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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
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采用线接触光弹流实验装置,在摆动工况下研究滚子在零卷吸速度条件下的弹流特性,探讨不同周期同一载荷下滚子摩擦副在零卷吸速度时油膜厚度的变化情况,以及载荷对零卷吸速度下滚子弹流特性的影响。结果表明:在滚子转速近零卷吸速度时,挤压效应起主导作用,油膜被封在接触区内,形成凹陷,并且该处油膜较为稀薄;在往复运动工况下,滚子周期性运动的次数影响零卷吸速度时滚子的油膜厚度,在起动瞬间滚子中部的油膜厚度最小,随着摆动次数的增加,滚子中部的油膜厚度逐渐增加,多次摆动后,油膜将达到相对稳定的厚度;载荷对滚子零卷吸速度下的弹流特性影响较大,随载荷的增大接触区增大,滚子端部最小油膜厚度变小,滚子端部边缘效应增大。 相似文献
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为了揭示重载变速工况下的弹流润滑特性,在自行开发的光干涉弹流实验装置上,开展了相关的实验研究。实验主要针对钢球点接触,在重载(0.83GPa)和超重载(1.44GPa)两种载荷和变卷吸速度工况条件下,对弹流油膜进行了测量,获得了有效的实验数据。结果表明:重载和超重载条件下形成的弹流油膜都具有马蹄形特征。但超重载的没有重载的马蹄形特征明显。卷吸速度为零时有明显的封油现象,随着卷吸速度的增加,由卷吸速度产生的流体效应使得膜厚增加。另外,在进行超重载实验时,随着实验时间的延长,镀铬膜玻璃表面会有较多划痕,甚至出现玻璃表面被压溃的现象。 相似文献
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载荷对凹陷表面的动态微弹流润滑特征的影响 总被引:1,自引:0,他引:1
研究了表面凹坑在不同接触载荷和滚滑率的情况下,通过弹流润滑区时对油膜压力和形状产生的干扰现象。根据对微弹流润滑特征分析发现,只有在表面存在相对滑动的条件下,进入弹流接触区的表面凹坑才随接触载荷 的增加被逐渐地压平变浅;而在纯滚动条件下,进入弹流接触区的表面凹坑深度几乎与载荷大小无关保持不变;所有条件下因表面凹坑进入弹流接触区产生的油膜干扰凹陷深度与载荷大小无关而保持一个稳定的值。 相似文献
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One of the main features of typical elastohydrodynamic lubricating (EHL) contacts is the unique horseshoe film shape, which can be readily observed by using interferometry and quite accurately modelled by the well-established EHL theory. However, an anomalous EHL film, characterized by a wedge shape together with a tiny dimple at the inlet region, is observed under pure sliding conditions with ultra slow speeds of 3–800 μm/s in an optical EHL test rig. The variations of the wedge and the inlet dimple with different sliding speeds and loads are investigated using a series of polybutene oils of high viscosities. It is found that the inclination of the wedge is dependent on sliding speeds, loads and oil viscosities. The dimple always occurs at the inlet. The appearance of an inlet dimple together with a wedge film shape is reported for the first time. The phenomenon can be attributed to a non-Newtonian characteristic of the lubricant: the limiting shear strength. Additionally, the influence of starvation on the film shape is also examined. 相似文献
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Preliminary experimental work has been carried out to identify some of the boundary slip phenomena of highly pressurised polybutenes
in an elastohydrodynamic lubrication (EHL) conjunction. The movement of the oil is signified using an entrapment that can
be readily formed by the impact of a steel ball against a layer of oil on a glass block in an optical EHL test apparatus.
The post-impact lateral movement of the entrapment was investigated under the conditions: (i) pure rolling, (ii) pure glass
block sliding (steel ball stationary) and (iii) pure ball sliding (glass block stationary). It was observed that under pure
rolling the entrapped oil travels within the contact region at the entrainment speed, which is correlated with EHL theory.
Under pure glass block sliding conditions, the speed of the entrapped oil core is less than the entrainment speed, and in
the extreme cases, this core can be nearly stationary. Under pure ball sliding conditions, the oil core moves at a speed greater
than the entrainment speed. The observation indicates that the oil/steel ball interface can sustain higher shear stress than
the oil/glass (chromium coated) interface and there is a boundary slip in terms of relative sliding at the latter interface
under the experimental conditions. Furthermore, the amount of slip increases with an increase in the pressure. These experiments
provide evidence of the existence of wall slippage, which leads to the abnormal EHL film profile characterised with an inlet
dimple as reported earlier. 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
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This article presents a study on the movement of an oil entrapment (or impact dimple) in a pure rolling elastohydrodynamic
lubricated (EHL) contact. The oil entrapment was formed by impacting a steel ball against a lubricated glass disc. The contact
was then activated under pure rolling conditions, and the movement of the entrapped oil was visualized by optical interferometry.
It was found that during the movement of the dimple within the EHL contact, there exists a critical value for the displacement
of dimple core. For the displacement of the dimple core less than the critical value, the dimple moves at the entrainment
velocity and the film thickness of dimple core remains almost constant. For displacement beyond the critical value, the dimple
slows down and its depth decreases rapidly. The effects of influential factors such as speed, initial dimple depth, load,
and initial gap size were theoretically and experimentally investigated. 相似文献
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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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In situ pressure measurements in dimpled elastohydrodynamic sliding contacts by Raman microspectroscopy 总被引:1,自引:0,他引:1
In situ pressure measurements within dimples formed in glass-steel point contacts under various sliding conditions were performed using Raman microspectroscopy. Experiments were conducted using a ball-on-disc type apparatus in which a circular contact is formed between a rotating glass disc and a rotating steel ball. Film thickness distributions were measured by duochromatic optical interferometry. Polyphenyl ether oil (5P4E) which has a high pressure-viscosity coefficient was used to produce a dimple in the contact area. Experimental results show that the pressure increases locally in the dimple zone and the pressure profile changes, accompanying the changes of the dimple location as a function of the slide-to-roll ratio. The maximum pressure is located downstream the maximum height of the dimple. The rheological response of the oil film under dimple occurrence conditions is discussed. 相似文献