The impact of surface effects on hydraulic motor startup friction and the coefficient of static friction
Abstract
A theoretical and experimental approach was used to perform a systematic analysis to find the optimal parameters of a textured surface for the purpose of reducing the coefficient of static friction. A textured surface implies using laser, mechanical, or in this case chemical means to produce regularly shaped and spaced depressions (or dimples) in metallic contacts. This research focused on high load metallic contact, such as in a hydraulic gerotor or geroler displacement machine. The theoretical approach used a DC-FFT algorithm to estimate the tangential load required to initiate motion between two real surfaces, the topography of which was acquired by a 3-D optical profilometer. Mathematical means were used to superimpose a textured surface on one of the surfaces. Once the tangential load was calculated, it was divided by the external normal load to predict the coefficient of static friction. These results were compared with experimental results measured by a specifically designed test rig. The test rig was originally developed by Jose Garcia, and modified for flat contacts. The results of both experimental and theoretical approaches imply that a higher area density of dimples produces a lower coefficient of friction, but that other variables such as depth and width of dimples do not follow such a clear trend. The experimental approach also suggests that the presence of lubricant tends to increase the coefficient of static friction for textured surfaces, perhaps due to increased adhesion.
Degree
M.S.
Advisors
Martini, Purdue University.
Subject Area
Mechanical engineering
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