On cavitation, post-cavitation and yield in amorphous polymer-rubber blends

The deformation behaviour of amorphous polymer-rubber blends is investigate d in terms of an axisymmetric unit cell model containing an initially spher ical rubber particle. The behaviour of the rubber is described by an incomp ressible non-Gaussian network theory, while for the matrix we adopt a recen t large strain elastic-viscoplasticity model that incorporates the intrinsi c softening upon yield and the subsequent progressive orientation hardening typical for amorphous glassy polymers. Guided by simple analytical estimat es, cavitation of the rubber particle is interpreted in terms of the unstab le growth of a pre-existing small void. It is shown that cavitation and yie ld are essentially coupled processes. On the macroscopic scale, both are so ftening mechanisms: If macroscopic yield takes place before the limit stres s for cavitation is reached, cavitation is prohibited. Furthermore, and con trary to common belief, it is found from the interfacial stress history tha t, using realistic material parameters, the rubber particle continues to si gnificantly affect plasticity in the matrix in the post-cavitation regime, i.e. after it has cavitated, so that cavitated particles cannot always be c onsidered to be equivalent to particle-sized voids. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.