Topography characterization of friction pairs during the real-time wear process in dry condition

At present, the prediction of wear failure is often based on temperature, friction coefficient, vibration, and other single or a few macroscopic parameters to judge the contact condition of the friction pairs. However, there are still deviations between the measured results and the actual situation. In the digital twin system for studying friction and wear phenomena, in-situ measurement and characterization of topography of friction pairs is a challenge problem which does not exist in other procedural twin systems. This paper investigates the relationship between in-situ measured macroscopic parameters and topographical parameters. First, the dynamic relationship between friction coefficient and fractal parameters is derived from the view of a microscopic contact, and the wear periods are determined based on the dynamic changes of fractal parameters. The derived friction-fractal formula is based on mechanical deformation and the Majumdar and Bhushan rough surface contact model, avoiding the assumptions based on specific wear mechanisms, then having the universal property. Second, the experimental verification is carried on which demonstrates good correspondence between the obtained topographical parameters based on the friction-fractal formula with the experimental results. The obtained friction-fractal formula provides a theoretical basis for predicting and analyzing the wear status of friction pairs in the critical equipment and supports the real-time contact state characterization of the friction pairs in the digital twin system.