Grain-level analysis of dynamic fragmentation of ceramics under multi-axial compression

Fragmentation of a small ceramic specimen subjected to a dynamic compressive load is analyzed numerically at the mesoscale level using a cohesive/volumetric finite element scheme. Special emphasis is placed on the effect of lateral confinement on the dynamic fragmentation process. The analysis is performed in plane strain condition and assumes intergranular crack motion. The scheme relies on Voronoi tessellation to generate the granular microstructure. A nonlinear kinematic description is used to account for the possible large deformations and/or rotations of the grains during the fracture event. A cohesive unilateral contact enforcement scheme is used to model the complex interaction between the fracture surfaces and the fragments formed. The brittle to ductile transition in the constitutive response along with the associated change in the mode of failure of this class of materials from axial splitting to shear localization are captured through detailed simulations. It is quantified together with the effect of the applied strain rate and granular microstructure on the dynamic fragmentation process. Results are in good agreement with the analytical wing crack model and experimental observations of dynamic fragmentation for this class of materials. The apparent ductility exhibited by confined ceramics is found to be associated with the suppression of lateral dilation rather than the onset of shear localization.