Attempts were made to measure thin lubricating films in ball-on-disk concentrated contacts using a fluorescence microscope. A normal CCD camera system could detect fluorescence from oil film of thickness down to 30 nm with a glass disk/steel ball configuration. However, there were two substantial problems that made accurate thickness determination difficult. One was light interference within thin films, which was overcome by introducing a transparent material for both the ball and the disk. The other problem was a significant background effect caused by cavities formed at the film exit, which had yet to be solved. Nevertheless, the fluorescent technique was useful in studying behaviours of lubricants and cavities. Tests in mixed lubrication conditions showed that changes in microtopography due to running-in gave rise to formation and growth of microcavities in the wake of surface asperities.
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