Notch-Sensitive Fracture Behavior of a Silicon Carbide Fiber-Reinforced Glass-Ceramic at Elevated Temperatures

The effect on high-temperature embrittlement of introducing a through-thickness notch in a multidirectional silicon carbide fiber-reinforced calcium-aluminosilicate glass-ceramic composite was investigatedthrough tensile testing, microdebonding, and light and scanning electron microscopy techniques. Thefracture mechanism of the composite changed from notch insensitive at room temperature to notch sensitiveat elevated temperatures due to increased fiber-matrix bond strength caused by oxidation effectsat interfaces exposed to the oxidative environment. Stress concentration and bending effects at the notchtip resulted in growth of the notch through fibers in a planar fashion covering the entire fracture surface.This was contrary to the case of an unnotched composite, for which two distinct fracture surface regionswere observed as planar embrittlement zones at the periphery and fibrous at the center. Cracks inthe notched composite were more closed relative to those in the unnotched one, except at the notchtip. Concentration of the stress at the notch tip increased the high-temperature embrittlement effecton the composite.