Fatigue strength of welded joints by considering the residual stress

Abstract

In this study, a fatigue life prediction model was proposed to evaluate the fatigue life of welded joints in 316L steel stainless considering (i) the as-weld Residual Stress (RS) relaxation and (ii) using the Crossland multi-axial fatigue criterion. Initially, a sequential coupling 3D thermo-mechanical finite element method was used to simulate the as-weld RS. Primary, the weld heating process was calculated by applying a heat source of double ellipsoidal distribution. Its movements along the weld direction were modeled by a user subroutine DFLUX. Secondly, the heat losses are considered by taking into account both the convection and the radiation. The behavior of the material was modeled by an elastoplastic model which combines isotropic and non linear kinematic hardening laws by using the Chaboche parameters. The latter model allows studying the redistribution of the residual stress under the cyclic load. The predicted results by the finite element method were in good agreement with the experimental data. After that, the equivalent fatigue stress was calculated (i) with considering the RS relaxation (ii) and without taking into account the RS (without thermal process). For the tensile test under 0.1 load ratio, the difference between the two cases is about 6%. The presence of the compressive RS in the high loaded point has a beneficial effect on the Crossland equivalent stress.