Complete numerical solutions are obtained for the steady-state line contact thermal elastohydrodynamic lubrication (TEHL) problems. The contact surfaces are arranged to run in opposite directions. The slide-roll ratios are allowed to be as high as infinity. The new theory reveals that the characteristics of the high slide-roll contacts are significantly different from those of the low slide-roll contacts. The unusual zero-entrainment films discovered by Dyson and Wilson and the abnormal surface-dimple phenomena observed by Kaneta et al. are explained.

A full numerical solution for the thermal EHL problem in circular contact formed by steel-glass conjunctions with slide-roll ratios larger than 2 has been carried out. An anomalous film profile, which is similar to that reported by Kaneta et al. (1996), has been obtained. The numerical results by the authors, involving three basic kinds of film profiles, the kinematic conditions for the formation of dimples, and the variations of dimples and traction behavior with operating conditions, have been carefully compared with the experiments by Kaneta et al., and provided a sound theoretical evidence of the dimple phenomena under steady-state conditions. The present study indicates that the temperature-viscosity-wedge effect seems to be an essential mechanism for the dimple phenomena.

Studies of elastohydrodynamic lubrication (EH L) frequently utilize the phenomenon of optical interference which is exhibited when an illuminated steel ball is in contact with a partially Crcoated glass disc in conjunction with a lubricant layer of known refractive index. The use of the steel and chromium surfaces enables lubricants having simila r refractive indices to glass to be examined. The EH L contact is composed of two microscopically thin layers: the Cr coating and the lubricant ®lm, bounded by the glass disc and the steel ball. That the two-beam interference method frequently used in optical EH L research may induce signi®cant errors in the measurement of ®lm thickness is reported in this paper. A theoretical analysis which includes consideration of the effects of both multibeam interference and optical absorption within the Cr ®lm and the steel surface is presented. The analysis is used to devise a multi-b eam intensity-based test technique which has been validated for a wide range of lubricant ®lm thickness measurements at a resolution of 1 nm and offers a practical minimum detectable ®lm thickness as thin as 1 nm.

The behaviours of point contact elastohydrodynamic lubrication (EHL) films under impact loads are investigated by direct observations using the optical interferometry technique. It has been found that when the initial impact gap is large, a central dimple is formed and the maximum film thickness occurs at the centre of the contact region. When the initial impact gap becomes small, a periphery dimple is generated and the maximum film thickness occurs at the contact periphery. When impact is applied to an oily Hertzian contact, the maximum film thickness of the periphery dimple is determined by the increasing rate of the Hertzian contact radius. The impact load under rolling/sliding conditions results in a crescent-shaped oil entrapment originally at the inlet of the EHL conjunction, which passes through the EHL conjunction approximately at the entrainment velocity. Some numerical results are also presented to show that the experimental observation in the periphery region is induced by the local squeeze effect.

This paper presents a deliberately designed elastohydrodynamical lubrication (EHL) experiment for the study of the individual effect of the limiting shear stress and wall slippage. Very slow entrainment speeds were employed to avoid influential shear heating and oils of high viscosities were chosen to ensure that the conjunction was under typical EHL. An anomalous EHL film, characterized by a dimple at the inlet region, was obtained. Literature revealed that this inlet dimple was reported in some numerical studies taking into consideration the limiting-shear-stress characteristics of the lubricant and wall slippage. It was found that even under the same kinematic conditions, different types of film shape would be generated by simple disc sliding and simple ball sliding. Simple disc sliding produces an inlet dimple with a comparatively thick inlet film thickness, which droops rapidly toward the outlet region. For simple ball sliding, there is also an inlet dimple but the central film thickness is rather uniform. However, by prerunning the conjunction at a zero entrainment velocity (at the same linear speeds but in opposite directions) before the sliding experiment, the slope of the central film of simple disc sliding becomes smaller. It is probably due to the modification of solid-liquid interface, i.e., the slippage level, by the highly pressurized and stressed prerunning conditions. With a prescribed prerunning, which can produce very similar films at simple disc sliding and simple ball sliding, variation of film thickness was studied and it was found that the inlet dimple film has obvious dependence on entrainment speeds, but was not sensitive to loads. The present experimental results can be considered as direct evidence for those numerical findings of the inlet dimple. Tentatively, an effective viscosity wedge is proposed to account for the formation of the inlet dimple.