Endochronic viscoplastic material models for filled PTFE

To describe the nonlinear material behaviour of polytetrafluoroethylene (PTFE), a viscoplastic material model of the overstress type is proposed based on experimental data. The approach starts with a rheological model without an elastic range, using a rate-independent elastoplastic model with an endochronic flow rule-and a nonlinear elastic law in, parallel connection with a nonlinear Maxwell model. The generalization to three dimensions is possible for both small and finite strains under the assumption that changes of the density are purely elastic. Numerical simulations show that the model can describe the short and long time material behavior of filled PTFE. (C) 2002 Elsevier Science Ltd. All rights reserved.