Effect of Thermal Expansion Mismatch and Fiber Coating on the Fiber/Matrix Interfacial Shear Stress in Ceramic Matrix Composites

A modified indentation technique has been used to measure the interfacial shear stress in a number of ceramic matrices containing silicon carbide fibers. It was shown that the frictional component of interfacial stress was essentially zero when matrix thermal expansion was lower than that of the fiber and increased linearly with thermal expansion mismatch when matrix thermal expansion was higher. The interfacial shear stress was lowered when the fibers were coated with BN. Lower matrix shear stresses resulted in a more extensive fiber pullout during the composite fracture.