The Effects of Surface Texture on EHL Point Contacts

1996 ◽  
Vol 118 (1) ◽  
pp. 59-66 ◽  
Author(s):  
Xiaolan Ai ◽  
Herbert S. Cheng
Keyword(s):  
Surface Texture ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Point Contact ◽  
Maximum Pressure ◽  
Point Contacts ◽  
Random Roughness ◽  
Minimum Film Thickness ◽  
Transverse Roughness ◽  
Effect Of Surface

The effect of surface texture on EHL point contact is studied numerically by using the multigrid method. Numerical simulations have been performed for waviness and random roughness with three different orientations, transverse, oblique and longitudinal. Results reveal a strong domination of unidirectional Couette flow in the EHL conjunction. The geometrical variations at inlet of the contact are transported downstream throughout the EHL conjunction. As a consequence, the oblique surface roughness striations are largely distorted, forming nearly longitudinal wavy passages. Results show that the oblique roughness induces local three dimensional EHL pressure fluctuations. The maximum pressure is higher than that of the transverse roughness. For sinusoidal waviness, oblique orientation gives the smallest minimum film thickness as compared with those of longitudinal and transverse waviness.

scholarly journals Bio-inspired design of ice-retardant devices based on benthic marine invertebrates: the effect of surface texture

2014 ◽  
Author(s):  
Homayun Mehrabani ◽  
Neil Ray ◽  
Kyle Tse ◽  
Dennis Evangelista
Keyword(s):  
Surface Texture ◽  
Marine Invertebrates ◽  
Freezing Point ◽  
Three Dimensional ◽  
Surface Pattern ◽  
Ice Formation ◽  
Cold Air ◽  
Three Dimensional Printing ◽  
Species Specific ◽  
Effect Of Surface

Growth of ice on surfaces poses a challenge for both organisms and for devices that come into contact with liquids below the freezing point. Resistance of some organisms to ice formation and growth, either in subtidal environments (e.g. Antarctic anchor ice), or in environments with moisture and cold air (e.g.vplants, intertidal) begs examination of how this is accomplished. Several factors may be important in promoting or mitigating ice formation. As a start, here we examine the effect of surface texture alone. We tested four candidate surfaces, inspired by hard-shelled marine invertebrates and constructed using a three-dimensional printing process. We screened biological and artifical samples for ice formation and accretion in submerged conditions using previous methods, and developed a new test to examine ice formation from surface droplets as might be encountered in environments with moist, cold air. It appears surface texture plays only a small role in delaying the onset of ice formation: a stripe feature (corresponding to patterning found on valves of blue mussels,Crassostrea gigas, or on the spines of the Antarctic sea urchinSterechinus neumayeri) slowed ice formation an average of 25% compared to a grid feature (corresponding to patterning found on sub-polar butterclams,Saxidomas nuttali). The geometric dimensions of the features have only a small (~6%) effect on ice formation. Surface texture affects ice formation, but does not explain by itself the large variation in ice formation and species-specific ice resistance observed in other work. This suggests future examination of other factors, such as material elastic properties and coatings, and their interaction with surface pattern.

Roughness Amplitude Reduction Under Non-Newtonian EHL Conditions

2005 ◽  
Author(s):  
A. D. Chapkov ◽  
C. H. Venner ◽  
A. A. Lubrecht
Keyword(s):  
Film Thickness ◽  
Pressure Fluctuations ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Point Contacts ◽  
Minimum Film Thickness ◽  
Roughness Amplitude ◽  
Average Film Thickness ◽  
Ehl Contact

The influence of surface roughness on the performance of bearings and gears operating under ElastoHydrodynamic Lubrication (EHL) conditions has become increasingly important over the last decade, as the average film thickness decreased due to various influences. Surface features can reduce the minimum film thickness and thus increase the wear. They can also increase the temperature and the pressure fluctuations, which directly affects the component life. In order to describe the roughness geometry inside an EHL contact, the amplitude reduction of harmonic waviness has been studied over the last ten years. This theory currently allows a quantitative prediction of the waviness amplitude and includes the influence of wavelength and contact operating conditions. However, the model assumes a Newtonian behaviour of the lubricant. The current paper makes a first contribution to the extension of the roughness amplitude reduction for EHL point contacts including non-Newtonian effects.

An Experimental Evaluation of the Hamrock and Dowson Minimum Film Thickness Equation for Fully Flooded EHD Point Contacts

1981 ◽  
Vol 103 (2) ◽  
pp. 284-294 ◽  
Author(s):  
K. A. Koye ◽  
W. O. Winer
Keyword(s):  
Experimental Data ◽  
Statistical Analysis ◽  
Film Thickness ◽  
Experimental Evaluation ◽  
Point Contact ◽  
Major Axis ◽  
Point Contacts ◽  
Lubricant Film Thickness ◽  
Minimum Film Thickness ◽  
Ellipticity Ratio

Fifty-seven measurements of the minimum lubricant film thickness separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Effect of Stiff Coatings on EHL Film Thickness in Point Contacts

2007 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Dong Zhu
Keyword(s):  
Film Thickness ◽  
Working Conditions ◽  
Coating Thickness ◽  
Point Contact ◽  
Thickness Variation ◽  
Point Contacts ◽  
Lubricant Film Thickness ◽  
Wide Range ◽  
Minimum Film Thickness ◽  
Coating Material Properties

This study investigates the influences of coating material properties and coating thickness on lubricant film thickness based on a point-contact isothermal EHL model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Numerical results indicates that the increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2, can be expressed in the following formulas: Imax=0.766M0.0248R20.0296L0.1379exp(−0.0245ln2L)H2=0.049M0.4557R2−0.1722L0.7611exp(−0.0504ln2M−0.0921ln2L) These formulas can be used to estimate the effect of a coating on EHL film thickness.

A Parametric Study on Fatigue Life for Mixed Elastohydrodynamic Lubrication Point Contacts

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Xiao-Liang Yan ◽  
Xiao-Li Wang ◽  
Yu-Yan Zhang
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Newtonian Flow ◽  
Lubrication Regimes ◽  
Close Relationship ◽  
Lubrication Characteristics ◽  
Effect Of Surface

The lubrication characteristics and fatigue life are numerically analyzed under full film and mixed lubrication regimes, in which the three-dimensional sinusoidal surfaces with changeable wavelengths in x and y directions are used, the geometry changes of the contact areas are described by the various ellipticity, and the non-Newtonian flow of lubricant is described by the sinh-law rheology model. The results show that the influences of characteristic shear stress, wavelength ratio, and ellipticity on lubrication characteristics and fatigue life are remarkable. The effect of surface topography on lubrication characteristics has a close relationship with speed. Increasing the ellipticity and decreasing wavelength ratio and characteristic shear stress can prolong the fatigue life.

Point Contact EHL Based on Optically Measured Three-Dimensional Rough Surfaces

1997 ◽  
Vol 119 (3) ◽  
pp. 375-384 ◽  
Author(s):  
Dong Zhu ◽  
Xiaolan Ai
Keyword(s):  
Rough Surface ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Peak Height ◽  
Machining Process ◽  
Maximum Pressure ◽  
Pressure Peak ◽  
Surface Profiles

This paper presents a numerical solution for the elastohydrodynamic lubrication in point contacts, using optically measured three-dimensional rough surface profiles as input data. The multi-grid computer program originally developed by Ai and Cheng (1993, 1994) is modified, so that both contacting surfaces can be three-dimensional measured rough surfaces moving at different velocities. Many different engineering surfaces are measured and analyzed in the present study, demonstrating that the numerical analysis is practical for real surfaces of bearings, cams, gears and other components, as long as a significant EHL film still exists. In addition, discussions are given in this paper for the effects of three-dimensional rough surface topography, which is related to machining process. It appears that, for the circular contact cases analyzed, surface roughness texture and orientation do not have a significant effect on the average film thickness, but they do affect the maximum pressure peak height and asperity deformation in the contact zone considerably.

Experimental Evaluation of EHD Film Shape and Its Comparison With Numerical Solution

2000 ◽  
Vol 122 (4) ◽  
pp. 689-696 ◽  
Author(s):  
I. Krˇupka ◽  
M. Hartl ◽  
R. Polisˇcˇuk ◽  
J. Cˇerma´k ◽  
M. Lisˇka
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Three Dimensional ◽  
Ccd Camera ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Point Contacts ◽  
Ehd Lubrication ◽  
Pure Rolling ◽  
Minimum Film Thickness

Colorimetric interferomentry has been applied to the study of EHD lubrication of point contacts under pure rolling conditions to obtain lubricant film shapes with high accuracy and resolution. An RGB CCD camera together with an extensive image processing software has enabled real time evaluation of chromatic interferograms. The classical numerical isothermal solution of EHD lubrication of point contacts has been used for the comparison with three-dimensional representations of film thickness distributions obtained from experiments. A good agreement was found between experimental and numerical EHD film shapes by comparing lubricant film profiles and positions of minimum film thickness. Both experimental results and numerical solution confirm the ratio between central and minimum film thickness to change significantly with operating conditions. [S0742-4787(00)00404-5]

Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part II—Ellipticity Parameter Results

1976 ◽  
Vol 98 (3) ◽  
pp. 375-381 ◽  
Author(s):  
B. J. Hamrock ◽  
D. Dowson
Keyword(s):  
Contact Problem ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Effective Radius ◽  
Radius Of Curvature ◽  
Line Contact ◽  
Point Contacts ◽  
Curvature Ratio ◽  
Minimum Film Thickness ◽  
Ellipticity Parameter

A numerical solution of the isothermal elastohydrodynamic problem for point contacts has been presented which reproduces all the essential features of the previously reported experimental observations based upon optical interferometry. In particular, the two “side lobes” in which minimum film thickness regions occur are shown to emerge in the theoretical solutions. The influence of the ellipticity parameter upon solutions to the point contact problem has been explored in the present paper. The ellipticity parameter (k) was varied from one (a ball on a plate) to eight (a configuration approaching line contact), and it has been shown that the minimum film thicknesses can be related to the well known line contact solutions by remarkably simple expressions involving either (k) or the effective radius of curvature ratio (Ry/Rx).

On the crucial role of ellipticity on elastohydrodynamic film thickness and friction

2016 ◽  
Vol 230 (12) ◽  
pp. 1503-1515 ◽  
Author(s):  
J-D Wheeler ◽  
N Fillot ◽  
P Vergne ◽  
D Philippon ◽  
GE Morales Espejel
Keyword(s):  
Film Thickness ◽  
Maximum Pressure ◽  
Fluid Viscosity ◽  
Point Contacts ◽  
Entrainment Velocity ◽  
Minimum Film Thickness ◽  
Elliptical Contact ◽  
Thickness Variations ◽  
Poiseuille Flows

The study reported here deals with elastohydrodynamic point contacts and it is focused on the influence of contact ellipticity. In five velocity–load reference cases, ellipticity was varied from slender to wide configurations, including the circular contact. For each case, Hertzian pressure, Hertzian area, load, and entrainment velocity were kept constant while the ellipticity was varied by changing the curvature radii. In this context, the maximum central film thickness did not occur for the infinitely wide contact, but for a slender configuration close to the circular case. Moreover, the minimum film thickness reached its optimum for a wide but finite elliptical contact. For low ellipticity ratios, specific film thickness features were obtained. In particular, very high central/minimum film thickness ratios are found. The cause of these behaviors was found in the change of the convergent shape. When the ellipticity was varied, the Poiseuille flows parallel and transverse to the entrainment direction were significantly modified and these modifications were quantitatively analyzed for the different cases. The competition between the Couette and the Poiseuille flows was totally different between the narrow and the wide elliptical contact, and this change was responsible for the film thickness variations with ellipticity. Ellipticity also had an effect on friction as it influenced the maximum pressure which in turn impacts the fluid viscosity.

Use of the Inverse Approach to Investigate the Stresses in Rough Elastohydrodynamic Contacts

2001 ◽  
Vol 124 (1) ◽  
pp. 109-113 ◽  
Author(s):  
K. Y. Li ◽  
C. J. Hooke
Keyword(s):  
Point Contact ◽  
Surface Profile ◽  
Companion Paper ◽  
Operating Conditions ◽  
Point Contacts ◽  
Roughness Effects ◽  
Inverse Approach ◽  
Transverse Roughness ◽  
Ellipticity Ratio ◽  
Good Agreement

The inverse approach, described in detail in a companion paper, is applied to two contacts. The first is a line contact with transverse roughness; the second a point contact with an ellipticity ratio of four containing an isolated transverse surface feature. In each case the surface profile was monitored as the operating conditions became more severe. These profiles were used to define the surface in a multi-level EHL solver and the pressures and subsurface stresses calculated. After allowing for the build up of residual stress, the maximum subsurface stress was compared with the yield strength of the rough surface. Good agreement was obtained indicating, first, that EHL theory is accurate for the rolling case examined and, second, that the Hooke-Venner hypothesis of equivalence between roughness effects in line and point contacts is valid.

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