薄膜润滑与润滑状态图

讨论了速度、固体表面能、滑动比、润滑剂粘度和化学性能对薄膜润滑状态下油膜厚度的影响,以及弹流润滑向薄膜润滑转化条件和液体膜失效条件。进而提出了新的润滑状态划分准则以及不同润滑机理下膜厚的变化情况。     

薄膜润滑的微极流体模拟

基于向列相润滑分子作用下薄膜润滑的有序模型,利用微极流体（Micropolar fluids）理论分析薄膜润滑的润滑特性,探求薄膜润滑的基本规律。结果表明,薄膜润滑下的摩擦学性质介于弹性流体动力润滑和边界润滑之间,弹流理论不能很好预测膜厚随工况参数的变化情况,而微极流体理论结果和试验值有较好的一致性。薄膜润滑下有序分子的存在所起作用相当于提高润滑剂的粘度,能够增加润滑油膜的厚度从而增加承载能力。在薄膜润滑下必须考虑微粒分子的角动量矩守衡。     

有序薄膜润滑的速度场

基于有序膜分子模型分析薄膜润滑中的速度场分布。薄膜润滑中有序膜分子的取向与向列相液晶分子有类似性,可用“向矢”表示。利用液晶理论可以分析薄膜润滑的速度场和润滑剂分子的取向,为分析薄膜润滑的特性提供依据。薄膜润滑区别于弹流润滑之处在于有序膜分子的弹性。粘弹比可以很好地表征这种差异。给出了不同粘弹比下的“向矢”角度和等效粘度的分布情况以及速度场的分布情况。     

高速小型复合陶瓷球轴承的润滑特性研究

为了寻求一种能够快速建立高速小型复合陶瓷球轴承弹流润滑数学模型的数值计算方法,基于Reynolds方程的情况下运用Fortran语言在Visual Studio中进行编译,通过给定初始压力分布,运用迭代法求得弹流润滑完全数值解,并获取最终的压力和膜厚值。结果表明:转速、载荷以及润滑油粘度会对轴承的接触区压力、膜厚产生影响,其中随着转速的增加,最小膜厚增加,最大压力减小;随着载荷的增加,最小膜厚减小,最大压力增大;而随着润滑油粘度的增加,膜厚增加,最大压力减小。通过与传统理论计算结果的对比,结果具有较好的一致性,研究结果对高速深沟陶瓷球轴承运用具有指导意义。     

海水润滑赛龙陶瓷轴承的摩擦学性能研究

分析海水润滑轴承的主要磨损形式,建立海水润滑赛龙陶瓷轴承的弹流润滑模型,通过数值计算发现在赛龙陶瓷/钢摩擦副间可以形成海水弹流润滑膜,轴承间水膜厚度分布有明显颈缩现象,但压力分布图中第二压力峰不明显;随着转速的增加,海水润滑膜膜厚及最小膜厚都变薄;相同条件下,赛龙陶瓷轴承用海水润滑比用纯水和油润滑时更不容易形成弹流润滑薄膜。     

渐开线齿轮润滑设计的多重网格数值模拟技术

针对石油矿场机械用齿轮的润滑设计问题，提出应用多重网格数值模拟技术进行分析设计的原理与方法，并用于分析典型齿轮的弹流润滑性能。计算结果表明，多重网格技术应用于齿轮弹流数值计算具有收敛速度快、数值稳定性好等优点。增大齿轮的模数、传动比和压力角，以及提高转速、增大润滑油粘度等参数可以提高齿面间的润滑油膜厚度，从而减少磨损、胶合等失效的发生。     

高速齿轮箱推力盘计入热效应的弹流膜厚数值计算与分析

本文对高速齿轮箱中具有节能效益的推力盘弹流润滑理论作了研究,获得了可用于生产实际的推力盘等温及热弹流润滑数值解计算程序。此外,计算和分析了表面速度、锥角、粘度和温度等对承载能力及最小膜厚的影响,并将本文数值解结果与用Dowson—Higginson 线接触理论拟合公式所得的最小膜厚值进行了比较,表明用拟合公式计算高速齿轮箱中推力盘弹流膜厚具有较大的误差。     

粘弹性流体动力润滑与润滑磨损

分析了等效微弹流接触表面形状与真实情况之间的差异。讨论了材料粘性对弹性变形的影响。将材料粘性引入微弹流模型中,给出了润滑条件下磨粒磨损计算模型以及发生润滑磨损的条件准则。利用所给模型对接触弹流润滑磨损问题进行了数值计算并给出了与试验结果的对比。     

高速单圆弧齿轮等温弹性流体动力润滑数值解

本文对高速单圆弧齿轮的等温弹流理论作了研究,成功地获得了可在IBM—PC/XT上执行的圆弧齿轮弹流数值解计算程序。由一系列的数值计算结果所绘制的线图,既可在微型机屏幕上显示,又可同时在小型绘图机上输出。在此基础上,计算和分析了轮齿表面平均速度、螺旋角和润滑剂粘度对承载能力及最小膜厚的影响;并将本文数值解结果与用Dowson—Higginson线接触理论拟合公式所得最小膜厚值进行了比较,表明用拟合公式计算单圆弧齿轮弹流膜厚与较为精确的数值解结果有较大的差别。     

水润滑复合材料齿轮非稳态热弹流润滑分析

在水润滑条件下,对改性聚醚醚酮复合材料齿轮副啮合时的非稳态热弹流润滑机理进行了数值模拟研究,并将计算结果与等温时变解的啮合点压力、膜厚等进行了对比。结果表明,水润滑条件下,复合材料齿轮的啮合点处存在弹流润滑;在考虑温度场的情况下,水膜压力受温度的影响不大,而轮齿啮入点一侧的膜厚要比等温解的膜厚小,而在啮出点一侧则正好相反。     

Effects of surface forces on pure squeeze thin film EHL motion of circular contacts

The pure squeeze thin film elastohydrodynamic lubrication (thin film EHL) motion of circular contacts with effects of surface forces taken into account is explored under constant load conditions. The difference between thin film EHL model and EHL model is apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner. Moreover, the viscosity is oscillatory due to its dependency on the hydrodynamic pressure which is affected by surface forces.     

Molecular dynamics characterization of thin film viscosity for EHL simulation

Molecular simulations were used to characterize changes in lubricant viscosity that may occur during thin film elastohydrodynamic lubrication (EHL). Molecular dynamics simulations were performed at variable wall speed and film thickness such that the effects of both parameters could be evaluated. Using this approach it was found that the viscosity of thin films under large shear is subject to both shear thinning and oscillation with film thickness. A composite model was developed that incorporated both effects. The expected impact that this model might have on an EHL interface was evaluated using a continuum simulation. An overall decrease in viscosity with some oscillation near the interface edges was predicted due to the molecularly modeled thin film effects.     

EHL simulation using the free-volume viscosity model

The free-volume viscosity model can accurately predict the temperature–pressure–viscosity relationship of lubricants. However, it is seldom used in elastohydrodynamic lubrication (EHL) simulation. This paper presents the application of the free-volume viscosity model in a Newtonian EHL simulation of a squalane-lubricated circular contact. Good agreement is observed between available experimental data and simulation results. The pressure–viscosity coefficients fit from viscometer data are also discussed. A recently developed definition of the coefficient is used to compare the coefficient value extracted from EHL film thickness interference measurements. Results indicate that the coefficient values from the curve fitting and EHL film thickness extraction agree well which has not been previously observed. Two factors help achieve this agreement: the new coefficient definition and smaller prediction error when using the Hamrock–Dowson formula in the cases studied. The effects of different pressure–viscosity relationships, including the exponential model, the Roelands model and the free-volume model, are investigated through an example with bright stock mineral oil. It is found that the real pressure–viscosity behavior predicted by the free-volume model yields a higher viscosity at the low-pressure area which results in a larger central film thickness. Therefore, due to use of the free-volume model, the present results are more consistent with experimental observations than previously reported numerical results.     

Inverse approach for estimating rheological characteristics of adsorption layer in thin film EHL contacts

A modified Reynolds equation is derived for thin film elastohydrodynamic lubrication (TFEHL) by means of the viscous adsorption theory. This TFEHL theory can be used to explain the deviation between the measured film thickness and that predicted from the convenient elastohydrodynamic lubrication (EHL) theory under very thin film conditions. Results show that the thinner the film, the greater the ratio of the adsorption layer to the total film thickness becomes, and the greater the value of the pressure–viscosity index (z′). An inverse approach is proposed to estimate the pressure distribution based upon the film thickness measurement and to determine the pressure–viscosity index of oil film, and the thickness (δ) and the viscosity ratio (η^*) of the adsorption layer in TFEHL circular contacts. Based on TFEHL theory, the inverse approach can reduce z′ error, and provides a reasonably smooth curve of pressure profile by implementing the measurement error in the film thickness. This algorithm not only estimates the pressure, but also calibrates the film shape. Consequently, it predicts z′, η^*, and δ with very good accuracy. It can also be used to evaluate the lubrication performance from a film thickness map obtained from an optical EHL tester. Results show that the estimated value of z′ is in very good agreement with the experimental data.     

Starved Grease Lubrication of Rolling Contacts

Many grease lubricated roller bearings operate in the starved elastohydrodynamic (EHL) regime where there is a limited supply of lubricant to the contact (1). Under these conditions the film thickness drops to a fraction of the fully flooded value (2) and, thus, it is difficult to predict lubrication performance, or bearing life, from conventional EHL models. In this regime film thickness depends on the ability of the grease to replenish the track rather than the usual EHL considerations. The conventional view of grease lubrication is that base oil bleeds from the bulk reservoir close to the track, replenishing the inlet and forming a fluid EHL film (3). Resupply, under starved conditions, will thus depend on both operating conditions and grease parameters. The aim of this paper is to evaluate the influence of these parameters on starved lubrication in a rolling contact. Starved film thickness has been measured for a series of greases and the results have been compared to the fully flooded values. These show that the degree of starvation increases with increasing rolling speed, base oil viscosity and thickener content but decreases at higher temperatures. In many cases an increase in absolute film thickness is obtained when moving from high viscosity base oil to a low one, this result is the reverse of normally accepted EHL rules. Taking the fully flooded film thickness as a guide to lubrication performance is therefore not valid as grease film thickness in the starved regime is determined by local replenishment rather than bulk rheological properties.     

Film Formation in EHL Point Contacts under Zero Entraining Velocity Conditions

The contacts of adjacent balls in a retainerless bearing are subjected to the zero entrainment velocity (ZEV). The existence of an effective elastohydrodynamic lubrication (EHL) film between contacts running under ZEV conditions has long been proven experimentally. However, the classical EHL theory predicts a zero film thickness under ZEV conditions. Mechanisms, such as the thermal viscosity wedge effect and immobile film theory, have been proposed to tentatively explain the phenomenon. However, detailed numerical results are needed to provide theoretical evidence for such film formations. This paper aims to simulate, based on the viscosity wedge mechanism, the film formation of EHL point contacts under ZEV conditions. Complete numerical solutions have been successfully obtained. The results show that the thermal viscosity wedge induces a concave film profile, instead of a parallel film (Hertzian) as postulated by some previous researchers. By the simulation solver developed, the variation of film thickness with loads, oil supply conditions and ellipticity parameters have been investigated. Some unique lubrication behaviors under ZEV conditions are demonstrated. Furthermore, preliminary quantitative comparisons with the latest optical EHL experiments are finished. Both results are in good correlation.     

Thin film elastohydrodynamic lubrication—a power-law fluid model

A 1-D modified Reynolds equation for power-law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL). The lubricating film between solid surfaces is modeled as three fixed layers, which are two adsorption layers on each surface and a middle layer between them. The comparisons between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the TFEHL model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity. The thickness and viscosity of the adsorption layer and the flow index influence the lubrication characteristics of the contact conjunction significantly. The film thickness increases with the increase of flow index. As the flow index becomes greater, the dimple in the film shape moves towards the center of the contacts. The effect of flow index produces an obvious difference in the pressure distribution. The greater the flow index, the greater the pressure spike, and the pressure spike tends to move toward the center. The larger the flow index, the more the velocity varies in both the middle layer and adsorption layers along the Z-axis. The greater the thickness and viscosity of the adsorption layer and the flow index, the greater the deviation in central film thickness versus speed between EHL model and TFEHL model produced in the very thin film regime.