Characterization of Damage Accumulation in a Carbon Fiber-Reinforced Silicon Carbide Ceramic Matrix Composite (C/SiC) Subjected to Mechanical Loadings at Intermediate Temperature

Creep-rupture and fatigue tests were conducted to identify the failure modes and degradation mechanisms of a [0/90] carbon fiber reinforced silicon carbide (C/SiC) composite at 550 and 650°C. When compared on a maximum stress versus time to failure basis at a given temperature, fatigue testing yielded longer lives than creep-rupture testing. Tests conducted at 550°C had longer lives than 650°C tests. The rate of modulus degradation was similar for both temperatures and loading modes. Examination of tested specimens revealed that oxidation of the carbon fibers was the dominant damage mechanism for C/SiC at these temperatures and test conditions. The oxidation damage occurred globally within the surface of the specimen gage section, and locally in the interior of the composite, around pre-existing matrix cracks and pores. The results of this study indicate that, under the test conditions employed here, specimen life is governed by a combination of time at temperature and time-averaged stress and is not cycle dependent.