A Porous Media Model for Thin Film Lubrication

1995 ◽  
Vol 117 (1) ◽  
pp. 16-21 ◽  
Author(s):  
J. A. Tichy
Keyword(s):  
Reynolds Equation ◽  
Squeezing Flow ◽  
Thin Film Lubrication ◽  
Porous Layers ◽  
Porosity Parameter ◽  
Porous Media Model ◽  
Molecular Length ◽  
Load Increase ◽  
Thickness Parameter ◽  
Film Lubrication

A rheological model has been developed which can be applied to boundary lubrication. The model is applicable to thin films in which the molecular length scale is the same order as the film thickness. The micro structure is simulated by porous layers attached to the contact surfaces. The model contains three material properties: (1) viscosity, (2) the thickness of the porous layer, and (3) a porosity parameter. A modified Reynolds equation is developed. Behavior in two types of contacts is calculated: squeezing flow between crossed cylinders (Chan and Horn’s, 1985 drainage experiment) and a one-dimensional converging wedge contact. The effect of the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the porosity parameter value tends to reduce the magnitude of the load increase.

The Present State of Lubrication and Its Relation to Rheology

1968 ◽  
Vol 90 (3) ◽  
pp. 526-530 ◽  
Author(s):  
J. K. Appeldoorn
Keyword(s):  
Thin Film ◽  
Reynolds Equation ◽  
Mathematical Treatment ◽  
Load Carrying Capacity ◽  
Thin Film Lubrication ◽  
Load Carrying ◽  
Viscoelastic Effects ◽  
Viscoelastic Liquids ◽  
Film Lubrication ◽  
Made In

In thick-film lubrication, Reynolds’ equation is generally satisfactory. However, the assumptions made in deriving this equation cannot be justified for non-Newtonian, viscoelastic liquids. It is concluded that no satisfactory mathematical treatment is yet available for calculating the load-carrying capacity of such liquids. In thin-film lubrication, elastohydrodynamic calculations indicate that the lubricant film may be quite thick even under heavily loaded conditions, but discrepancies exist between calculation and experiment. These can be explained by assuming non-Newtonian behavior, or unusual viscoelastic effects, but the assumptions are largely unfounded. There is virtually a complete absence of data on the behavior of liquids under impact loading. Such data are needed to resolve whether thin-film lubrication is primarily chemical or primarily physical.

Thin-Film Lubrication Theory for Newtonian Fluids With Surfaces Possessing Striated Roughness or Grooving

1973 ◽  
Vol 95 (4) ◽  
pp. 484-489 ◽  
Author(s):  
H. G. Elrod
Keyword(s):  
Reynolds Equation ◽  
Multiple Scale ◽  
Support Pressure ◽  
Load Carrying Capacity ◽  
Transient Effects ◽  
Thin Film Lubrication ◽  
Load Carrying ◽  
Bearing Design ◽  
First Time ◽  
Film Lubrication

Earlier work by others concerning the effects of striated roughness and grooving upon the load-carrying capacity of lubricating films is summarized, substantiated, and generalized. A multiple-scale double-variable technique is used on such lubrication problems for the first time. The present analysis applies to one-face roughness having striation wavelengths sufficiently long for the applicability of Reynolds equation. Transient effects are included. The final differential equation for support pressure is simple in form. In addition to predicting the effects of striated “Reynolds roughness”, this equation can be directly used in grooved-bearing design.

scholarly journals A New Approach for Estimating the Friction in Thin Film Lubrication

2010 ◽  
Vol 2010 ◽  
pp. 1-15 ◽  
Author(s):  
Dag Lukkassen ◽  
Annette Meidell ◽  
Peter Wall
Keyword(s):  
Surface Roughness ◽  
Variational Problem ◽  
Reynolds Equation ◽  
Main Idea ◽  
Thin Film Lubrication ◽  
New Approach ◽  
Fine Mesh ◽  
Load Carrying ◽  
Film Lubrication ◽  
Effect Of Surface

An important problem in the theory of lubrication is to model and analyze the effect of surface roughness on, for example, the friction and load carrying capacity. A direct numerical computation is often impossible since an extremely fine mesh is required to resolve the surface roughness. This suggests that one applies some averaging technique. The branch in mathematics which deals with this type of questions is known as homogenization. In this paper we present a completely new method for computing the friction. The main idea is that we study the variational problem corresponding to the Reynolds equation. We prove that the homogenized variational problem is closely related to the homogenized friction. Finally we use bounds on the homogenized Lagrangian to derive bounds for the friction. That these bounds can be used to efficiently compute the friction is demonstrated in a typical example.

Effects of adsorption layers and elastic deformation on thin-film lubrication of circular contacts with non-Newtonian lubricants

2018 ◽  
Vol 70 (2) ◽  
pp. 363-370 ◽  
Author(s):  
Li-Ming Chu ◽  
Jaw-Ren Lin ◽  
Cai-Wan Chang-Jian
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Power Law ◽  
Reynolds Equation ◽  
Present Model ◽  
Thin Film Lubrication ◽  
Content Type ◽  
Modified Reynolds Equation ◽  
Adsorption Layers ◽  
Film Lubrication

Purpose The modified Reynolds equation for non-Newtonian lubricant is derived using the viscous adsorption theory for thin-film elastohydrodynamic lubrication (TFEHL) of circular contacts. The proposed model can reasonably calculate the phenomenon in the thin-film lubrication (TFL) unexplained by the conventional EHL model. The differences between classical EHL and TFEHL with the non-Newtonian lubricants are discussed. Design/methodology/approach The power-law lubricating film between the elastic surfaces is modeled in the form of three layers: two adsorption layers on each surface and one middle layer. The modified Reynolds equation with power-law fluid is derived for TFEHL of circular contacts using the viscous adsorption theory. The finite difference method and the Gauss–Seidel iteration method are used to solve the modified Reynolds equation, elasticity deformation, lubricant rheology equations and load balance equations simultaneously. Findings The simulation results reveal that the present model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity in TFL with non-Newtonian lubricants. The thickness and viscosity of the adsorption layer and the flow index significantly influence the lubrication characteristics of the contact conjunction. Originality/value The present model can reasonably predict the average viscosity, the turning point and the derivation (log film thickness vs log speed) phenomena in the TFEHL under constant load conditions.

scholarly journals Impact of chosen force fields and applied load on thin film lubrication

Friction ◽  
2021 ◽  
Author(s):  
Thi D. Ta ◽  
Hien D. Ta ◽  
Kiet A. Tieu ◽  
Bach H. Tran
Keyword(s):  
Thin Film ◽  
Shear Stress ◽  
Surface Structure ◽  
Rheological Properties ◽  
Surface Potential ◽  
Applied Load ◽  
Velocity Slip ◽  
Thin Film Lubrication ◽  
Lubrication Performance ◽  
Film Lubrication

AbstractThe rapid development of molecular dynamics (MD) simulations, as well as classical and reactive atomic potentials, has enabled tribologists to gain new insights into lubrication performance at the fundamental level. However, the impact of adopted potentials on the rheological properties and tribological performance of hydrocarbons has not been researched adequately. This extensive study analyzed the effects of surface structure, applied load, and force field (FF) on the thin film lubrication of hexadecane. The lubricant film became more solid-like as the applied load increased. In particular, with increasing applied load, there was an increase in the velocity slip, shear viscosity, and friction. The degree of ordering structure also changed with the applied load but rather insignificantly. It was also significantly dependent on the surface structure. The chosen FFs significantly influenced the lubrication performance, rheological properties, and molecular structure. The adaptive intermolecular reactive empirical bond order (AIREBO) potential resulted in more significant liquid-like behaviors, and the smallest velocity slip, degree of ordering structure, and shear stress were compared using the optimized potential for liquid simulations of united atoms (OPLS-UAs), condensed-phase optimized molecular potential for atomic simulation studies (COMPASS), and ReaxFF. Generally, classical potentials, such as OPLS-UA and COMPASS, exhibit more solid-like behavior than reactive potentials do. Furthermore, owing to the solid-like behavior, the lubricant temperatures obtained from OPLS-UA and COMPASS were much lower than those obtained from AIREBO and ReaxFF. The increase in shear stress, as well as the decrease in velocity slip with an increase in the surface potential parameter ζ, remained conserved for all chosen FFs, thus indicating that the proposed surface potential parameter ζ for the COMPASS FF can be verified for a wide range of atomic models.

Mechanism of Boundary Lubrication and the Edge Effect

1965 ◽  
Vol 87 (3) ◽  
pp. 735-739 ◽  
Author(s):  
Y. Tamai ◽  
B. G. Rightmire
Keyword(s):  
Thin Film ◽  
Acid Solution ◽  
Palmitic Acid ◽  
Boundary Lubrication ◽  
Frictional Resistance ◽  
Copper Surface ◽  
Bulk Liquid ◽  
Attraction Force ◽  
Thin Film Lubrication ◽  
Film Lubrication

Experimental work was carried out on the boundary lubrication of a copper-copper couple with pure cetane, palmitic acid solution of cetane, and some other organic materials. The purpose was to get information about α and μlube, which appear in the friction equation: μ=αμsolid+(1−α)μlube, by using two different kinds of copper surface, a clean surface, and an oxidized surface. α was found to be small with palmitic acid solution, and the estimated shear strength of palmitic acid was high under the examined condition. α and μlube seemed to be properties which are independent of each other. α is closely related to the attraction force between the lubricant and the substrate, whereas μlube is related to the complexity of molecular structure of the lubricant. A comparison was made of bulk-liquid and thin-film lubrication. μlube was smaller in thin-film lubrication than it was in bulk-liquid lubrication. This suggests that the frictional resistance may be partly contributed by liquid in the edge space around the real contact.

The Optimization for the Shape Profile of the Slider Surface Under Ultra-Thin Film Lubrication Conditions by the Rarefied-Flow Model

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Chin-Hsiang Cheng ◽  
Mei-Hsia Chang
Keyword(s):  
Thin Film ◽  
Conjugate Gradient ◽  
Gradient Method ◽  
Direct Problem ◽  
Problem Solver ◽  
Thin Film Lubrication ◽  
Rarefied Flow ◽  
Slider Surface ◽  
Inverse Knudsen Number ◽  
Film Lubrication

The optimization of the surface shape for a slider to meet the specified load demands under an ultra-thin film lubrication condition has been performed in this study. The optimization process is developed based on the conjugate gradient method in conjunction with a direct problem solver, which is built based on the rarefied-flow theory. The direct problem solver is able to predict the pressure distributions of the rarefied gas flows in the slip-flow, transition-flow, and molecular-flow regimes with a wide range of characteristic inverse Knudsen number. First, the validity of the direct problem solver has been verified by a comparison with the existing information for some particular cases, and then the developed direct problem solver is incorporated with the conjugate gradient method for optimizing the shape profile of the slider surface. The performance of the present optimization approach has also been evaluated. Results show that the shape profile of the slider surface can be efficiently optimized by using the present approach. Thus, a number of cases under various combinations of influential parameters, involving the characteristic inverse Knudsen number and the bearing numbers in the x- and y-directions, are investigated.

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