The effect of stress triaxiality on the local cleavage fracture stress in a granular bainitic weld metal

Abstract

The local cleavage fracture stress σF measured at the cleavage initiation sites of a granular bainitic weld metal is only an apparent fracture parameter dependent on stress triaxialities at the local sites in the propagation controlled cleavage regime. This dependence can be explained by the stress triaxiality modified Smith equation in which the intrinsic cleavage fracture stress σF0 is introduced, considered to be an invariant characterizing a material's fracture property. In the nucleation controlled cleavage regime σF is temperature dependent and coincident with the local yield stresses defined by Von Mises criterion at the local sites. It is suggested that the modified Smith model would provide a unified physical basis for the intrinsic correlation among various macroscopic fracture properties as well as their temperature transition behaviors from the temperature dependence of material's yield strength.