Integration of a Molecular Viscosity Model and a Continuum EHL Solution for Simulation of Thin Film Lubrication

2005 ◽  
Author(s):  
A. Martini ◽  
Y. Liu ◽  
R. Q. Snurr ◽  
Q. Wang
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Molecular Model ◽  
Viscosity Model ◽  
Simulation Approach ◽  
Thin Film Lubrication ◽  
Molecular Film ◽  
Lubricated Contact ◽  
Molecular Viscosity ◽  
Film Lubrication

We present a simulation approach for thin film lubrication that integrates a molecular model of the film thickness-viscosity relationship in thin films with a continuum elastohydrodynamic (EHL) lubricated contact solution. Molecular simulation is used to characterize the effect of film thickness on viscosity in terms of solidification, shear thinning, and oscillation. This relationship is then incorporated into a traditional, continuum EHL solution. Film thickness distributions predicted by this integrated model are evaluated. It is found that the effect of the molecular film thickness-viscosity model is small compared to the increase in viscosity with pressure predicted by the Barus equation.

A New Postulation of Viscosity and Its Application in Computation of Film Thickness in TFL1

2002 ◽  
Vol 124 (4) ◽  
pp. 811-814 ◽  
Author(s):  
Chaohui Zhang ◽  
Jianbin Luo ◽  
Shizhu Wen
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Film Thickness ◽  
Solid Surface ◽  
Contact Area ◽  
Elastohydrodynamic Lubrication ◽  
Thin Film Lubrication ◽  
Lubrication Film ◽  
Viscosity Modification ◽  
Film Lubrication

In this paper, a viscosity modification model is developed which can be applied to describe the thin film lubrication problems. The viscosity distribution along the direction normal to solid surface is approached by a function proposed in this paper. Based on the formula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressible condition is solved and the outcome is compared to the experimental data. In thin film lubrication, according to the computation outcomes, the lubrication film thickness is much greater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequately low (i.e., film thickness is thin enough), the pressure distribution in the contact area is close to Hertzian distribution in which the second ridge of pressure is not obvious enough. The film shape demonstrates the earlobe-like form in thin film lubrication, which is similar to EHL while the film is comparatively thicker. The transformation relationships between film thickness and loads, velocities or atmosphere viscosity in thin film lubrication differ from those in EHL so that the transition from thin film lubrication to EHL can be clearly seen.

scholarly journals Molecular Dynamics Simulation on Thin-Film Lubrication of a Mixture of Three Alkanes

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3689
Author(s):  
Run Du ◽  
Anying Zhang ◽  
Zhihua Du ◽  
Xiaoyu Zhang
Keyword(s):  
Thin Film ◽  
Molecular Dynamics ◽  
Film Thickness ◽  
Md Simulation ◽  
Dynamics Simulation ◽  
Thin Film Lubrication ◽  
Thickness Change ◽  
Density Peaks ◽  
Initial Film ◽  
Film Lubrication

We used the COMPASS forcefield to perform molecular dynamics (MD) simulation of a mixture composed of three alkanes as the lubricant for the thin-film lubrication. The viscosity of the lubrication film in the non-working state, the final film thickness, and density distribution were investigated. The results reveal that the viscosity error among different initial film thicknesses in the non-working state is within 5%, which confirms the applicability of the model and the forcefield. The viscosity decreases oscillating as temperature increases. Whatever the initial film thickness is, the film thickness change rate with respect to pressure load is almost the same. When pressure increases, the density peaks increase. As the initial film thickness increases, the normalized thicknesses of adsorption and ordered layers decrease. In nanoscale, the density predicted by the MD simulation is higher than the prediction of the Tait equation, even if the adsorption layers is excluded.

A continuous viscosity model for thin film lubrication

2002 ◽  
Vol 35 (7) ◽  
pp. 459-465 ◽  
Author(s):  
Qu Quingwen ◽  
Wang Mei ◽  
Wang Lihua ◽  
Chai Shan
Keyword(s):  
Thin Film ◽  
Viscosity Model ◽  
Thin Film Lubrication ◽  
Film Lubrication

Study on Thin Film Lubrication With Second-Order Fluid

2002 ◽  
Vol 124 (3) ◽  
pp. 547-552 ◽  
Author(s):  
Ping Huang ◽  
Zhi-heng Li ◽  
Yong-gang Meng ◽  
Shi-zhu Wen
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Normal Stress ◽  
Journal Bearing ◽  
Deborah Number ◽  
Second Order ◽  
Thin Film Lubrication ◽  
Stress Changes ◽  
Load Carrying ◽  
Film Lubrication

The basic lubrication equations are deduced from the original second-order fluid constitutive equations. Two examples of lubrication, a plane inclined slider and a journal bearing, are calculated respectively. The Reynolds boundary conditions are used in the calculation of the journal bearing. In this calculation, it is found that the load carrying capacities of the slider and the journal bearing are of different tendencies with the increase of the Deborah number. Furthermore, the results show that with the decrease of the film thickness, the increase of the normal stress of second-order fluid is greater than that of Newtonian fluid. Finally, it is found that the distribution of the normal stress changes significantly at a certain thickness.

Velocity analysis for layered viscosity model under thin film lubrication

2001 ◽  
Vol 34 (8) ◽  
pp. 517-521 ◽  
Author(s):  
Qu Qingwen ◽  
Wang Mei ◽  
Chai Shan ◽  
Yao Fusheng
Keyword(s):  
Thin Film ◽  
Viscosity Model ◽  
Velocity Analysis ◽  
Thin Film Lubrication ◽  
Film Lubrication

Effect of surface roughness and deformation on Rayleigh step bearing under thin film lubrication

2017 ◽  
Vol 69 (6) ◽  
pp. 1016-1032 ◽  
Author(s):  
Rahul Kumar ◽  
Mohammad Sikandar Azam ◽  
Subrata Kumar Ghosh ◽  
Hasim Khan
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Coefficient Of Friction ◽  
Surface Deformation ◽  
Load Capacity ◽  
Performance Parameters ◽  
Thin Film Lubrication ◽  
Small Surface ◽  
Content Type ◽  
Film Lubrication

Purpose The aim of this paper is to study the effect of deterministic roughness and small elastic deformation of surface on flow rates, load capacity and coefficient of friction in Rayleigh step bearing under thin film lubrication. Design/methodology/approach Reynolds equation, pressure-density relationship, pressure-viscosity relationship and film thickness equation are discretized using finite difference method. Progressive mesh densification (PMD) method is applied to solve the related equations iteratively. Findings The nature and shape of roughness play a significant role in pressure generation. It has been observed that square roughness dominates the pressure generation for all values of minimum film thickness. Deformation more than 100 nm in bounding surfaces influences the film formation and pressure distribution greatly. Divergent shapes of film thickness in step zone causes a delay of pressure growth and reduces the load capacity with decreasing film thickness. The optimum value of film thickness ratio and step ratios have been found out for the maximum load capacity and minimum coefficient of friction, which are notably influenced by elastic deformation of the surface. Practical implications It is expected that these findings will help in analysing the performance parameters of a Rayleigh step bearing under thin film lubrication more accurately. It will also help the designers, researchers and manufacturers of bearings. Originality/value Most of the previous studies have been limited to sinusoidal roughness and thick film lubrication in Rayleigh step bearing. Effect of small surface deformation due to generated pressure in thin film lubrication is significant, as it influences the performance parameters of the bearing. Different wave forms such as triangular, sawtooth, sinusoidal and square formed during finishing operations behaves differently in pressure generation. The analysis of combined effect of roughness and small surface deformation has been performed under thin film lubrication for Rayleigh step bearing using PMD as improved methods for direct iterative approach.

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.

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