Effects of crack configuration and residual stress on fracture driving force for welded joint with embedded flaw

Abstract In this study, the effects of crack configuration and welding residual stress on the Weibull stress for high strength steel plate with embedded crack were investigated by conducting FEM analysis. Firstly, high strength wide steel plates (length: 200 mm, width: 200 mm, thickness: 25 mm) having an embedded crack which has height 6 or 9 mm, length 40 mm, depth 2 ~ 9.5 mm were created using iso-parametric elements with eight nodes. The welding residual stress of K-groove welded joint made by 780 MPa class steel was introduced around the embedded crack, and then these models were tensioned along the vertical direction to the crack surface. Finally, CTOD, overall strain, the Weibull stress and crack opening stress (local stress near the crack tip which is parallel to crack surface) were obtained in all cases. CTOD was calculated by tangential method. The Weibull stress of embedded crack without welding residual stress which has the same crack height and length as previously mentioned was found to have increased with decreasing crack depth at the same CTOD level, this means plastic constraint of shallow embedded crack was higher than one of deep embedded crack. The Weibull stress of shallow crack model with crack depth 2 mm at the same over all strain was bigger than the other cases caused by high crack driving force and plastic constraint. Based on the Weibull stress criterion, it can be found that the brittle fracture limit of embedded crack decrease with decreasing crack depth in all strain region. The Weibull stress of embedded crack with welding residual stress at the same CTOD level was higher than that with welding residual stress. This tendency was same as the relationship between the Weibull stress and over all strain before overall strain reaches yield strain. After yield strain, the Weibull stresses were almost same between embedded crack with and without welding residual stress. It can be found that the welding residual stress decrease the brittle fracture limit of embedded crack before overall strain reaches yield strain based on the Weibull stress criterion.