Fracture Prediction Beyond the Linear Elastic Range

Abstract

We have discussed the application of linear elastic fracture mechanics and some of its applications at length in the two preceding chapters. We recall that when the plastic zone was limited in extent, such that the full transverse constraint developed, the fracture surface was square, and material behavior could be described by a single parameter K Ic (or G c ). With thinner sections and less constraint, slant fracture may develop. Under these conditions slow crack growth may occur, and then the R curve approach can be used to describe fracture behavior. One exception to this generalization is the behavior of ferritic–pearlitic steels tested below and in the transition temperature region. Here, probably because of their sensitivity to strain rate, there is an abrupt onset of rapid crack extension, and a single parameter K c (or G c ) may still be adequate to describe fracture behavior [1]. We now turn to cases in which the assumption of small-scale yielding is inadequate and elastic–plastic or fully plastic behavior must be considered. Our emphasis again will be on cases in which full transverse constraint leads to in-plane deformation and a square fracture surface on a macroscopic level. However, a procedure analogous to R curves will be described for cases in which the fracture mode changes as the crack propagates and for tough materials which show stable tearing in plane strain.