Failure Pattern Formation in Brittle Ceramics and Glasses

摘要

When a high-speed projectile impacts a brittle material, such as glass or polycrystalline ceramic, severe damage and fragmentation is normally observed before projectile penetrates. AlON is a material being considered for a variety of transparent armor, sensor window, and radome applications. It is a polycrystalline ceramic that fulfills the requirements of transparency and requisite mechanical properties for transparent armor against armor piercing ammunition. AlON has a cubic, spinel crystal structure (Fd3m) that can be processed to transparency in a polycrystalline microstructure. It differs from glasses which do not have any periodic crystalline order, but it is akin to polycrystalline opaque ceramics, such as aluminum oxide. AlON was recently investigated by Strassburger, Patel, McCauley, and Templeton (2006) using EOI test in two different optical configurations. In the first, a regular transmitted-light shadowgraph set-up was used to observe wave and damage propagation. In the second, a modified configuration was used, where the specimens were placed between crossed polarizers, and the photoelastic effect was utilized to visualize the stress waves. Pairs of impact tests at approximately equivalent velocities were carried out in transmitted plane light (shadowgraphs) and crossed polarized light. AlON and fused silica specimens were impacted using solid cylinder steel projectiles with velocities ranging from 270 to 925 m/s.