Numerical analysis of void closure in metal forming

Abstract

Since voids in a billet or an ingot are detrimental to tensile strength of the material, they are required to be closed by metal forming processes. However, distributions of field variables, such as stress and strain, imposed by the processes are in general inhomogeneous and thus prediction of void closure is difficult. In previous studies, where stress triaxiality was low in magnitude, void closure was found to be predicted by the effective strain at the location of the void. The effective strain was obtained from numerical analysis of a non-void model. In the present study, this finding was further investigated for compressions of a rectangular block and a cylinder, where stress triaxiality was relatively high in magnitude. As a result, a closure criterion of spherical void was found as a function of the effective strain and stress triaxiality. The mode of void closure changed from collapse to contraction as stress triaxiality increased in magnitude.