Study On Mechanism For Filming And Failure Of Visco-plastic Fluid Hydrodynamic Lubrication

With the development of modern industry and science and technology,Significant changes have taken place in the operation conditions of fluid dynamicsystem applied to aeronautics and astronautics, ship, automobile manufacturing,electricity and other industries. Large-scale and high-speed of mechanical equipmentand the requirements of high precision and high efficiency lead to frictional parts inmachinery facing the increasingly harsh lubrication conditions. Some machinecomponents which have been well designed with traditional hydrodynamic lubricationtheory still can’t meet the established lubrication effect and performance, evenlubrication failure occurs. It makes people start to consider whether the traditionalhydrodynamic lubrication theory under harsh conditions can successfully predictlubrication failure or not. Therefore, the exploration of mechanism and failure ofdynamic lubrication in extreme cases is urgent need to address for the development ofmodern industry and science and technology.This paper deduces lubrication governing equations for visco-plastic fluiddynamic lubrication based on the visco-plastic rheological behavior of the fluidLubrication medium in high speed, high pressure and other working condition. Andthe flow characteristic, lubricating properties, lubrication failure, temperaturedistribution and boundary slip behavior of visco-plastic dynamic lubrication havebeen investigated.(1) The flow characteristic and lubricating properties of visco-plastic dynamiclubrication have been investigated. Visco-plastic rheological model has beenestablished. Visco-plastic dynamic lubrication Reynolds equation has been deducedby representative elemental volume analytical approach. The flow characteristic andlubricating properties of visco-plastic dynamic lubrication at different lubrication statehas been analyzed by solving the equation. The results show that, the formationmechanism of dynamic pressure lubricant film in visco-plastic dynamic lubrication iswedge-shaped effect as well, but dynamic pressure level of lubricant film in sliplubrication fields is depended on the ultimate shear stress and film thickness; Excessrelative slip velocity of two lubrication surfaces and undersized film thickness ratioare the primary cause for visco-plastic fluid lubrication failure.(2) The temperature distribution of visco-plastic lubricant film in visco-plasticdynamic lubrication has been investigated. The energy equation which is suitable forvisco-plastic dynamic lubrication has been deduced and solved. The results show that,because of the accumulation of viscous dissipation, the temperature of visco-plasticlubricant film rises continually along the direction of lubricant film converge and deviates form forecast of traditional lubrication theory; The influences of relative slipvelocity of two lubrication surfaces and film thickness ratio on temperate distributionof visco-plastic are prominent.(3) The boundary slip behavior in visco-plastic dynamic lubrication has beeninvestigated. The larger film thickness ratio is, the easier for formation of primaryboundary slip and harder for second boundary slip, and the lubrication tends to be inthe singe slip field lubrication state. Conversely, the lubrication tends to be in the noslip field lubrication state and double slip field lubrication state. The length ofboundary slip has remarkable variations with relative slip velocity of two lubricationsurfaces, film thickness ratio and viscosity of lubricant.