Cyclic fatigue of ceramic-matrix composites at ambient and elevated temperatures

Under cyclic loaning, the mechanical behaviour of ceramic-matrix composites changes with the number of cycles applied even at room temperature. In order to identify the microstructural mechanisms of damage due to cyclic fatigue, the macroscopic behaviour is experimentally observed from the lifetime diagram and the evolution of the stress/strain loops with the number of cycles applied. From this approach a micromechanical model has been developed where the cyclic fatigue effect is ascribed to interfacial wear between fibres and matrix. At high temperature, since the testing temperature is low enough to inhibit any physical and chemical change in the materials, the main effect of temperature is due to the release of residual thermal stresses. This phenomenon has been experimentally observed on two ceramic-matrix composites: SiC/SiC 2D and SiC/MAS L [0,90], where the signs of the residual thermal stresses are different. (C) 1996 Elsevier Science Limited