Characterization of R-curve behavior in Si3N4-based ceramics

The exponential function proposed by Ramachandran and Shetty (J. Am. Ceram. Soc., 74 (1991) 2634–2641) was employed to describe the R-curves measured by directly observing the stable growth of annealed indentation cracks in the tensile surface of the specimen during bending test of four grades of Si3N4-based ceramics. It was shown that this exponential function gives a satisfactory description for the experimental data measured from each individual crack. A detailed explanation for the physical meanings of the adjustable parameters included in this function was then presented. Some useful parameters, including the critical crack resistance, the threshold crack resistance and the flaw tolerance, were also deduced based on the analysis of the experimental data.