An oxide-oxide CMC with no interface, Nextel720~(TM)/alumina, was investigated under tension-tension fatigue condition at three frequencies (I, 100 and 900 Hz) to characterize the effects of cyclic frequency at room temperature. Cycles to failure at a stress level increased considerably with increase of the cyclic frequency from 100 to 900 Hz, but not much between 1 and 100 Hz. Local fiber/matrix interfacial bonding due to the frictional heating at the highest frequency of 900 Hz was observed during cycling. This may have caused an increase in the fatigue life/strength of the tested CMC system at the highest frequency of 900 Hz.
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