Finite Element Modelling of Inelastic Deformation of Ductile Polymers

Two uniaxial constitutive models, a nonlinear viscoelastic (NVE) model and a viscoplastic (VP) model, have recently been developed for time dependent inelastic analysis of ductile polymers. This study extends these models to provide a multiaxial formulation. The new multiaxial models are implemented in a general purpose finite element program, together with a conventional treatment of geometrical nonlinearity. The solution procedure is based on a simple explicit integration method that is suitable for the new material models and is easy to implement. Two example problems are studied to evaluate the performance of the new finite element procedure. Finite element simulations of a perforated high density polyethylene (HDPE) plate under remote uniaxial loading are performed, and finite element model simulations of an HDPE pipe section under parallel plate loading are also performed. The finite element modelling results are then compared with the measured experimental results. It is found that the finite element model provides good predictions of the inelastic deformation of HDPE under various loading histories, including cases that involve a highly nonlinear material and geometrical response.