Foreign Object Damage in SiC/SiC and Oxide/Oxide Ceramic Matrix Composites

Foreign object damage (FOD) of two different ceramic matrix composites (CMCs), MI SiC/SiC and oxide/oxide (N720/A), was assessed via impact testing at ambient temperature using impact velocities ranging from 100 to 400 m/s by 1.59-mm diameter steel ball projectiles.  Two different support systems of targets, full support and partial support, were employed for each of the CMCs.  The extent of impact damage as well as post-impact strength degradation of both CMCs increased with increasing impact velocity, and were greater in partial support then in full support, attributed to the additional backside tensile stress field in partial support.  The degree of relative post-impact strength degradation of the oxide/oxide composite was similar to that of the MI SiC/SiC composite.  Both of the CMCs were able to survive high energy (~1.3J) impacts without complete structural failure, which is in a notable contrast with gas-turbine monolithic silicon nitrides.  Impact damage morphology and response to static indentation by projectiles were also determined and will be discussed in terms of impact modeling.