Softening Due to Void Nucleation in Metals

The mechanics of void nucleation in an elastic-plastic solid stressed into the plastic range is studied with emphasis on the contribution of nucleation to softening of overall stress-strain behavior. Results for nucleation of an isolated spherical void in an infinite matrix under triaxial remote stressing are used to predict overall stress-strain behavior when interaction between voids is negligible. Calculations for nucleation of a void at a rigid spherical particle in a cylindrical cell model the simultaneous nucleation of a uniform distribution of voids. A strong dependence of the nucleation process on the matrix material specification is found when results based on isotropic hardening are contrasted with those based on kinematic hardening. At issue is the magnitude of the softening contribution due to void nucleation. This issue and the role of nucleation in promoting flow localization are discussed.