Tensile and fatigue behavior of oxide/oxide ceramic matrix composite with simulated foreign object damage in combustion environment

In this study, oxide/oxide ceramic matrix composite test coupons were quasi-statically indented and tested for tensile strength and fatigue life in a combustion environment. The combustion environment simulated the gas turbine engine environment in an aircraft. Two different dent sizes were created on two different sets of test coupons with a blunt conical indentor. During mechanical testing, the combustion flame simultaneously impinged on the dent region resulting in a maximum test coupon surface temperature of 1250 +/- 50 degrees C. For a life of 90 000 cycles, the fatigue limit in the combustion environment was 85% of the postindentation degraded tensile strength. Microscopy images of the failed test coupons showed damage modes of fiber fracture and matrix cracking at the dent site. The run-out test coupons which did not fail within 90 000 cycles showed residual strength that was not significantly different from that of their virgin counterparts.