An Ultrathin Liquid Film Lubrication Theory—Calculation Method of Solvation Pressure and Its Application to the EHL Problem

Abstract

This paper describes a new method for calculating the solvation pressure that acts between solid surfaces when the surfaces approach each other to within a very small distance in a liquid medium. Solvation pressure is calculated by solving the transformed Ornstein-Zernike equation for hard-spheres in a two-phase system with Perram’s method and using the Derjaguin approximation. Furthermore, the authors apply the new method to the elastohydrodynamic lubrication problem in which the film thickness is very small and solvation force and van der Waals force cannot be neglected. It will be shown that the calculation results agree well with experimental data. The results are then compared with two conventional solvation pressure models proposed so far, namely, Chan and Horn’s model, and, Jang and Tichy’s model. It is found that these two models neglect the elastic deformation of solid surface when obtaining the experimental parameter used in their models; thus they overestimate the solvation pressure resulting in the prediction of larger film thickness than the experiments.

Effect of lubricant molecular rheology on formation and shear of ultra-thin surface films

“…Then, discrete lubricant molecular behaviour pursues, followed by a stepwise drainage from the contact, roughly in accord with the molecular diameter of lubricant, which are assumed to be spherical. This finding conformed to the experimental observations of Chan and Horn [2] and predictions of Matsuoka and Kato [5]. Therefore, for fairly thin films, the pressures generated in the conjunction are due to a number of mechanisms, whose individual contributions vary according to the gap size, h(x, y) :…”

“…The analysis here shows that even with assumed steady state condition the transient nature of solvation and its interplay with hydrodynamics can result in non-uniform distribution of lubricant on surfaces. Now returning to figure 3, as the gap is reduced, fluid film discretization occurs (as noted by Matsuoka and Kato [5], and Al-Samieh and Rahnejat [1]). Layers of lubricant molecules are drained in a step-wise fashion from the conjunction, in this case at gap intervals of 1nm; the diameter of spherical molecules of OMCTS.…”

“…Matsuoka and Kato [5], Abd Al-Samieh and Rahnejat [4] and Al-Samieh and Rahnejat [1,11] also assumed the same for the bulk hydrodynamic behaviour of the lubricants such as those described above and used in the current analysis. Clearly, for the cavitated region: ρ = ρ c when p = p c .…”

“…Al-Samieh and Rahnejat [1] and Matsuoka and Kato [5] solved the Reynolds equation to obtain the hydrodynamic contribution. For the point contact geometry, the two dimensional Reynolds equation is:…”

Thin film lubrication in the past 20 years

“…A remarkable lubrication regime that solves the transition from boundary lubrication to EHL has been revealed, termed thin film lubrication (TFL) [4,5], which has been systematically investigated since the 1990s by a number of researchers, such as Johnston et al [18], Luo et al [19−22], Tichy [23,24], Hartal et al [25], Matsuoka and Kato [26], Gao and Spikes [27] and so on. Luo and Yian [28] suggested a gap-bridging model by describing the interlaced change of qualitative lubrication and quantitative parameters in 1989, which can be considered to be the embryo of the thin film lubrication model.…”