EVALUATION OF K(1C) DEPENDING ON SAMPLE-SIZE FOR CERAMICS

The functional relationships between fracture toughness and sample siz e, and between fracture strength and sample size, for single-edge-notc hed-beam (SENB) specimens were derived. Experiments for size effects o f fracture toughness on Al2O3 and Si3N4 ceramics were carried out, and the results were identical with the theoretical ones. It is pointed o ut that the size effects of K1c, the size requirement as well as the r equirement of proportional specimens are derived from the calculation formula of fracture toughness. The formula is invalid when the size of specimens used is smaller that the critical size. Theoretical and exp erimental results indicate that, under the critical size, fracture tou ghness size has a peak value which is about 20% higher than the real t oughness value. The larger the specimen, the more reliable and more st able the measured toughness value. This study presents a useful means for error analysis of K1c measurement and for the evaluation of reliab ility of structural ceramics.