Stick–slip boundary friction mode as a second-order phase transition with an inhomogeneous distribution of elastic stress in the contact area

Iakov A Lyashenko,Vadym N Borysiuk,Valentin L Popov

doi:10.3762/bjnano.8.189

Abstract

This article presents an investigation of the dynamical contact between two atomically flat surfaces separated by an ultrathin lubricant film. Using a thermodynamic approach we describe the second-order phase transition between two structural states of the lubricant which leads to the stick–slip mode of boundary friction. An analytical description and numerical simulation with radial distributions of the order parameter, stress and strain were performed to investigate the spatial inhomogeneity. It is shown that in the case when the driving device is connected to the upper part of the friction block through an elastic spring, the frequency of the melting/solidification phase transitions increases with time.

Highlights

The boundary friction mode occurs in tribological systems when the thickness of the lubricant layer separating two contacting surfaces is significantly smaller than the typical size of the surface roughness
We have presented the dynamical simulation of the boundary friction between a cylindrically shaped stamp and a flat surface
Using the method of dimensionality reduction (MDR) we have studied the stick–slip friction mode that occurs in the tribological system under shear deformation

Summary

Introduction

The boundary friction mode occurs in tribological systems when the thickness of the lubricant layer separating two contacting surfaces is significantly smaller than the typical size of the surface roughness. A specific case of boundary friction is friction between two atomically flat surfaces separated by a layer of lubricant with thickness of a few atomic diameters [1,2], or even monolayers [3]. Such type of friction mode plays an important role in applied mechanics as it often occurs in nanometer-sized tribological systems that are commonly used in aerospace technologies, computer memory devices and electronic positioning systems [4]. Stick–slip motion is known to cause fast destruction of the contact parts of microscopic devices, which is why it receives significant attention from the scientists and engineers

Objectives

Results

Conclusion