A non-unified creep plasticity constitutive model and a unified creep-plasticity model have been considered. In the non-unified model, creep and plastic strains were added separately; in the unified model, they were treated in a unified manner. These models were used to predict cyclic hardening and mean stress relaxation for isothermal loading conditions. The results indicate that certain instabilities occured in unified creep-plasticity simulations at low temperatures. Material behavior for thermal loading was studied using the two-bar structure. Both constitutive models were modified to handle material behavior changes with temperature. The thermal loading response was predicted satisfactorily with both models for most cases. However, certain model limitations were encountered in the unified model. The capabilities of both models are outlined and discussed.

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