【作者】 韩静；

【导师】 方亮；

【作者基本信息】 中国矿业大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 近年来，表面纹理作为一种可以显著改善表面摩擦学性能的方法得到国内外学者的广泛关注，成为当前摩擦学领域热点研究方向之一。为了寻找具有优异润滑性能的纹理几何形貌和参数组合，最大可能的改善摩擦性能，申请人利用理论分析和数值模拟的方法，针对宏观纹理表面动压润滑问题，围绕Reynolds方程的有效性评价、纹理表面动压润滑形成机理、几何形貌和参数对纹理表面动压润滑性能的影响规律、纹理表面的优化设计四个方面展开了系统讨论。首先基于Reynolds方程和Navier-Stokes方程在流体动压润滑条件下建立了纹理表面的润滑模型。通过理论分析和数值模拟发现Reynolds方程有效性的两个决定性因素是缩减的雷诺数和油膜厚度与纹理特征长度比。只有当这两个因素同时趋近于零时，Reynolds方程才不至于造成不可接受的误差；对于矩形微坑纹理表面，Reynolds方程有效性的评价准则为：油膜厚度与纹理特征长度的比值小于0.015，并且缩减的雷诺数小于0.20。推导出了基于Reynolds方程的矩形纹理表面动压润滑的解析解；得到了使润滑性能全局最优的无量纲微坑深度和宽度的解析表达，最优的无量纲深度和宽度组合为~0.87和~0.72。数值模拟验证了这一结果。进一步研究表明，即使在Reynolds方程不能有效使用的情况下，理论预测的最优微坑深度也能与数值计算结果相一致；这为工程应用中矩形纹理的优化设计提供了可靠、高效的理论依据。其次，提出和论证了单个微坑和整体轴承两个层面的纹理表面动压润滑形成机理，分析了纹理参数和工况条件对润滑形成机理的影响规律。并绘制了矩形沟槽纹理表面润滑机理“相图”。基于动压润滑形成机理和参数的影响规律，分析了润滑性能的提高对纹理形状的需求，由此设计了具有优异润滑性能的楔形纹理表面。通过与矩形、三角形、圆弧形、椭圆形纹理的对比发现楔形纹理在低雷诺数下具有最优的动压润滑性能；在此基础上，构建了楔形微坑的多纹理轴承，并分析了几何参数对其动压润滑性能的影响规律。压印方法在45#钢表面制备了阵列排布的球冠状微坑纹理表面，并采用销-盘实验和数值模拟方法评价了其摩擦性能。实验表明，只有合适的纹理尺寸才能够在特定的载荷下起到降低摩擦的作用，不适当的纹理尺寸不但起不到减摩的作用，甚至会起到反作用。数值模拟与该实验结果基本保持一致。最后，建立了具有纹理表面和光滑表面的单晶硅纳米薄膜的分子动力学模型，研究了单晶硅纳米薄膜纹理表面和光滑表面纳米力学性能和摩擦行为。结果表明纳米纹理的引入增加了摩擦力，降低了薄膜硬度，改变了摩擦法则，即：摩擦力与载荷的关系将从光滑表面的超线性关系转变为纹理表面的线性关系；纹理表面的摩擦力与载荷随纹理做周期性的振荡；摩擦力频谱包含了丰富的结构信息。纳米压痕中，相变是单晶硅纳米薄膜塑性变形唯一的机理；金刚石结构的Si-I转变为体心结构的Si-II和BCT5相是单晶硅纳米薄膜纳米压痕加载过程主要的相变机制；BCT5相的出现领先于Si-II相；卸载过程中高压Si-II和BCT5相全部转变为非晶相。更多还原

【Abstract】 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.更多还原