Solution strategies for FEM analysis with nonlinear viscoelastic polymers

The Schapery model is a very common model for nonlinear viscoelastic behaviour of polymers. Therefore this model has been implemented with a user subroutine into the FEM package MARC. Since explicit integration is relatively fast but is often accompanied by numerical instabilities and implicit integration is relatively slow but numerically stable, combined strategies have been programmed. Results show that the viscoelastic response of complex products can be calculated without numerical instabilities and with short calculation times. Full viscoelastic calculations and calculations using creep isochrones on dead weight loading of an HDPE bottle crate only differ from the onset of creep buckling.