自旋对弹流油膜影响的试验研究

利用自制的旋滑式光干涉弹流薄膜测量系统,对带有自旋的钢球—玻璃盘接触副形成的弹流油膜形状和厚度进行试验研究。采用新的方法来获得自旋,即通过调节接触副与玻璃盘旋转中心的距离改变自旋分量的大小。试验结果表明,自旋导致油膜厚度降低,油膜形状也失去了经典的马蹄形相对卷吸中心线的对称性。当卷吸速度增加时,油膜厚度增加,油膜形状的非对称性增强;载荷增加,油膜厚度减小,油膜形状的非对称性增强;偏心距增加,油膜整体厚度增加,两侧油膜厚度差别减小,油膜形状的对称程度增加。     

旋滚条件下弹流油膜的试验研究

应用光干涉方法,对旋滚条件下钢球-玻璃盘接触副形成的弹流油膜进行了试验研究.在试验中,通过调节接触副与玻璃盘旋转中心的距离即偏心距来获得不同程度的自旋分量.试验结果表明,纯滚条件下两侧缘处相等的最小油膜厚度由于自旋分量的引入不再相等,较小的最小膜厚具有较大的速度指数.侧缘处最小膜厚的速度指数大于中心膜厚的速度指数.随自旋的增加,油膜形状的非对称性增加,最小油膜厚度减小.随载荷和滚动速度的增加,自旋引起的油膜形状的非对称性增强.     

弹流润滑中局部油膜增厚的数值模拟

通过理论计算模拟了Kaneta等在光干涉弹流试验中观察到的,当接触区钢球表面和玻璃盘表面反向运动时出现的反常油膜局部增厚现象,即润滑固体表面在接触区出现凹陷.对钢球-玻璃盘接触副进行了热弹流问题的完全数值求解,发现润滑中的热效应是形成凹陷的根本原因.当盘快球慢时有凹陷出现;而盘慢球快时无凹陷出现.讨论了凹陷的深度、位置和形状随运动条件、粘压系数及载荷等的变化.     

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。     

挤压条件下弹流油膜的摩擦学现象研究

纯挤压条件下弹流油膜的研究已证实了油膜的中央凹陷。研究利用常载荷下的钢球在较小的初始间隙下冲击附有润滑油的玻璃盘,在接触区外围出现了外围凹陷,而不是熟知的中央凹陷。研究结果表明当初始的冲击间隙较大时,油膜的压力分布和厚度以及中心压力-时间曲线中的峰值和接近结束时的中央凹陷都与以前的自由落球问题相似。随着初始的冲击间隙减小,最大压力从接触区中心转换到圆周外围区,相应地,中央凹陷变得越来越不明显而在外围区出现了圆周凹陷,进一步的数值分析,发现当油膜足够厚时在小的初始间隙条件下也出现了外围凹陷。这主要是当初始的冲击间隙变小时,中央油膜厚度比大冲击间隙条件下润滑油被"冰冻"时薄很多,中央凹陷不明显;在外围区域,表面间隙很小,局部挤压效应变强,因此形成了外围凹陷。     

弹流膜厚的测试方法述评

论述了弹性流体动力润滑油膜工测试方法的进展，分析了各种膜厚测试方法的特点及应用范围。     

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。     

表面织构凹坑对弹流润滑点接触摩擦力和成膜能力影响研究

零件之间形成的润滑接触在工程中广泛存在,在零件表面人工织构特定的形貌,改善接触的摩擦磨损性能,是目前工程表面设计的热点和前沿。建立等温条件下的润滑点接触分析模型,并考虑润滑粘度和密度随压力变化以及接触弹性变形,研究了表面圆柱形凹坑的直径、间距和排列方向对弹流润滑接触摩擦系数的影响。结果表明,过大或过小的凹坑直径都不利于形成油膜,降低摩擦;凹坑间距越小,对油膜形成有利,摩擦系数就越低。     

铁路客车滚动轴承弹流润滑状态研究

采用非牛顿流体动力润滑ＥＨＬ（理论），地脂润滑线接触铁路客车动轴承在其实际运行工况下的润滑状态进行了研究。润滑脂流变模型Ｈｅｒｓｃｈｅｌ－Ｂｕｌｋｌｅｙ模型。数值计算２改进的Ｏｋａｍｕｒａ算法，并综合考虑了润滑脂流变参数及轴承具体工况参数变化等因素的影响。在数值计算基础上，得到了铁路客车滚动轴承在不同车速下的脂膜厚比λ值。     

齿面凹坑参数对面齿轮等温弹流润滑的影响

根据微分几何基本理论求出面齿轮曲率半径,由齿面相对运动求得面齿轮传动过程中卷吸速度,建立面齿轮等温弹流润滑模型,通过FORTRAN语言编程计算出齿面油膜厚度,分析凹坑直径和深度对油膜膜厚的影响,并通过实验验证理论计算的准确性。研究结果表明:齿轮从啮入到啮出过程中,油膜厚度沿啮合轨迹逐渐增大;当齿面凹坑直径在50~200μm时有增加油膜厚度的作用,其中凹坑直径为100μm时效果最优;当齿面凹坑深度在5~20μm时均有增加油膜厚度的效果,存在最优深度为10μm。     

The Influence of Moving Dent on Point EHL Contacts

A transient analysis for a dent passing through the conjunction of a point EHL contact was developed and solved numerically by using the multigrid method. Results show that the presence of sliding produces a noticeable pressure ridge and thus, a surface indentation at either leading side of the dent if the dent moves slower than the opposite surface, or at the trailing side if the dent moves faster than the opposite surface. The pressure ridge and surface indentation extend their lengths forward or backward from the dent in the sliding direction at a rate approximately half the sliding speed. The pressure fluctuation associated with the dent increases with increasing slide-to-roll ratio and dent depth, and decreases with increasing dent width in both x- and y-directions. The agreement between numerical simulation and experimental results obtained by Wedeven and Cusano (I) is remarkably close.     

Effect of Slide-to-Roll Ratio on Interior Stresses Around a Dent in EHL Contacts

The present, study extends the transient EHL point contact model and subsurface stress field calculation model to examine the influence of a surface dent on interior stresses in an EHL point contact under various slide-to-roll conditions. Results revealed that under the pure rolling condition the effect of a surface dent on the stresses is quite negligible. The presence of a shallow surface dent is unlikely to reduce the contact fatigue, life so long as pure rolling motion and good lubrication conditions are maintained. Unfortunately, the same cannot be said of the contact if it is operating in the boundary lubrication regime.

When sliding was introduced, the surface indentation generated significantly high pressure spikes with a strong directional preference. These high-pressure spikes cause severe stress concentrations either below the trailing edge of the dent, if it moves faster than the opposing surface, or below the leading edge of the dent, if it moves slower than the opposing surface. The maximum von Mises stress moved close to the surface and significantly increased in value as compared to the smooth surface solution. For the case of simple sliding, the maximum von Mises stress is even greater than the value calculated for the boundary lubrication case.

In regard to maximum tensile principle stresses, the presence of a dent increased the stresses only marginally over the smooth surface solutions. It is unlikely that surface indentation would significantly reduce the contact fatigue life due to Mode 1-type crack initiation.     

Influence of spinning on the rolling EHL films

Spinning cannot be ignored in some elastohydrodynamically lubricated contacts. In this paper, spinning is incorporated into an elastohydrodynamic lubrication (EHL) contact of pure rolling and its influences on EHL films are studied. Results show that with increase in spinning, the symmetry of the film shape gets lost, and the minimum film thicknesses, located respectively at the two side-lobes, decrease and show more dependence on loads. The speed indices of the film thickness at the side lobes are higher than those of the classical EHL theory predicted. Numerical work has also been carried out to clarify the experiment measurements.     

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。     

The Influence of DLC Coating on EHL Friction Coefficient

High hardness, high elastic modulus, low friction characteristics, high wear and corrosion resistance, chemical inertness, and thermal stability are factors that make diamond-like carbon (DLC) coatings the subject of many studies. For the same reasons they also seem suitable for use in, amongst others, machine components and cutting tools. While most studies in the literature focus on the influence of coatings on wear and friction in boundary lubrication and pure sliding contacts, few studies can be found concerning rolling and sliding elastohydrodynamic lubrication (EHL) friction, especially in the mixed and full film regime. In this article tests are carried out in a Wedeven Associates Machine tribotester where an uncoated ball and disc pair is compared to the case of coated ball against uncoated disc, coated disc against uncoated ball, and coated disc against coated ball. The tests are conducted at two different temperatures and over a broad range of slide-to-roll ratios and entrainment speeds. The results are presented as friction maps as introduced in previous work (Bj?rling et al. in J Eng Tribol 225(7):671, 2011). Furthermore a numerical simulation model is developed to investigate if there is a possibility that the hard, thin DLC coating is affecting the friction coefficient in an EHL contact due to thermal effects caused by the different thermal properties of the coating compared to the substrate. The experimental results show a reduction in friction coefficient in the full film regime when DLC-coated surfaces are used. The biggest reduction is found when both surfaces are coated, followed by the case when either ball or disc is coated. The thermal simulation model shows a substantial increase of the lubricant film temperature compared to uncoated surfaces when both surfaces are coated with DLC. The reduction in friction coefficient when coating either only the ball or the disc are almost the same, lower than when coating both the surfaces but still higher than the uncoated case. The findings above indicate that it is reasonable to conclude that thermal effects are a likely cause for the decrease in coefficient of friction when operating under full film conditions, and in the mixed lubrication regime when DLC-coated surfaces are used.     

单个边缘微观损伤对铝合金材料蚀坑应力集中效应的影响研究

为获取边缘微观损伤对铝合金蚀坑产生的应力集中效应的影响及影响规律,采用ANSYS有限元方法,构建7B04铝合金半椭球体简化蚀坑模型、单个半椭球体包含一个边缘微观损伤的蚀坑模型,并基于线弹性断裂力学,开展两种蚀坑模型的应力集中效应计算分析.研究发现:边缘微观损伤对半椭球体蚀坑应力集中效应的数值大小、作用区域以及作用区域大...     

倒角参数对滚子弹流润滑性能的影响研究

工程上常对滚子摩擦副的滚子进行端部倒角,倒角参数包括倒角长度与倒角半径。取润滑油为Eyring流体,用多重网格技术研究了此类滚子的弹流润滑性能,研究表明:最小膜厚位置可能出现在修形起始位置和滚子最边缘。当最小膜厚出现在修形起始位置时为正常工作状态;当最小膜厚出现在滚子最边缘时膜厚很薄,即将润滑失效。进而分别讨论了倒角长度和倒角半径对弹流润滑性能的影响,研究表明:应根据工况参数通过弹流计算设计端部倒角参数,以优化滚子的润滑状态和载荷分布,实现全膜润滑。     

表面横向粗糙峰对点接触热弹流润滑的影响

通过数值解研究丁固体表面的横向粗糙峰对钢球与玻璃盘形成的热弹流润滑接触区压力、膜厚以及温度分布的影响。计算中假设钢球是静止的．即滚滑比为2。结果表明在粗糙峰出现的位置上，压力、温度均有急剧的增加，并且固体表面的凹陷现象也变得更加复杂。     

A Limiting Solution for the Dependence of Film Thickness on Velocity in EHL Contacts with Very Thin Films

In recent years there have been substantial improvements in the capabilities of numerical modeling of elastohydrodynamic lubricant (EHL) films and it is now possible to analyze a very wide range of conditions rather than needing to rely on extrapolation using classical film thickness regression equations such as those of Dowson and Higginson. However, a new controversy has arisen concerning the film thickness-velocity dependence in EHL contacts at very low speeds and high loads, with some predictions showing a film thickness much less than that predicted by the classical equations. The present article applies the well-established limiting analysis, first presented by Grubin-Ertel, to the inlet of the EHL contact. It is shown that when the load is high and the speed is low (and the pressure gradient is very high in the inlet) an accurate resolution of the inlet pressure rise is critical for the determination of the film thickness. Discretization errors of this type might be responsible for discrepancies between the classical equations and some recently published numerical predictions.