A Constitutive Model for Plastics with Piecewise Linear Yield Surface and Damage

Reliable prediction of the behaviour of structures made from polymers is a topic under considerable investigation in engineering practice. Especially, if the structure is subjected to dynamic loading, constitutive models considering the mechanical behaviour properly are not available in commercial finite element codes yet. A constitutive model is derived including important phenomena like necking, crazing, strain rate dependency, unloading behaviour and damage. In particular, different yield surfaces in compression and tension and strain rate dependent failure, the latter with damage induced erosion, are taken into account. With the present formulation, standard verification tests can be simulated successfully. Also, an elastic damage model can be used to approximate the unloading behaviour of thermoplastics adequately.