Size Effects in Void Coalescence

The importance of the strain gradients that evolves at the onset of void coalescence at micron-scale is demonstrated through a detailed numerical study. Here, a 3D numerical framework is exploited to grain a parametric understanding of the influence of void size and void spacing, and a direct comparison to a recent extension of the coalescence criterion by Thomason is presented. Taking into account the intrinsic length scales inherited by the ductile failure process shows a clear increase in the level of the average volume stress, perpendicular to the plane of localization, at which void coalescence occurs. Oblate voids are particularly affected by the evolving strain gradients. The increase in stress level predicted in a gradient enhanced matrix material are, however, yet to be properly addressed in existing continuum models as both the Thomason criterion, as-well as the Gurson modeling framework, rest on conventional plasticity theory.