Measurements of the friction coefficient: discussion on the results in the framework of the time series analysis

Tribology studies the interaction between surfaces in relative motion with a particular focus on the principles of friction, wear and lubrication. The measurement of the friction coefficient (COF) is extremely sensitive to experimental friction force fluctuations thus making COF direct measurement not a trivial task. In this manuscript, a novel approach toward the understanding of the friction coefficient behavior during reciprocating tests is proposed. The proposed procedure represents a first approach for a deep investigation about measured COF distribution during tribological tests. It is based on the analysis of COF data measured during the tests in the framework of time series analysis and it was applied to several real tests in dry-friction showed as example of application. Output parameters (i.e., friction, traction force) were investigated to detect trends, connected to running-in period of the tribo-couple, seasonal, connected to the periodicity induced from reciprocating motion, and residual components. After “smoothing” the COF data set by removing the trend and seasonal components, the residual component was analyzed to check the stationary of the COF data set which represents the most characteristic interval in friction measurements.