Effect of fatigue damage on distribution of cracks in 3D C/SiC composites

X² goodness-of-fit test was introduced to investigate the distribution of the cracks on the matrix and the coating of 3D C/SiC composites before and after fatigue testing. The results show that the crack spacing of the matrix and the coating in the as-received composites obey the normal distribution N(143.75, 56.78²) and N(562.59, 100.09²), respectively. After fatigue testing, the crack spacing of the matrix and the coating obey the normal distribution N(105.48, 29.16²) and N(227.89, 25.23²), respectively. The distribution regularities are determined by the three dimensional braided structure of the composites. More cracks are brought in the matrix and the coating due to the fatigue stress, but the character of normal distribution is unchanged.