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.

A Thermal Elastohydrodynamic Theory for Individual Asperity-Asperity Collisions

1971 ◽  
Vol 93 (3) ◽  
pp. 383-394 ◽  
Author(s):  
P. E. Fowles
Keyword(s):  
Film Thickness ◽  
High Pressures ◽  
Numerical Solutions ◽  
Contact Region ◽  
Lubricant Film ◽  
Sliding Contact ◽  
Shear Stresses ◽  
Surface Shear ◽  
Sliding Speed

A thermal elastohydrodynamic theory is developed for the collision between two idealized asperities on surfaces in sliding contact. Numerical solutions are obtained for the pressure, temperature, and film thickness between the asperities as functions of their overlap, the sliding speed, and the time since the initiation of the collision for a given lubricant and asperity geometry. It is shown that extremely high pressures, temperatures, and surface shear stresses are to be expected at the center of the contact region. The tractions generated are shown to be of the same order as the load capacities. At the higher sliding speeds, overlapping asperities may pass over each other, separated at all times by a finite lubricant film. At the lower sliding speeds, boundary processes must take over before the completion of the collision.

Characteristics of Liquid Lubricant Films at the Nano-Scale

1999 ◽  
Vol 121 (4) ◽  
pp. 872-878 ◽  
Author(s):  
Jianbin Luo ◽  
Ping Huang ◽  
Shizhu Wen ◽  
Lawrence K. Y. Li
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Substrate Surface ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Thin Film Lubrication ◽  
Unusual Behavior ◽  
Running Time ◽  
Liquid Lubricant ◽  
Lubricant Viscosity

Characteristics of a liquid lubricant film at the nanometer scale are discussed in the present paper. The variations of the film thickness in a central contact region between a glass disk and a super-polished steel ball with lubricant viscosity, rolling speed, substrate surface tension, running time, load, etc. have been investigated. Experimental results show that the variation of film thickness in the thin film lubrication (TFL) regime is largely different from that in the elastohydrodynamic lubrication (EHL) regime. The critical transition point from EHL to TFL is closely related to lubricant viscosity, surface energy of substrates, and so on. The film in TFL is much thicker than that calculated from the Hamrock-Dowson formula. An unusual behavior of the lubricant film has also been observed when the effect of the running time on the film thickness is considered. The time effect and the formation mechanism of the enhanced film in the running process have been discussed.

Rough Air-Soft Elastohydrodynamic Lubrication

2013 ◽  
Vol 420 ◽  
pp. 30-35
Author(s):  
Khanittha Wongseedakaew ◽  
Jesda Panichakorn
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Modulus Of Elasticity ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Multilevel Methods ◽  
Inlet Temperature ◽  
Film Pressure ◽  
Air Inlet ◽  
Air Film

This paper presents the effects of rough surface air-soft elastohydrodynamic lubrication (EHL) of rollers for soft material under the effect of air molecular slip. The time independent modified Reynolds equation and elasticity equation were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel methods were used to obtain the film pressure profiles and film thickness in the contact region. The effects of amplitude of surface roughness, modulus of elasticity and air inlet temperature are examined. The simulation results showed surface roughness has effect on film thickness but it little effect to air film pressure. When the amplitude of surface roughness and modulus of elasticity increased, the air film thickness decreased but air film pressure increased. However, the air inlet temperature increased when the air film thickness increased.

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.

Formation of Lubricant Film in Rotary Sealing Contacts: Part II—A New Measuring Principle for Lubricant Film Thickness

1992 ◽  
Vol 114 (2) ◽  
pp. 290-296 ◽  
Author(s):  
G. Poll ◽  
A. Gabelli
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Lip Seal ◽  
Tribological System ◽  
Lip Seals ◽  
Magnetite Particles ◽  
Rotary Speed ◽  
Fluid Film Thickness ◽  
Insight Into

The development of models for the elastohydrodynamic lubrication of rotary lip seals requires the measurement of the film thickness under a real seal. A new method has been developed for this purpose which is based on the use of lubricant oils in which magnetite particles are suspended (so-called magnetic fluids). A change in the fluid film thickness will create a change in the impedance of the coil of the measuring circuit, the magnetic flux of which is directed through the oil film of the contact area. The advantage of this technique is that minimal modifications have to be applied to the tribological system under examination. Initial measurements carried out with a model rubber lip seal provided new insight into the build-up of a lubricant film as a function of the rotary speed and allowed comparison with the results of a theoretical model for the analysis of lip seal lubrication developed in parallel.

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).

Study on the Influence of Non-Newtonian Characteristics on Robots for Medical Application

2010 ◽  
Vol 29-32 ◽  
pp. 857-861
Author(s):  
Jian Ping Liu ◽  
Xin Yi Zhang ◽  
Qing Xuan Jia
Keyword(s):  
Film Thickness ◽  
Elastic Deformation ◽  
Reynolds Equation ◽  
Traction Force ◽  
Elastohydrodynamic Lubrication ◽  
Medical Application ◽  
Lubrication Theory ◽  
Newtonian Model

Considering lumen elastic deformation, Reynolds equation is deduced based on non-Newtonian model in this paper. Traction force and hydrodynamic mucus film thickness are calculated according to elastohydrodynamic lubrication theory. Compared with results based on Newtonian model and experiments, analysis based on non-Newtonian model reflects practical condition well. Lumen elastic deformation has some influence on traction force and mucus film thickness.

Experimental Investigation of Lubricant Flow Properties Under Micro Oil Supply Condition

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Shanhua Qian ◽  
Dan Guo ◽  
Shuhai Liu ◽  
Xinchun Lu
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Relative Length ◽  
Flow Properties ◽  
Oil Supply ◽  
Supply Condition ◽  
Lubricant Flow ◽  
Oil Pool ◽  
Disc Configuration

Lubricant flow properties of polyalphaolefin (PAO) oil have been experimentally investigated based on a ball-on-disc configuration under micro oil supply condition. The oil pool shape and central film thickness in the contact region were obtained using fluorescence microscopy and optical interferometry, respectively. It has been found that the relative length between the inlet meniscus and Hertzian center point in the oil pool to Hertzian radius was much larger than 1 in a smaller lubricant supply of 20 μl, and the corresponding contact region initially entered the elastohydrodynamic lubrication (EHL) region and then became starved with the increasing speed. The variations of the relative film thickness as a function of starvation degree and the ratio of relative length to Hertzian radius were proposed to explain the obtained results. Besides, the fluorescence technique was used to directly observe the inlet meniscus position of the oil pool and helped to gain more understanding of the lubricant flow properties under micro oil supply condition.

A Three-Dimensional Model of Line-Contact Elastohydrodynamic Lubrication for Heterogeneous Materials with Inclusions

2016 ◽  
Vol 08 (02) ◽  
pp. 1650014 ◽  
Author(s):  
Kun Zhou ◽  
Qingbing Dong
Keyword(s):  
Film Thickness ◽  
Half Space ◽  
Surface Deformation ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Line Contact ◽  
Lubricant Film Thickness ◽  
Equivalent Inclusion Method ◽  
Surface Contact

This paper develops a three-dimensional (3D) model for a heterogeneous half-space with inclusions distributed periodically beneath its surface subject to elastohydrodynamic lubrication (EHL) line-contact applied by a cylindrical loading body. The model takes into account the interactions between the loading body, the fluid lubricant and the heterogeneous half-space. In the absence of subsurface inclusions, the surface contact pressure distribution, the half-space surface deformation and the lubricant film thickness profile are obtained through solving a unified Reynolds equation system. The inclusions are homogenized according to Eshelby’s equivalent inclusion method (EIM) with unknown eigenstrains to be determined. The disturbed half-space surface deformations induced by the subsurface inclusions or eigenstrains are iteratively introduced into the lubricant film thickness until the surface deformation finally converges. Both time-independent smooth surface contact and time-dependent rough surface contact are considered for the lubricated contact problem.

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