An Attempt for Measuring the Crack Extension Resistance of Ceramics by Fracture Test in Bending

Abstract

R-curve properties for two kinds of SiC whisker reinforced Si₃N₄ ceramic composite were obtained by three-point bending test. Single edge notched beam specimens with sharp tip radius were fractured under a slow cross-head speed of 0.002mm/min in air. Crack extension Δa was calculated from the change of the specimen compliance. Crack extension resistance K_R was also calculated from the crack extension Δa and the fracture load during stable fracture. The extent of K_R increase in the R-curve was more remarkable in the composite containing whiskers with larger diameter. Some theoretical and technical problems for measuring the crack extension resistance of toughened ceramics were discussed in this letter.