基于 Evans-Johnson流变模型黏塑性流体弹流润滑的雷诺方程

分析了弹流润滑中润滑剂滑移的条件,指出了弹流润滑区域内可能存在6种润滑子区,首次基于Evans-Johnson流变模型为每个子区推得了雷诺方程.     

表面改性对滑动轴承弹流润滑的影响

考虑滑移边界条件,建立了极限剪应力模型和线接触弹流润滑模型,推导了润滑剂界面滑移速度,并修正了流体润滑Reynolds方程,针对界面改性后滑动轴承的润滑状态进行了探究。首先,分析了对轴瓦和轴颈界面均进行改性处理后,轴承润滑状态在整个弹流润滑接触区的变化;其次,分别研究了仅对轴瓦或者轴颈做改性处理的影响;最后,探究了界面改性对轴承摩擦因数的影响,并讨论了摩擦因数随载荷、速度的变化。结果表明,在弹流润滑的条件下,同时对轴瓦和轴颈进行表面改性处理时,油膜会在入口区形成凹陷,在出口区形成坍塌;仅对轴颈界面进行改性处理时,油膜会在整个接触区形成凹陷,对应的压力也会随之增加;相反,仅对轴瓦界面进行改性处理时,油膜厚度减小,压力降低;表面改性处理后,摩擦因数降低,并随载荷、速度的增大而减小。     

空间液体润滑剂弹流牵曳特性的研究

基于Johnson-Tevarrwerk模型对空间液体润滑剂的弹流牵曳特性进行理论研究,并采用高速球-盘式弹流牵曳力试验装置进行相同工况下的试验研究,证明Johnson-Tevarrwerk模型的理论分析很好地反映了空间液体润滑剂的弹流牵曳特性。研究结果表明:入口区的热效应不能忽略,等温牛顿模型不能用于空间液体润滑剂的弹流牵曳特性理论分析;在高滑滚比工况下,空间液体润滑剂弹流牵曳系数的非线性行为非常明显,高黏度空间液体润滑剂的流变行为必须由非牛顿流变模型描述。     

EMP径向滑动轴承计入边界滑移的热弹流分析

弹性金属塑料瓦（ＥＭＰ）径向滑动轴承是一种新型的轴承,轴瓦材料的特殊性使其热弹变形远大于普通金属瓦轴承,同时它所特有的边界滑移现象,对改善径向滑动轴承的润滑性能有较为明显的优越性。建立了计入边界滑移情况后对轴承３Ｄ热弹流分析的教学模型,并给出列,对其润滑机理进行了初步的分析。     

滑动条件下弹流润滑启动过程的实验观察

使用光干涉动态油膜厚度测量系统对不同启动条件下聚丁烯润滑油弹流油膜的形成过程进行了实验观测。结果表明,在纯滑动条件下,由于界面滑移弹流油膜存在反常的入口凹陷;卷吸速度相等时,较大的启动加速度产生较大的界面滑移,诱发较大的入口凹陷;不同的启动加速度,入口区的油膜形状和最小油膜厚度的变化也不相同。     

零卷吸预跑合对一类反常弹流油膜的影响

在极低速纯滑动的光弹流实验中,采用高粘度聚丁烯润滑剂形成的弹流油膜会在入口区出现凹陷,该反常的入口凹陷与极限剪切应力/界面滑移有关。针对盘纯滑和球纯滑2种不同的运动条件进行了油膜形状的测量,分析了零卷吸预跑合对油膜形状的影响。结果表明,一般地,纯玻璃盘滑动和纯钢球滑动产生的此类反常的油膜形状并不相同;当对弹流接触副采用零卷吸预跑合处理(即钢球和玻璃盘在接触区以大小相同方向相反的速度运动)之后,纯玻璃盘滑动形成的油膜形状有较大变化,油膜厚度增加,入口的楔形斜度下降,此时纯玻璃盘滑动和纯钢球滑动产生的油膜形状差别减小,甚至相同。     

单面界面滑移对阶梯轴承润滑性能的影响研究

由界面滑移理论模型可知,在传统阶梯轴承固体和液体交界处,如果界面处应力达到极限剪应力时,润滑剂就会发生界面滑移,此时润滑膜会失效,这将大大降低润滑膜的承载力。因此,很有必要研究界面滑移对轴承润滑性能的影响。考虑润滑油膜在阶梯轴承入口区静止接触表面上滑移而避免润滑油膜在轴承其他表面上滑移,给出了阶梯轴承润滑油膜承载能力和摩擦系数分析结果。算例得出,在一定工况下这种轴承的承载能力因界面滑移而提高,而其摩擦系数却因界面滑移而下降。     

液体润滑剂的黏度对边界滑移影响的实验研究

为了了解微纳米间隙中流体的流动特性,采用原子力显微镜对微纳米间隙中的固体和液体边界滑移进行了实验研究,主要研究了液体润滑剂的黏度对边界滑移的影响。实验中采用的固体样品为SiO2,液体样品为两种不同黏度的季戊四醇油酸酯,分子式为C77H140O8,黏度分别为32mm2/s和150mm2/s。采用相对速度法对实验数据进行了处理,结果表明,不同黏度的季戊四醇油酸酯和SiO2表面作用时都会发生边界滑移,黏度大,产生的滑移大。其原因是,随着黏度升高,邻近固体表面的液体分子与和固体表面相接触的液体分子之间的剪切力增大,可更加容易地克服固液界面间的作用力,更加容易产生边界滑移。     

界面极限滑移条件下的液膜密封流场平均速度分布规律

为研究液膜密封流场平均速度分布规律,及其与流-固界面剪切应力之间的关系,基于Couette流动模型建立存在边界速度滑移时的密封间隙流场速度计算模型,采用Mixture均相模型和Schnerr-Sauer空化模型,通过数值模拟考察界面无滑移(滑移速度为0)和无剪切(滑移速度最大)2种极限情况下不同转速时液膜轴向不同位置处的微流场径向、切向和轴向速度分布,并建立流体型槽界面剪切力-速度拟合模型。研究结果显示：液膜的切向速度远大于径向和轴向速度,三维合成速度分布规律主要由切向速度决定;流场在槽区内近台阶轴向1μm范围内压力梯度发生突变,但非槽区和槽区流场相对独立,非槽区可视为简单Couette流动,槽区为逆压梯度Couette流动;流-固界面粘附剪切应力的大小与液膜边界速度滑移密切相关,槽区界面剪切应力变小时,边界滑移速度和槽内外流场各方向速度均变大,且转速越高,数值越大;在不高于10 000 r/min时,空化效应对整体平均速度场的影响较小,但速度更高时,需量化空化效应,并对剪切应力-速度拟合模型进行修正。     

机械学专家温诗铸

(1)建立工程模型弹流润滑理论,奠定现代润滑设计的基础他相继在国际上提出以完备数值解为基础的考虑热效应的热弹流、考虑动态效应的非稳态弹流、考虑润滑剂非牛顿性的流变弹流以及分析粗糙表面的微观弹流等润滑理论,系统地建立了工程中各类弹流润滑问题的设计方法.在此基础上,导出当今普适性最高的润滑方程,并将上述各种实际因素全部纳入分析,建立了工程模型的弹流润滑理论,为现代润滑设计奠定基础.     

Energy Efficient Siloxane Lubricants Utilizing Temporary Shear-Thinning

This study investigates the rheologic properties, elastohydrodynamic film, and friction coefficients of several siloxane-based lubricants to assess their shear stability and their potential for energy efficient lubrication. Several siloxane-based polymers with alkyl, aryl, and alkyl-aryl branches were synthesized in order to examine the relationship between their molecular structures and tribological performance. Nuclear magnetic resonance spectroscopy and gel permeation chromatography were used to characterize the molecular structures and masses, respectively. Density, viscosity, elastohydrodynamic film thickness, and friction measurements were measured from 303 to 398 K. Film thickness and friction measurements were made at loads and speeds that cover the boundary, mixed, and full film lubrication regimes. These results illustrate that the shear characteristics of siloxane lubricants vary significantly with polymer length as well as branch structure and content. The findings provide quantitative insight into the features of siloxane molecular structure conducive to optimum film formation with minimum wear and elastohydrodynamic friction to enhance energy efficiency.     

Tribological Behavior of Some Candidate Advanced Space Lubricants

Performance of a variety of space lubricants was compared under boundary and elastohydrodynamic lubrication (EHL). The types of fluids studied were naphthenic mineral oil, paraffinic mineral oil, polyalphaolefin, and silahydrocarbon. The silahydrocarbon and the polyalphaolefin lubricants exhibited lower traction under similar conditions. A specific additive package increased the traction of the polyalphaolefin. Volatility characteristics of some of these fluids were also studied.     

Lubrication Properties of Polyalphaolefin and Polysiloxane Lubricants: Molecular Structure–Tribology Relationships

This study investigates the rheological properties, elastohydrodynamic film thickness, and friction coefficients of several commercially available polyalphaolefin (PAO) and polydimethylsiloxane (PDMS)-based lubricants to assess relationships between molecular structure and lubricant performance. Molecular structures and masses were determined by nuclear magnetic resonance spectroscopy and gel permeation chromatography, respectively. Density and viscosity are measured from 303 to 398?K, while elastohydrodynamic lubricant film thickness and friction measurements were made at temperatures, loads, and speeds that are representative of boundary, mixed, and full-film lubrication regimes. The results show that PDMS-based lubricants are thermally and oxidatively more stable than PAOs, while the viscosity of PDMS-based lubricants is generally less temperature sensitive than PAOs, except for highly branched polysiloxanes. In particular, this study provides quantitative insight into the use of PDMS-based lubricants to obtain low friction through the entire lubrication regime (boundary to full film) by optimal tuning of the molecular mass and chain branching.     

齿轮传动齿面摩擦因数计算方法的研究

从理论和实验2个方面,对复杂润滑状态下齿面摩擦因数的计算方法作了深入的系统研究。基于弹流润滑理论,综合研究了啮合周期内交变出现的完全弹流、混合润滑和边界润滑状态下齿面摩擦因数计算方法及其应用条件等。从齿面摩擦特性试验角度,对基于啮合点曲率半径等效原理的模拟试件和基于功率损失同摩擦功耗等效原理的试验齿轮的摩擦因数计算方法从实验原理、实验条件及结论进行了比较分析。指出了齿面摩擦因数动测实验的优越性;并补充了线外啮合冲击摩擦模型及其摩擦因数的计算方法。含系统误差与综合变形齿轮副在复杂润滑状态下的齿面摩擦因数的计算方法体系的完整构建,对全面地认识齿面摩擦规律,对齿轮失效、减摩降噪等研究具有积极的意义。     

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。     

界面滑移条件下弹流油膜的试验观察

在极低速纯滑动条件下完成高粘度聚丁烯弹流油膜的光干涉测量试验,观察到明显的油膜入口凹陷现象。试验结果表明,入口凹陷的深度随载荷的增加而增加,随卷吸速度的增加存在一个极大值。试验中润滑剂的粘度越高,入口凹陷越容易出现。纯滑动条件下,油膜厚度对速度和载荷的依赖关系明显偏离了经典的弹流理论。试验中观察到的入口凹陷证明了已有入口凹陷弹流数值分析的正确性。     

Lubricating Properties of Organic Phosphate Ester Aqueous Solutions

The lubricating properties of organic phosphate ester (DPZ) aqueous solution were investigated using the tribological testers and the home-built thin film interferometry. Experimental results indicate that DPZ can adsorb on the surfaces of rubbing pair, reduce the friction coefficient of boundary lubrication, and significantly improve the anti-seizure properties of water. Under the elastohydrodynamic lubrication (EHL), the lubricating film thickness decreases with the DPZ concentration increasing. It is thought that a preferential slip plane, which is created against the adjacent layer between the hydration sheath around the polar headgroups of DPZ molecules and bulk water, dramatically weakens the water film by breaking the H-bond network around surface.     

Reliable model of lubricant-related friction in internal combustion engines

A linear model of lubricant-related engine friction was developed. Based on lubrication fundamentals, the technique is comprised of three simple bench tests that respectively operate under thick fluid-film hydrodynamic lubrication, elastohydrodynamic lubrication, and boundary lubrication. With adequate configuration and appropriate test conditions, these bench tests are seen to simulate major friction losses in a typical internal combustion engine. Lubricant characteristics obtained in the bench tests were combined using SAS linear regression and correlated to ASTM Five-Car and Sequence VI engine tests. The linear model gave an excellent prediction of engine data. It further showed that hydrodynamic friction losses dominate lubricant-related engine friction, followed by boundary friction losses, and elastohydrodynamic or mixed friction losses. This simple, reliable, and inexpensive technique can be used as a research tool to study friction characteristics of crankcase lubricants and to develop superior fuel-efficient engine oils. Major findings from this study can be summarised as follows:

• 1 The linear model predicts that 5 to 6% fuel economy improvement over the industry high reference oil HR-4 is achievable with today's motor oil technology
• 2 Hydrodynamic friction losses in both ‘thick' and ’thin' fluid-film lubrication account for 63% of total friction losses caused by the engine oil while boundary friction losses amount to 37%.
• 3 Friction losses in the elastohydrodynamic (EHD) engine are significant, up to 22% of total friction losses. This, combined with the fact that EHD film thickness is the most significant parameter in the linear model, suggests that pressure effects (ie, high-temperature/high-shear/high-pressure viscosity, pressure-viscosity coefficients) are important.
• 4 Increasing fuel economy improvement is in general in the order: SAE 10W–40 < SAE 10W–30 < SAE 5W–30, providing that base stock and additive systems are unchanged.

     

Theoretical investigation of transient elastohydrodynamic lubrication with newtonian solid‐liquid lubricants

This paper reports a theoretical investigation of transient elastohydrodynamic lubrication of a line contact. A time‐dependent Reynolds equation and elasticity equations for compressible solid‐liquid lubricants were solved using finite volume and multigrid techniques. The lubricants used were mineral oils mixed with very small solid particles, MoS₂ and PTFE, which can be treated as Newtonian fluids. The two surfaces were initially at rest and in contact. The transient oil film pressure and oil film thickness were calculated numerically. This simulation showed the significant effects of solid particles on the lubrication characteristics.     

一种离子液体的热弹流润滑数值模拟

离子液体因微观结构与普通润滑油不同,使其具有较低的黏压系数。采用光干涉油膜测量技术标定一种离子液体的黏压系数,并通过等温数值计算验证其可靠性。使用标定的黏压系数,对该离子液体进行膜厚、温升、摩擦因数和接触区中心黏度等热弹流润滑数值计算,并与具有相同黏度的普通润滑油的算例进行比较。计算结果显示,离子液体与同黏度润滑油相比具有突出的摩擦学性能,体现在离子液体在较宽速度和滑滚比范围内有非常低的温升和摩擦因数,而膜厚仍保持在同黏度润滑油的40%以上。离子液体的这种热弹流特性主要归因于其较低的黏压系数。