MECHANISM OF BOUNDARY LUBRICATION UNDER POINT CONTACT

The acid number of the mixed solution of 150SN oil and oleic acid characterizes the volume content of oleic acid in the solution, based on which the adsorptive capability of oleic acid is studied on the 45 steel balls and disks. Boundary lubrication tests are carried out on a self designed ball-on-disk machine. The base oil is pure 150SN oil, and oleic acid as additive are added into the lubricant. Disks have surface roughness values (Ra) of 0.8μm and 0.4μm. The electrical contact resistance method is used to determine the lubrication status. Hypothesize that the molecular film is monomolecular layer in condensed state and the opposing surfaces are completely separated by molecular film. A boundary lubrication model is established according to experimental results and hypothesizes. The experimental and calculational results show that the adsorption of polar molecules on steel surface is the main factor to form the boundary lubrication film. Load and sliding speed contribute little to the friction coefficient of boundary lubrication. The properties of steel surface and additive for the lubricant significantly influence on the characters of boundary lubrication. The smaller the surface roughness value is, the smaller the friction coefficient of the boundary lubrication is.     

纳米级混合润滑研究

混合润滑是机械中广泛存在的润滑状态。从试验方面研究了由接触、边界润滑和薄膜润滑组成的点接触区混合润滑状态的特性,提出使用动态接触率来描述混合润滑状态,并研究了各种参数对动态接触率的影响。结果表明,在混合润滑状态下,动态接触率与接触中心平均膜厚成指数函数关系。速度和粘度的增大会减小动态接触率,载荷的增加则会增大接触率,极性添加剂分子的使用会减小实际粗糙峰之间的接触,从而降低动态接触率。另外,低速下,综合粗糙度小的摩擦副表面的接触率要大于粗糙度大的表面的接触率;随着卷吸速度的提高,粗糙度小的表面的动态接触率小于粗糙度大的表面的动态接触率。     

FRICTION IN GEAR TEETH UNDER EXTREME PRESSURE LUBRICATION

ＦＲＩＣＴＩＯＮＩＮＧＥＡＲＴＥＥＴＨＵＮＤＥＲＥＸＴＲＥＭＥＰＲＥＳＳＵＲＥＬＵＢＲＩＣＡＴＩＯＮＳｕｎＤｅｚｈｉ；ＹａｏＹｕｑｕａｎ；ＭａＸｉａｎｇｕｉ（ＮｏｒｔｈｅａｓｔｅｒｎＵｎｉｖｅｒｓｉｔｙ）ＡｂｓｔｒａｃｔＴｈｅｄａｔａｍｅａｓｕｒｅｄ...     

基于系统和时变观点的齿轮胶合分析

探讨了多种胶合英文术语的定义及相互关系，提出了初期胶合（轻微擦伤）的概念，并认为胶合以轻微擦伤为先导。作者建议对ＧＢ３４８１─８３《齿轮轮齿损伤的术语、特征和原因》进行修改。基于系统分析观点，将影响齿轮摩擦学性能的各种因素概括为环境、工况、结构、材料和润滑五个方面，并阐述了这五个方面的内涵。据此，又基于摩擦学的时变观点，阐述了具有时变观点的因素。在上述分析的基础上，提出了系统的和时变观点的齿轮胶合机理分析。     

系统时变观点的齿轮胶合机理的求解思路

基于系统的和时变的观点~［１］，提出了表征系统摩擦学状态的参数，并定量地研究了系统运行过程中的摩擦热和摩擦表面力学性能、摩擦体热膨胀、润滑油性能及润滑状态、边界膜润滑能力、接触状态、摩擦系数等的变化及其对系统工作状态的影响，提出了摩擦学系统工作状态参数和不同胶合磨损形式的判别式。在此基础上，提出了预测初期胶合发生及胶合程度的数值计算思路。     

Global and local analysis of gear scuffing tests using a mixed film lubrication model

Gear tests were performed in a FZG test rig in order to evaluate the influence of the operating conditions (torque, speed and oil bath temperature), gear geometry and base oil viscosity on gear scuffing.A mixed film lubrication model was used to evaluate the normal pressures and shear stresses in several points along the gear meshing line, for each load stage and for all the gear scuffing tests performed.The gear scuffing results were analyzed using two different approaches: one considering global gear parameters defined at the meshing line scale and another based on local parameters at the roughness asperity scale, determined using the mixed film lubrication model.The analysis at the roughness asperity level was used to complete the scuffing study performed with global gear contact parameters, explaining the occurrence of scuffing during ‘running-in’, justifying the zones in teeth flanks where the first scuffing marks appear and supplying indicators for low scuffing resistance at high oil bath temperatures.     

纳米级润滑膜的粘度修正与薄膜润滑计算

根据纳米级润滑膜的试验测试结果提出薄膜润滑状态的粘度修正公式 ,并在此基础上建立了润滑膜厚度计算的数值计算方程。将该数值计算结果与弹流理论计算值和试验值进行对比表明 ,在薄膜润滑条件下 ,膜厚与速度和润滑油粘度的关系与弹流润滑计算结果相差较大 ,可明显看出弹流润滑向薄膜润滑的过渡 ,所提出的粘度修正式与试验结果则有较好的一致性     

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。     

The comparisons of sliding speed and normal load effect on friction coefficients of self-mated Si3N4 and SiC under water lubrication

The effects of sliding speed and normal load on friction coefficients of self-mated Si₃N₄ and SiC sliding in water after running-in in water were investigated with pin-on-disk apparatus at sliding speeds of 30 to 120 mm/s, normal loads of 1 to 14 N in ambient condition. The results showed that, after running-in in water, for two kinds of self-mated ceramics, friction coefficient increases with both decreasing sliding speed and increasing normal load when normal load is larger than a critical normal load. Friction coefficient was independent of normal load when normal load is smaller than the critical load. The lubrication film of Si₃N₄ under water lubrication exhibited larger load carrying capacity than that of SiC did. Stribeck curves indicated that, for self-mated Si₃N₄ ceramics, hydrodynamic lubrication will change into boundary lubrication abruptly when the sommerfeld number is less than a critical value; while for self-mated SiC ceramics, hydrodynamic lubrication will change into mixed lubrication and then into boundary lubrication gradually when the sommerfeld number is below critical value.     

An investigation of the damping effects of various gas environments on a vibratory MEMS device

An experimental investigation of the damping effects in several different gas chemistries on a vibrating micromachined structure was conducted. A corresponding numerical study using an analytical model was also performed and the results correlated with the experimental observations. The analytical model is based on the compressible Reynolds equation. The theoretical and experimental quality factor show reasonable agreement for different gases. As expected, the quality factor decreases as the gas pressure increases. Both experiments and numerical predictions suggest that these various gases may not affect the mechanical behavior significantly, and could be used for their unique electrical properties, such as permittivities.     

薄膜润滑分层模型

根据轴承表面对液体分子的作用大于液体内部的作用,使液体的粘度随与表面的距离而变化,把润滑层分为三层,与表面紧邻为粘变层,中间为常规的等粘度层。由此根据液流连续性推导出广义雷诺方程。     

A cavitation algorithm for arbitrary lubricant compressibility

A general cavitation algorithm that accommodates for an arbitrary density–pressure relation is presented. It is now possible to model the compressibility of the lubricant in such a way that the density–pressure relation is realistic throughout the contact. The algorithm preserves mass continuity for cavitation caused by bearing geometry and surface topography. It is a commonly accepted physical assumption that the contribution of the pressure driven flow is negligible in the cavitated region. This phenomenon is adopted in the present algorithm, which is similar to that of Elrod, and is modeled by a switch function that terminates the pressure gradient at the cavitation regions. Results with this algorithm for different density–pressure relations are presented and discussed. The effects of inlet conditions, such as surface roughness and starvation, on the load carrying capacity of the contact are analyzed.     

非牛顿流体微观热弹流润滑理论

求得了非牛顿流体线接触微观热弹流润滑的准稳态数值解。结果显示,横向微凸体能够造成强烈的局部动压,且微凸体越高或越窄,动压效应便越强。     

油环轴承试验研究

提出了一种以整个轴承组件为试验对象,以泄油流量为贫油润滑状态度量指标的油环轴承试验新方法,设计、建立了实现这种方法的试验装置,具体试验研究了某引进技术高速油环轴承的润滑性能。试验在较宽的工况范围内测量轴承流量、热平衡温度及油环运动学参量等重要性能数据,试验结果及分析结论为改进油环轴承设计准则提供了依据。     

静压气体轴承超声速现象的研究与发展

简述了静压气体轴承的类型及发展,回顾了静压气体润滑轴承中超声速流动现象的理论与试验研究,比较分析了它们的特点与不足,指出供气压力低、承载能力小是传统气体轴承不可克服的缺点。根据气体动力学理论和已进行的相关试验。详细分析了超声速静压气体润滑轴承的性能优势,即没有供气压力的限制,承载能力可以随供气压力的提高成比例提高。计算流体力学的发展为超声速气体轴承的研究提供了有力的技术工具,根据气体轴承内各段不同的流动特点,采用分场计算的方法可以得到精确的气体润滑模型,最后指出了超声速静压气体轴承将成为气体轴承的一个新的发展方向。