Soft lubrication

TL;DR

This paper explores how soft substrates influence fluid-induced lubrication, revealing increased surface separation and optimal conditions for maximum normal force, with implications for biological and soft material applications.

Contribution

It introduces a model analyzing lubrication on soft elastic layers, identifying optimal material and geometric parameters for maximum normal force.

Findings

Soft substrates increase surface separation during lubrication.

An optimal combination of properties maximizes normal force.

Results applicable to bio-lubrication and soft elastic materials.

Abstract

We consider some basic principles of fluid-induced lubrication at soft interfaces. In particular, we show how the presence of a soft substrate leads to an increase in the physical separation between surfaces sliding past each other. By considering the model problem of a symmetric non-conforming contact moving tangentially to a thin elastic layer, we determine the normal force in the small and large deflection limit, and show that there is an optimal combination of material and geometric properties which maximizes the normal force. Our results can be generalized to a variety of other geometries which show the same qualitative behavior. Thus they are relevant in the elastohydrodynamic lubrication of soft elastic and poroelastic gels and shells, and in the context of bio-lubrication in cartilaginous joints.