Fatigue behavior of 2D laminate C/C composites at room temperature

Fatigue behavior was examined for three kinds of carbon fiber reinforced carbon matrix composites (C/Cs). The fatigue-tested materials included unidirectionally reinforced (UD), symmetric cross-ply laminated (CP) and symmetric quasi-isotropically laminated (QI) C/Cs. The fatigue fracture behavior of the C/Cs was classified into three regions based on applied strain, irrespective of the C/C types. In high applied strain region, fatigue fracture occurred in the same manner as in the static tensile tests. In the second region, where the applied stress is up to the fatigue limit, the strength of the C/Cs decreased slightly due to the degradation of the fiber strength caused by frictional wear along the fiber/matrix interface. The third region was at lower applied strain than the fatigue limit, in which no fatigue fracture occurred and the residual strength was recovered and sometimes enhanced due to damage at the fiber/matrix interface.