Friction at a Lubricated Line Contact Operating at Oscillating Sliding Velocities

[+] Author and Article Information
D. P. Hess, A. Soom

Department of Mechanical and Aerospace Engineering, University at Buffalo, Buffalo, NY 14260

J. Tribol 112(1), 147-152 (Jan 01, 1990) (6 pages) doi:10.1115/1.2920220 History: Received March 24, 1989; Online June 05, 2008


Although many contacts operate under unsteady loading and sliding conditions, friction behavior under such conditions is still not well understood. In this paper we report on a series of experiments that were run to examine friction-velocity characteristics of line contacts operating under unsteady sliding velocities in the mixed, elastohydrodynamic and hydrodynamic lubrication regimes. A periodic, time-varying velocity component was superimposed on a steady sliding speed in such a way that all three lubrication regimes could be covered in a cycle. It was found that as the frequency of oscillation was increased, a multi-valued friction coefficient appeared as a loop about the average (steady state) friction-velocity relation. It is shown that this behavior can be modeled by a characteristic time lag between a changing velocity and the corresponding steady state friction. The latter is described by a single equation that was matched to measured average friction data. In the mixed lubrication regime, which is where this lag most significantly affects friction behavior, the lag time increases with normal load and lubricant viscosity. It is shown that the time shift is not associated with a fixed characteristic distance. The observed delay arises due to entrainment and normal approach, which includes squeeze-films combined with rough surface contact deformations.

Copyright © 1990 by The American Society of Mechanical Engineers
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