Observations of fatigue damage process in SiC/SiC composites at room and elevated temperatures

Scanning Electron Microscope (SEM) in-situ observation of fatigue damage process of SiC/SiC composites was carried out at room and elevated temperatures. Although single edge V-notched specimens were used, fatigue crack initiated not only at the notch root but also at large pores far from the notch. The widespread damage means that the parameter of linear elastic fracture mechanics cannot be used to describe fatigue crack growth behavior of SiC/SiC materials. Instead, modulus of rigidity (MOR) may be used as a parameter to estimate fatigue damage process. The crack behavior was divided into two types of damage modes depending on the orientation of fiber bundles in front of a notch. No matter which type of damage mode, the final failure occurred at about 85% of the maximum value of MOR.