscous dynamic relaxation, but the associated cost may become tremendous: an important number of increment is necessary for the damping to dissipate the kinetic energy and the time increment must remain lower than the critical time step. This presentation aims at proposing an efficient and non-intrusive methodology to take into account initial in-service loads for the evaluation of transient dynamic loadings, by an alternate use of implicit and explicit solver. Efficiency will be demonstrated with a residual thermal stress simulation of composite materials, induced by the manufacturing process and influencing damage initiation. To our best knowledge, this pre-stress has never been accounted for in transient simulation using an explicit solver, such as impact, despite a wide literature about this topic. In a second time we will extend the methodology to compression after impact, and an impact simulation will be conducted on a stiffened panel initially subjected to a tensile load. Indeed, this component is representative of a fuselage part in the aeronautical industry. In conclusion, limits of the strategy and potential future developments will be exposed.
[485] ID:485-Decoupling elastic and thermal strains in operando X-ray diffraction measurements in directed energy deposition additive manufacturing using fast numerical strategy
Steve Gaudez (PSI), Daniel Weisz-Patrault (French National Centre for Scientific Research), Kouider Abdellah Abdesselam (Institu Polytechnique de Paris), Hakim Gharbi (Institut Polytechnique de Paris), Veijo Honkimäki (European Synchrotron Research Facility,), Steven Van Petegem (PSI) and Manas Upadhyay (Institut Polytechnique de Paris).
Abstract
Relatively fast numerical strategies have been developed for the simulation of temperature kinetics [1] and stresses [2] arising in directed energy deposition (DED). Operando synchrotron X-ray diffraction measurements during additive manufacturing of a 316L stainless steel thin-wall have recently been used to validate numerical predictions of residual elastic strain distribution taking place after complete cooling [3]. However, X-ray diffraction provides only the lattice strain coupling both thermal expansion and elastic strain, and it is demonstrated that the classic direct estimation of temperatures and cooling rates neglecting elastic strain leads to significant errors under DED conditions, which can be corrected by using numerical simulations.
To do so, the model[1] should be further validated so that it can be safely used to decouple thermal and elastic contributions in X-ray diffraction measurements. Indeed, despite the fact that infrared measurements have been used to validate simulations at the scale of the entire part, some local assumptions were necessary in [1] to reach short computation time, and the transient temperature distribution in the melt pool vicinity may be subjected to errors, and has not yet been properly validated against experiments. In this contribution, the transient thermal+elastic strain taking place during fabrication is derived from X-ray diffraction measurements. The resolution of acquired images is sufficient to observe strain distribution in the melt pool vicinity, but not sufficient to clearly identify the melt pool shape though. Good agreement is observed with the numerical counter-part, which thus demonstrate the ability of the fast numerical approach [1] to provide reliable results in the melt pool vicinity, and to be used to decouple thermal and elastic contributions in X-ray diffraction measurements as suggested in [3]. [1] Weisz-Patrault,D.(2020). Additive Manufacturing, 31, 100990. [2] Weisz-Patrault,D., Margerit,P., Constantinescu,A.(2022). Additive Manufacturing, 56, 102903. [3] Gaudez,S., Weisz-Patrault,D., Abdesselam,K.A., Gharbi,H., Honkimäki,V., van Petegem,S., Upadhyay,M.V.(2023)Preprint. Additive Manufacturing
[486] ID:486-Rate-Independent Phase-Field Framework for Hysteretic Behavior of Phase Transforming Solids
Omar El Khatib (TU Bergakademie Freiberg), Vincent von Oertzen (TU Bergakademie Freiberg) and Bjoern Kiefer (TU Bergakademie Freiberg).
Abstract
Phase-transforming solids are a distinct class of multifunctional materials renowned for their remarkable thermomechanical properties. These materials undergo microstructure evolution during specific stress- and temperature-induced phase transformations involving transitions between austenite and multi-variant martensite. The resulting hysteretic behavior, mainly characterized by energy dissipation, is crucial for understanding their performance. Experimental data suggests that phase-transforming solids exhibit rate-independent behavior under quasi-static loading conditions, implying that hysteresis loops retain a finite width even at extremely slow loading rates. The phase-field method has emerged as a powerful tool for modeling these intricate interface dynamics, with remarkable capabilities to capture complex interface topologies’ evolution accurately. Despite significant advancements in this field, see [1] and the references therein, notable gaps still exist in our understanding of these complex phenomena. Especially since most existing models often employ rate-dependent dissipation formulations, thus limiting their ability to replicate thermo-elastic hysteresis loops under quasi-static loading conditions. To address these limitations, this study builds upon a recently proposed thermomechanically coupled and variationally consistent phase-field approach that seamlessly integrates both rate-dependent and rate-independent driving force formulations, as detailed in [2]. Finite element simulations demonstrate the practical applicability of this approach, exploring microstructure formation in twinned martensite in shape memory alloy systems. The analysis includes rate-dependent and -independent stress- and temperature-induced hysteresis loops, the influence of driving force threshold values, and calibration of system parameters with experimentally observed martensite temperatures. This comprehensive modeling framework enhances our understanding and predictive capabilities for the thermo-elastic behavior of these unique materials, facilitating their efficient utilization in engineering applications.
References: [1] L. Xu, T. Baxevanis, D. C. Lagoudas, 2019, Smart Mater. Struct. 28(7), 074004. [2] O. El Khatib, V. von Oertzen, S. A. Patil, B. Kiefer, 2022, Proc. Appl. Math. Mech. 23(2), e202300273.
[487] ID:487-Energy-conserving equivariant GNN predictions of stiffness for lattice materials
Ivan Grega (University of Cambridge), Ilyes Batatia (University of Cambridge), Gabor Csanyi (University of Cambridge), Sri Karlapati (Amazon Research) and Vikram Deshpande (University of Cambridge).
Abstract
Lattices emerged in recent decades as a promising class of architected materials with a vast design space. Many machine learning models have been proposed as surrogate to numerical modelling in predicting their mechanical properties for rapid design applications. However, they are often not scalable, lack the appropriate physical constraints and hence are limited to a small fragment of the vast design space. Here we develop a graph-based neural network to predict the fourth-order stiffness tensor of any arbitrary periodic lattice. We build upon the equivariant MACE model and introduce positive semi-definite constraints that ensure energy conservation. To train the model, we assembled a generalised dataset of over 1 million unit cells with arbitrary crystal symmetries, stretching, bending and mixed behaviour, and varying degrees of complexity with an average connectivity from 3 to 16 and with up to 150 nodes per unit cell. We demonstrate an example application of the model in structural optimization.
[490] ID:490- On the triaxial compression of dense cohesive granular materials
Max Sonzogni (LMGC, Univ. Montpellier, CNRS), Jean-Mathieu Vanson (CEA, DES, IRESNE, DEC, Cadarache), Yvan Reynier (Univ. Grenoble Alpes, CEA, Liten, DEHT), Sebastien Martinet (Univ. Grenoble Alpes, CEA, Liten, DEHT), Katerina Ioannidou (LMGC, Univ. Montpellier, CNRS) and Farhang Radjai (LMGC, Univ. Montpellier, CNRS).
Abstract
Cohesive granular materials play a major role in nature and industry. Cohesive interactions between particles have various physico-chemical origins such as capillary bonding, Van der Waals forces, or cementing matrix. Despite extensive experimental and numerical work on these materials, their mechanical behavior under the action of external loading is still poorly understood, and the compaction behavior of cohesive granular materials is highly dependent on the loadings applied. In a previous study we established a link between the material properties, applied force and porosity of a cohesive granular sample submitted to an isotropic compaction [1]. Here we study the influence of the adhesion force under triaxial compression on dense granular samples. We find that shear stress increases linearly with void ratio in the critical state (state of continuous deformation). We show that the cohesive strength is linearly dependent on the adhesion force between the particles. Furthermore, the shear strength and the void ratio are linearly linked in the critical state. We also identify two limiting behaviors in the evolution of the microstructure based on the coordination number and the anisotropy of the contact network: an increase of coordination number at constant anisotropy for the most cohesive cases, and an increase of anisotropy at constant coordination number for the least cohesive cases. We show that these two microstructural parameters are linked together in the fabric space as a result of steric exclusions. [1] : M.Sonzogni, J.M.Vanson, Y.Reynier, S.Martinet, K.Ioannidou and F.Radjai, Soft Matter, submitted on 12/2023
[491] ID:491- Stiffness, strength, energy dissipation and reusability in architected polycrystals
Seunghwan Lee (Korea Advanced Institute of Science and Technology) and Hansohl Cho (Korea Advanced Institute of Science and Technology).
Abstract
Architecting heterogeneous materials on various (single) crystal lattices has been in a focal point of research with the recent progress in three-dimensional printing and additive manufacturing technologies across a wide range of length scales. In this work, we combine experiments and numerical simulations to design polycrystalline architected materials that exhibit superb elastic and inelastic features under extreme deformation conditions, inspired by polycrystalline metallic materials comprising single crystalline grains and their boundaries. First, we present a simple yet systematic design principle for the polycrystalline microstructures with varying grain sizes. We then fabricated the polycrystalline microstructures using a high-resolution, multi-material 3D printer and conducted large strain mechanical tests on the 3D-printed prototypes under plane-strain cyclic loading scenarios. Our experimental and numerical results revealed that elastic stiffness and plastic strength can be dramatically enhanced as the grain size decreases in these 3D-printed polycrystalline microstructures; furthermore, the connectivity (or strength) throughout the grain boundary network was found to play a crucial role in determining the grain size-dependent stiffness and strength, and their anisotropies. In addition to the grain size-dependent mechanical features, we examined catastrophic failure and “reusability” in the 3D-printed polycrystalline microstructures under large strain cyclic loading conditions, where we observed that cracks mainly initiate in the vicinity of two adjacent grains with a significant difference in their lattice orientations. Moreover, the high-angle grain boundaries were found to efficiently stop the crack propagation and mitigate the catastrophic failure throughout the polycrystalline network. Altogether, our work demonstrates a simple yet physically intuitive microstructure-topology-based approach for designing the polycrystalline architected materials that exhibit outstanding combinations of elastic and inelastic features involving stiffness, strength, energy dissipation, and reusability under harsh mechanical environments.
[493] ID:493- In-situ thermal monitoring during direct energy deposition: the links between process parameters, thermal cycles and microstructures
Marcia Meireles (ArcelorMittal Global R&D Montataire), Jérôme Favergeon (Laboratoire Roberval, Université de Technologie de Compiègne (UTC)), Morgan Dal (Laboratoire PIMM, Arts et Metiers Institute of Technology, CNRS, Cnam, HESAM Université) and Cristian Alvarez (ArcelorMittal Global R&D Montataire).
Abstract
Direct Energy Deposition (DED) technologies have undergone extensive research and investigation, finding applications across various industries such as medical, automotive, aerospace, tooling, and remanufacturing. Despite their versatile applications, ensuring the quality and repeatability of DED parts remains challenging due to the complex physical phenomena during production. In-situ temperature monitoring during DED plays a pivotal role in understanding process-property relationships and optimizing the process.
Adapted monitoring techniques were employed to analyze thermal behavior in solid and liquid states during the DED process of a low-carbon steel. A spatially and temporally resolved temperature measurement tool based on a commercial high-speed camera using a 2D mono-band technique was used to measure melt pool temperature, while an infrared camera was employed to measure temperature in solid zones. The application of these methodologies helped enhancing the understanding of the interconnections between process parameters, observed thermal phenomena, and part characteristics to achieve the desired build quality and microstructures.
Selective results will be presented to show the relationships between process parameters, melt pool geometry and temperatures. Moreover, the developed methodology allows a complete monitoring of local thermal history, and a metallurgical characterization has been performed to link the thermal history with the final microstructure. Such relationships is particularly important for low-carbon steel as the microstructure could evolve under the effect of tempering.
In conclusion, the in-situ temperature methodologies serve as insightful tools for selecting optimal process parameters and ensuring the desired properties of DED components.
[494] ID:494-Cyclic Softening of Ti-6Al-4V subjected to low cycle fatigue: Experiment and Modelling
Anish Ranjan (Indian Institute of Technology Bombay), Amit Singh (Indian Institute of Technology Bombay) and Sushil K Mishra (Indian Institute of Technology Bombay).
Abstract
Microstructures with bimodal and lamellar morphologies were prepared by heat treatment of titanium Ti-6Al-4V alloy at various temperatures. The electron backscatter diffraction (EBSD) analysis confirmed that the width of basal/{0001} macrozone reduces with increased heat treatment temperature. These samples were then subjected to tensile and interrupted strain-controlled low-cycle fatigue tests till a maximum of 200 cycles. The tensile response of bimodal microstructures was inferior compared to the lamellar microstructure. The energy dispersive spectrometry study revealed the alloying element partitioning phenomenon as a significant factor influencing tensile strength. Further, the total elongation is strongly dependent on the effective grain size. When subjected to the low cycle fatigue tests, bimodal microstructures also showed a large degree of cyclic softening. However, the lamellar samples failed at a significantly less number of cycles with limited cycling softening. EBSD study after 50, 100, and 200 cycles indicates a limited variation in the texture of the material. Chaboche isotropic-kinematic hardening model was implemented in Abaqus to predict the cyclic stress-strain response for bimodal and lamellar structures. Isotropic hardening parameters were calibrated based on the variation in cyclic yield strength (CYS) and cyclic stress amplitude (CSA). The stress-strain response predicted using the variation in CYS for bimodal microstructures was relatively accurate. However, for the lamellar microstructures, the preferable method of material parameter calibration was utilising the variation in CSA.
[495] ID:495-Tuning the adhesion properties of soft viscoelastic interfaces by dynamic excitation
Michele Tricarico (Politecnico di Bari) and Antonio Papangelo (Politecnico di Bari).
Abstract
Surface adhesion is a key material property in several engineering applications. In the past decades, many efforts have been made in mimicking nature to achieve outstanding adhesion performances. A well-known example is given by geckos, which are able to climb walls thanks to the hierarchical structure of their feet, that allows them to quickly adjust surface adhesion. Drawing inspiration by geckos, a controlled tuning of interface adhesion could potentially be crucial to a broad range of applications, such as soft robotics, space technology, micro-fabrication, and flexible electronics. When considering soft interfaces, an intricate correlation between viscoelasticity and adhesion exists: parameters like loading history, unloading speed and layer thickness can affect the detachment (i.e., pull-off force) of a rigid indenter from a soft viscoelastic substrate. Moreover, recently it has been demonstrated that surface adhesion of PDMS to a glass sphere can be successfully regulated via mechanical micro-vibrations: it is possible to enhance the apparent adhesion strength up to 77 times or reduce it to 0 with respect to the case with no vibrations, within a timescale comparable to that of geckos. Following up on these results, we have built a customised experimental set-up, that performs indentation tests on soft polymers films, mounted on a vibrating substrate (excited by shakers). We aim at studying the role of materials properties (i.e., crosslinking ratio), film thickness, loading/unloading velocities, and indenter geometry on the adhesive performances of the system. Subsequently we will explore the effects of micro-patterning of these soft interfaces. Micro-structured surfaces were manufactured via two‐photon polymerization lithography, using a Photonic Professional GT2 3D printer (NanoScribe), with sub-micron precision. We believe that our findings will contribute to the development of a new class of soft smart interfaces, with tuneable adhesion properties.
[496] ID:496-Multiperiodic responses and memory effects in frustrated sheets
Lishuai Jin (AMOLF), Colin Meulblok (Leiden University) and Martin van Hecke (Leiden University/AMOLF).
Abstract
Crumpled sheets and amorphous media exhibit memory effects and emergent computing capabilities but are difficult to control due to their highly disordered and uncontrolled geometry. Here we introduce an experimental platform that combines the geometric control of origami with the multistability of frustrated sheets, which allows to precisely and reproducibly couple and program multiple bistable hysteretic elements. We demonstrate that the geometry of the frustrated sheets controls the switching thresholds while the relative positions of the bistable elements set their interactions, giving rise to pathways (e.g., subharmonic orbits) inaccessible to systems of independent hysterons. Our work opens a new way for metamaterials with path-dependent responses and memory effects.
[497] ID:497- Influence of density on the mechanical properties of dry-formed cellulose fibre network materials
Magdalena Kaplan (Department of Engineering Mechanics, KTH Royal Institute of Technology), Adam Johansson (Yangi AB) and Sören Östlund (Department of Engineering Mechanics, KTH Royal Institute of Technology).
Abstract
Dry forming is an emerging technology in paper packaging production. In contrast to traditional papermaking techniques, the pulp fibres are dispersed in air instead of water. Because of the low water content, the material only has to be pressed and heated during a short amount of time. In consequence, the process has shorter lead times and significantly lowered energy consumption. However, water is an important factor in traditional paper making, as it highly contributes to the molecular interactions that create the fibre-fibre joints, which in turn hold the fibre network together. In the absence of water, these interactions will be much weaker, resulting in a substantially different material behaviour. The work presented here is a characterisation of the dry-formed material, where mechanical testing has been carried out in different loading modes. The most important modes of loading, based on what the material experiences in the forming process, were chosen as in-plane tension, out-of-plane compression, out-of-plane shear, and, additionally, combinations of these. Materials in the whole density range were considered, from uncompressed fluff pads, to fully formed sheets, at various densities. The results show similarities to conventional paper materials, although the dry-formed materials are in all cases weaker than wet-formed counterparts. As mentioned before, this is attributed to decreased fibre-fibre joint strength. From the experimental outcome, simple relations for some of the investigated mechanical properties versus density are proposed. In future work, the aim is to create a complete material model, which can be used to simulate the full forming process.
[498] ID:498-Assessing the energy absorption capability of sustainable hybrid composites
Albertino Arteiro (DEMec, Faculdade de Engenharia, Universidade do Porto), Pedro José Silva Campos (DEMec, Faculdade de Engenharia, Universidade do Porto), Denis Dalli (INEGI, Universidade do Porto), Teresa Duarte (DEMec, Faculdade de Engenharia, Universidade do Porto), Steve Foster (McLaren Racing Limited) and Giuseppe Tronci (McLaren Racing Limited).
Abstract
Energy absorption structures in both motorsport and aerospace applications are nowadays manufactured using carbon fibre reinforced polymer (CFRP) materials. Several new composite materials have been recently introduced to the market, including thin-ply CFRPs and more environmentally sustainable alternatives, such as thermoplastics and natural fibre composites (NFCs). There is a noticeable knowledge gap about the energy absorption capabilities of these novel materials, limiting their potential introduction to the design of such structures. While it is known that NFC materials such as flax fibre thermosets possess significantly lower mechanical properties (e.g. compressive strength) compared to high-grade CFRPs, energy absorption is not a simple reflection of these base properties, and thus such materials should not be disregarded at first glance. Furthermore, through laminate hybridisation, there is a realistic potential of matching the energy absorption offered by classical CFRPs while incurring a minimal weight penalty and simultaneously improving the sustainability of the structure. The present work aims to study the crashworthiness performance of hybrid composite laminates manufactured from thermoset NFCs and CFRPs. A quasi-static experimental study was performed on both monolithic and hybrid laminate tubular coupons of various curvatures. These were crushed in a stable progressive manner, enabling the determination of a steady-state crush stress and a corresponding specific energy absorption. Significant improvements were noted in the energy absorption levels of both monolithic flax and hybrid laminate coupons, in comparison to those presented in literature. Furthermore, a hybrid laminate Formula 1 Side Impact Structure (SIS) was manufactured and tested in collaboration with McLaren Racing, as a first demonstration of the potential use of NFCs in similar crashworthiness applications.
[499] ID:499-Constitutive modelling of injection moulded short-fiber reinforced polypropylene: characterisation and model application
Sten van den Broek (Eindhoven University of Technology), Tom Engels (Eindhoven University of Technology), Hans van Dommelen (Eindhoven University of Technology) and Leon Govaert (Eindhoven University of Technology).
Abstract
As a result of their high specific strength and stiffness, polymer-based composites are currently being used in a large variety of load-bearing applications where structural integrity and long-term durability is of the upmost importance. In the persistent pursuit for performance improvement, various reinforcements are added in the polymers, substantially affecting both short-term and long-term properties. A combination of a thermoplastic polymer matrix and short or long reinforcing fibers allows the use of injection moulding as a processing technique which, in turn, has increased production rates and facilitated the manufacturing of complex-shaped parts. This widespread use has led to an increased demand for the development of design tools that can predict the mechanical performance of such systems.
Unfortunately, there is an inherent complexity in the prediction of the mechanical performance of injection-moulded products based on fiber-reinforced thermoplastic polymers. The flow experienced during processing induces fibre orientation, which causes a pronounced directionality of mechanical properties (anisotropy). Moreover, the variation of flow conditions in the mould will lead to a spatial variation of these anisotropic properties throughout a product. Of course, the characteristic time- and temperature dependence of the polymer matrix introduces an additional complicating factor; specifically when there are several molecular deformation processes contributing.
In this study we took a previously developed anisotropic elasto-viscoplastic approach [1] and extended it to effectively describe the anisotropic, rate-dependent stress-strain response of a short-fiber filled polypropylene over a large range of strain rate and temperature (-25 to 100 C). The extension is based on experience in isotropic polymers [2] where the viscoelastic stress contribution of each molecular process is additively composed to the total response (multi-process, multi-relaxation time).
[1] A. Amiri Rad et al., Mech. Mater, 137 103141 (2019) [2] L.C.A. van Breemen et al.,J. Polym. Sci. B, 50, 1757-1771
[500] ID:500-Role of topology on the dynamic response of spinodal meta-materials
Vatsa Gandhi (University of Cambridge), Michael Espinal (Massachusetts Institute of Technology), Rishi Kommalapati (Massachusetts Institute of Technology), Pramod Kumbhar (University of Cambridge), Angkur Shaikeea (University of Cambridge), Carlos Portela (Massachusetts Institute of Technology) and Vikram Deshpande (University of Cambridge).
Abstract
Advancements in additive manufacturing have enabled fabrication of multi-functional architected meta-materials, allowing tailoring material properties (e.g., high stiffness-to-weight ratio) across a range of engineering applications including energy absorption, thermal insulation, and light weight structures such as sandwich panels in aerospace and automotive industries. Truss- and plate-based designs, the most common types of architected materials, are highly susceptible to stress concentrations, resulting in localized permanent damage. Therefore, there is a new paradigm shift towards spinodal shell-based architecture which avoids sharp joints to mitigate stress concentrations, and can therefore, achieve optimal stiffness while being particularly insensitive to defects. Due to their smooth, double curvature surface (e.g., eggshell), these shell lattices can be geometrically designed to control the anisotropic stiffness tensor and smoothly graded both as a function of relative density and topology. This provides a strong incentive to leverage their design capabilities to explore the effects on energy efficiency and wave guidance behaviour. In this work, both quasi-static and dynamic direct impact experiments are conducted on spinodal architectures to understand the role of strain-rate (~10^-4 – 10^2 s^-1) and topology on their mechanical behaviour. Specimens of different topologies (e.g., isotropic, columnar) and a constant relative density of 30% are manufactured using stereo-lithography with a tough resin. Through macroscopic load-displacement measurements, it was observed that these shell structures undergo more than 10x increase in strength when compressed dynamically, a feat unheard of in conventional architected materials. To further validate this, digital image correlation (DIC) is conducted to extract local surface-level displacement fields to explain the increased strain rate sensitivity and monitor the progression of local deformation modes (e.g., higher-order buckling) during compression. Lastly, these results are compared to experiments on conventional octet truss and sheet-based gyroid lattices, of the same material, to demonstrate the observed strain-rate sensitivity is indeed topology driven.
[502] ID:502-Size effects in the plasticity-assisted fracture of brittle polycristals
Jean-Michel Scherer (Mines Paris, Université PSL, Centre des Matériaux (MAT), UMR7633 CNRS, 91003 Evry, France) and Kaushik Bhattacharya (California Institute of Technology, Mechanical and Civil Engineering Department).
Abstract
Recent advances in experimental techniques have made it possible to characterize the bulk microstructure and map cracks inside millimeter-sized samples. Meanwhile, mathematical and numerical tools, have been developed and applied to model the nucleation and growth of cracks in brittle materials. The phase-field method, originally formulated to model complex crack on a macroscopic scale, has recently been extended to gain more and more physical insight. Recent developments include extensions to account for an anisotropic fracture energy landscape, coupling with plasticity [1], or diffusion of chemical species. In this context, we focus our scope at the microstructure scale, on materials where brittle fracture is initiated and governed by local plastic activity, e.g. silicon-iron, tungsten or steels at low temperatures. The seminal work of Hall [2] and Petch [3] has shown how grain size is related to size effects on the yield and fracture strength. The role of grain boundaries and grain size on the fracture toughness is less clear as the fracture toughness exhibits a non-monotonic evolution with grain size in the micrometer range [4]. We present advances in modeling the coupling between crystal plasticity and brittle fracture. We recall how local stress heterogeneities and singularites can arise from dislocation self-interactions and interactions with grain boundaries. Therefore, we develop a modelling framework designed to capture plasticity-induced brittle fracture that accounts for a material lengthscale. We outline the role of this lengthscale in capturing characteristic grain-size effects observed for brittle crack nucleation and propagation in polycrystals.
[1] Brach, S., Tanné, E., Bourdin, B., and Bhattacharya, K.. Computer Methods in Applied Mechanics and Engineering 353 (2019): 44-65. [2] Hall, E. O. Proceedings of the Physical Society. Section B 64.9 (1951): 747. [3] Petch, N. J. Progress in Metal Physics 5 (1954): 1-52. [4] Reiser, J., and Hartmaier, A.. Scientific reports 10.1 (2020): 2739.
[503] ID:503-A statistical framework for cellular reorientation under cyclic strain
Shuvrangsu Das (University of Cambridge), Patrick McGarry (University of Galway) and Vikram Deshpande (University of Cambridge).
Abstract
Cells avoid cyclic strain, as they orient perpendicular to the direction of applied cyclic strain on the underlying 2D substrate. This alignment is usually attributed to stress-fiber reorganization. However, experimental observations suggest that cell morphology and cytoskeletal stress-fiber organization are interconnected during cellular reorientation under cyclic loading. In this work, we developed a statistical mechanics framework that incorporates the stress-fiber organization, and cell morphology as well as their coupled evolution. The framework predicts the probability distribution of cell area, aspect ratio, and orientation, which agree well with the correspodning statistics obtained from experiments. Moreover, the framework proposes that cell achieve their final orientations by rotating from their initial configurations, instead of undergoing cellular straining. Our framework uncovers physical insights into the coupled dynamics of cell morphology and stress-fibers, and proposes a new mechanism governing cellular organization in cyclically strained tissues.
[504] ID:504-Reassessing rubber elasticity through full field X-ray measurements
Angkur Jyoti Dipanka Shaikeea (University of Cambridge), Zifan Wang (University of Cambridge), Shuvrangsu Das (University of Cambridge), Akshay Joshi (University of Cambridge) and Vikram Deshpande (University of Cambridge).
Abstract
The usage of engineering polymers, including rubbers, spans a wide range of applications in various industries, from aerospace to medicine. The comprehension of rubber elasticity, evolving from Hooke's law in the 1660s to Flory's ground-breaking work on polymer chains in the 1930s and 1940s (earning him the 1974 Nobel Prize), culminated in the formalization of understanding through the Neo-Hookean model in the 1940s. This model established the notion that, under isothermal conditions, stress is (non)linearly correlated with strain, with no consideration for other state variables. However, our research, utilizing an innovative X-ray tomography method, challenges this foundational concept. We perform in-situ experimentation in X-ray tomography to present evidence that prompts a re-evaluation of the established understanding. Our findings reveal the presence of a mobile un-crosslinked phase within rubbers and various engineering polymers, such as Nylon and HDPE, introducing an additional state variable into the equation. Consequently, spatial variations of stress (or strain) emerge as influential factors in determining their mechanical behaviour. This challenges the prevailing belief that the material properties of polymers can be solely defined on a local scale.
[505] ID:505-Data-driven games for computational multiscale mechanics of materials
Laurent Stainier (Centrale Nantes), Kerstin Weinberg (Universität Siegen) and Michael Ortiz (California Institute of Technology).
Abstract
As illustrated in a recent paper (Comput. Meth. Appl. Mech. Eng. 417A, 116399, 2023), the distance based data-driven paradigm for computational mechanics, labelled DDCM, can be revisited in the context of Game Theory. The classical DDCM formulation appears as a collaborative game, while an alternative adversarial game approach can also be derived. The latter approach offers the advantage to uncouple the data-driven constitutive description from the boundary-value field problem, allowing for easy integration in standard FE codes for example, at least in explicit dynamics or using matrix-free solvers.
We will illustrate how DDCM can be used in the context of computational multiscale mechanics of materials, both in its classical and in its game theoretical formulations. One important advantage of DDCM in the context of two-scale concurrent analysis lies in its capacity to efficiently reuse previously computed material response at the microscale (e.g. on a representative volume element), reducing the computational cost and leading to a goal-oriented sampling of the macroscopic material response.
[506] ID:506-Modelling the effects of manufacturing defects in composite structures with shell elements: a multi-scale framework based on second-order homogenisation
Aewis Kw Hii (Bristol Composites Institute, University of Bristol), Bassam El Said (Bristol Composites Institute, University of Bristol) and Stephen R Hallett (Bristol Composites Institute, University of Bristol).
Abstract
Manufacturing defects are frequently present within in-service composite components, and it is vital to understand and mitigate their impacts on structural performance and safety. This work presents a study demonstrating how shell elements can be constitutively enhanced to model the impact of manufacturing defects on the mechanical performance at the structural length-scale.
Owing to their accuracy and computational efficiency, shell elements are an effective tool for the mechanical performance analysis of large structures. When used in conjunction with Classical Laminate Theory and failure criterion, they provide accurate predictions of the structural stiffness and in-plane failure modes in composite components. However, a key shortcoming is that they cannot be used to model manufacturing defects like wrinkles and voids, nor geometric features like ply-drops and cut-plies, all of which are frequently present in as-manufactured components. To mitigate these modelling assumptions, design engineers often resort to applying sizeable knockdown factors to the component strength, derived from empirical estimates and costly experimental campaigns.
To address the issue, this contribution creates a multi-scale shell analysis framework based on second-order homogenisation and studies the influences of manufacturing defects on the overall shell strength and stiffness. The focus is on the bending and transverse shear modes, where the accuracy of the multi-scale approach to model defects at scale will be assessed. In the long run, this work is a step towards enabling engineers to determine the defects induced strength knockdowns in large components using only shell elements.
[507] ID:507- Incremental variational approach coupling gradient damage with poroelasticity of saturated media
Xiao-Dong Zhang (University of Lorraine), Long Cheng (University of Lorraine), Djimedo Kondo (Sorbonne University) and Albert Giraud (University of Lorraine).
Abstract
We aim at investigating the full coupling between gradient damage, poroelasticity and fluid flow phenomena in saturated porous media. To this end, we first extend the thermodynamics-based Biot-Coussy theory of porolelasticity in order to incorporate gradient damage processes. Inspired by Stainier 2013 (Adv. App. Meca., Vol 46, P. 69-126) in thermomechanics, we introduce the concept of kinetic porosity that allows to well clarify the interaction between skeleton deformation and fluid filtration in the connected pore space, this extension is then implemented to establish an incremental variational formulation expressed as a four-field minimization problem of an incremental total energy functional, which incorporates poroelastic energy, as well as the dissipation related to damage evolution and fluid flow in time increment. Moreover, by taking advantage of a suitable approximation of the kinetic porosity in the current time increment, the above mentioned minimization problem is reduced to a three-fields dependent one, involving the displacement and damage fields of the skeleton phase as well as the fluid pressure field, which is shown to result in the equilibrium state of the saturated porous media. An incremental variational principle is thus established (Zhang 2023, Ph.D. thesis, Univ. Lorraine). Subsequently, a variational model for the fully coupled problem is consistently proposed and is numerically implemented by means of a semi-staggered optimization algorithm. This procedure is applied in a benchmark modeling for which relevant solutions and numerical results related to hydraulic fracturing are available. The model is also employed for the evaluation of an Excavation Damage Zone (EDZ) around a waste storage underground gallery. The model is shown to be able to deliver sufficiently reliable predictions, which extends either in presence of coupled poroelastic effects or for pure elastic-damage couplings.
[508] ID:508-Development of new lean titanium alloys presenting increased work-hardening and defect tolerance through Reorientation Induced Plasticity
Odeline Dumas (4MAT, Université Libre de Bruxelles, Belgium), Harena Rakotozafy (4MAT, Université Libre de Bruxelles, Belgium), Loic Malet (4MAT, Université Libre de Bruxelles, Belgium), Frederic Prima (PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris, Paris, France) and Stephane Godet (4MAT, Université Libre de Bruxelles, Belgium).
Abstract
Defect tolerance trough high work-hardening in parts produced by additive manufacturing has been recently proven efficient in beta metastable Ti alloys. However, this alloy family does not meet the necessary yield strength levels of the aerospace industry. In the present study, alpha+alpha' microstructures are shown to exhibit never reached strength/work hardening balances. First, the proof of concept is evidenced in the well-known Ti-Al6-V4 alloy. It is shown that increased work-hardening is obtained by a novel deformation mechanism in the martensite of such dual-phase structures: Reorientation Induced Plasticity or RIP effect. Based on these findings, new alloy design rules are then proposed to increase the work-hardening behavior of lean alpha+beta alloys. They are shown to be particularly efficient on 3 different alloys. Reorientation Induced Plasticity is responsible for this unique behaviour. A large work-hardening level can be obtained while preserving high yield strength levels provided the compositions and annealing conditions are properly optimized.
[509] ID:509-Surrogate modelling of springback in thermoformed foam cores
Luis Octavio De Cunto (Aarhus University), Poul Henning Kirkegaard (Aarhus University) and Souhayl Sadik (Aarhus University).
Abstract
Thermoforming is a manufacturing process where heated viscoelastic materials, such as polymers, are moulded into specific shapes by applying heat, draping the softened material over a mould, and then allowing it to cool and solidify. During thermoforming, springback may occur as the material partially revert to their original shape when cooled after being stretched and moulded. This phenomena could lead to discrepancies in the geometry of the final shape with respect to the desired shape. Therefore, it is necessary to consider springback effects when designing the mould to be used in the process. In this project, a surrogate model is built in order to predict the springback during the thermoforming of foam core material panels. The surrogate model works by mapping the mould geometry (determined by a number of design parameters) with the surface of the material after thermoforming (determined by characteristic parameters of the final geometry). The training and testing data is built by performing Finite Element Simulations with ABAQUS software, sampling the space of possible surfaces, while Gaussian Processes (Kriging) models are used to build the surrogate, which is later used to navigate the design space and determine the optimal mould geometry.
[511] ID:511-What can we learn from detailed reconstructions of head injuries?
Svein Kleiven (KTH Royal Institute of Technology).
Abstract
Consequences of head injuries are not limited to the victim alone but have impact on the society as a whole through the large costs involved, not to mention the tragedies and the suffering. It should be noted that very little is understood about the true mechanisms associated with head injury, but many theories exist. Implementation or modification of security systems, such as a new helmet, is now a long and complex process. In recent years, biomechanical simulation models of head and human body acquired an increasingly larger place in the design of safety systems. One of the advantages with the finite element (FE) method is the possibility to model the anatomy with great detail, thus it is possible to study the kinematics of the head as well as the stresses and strains in the Central Nervous System (CNS) tissues. This presentation primarily focuses on summarizing current efforts, and to outline future strategies in human head injury prevention in sports. Multiple length scales are involved in the development of traumatic brain injury, where the global mechanics of the head level are responsible for local physiological impairment of brain cells. Prevention through safety helmets with innovative rotational protection systems are demonstrated.
[512] ID:512-Numerical study of the influence of woven roving mat reinforcement on shape deformation, fixity, and recovery of shape memory polymer composite beams
Md Saad Hussain Barsania (Research Scholar, Department of Aerospace Engineering, Indian Institute of Technology Madras) and K V Nagendra Gopal (Professor, Department of Aerospace Engineering, Indian Institute of Technology Madras).
Abstract
Shape memory polymers (SMPs) exhibit a distinctive capacity for significant deformations, followed by the restoration of their initial form upon exposure to particular external stimuli. This characteristic has enabled their recent use in many fields, particularly in biomedical devices and even for some aerospace applications. However, their use in structural applications has been limited due to their low strength and other mechanical properties. Incorporating reinforcing fibers into SMPs significantly enhances their mechanical properties though accompanied by a small reduction in their intrinsic shape memory properties. High glass transition temperatures (Tg) required for aircraft structural applications can be realized by optimizing the ratio of the SMP constituents. The current study is a finite element analysis based numerical investigation of the thermally stimulated response of glass fiber woven roving mat reinforced SMP laminate beams in terms of their deformation, shape fixity, and recovery. A 3D constitutive model for thermoset SMPs is implemented through a user-defined material (UMAT) subroutine in ABAQUS/Standard. The shape memory cycle begins at room temperature (Tl < Tg), heating to a high temperature (Th > Tg). After loading at high temperature (Th), the beam is cooled to low temperature (Tl) and then unloaded to assume a temporary shape. Upon reheating to high temperature (Th), it fully recovers its original state. The increase in strength of the SMPC and corresponding reduction in shape fixity were observed and quantified for different fiber volume fractions of the SMPC and compared with pure SMP. The study contributes valuable insight into optimizing SMPC structures for aerospace applications where a balance is required between high glass transition temperatures and high strength without much reduction in the shape memory effects.
[513] ID:513-Yield locus development of TIG Welded AA2219 alloy using cruciform samples
Priya Tiwari (IIT Bombay), Amir Hamza Siddiqui (IIT Bombay), Svs Narayan Murty (VSSC ISRO) and Sushil Mishra (IIT Bombay).
Abstract
AA2219, an aluminum-copper alloy, is extensively utilized in aerospace industries due to its exceptional weldability. Its robust strength, particularly at cryogenic temperatures, renders it a prime choice for applications such as cryogenic fuel tanks. The manufacturing of these fuel tanks predominantly involves welding processes, with TIG welding being a prevalent method.
This study characterizes AA2219 through uniaxial tensile tests conducted along and transverse to the weld direction. A specially designed cruciform sample ensures that the gauge area encompasses critical weld zones. Planar biaxial tensile tests are subsequently performed on these cruciform samples to elucidate the material behavior under welded conditions. The tests, executed in load control mode, encompass seven distinct load ratios (1:0, 2:1, 4:3, 1:1, 3:4, 1:2, and 0:1). The evolution of the yield locus is plotted and compared with that of the base material, revealing a substantial reduction in the material's safe zone post-welding. This reduction poses challenges for performing any forming operation. Fractography is employed to comprehend fracture behavior under various loading conditions. Additionally, Electron Backscatter Diffraction (EBSD) analysis is utilized to study microstructure evolution during the tests. The findings shed light on the mechanical response of AA2219 after welding, emphasizing the critical need to understand material properties for ensuring the structural integrity of components, particularly in applications demanding high strength at cryogenic temperatures.
[514] ID:514-A crack length control method for a Phase Field Fracture model in a fft-based scheme
Pedro Aranda (Polytechnical University of Madrid) and Javier Segurado (IMDEA Materials Institute).
Abstract
In fracture mechanics, the study of crack propagation in pre-cracked specimens with numerical simulations presents an unstable propagation with load and displacement control in many cases. In the case of the Phase Field Fracture model, the instability prevents the use of monolithic algorithms due to the non-convexity of the functional that needs to be minimized, forcing the use of stagger schemes that may require several hundred iterations to reach a stable configuration [1]. This problem is even greater when studying crack propagation through the microstructure in micromechanical problems. In this work, an energy dissipation control method [2] based on the crack length (CLCS) has been developed for Phase Field Fracture model to control the applied external load by imposing a monotonic crack growth. This technique allows the use of monolithic algorithms and the control allows to obtain the required stress/strain decrease path (snap-back behavior) corresponding to stable crack propagation. The technique has been implemented in a FFT based resolution framework [3] with a much higher computational efficiency in periodic micromechanical problems. The control technique is validated with a FEM based framework with CLCS in problems with analytical solution. The accuracy and efficiency of both proposed frameworks is studied. Finally, the resolution of multiple crack propagation in 2D and 3D microstructures of composite materials is presented.
REFERENCES [1] T. Gerasimov, L. De Lorenzis. A line search assisted monolithic approach for phase-field computing of brittle fracture. Computer Methods in Applied Mechanics and Engineering, 312:276–303, 2016. [2] Carpinteri A, Accornero F. Multiple snap-back instabilities in progressive microcracking coalescence. Engineering Fracture Mechanics, 187:272–281, 2018. [3] S. Lucarini, M. Upadyhay, J. Segurado, FFT based approaches in micromechanics: fundamentals, methods and applications. Modelling and Simulation in Materials Science and Engineering 30 023002, 2022.
[515] ID:515-DEM study of force transmission in flexible granular chain packings
Mohd Ilyas Bhat (Indian Institute of Science, Bangalore) and Tejas G Murthy (Indian Institute of Science, Bangalore).
Abstract
Flexible granular chains are linear chains of spherical beads connected by link elements, similar to roller blind chains. These chains form an exciting class of elasto-granular materials, wherein the inclusion of tension-transmitting link elements transforms the mechanical properties of parent cohesionless granular material. These chains exhibit an array of intriguing properties such as jamming at low packing density, strain stiffening, higher stiffness at small coordination numbers etc. Unlike other cohesionless granular materials, which flow and form conical piles on repose, the packings of these chains entangle and form stable vertical standing columns. This flow behaviour makes the study of force transmission and wall pressures in these chain packings an exciting problem to explore. We explore the static pressure distributions in 2D random chain packings and contrast their behaviour with the Janssen effect observed in conventional cohesionless granular materials. Although numerical methods such as Monte Carlo and MD have been employed to study the particle-level mechanics of flexible granular chains. However, most of these studies are carried out for drastically different length scales of molecular polymer melts. In our DEM contact model, the links connecting the beads in the chains are implemented as a combination of linear normal and angular stiffness, which constrains inter-particle elongation and the bending angle between three consecutive beads. We generate 2D chain packings in a vertical cylinder with varying chain length (M), column height, container size and deposition methods. Apart from the wall forces, we evaluate various micro-mechanical, topological and macroscopic parameters to elucidate force chain transmission and deformation of these chain packings. The ability of the chains to form tensile force chains drastically affects the saturation of the column base pressure. Moreover, the flexible geometry of the chains results in the formation of chain loops, leading to larger heterogeneity and anisotropy in contact force chains.
[516] ID:516- A multi-field mixed incremental variational framework for phase-field modeling of hydrogen-promoted fracture
Vikas Diddige (Institut für Mechanik und Fluiddynamik, TU Bergakademie Freiberg), Andreas Seupel (Sunfire GmbH), Stephan Roth (Institut für Mechanik und Fluiddynamik, TU Bergakademie Freiberg) and Björn Kiefer (Institut für Mechanik und Fluiddynamik, TU Bergakademie Freiberg).
Abstract
Certain metals, when exposed to a hydrogen environment---notably in hydrogen production, storage, and transport---experience a substantial deterioration in mechanical properties, an effect termed hydrogen embrittlement. To understand, predict, and counteract this hydrogen-assisted material degradation, sufficiently accurate material models are needed. According to the current hypothesis, hydrogen diffusion is driven by gradients of concentration and hydrostatic stress [1]. To capture this, a phase-field model is formulated as a multi-field problem coupling deformation, crack propagation, and diffusion to analyze hydrogen-promoted fracture. Here, the displacements, a fracture-related phase-field, the hydrogen lattice occupancy, and the chemical potential are considered as primary field variables. Approaches proposed in the literature often use an extrapolation of the hydrostatic stress calculated at the integration point level onto the nodes and later compute the gradient of hydrostatic stress [1]. This extrapolation process can introduce errors in the distribution of hydrostatic stresses throughout the material domain, potentially affecting the reliability of the simulation results. To address this, the model is reformulated into a mixed rate-type variational setting using a generalized Legendre transformation [2]. This introduces the chemical potential---whose gradient governs the hydrogen flux---as an additional variable dual to the hydrogen lattice occupancy. The primary field variables are obtained through the numerical solution of this saddle point problem. Moreover, the model's versatility in practical applications is enhanced by the ability to prescribe Dirichlet boundary conditions for the chemical potential and both homogeneous and inhomogeneous Neumann boundary conditions for the hydrogen flux on the specimen boundary. Furthermore, the inherent symmetry of the tangent moduli enables the use of symmetric solvers, and the flexibility of the framework easily accommodates additional fields of interest. Results for several representative boundary value problems are presented to demonstrate the applicability of the developed numerical framework.
[1] https://royalsocietypublishing.org/doi/10.1098/rspa.2013.0641 [2] https://doi.org/10.1016/j.jmps.2020.104093
[517] ID:517-Viscoelastic Constitutive Artificial Neural Networks (vCANNs) - a framework for data-driven anisotropic nonlinear finite viscoelasticity
Kian P. Abdolazizi (Hamburg University of Technology), Kevin Linka (Hamburg University of Technology, RWTH Aachen University) and Christian J. Cyron (Hamburg University of Technology, Helmholtz-Zentrum Hereon).
Abstract
The constitutive behavior of polymeric materials is often modeled by finite linear viscoelastic or quasi-linear viscoelastic models [1]. These popular models are simplifications that typically cannot accurately capture the nonlinear viscoelastic behavior of materials. For example, the success of attempts to capture strain (rate)-dependent behavior has been limited so far. In response to this issue, we introduce viscoelastic Constitutive Artificial Neural Networks (vCANNs), a novel physics-informed machine learning framework [2]. vCANNs rely on the concept of generalized Maxwell models with nonlinear strain (rate)-dependent properties represented by neural networks. With their flexibility, vCANNs can automatically identify accurate and sparse constitutive models for a wide range of materials. To assess the capabilities of vCANNs, extensive training was conducted using experimental stress-strain data from synthetic and biological materials subjected to diverse loading conditions, e.g., relaxation tests, cyclic tension-compression tests, and blast loads. The results show that vCANNs can learn to accurately and efficiently represent the behavior of these materials without human guidance. We showcase the seamless integration of vCANNs into existing finite element codes through illustrative examples. This integration underscores the practical applicability of vCANNs in the field of applied mechanics.
References
[1] K. Linka et al. [2021], 'Unraveling the local relation between tissue composition and human brain mechanics through machine learning', Frontiers in Bioengineering and Biotechnology 9:704738 , https://doi.org/10.3389/fbioe.2021.704738. [2] K.P. Abdolazizi, K. Linka, C.J. Cyron [2023], 'Viscoelastic Constitutive Artificial Neural Networks (vCANNs) - a framework for data-driven anisotropic nonlinear finite viscoelasticity', Journal of Computational Physics 499:112704, https://doi.org/10.1016/j.jcp.2023.112704.
[519] ID:519-A gradient crystal plasticity model with two length scale parameters
Aldo Marano (DMAS, ONERA, Université Paris Saclay, F-92322 Châtillon, France), Lionel Gélébart (Université Paris-Saclay, CEA, Service de Recherches Métallurgiques Appliquées) and Samuel Forest (Mines Paris, PSL University, MAT-Centre des matériaux, CNRS UMR 7633).
Abstract
The regularizing properties of gradient models for the simulation of plasticity localization problems are well known. In the case of crystal plasticity, they classically rely on a constitutive theory with a dependence on a tensorial measure of geometrically necessary dislocations (GNDs) density, associated to a length scale parameter. This length scale allows to control grain size effects on hardening induced by GNDs, but also to regularize the formation of kinks bands. However, this theory cannot yield a regularization of slip bands formation, due to the lack of dependence on the plastic distortion gradients components that are not associated to GNDs. In this work, we present a gradient crystal plasticity framework that introduces a dependence on a second tensorial measure of plastic slip gradients, associated to a second length scale parameter that yields a regularization of slip bands. The framework has been implemented within the FFT-based solver AMTIEX_FFTP. Analytical calculations and numerical simulations of single crystals and polycrystals will be presented. Our results show that these two length scales allow to control the characteristic size of slip and kink bands independently, and influence the competition between slip and kink banding. As a result, this framework allows capture important features of observed slip band networks in polycrystalline materials within crystal plasticity simulations. Finally, perspectives towards its application for the modeling of slip localization induced fatigue cracks will be discussed.
[520] ID:520-Fast cracks in amorphous polymers: unraveling the interplay between near-tip microcracking dynamics and macroscale fracture mechanics
Alizée Dubois (CEA DAM), Daniel Bonamy (CEA Saclay), Claudia Guerra (CEA Saclay), Julien Scheibert (Ecole Centrale Lyon) and Davy Dalmas (Ecole Centrale Lyon).
Abstract
Dynamic crack propagation is the key mechanism leading to catastrophic material failure. Linear Elastic Fracture Mechanics (LEFM) provides a predictive theoretical framework [1] and describes fracture experiments well as long as its application hypothesis are fulfilled and single cracks are considered. However, at high enough speeds, crack propagation involves small-scale, high-frequency, microcracking events that are difficult to account for via conventional continuum fracture mechanics. To shed light on these mechanisms, we re-examined an experimental dataset obtained on acrylic glass (PMMA) [2,3,4], which includes both measurements of crack speed and fracture energy at the macroscale, and catalogs with the micrometer/nanosecond resolved dynamics of the associated near-tip microcracking events. In the presentation, we will see how a simple geometrical model succeeds in reproducing quantitatively all the statistical features observed in the microcracking dynamics, and how macroscale crack speed and fracture energy emerge from the proper upscaling of this model.
References: [1] L.B. Freund, Dynamic Fracture Mechanics, Cambridge University Press, New York (1990). [2] J. Scheibert, C. Guerra, F. Célarié, D. Dalmas, and D. Bonamy. Brittle-quasibrittle transition in dynamic fracture: An energetic signature. Physical Review Letters, 104(4):045501 (2010) [3] C. Guerra, J. Scheibert, D. Bonamy, D. Dalmas, “Understanding fast macroscale fracture from microcrack post-mortem patterns” PNAS 109, 390-394 (2012). [4] D. Dalmas, C. Guerra, J. Scheibert, and D. Bonamy. Damage mechanisms in the dynamic fracture of nominally brittle polymers. International Journal of Fracture, 184(1-2):93–111 (2013).
[521] ID:521- Influence of irradiation and deformation on slip transfer in austenitic stainless steels
Thomas-Xavier Masset (CEA Paris-Saclay), Jérémy Hure (CEA Paris-Saclay) and Tanguy Benoît (CEA Paris-Saclay).
Abstract
Irradiation Assisted Stress Corrosion Cracking (IASCC) affects the internal structures of Pressurized Water Reactors, leading to the intergranular failure of austenitic stainless steel components. After irradiation, slip discontinuity at grain boundaries has been shown to strongly correlate with intergranular cracking. This is due to the impingement of slip bands at grain boundaries, which leads to high local stresses that may be responsible for cracking. As the irradiation level increases, fewer slip bands are observed for a given strain level, resulting in higher local stresses. Therefore, it is crucial to obtain a reliable criterion that can predict slip discontinuity at grain boundaries in austenitic stainless steel as a function of both deformation and irradiation level for the modelling of IASCC. However, no such criteria are currently available in the literature. In this study, in-situ SEM tensile experiments on an unirradiated and two proton-irradiated 304L specimens were conducted sequentially through two increments of plastic strain (2.5% up to 5%). The zones of interest were mapped using Electron Back Scattered Diffraction before deformation, followed by Scanning Electron Microscope images of the same zones after each strain increment. Slip transfer is evaluated for all defined grain boundaries, based on their local crystallographic orientations and the analysis of slip traces. The activated slip system in each grain is assessed using the Schmid criterion, assuming either uniaxial stress conditions or using FFT simulations based on the real microstructure. The experimental data at the irradiated state are consistent with the criteria reported in the literature for FCC materials. Finally, we discuss the effects of irradiation and deformation.
[523] ID:523- Insulin fluid dynamics and absorption via subcutaneous injection port: a computational study addressing flow obstructions and tissue heterogeneities
Daniele Bianchi (Università Campus Bio-medico di Roma), Lorenzo Zoboli (Università Campus Bio-medico di Roma), Francesco Luppino (Università Campus Bio-medico di Roma) and Alessio Gizzi (Università Campus Bio-medico di Roma).
Abstract
Over 33 million people in the EU suffer from diabetes. According to data from the International Diabetes Federation (IDF), the absolute number of diabetics in the EU is projected to increase from approximately 33 million in 2010 to 38 million in 2030. Many patients require multiple-dose insulin therapy to achieve acceptable glycemic control. Evidence suggests that a noninvasive or minimally invasive treatment option will help improve adherence for individuals whose reasons for nonadherence range from the inconvenience of therapy to needle aversion, especially in pediatric patients. Furthermore, insulin-induced lipohypertrophy is the most common local complication observed in diabetic patients undergoing insulin therapy, which reduces insulin absorption. This study couples a computational model capable of simulating insulin fluid dynamics through the port and subcutaneous tissue with a model of insulin absorption in the tissue. The computational model, based on finite element method, was utilised to analyse the operating conditions of the injection port. Specifically, the impact of an obstruction within the cannula delivering insulin to the subcutaneous tissue was examined. Moreover, the model can integrate both the physiological heterogeneity of the tissue and account for pathological tissue conditions such as lipodystrophies. The results highlight the influence of both obstruction and tissue heterogeneities on tissue absorption. Furthermore, the model can be employed to optimise the design of the injection port, thereby enhancing the device's effectiveness in diabetes therapy.
[524] ID:524-Experimental and numerical investigation of the inter-laminar shear behavior of flax/epoxy composite laminate
Fatiha Batouche (Laboratoire des Technologies Innovantes, Ecole Nationale Supérieure des Technologies Avancées, Algiers, Algeria), Mohamed Fayçal Ameur (Laboratoire des Technologies Innovantes, Ecole Nationale Supérieure des Technologies Avancées, Algiers, Algeria), Redouane Zitoune (Institut Clément Ader, UMR CNRS 5312, University of Toulouse, Toulouse, France), Claire Morel (Institut Clément Ader, UMR CNRS 5312, University of Toulouse, Toulouse, France) and Lotfi Toubal (Centre de Recherche sur les Matériaux Lignocellulosiques, Université du Québec à Trois-Rivières, QC, Canada).
Abstract
Background: Natural fiber reinforced polymers composites (NFRP) are currently very popular in the field of engineering, due to their excellent mechanical and physical properties and low manufacturing costs [1]. The study of the mechanical and failure behavior of thin flax/epoxy composites has been the subject of several research papers [1-2]. The objectives of this paper are to address the mechanical behavior and failure mechanisms that occur of thick flax/epoxy composite laminates, so far lacking in the scientific literature. Procedure: To achieve the objectives mentioned previously, experimental inter-laminar shear tests are proposed. These tests have been conducted on various thickness of the laminates (2mm, 4 mm and 8.5 mm). For the analysis of the mechanisms of failure, the tests have been recorded by CCD camera and the images have been used to measure the strain fields thanks to the DIC technique. The experimental results have been correlated to those obtained by Finite Elements Approach. The numerical model has been developed with cohesive elements in order to predict the damage between layers. Key findings: From the experimental results and the finite element analysis, the following conclusions can be drawn: • Failure of the laminates occurred due to delamination at the interface between the plies and the decohesion of the middle layer for all the specimens tested. • The Finite Element model show a good agreement with experimental results indicate the validity of the FE model at the macro-scale. However, at the meso-scale, some mechanisms of failure are not captured by the model. References: [1] I. El Sawi et al. An investigation of the damage mechanisms and fatigue life diagrams of flax fiber-reinforced polymer laminates, Journal of materials science, 2014. https://doi.org/10.1007/s10853-013-7934-0 [2] K. Mayssa et al. Evaluation of interlaminar shear of laminate by 3D digital holography, Optics and Lasers in Engineering, 2017. https://doi.org/10.1016/j.optlaseng.2016.12.014
[525] ID:525-Computational Study of the Effect of Structural Deformation on Osmotic Membrane Mass Transfer
Meisam Mohammadi Amin (Technical University of Denmark) and Ulrich Kruhne (Technical University of Denmark).
Abstract
Semi-permeable membranes are porous materials/structures that have several applications in different industries and daily life, for example as a key component in osmotic filtration systems. To date, fluid dynamics and osmotic mass transfer in membrane-bounded channels has been investigated mostly assuming undeformed configurations. However, many osmotic membrane processes, including Reverse Osmosis (RO) and Pressure-Retarded Osmosis (PRO), may undergo high-pressure conditions that cause significant membrane deformations due to pressure differences between the fluid channels. On the other hand, the deformations can change membrane channel spacing and configuration which have a great impact on both bulk flow conditions (pressure, velocity, etc.) and the osmotic-driven mass transfer through the membrane. To study such effects, a multi-physics computational model is implemented in this work, coupling a CFD solver (for fluid dynamics), a FSI model (for fluid-structure interactions) and mass transfer models (for osmotic transmembrane flow). The obtained results for a flat sheet membrane show that the hydrodynamics in the fluid-filled channels of membrane has significant impact on several process aspects, such as the pressure drop and osmotic fluxes. It is observed that alteration of the fluid velocity/pressure profiles and External Concentration Polarization (ECP) in adjacent deformed channels may lead to considerable change in transmembrane flux and Internal Concentration Polarization (ICP) values. This effect is most critical for the case that we use a high-pressure solution (deforming the membrane towards the low-pressure side) as the draw solution with high concentration of solute (strong ECP effect), a typical configuration in the PRO systems. It can be concluded that membrane deformations and flow redistribution effects may become even larger for thinner membranes or higher working pressures, where the use of meshes/spacers is inevitable. Therefore, process modelling and optimization tools are necessary for compromising between the structural stability of the membrane and the osmotic-driven mass transfer performance.
[527] ID:527-Magnetoactive elastomers: micromechanics and instability-driven microstructure transformations for tunable functions.
Stephan Rudykh (University of Galway).
Abstract
study the behavior of magnetoactive elastomers (MAE) undergoing large deformations while exited by magnetic fields. We analyze the role of the microstructures in the overall performance and stability of the soft active composites. We examine the coupled behavior of the active composites with (i) periodically and (ii) randomly distributed active particles embedded in a soft matrix [1], and (iii) periodic laminate composites and anisotropically structured composites with chain-like structures [2-4]. We identify the key parameters governing the magneto-mechanical couplings. Moreover, we find advantageous microstructures that give rise to significant enhancement of the coupling and actuation of the active materials [1]. Furthermore, we show that even very similar microstructures, such as periodic composites with hexagonal and rectangular representative volume elements, exhibit very different behavior in terms of their actuation and effective properties [1]. Next, we investigate the coupled magneto-elastic instabilities MAE. These instabilities may occur at different length scales [3, 5], and, potentially, they may be exploited to achieve new functionalities such as tunable band-gaps [6-10]. We explore the role of external magnetic fields, microstructure parameters, and consentient properties on the multiscale instabilities.
REFERENCES:
[1] E. Galipaeu et al. Int. J. Solids. Struct. 51: 3012-3024, 2014 [2] S. Rudykh and K. Bertoldi. J. Mech. Phys. Solids. 61: 949-967, 2013 [3] P. Pathak et al. Int. J. Mech. Sciences, 213: 106862, 2022 [4] A. Goshkoderia and S. Rudykh. Composites Part B 128: 19-29, 2017 [5] A. Goshkoderia et al. Phys. Rev. Lett. 124: 158002, 2020 [6] N. Karami-Mohammadi et al. J. Appl. Mech 86: 111001, 2019. [7] Q. Zhang and S. Rudykh. Mechanics of Materials 169:104325, 2022 [8] Q. Zhang et al. Int. J. Solids. Struct , 112396, 2023 [9] Q. Zhang et al. Ext. Mech. Lett. 59, 101957, 2023 [10] Q. Zhang et al. Int. J. Solids. Struct 289, 112648, 2024
[528] ID:528-Experimental study of micro-vascular networks embedded in carbon composites for High Energy Physics applications submitted to internal pressure
Matheo Dias ((2) Detector Technologies Group, European Organization for Nuclear Research (CERN), Switzerland), Diego Alvarez-Feito ((2) Detector Technologies Group, European Organization for Nuclear Research (CERN), Switzerland), François Boyer ((2) Detector Technologies Group, European Organization for Nuclear Research (CERN), Switzerland) and Philippe Olivier (University of Toulouse, Clement Ader Institute, UMR CNRS 5312).
Abstract
Carbon composite materials are ideal candidates for High Energy Physics (HEP) applications due to their low density, high stiffness-to-weight ratio and excellent thermal properties. They are widely used in the support structures of tracking detectors, where they play a key role in the thermal management of the silicon sensors and readout electronics. In state-of-the-art trackers such as those installed in the experiments at CERN’s Large Hadron Collider, lightweight composite structures provide the main heat path between the silicon modules and a network of metallic or plastic pipes containing a cooling fluid. However, despite the good results obtained with this approach, the performance targets of future HEP experiments call for even lighter and more efficient technologies. In this respect, the use of sacrificial materials to create micro-vascular networks in the composite laminates represents a very appealing solution to integrate the cooling circuit in the support structure. In this work, both experimental and numerical methods have been used to investigate the pressure resistance of channels embedded in carbon composite laminates. Modified poly(lactic) acid (PLA) preforms have been combined with a post-cure vaporization technique [1] to manufacture plates with longitudinal channels. Destructive tests have been carried out to determine the burst pressure of the plates as a function of the layup and the cross-section geometry of the channels. The deformation of the composite plates during the tests has been monitored using Digital Image Correlation (DIC). In parallel, a finite element model has been developed to predict the resistance of the plates, relying on cohesive elements to simulate the failure of the channels subject to internal pressure. Experimental delamination results obtained with mode I double cantilever beam (DCB) test specimens have been used to determine the input parameters for the numerical model.
[529] ID:529-Micro-mechanical study of residual stresses and strength of induction-cured thermoset composites
Andrejs Pupurs (Riga Technical University), Anish Niranjan Kulkarni (Riga Technical University) and Liva Pupure (Riga Technical University).
Abstract
Conventional manufacturing methods for lightweight composites are highly energy consuming. For example, oven curing has been estimated to consume approximately 20 MJ/kg largely due to excess heating of chamber volumes and molds. Electromagnetic induction heating on the other hand is a highly-promising alternative manufacturing method with low power consumption, high heating rates and flexibility to deliver contactless energy directly to the targeted location of the produced part. A prerequisite for this method are favorable electromagnetic properties of constituents that enable heat generation under the presence of electromagnetic field. Due to physical properties of carbon fibers, carbon/epoxy composites are suitable for induction heating. However, the heating mechanisms under induction heating are notably different from those in conventional oven curing - the fibers and their contact points act as heat sources and hence it is meaningful to study the development of fiber/matrix bonding strength and residual stresses in induction-cured composites. In the present study a series of micro-mechanical studies was performed experimentally and numerically. An induction heating rig consisting of a moving coil, thermal imaging camera and data processing unit, capable of ensuring a sufficiently uniform heat distribution during curing of highly anisotropic composites was developed and applied for manufacturing of unidirectional and cross-ply material samples. From unidirectional materials, longitudinal and transverse strength was determined, while micro-crack evolution and residual stresses were obtained from cross-ply material tests. Optical and scanning electron microscopy was used for quantification of micro-damage and for qualitative inspection of fracture surfaces. For reference the degree of cure was measured using DSC analysis. Obtained properties were compared with reference material obtained using conventional oven curing. Numerically, simulations of residual stress development during induction curing were performed using commercial FEM software using Schapery-based time-dependent material models. Boundary conditions corresponding to internal heat generation in carbon fibers were applied.
[530] ID:530-Hydrogen storage in Mg nanowires: ADP potentials
Pilar Ariza (University of Seville), Miguel Molinos (University of Seville) and Michael Ortiz (Caltech).
Abstract
Understanding the transport of hydrogen within metallic nanomaterials is crucial for the advancement of energy storage and the mitigation of hydrogen embrittlement. Using nanosized magnesium particles as a model, recent studies have revealed several highly nonlinear phenomena that occur over long time periods. The time scale of these phenomena is beyond the capability of established atomistic models such as molecular dynamics. In this work, we present a new approach, referred to as diffusive molecular dynamics (DMD) [1,2], to the simulation of long-term diffusive mass transport at the atomic scale. The basic assumption underlying DMD is that the time scale of diffusion is much larger than that of microscopic state transitions. In terms of numerical implementation, our approach involves the numerical integration of the master equation, and the numerical solution of a highly nonlinear optimization problem at every time-step. By working with atomic fractions, the characteristic time-step size of our DMD simulations can be much larger than those based on either AMD or KMC methods. In the present work, we focus on the characterization of thermodynamic and kinetic properties of magnesium hydride nanoparticles. Modeling phase transitions of Mg/MgH2 systems introduce an additional difficulty due to the change of lattice structure. We also note that the scope of DMD is not limited to metal hydrides and a broad range of multi-species systems of practical interest suggest themselves as worthwhile foci for future studies. REFERENCES [1] X. Sun, M.P. Ariza, M. Ortiz, K. Wang, Journal of the Mechanics and Physics of Solids, 125: 360-383, 2019. [2] G. Venturini, K. Wang, I. Romero, M.P. Ariza, M. Ortiz, Journal of the Mechanics and Physics of Solids, 73: 242-268, 2014.
[532] ID:532-Microscale Mechanical Testing of Lower Limb Vasculature
Cliona McCarthy (University of Limerick), John Mulvihill (University of Limerick) and Michael Walsh (University of Limerick).
Abstract
The estimated prevalence of peripheral arterial disease (PAD) is over 240 million people globally. End-stage treatment involves a bypass conduit to restore blood flow to limbs affected by critical limb ischemia. While conduit choices include xenografts and synthetic grafts, the use of autografts remains the gold standard, with better long-term outcomes for patients. The great saphenous vein (GSV) is the predominant autograft utilised, but approximately 40% of patients do not have sufficient GSV available. This leads to the over-use of synthetic grafts and consequently poorer patient outcomes due to their lower patency rates and an increased need for surgical revision. Currently, varicose (VV), and peripheral veins such as the popliteal (PV), superficial femoral (SFV) and tibial (TV) veins are not used as autograft options, despite a paucity of evidence demonstrating their lack of suitability as a conduit option. As the structure of the microenvironment influences the mechanical response of the surrounding tissue a robust investigation into the micromechanical and microstructural integrity of VV and peripheral veins would allow clinicians to make a more informed decision on whether these veins are suitable conduits. Consequently, this study micromechanically (using a novel mircoindentation approach) and structurally (using histology) characterises VV and peripheral veins to, for the first time, scientifically evidence their suitability as a bypass conduit, using the GSV for comparison analysis. Mechanical data show no significance between the Eeff of GSV and VV. The collagen content for GSV and VV was approximately 19% and 20% respectively. The results demonstrates, both mechanically and structurally, that VV have the potential to be used as a conduit option for patients who require bypass surgeries, thereby allowing for increased autograft options and improved long-term patient outcomes.
[533] ID:533-Micro-Mechanics Informed Neural Operator Framework for Multiscale Polycrystalline Material Behaviour
Rui Wu (University of Cambridge), Burigede Liu (University of Cambridge), Yannick Hollenweger (ETH Zurich) and Nikola Kovachki (NVIDIA).
Abstract
Advancements in computational solid mechanics have accelerated the development of materials, addressing the ongoing need for material optimization with previously un-attainable properties. The genesis of innovative materials and structural systems, such as high entropy alloys and mechanical metamaterials, relies on in-depth knowledge of the underlying physical principles across various scales, while the traditional single-scale modelling methods fail to meet this challenge. And it is still prohibitive to execute multi-scale simulations by cascading full-field single scale maps due to the limitation of computational resources. Developments in data-driven based approaches provide a solution, leveraging the neural network’s ability to process large amounts of data in an accelerated manner and approximate nonlinear maps, which makes it a promising computational tool in solving a variety of challenging physical systems.
In this work, we focus on polycrystalline materials, which are highly important to industry given their broad spectrum of applications. Establishing a precise and trustworthy link between the microstructures of polycrystals and their mechanical behaviours is essential for evaluating their properties and discovering innovative material alternatives. Therefore, building on the latest fundamental progress in AI-based tools, we develop the general micro-mechanics informed neural operator (MINO) for polycrystalline material systems, where the microstructural details are efficiently encoded and passed into the description of macroscopic material response to enable fast multi-scale predictions. In this framework we exploit recent advances in Fourier Neural Operators, which have been shown to be universal estimators for function space mappings. The MINO unlocks the potential for a more profound comprehension of unclear physics and heralds unprecedented opportunities for functionality/feature-lead material design. It promotes a more data-intensive and systematic research paradigm and will eventually enable expedited, property-specific material design with desirable functionalities.
[535] ID:595-Macro-elasticity of granular materials composed of polyhedral particles
Duc Chung Vu (LMGC, University of Montpellier), Lhassan Amarsid (CEA, DES, IRESNE, DEC, SESC, LDOP, Saint Paul les Durance), Jean-Yves Delenne (IATE, INRAE, Institut Agro, University of Montpellier), Vincent Richefeu (3SR, CNRS, University of Grenoble Alpes) and Farhang Radjai (LMGC, CNRS, University of Montpellier).
Abstract
By means of particle dynamics simulations, we investigate the orthotropic elastic moduli of dense packings of polyhedral particles with different number of faces. The samples are prepared by isotropic compaction under constant load and zero friction, leading to random close packed configuration of particles with highest density. Then, they were sheared under tri-periodic boundary conditions for different values of interparticle friction coefficient. During shearing, 16 instances corresponding to a wide variety of contact orientation anisotropies were stored and relaxed a static state before applying two distinct strain probes to measure the five independent elastic moduli of the sample. By comparing the simulation data with effective medium theory (EMT), our results clearly show that the elastic moduli are functions of two microstructural parameters: 1) a constraint number that accounts for contact types (face-face and face-edge contacts between polyhedra), and 2) the contact orientation anisotropy. The proposed expression of elastic moduli isolates the direct effect of particle shape, related to the nonaffine particle displacement field from the indirect effect, related to the granular microstructure. The effect of particle shape appears at two levels: on the one hand, through four parameters in the proposed expression, which are independent of friction coefficient, and, on the other hand, through the microstructure reflected by the values of constraint number and fabric anisotropy, which depend on both particle shape and interparticle friction coefficient [1].
[536] ID:536-Reassessing Strain Gradient Elasticity in Architected Solids: Unveiling Intriguing Meta Behaviours
Angkur Shaikeea (University of Cambridge), Vatsa Gandhi (University of Cambridge), David Hahn (University of California Berkeley), Xiaoyu Rayne Zheng (UCLA) and Vikram Deshpande (Cambridge University).
Abstract
While exploring the principles of elastic fracture mechanics within a 3D architected solid, a captivating observation emerged. Elastic brittle architected solids demonstrated a distinctive rising R-curve, reminiscent of ductile solids, resulting in an unexpected enhancement of toughness in a typically brittle system. This revelation broadens the horizons of mechanics of architected solids to theories such as strain gradient elasticity. Notably, an architected solid displays a considerable size effect when subjected to substantial strain/stress gradients, showcasing a softening behaviour in contrast to the stiffening observed in continuum solids. Thorough investigations through large-scale numerical calculations and in-situ measurements, employing micro-tomography techniques, have unveiled this elusive micromechanical behaviour in mechanical metamaterials. These findings carry substantial implications for the design of solids featuring micro-architectures, especially in the context of structural applications.
[537] ID:537-Twin branching in shape memory alloys: a 1D continuum model accounting for the energy dissipation effects
Seyedshoja Amini (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences), Mohsen Rezaee-Hajidehi (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences) and Stanislaw Stupkiewicz (Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences).
Abstract
In shape memory alloys, the competition between interfacial and elastic strain energy contributions leads to the phenomenon of twin branching, i.e. to the refinement of the twin laminates close to the macroscopic interface between twinned martensite and austenite. Recently, within a discrete setting, Seiner et al. (2020) developed an explicit, low-energy construction of the branched microstructure that is able to realistically predict the twin spacing and the number of branching generations. In this work, we propose a 1D continuum model of twin branching. The free energy of the branched twin microstructure is introduced which comprises two contributions that correspond to the interfacial energy and to the elastic strain energy associated with branching. The elastic strain contribution is calibrated using the respective upper-bound estimate derived by Seiner et al. (2020). The total free energy is then minimized, and the corresponding Euler-Lagrange equation is solved numerically using the finite element method. The results of our model show a good agreement with the model of Seiner et al. (2020) in a wide range of physically relevant parameters. Additionally, energy dissipation effects can be included in our continuum framework. Both rate-dependent and rate-independent dissipation is considered and its impact on the evolution of the branched microstructure is studied.
[538] High-fidelity Finite Element Simulations of Low-Velocity Impact on [05/903]s CFRP Beam Considering Accurate Experimental Conditions
Demirkan Coker (Department of Aerospace Engineering, Middle East Technical University), Onur Ali Batmaz (Department of Aerospace Engineering, Middle East Technical University), Mirac Onur Bozkurt (Department of Aerospace Engineering, Middle East Technical University) and Ercan Gurses (Department of Aerospace Engineering, Middle East Technical University).
Abstract
Composite materials are favored due to their exceptional strength-to-weight ratios. However, their weak interfacial characteristics make them vulnerable to out-of-plane loadings, including low-velocity impact (LVI). The increasing interest in numerical simulations for assessing composite resistance to LVI necessitates validation through direct damage observations. In a recent experimental study by Bozkurt and Coker (2021), [05/903]s CFRP beam specimens subjected to transverse impact loadings where strain fields are measured using the digital image correlation method, and damage evolution is captured in situ using an ultra-high-speed camera. In this study, we constructed the high-fidelity finite element (FE) model of the LVI experiments conducted by Bozkurt and Coker. The simulations utilize a user-implemented three-dimensional continuum damage model with the LaRC05 criterion for matrix cracking, and a built-in cohesive zone model for delamination in ABAQUS/Explicit. The influence of boundary supports on the global response is found to be significant, therefore, a heuristic boundary conditions approach that replicates the experiment boundaries through the assembly of spring elements is proposed. The simulation results then demonstrated excellent agreement with the experiments in terms of global impact response and damage pattern and sequence. Simulations reveal delamination propagation with crack tip speeds around ~5000 m/s, while experimental delamination crack tip speeds were measured at ~1000 m/s. However, when a crack tip definition based on the crack opening is introduced in the simulation, crack tip speeds in the range of 490-1500 m/s are measured consistent with experiments, implying that the sliding mode might be physically hidden in the experiments. Increasing the effective interface toughness to incorporate the macroscopic effects of experimentally-observed microscopic cracks at the interfaces demonstrated the potential use of delamination crack tip speeds as a benchmark for refining numerical simulations.
[539] ID:539-Designing achitected structures with tailored transport-thermal-mechanical performance using data-driven methods
Jinlong Fu (Queen Mary University of London), Hirak Kansara (Queen Mary University of London), Leo Guo (Delft University of Technology), Miguel Bessa (Brown University), Sid Kumar (Delft University of Technology) and Wei Tan (Queen Mary University of London).
Abstract
Shell-based architected materials, as exemplified by spinodoid topologies, provide a practical solution to address the prevalent stress concentration issues observed at junctions in truss-based structures, which often result in a reduction in mechanical performance. Despite the proven effectiveness of these structures, their development spans a broad design space. To seamlessly integrate them into crash energy absorbers, optimising the pertinent parameters becomes crucial for enhancing crush efficiency and energy absorption. A comprehensive understanding of the structures' behaviour under compression requires the inclusion of plasticity and damage models within finite element models. However, such inclusions increase computational costs, making optimisation with high-fidelity methods a costly endeavour. As an alternative approach, employing a probabilistic method through Bayesian Optimization strategically reduces the number of evaluations of resource-intensive observations. Results indicate that this approach offers a computationally efficient means of optimising functions with limited datasets.
Moreover, mapping physical properties to microstructural topology space poses a challenge, as multiple topologies can yield the same effective properties. We have proposed an inverse-design method for designing architected materials with diverse physical properties. The results demonstrate its effectiveness in addressing permeability-diffusivity-mechanical synergy, expanding the tunable scope of multi-physical performances, and tailoring functionally graded metamaterials with desired multi-functionality.
[540] ID:540-An extended version of the variational EIV approach for the homogenization of composites with generalized Maxwell matrix
Carole Nadot-Martin (Institut Pprime (UPR CNRS 3346)), Benjamin Tressou (Institut Pprime (UPR CNRS 3346)) and Mikael Gueguen (Institut Pprime (UPR CNRS 3346)).
Abstract
Polymer matrix composites are widely used in various industrial fields such as aeronautics and transport in general. Modelling their time-dependant macroscopic mechanical behaviour as a function of their microstructural organization is a common objective in the scientific community. Whatever the application, and before considering other dissipative processes, the very first stage remains a correct description of the viscoelasticity. Mean-field homogenization is here employed with new developments of the incremental variational approach originally proposed by Lahellec and Suquet (2007), also called EIV approach for “Effective Internal Variable” approach. The present paper has two objectives. The first one is to illustrate the possible association of the EIV approach to different linear schemes and, as a result, its possible application to various microstructures (fiber or particle-reinforced composites, strand-based wood composites). The second objective is to enlarge the application domain of the original EIV approach in terms of constituents’ viscoelastic laws that may be considered. Initially applied to phases described by simple viscoelastic laws involving a single, traceless, internal variable, (ex. Maxwell model and constant bulk modulus), the original formulation of the EIV model is here generalized to phases described by more representative viscoelastic laws involving several internal variables with both spherical and deviatoric parts. The generalized EIV approach is evaluated by comparison to reference solutions obtained by full-field finite element (FE) simulations for a fiber-reinforced microstructure. Linear viscoelastic laws with increasing complexity are considered for the matrix. At first, a classical Maxwell model is used as in Lahellec and Suquet’s original work, but now the internal variable (viscous strain) has a spherical part. Then, the matrix is described by a generalized Maxwell model with several branches. Different distributions of relaxation times are studied for bulk and shear moduli. In every case, the accuracy is satisfactory.
[541] ID:541-Deep-learning-based impact localization in PAEK/CF panels
Moises Zarzoso (IMDEA Materials Institute and Universidad Politécnica de Madrid), Davide Mocerino (IMDEA Materials Institute) and Carlos Gonzalez (IMDEA Materials Institute and Universidad Politécnica de Madrid).
Abstract
Structural health monitoring of aerostructures translates into a significant reduction in maintenance costs as well as lighter, more efficient component designs by providing real-time insight into the remaining lifespan throughout the whole life cycle. To perform this monitoring, the structure is required to be instrumented with a robust and sufficiently sensitive sensor system.
This work focuses on one of the most relevant applications of these systems, low energy impact damage localization. To this purpose, the monitoring relies on a mature technology, strain gauges. Thermoplastic PAEK/CF panels are instrumented with an array of gauges and tested under three-point bending conditions in pristine and impacted conditions.
In the deformed state, it is possible to compare the effect of damage in the strain field by means of its point values measured by strain gauges, using these compared values to infer damage extension. This is achieved through an artificial neural network trained on synthetic data generated by an accurately calibrated finite element simulation, this approach is known to be efficient in surrogate modelling of composites [1].
The resulting trained model performs as a digital twin of the composite panel, being able to predict with accuracy the location of impact as well as distinguish the impact energy that caused the damage. Several densities of strain gauges arrays are studied to assess the sensitivity of the monitoring system, while in-service robustness is achieved by ensuring the model performs effective predictions with malfunctioning gauges.
[1] J. Fernández-León, K. Keramati, C. Miguel, C. González, L. Baumela - A deep encoder-decoder for surrogate modelling of liquid moulding of composites. Engineering Applications Of Artificial Intelligence 120, 105945-105945, 2023.
[542] ID:542-An incremental variational homogenization approach of damage in brittle matrix composites
Ghita Ben El Barguia (Institut Jean le Rond D'Alembert, Sorbonne Université), Sophie Dartois (IJLRDA, Sorbonne Université), Noel Lahellec (LMA, Aix-Marseille Universite) and Djimedo Kondo (IJLRDA, Sorbonne Université).
Abstract
Brittle matrix-based composites generally exhibit damage due to microcracks growth when they are subjected to mechanical loadings. We aim at establishing a nonlinear homogenization model for composites with growing damage. To this end, we rely on an incremental variational homogenization approach available only for elasto(visco)plastic composites [5, 1, 6]. Following [5], we first introduce a linearization of the elastic-damageable laws of the phases. After implementing appropriate stationnarity conditions (see [2]), the resulting Linear Comparison Composite (LCC) is then homogenized by using Hashin- Shtrikman bounds. The incremental variational procedure is implemented for composites made up of linear elastic spherical particles embedded in a damageable matrix. In order to assess the model, we perform full-field (Finite Element) simulations on a 3D cell consisting of a damageable matrix containing a linear elastic spherical inclusion. A phase-field approach (see [3]) is used to predict the effective behavior of the composite, as well as the overall damage evolution. A full characterization of the local fields and their fluctuations are also provided (see detail in [2]). The numerical results provide a validation of the model, even the latter needs to be improved for a better account of the damage heterogeneity.
References [1] Agoras M., Avazmohammadi R., Ponte-Castaneda P., International Journ. Solids Struct., 97, 668–686, 2016. [2] Ben-El-Barguia G. An incremental variational approach and computational homogenization for composites with evolving damage, PhD, Sorbonne University, 2023. [3] Bourdin B., Francfort G.A., Marigo J.J., Journal of the Mechanics and Physics of Solids, 48, 797-826, 2000. [4] Fantoni F. et al., A phase field approach for damage propagation in periodic microstructured materials. Int. Journal of Fracture, 223, 53–76, 2020. [5] Lahellec N., Suquet P., J. Mech. and Phys. of Sol, 55, 1932–1963, 2007. [6] Lucchetta A. et al., Int. Jour. of Solids and Structures, 158, 243–267, 2018.
[543] ID:543-Defining Fracture Toughness for Hydrogels
John Bassani (University of Pennsylvania), Konstantinos Garyfallogiannis (University of Pennsylvania) and Prashant Purohit (University of Pennsylvania).
Abstract
Poroelastic hydrogels display dissipative behavior due to liquid diffusion, and defining fracture toughness is an open issue. Our primary interest is fibrous gels such as cartilage, blood clots, and carbon-nanotube-based sponges with absorbed oils which suffer a reduction in volume by the expulsion of liquid under uniaxial tension, which directly affects crack-tip fields and energy release rates. We have carried out experiments on fibrin gels coupled with a large-deformation continuum model to investigate the initiation of crack growth. The continuum model is formulated for isotropic fibrous gels that exhibit a range of behaviors volume increasing to volume decreasing in uniaxial tension by changing the ratio of two material parameters. The direction of liquid fluxes around cracks is shown to depend on whether the gel locally increases or decreases in volume. The energy release rate for cracks is computed using a surface-independent integral and it is shown to have two contributions — one from the stresses in the solid network, and another from the flow of liquid. The contribution to the integral from liquid permeation tends to be negative when the gel exhibits volume decrease, which effectively is a crack shielding mechanism. Both from correlations with experiments and from simulations based on a critical stretch fracture criterion, we show that both contributions are required to characterize the fracture toughness of these materials. Some historical perspective on fracture toughness of dissipated solids will also be discussed.
[544] ID:544-Modeling of hydrogen embrittlement in eutectic high entropy alloys: a FFT-based framework for Phase-Field fracture
Nabor Jiménez Segura (Department of Material Science - UPM), Gabriel Zarzoso (IMDEA Materials) and Javier Segurado (Department of Material Science - UPM).
Abstract
In the present work, a coupled chemo-mechanical model for hydrogen embrittlement is developed in a FFT-based environment. The problem is solved using an implicit staggered method. Thus, the three problems (mechanical, damage, and hydrogen diffusion) are solved sequentially until convergence is reached. The mechanical problem is solved for finite strains using the Fourier Galerkin method. In order to account for the fracture behaviour of the material, a phase-field method is implemented. To model the diffusion of hydrogen, the hydrogen population is subdivided into two classes: trapped hydrogen and (mobile) lattice hydrogen. According to Oriani postulate, these two populations must be in equilibrium. The resulting non-linear differential equation is solved for the chemical potential by means of a linearization.
[545] ID:545-Determination of Crystal Plasticity Parameters from In-Situ Synchrotron Diffraction
Martin Diehl (KU Leuven), Pushkar Dhekne (KU Leuven), Nikhil Prabhu (KU Leuven), Marc Seefeldt (KU Leuven), Matthias Bönisch (KU Leuven) and Kim Vanmeensel (KU Leuven).
Abstract
The predictive capabilities of crystal plasticity models depend critically on the availability of constitutive parameters that reflect the behavior of the material at hand. The large amount of parameters used in typical crystal plasticity models and the strong non-linear interactions between them renders the identification of these parameters a tedious task. This holds especially for the case of multiphase materials where the contribution of the individual phases to the overall mechanical behavior is hard to untangle. Here, we present results from parameter identification of a phenomenological crystal plasticity model for the hexagonal α-phase of Ti-6Al-4V α+β titanium alloy produced by laser powder bed fusion (LPBF). The lattice strain obtained from in-situ synchrotron diffraction experiments is used as input. An optimization procedure is used to adjust the constitutive parameters of a phenomenological crystal plasticity model until the experimental reference results are reproduced. The performance and robustness of the approach is investigated and the obtained parameters are discussed in comparison to data from the literature.
[546] ID:546-Real-time monitoring of the microstructure evolution during laser powder bed fusion
Steven Van Petegem (Structure and Mechanics of Advanced Materials, Paul Scherrer Institute).
Abstract
Laser-based powder bed fusion (LPBF) represents a highly versatile additive manufacturing method widely used for processing metals. Despite extensive research spanning several decades in this active scientific domain, numerous unanswered questions persist regarding the intricate interplay between process parameters and microstructural transformations. To enhance our comprehension of this relationship, we have developed two compact LPBF devices compatible with various synchrotron and neutron X-ray diffraction and imaging beamlines, enabling in situ investigations.
These setups enable the real-time monitoring of crystallographic phases, cracks, pores, and other phenomena during LPBF. They are capable of examining small samples with microsecond-scale time resolution or larger centimeter-sized samples with time resolutions spanning seconds to minutes. In this presentation, we highlight recent progress and outcomes from both setups. Specifically, we demonstrate the effectiveness of operando X-ray diffraction in tracing phase evolution, local cooling rates, and recrystallization. Additionally, our fast in situ X-ray radiography provides insights into cracking mechanisms and the kinetics of multi-material mixing. Integration with acoustic and optical sensors enhances these experiments, supplying essential input for machine-learning algorithms.
Furthermore, we explore the application of neutrons for in situ strain characterization through neutron diffraction and Bragg edge imaging, defect visualization via neutron dark-field imaging, and determination of magnetic phase fraction utilizing polarization contrast neutron imaging. Our findings contribute significantly to advancing our understanding of the LPBF process, offering valuable insights for informed decision-making and continuous improvement in additive manufacturing practices.
[547] ID:547-Operando tomographic microscopy during laser-based powder bed fusion.
Malgorzata Makowska (Paul Scherrer Institute), Fabrizio Verga (Inspire AG), Stefan Pfeiffer (Swiss Federal Laboratories for Materials Science and Technology), Federica Marone (Paul Scherrer Institute), Cynthia Chang (Technology Transfer Centre for Advanced Manufacturing, ANAXAM), Kevin Florio (ETH Zurich), Christian Schlepütz (Paul Scherrer Institute), Konrad Wegener (ETH Zurich), Thomas Graule (Swiss Federal Laboratories for Materials Science and Technology) and Steven Van Petegem (Paul Scherrer Institute).
Abstract
Laser-based Powder Bed Fusion (LPBF) of ceramics enables the fabrication of objects with complex three-dimensional shapes otherwise challenging or even impossible to produce with conventional manufacturing routes. However, the mechanical properties of LPBF-manufactured ceramics components are poor due to a large number of structural defects. Often, such defects are investigated by X-ray computed tomography. This allows studying in 3D the density and shape of pores and cracks in printed samples. Dynamic processes can be studied by fast in situ X-ray radiography, however, this method lacks 3D information.
In this work, we present the first results obtained by operando tomographic microscopy during LPBF of magnetite-modified alumina. This new technique allows tracking the 3D microstructural evolution during printing with a time resolution of 10ms. The experiments are performed at the TOMCAT beamline of the Swiss Light Source with an LPBF setup with a green laser. The effect of laser energy density on surface roughness, powder denudation zone and porosity formation mechanisms is investigated. Higher power results in a significant increase in the melt pool width, but not in its depth and no melt pool depression is observed. For the investigated ceramic system, the forces due to the recoil pressure do not significantly influence the melt pool dynamics. Increasing power allows for avoiding lack of fusion porosity, but enhances the formation of spherical porosity that is formed by either reaching the boiling point of liquid alumina or by introducing gas bubbles by injection of hollow powder particles into the liquid. The acquired information, not only provides an understanding of underlying processes but also is crucial for the development and verification of models used for the LPBF process simulations.
[548] ID:548-Advanced inverse formulations for 3DTFM: regularized and non-regularized strategies for traction reconstruction
Alejandro Apolinar-Fernández (Escuela Técnica Superior de Ingeniería, Universidad de Sevilla), Pablo Blázquez-Carmona (Escuela Técnica Superior de Ingeniería, Universidad de Sevilla), Raquel Ruiz-Mateos Brea (Escuela Técnica Superior de Ingeniería, Universidad de Sevilla), Jorge Barrasa-Fano (Biomechanics section, Department of Mechanical Engineering, KU Leuven), Hans Van Oosterwyck (Biomechanics section, Department of Mechanical Engineering, KU Leuven), Esther Reina-Romo (Escuela Técnica Superior de Ingeniería, Universidad de Sevilla) and José Antonio Sanz-Herrera (Escuela Técnica Superior de Ingeniería, Universidad de Sevilla).
Abstract
Traction Force Microscopy (TFM) integrates experimental and computational methods to study cellular tractions exerted on the extracellular matrix (ECM). The technique involves the measurement of displacements that result from cellular activity occurring in the interior of a certain material that imitates the ECM properties. Traction reconstruction is performed in two main ways: the forward method which, while computationally simple, suffers from important errors due to direct numerical differentiation of noisy displacement data; and the inverse method, which focuses on finding new displacements resembling the measured ones that fulfill specific conditions, offering better traction reconstructions.
The design of inverse methods for traction reconstruction is influenced by several factors, such as nonlinear effects, dimensionality (2D/3D), regularization, among others. Generally, solving the inverse problem involves some kind of matrix inversion, but noise in measured displacements can lead to problematic high maximum values in reconstructed tractions. To address this, Tikhonov regularization is commonly used, penalizing high norm values of computed tractions.
This study aims to compare different inverse methodologies, considering restriction imposition and regularization, to determine which one yields better traction reconstructions. We previously devised the Physics-Based Nonlinear Inverse Method (PBNIM), which enforces nullity of nodal forces at hydrogel nodes without regularization. Here, we implement regularization into PBNIM and develop the Mixed Physics-Based Nonlinear Inverse Method (M-PBNIM), which improves overall traction reconstruction by better estimating maximum tractions at the cell surface. However, regularization introduces the challenge of calibrating the regularization parameter, often done through non-conclusive procedures. Because of this, the non-regularized PBNIM stands out as the most suitable when regularization parameter calibration is omitted, provided that maximum tractions maintain acceptable values with errors comparable to the best inverse approaches. The conclusions emphasize the importance of considering not only traction reconstruction quality but also the efficiency and complexity of implementation when selecting an inverse method.
[549] ID:549-Metainterfaces: how to design a soft contact that obeys a specified friction law?
Antoine Aymard (Univ Lyon, CNRS, École Centrale de Lyon, ENTPE, LTDS, UMR5513, Ecully 69130, France), Emilie Delplanque (Univ Lyon, CNRS, École Centrale de Lyon, ENTPE, LTDS, UMR5513, Ecully 69130, France), Davy Dalmas (Univ Lyon, CNRS, École Centrale de Lyon, ENTPE, LTDS, UMR5513, Ecully 69130, France) and Julien Scheibert (Univ Lyon, École Centrale de Lyon, CNRS, ENTPE, LTDS, UMR5513, 69130 Ecully, France).
Abstract
Many devices, including sports shoes and robotic hands, involve frictional soft contacts. Optimizing those devices requires fine control of the interface’s friction law. We lack systematic methods to create dry contact interfaces whose frictional behaviour satisfies preset specifications. In this talk, a generic surface design strategy to prepare dry rough interfaces that have predefined relationships between normal and friction forces will be presented. Such metainterfaces circumvent the usual multiscale challenge of tribology, by considering simplified surface topographies as assemblies of spherical asperities. Optimizing the individual asperities’ heights enables specific friction laws to be targeted. Through various centimeter-scaled elastomer-glass metainterfaces, different types of achievable friction laws, including linear laws with a specified friction coefficient and unusual non-linear laws will be illustrated. This design strategy represents a scale- and material-independent, chemical-free pathway toward energy-saving and smart soft interfaces.
[550] ID:550-Simulation of Microstructure Evolution by Integrating Crystal Plasticity in the Multiphase-Field Method
Andreas Prahs (Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - MMS), Lukas Schöller (Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - MMS), Thea Kannenberg (Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - MMS), Daniel Schneider (Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT-MSS)) and Britta Nestler (Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - MMS).
Abstract
Crystal plasticity takes into account the crystal lattice and the corresponding slip systems that are characteristic of the underlying crystalline microstructure. The mechanical behavior of polycrystals is significantly affected by grain boundaries (GBs), which are considered as material singular surfaces in classical continuum mechanics [1]. Simulating the evolution of microstructure can be challenging and costly from a numerical perspective when tracking sharp interface (SI) grain boundaries (GBs). To avoid this issue, the CP can be implemented in the multiphase-field approach (MPFM) as suggested by [2]. Modeling surfaces as diffuse interfaces with finite thickness, the MPFM is an efficient method for treating evolving surfaces. In this talk, we provide a concise overview of how crystal plasticity is applied within the diffuse interface region [4] using the jump condition approach [3]. The consistency between the MPFM and SI solutions in a bicrystal is demonstrated through three-dimensional simulations. Additionally, the evolution of the polycrystalline microstructures following elastoplastic deformation are examined as an initial step towards the modeling recrystallization processes [5].
REFERENCES
[1] A. Prahs, T. Böhlke, Contin. Mech. Thermodyn, Vol. 32, 1417–1434, 2019.
[2] B. Nestler and H. Garcke and B. Stinner, Physical Review E, Vol. 71, No. 4, pp. 041609 1–6, 2005
[3] D. Schneider, F. Schwab. E. Schoof, A. Reiter, C. Herrmann, M. Selzer, T. Böhlke, B. Nestler, Comput. Mech., Vol. 60 (2), 203–217, 2017.
[4] A. Prahs, L. Schöller, F. Schwab, D. Schneider, T. Böhlke, B. Nestler, Comput. Mech., DOI: https://doi.org/10.1007/s00466-023-02389-6, 2023.
[5] T. Kannenberg, L. Schöller, A. Prahs, D. Schneider, B. Nestler, Comput. Mech., DOI: https://doi.org/10.1007/s00466-023-02423-7, 2023.
[551] ID:551-Discovering Tension-Compression Asymmetry in Plant Tissues Using inelastic Constitutive Artificial Neural Networks
Domen Macek (RWTH Aachen University), Tim Brepols (RWTH Aachen University) and Hagen Holthusen (RWTH Aachen University).
Abstract
Due to the fact that fibers in soft tissues can usually carry less compressive loadings, a tension-compression asymmetry is observed in the experiments. Unfortunately, it is not easy to determine the correct material model for such phenomena, especially when inelasticity is involved. Therefore, the inelastic Constitutive Artificial Neural Networks (iCANNs) presented in [1] can be used to overcome this problem. iCANNs provide a new framework for model finding that extends Constitutive Artificial Neural Networks (see [2]) to general inelastic material behavior. It assumes a multiplicative decomposition of the deformation gradient and is therefore able to capture finite deformations and deformation rates. The overall design of the iCANNs provides a priori thermodynamic consistency, objectivity, rigid motion of the reference configuration and independence of the rotational non-uniqueness. The network architecture combines a recurrent neural network with two individual feed-forward networks for the Helmholtz free energy and the pseudo potential. Since our focus here is to discover a model for tension-compression asymmetry in plant tissues, we first extend iCANNs further by multiplicatively decomposing the deformation tensor into positive and negative parts, and second, we assume an additive split of the isochoric part of Helmholtz free energy into positive and negative parts. We train the iCANNs on cyclic uniaxial stress-relaxation experiments for petiole of Stephania japonica, in order to find the material model describing the desired physical phenomenon. Furthermore, we present performance tests of the iCANNs on other data sets and discuss the accuracy of our approach.
REFERENCES [1] Holthusen, H.; Lamm, L.; Brepols, T.; Reese, S.; Kuhl, E. Theory and implementation of inelastic Constitutive Artificial Neural Networks. Computer Methods in Applied Mechanics and Engineering. (2023). DOI:10.48550/arXiv.2311.06380 [2] Linka, K.; Kuhl, E. A new family of constitutive artificial neural networks towards automated model discovery. Computer Methods in Applied Mechanics and Engineering. (2023) 403:115731. DOI:10.1016/j.cma.2022.115731
[552] ID:552-A computational modelling approach of viscoelasticity based on random fields for short fibre-reinforced composites with experimental verification
Eduard Klatt (Helmut-Schmidt-University) and Natalie Rauter (Helmut-Schmidt-University).
Abstract
The mechanical properties of short fibre-reinforced composites depend strongly on the injection moulding process. Due to its heterogeneous microstructure, fibre composite materials show not only a distinct anisotropy, but also spatially distributed viscoelastic properties on the component level. This is demonstrated experimentally at the macro level using tensile test specimens by investigating local deformation with a digital image correlation measurement system. Subsequently, on the micro level polished micrograph samples are used to investigate the entire cross-section by nanoindentation with a Berkovich tip. These experimental investigations show that the spatially distributed material properties are of stochastic nature and must therefore be considered in the modelling of short fibre-reinforced composites. A suitable modelling approach to describe the spatially distributed material properties in a 2D model are random fields, which are generated by utilizing the expansion optimal linear estimation method. This series expansion is based on a spectral decomposition of the correlation structure of the underlying microstructure. For modelling of the spatial distribution of material properties on the macro level using random fields, the information of the probabilistic characteristics of the microstructure, which given by probability density functions of fibre length, diameter and orientation are needed. These functions are obtained from the tensile test specimens by using computed tomography and are required for the generation of artificial microstructures. Subsequently, correlation structures are derived from the generated artificial structures for the generation of random fields. This approach allows the stochastic information of the fibre distribution to be considered in the modelling process. Since the microstructure depends, among other things, on the fibre content, this modelling approach is used for different fibre mass fraction. Finally, this modelling approach are compared with the experimental results.
[553] ID:553-Space-Fractional Continuum Mechanics as a Method of Capturing the Scale Effect
Paulina Stempin (Poznan University of Technology, Institute of Structural Analysis), Krzysztof Szajek (Poznan University of Technology, Institute of Structural Analysis) and Wojciech Sumelka (Poznan University of Technology, Institute of Structural Analysis).
Abstract
The work presents generalized (size-dependent) continuum mechanics, namely the space-fractional continuum mechanics, whose applicability is extended to problems with smaller characteristic lengths. This approach uses fractional calculus to account for information on the internal characteristic length of the microstructure and avoid the need to represent the complex original microstructure one-to-one. Fractional operators, as being defined on a specific interval, allow accounting for nonlocality, which should be understood that the current response of the model at a specific material point depends on information from its finite neighborhood.
The talk will focus on modelling the structural elements (beams and plates) defined in the framework of the aforementioned space-fractional continuum mechanics, which allows analysis over various scales (nano-micro-macro). The possibility of identifying damage in the structures at the nano/micro scale will also be addressed. Moreover, validation results lead us to the recognition that space-fractional continuum mechanics is an up-and-coming technique for modeling material bodies whose dimensions are of the order of the internal microstructure.
ACKNOWLEDGEMENTS This research was funded in part by the National Science Centre, Poland, grant number 2022/45/N/ST8/02421. For the purpose of Open Access, the authors have applied a CC-BY public copyright license to any Author Accepted Manuscript (AAM) version arising from this submission.
REFERENCES W.Sumelka, T.Blaszczyk. Fractional continua for linear elasticity. Archives of Mechanics, 66:147-172,2014. P.Stempin, W.Sumelka. Space-fractional Euler-Bernoulli beam model - Theory and identification for silver nanobeam bending. International Journal of Mechanical Sciences, 186:105902,2020. P.Stempin, W.Sumelka. Formulation and experimental validation of space-fractional Timoshenko beam model with functionally graded materials effects. Computational Mechanics, 68:697-708,2021. P.Stempin, W.Sumelka. Space-fractional small-strain plasticity model for microbeams including grain size effect. International Journal of Engineering Science, 175:103672,2022. P.Stempin, T.P.Pawlak, W.Sumelka. Formulation of non-local space-fractional plate model and validation for composite micro-plates. International Journal of Engineering Science, 192:103932,2023.
[554] ID:554-On The Role of Plastic Relaxation in Stress Assisted Grain Boundary Oxidation
Yinguang Piao (Imperial College London) and Dan Balint (Imperial College London).
Abstract
The influence of plasticity on high-temperature stress-assisted grain boundary oxidation of nickel-based superalloys used in applications such as turbine rotor discs is investigated using the method of Discrete Dislocation Plasticity (DDP). The misfit stress fields of triangular and nib-shaped intrusions are represented by a continuous distribution of edge dislocations whose extra half planes give the volumetric misfit of the oxide, which is implemented in a planar formulation of DDP by invoking the linear superposition principle. Volumetric misfit of an intrusion several microns in length generates high stresses in the parent material, which in turn leads to the nucleation of dislocation that are driven by the applied stress to the intrusion interface. Pile-up stresses on the order of 1 GPa cause localised growth and morphology change of the intrusion by stress-assisted diffusion. The analysis of the intrusion stress reveals that the morphology change relaxes the compressive stress inside the intrusion near its base, which increases its effective fracture resistance. Numerical experiments also show that an applied tensile stress increases the growth rate of the intrusion in defect-free samples, whereas in pre-strained samples it is found that dislocation pile-ups ahead of the oxide reduce the intrusion growth rate. This finding provides the first mechanistic explanation for reconciling an inconsistency in key experimental findings in the literature, which respectively identify a tendency for shorter and longer intrusions in samples subject to an applied load.
[555] ID:555-Mechanical response of coextruded multi-nanolayered films of PS/LDPE : How mechanical confinment enables to control PS damage mechanisms
Xavier Morelle (Laboratoire IMP, UMR CNRS 5223, INSA de Lyon), Emmanuel Fabing (Laboratoire IMP, UMR CNRS 5223, INSA de Lyon), Mohamadou Lamine Dia (Laboratoire IMP, UMR CNRS 5223, INSA de Lyon), Naïm Naouar (LaMCoS, UMR CNRS 5259, INSA de Lyon), Nawfal Blal (LaMCoS, UMR CNRS 5259, INSA de Lyon) and Khalid Lamnawar (Laboratoire IMP, UMR CNRS 5223, INSA de Lyon).
Abstract
To better apprehend the improved mechanical properties of highly structured multi-nanolayer films obtained by co-extrusion, as well as identifying the key parameters governing their structure-morphology, the present study focuses on model films made of low-density polyethylene (LDPE) and polystyrene (PS). Despite being two immiscible polymers with highly-mismatched rheological behavior (and without the need of compatibilizers), coextrusion by forced-layer-assembly allows to prepare well-controlled multilayer films with different level of confinement through the fine tuning of their number of layers. More specifically, the layer confinement of a semi-crystalline polymer, here LDPE, by a glassy amorphous polymer, here PS, was investigated. In comparison to each of the two base materials, the obtained multilayer architecture brings out the best of the two worlds by combining the ductility of LDPE with the high strength of PS, greatly outperforming the corresponding 50/50 randomly structured blend. Interestingly, we have demonstrated that increasing the number of layers of PS/LDPE system (while remaining in the processing window of stable continuous layers), thus increasing the level of layer confinement, allows to stabilize the brittle damage mechanisms (i.e. crazes) of PS, enabling to reach large strains without macroscopic failure. In parallel to the multi-layer morphology characterization by SEM and TEM, the orientation and crystalline structure of the coextruded films were also characterized by WAXS and DSC. The geometrical confinement of LDPE nanolayer did not affect the thermal properties of LDPE crystalline phase, but it did affect its crystalline morphology, evolving from an isotropic-spherulitic shape to a more lamellae-oriented form.
[556] ID:556- Influence of Thickness on the (Micro)structure and the Magnetic behavior of Kuamet6B2 Thin Walls
Saumya Sadanand (IMDEA Materials Institute), Marcos Rodriguez (IMDEA Materials), Amirhossein Ghavimi (Saarland University), Ralf Busch (Saarland University), Isabella Gallino (Saarland University), Paola Tiberto (Istituto Nazionale di Ricerca Metrologica), Enzo Ferrara (Istituto Nazionale di Ricerca Metrologica), Gabriele Barrera (Istituto Nazionale di Ricerca Metrologica) and Maria Teresa Perez Prado (IMDEA Materials Institute).
Abstract
The ongoing energy crisis demands extensive research into new alternatives for enhancing the energy efficiency of electric motors. As a probable solution to this, soft magnetic materials (SMM) portray excellent properties with high saturation flux density (BS) and low coercivity (HC)[1]. SMMs possess the ability to cater to this need, as they can substantially increase the efficiency of electric motors by reducing the core losses. Although promising, soft magnetic Fe-based amorphous metals need further research to overcome production challenges, as the need for high cooling rates to generate a significant fraction of the amorphous phase severely limits their production to thin ribbons resulting from rapid solidification processes such as melt spinning. Earlier work on additive manufacturing (AM) parameter optimization of a Fe-Si-B-based bulk metallic glass (BMG) has, however, shown promise for the fabrication of relatively large net-shape rotors [2]. This work investigates the effect of thickness on the (micro)structure and the magnetic behavior of Kuamet6B2 samples. The optimum combinations of parameters that fared well in terms of overall part density and amorphous degree of bulk samples have been applied in the current work to manufacture walls with thicknesses ranging from 500 µm to 1500 µm by laser powder bed fusion (LPBF). In particular, the wall thickness is correlated with the density, the defect structure, the meltpool morphology, the degree of amorphicity, and magnetic properties such as saturation magnetization (Js) and coercivity (Hc). To achieve this, complementary structural characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) have been utilized in conjunction with image analysis tools. The magnetic behavior was characterized using a vibrating sample magnetometer (VSM). The outcome of this work will provide guidelines for the design of soft magnetic bulk metallic glass components with more complex geometries and improved energy efficiency.
[557] ID:557- Influence of microstructure and interlocking on mechanical behavior of agglomerates of hexapod-shaped particles
Trieu Duy Tran (CEA, DES, ISEC, DMRC, University of Montpellier), Saeid Nezamabadi (LMGC, University of Montpellier), Jean-Philippe Bayle (CEA, DES, ISEC, DMRC, University of Montpellier), Lhassan Amarsid (CEA, DES, IRESNE, DEC, Cadarache) and Farhang Radjai (CNRS, LMGC, University of Montpellier).
Abstract
Despite the crucial role the agglomeration process plays in both nature and powder technology, the current understanding of the physical mechanisms determining the tensile strength of cohesive agglomerates consisting of fine particles is still limited. Specifically, the quantitative effects of particle shape in conjunction with cohesive-frictional interactions between particles have yet to be fully explained. One straightforward method to examine the influence of particle shape on the strength characteristics of granular materials is by employing hexapod-shaped particles. We used particle dynamics simulations to create agglomerates composed of hexapods and analyzed the effects of aspect ratio and interparticle friction on the force transmission and microstructure such as packing fraction, connectivity and elastic bulk modulus. We also investigate their mechanical behavior under diametral compression to showcase the effect of non-convex particle shape and interlocking on their tensile strength and we analyze the strength and fracture behavior as a function of aspect ratio, friction coefficient, and cohesive force between aggregates for irreversible cohesive interaction. We demonstrate that nonconvex form significantly increases the cohesive strength of the agglomeration for large enough aspect ratios. We show that the ability of thin hexapods to establish contact with their second neighbors and the function of friction in minimizing their disentanglement under diametral compression are connected with this amplifying effect of interlocking on the cohesive strength.
[558] ID:558-On the effect of the third stress invariant in ductile failure: microscopic and macroscopic aspects
Amine Benzerga (Texas A&M University) and R Vigneshwaran (Texas A&M University).
Abstract
The talk addresses two fundamental questions related by the effect of the third stress invariant in ductile failure: (i) What is the rationale for this effect? (ii) Are shearing states always “less ductile” than axisymmetric ones? To this end, the theory of unhomogeneous yielding is presented based on the concept of percolation of elastically unloaded domains through a network of pores. The concept is illustrated through standard single-void unit cells as well as many-void cells. It is shown that the concept of unhomogeneous yielding suffices to explain all known traits of J3 dependent failure, as gleaned from micromechanical simulations as well as available experiments. The theory also suggests that question (ii) may be answered with a negative depending on initial states. To further examine that, micromechanical voided cell calculations are carried out. The unit cell is subjected to proportional loading and fully periodic boundary conditions. The progression of elastic unloading in the unit cell is analyzed, leading to a precise detection of unhomogeneous yielding. Overall strain localization is determined by evaluating ``on the fly'' the tangent operator using a perturbation method. The connection between unhomogeneous yielding and strain localization is thus thoroughly investigated. Other critical strain measures used in the recent literature are monitored and their relevance to failure by void coalescence or strain localization is discussed. Our findings have far reaching implications since all available theories, of the critical strain type or Gurson-enhanced, assume a positive answer to question (ii). The effects of initial porosity and strain hardening in modulating the relative ductility under tension versus shear are further examined.
[559] ID:559-Rigorous generalized elasticity models for mechanical metamaterials
Michael Ortiz (Caltech), Pilar Ariza (University of Seville) and Sergio Conti (University of Bonn).
Abstract
Mechanical nanostructured metamaterials, when used in bulk applications, define a quintessential multiscale problem, with many orders of magnitude in scale separation between the micro and macro domains. Under such conditions, models--computational or otherwise--predicated on the explicit tracking of every individual member of the metamaterial are impractical and uncalled for, since locally large numbers of members deform collectively under applied loading and jointly exhibit well-defined effective behavior that can be characterized as a continuum material law. The identification of such an effective material model is the aim of homogenization theory and discrete-to-continuum techniques. However, mechanical materials fall outside conventional homogenization theory on account of the flexural, or bending, response of their members. We show that modern homogenization theory, based on calculus of variations and notions of Gamma-convergence, can be rigorously extended to account for bending and that the resulting homogenized metamaterials exhibit intrinsic generalized elasticity and retain a characteristic length scale even in the continuum limit. In particular, the homogenized metamaterials are nonlocal, have a built-in size effect and, for members of finite strength, an intrinsic fracture toughness. We illustrate these properties in specific examples including two-dimensional honeycomb and three-dimensional octet metamaterials.
[560] ID:560-Reduced order modeling of dynamics of cellular low-frequency resonant metamaterials for design and optimization
Alireza Amirkhizi (University of Massachusetts, Lowell), Weidi Wang (University of Massachusetts, Lowell), Willoughby Cheney (University of Massachusetts, Lowell), Erdem Caliskan (University of Tennessee, Knoxville) and Reza Abedi (University of Tennessee, Knoxville).
Abstract
In this study an approach for reduced order modeling (ROM) of the dynamics of cellular micro-architectured media is presented. The method relies on the sparse structural topology of repeating unit cells and extracts the effective ROM parameters based on matching its eigenfrequency spectrum with the continuum analysis of the same system. The process involves matching kinetic and potential energy of the two low and high fidelity models as well as the modal shapes, for all frequencies up to a certain desired limit. The focus on low frequency resonant media makes the method particularly effective. While Bloch-Floquet periodicity is used in this initial step, the application to finite structures has shown great success in frequency domain analysis. Additionally, time domain analysis of finite structures can also be performed using the same parameters. The approach can be used for design of graded structures; in other words, perfect periodicity is not required and if neighboring cells have similar architecture, the ROM approach is still capable of satisfactory match with far more computationally expensive (e.g. 4 orders of magnitude) high fidelity models. It is observed, however, that exterior cells may require adjustments to their ROM parameters, especially in time domain (e.g. impact) applications. Other optimization approaches are discussed in improving the matching performance of ROM with continuum analysis.
[561] ID:561-Cruciform Specimen Design and Optimization for Biaxial Testing of Carbon Fiber Reinforced Polymer Composites
Amir Hamza Nazir Ahmed Siddiqui (Indian Institute of Technology Bombay), Asim Tewari (Indian Institute of Technology Bombay), Sushil Mishra (Indian Institute of Technology Bombay) and Anirban Guha (Indian Institute of Technology Bombay).
Abstract
Composite materials are increasingly preferred for various structural applications due to their numerous advantages. However, most structures undergo complex loading, resulting in a multi-axial stress state within the material. Estimating material properties under biaxial loading is a complex process. The planar biaxial testing technique proves highly accurate for biaxial mechanical properties compared to other out-of-plane methods. Although planar biaxial tests precisely predict material deformation behavior, their applicability is confined to the design of cruciform specimens. Improper cruciform specimen design causes non-uniform strain distribution, leading to failure outside the gauge region. The present study aims to design a novel cruciform specimen to achieve uniform strain distribution and failure within the gauge region. An optimized cruciform biaxial specimen is initially developed using a commercial finite element method. Four cruciform geometries (A, B, C, and D) undergo systematic analysis through finite element simulations. Geometry D, featuring a square slot, is the most suitable for biaxial testing. Carbon fiber reinforced polymer composites (CFRP) are utilized in the study, manufactured through the resin transfer molding (RTM) process. Strain evolution during planar biaxial testing is recorded using the Digital Image Correlation method. Experimental biaxial tensile testing of the proposed cruciform design verifies the effectiveness of the optimized parameters, with digital image correlation revealing maximum and uniform strain distribution in the gauge region. The stress-strain curve shows linearity for equi-biaxial loading, with a failure strain of 0.55%. Fracture analysis confirms fiber fracture and fiber pull-out as observed failure mechanisms.
[562] ID:562-Micromechanical properties of MnO-SiO2-Al2O3 inclusions in iron
David Hernández-Escobar (Laboratory of Mechanical Metallurgy, École Polytechnique Fédérale de Lausanne, Lausanne, 1015, Switzerland), Sandor Lipcsei (Laboratory of Mechanical Metallurgy, École Polytechnique Fédérale de Lausanne, Lausanne, 1015, Switzerland), Alejandra Slagter (Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, USA) and Andreas Mortensen (Laboratory of Mechanical Metallurgy, École Polytechnique Fédérale de Lausanne, Lausanne, 1015, Switzerland).
Abstract
Oxide inclusions in the SiO2 – Al2O3 – MnO pseudo-ternary system are precipitated within iron by in-situ reaction, analyzed for their composition and characterised by means of micromechanical tests that give their intrinsic, in-situ mechanical properties such as their hardness and their stiffness, or the strength of their interface with the iron-based matrix. Preliminary results suggest that adjusting the MnO content of the resulting oxides inclusions can be used to obtain an inclusion stiffness close to that of the iron matrix, thus reducing the elastic inclusion/matrix mismatch in steel and making MnO-rich inclusion compositions attractive candidates if one seeks to minimize local stress concentrations in the alloy under mechanical loading.
[563] ID:563-Protection effectiveness of energy absorbing floors on elderly fall-related hip fractures using whole-body FE simulations
Qi Huang (KTH Royal Institute of Technology), Zhou Zhou (KTH Royal Institute of Technology) and Svein Kleiven (KTH Royal Institute of Technology).
Abstract
Falls among the elderly cause a huge number of hip fractures worldwide. Energy absorbing floors (EAFs) represent a promising strategy to decrease impact force and hip fracture risk during falls among the elderly. However, little is known about how the design features of floors influence biomechanical effectiveness. A high biofidelity while-body finite element model (THUMS) with updated soft tissue near the hip region was implemented in this study, to measure the attenuation in femoral neck force provided by four commercially available EAFs. The simulations were performed at the most serious sideways falling posture for a small-size elderly woman with a -10◦ trunk angle and +10◦ anterior pelvis rotation. At a pelvis impact velocity of 3 m/s, the peak force attenuation provided by four EAFs ranged between 4% and 20%. Similarly, the risk of hip fractures also demonstrates a comparable attenuation range. The results also exhibited that floors with higher internal energy during impact demonstrated greater force attenuation in sideways falls. By comparing the protective performance of existing EAFs, these results can improve the floor design that offers better performance and clinical effectiveness in high-fall-risk environments for the elderly.
[564] ID:564- In situ three-dimensional observation of plasticity onset in a Pt nanoparticle
Sarah Yehya (Université de Lyon, INSA-Lyon, MATEIS, CNRS UMR5510, F-69621 Villeurbanne, France), Thomas W. Cornelius (Aix-Marseille Univ., Université de Toulon, CNRS, IM2NP, Marseille, France), Marie-Ingrid Richard (Laboratory CEA Grenoble IRIG/MEM/NRS, 17 rue des Martyrs, FR-38054 Grenoble, France), Felisa Berenguer (Synchrotron SOLEIL - L’Orme des Merisiers, Saint-Aubin, BP 48 FR - 91192 Gif-sur-Yvette, France), Eugen Rabkin (Departement of Materials Science and Engineering, Technion - Israel Institute of Technology, 3200003 Haifa, Israel), Olivier Thomas (Aix-Marseille Univ., Université de Toulon, CNRS, IM2NP, Marseille, France) and Stéphane Labat (Aix-Marseille Univ., Université de Toulon, CNRS, IM2NP, Marseille, France).
Abstract
Crystal lattice defects can dramatically alter material properties and functionality. Furthermore, defects energy and mobility in nano-objects vary significantly from their bulk counterpart. Thus, the understanding of defects behavior is crucial to optimize material performance. Bragg coherent X-ray diffraction imaging (BCDI), a lensless imaging technique that relies on phase retrieval algorithms, allows for 3D characterization of morphology and strain with a 3D spatial resolution of 10 nm and picometer sensitivity of lattice displacement field. It has emerged nowadays as a revolutionary tool to image defects and strain fields in 3D. BCDI is thus an ideal technique to probe the stability of defects in nanocrystals during mechanical straining.
Here, we report three-dimensional defect characterization at the onset of plasticity in a 550 nm Pt nanoparticle from two recent successive synchrotron experiments: The first at ESRF-ID01 and the second at SOLEIL-CRISTAL. The former is an experiment that combines in-situ mechanical testing using a custom-built atomic force microscope with BCDI. The three-dimensional reconstructions from the Pt 111 coherent diffraction patterns show the nucleation of prismatic dislocation loops during indentation. The elastic field measured inside the crystal during indentation estimates that the shear stress required to generate defects is 6.4 GPa, which represents the upper theoretical limit of elasticity and is unprecedented for Pt nanoparticles.
In the latter experiment at the SOLEIL synchrotron, the complete dislocation network was imaged post-mortem and the Burgers vector for each dislocation line was determined by multi-reflection BCDI (Pt 111, Pt 002, Pt 020, and Pt 002 Bragg peaks) revealing sessile dislocations.
[565] ID:565- In-Silico Modeling of Atherosclerosis: Continuous and Agent-Based Hybrid Approach
Ricardo Caballero (I3A University of Zaragoza), Miguel A. Martínez (I3A University of Zaragoza) and Estefania Peña (I3A University of Zaragoza).
Abstract
In this work, we present an in-silico model that combines continuous convection-diffusion-reaction model and agent-based model to predict atheroma plaque growth. We explore how hemodynamics affect the mechanics and transport properties in the arterial wall, triggering cellular events that are related to atheroma plaque growth. The hybrid model has three modules coupled together: computational fluid dynamics (CFD), continuous module of continuous convection-reaction-diffusion (CRD) equations and agent-based model (ABM). The cellular processes included in the model are: mitosis and apoptosis of the cells; production and degradation of the extracellular matrix; production, phagocytosis and necrosis of macrophages, becoming foam cells (FCs) due to excess LDL in the wall; and the change of phenotype of smooth muscle cells (SMCs) from contractile to synthetic. Based on the results obtained in the continuous analysis for WSS and oxLDL concentration, atheroma plaque growth was reproduced in the ABM model. The transfer of information from the ABM to the continuous model was performed by segmentation of the output image provided by the ABM. The ABM shows the evolution of the atheroma plaque after 30 years, reproducing greater growth in the areas with higher concentrations of WSS and oxLDL.
[566] ID:566-A new numerical model for the elasto-plastic behavior of cellular materials
Yohann Trivino (LMGC, University Montpellier 2), Vincent Richefeu (Laboratoire 3SR, University Grenoble Alpes), Farhang Radjai (LMGC, University Montpellier 2), Komlanvi Lampoh (IATE, INRAE) and Jean-Yves Delenne (IATE, INRAE).
Abstract
We present a new model, based on the discrete element method, designed to simulate a dynamic rod system. Originally designed for the study of plant cell tissues, our approach shows remarkable adaptability to a variety of applications. The model is based on a set of equations governing the motion of bars in two-dimensional space. These equations are solved using a robust numerical integration scheme, with the resulting motion serving as the basis for calculating the forces distributed to the nodes by the bars. The results demonstrate a commendable fidelity in reproducing the anticipated behavior, attesting to the model's accuracy and reliability. Beyond its application to the elucidation of plant cell tissue dynamics, our model holds promise for the study of a wide range of systems. In conclusion, our proposed model, anchored in the discrete element method, not only successfully captures the subtleties of plant cell tissue dynamics, but also lends itself to broader scientific investigations.
[567] ID:567- Residual stress and surface integrity of selective laser melted 316L SS: A correlation between experimental and modelling results
Suryank Dwivedi (Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, India), Pratik Kumar Shaw (Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, India), Deepak Kumar (Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, India) and Amit Rai Dixit (Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, India).
Abstract
Selective Laser Melting (SLM) of metallic biomaterials, an additive manufacturing (AM) technique, offers rapid fabrication with improved bulk properties. This study investigates the impact of heat treatment on residual stress, bulk properties, and tribological performance of SLM 316L stainless steel (316L SS) components. Experimental analyses, including X-ray diffraction and microscopy, characterize residual stress and microstructural changes induced by varying heat treatment parameters (e.g., 650 °C and 950 °C). Micro-hardness measurements and tribological tests are also conducted to evaluate the mechanical and tribological behavior for both as-printed and heat-treated specimens. Surface integrity, such as surface roughness, morphology, and microstructure, reveals significant improvements at 650 °C and 950 °C compared to as-printed samples. A micro-hardness values range from 270 ± 4 to 357 ± 7 HV0.1, with a slight decay at 650 °C. Further, the tribological analysis shows similar behavior for as-printed and 650 °C specimens (COF: 0.34 and 0.33, respectively), with a slight improvement at 950 °C (COF: 0.29). The volumetric wear loss values were also calculated, and the outcomes aligned with the friction performance. Furthermore, the correlation between experimental and simulation results, using SIMUFACT Additive software, explores the residual stress distribution on all faces. The residual stress values for as-printed, 650 °C, and 950 °C specimens range from 354 MPa (compressive) to 722 MPa (tensile), 308 MPa (compressive) to 207 MPa (tensile), and 328 MPa (compressive) to 196 MPa (tensile), respectively. The results indicated that the as-printed part exhibits maximum tensile residual stress, decreasing with heat treatment strategies. The obtained residual stress values from the simulation results are also compared with the XRD data, and it found that maximum residual stress values are in line with simulation results, emphasizing the research's contribution to correlating experimental and simulation results for additively manufactured metallic components with tailored heat treatment strategies.
[568] ID:568-Phase-field Cosserat Crystal Plasticity Towards Modelling Nucleation In Recrystallization
Benoit Appolaire (Institut Jean Lamour, Université de Lorraine, CNRS), Flavien Ghiglione (Centre des Matériaux, MINES ParisTech - PSL University, CNRS), Anna Ask (Onera), Kais Ammar (Centre des Matériaux, MINES ParisTech - PSL University, CNRS) and Samuel Forest (Centre des Matériaux, MINES ParisTech - PSL University, CNRS).
Abstract
The microstructure of materials has a tremendous influence on their macroscopic properties, which naturally leads to seeking to tailor microstructures to reach wanted features. In the case of metals, it has been long recognized that grain boundaries control the macroscopic mechanical properties. Thus, the optimization of macroscopic properties through the design of grain boundaries has naturally grown over the years. Controlling the grain features at will requires a thorough understanding of the physical and mechanical phenomena occurring during thermomechanical processes, especially the phenomenon of recrystallization. Recrystallization can be roughly said to be composed of two steps: (i) nucleation and (ii) growth of the newly nucleated grains. While grain growth can be relatively well modelled, nucleation is still a challenging topic. The Kobayashi-Warren-Carter (KWC) phase field model is thought to be able to naturally account for such phenomena. It has been extended recently by Ask et al. in a new model with full coupling for material and lattice rotations, which also accounts for the evolution of dislocation densities. In this work, we aim at illustrating the capabilities of the modelling framework to handle grain nucleation occurring during recrystallization. Hence, we will consider conditions generating high lattice curvatures and stored energies such as slip or kink bands that are likely to promote nucleation of new grains. Thus, using a a three-dimensional version of the coupled model proposed by Ask et al., simple loading cases, such as torsion, will be tested on single and polycrystals to trigger grain nucleation.
[570] ID:570-A data-driven framework to establish surrogate constitutive models of viscoelastic porous elastomers
Mirac Onur Bozkurt (Imperial College London) and Vito L. Tagarielli (Imperial College London).
Abstract
Porous elastomers exhibit highly nonlinear and path-dependent material responses to large deformations. Predicting such complex behaviours analytically is unfeasible; therefore, traditional approaches often rely on test data to model these materials. Recent advancements in homogenization theory have enabled the development of high-fidelity predictions for complex material systems. Researchers have leveraged various machine learning techniques to establish constitutive models based on data containing homogenized material responses obtained from high-fidelity micromechanical simulations. In this research, we introduce a data-driven computational framework to implement surrogate constitutive models for porous elastomers undergoing large deformations. Explicit finite element (FE) simulations are conducted to compute the homogenised response of a cubic unit cell of an elastomer with constant initial porosity and material properties, subjected to a randomly imposed set of multiaxial strain states. The path-dependent stress response is predicted incrementally based on the current states of stress and strain, the prescribed strain increment, and the corresponding time increment. Average stress-strain measurements from FE simulations are utilized to assemble a training dataset for the surrogate macroscopic material model using simple neural networks. The prediction domain is gradually expanded to explore unseen initial porosities and material properties through active transfer learning. In addition to global stress predictions by the macroscopic surrogate model, the proposed framework approximates the corresponding local stress distribution in a porous unit cell via a coupled autoencoder architecture. The effectiveness of the proposed framework is demonstrated in producing material models with good accuracy and efficiency through several examples.
[571] ID:571-Continuum multi-physics modeling of cell and bacteria motility.
Alberto Salvadori (The Mechanobiology Research Center, Università degli studi di Brescia), Mattia Serpelloni (The Mechanobiology Research Center, Università degli studi di Brescia), Claudia Bonanno (The Mechanobiology Research Center, Università degli studi di Brescia) and Robert McMeeking (UCSB).
Abstract
Cellular motility emerges after polymerization of actin into an interconnected set of filaments. We portray this process in a continuum mechanics framework, claiming that polymerization promotes a mechanical swelling in a narrow zone about the nucleation loci, which ultimately results in cellular or bacterial motility. To this aim, a new paradigm in continuum multi-physics has been designed departing the well-known theory of Larché-Cahn chemo-transport-mechanics. In this note, we set up the theory of network growth and compare the outcomes of numerical simulations with experimental evidence.
[572] ID:572-Unraveling martensite micro-mechanics, by nano- to macro-scale in-situ testing & CP modelling
Johan Hoefnagels (Eindhoven University of Technology), Tijmen Vermeij (Eindhoven University of Technology), Ron Peerlings (Eindhoven University of Technology) and Marc Geers (Eindhoven University of Technology).
Abstract
Martensite damage in Dual-Phase steel has been analyzed extensively, but the exact deformation mechanisms that trigger or prevent damage initiation remain mostly unexplored. Whereas generally assumed to be hard and brittle, ‘1D’ nano-tensile tests have shown that lath martensite in fully martensitic steel in fact deforms in a highly anisotropic manner, showing large strains under favorable habit plane orientations. The question is whether this mechanism can also occur in dual-phase steels. Therefore, a range of novel methodologies have been developed for high-resolution and robust measurement, identification, and model validation of micromechanical deformation mechanisms. First, a new class of ’2D’ experiments is presented that enables one-to-one quantitative comparison between microstructure-resolved mechanics in experiments and simulations, by circumventing the notorious difficulty of dealing with an unknown 3D subsurface microstructure through a dedicated sample fabrication and testing routine of ’2D’ micrometer thin specimens and by discretization of the full 3D phase and grain geometry for advanced crystal plasticity modelling. Second, a novel nanomechanical testing and alignment framework, including a new nanoscale digital image correlation (DIC) patterning method, is introduced. Finally, the Slip System based Local Identification of Plasticity (SSLIP) method is presented to measure full-field crystallographic slip system activity maps from DIC data, which can directly be compared to numerical predictions. These methods have been applied to study lath martensite in DP steel in greater detail than before. It is shown, by a combination of ’1D’, ’2D’ and ’3D’ experiments and CP simulations, that strong anisotropic martensite plasticity, as previously observed in fully martensitic steel, also occurs in dual-phase steels due to the specific crystallography of the martensite islands. Moreover, it was found by detailed experimental-numerical comparison that the softer martensite plasticity mechanism that occurs over the habit plane also inhibits damage initiation in martensite notches.
[573] ID:573-Examining force-dependent density-reductions and tau mislocalization in dendritic spines with concomitant alterations in network dynamics in TBI-on-a-chip
Edmond A. Rogers (Purdue University), Tyler C. Diorio (Purdue University), Timothy Beauclair (Purdue University), Jhon Martinez (Purdue University), Shatha J. Mufti (Purdue University), David Kim (Purdue University), Nikita Krishnan (Purdue University), Vitaliy Rayz (Purdue University) and Riyi Shi (Purdue University).
Abstract
Using TBI-on-a-chip integrated with computational modeling, we have established a map of differential forces on the network adhered-MEA “chip” using finite element analysis. We found that while impacts induced an overall loss of dendritic spines, with the remaining spines revealing increased levels of mislocalized tau coupled with acrolein, such changes are not uniform. Specifically, these impact-induced changes are significantly intensified at the “edges” of the MEA, where we calculate the force to be higher (relative to the lower-forces experienced at the MEA “center”). Interestingly, acrolein exposure alone in the absence of impact is capable of partially mirroring all of these impact-induced phenomena. In addition to mechanical and biochemical investigations, we also show that impact, in a dose dependent fashion, causes a reduction of activity (spike rate), a functional deficit that can also be mimicked using acrolein. Further, we also show that impacts not only reduce activity, but also suppress, on average, the synchronization of the brain electrical activity, which again, can be partially recreated via acrolein exposure. These results reveal the quantitative relationship between mechanical forces and resulting biochemical, structural, and functional injuries, in the TBI-on-a-chip model, with greater spatial and temporal resolution then previously possible. Finally, this study, along with several previous reports utilizing TBI-on-a-chip, continue to implicate acrolein as a key culprit in post-TBI AD, suggesting that acrolein could provide a promising therapeutic target for slowing or even preventing the progression of TBI to AD.
[574] ID:574- Investigation of Dynamic Mechanical Properties of PP Thermoplastic
Justas Ciganas (Kaunas University of Technology), Arvydas Palevicius (Kaunas University of Technology) and Giedrius Janusas (Kaunas University of Technology).
Abstract
Polypropylene (PP) thermoplastics stand out because of their biocompatibility, high operating temperature, low macromolecular adsorption, and nontoxicity. In biology and medicine, PP plastic is used to create reaction tubes for various research. Additionally, plastic is used in medicine to produce human implants. When microfluidic chips are developed, PP plastic allows high structural strength, stiffness, and low adsorption. In addition, PP plastic can be used as a thermal micro actuator in MEMS devices. Because PP plastic is thermoplastic, it is usually formed by the hot embossing method. As a result of the wide use of PP thermoplastics, the hot embossing production method has been improved by using ultrasonic vibration. The improvement allows plastics to be imprinted at lower temperatures and have lower residual stresses, leading to savings in production costs and higher quality parts. To select suitable ultrasonic hot embossing formation parameters, it is necessary to perform a DMA study and determine the G' storage and G' loss modules. In this study, the test was performed with a stretching machine that has a vibration option. Strain, stress, and phase lag were recorded during the experiment. DMA material analysis allows for the analysis of viscoelastic materials such as PP properties and the use of these data with a finite element model. Irrespective of the forming temperature, the DMA measurements showed that the storage modulus increased with increasing forming frequency. The loss module increased with low frequency. As the frequency increased, the loss module decreased.
[575] ID:575-Dynamics of fluid-mediated approach of a soft solid to rigid interface
Joaquin Garcia-Suarez (EPFL) and Jacopo Bilotto (EPFL).
Abstract
A viscous, lubrication-like response can be triggered in a thin film of fluid squeezed between a rigid and flat surface and the tip of an incoming projectile. Under the assumption of the mediating fluid being incompressible, the impacting solid displays two limit regimes: one dominated by elasticity and the other by inertia. The transition between the two is predicted by a dimensionless parameter, which can be interpreted as the ratio between two time scales that are the time that it takes for the surface waves to warn the leading edge of the impactor of the forthcoming impact, and the characteristic duration of the final viscous phase of the approach. We will discuss the role of solid compressibility and elucidate why nearly-incompressible solids feature substantial "gliding" prior to contact at the transition between regimes, the largest size of entrapped bubble between the deformed tip of the impactor and the flat surface, and (c) a sudden drop in entrapped bubble radius past the transition between regimes. Finally, we argue also that the above timescale ratio (a dimensionless number) can govern the different dynamics reported experimentally for a fluid droplet as a function of its viscosity and surface tension.
[577] ID:577-No Yield Stress for Yield-Stress Fluids
Theo Tervoort (ETH Zürich), Gabriele Pagani (ETH Zürich), Leon Govaert (Eindhoven University of Technology) and Jan Vermant (ETH Zurich).
Abstract
This presentation focuses on simple yield-stress fluids, which are non-thixotropic viscoplastic soft materials exhibiting solid-like behavior at low stress levels and transitioning to non-Newtonian fluid-like flow above a critical stress. The most basic model to describe these materials is arguably the Bingham model [1], which assumes rigid behavior below a constant yield stress and Newtonian fluid behavior above it. More complex models include the Herschel-Bulkley [2] and Casson models [3], which account for non-Newtonian flow behavior beyond the yield stress.
Criticism has been raised regarding the assumption of a true yield stress below which only elastic deformation occurs [4]. This criticism arises from the observation of a limiting zero-shear viscosity plateau in typical yield-stress fluid systems like Carbopol microgels at various concentrations [5].
The nonlinear viscoelastic response of simple yield-stress fluids has received less attention but is the central focus of this presentation. By analyzing creep curves measured at different stress levels for Carbopol microgels, we will illustrate the validity of time-stress superposition for this system. This, in turn, allows us to formulate a comprehensive 3D nonlinear viscoelastic constitutive equation capable of describing nonlinear viscoelastic behavior, including creep and the transition to Herschel-Bulkley-like yielding, without the need for a conventional "yield stress."
References: 1. Bird, R. B., Dai, G. C. & Yarusso, B. J. The Rheology and Flow of Viscoplastic Materials. Rev. Chem. Eng. 1, 1–70 (1983). 2. Herschel, W. H. & Bulkley, R. Konsistenzmessungen von Gummi-Benzollösungen. Colloid Polym. Sci. 39, 291 (1926). 3. Casson, N. Rheology of disperse systems proceedings of a Conference. in Rheology of disperse systems (ed. Mill, C. C.) 84–104 (Pergamon Press, 1959). 4. Barnes, H. A. & Walters, K. The yield stress myth? Rheol. Acta 24, 323–326 (1985). 5. Roberts, G. P. & Barnes, H. A. New measurements of the flow-curves for Carbopol dispersions without slip artefacts. Rheol. Acta 40, 499–503 (2001).
[578] ID:578-Effect of Fiber-Fiber Adhesion on the Mechanics of Network Materials
Catalin Picu (Rensselaer Polytechnic Institute) and Nabeel Amjad (Rensselaer Polytechnic Institute).
Abstract
Most biological materials and many soft engineering materials are made from fibers stochastically distributed and oriented in two or three dimensions. These materials are referred to as ‘network materials’, as their mechanical behavior is controlled by the underlying fiber network. The parameters controlling the mechanical response are the structure of the network, fiber properties and fiber-fiber interactions. In this work we are concerned with the effect of inter-fiber adhesion on the overall mechanical behavior. We show that, in crosslinked networks, a yield point appears due to fiber-fiber adhesion and the yield stress scales linearly with the adhesion strength. The large deformation response is only weakly affected by the adhesive forces. Non-crosslinked networks evolve under the action of adhesive forces to produce cellular networks of fiber bundles. In the absence of friction, such networks are stabilized exclusively by adhesion. A phase diagram capturing the range of network stability in the space of system parameters will be discussed.
[579] ID:579-Higher-order nanobeams based on stress-driven integral elasticity
Francesco Marotti de Sciarra (Department of Structures for Engineering and Architecture), Raffaele Barretta (Department of Structures for Engineering and Architecture), Francesco Paolo Pinnola (Department of Structures for Engineering and Architecture) and Marzia Sara Vaccaro (Department of Structures for Engineering and Architecture).
Abstract
A nonlocal higher-order shear deformation beam theory is developed for bending of nanobeams based on the stress-driven model. Several distributions of the transverse shear strains are considered satisfying the zero traction boundary conditions on the surfaces of the beam. The higher-order shear deformation beam theories and the stress-driven nonlocal model provide the equations of nonlocal elastic equilibrium. Hence, it is shown that the stress-driven model is well-posed for higher-order shear deformation theories. The accuracy of the present approach is verified by comparing the obtained results with existing solutions.
[580] ID:580-Generalized structure tensor-based switchless constitutive relation for arterial tissues
Arvind (Indian Institute of Technology Madras) and Krishna Kannan (Indian Institute of Technology Madras).
Abstract
The collagen fibers which provide mechanical reinforcement to the arterial wall cannot sustain compressive loads. The existing Generalized Structure-Tensor (GST) based formulations emulate this through a tension-compression switch criterion based on the fiber stretch. This approach, however, has the following drawbacks: 1. discontinuous stresses at the switch point, 2. inconsistent predictions of the fiber stretch due to the conditional constitutive relations, i.e., the fibers predicted to be in compression according to the anisotropic terms can be in tension after the switch is employed, and 3. identical responses in longitudinal and transverse shear of unidirectional fibers, contrary to experimental observations.
To address these concerns, we introduce a matched invariant based on the Seth-Hill strain measure that auto-annihilates the contribution from fibers in pure compression. This leads to a unitary & switchless constitutive relation. The matched invariant inherently contains the I5 invariant and, consequently, the different shear modes yield distinct responses. The definition of the matched invariant is generalized for distributed fibers using the GST approach.
A vanishing matched invariant-based GOH (Gasser-Ogden-Holzapfel [1]) constitutive relation with the same number of material parameters is obtained as a particular case corresponding to the Green-Lagrange strain. The constitutive relation with the general Seth-Hill strain resembles an anisotropic Ogden-like relation that can better control the relative magnitude of normal and shear stresses. For deformations devoid of shear, the proposed relations exclude the compressed fibers in a manner similar to that of the angular integration-based model proposed by Li et. al [2]. As evidenced by extensive fitting to planar biaxial and uniaxial data for various arterial tissues, the resulting unitary constitutive relations have significantly improved descriptive and predictive capabilities. The proposed switchless constitutive relation solves the discussed issues with little added complexity. This formulation is equivalent to using a modified and deformation-dependent structure tensor instead of the conventional GST, thereby eliminating the major hurdles associated with the use of a switch criterion.
References: [1]. Gasser, T. C., Ogden, R. W., & Holzapfel, G. A. (2006). Hyperelastic modelling of arterial layers with distributed collagen fibre orientations. Journal of the royal society interface, 3(6), 15-35. [2]. Li, K., Ogden, R. W., & Holzapfel, G. A. (2018). Modeling fibrous biological tissues with a general invariant that excludes compressed fibers. Journal of the Mechanics and Physics of Solids, 110, 38-53.
[581] ID:581- A first-order hyperbolic Arbitrary Lagrangian Eulerian conservation formulation for non-linear solid dynamics in irreversible processes
Antonio Javier Gil (Swansea University), Chun Hean Lee (University of Glasgow), Thomas Di Giusto (Swansea University) and Javier Bonet (CIMNE, Universitat Politecnica de Catalunya).
Abstract
The presentation introduces a computational framework using a novel Arbitrary Lagrangian Eulerian (ALE) formalism in the form of a system of first-order conservation laws. In addition to the usual material and spatial configurations, an additional referential (intrinsic) configuration is introduced in order to disassociate material particles from mesh positions. Using isothermal hyperelasticity as a starting point, mass, linear momentum and total energy conservation equations are written and solved with respect to the reference configuration. In addition, with the purpose of guaranteeing equal order of convergence of strains/stresses and velocities/displacements, the computation of the standard deformation gradient tensor (measured from material to spatial configuration) is obtained via its multiplicative decomposition into two auxiliary deformation gradient tensors, both computed via additional first-order conservation laws.
Crucially, the new ALE conservative formulation will be shown to degenerate elegantly into alternative mixed systems of conservation laws such as Total Lagrangian, Eulerian and Updated Reference Lagrangian. Hyperbolicity of the system of conservation laws will be shown and the accurate wave speed bounds will be presented, the latter critical to ensure stability of explicit time integrators. To consider more general irreversible processes such as thermo-elasticity and thermo-visco-plasticity, incorporation of the first law of thermodynamics, expressed in terms of the entropy density, will be introduced as an additional conservation law.
For spatial discretisation, a vertex-based Finite Volume method and a Smooth Particle Hydrodynamics alternative are employed and suitably adapted. To guarantee stability from both the continuum and the semi-discretisation standpoints, an appropriate numerical interface flux (by means of the Rankine–Hugoniot jump conditions) is carefully designed and presented. Stability is demonstrated via the use of the time variation of the Ballistic energy of the system, seeking to ensure the positive production of numerical entropy. A range of three dimensional benchmark problems will be presented in order to demonstrate the robustness and reliability of the framework, including high velocity impact thermally coupled scenarios.
[582] ID:582-The effect of grain boundaries on the fracture toughness of hard coatings
Yinxia Zhang (KIT - Institute for Applied Materials), Matthias Bartosik (University of Leoben), Ujjval Bansal (KIT - Institute for Applied Materials), Subin Lee (KIT - Institute for Applied Materials) and Christoph Kirchlechner (KIT - Institute for Applied Materials).
Abstract
Grain boundaries (GBs) play a pivotal role in the design and performance of hard coatings. Our study focuses on understanding their impact on the fracture toughness of around 2 µm thick sputtered AlN, CrN/AlN multi-layered, and CrN hard coatings. For this purpose, we employed bridge notch cantilever bending tests on columnar grain boundary structures, aligning the notches both parallel and perpendicular to the coating’s growth direction. Our bridge geometry was optimized in such a way that the crack initiation occurs at the material bridges. Subsequently, the crack arrests and forms a natural sharp through thickness crack at which final fracture occurs. This way, not only three different fracture toughness values can be obtained from a single experiment, but also a very localized determination of the toughness value becomes possible with much reduced scatters in the data. We found that the GB orientation greatly influences the microscale fracture toughness. Notably, the deflection of cracks running perpendicular to the growth direction resulted in a significant increase of the fracture toughness, by around 10%. Furthermore, we observed that an epitaxial structure without GBs exhibits a higher fracture toughness compared to the columnar grain structure. The bridge with the epitaxial structure demonstrated a fracture toughness of 4.1±0.4 MPa·m1/2, which is higher compared to 3.0 ± 0.3 MPa·m1/2 of the bridge with the columnar grain structure. In the talk, the method of crack arrest upon bridge failure and its use for the determination of fracture toughness values in confined volumes will presented and discussed.
[583] ID:583-The role of fiber breakage in compression after impact of thermoplastic composites: insights from novel experimental techniques.
Fernando Naya (Universidad Carlos III de Madrid), Jesús Pernas-Sanchez (Universidad Carlos III de Madrid), Cristina Fernández (Universidad Carlos III de Madrid) and Pablo Zumel (Universidad Carlos III de Madrid).
Abstract
The post-impact strength of CFRP composite materials stands as a crucial design parameter for aeronautical structures, dictating their damage tolerance. In low velocity impact tests, the laminate demonstrates a partial return of energy to the indenter above a certain threshold, exhibiting elastic recovery. The remaining energy undergoes absorption and dissipation within the laminate, manifesting as damage (both interlaminar and intralaminar), plastic deformation of the polymer matrix, and breakage of carbon fibers. Despite its significance, quantifying the contribution of individual damage mechanisms to the overall energy absorption process remains a challenge due to experimental complexities. Herein, we introduce a novel experimental approach leveraging local induction heating to isolate the influence of fiber breakage during the damage process. This methodology mimics the extent and location of damage incurred in standard low-velocity impacts while preserving fiber integrity. Our study compares the residual strength and stiffness of AS4/PEEK laminates subjected to impacts across a range of energies (20-70J) with those damaged by electromagnetic currents, ensuring equivalent damage extensions. The findings underscore the profound impact of carbon fiber breakage on laminate stiffness, while strength remains largely unaffected. This reaffirms delamination as the primary contributor to strength loss in post-impact compression scenarios.
[584] ID:584-Strain rate influence on the compressive behaviour of holed woven CFRP laminates
Jose Manuel Rodriguez-Sereno (Universidad Carlos III de Madrid), Jesus Pernas-Sanchez (Universidad Carlos III de Madrid), Jose Alfonso Artero-Guerrero (Universidad Carlos III de Madrid) and Jorge Lopez-Puente (Universidad Carlos III de Madrid).
Abstract
The study of carbon fibre composite (CFRP) laminates at high strain rates is one of the main challenges in the aeronautical industry. Several researchers have studied the effect of strain rate on CFRP laminates with a woven structure. Dynamic compression tests are mainly performed using the Hopkinson bar system (SHPB). The research community has not yet agreed on a robust methodology that accurately describes the formulation representing the high strain rate response of woven CFRP laminates. Over the past decades, several researchers have studied the effect of holes in CFRP to describe the effect of the stress concentration factor. Although many studies have developed numerical simulations to analyse the fracture process in CFRP based on fracture mechanics theories, there is little information on the strain rate dependence of woven fabric CFRP laminates with holes. In this work, a constitutive model is proposed to describe the mechanical behaviour of woven CFRP laminates including the strain rate dependence on the compressive properties. Finally, a FE modelling has been carried out using Abaqus/Explicit software of compression tests on CFRP laminate specimens with holes, at different strain rates (Quasi-Static and dynamic) using different fibre orientations. The results of the simulations have been validated based on the results of an experimental campaign.
[585] ID:585- On the influence of cryogenic temperatures on CFRP laminates subjected to impulsive loadings
Jose Alfonso Artero-Guerrero (Universidad Carlos III de Madrid), Jesús Pernas-Sanchez (Universidad Carlos III de Madrid), Jorge Lopez-Puente (Universidad Carlos III de Madrid), Juan Royo (Airbus Operations S.L.), Vasilis Votsios (Airbus Operations S.L.), Miguel Miranda (Airbus Operations S.L.) and Esteban Martino (Airbus Operations S.L.).
Abstract
The use of LH2 as a possible alternative for a sustainable propellant in the aeronautic industry represents a major step for developing a zero-emissions aircraft. This fuel must be stored and handled at cryogenic temperatures. Therefore, composite structures under cryogenic temperatures has become a interesting scientific and industrial topic in recent years. The influence of cryogenic temperatures on material performance has to be investigated including different loading scenarios such as impact events.
On this work, authors have characterized Carbon Fiber Reinforced Polymer (CFRP) laminates under quasistatic and dynamic conditions for ambient and cryogenic temperatures (-150ºC). Characterisation campaign is focused on the transversal and off-axis behaviour of CFRP laminate under compressive loadings. For dynamic conditions, a Split-Hopkinson Pressure Bar (SHPB) has to be used in order to reach strain rate up to 500 1/s. Moreover, drop weight tower test has been performed for ambient and cryogenic temperatures (-150ºC) at quasi-isotropic laminates. Finally, after an ultrasonic inspection, compression after impact test has been carried out to evaluate the residual performance of the impacted laminated. The analysis of the complete testing campaign deepen the understanding of the performance of the matrix and matrix-fibres interaction under these extreme conditions.
[586] ID:586-Deformation behavior Analysis of P91 Martensitic Steel: Micropillar Tests and Crystal Plasticity Modelling
Samaneh Isavand (University of Limerick), Pavan Sreenivasa Rao (University of Limerick), Andrey Bondarev (University of Limerick), Sean Leen (University of Galway) and Noel Odowd (Noel.ODowd@ul.ie).
Abstract
This study investigates the deformation mechanisms of P91 martensitic steel at room temperature employing micropillar compression tests and crystal plasticity finite element (CPFE) modelling. The active slip systems were identified through micropillar compression tests, where micropillars were milled using a focused ion beam instrument. These micropillars were extracted from grains within the polycrystal P91 with different crystallographic orientations suited for activating various slip plane families in a body-centered cubic (BCC) structure. The CPFE model, describing the cumulative rate dependent behaviour of each slip system within the single crystal, was calibrated for each slip family through the stress-strain curves of the micropillar compression tests. The scanning electron microscopy (SEM) images of the deformed micropillars were compared with the corresponding prediction of the CPFE models to evaluate the predictive capacity of the finite element models. The accuracy of slip trace predictions, specifically regarding the angle of slip trace and shape of the deformed micropillars for {110}, {112}, and {123} slip plane families was verified.
[587] ID:587-Computational homogenization and topology optimization of flexoelectricity-based metamaterials for apparent piezoelectricity
David Codony (Universitat Politècnica de Catalunya), Jordi Barceló-Mercader (Universitat Politècnica de Catalunya), Francesco Greco (Universitat Politècnica de Catalunya), Alice Mocci (Universitat Politècnica de Catalunya), Hossein Mohammadi (Universitat Politècnica de Catalunya), Sonia Fernández-Méndez (Universitat Politècnica de Catalunya) and Irene Arias (Universitat Politècnica de Catalunya).
Abstract
We present a method for the numerical computation of representative volume element (RVE) in the context of high-order electromechanical theory, which relies on the construction of a generalized-periodic Cartesian B-Spline approximation space [1]. The geometry is unfitted to the mesh, and described by a periodic level set function. The imposition of generic macroscopic fields (strains/stresses and electric fields/electric displacements) is naturally allowed as strong Dirichlet/Neumann macroscopic conditions.
We apply the proposed method to study non-piezoelectric architected metamaterials with ap parent piezoelectric behavior thanks to the flexoelectric effect (coupling between polarization and strain gradient). In particular, we perform multi-objective topology optimization of flexoelectric metamaterial RVEs by means of genetic algorithms [2]. We find the Pareto fronts where area fraction is minimized and different apparent piezoelectric coefficients (stress/strain sensor/actuator) are maximized.
Overall, we find RVE topologies exhibiting a competitive apparent piezoelectric behavior as compared to reference piezoelectric materials such as quartz and PZT ceramics.
References [1] J. Barceló-Mercader, D. Codony, A. Mocci, and I. Arias, “Computational homogenization of higher-order electro-mechanical materials with built-in generalized periodicity conditions”, arXiv preprint arXiv:2311.08196, 2023. [2] F. Greco, D. Codony, H. Mohammadi, S. Fernández-Méndez, and I. Arias, “Topology optimization of flexoelectric metamaterials with apparent piezoelectricity,” Journal of the Mechanics and Physics of Solids, vol. 183, p. 105477, 10 2023.
[588] ID:588-Multiscale modelling of the effect of surface piezoelectricity in finite samples
Monica Dingle (Universitat Politècnica de Catalunya), David Codony Gisbert (Universitat Politècnica de Catalunya) and Irene Arias Vicente (Universitat Politècnica de Catalunya).
Abstract
Energy transduction, i.e. the ability to transform mechanical energy into electrical energy and vice-versa is the core of current technologies for sensors, actuators and energy harvesters which are extensively used in a wide range of applications, such as consumer electronics, car sensors and diagnosis techniques to name a few. Most of these technologies rely on piezoelectricity, the coupling between polarization and strain. In recent decades, flexoelectricity, a universal electromechanical coupling, has received increasing attention as a promising alternative for electromechanical applications. Flexoelectricity is the two-way coupling between strain gradient and polarization, and conversely the coupling between polarization gradient and strain [1]. It is a gradient effect and thus scales inversely to size, becoming relevant only at sub-micron sizes in most materials. Nevertheless, developments in nanotechnologies have enabled a miniaturization of electromechanical devices reaching sizes where flexoelectricity becomes important [2]. Thus, a full understanding of the underlying physical mechanisms becomes essential towards developing engineering tools to optimize the performance of piezoelectric devices and to design new active metamaterials exploiting flexoelectricity [3, 4]. One aspect which remains elusive is the effect of surfaces on the overall flexoelectric response of finite samples [5]. Surface piezoelectricity has been claimed as one possible source of discrepancy between theoretical estimates and experimental measures of flexoelectric coefficients [1]. In this work, we develop a model to account for surface effects in a mathematical and computational framework for flexoelectricity and explore avenues towards the differential characterization of both mechanisms.
References
[1] P. Zubko, G. Catalan, and A. K. Tagantsev, “Flexoelectric effect in solids,” Annual Review of Materials Research, vol. 25, pp. 946–974, 2013. [2] B. Wang, Y. Gu, S. Zhang, and L.-Q. Chen, “Flexoelectricity in solids: Progress, challenges, and perspectives,” Progress in Materials Science, vol. 106, p. 100570, 2019. [3] A. Mocci, J. Barceló-Mercader, D. Codony, and I. Arias, “Geometrically polarized architected dielectrics with apparent piezoelectricity,” Journal of the Mechanics and Physics of Solids, vol. 157, p. 104643, 2021. [4] F. Greco, D. Codony, H. Mohammadi, S. Fernández-Méndez, and I. Arias, “Topology optimization of flexoelectric metamaterials with apparent piezoelectricity,” Journal of the Mechanics and Physics of Solids, vol. 183, p. 105477, 10 2023. [5] A. S. Yurkov and A. K. Tagantsev, “Strong surface effect on direct bulk flexoelectric response in solids,” Applied Physics Letters, vol. 108, no. 2, p. 022904, 2016.
[589] ID:589- Experimental Characterisation of Notch non-Linearities in Pseudo-Ductile Composite Laminates
Anbazhagan Subramani (University of Girona), Joël Cugnoni (University of Applied Sciences and Arts Western (HES-SO), HEIG-VD), Pere Maimí Vert (University of Girona), Josep Costa Balazant (University of Girona) and Robin Amacher (LPAC, École Polytechnique Fédérale de Lausanne (EPFL)).
Abstract
Thin-ply composites (t_ply=20-80 g/m^2) are gaining popularity due to their minimal manufacturing defects and uniform mechanical properties. However, they suffer from increased brittleness and notchsensitivity due to reduced strain redistribution capabilities [1]. Hybridisation using Low Elongation (LE) and High Elongation (HE) layers, specifically the [HE/LE/HE] sub-laminate design, introduces pseudo-ductility by inducing fragmentation in the LE layer, leading to a metal-like behaviour. However, the relationship between ply thickness, translaminar toughness, and notch sensitivity complicates ascertaining the improvements solely attributable to pseudo-ductility [2, 3]. Studies by Czél and Tavares highlight a reduction in notch sensitivity in hybrid laminates but with varying results depending on specimen size and design [4, 5]. This study develops pseudo-ductile hybrid laminates without significantly increasing sub-laminate thickness, ensuring comparable unnotched tensile strength to the LE counterpart of the same laminate stacking sequence. We characterised the unnotched and notched strengths of both laminates, employing Digital Image Correlation (DIC) to analyse damage mechanisms. Then, we identified and analysed strain non-linearities using the DIC images to differentiate the damage mechanisms in both laminate types. Further, we also employed DIC to examine full-field pseudo-ductile strains and damage incrementally. Our findings provide a clear pathway to delineate and compare damage mechanisms between reference and hybrid materials, showcasing the effectiveness of our proposed methodology.
References [1] Amacher, R., Cugnoni, J., Botsis, J., Sorensen, L., Smith, W., & Dransfeld, C. (2014). Thin ply composites: Experimental characterization and modeling of size-effects. Composites Science and Technology, 101, 121-132. [2] Furtado, C., Arteiro, A., Linde, P., Wardle, B. L., & Camanho, P. P. (2020). Is there a ply thickness effect on the mode I intralaminar fracture toughness of composite laminates?. Theoretical and Applied Fracture Mechanics, 107, 102473. [3] Subramani, A., Maimí, P., Guerrero, J. M., & Costa, J. (2023). Nominal strength of notched seudo-ductile specimens. Theoretical and Applied Fracture Mechanics, 128, 104120. [4] Czél, G., Jalalvand, M., Fotouhi, M., Longana, M. L., Nixon-Pearson, O. J., & Wisnom, M. R. (2018). Pseudo-ductility and reduced notch sensitivity in multi-directional all-carbon/epoxy thin-ply hybrid composites. Composites Part A: Applied Science and Manufacturing, 104, 151-164. [5] Tavares, R. P. (2020). Mechanics of deformation and failure of fibre hybrid composites (Doctoral dissertation, Universidade do Porto (Portugal))
[590] ID:590-Simulation of indirect tensile tests of cylindric specimens and extension of the size-effect curves of concrete
Beatriz Sanz (Universidad Politécnica de Madrid), Jaime Planas (Universidad Politécnica de Madrid) and Camilo Ramos (Corporación Universitaria Minuto de Dios).
Abstract
New types of concrete have emerged in the last decades, which require research about their fracture behaviour. As an example, a recen study carried out in collaboration with the Spanish Association of Railway Sleeper Element Manufacturers manifested that the size-effect curves of concrete should be extended in order to be applied to new mixtures. In that work a new implementation of the method proposed by Planas, Elices and Guinea, which combines diagonal splitting tensile tests and three-point bending tests of notched specimens to determine the main fracture properties of quasi-brittle materials, was offered with the appropriate modifications in order to perform the tests by using the factory facilities, and a round-robin test was carried out with the collaboration of ten laboratories, obtaining satisfactory results. However, it was found that some mixtures present a diameter to brittleness length ratio with values out of the ranges considered by Rocco et al in their size-effect study, manifesting the need of extending the available curves. The current works presents a numerical study for the extension of the size-effect curves of cylindrical specimens for low diameter to brittleness length ratios, by using elements with an embedded cohesive crack within the finite element framework COFE (Continuum Oriented Finite Element) and bi-dimensional models of the specimens in dimensionless numerical simulations. In the presentation, the main aspects of the simulations will be explained together with the analysis of the main cases for verification of the method, the extended curves of cylindrical specimens will be presented for the ranges of width of bearing bands and diameter of cylinders considered by Rocco el al, and it will be discussed how to proceed in the interpretation of the experimental results to determine the tensile strength and brittleness length of concrete.
[591] ID.591- Enhanced the Mechanical Strength of 3D printed PEEK Parts
Mojtaba Tafaoli-Masoule (Mechanical Engineering Department, Babol Noshirvani University of Technology, Iran), Mohsen Shakeri (Mechanical Engineering Department, Babol Noshirvani University of Technology, Iran), Abolfazl Zahedi (Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborugh University, UK) and Mohammad Vaezi (Mechanical Engineering Department, Babol Noshirvani University of Technology, Iran).
Abstract
Polyether-ether-ketone (PEEK) stands out as a semi-crystalline engineering thermoplastic uses in many industries such as automotive, aerospace, and medical sectors. This material now solves the challenges of customized medical scaffolds through promising results of nontoxicity, high mechanical strength, lightweight nature, biocompatibility, and resilience at elevated temperatures. The main drawback of PEEK is printability. The common procedure to print PEEK components is Fused Deposition Modeling (FDM) has many process parameters to adjust. Changing the 3D working parameters in PEEK FDM significantly influences mechanical strength and product quality, presenting a common challenge in ensuring high-quality and robust outputs. This challenge needs to be addressed specifically when PEEK supports complicated surgery and in the construction of customized artificial implants. This research introduces an innovative modeling approach employing artificial neural network (ANN) and an elitist genetic algorithm (GA) to optimize process parameters to enhance the mechanical strength of PEEK printed components. The wide range of nozzle and bed temperatures, print speeds, and layer thicknesses are investigated thoroughly. SEM microstructure analyses of specimens printed with varied parameter values further enrich the comparative evaluation. The result reveals the best possible options to print PEEK materials. By optimizing adjustable parameters crucial to mechanical strength using genetic algorithms, the study compares results with existing literature and previous Taguchi orthogonal array designs. The proposed methodology extends beyond mechanical strength investigation, offering insights applicable to diverse mechanical properties.
[592] ID.592-Challenging pressure-free debinding/sintering of Magnesium alloy: application to 3D printed parts by direct-ink writing
Julien Moreau (Mateis (UMR5510)), Xavier Boulnat (Mateis (UMR5510)), Michel Pérez (Mateis (UMR5510)), Olivier Dezellus (LMI(UMR5510)) and Benoit Ter Ovanessian (Mateis (UMR5510)).
Abstract
Additive manufacturing (AM) processes allow for the personalisation of orthopaedic implants. However, permanent implants are not always suitable, since the implant is no more needed once the fracture is repaired. As such, degradable implants, among which Iron (Fe), Zinc (Zn) or Magnesium (Mg) are being studied, would allow a temporary repair function and will degrade after few months. But AM of such alloys, especially Mg, is extremely challenging. Beside laser powder bed fusion (L-PBF), the sinter-based AM techniques are promising to tailor porosity at various scales, leading to customised properties. However, the sintering process of magnesium is the main challenge to overcome as magnesium is one of the most reactive metal for oxidation issue. In this presentation, we will present a sinter-based AM technique to 3D print Mg parts, called robocasting or direct-ink writing. This 3D printing process consists of (i) extruding a paste filled with metallic particles (ii) debinding the organic components of the paste and (iii) pressureless sintering the final structures. The presentation will focus on optimising the debinding and sintering of the parts. We propose to study the liquid phase sintering of MgZnZr (ZK30) alloy. Due to the high reactivity of Mg, a thin oxide layer of approximately 7 nm forms at the surface of the particles. This thin layer acts as a diffusion barrier, thus to perform sintering this barrier must be overcome. Compared to pure Mg, the use of an alloy aims at tailoring the liquid phase proportion to sinter the parts. Using thermodynamic calculations and various in situ experiments such as differential scanning calorimetry (DSC), we optimized the sintering conditions in order to retain the complex shape of the printed material. The sintering set-up is described (atmosphere, temperature, type of confining materials). We managed to sinter, in a reproducible way, various 3D printed parts. Post mortem analyses were carried out, from micro-tomography to microstructural characterization, to link the sintering conditions to the properties of the sintered parts.
[593] ID:593- Aluminium alloys for Additive Friction Stir Deposition manufacturing
Maureen Puybras (Mateis (UMR5510)), Michel Perez (Mateis (UMR5510)) and Thomas Dorin (IFM - Deakin University).
Abstract
The goal of this study is to provide new alloy solutions for the MELD manufacturing technology, a solid-state additive manufacturing technique, based on the additive friction stir deposition. Post deposition treatements are usually necessary to enhance mechanical properties of the printed parts. In order to take into account environmental issues, the aim of this presentation is to present an example of application that does not require post-process thermal treatments. Al-Mg alloys, hardened by magnesium in solid solution, were the ideal candidate. This type of alloy, mainly used in the construction of boat hulls, is known to form Al3Mg2 precipitates at grain boundaries. The susceptibility to stress corrosion cracking as result of alloy ageing, known as “sensitization” is the consequence of this precipitation in such a corrosive environment. To overcome this issue, the addition of Al3(Sc,Zr) core-shell dispersoids, potential heterogeneous nucleation sites for Mg, was studied. Thanks to isothermal artificial ageing treatments punctuated by measurements of thermoelectric power, it was shown that the presence of Al3(ScZr) dispersoids in the alloy accelerated Mg precipitation. Atom probe tomography analyses subsequently confirmed the segregation of Mg on the surface of these dispersoids.
This presentation will focus on the influence of the MELD process on (i) the alloy microstructure, (ii) Mg precipitation and (iii) Al3(ScZr) dispersoids stability.
After MELD, the microstructure appears finer, equiaxed and homogeneous. EBSD analyses shows a grain size for binary AlMg alloy independent of the tool rotation rate. However, the grain size of AlMgScZr alloys increases with rotation rate, questioning the stability of dispersoids under shear. Dispersoids have been studied with TEM and APT before and after the MELD process. Mg precipitation kinetics and corrosion sensitivity were finally characterised to outline the influence of the MELD on sensitization.
[595] ID:595- Optimization of Easy Open Ends for Food Can Packaging: A Comprehensive Material Analysis Approach
Eneritz Cereza (Mondragon Unibertsitatea), Nagore Otegi (Mondragon Unibertsitatea), Joseba Mendiguren (Mondragon Unibertsitatea) and Borja Erice (Mondragon Unibertsitatea | IKERBASQUE).
Abstract
Easy open ends (EOE) play a pivotal role in food can packaging, where efficient material utilisation through shell thickness reduction not only brings economic benefits but also contributes to ecological sustainability. The EOE components, the tab and the end, are independently manufactured and then riveted together. The V-shape score line featured in the latter, represents the weakest part of the assembly, necessitating special attention. The structural integrity and functionality of both components is crucial for ensuring the optimal performance during the can manufacturing and performance process. To address this, materials commonly used in the food packaging industry families were selected: i) two steels grades, TH550 (tab) and ML460 (end) and ii) two aluminium alloys 5182-H48 (tab) and 3104-H26 (end). Their elastoplastic properties were characterised and represented with Hill-48 plasticity and combined Swift-Vode hardening models for the FEM forming analysis. To ensure the material’s performance robustness during the forming operation, the Hosford-Coulomb ductile fracture initiation criterion’s properties were also calibrated for the as-received materials. for the sake of simplicity, the score line was treated as an independent virtual material with continuous thickness properties. The score geometrical feature was removed and instead represented by the said material maintaining a reasonable mesh size throughout the whole component. Finally, experimental performance tests were conducted to assess the validity of the FEMs, showing good agreement.
[596] ID:596-Fracture mechanisms in largely strained steels due to self-contacting surface defects: experiments and modelling
Borja Erice (Mondragon Unibertsitatea / IKERBASQUE), Maria Jesus Perez-Martin (Department of Structural Engineering & Centre for Advanced Structural Analysis, NTNU), Martin Kristoffersen (Department of Structural Engineering & Centre for Advanced Structural Analysis, NTNU), David Morin (Department of Structural Engineering & Centre for Advanced Structural Analysis, NTNU), Tore Borvik (Department of Structural Engineering & Centre for Advanced Structural Analysis, NTNU) and Odd Sture Hopperstad (Department of Structural Engineering & Centre for Advanced Structural Analysis, NTNU).
Abstract
Wrinkles can be found on the surface of largely compressed areas of metallic materials. These surface instabilities can be observed in structural elements that are of interest for the automotive and offshore industries, such as bent tubes or pipes, pressure vessels or die formed sheet metal pieces. Wrinkles are understood as undulations or surface roughness that might set in due to large straining in metallic materials. Typically, they present distinct geometrical features that are periodically repeated on the surface and they are dimension-wise significantly smaller than any of the dimensions that define the rest of the solid. They fold and self-contact, creating surface defects when the structural elements are increasingly compressed, and may lead to a ductile-to-brittle transition if subsequently strained in tension. Eventually, the self-contact grows unsteadily evolving into a crease, a specific type of singularity.
To analyse such an effect, a finite element model of a half-space plane-strain material block with an imperfection was subjected to different levels of compression followed by reverse tensile straining. The existence of a critical strain, for which the self-contact defect acted as a crack during the tensile straining phase predicted by the model was confirmed by reverse compression-tension tests performed at two different strain rates. A post-mortem fractographic analysis allowed to link the ductile-to-brittle transition strain to the morphology of the fracture surfaces. This experimental analysis demonstrated that the findings from the numerical simulations using strain localisation theory were in line with the experimental results.
[597] Thermal history prediction by Machine Learning in Additive Manufacturing
José Ángel Bejarano Vázquez (CENIM-CSIC), Isaac Toda Caraballo (CENIM-CSIC) and Lucía Morales Rivas (CENIM-CSIC).
Abstract
In the scope of understanding the factors controlling the defects that commonly appear in the microstructures of materials produced by Additive Manufacturing (AM), a first step is the prediction of the thermal history at which the material is subjected by means of different printing parameters. The extremely large amount of different combinations of printing parameters (laser power, hatch distance, laser scanning speed…) adds to the different printing geometries which also can vary the influence of such printing parameters. Its computation by means of Finite Element Modelling is the logical choice, but is time consuming and cannot be used in large computational optimization processes.
This work therefore aims at developing a fast and accurate predictive methodology to calculate temperature history at during the AM process. First, a Finite Element Method (FEM) model was developed to extract thermal profiles at key points for Selective Laser Melting processes, optimized for computational efficiency for more than 3000 different printing parameters combinations. Subsequently, different Machine Learning (ML) methodologies are tested as predictive models to determine the most robust approach. The models employed include XGBoost, Random Forest, Extremely Randomized Trees (ERT), and Feedforward Neural Networks (FNN). These models were fed with the dataset, yielding optimal predictive outcomes for both ERT and FNN with very good performance. It demonstrates that it is viable to develop models based on ML for predicting thermal profiles in AM using as input the printing parameters. It also determines the performance difference among several of the ML models. This has led finally to a predictive model that offers quasi-instantaneous predictions with minimum error as compared to the computationally expensive FEM simulations.
[598] ID:598- Identification of the corrosion fatigue crack initiation and propagation lives using in-situ electrochemical measurements of the LPBF 316L
Xavier Majnoni D'Intignano (I2M, CNRS, Arts et Métiers Institute of technology, Bordeaux, France), Mohamed El May (I2M, CNRS, Arts et Métiers Institute of technology, Bordeaux, France), Nicolas Saintier (I2M, CNRS, Arts et Métiers Institute of technology, Bordeaux, France), Olivier Devos (I2M, CNRS, University of Bordeaux, Bordeaux, France), Sébastien Mercier (ONERA, Châtillon, France) and Charles Bianchetti (ONERA, Châtillon, France).
Abstract
The 316L stainless steel produced by Laser Powder Bed Fusion (LPBF) demonstrates excellent resistance to pitting corrosion compared to conventional 316L stainless steel, with comparable fatigue strength. Nevertheless, its fatigue performance remains highly dependent on manufacturing parameters. However, few studies have focused on the coupling of these two phenomena, as occurs during corrosion fatigue tests. The main objective of this work is to study the interactions that take place between the cyclic loading applied, the microstructure of the material and the corrosion mechanisms involved in these tests. Firstly, heat treatments were applied in order to modify the microstructure of LPBF 316L on several scales. Each microstructure obtained was then characterised. Corrosion tests conducted in a solution containing 0.6 M NaCl were used to investigate the different electrochemical interactions of each metallurgical state with the environment. Secondly, uniaxial high cycle fatigue tests (1e6 cycles) were carried out in air and in a solution containing 0.6 M NaCl with a loading ratio R = 0.1. The electrochemical behaviour of the passive film was studied during the corrosion fatigue tests by monitoring the open circuit potential (OCP) and performing electrochemical impedance spectroscopy (EIS) measurements. The corrosion fatigue crack initiation was related to the passive film strength under cyclic loading and the presence of additive manufacturing process defects. Through in-situ electrochemical measurements, a decrease in the OCP has been observed in correlation with crack propagation. Subsequently, a specific number of cycles associated with this propagation was determined. Based on these results, the Paris law parameters were calibrated. These results have enabled us to identify the role of heat treatment on the corrosion fatigue crack initiation and propagation in LPBF 316L.
[599] ID:599-Fatigue resistance of chemically pre-aged Short Fiber Reinforced Polyamides
Carole Nadot-Martin (Institut Pprime), Florent Alexis (Institut Pprime), Sylvie Castagnet (Institut Pprime), Peggy Havet (Valeo Thermal Systems – BG Material Laboratory) and Gilles Robert (Polytechnyl sas (DOMO Chemicals)).
Abstract
The present talk deals with the effect of acid aqueous environment on the fatigue lifetime of Short Fiber Reinforced Thermoplastics (SFRP) employed for automotive components. In this context, two polyamides (PA6 and PA66) containing 35% weight ratio of short glass fibers were aged for 1000h at pH=2,5 and T=60°C and compared with unaged materials. At first, the effects of chemical pre-aging was characterized from Scanning Electronic Microscopy and Differential Scanning Calorimetry and then the monotonic tensile properties were studied. The results showed a slight embrittlement of the aged materials and no stiffening, consistently with the molecular chain breakage due to hydrolysis and with the unaffected crystallinity ratio. Fibers were debonded from the matrix on an outer layer of 200 µm thickness. Then, stress-controlled uniaxial fatigue tests were performed at constant amplitude, frequency (1Hz) and load ratio (R=0.1) for three orientations (0°, 45° and 90°) with respect to the injection direction. An in-situ device was specifically developed to test immersed samples in acid solution, with the challenge to ensure stability and homogeneity of the solution and of the strain measurement all along fatigue tests. A slight decrease of fatigue lifetime was evidenced for pre-aged samples, especially when fibers were mainly aligned with the tensile direction (0°). Such decrease was not observed in samples aged and tested in water.