Study On The Lubrication And Friction Properties Of Macroscale And Microscale Surface Texture

As a method to improve the tribology properties greatly, the surface texture hasdrawn wide range of interest and became one of the hottest research points intribology, recently. In the present paper, in order to look for the texture shapes andgeometric parameters with outstanding lubrication performance and friction property,the topic of hydrodynamic lubrication on micro-texture surface was discussed mainlyfrom four parts, effectiveness evaluation of the Reynolds equation to textured surface,the mechanisms of hydrodynamic lubrication, the effects of texture shape andgeometric parameters on hydrodynamic lubrication property, and the optimizationdesign of textured surface.Firstly, the lubrication model of textured surface was proposed in hydrodynamiclubrication contact on the basis of Reynolds equation and Navier-Stokes equations.This lubrication model was used to verify the availability of Reynolds equation. Thetheoretical analysis and numerical simulation results indicated that the availability ofReynolds equation depended on two factors, reduced Reynolds number and the ratioof oil film thickness to length of calculated cell. For rectangular texture, the criterionfor validity of the Reynolds equation is that the ratio of oil film thickness to length ofcalculated cell less than0.015and the reduced Reynolds number less than0.20.The analytic solutions of the hydrodynamic pressure on rectangular texturesurface were derived based on the Reynolds equation. And the analytical expressionof the dimensionless dimple depth and width with best lubrication property wasobtained. The correspondent optimal group values were dimensionless dimple depth~0.866and dimensionless dimple width~0.718, which were fitted very well with thenumerical simulation even though the Reynolds equation is unavailable. Those resultscan provide us a reliable, highly-efficient designing idea using rectangle texture incommercial applications.Secondly, for both single texture surface and finite length multi-texture surface,the hydrodynamic mechanism was proposed, on which the effet of texture parametersand operating condition were discussed. And the “phase map” of pressure-buildupmechanism of rectangular surface texture was mapped. Based on those studies, therequirements of high lubrication performance to texture shapes and geometricparameters were also discussed. And the wedge-shaped texture with great lubricationproperty was designed. By comparing with the rectangle, triangle, circular, ellipse shape, it was found the lubrication properties of wedge-shaped texture were betterthan others under the small Reynolds number. And then, the multi-texture surface withwedge-shaped texture was proposed and the effect of its geometric parameters onhydrodynamic lubrication was studied.Array arranged spherical cap-shaped micro-dimples were imprinted on thesurface of45#steel, of which the lubrication and friction performance were studiedby pin-on-disc sliding experiment and numerical simulation. The experimental resultsshowed that only the reasonable texture size could decrease the friction force underthe specified load. However, the unreasonable texture size couldnot decrease thefriction, but even increase the friction.The numerical simulation results basicallyagree with it.At the last part of this paper, the Molecular Dynamics model of monocrystallinesilicon nano-film with smooth and nano-textured surface were built. Based on this, themechanical property and friction behavior of nano-textured surface were studied. Itwas resulted that the existence of nano-texture on monocrystalline silicon nano-filmincreased the friction force, decreased the hardness, and leaded to different frictionlaw, that is, the relationship between friction force and load is liner different from thesuperliner with smooth surface. The friction force and the load oscillated with theperiodicity of textures. This frequency spectrum character of friction force containedrich structural information. In the nano-indentation, the phase transformation is theonly mechanism of plastic deformation for monocrystalline silicon nano-film. And thedominant mechanism of its phase transformation was the diamond structure Si-Itransformed into body centered cubic structure, Si-II and BCT5, in which the BCT5appeared or developed earlier than Si-II. In unloading process, both the high pressurephase Si-II and BCT5transformed into amorphous phase.