Durability and Damage Development in Woven Ceramic Matrix Composites Under Tensile and Fatigue Loading at Room and Elevated Temperatures

This paper investigates the damage development in SiC/SiNC woven composites under tensile and cyclic loading both at room and elevated temperatures. The ultimate strength, failure strain, proportional limit, and modulus data at a temperature range of 23°C–1250°C are generated. The tensile strength of SiC/SiNC woven composites has been observed to increase with increased temperatures up to 1000°C. The stress/strain plot shows a pseudo-yield point at 25 percent of the failure strain εf, which indicates damage initiation in the form of matrix cracking. The evolution of damage above 0.25 εf both at room and elevated temperature comprises of multiple matrix cracking, interfacial debonding, and fiber pullout. Although the nature of the stress/strain plot shows damage-tolerant behavior under static loading both at room and elevated temperature, the life expectancy of SiC/SiNC composites degrades significantly under cyclic loading at elevated temperature. This is mostly due to the interactions of fatigue damage caused by the mechanically induced plastic strain and the damage developed by the creep strain. The in-situ damage evolutions are monitored by acoustic event parameters, ultrasonic C-scan, and stiffness degradation. Rate equations for modulus degradation and fatigue life prediction of ceramic matrix composites both at room and elevated temperatures are developed. These rate equations are observed to show reasonable agreement with experimental results. [S0094-4289(00)02304-5]