Effect of thermal shock on ballistic impact damage in ceramic matrix composites

This paper presents experimental characterization of foreign object damage in three-dimensionally woven SiC/SiC composite (3D-CMC) plates with and without thermal shock. Thermal shock tests were performed using a micro-gas turbine engine which can give a sudden change in the temperature of combustion gas with the aid of an afterburner. Ballistic impact damage was introduced by collision of a flying sphere to 3D-CMC plates. A steel sphere with a diameter of 1.5 to 4.0 mm collided against target materials at the impact speed ranging from 200 to 1100 m/s. The damages on the surface of the specimen were observed by using optical microscopy. The damage consisting of a crater and breakage of fiber bundles was observed on the front (collision) surface. The surface damage area increases with increasing impact energy. The surface damage of thermally-shocked specimens was larger than that of virgin specimens. A spall fragment was ejected from the back surface at the impact energy larger than critical one (12 to 20 J) in both specimens while the fragment was broken into pieces only in the thermally-shocked specimens. The critical impact energy for spall depends on mass of a projectile and is not affected by thermal shock.