Beyond Quality and Quantity: Contact Distribution Encodes Frictional Strength

TL;DR

This paper reveals that the spatial distribution of contact points at an interface significantly influences static frictional strength, outperforming traditional measures like contact area and contact quality.

Contribution

The study introduces a novel approach showing that contact distribution encodes frictional strength, enabling better predictions without relying on contact quality or quantity.

Findings

Contact distribution predicts static friction more accurately than contact area.

Linear regression on contact images improves friction prediction by 3-7 times.

Spatial contact patterns encode key information about interfacial frictional strength.

Abstract

Classically, the quantity of contact area $A_R$ between two bodies is considered a proxy for the force of friction. However, bond density across the interface - quality of contact - is also relevant, and contemporary debate often centers around the relative importance of these two factors. In this work, we demonstrate that a third factor, often overlooked, plays a significant role in static frictional strength: the distribution of contact. We perform static friction measurements, $\mu$, on three pairs of solid blocks while imaging the contact plane. By using linear regression on hundreds of image-$\mu$ pairs, we are able to predict future friction measurements with 3 to 7 times better accuracy than existing benchmarks, including total quantity of contact area. Our model has no access to quality of contact, and we therefore conclude that a large portion of the interfacial state is encoded in the spatial distribution of contact, rather than its quality or quantity.