INFLUENCE OF SURFACE-ROUGHNESS SKEWNESS ON ROLLING-CONTACT FATIGUE LIFE

Rolling element bearings operating under mixed or boundary lubrication conditions experience a higher metallic contact ratio (MCR) between the surfaces, and a corresponding decrease in rolling contact fatigue life. This paper evaluates the effects of randomly distributed small indentations, or pits, on the lubricating properties when operating under these mixed or boundary lubrication conditions. Rings and needle rollers were textured with randomly distributed small indentations, or pits, for evaluation. Skewness (Sk) was used as a measure of surface finish to characterize the degree to which the material of these modified parts was above the mean line, a positive value, or below the mean line, a negative value. Fatigue life tests were conducted on these rolling elements, whose skewness ranged from -1.2 to -2.0, under mixed or boundary lubrication conditions. Test results showed rolling bearing fatigue life to increase with a decrease in skewness as related to the depth, width, and distribution of the surface indentations, or pits, on the parts.