The effect of statistically heterogeneous void nucleation on metal failure in shear

Ductile fracture consists of the nucleation, growth, and coalescence of microvoids observed as dimples on the fracture surface. Typical alloys contain diverse heterogeneities that are stochastically distributed, so that void nucleation is essentially heterogeneous and statistical. The scenarios of homogeneous vs. stochastic heterogeneous void nucleation are systematically compared under simple shear deformation in two limiting cases: (1) a uniform sheet that can be viewed as representing the initial stages of plastic deformation, and (2) the same sheet with an embedded central pore, the latter representing the prevailing situation for which large voids have already nucleated and grown. The homogeneous case provides a reference to which the statistically heterogeneous cases are compared. In the uniform sheet model, heterogeneous void nucleation decreases the porosity accumulation and the stress triaxiality. However, when embedding a geometrical pore at the center of the simulation cell, the averaged triaxiality increases irrespective of the void nucleation heterogeneity. The overall ductile failure process can be thought of as a gradual evolution from the initial stage (1) of a homogeneous sheet with heterogeneous void nucleation towards the final stage of a similar void-containing sheet (2), with the associated evolutions of the stress and porosity fields presented here.