bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of the Effect of Fluid Inertia and End Leakage in the Finite Squeeze Film Damper
Authors: Tichy J. A.
Published: October 2009

A modified form of Reynolds’ equation is obtained by integrating the thin film equations across the film and approximating the nonlinear inertia terms using the lubrication theory velocity field. The resulting nonhomogeneous partial differential equation is tackled by the classical separation of variables technique, and the corresponding eigenvalue problem solved by a computer library routine. The end boundary condition is that the local exiting flow rate is proportional to the pressure difference across the end seal. The results show a large effect of inertia in terms of pressure amplitude and phase shift, but the phase shift is reduced at large eccentricity. End leakage and bearing length change the pressure amplitude for the inertialess and inertia cases, but in equal measure. Hence conclusions reported in the literature regarding the effect of inertia in long or short dampers generally hold for finite bearings.
The Influence of Pad Flexibility on the Dynamic Coefficients of a Tilting Pad Journal Bearing
Authors: Lund Jorgen W. , Pedersen Lars Bo
Published: October 2009

An approximate method is developed to include the flexibility of the pad in the calculation of the stiffness and damping properties of a tilting pad journal bearing. It is a small-amplitude perturbation solution in which the pad deformation is accounted for solely by the change in clearance. A comparison of results with those obtained from a more complete elasto-hydrodynamic solution shows good agreement.
A Finite Element Analysis of the Navier-Stokes Equations Applied to High Speed Thin Film Lubrication
Authors: Medwell J. O. , Gethin D. T. , Taylor C.
Published: October 2009

The performance of a cylindrical bore bearing fed by two axial grooves orthogonal to the load line is analyzed by solving the Navier-Stokes equations using the finite element method. This produces detailed information about the three-dimensional velocity and pressure field within the hydrodynamic film. It is also shown that the method may be applied to long bearing geometries where recirculatory flows occur and in which the governing equations are elliptic. As expected the analysis confirms that lubricant inertia does not affect bearing performance significantly.
The Transmission Loss in Squeeze-Film Flow of Newtonian and Some Viscoelastic Fluids
Authors: Phan-Thien N.
Published: October 2009

It is shown that the difference between the forces acting on the top and bottom plates of a squeeze-film bearing, or the transmission loss, is entirely an inertia phenomenon and arises due to the acceleration of the top plate (the bottom plate is stationary). Its magnitude is given by half of the mass of the fluid film multiplied by the top plate acceleration. This is valid for Newtonian and some Oldroyd-B fluid provided that edge effects are negligible and no bifurcation of solution occurs.
Inertia Effect in Hydrodynamic Lubrication With Film Rupture
Authors: You H. I. , Lu S. S.
Published: October 2009

The modified Reynolds equation in conjunction with the modified Coyne-Elrod rupture model is used to investigate the inertia effect on the pressure distribution in converging-diverging bearings. The modified Reynolds equation is solved analytically for infinitely long bearings, including the cylinder-plane bearing and the journal bearing. The results showed that the fluid inertia tends to stretch the fluid film and to move the film rupture point farther downstream. The effects are profound even at a moderate value of the reduced Reynolds number, Re* ≈ 0.13 based on the minimum film thickness.
Future Directions in Tribology Research
Authors: Jahanmir S.
Published: October 2009

A symposium was recently held at the National Science Foundation in which a small group of internationally recognized tribologists from academia, federal laboratories, and private industry was invited to discuss and recommend future directions for basic research in tribology. This symposium was followed by a session at the ASME/ASLE Tribology Conference (October 20–22, 1986, Pittsburgh, PA) where representatives from private industry were invited to assess the experts’ recommendations and express the research needs of their respective industries. Among the many research topics that were discussed, four specific areas were emphasized as being in need of immediate attention. They were: 1. predictive models for friction, wear and failure; 2. microscopic and chemical aspects of lubrication; 3. mechanisms and prevention of wear at a microscopic level; and, 4. materials and lubricants for high temperature applications. It was noted that many of these areas are extremely complex and could benefit by interdisciplinary teams collaborating in universities, federal laboratories, and the private sector. The participants expressed the view that there is a great need for the transfer of basic research results to the users in industry.
Effect of Shear Surface Boundaries on Stress for Shearing Flow of Dry Metal Powders—An Experimental Study
Authors: Craig K. , Buckholz R. H. , Domoto G.
Published: October 2009

This paper studies the rapid simple shearing flow of dry cohesionless metal powders contained between parallel rotating plates. In this study, an annular shear cell test apparatus was used; the dry metal powders are rapidly sheared by rotating one of the shear surfaces while the other shear surface remains fixed. Such a flow geometry is of interest to tribologists working in the area of dry or powder lubrication. The shear stress and normal stress on the stationary surface are measured as a function of the following parameters: shear surface boundary material and roughness, the shear-cell gap thickness, the shear-rate and the fractional solids content. Both the fractional solids content and the gap thickness are kept at prescribed values during stress measurements. In this experiment the metal powder tested is different from the shear transmission surface material; the effect on the measured normal and shear stress data are reported. The results show the dependence of the normal stress and the shear stress on the shear-rate, particle density and particle diameter. Likewise, a significant stress dependence on both the fractional solids content and the shear-cell gap thickness was observed.
An Elastic-Plastic Model for the Contact of Rough Surfaces
Authors: Chang W. R. , Etsion I. , Bogy D. B.
Published: October 2009

An elastic-plastic asperity model for analyzing the contact of rough surfaces is presented. The model is based on volume conservation of an asperity control volume during plastic deformation. Numerical results obtained from this model are compared with other existing models that are either purely elastic or purely plastic. It is shown that these models are limiting cases of the more general elastic-plastic model presented here. Some of the results obtained deviate appreciably from previous analyses which do not consider asperity volume conservation.
High Knudsen Number Molecular Rarefaction Effects in Gas-Lubricated Slider Bearings for Computer Flying Heads
Authors: Mitsuya Y. , Ohkubo T.
Published: October 2009

This paper presents a study into the gas lubrication capability of an ultra-thin 0.025 μm film (converted value for ambient air film). The experimental results obtained using subambient helium as the lubricating film are compared with the calculated results using the modified Reynolds equation considering flow slippage due to the molecular mean free path effects. This comparison confirms that the slip flow model holds true within the range of the present experiments, and that the modified Reynolds equation is applicable for designing the computer flying heads operating at such thin spacing. The reason for the excellent agreement is discussed considering the locality of rarefaction effects on the lubricating surfaces and the anisotropy of these effects between the film thickness and the slider width.
Solid Slider Bearings Lubricated by Their Own Melting or Sublimation
Authors: Beretta Gian Paolo , Niro Alfonso , Silvestri Mario
Published: October 2009

We study the steady-state hydrodynamic lubrication of a solid-solid sliding bearing with spontaneous fusion or sublimation of the solid slider substance. Lubrication is sustained by the fluid film produced by fusion or sublimation. Our analysis extends the recent literature on liquid film lubrication of a melting solid slider to the interesting case of gaseous film lubrication of a sublimating solid slider. The results are in the form of analytical expressions showing the explicit influence of every parameter of the problem, together with conditions specifying the range of validity, and conditions guaranteeing that fusion or sublimation develop the necessary supply of lubricant. For substances like water and bismuth that contract upon melting, we extend the results to the interesting range of conditions dominated by the effect of pressure on the melting temperature.
An Experimental Study of the “Hot-Spots” Occurring During the Oxidational Wear of Tool Steel on Sapphire
Authors: Quinn T. F. J. , Winer W. O.
Published: October 2009

This paper describes some interesting preliminary results obtained with tool steel pins sliding against a rotating sapphire disk without lubrication. It is shown (i) that mild (oxidational) wear of the pin surface can be obtained with this combination of materials, (ii) that the “hot-spots” between the pin and the disk surfaces can be seen and photographed for size analysis, and (iii) that the temperature of the hot-spots can be estimated from the photographs. Some scanning electron micrographs were also taken of the pin surfaces at the end of the experiments, the objective being to complement the optical analyses, and thereby provide information about the number, size, and temperature of the hot-spots. The revelance of these estimates to the mechanisms involved in mild (oxidational) wear is also discussed.
Analysis of Starved Thrust Bearings Including Temperature Effects
Authors: Artiles A. , Heshmat H.
Published: October 2009

A method of analysis is described treating starvation in finite thrust bearing pads. A variable-size finite difference mesh is used to represent the two-dimensional temperature and pressure fields. A combination of Newton-Raphson iteration, direct iteration, and column matrix methods are used to solve for the start-of-film and minimum film thickness as well as the coupled two-dimensional energy and Reynolds equations. A parametric study describes the performance characteristics of the tapered land thrust bearing (flowrates, extent of fluid film, temperature rises, load capacity and torque) for different minimum film thicknesses and levels of starvation. This study considered variations in the geometrical parameters such as pad aspect ratio (L/R2=1/3, 1/2, 2/3) and extent of the pad (β=27, 42, and 57 deg) with an optimum taper ratio (β1/β=0.8). It is found that the effects of starvation are fairly small near the flooded condition but accelerate rapidly below the 50 percent starvation level. The start of the film (θ1) depends mostly on the level of starvation, and is essentially independent of the geometrical parameters, operating conditions or film thickness.
On Random Reynolds Roughness
Authors: Gans R. F.
Published: October 2009

Lubricant fluxes and lubrication forces have been calculated for statistical realizations of a piecewise planar slider running over a smooth base with an incompressible lubricant. The statistics of the response are not simply related to those of the roughness. The standard deviation of the force increases approximately as the fourth power of the roughness deviation for probable contact situations.
A New Running Torque Formula for Tapered Roller Bearings Under Axial Load
Authors: Aihara S.
Published: October 2009

Conventional formula for calculating the running torque of tapered roller bearings often showed discrepancy from actual running torque, particularly under axial load. Therefore, an equation was formulated based on the knowledge of EHL rolling resistance and EHL oil film thickness. Careful examination of actual bearing running torque suggested the load dependency of EHL rolling resistance which previous theory did not include. Such load effect was confirmed by means of two disc machine and the equation was partly corrected. A new running torque formula of a tapered roller bearing under axial load was proposed and good agreement with actual bearing torque was confirmed.
Heat Partition and Transient Temperature Distribution in Layered Concentrated Contacts. Part I—Theoretical Model
Authors: Rashid M. , Seireg A.
Published: October 2009

The study reported in this paper deals with the development of a generalized and efficient computer-based model for parametric evaluation of heat partition and transient temperatures in dry and lubricated layered concentrated contacts. The program utilizes finite differences with the alternating direction implicit method. It is capable of treating this general class of problems provided that the heat generation distribution and the layer properties and thicknesses are known.
Thermal Effects in Rolling/Sliding Contacts: Part 2—Analysis of Thermal Effects in Fluid Film
Authors: Sadeghi Farshid , Dow Thomas A.
Published: October 2009

A two dimensional numerical solution to the problem of thermal elastohydrodynamic lubrication of rolling/sliding contacts was obtained using a finite difference formulation. The technique involves the simultaneous solution of the thermal Reynolds’ equation, the elasticity equation, and the two dimensional energy equation. A pressure and temperature dependent viscosity for a synthetic paraffinic hydrocarbon lubricant (XRM-109F) was considered in the solution of the Reynolds’ and energy equations. The experimental pressure and surface temperature measurements obtained by Dow and Kannel [1] were used in evaluating the results of the numerical analysis for the cases of pure rolling and slip conditions.
Friction Induced Strengthening Mechanisms of Magnesia Partially Stabilized Zirconia
Authors: Aronov V.
Published: October 2009

Experimental investigation of the wear behavior of Magnesia Partially Stabilized Zirconia (Mg-PSZ) rubbed against itself showed that up to three orders of magnitude increase in the wear resistance can be achieved in a particular temperature range that depends on both the sliding speed and the ambient temperature. XRD analysis revealed that thermally induced phase transformation takes place on the frictional interface. Surface analysis show that wear rates at maximum wear resistance are controlled by the crack generation kinetics rather than by crack propagation kinetics. The plastic strain before fracture varies with temperature. The maximum plastic strain was observed at the temperature of maximum wear resistance. A phenomenological model is presented that provides an explanation for the wear temperature behavior of Mg-PSZ. The model is based on the following chain of events that takes place on the frictional interface: spatial overheating of the surface areas, phase transformation of the overheated areas, cooling, volume expansion, and development of a compressive stress field in the near surface volumes.
A Note on Film Rupture in Hydrodynamic Lubrication
Authors: Ota Terukazu
Published: October 2009

A theoretical and experimental study has been made for a film repture in hydrodynamic lubrication. A model is proposed on boundary conditions at the film rupture point. It contains a pressure correction term as a parameter, which simplifies that derived by Coyne and Elrod, and the so-called separation boundary condition. Some experiments have been conducted for a flow in a cylinder-plane geometry. It is found that numerical results using the present model agree reasonably well with the present and previous experimental data.
Failure of Steel Couples Under Boundary Lubrication: Influence of Steel Composition, Microstructure, and Hardness
Authors: Habig K.-H. , Feinle P.
Published: October 2009

If oil-lubricated sliding or rolling couples are overloaded, separating oil films can be broken through so that the friction coefficient increases severely. Thereby an instantaneous failure of tribosystems can be caused. This type of failure was investigated by means of an Amsler-wear-test-machine with two contacting and rotating disks that were immersed into a tempered oil bath. The load was increased in steps until failure was indicated by an increase of the coefficient of friction. The results reveal a strong influence of the chemical composition and of the microstruture of the steels while hardness does not show an influence. Failure is restricted if protective reaction layers can form on the stressed surfaces. As most of the alloying elements reduce the formation of such layers failure load is lowered by them. Unalloyed ferrite is able to form thick reaction layers causing a high failure load. Less reactive components of the microstructure like cementite, martensite, and above all austenite decrease the failure load.
The Wear Process During the “Running-In” of Steel in Lubricated Sliding
Authors: Suzuki M. , Ludema K. C.
Published: October 2009

Steel cylinders were slid against flat steel disks, using a liquid lubricant, in order to study the progression of events associated with “running-in.” It was found that, when using mineral oil, the electrical contact resistance varied over a small range of high values indicating no metallic contact, whereas with engine oil a high resistance with an intermittent negligible contact resistance was found. A surface film forms from the additives in the engine oil which produces lower wear, slightly higher friction, a retarded running-in, and a rougher surface finish in the direction of sliding than does the mineral oil. A film which is composed only of Fe3O4 is formed when mineral oil is used. In addition, the mineral oil lubricated surfaces develop a conforming waviness across the sliding tracks. The oxide must have enhanced this surface conformity since it was not seen in the surfaces lubricated with engine oil. The role of the oxide may be further seen in experiments in which wear debris that accumulated in the entrance region of specimen contact was removed at frequent intervals. Little conforming waviness was seen in the latter case, suggesting that oxide which gathered in the entrance region abraded grooves in the steel surfaces. After the oxides were dislodged the friction increased and the contact resistance decreased for a time, indicating that the oxide acted like a solid lubricant.
Transient Contact of Two Sliding Half-Planes With Wear
Authors: Azarkhin A. , Barber J. R.
Published: October 2009

We study the transient contact of two sliding bodies with a simple geometry. The model employs the Archard law of wear in which the rate of material removal is proportional to pressure and speed of sliding. The problem is formulated in terms of two governing equations with unknown pressure and heat flux at the interface. The equations are solved numerically, using appropriately chosen Green’s functions. We start with a single area of contact. As a result of frictional heating and thermal expansion, the contact area shrinks, which leads to further localization of pressure and temperature. The role of wear is twofold. By removing protruding portions of the two bodies, wear tends to smoothen out pressure and temperature. On the other hand, it causes the contact area to grow sufficiently large to become unstable and bifurcate. Areas carrying load are eventually removed by wear, and the contact moves elsewhere. The system develops a cyclic behavior in which contact and non-contact areas interchange.
Friction, Wear, and Interfacial Electrical Resistance. Part I: The Hoop Apparatus
Authors: Kuhlmann-Wilsdorf D. , Chang Y. J. , Johnson L. B. , Bredell L. J.
Published: October 2009

An apparatus has been developed for the gathering of data from which, through suitable analysis, detailed information on the momentary condition of a sliding interface may be obtained. The information includes the number of the contact spots, the electrical resistivity of the interfacial film, and the flash temperature at the contact spots. The apparatus provides for the continuous simultaneous recording of the coefficient of friction and of the interfacial electrical resistance of a slider in stick-slip motion at constant load and controllable average speed, and/or of the interfacial resistance of a slider at constant speed under controllable load. Loads between 0.3 and 10N and speeds up to 0.15m/s may be selected, in a variety of atmospheres and ambient pressures, as the apparatus is enclosed in a bell jar. It consists of a rotating cylindrical metal hoop inside of which a metal slider moves under the forces of friction and gravity, giving stick-slip behavior full play, and a slider in fixed position subjected to controllable, hydrostatically applied loads. The entire apparatus can be used with a controlled atmosphere or vacuum. The motion of the stick-slip slider, from which the coefficient of friction is inferred, is recorded on one pen of a three-pen strip-chart recorder and the electrical contact resistances between the two sliders and the hoop on the other two pens. The dependence of contact resistance on load, obtainable from the fixed slider without removing the bell jar, permits a determination of the number of contact spots provided the constriction resistance is not negligibly small compared to the film resistance. Deliberate changes of the contact spot temperature can be made by adjusting the current through the slider/hoop interfaces.
The Stresses Induced in a Half-Space by an Arbitrary Axisymmetric Pressure Distribution
Authors: Hills D. A. , Sackfield A.
Published: October 2009

A general method is described for deducing the stresses induced in a half-space by an axisymmetric pressure distribution applied over a small area of the surface. The technique is illustrated by re-evaluating the solution to Hertz’ contact problem, and deducing the stresses induced in a fourth-order contacting pair.
A Reynolds-Eyring Equation for Elastohydrodynamic Lubrication in Line Contacts
Authors: Conry T. F. , Wang S. , Cusano C.
Published: October 2009

A new Reynolds equation, based on the Eyring theory of non-Newtonian flow, is derived for flow in one dimension. It is shown that this new equation reduces to the traditional Reynolds equation as the Eyring model approaches the Newtonian model in the limit. Numerical solutions are presented for a selected oil at two different temperatures. The central film thickness decreases with increasing dimensionless viscosity parameter and slide/roll ratios. A transition zone is noted through which the ratio of minimum to central film thickness passes as the pressure distribution goes from near Hertzian to a distribution that appreciably deviates from Hertzian.
An Analysis of the Steady-State Performance of the Cylindrical-Spherical Floating Ring Bearing
Authors: Clarke D. M. , Fall C. , Hayden G. N. , Wilkinson T. S.
Published: October 2009

A steady-state analysis based on the short bearing approximation is presented for the cylindrical-spherical floating ring bearing, where the inner surface of the ring is cylindrical whilst the outer is spherical. Performance characteristics are compared with Li and Rohde’s theoretical work on the conventional cylindrical-cylindrical bearing. Excellent agreement is obtained, especially for (L/D) = 0.5. The present analysis of both the inner and outer lubricant films, the thickness of the latter varying axially, takes account of striated flow downstream of cavitation inception. The importance of this is demonstrated when considering power loss prediction.
Magnetic Bearing With Rotating Force Control
Authors: Chen H. M. , Darlow M. S.
Published: October 2009

A common attractive type active Magnetic Bearing (AMB) was designed and tested with three parallel feedback control loops. The feedback of the measured AMB journal displacement provides the bearing stiffness. Two special circuits, called Velocity Observer and Acceleration Observer, are formulated for estimating the AMB journal velocity and acceleration based on the same measured displacement without performing differentiation. The feedback control using the estimated velocity provides the AMB damping. The feedback control using the estimated acceleration creates a rotating force which cancels the imbalance force and other external disturbances. The rotating force control can be switched on or off in the designed speed range without causing rotor instability. This additional vibration suppression mechanism greatly enchances the versatility of AMB.
Piston Friction Force of a Small High Speed Gasoline Engine
Authors: Takiguchi M. , Machida K. , Furuhama S.
Published: October 2009

This paper clarified piston friction forces and conditions of lubrication in the high engine speed range through the improvement of piston friction measuring instruments. Measurements of piston friction forces of the two-ring package have been also done. It is found that the effect of the two-ring package on the reduction of friction forces is greater than expected by means of the oil starvation phenomenon.
The Analysis of a Self-Acting Flexible Foil Slider Bearing
Authors: Hardie C. E. , Ettles C. M. McC.
Published: October 2009

The flexible foil slider bearing is an alternate approach to the design of low clearance slider bearings used in direct access storage devices. The flexible foil, or membrane design will be presented as a slider bearing with high film stiffness that can achieve competitive flying heights. The elastohydrodynamics of the membrane slider design will be examined. A steady-state analysis will examine the effects on membrane shape of various physical parameters such as membrane stiffness, and membrane surface backing pressure. A transient analysis will assess the fluid film stiffness of the membrane slider. The membrane slider design has impressive compatibility between the slider and the disk surface for single impulse disturbances as well as continuous or ripple disturbances.
In Situ Estimation of the Dynamic Characteristics of an Uncavitated Squeeze-Film Damper
Authors: Burrows C. R. , Sahinkaya M. N. , Kucuk N. C. , Tong M. L.
Published: October 2009

A modified form of the author’s frequency-domain estimation algorithm has been applied to estimate the inertia and damping coefficients of an uncavitated squeeze-film bearing. These estimates are obtained in situ from measurements on a specially designed rig. The experiments provided further evidence that oil-film inertia coefficients may be significant and showed that theoretical predictions are inadequate.
Calculation of Clearances in Soft Point Contacts
Authors: Hooke C. J.
Published: October 2009

The clearances in highly deformed contacts are formed in a narrow region on the upstream side, are convected through the contact with little change and emerge downstream where a restriction forms in a narrow exit zone. The paper describes how this behavior simplifies the lubrication analysis. Expressions for the minimum film thickness under point contacts are obtained for the elastic isoviscous regime.
Elasto-Plastic Finite Element Analysis of Repeated, Two-Dimensional Rolling-Sliding Contacts
Authors: Ham G. , Rubin C. A. , Hahn G. T. , Bhargava V.
Published: October 2009

The stresses, strains, and deformations produced by repeated, two-dimensional rolling-sliding contact are analyzed using a modified finite element model developed by Bhargava et al. [1]. Rolling and sliding are simulated by translating an appropriate set of normal and tangential surface tractions across an elastic-perfectly plastic half space. The study examines a peak-pressure-to-shear strength ratio of po/k = 4.5 and normal to tangential force ratios of T/N = 0.20 and T/N = 0.17. The calculations describe the residual stresses, displacements and the continuing cyclic radial, shear and equivalent strains generated at various depths in the rim. The results are compared with previous calculations by Johnson and Jefferis [2] of rolling-sliding contact and with pure rolling. The present work predicts much higher deformations than previously calculated.
Adhesion Model for Metallic Rough Surfaces
Authors: Chang W. R. , Etsion I. , Bogy D. B.
Published: October 2009

An improved DMT adhesion model in conjunction with an elastic-plastic contact model is used to study adhesion of contacting metallic rough surfaces. The effects of surface roughness and surface energy of adhesion on the pull-off force and on the significance of the adhesion force are investigated. It is shown that for clean surfaces the adhesion is quite large even for relatively rough surfaces. Adhesion is negligible only for contaminated rough surfaces or at very high external loading.
Tribological Improvement of Ag Films by Ion Beam Enhanced Deposition
Authors: Hirano Motohisa , Miyake Shojiro
Published: October 2009

This paper investigates the tribological properties of Ag film fabricated by ion enhanced deposition at atmospheric room temperature, whereby 150 keV Ar ion bombardment and Ag ion plating are performed simultaneously. In the absence of a lubricant, friction test apparatus employing ball-plate geometry is used. Also, properties such as film crystallinity, morphology and concentration profile are examined to study the high energy ion bombardment effect related to the film’s tribological properties. The activation of the mutual diffusion process which results from simultaneous ion bombardment during ion plating, as well as promotion of the crystallization in the ion bombarded film due to subsequent annealing, can greatly extend the mixing layer, and thus enhances the sliding life of the Ag film.
Rolling Bearing Life Prediction. Corrections for Material and Operating Conditions. Part II: The Correction Factors
Authors: Tallian T. E.
Published: October 2009

Computer based rolling bearing analysis programs exist which provide models for load and stress distribution, EHD conditions, heat balance and fatigue life prediction for rolling bearings and machine assemblies comprising such bearings. Fatigue life prediction is generally based on the ANSI standard. This two-part paper offers correction factors for refining the life prediction by modeling effects of material and operating variables. The corrections can be applied to the ANSI-predicted life of a complete bearing or to predicted lives of stressed volume elements in the bearing, with subsequent summation over the stressed volumes. Formulations are presented with a view to their incorporation into dynamic bearing analysis computer programs. This second part of the paper comprises the equations for the correction factors, the complete life correction, an Appendix showing logic flow for the calculations, and figures illustrating the behavior of the correction factors.
Control of Surface Finishing Residual Stresses in Magnetic Recording Head Materials
Authors: Chandrasekar S. , Bhushan B.
Published: October 2009

Surface finishing of magnetic recording head materials, such as ferrites, by diamond grinding and lapping results in a residual compressive stress on the surface. Residual stresses alter the magnetic properties of the ferrite causing the recording head performance to deteriorate. Hence, they need to be minimized. This paper considers the role of two processing techniques—annealing and chemical lapping—in controlling residual stress in ferrites. The effect of these processing techniques on various mechanical and physical properties of finished ferrites and the mechanism of residual stress control are discussed.
Analysis of an Unpressurized, Laterally Restrained, Elastomeric O-Ring Seal
Authors: Dragoni E. , Strozzi A.
Published: October 2009

An unpressurized, elastomeric O-Ring seal inserted into a rectangular groove is analysed numerically and experimentally. The salient parameters characterizing the seal deformed geometry and stress field are investigated. The results gathered are confronted to those holding for a laterally unrestrained toroidal seal. Based on such a comparison, an analytical model is developed which accounts for the lateral restraining effects.
Effect of Peclet Number in Thermo-Mechanical Cracking Due to High-Speed Friction Load
Authors: Ju F. D. , Liu J. C.
Published: October 2009

The present paper discussed the critical depth, i.e., the depth at which the thermal tensile stress reaches a maximum, caused by the frictional excitation of a fast moving asperity. In the study, the critical depth was computed directly by maximizing the thermal tensile stress with respect to positions under the asperity inside the material. The relationship between critical depth and Peclet number for all materials in the two-dimensional formulation may be simplified to satisfy the exponential form R(ηcr)2.275=20.4368. Stellite III was chosen as the indicator material. Other parametric effects including mechanical properties and thermal properties were tested with materials having diverse property values. These tests confirmed that for the two-dimensional formulation, the Peclet number is the only one which dominates the critical depth.
A Highly Accurate Approach That Resolves the Pressure Spike of Elastohydrodynamic Lubrication
Authors: Bissett E. J. , Glander D. W.
Published: October 2009

We propose an accurate numerical method to solve the classical line contact problem of elastohydrodynamic lubrication. The method incorporates a second order accurate discretization and a straightforward automatic local mesh refinement procedure. Using these elements, we remove discretization errors which have produced significant inaccuracies in previously published results, and we completely resolve the pressure spike which is shown to be smooth on a sufficiently small length scale.
Dynamic Identification of Convergent Externally Pressurized Gas-Bearing Gaps
Authors: Plessers P. , Snoeys R.
Published: October 2009

The dynamic behavior of externally pressurized gas bearings is described by means of frequency response functions, from which dynamic stiffness and damping coefficients are derived. A numerical method is presented to calculate the frequency response function for plane circular thrust bearings with convergent gap geometry. A test procedure is described for measuring the frequency response function of an air film in order to verify computational, results. The comparison reveals a fairly good agreement between measured and calculated frequency responses. Finally, the effect of bearing parameters on the frequency response function of the air film is investigated.
Dynamic Stability of Mechanical Structures Containing Externally Pressurized Gas-Lubricated Thrust Bearings
Authors: Plessers P. , Snoeys R.
Published: October 2009

A stability criterion is presented to evaluate instability phenomena in mechanical systems containing externally pressurized gas bearings. For this criterion, the gas bearing films and the supporting structure are characterized separately by means of frequency response functions. The overall system may be considered as a feedback-loop for which the Nyquist criterion will define stability limits. The analysis demonstrates the interaction between the dynamics of the supporting structure and the air gap. The stability criterion is generalized for systems containing more than one gas film. The stability criterion is verified experimentally.
An Analysis of Speed, Temperature, and Performance Characteristics of Automotive Drum Brakes
Authors: Day A. J.
Published: October 2009

Finite element analysis techniques have been used to simulate braking friction in a large, heavy duty twin leading shoe brake. Temperature, lining wear and pressure distributions, and thermal distortions of the brake drum which are generated during high pressure brake applications from two different road speeds have been predicted and compared with experimental data. Two different types of brake lining, a conventional asbestos-based resin-bonded composite friction material and a heavy duty resin-bonded semi-metallic type of friction material have been studied in this way, and it is shown that observed in-stop and speed-related brake performance are strongly dependent upon the rate of frictional energy transformation at the lining/drum interface, which defines the development of interface transient temperatures. By relating the measured friction characteristic of the friction material to predicted lining friction surface temperatures good correlation between predicted and actual brake performance is demonstrated.
Analysis of an Eddy Current Journal Bearing
Authors: Connor K. A. , Tichy J. A.
Published: October 2009

Nearly all magnetic bearings which have found use in modern technology are based on the attractive force between a magnet and a magnetic material. A distinct disadvantage is that such devices are inherently unstable and require active feedback for operation. In the present study an eddy current bearing is analyzed which uses repulsive forces to levitate a rotor, as in proposed advanced rail transportation systems. The journal bearing is considered to be a series of one-dimensional pads wrapped around a shaft. Maxwell’s equations are solved for the equivalent Cartesian geometry pad and rotor. This system is modeled as a sinusoidally varying surface current backed with an infinitely permeable (magnetic) pad which is separated from a conductive nonmagnetic rotor by a free gap. The magnetic forces are found to vary inversely with gap size, a necessary condition for stability. The behavior of an eddy current journal bearing is calculated and compared to that of fluid film bearings. Load, “friction” (which may also serve as propulsion), and attitude angle are determined as a function of eccentricity ratio, a slip parameter, clearance ratio and a number of pads. The approximate results presented may serve as guidelines for development work and subsequent analysis.
Thermohydrodynamic Analysis of Wide Thrust Bearings Operating in Turbulent Inertial Flow Regimes
Authors: Chowdhury S. J. , Ahmadi G.
Published: October 2009

Wide thrust bearings operating in turbulent inertial flow regimes are studied. Isothermal and thermohydrodynamic performances of the bearing are analyzed. Integro-differential equations of motion, continuity, and energy equations are solved to yield pressure, mass-mean velocity, and temperature distributions. The effects of contraction ratio and film Reynolds number on the pressure field, load bearing capacity, flow rate and frictional resistance force of the bearing are examined. The effect of film temperature variation on the performance of bearing is studied and the result is compared with the isothermal case. It is observed that the viscous heating reduces the load bearing capacity to a significant extent. The effects of including the inertial terms are also considered. The results for inertial and noninertial cases are plotted and compared. It is shown that with the inclusion of the inertial terms the load bearing capacity somewhat increases. The results obtained are compared with the existing data and reasonable agreement is observed.
Finite Element Solution for the Rarefied Gas Lubrication Problem
Authors: Kubo Masahiro , Ohtsubo Y. , Kawashima N. , Marumo H.
Published: October 2009

This paper is useful in analyzing the performance of finite-width-air bearings in the rarefied gas region, using a newly developed finite element method. The linearized Boltzmann equation was solved by numerical iteration and a pressure equation was obtained, coupled with a continuous equation. The finite element method was developed for solving the pressure equation. The results were compared with a two moment approximate solution for the Boltzmann equation, which corresponds to the conventional slip flow analysis developed by Burgdorfer. An analysis of tapered flat slider flying characteristics in the rarefied gas regime, e.g., when the inverse Knudsen number in the trailing edge = 1, showed that the present exact solution for the Boltzmann equation was different from the two moment approximate solution by more than 10 percent in load capacity value, when the dimensionless load was not so large as when it is used for actual slider design.
Observations of Liquid Droplet Behavior and Oil Film Formation in O/W Type Emulsion Lubrication
Authors: Nakahara T. , Makino T. , Kyogoku K.
Published: October 2009

The behavior of liquid droplets in O/W type emulsions flowing between a flat glass plate and a metal roller was observed by means of a microscope. The behavior of the droplets introduced into the EHL film was found to be related to the streamlines of the continuous water phase in the vicinity of the inlet zone. It was observed that the oil droplets which penetrated into the EHL zone formed an oily pool (an oily film zone) containing water droplets in the inlet zone close to the EHL zone. This oily pool was a W/O emulsion rich in oil caused by phase inversion. The effects of oil concentration, emulsifier content and rolling speed on the area of the oily pool were investigated, and it was found that the extent of the oily pool was influenced by the rolling speed as well as oil concentration. The EHD film thickness was measured by means of optical interferometry with use of two wavelengths, and the measured results were compared with the calculated ones employing the starvation theory of Wolveridge et al. and the empirical equation of Wymer and Cameron for the region of the oil pool. It was found that course droplets play an important role in film formation by causing the formation of the oily pool in the low speed range. In the high speed range, however, a fine O/W emulsion forms the film.
Analysis of Eccentric Annular Incompressible Seals: Part 1—A New Solution Using Fast Fourier Transforms for Determining Hydrodynamic Force
Authors: Nelson C. C. , Nguyen D. T.
Published: October 2009

A new analysis procedure is presented which solves for the flow variables of an incompressible-flow annular pressure seal in which the rotor has a large static displacement from the centered position. The analysis begins with a set of governing equations based on a turbulent bulk-flow model and Moody’s friction equation. No simplification of these bulk-flow equations are required for the solution procedure. Perturbation of the flow variables yields a set of zeroth and first-order equations. The zeroth-order equations (which model the large static displacement) are integrated by means of an efficient new method which employs Fast Fourier Transforms. Further integration of the zeroth-order pressures yields the hydrodynamic reactive force. Predictions for the hydrodynamic forces from this analysis procedure are in excellent agreement with available experimental results.
Asymptotic Analysis of a Narrow Gas-Lubricated, Flat Sector Thrust Bearing
Authors: Shepherd J. J.
Published: October 2009

The method of matched expansions is employed to analyze the steady state operation of a finite gas-lubricated flat sector bearing for the case where the ratio of radial to circumferential dimensions is small and the relevant bearing number, Λ, is moderate. This technique yields general expressions for the pressure distribution, load bearing capacity, power loss and center of pressure location that are valid for a significant and continuous range of bearing dimensions, orientations and operating conditions. Comparisons are made, where possible, with the existing results from the literature obtained by numerical methods.
Thermohydrodynamic Analysis of Journal Bearings Considering Cavitation and Reverse Flow
Authors: Ott H. H. , Paradissiadis G.
Published: October 2009

The flow field of a hydrodynamic journal bearing is calculated by the iterative solution of the system of Reynolds and energy equations. In the case of reverse flow at the film inlet, the temperature profile there can not be prescribed as a boundary condition but has to be determined from the flow in the film. This is achieved by a separate integration of the energy equation in the reverse flow area. The flow in the cavitation regions is approximated by a theoretical model leading to a form of the energy equation similar to that for pressure regions, thus enabling the integration of the energy equation over the whole film.
An Interior Collocation Method for Static and Dynamic Analysis of Finite Length Gas Journal Bearings
Authors: Arakere N. , Nelson H. D.
Published: October 2009

The general Reynolds equation for self-acting, finite length gas-lubricated journal bearings is solved using an interior collocation method. The method assumes an approximate solution to the governing differential equation in the form of a series of trial functions, wn, with n unknown coefficients. The coefficients are evaluated by substituting the assumed solution in the governing differential equation, and forcing the residual (error) at n collocation points in the computational domain to be zero. The effectiveness of the collocation method is demonstrated by using the technique for the static and dynamic analysis of a journal supported by a plane gas bearing. The results from the collocation method agree very well with those obtained from a finite difference technique. Periodic orbit plots for a single journal in a finite bearing are presented for various journal unbalances and speeds. The collocation method is shown to be an order of magnitude computationally faster than the finite difference method. The method can be extended to other bearing types such as slider, hydrostatic and tilting pad bearings.
Wear Behavior of Laser Surface-Hardened Gray and Ductile Cast Irons. Part 2—Erosive Wear
Authors: Molian P. A. , Baldwin Mark
Published: October 2009

A 1.2-kW, continuous wave, CO2-gas laser was used to transformation harden or melt the surface of gray and ductile cast irons. Effects of surface-hardened layers on solid particle erosion showed that the erosion rate decreased with an increase in surface hardness and case depth. The order of matrix microstructures that increased the erosion rate were ledeburite, tempered martensite, and pearlite. These results were opposite to those observed in bulk-hardened alloys. Erosion mechanisms of brittle, gray iron included micromachining in the untreated condition and grain boundary cracking in the laser-treated condition. In contrast, erosion modes of ductile iron were plastic flow followed by cracking in the untreated condition and platelet formation and fatigue in the laser-treated conditions. The beneficial effects of surface hardening on erosion were examined and discussed.
Finite Element Analysis of a Layered Elastic Solid in Normal Contact With a Rigid Surface
Authors: Komvopoulos K.
Published: October 2009

Based on the finite element method, the elastic contact problem of a layered semi-infinite solid compressed by a rigid surface is solved numerically. The case of a surface layer stiffer than the substrate is considered, and general solutions for the subsurface stress and deformation fields are presented for relatively thin, intermediate, and thick layers. Additionally, the stresses in a compressed homogeneous half-space having the substrate properties have been obtained for comparison. The significance of the layer thickness relative to the size of the half-contact width, the friction coefficient at the contact zone, and the stiffness of the layer are critically examined and the conditions under which the layer is beneficial are addressed. Furthermore, the mechanisms of microcrack initiation at the layer surface or interface, layer debonding, and onset of plastic flow in the layered solid are explained qualitatively, in light of the governing stresses, and the regimes of their prevalence are approximately determined.
Sliding of a General Axisymmetric Point Contact
Authors: Sackfield A. , Hills D. A.
Published: October 2009

The complete stress field generated beneath an arbitrarily profiled axisymmetric indentor is found, both for normal indentation, and sliding. It is shown that a shallower profile than that of a sphere, i.e., one having a larger radius of curvature at the point of first contact, associated with a “flatter” pressure distribution, gives rise to a milder stress state, so that a heavier load may be sustained over a given contact disk without yielding.