Extension of generalized plasticity to finite deformations and non-linear hardening

The generalized plasticity model, as presented by Lubliner (1991), Lubliner et al. (1993) and Auricchio et al. (1992), is a generalization of classical rate-independent plasticity with a yield surface. This material model is able to describe a reloading transient during the reloading process of a specimen, which is shown in the asymptotic approach of the reloading curve to the initial load curve in the stress-strain diagram, as observed in Lubhahn and Felger (1961) for copper or in Greenstreet et al. (1971) for graphite. In the present paper an advantageous extension of the generalized plasticity model to finite plastic strain regimes is given. Classical plasticity and the model in Auricchio and Taylor (1995) for linear kinematic and isotropic hardening rules are included as special cases in the proposed concept. It will be shown that the suggested modification yields a mathematically simple structure of the constitutive relations and an efficient stress algorithm, adaptable to finite element programs similar to that in Auricchio and Taylor (1995). Special attention is focused on a correct treatment of the loading criteria. (C) 1999 Elsevier Science Ltd. All rights reserved.