Search Results

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.

Reliability research in hybrid ceramic bearings involves life testing of hybrid bearings and ceramic specimens. New materials for bearings like advanced ceramics have emerged for evaluation in recent years. In fatigue testing to determine the stress-life relationship, the number of sample size in life testing can be limited by consideration of cost and testing time. In the testing of ceramics, some researchers have relied on the use of a stepwise multiple loading approach to increase the failure data points. In this paper, a maximum likelihood method is applied to test data with multiple loads to estimate the stress-life exponent. This method treats the data at different loads or steps at once. Test data from three fatigue experiments using silicon nitride materials have been analyzed to obtain the stress-life exponents. Also, Weibull plots of the ‘equivalent lives' have been presented for all test specimens tested at different loads and load steps.

This paper describes the methodology and some computer-aided procedures for analyzing the contact of roller and a drawn cup bearing ring inside a housing of material of low tensile strength. The analysis can be used to predict the onset of plastic yielding in the housing. It also discusses the role of stresses arising from the press fit between the cup and the housing in preventing the relative slippage at the cup/housing interface and fretting corrosion. Illustrative examples are shown for a heavy duty drawn cup bearing with aluminum housing for a multitude of loads and cup thicknesses.

Microplastic deformation associated with rough surface and dents are found to generate tensile residual stress, which can be a source of surface fatigue. Both pre-existing hoop stress and friction-induced lateral normal stress parallel to surface are found to have an effect on the plastic strains and tensile residual stress. This finding can possibly explain many reported experimental observations that in rolling/sliding contact, the slower surface is more susceptible to surface fatigue than the faster mating surface. Micropitting probability and wear volume loss can be formulated based on Mode I crack growth process using the tensile residual stress as the fatigue criterion.