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Research Papers: Elastohydrodynamic Lubrication

Effect of Roughness Orientation on the Elastohydrodynamic Lubrication Film Thickness

[+] Author and Article Information
Dong Zhu

School of Aeronautics and Astronautics,
Sichuan University,
Chengdu, 610065, China
e-mail: DongZhu@Mail.com

Q. Jane Wang

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received June 30, 2012; final manuscript received December 8, 2012; published online March 28, 2013. Assoc. Editor: Xiaolan Ai.

J. Tribol 135(3), 031501 (Mar 28, 2013) (9 pages) Paper No: TRIB-12-1104; doi: 10.1115/1.4023250 History: Received June 30, 2012; Revised December 08, 2012

Effect of roughness orientation on lubricant film thickness has been an important issue of surface design, attracting much attention since the 1970 s. A systematical study, however, is still needed for various contact types in an extended range of operating conditions, especially in mixed lubrication cases with film thickness to roughness ratio (λ ratio) smaller than 0.5. The present study employs a deterministic mixed elastohydrodynamic lubrication (EHL) model to investigate the performance of lubricating films in different types of contact geometry, including the line contact, circular contact, and elliptical contacts of various ellipticity ratios. The speed range for analyzed cases covers 11 orders of magnitude so that the entire transition from full-film and mixed EHL down to dry contact (corresponding λ ratio from about 3.5 down to 0.001 or so) is simulated. Three types of machined surfaces are used, representing transverse, longitudinal, and isotropic roughness, respectively. The line contact results are compared with those from the stochastic models by Patir and Cheng (“Effect of Surface Roughness Orientation on the Central Film Thickness in EHD Contacts,” Proc. 5th Leeds-Lyon Symp. on Tribol., 1978, pp. 15–21) and the influence of roughness orientation predicted by the deterministic model is found to be less significant than that by the stochastic models, although the basic trends are about the same when λ > 0.5. The orientation effect for circular or elliptical contact problems appears to be more complicated than that for line contacts due to the existence of significant lateral flows. In circular contacts, or elliptical contacts with the ellipticity ratio smaller than one, the longitudinal roughness may become more favorable than the isotropic and transverse. Overall, the orientation effect is significant in the mixed EHL regime where theλratio is roughly in the range from 0.05 to 1.0. It is relatively insignificant for both the full-film EHL (λ > 1.2 or so) and the boundary lubrication/dry contact (λ < 0.025 ∼ 0.05).

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Figures

Grahic Jump Location
Fig. 1

Roughness effect on line contact EHL film thickness predicted by stochastic models (from Zhu et al. [7])

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Fig. 2

Three types of machined rough surfaces used

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Fig. 3

Four types of contact geometry analyzed. The greater the contact ellipticity, the less the lateral flows, and the stronger the entraining action in the direction of motion.

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Fig. 4

A set of deterministic solutions at k = 2 showing the entire transition U* = 0.9113 × 10−20 ∼ 0.4557 × 10−9, W* = 0.5478 × 10−4, G* = 2829.7, Ph = 2.277 GPa, S = 20%, σ = 600 nm

Grahic Jump Location
Fig. 5

Summarized results for the cases of k = 2 with transverse roughness U* = 0.9113 × 10−20 ∼ 0.4557 × 10−9, W* = 0.5478 × 10−4, G* = 2829.7, Ph = 2.277 GPa, S = 20%, σ = 600 nm

Grahic Jump Location
Fig. 6

Effect of roughness orientation on film thickness (λ) ratio for various types of contact geometry

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Fig. 7

Contact load ratio Wc for line contacts, k = ∞

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Fig. 8

Line contact results replotted in the way of Patir and Cheng [4]. Right graph is an enlargement focusing on the range of Λ > 0.1.

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Fig. 9

Rough surface line contact EHL film thickness variations in comparison with that of smooth surfaces

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Fig. 10

Elliptical contact results of k = 2 and k = 1/2 replotted in the way of Patir and Cheng [4]

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