Relaxation and Stability of Welding Residual Stresses in High Strength Steel under Mechanical Loading

The relaxation of near surface welding residual stresses in S1100QL under static and cyclic mechanical loadings was studied. By increasing static loads the residual stress relaxes continuously. Under cyclic loading the residual stresses behave depending on the initial status, local yield strength and maximum applied load. If the von Mises stress as a function of residual stress, load and mean stresses, exceeds the local yield strength, plastic deformation and thus relaxation occurs. The first load cycle is of importance in which a considerable portion of the initial residual stress field relaxes. Afterwards regardless of whether in high or low cycle fatigue conditions, the relaxation rates were the same and comparatively smaller than the first relaxation. When no relaxation in the first load cycle occurred, the number of cycles did not change the residual stress. The specimens were loaded until failure or a maximum of 2x10(6) numbers of cycles.