A VIEW ON DUCTILE‐FRACTURE MODELLING

Abstract

Theoretical models of ductile fracture are reviewed in terms of experimental results from metallurgical studies of ductile fracture in metals and alloys. It is shown that the plastic limit‐load model, which is based on a criterion of void coalescence by internal microscopic necking of the intervoid matrix, is fully consistent with scanning electron microscope (SEM) observations of both the ductile‐fracture surface and the microstructure immediately adjacent to the fracture surface. On the other hand, the dilational‐plastic models of ductile fracture, which are based on the dilational‐growth of spherical voids to some arbitrary critical void‐volume fraction, are inconsistent with the microstructural observations of ductile fracture. This inconsistency between the dilational‐plastic models and experimental results is shown to be the combined effect of neglecting the controlling influence of extensional void‐growth and the failure to incorporate a physically realistic criterion of void coalescence.The problems of modelling the ductile crack‐growth process by both analytical and numerical (finite element) studies, where problems of uniqueness of the plastic velocity field may occur, are also considered. The limitations of the finite‐element method in modelling void‐coalescence problems, where the equations of plasticity are of second‐order hyperbolic form, are also discussed.