讨论了速度、固体表面能、滑动比、润滑剂粘度和化学性能对薄膜润滑状态下油膜厚度的影响，以及弹流润滑向薄膜润滑转化条件和液体膜失效条件。进而提出了新的润滑状态划分准则以及不同润滑机理下膜厚的变化情况。

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。

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.

The determination of hydrodynamic film failure has become one of the key aspects in the study of thin film lubrication (TFL) since the hydrodynamic effect of fluid film at nano-scale can be observed with recently developed experimental techniques. In the present paper, the relative optical interference intensity, (ROH) technique with a resolution of 0.5 run in the vertical direction has been used to measure the film thickness. Experimental results show that the hydrodynamic effect can be clearly observed even at very low speed if the contact pressure is sufficiently low or if the viscosity of lubricant is comparatively high. When the pres-sure increases to a certain degree, the fihn will suddenly drop to the dimension of several layers q/molecules and this is where the failure of the fluid film has taken place. For different viscosity of lubricants, the fluid film failure occurs at different rolling speeds and pressures. In addition, when the normal load becomes high-er, a higher speed or larger viscosity is required to form the fluid film in the contact region. Finally, the effects of pressure, viscos-ity, and velocity on the occurrence of fluid film failure have been examined and a relationship involving the three parumeters is proposed.