Damage analysis of 2D C/SiC composites subjected to thermal cycling in oxidizing environments by mechanical and electrical characterization

Damage in 2D C/SiC composites subjected to thermal cycling in wet oxygen atmosphere was analyzed by both mechanical testing and electrical resistance measurement. The microstructures were observed on a scanning electron microscope and a novel monitoring system was developed to acquire automatically and analyze the resistance of composites during their dynamic damage. Results show that under cyclic temperature, matrix cracks and delaminates transversely as regular spacing and superficial fibers are susceptible to oxidation through the opening cracks, leading to two types of major fiber failure pattern: (i) physical fracture under thermal cycling and (ii) chemical recession in oxidizing atmosphere. They are considered to be responsible for mechanical degradation with increasing thermal cycles. In electrical testing, resistance decreases upon heating and increases with cooling in each cycle. As cycling progresses, the baseline resistance decreases continuously and then levels off after about 35 cycles, which is consistent with the statistical result (about 38 times) of mechanical testing.