Bearing defect data from 8,000 railroad roller bearings are analyzed to determine their defect modes and defect rate distributions. Cone bore growth, brinelling, and fatigue are identified as the predominant defect modes as bearings age at least through age 12 years. The results of the study show that, after only two years of service, ten percent of all railroad roller bearings exhibit a defect of one type or another for which at least one component would be condemned if it were in a rework shop. The present AFBMA method of calculating fatigue spalling, modified to account for lubricant film thickness effects, correlates reasonably well with the observed incidence of spalling (10 percent fatigue life of about 11 years). The problem lies in the fact that the AFBMA calculation procedure ignores the other competing defect modes which contribute far more to the overall defect rate than does spalling. The relationship between “defect rate” and “failure rate” is not direct, of course, and an examination of “condemning limit” definitions relative to the progression of bearing failure in service is needed.

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