Soft lubrication

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Original entry by Joerg Fritz, AP225 Fall 2009


"Soft lubrication"

J.M. Skotheim and L. Mahadevan: Physical Review Letters, 2004, 92, pp 245509-1 to 245509-4


Lubrication theory, Elsticity, Soft interface, Poroelasticity, Adhesion


Fig.1 Schematic illustrating the geometry and physics of soft lubrication. The thin non-conforming interface creates an anti-symmetric pressure distribution. This pressure distribution leads to a deformation of the elastic layer. This creates a different gap geometry and thus a new pressure distribution.

Nature is full of examples for soft lubrication. From the ejection of fungal spores over the flow of red blood cells in arteries to the movement of joints, the concept of reducing wear and adhesion between two surfaces with a thin film of water is ubiquitous. This gives rise to a very interesting problem that couples fluid mechanics and the elasticity of soft (e.g. biological) materials. This paper examines a model problem for symmetric nonconforming surfaces moving tangentially to each other, where a thin elastic layer covers one or both of them. The main result is that an optimal combination of material and geometric properties exists, which maximizes the normal force.

An exemplary scaling


Fig.2 A table summarizing the scalings for all cases considered in this paper.