Study On Contact Fatigue Reliability Of Vehicular Cylindrical Roller Bearing With A Local Defect

As a key component of the transmission system,driving system and other mechanisms in the vehicle,the cylindrical roller bearing plays an important role in supporting and guiding the rotating shaft.Due to the complex and changeable driving conditions of the vehicle,the cylindrical roller bearing operates under time-varying load conditions for a long time,and the raceway surface of the bearing is prone to the crack,pitting,spalling and other local defects,which worsens the stress-strain and contact states and weakens the fatigue life and reliability of the cylindrical roller bearing.In order to ensure the reliable operation of the cylindrical roller bearing,the vehicle stability and personal safety,a vehicular cylindrical roller bearing is taken as the research object in this thesis,and the potential rules about the dynamic behavior,contact behavoir,contact fatigue life and reliability of the vehicular cylindrical roller bearing with a local defect are discussed.The conclusions can provide references for the production,operation and maintenance of vehicular cylindrical roller bearings.The main research contents and achievements of this thesis are as follows:(1)The dynamic behavior of the vehicular cylindrical roller bearing with a local defect is studied by considering nonlinear motion characteristics,complex contact and friction.A transient dynamic finite element model of the vehicular cylindrical roller bearing with an ellipsoidal defect is established by using the local mesh encrypting method,the dynamic performance of the defective bearing is analyzed,and the influences of defect dimension parameters and loading parameters on dynamic behavior are discussed.The results show that under the influence of the local defect,the radial vibration of the outer ring of the cylindrical roller bearing increases significantly.Compared with the situation of the normal bearing,the Root Mean Square Error(RMSE)values of radial vibration displacement,velocity and acceleration of the defective bearing increase by 4.4%,18.75%and 19.86%,respectively.Meanwhile,the RMSE value of roller acceleration increases by 32.06%.The local defect causes the increase of the stress and strain in the outer ring and the roller,and leads to the transfer of the equivalent stress peak area of the outer ring from near the end faces of the outer ring to the defective area.In addition,the increasing defect dimensions,inner ring speed and radial load will aggravate the radial vibration amplitude of the outer ring,and deteriorate the stress-strain state of the outer ring and the roller.(2)Based on the most dangerous stress and strain location of the defective bearing in the cycle and the Hertz contact theory,a static contact finite element model of the defective vehicular cylindrical roller bearing is established and solved by considering the factors of multi-body contact,friction and linear elasticity of materials,and the influences of the local defect,defect dimensions and radial load on the stress-strain and contact performance of the cylindrical roller bearings are investigated.The results show that the contact pressure of the cylindrical roller bearing under the radial load presents a symmetrical distribution about the origin and a zonal distribution along the axial direction.The defect causes the interruption of the pressure distribution in the defect area,and leads to the increase of the stress,strain and contact pressure of the defective bearing components.Moreover,the expansion of defect and the increasing radial load will increase the stress,strain and contact pressure of the defective bearing components,and the contact pressure increment at the bottom roller reaches the maximum value.(3)The fatigue load spectrum of defective bearing is obtained by Rain-flow counting method,and based on the influence of the material fatigue behavior and the static contact model of the defective bearing with stress results,a finite element model of the contact fatigue life of the defective vehicular cylindrical roller bearing is established,and the rules of the fatigue life of the cylindrical roller bearing under the local defect and different defect dimensions are analyzed based on Miner’s linear cumulative damage theory.The results show that the fatigue life and safety factor of the outer ring and the bottom roller of the defective bearing show a"rise-fall-rise"trend along the axial direction.The local defect weakens the minimum fatigue life and safety factor of the defective bearing components,and leads to the minimum fatigue life of the cylindrical roller bearing decreases from 2.52×10~9 cycles(157.5 million revolutions)to 6.86×10~8 cycles(42.9million revolutions).Additionally,the fatigue behavior of the defective bearing components declines with the increasing defect dimensions,which aggravates the fatigue failure risk of the cylindrical roller bearing.(4)Based on the obtained minimum fatigue life of the defective bearing and the probability distribution preformances of the input variables such as material properties and external loads,the contact fatigue reliability model of the defective vehicular cylindrical roller bearing is established.The relationships between the fatigue reliability of the cylindrical roller bearing and input variables are revealed by the Central Composite Design(CCD)method and Latin Hypercube Sampling(LHS)method,and the evolutions of the fatigue reliability of the cylindrical roller bearing under the local defect and different defect dimensions are explored.The results show that the minimum fatigue life of the cylindrical roller bearing is negatively correlated with the elastic modulus and radial load,while positively correlated with the Poisson’s ratio.The local defect increases the influence of the minimum fatigue life of the cylindrical roller bearing by material properties,but reduces that by radial load.The minimum fatigue life of the cylindrical roller bearing follows Weibull distribution approximately,and the reliability of the defective bearing decreases under a certain fatigue life.In addition,the increasing defect dimensions reduces the fatigue reliability of the defective bearing,and improves the probability of fatigue failure of the cylindrical roller bearing.