Fluid distribution in a friction gap during mixed lubrication

To enable a robust measurement of the lubricant distribution between two rough topographies under starved regimes, measurements on a scaled friction gap with transparent topographies and coloured fluid were carried out. Therefore, the disc-to-disc tribometer “fluid contact triboscope (FLUCS)” was developed, as a further development of the wear debris investigator. Highspeed videos through the transparent topography are used to calculate the fluid height from the colour intensity of the fluid. In order to quantify the share of solid and fluidic friction, the shear area of the fluid is determined quasi in-situ. For this purpose, tracer particles were added to the fluid and its flow was analysed using particle tracking velocimetry (PTV). By varying the amount of fluid, the influence of the friction regime on the fluid distribution, fluid height, gap height, coefficient of friction, and lubricant flow was analysed. The results show the formation of characteristic fluid lines, which are favored by high viscosities, relative velocities, and topographic roughnesses. The measured coefficient of friction over the fluid quantity shows a Stribeck-like character and is interpreted in terms of the friction regimes.