外加电场作用下双电层电粘度对水润滑特性的影响

根据双电层理论,建立了外电场作用下流体润滑中的双电层引起的电粘度效应的数学模型,并通过组合滑块水润滑试验考察了双电层的电粘度效应对流体润滑性能的影响。结果表明,外加电场作用下,双电层电粘度效应对摩擦因数具有明显影响;当速度较低时,随着外加电压的增加,摩擦因数明显增大;随着速度的增加,摩擦因数增大幅度减小;试验结果同所建立的数学模型相符。     

双电层电粘度对薄膜润滑影响的试验研究与数值分析

由于固液界面处存在双电层,理论和试验研究都表明该效应对薄膜润滑有较为明显的影响。首先,利用自行设计的外加电场重构双电层装置进行了组合滑块水润滑试验,结果分析表明:双电层所引起的电粘度效应对流体润滑中摩擦因数有明显影响,另外当摩擦副的材料不同时,摩擦因数的变化规律不同。然后,又对KCl(氯化钾)溶液进行了组合滑块试验,进一步研究了离子浓度对电粘度效应的影响,在不同速度和溶液浓度的工况下,对摩擦因数进行了测量。结果表明:低浓度溶液使摩擦因数明显增加,浓度高时摩擦因数减小;随着速度的增加,双电层效应对摩擦因数的影响减小。最后,对试验工况进行了数值分析。     

离子双电层动态输运特性及电场对液体油膜压力的影响

随着流体动压润滑向纳米尺度发展,离子双电层对润滑性能的影响不能忽视。考虑到润滑过程中摩擦副相对速度是可变的,提出一种考虑离子动态输运特性与流场及电场耦合的离子双电层润滑模型,分析摩擦副相对运动速度和Zeta电势差对润滑膜的影响。分析结果表明：摩擦副相对运动造成了电势不均衡分布,平衡电势偏向于运动壁面Zeta电势,且相对速度的增大加剧了不均衡性;Zeta电势差对润滑液体承载能力影响显著,当Zeta电势差从0开始增大时,双电层电黏度效应及润滑液体承载能力先增大后减小。提出的模型实现了速度可变的双电层润滑瞬态仿真,为变工况下的双电层润滑性能分析奠定理论基础。     

薄膜润滑中双电层效应影响分析

根据Poisson—Boltzmann双电层理论,详细推导了润滑区中双电层产生的流动电场,并进一步建立了考虑双电层电粘度效应的薄膜润滑数学模型。然后,对润滑中双电层效应进行了数值分析,对不同的电粘度公式进行了比较,结果表明薄膜润滑中,双电层的电粘度效应使流体粘度显著增加,同时润滑膜厚也明显增加。     

润滑液对电控摩擦的影响研究

研究了二氧化硅/黄铜摩擦副在不同水基润滑液中的摩擦行为对外加电场的响应,发现中性的盐类水溶液做润滑液时外加电压使摩擦副的摩擦因数大幅增加。不同的盐溶液做润滑液时,摩擦因数对外加电压的响应速度不同,其中溶解度高的长链有机钠盐溶液做润滑液时二氧化硅/黄铜的摩擦因数对电场的响应速度快且稳定性好。而碱类和酸类溶液做润滑液时,外加电压使二氧化硅/黄铜摩擦副的摩擦因数减小。     

工况条件对微型汽车离合器摩擦副摩擦因数的影响

分析了影响摩擦因数的因素,设计了一套试验方案,在高温摩擦磨损试验机上研究了工况条件对微型汽车离合器摩擦副摩擦因数的影响规律.结果表明:微型汽车离合器摩擦副的摩擦因数随工作载荷和滑动速度的增加先减小,然后逐渐趋于稳定;随着温度的上升,摩擦副的摩擦因数先下降,当温度上升到摩擦片的软化温度时,摩擦因数开始回升,当温度继续上升到摩擦片的分解温度时,摩擦因数又开始下降.     

有无电流条件下温度对碳/铜摩擦副摩擦磨损性能的影响

通过销-盘摩擦磨损试验,研究了碳/铜摩擦副在有无电流条件下的摩擦学性能。结果表明:试验过程中摩擦副温度不断地升高,且有电流时摩擦副温度比无电流时高,滑板材料的磨损量随着温度的升高而增大;当无电流通过时,摩擦因数随温度的升高先增大后减小,当有电流通过时,摩擦因数随温度的升高而减小。观察碳滑板磨损前后表面形貌发现:磨损表面随摩擦副温度的升高变得越来越光滑;当无电流通过时,磨粒磨损和黏着磨损是主要磨损类型,当有电流通过时,磨损类型以氧化磨损和电弧烧蚀为主。碳滑板材料磨损表面EDS分析发现,元素转移和氧化现象在磨损过程中时有发生。     

压铸镁合金AZ91D摩擦磨损性能的研究

采用MM-200型磨损试验机，研究了干滑动摩擦条件下载荷和磨损时间对液态压铸成形镁合金AZ91D摩擦磨损性能的影响，借助扫描电镜探讨了材料的磨损机理。试验结果表明：当滑动速率为0．618m／s、载荷为20～250N时，液态压铸镁合金的磨损速率和摩擦因数均随着载荷的增大而增大，当载荷增大到250N之后，试样的磨损质量反而减小；随着磨损时间的增加，压铸镁合金的磨损质量损失呈线性比例增大，其摩擦因数在0．220～0．235范围内波动；T4和T6热处理对高载荷下镁合金材料的耐磨性能有一定的影响；随着载荷的增大，各种状态下镁合金材料的磨损机制均发生了由氧化磨损、剥层磨损、粘着磨损到熔化磨损的转变。     

大滑滚比工况下弹流摩擦试验研究

针对大滑滚比工况,在自行改造的双盘摩擦磨损试验机上,完成了一系列线接触弹流摩擦试验;测量了不同工况下的摩擦因数,对试验结果进行了全面的分析,得到了一系列摩擦曲线,反映了多种具体工况下,各工况参数对摩擦因数的影响.结果表明:载荷比较小时,摩擦因数对载荷或转速的变化非常敏感;随着载荷的增大,摩擦因数对载荷与转速的敏感程度急剧下降;大滑滚比工况下,摩擦因数随滑滚比的变化幅度不大;摩擦因数随载荷增大而减小,且减小幅度随载荷增大而减小;摩擦因数随转速增大而减小,且减小幅度随转速增大而减小.     

基于分形理论的滑动摩擦表面接触力学模型

依据分形理论,考虑微凸体变形特征及摩擦作用的影响建立滑动摩擦表面接触力学模型。采用一个三次多项式来表达弹塑性变形微凸体的接触压力与接触面积的关系,从而满足在变形状态转变临界点处的微凸体接触面积与接触压力转化皆是连续和光滑的条件。推导出滑动摩擦表面临界弹性变形微接触面积、临界塑性变形微接触面积、量纲一真实接触面积的数学表达式。理论计算结果表明,表面形貌一定时,真实接触面积随着载荷的增大而增大;载荷一定时,真实接触面积随着特征尺度系数的增大而减小,随着分形维数的增大先增大后减小;当表面较粗糙时,摩擦因数对真实接触面积的影响很小;随着表面光滑程度的增大,摩擦因数对真实接触面积的影响增大,真实接触面积随着摩擦因数的增大而增大,特别是当摩擦因数较大时,真实接触面积增大的幅度也较大。接触力学模型的建立,为研究滑动摩擦表面间的摩擦磨损性能提供了依据。     

Theoretical analysis and experimental study on the influence of electric double layer on thin film lubrication

A new mathematical model for thin film lubrication is established by taking into account the effect of an electric double layer. In the present paper, experiments are carried out on a self-made tester. With a composite block and a rotating disk, influence of electric double layer on thin film lubrication is studied. Two different methods are used to reconstruct the field of electric double layer so as to change its effect. One is to change the ionic concentration of lubricants by adding additives, and the other is to apply an external electric field on friction pairs. According theoretical analysis, both the methods will apparently change the electro-viscosity of the lubricant film so as to change the lubrication performances. After theoretical calculation of electro-viscosity is amended according to the experimental results, the equations of electro-viscosity are presented. The results show that the equivalent viscosity of fluid induced by the effect of electric double layer apparently increases with the decrease of thickness of the film while the lubrication film is thin enough. The effect of electro-viscosity is weakened as the thickness of the film increases. Moreover, the effect of electro-viscosity increases with the increase of external electric field at first. When the voltage reaches a certain value, the electro-viscosity begins to decrease. __________ Translated from Tribology, 2005, 25(6) (in Chinese)     

Modeling and analysis of interfacial electro-kinetic effects on thin film lubrication

At the interface between a solid and a following liquid, charge migration within the electric double layer causes an electro-viscous force to develop which manifests itself as an enhanced fluid viscosity. Based on the Poisson–Boltzmann equation, a new mathematical model of the electro-viscosity is developed. Numerical analysis is carried out taking into account the influence of the electric double layer on thin film lubrication. Analysis results show that the electro-viscosity leads to a significant increase in the film thickness in the thin film regime (below 100 nm).     

外加电场对3种陶瓷/金属摩擦副摩擦行为的影响

使用自制面接触往复式滑动摩擦磨损实验机,采用质量百分比浓度为１％的硬脂酸锌水基乳化液作为润滑剂,研究了边界润滑状态下外加直流电场的几处施加方式对３种摩擦副在低速滑动时摩擦行为的影响。实验结果显示,外加电压的存在显示地改变了３种摩擦副的摩擦系数以及摩擦系数曲线的平稳程度,摩擦系数是最大相对增加量和最大相对减少量分别达到２００％和４０％。摩擦系数的改变与外加直流电压的通断是对应的,不同摩擦副对电压接通     

Investigation of the Stability and Tribological Performance of Ionic Nanoliquids

In previous studies, nanoparticles and ionic liquids (ILs) have been used separately as oil additives and have been shown to reduce friction and wear. In this study, the stability and tribological performance of ionic nanoliquids (INLs), which combine nanoparticles and miscible ionic liquids together as oil additives, were investigated. Zinc oxide nanoparticles were dispersed in a mixture of polyalphaolefin (PAO) oil and ionic liquid (tetradecyltrihexylphosphonium bis (2,4,4-trimethylpentyl phosphinate)) using an ultrasonic homogenizer. The coefficient of friction was studied using a tribometer with a ball-on-disk configuration. The wear track was measured using a Bruker Contour GT-K Optical Profiler and the wear volume was calculated. The effects of concentration and load on the coefficient of friction and wear were investigated. The effects of ultrasonic mixing time and nanoparticle concentration on the stability of the solutions were also studied.     

双电层对润滑薄膜厚度与压力的影响

利用修正的Reynolds方程对在不同金属-陶瓷（Fe和Cu及陶瓷材料Al2O3,SiN4、ZrO2和SiO2）水润滑中的双电层的影响进行了分析。通过数值计算,分别对流体润滑、弹流润滑的线、点接触的情况做了计算。计算结果表明:在膜厚较薄（几十纳米）时,双电层电势对润滑膜的厚度有较明显的影响,使最小膜厚明显增加,随着膜厚的增加这种影响将迅速减弱。而双电层的存在对润滑膜的压力分布影响不大。     

Effects of external electric fields on frictional behaviors of three kinds of ceramic/metal rubbing couples

In this paper, effects of external electric fields on frictional behaviors of Al₂O₃/brass, Al₂O₃/stainless steel and Al₂O₃/carbon steel couples under boundary lubricating conditions were studied on a self-made plate/plate type tribotester. Emulsion of 1 wt% zinc stearate dispersed into deionized water was used as lubricant in the experiments. The experiment results have shown that external electric fields affect the friction coefficient and its fluctuation of each rubbing couple substantially. The three couples showed different rates of change in friction coefficient and different tendency of change as the field was turned on and off during the rubbing process. Results acquired from experiments carried out in a wide range of external voltage, from 0 to 110 V, indicating that friction coefficient of Al₂O₃/brass couple increases monotonously with the intensity of the external electric field, although no linear relationship was found between them.