Static friction boost in edge-driven incommensurate contacts

TL;DR

This study investigates how static friction in incommensurate 2D contacts varies with size and loading configuration, revealing a sharp increase under edge-loading due to localized dislocations, supported by atomistic simulations.

Contribution

It demonstrates that static friction scaling and magnitude depend on loading configuration, highlighting the role of localized dislocations in incommensurate contacts.

Findings

Static friction increases sharply under edge-loading at a critical size.

Sublinear scaling persists despite localized commensurate regions.

Atomistic simulations support the relevance of elasticity effects in real contacts.

Abstract

We present a numerical investigation of the size scaling of static friction in incommensurate two dimensional contacts performed for different lateral loading configurations. Results of model simulations show that both the absolute value of the force $F_s$ and the scaling exponent $\gamma$ strongly depend on the loading configuration adopted to drive the slider along the substrate. Under edge-loading a sharp increase of static friction is observed above a critical size corresponding to the appearance of a localized commensurate dislocation. Noticeably, the existence of sublinear scaling, which is a fingerprint of superlubricity, does not conflict with the possibility to observe shear-induced localized commensurate regions at the contact interface. Atomistic simulations of gold islands sliding over graphite corroborate these findings suggesting that similar elasticity effects should be at play in real frictional contacts.