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 depe nds 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 en ergy consumption during material processing. In order to optimise metal for ming processes, the work hardening and softening should be analysed to incl ude the influence of deformation conditions within the constitutive model. This paper developed a constitutive model based on the Estrin and Mecking p henomenological model for cyclic hardening without prestraining whilst usin g a combined Estrin and Mecking model and Avrami equation for cyclic soften ing with prestraining. As cyclic softening is largely dependent on the work hardening previously achieved and on deformation conditions, the constitut ive model takes account of these conditions in addition to those used in co nventional constitutive models. (C) 1999 Elsevier Science S.A. All rights r eserved.