R-CURVE MEASUREMENT OF SILICON-NITRIDE CERAMICS USING SINGLE-EDGE NOTCHED BEAM SPECIMENS

R-curve behaviour of three kinds of silicon nitride-based ceramics has been studied using the single-edge notched beam (SENB) technique. If the notch is deep enough, the specimen shows stable fracture during th e bending test, even when the sample is a brittle material. The condit ions required to obtain stable fracture in the bending test are clarif ied by the analysis. The crack length of the specimen was also calcula ted from the changing load during the fracture test. In this study, co arse-grained silicon nitride shows a large increase of the R-curve. On the other hand, silicon nitride with silicon carbide whiskers shows n o R-curve increase. The rise of the R-curve should be related to the m icrostructure of the ceramics, and especially to the grain size of the specimen, because silicon carbide whiskers are not large compared to the silicon nitride grains, and silicon carbide can reduce the grain g rowth of silicon nitride during sintering.