Nonlinear mechanical response of amorphous polymers below and through glass transition temperature

Abstract

The mechanical response of various amorphous polymers such as poly-(methyl methacrylate), polycarbonate, polystyrene, and poly(ethylene terephthalate) were studied experimentally and theoretically. First, usual stress-strain constitutive equations were determined below and through their glass transition temperature. Further measurements were done to specify the double component of nonelastic strain (anelastic and viscoplastic). 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 recalled in this article: the existence of quasi point defects corresponding to nanofluctuations of specific volume (concentration); the hierarchically constrained nature of molecular dynamics; and under the application of a stress, the nucleation and growth of shear microdomains (anelastic strain) until they ultimately merge irreversibly with one another (viscoplastic strain). Recently, developments based on the description of the dislocation dynamics were introduced. To account for strain hardening effect at large strains, the rubberlike elasticity formalism was included. The accuracy of the analysis in describing a high stress mechanical test was illustrated in a large range of temperatures. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2517–2528, 1997