Study On Tribological Properties Of Cylindrical Roller Bearing Coated With Molybdenum Disulfide Matrix Composites

Bearings play an important role in the rapid development of aerospace technology.In order to meet the special operating conditions and working environment of China’s space station,excellent surface tribological properties of bearing surface are obtained through coating a layer of molybdenum disulfide matrix antifriction composite coating,which has become an important way to improve the lifetime of bearing.However,composite coated bearings still need to face problems such as friction,wear,and coating peeling failure during operation.In order to maintain stable operation of the space station,achieve better lubrication efficiency,and improve the service life of bearings,it is of great significance to carry out research on the tribological properties of composite coatings.In this thesis,cylindrical roller bearing coated with molybdenum disulfide matrix composites is taken as the object,numerical methods such as finite element simulation are used to deeply study the contact performance,thermal performance,coating-substrate adhesion performance,and friction and wear performance of composite coating bearings,with a view to providing a useful reference for the research of surface coating bearings.The main research content and results are as follows:(1)Based on the theories of contact mechanics and elastic mechanics,a finite element model for the contact between the inner ring and roller of a cylindrical roller bearing coated with a molybdenum disulfide matrix composite coating is established.A high-quality element is generated for the coating thickness,and the validity of the model is verified based on the Hertz contact theory.Furthermore,the effect of molybdenum disulfide matrix composite coating on the contact performance of the cylindrical roller bearing is studied,and contact performances of coated bearing with different slip-roll ratio,friction coefficients,loads are analyzed.The research results show that compared to the results without coating,the von Mises stress and contact pressure of the coated bearings are lower,and the usage of the coating increases the contact width between the roller and the inner ring,making the stress distribution range wider,reducing the contact pressure and von Mises stress as a whole,and significantly reducing the edge stress concentration.Excessive slip-roll ratio will cause more severe wear on the roller edges and corresponding areas of the inner ring.The increase of friction coefficient has a greater impact on the von Mises stress of the roller than on the inner ring.The logarithmic strain of both the inner ring and the roller increases with the increase of friction coefficient.(2)Based on thermodynamic theory and taking into account the interaction between temperature and stress fields,a finite element model of cylindrical roller bearings coated with molybdenum disulfide matrix composite coating on the inner ring is established.A fully thermally coupled simulation is conducted based on the ABAQUS "Dynamic,Tempdisp,Explicit" module to analyze the temperature field distribution and temperature evolution rules of various components of the bearing.The results show that the highest temperature of the bearing inner ring is located on the surface of the coating.With the increase of rotational speed,load,and friction coefficient,the heat production of the bearing increases,and the temperature difference between the coating and the substrate gradually increases.The coating is more susceptible to external conditions than the substrate.The highest temperature on the coating of the bearing inner ring is mostly located in the inner region on both sides of the contact between the roller and the inner ring.This area is more susceptible to high temperatures,resulting in reduced bearing lubrication performance.Under different rotational speeds,loads,and friction coefficients,the highest temperature relationship for the outer ring,roller,and cage is roller>cage>outer ring.With the increase of rotational speeds,loads,and friction coefficients,the greater the temperature difference between the three components above.(3)Based on the bilinear traction-separation theory,the key technology of cohesive element is adopted to overcome the problems of the inability to characterize the bonding properties between the composite coating and the substrate on the surface of cylindrical roller bearings,as well as the evolution of the bonding interface delamination.A finite element model of the coating-substrate containing cohesive zone is created,and based on the indentation model,the evolution laws of the mechanical properties of the composite coating on the bearing surface and the evolution laws of the coating-substrate bonding properties are explored.The results show that the coating-substrate bonding interface is mainly affected by shear stress,and there is a maximum shear stress at a radial distance of contact width.As the indentation depth increases,initial shear delamination occurs within the contact radius.When the indentation depth reaches the coating thickness,there is no delamination outside the region.It is found that under high interfacial strength and interfacial toughness,it would increase the difficulty of delamination at the coatingsubstrate bonding interface.Under this condition,the coating-substrate bonding ability is strong.Under high cohesion conditions,the maximum principal stress criterion by the coating will increase,making the coating more prone to surface cracks.With high elastic modulus,the indentation simulation results show that there are two delaminations at the coating-substrate bonding interface.The first delamination is located within the contact radius,which is a shear delamination.The second delamination is located outside the contact half width region,where the coating is mainly affected by tensile stress and is an interfacial tensile delamination.With the increase of elastic modulus,the shear delamination distance becomes shorter,while the tensile delamination distance becomes longer.Under ideal bonding conditions,residual tensile stress makes the coating more prone to surface cracks.At the same indentation depth,residual tensile stress leads to larger indentation load,while residual compressive stress is the opposite.(4)Based on Archard’s wear theory,a study on friction and wear of cylindrical roller bearing coating is conducted.Based on the pin on disk wear finite element model,the secondary development of the UMESHMOTION subroutine and ALE adaptive mesh technology are used to overcome the limitations of experimental methods.The wear depth distribution and contact pressure distribution of the pin on disk wear finite element model are obtained.The results show that as the reciprocating sliding distance increases,the wear depth of the spherical pin increases,and the wear area expands.The deepest wear point is located at the geometric center of the spherical pin,with good symmetry.The wear morphology of the spherical pin head gradually becomes flat as the amount of reciprocating slip increases,and the wear morphology of the contact area of the grinding disc can be seen as a groove shape from the wear depth curve.The contact pressure of the spherical pin decreases with the increase of the sliding distance,and the contact pressure is the largest at the initial stage of wear,while it remains stable after reaching a certain reciprocating sliding distance.Considering the friction heat generation,the maximum temperature of the spherical pin and the grinding disc is located at the contact center,and the contact center axis is symmetric along the x-direction.The high-temperature area is also the core wear area,and the high-temperature area continues to expand after the wear of the spherical pin head.However,the heat is still concentrated in the center of the wear area.The grooves generated by the wear increase the contact area,and the heat generation in the edge area also increases,while the temperature outside the wear area decreases significantly.