Residual Stress Evolution in Welded Joints Subject to Four-Point Bending Fatigue Load

Residual stresses, introduced into a component by manufacturing processes, significantly affect the fatigue behaviour of the component. External load application produces an alteration in the initial residual stress distribution, so it is reasonable to suppose that residual stress field into a component subject to a cyclic load presents an evolution during the total life. In this work, the authors analysed the evolution that the residual stress field, pre-existing in a butt-welded joint, suffers following the application of cyclic load. The comparison between two residual stress measurements, carried out on the same joint before and after the cyclic load application, allowed to obtain interesting information about the residual stress evolution. It was found that in particular condition, unlike the general opinion, a cyclic load application produces an increasing in the residual stress level rather then a relaxation. This phenomenon is to take well in account in order to avoid unexpected failure in components subjected to a fatigue load.