Soft Elasto-Hydrodynamic Lubrication

This article examines the use of ferrofluids to control starvation in lubricated contacts. Starvation in a ball–plate contact is experimentally studied under sliding–rolling conditions using a Mini Traction Machine (MTM). Friction is measured and the experimental results are presented in the form of Stribeck curves. The volume of lubricant is controlled in such a way that no free bulk oil is present in the vicinity of the contact. An abrupt change in the slope of the Stribeck curve in the Hydrodynamic Lubrication zone is interpreted as the onset of starvation. It is then shown that the use of ferrofluids in the presence of a magnetic field distribution can change the conditions at which this onset of starvation occurs. Different magnetic field distributions are tested for different values of load and ferrofluid viscosity. It is proposed that ferrofluid lubricants in conjunction with a suitably positioned magnetic field can be used to promote replenishment, and thus control and reduce lubricant starvation.     

Elasto-Hydrodynamic Lubrication of Rolling-Contact Surfaces

An X-ray technique is described for the measurement of the thickness and shape of thin oil films (from 5 to 50 millionths of an inch thick) formed between the rolling and rolling-sliding surfaces of hardened steel rollers as in rolling bearings and gears. The film thickness with white mineral oil, diester-base, and silicone lubricants was found to vary with temperature (viscosity), speed, and load in much the same way as expected from elasto-hydrodynamic considerations. The shape of the elastically flattened contact regions on the rollers appeared to change with rolling speed in such a way as to explain why ball bearings and gears have longer fatigue life (in revolutions) at high speed than at low speed.

The experimental results are compared with lubrication theory in which the elastic deflections of the bearing surfaces are combined with the viscous flow of the lubricant under pressure. Although there is general agreement between theory and experiment, possible modifications to the theory to account for the increasing discrepancy with experiment at high speed, load, and viscosity are discussed.     

激光微造型表面固体润滑性能研究

采用声光调Q二极管泵浦固体光源(DPSS)Nd:YAG激光器,在45#钢试样表面进行表面微造型加工。以聚酰亚胺(PI)和二硫化钼(MoS2)复合固体润滑材料作为固体润滑剂,通过两步加温固化黏结工艺成功制备微造型固体润滑试样。在MMW-1A型摩擦磨损试验机上进行光滑无润滑试样、光滑表面固体润滑试样和微造型固体润滑试样的摩擦性能对比试验,以及微造型固体润滑试样在不同转速和压力下的摩擦性能试验。结果表明,在经过激光加工的微凹坑中填充复合固体润滑材料的试样,在摩擦过程中微凹坑中填充的固体润滑材料能有效转移到在摩擦表面,补充消耗掉的润滑材料,因而表现出更好的摩擦学性能。     

A Review of Elasto-Hydrodynamic Lubrication Theory

The development and understanding of elastohydrodynamic lubrication (EHL) can be traced back to the beginning of the previous century. However, it was not until 1949 that the first real solution of the problem was published. Since then, the technology has evolved enormously. In the current article a summary of these developments is given. Smooth surface EHL has become well established. Numerical methods, analytical solutions, and experimental techniques have become mature. Focus areas of research today are thermal EHL, starved EHL, friction (non-Newtonian lubricants), roughness, and grease. The scope of EHL is so wide that the authors needed select the topics of focus in this article. Therefore, in addition to the general overview of the areas of friction, analytical methods, starved EHL, and grease EHL are highlighted in this article.     

基于流体动压润滑效应的人工髋关节材料表面织构优化研究

以销-盘试验为模型,基于有限差分法,以Reynolds方程为理论基础,建立含有表面织构的人工髋关节材料的摩擦表面在全膜润滑下的数值模型,分析表面织构各个参数对两摩擦表面间油膜压力分布的影响。结果表明,在该模型条件下,销-盘摩擦表面间能够形成流体动压润滑,不同的表面织构参数对销盘摩擦表面间的油膜压力分布产生较大的影响。通过该模型可得到实现最佳摩擦表现的最优化的表面织构参数,从而为人工髋关节材料销-盘实验的设计提供参考。     

缸套表面环槽织构润滑性能数值分析

为了改善缸套-活塞环摩擦副润滑性能,在缸套表面采取了环槽织构措施,通过数值计算的方法,研究了环槽形新型织构的润滑摩擦机理,并对比分析了环槽与圆形凹腔织构润滑性能的差异。结果表明:当活塞环经过环槽织构时,在运动方向上,环槽中心圆柱前槽与后槽分别产生油膜压力较小与较大的动压润滑效应,即环槽能产生二次动压效应;与相同外径的圆形凹腔织构相比,存在一个最佳槽宽能有效改善润滑摩擦性能,在此数值以外,合适的槽宽能使环槽润滑性能较好,相比于圆形凹腔织构,润滑油膜压力分布更为均匀,最小膜厚比增加,摩擦力和摩擦平均有效压力均呈下降趋势,其原因是二次动压效应与面积占有率对环槽影响的叠加中,前者占据了主导地位;过小的槽宽会使得环槽织构润滑效果恶化。     

A Direct Solution of the Elasto-Hydrodynamic Lubrication Problem

A numerical scheme, suitable for digital computer use, is presented for the solution of the elasto-hydrodynamic problem. The variation of viscosity with pressure, compressibility, and, of course, surface deformations are included in this analysis. The method is applicable over a wide range of loads—from the lightly loaded situation where there is simple hydrodynamic lubrication up to the heavily loaded cases where the pressure distribution is closely related to the Hertzian pressure distribution for the contact of unlubricated surfaces. A series of solutions are presented which show the importance of the various effects and a study is made showing the transition region between the hydrodynamic and Hertzian pressure distributions.     

织物纹理在润滑条件下摩擦学性能的研究

对涤纶织物表面的纹理进行摩擦学性能试验研究。将表面为斜纹、平纹、仿平的3种纹理的涤纶织物试样分别黏附在45#钢盘表面,与直径为4mm的GCr15销配副,分别在机油和石蜡润滑下,在UMT-Ⅱ销-盘试验机上进行试验,研究其在不同速度和载荷下的摩擦学性能。结果表明,不同纹理的涤纶织物,相对于光滑试样均能显著降低摩擦因数,但其需要相对较长的跑合时间才能进入稳定的摩擦状态;润滑液黏度较高时,带有斜纹纹理的涤纶织物摩擦因数最低,润滑液黏度较低时,带有仿平纹理的涤纶织物摩擦因数最低。     

Improved Tribological Behavior of DLC Films Under Water Lubrication by Surface Texturing

Textured diamond-like carbon (DLC) films with the pattern of parallel grooves were developed by depositing DLC on textured stainless substrates in a PVD system. The texturing effects on tribological performance of DLC in water-lubricated condition were investigated. Results show that introducing specific patterns into DLC film not only retains the low friction coefficients, but also dramatically extends coating lifetime through affecting the coating delamination behavior and graphitization process during friction. Besides the adherence difference induced by surface texturing which could influence the delamination, another possible mechanism, “buffer stripes”, which is characteristic of the lateral soft/hard periodical structure, was proposed by us based on the Micro-Raman spectroscopy and nanoindentation analysis. Additionally, a much lower graphitization for textured DLC during friction may also be responsible for the improved wear resistance.     

缸套表面织构润滑性能理论及试验研究

通过将激光表面织构技术应用于发动机缸套表面,建立缸套-活塞环摩擦副混合润滑理论模型,并以桶面环为例,计算缸套表面织构对摩擦副润滑摩擦性能的影响规律。计算结果表明：缸套通过激光表面织构后,其润滑摩擦性能得到改善,凹腔织构效果要优于沟槽织构效果,在各行程中部油膜厚度最大增加了29%左右,而摩擦力峰值下降30%左右。通过发动机对比台架试验发现：相对于原机,配套表面织构缸套后发动机燃油消耗率呈现出下降趋势,在低转速下改善效果最为显著,燃油消耗率最大降低了9.8 g/(kW•h),降幅为4.62%,证实了表面织构技术对于降低发动机摩擦损失是有效的;同时发动机的其他性能指标也有不同程度改善,漏气量、烟度、全损耗系统用油消耗率等参数都有所下降,烟度下降明显,漏气量最大降幅为34.6%,全损耗系统用油消耗率降低了33.8%。     

直动滚子盘形凸轮弹流润滑分析

磨损是直动滚子盘形凸轮机构的主要失效形式之一,润滑形态是影响凸轮磨损的主要因素,利用弹流润滑理论,探讨直动滚子盘形凸轮机构的最小油膜厚度及其膜厚比的计算,为凸轮的摩擦学优.化设计提供参考.     

柴油机缸套表面微沟槽织构润滑性能仿真分析

针对缸套表面织构微沟槽形貌,建立了缸套-活塞环摩擦副混合润滑理论模型,并采用MATLAB编程计算来分析微沟槽形貌参数对其润滑摩擦性能的影响规律。结果表明：缸套表面微沟槽可以形成很好的油膜压力,有效地改善缸套-活塞环间的润滑状态;随着微沟槽角度的增大,最小膜厚比逐渐增大,其润滑效果也越来越好,综合考虑摩擦润滑性能和机油耗性能情况下,最佳的微沟槽角度为60°。在上止点附近,面积占有率变化Sp对量纲一摩擦力影响较大;在其他区域,面积占有率对摩擦力影响不大;综合考虑油膜厚度与摩擦力,当Sp=0.15时效果最好。随着微沟槽深宽比e的增大,量纲一摩擦力不断增大,当e从0.025增大到0.150时,平均量纲一摩擦力增大了2.3倍,但深宽比过大,润滑效果将会减弱。研究结果认为,最佳深宽比的范围为0.05~0.08。
     

弹流润滑球轴承-转子系统载荷特性分析

基于点接触弹性流体动力润滑理论,搭建了球轴承在弹流润滑状态下刚度-阻尼的计算公式,依据该动态刚度-阻尼建立了球轴承-转子系统动力学微分方程,采用数值方法求解系统在不同参数条件下的轴心轨迹、相图、分岔图,分析径向载荷对轴承-转子系统动力学特性的影响。研究表明,在弹流润滑油膜的作用下,具有动态刚度和阻尼的滚动轴承-转子系统显示出了更为复杂的非线性动力学特性;径向载荷是影响轴承转子系统的重要因素之一,较大的径向载荷有利于系统周期性运转。     

弹流润滑中圆柱滚子轴承接触体内应力分析

基于现代弹性流体动力润滑理论和弹性力学理论,建立了高速圆柱滚子轴承非等温时变的弹流分析模型、轴承套圈与滚动体接触时接触体内应力分析仿真模型。用数值分析方法对模型求解,并用Tecplot软件对轴承接触体内应力分布进行仿真。仿真结果分析表明,弹性流体动力润滑中轴承速度及其所受载荷是影响轴承接触体内部应力分布的主要因素;在不考虑其它因素情况下,接触区内中部靠接近表面的区域接触应力最高,改善接触体表面压力,可以有效改善接触体内等效应力分布。     

Optimization of Surface Texturing for Contact Between Steel and Ultrahigh Molecular Weight Polyethylene Under Boundary Lubrication

In this study, we developed a design method for surface texturing optimization and evaluated it experimentally. Square patterns composed of different fractions of pore shapes were prepared by using a nanosecond pulse laser on AISI 1045 steel surfaces. A pore diameter of 75 μm was used to design the area densities. The area density was 5–25 %, and the pore depth was 20–75 μm. Different area densities and pore depths were examined for optimization, and pin-on-disk sliding tests were performed using ultrahigh molecular weight polyethylene pins. The results showed that all of the coefficients of friction of the textured specimens were reduced regardless of the area density and aspect ratio. Optimization was performed according to the measured dimensions of the pores, and the optimized area density and pore depth under the current sliding conditions were found to be 25 % and 25 μm, respectively.     

A Study on the Tribological Behavior of Surface Texturing on Babbitt Alloy under Mixed or Starved Lubrication

Aiming at improving the tribological performances of sliding bearings in mixed or starved lubrication regime, textures in square and linear radiating arrays are ablated on the surface of Babbitt alloy disks by laser radiation. Series of pin-on-disk wear tests and computational fluid dynamics (CFD) analysis are conducted to investigate the influence of distribution and geometry of the textures under various operating conditions. Results suggest that surface texturing suitably interacts with the material properties of Babbitt metal favorably improving its tribological performance. Friction coefficients of the disks with textures arrayed in square are generally much lower and more stable as compared to their counterparts with textures arrayed in linear radiation. Also, textures arrayed in a square with an area density of 8.6 % allow the lowest friction coefficient, as low as 0.015, to be achievable. Theoretical analysis sheds the light that proper texture arrangements tend to generate favorable distribution of micro-hydrodynamic pressure to improve the tribological performance of Babbitt alloy significantly.     

山高刀具助力首都航天机械公司高精高效生产

<正>未来的某一天,我们将会看到这样的景象:来自世界任何一个角落的用户都能享受到由中国的卫星导航系统所提供的定位、导航、授时服务。事实上,这个"未来"并不遥远,我国的第二代卫星导航系统——北斗卫星导航系统将在2020年之前把这个美丽的设想变成现实。     

The Synergetic Effects of Surface Texturing and MoDDP Additive Applied to Ball-on-Disk Friction Subject to Both Flooded and Starved Lubrication Conditions

This paper reports a novel work on the synergetic effects of microscale surface texturing and lubricant friction modifier additive of molybdenum dialkyldithiophosphate (MoDDP) subject to both flooded and starved lubrication conditions. The experiments were performed on reciprocating ball-on-disk friction in GTL8 base oil with and without MoDDP. In the flooded lubrication condition, the test results demonstrated that the presence of the MoDDP additive contributed to lower friction coefficients and also more pronounced effect of surface textures on friction than in the case of the bare base oil. In the starved lubrication experiments, textured and texture-free surfaces in the oils with and without MoDDP additive were tested until an abrupt rising of friction coefficient was detected. The results showed that the magnitude of friction coefficient before terminating each test was the almost same for various tests, while the endurance time in different test conditions was significantly different. The textured surface exhibited longer endurance time than the texture-free surface, especially when the MoDDP additive was used. The mechanism of the synergetic effects of surface textures and MoDDP additive has been discussed based on the experimental observations in the following sections. This study provides a new idea for the application of surface texture in boundary lubrication when lubricant additive is contained in the lubricating oils.     

Surface Roughness Effect on Slider Bearing Lubrication

The effect of roughness of surfaces of a slider bearing on the load-carrying capacity and friction force, is studied. The distinction is made between waviness and roughness, the latter being treated as a random quantity which may be characterized by a probability density function, determined experimentally. Results can be obtained in closed form suitable for calculation if a Beta distribution is assumed. Actually, this can approximate quite closely a Gaussian distribution, yielding quite accurate results. However, the procedure developed can be carried out for any desired distribution.     

表面织构排布形式对其润滑特性的影响

建立不同排布形式表面织构的几何模型,基于N S方程并采用CFD方法分析其油膜压力分布,并考察其流场流动情况和不同间距对承载能力的影响。结果表明,不同排布形式的表面织构对润滑特性有很大的影响,其中,交错排布的表面织构具有最高的承载力。微凹坑之间存在最优间距,使其所产生动压效应的作用发挥得最充分。交错排布的微凹坑织构最优面积率比均匀排布的微凹坑织构有了很大的提高。