An approach to the coupled behaviour of polymers subjected to a thermo-mechanical loading in a gaseous environment

A thermo-diffuso-mechanical modelling is presented here in order to describe the behaviour of polymers under high temperature and strongly fluctuating gas pressure. The elementary volume is considered as a homogeneous non-reacting mixture of polymer and gas. Moreover, it is described within the formal framework of the thermodynamics of irreversible processes with internal variables and generalized normality rule. Introducing quadratic thermodynamic potentials results in linear constitutive laws, which take into account all direct couplings between thermal, diffusion and mechanical phenomena. Based on the assumptions of isotropy and small perturbations, the general macroscopic continuum formulation obtained is successively applied to an elastic, then to a viscoelastic mechanical behaviour. Implementing the thermo-diffuso-elastic model in ABAQUS™ software via a user subroutine allows a qualitative study of the direct couplings. Some of its main results are discussed here. Such a tool will facilitate the analysis of decompression tests and the polymer characterization. It will also contribute to the identification of the effects of both direct and indirect couplings.