Impact failure mechanisms in alumina tiles on finite thickness support and the effect of confinement

The quasi-static and the dynamic damage mechanisms in alumina tiles backed by finite thickness support plates and subjected to a variety of boundary conditions were investigated. The tile/plate assemblies were impacted by NATO 0.3 cal. armor piercing (AP) rounds with hardened and sharpened steel core. The alumina tile samples were 50×50 mm² area, their thicknesses ranging from 3 to 12 mm. The backup plates were made from 5 and 10 mm thick steel, aluminum, and Spectra^TM composite. The tiles were mounted in a special confinement frame, which enabled the tile samples to be subjected to biaxial compressive stresses, hence the confinement effect on the ballistic failure mechanisms could be examined. Several parameters associated with impact of ceramic tiles are discussed: the irreversible plastic deformation of the backup plate, the number of radial cracks, and changes in damage mechanisms with changing tiles' thickness. It is shown that the support plate plays a major role in the survivability of the alumina tile, and from a certain assembly thickness it may be considered as a semi-infinite. Furthermore, while suppressing the lateral movement of the fragments reduces the damage to the tile, biaxial compressive confinement gives only limited additional protection.