# Relaxation Tribometry: A Generic Method to Identify the Nature of Contact Forces

## TL;DR

This paper introduces a comprehensive method for analyzing contact forces in relaxation tribometry by identifying six force components from oscillation signals, including two novel terms affecting frequency.

## Contribution

It presents a generalized force model with six terms, including two new ones, and a technique to distinguish them based on oscillation signatures in relaxation tribometry.

## Key findings

- Six force components can be uniquely identified from oscillation data.
- Two newly proposed force terms influence oscillation frequency, not amplitude.
- Method demonstrated on PDMS sphere/glass plate contact.

## Abstract

Recent years have witnessed the development of so-called relaxation tribometers, the free oscillation of which is altered by the presence of frictional stresses within the contact. So far, analysis of such oscillations has been restricted to the shape of their decaying envelope, to identify in particular solid or viscous friction components. Here, we present a more general expression of the forces possibly acting within the contact , and retain six possible, physically relevant terms. Two of them, which had never been proposed in the context of relaxation tribometry, only affect the oscillation frequency, not the amplitude of the signal. We demonstrate that each of those six terms has a unique signature in the time-evolution of the oscillation, which allows efficient identification of their respective weights in any experimental signal. We illustrate our methodology on a PDMS sphere/glass plate torsional contact.