Effect of flaws on the strength of Si3N4

Fracture-mechanics analysis and fractographic studies were performed to assess the effect of surface flaws on the strength of Si₃N₄. The critical surface-flaw size calculated from fracture-mechanics analysis was in agreement with the fractographically observed flaw size. A comparison of the results of fracture-mechanics calculations with fractographic observations indicates that the failure-initiating flaws grow subcritically before failure. The subcritical growth of these flaws and hence the strength is greatly influenced by the microstructure and grain-boundary phases. Paper was presented at the 1986 SEM Fall Conference on Experimental Mechanics held in Keystone, CO on November 2–5.