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TECHNICAL PAPERS

An Elastohydrodynamic Lubrication Model for Coated Surfaces in Point Contacts

[+] Author and Article Information
Yuchuan Liu1

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, #B224, Evanston, IL 60208ycliu@northwestern.edu

W. Wayne Chen, Q. Jane Wang

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, #B224, Evanston, IL 60208

Dong Zhu

Innovation Center, Eaton Corporation, 26201 Northwestern Highway, Southfield, MI 48037

Shuangbiao Liu2

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, #B224, Evanston, IL 60208

1

Corresponding author.

2

Presently at: Technology and Solutions Division, E854, Caterpillar Inc., Peoria, IL 61656-1875.

J. Tribol 129(3), 509-516 (Feb 02, 2007) (8 pages) doi:10.1115/1.2736433 History: Received August 17, 2006; Revised February 02, 2007

An elastohydrodynamic lubrication (EHL) model for coated surfaces in point contacts has been developed by combining the elastic deformation formulation for the coated surfaces with an EHL model. Inverse fast Fourier transform (IFFT) is employed first to obtain the influence coefficients (ICs) from the frequency response function (FRF). The subsequent calculation of elastic deformation is performed using the efficient algorithm of discrete convolution and fast Fourier transform (DC-FFT). The coating EHL model is verified by the comparison to available numerical results. The effects of coating on lubrication under various loads, speeds, rheological models, and pressure-viscosity behaviors are numerically investigated. Similar to the observations from dry contact, stiffer coatings in EHL tend to reduce the nominal contact radius but increase the maximum contact pressure, and vice versa for more compliant coatings. However, as coating thickness increases, the influence of coatings on film thickness, including the central and the minimum film thicknesses, does not follow a monotonic variation, and therefore, cannot be predicted by any simple film thickness equation. The reason for that is the pressure viscosity effect which tends to counterbalance the effect of coating. The average friction coefficient in lubricant film increases in stiff coating cases but decreases for compliant coating cases. Furthermore, two possible approaches to improving the minimum film thickness thus reducing friction and wear in mixed lubrication are indicated: a thin stiff coating for conventional EHL and a thick compliant coating for soft EHL.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Description of the EHL with coated surfaces in a point contact

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Figure 2

Verification of the elastic deformation computated using the ICs obtained from FRF in refined mesh under a Hertzian contact pressure

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Figure 3

Reproduced O’ Sullivan and King’ results using the present model

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Figure 4

Effect of Poisson’s ratio on contact pressure and contact radius

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Figure 5

Effect of coating on maximum contact pressure

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Figure 6

Effect of coating on nominal contact radius

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Figure 7

Effect of coating on friction in the lubrication film

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Figure 8

Effect of coating on central film thickness

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Figure 9

Effect of coating on minimum film thickness

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Figure 10

Film thickness and pressure profiles for the cases with variable Young’s modulus at a fixed coating thickness

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Figure 11

Film thickness and pressure profiles for the cases with variable coating thickness at a fixed Young’s modulus

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Figure 12

Comparison between low speed and high speed cases: (a) central film thickness ratio; (b) minimum film thickness ratio; (c) average friction coefficient ratio

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Figure 13

Comparison between lightly loaded and heavily loaded cases: (a) central film thickness ratio; (b) minimum film thickness ratio; (c) average friction coefficient ratio

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Figure 14

Comparison between non-Newtonian and Newtonian cases (a) central film thickness ratio; (b) minimum film thickness ratio

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Figure 15

Comparison between high coefficient and low coefficient cases: (a) central film thickness ratio; (b) minimum film thickness ratio

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