A multi-scale plastic-damage model for strain-induced morphological anisotropy in semi-crystalline polyethylene

Abstract

In this article, we present a multi-scale plastic-damage model for strain-induced morphological anisotropy in semi-crystalline polyethylene formulated within a continuum-based micromechanical framework. The crystallographic shear in the crystalline lamellae and the molecular alignment/relaxation of the amorphous phase are two underlying inelastic processes integrated in the constitutive representation. The cavitation damage accumulation related to the progressive nucleation and anisotropic growth of nano-sized cavities in the amorphous phase is also integrated and treated separately for the elastic–viscoplastic intermolecular interactions and for the viscohyperelastic network interactions. The mechanical coupling between the deformation modes in the amorphous and crystalline domains is obtained by considering the crystalline–amorphous interfacial interaction in the micro-macro homogenization procedure. We compare the model output to tensile experimental observations from the literature of high-density polyethylene, in terms of stress–strain response and inelastic volumetric strain, during stretching and stretching-retraction-recovery sequences upon large-strain plastic deformation at different strain rates and temperatures. We analyze the effect of strain-induced morphological anisotropy on the internal cavitation damage distributions by means of pole figures. The key role of the cavitation damage on the macroscopic and internal responses is studied.