# Shear-Induced Anisotropy in Rough Elastomer Contact

## TL;DR

This study reveals how shear forces induce anisotropy in micro-junction shapes within rough elastomer contacts, affecting macroscopic contact properties and highlighting a previously overlooked aspect in contact mechanics models.

## Contribution

It demonstrates shear-induced anisotropy in micro-junctions and links it to macroscopic contact behavior, extending understanding of rough elastomer contact mechanics.

## Key findings

- Micro-junction shapes vary with shear force.
- Anisotropy saturates in macroscopic sliding.
- Scaling law applies over four orders of magnitude.

## Abstract

True contact between randomly rough solids consists of myriad individual micro-junctions. While their total area controls the adhesive friction force of the interface, other macroscopic features, including viscoelastic friction, wear, stiffness and electric resistance, also strongly depend on the size and shape of individual micro-junctions. Here we show that, in rough elastomer contacts, the shape of micro-junctions significantly varies as a function of the shear force applied to the interface. This process leads to a growth of anisotropy of the overall contact interface, which saturates in macroscopic sliding regime. We show that smooth sphere/plane contacts have the same shear-induced anisotropic behaviour as individual micro-junctions, with a common scaling law over four orders of magnitude in initial area. We discuss the physical origin of the observations in the light of a fracture-based adhesive contact mechanics model, described in the companion article, which captures the smooth sphere/plane measurements. Our results shed light on a generic, overlooked source of anisotropy in rough elastic contacts, not taken into account in current rough contact mechanics models.