Void growth dependence on loading path and mean stress from large-scale numerical simulations

Abstract

Direct numerical simulation of a large population of voids nucleated from randomly distributed spherical particles is used to assess the load path and mean stress dependence of void growth. The voids are formed by particle failure, and they grow by expansion of the void surfaces through the arbitrary Lagrange/Eulerian mesh. Boundary conditions simulating uniaxial extension and simple shear with varying levels of imposed volume strain provide a range of stress triaxialities and distinct load paths. Volume averages of the void fraction and the mean and effective stresses are extracted from the simulation as measures of the state and loading during dilatational plastic flow.Comparison of the numerical results with the Gurson model shows that the mean stress dependence on the volume fraction follows the Gurson model relatively well at high stress triaxialities but deviates substantially at low triaxialities. Conversely, the effective stress from the Gurson model agrees with the numerical results reasonably well at low stress triaxiality but it deviates appreciably at high stress triaxialities. The results from the simple shear loading are in closer agreement with the Gurson model than the extension results, suggesting load path dependence.