Development of constitutive models for metal forming with cyclic strain softening

Many cold and hot worked metals undergo strain hardening and softening when subjected to cyclic plastic straining. The degree of strain softening depends on the amount of prior cold work or heat treatment introduced into the material and upon the magnitude and the number of cycles of applied cyclic plastic strain. Cyclic strain softening leads to a lower Bow stress, higher ductility, reduced tensile strength upon subsequent straining and lower energy consumption during material processing. In order to optimise metal forming processes, the work hardening and softening should be analysed to include the influence of deformation conditions within the constitutive model. This paper developed a constitutive model based on the Estrin and Mecking phenomenological model for cyclic hardening without prestraining whilst using a combined Estrin and Mecking model and Avrami equation for cyclic softening with prestraining. As cyclic softening is largely dependent on the work hardening previously achieved and on deformation conditions, the constitutive model takes account of these conditions in addition to those used in conventional constitutive models. (C) 1999 Elsevier Science S.A. All rights reserved.