Contact of Single Asperities with Varying Adhesion: Comparing Continuum Mechanics to Atomistic Simulations

TL;DR

This study compares continuum mechanics predictions with atomistic simulations for nanometer-scale contacts, revealing significant effects of atomic roughness on contact properties and the limitations of continuum theory in such regimes.

Contribution

It demonstrates how atomic-scale roughness impacts contact mechanics and evaluates the accuracy of continuum theory in nanoscale contact analysis.

Findings

Atomic roughness significantly alters contact area and stress distributions.

Continuum theory can misestimate contact parameters at the nanoscale.

Friction and lateral stiffness vary greatly due to atomic effects.

Abstract

Atomistic simulations are used to test the equations of continuum contact mechanics in nanometer scale contacts. Nominally spherical tips, made by bending crystals or cutting crystalline or amorphous solids, are pressed into a flat, elastic substrate. The normal displacement, contact radius, stress distribution, friction and lateral stiffness are examined as a function of load and adhesion. The atomic scale roughness present on any tip made of discrete atoms is shown to have profound effects on the results. Contact areas, local stresses, and the work of adhesion change by factors of two to four, and the friction and lateral stiffness vary by orders of magnitude. The microscopic factors responsible for these changes are discussed. The results are also used to test methods for analyzing experimental data with continuum theory to determine information, such as contact area, that can not be measured directly in nanometer scale contacts. Even when the data appear to be fit by continuum theory, extracted quantities can differ substantially from their true values.