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Research Papers: Elastohydrodynamic Lubrication

Plasto-Elastohydrodynamic Lubrication (PEHL) in Point Contacts

[+] Author and Article Information
Ning Ren, W. W. Chen, Q. Jane Wang

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

Dong Zhu

State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China

J. Tribol 132(3), 031501 (Jun 24, 2010) (11 pages) doi:10.1115/1.4001813 History: Received December 14, 2009; Revised April 27, 2010; Published June 24, 2010; Online June 24, 2010

Elastohydrodynamic lubrication (EHL) is an important branch of the lubrication theory, describing lubrication mechanisms in nonconformal contacts widely found in many mechanical components such as various gears, rolling bearings, cams and followers, metal-rolling tools, traction drives, and continuous variable transmissions. These components often transmit substantial power under heavy loading conditions. Also, the roughness of machined surfaces is usually of the same order of magnitude as, or greater than, the estimated average EHL film thickness. Consequently, most components operate in mixed lubrication regime with significant asperity contacts. Due to very high pressure concentrated in small areas, resulted from either heavy external loading or severe asperity contacts, or often a combination of both, subsurface stresses may exceed the material yield limit, causing considerable plastic deformation, which may not only permanently change the surface profiles and contact geometry but also alter material properties through work hardening as well. In the present study, a three-dimensional plasto-elastohydrodynamic lubrication (PEHL) model has been developed by taking into account plastic deformation and material work-hardening. The effects of surface/subsurface plastic deformation on lubricant film thickness, surface pressure distribution, and subsurface stress field have been investigated. This paper briefly describes the newly developed PEHL model and presents preliminary results and observed basic behavior of the PEHL in smooth-surface point contacts, in comparison with those from corresponding EHL solutions under the same conditions. The results indicate that plastic deformation may greatly affect contact and lubrication characteristics, resulting in significant reductions in lubricant film thickness, peak surface pressure and maximum subsurface stresses.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

EHL pressure peaks due to severe asperity contacts. Left: EHL solution from smooth surfaces. Right: mixed EHL solution from machined rough surfaces. Predicted Ph=1.727 GPa, max. von Mises stress 3.222 GPa. Materials: steel versus steel.

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Figure 2

Strain field due to a unit surface force

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Figure 4

Comparison of PEHL results with those of elastic-plastic indentation by Hardy (21). P/Py, originally used by Hardy (21), is the same as W/Wy elsewhere.

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Figure 5

Comparison of PEHL results with those of elastic-plastic indentation by Kral (22)

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Figure 6

A Typical PEHL solution in comparison with its corresponding EHL solution

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Figure 7

von Mises stress results from PEHL solutions in comparison with those from corresponding EHL Solutions (cross section views at Y=0)

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Figure 8

PEHL results under different loads in comparison with those from corresponding EHL solutions (cross section views at Y=0, ET/E=0)

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Figure 9

PEHL solutions under different loads (cross section views at Y=0)

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Figure 10

Effect of load increase on PEHL pressure and film thickness

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Figure 11

Effect of work-hardening on PEHL pressure and film thickness

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