In most general purpose finite element programs, the rate-independent elastoplastic constitutive relations use the classical isotropic and kinematic hardening models, or some modification of them through mostly ad hoc rules. Numerous experimental observations indicate that materials can have very complex behaviour, and the classical inelastic models are quite inadequate for simulating these responses. A hierarchy of plastic constitutive models which includes rate-independent, rate-dependent and finite deformation models have been recently developed by Ellyin and Xia [1–3]. As a further step towards practical application, the rate-independent model has been developed into a package for a user defined material model. For example, it has been implemented in the ADINA code user defined material model for the two- and three-dimensional elements. The performance and validation of the model is verified by numerous examples involving different types of loading paths and histories. The results are compared with the experimental data. It is clearly shown that this model is far superior to those currently available, yet it is relatively simple to implement.
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