Viscous Heating in Compressed Liquid Films

Bair, Scott

doi:10.1007/s11249-019-1252-x

Cited by 8 publications

(13 citation statements)

References 31 publications

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“…[45]. Finally, Bair has also recently questioned the ability of NEMD thermostats to maintain isothermal conditions at the high shear rates [46] employed by Jadhao and Robbins [24,30]. The energy released in these NEMD simulations is certainly considerable; however, the thermostatting methods applied have been shown to maintain isothermal conditions up to even higher strain rates (10 12 s −1 ) [47] than those considered by Jadhao and Robbins [24,30].…”

Section: Shear Thinningmentioning

confidence: 99%

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%

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

2021

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“…52 They showed that the transition from Carreau to Eyring is generic, as soon as the alignment of squalane molecules saturates. However, Bair 59 reproduced a similar trend of transition from power-law to sinh-law in Couette viscometers when they were operating above some viscous power. The transition may be caused by viscous heating and thermal softening, which is exactly the reason why Eyring 60 used the sinh-law to describe the experimental observations on capillary and circular Couette viscometers.…”

Section: Shear-thinning Rheological Fluid Modelsmentioning

confidence: 62%

Two-dimensional generalized non-Newtonian EHL lubrication: Shear rate-based solution versus shear stress-based solution

Liu

Zhang

Schneider

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part J:

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Lubricant behaves non-Newtonian at high shear stress and high shear rate. The non-Newtonian shear behavior of oil such as shear-thinning, viscoelasticity, and limiting shear stress could have influences on almost all characteristics of an elastohydrodynamic lubrication (EHL) contact, that is, the central film thickness, the coefficient of friction, and the temperature rise in the lubricating film. For example, for lubricants of large molecular weight or of polymer blended ones, there can be inlet shear-thinning, which would reduce the EHL film thickness. For the EHL traction in a rolling/sliding EHL contact, it cannot be reasonably predicted without the consideration of non-Newtonian rheology. In EHL numerical studies, the non-Newtonian properties and the constitutive equations are expressed by the concept of generalized viscosity [Formula: see text], which can be either a function of shear rate [Formula: see text] or a function of shear stress [Formula: see text]. In this way, a non-Newtonian lubrication problem could be solved as a generalized Newtonian problem based on solvers for a Newtonian EHL problem. According to the function of the generalized viscosity [Formula: see text], numerical solutions can be classified into shear rate-based ones and shear stress-based ones. In this work, these two kinds of numerical solutions are revisited. And their efficiency is compared for a two-dimensional (2D) non-Newtonian point contact EHL problem (here 2D means non-Newtonian flow in both the x and y directions). Results show that the shear rate-based numerical solution has a higher efficiency than the shear stress-based one. The shear rate-based 2D generalized Newtonian method is more suitable to analyze multiple EHL contacts in angular contact ball bearings and gears with complex 2D flow and/or transient EHL lubrication problems.

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“…The improved Yasutomi correlation (2,3,4) was applied to the Bair [11] and NRL [17] data to arrive at the parameters listed in Table 1. The results of Irving and Barlow [13] were presented as a correlation and were not used although the agreement is good as shown in Figure 1.…”

Section: The Improved Yasutomi Correlationmentioning

confidence: 99%

“…See for example reference [3]. When the glass transition is approached by compression from ambient pressure, as in TEHL,  may increase by an order-of-magnitude [4] from 0.03 to 0.3 K -1 . For accuracy and relevance, modelling of TEHL must include this behavior known as fragility.…”

Section: Introductionmentioning

confidence: 99%

The Role of Fragility in Thermal Elastohydrodynamics

Bair

Habchi

2023

Tribol Lett

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Temperature primarily influences thermal elastohydrodynamic lubrication (TEHL) through the temperature dependence of the viscosity of the liquid. The pressure and temperature dependences of viscosity increase rapidly as the glassy state is approached from the liquid state, a property known as fragility. The glass temperature increases with pressure and reaches to ordinary temperatures at TEHL pressures. It is astounding, therefore, that most TEHL analyses have ignored fragility by utilizing a viscosity correlation incapable of describing this behavior. Here, a low viscosity fragile oil is characterized for low-shear viscosity to 1.6 GPa and TEHL line contact simulations show, not only a substantial effect on friction, but significant differences in minimum film thickness when fragility is not ignored, as is customary in classical TEHL. The influence on friction manifests even under moderate load and speed conditions, while that on film thickness seems to be restricted to high loads.

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Viscous Heating in Compressed Liquid Films

Cited by 8 publications

References 31 publications

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

Contributions of Molecular Dynamics Simulations to Elastohydrodynamic Lubrication

Two-dimensional generalized non-Newtonian EHL lubrication: Shear rate-based solution versus shear stress-based solution

The Role of Fragility in Thermal Elastohydrodynamics

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