Ordinary shear thinning behavior and its effect upon EHL film thickness

2003 ◽  
pp. 693-699 ◽  
Author(s):  
Scott Bair ◽  
Farrukh Qureshi
Keyword(s):  
Film Thickness ◽  
Shear Thinning

scholarly journals Analysis of misaligned journal bearing lubrication performance considering the effect of lubricant couple stress and shear thinning

2021 ◽  
Vol 37 ◽  
pp. 282-290
Author(s):  
Junchao Zhu ◽  
Haiyu Qian ◽  
Huabing Wen ◽  
Liangyan Zheng ◽  
Hanhua Zhu
Keyword(s):  
Film Thickness ◽  
Couple Stress ◽  
Journal Bearing ◽  
Shear Thinning ◽  
Inlet Temperature ◽  
Stress Effect ◽  
Misalignment Angle ◽  
Oil Film ◽  
Stress Coefficient ◽  
Lubrication Performance

ABSTRACT This paper investigates journal bearings, and builds a lubrication model taking into account misalignment, the lubricant couple stress effect and shear thinning. In order to explore the sensitivity of couple stress fluid lubrication performance to oil film thickness, we introduce the critical oil film thickness coefficient. The results show that the sensitivity increases with the increase of the couple stress coefficient, and it is highest in the area of minimum oil film thickness. Compared with a parallel journal, increases in the misalignment angle strengthen the effect of couple stress. Shear thinning also plays an important role in bearing lubrication performance. For a low oil inlet temperature, the effect of shear thinning increases with the increase of the couple stress parameter. For a high oil inlet temperature, the influence is negligible. An increase in the misalignment angle will not further enhance the effect of shear thinning.

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

2008 ◽  
Author(s):  
I. I. Kudish ◽  
P. Kumar ◽  
M. M. Khonsary ◽  
S. Bair
Keyword(s):  
Film Thickness ◽  
Scale Effects ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Effective Pressure ◽  
Practical Advantage ◽  
Inlet Zone ◽  
Real Machine

The prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the properties have been obtained from a measurement of the central film thickness in an optical EHL point contact simulator and the assumption of a classical Newtonian film thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient which compensates for shear-thinning. We have shown by a perturbation analysis and by a full EHL numerical solution that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact within a real machine may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning in the inlet zone.

New Central Film Thickness Equation for Shear Thinning Lubricants in Elastohydrodynamic Lubricated Rolling/Sliding Point Contact Conditions

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Puneet Katyal ◽  
Punit Kumar
Keyword(s):  
High Pressure ◽  
Equation Of State ◽  
Film Thickness ◽  
Point Contact ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Numerical Approach ◽  
Present Formulation ◽  
Contact Conditions ◽  
Doolittle Equation

This paper offers central film thickness formula pertaining to shear-thinning lubricants under rolling/sliding point contact conditions. The shear-thinning behavior of the lubricants is modeled using Carreau viscosity equation and the piezo-viscous response employed herein is the free-volume based Doolittle equation in conjunction with Tait's equation of state for lubricant compressibility. The present formulation is based on reciprocal asymptotic isoviscous piezo-viscous coefficient as it is a more accurate measure of the high pressure piezo-viscous response of elastohydrodynamic lubricated (EHL) lubricants compared to the conventional pressure–viscosity coefficient. Comparisons between simulated, curve-fitted values, and experimental results validate both the employed numerical approach and rheological model.

The Generalized Newtonian Fluid Model and Elastohydrodynamic Film Thickness

2002 ◽  
Vol 125 (1) ◽  
pp. 70-75 ◽  
Author(s):  
Scott Bair ◽  
Farrukh Qureshi
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
Fluid Model ◽  
Shear Thinning ◽  
Nonequilibrium Molecular Dynamics ◽  
Generalized Newtonian Fluid ◽  
Flow Curves ◽  
Liquid Behavior ◽  
Inlet Zone ◽  
Film Thinning

The nature of real shear-thinning in elastohydrodynamic contacts is well-known from both experimental measurement and nonequilibrium molecular dynamics to follow a power-law. Shear-thinning will affect the film thickness when the Newtonian limit is low enough to occur in the inlet zone (less than about 1 MPa shear stress). Then kinetic theory tells us that film thinning should occur for molecular weight greater than 2000 kg/kmol. We present a review of generalized Newtonian models, flow curves for real lubricants and comparison of calculated and measured film thickness. The calculations utilize measurable liquid behavior, in contrast to most previous work.

A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction

2007 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Scott Bair ◽  
Philippe Vergne
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
High Viscosity ◽  
Viscosity Models ◽  
Pure Rolling ◽  
Volume Viscosity ◽  
Traction Coefficient ◽  
Simulation And Experiment

We present a realistic elastohydrodynamic lubrication (EHL) simulation in point contact using a Carreau-like model for the shear-thinning response and the Doolittle-Tait free-volume viscosity model for the piezoviscous response. The liquid is a high viscosity polyalphaolefin which possesses a relatively low threshold for shear-thinning. As a result, the measured EHL film thickness is about one-half of the Newtonian prediction. We derived and numerically solved the two-dimensional generalized Reynolds equation for the modified Carreau model based on Greenwood [1]. Departing from many previous solutions, the viscosity models used for the pressure and shear dependence were obtained entirely from viscometer measurements. Truly remarkable agreement is found in the comparisons of simulation and experiment for traction coefficient and for film thickness in both pure rolling and sliding cases. This agreement validates the use of a generalized Newtonian model in EHL.

The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Ivan Krupka ◽  
Martin Hartl ◽  
Scott Bair
Keyword(s):  
Film Thickness ◽  
Ambient Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Component Mixture ◽  
Base Oil ◽  
Viscosity Models ◽  
Viscosity Behavior ◽  
Pure Rolling

Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components.

Correlation of Polysiloxane Molecular Structure to Shear-Thinning Power-Law Exponent Using Elastohydrodynamic Film Thickness Measurements

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Thomas J. Zolper ◽  
Paul Shiller ◽  
Manfred Jungk ◽  
Tobin J. Marks ◽  
Yip-Wah Chung ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Shear Rate ◽  
Film Thickness ◽  
Power Law ◽  
Shear Thinning ◽  
Macromolecular Structure ◽  
Polymeric Fluid ◽  
Power Law Exponent ◽  
Elastohydrodynamic Film Thickness ◽  
Thickness Measurements

Siloxane-based polymers (polysiloxanes) are susceptible to temporary shear-thinning that manifests as a reduction of elastohydrodynamic film thickness with increasing entrainment speed or effective shear rate. The departure from Newtonian film thickness can be predicted with the power-law exponent ns, an indicator of the severity of shear-thinning in a polymeric fluid that is influenced by the macromolecular structure. In this paper, a combination of extant rheological and tribological models is applied to determine the power-law exponent of several polysiloxanes using film thickness measurements. Film thickness data at several temperatures and slide-to-roll ratios are used to validate the methodology for several siloxane-based polymers with alkyl and aryl branches.

Investigation of Shear-Thinning Behavior on Film Thickness and Friction Coefficient of Polyalphaolefin Base Fluids With Varying Olefin Copolymer Content

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Thomas J. Zolper ◽  
Yifeng He ◽  
Massimiliano Delferro ◽  
Paul Shiller ◽  
Gary Doll ◽  
...  
Keyword(s):  
Film Thickness ◽  
Molecular Mass ◽  
Gel Permeation Chromatography ◽  
Shear Thinning ◽  
Hydrodynamic Friction ◽  
Lubrication Regimes ◽  
Film Forming ◽  
Molecular Masses ◽  
Shear Characteristics ◽  
The Relationship

This study investigates the rheological properties, elastohydrodynamic (EHD) film-forming capability, and friction coefficients of low molecular mass poly-α-olefin (PAO) base stocks with varying contents of high molecular mass olefin copolymers (OCPs) to assess their shear stability and their potential for energy-efficient lubrication. Several PAO–OCP mixtures were blended in order to examine the relationship between their additive content and tribological performance. Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy were used to characterize the molecular masses and structures, respectively. Density, viscosity, EHD film thickness, and friction were measured at 303 K, 348 K, and 398 K. Film thickness and friction were studied at entrainment speeds relevant to the boundary, mixed, and full-film lubrication regimes. The PAO–OCP mixtures underwent temporary shear-thinning resulting in decreases in film thickness and hydrodynamic friction. These results demonstrate that the shear characteristics of PAO–OCP mixtures can be tuned with the OCP content and provide insight into the effects of additives on EHD characteristics.

Elastohydrodynamic film thickness for shear-thinning lubricants

1998 ◽  
Vol 212 (3) ◽  
pp. 179-191 ◽  
Author(s):  
J. A. Greenwood ◽  
J. J. Kauzlarich
Keyword(s):  
Shear Rate ◽  
Film Thickness ◽  
Gas Turbines ◽  
Shear Thinning ◽  
Mineral Oil ◽  
High Shear ◽  
Newtonian Viscosity ◽  
Special Cases ◽  
Rolling Element ◽  
Low Shear

Mineral oils and synthetic lubricants that are thickened by polymers of large molecular weight are being promoted for automobiles as well as aircraft gas turbines. These multiweight lubricants are found to have a complicated Newtonian and non-Newtonian viscosity depending upon shear rate in the bearing. In general, polymer-thickened mineral oil lubricants show a first Newtonian behaviour at a low shear rate, shear-thinning non-Newtonian behaviour at a higher shear rate and a second Newtonian behaviour at a very high shear rate, with a second Newtonian viscosity approximately equal to the base oil viscosity. Because of high shear thinning in the inlet region of rolling element bearings, predicting the film thickness using the low shear rate first Newtonian viscosity can be in error, in particular examples, by a factor of ½ for mineral oil plus 4% methacrylate thickener and 1/7 for mineral oil plus 20% polybutene thickener. The case of naturally shear-thinning silicone fluids is analysed and it is shown that the elastohydrodynamic (EHD) film thickness is nearly the same for silicones with widely varying first Newtonian viscosity. A general EHD analysis for shear-thinning lubricants in pure rolling is presented and shown to agree with known special cases. A closed-form EHD equation for power law shear-thinning lubricants is derived, which gives very accurate results for a bearing where the inlet state of the rolling element falls in the region where the non-Newtonian viscosity is expected. A comparison with some published experimental results by Bair and Khonsari is presented.

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