Quasi-static impact damage in confined ceramic tiles

The effect of confinement on the failure mechanisms in dense alumina tiles during the penetration of a projectile was investigated and the role played by lateral mechanical confinement in inhibiting some failure modes was examined. Alumina tiles were placed in a confinement frame which simply and accurately allows high biaxial compressive pre-stresses. The confinement frame is a modular system which enables the application of various boundary conditions on the impacted tile to be generated. Tile samples were supported by semi-infinite support blocks made of steel or aluminum, and were confined by steel wedges. In the tests carried out under ballistic penetration conditions, the confined tiles were impacted by 0.3 cal. NATO AP (armor piercing) projectiles. These contained a hardened steel cone-shaped core with a sharp tip. In this investigation, the effect of reflected stress waves was small or even negligible, since the tile/support impedance mismatch was low, so that quasi-static failure mechanisms pre-dominated. The effect of tile thickness on the damage mechanisms was also examined. Under the described test conditions, the major failure modes were radial cracks, cone crack, and fragmentation of the cone. Confined tiles exhibited reduced damage; damage in the form of radial cracks was reduced, and cone crack and fragmentation of the cone were inhibited. Based on the theory of a plate on an elastic foundation, the quasi-static loads that initiate the radial cracks were formulated. This model assists in understanding the initial damage mechanism.