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Research Papers: Elastohydrodynamic Lubrication

Elastohydrodynamic Lubrication Model With Limiting Shear Stress Behavior Considering Realistic Shear-Thinning and Piezo-Viscous Response

[+] Author and Article Information
Punit Kumar

Department of Mechanical Engineering,
National Institute of Technology Kurukshetra,
Haryana 136119, India
e-mail: punkum2002@yahoo.co.in

Parinam Anuradha

Department of Mechanical Engineering,
U.I.E.T., Kurukshetra University, Kurukshetra,
Haryana 136119, India
e-mail: panuradhasachdeva@gmail.com

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received May 29, 2013; final manuscript received November 24, 2013; published online January 20, 2014. Assoc. Editor: Dong Zhu.

J. Tribol 136(2), 021503 (Jan 20, 2014) (8 pages) Paper No: TRIB-13-1111; doi: 10.1115/1.4026111 History: Received May 29, 2013; Revised November 24, 2013

This paper addresses a largely ignored aspect pertaining to the elastohydrodynamic lubrication (EHL) traction behavior of fragile lubricants which undergo transition to glassy state at typical EHL contact zone pressures. For such lubricants, a conventional EHL model predicts extremely high and unrealistic values of traction coefficient, especially under near pure rolling conditions where thermal effect is negligible. Therefore, an EHL model incorporating the effect of limiting shear stress and the associated wall slip phenomenon is presented herein. Unlike the other such investigations involving limiting shear stress behavior, the present model employs Carreau-type power-law based models to describe the rheology of lubricants below the limiting shear stress along with realistic pressure-viscosity relationships (WLF and Doolittle-Tait). The use of Carreau-type shear-thinning model in this analysis allows the simultaneous prediction of minimum film thickness and traction coefficient for lubricants which shear-thin in the inlet zone and exhibit limiting shear stress behavior in the contact zone, a feature absent in the existing EHL models utilizing ideal visco-plastic or some other unrealistic rheological model. Using published experimental data pertaining to the shear-thinning and pressure-viscosity response of two fragile lubricants (L100 and LVI260), it has been demonstrated that the present model can explain the appearance of plateau in the experimental traction curve. Also, the influence of shear-thinning parameters and the pressure-viscosity coefficient on the predicted limiting shear stress zone has been studied.

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References

Figures

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Fig. 1

Variation of viscosity within the EHL conjunction for (a) Polybutene - L100, (b) Mineral oil - LVI260

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Fig. 2

Variation of traction coefficient with slide to roll ratio for (a) Polybutene - L100, (b) Mineral oil - LVI260

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Fig. 3

Effect of slip on EHL film shape at (a) S = 0.03, (b) S = 0.06

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Fig. 4

Comparison of shear-thinning behavior for three combinations of n and Gcr

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Fig. 5

Variation of LSS zone with slide to roll ratio for different sets of shear-thinning parameters (n and Gcr) with (a) α = 23.9 GPa−1, (b) α = 28.3 GPa−1

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Fig. 6

Variation of LSS zone with rolling velocity for (a) α = 23.9 GPa−1, (b) α = 28.3 GPa−1

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Fig. 7

Variation of LSS zone with maximum Hertzian pressure for (a) α = 23.9 GPa−1, (b) α = 28.3 GPa−1

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