A Friction Model of Fractal Rough Surfaces Accounting for Size Dependence at Nanoscale

TL;DR

This paper develops a theoretical model for nanoscale friction on fractal rough surfaces, incorporating size dependence revealed by molecular simulations, and predicts how friction varies with roughness, load, and material properties.

Contribution

It introduces a novel friction model that accounts for size dependence at the nanoscale for fractal rough surfaces, bridging atomic simulations and macroscopic predictions.

Findings

Friction coefficient decreases with increasing contact area.

Friction coefficient decreases with increasing external load.

Model provides guidelines for designing friction pairs.

Abstract

Traditional laws of friction believe that the friction coefficient of two specific solids takes constant value. However, molecular simulations revealed that the friction coefficient of nanosized asperity depends strongly on contact size and asperity radius. Since contacting surfaces are always rough consisting of asperities varying dramatically in geometric size, a theoretical model is developed to predict the friction behavior of fractal rough surfaces in this work. The result of atomic-scale simulations of sphere-on-flat friction is summarized into a uniform expression. Then, the size dependent feature of friction at nanoscale is incorporated into the analysis of fractal rough surfaces. The obtained results display the dependence of friction coefficient on roughness, material properties and load. It is revealed that the friction coefficient decreases with increasing contact area or external load. This model gives a theoretical guideline for the prediction of friction coefficient and the design of friction pairs.