bluuebunny/crossref_metadata_2025 huggingface dataset:
The Measurement and Finite Element Analysis of the Dynamic Stiffness of Nonuniform Clearance, Gas, Thrust Bearings
Authors: Holster P. , Jacobs J. , Roblee J.
Published: June 2008

This paper presents an overview of a finite-element-method (FEM) approach for the calculation of the dynamic stiffness of circular, externally pressurized gas thrust bearings with a nonuniform clearance. Some observations are made about the characteristic behavior of gas bearings subject to dynamic loading. The primary emphasis of this paper, however, is the development and qualification of a test apparatus and the necessary test techniques for measuring dynamic stiffness up to 250 N/μm at frequencies up to 2000 Hz. A thorough, experimental verification of the FEM model is reserved for a later paper.
Measured and Predicted Force and Stiffness Characteristics of Industrial Magnetic Bearings
Authors: Imlach J. , Blair B. J. , Allaire P. E.
Published: June 2008

Closed-loop stiffness and load capacity (force) equations have been developed for industrial magnetic bearings. Two sets of magnetic bearings have been constructed using these equations as a design basis. These bearings have been installed in two canned motor pumps. The predicted force and stiffness values from the equations are compared to experimental measurements to determine their validity. When obvious sources of error were eliminated, agreement within 10 percent was obtained for development pump’s magnetic bearings. Agreement was generally better for this pump than for the demonstration pump. By employing these equations, along with easily measured current and displacement information from magnetic bearing equipped machinery, actual stiffness’ and bearing loadings can be determined for operating equipment. Thus, the range of information available from magnetic bearings is extended to include static and dynamic loadings as well as shaft orbits and critical speed and damping information (Humphris et al., 1989). This enhances their use as diagnostic and preventative maintenance tools which are built into machinery and can be used on line.
The Rotordynamic Coefficients of Mechanical Seals Having Two Flexibly Mounted Rotors
Authors: Wileman J. , Green I.
Published: June 2008

The Reynolds equation is derived for a mechanical seal in which both elements are flexibly mounted to rotating shafts. Stiffness and damping coefficients for the fluid film are calculated for the three degrees of freedom of each element based upon a small perturbation analysis. The analogous coefficients for simpler configurations (e.g., flexibly mounted rotor, flexibly mounted stator) contained in the literature are shown to be obtainable as degenerate cases of the more general results presented in this work.
The Collapse of Sliding Micro-EHL Films by Plastic Extrusion
Authors: Hamer J. C. , Sayles R. S. , Ioannides E.
Published: June 2008

In the mixed lubrication regime, where surface roughness may exceed the elastohydrodynamic film thickness, sliding micro-ehl films appear to collapse during their passage through the contact. A possible explanation for this can be found if the film is treated as a plastic solid. In this work, the collapse velocity is found by simultaneously solving the plastic extrusion equations and the elastic pressure equations for the film trapped between approaching asperities. The velocity of collapse is shown to be very sensitive to the asperity wavelength, slide-roll ratio, and the velocity profile between the sliding asperities.
Effect of Hydrodynamic Thrust Bearings on Lateral Shaft Vibrations
Authors: Mittwollen N. , Hegel T. , Glienicke J.
Published: June 2008

A computational method for the prediction of static and dynamic characteristic data of tilting pad and fixed pad thrust bearings for high surface velocities and high thermal loads is developed and verified. Furthermore, a convenient model is presented, which allows the determination of the dynamic coefficients for the gyrating movement of the thrust collar, where it is sufficient using the purely axial dynamic single pad coefficients only. Introducing these coefficients into an accordingly modified rotor dynamics program, the lateral vibrations of a high speed rotor with sliding bearings are calculated and a considerable effect of the thrust bearings is shown. These theoretical results are also verified experimentally through vibration measurements at a high speed rotor test rig.
Stiffness and Damping of Compressible Lubricating Films Between Computer Flying Heads and Textured Media: Perturbation Analysis Using the Finite Element Method
Authors: Mitsuya Y. , Ota H.
Published: June 2008

Averaged static and dynamic lubrication equations are derived in the general form containing anisotropic film thicknesses dependent on roughness orientation. Solving these equations lead to a presentation of the dynamic characteristics of lubricating films existing between computer flying heads and textured media. Squeeze effects owing to moving roughness accompanying high-frequency spacing variation are found to be given as a function of arithmetically averaged film thickness minus harmonically averaged film thickness. The calculation procedure using the finite element method is then presented for the averaged static and dynamic lubrication equations. Stiffness and damping coefficient are demonstrated indicating the effects of roughness orientation and roughness movement. Under the fixed static film conditions, the roughness decreases the stiffness. In contrast to this, the roughness only slightly affects the damping coefficient. Under fixed load and loading point conditions, these relationships are inversed. It is interesting to note that damping coefficients are decreased by longitudinal roughness and are increased by moving transverse roughness. The reason for this tendency is considered to be that the moving transverse roughness serves to generate the squeeze damping force.
Closed-Form Expression for Temperature in a Semi-Infinite Solid Due to a Fast Moving Surface Heat Source
Authors: Tichy J. A.
Published: June 2008

In the thermal analysis of an asperity on a sliding surface in frictional contact with an opposing surface, conditions are often idealized as a moving heat source. The solution to this problem at arbitrary Pe´cle´t number in terms of a singular integral is well known. In this study, closed-form solutions are found in terms of the exponential integral for high Pe´cle´t number. Fortunately, the closed-form solutions are accurate at Pe´cle´t number of order one. While several restrictions are necessary, the closed-form expressions offer considerable numerical savings relative to evaluations of the convolution integral.
Investigation of Surface Deformation When a Hard Wedge Slides Over a Soft Surface
Authors: Kopalinsky E. M.
Published: June 2008

In experiments a tool steel wedge was indented into the surface of an aluminum specimen and then slid along it. The resulting deformation was measured using a grid printed on a plane of flow and the strain distribution near the surface was determined from an analysis of the observed deformation. Results are given for various wedge angles and lubrication conditions. The relevance of the results to a slipline field model of asperity deformation, which has been used to predict friction and wear for metal surfaces in sliding contact, is considered.
Frequency Effects on the Stability of a Journal Bearing for Periodic Loading
Authors: Vijayaraghavan D. , Brewe D. E.
Published: June 2008

In this paper, stability of a journal bearing is numerically predicted when an unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the JFO theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load vibration and frequency of journal speed are also investigated. The journal trajectories, transient variations in fluid film forces, net surface velocity and minimum film thickness and pressure profiles are also presented.
A Mixed Lubrication Model Applicable to Bearing/Seal Parts of Hydraulic Equipment
Authors: Yamaguchi Atsushi , Matsuoka Hiroshi
Published: June 2008

A mixed lubrication model applicable to the bearing/seal parts is presented which enables forecasts of both friction and flow rate. The model is based on the combination of the Greenwood-Williamson model for nonlubricated rough surfaces in contact and Patir and Cheng’s mean flow model. It introduces an adsorbed film model and includes effects of EHL and cavitation. Regardless of the assumptions introduced, the model agrees well with experimental results of parallel sliding surfaces lubricated with liquids ranging from mineral oils to water.
Temperature Distributions and Heat Transfer in Journal Bearings
Authors: Fitzgerald M. K. , Neal P. B.
Published: June 2008

The paper contributes to the stock of thermal data for axial-groove journal bearings. Test results are presented for 76 mm diameter bearings of two length/diameter ratios and two values of diametral clearance. Data presented include bush temperature distribution, journal surface temperature, and oil flow rate for a range of load and speed. Heat transfers from the oil film to the bush and the journal are estimated from the temperature data. Bush heat transfer is shown to depend primarily on the film Peclet number with load as a significant secondary factor. The consequences of neglecting the effect of bush heat transfer in the prediction of operating temperature are discussed.
The Effect of Tribofilm Formation and Humidity on the Friction and Wear Properties of Ceramic Materials
Authors: Komvopoulos K. , Li H.
Published: June 2008

The processes of tribofilm formation and disruption and the predominant tribo-mechanisms of unlubricated ceramic materials were investigated experimentally. Sliding experiments in humidity controlled atmospheres revealed that the formation of interfacial tribofilms significantly affects the steady-state friction and wear properties of ceramics. Scanning electron microscopy and various composition analysis techniques demonstrated that although tribochemical reactions might occur, the principal mechanisms of tribofilm formation were the generation, agglomeration, and compaction of fine wear debris produced from both sliding surfaces. The tribofilms exhibited different tribological characteristics, depending on their elemental compositions and the humidity. For all the ceramic pairs tested, the steady-state coefficients of friction decreased with relative humidity. In contrast to the conventional fracture toughness approach, surface profilometry and microscopy studies showed that the highest wear rates were encountered with the toughest ceramic. Plowing grooves parallel to the direction of sliding, fine wear debris of round and cylindrical shapes, microcracking, and localized delamination of the tribofilms were identified. Microscopic observations suggested that damage of the subsurface material adjacent to the interface of the tribofilms was immeasurable. Qualitative comparison of the topographical features of worn surfaces indicated that, depending on the humidity and the type of ceramic, microplasticity, microfracture, and delamination of the tribofilms were the prevailing steady-state tribomechanisms.
A Steady-State Model of a Floating Ring Bearing, Including Thermal Effects
Authors: Clarke D. M. , Fall C. , Hayden G. N. , Wilkinson T. S.
Published: June 2008

A steady-state model of a conventional floating ring bearing is presented, specifically, to assess the feasibility of its use in the power generating industry. It necessitates the numerical solution of the Reynolds and energy equations for both inner and outer lubricant films. Oil recirculation and heat and mass transfer between the films are included. For the application considered, the oil temperatures and eccentricity ratios encountered are not excessive.
Approximations in Hydrodynamic Lubrication
Authors: Dai R. X. , Dong Q. , Szeri A. Z.
Published: June 2008

In this numerical study of the approximations that led Reynolds to the formulation of classical Lubrication Theory, we compare results from (1) the full Navier-Stokes equations, (2) a lubrication theory relative to the “natural,” i.e., bipolar, coordinate system of the geometry that neglects fluid inertia, and (3) the classical Reynolds Lubrication Theory that neglects both fluid inertia and film curvature. By applying parametric continuation techniques, we then estimate the Reynolds number range of validity of the laminar flow assumption of classical theory. The study demonstrates that both the Navier-Stokes and the “bipolar lubrication” solutions converge monotonically to results from classical Lubrication Theory, one from below and the other from above. Furthermore the oil-film force is shown to be invariant with Reynolds number in the range 0 < R < Rc for conventional journal bearing geometry, where Rc is the critical value of the Reynolds number at first bifurcation. A similar conclusion also holds for the off-diagonal components of the bearing stiffness matrix, while the diagonal components are linear in the Reynolds number, in accordance with the small perturbation theory of DiPrima and Stuart.
Shear Strength and Tribological Properties of Stearic Acid Films—Part I: On Glass and Aluminum-Coated Glass
Authors: Timsit R. S. , Pelow C. V.
Published: June 2008

The mechanical shear strength of dry and lubricated interfaces is evaluated by measuring the frictional force during sliding of a hemispherical pin in contact with a flat slide. The solids investigated include bare glass and aluminum-coated glass and interfaces are generated from pairings of these materials. Lubrication is obtained by depositing a stearic acid Langmuir-Blodgett layer on the slide. Shear strength is measured at contact stresses ranging from ~ 0.05 to 0.8 GPa and at a sliding speed of 60 μm s−1. The shear strength of dry interfaces is found to increase with contact stress, and increases slightly with aluminum film thickness. Because stearic acid adheres to glass and aluminum, the shear strength of lubricated interfaces originates from the interaction of two stearic acid layers generated from molecular redistribution over the surfaces during sliding. For lubricated interfaces, the shear strength increases nearly linearly with contact stress, in agreement with the results of earlier work. The shear strength of stearic acid is found to depend slightly on the combination of sliding materials. Lubricant durability is found to be largest in glass/glass sliding interfaces.
The Subsynchronous Dynamic Behavior of Tilting-Pad Journal Bearings
Authors: White M. F. , Chan S. H.
Published: June 2008

Tilting-pad journal bearings are being increasingly used to avoid bearing instability problems. This paper describes the theory and results from a design program which has been developed for tilting-pad journal bearing calculations. The present approach is based on the numerical solution of the Reynolds equation using a one-dimensional finite element technique which considers temperature and viscosity changes and can also take into account the effect of turbulent flow. Computed results of dynamic stiffness and damping coefficients show very good agreement with data from the literature. The effects of various factors which may influence the bearing dynamic characteristics are discussed. For bearings with small preloads and operating at high Sommerfeld numbers, the effective damping at subsynchronous frequencies is considerably lower than that predicted for synchronous vibration. The stiffness is also affected by frequency. This frequency effect is attenuated by increased bearing preloads and offsets. Such factors have important consequences on the stability of high speed turbomachinery supported by tilting-pad journal bearings.
Moisture Effects Including Stiction Resulting From Adsorbed Water Films
Authors: Gao Chao , Kuhlmann-Wisldorf D. , Makel D. D.
Published: June 2008

Stiction resulting from moisture effects at small elastic contact spots has been identified and studied using bundles of fine, gold-plated copper fibers sliding on a gold-plated copper surface. The relevant measurements were made in the hoop apparatus which permits simultaneous monitoring of the momentary coefficient of friction and electrical contact resistance. Previous studies made with the hoop apparatus have shown that under the action of high local pressure, adsorbed moisture is expelled from between the contact spots leaving only one monomolecular layer of adsorbed water on each of the contacting surfaces. Additional details of the observations are varied and permit a refined analysis. Stiction results during periods of very slow motion or rest through local energy reduction at the spots as excess water is slowly drained in the course of molecular ordering of the two absorbed layers. Complex variations of kinetic friction with humidity and sliding speed are explained through the interplay of excess molecules between the contact spot surfaces, meniscus formation, fluid drag about the spots, and shear thinning in that flow.
DDC Lubrication: A New Concept in Tribology
Authors: To̸nder K.
Published: June 2008

A new lubrication concept is presented, Deep Disconnected Cavities. It differs from the lubrication of microcavities, previously treated by other authors, by the deepness of the cavities. The validity of Reynolds’ equation and nonturbulent conditions are assumed. By a Taylor expansion scheme, it is shown that the roughness effects are expressible in terms of roughness factors modifying the Reynolds equation, similar to those proposed by Patir and Cheng (1978). Unlike those established for ordinary roughness, the DDC factors are independent of local film thickness and roughness amplitude (cavity depth), and may therefore be used to modify standard hydro-dynamic parameters. By a different mathematical approach, involving upper and lower bounds on the various hydrodynamic quantities, it is found that Reynolds’ equation and all the other hydrodynamic expressions may be written just as for smooth surfaces, with the following modifications: 1. The film thickness should be expressed by the minimum gap function, and not by the mean gap function. 2. There are, in general, three effective viscosities, lower than the physical one, two of which are associated with the x and y directions respectively and appear in the modified Reynolds equation as well as in the flow terms. The third one appears only in the expression for shear stress.
A Nonlinear Model for Short Length, Cylindrical Squeeze Films With Large Planar Motions
Authors: Lu Yong , Rogers R. J.
Published: June 2008

A rotating shaft vibrating in a squeeze film bearing and a tube in a heat exchanger oscillating with fluid-filled cylindrical supports both involve cylindrical squeeze films. Many theoretical and experimental results show that the squeeze film force consists of both a damping force and an inertia force. For relatively large amplitude motions or when the initial eccentricity is large, the time waveform of the squeeze force is significantly nonlinear. In order to predict the transient response of a rotor with squeeze film bearings or a heat exchanger tube subject to flow induced vibration, the nonlinear instantaneous squeeze force must be calculated. This paper presents a model for the instantaneous cylindrical squeeze film force for planar motion. The squeeze film model for a two-dimensional plate shows that there are three nonlinear terms included in the squeeze force. Based on this model, an equation for the short length, cylindrical squeeze film force for moderately large eccentricities is developed. The equation includes the three nonlinear terms: the viscous term, the unsteady inertia term, and the convective inertia term. All three terms are functions of instantaneous eccentricity. The equation predicts the nonlinear multi-harmonic and unsymmetrical time waveforms of the instantaneous squeeze film force for planar motions with both in-line and out-of-line initial eccentricities. The results are compared with experimentally measured squeeze force waveforms obtained with a length to diameter ratio of 0.75 and instantaneous eccentricities less than 0.75. The squeeze force waveforms for this finite length geometry can be reasonably predicted if correction coefficients, which account for the circumferential flow, are applied to the three nonlinear force terms. These coefficients are themselves functions of frequency, initial eccentricity and amplitude.
A Computational Method for Cavitation in a Wavy Mechanical Seal
Authors: Payvar P. , Salant R. F.
Published: June 2008

A stable and convergent computational method is presented for the calculation of the flow field in the film between the faces of a wavy mechanical seal. The method is particularly useful for situations in which cavitation may occur in the film. The boundary conditions are formulated so as to allow for the occurrence of cavitation nodes on the low pressure boundary. Numerical results are presented for a particular wavy seal to demonstrate the validity of the method over a wide range of the two most important parameters governing the occurrence and the extent of the cavitation zone.
The High Pressure High Shear Stress Rheology of Liquid Lubricants
Authors: Bair S. , Winer W. O.
Published: June 2008

A limiting shear stress model of liquid lubricant shear rheology is offered which accurately represents all available primary data. The model is of the nonlinear Maxwell type with shear modulus taken into the time derivative and broadening of the viscous-plastic transition with pressure. Property relations for viscosity, limiting stress and shear modulus are refined for a polyphenyl ether in particular. The model, with simplifying assumptions, is compared with disk machine results. This model, with change of yield criterion, may be applicable to some shear thinning liquids at low pressure. Limiting shear stress varies with pressure in the same manner as the ultimate shear strength of solid polymers.
The Influence of Air-Bearing Surface Geometry on the Dynamics of Sliders
Authors: Suk M. , Ishii T. , Bogy D.
Published: June 2008

We investigate the influence of crown on slider dynamics during the takeoff stages of disk drives using the multi-channel laser interferometer. We show that a two-dimensional analysis of slider dynamics during takeoff/landing cannot explain all the observed phenomena. We also examine the crown effect on slider motion while it is flying on a thin film disk with a crater-like surface defect. Finally, we measure the spacing variation of the slider as a function of disk speed. It is observed that the initial motion of negative crown sliders during takeoff can be quite similar to positive crown sliders, although the process is quite different. Furthermore, the results suggest that the negative crown sliders may lead to more disk wear due to longer sliding distances. We observed that during steady flying conditions the craterlike surface defect on the disk produced significantly larger motions for negative crown sliders than positive crown sliders. Lastly, we found that both the waveform and magnitude of the low frequency component of the spacing fluctuation is independent of the slider flying height.
Three-Dimensional Temperature Distribution in EHD Lubrication: Part I—Circular Contact
Authors: Kim Kyung Hoon , Sadeghi Farshid
Published: June 2008

A complete numerical solution of Newtonian thermal compressible elastohydrodynamic lubrication of rolling/sliding point (circular) contact has been obtained. The multilevel multigrid technique was used to solve the simultaneous system of thermal Reynolds, elasticity and the energy equations with their boundary conditions. The effects of various loads, speeds, and slip conditions on the lubricant temperature, film thickness, and friction force have been investigated. The results indicate that the temperature rise in the contact is significant and thermal effects cannot be neglected.
Study on Oil Film and Pressure Distribution of Micro-EHL
Authors: Ping Huang , Shizhu Wen
Published: June 2008

Micro-EHL problems of line contact have been solved by Newton-Raphson method. The results are given from the zero roughness amplitude to the value higher than the film thickness in the smooth surface solution. With the increase of the roughness amplitude, cavitations may be found inside the contact region. This situation is predicted by a critical roughness amplitude. The solutions are also given after the roughness exceeds to the critical value. From the results it is found that the film thickness is still thick enough even if the roughness is very high. The other factors to influence on the pressure and film thickness, such as loads, roughness wavelengths and oil compressibility, are considered as well.
Computation of Cavity-by-Cavity Flow Development in Generic Labyrinth Seals
Authors: Rhode D. L. , Nail G. H.
Published: June 2008

A recently developed version of a swirl-flow finite difference computer code was improved and employed in predicting the compressible flow of air through generic labyrinth seals. The cavity-by-cavity flow field development from the seal inlet is computed, and the distribution of various field variables is examined. Results are given for straight-through seals of corresponding teeth-on-stator and teeth-on-rotor types. The teeth-on-rotor seal gives greater leakage resistance than the equivalent teeth-on-stator design. Also, it exhibits a greater swirl velocity development. These previously unavailable predictions of swirl velocity development are provided for the refinement of simpler models, as investigators have asked for these results.
Interferometric Studies of Effects of Striated Roughness on Lubricant Film Thickness Under Elastohydrodynamic Conditions
Authors: To̸nder K. , Jakobsen J.
Published: June 2008

Experimental results for striated roughness, obtained from an interferometric EHD test rig, are presented. The roughnesses are straight-edged grooves etched in a flat sapphire surface, yielding fringes over the flat lands. A new feature is the method of recording: Visual inspection, serial photography and digital analysis of the photographs, gives the relative light intensity in the central region of the contact zone. This permits the construction of curves relating light intensity and thence film thickness to speed. We find: transversely oriented grooves produce a higher central film thickness than do longitudinal ones, and films generated by smooth surfaces are thicker still. The slopes of the curves, on log-log paper, all tend to the value 0.67. The curves for rough surfaces are very different at low speeds, due to the escape of lubricant along the grooves.
An Expression of Reynolds Stresses in Turbulent Lubrication Theory
Authors: Tieu A. K. , Kosasih P. B.
Published: June 2008

This paper proposes an alternative model of Reynolds stresses for turbulent lubrication theory. The approach relies on Prandtl’s mixing length theory which is based on a modified Van Driest mixing formula [1]. However, unlike the previous theories [2, 3] the proposed equation is capable of accounting for the effect of shear stress gradient on the mixing length. Thus it is well suited to turbulent flow analysis in bearings where the presence of shear stress gradient due to the effect of pressure gradient should be considered. A series of velocity measurements in thin channels in the low Reynolds number turbulent flow range are analysed using the theory. The data analysis shows a strong effect of shear stress gradient on the viscous sublayer in the low Reynolds number regime. As a result, a new model of mixing length applicable to the turbulent lubrication analysis in thin film at low or high Reynolds numbers or under low or high shear stress gradient is presented.
Lubricant Removal, Degradation, and Recovery on Particulate Magnetic Recording Media
Authors: Novotny V. J. , Karis T. E. , Johnson N. W.
Published: June 2008

Lubrication of particulate magnetic recording media improves their mechanical durability in sliding and flying by several orders of magnitude compared with unlubricated media. Lubricant removal, degradation, and recovery were studied using microslit scanning Fourier transform infrared spectroscopy and microspot scanning X-ray photoelectron spectroscopy. These techniques measure the total and surface lubricant amounts in the porous film, respectively. Lubricant dynamics were compared for two physisorbed polyperfluoroalkylether lubricants of similar molecular weight but different molecular structure—Y with a CF3 side group and Z with linear chains. The bulk viscosity of Y was about ten times higher than the viscosity of Z. In sliding, the lubricant removal rate of Y was significantly higher than that of Z while in flying the removal rates were reversed. Removal rates in sliding were orders of magnitude higher than those in flying. Effective lateral diffusion coefficients estimated from the rate of lubricant reflow back to the depleted tracks were close to inversely proportional to the bulk viscosity. During sliding and flying both lubricants degraded as evidenced by chemically altered lubricant detected on the surfaces after dissolution of undegraded lubricant.
Effects of Elastic Moduli of Contact Surfaces in Elastohydrodynamic Lubrication
Authors: Kaneta M. , Nishikawa H. , Kameishi K. , Sakai T. , Ohno N.
Published: June 2008

Using the optical interferometry technique the film profile in circular elastohydrodynamic contacts is examined with several kinds of fluid under wide ranges of loads and speeds. It is found that under a sliding condition a deep conical depression (dimple) occurs in the contact surface in place of the flat plateau predicted by the EHL theory. This dimple phenomena can be explained by the squeeze film effect acting parallel to the contact plane attributable to the difference in surface deflections of the contact bodies. That is, if the contacting bodies are different in their elastic moduli, EHL film shape is markedly influenced by the slide/roll ratio even if the rolling or entrainment velocity is kept constant. This result suggests that the establishment of a new EHL theory, which takes into consideration the effects of the difference in elastic moduli of the contacting surfaces and surface pressure components parallel to the contact tangent plane, is necessary for deeper understanding of the EHL regime.
The Behavior of Non-Newtonian Thermal EHL Film in Line Contacts at Dynamic Loads
Authors: Yang Peiran , Wen Shizhu
Published: June 2008

The behavior of the thermal elastohydrodynamic lubrication film in line contacts at dynamic loads is investigated numerically with a forward-iterative procedure. The lubricant is assumed to be an Eyring fluid. The results show that the effects of the dynamic loads upon the time depending EHL film include two aspects: to retard the change and to increase the thickness of the film. In the case the load frequency is very high, a pressure peak which is round in shape can be found in the inlet zone of the contact.
Accounting for Transducer Dynamics in the Measurement of Friction
Authors: Streator J. L. , Bogy D. B.
Published: June 2008

In many studies of sliding interfaces, the measurement of friction is complicated by quasi-harmonic vibrations of the transducer system. An analytical technique is introduced which accounts for the dynamic characteristics of a force transducer under periodic excitation, and is used to compute the forcing function in the sliding interface. The force transducer is modeled as an elastic cantilever-beam with an attached rigid mass. The forcing function is obtained by solving the time-dependent, fourth-order partial differential equation of Euler-Bernoulli beam theory. The solution is facilitated by the application of Fourier series expansions in time and eigenfunction expansions in space. Results of the method are compared to previous analyses of friction-induced vibration in which the elasticity of the transducer is modeled as a simple spring and the rigid body as a lumped mass, leading to a single degree-of-freedom (DOF) governing equation. It is found that a single DOF calculation based on instantaneous measurement of displacement agrees surprisingly well with the results of the Euler-Bernoulli analysis. A single DOF model based on instantaneous measurement of strain and a static displacement-strain calibration factor agrees well with the Euler-Bernoulli analysis for a low frequency range but deviates at higher frequencies.
A Higher Order Perturbational Approach in the Lubricated EHL Contacts With Non-Newtonian Lubricant
Authors: Wang Jianming , Zhang He Hao
Published: June 2008

In previous papers [7–9], investigations have been made on the influence of several kinds of non-Newtonian lubricants on the line contact EHL by using a first-order perturbational method. The practical engineering applications have been also tried successfully through papers [10–14]. However, when the slide/roll ratio reduces to zero the derived Reynolds equations become either the exact equations for a Newtonian lubricant or totally invalid. This, of course, is not the case for a natural non-Newtonian fluid. The facts show the limitation of the first-order method and also implies that with a tendency of decreased slide/roll ratio the first-order perturbational approach may bring a larger error and cannot describe accurately the behavior of non-Newtonian lubricants in the lubricated region. To improve it, a higher-order perturbational procedure is proposed in this paper.
Simplified Contact Fatigue Life Prediction Model—Part I: Review of Published Models
Authors: Tallian T. E.
Published: June 2008

Part I of this two-part paper reviews eleven published spalling fatigue life models, to identify consensus parameters and relationships and to compare model strengths and limitations, as a basis for the construction of a simplified, readily calculated engineering model encompassing the major life variables, based on explicit assumptions and derivations. Part II of the paper presents the new model. It uses the applied alternating shear stress field to define the critical stress as a function of depth, and computes life as crack propagation time through this field. The model defines surface defects as critical defects. Material fatigue susceptibility, fatigue limit stress and the defect severity distribution are the main endurance parameters. In addition to Hertz pressure, life-modifying variables are: interface traction, surface microgeometry and EHD film. It is shown that the new model is capable of representing the influence of all major consensus parameters on life, by relationships that fall within the bounds of previously published behavior.
Magnetic Bearing Sizing for Flexible Rotors
Authors: Maslen E. H. , Allaire P. E.
Published: June 2008

Magnetic bearing load capacity in flexible rotor systems must be adequate to accommodate external loads acting on the rotor. The first part of this paper develops the theoretical basis for computing the bearing load capacity requirements of flexible rotors subject to bounded external harmonic loads and strict motion constraints. The second part of this work illustrates the application of the theory to a specific example: a fairly simple three disk flexible rotor subject to mass unbalance loads. Load capacity requirements are computed for the example shaft at its first three free-free forward whirl critical speeds. Based on the bounds obtained, two bearing design cases are examined: one with 45 N load capacity and the other with 223 N load capacity. The performance of the rotor is not improved with the higher capacity bearing and neither is capable of adequately constraining the rotor at its second critical speed. It is concluded that this shaft cannot be operated above its second free-free critical speed without a midspan bearing.
The Tribological Reaction Accompanying Friction and Wear of Silicon Nitride Containing Titanium Nitride
Authors: Imada Y. , Kamamura K. , Honda F. , Nakajima K.
Published: June 2008

Effect of humidity in atmosphere gas, air, or argon, is investigated for the tribochemical reaction in Si3N4 – 23 percent TiN-Si3N4 – 23 percent TiN sliding contact system using a pin-on-plate type testing machine by reciprocal movement of pin against plate. An examination is also conducted on Si3N4 – Si3N4 couple in comparison with the above system. The experimental results have shown that the wear rate decreases with increasing humidity, and the wear property is somewhat improved by adding a suitable amount of TiN to Si3N4. Reaction products formed on the interface under the sliding contact are analysed by using EPMA and XPS. It is confirmed that SiO2 (or TiO2) is produced on the surface during friction and wear, and the amount of SiO2 (or TiO2) increases with the increase of humidity. Formation of NH3 caused by development of tribochemical reaction on friction surface is examined by a spectrometric study using Nessler’s reagent. The results show that the formation of NH3 is connected directly with the amount of SiO2 (or TiO2), and that three types of formation rate are observed depending on the humidity.
Squeeze Film Dynamics of Two-Phase Seals
Authors: Yasuna J. A. , Hughes W. F.
Published: June 2008

A dynamic analysis of two-phase face seals including squeeze film effects and thermal transients is presented. Axial responses to perturbations from equilibrium for various sets of typical seal operating conditions are examined, and the sensitivity of these responses to certain parameters is discussed. Sample calculations indicate damped transient responses which often decay as steady state is approached asymptotically. In some cases, however, stable and unstable oscillations are observed.
Seizure Strength Improvement for Phosphate-Stearate Coatings Involved in Cold Forging of Steel
Authors: Hivart Ph. , Bricout J. P. , Oudin J. , Dauphin J. Y.
Published: June 2008

A seizure test particularly well suited to evaluate the mechanical strength of phosphate-stearate coatings has been developed. Test results, including tangential friction force and time at the onset of seizure, are related to the effective phosphate bonding and to lubricant reactive effects. It is shown that seizure is delayed if the phosphate coating is annealed at 500°C just before soaping. The γ-Zn3 (PO4)2 formation which occurs with a decrease in volume induces cracking along hopeite needles and causes an increase in reactive surface for soaping and, therefore, an increase in the quantity of zinc phosphate converted into zinc stearate. Improvement of the phosphate coating by annealing at 500°C before soaping may be an attractive alternative to the use of molybdenum disulfide lubricants.
Contact Stress Analysis of a Layered Transversely Isotropic Half-Space
Authors: Kuo C. H. , Keer L. M.
Published: June 2008

The three-dimensional problem of contact between a spherical indenter and a multi-layered structure bonded to an elastic half-space is investigated. The layers and half-space are assumed to be composed of transversely isotropic materials. By the use of Hankel transforms, the mixed boundary value problem is reduced to an integral equation, which is solved numerically to determine the contact stresses and contact region. The interior displacement and stress fields in both the layer and half-space can be calculated from the inverse Hankel transform used with the solved contact stresses prescribed over the contact region. The stress components, which may be related to the contact failure of coatings, are discussed for various coating thicknesses.
SEM Studies of Wear Mechanisms in Magnetic Thin Film Disks With Different Overcoats
Authors: Ganapathi S. K. , Balanson R. D. , Talke F. E.
Published: June 2008

Scanning Electron Microscopy and optical profilometer studies were conducted to study the wear of unlubricated thin-film magnetic recording disks overcoated with carbon as well as silver and zirconia. The results indicate that wear of the carbon overcoat occurs in the form of localized damage, or “pits,” accompanied by a gradual “thinning” of the carbon overcoat in the wear track. A similar pitting behavior is found for zirconia overcoated disks, but the pits resemble cracks in the overcoat, while the wear of silver disks resembles that of typical metal-metal sliding interfaces.
Gas Bearing of Infinite Stiffness
Authors: Kazimierski Zbyszko , Brzeski Lech , Horodko Longin
Published: June 2008

The experiences gathered during the theoretical and experimental investigations of the thrust and journal high stiffness bearing (H.S.B.) allowed to improvement of their characteristics. New elements of the throttling system were introduced into the journal H.S.B. to make possible this improvement. It was shown that the H.S.B. can reach infinite stiffness in a wide range of the loading forces having at the same time zero or submicronic shaft displacement. Additionally, the load-displacement characteristic of the H.S.B. may have the prescribed negative displacement to make possible the full compensation of elastic deformation of connected machine parts. The influence of journal rotation on the H.S.B. load-displacement characteristics is discussed in this paper. The H.S.B. of presented characteristics may be applied to many precise devices, e.g., to ultra-precision grinding machines.
Formation of Lubricant Film in Rotary Sealing Contacts: Part II—A New Measuring Principle for Lubricant Film Thickness
Authors: Poll G. , Gabelli A.
Published: June 2008

The development of models for the elastohydrodynamic lubrication of rotary lip seals requires the measurement of the film thickness under a real seal. A new method has been developed for this purpose which is based on the use of lubricant oils in which magnetite particles are suspended (so-called magnetic fluids). A change in the fluid film thickness will create a change in the impedance of the coil of the measuring circuit, the magnetic flux of which is directed through the oil film of the contact area. The advantage of this technique is that minimal modifications have to be applied to the tribological system under examination. Initial measurements carried out with a model rubber lip seal provided new insight into the build-up of a lubricant film as a function of the rotary speed and allowed comparison with the results of a theoretical model for the analysis of lip seal lubrication developed in parallel.
A Rolling Contact Fatigue Study of Hard Carbon Coated M-50 Steel
Authors: Wei R. , Wilbur P. J. , Kustas F. M.
Published: June 2008

Hard carbon coatings with diamond-like properties were applied on AISI M-50 steel rods which were subjected to rolling contact fatigue (RCF) testing at a cyclic Hertzian stress level of 5.5 GPa. The coatings were produced using a single, broad beam ion source that directed 450 eV ions, derived from a methane discharge, onto the rods. Results from preliminary tests show that hard carbon coatings alter the fatigue failure characteristics of this material substantially. They caused the B50 lifetime to increase from 7.5 × 106 stress cycles for uncoated material to 13 × 106 but they also caused the B10 lifetime to decrease from 4 × 106 stress cycles for the uncoated material to less than 1 × 106. The coatings induced an order of magnitude increase in lifetime for some tests. Scanning electron microscopy, surface profilometry and microhardness tests were used to examine coating morphologies, investigate coating/base material interfaces and demonstrate hardness increases.
A Thermohydrodynamic Analysis of a Twin Axial Groove Bearing Under Different Loading Directions and Comparison With Experiment
Authors: El-Deihi M. K. I. , Gethin D. T.
Published: June 2008

A rigorous thermohydrodynamic analysis of loading direction effects in a cylindrical bore bearing is presented and compared with experimental data. The results show that for good comparison between measured and predicted behavior, careful attention must be paid to thermal boundary condition specification. However, for the types considered, the global performance was not affected markedly. The calculations demonstrate that this bearing type is very sensitive with respect to loading direction and when compared with other work it shows that a rigorous thermohydrodynamic analysis is necessary for accurate prediction of thermal behavior.
Film Thickness, Friction, and Scuffing Failure of Rib/Roller End Contacts in Cylindrical Roller Bearings
Authors: Aramaki H. , Cheng H. S. , Zhu D.
Published: June 2008

The lubrication performance of rib/roller end contacts of cylindrical roller bearings was studied both theoretically and experimentally for end-crowned rollers and inclined ribs. A partial EHL program was used to calculate the film thickness and the friction in the rib/roller end contact. Calculated minimum film thickness shows a strong load dependence although the central film thickness is still a weak function of the load. The influence of the contact position on the film thickness was also investigated for roller skewness and design tolerance. It was found that the contact location affects the minimum film thickness strongly in spite of a weak influence on the central film thickness. Friction and scuffing experiments were conducted on a special rig, which can achieve arbitrary slide/roll ratio to simulate the rib/roller end contacts. Good agreements were found between measured and calculated friction based on the assumption that the lubricant was Newtonian. In scuffing experiments, scuffing propagation was observed on the rib contact surface. The critical load for scuffing is strongly correlated with the sliding velocity. The critical load at high speeds is lower than that at low speeds although the friction at high speeds is lower. These data imply the importance of the contact location and the wear process for film breakdown.
Thermal Non-Newtonian Elastohydrodynamic Lubrication of Line Contacts Under Simple Sliding Conditions
Authors: Wang Shao , Conry T. F. , Cusano C.
Published: June 2008

A computationally simple formulation for the stationary surface temperature is developed to examine the thermal non-Newtonian EHD problem for line contacts under simple sliding conditions. Numerical results obtained are used to develop a formula for a thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for the maximum surface temperature and traction coefficient are also presented. The thermal effects on film thickness and traction are found to be more pronounced for simple sliding than for combined sliding and rolling conditions.
Rolling Element Bearing Fatigue Damage Propagation
Authors: Hoeprich M. R.
Published: June 2008

Rolling element bearing fatigue spalls were propagated for several test conditions well beyond the laboratory criteria of 6.5 square millimeters used in the author’s laboratory. Usually more than one mode of fatigue spall propagation is involved when large spalls develop. The information provided in this paper can be used to gain an appreciation of the total useful life of a bearing and to allow a more accurate diagnosis of fatigue spall damage.