Growth behavior of a crack parallel to a weld line between two different steels (effect of crack position on fracture mode)

It was shown previously that a crack in a weld line between two different steels may cause mode II type fracture, even under so-called mode I type loading, due to the difference of material properties. In this study, the fracture experiments of the specimen in which a crack parallel to a weld line between high-tension steel and mild steel exists in its neighborhood are carried out. It is shown that mode II type fracture occurs when a crack is in the heat affected zone, the fracture mode changes to mode I type with the distance of crack position from the weld line and mode I type fracture occurs when a crack exists in each mother material. After that, finite element analyses corresponding to the experiments are carried out taking material properties in the weld line and heat affected zone into account, and the CED (crack energy density) in an arbitrary direction is evaluated through the results of finite element analyses. The applicability of fracture criterion based on the CED in an arbitrary direction is demonstrated to the crack growth initiation behavior of a crack parallel to a weld line between two different steels. Moreover, the effect of inhomogeneity by welding on the fracture resistance with the crack position is investigated based on the CED in an arbitrary direction.