evaluating the effects of overload and welding residual stress in fatigue crack propagation

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 happening. 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.