Yoshinobu Akamatsu

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 sur...

Effects of Low Speed on Roller Bearing Fatigue Life

Two test series were conducted to study the effect of low speed and high load on the rolling-element fatigue life of 30 mm and 40 mm bore cylindrical roller bearings at inner race speeds from 19 to 3725 rpm and lubricant film parameter Lambda (λ) ratios from 0.03 to 1.2. Maximum Hertz stress ranged from 2.24 to 4.2 GPa (325 to 609 ksi). A total of 387 bearings were tested out of which 123 failed. Bearing life was directly related to transit contact lime (TT). As TT increases, life also increases. That is, bearings which run slower have longer lives in terms of bearing revolutions. A transit time life factor (LF) is suggested to be used with STLE life factors for slow moving industrial equipment roller bearings. Both TT and the total number of stress cycles affect the magnitude of measured surface residual stress induced during bearing operation. There was a relation observed between the decomposition of retained austenite and induced compressive residual stress measured on the inner-race surface. Presente...