Comment on “History, Origins and Prediction of Elastohydrodynamic Friction” by Spikes and Jie

Bair, Scott; Vergne, Philippe; Kumar, Parveen; Poll, Gerhard; Křupka, Ivan; Hartl, Martin; Habchi, Wassim; Larsson, Roland

doi:10.1007/s11249-015-0481-x

Cited by 48 publications

(56 citation statements)

References 34 publications

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“…There is still much debate regarding the most suitable shear thinning model to describe lubricant behaviour under high pressure, high shear rate, and elastohydrodynamic lubrication (EHL) conditions [41,122,123]. NEMD simulations have been used to investigate this behaviour and can give unique insights into behaviour under conditions which are challenging to probe experimentally [124][125][126].…”

Section: Shear Thinningmentioning

confidence: 99%

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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Nonequilibrium molecular dynamics (NEMD) simulations have provided unique insights into the nanoscale behaviour of lubricants under shear. This review discusses the early history of NEMD and its progression from a tool to corroborate theories of the liquid state, to an instrument that can directly evaluate important fluid properties, towards a potential design tool in tribology. The key methodological advances which have allowed this evolution are also highlighted. This is followed by a summary of bulk and confined NEMD simulations of liquid lubricants and lubricant additives, as they have progressed from simple atomic fluids to ever more complex, realistic molecules. The future outlook of NEMD in tribology, including the inclusion of chemical reactivity for additives, and coupling to continuum methods for large systems, is also briefly discussed.

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Section: Shear Thinningmentioning

confidence: 99%

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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“…11 should represent the Eyring stress, s e , while the constant c 0 should correspond to the value log e (2g p /s e ) where g p represents the low shear rate viscosity within the contact. It should be noted, however, that the most appropriate rheological model to describe the relationship between fluid stress and strain in high pressure EHD contacts is still a topic of considerable debate [31,40,41] and the fit values in Tables 4 and 5 are provided to enable readers to construct isothermal EHD friction curves and not to espouse any particular model of EHD rheology. Fig.…”

Section: Isothermally Corrected Shear Stress and Friction Coefficientmentioning

confidence: 99%

Effect of Base Oil Structure on Elastohydrodynamic Friction

2016

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The EHD friction properties of a wide range of base fluids have been measured and compared in mixed sliding-rolling conditions at three temperatures and two pressures. The use of tungsten carbide ball and disc specimens enabled high mean contact pressures of 1.5 and 2.0 GPa to be obtained, comparable to those present in many rolling bearings. The measurements confirm the importance of molecular structure of the base fluid in determining EHD friction. Liquids having linear-shaped molecules with flexible bonds give considerably lower friction than liquids based on molecules with bulky side groups or rings. EHD friction also increases with viscosity for liquids having similar molecular structures. Using pure ester fluids, it is shown that quite small differences in molecular structure can have considerable effects on EHD friction. The importance of temperature rise in reducing EHD friction at slide-roll ratios above about 5% has been shown. By measuring EHD friction at several temperatures and pressures as well as EHD film thickness, approximate corrections to measured EHD friction data have been made to obtain isothermal shear stress and thus EHD friction curves. These show that under the conditions tested most low molecular weight base fluids do not reach a limiting friction coefficient and thus shear stress. However, two high traction base fluids appear to reach limiting values, while three linear polymeric base fluids may also do so. Constants of best fit to a linear/logarithmic isothermal shear stress/strain rate relationship have been provided to enable reconstruction of isothermal EHD friction behaviour for most of the fluids tested.

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“…1 The Eyring model is also based on the ℎ function. As Eyring [14] derived his model from measurements at a capillary viscometer where a proper separation of shear thinning and thermal effects is not possible (Bair et al [5]), some relation between the temperature dependency of | and primary measured data may be assumed. …”

Section: Contact-local Approachmentioning

confidence: 99%

“…A widely used model that does not take into account limiting shear stress, but which presents good numerical practicability (Bartel [9]) has been proposed by Eyring [14]. Bair et al [5] show that the Eyring model cannot provide a good representation of the shear thinning behavior of lubricants. Furthermore, shear stresses are not limited and can become infinitely large.…”

Section: Introductionmentioning

confidence: 99%