In many forming processes, the mechanical properties of the workpiece material are deteriorated by the growth of voids during plastic deformation. In this study we present a new constitutive relation for void growth based on mechanical analyses of an isolated void growing in metallic media under various conditions of stress triaxiality. Incompressible, strain hardening, viscoplastic behavior of matrix material is characterized by an internal state variable model. Systematic variations in shear strength, mean stress, porosity and deviatoric deformation rate provided families of growth rate curves that were collapsed by appropriate scaling into two master curves. The forms of these curves and the scaling factors needed to obtain two master curves motivated the mathematical structure of the constitutive relation for void growth. A new macroscopic process model is formulated by using two state variables, one for strain hardening from slip dominated plastic distortion and the other for damage from void growth. Application of the model to strip drawing operations is given via implementation in a finite element formulation. The predicted density changes as a result of void growth are compared to those from experiments reported by others.
展开▼
