A Two Surface Plasticity Model With Bounding Surface Softening

Two surface plasticity models have been used increasingly in recent years to model not only uniaxial, cyclic plasticity but also multiaxial and nonproportional histories. A two surface model is presented here which predicts the increased hardening due to out-of-phase cycling in a natural way. It includes a mechanism by which the bounding surface contracts when the yield surface is not in contact. This provides a mechanism that is useful for modeling cycling behavior. Predictions of the model with experiments at moderate strain are presented.