An oxide-oxide CMC with no interface, Nextel720/alumina, was investigated under tension-tension fatigue condition using the capabilities provided by a unique burner rig facility which simulated both the load and combustion conditions of hot-section components of gas turbine engines such as turbine blades and vanes. A set of fatigue tests performed using the burner rig (stress ratio, R = 0.05 and frequency = 1 Hz) provided S-N data and damage details, which were analyzed for the role and effects of oxidation on the failure and damage mechanisms. These test results were then compared with those obtained from fatigue tests (R = 0.05 and 1 Hz) in a standard furnace under laboratory air environment. The fatigue strength for 90,000 cycles, i.e. 25 hours was equal to 150 MPa, i.e. 90% of the ultimate tensile strength of the material under the combustion environment condition, Residual tensile strength of fatigue tested specimen at room temperature was almost equal to that of the virgin material which showed that there was no degradation in the test material from the combined fatigue and combustion exposure. Normalized fatigue strength, i.e. ratio of the fatigue strength and ultimate tensile strength at a certain number of cycles to failure, as well as damage mechanisms were almost similar in combustion and laboratory air environments. This suggested that the combustion environment condition was not damaging to the Nexte1720/alumina.
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