An original experimental method for measuring friction coefficient during tribofilm formation by accumulating free sliding oscillating responses

A new experimental approach is proposed to investigate the friction behaviour and highlight the relationship with the tribofilm formation. It is based on the accumulation of several free dynamic responses of a single-degree-of-freedom damped oscillating system on the same sliding surfaces. By analysing the decreasing amplitude of the damped free dynamic responses and their associated energy decays, it is not only possible to describe the evolution of the tribological behaviour, but also to accurately identify velocity-dependent and velocity-independent friction contributions as the gradually formation of tribofilm. To demonstrate the relevance of this original technique, two tribosystems were studied, each lubricated with either base oil or formulated one, and by comparing the results with those obtained by a conventional linear tribometer. •An original experimental technique allows to characterize friction coefficient during tribofilm formation.•Accumulation of the free dynamic responses of a single-degree-of-freedom oscillatoron the same friction track allows to increase the sliding distance and form tribofilm.•Friction characteristics are obtained from the free damped responses by analysing the envelop or energy decay and without measuring the tangential force.•Velocity-dependent and velocity-independent friction contributions can be identified during the progressive tribofilm formation.•Comparing with conventional tribometers, the proposed approach was validated by testing base and formulated oil, and appears to be in future effective and suitable to study the performance of new lubricant formulations.