Lubricated sliding friction: Role of interfacial fluid slip and surface roughness

Abstract

We derive approximate mean field equations for the fluid flow between elastic solids with randomly rough surfaces including interfacial fluid slip and shear thinning. We present numerical results for the fluid flow and friction factors for realistic systems, in particular, we consider the case of an elastic cylinder with random surface roughness in relative sliding contact with a flat rigid (low-energy) countersurface. We present experimental data for the sliding friction between rubber stoppers and glass barrels lubricated with baked-on silicone oil. We find that the frictional shear stress acting in the rubber asperity contact regions is nearly velocity independent for velocities in the 10-1000 μm/s range, and very small τ f ≈ 0.04 MPa, while for bare glass in silicone oil τ f is much larger and velocity dependent.

Rubber Adhesion and Friction: Role of Surface Energy and Contamination Films

“…On the silanized surface the contamination film binds weaker than on the clean surface but, nevertheless, it appear that in many cases there is negligible slip between the contamination film and the silanized glass surface. This differ from the result of a recent study where slip was observed between a rubber stopper and a glass barrel with baked-on silicone oil (Rotella et al, 2020). In wet conditions the silanazed glass surface result in a higher maximum friction coefficient than the hydrophilic glass surface.…”

“…For a silanized glass surface (see Figure 2C) some of the slip may be localized to the interface between the hydrophobic coating and the contamination film (Rotella et al, 2020), but the experimental results presented below indicate that the main slip again occur either within the contamination film or at the interface between the rubber and the contamination film. We will show below that the contamination film may be derived mainly from the rubber rather than from other origins.…”

Rubber Wear and the Role of Transfer Films on Rubber Friction on Hard Rough Substrates

“…However, the study in Ref. [12] indicates that even for very inert substrate the main slip may occur either within the contamination film or at the interface between the rubber and the contamination film.…”

Interfacial fluid flow for systems with anisotropic roughness

“…Fluid flow at the interface between elastic solids is a complicated topic, in general involving elastic deformations, complex fluid rheology and interfacial fluid slip [1]. In particular, the influence of the surface roughness on the fluid flow dynamics is a highly complex topic.…”

“…These factors depend on the average surface separationū, which will vary throughout the nominal contact region;ū is the local interfacial surface separation u(x, y) averaged over the surface roughness [2,3]. In several publications it has been shown how to calculate the fluid flow factors, which enter in the (modified) Reynolds equation, and the friction factors, which enter in the expression for the shear stress acting on the solids [1,[4][5][6][7][8][9][10].…”