Fatigue of C/C composites in bending and in shear modes

The fatigue of C/C composites was investigated in bending and shear modes. In bending, a large stress ratio resulted in a decrease in strength; the decrease became small without water present. However, a large ratio led to a decrease in Young's modulus, regardless of the presence of water. In shear, degradation in strength or fatigue life decreased with increasing the ratio. For specimens fatigue degraded in air, static strength in water decreased as compared with that in air. It is strongly suggested that fatigue degradation in C/C composites is promoted by a combination of stress corrosion and crack propagation promoted by a wedge effect.