ABSTRACT. Gears are one of the most basic components of any mechanical machine or design. Gear durability has an important influence on the durability and service life of machines. Mechanical gears usually work under cyclic loading and thus are subject to fatigue failure. The stress distribution in gears is not uniform.This process aims to identify stress concentration areas, where damage is likely to occur. High stress concentration is observed locally in contact areas and in regions near the root of gear teeth. On the other hand, assessing stress distribution also allows to identify areas that can reduce mass. This study uses numerical simulation by finite element method to analyze stress field in straight tooth pair of spur gears. The influence on the stress field of the gear’s geometric parameters such as the arc radius of the tooth, the position and shape of the mass loss holes will be investigated. Furthermore, reducing the local stress concentration is crucial. Some previous works have proposed the employment of small holes in the region around gear teeth, namely the stress-relieving holes. The present work focuses on investigation of stress distribution in spur gears under two conditions: with and without stress-relieving holes. For this purpose, a finite element model of spur gears is developed. The numerical model is also used to examine how factors such as position, size and shape of the holes may affect the stress distribution in spur gears.

ABSTRACT. In this study, the foot water is calculated by the factors of collecting parameters and tides, calculated waves are analyzed by the tidal integrated numerical model, Toring sea and storm surge (SuWAT - Surge, Wave and Tide). The SuWAT model has been applied to calculate storm surge in a number of storms that have made landfall on the northern coast (such as storms Franki-96, Washi-05, Xangxane-06, Kalmeagy-14) with some calculation options different. The results show that the influence of the tide on the rising water level is negligible in places with low tidal amplitude and with storm landing at high tide, the water will be lower than when the storm makes landfall at low tide; The water surge due to atmospheric pressure is only significant in the offshore area when the storm intensity is still strong. Meanwhile, in the area, shoreline rise due to wind stress and wave stress accounted for the majority of the total water level rise during storms. With storm parameters, the storm surge at Hon Dau station reached the maximum value with the case where the storm's movement speed was 1 hour slower than the actual one. The magnitude of the water decreased as the pressure in the storm increased, but the magnitude increased at three different stations. Water level rise at 3 stations Cua Ong, Hon Dau, and Hon Ngu increased with wind speed, however, Hon Ngu station had a higher rate of increase. The magnitude at Cua Ong station increases slowly. The water surge at Cua Ong station is dominated by wind speed more than at Hon Ngu station. The research results will be very useful in warning and forecasting storm surge in the area.

ABSTRACT. Aluminum alloy is one of the lightest alloys available, making it valuable in high stress situations. Type 7075 aluminum is widely used in the friction stir welding process (FSW) for many fields such as aerospace/ aviation, railway, marine, and many other industries. Friction stir welding is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. Three-dimensional FSW makes the experimental investigation more costly, time-consuming and complex setting. Therefore, Finite Element Methods (FEMs) has been used to overcome the complexity and reduce costs. In this study, the numerical model of the FSW process with different threaded tools based on Coupled Eulerian-Lagrangian formulation is investigated by ABAQUS software. The FWS tool (AISI H13 steel) is treated as Lagrangian component and modeled by isotropic linear-elastic material. The workpiece material (AA 7075 – T6) is treated as Eulerian component and used the elastic-plastic Johnson – Cook. The main objective of this research would investigate influence of combining threaded and triflat in tool profiles through void information and temperature field distribution in AA 7075 aluminum. The results of this research present the difference of temperature distribution between the numerical simulation and experiments. The results also point out that the Eulerian Volume Fraction option can be used to evaluate and analyze void formation pretty well. However, there are still a number of issues with this finite element model of the friction stir welding that is difficult to describe entirely weld behavior as the real processes of friction stir welding.

ABSTRACT. Deep drawing is the most advanced sheet metal forming technique. In today’s demanding environment is the global environment and energy saving, the process has been supposed to play a vital role in light-weight component industry [1]. Light-weight, high strength, low density and extreme corrosion aspects must be almost guaranteed in a deep drawn product. However, due to those requirements, thinning and wrinkling and other defects will be increased also. The success of methods, as well as the quality of the products, are influenced by numerous elements such as blank-holder pressure, punch force, speed of punch, blank shape, thickness variation, surface-to-surface friction coefficient, material characteristic,… In addition, worldwide manufacturers keep getting the most goods done in less time. Indeed, the increasing of productivity should be also dealt because it proportionally relates to the stamping speed. This paper investigates the influence of punch velocity on deformation behavior of aluminum alloy 5052–H112. Finite Element Method was used to perform Nakajima test at several of punch velocities of specimen widths and monitor fluctuations in magnitude of von Mises stress, the major strain and minor strain. Forming Limit Curve (FLC) was obtained at different velocities and almost uniform. Stretching and sliding across the top of the punch resulted in thinning of sheet metal. Beside this, the action of punch stroke resulted in the production of more von Mises concentrated stress and the largest specimen in widths had shown the peak value of von Mises stress compared with the other specimens at all different velocities. Furthermore, the ratio of the major strain to the minor strain is influenced by the mass of material at the contact area and keeps consistent over the variation in velocities of punch. This will pave the way for future studies of the optimization of the stamping speed in deep drawing.

ABSTRACT. The high precision and the product surface finish quality are the main characteristics of these precision machine tools. Machining with different tool paths at different feedrates is applied to increase productivity. Today, machine tools using high-speed machining methods are developed to shorten machining times and increase production capacity. However, the vibration of high-speed machine tools is the main cause of the product quality reduction. The effect of the machining speed on the vibration diagnostic process of the machine is a problem that needs to be investigated in order to choose the appropriate machining mode. This paper describes the vibration analysis methods of machine tools such as: based on simulated results to determine the natural frequencies of vibration and dynamic modeling of the ball-screw feed drive system. Analysis of structural simulation results shows that the higher the rigidity of the machine, the lower the vibration amplitude, the greater the ability to absorb and suppress vibrations for the machine tool without using dampers. Meanwhile, the combination of the measurement analysis and dynamics modeling on machine tools is an effective method for optimizing speed and controlling machining vibrations arising. First, the finite element method (FEM) is applied to determine the stiffness analysis and the natural vibration frequency of the machine tool. The simulation results are analyzed and determined by comparing with experimental measurement results. The vibration frequency of the ball-screw drive system during machining at different feedrates is also modeled and verified by the measurement results. Finally, the results from proposed methods are used to predict the vibration frequency of the system especially the ball-screw through the feed drive or rotational speed. In addition, the purpose of the proposed method is to prevent resonance by way of the forced frequency away from the natural frequency in high speed machining. This paper proposes a survey method can be applied for high-speed machine tools with different structures to choose appropriate machining feedrate.

ABSTRACT. Today, freight is an extremely important industry for the world we are living. Fast transportation, large volume,…will optimize the cost, time and effort. Besides, ensuring the products safety is a matter of concern. During transporting, it is inevitable that the vibration caused by the engine, rough road surface,…the cargo inside can be damaged. Automobile industries have prime importance to vibration testing. Sine vibration testing is performed when we have been given with only one frequency at given time instant. Trend to perform random vibration testing has been increased in recent times. As random vibration considers all excited frequencies in defined spectrum at known interval of time, it gives real-time data of vibration severities. The vibration severity is expressed in terms of Power Spectral Density (PSD). KLT box is an industrial stacking container conforming to the VDA 4500 standard which was defined by German Association of the Automotive Industry (VDA) for the automotive industry. The aim of this paper is study about random vibration and power spectral density analysis, how it can be used to predict the impact of hash road to the KLT box on container/ truck during transportation. Finite element model is developed in ANSYS, modal analysis and random vibration analysis were done.

ABSTRACT. Nowadays, CNC milling machines appear in most manufacturing fields and are widely used in industries. Besides, the CNC controller used LinuxCNC software (LinuxCNC controller) is considered with relatively cheap cost and compact size. Therefore, it can be applied to the needs of self-manufacturing CNC machines and meet the tastes of the Vietnamese market. However, during long-term operation, the heat generated by the electrical components inside the control cabinet is unavoidable. The high ambient temperature inside the control cabinet can affect the stability and responsiveness of electrical components, reducing the accuracy of CNC machines. The investigation based on experimental measurements will produce the best estimates, but such things take a lot of time, effort, and money. By the way, the Ansys CFX simulation software is considered a reliable solution to support the experimental survey methods.  ​In this paper, firstly, the authors have designed and modeled the enclosure of the electrical cabinet along with the equipment inside the control cabinet into a 3D model. Then, the authors applied Ansys CFX software to simulate temperature change inside the control cabinet after applying the cooling methods. The authors propose a solution to limit the high ambient temperature inside the control cabinet and based on the simulation results to evaluate the efficiency, from which the appropriate method can be selected. For small-scale factories without cooling systems, this survey method can be the right solution. To evaluate the effectiveness of the proposed method for reducing heat, the authors measured and evaluated the position tracking errors of the CNC milling machine. Besides, some products have been processed to compare and evaluate the quality. Finally, based on the results obtained in the paper, some conclusions are made to verify the effectiveness of this research method.

ABSTRACT. Crash-dynamics research has always concentrated significantly in the safety, survivability of passengers in a car crash. To identify the capability of energy absorption of a crash box, a thin-walled structure will be modeled and simulated by ABAQUS software. Investigate the influence of material, cross-sectional, thickness factors on the energy absorption capacity of the tube, using MCDM – Multi-Criteria Decision-Making to get the best option and testing the improvement while filling the tube with Foam material. In this study, beside the cross-sectional, aluminum alloys and steel materials and thickness are factors that influence the energy absorption evaluation criteria, the foam material with difference density are surveyed to compare effectiveness between the foam-filled and hollow crashboxes. The results show that the folds of the foam-filled tube after deformation along the compressive direction will be more continuous and stable. More, the higher foam density, the greater the energy absorption. This prevents the crashbox from deviating from the direction of the force, help directing the collapse of the tube, thereby improving energy absorption without significantly increasing the weight of the structure

ABSTRACT. This paper presents an enhancement of void growth-based damage criterion for anisotropic material. With assuming principal directions are coincident with rolling, transverse and normal orientations of sheet, respectively, manipulating original model to suitable for anisotropic behavior of material has performed via a rotation tensor. A coupled fracture model, which formed by incorporating a void growth based - damage criterion together with an anisotropic yield function, is introduced to prediction of ductile rupture in sheet metals. The proposed damage model is used to predict forming limit diagram (FLD) of aluminum alloy sheet AA5052-H32 which its elaso-plastic behavior is assumed to obey the Barlat-Lian89 yield criterion. The forming limit diagram of sheet AA5052-H32 is predicted by the proposed model. For 0-dgree direction, the predicted result by numerical simulation is compared with that of experiment whereas the forming limit diagram by two 45-degree and 90-degree directions with respect to rolling direction is archived via the desk study.