Tension-tension fatigue of a cross-woven C/SiC composite

The tension-tension fatigue behavior of a cross woven C/SiC composite was studied in terms of damage modes and damage development. The fatigue stress versus life diagram (S-N) curve and an endurance limit of 320–340 MPa (about 80% tensile UTS) for 106 cycles were obtained for the C/SiC composite. Different fatigue behaviors were found for samples that failed during fatigue and for samples that survived 106 cycles. Seven fatigue damage modes were observed, the development of which were used to explain the different fatigue behaviors. For the fatigue-failed samples, the degrees of damage of the seven modes increased with increase of cycles, leading to an increase in elapsed strain and a decrease in composite modulus. For fatigue-survived samples, the development of all the damage modes except for fiber breaking caused an initial increase of elapsed strain and decrease of composite modulus, but at high cycles, fiber bundle realignment and straightening in these samples led to partial recovery of the modulus and cessation of the damage development.