Prediction of ductile fracture toughness

Inspired by recent multiscale modeling of void/microvoid interaction in ductile fracture, a new analysis of literature data on ultrahigh strength martensitic steels shows that J_IC toughness normalized by primary inclusion mean spacing is parabolically related to the measured critical primary void size ratio. Interpreting this critical ratio as a measure of the critical intervoid ligament strain for primary void coalescence by finer scale microvoid instability, calculation of the critical strain from Rice-Tracey void growth shows that J_IC toughness is exponentially related to the critical microvoid instability strain. This represents a far stronger sensitivity to critical strain than the previously assumed linear scaling. An approximate correlation of this critical strain to macroscopic fracture ductility allows an estimate of fracture toughness.