Residual stress relaxation of welded steel components under cyclic load

It is a well known fact that the fatigue strength and the life of welded steel components are affected, to a considerable extent, by residual stresses distributed around their weldments. When externally applied load is superimposed on residual stresses, unexpected deformations and failure of the components can occur. These residual stresses are not constant, but are relaxed or redistributed during in-service. Under monotonic load relaxation takes place when the sum of external and residual stress locally exceeds the yield stress of material used. It is noteworthy that under cyclic load the residual stress is considerably relieved by the first or the early cycles of load, and then is gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon of and mechanism of stress relaxation are still not clear, and only a few comprehensive models have been proposed to predict amount of relaxed residual stress. In this study, the characteristics of residual stress relaxation under monotonic and cyclic load were investigated, and a model for quantitatively predicting the amount of residual stress relaxation is proposed.