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Research Papers

Effects of Couple Stress on Elastohydrodynamic Lubrication at Impact Loading

[+] Author and Article Information
Hsiao-Ming Chu

Department of Mechanical and Automation Engineering, I-Shou University, Kaohsiung 840, Taiwan

Wang-Long Li1

Institute of Nanotechnology and Microsystems Engineering, National Cheng Kung University, No.1 University Road, Tainan 701, Taiwanli.dragonpuff@gmail.com and dragon@mail.mina.ncku.edu.tw

Yuh-Ping Chang

Department of Mechanical Engineering, Kun Shan University, Tainan 710, Taiwan

Huan-Chang Huang

Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan

1

Corresponding author.

J. Tribol 130(1), 011010 (Dec 26, 2007) (8 pages) doi:10.1115/1.2805430 History: Received February 21, 2007; Revised September 11, 2007; Published December 26, 2007

In this paper, pure squeeze elastohydrodynamic lubrication motion of circular contacts with couple stress lubricant is explored at impact loading. On the basis of microcontinuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation equation and ball motion equation, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the couple stress is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length of the couple stress fluid increases, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, and the diameter of the dimple, the rebounding velocity, the maximum value of the relative impact force, and the acceleration decrease. Furthermore, the fact that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period is proved numerically in this analysis. As the effect of couple stress increases, the first and second peaks form earlier; as the total impact time decreases, the pressure of the first peak increases and that of the second peak decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increases with increasing the characteristic length of the couple stress fluid.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry of EHL of circular contacts under pure squeeze motion

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Figure 2

Compare the results of the numerical method performed by Larsson and Högund with the numerical results by using the present method

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Figure 3

Dimensionless central pressure versus time with three different characteristic lengths (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 4

Dimensionless pressure distribution versus time with three different characteristic lengths (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 5

Dimensionless film thickness distribution versus time with three different characteristic lengths (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 6

Effects of characteristic length on the film thickness during the total impact time (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 7

Effects of characteristic length on Cw during the total impact time (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 8

Effects of characteristic length on the squeeze velocity and acceleration before T=1.2×109 (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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Figure 9

Effects of characteristic length on the squeeze velocity and acceleration during the total impact time (v00=−0.1m∕s, h00=20μm, m=0.263kg, G=3500)

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