Friction Mapping as a Tool for Measuring the Elastohydrodynamic Contact Running-in Process

Report No. ARL-TR-7501
Authors: Stephen Berkebile; Nikhil Murthy
Date/Pages: October 2015; 36 pages
Abstract: Elastohydrodynamically lubricated gear and bearing contacts typically demonstrate a period of wear called "running-in" when they are first put into service, during which time the friction coefficient of the 2 mating surfaces drops rapidly. The running-in process depends on numerous contact conditions and material properties. These dependencies are important to understand, since running-in has lasting consequences for the operation, efficiency, and failure conditions of the contact. In this report, we demonstrate friction mapping as a method to characterize the running-in process, using a high-speed ball-on-disc tribometer to measure the coefficient of friction as a function of entrainment velocity and slip for different contact histories. We observe that the final state friction coefficient and surface morphology, once the running-in process is complete, does not depend significantly on the ramp direction, nor on the particular range for those measured here. However, the running-in occurs at different rates and at different entrainment velocity and slip values, depending on the ramp direction and extent of mapping range.
Distribution: Approved for public release
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Last Update / Reviewed: October 1, 2015