bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of Deformation of Steel Coated With Ceramics in Rolling-Sliding Contact
Authors: Ishikawa Hiromasa , Ishii Hiroshi , Uchida Takeshi
Published: June 2008

The stresses, strains, and deformations produced by repeated, two-dimensional rolling-sliding contacts are analyzed both in the coated layer of ceramics SiC and in the substrate of two types of steels using a finite element method. Rolling and sliding are simulated by translating an appropriate set of normal and tangential surface tractions across the surface of an elastic-plastic model. A peak-pressure to shear-strength ratio of p0/k = 5 and normal to tangential force ratios of T/P = 0.2 are examined. The effect of thickness of the coated layer on the mechanical behavior of the substrate is discussed.
The Effect of Initial Curvature in a Flexible Disk Rotating Near a Flat Plate
Authors: Carpino M.
Published: June 2008

The effect of initial curvature in a disk which is rotated close to a rigid flat plate is analyzed in this paper. When the unconstrained disk is not rotating, it has an initial curvature perpendicular to the axis of rotation. A thin gas film separates the disk from the rigid plate when the disk is rotating. The governing equations for this system are presented and solved.
The Short-Time Compressibility of Elastohydrodynamic Lubricants
Authors: Ramesh K. T.
Published: June 2008

Elastohydrodynamic (EHD) lubricants are subjected to very large pressures (several GPa) for very short times (10−4 seconds) in typical EHD contacts. However, measurements of EHD lubricant compressibilities to date have primarily been made for quasistatic deformations and only for relatively low pressures. This paper presents some experimental results on the variation of the density of the lubricant 5P4E over a very wide range of pressures and over two distinct timescales, from 10−6 seconds to 10−4 seconds. The very short time (10−6 seconds) data are obtained from plate-impact experiments, and the data near 10−4 seconds are obtained with a new experimental technique using the compression Kolsky bar. It is observed that the commonly used Dowson-Higginson relationship represents too stiff a response at the high pressures for these short times, at least for this synthetic lubricant. A full finite deformation analysis of the plate impact problem is used to obtain the material response function for the large compressibilities observed. On the basis of these results, we suggest a new form of the pressure-density relationship for an elastohydrodynamic lubricant that appears to hold over the entire range of pressures and for time durations on the order of those actually occurring in elastohydrodynamic lubrication.
Film Collapse in EHL and Micro-EHL
Authors: Shieh Jinn-an , Hamrock Bernard J.
Published: June 2008

The pressure, film thickness, and streamline patterns within the lubrication conjunction in elastohydrodynamic and microelastohydrodynamic lubrication are presented for various operating parameters. The circular non-Newtonian fluid model was used and periodic stationary surface irregularities were considered. Results obtained from different operating parameters are compared to illustrate the reason why film collapses occur in EHL and micro-EHL problems. Effects of speed, slide-roll ratio, and surface irregularity were studied in establishing when film collapse is more likely to occur. The occurrence of vortices and the location of the stagnation point within the conjunction are shown for the operating parameters considered.
On Mixed Squeeze Films of Infinite Width Plates
Authors: Chengwei Wu
Published: June 2008

A mixed squeeze film model between two rough squeezing plates is established in the present paper. The squeeze behavior in the presence of full and partial fluid film between two rough surfaces is analyzed by using Patir and Cheng’s average flow model and Greenwood and Tripp’s roughness contact model. For one-dimensional squeeze films, transverse and isotropic surface roughness (γ ≤ 1) leads to an increasing squeeze film damping coefficient and a longer sinkage time in comparison with smooth surfaces. But, longitudinal roughness (γ > 1) leads to a decreasing squeeze film damping coefficient and a shorter sinkage time. When the roughness orientation parameter γ is kept constant, increasing roughness amplitude causes an early roughness contact and an increasing contact rigidity.
Micro-Tribological Studies on Fluorinated Carbon Films
Authors: Miyake S. , Kaneko R. , Kikuya Y. , Sugimoto I.
Published: June 2008

Micro-tribology is a key technology in micro-mechanics and the magnetic recording head-media interface. The atomic-scale surface state is very important in micro-tribology. However, the concepts of micro-tribological material design are not clear. The top-surface must be modified to improve micro-tribological properties. To improve adhesion and strength, hard carbon films containing silicon deposited by an electron cyclotron resonance (ECR) plasma depositor are examined for friction and wear using a reciprocating tribometer. Fluorinated silicon-containing films are deposited to reduce atomic-scale wear. Micro-tribological properties of this film are investigated by ultra-low load wear-testing, leading to the following conclusions: (1) The micro-tribological characteristics of silicon-containing carbon film are improved by fluorination. Fluorination decreases the surface energy, evaluated by contact angle to the water, and reduces the micro-wear on an atomic scale. (2) The adhesion to the substrate and the strength of the carbon film are greatly improved by adding small quantities of silicon. These films also have significantly longer lubricating lives.
Non-Newtonian Thermal Elastohydrodynamic Lubrication
Authors: Sui P. C. , Sadeghi F.
Published: June 2008

A numerical solution to the problem of thermal and non-Newtonian fluid model in elastohydrodynamic lubrication is presented. The generalized Reynolds equation was modified by the Eyring rheology model to incorporate the non-Newtonian effects of the fluid. The simultaneous system of modified Reynolds, elasticity and energy equations were numerically solved for the pressure, temperature and film thickness. Results have been presented for loads ranging from W = 7 × 10−5 to W = 2.3 × 10−4 and the speeds ranging from U* = 2 × 10−11 to U* = 6 × 10−11 at various slip conditions. Comparison between the isothermal and thermal non-Newtonian traction force has also been presented.
On The Fluid-Solid Interaction in Reference to Thermoelastohydrodynamic Analysis of Journal Bearings
Authors: Khonsari M. M. , Wang S. H.
Published: June 2008

Thermohydrodynamic analysis of journal bearings is extended to include provisions for the shaft thermal dilation as well as the bush thermoelastic deformation. Numerical solutions using a combination of the finite difference and finite element methods are presented. Comparison of the simulation results with those obtained experimentally yielded satisfactory agreement. It was found that while the shaft and bush thermal expansion and the bush elastic deformation are individually important, the collective effect of these factors must be considered for meaningful end results.
Three-Dimensional Thermoelastic Solutions of Thrust Bearings Using Code Marmac1
Authors: Ettles C. M. , Anderson H. G.
Published: June 2008

The benefits of three-dimensional modeling of thrust bearings are described and illustrated with examples. Data are given for the convection coefficients on the back face of pads and attention is drawn to improvements in bearing performance given by reducing the thermal resistance of pads. The importance of pad support in large bearings is illustrated by a case study in which the size of the support disk is varied. Improved performance can be obtained if the disk is sized correctly. Further improvement is obtained if part of the disk support is cut away.
p-Version Finite Element Analysis of Gas Bearings of Finite Width
Authors: Nguyen S. H.
Published: June 2008

Steady-state compressible isothermal lubrication problems are analyzed by the p-version finite element formulation in conjunction with the Newton-Raphson iteration procedure. Test examples confirm that this is an effective formulation for solving finite width bearing problems, and that, even for high bearing number (Λx > 1000) and coarse mesh situations, numerical solutions are accurate and converge rapidly.
Flow of a Power-Law Fluid in a Rayleigh Step
Authors: Elkouh A. F. , Yang Der-Fa
Published: June 2008

An exact solution of the lubrication equations of motion for flow in a Rayleigh step of infinite width is presented. The fluid is assumed to be incompressible, and the non-Newtonian behavior of the fluid is described by a power-law model. The dimensionless pressure gradient and load capacity are obtained by the solution of a system of six algebraic equations. Optimum dimensions and load capacity for Rayleigh step bearing are presented.
Elasto-Plastic Finite Element Analysis of Repeated Three-Dimensional, Elliptical Rolling Contact With Rail Wheel Properties
Authors: Kulkarni S. M. , Hahn G. T. , Rubin C. A. , Bhargava V.
Published: June 2008

This paper presents an elasto-plastic analysis of the repeated, frictionless, three-dimensional rolling contact similar to the ones produced by the rail-wheel geometry. This paper treats an elliptical contact rolling across a semi-infinite half space. The contact shape and loading: semi-major axis (in the rolling direction), w1 = 8 mm, and semi-minor axis, w2 = 5.88 mm, reflect standard rail and wheel curvatures and a wheel load of 149 KN (33,000 lb). A three-dimensional, elasto-plastic finite element model, developed earlier, is employed together with the elastic-linear-kinematic-hardening-plastic (ELKP) idealization of the cyclic plastic behaviour of a material similar to rail and wheel steels. The calculations present the displacements, the stress-strain distributions, stress-plastic strain histories and the plastic strain ranges in the half-space. The cyclic plasticity approaches a steady state after one contact with further contacts producing open but fully reversed stress-strain hysteresis loops, i.e., plastic shakedown.
A Theory for Dry Wear Based on Energy
Authors: Qiu Xiangjun , Plesha M. E.
Published: June 2008

A model for wear based on energy is developed. The model accounts for the volume of wear material produced during sliding and includes the possibility of debris reattachment to the contact surfaces. Fourier analysis of contact surface geometries allow the model to be transformed from space-variable form to spectral form, which is more convenient for many applications such as implementation in analysis software. As special cases, Archard’s wear law is obtained and an exponential wear model, which currently sees wide use for treatment of sliding wear in dilatant contact problems, is deduced.
Atomic Force Microscopy of Magnetic Rigid Disks and Sliders and Its Applications to Tribology
Authors: Bhushan Bharat , Blackman G. S.
Published: June 2008

Surface topography measurements of magnetic rigid disks and a slider are made using an atomic force microscope (AFM) and a conventional noncontact optical profiler (NOP). The lateral resolution for the surface topographs spans the range of 1 μm down to 2 nm. Topography measurements are used to predict summit statistics and the real area of contact statistics. We find that contact statistics predictions are a strong function of the lateral resolution of the roughness measurement tool. As the magnetic slider comes into contact with the disk surface, the nanoasperities (detected by AFM) plastically deform instantly and subsequently the load is supported by the elastic deformation of microasperities (detected by NOP). AFM also allows the measurements of lubricant-thickness distributions on smooth surfaces. Examples for magnetic disks are presented.
Performance and Stability of a Hybrid Spherical Gas Gyrobearing
Authors: Sela N. M. , Blech J. J.
Published: June 2008

A new spherical Gas Gyrobearing configuration is presented. The static performance is evaluated for general eccentricity, and data is presented for load capacity, gas flow rate and error torque, over a range of eccentricities and gas feed pressures. The dynamic stability of the rotor about an equilibrium point, assuming small perturbations, is analyzed using the step-jump method. Finally, a nonlinear path simulation was performed, by simultaneously solving the Reynolds equation and the rotor’s equations of motion.
On the Maximum Temperature in Double-Layered Journal Bearings
Authors: Khonsari M. M. , Wang S. H.
Published: June 2008

Thermohydrodynamic analysis of a full journal bearing with a realistic model for the bushing made of two distinct layers is presented. The governing equations and an efficient numerical solution technique are discussed. It was found that the maximum bearing temperature is more sensitive to the thermal conductivity of the bearing liner than that of the backing metal. Results are provided for estimating the maximum bearing temperature.
Interrelated Rotordynamic Effects of Cylindrical and Conical Whirl of Annular Seal Rotors
Authors: Baskharone E. A. , Hensel S. J.
Published: June 2008

A comprehensive approach for computing the dynamic coefficients of an annular seal is presented. The coefficients are partly those associated with a uniform lateral eccentricity mode of the rotor (known as the cylindrical whirl mode) and with an angular eccentricity (which gives rise to a conical whirl type). The rotor excitation effects in both cases are treated as interrelated by recognizing the fluid-exerted moments resulting from the lateral eccentricity and the net fluid force resulting from the angular eccentricity. In all cases, the rotor is assumed to undergo a whirling motion around the housing centerline. The computational procedure is a finite-element perturbation model in which the zeroth-order undisplaced-rotor flow solution in the clearance gap is obtained through a Petrov-Galerkin approach. Next, the rotor translational and angular eccentricities, considered to be infinitesimally small, are perceived to cause virtual distortions of varied magnitudes in the finite element assembly which occupies the clearance gap. Perturbations in the flow variables including, in particular, the rotor surface pressure, are then obtained by expanding the finite-element equations in terms of the rotor eccentricity components. The fluid-exerted forces and moments are in this case computed by integration over the rotor surface, and the full matrix of rotordynamic coefficients, in the end, obtained. The computational model is verified against a bulk-flow model for a sample case involving a straight annular seal. Choice of this sample model for validation was made on the basis that no other existing model has yet been expanded to account for the mutual interaction between the cylindrical and conical rotor whirl, which is under focus in this study.
The Flow of Layered Liquid Crystals in a Thin Wedge With Dislocations
Authors: Rhim Y. , Tichy J.
Published: June 2008

The velocity, displacement, and stress field of layered liquid crystals with dislocations in a lubricating gap are investigated numerically. Galerkin’s weighted residual finite element method is employed to solve a set of five highly nonlinear coupled differential equations in terms of two spatial coordinates. In addition to the usual continuity and momentum equations, equations are required for a body force term governing permeation through the layers and elastic displacement of the layers. The last equation contains a fourth derivative term which gives rise to dislocations and numerical complications. The results show a strong increase in load relative to an equivalent viscous lubricant. The load increase depends strongly on the magnitude of a permeation parameter.
A Dynamic System Model for Lubricated Sliding Wear and Running-In
Authors: Hu Y. Z. , Li Na , To̸nder Kristian
Published: June 2008

Running-in should be regarded as a self-adapting and convergent process of a dynamic system. The effect of surface roughness on dynamic behavior of a lubricated sliding wear system has been explored in this paper. With the RMS σ of a composite roughness considered as the characterizing parameter of the mating surfaces, two state equations: the wear equation concerning the effect of roughness and the rate of equation concerning changes in RMS, have been established. The optimum roughness of a wear system corresponding to the minimum wear rate and the equilibrium roughness produced by the running-in, the stability of the wear system and its critical load capacity can be predicted and simulated by this dynamic model.
Some Parameters Affecting Tactile Friction
Authors: Dinc¸ O. S. , Ettles C. M. , Calabrese S. J. , Scarton H. A.
Published: June 2008

The friction of a sliding tactile contact was measured in an apparatus which simulated a keyboard. Results were taken for several materials. The friction coefficient was found to decrease with increasing load and with increasing speed. Experiments at varying humidity and surface roughness helped to define the friction mechanisms. It is concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface. Increased bridging due to higher humidity causes increased friction from viscous shearing effects, while increased roughness allows fewer bridges to form, decreasing the friction.
Measurement of Rotordynamic Coefficients for a Hydrostatic Radial Bearing
Authors: Murphy B. T. , Wagner M. N.
Published: June 2008

Measurement of rotordynamic coefficients is presented for a pair of hydrostatic radial bearings, including direct and cross-coupled stiffness and damping. Two different hydrostatic configurations were tested: (1) an externally fed bearing 74.7 mm (2.95 in.) in diameter with a nominal direct stiffness of approximately 210 MN/m (1.2 million lb/in.) and (2) an internally fed bearing 54.6 mm (2.15 in.) in diameter with a nominal direct stiffness of approximately 88 MN/m (0.5 million lb/in.). Each bearing had 6 equally spaced hydrostatic pressure pockets, stationary for the externally fed bearing and rotating for the internally fed bearing. Also, both bearings had extended exit regions to provide additional damping. The top rotational speed was 22,700 rpm and the maximum axial Reynolds number was 50,000 using a freon derivative, Freon-113, as the working fluid. The test apparatus was a “synchronous rig” as an intentionally eccentric journal was used as the sole source of excitation. Data reduction was done by performing a matrix solution to separate damping from stiffness. Results show the internally fed bearing to be 20 percent less stiff than predicted, and to have a significant amount of damping which agrees well with predictions. The internally fed bearing was found to be approximately 60 percent less stiff than predicted, and to be roughly neutral in terms of damping, as predicted.
On the Thermal Effects in the Design of Tilting-Pad Bearings Subjected to Inlet Pressure Build-Up
Authors: Kim K. W. , Rodkiewicz C. M.
Published: June 2008

The presented analytical consideration of tilting-pad bearings incorporates simultaneously the changes in viscosity (due to viscous dissipation) and in the nonambient inlet pressure (due to momentum depletion within the fore-region). The solution provides the following quantities: film temperature distributions, pressure distribution, maximum temperature of the pad, load capacity, friction force, coordinate of the center of pressure, and coordinate of the pivot point. Comparison with the case when the inlet pressure is assumed to be ambient indicates the significance of the pressure build-up in the fore-region.
Static Characteristics of Magnetized Journal Bearing Lubricated With Ferrofluid
Authors: Zhang Y.
Published: June 2008

The static characteristics of magnetized journal bearing, which is lubricated with ferrofluid, are investigated. The magnetic force acting on the ferrofluid is obtained using a solenoid model for the magnetized bearing. The model suggests that the position of oil film should be located with the positive magnetic force region. In the study we found that the main feature of the magnetic force is the ability to change the size of the cavitation region, and then all the static characteristics. The pressure resulting from the magnetic force should be incorporated into the Reynolds equation and it cannot be separately treated. The study shows that the bearing load increases in the magnetic bearing and the friction coefficient decreases if they are compared with those of a submerged bearing. Due to the symmetrical distribution of the magnetic force and its zero resultant force to the bearing load, a strong magnetic field may have the same effect on the bearing lubrication as a moderate magnetic field does. The paper focuses particularly on how the magnetic force influences bearing cavitation.
Extension of Transonic Flow Computational Concepts in the Analysis of Cavitated Bearings
Authors: Vijayaraghavan D. , Keith T. G. , Brewe D. E.
Published: June 2008

In this paper, an analogy between the mathematical modeling of transonic potential flow and the flow in a cavitating bearing is described. Based on the similarities, characteristics of the cavitated region and jump conditions across the film reformation and rupture fronts are developed using the method of weak solutions. The mathematical analogy is extended by utilizing a few computational concepts of transonic flow to numerically model the cavitating bearing. Methods of shock fitting and shock capturing are discussed. Various procedures used in transonic flow computations are adapted to bearing cavitation applications, e.g., type differencing, grid transformation, an approximate factorization technique, and Newton’s iteration method. These concepts have proved to be successful and have vastly improved the efficiency of numerical modeling of cavitated bearings.
Measurements of Asperity Temperatures of a Read/Write Head Slider Bearing in Hard Magnetic Recording Disks
Authors: Bair S. , Green I. , Bhushan B.
Published: June 2008

An infrared temperature measurement system was used to measure hot spots in a magnetic head rigid disk interface. The system employed the spectral distribution as well as intensity of sampled radiation to determine both the temperature and effective area of microscopic sources at elevated temperature. Flash temperatures between particulate and thin-film rigid disks and a simulated transparent sapphire slider at various operating conditions were measured.
Nonlinear Effects in a Plain Journal Bearing: Part 1—Analytical Study
Authors: Choy F. K. , Braun M. J. , Hu Y.
Published: June 2008

Hydrodynamic/hydrostatic journal bearings have been widely used in various types of high speed rotating machinery. For space applications, the issue of using cryogenic fluids as working lubricants has steadily gained in significance. The primary goal of this paper is to model the nonlinearities that occur in a hydrodynamic journal bearing with both cryogenic and oil lubricants. Results will be examined through bearing fluid film pressure distribution and bearing linear and nonlinear stiffness characteristics. The numerical model that couples a variable property Reynolds equation with the dynamics of the rotor is solved by means of a finite difference solution technique. The procedure for the fluid film pressure solution involves an iterative scheme that solves the Reynolds equation coupled with the equations of state for liquid oxygen (LO2). The pressure curve is then integrated to calculate bearing supporting forces. A two-dimensional Newton-Raphson iteration method is used to locate the journal equilibrium position from which both linear and nonlinear bearing stiffness are evaluated by means of the small perturbation technique. The effects of load on the linear/nonlinear plain journal bearing characteristics are analyzed and presented in a parametric form. The relationship between the accuracy of the linear solution and the various orders (3rd, 5th, and 7th power for ΔX) of the nonlinear approximation are also discussed. The validity of both linear and nonlinear solutions at various distances from the journal equilibrium position is also examined. A complete parametric study on the effects of load, temperature, operating speed, and shaft misalignment will be given in Part 2 of this paper.
Temperature Measurements by Infrared Thermography in the Interface of a Radial Face Seal
Authors: Tournerie B. , Reungoat D. , Frene J.
Published: June 2008

Mechanical seal functioning can be greatly affected by thermal effects and particularly by the coupling of seal face geometry and heat dissipation in the interface. It is necessary to develop new investigation means in order to study accurately such very delicate phenomena. This paper deals with the feasibility of temperature measurements by means of infrared thermography technique. The capabilities of the infrared camera which has been used are examined. A radiation analysis leads to the evaluation of the contributions to the radiant energy received by the camera detector. A first series of results demonstrates clearly the efficiency of the technique. It is shown how the face rotor coning and heat exchanges can be combined in the case of a thermally stable seal operation.
Test Results for Rotordynamic Coefficients of the SSME HPOTP Turbine Interstage Seal With Two Swirl Brakes
Authors: Childs D. W. , Baskharone Erian , Ramsey Christopher
Published: June 2008

Test results are presented for the HPOTP Turbine Interstage Seal with both the current and an alternate, aerodynamically designed, swirl brake. Tests were conducted at speeds out to 16,000 rpm, supply pressures up to 18.3 bars, and the following three inlet-tangential-velocity conditions: (a) no preswirl, (b) intermediate preswirl in the direction of rotation, and (c) high preswirl in the direction of rotation. The back pressure can be controlled independently and was varied to yield the following four pressure ratios: 0.4, 0.45, 0.56, and 0.67. The central and simplest conclusion to be obtained from the test series is that the alternate swirl brake consistently outperforms the current swirl brake in terms of stability performance. The alternate swirl-brake’s whirl-frequency ratio was generally about one half or less than corresponding values for the current design. In many cases, the alternate design yielded negative whirl-frequency-ratio values in comparison to positive values for the current design. The alternate design can be directly substituted into the space currently occupied by the current design. There is no change in leakage performance.
Stability Characteristics of a Journal Bearing Mounted in an Uncentralized Squeeze Film Damper
Authors: Sato Yuichi , Fujino H. , Sakakida H. , Hisa S.
Published: June 2008

This paper describes the stability of a journal bearing mounted in an uncentralized squeeze film damper. It is known that mounting a journal bearing in a centralized squeeze film damper improves the bearing stability. From a practical viewpoint, however, it is difficult to centralize journal bearings which support a heavy rotor, such as a steam turbine. Experimentally, we show that a journal bearing can be stabilized by mounting in an uncentralized squeeze film damper. The effect of clearance of a squeeze film damper is investigated. By using short bearing analysis, rotor trajectories are calculated. Calculated results also shows stability improvement.
Torque of Tapered Roller Bearings
Authors: Zhou R. S. , Hoeprich M. R.
Published: June 2008

An analytic tapered roller bearing torque model is presented along with laboratory test data. Initial results of this proposed model are favorable. An accurate general purpose torque prediction tool could be obtained by extending the concepts presented in conjunction with a more comprehensive analysis of actual bearing operating conditions. By using EHL (Elastohydrodynamic Lubrication) theory and micro-macro contact analysis, the bearing torque can be determined by predicting each torque component for each roller due to raceway rolling, raceway moments due to EHL pressure distribution, and frictional force of rib-roller end contact. The roughness effect of contact surfaces, effect of EHL film thickness parameter (the ratio of film thickness to composite surface roughness), and thermal EHL effects are also included. A bearing torque test rig, which can measure the torque of cup race, cone race, and rib separately, was built and used to provide test data. Good agreement between the experimentally measured bearing torques and the predictions of the new torque model has been obtained. This torque model will provide a greater fundamental understanding and is more versatile over a wide range of operating conditions.
Dynamic Load Capabilities of Active Electromagnetic Bearings
Authors: Bornstein K. R.
Published: June 2008

Magnetic bearings are finding increasing use in a wide range of applications. It is well known that the static capacity of a bearing can be determined by its saturation point. The static capacity has often been the prime criterion for the selection of magnetic bearing size. The dynamic capacity of a bearing is a much more complicated function. This paper will develop equations to express the dynamic load capacity of a magnetic bearing in terms of its amplifier size, the frequency of excitation, the magnetic airgap, the method of force actuation, and certain nondimensional terms.
Re-Examination of Film Rupture Boundary Condition in Hydrodynamic Lubrication Under Inertia Effect
Authors: Mori A. , Mori H.
Published: June 2008

This paper presents discussions on the choice and handling of film rupture boundary conditions for the hydrodynamic lubrication under the effect of lubricant inertia forces. Many researchers have analyzed this inertia effect in converging-diverging hydrodynamic wedge and squeeze films without careful consideration of the problem caused by the film rupture boundary conditions used. To reveal the importance of the problem, the marked difference in pressure distribution produced by the difference in boundary conditions is presented for an infinitely long, steadily loaded, cylindrical journal bearing.
Performance of Air-Lubricated Hydrodynamic Bearing Spindles for Laser Scanners
Authors: Tanaka K. , Muraki H.
Published: June 2008

This paper reports on the performance of air-lubricated bearing spindles for high-speed laser scanners using newly developed bearings. Experimental results confirmed that these spindles have adequate performance including floating stability, endurance, vibration-resistance at high-speeds, and start-stop endurance for laser scanners. These spindles are already mass-produced and used in laser printers and digital color copiers, so their high performance and endurance are proven.
Thermohydrodynamic Performance of a Tilting Pad Journal Bearing With Spot Lubrication
Authors: Tanaka M.
Published: June 2008

A new method of lubricant feeding is presented for tilting pad journal bearing and its effect on the thermohydrodynamic performance of the bearing is investigated theoretically and experimentally for various operating conditions. The new method can significantly reduce the maximum pad temperature compared with conventional methods, and its effect becomes pronounced with the increase in operating shaft speed. The method is promising for high speed journal pad bearing which is rapidly decreasing a safety margin against seizure due to the dangerously rising maximum pad temperature.
Modeling of Temperatures in the Conjunction of a Vapor-Lubricated Four-Ball Wear Tester
Authors: Hsu C. J. , Duda J. L. , Klaus E. E.
Published: June 2008

Recent studies have shown that solid films formed from vapor-delivered lubricants can provide effective lubrication for load-bearing systems at elevated temperatures. A model is developed to describe the processes occurring in the conjunction between two load-bearing surfaces which are being lubricated by a film deposited from a vapor phase. This analysis combines models of the chemical kinetics of the deposition process and the wear process under ideal conditions in which all the wear is due to the reaction of the lubricant vapor with this surface material. The analysis is applied to the case of 1/2 in. M50 steel ball bearings being lubricated in a four-ball wear tester by a vapor at 370°C containing 0.5 mole percent tricresyl phosphate in a nitrogen carrier gas. Under conditions of 600 rpm and a 10 kg load, the analysis indicates that the temperature in the conjunction is 540°C. This analysis elucidates the coupled processes which take place during vapor-deposited lubrication at elevated temperatures.
Some Factors Affecting the Design of Spring Supported Thrust Bearings in Hydroelectric Generators
Authors: Ettles C. M.
Published: June 2008

A size effect exists for thrust bearings, requiring increasing attention to the control of deformation as the size is increased. One method of controlling deformation is to mount the pad on a set of closely packed springs. The extent (or proportional area) of spring support is important for thin pads. Support over the whole back face of the pad causes a concavity due to elastic deformation. The bearing must then run sufficiently hot so that this is countered by thermal deformation, which always acts to produce a convexity. The effects on performance of pad thickness, the thermal gradient in the pad and the extent and pattern of the springs is described. Two case studies are presented using a 3-D thermoelastic analysis. The use of comparatively thick pads is recommended.
Hydrodynamic Thrust Bearings: Theory and Experiment
Authors: Tieu A. K.
Published: June 2008

In this paper results from experimental studies and computer simulation of hydro-dynamic tilting thrust bearings are presented. The bearing performance in terms of outlet film thickness, friction coefficient, and bearing temperature was measured in a high speed thrust bearing test rig. The numerical simulation involves the solution of the generalized Reynolds equation and the energy equation, which considers thermal effects on the oil viscosity and the squeezing of the oil film.
Performance Characteristics of Compliant Journal Bearings
Authors: Lin C. R. , Rylander H. G.
Published: June 2008

This investigation of compliant journal bearings is directed toward the fundamental behavior characteristics which are necessary when compliance is factored into the final design. Analytical determintation of performance characteristics are shown as a function of the bearing flexibility. As the deformation coefficient increases, load capacity decreases, the cavitation angle and friction coefficient increase, attitude angle may increase or decrease, stability is improved for attitude angles less than 0.8, and minimum film thickness will occur near the two sides of the bearing.
Subsurface Stresses in Micro-EHL Line Contacts
Authors: Elsharkawy A. A. , Hamrock B. J.
Published: June 2008

The circular non-Newtonian fluid model associated with a limiting shear strength and the system approach were used to calculate the pressure, surface shear stress, and film thickness profiles in an elastohydrodynamically lubricated conjunction under isothermal conditions. The calculated pressure and surface shear stress were used to evaluate the maximum shear stress and the von Mises equivalent stress distributions in the solids. The effect of the slide-roll ratio for smooth lubricated surfaces, the effect of a single moving irregularity located on one of the smooth lubricated surfaces, and the effect of the amplitude and wavelength of a stationary sinusoidal wavy surface on the pressure, surface shear stress, and film thickness profiles, and hence on the subsurface stress pattern in the solids, were studied.
Hydrodynamic Lubrication in Axisymmetric Stretch Forming—Part 1: Theoretical Analysis
Authors: Wilson W. R. D. , Hector L. G.
Published: June 2008

An improved theoretical model for the hydrodynamic lubrication of axisymmetric, sheet metal stretch forming is presented. The infinite initial film thickness problem, encountered in a previous model, is removed by accounting for the squeeze action occurring during the initial stages of the process. Both isoviscous and thermoviscous theories are developed assuming that the lubricant is a Newtonian fluid. In the thermoviscous model, the lubricant viscosity is assumed to vary exponentially with temperature. The influence of plastic heating of the sheet on the entrainment and transport of the lubricant film is examined. The effects of variable punch speed are also investigated.
Hydrodynamic Lubrication in Axisymmetric Stretch Forming—Part 2: Experimental Investigation
Authors: Hector L. G. , Wilson W. R. D.
Published: June 2008

In order to test the validity of the theoretical model discussed in Part 1, an experimental technique, employing optical interferometry, has been developed to measure lubricant film thickness during axisymmetric stretch forming. Specially fabricated, transparent punches are used for both double and multiple beam interference studies. The choice of workpiece material, lubricant, and forming speed ensures that the punch/sheet conjunction will be hydrodynamically lubricated during most of the process. Interference patterns, due to the variable film of lubricant separating the punch and sheet surfaces, are formed as the sheet wraps around the punch. These patterns provide a contour map of the lubricant film thickness along the punch/sheet conjunction. The measured film thickness, as taken from an interpretation of the patterns, is compared with the theoretical predictions of Part 1.
Prediction of Bulk Moduli for Mineral Oil Based Lubricants, Polymer Solutions, and Several Classes of Synthetic Fluids
Authors: Song H. S. , Klaus E. E. , Duda J. L.
Published: June 2008

This study involves the development of correlating equations for the prediction of the bulk moduli of mineral oil-based lubricants, polymer containing lubricants, and several classes of synthetic fluids including methyl silicones, perfluoropolyether, polybutenes, poly α-olefin, polyphenyl ethers, and esters. This technique only requires the viscosity, the density, and deviation factor which is related to structural effects and free volumes of the fluids. Although prediction techniques are available in the literature for mineral oils, this is the first study to consider the predictions of the bulk moduli of polymer solutions and nonmineral oil based fluids.
Friction in a Cone Clutch and in a Friction Drive With Wedge-Type Bodies
Authors: Vyrabov R. V.
Published: June 2008

Mathematical relationships obtained on the basis of the friction theory in a wedge pair are widely used in technical calculations. With the help of them the limit circumferential force in cone clutches and friction drives with wedge-type bodies (wedge roller transmissions, variable-speed friction block belt drives, V-belt transmissions and etc.) are determined. This may seem to be a simple problem which could be solved without difficulties, however the classical equations used can not be derived in stringent terms and was not confirmed experimentally. The aim of this paper is to clarify this problem.
Tribochemical Effects of Various Gases and Water Vapor on Thin Film Magnetic Disks With Carbon Overcoats
Authors: Strom B. D. , Bogy D. B. , Bhatia C. S. , Bhushan B.
Published: June 2008

Friction tests on thin film magnetic disks with carbon overcoats were performed using commercial read/write heads as sliders. The results provide evidence that the thin film overcoats wear through chemical means in the presence of gaseous oxygen, and through mechanical means in the absence of oxygen. When small concentrations of water are present, friction behavior resembling that of an oxidizing environment is observed, suggesting oxidation of the carbon film preceded by dissociation of adsorbed water.
Analysis of Variable Fluid Properties, Turbulent Annular Seals
Authors: San Andres Luis A.
Published: June 2008

A computational analysis for calculation of the dynamic force response in turbulent flow annular pressure seals of arbitrary nonuniform clearance is presented. Cryogenic liquids are considered as barotropic. The fluid motion is described by a bulk flow model and Moody’s friction factor is introduced to accomodate surface roughness effects. The numerical solution scheme is computationally efficient and accurate for seal operation at arbitrary eccentricity ratios. Numerical predictions show good agreement with available experimental results. The effects of eccentricity and liquid properties on the performance of the Space Shuttle Main Engine High Pressure Fuel Turbopump interstage seal at full power level are discussed as a reference case.
A Surface Pitting Life Model for Spur Gears: Part I—Life Prediction
Authors: Blake J. W. , Cheng H. S.
Published: June 2008

Surface pitting is a major failure mode for gears. Estimation of failure probability and service life are important in gear design. Current techniques give only a pass/fail rating based on semi-empirical methods. A predictive model for estimating service lives and failure probabilities has been developed. This paper discusses the life prediction analysis, which is based on propagation of a surface breaking crack under rolling/sliding contact conditions. The effects of both surface roughness and non-metallic inclusions can be included. While predicted lives are lower than expected, trends observed through parametric variation are consistent with service behavior.
A Surface Pitting Life Model for Spur Gears: Part II—Failure Probability Prediction
Authors: Blake J. W. , Cheng H. S.
Published: June 2008

A predictive pitting model for estimating failure probabilities and service lives has been developed. This paper presents the failure probability analysis and a discussion of the model’s application to spur gears. Probability estimates are based on an initial crack size distribution and on possible interaction between cracks and inclusions. Plots of the fraction of components experiencing pitting (percent) versus life show less spread than would be expected. However, trends predicted based on parametric variation are consistent with service behavior. The model is applied by linking the pitting model with a spur gear performance code. Results are compared with AGMA standards.
Experimental Investigation of a New Concept Viscous Pump
Authors: Green I. , Mainland M. , Etsion I.
Published: June 2008

A new concept viscous pump that was described earlier in the literature was built and tested to evaluate its performance. It was found that the new concept is feasible and has promising features for use in various applications where high level of cleanliness is required. The pressure-flow characteristic is linear with an easy and accurate flow control which can be attractive in metering pumps.
Effect of Roughness and Sliding Friction on Contact Stresses
Authors: Bailey D. M. , Sayles R. S.
Published: June 2008

The stress distributions associated with smooth surfaces in contact are rarely experienced in practice. Factors such as surface roughness, lubricant films, and third body particulates are known to influence the state of stress and the resulting rolling contact fatigue life. This paper describes a numerical technique for evaluating the complete subsurface field of stress resulting from the elastic contact of nonconforming rough bodies, based on measurements of their profile. The effect of sliding friction is included. The presence of asperities within the contact region gives rise to high shear stresses near the surface. Realistic coefficients of friction for lubricated sliding contacts (i.e., μ ≈ 0.1) causes the “smooth body” shear stresses to interact with the asperity stresses to produce a large, highly stressed region exposed to the surface. The significance of these near-surface stresses is discussed in relation to modes of surface distress which lead to eventual failure of the contacting surfaces.
Modeling the Flying Characteristics of a Rough Magnetic Head Over a Rough Rigid-Disk Surface
Authors: Crone R. M. , Jhon M. S. , Bhushan B. , Karis T. E.
Published: June 2008

The volumetric information storage density of rigid disk drives continues to increase through decreases in the slider-disk separation (i.e., the flying height). Reductions in slider-disk separations are achieved primarily through smoother surfaces on the magnetic media. The limiting factor in decreasing the slider-disk separation is the interactions that occur between the slider and the diminishing surface roughness and the impact that this roughness has on the transient and steady-state flying characteristics of the recording head. In this paper, we present a new finite element algorithm to solve the modified Reynolds equation that is specifically designed to utilize state of the art vector/parallel hardware. To the authors’ knowledge, this is the first numerical simulation of the flying characteristics of a finite width slider over a rigid disk surface which directly incorporates three-dimensional surface roughness. The effects that the magnitude, orientation, shape, and location (i.e., roughness on the disk or slider) of the surface roughness has on the steady-state slider flying characteristics are presented.
An Appraisal of a Proposed Active Squeeze Film Damper
Authors: Mu C. , Darling J. , Burrows C. R.
Published: June 2008

A theoretical model for an active squeeze film damper (SFD) is introduced. The design makes it possible to change the radial clearance and land length of the SFD by adjusting the position of the damper ring. Expressions for the oil film forces are obtained. The vibration control of a flexible rotor is taken as an example of the application of the new design. The possibility of controlling rotor vibrations is demonstrated by means of numerical experiments.
A Study of the Relative Surface Conformity Between Two Surfaces in Sliding Contact
Authors: Wang Fu-Xing , Lacey P. , Gates R. S. , Hsu S. M.
Published: June 2008

The surface roughnesses of two surfaces in a wear contact can change throughout the course of the wear process. This may or may not change the lubrication mechanism of the system depending on the real area of contact as influenced by the changes in the surface roughness. The present work examines the changes in surface roughness within the contact area, as well as the relative mating of the two surfaces. To quantify the similarity between the two wear surfaces, a new concept, the relative surface conformity, has been defined and developed. To effectively measure this parameter, a computer program was written to input the wear scar profilometry traces and to calculate the relative surface conformity of the two. Finally, the relative surface conformity was shown to rise with increasing test duration, during running in.
Theoretical Evaluation of Capacitance, Capacitive Reactance, Resistance and Their Effects on Performance of Hydrodynamic Journal Bearings
Authors: Prashad H.
Published: June 2008

A theoretical approach is developed to determine capacitance, capacitive reactance, active resistance, and impedance of hydrodynamic journal bearings under different conditions of operation. It has been established that the bearing capacitance increases with eccentricity and L/D ratios but reduces with increase in clearance ratio. On the contrary, resistance and capacitive reactance of a bearing increase with the clearance ratio but reduce with increase in the eccentricity and L/D ratios. However, the bearing impedance is more affected by the resistance than the capacitive reactance. The bearing behaves like a capacitor till the ratio of capacitive reactance to active resistance is less than unity, and acts like a variable resistor as this ratio exceeds unity. This analysis has a potential to analysis safe load carrying capacity at different speeds of operation by determining the bearing capacitance. Also, this may act as a guide to select the bearing design parameters for safe and reliable operation of a hydrodynamic journal bearing.