Constitutive modelling of plasticity of fcc metals under extremely high strain rates

A reliable and accurate description of the constitutive behavior of metals under the coupled effect of extremely high strain rate has become more and more important. The conventional constitutive models available, however, do not apply when the strain rate is beyond 10(4) s(-1). This paper establishes a new constitutive model to describe the fcc crystalline plasticity at the extreme strain rate beyond which the material sensitivity to strain rate increases dramatically. The new model distinguishes the mobile dislocations from the total dislocations and incorporates the change of mobile dislocation density to count for the microstructural evolution of the material. A unified constitutive model is then proposed. An optimization method was used to obtain globally optimal parameters in the model. The flow stress predictions by the unified model show a very good agreement with experiments within the whole strain rate range from 1 x 10(-4) s(-1) to 6.4 x 10(5) s(-1). The flow stress upturn phenomenon in OFHC copper was satisfactorily described. (C) 2011 Elsevier Ltd. All rights reserved.