23. Experimental Study of the Dynamic Fragmentation in Transparent Ceramic Subjected to Projectile Impact

Transparent ceramics, such as monocrystalline sapphire, are very interesting materials for many applications including armor systems. Indeed, these technical ceramics present a very high compressive strength, a high Hugoniot Elastic Limit and a low density. However, due to their brittleness and low tensile strength, a fragmentation of the ceramic target occurs under ballistic impact. In the present study, the fragmentation process in a transparent ceramic subjected to projectile impact is investigated. To achieve this goal, edge-on impact tests have been performed at various impact speeds. The use of an ultra-high speed camera at a frame-rate set to one million frames per second allows visualizing “in real time” the whole fragmentation process resulting from the initiation and propagation of multiple cracks in the targets. Depending on the impact speed, cracks initiate from the impacted edge, the rear edge or from the two lateral surfaces of the targets. It is also observed that cracks propagate following specific directions related to crystallographic planes. Finally, the impact velocity and the orientation of the crystal are seen to play a major role on the final cracking pattern of the target.