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In this article, the life of metals under fatigue loading with variable amplitude has been investigated. For this purpose, the continuum damage mechanics method is used to model the damage parameter, in which the amount of dissipated energy in each cycle per volume is known as the damage index. The damage model introduced in this article has the ability to be used in problems with variable amplitude, therefore, in this study, a specimen of Q235 steel was simulated in Abaqus software and from two subroutines UMAT and UMATHT to simultaneously extract dissipated energy in Each cycle and its corresponding temperature were used. In order to investigate the fatigue life under variable amplitude loading, Two blocks with different amplitudes have been considered. Different types have been considered for these two blocks, and their results show that the introduced damage model has a high sensitivity to the loading history and sequence; Also, there is a good agreement between the results of this research and the experimental results.

In this paper, the effect of notch depth on the fracture toughness (KIC) and the plastic region of the crack tip material using the Charpy V-Notch test (CVN) data extracted from API X65 with different notch depth were conducted and the fracture energy was measured. Also, computer simulation of the experiment with a three-dimensional model was performed based on Gurson's modified damage law in Abaqus software. To obtain KIC values, equations based on the yield stress (σYS) and the failure energy of the Charpy V-Notch test (CVN) obtained from the steel was used. The estimated KIC data and plastic region of the crack tip, decreased with increasing notch depth.

Use of adhesively bonded joints in structures has been increased in recent years because of their advantages. In structural applications, fatigue is generally considered to be the most important form of loading in respect to long-term service life. In this paper, experimental tests have been performed in order to examine the fatigue damage process of double lap adhesive joints, composed of E-glass laminates and epoxy adhesive with TiO2 particles, under fatigue loading and then a method was proposed for fatigue life prediction based on initial stiffness. The scatter in results shows that the fatigue life is mostly dependent on initial stiffness. According to this, an exponential equation based on the initial stiffness has been proposed to have an initial estimation of fatigue life of the adhesive joints. In addition to the initial stiffness, stiffness degradation of the joints under fatigue loading influences on their final performance and therefore the initial estimation of fatigue life based on the initial stiffness could be modified. Also to have an online control of the fatigue damage process during the fatigue loading, a damage index using stiffness degradation was introduced.

Friction stir welded butt joints were performed on sheets made of AA2024-T351 aluminum alloy at tool rotational speeds of 400, 630, 800 rpm and traverse speeds of 8, 16, 25 mm/min. The fatigue crack propagation rate was investigated according to standard ASTM-E647 in CT specimens. FE simulation of FSW process was implemented for different welding conditions and next the fatigue crack propagation was simulated using XFEM method. In this analysis, to assess the damage in the joints, maximum stress criterion is used. The maximum principal stress in element was the fracture criterion. Numerical results are in good agreement with the experiments so the simulation is reliable. The obtained results show that the tool rotational and traverse speed affect the fatigues crack growth rate. For all welded specimens crack propagation rate was slower than that of the base metal for low values of ∆K (∆K≤13 Mpa) but is much faster at high values of ∆K. Furthermore fatigue properties of specimens that welded with lower speeds are better than base metal and increase in rotational or traverse speeds of the tool will increase the crack propagation rate of the welded specimens.

In this study, microstructure, microhardness and residual stress in the butt jointed friction stir welded aluminum alloy 2024-T351 plates with different tool’s rotational and traverse speed is studied. According to the 2024-T351 aluminum is a heat treatable alloy, Hardness test results showed that increasing rotational speed or decreasing traverse speed of the tool reduced hardness in the weld zone. Then, using standard X-ray diffraction, which is a non-destructive method, residual stress in the welded samples is determined.A thermal model of friction stir welding process is simulated by using finite element method in the ABAQUS software. Comparison of residual stress results that obtained from the numerical solution with experimental measurements show that, the numerical model can predict the residual stress fields in friction stir welding joints reasonably.The results show that, increasing rotational speed, cause to higher residual stress in the weld zone, due to generation the higher thermal gradient and also, The higher tool traverse speed will induce a greater high-stress zone with a higher stress value in the weld, because of, a lower heat input and result in the relatively harder metal in the weld zone, causes a greater resistance to the plastic extrusion.

Cold working a hole decreases tendency of fatigue crack near the hole to initiate or growth. It is due to creation some compressive tangential residual stresses around the hole. Determination of mentioned residual stresses with a non-destructive, simple and non-expensive method is the key step in design process of holed components. In this article, residual stresses have been determined by mounting some strain gages around the hole and in fact surface strains during cold working process have been introduced as a feature for residual stress field. Delineation the numbers of needed strain gages and also proper place for mounting them around the cold worked hole is the main object of this research. Results have a good agreement with test result of cold working on specimens made of Al2024. According to the results, mounting two strain gages at same radius in opposite side of hole edge; which one in radial and another in tangentially direction; is needed for determining the residual stress field. Also, strain gages should be mounted in elastic zone. Mounting the gages in plastic zone led to have errors and unreliable results.

In this research, accumulation of plastic strain and softening behavior of stainless steel SS316L cylindrical shell under cyclic bending and combined loads (bending-torsion) are studied. Cyclic bending was under force-control and displacement-control but Combined loading was under displacement-control. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Under force-control loading with non-zero mean force, plastic strain was accumulated in continuous cycles that it was called ratcheting. Based on experimental results, linear relation was observed between plastic energy and rate of plastic deformation that shows the rigidity of fixtures using in experimental tests. Under displacement-control loading, softening behavior was observed due to growth of ovalization and the rate of softening became higher by using of the higher displacement amplitude. The crack growth up to failure is oblique in combined load due to torsion and bending loads whereas the crack growth is peripheral in bending load. The numerical analysis was carried out by ABAQUS software and nonlinear isotropic/kinematic hardening was compared with isotropic hardening and observed the nonlinear isotropic /kinematic hardening model simulates the softening behavior and accumulation of plastic strain of cylindrical shells under cyclic bending accurately.

The performance specifications of vehicles on the road are the result of dynamic interaction of various components of the vehicle structure. But the car tire because it is directly in contact with the road surface and plays an important role. Indeed the tire is the generator of the forces and moments which control vehicle motion. However the tire’s structure is relatively complex but defining specific parameters can simplify modeling the behavior of complexity of the structure and behavior of the tire is too comprehensive so that ever theory that could answer many questions in predicting tire performance is not provided. Theories presented by embellishment from relations or parameters that are obtained through empirical-rather than mathematical analysis and physical-are mixed. Here our purpose to describe the effect of the geometry of the tire and the inflated pressure on the tire side force which plays an essential role in the tire dynamic behavior.

A7075 aluminum alloy is considered as a high-strength alloy which is used making under-pressure tubes according to ASTM B210M–05 standard. Finding an appropriate model for investigating Bauschinger effect factor in A7075 aluminum alloy behavior plays an important role analyzing the process of autofrettaged tubes. For this purpose، the results of experimental data of uniaxial tension- compression tests have been used. In order to carry out the tests، an Instron servo-hydraulic machine has been used. The samples were made having 12. 5 mm based on ASTM standard E8M-97a. The fact that plastic strain created in these alloys is considered as unloading characteristic، to model the material behavior، the series of these tests on the basis of plastic deformation is done differently. In this research، tests were done at plastic strains up to 4. 3%. Also in this paper، many important problems including the amount of plastic strain on determining Young’s modulus and Bauschinger effect factor were tested. In this research، to determine the amount of tension- compression yield، the amount of offset has been considered as 0. 01%.

This paper presents the results of the experimental and analytical investigation carried out using a steel forged material، EA4T، subjected to impact loading conditions within the strain rate domain101-103 (1/s). The standard three point bend test specimens manufactured according to ASTM 399 standard were subjected to impact loadlevels correspondingto preset defined impact energy levels by applying the Izod impact testing equipment. The specimens were also modeled and the loading condition was simulated using the finite element commercial software، ABAQUS v6. 11. Both the experimental findings and the finite element analysis results indicated that the crack initiation conditions were satisfied when the impact energy applied to the specimen reached a specifiedlevel. It was found that for a lower level of applied impact energy، the impact loading resulted in improving the fatigue characteristic of the material. In contrast، application of the higher impact energy caused the crack to propagate further. The other finding of the study was that increasing the plastic zone size decreased the crack propagation rate (da/dE).

The concept of random tessellation is extensively used in wide area of natural sciences, especially material sciences. In this paper a simple but complete explanation of the random tessellation and mathematical tools requirements is presented. Then introducing the algorithm and the program for display random tessellation diagram was written. This program, with high speed and simple algorithm for random tessellation has the ability to change the level of statistical parameters such as number, mean, variance of the area of the grain. The ability to model microstructures of metals and grains for mechanical application, such as estimation of mechanical properties and crack propagation model at microstructure scale in FEM software is very important. More, an application of random tessellation for finding of equivalent mechanical properties was mentioned. In this paper by increasing the number of grains, in other words, decreasing the size of the grain, property’s values were changed and approached to the experimental global values and isotropic properties.

Using ceramic coatings has increased in popularity due to their compatibility with bone, absence of the fibrous layer at the coating-implant interface, and the stronger coating-bone bonding. Among these coatings, hydroxyapatite (HA) and fluoroapatite (FA) are more popular. For the first time in this paper, modeling and stress analysis have been carried out for 24 implants in an axisymetric form using the finite element technique. Twelve of these samples belong to IMZ and the rest are from Dyna system. All implants had HA and FA coatings with thicknesses between 10 to 100 microns. The stress analysis results show that the stress concentration at the implant-coating and bone-coating bonding surfaces decreases with the increase of coating thickness. In addition, stress concentrations for implants with FA coatings are always more than those with HA coatings. In all implants, stress concentration has been observed around the bone crest.