Mechanisms of Residual Stress Relaxation and Redistribution in Welded High-Strength Steel Specimens under Mechanical Loading

Abstract

In this article, the relaxation of surface and near-surface welding residual stress fields in S690QL under static and cyclic loadings has been studied. The influence of local mechanical properties in the weld metal, heat-affected zone and in the base metal upon relaxation and redistribution of residual stress were considered. Welded specimens were loaded statically and cyclically. Under static loading, the variation of the residual stress field under tension and compression was investigated and it was observed that, by increasing the load, residual stress relaxes continuously. However, the relaxation under compression sets in with delay, since the tensile residual stresses should be first overcome. Under cyclic loading, with or without mean stress, the behaviour of the residual stresses depends on the initial residual stress, local yield strength and maximum applied load. If the von Mises stress, which is a function of residual stress, load and mean stress, exceeds the local yield strength, plastic deformation and thus a relaxation occurs. In the case of relaxation, the first load cycle is of importance, in which a considerable amount of the initial residual stress field is relaxed. After the first relaxation, no significant variation of the residual stress field in the fatigue crack free phase could be observed. When no residual stress relaxation in the first load cycle occurred, the number of load cycles did not change the residual stress field. The specimens were loaded until failure or maximum 2×106 cycles.