A Constitutive Law for Porous Material and Its Application to Ductile Fracture Analysis

A model for the onset of ductile fracture in porous media is proposed and applied to the onset of void coalescence in the neck of a tensile specimen. A constitutive law for a rigid-work hardening porous solid is developed, based on an anisotropic yield function introduced by the authors in a previous report. The constitutive law embodies the void evolution model suggested by Rice and Tracey. The onset of void coalescence is based on a criterion of internal necking of the matrix ligaments between the voids. This model was developed by Thomason for the plane strain case. The model is extended in the present study to include axial symmetry, and then it is shown that the extended model coincides qualitatively well with the fracture strain variation obtained experimentally by Edelson and Baldwin for sintered porous materials.