一个表面带单粗糙峰的线接触时变微弹流润滑数值分析

通过数值求解研究了一个固体表面的单粗糙峰对两固体形成的线接触时变弹流润滑区压力、膜厚分布曲线的影响。结果表明：粗糙峰的出现，使其对应位置上的压力、膜厚发生急剧变化；粗糙峰的移动，对压力和膜厚的变化、固体表面的凹陷现象以及Hertz接触区的出口颈缩均有不同的影响；另外，压力峰和油膜形状随着粗糙峰幅值和半波长的变化而变化。结果亦表明：准稳态解比时变解过高地估计粗糙峰对压力和膜厚的影响。     

指数率水基磁流体滑动轴承单峰时变热弹流润滑分析

利用考虑热、磁场、时变和指数率非牛顿效应的雷诺方程,对水基磁流体滑动轴承进行微观弹流润滑分析。对比稳态解与时变解,并探讨速度、载荷对水基磁流体润滑膜压力、膜厚和温度的影响。结果表明:考虑时变效应时水基磁流体的润滑膜的膜厚、压力和温度发生了明显变化,故在实际中不能用稳态解代替时变解;单个粗糙峰的存在,引起了水基磁流体润滑膜的局部最高压力峰和温度峰,由于局部压力峰的存在,使单个粗糙峰被迫压平,膜厚减小;随着速度的增加,水基磁流体润滑膜的压力峰减小,膜厚增大,温度增大;随着载荷的增加,水基磁流体润滑膜的压力峰增大,膜厚减小,温度增大。     

单粗糙峰对直齿圆柱齿轮热弹流润滑的影响

建立了单粗糙峰函数模型,给出了考虑单粗糙峰时的膜厚方程.应用多重网格技术研究了单粗糙峰的幅值和波长对直齿圆柱齿轮热弹流润滑的影响,并将单粗糙峰在不同幅值和波长情况下的中心压力、中心膜厚、最大温升和最小膜厚沿啮合线的变化与光滑解进行了比较.结果表明:单粗糙峰幅值和波长对齿轮热弹流润滑有着不同的影响,其中中心压力和最大温升随幅值的增大而增大,随波长的增大而减小,中心膜厚随幅值的增大而减小,随波长的增大而增大;与光滑解相比,粗糙峰的存在对弹流润滑产生较大的影响,使中心压力变大、中心膜厚变薄、最大温升值变大.     

单粗糙峰对摆线针轮弹流润滑的影响

以弹流润滑理论为基础,利用多重网格法,研究了啮合表面单粗糙峰的存在对摆线针轮时变弹流润滑的影响,并将不同幅值和波长条件下的粗糙解与光滑解进行了比较。结果表明,粗糙峰幅值越大,波长越小,油膜压力越高;随着幅值的增加,在啮合大部分区域,中心油膜值变大,而在啮合的开始和结束阶段的膜厚值要略低于光滑解,波长变化对中心膜厚基本无影响;随着幅值和波长的增加,最小油膜值相应增大,有利于润滑状况的改善。     

波动表面的等温弹流润滑分析

对具有波动表面的弹流润滑问题建立了数学模型,得到一种普遍的波动表面的点接触非稳态弹流数值算法.以准稳态解为初始条件,逐个周期求出了波动表面的等温牛顿流体弹流润滑的数值解,研究了两接触表面均带横向或纵向粗糙度的等温弹流润滑问题,分析了粗糙峰对压力和膜厚的时变影响,对比了接触表面带不同粗糙度的润滑性能,讨论了幅值和波长对压力和膜厚的影响.结果表明:接触区两表面的粗糙峰的叠加将产生更高的局部压力峰,膜厚变薄,粗糙峰的振幅越大,波长越短,对点接触弹流润滑越不利.     

水基磁流体轴承的微观弹流润滑分析

采用多重网格法和多重网格积分法对水基磁流体润滑轴承进行弹流润滑分析,在雷诺方程中考虑了热、非牛顿、磁场和时变的影响,探讨了粗糙度因素对弹流润滑性能的影响。分析中对比了轴-轴承双面和轴承单面带有正弦粗糙度时的润滑膜膜厚和压力的分布,并研究了双面都带有粗糙度相位不同时润滑膜压力和膜厚的分布。数值分析结果表明,两个表面都存在相同的粗糙度时,在波峰相对处的膜厚更小,压力更大,在波谷相对处的膜厚更大,压力更小;随着一个表面的粗糙峰远离另一个表面的粗糙峰时,膜厚和压力波动减小,润滑膜的最小膜厚逐渐增大,最大压力逐渐减小,直到润滑膜的粗糙峰与粗糙谷相对时,膜厚和压力不在波动,最小膜厚达到最大,最大压力达到最小。然后当这个表面粗糙峰再继续接近下一个表面粗糙峰时,膜厚和压力的波动增大,润滑膜的最小膜厚又开始减小,最大压力又增大,直到润滑膜的粗糙峰与粗糙峰相对时,膜厚和压力波动最大,最小膜厚达到最小,最大压力达到最大。     

考虑纵向粗糙度的点接触微观热弹流润滑数值分析

主要研究了纯滑动点接触热弹流润滑在考虑纵向单粗糙峰／单粗糙谷这一因素时，油膜的厚度、压力、温度随粗糙波高度、波长的变化而变化的情况，结果表明粗糙度对油膜的压力、膜厚和温度均有很大影响。     

表面粗糙峰/谷对大滑滚比线接触热弹流润滑接触的影响

假设在一个表面上存在单个粗糙峰或粗糙谷，采用数值分析方法研究大滑滚比下粗糙表面对线接触热弹流润滑接触的影响。研究发现：粗糙峰和粗糙谷造成油膜压力、膜厚和温升曲线的局部波动，其中压力的波动最为明显；在滑滚比较小时，粗糙峰和粗糙谷对压力、膜厚和温升曲线的影响较大， 随着滑滚比的增加，影响逐渐降低； 随着滑滚比的增加，粗糙峰幅值增加对压力、膜厚和温升曲线造成的波动也逐渐减弱。研究结果对于揭示滚珠丝杠或无保持架轴承等的润滑油膜形成和失效有重要意义。     

摆线针轮传动时变微观弹流润滑数值分析

结合摆线针轮传动中啮合点处综合曲率半径、卷吸速度、轮齿载荷随时间变化的特点,利用多重网格技术,得到了摆线针轮时变微观弹流润滑的完全数值解,分别讨论了单独粗糙峰和粗糙谷对弹流润滑的影响,并与其光滑解进行了比较。结果表明,粗糙度的存在,能较大程度影响油膜压力,但对油膜厚度影响轻微;并且粗糙峰和粗糙谷对油膜压力影响有明显的不同表现。     

粗糙峰和粗糙谷对直齿圆柱齿轮热弹流润滑的影响

利用多重网格技术,研究了表面粗糙度对渐开线直齿圆柱齿轮非牛顿热弹流润滑的影响。从同一啮合线和不同啮合时刻两方面,分别讨论了粗糙峰和粗糙谷对直齿圆柱齿轮弹流润滑的影响,并且将这些解与光滑解进行比较。结果表明,粗糙峰和粗糙谷分别给接触区内带来了压力的单峰和双峰,但对膜厚的影响却不大。     

渐开线直齿轮瞬态微观热弹流润滑分析

考虑了瞬态效应、轮齿表面油膜温度场和轮齿表面纵向粗糙度等因素,对渐开线直齿圆柱齿轮的弹流润滑问题进行研究。载荷由双齿或单齿承担,根据实际载荷谱简化的轮齿载荷曲线,利用压力求解的多重网格法和弹性变形求解的多重网格积分法以及温度求解的逐列扫描技术,得到渐开线直齿轮瞬态微观热弹流润滑问题的完全数值解,讨论了轮齿间油膜的厚度、压力、温度沿啮合线的变化规律。数值计算结果表明,齿轮表面纵向粗糙度对轮齿间油膜的压力、膜厚、温升都有较大影响。考虑轮齿表面粗糙度后,油膜压力和温升明显增大,并随压力的增加而影响越来越显著,粗糙峰使油膜压力分布和温度分布产生振荡,轮齿表面的粗糙峰对摩擦因数影响较小,摩擦因数和最高温升在节点两侧最大。     

Influence of surface roughness features on mixed‐film lubrication

An optical technique (three‐dimensional spacer layer imaging) has been developed to map accurately lubricant film thickness in thin‐film elastohydrodynamic (EHD) contacts. This experimental technique has been used to study the influence of surface roughness features, asperity height, and slope on EHD film thickness and pressure. Single ridges transverse to the entrainment direction were used to represent asperities. It was found that the ridges with lower slopes generate films of greater minimum thickness. Below a certain entrainment speed, the minimum film thickness declined at a rate dependent on the ridge slope. At low speeds, the ridges with higher slopes entrapped a larger volume of lubricant ahead of the ridge and along the entrainment direction. For all speeds, the highest ridges entrapped the most lubricant. Both ridge slope and ridge height had a negligible effect on mean film thickness in the contact. Asperity pressure increased with higher ridge slope, but was not influenced by entrainment speed. An increase in pressure was found where lubricant is entrapped upstream of a ridge.     

法向振动下的非牛顿热弹流润滑分析

假设润滑剂为Ree-Eyring非牛顿流体,考察了法向振动对线接触热弹流润滑性能的影响;法向振动由两固体间刚体位移随时间的简谐变化来表征,求得了稳态工况及一个振动周期内各时刻的瞬态解;并讨论了振动的频率和振幅对压力、膜厚、温度、摩擦因数等参数的影响.结果表明：时变效应导致了接触区内的动态凹陷现象;频率的变化主要影响膜厚的大小和凹陷的形状,而振幅的变化会很大程度上改变承载系数的变化幅度.     

Numerical evaluation of pressure from experimentally measured film thickness in EHL point contact

This paper is concerned with elastohydrodynamic lubrication, especially the determination of lubricant film thickness and contact pressure within a point contact of friction surfaces of machine parts. A new solution technique for numerical determination of contact pressure is introduced. The direct measurement of contact pressure is very difficult. Hence, input data of lubricant film thickness obtained from the experiment based on colorimetric interferometry are used for the calculation of pressure using the inverse elasticity theory. The algorithm is enhanced by convolution in order to increase calculation speed. The approach described in this contribution gives reliable results on smooth contact and in the future, it will be extended to enable the study of contact of friction surfaces with asperities. Copyright © 2007 John Wiley & Sons, Ltd.     

Average flow model with elastic deformation for CMP

We present a three-dimensional (3D) average flow model considering elastic deformation of pad asperities for chemical mechanical planarization. To consider the contact deformation of pad asperities in the calculation of the flow factor, 3D contact analysis of a semi-infinite solid based on the use of influence functions is conducted for computer-generated rough surfaces. The average Reynolds equation and boundary conditions of both force and momentum balance are used to investigate the effects of pad roughness and external pressure conditions on a film thickness and wafer position angles. It is found that the position angles decrease with the increasing of the applied pressure and the roughest pad has the highest position angles at any given load. Comparing elastic and rigid pads, the minimum film thickness formed between the elastic pad and the wafer is thinner than that between the rigid pad and the wafer.     

A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique

A laser induced fluorescence technique was used to investigate the build-up of lubricant films in compliant contacts operating in the isoviscous elasto-hydrodynamic regime (I-EHL). The described technique utilises an optimised optical set-up with a relatively high signal-to-noise ratio and was shown to be able to produce film thickness maps of the complete contact area and measure a very wide span of thicknesses, from 50 nm to 100 μm. Maps of film thickness were obtained over a range of entrainment speeds and loads for three different contact configurations and two elastomer materials, polydimethylsiloxane (PDMS) and a fluorocarbon rubber (FKM) which is typically used in rotary seal applications. In a model contact of a nominally smooth PDMS ball sliding on a glass flat, a crescent shaped area of reduced film thickness was observed towards the contact exit. In contrast to typical elasto-hydrodynamic contacts, no side-lobes of reduced film thickness were recorded, while the central film region exhibited a converging wedge shape. The elliptical contact of an FKM O-ring rolling on a flat glass showed a central region of flat film while areas of minimum film thickness were located near the contact edges either side of the centre. The highly conformal contact of relatively rough FKM O-ring sliding against a concave glass lens, a geometry more representative of that found in elastomeric seals, showed discrete regions of reduced film, corresponding to surface roughness asperities. With rising entrainment speed, some lift-off was observed, with surface roughness asperities appearing to be increasingly compressed. Measured films thicknesses were compared to existing theoretical predictions for I-EHL contacts and the level of agreement was found to be highly dependent on contact geometry and applied conditions.     

A partial elastohydrodynamic theory for the running-in process of hobbed gears

The running-in process of hobbed gears has been studied experimentally. The initial wear was found to be small although it increased with running speed and load. To explain the results, a simulation procedure was developed that was based on a random surface model and a proposed relation between film thickness, surface roughness and running conditions. A new oil model was used for the analysis of conditions between meshing rough flanks. The wear and deformation of asperities during the running-in period is due to direct contact between the asperities. The parameters determining wear and deformation are the adhesion and temperature between the asperities in contact.     

Research on the Friction Behaviors of Two Rough Surfaces Covered with Boundary Film

Boundary film plays an important role in improving the lubricating characteristics of mixed lubrication. But due to the complication of surface profile and the microscale of boundary film, progress made on the boundary lubrication is relatively less than that of fluid film lubrication. A friction model of two rough surfaces covered with the boundary film is studied in the paper. The rough surface is modeled by a collection of spherical asperities with the same curvature radius and the Gaussian height distribution, the shearing force of asperities over the boundary film is expressed by the linear equation, and the plowing force of asperities over the solid flat is modeled by considering the possibility of asperities being sheared off. Then, the friction behaviors are researched by analyzing the effects of boundary film and surface topography in different values. The results demonstrate that the effects of boundary film on the friction coefficient are enhanced with the increase in the thickness of boundary film and are weakened with the increase in the contact load. And surface profile parameters also affect the friction behaviors of boundary lubrication, the smoother the surface is, the more significant the boundary lubricating effect is.