Void behaviors from low to high triaxialities: Transition from void collapse to void coalescence

This paper examines the critical strain to onset of void collapse and void coalescence via homogenization based micromechanics analyses. The critical strains are established by examining the energetics of a voided unit cell throughout its loading history. Cells of varying initial void volume fraction f(0) are subjected to a full range of the Lode parameter L and stress triaxiality T ranging from low (and negative) to high, and loci of strain to onset of void collapse and void coalescence are obtained. Numerical results show that the loci are discontinuous functions of T, with the existences of transition zone separating loci of strain-to-onset of void collapse and that of void coalescence; within the zones neither of the two void behaviors is predicted at low triaxiality. Stress state dependence of void collapse and void coalescence are investigated and presented in the form of phase maps, analogous to phase diagrams; they illustrate and distinguish clearly in the T - L space, regions in which void collapse, void coalescence and neither of the two are possible. (C) 2016 Elsevier Ltd. All rights reserved.