In this contribution the applicability of the microphysically based "unified" model firstly introduced by Estrin is investigated resulting in a proposal for a modified version. The original constitutive equations are restricted to isotropic hardening. For the description of kinematic hardening the material model is extended by introducing the concept of effective stresses.

For the identification of the parameters of the model a specially structured evolution strategy can be applied successfully. From experimental and microphysical considerations a starting- parameter vector can be derived by which the convergence of the iteration process is strongly accelerated.

As a technical application of the material law the casing structure of an extrusion press is investigated. Results derived from both, Estrin's model and the extended model, are compared. The applied finite element formulation employs implicit time integration and full Newton-Raphson technique based on a consistent linearization of the constitutive equations.

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