Modeling of shear instabilities observed in cylinder collapse experiments performed on ceramic powders

Brittle materials fail by microcracking and fragmentation when subjected to multiaxial loading. In some cases full comminution occurs and the material behavior becomes governed by the flow of particles. In this work a granular model developed by Anand and co-workers, based on a two-mechanism elastoplastic formulation, is extended to include rate effects and incompressibility at zero void ratio. The model parameters for Alumina and Silicon Carbide ceramic powders are identified using stress histories obtained by means of pressure-shear plate impact experiments. The model is then used to simulate the shear banding mechanism experimentally observed in thick-wall cylinder collapse experiments performed on ceramic powders (Nesterenko and co-workers). The proposed model captures the main physics of the problem and provides valuable insight in the deformation process. Initiation site and speed of propagating instabilities are obtained from the simulations.