Novel Friction Law for the Static Friction Force based on Local Precursor Slipping

TL;DR

This paper introduces a new static friction law showing that the maximum static friction coefficient varies with load and contact area due to local precursor slips, challenging traditional constant assumptions.

Contribution

The study experimentally demonstrates a novel static friction law influenced by local precursor slips, expanding understanding beyond classical models.

Findings

Maximum static friction coefficient decreases with increased load.

Static friction coefficient decreases with reduced apparent contact area.

Local precursor slips precede bulk sliding, affecting static friction behavior.

Abstract

The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force. It is commonly believed that the maximum static friction force is proportional to the loading force and does not depend on the apparent contact area. The ratio of the maximum static friction force to the loading force is called the static friction coefficient mM, which is considered to be a constant. Here, we conduct experiments demonstrating that the static friction force of a slider on a substrate follows a novel friction law under certain conditions. The magnitude of mM decreases as the loading force increases or as the apparent contact area decreases. This behavior is caused by the slip of local precursors before the onset of bulk sliding and is consistent with recent theory. The results of this study will develop novel methods for static friction control.