Fundamental Differences Between Newtonian and Non-Newtonian Micro-EHL Results

[+] Author and Article Information
L. Chang, W. Zhao

Department of Mechanical Engineering, Pennsylvania State University, University Park, PA 16082

J. Tribol 117(1), 29-35 (Jan 01, 1995) (7 pages) doi:10.1115/1.2830603 History: Received January 14, 1994; Revised March 24, 1994; Online January 24, 2008


Numerical analyses of micro-EHL problems have shown remarkably different results with Newtonian and non-Newtonian rheological models. However, no consensus has been reached whether a Newtonian model can be used in micro-EHL analysis. It is difficult to prove the point numerically as researchers use different numerical methods, grid sizes, time steps, and convergence criteria. This paper analytically studies the fundamental differences between Newtonian and non-Newtonian micro-EHL results. Algebraic governing equations are derived in terms of dimensionless parameters of the problem. Results are obtained for a range of key dimensionless parameters of practical interest. These results suggest that Newtonian and non-Newtonian micro-EHL results would be qualitatively different and the differences would be most pronounced with surface roughness of short wavelengths. Since surface roughness of machine elements contains substantial short-wavelength contents, a Newtonian rheological model is likely to generate misleading micro-EHL results under all operating conditions under which the shear-thinning effect of the lubricant is significant.

Copyright © 1995 by The American Society of Mechanical Engineers
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