Separation and hierarchic order of key influences on the ballistic strength of opaque and transparent ceramic armor

A complex study was performed over several years with laboratory-made ceramic tiles to enable ballistic tests with a separate variation of selected influences keeping other factors constant. These investigations were aimed at answering the question about influences of different microstructures and of associated mechanical properties depending on systematic variations of the backing materials. Contradictive findings of the past are explained now by the observation that the ballistic strength of Al2O3 and spinel ceramics and single crystals with different backings (steel, aluminum, glass) is governed by a few major influences subject to a strict hierarchy: (1) Top priority is the mode of ceramic fragmentation governed by the microstructure and by the dynamic stiffness of the ceramic/backing target; these influences also affect the relative importance of dwell and penetration. (2a) On a lower rank, Young's modulus and dynamic stiffness of the ceramic are responsible for projectile deformation during dwell. (2b) On penetration, the abrasive benefit of a high ceramic hardness depends on the size of the ceramic debris, i.e. on ceramic fragmentation. In contrast, all strength data are weakly correlated with the ballistic efficiency. This result is readily understood regarding the need of ceramic failure for maximum projectile erosion.