ABSTRACT. Continuum kinematics-inspired peridynamics (CPD) is a peridynamic (PD) formulation that uses the same kinematic measures as classical continuum mechanics (CCM), providing a geometrically exact formulation [2]. PD is a non-local continuum formulation, wherein the behaviour of each material point is influenced by material points within a finite neighbourhood of that point [3]. By incorporating non-locality as a fundamental modelling concept, the range of interactions considered at each point is expanded, encompassing influences beyond its immediate neighbours. Simultaneously, the integral formulation simplifies the representation of spatial discontinuities by eliminating the need for explicit spatial gradient computations, making it highly suitable for modelling the intricate and heterogeneous nature of biological tissues. The implementation emphasises the complexities associated with incompressibility in material modelling.

This contribution focuses on the implementation of CPD in Julia [1]. Several key aspects render Julia an ideal choice for the implementation of CPD. Julia is renowned for its computational performance, underpinned by its just-in-time compilation that allows for the efficient execution of numerical simulations [1]. Julia's performance-oriented design is well-suited for implementing and executing complex simulations efficiently. Julia has built-in support for parallel computing which empowers researchers to harness the full potential of multi-core processors and distributed computing environments. This capability proves invaluable, especially for large-scale simulations, where parallelization can lead to substantial acceleration in computational tasks. Additionally, Julia seamlessly connects with external libraries, simplifying the integration of existing numerical tools.

The implementation of CPD in Julia offers a robust and powerful tool for simulating the intricate behaviour of materials where non-local effects are important, as well as in the presence of discontinuities. This work not only contributes to advancing the capabilities of PD simulations but also demonstrates the synergy between innovative computational frameworks and high-performance programming languages like Julia in tackling complex engineering and scientific challenges.

References: [1] Bezanson, J., Edelman, A., Karpinski, S., & Shah, V. B. (2017). Julia: A Fresh Approach to Numerical Computing. SIAM Review, 59(1), 65-98. doi:10.1137/141000671. [2] Javili, A., et al. (2020). The Computational Framework for Continuum-Kinematics-Inspired Peridynam-ics. Computational Mechanics, 66(4), 795–824. [3] Silling, S. A. (2000). Reformulation of Elasticity Theory for Discontinuities and Long-Range Forces. Journal of Mechanics and Physics of Solids.

ABSTRACT. This research presents the results of experimental and numerical investigations on water ingress trapped in honeycomb panel. Ingress of atmospheric water in aircraft honeycombs may cause minor or major damages of aircraft. The percentage of water/ice filling honeycomb cells is an important factor related to possible cell wall damage. This study is focused on the analysis of the influence of panel orientation (horizontal, vertical and inclined at 30°, 45° and 60°) on the efficiency of water detection, The numerical analysis was conducted by using the ThermoCalc-3D software to evaluate the detectability of water ingress in the cases where a test panel is placed in different spatial orientations. The samples with water and ice were tested and analysed by using several data processing algorithms available in the ThermoFit software to enhance water detection performance. The signal-to-noise ratio (SNR) concept was used for comparing efficiency of image processing algorithms in the inspection of water ingress in honeycomb panels with varying water content, spatial orientation and water/ice phase transformation.

ABSTRACT. This project explores a novel configuration and control system for a VTOL (vertical take-off and landing) UAV (unmanned aerial vehicle) in an attempt to increase the efficiency. The project includes the design, build and test of the quadcopter. The power draw data of the drone in different configurations are gathered and then compared to each other. This data includes the power consumption for static hover at a constant altitude and forward flight at a constant altitude.

ABSTRACT. Water treatment systems are crucial for providing clean, drinkable water, particularly in countries with limited water resources. In recent years, climate change has led to significant water shortages in the Western Cape region, especially affecting the city of Cape Town. Automation and control engineering play a vital role in enhancing the efficiency and performance of water treatment systems. Although numerous water treatment systems have been designed and developed in the literature, most automation and control methods focus on waste treatment, seawater, and desalination systems. There are few, if any, that fully and specifically address the automation and control engineering needed for borehole water treatment. This paper aims to fill that gap by designing an automated borehole water treatment system using the Siemens LOGO programmable logic controller and reverse osmosis methods. The automated water treatment plant includes several processes, such as filtration, chemical dosing, disinfection, and monitoring of critical parameters. The experimental results indicate that the water quality has improved, achieving a pH level of 6.6, which makes the water safe for drinking. Further investigation is needed to evaluate the effectiveness of the water treatment system using samples from boreholes around Cape Town. This assessment will test various physicochemical parameters, including hardness, turbidity, sulfate, phosphate, copper, lead, iron, and residual chlorine.

ABSTRACT. This project investigates the fracture toughness (FT) of compact tension (CT) specimens produced from Inconel 718 (IN718) using laser-powder bed fusion (L-PBF). IN718 was selected due to its extensive use in the aerospace industry. Two types of heat treatments involving homogenisation and aging were examined. Fatigue pre-cracking and fracture toughness tests were performed at room temperature. A higher temperature homogenisation heat treatment reduced anisotropy, while a lower temperature homogenisation resulted in the retention of columnar dendritic structures. The fracture toughness for the higher temperature homogenisation was measured at 303 kJ/m², whereas the lower temperature homogenisation resulted in a fracture toughness of 165 kJ/m². Both heat treatments improved the fracture toughness compared to that of wrought IN718, which is reported as 79 kJ/m³.

ABSTRACT. Unbound granular material (UGM) is commonly used in flexible pavement roads to handle dynamic stress with varying frequency. The flexible pavement roads are key components of societal infrastructure, ensuring safe and efficient traffic flow. In South Africa, as elsewhere, these important road networks are subjected to wear and tear from heavy automotive traffic, resulting in significant maintenance expenses. Using the Finite Element Analysis (FEA) via ABAQUS, we methodically investigate the interactions of the unbound road pavement material. We further examined how loading frequency affects the mechanical properties of UGM utilizing repeated load tests. A thorough examination of several damage mechanisms, focusing on phenomena such as surface sliding, intermittent drag, and the creation of undulations. The equivalent plastic strain, displacements, period and frequency of undulations of granular materials under six loading frequencies were analysed. Moreover, the loading stress and gradation of material had interaction effect with loading frequency.

ABSTRACT. Evaluating the modulus of bone requires the testing of small compression specimens. This, however, requires accurate displacement measurement which is adversely affected by the compliance of large standard universal testing machines. This paper serves as a continuation of work done by Daras et al. It presents a custom compression test set-up (i.e. a sub-press) that facilitates routine quasi-static compression tests on small specimens by eliminating the effect of testing machine compliance on the results. The displacement of the sub-press was recorded using a combination of Hall effect sensors and multipole magnetic strips, which offer a resolution of less than one micron. The results of quasi-static compression tests on small polymer and aluminium specimens are reported. The specimen moduli are obtained by measuring the stiffness of specimens of two different heights and using this data to calculate and account for the machine compliance of the sub-press. Additional tests on cortical bone specimens demonstrate the application of the sub-press.

ABSTRACT. Drop foot is a condition where the muscles responsible for lifting the front part of the foot are weakened or paralysed, resulting in dragging or scuffing of the toes along the ground while walking. The most common treatment for drop foot is ankle-foot orthoses (AFOs). These devices require experimental testing and BS EN ISO 22675:2016 (2016) sets out the test methods and requirements for testing prostheses, specifically ankle-foot devices and foot units. Commercial daily wear AFOs fix the foot in a set position and and a proposed articulating daily-wear AFO design requires testing. The standard testing machine thus requires modifications to simulate an articulating ankle to allow for the testing of the proposed articulating AFO. The testing machine has specifcations set out by the standard and additional specifications is used to describe drop foot. During evaluation, the testing machine was able to meet all requirements with the required accuracy.

ABSTRACT. Kirschner wires (K-wires) are an essential part of the Ilizarov external fixator, as it contributes to the overall rigidity of the frame to promote bone healing through axial bone movement. The tension of the wires and their ability to cause interfragmentary movements are an essential part of the Ilizarov technique. In this study, two different brands of fixation devices will be used to determine the behaviour and deformation of K-wires when subjected to loading. Each frame will be experimentally tested by loading the frame with 800 N for 450 cycles using an Instron load frame machine. It is expected to find both plastic deformation in the wires as well as slip through the fixation bolts. The tension loss is expected to start as soon as the fixation bolts are tightened, and it is expected that around 70% of the wire pretension is lost after loading is complete. The design and overall efficacy of the frame can be optimised knowing how the frame behaves upon loading and what the contributing factors are for the undesirable biomechanical environment created by the current design of the Ilizarov frame.

ABSTRACT. This research focuses on evaluating the accuracy of Digital Image Correlation (DIC), a non-contact optical technique used for full-field deformation and strain measurements in fields such as experimental mechanics and aerospace. A key factor influencing DIC accuracy is the quality of speckle patterns applied to test surfaces. Using finite element (FE) methods, this study generates numerically deformed images to provide ground truth references for assessing DIC accuracy. A Python-based tool was developed to synthesise these deformations and examine the impact of various speckle patterns

ABSTRACT. Development of a finite volume 1D thermofluid network modelling methodology for the human cardiovascular system

N Cilliersa, Prof R Laubscherb & Prof P Rousseauc

a Department of Biomedical Engineering, University of Stellenbosch, Stellenbosch, South Africa b Department of Mechanical & Mechatronic Engineering, University of Stellenbosch, Stellenbosch, South Africa c Department of Mechanical & Mechatronic Engineering, University of Stellenbosch, Stellenbosch, South Africa

Introduction: It is well-documented that cardiovascular disease (CVD) is the world’s number one cause of death. The prominent diseases causing these high mortality rates are ischemic heart disease and ischemic stroke. Both ischemic heart disease and ischemic stroke are caused by the narrowing or blockage of arteries, known as atherosclerosis, resulting in obstruction and reduced blood flow rates to important organs1. As the number of people affected by CVD continues to increase rapidly, a need to quickly and accurately diagnose various pathologies associated with CVD has arisen. The ability to simulate CVD progression has valuable diagnostic and prognostic potential in the field of cardiovascular health. Such a simulation could be used to detect and accurately describe the pressure differences experienced in the main arteries of the body, as well as variations in arterial structure caused by CVD pathologies, such as atherosclerosis or stenosis2. Conventional haemodynamic simulation approaches involve three-dimensional computational fluid dynamics (CFD) models incorporating fluid-solid interaction (FSI). FSI is important since the blood vessels undergo deformations, i.e. changes in geometry, due to the force exerted by blood flow, causing changes in the blood pressure that, in turn, affect the vessel wall3. Although it can inherently account for intricate spatial and geometric features4, these three-dimensional models are computationally expensive. These models, therefore, require very long run times5 and do not allow for the entire system to be considered. Since these simulations are inherently transient or dynamic, i.e. time-dependent, a computationally efficient alternative to the existing CFD models needs to be developed. It is also important to know what the effects of the disease will be on the system as a whole, and how it will evolve over time. The present research aims to develop a dynamic, finite-volume one-dimensional thermofluid network-based modelling methodology of the human cardiovascular system. It will allow for the computation of blood flow rate and pressure differences in the human arterial system over time for only one spatial dimension. Therefore, these models offer lower computational complexity compared to the three-dimensional models. Despite its simplicity, it effectively describes pressure changes in arteries and arterial structure variations, such as blood vessel tapering, or bifurcations present in arterial branches.

1D Network formulation: The network methodology, when applied with finite differencing, is the technique used to model the behaviour of the fluid flow, pressure distributions and area changes throughout the system, in this case, blood vessels. The system is discretised as a network of nodes and elements.

Figure 1: Graphical representation of network discretisation of a reverse-tapering artery

Figure 1 shows where the nodes (squares) and elements (circles) should be placed in a course network discretisation of an artery. Each node represents a control volume and each element, or branch, represents a flow path between the nodes. The physical characteristics of arteries, such as their wall thickness, elasticity and reference diameters, vary along the length. Therefore, the cross-sectional area at each of the nodes is a function of these physical characteristics, as well as the pressure of the blood flowing through it. Mass balance is applied to each of the nodes, giving rise to the following equation when integrated over a finite control volume: , (1) with m ̇_i and m ̇_e the in and out mass flow rates respectively, and m ̇_s the mass source. Although the aim is to develop a dynamic model, this paper will only describe the steady state analysis that is currently being finalised. Therefore, the mass balance reduces to: . (2) Eq. (1.2) requires that the net mass flow into/out of the control volume, or node, plus any mass source terms must be equal to zero for mass balance to be ensured. Momentum balance is applied over each of the elements while assuming incompressible flow. Therefore, we get for each element that: (3) where L is the finite length of the control volume. For steady flow we get: , (4) where, A segregated approach can be applied to solve the system of governing equations that arise from the mass and momentum balance equations. This approach begins by assigning mass source and pressure boundary conditions. Next, initial values for stagnation pressure are guessed at each of the nodes, excluding the pressure boundary nodes, alongside mass flow rates for each of the elements. The momentum balance equation is then rearranged to express the mass flow rate of the elements in terms of the stagnation pressures at each node. Using these new mass flow rates, the component characteristics are updated accordingly. The mass flow rates expressed in terms of pressure are substituted into the mass balance equation. This substitution leads to the formation of a system of linear equations that must be solved. By solving this system, the stagnation pressures can be determined. Subsequently, the mass flow rates are updated using the newly calculated stagnation pressures. This process is repeated iteratively—specifically, the steps from determining the mass flow rates using the stagnation pressures to computing the new stagnation pressures—until convergence is achieved. The next sections will present results of two simple steady state case studies to demonstrate the methodology.

Case Study 1: An artery with a constant elasticity and vessel wall thickness, but with increasing reference diameter throughout its length, is investigated. The artery is discretised into 21 nodes and 20 elements.

Figure 3: Graphical representation artery and its network discretisation in Case Study 1

As seen is Figure 4, the reference diameter across the nodes increases, the stagnation pressure decreases and velocity increases, since the increase in lumen area of the artery results in a decrease in pressure, in accordance with Poiseuille’s law.

Figure 4: Graph of results for Case Study 1 Case Study 2: An artery that has an increase in reference diameter, vessel wall thickness and elasticity towards its middle and tappers down on either side is investigated. Again, the artery is discretised into 21 nodes and 20 elements. Figure 5: Graphical representation of the artery in Case Study 2

Figure 6: Graph of results for Case Study 2

In Figure 6, as the area increases, the velocity decreases proportionally. There is a less steep decrease in pressure at the nodes where vessel wall thickness, reference diameter and elasticity increase. This slow decrease in pressure can be attributed to Bernoulli’s principle and the decrease in velocity around this region.

References: 1. Whang, W., Coronary Heart Disease, in Encyclopedia of Behavioral Medicine, M.D. Gellman and J.R. Turner, Editors. 2013, Springer New York: New York, NY. p. 503-505. 2. Formaggia, L., D. Lamponi, and A. Quarteroni, One-dimensional models for blood flow in arteries. Journal of Engineering Mathematics, 2003. 47(3): p. 251-276. 3. Rostam-Alilou, A.A., et al., Fluid-structure interaction (FSI) simulation for studying the impact of atherosclerosis on hemodynamics, arterial tissue remodeling, and initiation risk of intracranial aneurysms. Biomech Model Mechanobiol, 2022. 21(5): p. 1393-1406. 4. Xiao, N., J. Alastruey, and C. Alberto Figueroa, A systematic comparison between 1-D and 3-D hemodynamics in compliant arterial models. Int J Numer Method Biomed Eng, 2014. 30(2): p. 204-31. 5. Reymond, P., et al., Validation of a one-dimensional model of the systemic arterial tree. Am J Physiol Heart Circ Physiol, 2009. 297(1): p. H208-22.

ABSTRACT. A 3D CFD simulation was undertaken in ANSYS Fluent Inc to model the thermal behaviour of a low-cost naturally ventilated greenhouse in Southern African conditions. The computational domain included the greenhouse and its immediate cylindrical surroundings. The radiative transfer equation was solved using the discrete ordinate method; turbulence using the standard k-ε model. Experimental data was used for boundary conditions. Preliminary results indicate that the experimental greenhouse temperatures lag the solar radiation and numerical results by two-hours. The next phase will incorporate the soil inertia to address the time-lag and temperature discrepancies identified in the thermal field.

ABSTRACT. This study investigates the optimization of friction stir process (FSP) parameters to enhance the mechanical properties of AA5083-based composites reinforced with coal. The Taguchi method is employed to optimize key process parameters, including rotational speed, traverse speed, and tilt angle. These parameters were selected due to their significant influence on material flow, heat generation, and reinforcement distribution during FSP.

ABSTRACT. This research focuses on optimizing pre-cooling processes for citrus fruits to mitigate chilling injuries—a critical issue affecting the quality and marketability of South African citrus exports. Chilling injuries are a major concern, particularly given the stringent post-harvest cooling requirements mandated by international phytosanitary standards. Despite their significance, there is a scarcity of targeted research on the specific cooling rates that most effectively prevent these injuries. This study aims to address this gap by constructing small-scale cooling tunnels to experiment with various cooling rates to identify trends. Concurrently, the project will aim to simulate and validate industrial-scale pre-cooling facilities to assess current practices in the field. By synthesizing experimental data with simulation outcomes, the research intends to develop comprehensive industry guidelines for optimal pre-cooling techniques. This project aspires to enhance the quality and marketability of South African citrus fruits, establish new industry standards for pre-cooling processes, and reduce economic losses due to fruit quality degradation and rejection in international markets. Additionally, this study will engage with key industry stakeholders to ensure the practicality and applicability of the findings, fostering collaboration between academia and industry. The goal is to contribute to the sustainable and profitable export of citrus fruits, ensuring long-term benefits for South Africa's agricultural sector.

ABSTRACT. This paper investigates a numerical method for modelling failure mechanisms of continuous unidirectional carbon fiber reinforced polymer (UD-CFRP) composites under tensile and bending stresses. The study highlights the challenges in accurately determining material properties of CFRP composites, which complicates testing and modelling. Specimens were manufactured from 50mm-wide unidirectional carbon fiber tape using vacuum-assisted resin infusion (VARI), and ASTM standards (D3039M-14 for tensile and D7264M-15 for flexural properties) guided the experiments to obtain essential material properties for building engineering material data in FEA model. Tests were conducted on specimens with varying ply counts (4, 6, and 8), keeping a consistent 40:1 support span-to-thickness ratio for the 3-point bending test. Results indicated that laminates with fewer plies had higher flexural and tensile stresses, with 4-ply specimens reaching an average ultimate tensile stress of 1635 MPa, compared to 1205 MPa and 1026 MPa for the 6- and 8-ply specimens, respectively. Similar trends were observed in bending tests, where 4-, 6-, and 8-ply specimens showed average flexural stresses of 985 MPa, 928 MPa, and 862 MPa. Finite element analysis (FEA) results for tensile matched well with experimental findings, identifying delamination as the primary failure mechanism. The study suggests that a more accurate modelling of laminate interfaces is required to effectively capture stepwise delamination and progressive failure.

ABSTRACT. The aerodynamic force coefficients of a motorcycle with inverted Eppler E423 airfoil wings were investigated. The force coefficients were evaluated at different angles of attack at different velocities to determine if an angle of attack exists for which there is a maximum downforce produced at a specific motorcycle velocity. A wind tunnel experiment was performed using a force balance and a Fused Deposition Modelling (FDM) 3D printed scale model. The experiment was used to validate a Computational Fluid Mechanics (CFD) simulation strategy which was subsequently performed on a full scale model of the motorcycle with wings.

ABSTRACT. The abstract is attached as a PDF.

DEVELOPMENT OF A 2D WAGON-TRACK MULTI-BODY SIMULATION M.S. Perumal^(a), B.M. Nickerson^(a), A. Bekker^(a) ^(a)Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Stellenbosch, South Africa

2 Introduction: Understanding train-track dynamic interaction is a fundamental component in the field of railway engineering interaction allows one to develop insight into the forces generated on the track and train such as rail and wheel response forces. This can be used to determine imperfections in the rail and wheels. A wheel flat is a typical example of an imperfection and can lead to economic losses for the train and track owners. In severe cases, it can result in derailments . A Two Dimensional Wagon Track Model (2DWT) is a simulation tool that assists with understanding the vertical dynamics of the track and train system. It is envisioned that by leveraging the accessibility of Machine Learning (ML) and the 2DWT model, a neural network can be developed to detect wheel imperfections. Thus, the aim of this research is to categorize wheel flats using a neural network trained on simulation data generated using a 2DWT model. The following work addresses the development of the 2DWT model. Since this research is sponsored by the Gibela Rail Transport Consortium, an X’Trapolis Mega Train (Figure 1) will be used to determine the effectiveness of this approach.

[X’Trapolis Mega train-set.]

Methodology: The proposed method of characterizing the wheel flat is by:

1. Developing a 2DWT model. (focus of this abstract)

2. Generating simulated data sets.

3. Training a neural network on simulated data.

4. Deploying the system on an instrumented rail section.

Model Details: Currently, a 2DWT model that consists of three subsystems, namely: the wagon, track and interface subsystem has been developed and is shown in Figure 2.

[Vertical track and train interaction system model.]

The governing equations of motion (EOM’s) are as follows .

Car body bounce: $$\begin{gathered} M_{c}\ddot{Z_c} + 2C_{s2}\dot{Z_c}+2K_{s2}Z_c-C_{s2}(\dot{Z_{t1}}+\dot{Z_{t2}}) \\-K_{s2}({Z_{t1}}+{Z_{t2}}) = 0 \label{eqn: carbounce}

\end{gathered}$$

Car body pitch: $$\begin{gathered} J_{c} \ddot{\psi}_{c} + 2C_{s2}l_{c}^{2} \dot{\psi}_{c} + 2K_{s2}l_{c}^{2}\psi_{c} - C_{s2}l_{c}(\dot{Z}_{t1} - \dot{Z}_{t2}) \\- K_{s2c}l_c(Z_{t1} - Z_{t2}) = 0 \label{eqn: carpitch}

\end{gathered}$$

Bogie 1 bounce: $$\begin{gathered} M_{t}\ddot{Z_{t1}} + (C_{s2}+2C_{s1})\dot{Z}_{t1} + (K_{s2}+2K_{s1})Z_{t1} \\- C_{s1}(\dot{Z}_{w1}+\dot{Z}_{w2}) - K_{s1}({Z}_{w1}+{Z}_{w2}) - C_{s2}(\dot{Z}_c+l_c\dot{\psi}) \\ - K_{s2}({Z}_c+l_c{\psi}) = 0 \label{eqn: bogiebounce}

\end{gathered}$$

Bogie 1 pitch: $$\begin{gathered} J_c\ddot{\psi}_{t1}+2C_{s1}l_t^{2}\dot{\psi}_{t1}+2K_{s1}l_t^{2}{\psi}_{t1} -C_{s1}l_t(\dot{Z}_{w1} \\-\dot{Z}_{w2}) -K_{s1}l_t({Z}_{w1}-{Z}_{w2}) = 0 \label{eqn: bogiepitch}

\end{gathered}$$

Wheel 1: $$\begin{gathered} M_{w}\ddot{Z}_{w1}+C_{s1}(\dot{Z}_{w1}-\dot{Z}_{t1})+K_{s1}({Z}_{w1}-{Z}_{t1}) \\- C_{s1}l_t\dot{\psi}_{t1}-K_{s1}l_t{\psi}_{t1} + P_{1}(t) = 0 \label{eqn: wheel1}

\end{gathered}$$

Equations [eqn: bogiebounce] and [eqn: bogiepitch] are adjusted for the second bogie. While variants of equation [eqn: wheel1] are present for each of the four wheels.

The rail is modelled as an Euler-Bernoulli beam: $$\begin{gathered} \ddot{q}_k(t) + \sum_{i=1}^{N}C_{pi}Y_k(x_i)\sum_{k=1}^{K}Y_k(x_i)\dot{q}_k(t) \\ + \frac{EI}{m_r}\left( \frac{k\pi}{l}\right)^4 q_k(t) + \sum_{i=1}^{N}K_{pi}Y_k(x_i)\sum_{k=1}^{K}Y_k(x_i)\dot{q}_k(t) \\ - \sum_{i=1}^{N}C_{pi}Y_k(x_i)\dot{Z}_{si}(t) - \sum_{i=1}^{N}K_{pi}Y_k(x_i){Z}_{si}(t) \\ = \sum_{j=1}^{4}P_j(t)Y_{k}(x_{Gj}) \label{eqn: rail}

\end{gathered}$$

Where N is the number of sleepers and K is the number of modes. P_(j) is the contact force between the wheel and rail and follows Hertzian contact rules. The EOM’s for the ballast and sleepers are below:

Sleepers: $$\begin{gathered} M_{si}\ddot{Z}_{si}(t)+(C_{pi}+C_{bi})\dot{Z}_{si}(t) + (K_{pi}+K_{bi})Z_{si}(t) \\- C_{bi}\dot{Z}_{bi}(t) - K_{bi}Z_{bi}(t)- C_{pi}\sum_{k=1}^{K}Y_k(x_i)\dot{q}_k(t) \\-K_{pi}\sum_{k=1}^{K}Y_k(x_i){q}_k(t) = 0 \label{eqn: sleeper}

\end{gathered}$$

Ballast: $$\begin{gathered} M_{bi}\ddot{Z}_{bi}(t) + (C_{bi}+C_{fi}+2C_{wi})\dot{Z}_{bi}(t) + \\(K_{bi}+K_{fi}+2K_{wi}){Z}_{bi}(t) -C_{bi}\dot{Z}_{si}(t)-K_{bi}{Z}_{si}(t) \\- C_{wi}\dot{Z}_{b(i+1)}(t)- K_{wi}{Z}_{b(i+1)}(t)- C_{wi}\dot{Z}_{b(i-1)}(t) \\- K_{wi}{Z}_{b(i-1)}(t) = 0 \label{ballast}

\end{gathered}$$

where the mode shape is given by: $$\begin{aligned} Y_k(x) = \sqrt{\frac{2}{m_rl}} \sin\left(\frac{k\pi x}{l}\right) \label{mode_shape}

\end{aligned}$$

The beam’s displacement is a summation of the product of the mode shape and temporal modal coordinate (Equation [eqn: rail]). It is known that higher order mode shapes are required for high frequency excitations. However, to the best of the authors knowledge, published literature does not indicate the required number of mode shapes per unit length of the beam, whilst some research suggests that at least 60 modes is sufficient .

Findings: This research has established the relationship between the number of modes and the length of the rail. In addition to capturing higher frequency responses, the number of modes must be increased as the length of the rail increases. This is not due to higher excitation frequencies, but rather due to a loss in resolution of the transverse displacement when increasing the length of the rail. Figure [fig:ICvModes] shows the relationship between the rail length and the number of modes. For short rail lengths (<200 sleepers), and when using 100 modes or more, the wagon displacement should remain at 37.64 mm, regardless of the number of sleepers used, this can be done by increasing the number of modes as the rail length increases.

References:

ABSTRACT. During start-up and shutdown, vibrating screens often operate at frequencies higher than their natural frequencies before stabilizing at the normal operating frequency. These excessive vibrations can cause damage to the machine and shorten its lifespan. Therefore, it is crucial to implement isolators that can dampen these large vibrations. By understanding the material properties of isolators, they can be designed with specific characteristics to reduce the risk of machine damage. This study proposes a hyper-viscoelastic model to describe the mechanical behaviour of silicone rubber. The hyperelastic behaviour of silicone rubber is modelled using the three-parameter Mooney-Rivlin model, with the hyperelastic parameters determined through inverse Finite Element (FE) modelling based on experimental indentation and Digital Image Correlation(DIC) data. The time-dependent characteristics of the silicone rubber are captured using a four-parameter Generalized Maxwell (GM) model, with viscoelastic material parameters obtained through a least-squares fit of experimental stress relaxation data. The material characterization is validated by physical testing and compared with FE model results.

ABSTRACT. This paper investigates the accuracy to which fatigue life can be predicted in a specimen, with and without non-metallic welded inclusions in a butt-welded joint using finite element analyses.

See attached abstract

ABSTRACT. The study uses a milling machine to explore the correlation between preset and actual speed during the friction stir welding of AA6082-T651. The results show that the actual speed was 95% of the preset speed. Joints at 95% speed achieved UTS of 87MPa, while those at 100% achieved 81.8 MPa. The joints achieved 35.8% to 38.8% of the parent material's ultimate tensile strength. The microhardness ranged from 15HV to 95HV, with the heat-affected zone being the harder zone at 597rpm.

ABSTRACT. The blast wave propagation of cuboid-shaped explosive charges with varying aspect ratios remains underexplored in current literature, despite spherical and cylindrical-shaped explosive charges being well understood and documented. This paper presents an experimental study carried out to investigate the blast wave propagation of a 50 g plastic explosive (PE4) cuboid-shaped charge with an aspect ratio of 1:1:1 in free air. The results were compared with the 50 g PE4 spherical explosive charge at two scaled distances (Z) of 1.5 and 1.8 m/kg1/3. There was a significant variation in overpressure between the directions normal to the face and vertex of the cuboid charge when compared to the overpressure generated by a spherical charge at the same locations highlighting the influence of charge geometry on the blast wave.

ABSTRACT. This study highlighted the importance of carrying out flexural tests on the newly developed or manufactured sandwich panels made from CFRP and GFRP face sheets and PVC foam. The flexural behaviour depicted by the force-deflection curve and obtained as per the ASTM D790 testing standard can be categorised into three stages namely: (a) linear behaviour within 2 mm deflection for both panels (b) fracture or failure behaviour (c) gradual decrease of force with increase in deflection. The determined maximum flexural strength values for CFRP and GFRP panels were 23.15 MPa and 22.60 MPa respectively. These findings are significant to optimise the structures for use in specific applications.

ABSTRACT. A cost-effective approach to the decarbonization of the public transportation sector is through the electric conversion of large passenger vehicles in which internal combustion engine (ICE) buses are retrofitted with electric powertrain components. This could however have a potential influence on the safety performance of the vehicle. This study investigates the influence of electric conversion on the safety performance of a large passenger vehicle with regards to the rollover safety requirements of UN ECE Regulation No.66. A finite element (FE) analysis was conducted to quantify the energy absorption capability of a rollover hoop and subsequently calculate the energy absorption capability of the superstructure. The FE analysis was validated by experimental quasi-static loading tests of the rollover hoop. The results of this study provides a framework for performing an electric conversion of an ICE-powered bus while ensuring that the superstructure has sufficient strength to protect the occupants during a rollover event.

ABSTRACT. Rapid sand casting integrates binder jetting, an additive manufacturing (AM) technique, to produce moulds suitable for metal casting. Unlike traditional moulding, binder jetting involves configuring multiple process parameters such as recoater speed, drop mass (binder concentration), print resolution, layer thickness, binder print orientation, and activator concentration to fabricate moulds. Numerous studies have reported discrepancies in thermophysical properties between 3D printed sand mould and conventional mould as a result of the distinct operating process of binder jetting. This study aims to develop an artificial neural network model of rapid sand casting to predict, optimise and customise the properties of 3D sand printed mould with varied parameter of the Voxeljet VX1000 printer.

ABSTRACT. Rapid Sand Casting (RSC) has gained recognition as a method for advancing conventional metal casting through the rapid prototyping of sand molds and cores using binder jetting. While RSC has addressed many challenges in traditional sand mold production, it has yet to be applied in high-tech industries such as aerospace, automotive and biomedical. This research aims to assess the feasibility, consistency, and reliability of RSC products for such applications. The study evaluates the variability in mechanical properties of binder-jetting-produced sand castings using descriptive and inferential statistical. The results highlight factors contributing to variability and reveal some outcomes that occurred by chance. This work lays the foundation for qualifying RSC for high-tech applications, opening the door to its broader use in advanced industries.

ABSTRACT.  

A South African company that produces industrial inkjet inks experienced problems with blockages in the inkjet print heads of customers using their ink. After observing the challenges that this company was still experiencing despite using the conventional methods such as printing nozzle statuses for problem diagnoses, flushing, or cleaning the components out, an NDT investigation was done using the following methods: Liquid Penetrant to quantify the blockages, gamma x-ray, computed tomography, and microscopy. Further destructive testing was done to investigate the state of blocked printheads versus new printheads physically, to assess the differences in appearance of some of the internal structural parts of the print heads. The results of these physical experiments did not produce enough information to solve the problem, there was still a lack of clarity when using the afore-mentioned NDTs and destructive testing due to the micro-scale size of the nozzles and complexity of the ink channels within the print head, which led to limitations in what could be viewed internally from the results of the poor image qualities produced from scans and observed under the microscope. ANSYS CFD software is currently being investigated as a potential tool to use for an in-depth understanding of these components and their weak areas, the geometry for both the piezoelectric membrane actuator that produces the droplet and the movement of the droplet through the nozzle is represented using Ansys.

ABSTRACT. Aerodynamic drag has a large influence on the fuel efficiency of road freight vehicles and thus their carbon emissions. Reducing this drag force is a major focus in the transport industry. This study considers the shape optimisation of a truck bumper for overall drag reduction using computational fluid dynamics (CFD) models. The optimisation methodology makes use of a local surrogate modelling approach to approximate the expensive CFD model. The surrogate model used in this study is a second-order polynomial model, while an optimal Latin hypercube sampling technique is used as the sampling method. Five design variables are used to control the shape of the bumper. The results show that an 8.55 % improvement in the overall drag of the truck can be achieved by only modifying the shape of the bumper.

ABSTRACT. The key research question centres on optimising acceleration in an electric motor for a Formula Student electric race car. This study aims to uncover insights overlooked in previous research, particularly within the context of which drivetrain configuration will be the most cost effective

This research will exclusively focus on the powertrain. Other vehicle components such as aerodynamics, suspension, and braking systems will not be the primary focus of this study, although their interactions with the powertrain will be considered. The study considers the integration of the Battery Management System that leverages State of Charge algorithms to enhance motor performance. And cooling system necessary for achieving optimised thermal conditions in the electric motors and battery packs.

The research is limited by the available resources at the university. This includes the use of existing laboratory facilities, software tools, and components from previous projects. The study will operate without external funding. This limitation necessitates a focus on designs that can be implemented with minimal financial investment.

ABSTRACT. Laser-powder bed fusion (L-PBF) employs a laser beam to melt a specific geometry within a powder bed, layer by layer, creating a three-dimensional part. This method has quickly become a popular choice for manufacturing nickel superalloys, particularly in aerospace applications where Inconel 718 (IN718) is typically employed. The properties of the finished material are significantly affected by the parameters of the L-PBF process. This study used a design of experiments (DOE) approach to examine the impact of laser power and scanning speed on the as-built density and hardness of L-PBF IN718. The microstructures of specimens demonstrating optimal density and hardness within the defined design parameters were analysed. An opportunity for reducing the laser power and scanning speed while producing an isotropic and mechanically sound material was sought.

ABSTRACT. This paper highlights the role of Work-Integrated Learning (WIL) in mechanical engineering education by showcasing a project where a student designed and built a walkway platform. The project aimed to assist a crane operator and facilitate maintenance tasks. Research, including a literature review and interviews with industry experts, guided the design process, focusing on material selection, load capacity, and structural stability. The platform successfully supported a 2.5 kN load, surpassing the 200 kg target. Collaboration with the Health and Safety department and proactive project management, such as using Gantt Charts, were crucial to the project's success and safety.

ABSTRACT. Coordinate Measuring Machines (CMMs) play a crucial role in ensuring precision and quality in manufacturing industries. This paper introduces a novel CMM design system featuring a single displacement sensor while upholding the Abbé principle. The proposed system integrates a single displacement sensor fixed to a common metrology frame alongside the probe. The sensor's functional line is set at a 45° angle to each plane surface (x-y, x-z, and y-z), directed towards the probe's tip at a fixed distance. A manipulation system facilitates translation in the x and y directions, providing a volumetric working space of 40 x 40 x 40 mm. A comprehensive kinematic model is developed to ascertain the probe's position and distances travelled in each axis. A fully functional prototype is constructed to validate the concept, with measurements conducted on a standardized calibrated gauge block for validation. Results demonstrate measurement uncertainties of 12 µm, 16 µm, and 18 µm in the x, y, and z directions, respectively for a volumetric size of 20 x 20 x 8 mm. These findings underscore the feasibility and potential benefits of the novel CMM system. Future research avenues include further error analysis, system refinement, and real-world application in manufacturing environments.

ABSTRACT. Planar Biaxial Tensile Testing (PBT) is used for evaluating the mechanical properties of biological tissue, as it’s a better approximation of the in vivo loading conditions than uniaxial tensile testing. PBT applied to biological material specimens requires intricate gripping and mounting systems. Specimen preparation necessitates careful attention due to the small sizes, soft tissue samples, and limitations of available tissue. To complement PBT, Digital Image Correlation (DIC) is employed to capture full-field displacement, offering detailed strain mapping across the specimen’s surface.

ABSTRACT. Intramyocardial biomaterial injections after myocardial infarction offer promise in delaying heart failure by supporting damaged tissue, reducing wall stress, and preventing thinning. Polyethylene glycol (PEG) hydrogels are widely used as injectable materials; however, studies have noted significant post-injection material loss due to heart motion, leading to low retention rates. Most computational research has focused on the impact of biomaterials in a gelled state within the infarcted region, simulating early-stage injections with layered sheets and delayed treatments with spherical inclusions. This study focuses on biomaterial’s dynamic flow and displacement during and after delivery into myocardial tissue for treating acute infarction.

A subject-specific biventricular finite element model of a rat heart, incorporating a left ventricular acute infarct, was developed from µCT data shown. A detailed microstructural tissue block model was also created using confocal imaging to analyse biomaterial flow and tissue deformation during cardiac motion. Sub-modelling applied deformations from the biventricular model to the tissue block, facilitating simulations of PEG hydrogel injection.

The hydrogel displayed sinusoidal velocity patterns aligned with systole and diastole, with pronounced effects at the inlet and fluctuating outflows at the outlet, indicating that cardiac motion creates preferential flow pathways. Interstitial cavity volume increased slightly with the cardiac cycle, correlating with rises in volume-averaged maximum principal strain within the tissue, suggesting that myocardial deformation impacts hydrogel distribution. Observed strain rates and wall shear stress fluctuations highlight mechanical variations across the cardiac cycle, which is critical for understanding hydrogel-tissue interactions. The study highlights the influence of myocardial cavity geometry on hydrogel flow, particularly in narrow regions, which can accelerate hydrogel loss post-infarction.