Internal state variable description of dynamic fracture of ductile solids

Abstract

The paper aims at the description of ductile fracture phenomenon in dynamic processes in inelastic solids by means of internal state variable structure. Dynamical test data for aluminum and copper have been discussed. Particular attention is given to postshot photomicrographic observations of the residual porosity and on investigation of fracture mechanisms and spalling phenomenon. Spalling process has been described as a sequence of the nucleation, growth and coalescence of microvoids. Heuristic considerations of the growth and nucleation of microvoids are presentedGeneral evolution equation for porosity parameter is postulated. This equation describes the work-hardening viscoplastic response of solid and takes also account of the interactions of microvoids. An elastic-viscoplastic model of a material with internal imperfections is proposed. Internal imperfections are generated by the nucleation, growth and coalescence of microvoids. The model describes the dynamical behavior of dissipative solids observed experimentally as well as the mechanisms of fracture. A dynamical criterion of fracture (spalling) of metals is proposed. The criterion describes the dependence of fracture phenomenon upon the evolution of the constitutive structure.As an application of the theory the dynamic fragmentation process is considered. Prediction of fragment size is based on a very simple evolution equation assumed for the porosity parameter. The procedure of the determination of the interaction material functions has been developed.