A study on evaluation of ductile crack initiation using strain hardening exponent for steels

Abstract Evaluation method of ductile crack initiation limit without depending on materials was investigated. Ductile crack initiation behaviors were experimentally and analytically comprehended using aluminum alloy as non-ferrous metal in addition to two different steels. It was found that their limit characteristics of ductile crack initiation for materials used were different in the case of using a conventional method based on stress triaxiality factor and equivalent plastic strain. It is considered that from cross section observations, ductile crack initiation for steels is caused by shear fracture between grown voids at the center of specimen. Therefore, Mohr-Coulomb fracture criterion, which is related to normal stress and shear stress, was applied to the evaluation of steels. As a result, it was found that strain hardening exponent of the materials could be a new parameter. Using strain hardening exponent in addition to stress triaxiality factor and equivalent plastic strain, ductile crack initiation limit of different steels whose fracture mechanisms are similar, can be evaluated with a master curve.