Texture-induced modulations of friction force: the fingerprint effect

TL;DR

This study uncovers a quasi-static, texture-induced mechanism causing periodic force oscillations in soft solid friction, with implications for tactile sensing and material design.

Contribution

It introduces a new mechanical model explaining force modulations due to surface patterning and non-linear friction in soft contacts.

Findings

Force oscillations are set by groove period and sliding velocity.

A quantitative model predicts force modulation amplitude based on load and surface roughness.

The effect is relevant for soft solids and tactile sensing applications.

Abstract

Dry solid friction is often accompanied by force modulations originating from stick-slip instabilities. Here a distinct, quasi-static mechanism is evidenced leading to quasi-periodic force oscillations during sliding contact between an elastomer block, whose surface is patterned with parallel grooves, and finely abraded glass slides. The dominant oscillation frequency is set by the ratio between the sliding velocity and the period of the grooves. A mechanical model is proposed that provides a quantitative prediction for the amplitude of the force modulations as a function of the normal load, the period of the grooves and the roughness characteristics of the substrate. The model's main ingredient is the non-linearity of the friction law. Since such non-linearity is ubiquitous for soft solids, this "fingerprint effect" should be relevant to a large class of frictional configurations and might in particular have important consequences in human (or humanoid) active digital touch.