An Endochronic Viscoplastic Approach for Materials with Different Behavior in Tension and Compression

To describe viscoplastic materials with different behavior intension and compression via the example of filled PTFE(Polytetrafluorethylen), an endochronic viscoplastic materialmodel is proposed. The approach is based on a rheological modelwithout an elastic range, using a rate-independent elastoplasticelement with an endochronic flow rule and a nonlinear elastic lawin parallel connection with a nonlinear Maxwell model. The SDE(strength differential effect) due to different experimentalresults in tension and compression tests is described by twointernal variables and their evolution equations. Numericalsimulations show that the model can describe the short and longtime material behavior of filled PTFE under isothermal loading inboth, tension and compression.