CHARACTERIZATION OF INTEGRATED DATA ON INHERENT FLAWS IN ENGINEERING CERAMICS(Special Issue on Hierarchical Estimations of Materials Strength)

Abstract

Integrated data on inherent flaws in engineering ceramics were characterized for quantitative analyses of them. For this purpose, a ceramic strength database utilized on a personal computer was temporarily constructed so that collected data on flaws could be compiled as records in the database. It was clarified that distributions of the equivalent crack length l for several ceramics were nearly fitted to normal distribution functions. The distribution of l was investigated for every type of flaw, and it was found to shift toward a longer length region in the order of embedded, surface, and corner flaws. The flaw data were also correlated with strength and microstructural parameters. In the relation to the strength, the strength was reduced as a whole with the decrease in the crack length, while the lower bound of strength scatter was predicted by a modified relation of the fracture mechanics criterion for long cracks. It was revealed that the flaw size increased with the increase in the grain size or the porosity. The relation of a Petch-Hall type was observed between the grain size and the mean strength estimated by using the mean value of l. Some useful suggestions were offered for the improvement of ceramic strength.