Test methods for evaluating fiber/matrix interfacial properties of various carbon-carbon composites up to elevated temperatures

Experimental techniques for evaluating the interfacial properties between the fiber bundle and the matrix of carbon-fiber-reinforced carbon matrix composites (C/Cs) were examined. The C/Cs examined were unidirectionally reinforced (UD-), plain-woven (2D-) and three-dimensinally reinforced (3D-) C/Cs. Specially arranged fiber bundle push-out and pull-out tests were conducted for the three C/Cs. In these tests, a fiber bundle in the specimens was extruded or pulled out by external compressive or tensile loads. Post-fracture observations revealed that a shear fracture was successfully induced around the loaded bundle interface by the test methods examined in this paper. In particular, the interfacial properties of the 3D-C/C were evaluated up to 2273 K in vacuum. The interfacial shear strength and initial sliding stress of the 3D-C/C monotonically increased with the test temperature. The relief of the residual thermal stress in the carbon matrices and the increase in the frictional resistance at the debonded interface were considered to be the major mechanisms that caused the enhancements.