NONLINEAR MECHANICAL RESPONSE OF AMORPHOUS POLYMERS BELOW AND THROUGHCLASS TRANSITION-TEMPERATURE

The mechanical response of various amorphous polymers such as poly (me thyl methacrylate), polycarbonate, polystyrene, and poly(ethylene tere phthalate) were studied experimentally and theoretically. First, usual stress-strain constitutive equations were determined below and throug h their glass transition temperature. Further measurements were done t o specify the double component of nonelastic strain (anelastic and vis coplastic). The analysis of all of the data was performed on the basis of a molecular theory of nonelastic deformation of amorphous polymers proposed by Perez et al. The main assumptions of this modeling are re called in this article: the existence of quasi point defects correspon ding to nanofluctuations of specific volume (concentration); the hiera rchically constrained nature of molecular dynamics; and under the appl ication of a stress, the nucleation and growth of shear microdomains ( anelastic strain) until they ultimately merge irreversibly with one an other (viscoplastic strain). Recently, developments based on the descr iption of the dislocation dynamics were introduced. To account for str ain hardening effect at large strains, the rubberlike elasticity forma lism was included. The accuracy of the analysis in describing a high s tress mechanical test was illustrated in a large range of temperatures . (C) 1997 John Wiley & Sons, Inc.