Quantitative Compressibility Effects in Thermal Elastohydrodynamic Circular Contacts

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
W. Habchi ◽  
S. Bair
Keyword(s):  
Equation Of State ◽  
Film Thickness ◽  
Transport Properties ◽  
Research Committee ◽  
Viscosity Coefficients ◽  
Film Forming ◽  
Volume Compression ◽  
Relative Errors ◽  
Compressibility Effects ◽  
Source Of Error

This paper investigates the effects of lubricant compressibility on the film-forming performance of thermal elastohydrodynamic lubricated (EHL) circular contacts. Numerical film thickness predictions using the classical Dowson and Higginson relationship are compared to those that would be obtained using a more realistic compressibility model, all other parameters kept unchanged. This allows an isolation of the realistic compressibility effects on the film-forming performance. For realistic predictions, the authors consider two model liquids from the 1953 report of the ASME Research Committee on Lubrication, the most and the least compressible. The compressibility of these liquids is modeled using the Tait equation of state (EoS) while all other transport properties are kept unchanged for the sake of isolating compressibility effects. In addition, the same typical generalized-Newtonian behavior is assumed for both model liquids. The results reconfirm the well-known observations that minimum film thickness is very little affected by lubricant compressibility while central film thickness decreases linearly with the increase in volume compression of the lubricant. It is also observed that the relative errors on central film thicknesses induced by the use of the Dowson and Higginson relationship for compressibility increase with load and temperature and are very little affected by mean entrainment speed. Compressibility is shown to be a significant source of error in film-derived measurements of pressure-viscosity coefficients especially at high temperature. The thermodynamic scaling that provides an accurate and consistent framework for the correlation of the thermophysical properties of liquids with temperature and pressure requires an accurate equation of state. In brief, this paper highlights the importance of using realistic transport properties modeling based on thermodynamic scaling for an accurate numerical prediction of the performance of EHL contacts.

scholarly journals Analytical Formula for the Ratio of Central to Minimum Film Thickness in a Circular EHL Contact

Lubricants ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 80 ◽  
Author(s):  
Petr Sperka ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Experimental Data ◽  
Film Thickness ◽  
Analytical Formula ◽  
Numerical Calculations ◽  
Constant Ratio ◽  
Viscosity Coefficients ◽  
Wide Range ◽  
Minimum Film Thickness ◽  
Film Parameter ◽  
Ehl Contact

Prediction of minimum film thickness is often used in practice for calculation of film parameter to design machine operation in full film regime. It was reported several times that majority of prediction formulas cannot match experimental data in terms of minimum film thickness. These standard prediction formulas give almost constant ratio between central and minimum film thickness while numerical calculations show ratio which spans from 1 to more than 3 depending on M and L parameters. In this paper, an analytical formula of this ratio is presented for lubricants with various pressure–viscosity coefficients. The analytical formula is compared with optical interferometry measurements and differences are discussed. It allows better prediction, compared to standard formulas, of minimum film thickness for wide range of M and L parameters.

scholarly journals The Unresolved Definition of The Pressure-Viscosity Coefficient

2021 ◽  
Author(s):  
Scott Bair
Keyword(s):  
High Temperature ◽  
Equation Of State ◽  
Low Temperature ◽  
Film Thickness ◽  
Pressure Dependence ◽  
Analytical Calculation ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Classical Approach ◽  
Definition Of

Abstract In the classical approach to elastohydrodynamic lubrication (EHL) a single parameter, the pressure-viscosity coefficient, quantifies the isothermal pressure dependence of the viscosity for use in prediction of film thickness. Many definitions are in current use. Progress toward a successful definition of this property has been hampered by the refusal of those working in classical EHL to acknowledge the existence of accurate measurements of the piezoviscous effect that have existed for nearly a century. The Hamrock and Dowson pressure-viscosity coefficient at high temperature requires knowledge of the piezoviscous response at pressures which exceed the inlet pressure and may exceed the Hertz pressure. The definition of pressure-viscosity coefficient and the assumed equation of state must limit the use of the classical formulas, including Hamrock and Dowson, to liquids with high Newtonian limit and to low temperature. Given that this problem has existed for at least fifty years without resolution, it is reasonable to conclude that there is no definition of pressure-viscosity coefficient that will quantify the piezoviscous response for an analytical calculation of EHL film thickness at temperatures above ambient.

Effects of polymers concentration on EHL film-forming in point contacts

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Liangwei Qiu ◽  
Xiaoyang Chen ◽  
Fakai Dong
Keyword(s):  
Film Thickness ◽  
Peer Review ◽  
Point Contact ◽  
High Concentration ◽  
Content Type ◽  
Base Oils ◽  
Low Viscosity ◽  
Lubricant Oil ◽  
Pure Rolling ◽  
Film Forming

Purpose This paper aims to experimentally investigate the film-forming capability of base oils containing poly-methacrylate (PMA) and poly-isobutene (PIB), in a point contact under pure rolling. Design/methodology/approach By using the relative light intensity method, the film thickness is calculated from the interferometer images which are captured by multiple-contact optical elastohydrodynamic lubricated test rig. Findings The test results reveal that polymers, both PMA and PIB, have a significant contribution to the film-forming capability of base oils and the film thickness increases with concentration. The forming-film capabilities for PMA and PIB in base oils are similar at low concentration, while PIB gives a higher film thickness than PMA at high concentration. Shear-thinning phenomenon are observed in all polymer-based oils. Originality/value The polymer usually as an additive is added into the low viscosity base oils to improve the properties of lubricant oil. This paper reports the lubricated properties of PMA and PIB with different concentrations in base oils and to evaluate their functional mechanism in a point contact. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0263/

scholarly journals Elastohydrodynamics of a Worm Gear Contact

2000 ◽  
Vol 123 (2) ◽  
pp. 268-275 ◽  
Author(s):  
S. Kong ◽  
K. Sharif ◽  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Film Thickness ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Worm Gear ◽  
Simulation Technique ◽  
Elastic Contact ◽  
Gear Teeth ◽  
Film Forming ◽  
Worm Gears ◽  
Gear Contact

The paper is concerned with prediction of elastic contact and elastohydrodynamic film thickness in worm gears. Using the undeformed geometry of the gap between gear teeth in contact a three-dimensional elastic contact simulation technique has been developed for calculation of the true area of elastic contact under load relative to the wheel and worm surfaces. A parallel investigation of elastohydrodynamic lubrication effects has been carried out using a special non-Newtonian, thermal solver which takes account of the nonsymmetrical and spin aspects of worm contacts. An interesting feature of the results obtained is the discovery of regions of poor film forming due to entrainment failure at the edges of the contact.

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.

Equation of state of bcc-Mo by static volume compression to 410 GPa

2014 ◽  
Vol 116 (22) ◽  
pp. 223504 ◽  
Author(s):  
Yuichi Akahama ◽  
Naohisa Hirao ◽  
Yasuo Ohishi ◽  
Anil K. Singh
Keyword(s):  
Equation Of State ◽  
Volume Compression
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