Effect of Alternated Multiaxial Stress State on Fatigue Strength and Relaxation of Residual Stress in Welded S355 Steel with Nonlinear and Combined Hardening

This work aims to analyse the effect of the alternated multiaxial stress state on the relaxation mechanisms of residual stresses and the integrity of welded S355 steel, presenting a nonlinear and combined hardening behaviour. The first part of this work proposes a model to predict the residual stresses introduced by the thermal effect of the welding process. The stresses resulting from the thermal cycle were integrated into a second model in which the material was subjected to a cyclic load to analyse the relaxation process. To ensure a good accuracy of the relaxation results, the kinematic and isotropic hardening were combined in a nonlinear model. In the last part of this paper, a multiaxial fatigue strength analysis was carried out, taking into account the effect of residual stresses and the relaxation process. The results show a considerable relaxation of the residual stresses if they are subjected to low load levels applied under specific conditions. The relaxed residual stresses can have a considerable effect on fatigue strength. Also, the importance of the consideration of the relaxation process on the accuracy of the fatigue strength results is illustrated.