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.

Experimental study of ultrathin liquid lubrication film thickness at the molecular scale

1997 ◽  
Vol 211 (2) ◽  
pp. 139-150 ◽  
Author(s):  
H Matsuoka ◽  
T Kato
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Film Thickness ◽  
Solid Surface ◽  
Experimental Measurements ◽  
Dynamic Measurements ◽  
Lubrication Film ◽  
Solid Specimen ◽  
Molecular Scale ◽  
New Apparatus

Ultrathin liquid lubrication film thicknesses at the molecular scale are measured by a new apparatus developed by the authors. Mica is used as the solid specimen and octamethylcyclotetrasiloxane (OMCTS), cyclohexane and n-hexadecane are used as liquid specimens. From experimental measurements, discretization of the lubrication film thickness is observed when the thickness is less than about 10 times the molecular diameter of the intervening liquid. Analysis of experimental data shows that the discretization of the lubrication film thickness is due to the solvation force. Dynamic measurements show that the solvation force is almost the same as the non-sliding case and is independent of the sliding speed of the solid surface.

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.

scholarly journals Molecular behaviors in thin film lubrication—Part two: Direct observation of the molecular orientation near the solid surface

Friction ◽  
2019 ◽  
Vol 7 (5) ◽  
pp. 479-488 ◽  
Author(s):  
Ming Gao ◽  
Haoyu Li ◽  
Liran Ma ◽  
Yuan Gao ◽  
Linwei Ma ◽  
...  
Keyword(s):  
Thin Film ◽  
Direct Observation ◽  
Solid Surface ◽  
Molecular Orientation ◽  
Thin Film Lubrication ◽  
Film Lubrication

Rheological Characteristics for Thin Film Elastohydrodynamic Lubrication

2005 ◽  
Vol 21 (2) ◽  
pp. 77-84 ◽  
Author(s):  
H.-M. Chu ◽  
R. T. Lee ◽  
S. Y. Hu ◽  
Y.-P. Chang
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Pressure Distribution ◽  
Relative Viscosity ◽  
Elastohydrodynamic Lubrication ◽  
Surface Forces ◽  
Hertzian Contact ◽  
Surface Films ◽  
Thin Film Lubrication ◽  
The Status

ABSTRACTThis paper uses three lubrication models to explore the differential phenomenon in the status of thin film lubrication (TFL). According to the viscous adsorption theory, the modified Reynolds equation for thin film elastohydrodynamic lubrication (TFEHL) is derived. In this theory, the film thickness between lubricated surfaces is simplified as three fixed layers across the film, and the viscosity and density of the lubricant vary with pressure in each layer. Under certain conditions, such as a rough or concentrated contact of a nominally flat surface, films may be of nanometer scale. The thin film elastohydrodynamic lubrication (EHL) analysis is performed on a surface forces (SF) model which includes van der waals and solvation forces. The results show that the proposed TFEHL model can reasonably calculate the film thickness and the average relative viscosity under thin film EHL. The adsorption layer thickness and the viscosity influence significantly the lubrication characteristics of the contact conjunction. The differences in pressure distribution and film shape between surface forces model and classical EHL model were obvious, especially in the Hertzian contact area. The solvation force has the greatest influence on pressure distribution.

Rheological Characteristics for Thin Film Elastohydrodynamic Lubrication with Non-Newtonian Lubricants

2007 ◽  
Vol 23 (4) ◽  
pp. 359-366
Author(s):  
H.-M. Chu ◽  
Y.-P. Chang ◽  
W.-L. Li
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Velocity Distribution ◽  
Adsorption Layer ◽  
Elastohydrodynamic Lubrication ◽  
Middle Layer ◽  
Flow Index ◽  
Thin Film Lubrication ◽  
The Difference ◽  
Index Ratio

AbstractThe modified Reynolds equation for power law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL). The differences between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the proposed model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity under thin film lubrication. The thickness (δ), the viscosity (m1), and the flow index (n1) of the adsorption layer influence significantly the lubrication characteristics of the contact conjunction. Furthermore, the film thickness increases with the increase of n1 and the film thickness affected by m1 is greater than that affected by n1, but the effect of n1 produces a very small difference in the pressure distributions. In addition, the greater n1, the smaller the change of velocity distribution in the adsorption layer, and the greater the change of velocity distribution in the middle layer. The larger δ and n1, the larger the deviation on log (film thickness) vs. log (speed) produced in the very thin film regime. In the region of the flow index ratio between 1.0 and 1.3, the difference in film thickness is significant. When the flow index of the adsorption layer is 1.6 times greater than the flow index of the middle layer, the adsorption layer is generally looked upon as a “solid-like”.

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.

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.

Sign in / Sign up

Export Citation Format

Share Document