Research on Rolling Contact Fatigue Damage Behavior of M50 Bearing Steel in Aeroengine Rolling Bearing

Author:Guan Jian

Supervisor:wang li qin


Degree Year:2019





High-end equipment and technology have been highly developed in the field of aerospace.Rolling bearing is now facing severe working condition,such as alternate heavy load,continuous overload and transformation of lubrication state.Such severe working condition will induce high contact pressure and shear stress.The rolling contact fatigue damage rate on the surface friction pairs is increased and failure of rolling bearing in the early stage will occur.The reliability and life of the equipment are limited.In order to enhance the reliability and fatigue life of rolling bearing,M50 bearing steel is applied as the major steel in bearing of high-end equipment.The thermo-hardness of M50 bearing steel is more excellent than common bearing steel due to the alloy element content.Alloy element and carbon element are likely to combine into carbides,which are easy to be crashed down.Meanwhile M50 bearing steel is extremely sensitive to the inclusions and voids in it.Hence the investigation of fatigue damage mechanism,the establishment of life prediction method are quite significant for M50 bearing steel.The fatigue failure prediction model of M50 bearing steel containing inclusions with non-regular shape is established on the basis of Voronoi finite element model and continuum damage mechanics.Voronoi finite element method can simulate the microstructure and size of grains.The model built in this paper considers the load sequence effect and material properties instead of crack size.The effects of bearing load and lubrication state on fatigue damage are investigated combining quasi-dynamic method.The critical value of load under which the roller bearing can work without rolling contact fatigue damage is given.Fatigue damage will not occur when the load is less than the critical value.The effects of inclusion parameters(elastic modulus,size and depth)on stress distribution and fatigue damage are investigated.The results show that higher elastic modulus,larger size and shallower depth will induce more severe fatigue damage.The critical value of inclusion’s size and depth is determined.The model containing real inclusions is completed by the combination of image processing and finite element method.The fatigue damage induced by inclusion is more severe when the morphology of inclusion is more complicated.The fatigue damage evolution of the micro-domain containing a large amount of inclusions is analyzed.The results show that fatigue crack initiates from the site between two inclusions.The increasing of friction coefficient will urge fatigue cracks to grow to the contact surface.Fatigue damage and cracks will not generate when depth exceeds the critical value as the stress concentration effect induced by inclusion is weak.Fatigue cracks extend to a deeper depth with the increasing of inclusion’s elastic modulus.The results can provide theoretical support for heating technology of bearing steel.The refining of large inclusions can weaken the fatigue damage in bearing steel.The effects of load cycling on material hardening and the condition of shot peening and ion implantation on residual stress are analyzed.Load cycling and residual stress can separately increase the hardening exponent and stress amplitude in the model.The variation of the parameters will reduce the rate of fatigue damage accumulation and prolong the fatigue life of M50 bearing steel.The effects of surface roughness on fatigue damage accumulation and crack propagation are analyzed.The simulation results show that transverse texture,negative skewness value,lower mean square value and kurtosis are beneficial for inhibiting cracks propagation and prolonging fatigue life.High contact pressure and friction are generated in local area under mixed lubrication state.The increasing of friction coefficient of local area will accelerate the crack propagation rate and reduce the fatigue life.The increasing of local area’s radius can also reduce the fatigue life and the fatigue life will remain stable when radius exceeds a certain value.Finally,the fatigue test of M50 bearing steel is completed on the ball-disk test rig in order to analyze the fatigue damage mechanism.The surface damage morphology is not alike under different loading sequence.More fatigue pitting is observed under high-low loading sequence.The fatigue damage model is used to simulate fatigue damage evolution under the same working condition in the tests and the result of theoretical analysis is matched with the observation in tests.It is proved that the model in this paper is reliable.The relation between fatigue cracks induced by inclusion and rolling direction is then investigated.The result shows that the direction of crack is merely affected by rolling direction.The elastic modulus,depth,and azimuth of inclusion will only affect the depth and shape of the crack.The Weibull distribution of fatigue life is separately obtained by theoretical model and fatigue tests.It can be seen that the model in this paper is able to predict the fatigue life of bearing steel.