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Occurrence of Wall Slip in Elastohydrodynamic Lubrication Contacts

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Abstract

Preliminary experimental work has been carried out to identify some of the boundary slip phenomena of highly pressurised polybutenes in an elastohydrodynamic lubrication (EHL) conjunction. The movement of the oil is signified using an entrapment that can be readily formed by the impact of a steel ball against a layer of oil on a glass block in an optical EHL test apparatus. The post-impact lateral movement of the entrapment was investigated under the conditions: (i) pure rolling, (ii) pure glass block sliding (steel ball stationary) and (iii) pure ball sliding (glass block stationary). It was observed that under pure rolling the entrapped oil travels within the contact region at the entrainment speed, which is correlated with EHL theory. Under pure glass block sliding conditions, the speed of the entrapped oil core is less than the entrainment speed, and in the extreme cases, this core can be nearly stationary. Under pure ball sliding conditions, the oil core moves at a speed greater than the entrainment speed. The observation indicates that the oil/steel ball interface can sustain higher shear stress than the oil/glass (chromium coated) interface and there is a boundary slip in terms of relative sliding at the latter interface under the experimental conditions. Furthermore, the amount of slip increases with an increase in the pressure. These experiments provide evidence of the existence of wall slippage, which leads to the abnormal EHL film profile characterised with an inlet dimple as reported earlier.

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Abbreviations

d :

Displacement, μm.

h c :

The film thickness at the dimple core/the dimple depth defined as the maximum film thickness within the dimple, μm.

h minL :

Minimum film thickness at the inlet edge of the dimple along the central entrainment, μm.

h minR :

Minimum film thickness at the outlet edge of the dimple along the central entrainment, μm.

h o,c :

Initial dimple depth defined as the maximum film thickness within the dimple, μm.

ub, ug:

Speeds of the steel ball and the glass block, respectively, at the contact point, μm/s.

u c :

Dimple core (fringe centre) speed, μm/s.

u e :

Entrainment speed, μm/s, u e = (u b + u g)/2.

u s :

Relative speed of the oil to the glass surface at the interface, μm/s.

w :

Applied load, N.

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Acknowledgements

The authors would like to extend their thanks to the City University of Hong Kong for providing financial support for this work (SRG 7002094). The authors are also grateful to Mr. X. M. Li for his kind assistance in this study.

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Authors and Affiliations

  1. Department of Manufacturing Engineering and Engineering Management, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, People’s Republic of China

    F. Guo & P. L. Wong

  2. School of Mechanical Engineering, Qingdao Technological University, 11 Fushun Road, Qingdao, 266033, People’s Republic of China

    F. Guo & M. Geng

  3. Department of Mechanical and Electronic Systems Engineering, Kyushu Kyoritsu University, Kitakyushu, 807-8585, Japan

    M. Kaneta

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  1. F. Guo
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  2. P. L. Wong
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  3. M. Geng
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  4. M. Kaneta
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Correspondence to F. Guo.

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Guo, F., Wong, P.L., Geng, M. et al. Occurrence of Wall Slip in Elastohydrodynamic Lubrication Contacts. Tribol Lett 34, 103–111 (2009). https://doi.org/10.1007/s11249-009-9414-x

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