Foreign object damage phenomenon by steel ball projectiles in a SiC/SiC ceramic matrix composite at ambient and elevated temperatures

Foreign object damage (FOD) phenomenon of a gas-turbine grade SiC/SiC ceramic matrix composite (CMC) was determined at 25 degrees and 1316 degrees C using impact velocities ranging from 115 to 440 m/s by 1.59-mm diameter steel ball projectiles. Two types of target-specimen support were employed at each temperature: fully supported and partially supported. For a given temperature, the degree of impact damage increased with increasing impact velocity, and was greater in partial support than in full support. The elevated-temperature FOD resistance of the composite, particularly in partial support at higher impact velocities >= 350 m/s, was significantly less than the ambient-temperature counterpart, attributed to a weakening effect of the composite. In full support, frontal contact stresses played a major role in generating composite damage; whereas, in partial support both frontal contact and backside tensile stresses were combined sources of damage generation. Formation of cone cracks initiating from impact site was also one of the key damage features. The SiC/SiC composite was able to survive higher energy impacts without complete structural failure, as compared with gas-turbine grade AS800 and SN282 monolithic silicon nitrides.