Terminal ballistic tests with armor piercing 7.62 mm projectiles were performed on high quality 96% and 99.8% alumina ceramic tiles backed with both thick and thin aluminum plates. The dynamic failure mechanism of unconfined alumina ceramic tiles was sought by the examination of fracture and deformation structure in the recovered targets. Various impact velocities ranging from 420 to 810 m/s allowed, to some extent, to the determination of successive failure steps. The results suggest that nonconventional material behaviour such as fragmentation, frictional effects during fragment flow and conoid fracture are highly effective in the penetration resistance of ceramics. The reduced backup rigidity was found to disturb the formation of conoid zone in ceramic tiles, by causing premature tensile fracture at the back face of ceramics. This results in a decrease in the penetration resistance of ceramics and reduced load distribution to backup material, which is of crucial importance in two component armour systems.