# Tuning friction with composite hierarchical surfaces

## TL;DR

This paper explores how composite hierarchical surface structures with varying roughness and stiffness can be engineered to effectively control and reduce static friction, advancing surface design techniques.

## Contribution

It introduces a novel approach to tuning friction through hierarchical composite surfaces combining geometrical and material property variations.

## Key findings

- Hierarchical arrangements significantly reduce static friction.
- Varying local roughness and stiffness effectively modulates friction.
- Composite surface design offers new friction control strategies.

## Abstract

Macroscopic friction coefficients observed in experiments are the result of various types of complex multiscale interactions between sliding surfaces. Therefore, there are several ways to modify them depending on the physical phenomena involved. Recently, it has been demonstrated that surface structure, e.g. artificial patterning, can be used to tune frictional properties. In this paper, we show how the global friction coefficients can also be manipulated using composite surfaces with varying roughness or stiffness values, i.e. by combining geometrical features with the modification of local friction coefficients or stiffnesses. We show that a remarkable reduction of static friction can be achieved by introducing hierarchical arrangements of varying local roughness values, or by introducing controlled material stiffness variations.