A modified fraction model with a nonhardening strain region.

Abstract

A modified fraction model, which is one of the viscoplastic constitutive models, can be extended to represent the cyclic hardening or softening behavior of material by introducing the concept of a nonhardening strain region. The procedure for determining the material constants of the model is precisely described through the example of 21/4 Cr-1 Mo steel at 600°C. The data required for determining the material constants are the rate dependent stress-strain curves and the cyclic hardening or softening behavior of the material. Several example calculations and comparison with the test data have revealed that the proposed model can represent the plastic, creep and plastic creep interaction behavior of the material as well as the cyclic hardening or softening behavior in the viscoplastic regime.