Research On Mixed Lubrication Performance And Fatigue Life Of High-speed Rolling Bearing

With the progress and development of aviation science and technology, the main shaftbearings in aircraft engine are required to work reliably under higher speed, highertemperature and heavier load conditions, which bring serious challenges to the design andmanufacturing technology of rolling bearings. Under the above severe working conditions,the rolling elements and raceways are operating in more harsh mixed lubrication regime,and thus the effects of the non-Newtonian characteristics of lubricants and surfacetopography on the lubrication properties and fatigue failure become more significant. Inaddition, the high sliding speed, spin speed and centrifugal force under high speedoperation conditions will have impact on the performance of thermal elastohydrodynamiclubrication (TEHL), which will ultimately affect the temperature, power loss and fatiguelife of bearings. However, there is still a lack of systematic research about the influence ofthese factors on the performance of high-speed rolling bearings.According to the operating conditions of aero engines main shaft bearings, a fatiguelife prediction model is established and systematic investigations about the temperaturecharacteristics, power loss and fatigue life of both hybrid ceramic bearings and steelbearings are conducted on the basis of the mixed lubrication model considering thenon-Newtonian and surface topography effects. The main contents are as follows:The effects of non-Newtonian characteristics of lubricants, material of the contact pair,surface topography, ellipticity and other factors on the performance of mixed lubrication areinvestigated. The results show that as the characteristic shear stress of the lubricantsincreases, the film thickness increases, but the magnitude of the pressure ripple increases.Rough surfaces with transverse texture features are more beneficial to the mixed lubricationproperties. The influence of roughness parameters skewness and kurtosis on the filmthickness is weak, but that on the maximum pressure is obvious. The maximum pressureand average film thickness decrease with the increase of ellipticity.Based on researches about the mixed lubrication properties considering thenon-Newtonian and surface topography effects, three-dimensional subsurface stress andfatigue life prediction models are established. Then, the influence of non-Newtoniancharacteristics of lubricants, material properties, surface texture and other factors on thesubsurface stress and fatigue life are studied. The results indicate that the frictioncoefficient and subsurface stress increase with the increase of the characteristic shear stress of lubricants, which eventually leads to reduction of fatigue life. The impact degree oflubricant viscosity on fatigue life depends on the lubrication conditions. Under mixedlubrication conditions, the fatigue life increases when the surface texture features changefrom vertical to transverse. The fatigue life decreases with the increase of the roughnessparameter skewness, while it undergoes apparent fluctuations with the increase of kurtosis.As the kurtosis increases, the influence of skewness on fatigue life becomes moresignificant, and vice versa. The increase of ellipticity contributes to the decrease ofsubsurface stress and increase of fatigue life.A non-Newtonian TEHL model considering spinning motion is established, and anefficient numerical solution method is developed. Then, the influence of entraining velocity,slide-roll ratio, and spinning speed on the temperature, power loss and fatigue life areanalyzed. The results demonstrate that the influence of entraining velocity on the rollingcontact fatigue (RCF) life has a close relationship with the ellipticity. The increase ofslide-roll ratio leads to a significant increase in the temperature and decrease in the fatiguelife, and the influence of slide-roll ratio depends on the entrainment velocity. The oil filmtemperature and the power loss increase with the increase of spinning speed. Although thefriction coefficient decreases in the presence of spinning, the RCF life is slightly decreased.The non-Newtonian TEHL model and the kinetic model of rolling bearings arecombined to study the temperature, power loss and fatigue life of hybrid ceramic ballbearings and steel bearings. The results suggest that an increase in the raceway curvatureratio will leads to reduce of total power loss significantly. Comparing with steel bearing, thehybrid ceramic bearing presents higher pressure, higher temperature and shorter fatigue lifeat low speed, while it shows lower temperature and longer fatigue life at high speed.Tribological properties of ceramic balls and steel balls under different lubricationregimes are studied experimentally. The results show that under mixed lubricationconditions, the friction coefficient of ceramic-on-steel contact pairs is larger than that ofsteel-on-steel contact pairs. The friction coefficients for ceramic ball and steel ball samplesare almost identical under full-film lubrication conditions. After the centrifugal force beingconsidered, the coefficient of friction for ceramic ball samples is less than that for steel ballsamples.