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Research Papers: Elastohydrodynamic Lubrication

On the Stribeck Curves for Lubricated Counterformal Contacts of Rough Surfaces

[+] Author and Article Information
Dong Zhu, Jiaxu Wang

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

Q. Jane Wang

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

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 11, 2014; final manuscript received October 19, 2014; published online November 17, 2014. Assoc. Editor: Xiaolan Ai.

J. Tribol 137(2), 021501 (Apr 01, 2015) (10 pages) Paper No: TRIB-14-1130; doi: 10.1115/1.4028881 History: Received June 11, 2014; Revised October 19, 2014; Online November 17, 2014

The “Stribeck curve” is a well-known concept, describing the frictional behavior of a lubricated interface during the transition from boundary and mixed lubrication up to full-film hydrodynamic/elastohydrodynamic lubrication. It can be found in nearly every tribology textbook/handbook and many articles and technical papers. However, the majority of the published Stribeck curves are only conceptual without real data from either experiments or numerical solutions. The limited number of published ones with real data is often incomplete, covering only a portion of the entire transition. This is because generating a complete Stribeck curve requires experimental or numerical results in an extremely wide range of operating conditions, which has been a great challenge. Also, numerically calculating a Stribeck curve requires a unified model with robust algorithms that is capable of handling the entire spectrum of lubrication status. In the present study, numerical solutions in counterformal contacts of rough surfaces are obtained by using the unified deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed. Stribeck curves are plotted in a wide range of speed and lubricant film thickness based on the simulation results with various types of contact geometry using machined rough surfaces of different orientations. Surface flash temperature is also analyzed during the friction calculation considering the mutual dependence between friction and interfacial temperature. Obtained results show that in lubricated concentrated contacts, friction continuously decreases as speed and film thickness increase even in the full-film regime until extremely high speeds are reached. This is mainly due to the reduction of lubricant limiting shear stress caused by flash temperature rise. The results also reveal that contact ellipticity and roughness orientation have limited influence on frictional behaviors, especially in the full-film and boundary lubrication regimes.

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References

Figures

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Fig. 1

Schematic of the Stribeck curve (from Ref. [11])

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Fig. 2

Measured sliding friction in an EHL circular contact (from Ref. [9], test conducted by Wedeven Associates, Inc.)

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Fig. 3

Three types of machined rough surfaces used (from Ref. [33])

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Fig. 4

Four types of contact geometry analyzed (from Ref. [33]). The greater the contact ellipticity, the less the lateral flows, and the stronger the entraining action in the direction of motion.

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Fig. 5

A set of deterministic solutions at k = 2 Showing the entire transition U *= 0.9113 × 10−20 ∼ 0.4557 × 10−6, W *= 0.5478 × 10−4, G *= 2829.7, Ph = 2.277 GPa, S = 20%, σ = 600 nm, and λ = 0.00086 ∼ 75.16

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Fig. 6

Flash temperature results for surface 1 corresponding to the solutions in Fig.5U*= 0.9113 × 10−20 ∼ 0.4557 × 10−6, W*= 0.5478 × 10−4, G*= 2829.7, Ph = 2.277 GPa, S = 20%, σ = 600 nm, and λ = 0.00086∼75.16. (a) Contour maps of flash temperature increase on surface 1 and (b) maximum flash temperature rise as a function of speed.

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Fig. 7

Summarized results for the cases of k = 2 with transverse roughness U *= 0.9113 × 10−20 ∼ 0.4557 × 10−6, W *= 0.5478 × 10−4, G *= 2829.7, Ph = 2.277 GPa, S = 20%, σ = 600 nm, and λ = 0.00086 ∼ 75.16

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Fig. 8

Contact load ratio and friction coefficient as functions of film thickness ratio (λ) for various types of contact geometry (transverse roughness)

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Fig. 10

Friction coefficient as functions of film thickness ratio (λ) for various types of contact geometry and roughness orientation

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Fig. 9

Friction coefficient as functions of speed for various types of contact geometry and roughness orientation

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