Thermo-mechanical coupling failure mechanisms of reusable SiCf/SiC composites with PyC interphase

The extreme and repeated aerothermal environments working on reusable launch vehicles bring challenges for the design of hot structure. Due to the outstanding high-temperature resistant, SiCf/SiC composite is an excellent candidate material for hot structures in re-entry vehicles. In this paper, the thermo-mechanical coupling failure mechanisms of SiCf/SiC composite are investigated comprehensively. Experimental results reveal different failure mechanisms of SiCf/SiC composites subjected to monotonic quasi-static tension at room temperature and high temperature, cyclic thermal fatigue and thermo-mechanical coupling fatigue. Cyclic thermal environment causing oxidation of interphase layer and embrittlement of fiber plays a significant role in decrease of load bearing capacity of SiCf/SiC composites. The long-term periodic fatigue load that is superimposed on the cyclic thermal condition would further deteriorate the performance of materials. To better understand the damage evolution process, a thermo-mechanical coupling fatigue model is proposed to describe the degradation of SiCf/ SiC composites for different stress levels. The service life of SiCf/SiC composites is obtained, which could be used to evaluate the reusable performance of SiCf/SiC hot structure. The results of this study provide novel insights into the design of SiCf/SiC composites for reusable launch vehicles under prolonged and repeated service environment.