Observations of Shear Localization in Liquid Lubricants Under Pressure

Bair, Scott; Qureshi, Farrukh; Winer, W. O.

doi:10.1115/1.2921667

Cited by 68 publications

(34 citation statements)

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“…In the field of tribology, shear localisation has only been directly observed experimentally in viscous model lubricants, such as polybutadiene and polyphenyl ethers (e.g., 5P4E) [196][197][198][199][200][201]. However, it has also been inferred from film thickness measurements in realistic mineral oils [202,203] and there is currently a growing consensus that this phenomenon may also be important for more realistic lubricants under extreme EHL conditions [185].…”

Section: Shear Localisationmentioning

confidence: 96%

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 Localisationmentioning

confidence: 96%

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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“…It is conceivable that when the applied shear stress exceeds this value, slip may occur within the lubricant film. Some evidence to support was provided by Bair et al [23], albeit for considerably thickener films, which showed oil samples within a high pressure rheometer that fractured under high pressure forming slip bands [23]. Recently, important work by Ponjavic et al [24], using fluorescence microscopy to obtain through-thickness velocity profiles, has shown that oligomer polybutene exhibits wall-slip under EHL conditions [24].…”

Section: Introductionmentioning

confidence: 92%

“…This assumption requires verification as there is a possibility that slip occurs at a point midway through the thickness of the film, as for instance observed by Bair [23] using a high pressure rheometer.…”

Section: Location Of Slip and Validation Of Assumptionmentioning

confidence: 99%

Wall slip in an EHL contact lubricated with 1-dodecanol

Wang

Reddyhoff

2017

Tribology International

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A study was conducted of the factors that cause anomalous EHD film shapes in 1-dodecanol lubricated contacts -i.e. a thickened central plateau and an exaggerated outlet constriction. This has led to the hypothesis that, in the region where pressures exceed ~0.44 GPa, dodecanol experiences slip, which reduces the average lubricant velocity and causes an elevated film thickness in order to maintain flow continuity. The analysis suggests that slip must be occurring at, or close to, the faster moving surface, since a discontinuity in the flow midway through the thickness of the film would not affect the average speed of the lubricant. Based on this hypothesis, an equation has been derived to predict the anomalous central film thickness as a function of applied slide-roll ratio and this has been validated by comparison with experimentally measured central film thickness values. Further support of this hypothesis is provided by traction test results showing a discontinuity occurring close to the onset of slip.

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“…In 1993 Bair and Winer studied velocity profiles by tracking micro-sized dispersed particles in three lubricants sheared between two flat surfaces at high shear stress [106]. The lubricant films were observed from the side, which meant that their thickness, of 150 m, was much greater than a normal EHD film.…”

Section: Probing the Velocity Profile In Ehd Contactmentioning

confidence: 99%

History, Origins and Prediction of Elastohydrodynamic Friction

2014

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There is currently considerable debate concerning the most appropriate rheological model to describe the behaviour of lubricant films in rolling-sliding, elastohydrodynamic contacts. This is an important issue since an accurate model is required in to predict friction in such contacts. This paper reviews the origins of this debate, which primarily concerns a divergence of views between researchers using high pressure, high shear rate viscometry and those concerned with the measurement and analysis of elastohydrodynamic friction; the former advocate a Carreau-based shear stress/strain rate model while the latter generally favour an Eyring-based one. The crucial importance of accounting for shear heating effects in analysing both viscometric and friction data is discussed. The main criticisms levied by advocates of a Carreau-based model against Eyring's model are discussed in some detail. Finally the ability of both types of rheological model to fit elastohydrodynamic friction measurements for a quite simple, well-defined base fluid is tested, using previously-measured pressure-viscosity behaviour for the fluid. Both models appear to fit the experimental data over a wide temperature range quite well, though fit of the Eyring model appears slightly closer than that of the Carreau-Yasuda model. Friction data from a wider range of welldefined fluid types is needed to identify categorically the most appropriate model to describe elastohydrodynamic friction.

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Observations of Shear Localization in Liquid Lubricants Under Pressure

Cited by 68 publications

References 0 publications

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

Wall slip in an EHL contact lubricated with 1-dodecanol

History, Origins and Prediction of Elastohydrodynamic Friction

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