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Rolling bearings are rated for their capabilities to withstand rolling contact fatigue. All other means of bearing failure are considered preventable through proper attention to bearing manufacture, mounting, lubrication, and minimization of contaminant ingress. The standard methods for calculation of rolling bearing capacities and fatigue lives are based on the 1947 and 1952 publications of Lundberg and Palmgren. They defined separate material factors for ball bearings and roller bearings fabricated from 52100 steel, through-hardened to at least 58 Rockwell C; the fatigue life predictions, were strongly influenced by these capacity-multiplying factors. The standard was in use for less than five years, when it became apparent bearings fabricated from ever-cleaner materials; for example vacuum degassed and vacuum melted steels, were out-performing standard life predictions. Moreover, tapered and cylindrical roller bearings routinely fabricated from carburizing steels such as SAE 4118, 4320, 8620, etc. were not directly covered by the standards. This deficiency is accommodated by the use of material-life factors applied to the Lundberg-Palmgren life equations. The Society of Tribologists and Lubrication Engineers (STLE) recommends the use of separate material-life factors to cover basic steel metallurgy, heat treatment, and metal shaping. It has been demonstrated that, together with other life factors for lubrication effectiveness and contamination, this cascading of life factors is insufficiently accurate to predict life because in most cases, these effects on bearing endurance are interdependent.
In 1985, Ioannides and Harris published a rolling bearing life prediction method based on applied and induced contact stresses and body stresses. The resultant material stresses could be combined by classical strength of materials methods of superimposition; these resultant stresses could then be compared against fatigue limit stress as the material strength criterion to determine resistance to fatigue. From 1992 through 2000, the United States Navy funded a research project to establish appropriate fatigue limit stress values for common and special rolling bearing materials and to employ such values in computerized calculation tools to effectively apply this technology to modern bearing applications. This paper presents these developments.
Ball bearings, roller bearings, rolling bearings, fatigue life, fatigue limit stress, stress-life method
Professor of Mechanical Engineering, Pennsylvania State University, University Park, PA