Study on the Failure Assessment Diagram of Ceramics

在室温至1200 ℃范围内研究了陶瓷的断裂行为。在此基础上，提出了陶瓷加工区尺寸的判据。结果表明：（1）用同一材料，研究了断裂应力σ_F和断裂韧性K_的统计特性<1C>。结果表明，σ_F和K_F的离散特征明显<1C>符合威布尔分布。2<1C>）在室温至1200 ℃范围内，断裂应力σ_F随温度的升高而减小。而断裂韧性K_<1C>有增大的趋势。3）对于含短裂纹的陶瓷材料，用线性断裂力学方法无法评价其强度性能。陶瓷的断裂应力与裂纹长度有关。提出的工艺区尺寸准则可作为陶瓷断裂行为的合理评价方法。此外，过去五种其他类型的陶瓷进行了检查。4）提出了基于工艺区尺寸准则的缺口材料性能评价方法。5）提出了基于概率概念和过程区尺寸准则的陶瓷失效评定图。通过这种方式，可以轻松且保守地评估陶瓷的可靠性。

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.