VOID GROWTH IN GLASSY-POLYMERS

This paper deals with a study of voids in amorphous glassy polymers th at exhibit elastic-viscoplasticity with rate dependent yield, intrinsi c softening and progressive strain hardening at large strains. The stu dy is motivated by the plastic deformation in voided polymer-rubber bl ends caused by cavitation of the rubber particles, and thus attempts t o contribute to the understanding of the toughening mechanisms in blen ds. Axisymmetric cell analyses are presented to study the plastic defo rmation around initially spherical voids and their resulting growth in terms of size and shape up to large overall strains. This void growth is demonstrated to inherit particular properties from the typical fea tures of plasticity in glassy polymers, viz. small strain softening an d large strain hardening. The role of strain localization into shear b ands and their subsequent propagation in controlling void growth is hi ghlighted. Furthermore, an approximate constitutive model is presented for the description of the macroscopic overall behaviour of porous gl assy polymers. This model includes a modification of existing porous p lasticity models to account for elasticity effects on the initiation o f overall plasticity, which are important in polymers because of their relatively high yield strain. Its predictions are compared with the r esults from the numerical cell analyses. (C) 1997 Elsevier Science Ltd .