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Research Papers: Elastohydrodynamic Lubrication

Estimation of Cavity Length in EHL Rolling Point Contact

[+] Author and Article Information
K. Stadler1

 University of Pisa, SKF GmbH, Gunnar-Wester-Strasse 12, 97421 Schweinfurt, Germanykenred.stadler@skf.com

N. Izumi1

Department of Mechanical Engineering Science, Kyushu University, 744 Motooka, Nishiku, Fukuoka 8190395, Japanizumi@mech.kyushu-u.ac.jp

T. Morita, J. Sugimura

Department of Mechanical Engineering Science, Kyushu University, 744 Motooka, Nishiku, Fukuoka 8190395, Japan

B. Piccigallo

Dipartimento Genio Navale, Naval Academy of Livorno, Viale Italia, 57100 Livorno, Italy

1

Corresponding authors.

J. Tribol 130(3), 031502 (Jun 23, 2008) (9 pages) doi:10.1115/1.2919780 History: Received October 04, 2007; Revised April 11, 2008; Published June 23, 2008

Reciprocating lubricated contacts sometimes suffer from oil starvation due to cavitation at the reversal of motion. However, the behavior of cavities is not well understood such that starvation can be theoretically predicted. In this study, the length of cavity in a steady state elastohydrodynamic lubricated point contact was calculated. For numerical simulation, a modified Elrod algorithm was used. An equation was obtained for the cavity enclosed in the oil meniscus. The equation was constructed with Moes dimensionless parameters M and L, assumed pressure of cavity, and viscosity pressure index of the lubricant. The dimensionless cavity length (or the ratio of cavity length by Hertzian contact radius) is proportional to the product of Ma and Lb. Careful examination of the equation elucidated that the cavity length is dominated by the viscosity, sum velocity, cavity pressure, and geometry of the contact. Experimental measurements with a ball-on-disk apparatus have shown good agreement. The validity of the equation suggests that the algorithm is applicable for complete transient simulations. In practice, the estimated cavity length can be a parameter for starvation.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Observations and schematic showing (a) an enclosed type cavity and therefore a cavity pressure lower than the ambient pressure can be assumed; (b) cavity breaking through the oil meniscus and therefore an ambient pressure can be assumed

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Figure 2

Measurement of the reference cavity pressure by using a syringe (schematic)

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Figure 3

Relaxation scheme for starved or cavitated lubricated contacts

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Figure 4

Numerical simulation (θ) (left), interferogram (right) ∅25.4mm steel ball/glass plate, 5N, 20mm∕s, BS oil, pcav=−0.1013MPa

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Figure 5

Dimensionless midplane pressure P, film thickness H, and amount of oil θH in X-direction, ∅25.4mm steel ball/glass plate, 5N, 20mm∕s, BS oil, pcav=−0.1013MPa

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Figure 6

Dimensionless midplane pressure P, film thickness H, and amount of oil θH in X-direction, ∅25.4mm steel ball/glass plate, 30N, 50mm∕s, BS oil; (a) pcav=−0.1013MPa enclosed type cavity and (b) pcav=0 (zero gauge pressure) open type cavity

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Figure 7

Definition of cavity length Xc

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Figure 8

Central film thicknesses Hcen simulated and calculated by Hamrock (21) for a ∅25.4mm steel ball/glass plate, for several M and L Moes parameter (empty and filled circles for better differentiation only)

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Figure 9

Cavity length over M for different L (empty and filled circles for better differentiation only)

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Figure 10

Cavity length over L for different M (empty and filled circles for better differentiation only)

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Figure 11

Dependency of the dimensionless cavity length on pcav (e.g., M=100, L=10, α=26.3GPa−1, η0=1.375Pas)

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Figure 12

Dependency of the dimensionless cavity length on pressure viscosity index α

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Figure 19

Effect of an air bubble on the cavity length

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Figure 18

Correlation of the dimensionless cavity length on Hcen (Points close together—PE regime; spread points—isoviscous rigid (IR) or isoviscous elastic (IE) regime)

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Figure 17

Correlation of estimated cavity length and experimental measured cavity length for different oils

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Figure 16

Correlation of estimated cavity length without α correction and experimental measured cavity length for different oils

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Figure 15

Representative half cycles showing a constant cavity length for constant velocity (BS oil, W=20N); 500fps—picture selection for 100fps

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Figure 14

Trapezoid velocity pattern for cavity length measurements

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Figure 13

Schematic of the experimental apparatus

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