Inelastic response of alumina

This paper investigates the effects of microcracking, plasticity, and strain rate dependent pore closure on the inelastic deformation wave profiles of a low density (3.55 mg/m³) and a high density (3.88 mg/m³) aluminas. This is accomplished by means of numerical simulations of the measured plane shock wave profiles in these aluminas. The wave profiles were generated over a wide range of impact velocities (80 m/s to 2200 m/s). An internal-state-variable based ceramic model was used in the simulations to describe the inelastic strains due to microcracking, microplasticity, and pore collapsing. The microcrack size, number of microflaws, and limiting speed of the crack growth controlled the shape of the inelastic wave portion of the velocity profile at low velocity impact. The porosity content and the strain rate sensitivity parameter did not significantly influence the shapes of the low velocity profiles. However, these two parameters greatly influenced the profile shapes when the ceramic was shocked at high velocities well above the Hugoniot elastic limit. The simulations of high velocity experiments clearly demonstrated the need for describing the pore collapse process in order to match the measured wave profiles.