Static friction at fractal interfaces

TL;DR

This paper investigates how multiscale fractal surface structures influence static friction, revealing that higher fractality increases friction in elastic asperities, while adhesive interactions can minimize friction at intermediate fractality levels.

Contribution

It introduces a spline-assisted-discretization method to analyze asperity interactions on fractal surfaces, linking surface fractality with static friction behavior.

Findings

Higher fractality increases friction in elastic asperities.

Adhesive strength affects overall friction depending on surface fractality.

Optimal fractality (~1.3-1.5) minimizes friction in adhesive systems.

Abstract

Tribological phenomena are governed by combined effects of material properties, topology and surface-chemistry. We study the interplay of multiscale surface structures with molecular-scale interactions towards interpreting static frictional interactions at fractal interfaces. By spline-assisted-discretization we analyse asperity interactions in pairs of contacting fractal surface-profiles. For elastically deforming asperities, force analysis reveals greater friction at surfaces exhibiting higher fractality, with increasing molecular-scale friction amplifying this trend. Increasing adhesive strength yields higher overall friction at surfaces of lower fractality owing to greater true-contact-area. In systems where adhesive-type interactions play an important role, such as those where cold-welded junctions form, friction is minimised at an intermediate value of surface profile fractality found to be around 1.3 to 1.5. Results have implications for systems exhibiting evolving surface structures.