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Research Papers: Elastohydrodynamic Lubrication

Experimental and Numerical Investigations of the Stribeck Curves for Lubricated Counterformal Contacts

[+] Author and Article Information
Tao He

School of Aeronautics and Astronautics,
Sichuan University,
Chengdu 610065, China

Dong Zhu

School of Aeronautics and Astronautics,
Sichuan University,
Chengdu 610065, China
e-mail: DongZhu@Mail.com

Jiaxu Wang

School of Aeronautics and Astronautics,
Sichuan University,
Chengdu 610065, China;
State Key Laboratory of Mechanical Transmissions,
Chongqing University,
Chongqing 400044, China

Q. Jane Wang

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208;
State Key Laboratory of Mechanical Transmissions,
Chongqing University,
Chongqing 400044, China

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received April 7, 2016; final manuscript received June 26, 2016; published online August 24, 2016. Assoc. Editor: Xiaolan Ai.

J. Tribol 139(2), 021505 (Aug 24, 2016) (13 pages) Paper No: TRIB-16-1117; doi: 10.1115/1.4034051 History: Received April 07, 2016; Revised June 26, 2016

The Stribeck curve is an important means to demonstrate the frictional behavior of a lubricated interface during the entire transition from boundary and mixed to full-film lubrication. In the present study, a new test apparatus has been built that can operate under rolling–sliding conditions at a continuously variable speed in an extremely wide range, approximately from 0.00006 to 60 m/s, covering six orders of magnitude. Hence, a complete Stribeck curve can be measured to reveal its basic characteristics for lubricated counterformal contacts. The measured curves are compared with numerical simulation results obtained from an available unified mixed elastohydrodynamic lubrication (EHL) model that is also capable of handling cases during the entire transition. A modified empirical model for the limiting shear stress of lubricant is obtained, and a good agreement between the measured and calculated Stribeck curves is achieved for the tested base oils in all the three lubrication regimes, which thus well validates the simulation methods employed. Both the experimental and numerical results indicate that the Stribeck curves for counterformal contact interfaces behave differently from those for conformal contacts. When the rolling speed increases at a fixed slide-to-roll ratio, the friction continuously decreases even in the full-film lubrication regime due to the reduction of the lubricant limiting shear stress caused mainly by the rise of the surface flash temperature. In addition, the test results indicate that the boundary additives in a commodity lubricant may have considerable influence on the boundary lubrication friction but that on the friction in the mixed and full-film lubrication appears to be limited.

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References

Figures

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Fig. 3

Rolling–sliding test apparatus constructed

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Fig. 2

Measured friction in a lubricated circular contact

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Fig. 1

Schematic of the Stribeck curve for journal bearings (from Ref. [6])

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Fig. 4

A sample of measured Stribeck curve: (a) friction versus rolling speed and (b) friction versus calculated λ ratio

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Fig. 5

Comparison between measured and calculated Stribeck curves at different loads for 4503(32) base oil G* = 5031, W* = 0.1217 × 10−5–0.8521 × 10−5, U* = 0.6470 × 10−15–0.2265 × 10−9: (a) friction versus rolling speed and (b) friction versus calculated λ ratio

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Fig. 6

Comparison between measured and calculated Stribeck curves at different loads for 75 W/90 base oil G*= 5009, W*= 0.1217 × 10−5–0.8521 × 10−5, and U*= 0.1436 × 10−14–0.5025 × 10−9

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Fig. 7

Sample numerical solutions of film thickness, pressure, and flash temperature rise on surface 1 lubricant: base oil of MTF 75 W/90, load: 500 N

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Fig. 8

Comparison between commodity 4503(32) and its base oil

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Fig. 9

Comparison between commodity 75 W/90 and its base oil

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Fig. 10

Stribeck curves for commodity gear oil Mobil 600 XP 68—kinematic viscosities: 67.9 cSt at 40 °C and 8.8 cS at 100 °C; density: 0.88 g/cm3 at 15.6 °C

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