A variational principle of elastoplasticity and its application to the modeling of frictional materials

Starting from a thermomechanical description of elastoplasticity, a stress-based variational principle is derived. The principle, which generalizes von Mises’s principle of maximum plastic dissipation, reproduces the conventional elastic/hardening-plastic framework applicable to metals as a special case and further proves to be suitable for developing constitutive models for frictional materials. Application of the principle to the isotropic and triaxal compression behaviour of sands is considered by means of a non-conventional extension of the modified Cam clay model. The new model allows for the specification of arbitrary stress-dilatancy relations without altering the yield potential or introducing a separate flow potential. Moreover, the elastoplastic tangent modulus is always symmetric, regardless of the degree of apparent nonassociativity.