Interface Defeat and Penetration: Two Modes of Interaction between Metallic Projectiles and Ceramic Targets

Abstract: Ceramics constitute an important group of low-density armour materials. Their high intrinsic strength makes it possible to design ceramic armour systems capable of defeating projectiles directly on the ceramic surface. This capability, named interface defeat, signifies that the projectile material is forced to flow radially outwards on the surface of the ceramic without penetrating significantly.This thesis presents impact experiments between long-rod projectiles and ceramic targets. The projectile/target interaction was studied using flash X-ray technique. Transition velocities (the impact velocity at which interface defeat can no longer be maintained and penetration starts) were estimated for different combinations of metallic projectiles and ceramic targets and compared to critical velocities estimated on a theoretical basis. Replica scaling experiments were also performed in order to investigate the possible influence of scale.All ceramic materials tested showed a distinct transition from interface defeat to penetration. Experiments with different silicon carbides showed that the transition velocity correlated better with the fracture toughness than with the hardness of the ceramic materials. For conical projectiles, penetration occurred along a conical surface crack and at a lower transition velocity than that observed for cylindrical projectiles. Experiments with unconfined alumina targets in different scales showed only a slight increase in dimensionless final penetration with length scale.A unique transition velocity seems to exist for each combination of projectile, target material and target configuration. This velocity was found to depend on both the strength (hardness) and the brittleness (fracture toughness) of the ceramic. The lower transition velocity of conical projectiles compared with cylindrical ones is mainly due to the radially expanding load and the penetration of projectile material into surface cracks. The results of the experiments in different scales indicate that replica scaling is valid for penetration in ceramics.