Your EHD Rig May Not Be As Elastohydrodynamic As You Think

2021 ◽  
Vol 143 (8) ◽  
Author(s):  
Scott Bair ◽  
Wassim Habchi
Keyword(s):  
Film Thickness ◽  
Short Note ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Experimental Investigations ◽  
Poor Agreement ◽  
Elastic Regime ◽  
The Poor ◽  
The Subject ◽  
Primary Instrument

Abstract The concentrated contact formed between a steel ball and a glass disc—the optical elastohydrodynamic lubrication (EHD) rig—has been the primary instrument for experimental investigations of elastohydrodynamic film thickness. It has been a source for values of pressure-viscosity coefficient, a difficult-to-define property of liquids. However, comparisons with the pressure dependence of the viscosity obtained in viscometers show little agreement. There are multiple reasons for this failure including shear-thinning and compressibility of the oil. Another reason for the poor agreement is the subject of this short note. The optical EHD rig using glass as one surface will only be in the piezoviscous-elastic (EHD) regime when the pressure-viscosity coefficient is large. For low values, it would be operating in the isoviscous-elastic regime (soft EHD).

Experimental Investigations Into the Behavior of Elastohydrodynamic Lubricating Films

1982 ◽  
Vol 104 (1) ◽  
pp. 91-98 ◽  
Author(s):  
G. S. A. Shawki ◽  
M. O. A. Mokhtar ◽  
A. A. Abdel-Ghany
Keyword(s):  
Temperature Distribution ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Contact Temperature ◽  
Experimental Investigations ◽  
Capacitive Transducer ◽  
Full Contact ◽  
The Subject ◽  
Critical Reduction ◽  
Lubrication Conditions

This paper presents the results of experimental investigations conducted on a disk machine specially designed and constructed to determine film behavior under elastohydrodynamic lubrication conditions. Oil film thickness is measured by a novel electronic technique utilizing a capacitive transducer. Besides film geometry, measurements include temperature distribution and frictional traction in the film, all taken under pure sliding conditions. Recordings of full contact profile confirm by way of example the development of a critical reduction in film thickness towards the exit end of the Hertzian zone, this being accompanied by a critical increase in contact temperature. Further work on the subject is proceeding.

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.

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.

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Ilya I. Kudish ◽  
P. Kumar ◽  
M. M. Khonsari ◽  
Scott Bair
Keyword(s):  
Film Thickness ◽  
Scale Effects ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Effective Pressure ◽  
Carreau Fluid ◽  
Practical Advantage ◽  
Inlet Zone ◽  
Real Machine

The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness 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 of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations.

New equations for enhanced film thickness in line contacts under pressurized ambient conditions

2016 ◽  
Vol 231 (5) ◽  
pp. 616-622 ◽  
Author(s):  
Niraj Kumar ◽  
Punit Kumar
Keyword(s):  
Film Thickness ◽  
Ambient Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Ambient Conditions ◽  
Alternative Approach ◽  
Film Forming ◽  
Highly Sensitive ◽  
Minimum Film Thickness ◽  
Line Contacts

An elastohydrodynamic lubrication model is proposed for line contacts under pressurized ambient conditions often encountered in hydraulic pumps, submarine machinery and many other submerged systems. It has been demonstrated that the film forming behavior under such conditions is essentially different from that in conventional elastohydrodynamic lubrication contacts. The numerical simulation results are regressed to develop new central and minimum film thickness equations for Newtonian fluids as functions of ambient pressure, speed, load, and material parameters. An alternative approach is also discussed which involves the use of existing film thickness formulas with ambient viscosity and pressure–viscosity coefficient pertaining to the desired pressure range. A film thickness enhancement of more than 100% over conventional elastohydrodynamic lubrication case is observed. This enhancement is shown to be highly sensitive to the pressure–viscosity coefficient. Besides, the effect of shear-thinning behavior is also investigated and it is found to lower the film thickness enhancement, especially at high ambient pressures.

Elastohydrodynamic Lubrication at Impact Loading

1994 ◽  
Vol 116 (4) ◽  
pp. 770-776 ◽  
Author(s):  
Roland Larsson ◽  
Erik Ho¨glund
Keyword(s):  
Film Thickness ◽  
Impact Velocity ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Lubricant Layer ◽  
Maximum Pressure ◽  
Damping Capacity ◽  
Lubricating Film ◽  
Static Conditions ◽  
Ball Mass

Experimental and theoretical studies of elastohydrodynamically lubricated contacts normally assume static or quasi-static conditions. Nonsteady conditions are, however, very common, e.g., in machine elements such as ball bearings, gears, and cam-follower mechanisms. In this paper, the case of a ball impacting a flat lubricated surface is investigated theoretically. This case implies transient conditions and the lubricating effect is due to pure squeeze action in the contact. Pressure and film thickness distributions are computed during impact and rebound. The results of the analysis show the effects of ball mass, initial impact velocity, lubricant properties, and the thickness of the applied lubricant layer on, for example, minimum film thickness, maximum impact force, and maximum pressure. Increasing impact velocity increases the minimum value of film thickness achieved during the total impact time. The damping capacity of the lubricating film is very high at low impact velocity and small ball mass. In fact, the damping is so high that no rebound occurs if the velocity or the ball mass are smaller than certain critical values. The thickness of the lubricant layer has very little influence on the results if it is thicker than a certain value. If the pressure-viscosity coefficient is increased, the film becomes thicker.

The Application of Elastohydrodynamic Lubrication Theory to Individual Asperity-Asperity Collisions

1969 ◽  
Vol 91 (3) ◽  
pp. 464-475 ◽  
Author(s):  
P. E. Fowles
Keyword(s):  
Film Thickness ◽  
High Pressures ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Lubrication Theory ◽  
Lubricant Film ◽  
Collision Process ◽  
Sliding Speed

Conventional elastohydrodynamic theory is modified and applied to the collision between two idealized surface asperities in an isothermal sliding system. Solutions for the pressure and film thickness between the asperities as functions of their overlap, the sliding speed, the pressure-viscosity coefficient of the lubricant, and the time since the initiation of the collision are obtained numerically for the first half of the collision process. It is shown that extremely high pressures and small film thicknesses are to be expected at the center of the contact region assuming the rheology of the lubricant film can be represented by that of the bulk lubricant.

scholarly journals A smart friction control strategy enabled by CO2 absorption and desorption

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jing Hua ◽  
Marcus Björling ◽  
Mattias Grahn ◽  
Roland Larsson ◽  
Yijun Shi
Keyword(s):  
Ionic Liquids ◽  
Film Thickness ◽  
Intelligent Control ◽  
Control Strategy ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Co2 Absorption ◽  
Full Size ◽  
Friction Control ◽  
Lubricated Contact

Abstract Intelligent control of friction is an attractive but challenging topic and it has rarely been investigated for full size engineering applications. In this work, it is instigated if it would be possible to adjust friction by controlling viscosity in a lubricated contact. By exploiting the ability to adjust the viscosity of the switchable ionic liquids, 1,8-Diazabicyclo (5.4.0) undec-7-ene (DBU)/ glycerol mixture via the addition of CO2, the friction could be controlled in the elastohydrodynamic lubrication (EHL) regime. The friction decreased with increasing the amount of CO2 to the lubricant and increased after partial releasing CO2. As CO2 was absorbed by the liquid, the viscosity of the liquid increased which resulted in that the film thickness increased. At the same time the pressure-viscosity coefficient decreased with the addition of CO2. When CO2 was released again the friction increased and it was thus possible to control friction by adding or removing CO2.

Some important aspects of thermal elastohydrodynamic lubrication

2010 ◽  
Vol 224 (12) ◽  
pp. 2588-2598 ◽  
Author(s):  
P Kumar ◽  
P Anuradha ◽  
M M Khonsari
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Thermal Expansivity ◽  
Viscous Heating ◽  
Line Contact ◽  
Rheological Equation ◽  
Transient Conditions ◽  
The Subject ◽  
Thermal Ehl

Thermal effect in elastohydrodynamic lubrication (EHL) has been the subject of study for the last four decades; however, some important aspects related to the physical behaviour of the lubricant in response to pressure, temperature, and shear rate remain largely neglected. This paper presents a brief review of the thermal EHL literature and sheds light on the importance of accurate characterization of the lubricant properties such as viscosity, density, rheology, and thermal conductivity. Full thermal EHL line contact simulations under steady-state and transient conditions show that using the ambient value of thermal expansivity, which has been the usual trend, may overestimate the central film thickness and introduce unrealistic features in transient EHL characteristics. Also, it is demonstrated that the most extensively used rheological equation – the sinh law – for characterizing the behaviour of shear-thinning lubricants underestimates the effect of viscous heating on EHL traction and film thickness.

PENERAPAN STRATEGI PEMBELAJARAN GO TO YUOR POST UNTUK MENINGKATKAN HASIL BELAJAR IPS SISWA KELAS VI SDN 024 TARAI BANGUN KECAMATAN TAMBANG KABUPATEN KAMPAR

2017 ◽  
Vol 1 (1) ◽  
pp. 85
Author(s):  
Delfi Yendri
Keyword(s):  
Social Sciences ◽  
Data Collection ◽  
Student Learning ◽  
Learning Outcomes ◽  
Learning Strategies ◽  
Student Learning Outcomes ◽  
Student Activity ◽  
The Poor ◽  
The Subject ◽  
Data Collection Activity

This research is motivated by the poor results of Study Social Sciences (IPS) Student Class VI SDN 024 Tarai Bangun Kecamatan Tambang. This study aims to determine the resulting increase studying social sciences (IPS) student class VI SDN 024 Tarai Bangun Kecamatan Tambang through the application of learning strategies go to yuor post, which carried out for 1 month. The subjects were VI SDN 024 Tarai Bangun Kecamatan Tambang by the number of students as many as 38 people. Form of research is classroom action research. The research instrument consists of instruments and instrument performance data collection activity observation sheet form teacher and student activity. Based on the research, the conclusion to this study is based on the analysis and discussion in chapter IV can be concluded that the application of learning strategies go to yuor post can improve learning outcomes in the subject of social sciences grade VI SDN 024 Tarai Bangun Kecamatan Tambang. Evidenced by the increase in learning outcomes before action to the first cycle, to cycle II. Before the act of student learning outcomes classified as unresolved with an average of 59%, an increase in the first cycle by an average of 69%. While the results of student learning in the second cycle must be increased by an average of 75% with the category completed.

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