Abstract
Rolling fatigue tests were carried out on hot isostatically pressed silicon nitride bearing balls. At three load levels of the maximum Hertzian contact pressure pmax=5900, 6740 and 7110MPa, 13 balls each were tested, and the life distribution was studied. It was found that the rolling fatigue life followed approximately a 2-parameter Weibull distribution with the shape parameter of α≅1 at each load level. The relationship pmaxκL50=const (κ≅10) was found between pmax and the median life L50. Microscopic observation of flaking was also performed, and two types of flaking were found. One is flaking with the depth of the order of 100μm, and the other is a shallower one. The depth of the former type was found to coincide approximately with the depth at which the maximum shear stress occurred. At lower load levels, the former type was dominant. Frequency of appearance of the latter type increased with an increase in load level. Comparing the shape parameter of α≅1 and the exponent of κ≅10 mentioned above with those for the cyclic bending fatigue of plain specimens of silicon nitride, it was suggested that the mechanism of rolling fatigue of silicon nitride was different from that of cyclic bending fatigue of the same material.
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