Ultra-thin lubricating films under transient conditions

Abstract

The mechanism of fluid film lubrication in ultra-thin conjunctions under counterformal concentrated circular point contacts is discussed in this paper. The significance of squeeze film action in increased load carrying capacity is highlighted. The numerical predictions made in acceleration-deceleration motion of a ball against a flat race is found to conform with the experimental findings of other research workers for polar branched lubricants down to a film thickness in the region of 20 nm. This conformance with the experimental findings has enabled a fundamental understanding of the multi-physics of film formation when conditions promoting the formation of ultra-thin films of the order of few nanometres have been employed, with the use of a non-polar lubricant. This paper provides the first ever solution of the combined effect of viscous, surface and molecular forces under transient conditions.

Thermohydrodynamics of lubricant flow with carbon nanoparticles in tribological contacts

“…These forces would include electrostatic repulsion as well as long range van der Waal interactions. They also become dominant with reduced contact load, thinness of lubricant film (mixed and boundary regimes of lubrication) as well as smoothness of contacting surfaces [10,33]. The aggregation of nanoparticles and the attachment/adsorption of particles to the solid boundaries is a function of these forces, as well as the Faxen viscous force in their detachment, also not included in this preliminary analysis.…”

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

“…A solution can now be obtained for θ, h, p, δ, ρ and η, by representing equation (7) in finite differences and obtaining a solution through low relaxation effective influence Newton-Raphson method with Gauss-Seidel iterations (Al-Samieh and Rahnejat [1], Teodorescu et al [16] and Chong et al [20]). The procedure places the hemispherical feature at consecutive reducing separations h 0 from the surface of the flat semi-infinite plane.…”

“…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:…”

“…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 .…”

“…OMCTS is a non-polar fluid with molecular diameter of around 1nm. Al-Samieh and Rahnejat [1] have shown that near molecularly smooth surfaces the behaviour of such a fluid is dominated by the solvation effect for films of up to several molecular diameters deep. Chan and Horn [2] have shown that there is discretised drainage of OMCTS from such conjunctions, indicating its near surface solvation effect.…”