Transition from Ductile Tearing to Cleavage Fracture — a Statistical Model

Abstract

The fracture resistance of ferritic steels in the ductile/brittle transition regime is controlled by the competition between ductile tearing and cleavage fracture. In a typical situation, a crack begins to grow by ductile tearing but ultimately failure occurs by catastrophic cleavage fracture. In this work, the process of ductile tearing is modeled by void-containing cell elements embedded within a conventional elastic-plastic continuum [see Shih and Xia (1994), Xia and Shih (1995a,b,c) and Xia, Shih and Hutchinson (1995) for more details]. Under increasing strain, the voids grow and coalesce to form new crack surfaces thereby advancing the crack. The fields that evolve ahead of the advancing crack are used in conjunction with a statistical model based on the weakest link concept to compute a stress measure pertinent to cleavage, referred to as Weibull stress, and the probability of failure by cleavage. The statistical model also takes into account the competition between the nucleation of voids from carbide particles and the nucleation of unstable microcracks from such inclusions precipitating catastrophic cleavage fracture.