فهرست مطالب

  • Volume:15 Issue: 3, Sep 2022
  • تاریخ انتشار: 1401/10/05
  • تعداد عناوین: 10
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  • Majid Farhang, Mohammadreza Farahani *, Mohammad Nazari, O. Sam Daliri Pages 1-9
    Friction stir welding was performed on AA2024- T6 aluminum plates using different rotation and traverse speeds with the objective of improving the mechanical strength and microstructure properties. The influence of the traverse and rotation speed on the microstructures, mechanical properties and residual stresses of the welded Aluminum plates were investigated. By increasing the rotation speed, stirred zone grain size became larger. Besides, the homogenous second phase distribution was obtained. Furthermore, by increasing both rotational and traverse speeds, hardness of the thermo-mechanically affected zone and the stirred zone increase to base metal hardness. These welded plates that were fractured at advancing side have a maximum tensile strength equal to 71% of base plate strength which was obtained at 31.5 mm/min traverse speeds and 1120 rpm rotational speed. The longitudinal residual stress was diminished with decreasing of rotational speed by 1120 rpm at a constant traverse speed. In this conditions and by increasing the traverse speed by 31.5 mm/min, the maximum tensile strength was obtained as many as 48%. It was attributed to more plastic deformation and minimum grain size in the weld zone due to higher traverse speed.
    Keywords: Al 2024-T6, Friction Stir Welding, Mechanical Properties, Residual stress
  • Aliasghar Meraji, Saied Mahjoub Moghadas * Pages 11-26
    Vertical vibrations in the ambulance patient compartment due to road disturbances can cause serious injury to patients. In the present study, after extracting the vibrations entering an ambulance with passive suspension system, the use of a new active vibration isolation system between the patient's Compartment and the ambulance body is proposed. This isolation system includes an air spring, a linear shaft motor and a suitable active controller, which is abbreviated as AVI system. In this paper, instead of using one AVI system to control the vibrations of the stretcher, four AVI systems are used to control the vibrations of the patient's Compartment. The accurate modelling for ambulance with passive suspension system in both types non-isolated and active isolated patient's Compartment has been done by SOLIDWORKS software. Then by extracting the mathematical model, differential equations and state space model, the comparison of both types was done using MATLAB-SIMULINK software and finally the results were optimized using the Model Reference Adaptive Control (MRAC). In this control method, the functional parameters automatically adapt themselves by changing the position of the centre of gravity. The results obtained according to the IS02631 standard, show that with the present method, vertical vibrations are reduced by more than 80%.
    Keywords: Active vibration isolator, Adaptive control, Ambulance suspension system, IS0 2631 standard, patient's compartment
  • Ali Massah, Nathan Jafarian Jam *, Ehsan Soury Pages 27-37
    Injection molding is one of the common processes for producing plastic parts. In this process, the mold is filled immediately and then the part and mold will be cooled down during the packing time. In the end, the part will be ejected from the mold. In this study, the effects of the most important processing parameters such as packing time, melt and mold temperature have been investigated on shrinkage and warpage of the products experimentally and numerically. According to previous reports, a thin sheet is defined by a length to thickness ratio of at least 100. MOLDFLOW software has been utilized to obtain the numerical results. For the empirical study, 64 specimens have been produced in different production conditions. These samples have been scanned by a 3D scanner and results have been analyzed by CATIA software. The findings show that increasing melt and mold temperature decreases the warpage amount and rises the shrinkage in the specimens. Also increasing the packing time up to 2 seconds increases the warpage and decreases the shrinkage noticeably but in longer packing times the variations will be less remarkable. Moreover, findings show that the general trend in simulated and experimental results are similar in all reported values of shrinkage and warpage, in which the maximum calculated errors for both of them are approximately 10%.
    Keywords: HDPE, Injection molding, melts, mold temperature, Packing Time, Shrinkage, warpage
  • Behnam Yasemi, Hamid Soleimanimehr *, Hossein Khodarahmi, Sadegh Rahmati, Najmeh Khazraiyan Pages 39-46
    This paper deals with the numerical simulation of segmented projectiles. A segmented projectile is a subset of kinetic energy projectiles. The segmented projectile is made of tungsten and the target is semi-infinite and is made of 4340 steels. Due to the disadvantages of segmented projectiles with, the simulation of segmented projectile with is discussed. Projectiles with aspect ratio greater than one are known as short-rod projectiles. This aspect ratio range forms both the primary and secondary phase of penetration. Numerical simulation was performed by AUTODYN software with Smoothed Particle Hydrodynamic (SPH) method. The use of SPH approach is most consistent with the experimental results. In order to have effective segmented projectiles, greater speeds were used in the simulations. In this range of velocity, due to the hydrodynamic penetration and complete erosion of the rods, the maximum penetration depth is obtained. After a relatively good correlation between the simulation results and the experimental and Hydrocode results, the numerical analysis of the segmented projectiles is performed. The results show an increase in the penetration depth of segmented projectile relative to the continuous type. In the following, the relationship between velocity increase and penetration depth and crater diameter of this type of projectile is investigated. An increase in penetration depth of 40 to 60% has been observed in this type of projectile compared to the continuous projectiles. An increase in penetration depth and crater diameter is observed with increasing impact velocity.
    Keywords: Aspect Ratio, numerical simulation, SPH, Segmented Projectile
  • Hossein Ahmadi Rashid, AMIR GHIASVAND *, Maziar Mahdipour Jalilian, Mahdi Kazemi Pages 47-54
    In this paper, analytical and finite element solutions of mechanical buckling of a thick Functionally Graded (FG) plate have been investigated. Boundary conditions have been assumed as simply supported at all edges and three different loadings have been applied. In analytical section the procedure of developing the critical buckling force by third order shear theory has been presented and then the stability Equations have been reduced from 5 to 2. In continue, the problem has been solved using numerical simulation by ABAQUS. To validate the FEM, results have been compared and validated with analytical solution. The results show that the bi-axial compression loading case with the loading ratio of R to one and R to zero are the most possible and most unlikely case in buckling occurrence, respectively.
    Keywords: Buckling, Finite Elements Analysis, Functionally graded materials (FGM), Third Order Shear Theory
  • Reza Tarighi *, M.H. Kazemi, MohammadHosein Khalesi Pages 55-69

    In this paper, a new approach to the use of genetic algorithms and the predictive control method, for goal tracking is presented. A hypothetical rocket is modelled for the analyses. Rocket guidance algorithm is developed to achieve a desired mission goal according to some performance criteria and the imposed constraints. Given that goals can be fixed or moving, we have focused and expanded on this issue in this study and also the dynamic modelling of flying objects with six-degrees-of-freedom (DOF) is used to make the design more similar to the actual model. The predictive control method is used to predict the next step of rocket and aim movement. At each step of the problem, the rocket distance to the aim is obtained, and a trajectory is predicted to move the rocket towards the purpose. The objective function of this problem, in addition to the distance from the rocket position to the target, are also parameters of the dynamic model of the rocket. Therefore, these parameters are optimized at each step of the problem solving. Ultimately, the rocket strikes the intended aim by following this optimal path. Finally, for the validation of the model, numerical results are obtained for both Genetic Algorithms (GA) and Particle Swarm Optimization (PSO). Simulation results demonstrate the effectiveness and feasibility of the proposed optimization technique.

    Keywords: Genetic Algorithm, optimal path design, Optimization Algorithms, Particle swarm Algorithm, Predictive control
  • Sirvan Mohammadi *, Sadegh Daryaei Pages 71-87
    In this research, using the 3D finite element method and considering different materials for a composite patch, the effect of separate and simultaneous use of stop holes and composite patch (one-sided and two-sided) on reduction of SIF in a curved plate including mixed-mode crack is investigated. Glass-epoxy, graphite-epoxy, carbon-epoxy, and boron-epoxy are used for repair patches.  For the one-sided patch, the effects of different geometric parameters on the efficiency of the repair are investigated. For all four composite patches, as the thickness of the patches increases, KI and KII decrease, but with increasing the patch length, KI and KII increase. The research results also show that with increasing the width of the glass-epoxy patch, KI and KII almost do not change, but for other patches, as the patch width increases, the SIF increases. The effect of the radius of curvature of the plate on the efficiency of various repair methods is also investigated. In all repair methods studied, SIF decreases with increasing radius of curvature of the curved plate. Different repair methods are compared and the best method with the highest efficiency is introduced. The best repair mode is the hybrid repair method (stop-holes and two-sided boron-epoxy patch), which reduces KI and KII by 84.50 and 86.6%, respectively. Finally, the effect of adhesive thickness used for patch bonding on hybrid repair method efficiency and durability is investigated. for all four materials of patches understudy, KI and KII increase with increasing the thickness of the adhesive, but on the other hand, as the thickness of the adhesive increases, the maximum Von Mises stress in the adhesive decreases.
    Keywords: Composite patch, Crack repair, Crack stop holes, Fracture mechanics, Stress intensity factor
  • Sajjad Dehghanpour *, Ali Alavi Nia Pages 89-97
    In this paper, deformations and energy absorption capacities of thin-walled tubes with different section geometries (circle, square, rectangle, hexagon and triangle) under quasi-static in-plane loading are investigated. The tubes have the same material properties, mass, volume, lengths and average section area and the loading conditions are similar for all of the specimens. In order to investigate the behaviour of the tubes, more than 100 tests are carried out and numerical simulations are performed. The numerical results are in good agreement with experimental data and show that the section geometry has an important effect on energy absorption capacity so that the circular and square sections have the least and the most capability of energy absorption, respectively. Furthermore, for a specific tube, the absorbed energy increases with the wall thickness. The first peak load in load-displacement curves has the greatest and the smallest values for rectangular and circular sections, respectively.
    Keywords: energy absorption, In-plane loading, peak load, Quasi-Static, Thin-walled tube
  • Alireza Alaghemand, Ali Fattah Pages 99-107

    A microchannel device was designed and utilized to separate Michigan Cancer Foundation-7 cells from white blood cells using both wall-induced lift and di-electrophoresis forces. Using COMSOL Multiphysics simulator, the label-free separation process is performed based on the radius size of the particles. The best performance of the structure is obtained with the efficiency of 100% and 99% for cancer and white blood cells separation processes, respectively. For the proposed microfluidic structure, in addition to the highest available efficiency and high separation speed of 12 um/s, the low DC voltage of 6 V is applied, which causes negligible damage to the blood cells.

    Keywords: Cancer Cells, COMSOL, Dielectrophoresis, Microfluidics, Separation
  • AmirHosein Samimi, MohammadReza Karamooz-Ravari, Reza Dehghani Pages 109-117

    Lattice structures have attracted a great deal of attention for being used in different industries due to unique properties such as high strength-to-weight ratio and high damping coefficient. These metamaterials might suffer from dimensional inaccuracies, i.e., variable strut’s diameter, wavy struts, micropores, and deviation from the designed cross-sectional area, which arise from the fabrication process. These inaccuracies can drastically affect their mechanical response. In this paper, the effects of different dimensional inaccuracies, including variable struts’ diameter, wavy struts, and material concentration at nodes, on the frequency response of different cellular lattice structures are studied. To do so, a finite element model is constructed using Timoshenko beam elements, and the natural frequencies are obtained for four different lattices. The obtained results show that, by increasing the average diameter, the natural frequency increases drastically, whereas by increasing the amount of variation in the struts’ diameter and waviness the natural frequency decreases by a small amount. It is also observed that the lattice structures whose main deformation mechanism is axial loading are more sensitive to the change of average struts’ diameter. In addition, the natural frequency increases as the concentration of material in the vicinity of the nodes increases. The effect of material concentration inaccuracy is more pronounced for the first lattice for which the number of struts meeting at one node is the smallest.

    Keywords: Beam, Lattice Structures, Natural Frequency, Vibration