Fluorescence Tracking and µ-PIV of Individual Particles and Lubricant Flow in and Around Lubricated Point Contacts

Abstract

This paper deals with optical experimental methods for improving current knowledge on particle entrapment in elastohydrodynamic (EHD) contacts. Particular attention was paid to the possibilities offered by fluorescence-based techniques for mapping lubricant flow and tracking contaminant trajectories. A ball-on-disc tribometer, a fluorescent medium, and particle image velocimetry (PIV) equipment were used together for this purpose. This original experimental set-up enabled us to obtain lubricant streamlines and velocity vector maps in the contact area. Moreover, it allowed us, for the first time, to capture the details of trapping as the rejection of contaminating particles, in the context of lubrication, as it happened. Dynamic in situ observations clearly showed that the entrapment of debris-like particles was competing against the backflow occurring upstream, in particular in elliptical contacts. The results reported in this work confirm and expand previous results obtained with different methods, i.e. using a twin-disc machine and CFD computations. Finally, we briefly describe as future work the potential for applying these fluorescence-based methods to questions that are still under debate in the lubrication community.