In this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as function depending on SIFs resulted by external load, weld residual stress and overload. Weight function is applied to calculate SIF resulted by weld residual stress. Also, a method is introduced to determine overload SIF and overload stress ratio. Then fatigue crack propagation equation is modified for our purpose. In other words, a simple and efficient method is presented in this paper for predicting fatigue crack propagation rate in welded joints when the overload is happen. Finally for evaluating this modified equation, experimental methods are applied. Test samples were M(T) geometry made of aluminum alloy with a longitudinal weld by the Gas Tungsten arc welding process. Modified equation has a good agreement with the experimental model presented in this field. تفاصيل المقالة

In this paper, thermal effect of plasma arc welding is investigated, and temperature field of ferrite stainless steel is acquired. Thermal effect of plasma arc and subsequently the generated temperature field in the work piece is the key for analysis and optimization of this welding process, which is the main goal of this paper. Finite element simulation of welding process by SIMPLEC method and ANSYS software is achieved, using FSI solver for getting stainless steel temperature field, effect of parameters variation on temperature field, and process optimization for different situations of plasma and shielding gases (Argon, Helium, and mixture of both). Lastly, the results of other papers are used to verify the correctness of this paper’s results. The temperate field results have determined the effects of welding parameters, and are used to optimize plasma welding process for improving weld quality. Optimization results for different gases indicates that due to special heat of Helium gas, there is extra potential with respect to Argon gas to narrow the plasma arc and concentrate inlet heat over stainless steel. تفاصيل المقالة

In this paper, a new method is introduced for evaluating effects of residual stress on fatigue life. The ability of ultrasonic method using longitudinal wave with critical angle of refraction or LCR wave in measuring and removing residual stresses due to welding was used. Two plates of alloy 2024-T351 were welded to each other. To measure their residual stress field acoustoelastic property was used and the changes in the speed of ultrasonic propagation of elastic waves when passing through the residual stress fields was investigated. In order to exert the effects of residual stress on fatigue life, the relations between the coefficients of effective stress intensity (SIF) and Fatigue Crack Propagation (FCP) rate in a state that the parts were welded together with residual stress under cyclic loading were obtained. Finally, ultrasonic waves with a certain frequency were used to remove the residual stresses. Also, the relationships between stress intensity factor and fatigue crack propagation rate were modified to predict fatigue life after removal of residual stresses. This method resulted in a 31% increase in fatigue life. The main reason for the increase in life was the plastic area created by the ultrasound wave. Therefore, it can be said that introduced method are suitable for using to remove residual stress due to welding. تفاصيل المقالة

This paper is introduced new method for predicting of fatigue crack propagation (FCP) in residual stress (RS) field due to welding. If there is stress in the material and is subjected to loading, the effects of loading and RS must be considered simultaneously. For this purpose, stress intensity factor (SIF) in liner elastic fracture mechanics (LEFM) approach and J-integral in elastic-plastic fracture mechanics (EPFM) approach are used. The superposition principle based on LEFM is used to consider the RS effects on the cycle ratio and SIF. To achieve more appropriate results based on EPFM, the J-integral is modified to consider the simultaneous effects of RS and external loading. Finally, the FCP equations are modified to consider into calculation the simultaneous influences of RS and cyclic loading. Results from FCP equation based on J-integral are in good agreement with experimental results. The obtained results show that the MLPG method is suitable for calculating the residual stress and the modified J-integral method is the best method for predicting FCP in the RS field caused by welding. تفاصيل المقالة