On the Impact Strength Characteristics of Fine-Ceramics involving the Surface Damage by Repeated Impact Load.

工程陶瓷的机械性能有两个相反的方面；为了表征精细陶瓷的断裂韧性，从两个不同的角度进行了一系列实验：一个是室温和高达1200℃高温的冲击三点弯曲试验，另一个是反复冲击载荷的表面损伤试验。对前一次测试的结果进行了评估。考虑到陶瓷的未来应用，后一个实验使用了陶瓷/钢的钎焊接头。在这项研究中使用了三种工程陶瓷；本研究的主要结论总结如下：（1）室温冲击三点弯曲试验结果：在各温度水平下比较，氮化硅的冲击弯曲强度均高于静态弯曲强度。此外，冲击弯曲下的强度分布与静态弯曲下的强度分布几乎相同。由此得出结论，氮化硅在高温下具有优异的冲击强度。另一方面，当在低失效概率下进行评估时，碳化硅在高温下表现出低冲击强度。 (2)表面损伤试验结果：氮化硅表面损伤观察表明，宏观裂纹从陶瓷盘中心呈放射状扩展；用钢锤压痕。

Engineering ceramics have two opposite aspects in their mechanical properties; low fracture toughness and high strength at high temperature together with excellent wear properties.In order to characterize the fracture toughness of fine ceramics, a series of experiments was carried out from two different points of view: One is impact 3-point bending test at room and high temperatures upto 1200゜c, and another is surface damage test by repeated impact load. The results of the former test were evaluated statistically. Brazed joints of ceramics/steel were used for the latter experiment considering the future application of ceramics. In this study were used three sorts of engineering ceramics; sintered silicon nitride, reaction sintered silicon carbide and alumina.Major conclusions of this study are summarized as follows: (1) Results of impact 3-point bending test at room thigh temperature: The impact bending strength of silicon nitride is higher than the static bending strength when compared at each temperature level. And further the scatter of strength under impact bending is almost the same as that of static bending. Thus, it is concluded that silicon nitride has excellent impact strength at high temperature. On the other hand, silicon carbide shows low impact strength at high temperature when evaluated at low failure probability. (2) Results of surface damage tests: Observations of surface damage of silicon nitride indicated that macro-cracks propageted radially from center of ceramics disc; the indentation by steel hammer.