Reply to the Comment by Scott Bair, Philippe Vergne, Punit Kumar, Gerhard Poll, Ivan Krupka, Martin Hartl, Wassim Habchi, Roland Larson on “History, Origins and Prediction of Elastohydrodynamic Friction” by Spikes and Jie in Tribology Letters

Spikes, H. A.; Zhang, Jie

doi:10.1007/s11249-015-0483-8

Cited by 27 publications

(19 citation statements)

References 28 publications

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“…High-pressure viscometers can reach shear rates of only ~ 10 4 s −1 at EHL pressures (> 1 GPa) for low-viscosity fluids before shear heating becomes uncontrollable [15]. At similar pressures, tribometer experiments under thin-film EHL conditions can reach much higher shear rates (10 6 s −1 ) before shear heating becomes excessive [16], but it has been debated how useful the rheological data from such experiments are to predict EHL friction [3][4][5]. On the other hand, non-equilibrium molecular dynamics (NEMD) simulations are ideally suited to study the rheology of fluids at high shear rates, since thermostats can be used to suppress shear heating.…”

Section: Shear Thinningmentioning

confidence: 99%

“…Numerical methods, analytical solutions, and experimental techniques have all advanced significantly over the last few decades [2]. However, the measurement and prediction of EHL friction remains a significant challenge and continues to attract much controversy [3][4][5]. In addition to the aforementioned methods, molecular dynamics (MD) simulations have emerged as tools capable of giving unique insights into the nanoscale behaviour of lubricants, including under EHL conditions [6].…”

Section: Introductionmentioning

confidence: 99%

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Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

2021

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The prediction of friction under elastohydrodynamic lubrication (EHL) conditions remains one of the most important and controversial areas of tribology. This is mostly because the pressure and shear rate conditions inside EHL contacts are particularly severe, which complicates experimental design. Over the last decade, molecular dynamics (MD) simulation has played an increasingly significant role in our fundamental understanding of molecular behaviour under EHL conditions. In recent years, MD simulation has shown quantitative agreement with friction and viscosity results obtained experimentally, meaning that they can, either in isolation or through the use of multiscale coupling methods, begin to be used to test and inform macroscale models for EHL problems. This is particularly useful under conditions that are relevant inside machine components, but are difficult to obtain experimentally without uncontrollable shear heating.

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Section: Shear Thinningmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

2021

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“…41 The subject has been extensively analysed by Bair and it is currently a subject of heated debate. 42–44…”

Section: Discussionmentioning

confidence: 99%

“…41 The subject has been extensively analysed by Bair and it is currently a subject of heated debate. [42][43][44] It is also found that such predictions depend on an accurate description of the local pressure-viscosity coefficient, , which can only be predicted from high pressure viscometer measurements. This type of rheometer is not commercially available and therefore few lubricants have been characterised by research centres up to the pressure levels encountered in EHL contacts.…”

Section: Discussionmentioning

confidence: 99%

Partial EHL friction coefficient model to predict power losses in cylindrical gears

Arana

Larrañaga

Ulacia

2018

Proceedings of the Institution of Mechanical Engineers, Part J:

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The accurate prediction of friction coefficient and power losses in the gear mesh is a key subject to several gear-related fields of study. However, there is still not a unified method for large ranges of operating conditions, different gear geometries and lubricant types. The current paper meets this demand by modelling partial EHL friction with an asperity-fluid load sharing approach where fluid traction is calculated with the Ree-Eyring equation and the reference stress behaviour is predicted from piezoviscosity coefficient. It will be shown that only an accurate description of the lubricant’s viscosity behaviour is required to compute friction in gears. Finally, mesh power losses are predicted considering thermal effects and numerical predictions are compared to experimental results showing good agreement.

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“…On the other hand, researchers dealing with high pressure rheometry are advocating a Carreau based model [4]. Several articles that heated up the debate were published in 2014 and 2015 by Spikes and Jie [4,5], Bair and his co-authors [6], and it seems that there is still no consensus on this topic.…”

Section: Introductionmentioning

confidence: 99%

A Computational Fluid Dynamics Study on Shearing Mechanisms in Thermal Elastohydrodynamic Line Contacts

et al. 2019

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A computational fluid dynamics (CFD) model of the thermal elastohydrodynamically lubricated (EHL) line contact problem has been developed for the purpose of exploring the physical processes that occur inside a thin EHL film subjected to shearing motion. The Navier-Stokes equations are solved by using the finite volume method (FVM) in a commercial CFD software, ANSYS Fluent. A set of user-defined functions (UDF) are used for computing viscosity, density, heat source, temperature of moving surfaces and elastic deformation of the top roller according to well-established equations commonly used in the EHL theory. The cavitation problem is solved by taking into account multiphase mixture flow. The model combinations of Houpert and Ree-Eyring and of Tait and Carreau were used for modeling the non-Newtonian behavior of Squalane and the results were compared. Both rheological models suggest the existence of shear-band and plug-flow at high fluid pressure. Due to the differences in viscosity at GPa-level pressure, the chosen model has substantial influence on the computed shear stress and temperature distributions in the high-pressure region. This shows the importance of using correct rheology information in the whole range of pressure, temperature, and shear strain rate.

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Reply to the Comment by Scott Bair, Philippe Vergne, Punit Kumar, Gerhard Poll, Ivan Krupka, Martin Hartl, Wassim Habchi, Roland Larson on “History, Origins and Prediction of Elastohydrodynamic Friction” by Spikes and Jie in Tribology Letters

Cited by 27 publications

References 28 publications

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

Partial EHL friction coefficient model to predict power losses in cylindrical gears

A Computational Fluid Dynamics Study on Shearing Mechanisms in Thermal Elastohydrodynamic Line Contacts

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