Multifractal analysis of stress time series during ultrathin lubricant film melting

TL;DR

This paper investigates the multifractal properties of stress time series during ultrathin lubricant film melting, revealing how noise influences self-similar regimes and the nature of correlations in different friction states.

Contribution

It introduces a multifractal analysis of stress signals in lubricant melting, highlighting the role of noise and correlations in different friction regimes, which is a novel application in this context.

Findings

Self-similar melting occurs with dominant temperature noise.

Multifractality arises from correlations and power-law stress distribution.

Different friction regimes exhibit distinct multifractal characteristics.

Abstract

Melting of an ultrathin lubricant film confined between two atomically flat surfaces is we studied using the rheological model for viscoelastic matter approximation. Phase diagram with domains, corresponding to sliding, dry, and two types of $stick-slip$ friction regimes has been built taking into account additive noises of stress, strain, and temperature of the lubricant. The stress time series have been obtained for all regimes of friction using the Stratonovich interpretation. It has been shown that self-similar regime of lubricant melting is observed when intensity of temperature noise is much larger than intensities of strain and stress noises. This regime is defined by homogenous distribution, at which characteristic stress scale is absent. We study stress time series obtained for all friction regimes using multifractal detrended fluctuation analysis. It has been shown that multifractality of these series is caused by different correlations that are present in the system and also by a power-law distribution. Since the power-law distribution is related to small stresses, this case corresponds to self-similar solid-like lubricant.