An endochronic viscoplastic approach for materials with different behavior in tension and compression

To describe viscoplastic materials with different behavior in tension and compression via the example of filled PTFE (Polytetrafluorethylen), an endochronic viscoplastic material model is proposed. The approach is based on a rheological model without an elastic range, using a rate-independent elastoplastic element with an endochronic flow rule and a nonlinear elastic law in parallel connection with a nonlinear Maxwell model. The SDE (strength differential effect) due to different experimental results in tension and compression tests is described by two internal variables and their evolution equations. Numerical simulations show that the model can describe the short and long time material behavior of filled PTFE under isothermal loading in both, tension and compression.