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Research Papers: Elastohydrodynamic Lubrication

Three-Dimensional Plasto-Elastohydrodynamic Lubrication (PEHL) for Surfaces with Irregularities

[+] Author and Article Information
Ning Ren, Q. Jane Wang1

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

Dong Zhu

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

1

Corresponding author.

J. Tribol 133(3), 031502 (Jul 07, 2011) (10 pages) doi:10.1115/1.4004100 History: Received June 20, 2010; Revised March 31, 2011; Published July 07, 2011; Online July 07, 2011

Elastohydrodynamic lubrication (EHL) is one of the most common types of lubrication, which widely exists in many machine elements such as gears, rolling bearings, cams and followers, metal rolling tools, and continuous variable transmissions. These components often transmit substantial power under heavy loading conditions that may possibly induce plastic deformation of contacting surfaces. Moreover, the roughness of machined surfaces is usually of the same order of magnitude as, or greater than, the average EHL film thickness. Consequently, most components operate in mixed lubrication with considerable asperity contacts, which may result in localized pressure peaks much higher than the Hertzian pressure, causing subsurface stress concentrations possibly exceeding the material yield limit. Plastic deformation, therefore, often takes place, which not only permanently changes the surface profiles and contact geometry, but alters material properties through work-hardening as well. Available mixed EHL models, however, do not consider plastic deformation, often yielding unrealistically high pressure spikes and subsurface stresses around asperity contact locations. Recently, a three-dimensional (3D) plasto-elastohydrodynamic lubrication (PEHL) model has been developed for investigating the effects of plastic deformation and material work-hardening on the EHL characteristics and subsurface stress/strain fields. The present paper is a continuation of the previous work done by Ren (2010, “PEHL in point contacts,” ASME J. Tribol., 132 (3), pp. 031501) that focused on model development and validation, as well as investigation of fundamental PEHL mechanisms in smooth surface contacts. This part of the study is mainly on the PEHL behavior involving simple surface irregularities, such as a single asperity or dent, which can be considered as basic elements of more complicated surface roughness. It is found that considerable plastic deformation may occur due to the pressure peaks caused by the surface irregularity, even though sometimes external loading is not heavy and the irregularity is concave. The plastic deformation may significantly affect contact and lubrication characteristics, resulting in considerable reductions in peak pressure and maximum subsurface stresses.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Plastic deformation and hardening laws

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Figure 2

Sample PEHL Results with a single stationary asperity

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Figure 3

Subsurface plastic strain and von Mises Stress fields

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Figure 4

Effect of asperity height

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Figure 5

Effect of asperity radius

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Figure 6

Snapshots of pressure and film thickness distributions and residual stress field with a moving asperity at different time steps

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Figure 7

Sample PEHL Results with a single stationary dent

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Figure 8

Effects of dent depth and radius

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Figure 9

Snapshots of pressure and film thickness distributions and residual stress field with a moving dent at different time steps

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