Effect of pitting degradation on ductile fracture initiation of steel butt-welded joints

Monotonic tensile experiments and corresponding finite element (FE) analyses including a ductile fracture damage criterion have been conducted to investigate the ductility degradation behaviours of steel butt-welded joints with corrosion pits. The results showed that the ultimate elongation of welded joint samples rapidly decreased because the existence of pits led to the earlier initiation of ductile cracks after necking. Pit location was the main factor affecting ductility degradation, pits located in the weakest region of sectional stiffness were the biggest threat to the overall deformability of welded joints. In addition, both pit depth and aspect ratio had a significant effect on local ductile crack initiation and propagation, the local stress triaxiality and plastic strain accumulation increased steadily with the increase of pit size, resulting in the decrease of equivalent plastic fracture strain. Furthermore, based on the parametric numerical analyses, equivalent ductile fracture criterion considering pitting parameters was proposed to replicate the effects of actual pits on ductility degradation.