R-Curve Behavior of Si3N4/BNNT Composites

The crack propagation rsistance behavior of Si₃N₄ ceramics reinforced by boron nitride nanotubes (BNNT) has been discussed in the work. And, bending strength and fracture toughness of Si₃N₄/BNNT composites were tested by three point bending method. It is shown that crack propagation resistance of BNNT/Si₃N₄ composites is increased distinctly owing to addition of BNNT. It is attributed to the pinning and bridging roles of BNNT. One kind of mathematical model was constructed for calculating crack propagation resistance of Si₃N₄ ceramics and BNNT/Si₃N₄ composites. Crack resistance curve (R-Curve) of Si₃N₄ ceramics and BNNT/Si₃N₄ composites was also calculated. Crack propagation of them was simulated using finite element methods. The results show that strong shielding area is formed in crack tip owing to existence of BNNT and crack propagation is prevented by strong stress shielding roles.