Revealing thermal shock behaviors and damage mechanism of 3D needled C/C-SiC composites based on multi-scale analysis

Understanding thermal shock behaviors and related damage mechanism of needled C/C-SiC composites is of much significance to their engineering application. In this study, a multi-scale framework is developed to characterize the degeneration of mechanical properties and damage accumulation in the needled composites comprehensively across different scales under cyclic thermal shock. Thermal shock temperature and thermal shock cycles are involved in the simulation, and the outcomes are verified with experiments performed in an inert atmosphere. The results show that the strength of C/C-SiC composites decreases continuously as the test temperature and thermal shock cycles increase. Meanwhile, the fracture of the material mainly occurs in the short -fiber felt. The damage initiates in the short -fiber felt near the contact area of the non-woven (NW) fiber tow and the needle-punched (NP) fiber tow when the test temperature is low (about 900 degrees C), and gets severe as temperature increases. With the increase of thermal shock cycles at 1700 degrees C, the fracture of the composites is more significant, and spreads from inside to the outer surface. Based on the multi-scale simulation and the microstructure of the composites after TSR tests, the primary damage mechanisms in the short -fiber felt are identified as ceramic-matrix damage and interface debonding.