Durability and damage development in woven ceramic matrix composites undertensile 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. T he ultimate strength, failure strain, proportional limit, and modulus data at a temperature range of 23 degreesC-1250 degreesC are generated. The tens ile strength of SiC/SiNC woven composites has been observed to increase wit h increased temperatures up to 1000 degreesC. The stress/strain plot shows a pseudo-yield point at 25 percent of the failure strain (epsilon (f)), whi ch indicates damage initiation in the form of matrix cracking. The evolutio n of damage above 0.25 epsilon (f) both at room and elevated temperature co mprises of multiple matrix cracking, interfacial debonding, and fiber pullo ut. Although the nature of the stress/strain plot shows damage-tolerant beh avior under static loading both at room and elevated temperature, the life expectancy of SiC/SiNC composites degrades significantly under cyclic loadi ng at elevated temperature. This is mostly due to the interactions of fatig ue 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 cera mic matrix composites both at room and elevated temperatures are developed. These rate equations are observed to show reasonable agreement with experi mental results. [S0094-4289(00)02304-5].