Effects of cyclic loading and temperature on a SiC-coated carbon/carbon composite in a combustion environment

The damage mechanism of SiC-coated carbon/carbon composites subjected to cyclic loading in a combustion gas environment was investigated. At the maximum cyclic stresses <90 MPa, the hysteresis and ratchetting strain responses indicated that the damage evolutions were similar at both 1300° and 1800°C. As the applied stress was sufficient to open the coating cracks, rapid failure of the composite was observed. Because of the enhancement mechanism caused by the cyclic loading, the residual strengths of the cyclic-loaded specimens exposed to the combustion environment were higher than those of the specimens not exposed to cyclic loading. Acoustic emission activities throughout the tensile tests of the cycled specimens showed that little damage was produced before the applied tensile load exceeded the maximum history load of the cyclic loading tests.