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Elastohydrodynamic Lubrication

Mixed Elastohydrodynamic Lubrication in Finite Roller Contacts Involving Realistic Geometry and Surface Roughness

[+] Author and Article Information
Dong Zhu, Jiaxu Wang

 State Key Laboratory of Mechanical Transmissions,  Chongqing University, Chongqing 400044, P. R. C.

Ning Ren1

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

Q. Jane Wang

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

1

Currently employed by Ashland, Inc., Lexington, Kentucky.

J. Tribol 134(1), 011504 (Mar 06, 2012) (10 pages) doi:10.1115/1.4005952 History: Received July 09, 2011; Revised January 30, 2012; Published March 05, 2012; Online March 06, 2012

Concentrated (or counterformal) contacts are found in many mechanical components that transmit significant power. Traditionally, concentrated contacts can be roughly categorized to point and line contacts. In point contacts, the contact area is small in both principal directions, while in line contacts, it is small in one direction but assumed to be infinitely long in the other direction. However, these two types of geometry are results of simplification that does not precisely cover all the contact conditions in engineering practice. Actually most line contact components are purposely designed to have a crown in the contact length direction in order to accommodate possible non-uniform load distribution and misalignment. Moreover, the contact length is always finite, and at two ends of the contact there usually exist round corners or chamfers to reduce stress concentration. In the present work, the deterministic mixed EHL model developed previously has been modified to take into account the realistic geometry. Sample cases have been analyzed to investigate the effects of contact length, crowning, and end corners (or chamfers) on the EHL film thickness and the stress concentration, and also to demonstrate the entire transition from full-film and mixed EHL down to a practically dry contact under severe operating conditions with real machined roughness. It appears that this modified model can be used as an engineering tool for roller design optimization through in-depth mixed EHL performance evaluation.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Idealized line contact EHL

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Figure 2

Idealized point/elliptical contact EHL

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Figure 3

Geometry of a typical roller

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Figure 4

Deviation of a roller profile from straight cylinder. The solid line represents the true surface profile, while the dashed line shows the simplified geometry described by Eq. 1.

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Figure 5

Five different types of roller contact (H – film thickness contour, P – pressure contour)

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Figure 6

Effect of roller length – straight rollers

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Figure 7

Effect of roller length – straight rollers with round corners

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Figure 8

Effect of Crown Radius. Load 1200 N/mm, Roller Length 10 mm, Ph  = 1.4844 GPa.

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Figure 9

Effect of crown radius – two more sets of cases. (a) Load 1200 N/mm, roller length 5 mm, Ph  = 1.4844 GPa, and (b): load 600 N/mm, roller length 10 mm, Ph  = 1.0496 GPa.

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Figure 10

Effect of round corner radius, load 1200 N/mm, roller length 5 mm, crown radius 1270 mm, Ph  = 1.4844 GPa

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Figure 11

Continuous transition from full-film and Mixed EHL to dry contact with two shaved surfaces

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Figure 12

Contact load ratio and friction as functions of speed or film thickness ratio over the entire transition

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