Boundary Lubrication and Its Stability

2008 ◽  
Author(s):  
Kamaljit Singh ◽  
Saurabh Baghmar ◽  
Jagdish Sharma ◽  
M. V. Khemchandani ◽  
Q. J. Wang
Keyword(s):  
Solid Surface ◽  
Boundary Lubrication ◽  
Surface Forces ◽  
Aluminum Surface ◽  
Boundary Lubrication Friction ◽  
Lennard Jones ◽  
Boundary Lubricant ◽  
Zone Of Influence ◽  
En 31 ◽  
Experimental Values

The interaction between lubricant molecules and the solid surface to be lubricated depends upon the surface forces which can be attractive, and repulsive. It thus forms an interactive zone above the solid surface having a band width and height of surface potential and is considered as ‘Zone of Influence’-(ZOI). Its value will vary with the nature of surface finish, distribution of alloying constituents on surface matrix and its size which play very important role in prediction of stability and failure of boundary lubrication friction including absorption and desorption of lubricant molecules. A theoretical model for the formation of boundary lubrication is proposed by combining Lennard Jones (6–12) potential to incorporate for estimating the critical temperature of boundary lubricant, friction coefficient and variation of ZOI for a given condition. Experimental values using EN 31 Ball sliding against the aluminum surface with 0.4% stearic acid as lubricant data agrees well with theoretical values.

Numerical Method of Analyzing Contact Mechanics between a Sphere and a Flat Considering Lennard-Jones Surface Forces of Contacting Asperities and Noncontacting Rough Surfaces

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Numerical Method ◽  
Contact Mechanics ◽  
Rough Surfaces ◽  
Present Theory ◽  
Adhesive Contact ◽  
Adhesive Force ◽  
Surface Forces ◽  
Contact Theory ◽  
Magnetic Disk ◽  
Lennard Jones

A new numerical method of analyzing adhesive contact mechanics between a sphere and a flat with sub-nanometer roughness is presented. In contrast to conventional theories, the elastic deformations of mean height surfaces and contacting asperities, and Lennard-Jones (LJ) surface forces of both the contacting asperities and noncontacting rough surfaces including valley areas are taken into account. Calculated contact characteristics of a 2-mm-radius glass slider contacting a magnetic disk with a relatively rough surface and a 30-mm-radius head slider contacting a currently available magnetic disk with lower roughness are shown in comparison with conventional adhesive contact theories. The present theory was found to give a larger adhesive force than the conventional theories and to converge to a smooth sphere-flat contact theory as the roughness height approaches zero.

Intermolecular forces and properties of fluid. I. The automatic calculation of higher virial coefficients and some values of the fourth coefficient for the Lennard-Jones potential

1960 ◽  
Vol 254 (1279) ◽  
pp. 487-498 ◽  
Keyword(s):  
Virial Coefficient ◽  
Mathematical Problem ◽  
Virial Coefficients ◽  
Intermolecular Forces ◽  
Lennard Jones Potential ◽  
Intermolecular Potentials ◽  
Jones Potential ◽  
Lennard Jones ◽  
Experimental Values ◽  
First Time

The prediction of the virial coefficients for particular intermolecular potentials is generally regarded as a difficult mathematical problem. Methods have only been available for the second and third coefficient and in fact only few calculations have been made for the latter. Here a new method of successive approximation is introduced which has enabled the fourth virial coefficient to be evaluated for the first time for the Lennard-Jones potential. It is particularly suitable for automatic computation and the values reported here have been obtained by the use of the EDSAC I. The method is applicable to other potentials and some values for these will be reported subsequently. The values obtained cannot yet be compared with any experimental results since these have not been measured, but they can be used in the meantime to obtain more accurate experimental values of the lower coefficients.

A Boundary Lubrication Friction Model Sensitive to Detailed Engine Oil Formulation in an Automotive Cam/Follower Interface

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Rupesh Roshan ◽  
Martin Priest ◽  
Anne Neville ◽  
Ardian Morina ◽  
Xin Xia ◽  
...  
Keyword(s):  
Boundary Lubrication ◽  
Fuel Efficiency ◽  
Lubricant Additive ◽  
Friction Model ◽  
Operating Conditions ◽  
Valve Train ◽  
Engine Oil ◽  
Contact Friction ◽  
Boundary Lubrication Friction ◽  
Base Oil

Theoretical studies have shown that in severe operating conditions, valve train friction losses are significant and have an adverse effect on fuel efficiency. However, recent studies have shown that existing valve train friction models do not reliably predict friction in boundary and mixed lubrication conditions and are not sensitive to lubricant chemistry. In these conditions, the friction losses depend on the tribological performance of tribofilms formed as a result of surface–lubricant additive interactions. In this study, key tribological parameters were extracted from a direct acting tappet type Ford Zetec SE (Sigma) valve train, and controlled experiments were performed in a block-on-ring tribometer under conditions representative of boundary lubrication in a cam and follower contact. Friction was recorded for the tribofilms formed by molybdenum dithiocarbamate (MoDTC), zinc dialkyldithiophosphate (ZDDP), detergent (calcium sulfonate), and dispersant (polyisobutylene succinimide) additives in an ester-containing synthetic polyalphaolefin (PAO) base oil on AISI E52100 steel components. A multiple linear regression technique was used to obtain a friction model in boundary lubrication from the friction data taken from the block-on-ring tribometer tests. The model was developed empirically as a function of the ZDDP, MoDTC, detergent, and dispersant concentration in the oil and the temperature and sliding speed. The resulting friction model is sensitive to lubricant chemistry in boundary lubrication. The tribofilm friction model showed sensitivity to the ZDDP–MoDTC, MoDTC–dispersant, MoDTC–speed, ZDDP–temperature, detergent–temperature, and detergent–speed interactions. Friction decreases with an increase in the temperature for all ZDDP/MoDTC ratios, and oils containing detergent and dispersant showed high friction due to antagonistic interactions between MoDTC–detergent and MoDTC–dispersant additive combinations.

Nanobubble Formation at the Solid-Liquid Interface Studied by Atomic Force Microscopy

2005 ◽  
Vol 899 ◽  
Author(s):  
Abhinandan Agrawal ◽  
Gareth H. McKinley
Keyword(s):  
Atomic Force Microscopy ◽  
Solid Surface ◽  
Silicon Oxide ◽  
Slip Length ◽  
Hydrophobic Surface ◽  
Force Microscopy ◽  
Atomic Force ◽  
Experimental Values ◽  
Solid Liquid ◽  
Wafer Surfaces

AbstractThe formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase. While nanobubbles do not form on flat hydrophilic (silicon oxide wafer) surfaces immersed in water, they appear spontaneously at the interface of water against smooth, hydrophobic (silanized wafer) surfaces. From the experimental observations we draw the conclusion that the features observed in the AFM images are deformable, air-filled bubbles. In addition to the hydrophobicity of the solid surface, differences in solubility of air between two miscible fluids can also lead to formation of nanobubbles. We observe that nanobubbles appear at the interface of water against hydrophilic silicon oxide surfaces after in-situ mixing of ethanol and water in the fluid-cell.The shapes of the nanobubbles are well approximated by spherical caps, with width much larger than the height of the caps. We quantify the morphological distribution of nanobubbles by evaluating several important bubble parameters including surface coverage and radii of curvature. In conjunction, with an analytical model available in the literature, we use this information to estimate that the present nanobubble morphology may give rise to slip lengths ∼1–2 µm in pressure driven flows for water flowing over the hydrophobic surface. The consistency of the calculated slip length with the experimental values reported in the literature, suggests that the apparent fluid slip observed experimentally at hydrophobic surfaces may arise from the presence of nanobubbles.

Variation with load of the coefficient of friction and metallic transfer under conditions of boundary lubrication

1952 ◽  
Vol 212 (1111) ◽  
pp. 516-519 ◽  
Keyword(s):  
Coefficient Of Friction ◽  
Boundary Lubrication ◽  
General Pattern ◽  
Copper Plate ◽  
Experimental Conditions ◽  
Average Hardness ◽  
Boundary Lubricant ◽  
The Coefficient Of Friction ◽  
Fixed Load ◽  
Molecular Layers

Several papers have been published recently which show for a number of metals that, under certain experimental conditions, several molecular layers of boundary lubricant are necessary to give effective lubrication, i.e. a coefficient of friction of 0.1 or less. Recent experiments by the authors suggest that these results represent parts of a more general pattern. In the previous work, the experiments were carried out at a fixed load; in the present, the load has been varied. The apparatus used was a copy of that described by Bowden & Leben (1939) for studying friction at low speeds of sliding. A hemispherical copper slider of radius 0-45 cm was caused to slide upon a flat copper plate at a speed of approximately 1 cm/min. Several specimens were used; their average hardness was 100 v .p .h .

Measurement of Boundary Lubricant Viscosity at Metal-Deformation Pressures (3000 Atmospheres, 20 Tons/Sq In.)

1967 ◽  
Vol 89 (3) ◽  
pp. 272-281 ◽  
Author(s):  
G. W. Rowe
Keyword(s):  
Boundary Lubrication ◽  
Flat Surface ◽  
Hydrodynamic Lubrication ◽  
Elastohydrodynamic Lubrication ◽  
Wire Drawing ◽  
Average Pressure ◽  
Boundary Lubricant ◽  
Metal Deformation ◽  
Local Pressures ◽  
Lubricant Viscosity

In many metalworking operations, such as rolling and wire drawing, the average pressure acting between the workpiece and the tool will be of the order of the yield stress of the metal, usually 20–50 tons/sq in. The lubricant temperature may also rise by 60 deg C or more. Any consideration of hydrodynamic lubrication in these operations should thus take account of the large viscosity changes which may occur under such pressures and temperatures. In addition, it is probable that the rate of shear will be important [1], but this will not be considered in this paper. Local pressures of the same order are developed in typical boundary-lubrication apparatus using a hemispherical slider on a flat surface under kilogram loads [2]. Information on the pressure and temperature coefficients of viscosity for lubricants is therefore important also in studies of boundary lubrication and elastohydrodynamic lubrication [3], especially in the presence of boundary additives [4]. This paper describes a simple apparatus for viscosity measurement at temperatures up to 70 deg C and pressures up to 20 tons/sq in. (3000 atmospheres) or with future modifications up to 45 tons/sq in., together with some results for fluids with and without boundary additives.

The Effects of Temperature on the Solid-Surface Luminescence Properties of Benzo(f)quinoline Adsorbed on Filter Paper

1989 ◽  
Vol 43 (4) ◽  
pp. 616-621 ◽  
Author(s):  
S. M. Ramasamy ◽  
R. J. Hurtubise
Keyword(s):  
Quantum Yield ◽  
Solid Surface ◽  
Filter Paper ◽  
Rate Constants ◽  
Protonated Form ◽  
Solid Matrix ◽  
Phosphorescence Lifetime ◽  
Phosphorescence Quantum Yield ◽  
Surface Luminescence ◽  
Experimental Values

Experimental values of fluorescence quantum yield, phosphorescence quantum yield, and phosphorescence lifetime were acquired at temperatures from 23° to −180°C for the protonated form of benzo( f)quinoline adsorbed on filter paper. From the experimental values, triplet formation efficiencies, rate constants for phosphorescence, and rate constants for the radiationless transition from the triplet state were calculated. The results showed the various interrelationships of the solid-surface radiative and nonradiative processes. In addition, the results indicated that the modulus of the solid matrix is an important factor in enhancing phosphorescence quantum yield.

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