A two-phase model for the mechanical behaviour of semicrystalline polymers. Part I: Large strains multiaxial validation on HDPE

Due to their microstructural properties, semicrystalline polymers (SCPs) generally present the ability to undergo large plastic strains. In structure with plastic components, large strains can thus be locally reached, during creep or in crack tip for examples. On the other hand, the stresses state is generally tridimensional. It is consequently important to develop mechanical models able to predict the tridimensional and large strains behaviour of SCPs, in order to design structures. The proposed model consists of an extension to large strains of a model previously proposed for moderate strains [Cangémi, L., Meimon, Y., 2001. A two-phase model for the mechanical behaviour of semicrystalline polymers. Oil Gas Sci. Technol. – Rev. IFP 56 (6), 555–580]. The model is based on a two-phase representation of SCPs at a mesoscopic level. The thermodynamics of porous media permits to introduce a mechanical coupling between the two phases. The main features of SCPs (mean stress dependence, volume change, viscosity, hardening) are described from a specific yield surface and a viscoplastic formalism. A cavities nucleation criterion is also included to predict the dilatant volume strain of SCPs obtained under specific loading conditions.The large strains model is validated for HDPE under uniaxial tension, simple shear, uniaxial compression and plane strain compression conditions, from literature data and experimental data performed in the study.