Influence Of Inhomogeneities On The Lubrication,Contact And Vibration In Rolling Bearings

As a key fundamental mechanical element,the precision of rolling bearing directly affects the performance of equipment.Under high-speed/heavy-load conditions,the precision of bearings may degrade during operation: on the one hand,due to the deformation and wear in service,the rotation error will be amplified,and then result in recession of bearing precision;on the other hand,due to impurity of bearing material,non-metallic inclusions in material will induce the inelastic displacement on raceway and therefore the change of contact pressure,the aggravation of stress concentration.The current studies mainly focus on the impact of inclusions on stress distribution and rolling contact fatigue,while its effect on precision retentivity has not been taken into account.In present thesis,a multi-factor coupled lubrication contact model and a rolling bearing dynamic model with the consideration of material inhomogeneities are established,and the influences of material inhomogeneity on the lubrication,contact and vibration of rolling bearings are studied.The main contents are as follows:(1)With consideration of the coupled effect of material impurity,surface roughness,plastic deformation etc.,an elastic-plastic contact model is established.Based on the conjugate gradient method(CGM)and fast Fourier transform(FFT)based method,the model is solved with high efficiency and good convergence.The various simulations are conducted for the effects of non-Gaussian rough surfaces,material inhomogeneities and hardened layer of heat treatment and the results show that different kinds of rough surfaces have great influence on the elastic-plastic contact behavior,where the negative skewness surface results in smaller average contact pressure and larger contact area;the hard inhomogeneity causes surface bulge and then increases the local contact pressure,while the soft inhomogeneity has the opposite effect;hard inhomogeneities in the high stress region always generate stress concentration.The hardened layer of heat treatment should be at least ten times of Hertz contact radius.(2)It is established a multi-factor coupled lubrication contact model in which the coupled influence of material inhomogeneity,oil supply condition,surface roughness and plastic deformation etc.is fully considered.The results show that the influence of inhomogeneity on the contact pressure and the film thickness is smaller than the surface roughness;the effect of roughness on the stress distribution is limited to the surface layer,while the effect of inhomogeneity is confined to the interior and vicinity of the inhomogeneity.In the oil-air lubrication,the size and position of oil drops have a great effect on the lubrication performance.(3)A rolling bearing dynamic model with consideration of material inhomogeneity is proposed,and the effect of inhomogeneities in the races on bearing vibration is investigated systematically for the first time.Through studying the effect of different sizes,depths,shapes,numbers and distributions of inhomogeneities on bearing vibration,it is found that the inhomogeneity in inner raceway makes the system motion more complicated,where the periodic motion becomes multiple periods or even chaos and more vibration occurs at low or side-band frequency;however,the inhomogeneities in outer raceway have smaller effect.The size and depth of inhomogeneity on the bearing vibration is obvious,and the larger and shallower inhomogeneity leads to more vibration,while the shape and number of inhomogeneity have less effect on the bearing vibration.(4)The vibration experiment and modeling analysis of ball-ring system and rolling bearing system are carried out,which verify the dynamic model of bearings considering material inhomogeneity and validate the effect of bearing vibration caused by the material inhomogeneity.