Mechanical Behavior of a Continuous-SiC-Fiber-Reinforced RBSN-Matrix Composite

The results of a detailed study are presented on the toughening of reaction‐bonded silicon nitride reinforced with large‐diameter SiC monofilaments at ambient and elevated temperatures. Composite stiffness, strength, toughness, and R‐curve behavior were investigated at ambient temperature, with strengths measured up to 1400°C. At elevated temperature, toughening mechanisms were explored by investigating crack initiation and growth under creep conditions. The results show that, at ambient temperature, the composite exhibited noncatastrophic failure with substantial toughening associated with contributions of both fiber pullout and elastic bridging of fibers in the crack wake, consistent with predictions using available models. Limited R‐curve measurements suggest that large‐scale bridging effects may be present. At elevated temperature, crack initiation occurred in the matrix at about 1000°C, but in the fiber at higher temperatures. Growth of cracks is governed by time‐dependent bridging of unbroken fibers in the crack wake, consistent with a model based on fiber pullout by viscous sliding of fibers out of the matrix along amorphous interfacial layers.