Sliding Friction of Hard Sliders on Rubber: Theory and Experiment

TL;DR

This study combines theory and experiments to analyze sliding friction of steel sliders on rubber, revealing how viscoelastic dissipation and surface asperities influence friction under different conditions.

Contribution

It introduces a viscoelastic model that accurately predicts friction for lubricated rubber sliding and explores the effects of temperature and surface asperities on friction mechanisms.

Findings

Lubricated friction matches viscoelastic model predictions at room temperature.

Friction increases at low temperatures due to asperity penetration and adhesion.

Interfacial shear stress varies linearly with the logarithm of sliding speed.

Abstract

We present a study of sliding friction for rigid triangular steel sliders on soft rubber substrates under both lubricated and dry conditions. For rubber surfaces lubricated with a thin film of silicone oil, the measured sliding friction at room temperature agrees well with theoretical predictions obtained from a viscoelastic model originally developed for rolling friction. On the lubricated surface, the sliding friction is primarily due to bulk viscoelastic energy dissipation in the rubber. The model, which includes strain-dependent softening of the rubber modulus, accurately predicts the experimental friction curves. At lower temperatures ($T = -20^\circ {\rm C}$ and $-40^\circ {\rm C}$), the measured friction exceeds the theoretical prediction. We attribute this increase to penetration of the lubricant film by surface asperities, leading to a larger adhesive contribution. For dry surfaces, the adhesive contribution becomes dominant. By subtracting the viscoelastic component inferred from the lubricated case, we estimate the interfacial frictional shear stress. This shear stress increases approximately linearly with the logarithm of the sliding speed, consistent with stress-augmented thermal activation mechanisms.