Dynamic Failure Behavior of Polycrystalline Alumina Under Impact Loading

Plate impact experiments and impact recovery experiments were performed on $92.93wt.%$ aluminas using a $100mmdia$ compressed-gas gun. Free surface velocity histories were traced by a velocity interferometry system for any reflector (VISAR) velocity interferometer. There is a recompression signal in free surface velocity, which shows evidence of a failure wave in impacted alumina. The failure wave velocities are $1.27km∕s$ and $1.46km∕s$ at stresses of $7.54GPa$ and $8.56GPa$⁠, respectively. It drops to $0.21km∕s$ after the material released. SEM analysis of recovered samples showed the transit of intergranular microcracks to transgranular microcracks with increasing shock loading. A failure wave in impacted ceramics is a continuous fracture zone, which may be associated with the damage accumulation process during the propagation of shock waves. Then a progressive fracture model was proposed to describe the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. Numerical simulation of the free surface velocity was performed in good agreement with the plate impact experiments. And the longitudinal, lateral, and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.