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For about three decades, the Lambda ratio, i.e. the ratio of Ehd film thickness to the composite surface roughness has been used as an indicator for bearing lubrication as well as the basis for bearing load rating improvement. Although the film thickness and the Lambda ratio are relatively independent of load, the initiation of surface fatigue, or micropitting is load dependent. Furthermore, in the low Lambda region, the bearing surface fatigue and life ratio are more dependent on roughness than on film thickness. This paper reexamines the role of Lambda ratio and other parameters on bearing surface fatigue and bearing life ratio, by taking into consideration the severity of asperity interactions and microplastic deformation,

A close examination has been made on the result of experimental research on surface fatigue in the low Lambda regimes. These experiments consist of two kinds. One is the endurance test of needle bearings, ball bearings and roller bearings with different surface and lubrication conditions. The other is the test with disk machines to observe peeling (or micropitting). The study shows that the Lambda ratio is not the only parameter which affects the surface fatigue of bearings. In most cases, the life ratio depends more strongly on the composite rms surface roughness than on film thickness. Thus, in addition to the Lambda ratio, the effects of asperity height/tip radius ratio, nominal contact pressure, mean separation, lubricant inlet starvation, surface defect, hardness and the compressive residual (or tensile hoop) stress on surface fatigue, should be taken into account.