Abstract
A novel methodology, based on the use of phosphorescence imaging, is applied to determine the local through-thickness velocity profile of lubricant in an elastohydrodynamic contact. The technique has spatial and temporal resolutions of 40 μm and 340 μs respectively and thus allows lubricant rheology to be investigated at conditions close to service conditions. The capability of the newly-developed method is verified by examining the flow of 5P4E polyphenyl ether, a lubricant base fluid used in very high temperature applications and is well-known for its high viscosity-pressure coefficient. Experimental results highlight the effect of the contact pressure on the velocity profile of this fluid in lubricated contacts. At low pressures, the velocity profile of 5P4E is close to linear, characteristic of Couette flow. As the local pressure increases, its velocity profile progressively deviates from a Couette profile and shear banding is evident at high pressure.
Highlights
Elastohydrodynamic (EHD) lubrication is present in lubricated machine components that have mechanical parts rolling against one another, for example ball or roller bearings, cams and gears
It should be noted that all predictions of friction coefficient and film thickness of lubricant films in EHD contacts rely on the assumption that the velocity profile of the lubricant film is linear
Through-thickness velocity profiles in an EHD contact at high speed have been obtained by phosphorescence imaging
Summary
Elastohydrodynamic (EHD) lubrication is present in lubricated machine components that have mechanical parts rolling against one another, for example ball or roller bearings, cams and gears. In this lubrication regime, the lubricant film is subject to extremely high pressures, in the range of gigapascals, combined with shear rates that can reach up to 108 s−1. It is important to measure directly the flow of lubricants in EHD contacts to improve the understanding and prediction capability of rheological behaviour of EHD lubricants
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