Co-Operative Research on Fatigue Failure at Contact Surface

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In order to clarify the mechanism of surface fatigue in contact, two-roller test, three dimensional rolling contact test (simulated the contact condition of rail and wheel), fretting test and repetitive compression test were conducted. By two roller tests, following conclusions were obtained: (1) Asperity interaction of surface roughness is most important factor for occurrence of rolling fatigue, i. e., pitting, micro pitting and spalling. (2) In especial, the running-in condition is controlled by the asperity contact frequency Naf, defined by the number of contact positions of higher hardness roller with different microgeometries which are brought into contact with any one position of mating lower hardness roller, and Naf controls the severity of asperity contact and the occurrence of rolling fatigue. (3) The rolling fatigue limits under severe asperity contacts are determined by the limiting Hertzian pressure where running-in occurs or not. (4) Micro-Pitting of carburized steel are c … More ontrolled by the value of roughness which is limit of occurrence of running-in. By fretting tests, it was clarified that the tangential traction have an influence on the contact fatigue by promoting the occurrence of tensile stresses which always appear in three dimensional contacts, owing to macro geometrical condition or micro asperity contacts. The occurrences of fatigue cracks in the macro geometrical three dimensional contact (i. e. the simulated rail-and-wheel contact) and the repetitive compression tests certify above conclusion. The gear tests and the repetitive compression tests also showed that particles of solid, e. g. the particles of solid lubricants contained in gear oil, are possible to be the sources of stress concentrations, and therefore it should be small enough. By the analysis of cracking from the failure mechanics, the propagations of cracks were predicted. Furthermore, it was shown that the running-in condition or the severity of asperity contacts can be estimated from the cross-corelation function of roughness profile measured three-dimensionally. Less