Rheological Models for Thin Film EHL Contacts

1995 ◽  
Vol 117 (1) ◽  
pp. 22-28 ◽  
Author(s):  
Siyoul Jang ◽  
John Tichy
Keyword(s):  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Classical Case ◽  
Solid Surfaces ◽  
Nanometer Scale ◽  
Rheological Models ◽  
Flat Surfaces ◽  
Porous Layers ◽  
Viscous Fluid Model

Rheological behavior in concentrated contacts has been studied extensively. In certain conditions such as a rough concentrated contact or sliding of nominally flat surfaces, films may be of molecular (nanometer) scale. The question arises as to whether the application of any viscous fluid model is appropriate. In this study, elastohydrodynamic lubrication analysis is performed on three candidate rheological models: (1) the classical case of viscosity variation with pressure, (2) an isoviscous model which idealizes porous layers on the solid surfaces representing the molecular microstructure, and (3) an isoviscous model which includes van der Waals and solvation surface forces. The latter two models predict behavior similar to classical behavior. The study is not sufficiently sensitive to determine which model best predicts experimental results, but some credence must be given to the latter two because experimental evidence suggests that Reynolds’ equation is not valid for molecularly thin films.

EHL of Coated Surfaces: Part II—Non-Newtonian Results

1994 ◽  
Vol 116 (4) ◽  
pp. 786-793 ◽  
Author(s):  
A. A. Elsharkawy ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Half Space ◽  
Hard Coatings ◽  
Surface Shear Stress ◽  
Coating Materials ◽  
Surface Shear ◽  
Pressure Profiles

A complete non-Newtonian elastohydrodynamic lubrication solution for multilayered elastic solids is introduced in this paper. A modified form for the Reynolds equation was derived by incorporating the circular non-Newtonian fluid model associated with a limiting shear strength directly into the momentum equations that govern the instantaneous equilibrium of a fluid element inside the lubricated conjunction. The modified Reynolds equation, the elasticity equations of multilayered elastic half-space, the lubricant pressure-viscosity equation, the lubricant pressure-density equation, and the load equilibrium equation were solved simultaneously by using the system approach. The effects of the surface coating on pressure profiles, film shapes, and surface shear stress profiles are shown. Furthermore, the effects of coating thickness on the minimum film thickness and on the coefficient of friction are presented for different coating materials. The results show that for hard coatings non-Newtonian fluid effects on the pressure profiles and film shapes are significant because of the increase in the contact pressure.

A Layered-Rheology Model for Thin Film Elastohydrodynamic Lubrication of Circular Contacts

2015 ◽  
Vol 764-765 ◽  
pp. 160-164
Author(s):  
Li Ming Chu ◽  
Hsiang Chen Hsu
Keyword(s):  
Thin Film ◽  
Power Law ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Middle Layer ◽  
Solid Surfaces ◽  
Flow Index ◽  
Lubricating Film ◽  
Lubrication Characteristics ◽  
Adsorption Layers

The modified Reynolds equation for power-law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL) of circular contacts. The lubricating film between solid surfaces is modeled as three fixed layers, which are two adsorption layers on each surface and a middle layer. The differences between classical EHL and TFEHL with non-Newtonian lubricants are discussed. Results show that the TFEHL power law model can reasonably calculate the pressure distribution, the film thickness, and the velocity distribution. The thickness and viscosity of the adsorption layer and the flow index influence significantly the lubrication characteristics of the contact conjunction.

A Circular Non-Newtonian Fluid Model: Part I—Used in Elastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 486-495 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Shear Strength ◽  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Load Parameter ◽  
Viscosity Term ◽  
Pure Rolling ◽  
The Coefficient Of Friction

A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. Results show that the calculation of the central and minimum film thicknesses from the classical Reynolds equation is still valid for pure rolling conditions. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied. Such parameters as the pressure profile, the film shape, the coefficient of friction, the dimensionless shear stress at surface a, and the velocitiy contour in the conjunction were considered.

Finite Element System Approach to EHL of Elliptical Contacts: Part I—Isothermal Circular Non-Newtonian Formulation

1998 ◽  
Vol 120 (4) ◽  
pp. 695-704 ◽  
Author(s):  
Hsing-Sen S. Hsiao ◽  
Bernard J. Hamrock ◽  
John H. Tripp
Keyword(s):  
Finite Element ◽  
System Approach ◽  
Reynolds Equation ◽  
Solution Method ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Weak Form ◽  
Weighting Method ◽  
Element System ◽  
User Friendly

The column continuity equation is used in formulating a modified Reynolds equation for elastohydrodynamic lubrication of elliptical contacts. A finite element method (FEM), here the Galerkin weighting method with isoparametric Q9 elements, is used to discretize the weak form of the Reynolds equation. In addition to the nodal pressures and the offset film thickness, the locations of the two-dimensional irregular free boundary are explicitly solved for by simultaneously forcing the essential and the natural Reynolds boundary conditions. Newton-Raphson’s iterations with a user-friendly yet efficient meshless scheme (i.e., automatic meshing-remeshing) are finally applied to solve these equations. A decoupled circular non-Newtonian fluid model is adapted in a way to illustrate the implementation of this new solution method. Extensive results will be given in Part II.

Non-Newtonian Thermal Elastohydrodynamic Lubrication

1991 ◽  
Vol 113 (2) ◽  
pp. 390-396 ◽  
Author(s):  
P. C. Sui ◽  
F. Sadeghi
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Traction Force ◽  
Elastohydrodynamic Lubrication ◽  
Simultaneous System ◽  
Energy Equations ◽  
Rheology Model ◽  
Generalized Reynolds Equation

A numerical solution to the problem of thermal and non-Newtonian fluid model in elastohydrodynamic lubrication is presented. The generalized Reynolds equation was modified by the Eyring rheology model to incorporate the non-Newtonian effects of the fluid. The simultaneous system of modified Reynolds, elasticity and energy equations were numerically solved for the pressure, temperature and film thickness. Results have been presented for loads ranging from W = 7 × 10−5 to W = 2.3 × 10−4 and the speeds ranging from U* = 2 × 10−11 to U* = 6 × 10−11 at various slip conditions. Comparison between the isothermal and thermal non-Newtonian traction force has also been presented.

Two Dimensional Modified Reynolds Equation Including Pressure Dependent Viscosity Effect

2012 ◽  
Author(s):  
Jung Gu Lee ◽  
Alan Palazzolo
Keyword(s):  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Maximum Pressure ◽  
Elastic Solids ◽  
Pressure Distributions ◽  
Pressure Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity ◽  
Modified Equation

The Reynolds equation plays an important role for predicting pressure distributions for fluid film bearing analysis, One of the assumptions on the Reynolds equation is that the viscosity is independent of pressure. This assumption is still valid for most fluid film bearing applications, in which the maximum pressure is less than 1 GPa. However, in elastohydrodynamic lubrication (EHL) where the lubricant is subjected to extremely high pressure, this assumption should be reconsidered. The 2D modified Reynolds equation is derived in this study including pressure-dependent viscosity, The solutions of 2D modified Reynolds equation is compared with that of the classical Reynolds equation for the ball bearing case (elastic solids). The pressure distribution obtained from modified equation is slightly higher pressures than the classical Reynolds equations.

The Effects of Vibrations on Particle Motion in a Viscous Fluid Cell

2008 ◽  
Vol 75 (3) ◽  
Author(s):  
Samer Hassan ◽  
Masahiro Kawaji
Keyword(s):  
Viscous Fluid ◽  
Drag Force ◽  
Particle Motion ◽  
Fluid Model ◽  
Resonance Phenomenon ◽  
Fluid Viscosity ◽  
Mass Force ◽  
Amplitude Data ◽  
Viscous Fluid Model ◽  
Fluid Cell

The effects of small vibrations on particle motion in a viscous fluid cell have been investigated experimentally and theoretically. A steel particle was suspended by a thin wire at the center of a fluid cell, and the cell was vibrated horizontally using an electromagnetic actuator and an air bearing stage. The vibration-induced particle amplitude measurements were performed for different fluid viscosities (58.0cP and 945cP), and cell vibration amplitudes and frequencies. A viscous fluid model was also developed to predict the vibration-induced particle motion. This model shows the effect of fluid viscosity compared to the inviscid model, which was presented earlier by Hassan et al. (2004, “The Effects of Vibrations on Particle Motion in an Infinite Fluid Cell,” ASME J. Appl. Mech., 73(1), pp. 72–78) and validated using data obtained for water. The viscous model with modified drag coefficients is shown to predict well the particle amplitude data for the fluid viscosities of 58.5cP and 945cP. While there is a resonance frequency corresponding to the particle peak amplitude for oil (58.0cP), this phenomenon disappeared for glycerol (945cP). This disappearance of resonance phenomenon is explained by referring to the theory of mechanical vibrations of a mass-spring-damper system. For the sinusoidal particle motion in a viscous fluid, the effective drag force has been obtained, which includes the virtual mass force, drag force proportional to the velocity, and the Basset or history force terms.

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