Reduction of friction by normal oscillations. I. Influence of contact stiffness

TL;DR

This paper provides a theoretical analysis of how normal oscillations influence sliding friction, emphasizing the role of contact stiffness and oscillation amplitude, with implications for different contact shapes and large amplitude oscillations.

Contribution

It introduces a detailed analysis of contact stiffness effects and large oscillation amplitudes on friction, considering different contact geometries, which was not extensively covered before.

Findings

Friction depends on two dimensionless parameters: sliding velocity and oscillation amplitude.

Contact shape influences the frictional response under oscillations.

Large oscillation amplitudes can cause contact loss and 'jump' phenomena.

Abstract

The present paper is devoted to a theoretical analysis of sliding friction under the influence of oscillations perpendicular to the sliding plane. In contrast to previous works we analyze the influence of the stiffness of the tribological contact in detail and also consider the case of large oscillation amplitudes at which the contact is lost during a part of the oscillation period, so that the sample starts to "jump". It is shown that the macroscopic coefficient of friction is a function of only two dimensionless parameters - a dimensionless sliding velocity and dimensionless oscillation amplitude. This function in turn depends on the shape of the contacting bodies. In the present paper, analysis is carried out for two shapes: a flat cylindrical punch and a parabolic shape. Here we consider "stiff systems", where the contact stiffness is small compared with the stiffness of the system. The role of the system stiffness will be studied in more detail in a separate paper.