Fracture mechanism of Hi-Nicalon SiC fibers annealed at high temperature

Hi-Nicalon silicon carbide fibers were annealed at 1400°C, 1600°C and 1800°C for 10 h in argon atmosphere, respectively. The strength of fibers was determined by monofilament tensile testing machine. The tensile strength was statistically analyzed with Weibull distribution and the fracture surfaces of the fibers were observed by SEM. The results indicate that the strength of the fibers obeys Weibull distribution, and the tensile strength decreases with the increase of annealing temperatures. After being annealed at 1800°C for 10 h, the specimens show cleavage fracture. Statistical analysis reveals that the defects in fibers' surface have negligible effect on their strength, most of cracks initiate at the inner region of fibers, and the specimens show brittle/flat fracture.