Fatigue assessment of the welded joints containing process relevant imperfections

Internal weld imperfections and defects affect the fatigue behavior of the welded joints significantly. Their effects become more important when the weld seam does not have a sharp weld toe transition. These imperfections and defects in the welded area are classified by different instructions such as the DVS-guideline or the IIW recommendation. These instructions and guidelines introduce different FAT classes for the same weld imperfection type. FAT is the magnitude of the stress to failure in two million cycles. Furthermore, they do not take into account the importance of the position and the size of weld imperfections. This introduces uncertainty for the user due to differences between guidelines and the lack of information. As a result, in order to eliminate the inconsistency in the available weld recommendations and guidelines, it is necessary to perform a new investigation on different weld imperfections. This study considers the effects of imperfections on the weld quality both experimentally and numerically. The experimental study considered the effect of weld imperfections on weld quality with respect to the post weld treatment procedure on the weld seam. Then, a numerical method was introduced and validated by experimental results to predict the fatigue life in crack initiation and propagation steps. Fatemi-Socie approach as a fatigue damage model and fracture mechanics estimated the fatigue life in the crack initiation and propagation steps, respectively. The experimental and numerical results were plotted in S-N diagrams, and based on this work, new FAT classes were recommended. It was seen that if the type of weld defect is a single pore, the suggested value by IIW recommendation is more realistic than the other guidelines.