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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。 相似文献
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It is well known that a sliding speed influences a lubricant film thickness of elastohydrodynamic rolling–sliding contacts significantly. The effect of sliding is described quite well for unidirectional rolling and sliding; however, there are a limited number of papers dealing with sliding in different directions. This study describes how the sliding direction influences elastohydrodynamic film shape under high sliding conditions. An optical ball-on-disc tribometer together with thin-film colorimetric interferometry method is used for a film thickness measurement. The results show that the sliding direction influences lubricant film shape and the effect is connected with dimple phenomena. The temperature–viscosity wedge effect is discussed as a possible mechanism. The results are important for a film thickness prediction under high sliding conditions and provide experimental evidence for an extension of elastohydrodynamic lubrication (EHL) theory. 相似文献
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Cases of elastohydrodynamic lubrication (EHL) point contacts running under opposite sliding conditions have been studied with consideration of the thermal effect for various loads and entrainment velocities. A thermal EHL solver has been developed and proven to be able to deal even with extreme cases under an infinite slide–roll ratio. Results show that film profiles featuring a dimple can be formed in the contact zone when the slide–roll ratio exceeds a certain level. Moreover, the present study provides theoretical evidence for the lubricating film build up in the case where the two bounding surfaces run with equal but opposite velocities. An effective lubricating film under zero entrainment speeds was experimentally proven by Dyson and Wilson [1] (Proc Instn Mech Engrs, 1968–1969 183(3P) 81) in the 1960's, which, however, cannot be explained by the isothermal EHL theory. 相似文献
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The authors showed in previous experiments with high viscosity polymeric lubricants that a non-classical elastohydrodynamic
(EHL) film, which featured an inlet dimple, could be generated under pure sliding conditions. The phenomenon was tentatively
attributed to boundary slippage. In this paper, much greater sliding is introduced in the experiments to gain further insight
into film formation under boundary slippage. By putting all of the results on a load versus entrainment speed chart, it is
found that the required conditions for the formation of the inlet dimple fall into an open triangular region in the chart.
The existence of the inlet dimple can be maintained for a larger speed range with a higher load. The minimum speed required
(the lower speed bound for the dimple existence) decreases only marginally with an increase in load but the speed of the disappearance
of the dimple (the upper speed bound) increases with an increasing load. Interferograms show that with an increase in the
slide-roll ratio, i.e., expanded boundary slippage, a bump occurs before the exit constriction, which indicates an obvious
drop in film thickness, and the location of the minimum film thickness in the whole EHL contact moves from the outlet constriction
to the center of the bump. The observed inlet dimple and bump have already been described in the previous numerical results
that consider boundary slippage, and provide more justification for the boundary slippage postulation in the experimental
films. 相似文献
6.
The study aimed to determine the formation of an adsorption film at elastohydrodynamic lubricated (EHL) contacts and its effects on EHL film shape and friction. Experiments were conducted on an optical EHL test rig with surfaces of different surface energies. A new type of “abnormal” EHL film shape characterized with three dimples in the inlet of the contact was obtained in pure ball sliding experiments with long-chain polybutene. The adsorption layer was inferred to be the main cause for the “tri-dimple” phenomenon. The “tri-dimple” formation was examined. Under a fixed speed, a single inlet dimple gradually broke into three dimples with increasing number of ball rotation, and it happened with slight increase in friction force. Three zones, namely a central and two lateral zones, of the contact were classified and characterized with different levels of influence on the adsorption layer. 相似文献
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An optical interferometric technique has been used to investigate fluid film thickness in sliding, isoviscous elastohydrodynamic contacts (I-EHL). Monochromatic two-beam interferometry has been employed to map lubricant film thickness across a range of applied loads and entrainment speeds. The contact was formed between an elastomer sphere and plain glass disc, illuminated under red light, λ= 630 nm. Experimental work has employed sunflower oil and glycerol/water solutions as the test lubricants, due to their similar refractive indices and varying viscosity. A black-and-white-image-intensified camera has been employed to capture interference images and a computer processing technique used to analyse these images, pixel by pixel, and create film thickness maps based on their gray-scale intensity representations. Comparison of film thickness results to theoretical models shows reasonable qualitative agreement. Experimental results show both a reduced horseshoe, which is limited to the rear of the contact, and wedge-shaped film thickness profile within the Hertzian contact region. This is unlike conventional hard EHL contacts where the horseshoe-shaped pressure constriction extends around the contact toward the inlet. Experimental results suggest that film thickness profiles take on a convergent wedge shape similar to that used in many hydrodynamic bearings. It is likely that this wedge is largely responsible for generating fluid pressure and therefore the load-carrying capacity of the contact. 相似文献
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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。 相似文献
10.
This paper describes interferometry measurement of the film profiles of sliding elastohydrodynamic lubrication (EHL) contacts
with spin. In the custom-made EHL test rig, spin motion is introduced through adjusting the center offset of the ball-on-disc
contact with respect to the disc rotation axis. A parameter, spin ratio S
sp, is employed to represent the spin level, which is defined as the ratio of the Hertzian contact radius to the center offset.
Experimental results show that with spin the film shape is obviously skewed, and the film thicknesses at the two side lobes
are no longer the same; therefore, the symmetry of the classical horseshoe film shape is lost. The film thickness dependences
on entrainment speeds are significantly influenced by the spin ratio S
sp, and high spin ratios induce high speed indices. At a fixed spin ratio S
sp, with increasing sliding speeds the film thickness difference between the two side lobes becomes large, and the horseshoe
film shape is more distorted. When applied loads are raised, more spin is introduced, film thickness decreases, and film shape
is obviously twisted. 相似文献