Fatigue assessment of weld toe and weld root failures in steel welded joints according to the peak stress method

The peak stress method is an engineering, finite element (FE)-oriented application of the local approach based on the notch-stress intensity factors (NSIFs), which quantify the intensity of the local, linear elastic stress field at the potential crack initiation points (either the weld toe or the weld root). All effects due to plate thickness, joint shape and loading mode (axial or bending) are fully included in the NSIFs, such that a single design curve is sufficient to assess the fatigue strength of arc-welded joints in structural steels, tested in the as-welded conditions. The design stresses to analyse the fatigue strength are the peak stresses evaluated by FEM at the weld toe or the weld root, which are modelled as sharp notches with a tip radius equal to zero. The mean value of the FE size adopted to calculate the singular peak stresses can be chosen within a range of applicability, while the FE pattern of elements to use is the free mesh generated automatically by the Ansys™ numerical code. Due to the rather coarse meshes required to apply the PSM and its suitability to be used directly with results of 3D FE analyses, the method is rather useful in everyday design practice.