Self-sustained lift and low friction via soft lubrication

TL;DR

This paper demonstrates how a soft lubricated interface can produce self-sustained lift and significantly reduce friction in the motion of a submerged cylinder, with implications for natural and engineered low-friction systems.

Contribution

It introduces a minimal experimental setup and a scaling model explaining elastohydrodynamic lift and low friction in soft wet solids, confirming recent theoretical predictions.

Findings

Emergent steady-state sliding with reduced friction.

Elastohydrodynamic lift explains self-sustained lubrication.

Potential applications in reducing wear and landslides.

Abstract

Relative motion between soft wet solids arises in a number of applications in natural and artificial settings, and invariably couples elastic deformation and fluid flow. We explore this in a minimal setting by considering a fluid-immersed negatively-buoyant cylinder moving along a soft inclined wall. Our experiments show that there is an emergent robust steady-state sliding regime of the cylinder with an effective friction that is significantly reduced relative to that of rigid fluid-lubricated contacts. A simple scaling approach that couples the cylinder-induced flow to substrate deformation allows us to explain the emergence of an elastohydrodynamic lift that underlies the self-sustained lubricated motion of the cylinder, consistent with recent theoretical predictions. Our results suggest an explanation for a range of effects such as reduced wear in animal joints and long-runout landslides, and can be couched as a design principle for low-friction interfaces.