The effect of applied stress on damage mode of 3D C/C composites under bend-bend fatigue loading

The bend-bend fatigue behavior of 3D integral braided carbon/carbon composites (3D C/C) was examined. Fatigue test was conducted under load control at a sinusoidal frequency of 10 Hz to obtain stress-fracture cycles (S-N) relationship. The fatigue limit of the C/C was found to be 203 MPa (92% of the static flexural strength), the lag loops of fatigue load-displacement were transformed from elasticity to anelasticity and the flexibility of specimens were enhanced with increase in applied stress. It is revealed that the interfacial sliding abrasion played an important role in the fatigue failure process, and the extent and speed of sliding abrasion were controlled by the level of applied stress.