Abstract
A quantitative method for assessing the influence of steel cleanliness on the fatigue life of rolling bearing raceways is presented. The approach systematically accounts for the effect of the highly variable stress state within raceways. Finite element analysis is used to determine the stress state in the bearings. A fracture mechanics model for the safe stress amplitude as a function of inclusion size is employed from Lewis and Tomkins. The size and number of large inclusions in a large volume of steel are estimated by the Generalised Pareto Distribution. These three elements are combined to determine the failure probability of the raceway in an example rolling bearing. A sensitivity analysis to the various microstructural input parameters is conducted. It is found that the size distribution of the larger inclusions is the most important factor in controlling the fatigue resistance of rolling bearings, and that residual stresses must be considered to produce realistic predictions.
Highlights
Lifing methods for rolling element fatigue were developed by Lundberg and Palmgren in the 1940s and 50s by analysis of many hundreds of tests on small bearings at contact stresses well in excess of 2500MPa [1, 2]
Significant cyclic strain-induced metallurgical changes occur [3]. These changes consist of the formation of white etching areas (WEAs) and dark etching areas (DEAs) close to the running surface that are orientated at specific angles
It is found that finite element analysis is required for accurate simulation of doubly curved surfaces which undergo large deformations
Summary
Lifing methods for rolling element fatigue were developed by Lundberg and Palmgren in the 1940s and 50s by analysis of many hundreds of tests on small bearings at contact stresses well in excess of 2500MPa [1, 2] Under these conditions, significant cyclic strain-induced metallurgical changes occur [3]. They carried out a small number of tests on 6309 deep groove ball bearings under two different steel qualities and lubrication conditions (high and low , where λ is the ratio of oil film thickness to combined surface finish of the surfaces) They concluded that values of the shear stress fatigue limit τu = 300 and 350MPa applied to the bad and good quality steels, whilst values of von Mises stress σuM= 519 and 606MPa were correspondingly obtained. This is a simplified model, but introducing a more sophisticated model will not have an observable qualitative effect on the final results
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