The mechanism of the transition from elastohydrodynamic lubrication (EHL) to thin film lubrication (TFL) has been studied with a technique of relative optical interference intensity for measuring the film thickness. The resolution of the instrument could reach 0.5nm in the vertical direction and 1.5 um in the horizontal direction. The factors influencing the measurement precision and the differences between EHL and TFL are discussed. Film thicknesses with different lubricants, velocities, and loads are measured. The experimental data show that the variation of the film thickness in TFL is not the same as that in EHL. As the rolling speed decreases, a turning point in the film thickness curve is found, which distinguishes TFL from EHL. Consequently, a TFL model with a fluid layer, an ordered liquid layer, and an adsorbed layer is proposed. Finally, the functions of the layers are discussed in detail.

The technique of relative optical interference intensity (ROII) was used to investigate the effect of molecular ordered degree of cholesterol esters in hexadecane on lubricating properties in thin film lubrication (TFL) regime. The results indicate that transition from TFL to elastohydrodynamic lubrication (EHL) occurs when the rolling speed varies in the range from 30 to 70mm/s for pure hexadecane. However, when cholesterol liquid crystal (LC) was added into hexadecane, the tran-sition phenomenon disappears. The film thickness is closely related to the number of carbon atoms in LC alkyl chain, the LC polarity, the concentra-tion of LC in hexadecane liquid, and the applied external DC voltage. When the thickness of these lubricant films increases to about 30 nm, it nearly keeps constant and hardly changes with the volt-age. The formation mechanism of the thin lubri-cating film in the nano scale is discussed.

利用考虑微结构与微旋效应的微极流体理论来研究薄膜润滑的特性。微极效应将引起等效黏度的增加，从而影响油膜厚度。它对压力分布和膜厚形状的影响很小。数值模拟结果表明，等效黏度的增加效应与实验值有很好的类似性。

In this paper, a viscosity modification model is developed which can be applied to describethe thin film lubrication problems. The viscosity distribution along the directionnormal to solid surface is approached by a function proposed in this paper. Based on theformula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressiblecondition is solved and the outcome is compared to the experimental data. In thin filmlubrication, according to the computation outcomes, the lubrication film thickness is muchgreater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequatelylow (i.e., film thickness is thin enough), the pressure distribution in the contactarea is close to Hertzian distribution in which the second ridge of pressure is not obviousenough. The film shape demonstrates the earlobe-like form in thin film lubrication, whichis similar to EHL while the film is comparatively thicker. The transformation relationshipsbetween film thickness and loads, velocities or atmosphere viscosity in thin film lubricationdiffer from those in EHL so that the transition from thin film lubrication to EHL canbe clearly seen.

Thin film lubrication (TFL) is a condition in which the lubricating features between twosurfaces in relative motion are determined by the combination of the properties of the surfaces andthe lubricant and viscosity of the lubricant. The effects imposed by couple stress on lubricationcharacteristics cannot be disregarded in this regime where the ordered molecules dominate thefluid field. There are different tensor measures and constitutive equations in this case other thanNewtonian case. The lubrication of two-phase (solid phase and liquid phase) fluid is investigated inthis paper. The existence of couple stress will enhance the lubricant viscosity and hence increasethe film thickness and improve the load-carrying capability. Size-dependent effects can be seen inthe lubrication with couple stress, and the thinner the lubricating film is, the more obvious the effectwill be.