A new model for the fatigue life prediction considering residual stress relaxation

The fatigue life of a welded joint is sensitive to welding residual stresses remained in the joint. This paper reports a new fatigue life prediction model for welded joints. The effects of residual stresses are assumed to be equivalent to those of mean stresses. The keystones of present model are hot-spot stress, equivalent stress model to take account into the effects of residual stresses, and residual stress relaxation model. Hot-spot stress is a very effect reference stress because the fatigue test data from many kinds of joints can be plotted on one curve by this stress. The residual stress relaxation model decreases residual stresses cycle by cycle, and the equivalent stress is updated, also cycle-by-cycle, by hot-spot stress and residual stress. The fatigue damage is calculated by Miner's linear damage rule with the equivalent stress. This fatigue life prediction model needs two kinds of fatigue test with different residual stresses. Once being tuned by two specific fatigue tests, this model can be applied to arbitrary stress ratios and many kinds of joints. Finally the present model was conceived, by a couple of experiments, as promising one.