窒化けい素セラミックスの疲労強度に及ぼす欠陥の影響

概要

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Microstructure of engineering ceramics, especially the distribution of defects and the density, sometimes varies wity the lot of manufacture. For this reason,it is important to investigate the influences of the microstructure upon the mechanical properties. In this study, the rotating bending fatigue tests were carried out on two lots of Si_3N_4 ceramics, and the influences of the defects and density upon the fatigue strength were investigated. Bulk densities of lots A and B were 3.02 g/cm^3 and 3.16 g/cm^3, respectively. Average static bending strength of lot B was about 20 percent higher than that of lot A due to the differences in defects distribution and fracture toughness. However, the two lots scarcely differed in rotating bending fatigue strength. This is considered to be because the fatigue strength laegely depends on the size and kind of defects. Fatigue strength was predicted on the basis of a fatigue datum in the case when the fracture origin was the largrst pore defect. Crack propagation rate was assumed to be in proportion to the power of the stress intensity factor. Consequently, when the fracture origin was a pore defect with inclusion or a micropore cluster, the fatigue strength was higher than the predicted value, in most cases. Therefore, the fatigue life prediction based on pore defects leads to reliable estimation.
社団法人日本材料学会の論文
1992-01-15