Assessment method of ductile and brittle fracture initiation in high strength steels

In this paper, ductile and quasi-cleavage fracture behaviour of a 1300MPa class bolt steel was mainly investigated. Ductile crack initiation behaviour was estimated by the relationship between stress triaxiality and the equivalent plastic strain, which we call ductile crack initiation curve. Quasi-cleavage fracture initiation behaviour was estimated by the Weibull stress approach. Round notched bar tension tests and the corresponding FEM analyses were executed for estimation of the ductile crack initiation curve and the Weibull stress. It was found that the ductile and quasi-cleavage fracture initiation behaviour can be estimated quantitatively by the ductile crack initiation curve and the Weibull stress criterion.