Thermoelastic Instability With Consideration of Surface Roughness and Hydrodynamic Lubrication

1999 ◽  
Vol 122 (4) ◽  
pp. 725-732 ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Thermal Conductivity ◽  
Surface Roughness ◽  
Film Thickness ◽  
Hot Spots ◽  
Critical Speed ◽  
Hydrodynamic Lubrication ◽  
Lubricant Film Thickness ◽  
Governing Equations ◽  
Thermoelastic Instability ◽  
Liquid Lubricant

An idealized model consisting of a surface with high thermal conductivity separated by a film of liquid lubricant from a rough surface with low thermal conductivity is developed to study thermoelastic instability. The governing equations are derived and solved for the critical speed beyond which thermoelastic instability leading to the formation of hot spots is likely to occur. A series of dimensionless parameters is introduced which characterizes the thermoelastic behavior of the system. It is shown the surface roughness and the lubricant film thickness both play an important role on the threshold of instability. [S0742-4787(00)00104-1]

On the Formation of Hot Spots in Wet Clutch Systems

2001 ◽  
Vol 124 (2) ◽  
pp. 336-345 ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Hot Spots ◽  
Friction Material ◽  
Mechanical Seal ◽  
Comprehensive Model ◽  
Governing Equations ◽  
Thermoelastic Instability ◽  
Wet Clutch ◽  
Special Case

A comprehensive model is developed for analyzing the onset of thermoelastic instability in a wet clutch. For this purpose, appropriate governing equations are derived that take into account the porosity and deformability of the friction material. The effect of the thickness of the separator disk and that of the friction material are also included. The model is general and can be used to describe TEI in a variety of other systems such as in a mechanical seal, as a special case. A series of simulations are presented that predict the thermoelastic behavior of a wet clutch from an instability viewpoint.

On the Growth Rate of Thermoelastic Instability

2004 ◽  
Vol 126 (1) ◽  
pp. 50-55 ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Growth Rate ◽  
Surface Roughness ◽  
Hot Spots ◽  
Wave Speed ◽  
Failure Process ◽  
Finite Thickness ◽  
Critical Value ◽  
Frictional Heat ◽  
Operating Speed ◽  
Thermoelastic Instability

Thermoelastic instability (TEI) is known to be directly related to the occurrence of hot spots in friction systems, such as brakes, seals, and clutches. TEI is a failure process where the local frictional heat, thermal expansion, contacting pressure and temperature grow rapidly over a certain critical value of the operating speed. In this article, we examine the rate of growth of instability and establish a link between the wave speed and the configuration of hot spots as well as its penetrating depth. The analysis includes provision for surface roughness and is capable of treating bodies of finite thickness with or without liquid lubrication.

scholarly journals Hydrodynamic lubrication of rough surfaces

1982 ◽  
Vol 383 (1785) ◽  
pp. 439-446 ◽  
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
Rough Surfaces ◽  
Homogenization Method ◽  
Squeeze Film ◽  
Spatial Average

Using the two-space homogenization method we derive an averaged Reynolds equation that is correct to O (< H 6 > — < H 3 > 2 ), where H is the total film thickness and the angle brackets denote a spatial average. Applications of this mean Reynolds equation to a squeeze-film bearing with a sinusoidal or an isotropic surface roughness are discussed.

Micropitting in Wind Turbine Gearboxes: Calculation of the Safety Factor and Optimization of the Gear Geometry

2011 ◽  
Vol 86 ◽  
pp. 898-903
Author(s):  
Hanspeter Dinner
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Wind Turbine ◽  
Contact Pressure ◽  
Safety Factor ◽  
Lubricant Film Thickness ◽  
Metallic Contact ◽  
Small Cracks ◽  
Gear Geometry ◽  
Specific Sliding

If the contact pressure between mating flanks of a gear set is increased, the lubricant film thickness in between is reduced to a level where the asperities of the flanks start to touch. This case where the surface roughness is of similar value as the EHD film thickness is called “mixed friction”. Due to the metallic contact of the asperities and the movement of the flanks with respect to each other, the flanks are damaged. The damaged flanks appear dull or greyish, hence the name “grey-staining” (or “Graufleckigkeit” in German), see e.g. [4] or [1]. Micropitting are small cracks on the surface of the gears (as opposed to pitting, where the cracks form below the surface), which grow into the material. The size of the damages is about 10-20 mm depth, 25-100 mm length and 10-20 mm width. Micropitting is mainly observed with case carburized gears but may also be found in nitrided, induction hardened or through hardened gears. Micropitting mainly occurs in areas of negative specific sliding. Negative specific sliding is to be found along the path of contact between point A and C on the driving gear and between point C and E on the driven gear.

Hydrodynamic Lubrication in Axisymmetric Stretch Forming—Part 2: Experimental Investigation

1991 ◽  
Vol 113 (4) ◽  
pp. 667-674 ◽  
Author(s):  
L. G. Hector ◽  
W. R. D. Wilson
Keyword(s):  
Experimental Investigation ◽  
Film Thickness ◽  
Hydrodynamic Lubrication ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Stretch Forming ◽  
Workpiece Material ◽  
Contour Map ◽  
Theoretical Predictions ◽  
Interference Studies

In order to test the validity of the theoretical model discussed in Part 1, an experimental technique, employing optical interferometry, has been developed to measure lubricant film thickness during axisymmetric stretch forming. Specially fabricated, transparent punches are used for both double and multiple beam interference studies. The choice of workpiece material, lubricant, and forming speed ensures that the punch/sheet conjunction will be hydrodynamically lubricated during most of the process. Interference patterns, due to the variable film of lubricant separating the punch and sheet surfaces, are formed as the sheet wraps around the punch. These patterns provide a contour map of the lubricant film thickness along the punch/sheet conjunction. The measured film thickness, as taken from an interpretation of the patterns, is compared with the theoretical predictions of Part 1.

Lubrication of 2D Soft Elasto Hydrodynamic Contacts: Extension of the Amplitude Reduction Theory

2011 ◽  
Author(s):  
F. Mora ◽  
P. Sainsot ◽  
A. A. Lubrecht ◽  
Y. le Chenadec
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Reduction Theory ◽  
Lubricant Film Thickness

This paper is an extension of the Amplitude Reduction Theory to soft ElastoHydrodynamic contacts. The ART permits a quantitative prediction of the influence of surface roughness on the lubricant film thickness modification as a function of the operating conditions.

Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording

2011 ◽  
Author(s):  
Norio Tagawa ◽  
Takao Miki ◽  
Hiroshi Tani
Keyword(s):  
Film Thickness ◽  
Laser Heating ◽  
Temperature Programmed Desorption ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Lubricant Depletion ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Temperature Programmed ◽  
Thermally Assisted Magnetic Recording

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

The Effects of Three-Dimensional Model Surface Roughness Features on Lubricant Film Thickness in EHL Contacts

2003 ◽  
Vol 125 (3) ◽  
pp. 533-542 ◽  
Author(s):  
Jian W. Choo ◽  
Romeo P. Glovnea ◽  
Andrew V. Olver ◽  
Hugh A. Spikes
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Three Dimensional ◽  
Lubricant Film ◽  
Imaging Method ◽  
Dimensional Model ◽  
Lubricant Film Thickness ◽  
Model Surface ◽  
Three Dimensional Model ◽  
Spacer Layer

The Spacer Layer Imaging method has been used to investigate the influence of three-dimensional roughness features on the thickness and shape of elastohydrodynamic (EHL) films. An array of near-hemispherical bumps was employed to represent asperities. A micro-EHL film developed at the bumps whose orientation depended on that of the inlet boundary at the location at which the bump had entered the contact. Rolling-sliding conditions induced a micro-EHL film with a classical horseshoe shape at the bumps. The flow of lubricant around the bumps appeared to differ between thin and thick films.

Isothermal Hydrodynamic Lubrication in Hydrostatic Extrusion of a Work-Hardening Material

1979 ◽  
Vol 101 (3) ◽  
pp. 386-389 ◽  
Author(s):  
S. Thiruvarudchelvan
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Numerical Method ◽  
Work Hardening ◽  
Critical Speed ◽  
Hydrodynamic Lubrication ◽  
Hydrostatic Extrusion ◽  
Extrusion Pressure ◽  
Hydrodynamic Conditions ◽  
Hardening Material

Using a numerical method the film thickness and the pressure distribution in hydrostatic extrusion of a work-hardening material under hydrodynamic conditions are determined. A minimum or critical speed for full fluid lubrication to develop is predicted. The effect of the length of die-land on the critical speed, and the effect of speeds above the critical speed on the extrusion pressure are also presented.

Hot Spotting and Judder Phenomena in Aluminum Drum Brakes

2002 ◽  
Vol 125 (1) ◽  
pp. 44-51 ◽  
Author(s):  
Kwangjin Lee ◽  
Frank W. Brooks,
Keyword(s):  
Surface Finish ◽  
Material Properties ◽  
Hot Spots ◽  
Critical Speed ◽  
Concave Surface ◽  
Thermoelastic Instability ◽  
Critical Speeds ◽  
Circumferential Groove ◽  
Drum Brakes ◽  
Test Schedule

Hot spotting and judder phenomena were observed in automotive aluminum drum brakes. A vehicle judder test schedule was developed to determine the critical speed for thermoelastic instability (TEI). The brake material properties relevant to the TEI analysis were measured as a function of temperature. The critical speeds for the brake systems with different drum materials were determined by the judder schedule and they are compared with the analytical predictions of Lee (2000). The brake drums and linings were then modified and tested in order to investigate its effects on the hot spotting and judder propensity. The design modifications include brake linings with a different compound, stress-relieved drums, linings with a convex or concave surface finish, three-segmented linings, and linings with a circumferential groove. The linings with a circumferencial groove effectively reduce the size of hot spots and the best judder rating was achieved.

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