A New Nonlinear Viscoelastic Model for Polymers

This paper presents a new nonlinear viscoelastic model that has been recently implemented in the commercial finite element code, Abaqus.  The model is intended to accurately predict nonlinear response of elastomers and other polymers subjected to large deformations.  It consists of an arbitrary number of viscoelastic networks and an elastic equilibrium network, which are connected in parallel. In the model the multiplicative decomposition of the deformation gradient into elastic and inelastic parts is assumed. In this approach there exists an intermediate, stress-free configuration from which the elastic response is computed. The elastic response is specified using any of the hyperelastic models available in Abaqus. The viscous response is obtained assuming the existence of the creep potential, which is used to compute the flow rule. The flow rule is expressed as a function of stress invariants and internal variables, and different evolution laws for the internal variables are allowed within the framework of the model. Finally, in order to validate the model, it is used to predict the response of the PC-ABS thermoplastic material for a series of relaxation tests, and the resulting numerical solutions are compared with the experimental results.