Understanding the deformation of ceramic materials at high strain rates.

Ceramic hardness and plasticity have been highlighted as important characteristics in ballistic performance; both of which can be measured and semi-quantified from indentation experiments, respectively. However, relatively little work has investigated the accompanying type, on-set and evolution of indentation-induced damage that may also be contributing an influential role. Pressureless sintered SiC and spark plasma sintered B4C, SiC-AlN-C and range of SiC-B4C composite samples were investigated and their indentation damage characterised by cross- sectioning and serial ceramographic polishing techniques. Observations were compared with their surface and sub-surface sphere impact-induced damage and used to correlate with, and explain differences in, ballistic performance against an armour-piercing projectile. The results conclude that 19.62 N Knoop hardness and predicted transition velocities correlate with V50 ballistic performance, supporting the importance of high ceramic hardness and the propensity to sustain projectile dwell in ballistic performance. The type and evolution of indentation-induced damage appears less significant, although variability in indentation behaviour does appear to correlate to variability in ballistic performance. Despite the shallow indentation damage depth and high crack propagation resistance of SiC-AlN-C, the early on-set of concentrated damage beneath indentations (and impact craters) resulting in a decrease in hardness, appears to be the dominate factor governing the low ballistic performance of this material. In contrast, the high hardness, plasticity and apparent residual strength of the sub-surface indentation damage zone of SiC-B4C composites appears to offer the greatest ballistic performance potential. This work provides further evidence to support the use of indentation as a possible screening method to rank the ballistic performance potential of candidate armour ceramics