Collapse and coalescence of spherical voids subject to intense shearing: studied in full 3D

Micro-mechanical 2D cell model studies have revealed ductile failure during intense shearing to be governed by the interaction of neighbouring voids, which collapse to micro-cracks and continuously rotate and elongate until coalescence occurs. For a three-dimensional void structure, this implies significant straining of the matrix material located on the axis of rotation. In particular, the void surface material is severely deformed during shearing and void surface contact is established early in the deformation process. This 3D effect intensifies with decreasing stress triaxiality and complicates the numerical analysis, which is also reflected in published literature. Rather than moving towards very low triaxiality shearing, work has focused on extracting wide-ranging results for moderate stress triaxiality (T similar to 1), in order to achieve sufficient understanding of the influence of initial porosity, void shape, void orientation etc. The objective of this work is to expand the range of stress triaxiality usually faced in 3D cell model studies, such that intense shearing is covered, and to bring forward details on the porosity and void shape evolution. The overall material response is presented for a range of initial material configurations and loading conditions. In addition, a direct comparison to corresponding 2D cell model predictions for circular cylindrical voids under plane strain shearing is presented. A quantitatively good agreement of the two model configurations (2D vs. 3D) is obtained and similar trends are predicted. However, the additional layer of matrix material, connecting voids in the transverse direction, is concluded to significantly influence the void shape evolution and to give rise to higher overall ductility. This 3D effect is demonstrated for various periodic distributions of voids.