Study On Non-newtonian Mixed Lubrication Of Point Contact With Surface Roughness

There are four parts in the thesis,i.e.,effects of the surface wear on the lubrication performance of non-Newtonian thermal elastohydrodynamic lubrication,the single layer mesh iterative method for solving pressures in point contact mixed lubrication,research on the steady state and transient mixed lubrication problems of the non-Newtonian fluid,measurements of the friction coefficient in point contact mixed lubrication.Firstly,a mathematical model of the non-Newtonian thermal elastohydrodynamic lubrication in point contact with wear has been established.Effects of the wear half width on the film pressure,thickness and temperature have been studied,and influences of different cases on variations in the minimum film thickness versus the wear half width have been discussed.Moreover,comparison has been made with Newtonian fluid results.Results show that,the central film thickness increases with the increase of the wear half width.The value of the minimum film thickness is relatively stable when the wear band edge is far from the position of the minimum film thickness of the smooth surface in the same working condition.On the contrary,the minimum film thickness decreases,and its position is always in the vicinity of the wear band edge.And different working conditions have some influences on the stable range of the minimum film thickness.Compared with the Newtonian fluid,the oil film temperature and the friction coefficient decrease obviously.Secondly,a model of the isothermal steady-state mixed lubrication with Newtonian fluid has been built.The single layer iterative method for solving pressure has been investigated.Comparison of solution with the multi-grid method has been carried out,respectively.The numerical result obtained with the single Gauss-Seidel iteration and Jacobi iteration has been given.Furthermore,influences of the lubricant viscosity on the mixed lubrication have been discussed.Results show that,the proposed algorithm is feasible compared with the multi-grid method.The difference of the calculation results used the single Gauss-Seidel iteration or the Jacobi iteration is little,so the single Gauss-Seidel iteration method can be adopted.And the lower the viscosity of the lubricant,the more easily the contact area is in a mixed lubrication status.Thirdly,the non-Newtonian point contact mixed lubrication model under the steady state and transient condition has been established,respectively.Full numerical solutions for the ideal smooth surface and the rough surface with different entrainment velocities have been calculated,respectively.Distributions of the pressure and the film thickness have been studied during the speed variation process containing three stages,i.e.,the acceleration,the uniform speed and the deceleration.Results show that,the film thickness decreases gradually with the decrease of the entrainment velocity both for the smooth and the rough surface.The boundary lubrication region continuously becomes larger from two sides of the contact region.During the acceleration,the film thickness begins to increase from the entrance and extends to the outlet.Due to the squeezing effect,the film thickness of the rough surface is larger than that of the smooth surface under transient condition.However,during the deceleration,the film thickness decreases and the rate of the reduction at the entrance becomes quickly.In addition,the second pressure peak and the exit film constriction exist.Finally,with the MMW-1 type vertical universal friction and wear testing machine,effects of the speed,the load,the surface roughness and the viscosity on the friction coefficient have been studied by the experiment.Results show that,under certain conditions,the greater the load,the longer the time required for transformation from the mixed lubrication status into the fluid lubrication status.The greater the surface roughness,the more slowly the friction coefficient changes with the velocity.The larger the viscosity of the lubricating oil,the faster the friction coefficient decreases with the velocity.