Rheological Behavior of Confined Fluids in Thin Lubricated Contacts

Tichy, John

doi:10.1115/1.1354204

Cited by 5 publications

(6 citation statements)

References 12 publications

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“…As film thickness, h, decreases to nanometer and molecular scale, there will be a transition of lubrication mode from EHL to boundary lubrication, during which the source of friction also changes from fluid traction to the shear strength of boundary films. The transition is believed due to the changes in rheological properties of thin lubricating films [15,16], which is a research subject known as thin film lubrication or thin film rheology, received great attentions recently [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Transition of frictional states and surface roughness effects in lubricated contacts

Wang

et al. 2008

Proceedings of the Institution of Mechanical Engineers, Part J:

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In order to investigate frictional performances in different lubrication regimes and effects of surface roughness, the friction on engineering surfaces with different roughness patterns and amplitudes were measured. Results show a smooth transition of lubrication states from full-film hydrodynamic lubrication to mixed and boundary lubrication. Data from the tests also suggest that the transition of friction regimes is affected by roughness amplitude. It is observed that not only the smoother surfaces give rise to the lower critical velocities of transition from full-film to mixed lubrication, but also the friction coefficients at the point of the transition are much smaller for the smoother surfaces. For the transition from mixed to boundary lubrication, however, effects of roughness amplitude are insignificant. As a result, it is concluded that under the same contact conditions, different features in roughness cause the system to transit in different routines from one lubrication regime to another. Furthermore, a computer model, based on the deterministic solution of mixed lubrication combined with modelling of rheological variation in ultra-thin films, has been presented to predict friction in overall lubrication regimes. At last, the comparisons of simulation and experimental results show satisfactory agreements.

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Section: Introductionmentioning

confidence: 99%

Transition of frictional states and surface roughness effects in lubricated contacts

Wang

et al. 2008

Proceedings of the Institution of Mechanical Engineers, Part J:

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“…The following assumptions of the rheology of the thinfilm lubricant, including the increased relaxation time, development of yielding stress, and power-law viscosity behavior, are based on the experimental results of previous studies. [2,[8][9][10]13,14]…”

Section: Dynamic Rheological Model Of the Thin-film Lubricationmentioning

confidence: 99%

“…When a lubricant is confined within the contact area, a near-surface lubricant layer may stick onto the solid surface by chemical or physical adsorption to protect the surface, resulting in a high-viscosity layer adjacent to the solid surface. [2,14] This high-viscosity layer has two effects. Firstly, the highviscosity layer mainly results from the polar additives in the oil, which is generally immobile on the substrate during shearing.…”

Section: Shear Stress Of the Adsorbed Thin-film Layermentioning

confidence: 99%

“…Liquid viscosity is a crucial lubricant parameter for the hydrodynamic lubrication of machines based on the conventional Reynolds equations. However, the conventional Reynolds equations are limited to describing and predicting the properties of boundary or thin-film lubrication, [1,2] since boundary lubrication is often defined as the lubrication regime in which liquid bulk properties like viscosity are no longer dominant over friction. Generally, the transition from hydrodynamic lubrication regime to boundary lubrication regime can be clarified in a typical Stribeck curve, as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

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A dynamic rheological model for thin-film lubrication

Zhang¹,

Huang²,

Guo³

et al. 2013

Chinese Phys. B

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In this study, the effects of the non-Newtonian rheological properties of the lubricant in a thin-film lubrication regime between smooth surfaces were investigated. The thin-film lubrication regime typically appears in Stribeck curves with a clearly observable minimum coefficient of friction (COF) and a low-COF region, which is desired for its lower energy dissipation. A dynamic rheology of the lubricant from the hydrodynamic lubrication regime to the thin-film lubrication regime was proposed based on the convected Maxwell constitutive equation. This rheology model includes the increased relaxation time and the yield stress of the confined lubricant thin film, as well as their dependences on the lubricant film thickness. The Deborah number (De number) was adopted to describe the liquid-solid transition of the confined lubricant thin film under shearing. Then a series of Stribeck curves were calculated based on Tichy's extended lubrication equations with a perturbation of the De number. The results show that the minimum COF points in the Stribeck curve correspond to a critical De number of 1.0, indicating a liquid-to-solid transition of the confined lubricant film. Furthermore, the two proposed parameters in the dynamic rheological model, namely negative slipping length b (indicating the lubricant interfacial effect) and the characteristic relaxation time λ 0 , were found to determine the minimum COF and the width of the low-COF region, both of which were required to optimize the shape of the Stribeck curve. The developed dynamic rheological model interprets the correlation between the rheological and interfacial properties of lubricant and its lubrication behavior in the thin-film regime.

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“…Tichy [118,128,130,316,317] and others argue that continuum hydrodynamics modeling can remain a valid tool at the nanometer scale when one is interested in ensemble averages of time scales much longer than the molecular relaxation time, so that the transport of even a small number of molecules can be described using continuum theories. It is well-known that confined water can exhibit reduced mobility and antisymmetric transport properties [27]; however, precise guidelines for assessing the validity of continuum mechanics at the length scale of interfacial water (~1 nm) have yet to be developed.…”

Section: Validity Of Continuum Descriptionmentioning

confidence: 99%

Studies of the viscoelastic properties of water confined between surfaces of specified chemical nature.

Houston¹,

Grest²,

Moore³

et al. 2010

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This report summarizes the work completed under the Laboratory Directed Research and Development (LDRD) project 10-0973 of the same title. Understanding the molecular origin of the no-slip boundary condition remains vitally important for understanding molecular transport in biological, environmental and energy-related processes, with broad technological implications. Moreover, the viscoelastic properties of fluids in nanoconfinement or near surfaces are not well-understood. We have critically reviewed progress in this area, evaluated key experimental and theoretical methods, and made unique and important discoveries addressing these and related scientific questions. Thematically, the discoveries include insight into the orientation of water molecules on metal surfaces, the premelting of ice, the nucleation of water and alcohol vapors between surface asperities and the lubricity of these molecules when confined inside nanopores, the influence of water nucleation on adhesion to salts and silicates, and the growth and superplasticity of NaCl nanowires.

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Rheological Behavior of Confined Fluids in Thin Lubricated Contacts

Cited by 5 publications

References 12 publications

Transition of frictional states and surface roughness effects in lubricated contacts

Transition of frictional states and surface roughness effects in lubricated contacts

A dynamic rheological model for thin-film lubrication

Studies of the viscoelastic properties of water confined between surfaces of specified chemical nature.

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