Effect of Film Thickness on Slip and Traction Performances in Elastohydrodynamic Lubrication by a Molecular Dynamics Simulation

The nonequilibrium molecular dynamics simulations were carried out to study the slip and traction properties of a traction fluid with effect of film thickness, under high-temperature and -pressure conditions. The thinnest film of about 14 Å presents a solid-like structure which shows a two-layer discrete distribution. The film of about 24 Å corresponds to the intermediate state between the solid-like and liquid phases. With the increasing film thickness, a continuous bulk structure confined by solid-like phases appears in the central region, leading to relatively loose interlayer structure. The velocity profile across the film was then analyzed to obtain the shear property. It indicates that the thinnest film shows a plug-slip shear, the relatively thick films show a shear localization, and the thickest film of about 86 Å shows a stick–slip phenomenon. The slip length increases and then reaches the maximum as the film thickness increases to 63 Å, which is related to the change of solid-like phase near the inner surface of slab. Finally, the traction coefficient illustrates the locally lowest value of 0.08 in the moderate film of 42 Å while the highest value is reached in the two-layer system. The inverse proportion relationship between slip length and traction coefficient is obtained. This study is helpful to understand the flow and traction characteristics and their relationship in elastohydrodynamic lubricant for the important use in new infinitely variable transmission systems.