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The stress-rupture and stress-relaxation behavior of carbon fiber-reinforced melt-infiltrated silicon carbide composites was investigated in ambient air at 1000°C. It was found that the compliance of the material increases continuously with time when subjected either to a constant composite stress or strain in air at 1000°C. The changes in compliance are explained based on the oxidation of the fiber coating, and on the oxidation, loss of cross-sectional area and rupture of the reinforcing fibers. In the case of stress-rupture, the load previously carried by failed fibers is redistributed to their surviving neighboring fibers inducing further fiber failure. During stress-relaxation, fiber failure is reflected directly on the reduction of the load carried by the composite.
By monitoring the expansion of the specimens during heating, prior to the application of the stress or strain, it was possible to determine the liner coefficients of thermal expansion of the material between 200°C and 1000°C.
ceramic-matrix composites, stress-rupture, stress-relaxation, oxidation, thermal expansion, melt infiltration, silicon carbide, carbon
Group leader, Mechanical Characterization and Analysis Group, Oak Ridge National Laboratory, Oak Ridge, TN
Senior scientist, Dynacs Engineering Co., NASA Glenn-Research Center, Cleveland, OH