考虑基体变形的混合润滑结合面接触特性

为研究混合润滑状态下粗糙表面基体变形对结合面接触特性的影响,建立了考虑基体变形的结合面接触刚度模型。首先,通过单微凸体-基体系统模型分别求解微凸体和基体的接触刚度,利用不动点迭代法获得微凸体真实变形量;其次,基于分形理论建立结合面固体接触刚度模型,通过固体接触刚度获得液体介质的接触刚度。根据仿真结果分析了基体变形、粗糙表面形貌以及润滑介质对结合面接触特性的影响规律。结果表明:当真实接触面积一定时,通过新模型计算的法向载荷小于忽略基体变形的模型;在接触前期,结合面的接触刚度主要由液体介质接触刚度主导,随着真实接触面积的增加,液体接触刚度占总刚度的比率越来越小,最后转变为固体的接触刚度主导结合面的接触刚度。该模型为研究混合润滑状态下结合面的接触特性提供了理论基础。     

三维真实粗糙结合面法向接触刚度研究

针对目前建立结合面粗糙表面模型主要以统计数方法和分形方法居多的情况,利用LEXT OLS4000测量仪测量得到真实表面形貌数据,基于小波理论对数据进行了降噪、分解和重构等顸处理,将数据导入到Pro/E中建立真实表面模型,运用ANSYS对结合面进行接触分析.带粗糙面的微元体被等效为无厚度界面和相同大小的光滑微元体串联,得出无厚度界面法向接触刚度.研究表明:表面形貌造成的接触应力分布不均匀和局部塑性变形导致结合面法向接触刚度随着压力的增加先增大后减小,并随着表面粗糙度参数值的增加而降低;不同的加工方式也影响着结合面的法向接触刚度.     

硬岩掘进装备支撑系统界面接触刚度非线性特性

隧道岩石表面形貌和岩石力学特性对撑靴接触界面刚度特性关系密切。根据隧道岩石形貌特点,采用分形数学模型分析不同分形参数与表面粗糙度之间的关系,通过投影方法建立三维隧道岩石粗糙表面数值分析模型。考虑岩石隧道表面粗糙度,岩石力学特性、撑靴数量以及复合岩层等工况,分析不同参数下撑靴载荷与法向接触刚度之间的关系。结果表明：掘进装备的支撑系统界面法向接触刚度随着法向力、分形维数、弹性模量的增大而增大,随着特征尺度系数的增大而减小;撑靴数量的增加会带来界面法向刚度增加。在相同载荷下,双撑靴的接触刚度接近单撑靴接触刚度的两倍;岩石成分比例相同时,其法向刚度最小;当岩石成分比例不同时,较小弹性模量岩石成分越高,其法向刚度越大;岩石成分比例不同的情况下,其法向刚度相差不大。     

空间应用高速转子轴承润滑特性分析

针对空间用高速转子轴承的润滑失效问题,综合考虑接触几何、真实粗糙表面形貌、弹性变形、润滑剂流变特性以及滚珠高速自旋特性等因素的影响,建立角接触球轴承的混合润滑统一模型;分析转速、载荷、真空、高低温等工况环境条件对轴承微观传动界面接触与润滑特性的影响规律,并针对算例给出各种润滑状态之间的临界转速。结果表明:随着转速的提高,轴承接触界面润滑状态逐渐改善;除了极低转速,轴承接触界面压力峰值总体随载荷增大而增加;油膜厚度随着大气压强的增大而增大,界面压力峰值随着大气压强的增大而减小;油膜厚度随着温度的增加而减小,界面压力随温度的升高而增大;低速条件下离心力、微重力引起的入口区域乏油对润滑特性影响较小。     

高速轮轨粗糙表面法向和切向接触刚度研究

为准确计算高速轮轨粗糙表面法向和切向接触刚度,基于W-M函数分形理论建立高速轮轨表面粗糙度三维数值模型;分析轮轨法向和切向接触刚度理论,运用有限元法离散轮轨接触面建立轮轨粗糙表面接触有限元简化模型;基于罚函数的面-面接触算法定义轮轨接触,加载位移载荷计算轮轨法向和切向接触刚度。计算结果表明:接触载荷作用下考虑轮轨表面粗糙度可更为准确地计算法向和切向接触刚度;轮轨法向接触刚度受法向载荷影响较大,且随着法向载荷的增加而增加,而摩擦因数对法向接触刚度的影响甚微;轮轨切向接触刚度随着法向载荷和摩擦因数的增加而增加,随着切向载荷的增加而减小。     

弹性状态下粗糙表面法向接触刚度的研究

粗糙表面接触问题是一类重要和具有实用价值的实际工程问题。采用Ｈｅｒｔｚ理论和粗糙表面随机接触模型, 研究弹性状态下粗糙表面法向接触刚度,推导出在不同接触体的法向接触刚度公式。由推导的理论公式可知,粗糙表面 在随机接触模型中接触刚度跟载荷成正比,与表面粗糙度均方值成反比     

弹性状态下粗糙表面的法向接触刚度

粗糙表面接触问题是一类重要和具有实用价值的实际工程问题。采用Hertz理论和粗糙表面随机接触模型,研究弹性状态下粗糙表面法向接触刚度,推导出在不同接触体的法向接触刚度公式。由推导的理论公式可知,粗糙表面在随机接触模型中接触刚度跟载荷成正比,与表面粗糙度均方值成反比。     

一种点接触粗糙表面摩擦行为的预估方法研究

针对润滑状态下连接界面的接触问题,对流体动力油膜和粗糙表面的摩擦特性进行了研究,提出了一种点接触粗糙表面摩擦行为的预估方法。首先,基于载荷分配思想建立了粗糙表面摩擦模型,利用Hertz理论中的最大接触压力分别确定了微凸体高度分布服从高斯分布、指数分布以及三角分布时粗糙表面的接触载荷;然后,通过弹性流体动力润滑膜厚公式求解了流体动力油膜承担的载荷;最后,绘制了滑动速度-摩擦系数曲线,模拟了整个润滑过程中连接界面摩擦系数的变化。研究结果表明:仿真结果与试验数据具有一致性,且不同法向载荷、粗糙表面形貌、润滑剂粘度以及假设的微凸体高度分布对摩擦系数的影响程度不同;微凸体假设为高斯分布时,仿真结果更接近试验数据;该方法可以为机械结构的润滑状态预测提供理论基础。     

具有微织构形貌的结合面法向接触刚度分形模型的研究

研究微织构结合面上的表面形貌参数对结合面法向接触刚度的影响。根据微织构表面的形貌特征,将微织构表面分为织构前表面和织构区域两部分,由分形接触理论计算出织构前表面上微凸体的基本参数,忽略织构区域底部未接触部分,将微凸体在接触载荷作用下的变形分为三个阶段:弹性阶段、弹塑性阶段、塑性阶段。由接触力学理论,首先建立织构前表面上单个微凸体的法向接触刚度模型。然后由微观到宏观,结合微织构表面的织构形貌特征,构造整个宏观微织构结合面的法向接触刚度计算模型,研究不同的表面形貌参数对于微织构界面上法向接触载荷、微凸体因载荷产生的变形以及法向接触刚度的影响。经过仿真分析之后,结果表明,当微织构结合面的法向接触载荷不断增大时,结合面的法向接触刚度总体呈单调上升趋势;并且随着织构密度的增加,结合面上由于织构形貌的存在,使得一部分微凸体未产生变形,从而减小结合面的法向接触刚度,并且当法向载荷增加时,这种效果会更加明显;在相同的接触载荷下,塑性指数越高,处于塑性变形状态的微凸体就越多,从而使具有微织构形貌的结合面的法向接触刚度变大。     

考虑软三体接触的粗糙界面混合润滑模型研究

软三体颗粒润滑是利用大量松散的固体软颗粒在界面中的承载和剪切行为实现特殊环境下界面的减摩,因此研究软颗粒介质摩擦界面在剪切过程中的受力情况,对软三体颗粒润滑机理的分析以及润滑装置的设计都具有重要意义。研究中将第三体颗粒类比为流体,基于雷诺方程、黏度方程、Greenwood和Williamson接触模型（G-W模型）等建立了含大颗粒粗糙界面的混合润滑模型。该模型中摩擦副的总载荷及总摩擦力由流体、微凸体和大颗粒三部分共同构成。通过采用有限差分法对上述物理模型进行求解分析,探究膜厚比、第三体大颗粒的质量浓度、粒径以及试件的表面形貌、弹性模量对三体接触界面的承载和摩擦力的影响情况,进而分析大颗粒粒径和接触表面粗糙度耦合时软三体接触界面的力学性能。基于对所构建的软三体接触界面混合润滑模型的研究可知：合理选择大颗粒质量浓度、粒径以及试件的表面形貌、弹性模量有助于提高承载、减小摩擦力,使得软三体颗粒流具有更好的减摩润滑性能。     

Investigation into the Normal Contact Stiffness of Rough Surface in Line Contact Mixed Elastohydrodynamic Lubrication

In this work, the statistical asperity microcontact models in combination with the acoustic spring model and the load sharing concept are utilized to study the interfacial normal contact stiffness for a rough surface in line contact elastohydrodynamic lubrication (EHL). Two different statistical microcontact models of Greenwood and Williamson (GW) and Kogut and Etsion (KE) are employed to derive the normal contact stiffness expressions for a dry rough line contact considering the purely elastic contact and the multiple regimes elastic–elastoplastic–fully plastic contact, respectively. The liquid film stiffness is calculated based on the relationship between film thickness and bulk modulus of the lubricant. The lubricant film thickness equations are employed in conjunction with the load sharing concept and the empirical formulas for the maximum contact pressure in a dry rough contact are fitted for the GW model and the KE model, to evaluate the relationship between film thickness and motion velocity for the purely elastic GW microcontact model and the multiregime KE microcontact model, respectively. The comparison with experimental results shows that the KE model predicts closer total contact stiffness results than the GW model. The stiffness contributions from the solid asperity contact and lubricant film are obtained and effects of surface roughness, applied load, motion velocity, and type of lubricant on the normal contact stiffness are analyzed.     

A molecular dynamics simulation of 3D rough lubricated contact

In this paper, a molecular dynamics simulation of three dimensional rough surface contact under different lubricated conditions was carried out. At atomic scale, mixed lubrication involves nano-asperity contact where the load is supported not only by asperities but also by a sufficient amount of confined lubricant. The contact area and pressure distribution of various lubricated conditions, e.g. dry, partially lubricated and fully lubricated, were presented. It has been found that cavities were formed between upper and lower surfaces under the load, and confined lubricant molecules were able to fill the cavity and support the load, resulting in the decrease of contact area and thus the protection of surface topography.     

过盈配合单向分形界面微观接触面积研究

通过对模拟压缩机叶轮和轴过盈配合的试件表面轮廓进行分析,发现切削加工的粗糙配合表面具有单向粗糙度特征,同时垂直加工纹理方向的表面轮廓具有明显分形特性。基于M-B分形接触的修正模型,建立了具有单向粗糙度分形特征表面的理论接触模型,推导出接触面积与法向载荷的函数关系式。结合真实粗糙表面,建立了具有分形特性的单向粗糙度实体模型,利用有限元分析软件对实体模型进行了仿真分析,验证了接触面积与法向载荷函数关系的正确性。     

依据各向异性分形几何理论的固定结合部法向接触力学模型

基于各向异性分形几何理论,考虑微凸体变形特点、表面微凸体承受法向载荷的连续性和光滑性原理,以及区分微凸体分别处于弹性、塑性变形时的一个微凸体实际微接触面积,建立固定结合部法向接触力学模型。采用二变量Weierstrass-Mandelbrot函数模拟各向异性三维分形轮廓表面。推导出划分弹塑性区域的临界弹性变形微接触截面积、结合部量纲一法向载荷、结合部量纲一法向接触刚度的数学表达式。数值仿真结果表明：当表面形貌的分形维数、分形粗糙度一定时,真实接触面积随着结合部法向载荷的增大而增大;结合部法向接触刚度随着真实接触面积、结合部法向载荷、相关因子或材料特性参数的增大而变大;当分形维数由1变大时,结合部法向接触刚度随着分形维数的变大而增大;当分形维数增加到趋近于2时,结合部法向接触刚度有时却会随着分形维数的增加而降低。结合部法向接触力学模型的构建,有助于分析固定接触表面间的真实接触情况。     

Roughness and Lubricant Effect on 3D Atomic Asperity Contact

Large-scale molecular dynamics simulations were performed to study the sliding process of rough surfaces with and without lubricant. In the dry contact, a linear relationship has been observed between the load and the contact area for surfaces with large root mean square (RMS) roughness. However, it becomes nonlinear when the RMS is small. In the presence of adhesion, small roughness results in a large friction force when the surfaces are flattened and the contact area reaches 60 %. In order to confirm this observation, nonadhesive models have been established with an observation that under the combined influence from roughness and adhesion, the contact area plays a crucial role to determine whether the dry sliding is under the domination of roughness or adhesion. In the lubricated sliding, an increase in friction force has been found for the partially lubricated condition because the asperity contact still accounts for a great deal of resisting force. Besides, the lubricant exerts a comparable resisting force to the sliding.     

双粗糙平面法向接触建模方法的有限元对比分析

基于统计学方法,Greenwood和Tripp(GT模型)提出双粗糙平面法向接触(双粗模型)可以等效为单粗糙平面与刚性平板之间的接触(单粗模型),但这种等效处理缺乏对接触应力场分析以及材料硬化的考虑。为进一步研究GT模型,基于高斯粗糙表面数字化表征,通过控制自相关长度和滤波方法,得到双粗糙平面及其等效单粗糙平面;借助有限元软件ABAQUS对2组模型法向接触进行建模及分析。结果表明:2组模型预测的接触刚度和接触面积符合较好,但接触压力与接触面积关系存在差异;2组模型预测的等效应力和接触压强的应力幅值以及云图的分布区域大致相近,但双粗模型由于存在大量微凸体侧接触,弱化接触状态以及材料硬化,因而应力幅值偏低。     

Modeling Sliding Contact of Rough Surfaces with Molecularly Thin Lubricants

The sliding contact between two rough surfaces in the presence of a molecularly thin lubricant layer is investigated. Under very high shear rates, the lubricant is treated as a semi-solid layer with normal and lateral shear-dependent stiffness components obtained from experimental data. The adhesive force in the presence of lubricant is also adapted from the Sub-boundary lubrication model and improved to account for variation in surface energy with penetration into the lubricant layer. A model is then proposed, based on the Improved sub-boundary lubrication model, which accounts for lubricant contact and adhesion and its validity is discussed. The model is in good agreement with published experimental measurements of friction in the presence of molecularly thin lubricant layers and suggests that a molecularly thin lubricant bearing could be successfully used to reduce solid substrate damage at the interface.     

An Advanced Rough Surface Continuum-Based Contact and Sliding Model in the Presence of Molecularly Thin Lubricant

A model of molecularly thin lubricant layer behavior for rough, sliding contact is presented in this work as a function of lubricant layer morphology. Building on previous work by the authors where the lubricant layer was assumed to be uniform in thickness and morphology, lubricant contributions to contact are presently treated at the asperity level and the effects of lubricant bonding ratio and coverage are accounted for. Effective stiffnesses for lubricated asperities are used to calculate the bearing and shear forces, while variable surface energy is modeled at the asperity level and used within an improved continuum adhesive formulation. Contributions from asperities in lubricant and solid contact for partial coverage are determined within the context of a statistical mechanics model. The proposed model can be used to study the mixed nanolubrication regime expected during light contact or “surfing” recording in magnetic storage, where sustained nanolubricant contact would partially deplete mobile molecules from the contact interface.     

基于接触分形理论的机械结合面法向接触刚度模型

为能够从理论上建立起具有尺度独立性的机械结合面法向接触刚度的理论模型,从而解决以往研究 荼存在的缺陷与不足,在一定的假设下,基于球体与平面的赫兹接触理论和接触分形理论,首次从理论上给出了具有尺度独立性的机械结合面法向接触刚度分形模型,并取得了与实验一致的数字仿真研究结果。