Restitution of Impacting Projectiles in Ceramic Matrix Composites Subject to Foreign Object Damage

Accurate assessments of rebound velocity of a projectile in impact events for ceramic matrix composites (CMCs) are important since the rebound velocity affects the degree of resultant impact damage in both CMC targets and projectiles. A series of in-depth characterizations of coefficients of restitution (COR), which is defined as rebound velocity divided by impact velocity of a projectile, was made using various types of gas-turbine grade CMCs in conjunction with dynamic imaging and data-acquisition systems. Both the impact aspects and the COR were characterized as a function of impact velocities ranging from 150 m/s to Mach 1 and were analyzed with respect to materials' key properties. An important experimental observation was that regardless of types of CMCs employed, the corresponding CORs at an impact velocity of 350 m/s (i.e., Mach 1) yielded consistently the same value close to 0.1-0.2. The temperature effect in COR was found to be minor to 1100 degrees C as assessed with the specialty SiC/SiCs, also independent of environmental barrier coatings (EBCs). The COR were also determined in other materials systems such as advanced monolithic ceramics and some metallic materials in an attempt to construct an overall COR map in response to related foreign object damage (FOD) events.