Study on the Failure Assessment Diagram of Ceramics

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Fracture behaviour of ceramics was examined in the range at a room temperature to 1200^ﾟC. Based on these results, a process zone size criterion for ceramics was proposed. In results, it was possible to assess the fracture characteristics of ceramics quantitatively, and gave following conclusions.1)Using the same material, the statistical properties of fracture stress-sigma_F and fracture toughness K_<1C> was examined. In results, the dispersion characteristics of sigma_F and K_<1C> evidently conformed to the Weibull distribution. And the value of shape parameter alphafor K_<1C> is large than that for sigma_F.2)In the range at a room temperature to 1200^ﾟC, fracture stress sihma_F tend to decreased with a gain of temperature. On the other hand, fracture toughness K_<1C> tend to increased.3)It was impossible to evaluate the strength properties for ceramics with short crack by linear fracture mechanics. Fracture stress of ceramics show dependence on crack length. The proposed process zone size criterion can be accepted as a rational evaluation method for the fracture behaviour of ceramics. Furthermore, the past five other types of ceramics was examined. those data agreed fairly well process zone size criterion.4)A evaluation method for notched material was also proposed based on process zone size criterion. It was possible to assess the dependence of fracture toughness for notch tip radius quantitatively on three other types of ceramics.5)A failure assessment diagram for ceramics was proposed based on probabilistic concept and process zone size criterion. In this way, it was possible to assess the reliability for ceramics easily and conservatively.