bluuebunny/crossref_metadata_2025 huggingface dataset:
The High Shear Stress Rheology of Liquid Lubricants at Pressures of 2 to 200 MPa
Authors: Bair S. , Winer W. O.
Published: June 2008

The steady shear flow characteristics of two liquid lubricants were measured in a new rheometer at shear stresses to 10 MPa. All measurements were performed well below the glass transition pressure. Both Newtonian and rate-independent (limiting shear stress) behaivor was observed.
Test Results for Turbulent Annular Seals, Using Smooth Rotors and Helically Grooved Stators
Authors: Childs D. W. , Nolan S. A. , Kilgore J. J.
Published: June 2008

Test results, consisting of leakage data, friction factors, and rotordynamic force coefficients, are presented for seven annular seals using smooth rotors and helically-grooved stators. All seals have the same nominal clearances and groove depths. The helix angles vary from zero (circumferential grooving) to 70 deg. The number of grooves and the leakage rates increase steadily with increasing helix angles. Helically-grooved stators leak more than smooth seals for helix angles greater than 30 deg. The effective direct stiffness of the seals first decreases and then increases with increasing helix angles. Contrary to theoretical predictions (Kim and Childs 1987), the effective net damping was relatively insensitive to changes in the helix angles.
A Theory of Thermo-Elastohydrodynamic Lubrication of Liquid-Solid Lubricated Cylinders
Authors: Khonsari M. M. , Wang S. H. , Qi Y. L.
Published: June 2008

The purpose of this research is to extend the theory of the concentrated thermo-elastohydrodynamic line contact to include the influence of the existence of solid lubricant dispersed in liquid-base lubricant. The combined effects of the rheological characteristics of the oil and the mechanical properties of the particles and those of the bounding surfaces are taken into consideration in theoretical development. Results are presented for the pressure distribution, the oil film thickness, the temperature rise, and the coefficient of friction for two commonly used solid lubricants namely MOS2 and graphite.
A Continuous Boiling Model for Face Seals
Authors: Yasuna J. A. , Hughes W. F.
Published: June 2008

Mechanical face seals with phase change have extensive engineering applications, yet little theory exists to predict dynamic and thermodynamic behavior. At present, numerical solutions exist for two operating extremes—for low leakage laminar flow where boiling is assumed to occur discretely, and for high leakage, turbulent adiabatic flow. A model is presented herein which allows for continuous boiling, and considers thermal convection effects in laminar flow. Sample calculations and results are compared to the discrete boiling model, and as leakage increases and convection effects become more important boiling may occur over a large portion of the seal face. It is shown that contrary to the discrete boiling model, there may exist a narrow range of stable or bistable operation even when saturation conditions exist near the seal inlet. Instability will invariably occur however if the seal is sufficiently perturbed. This analysis is intended to explain some of the anomalous behavior observed in typical sealing applications, and to act as a guide for experimental verification.
Compatibility Between Tool Materials and Workpiece in Sheet-Metal Ironing Process
Authors: Dohda K. , Kawai N.
Published: June 2008

To assess the tool-workpiece compatibility in metal forming, a friction test is carried out on a strip-ironing type tribometer, which can estimate quantitatively the effect of new surface generation during the process and sliding travel on galling. The workpiece is mild steel and the die materials are tool steels of various kinds, cemented carbide, ceramics, and surface treated steels. The compatibility is estimated through examination of the frictional characteristics, observation of the frictional surface, and the surface appearance of products. The effect of lubricants on compatibility is also examined.
Transfer of Aluminum to Steel in Sliding Contact: Effects of Lubricant
Authors: Nautiyal P. C. , Schey J. A.
Published: June 2008

The mechanism of metal transfer was investigated in twist-compression experiments with 6061-T6 aluminum specimens rotating against hardened steel anvils. Mineral oils of 4.5, 30 and 284 mm2/s viscosity at 38 C were used neat and with fatty acids, alcohols, and P and CI EP additives. Even though the initial squeeze films disappeared, sooner with the light oil and later with the heavier oil, the oils limited metal transfer and retransfer and gave a steady-state friction value of 0.2. The heaviest oil maintained a fluid film with a friction value of 0.03 and restricted metal transfer to a thin patchy coating in the valleys of the lapped anvil surface. Some additives limited metal transfer even with the lighter oils. It appeared that stearic acid and stearyl alcohol were effective in reducing friction and metal transfer by forming a boundary film, enhanced in the case of the alcohol by the formation of a gel-like layer. A chlorine-rich aluminum compound formed with chlorinated paraffin.
The Determination of Squeeze Film Dynamic Coefficients From Transient Two-Dimensional Experimental Data
Authors: Roberts J. B. , Ellis J. , Hosseini Sianaki A.
Published: June 2008

A state variable filter (SVF) method of identifying parameters in lumped-parameter systems is extended to accommodate multi-degree-of-freedom problems. The method is computationally efficient and can be used with both transient and forced squeeze-film response data. In this paper the method is successfully applied to the analysis of transient simulated data both with and without signal noise. Finally the method is shown applied in the analysis of two-dimensional transient experimental data from a squeeze-film bearing rig. The identified results for the dynamic film coefficients compare well with results from earlier single-degree-of-freedom experimental trials.
Sliding Failure Model for Magnetic Head-Disk Interface
Authors: Engel P. A. , Bhushan B.
Published: June 2008

A mechanical model is presented for the “time to failure” of a sliding magnetic head-disk interface system. The principal physical variables include the sliding speed, surface topography, elastic mechanical properties, coefficient of friction, and wear rate. Surface protrusions, such as asperities and debris particles, induce impact and sliding encounters which represent a damage rate. Failure occurs when a specific damage rate, a characteristic for the system, is reached. Modeling uses a set of topographic parameters describing the changing, wearing surface.
Thermomechanical Behavior of Multilayered Media: Results
Authors: Leroy J. M. , Floquet A. , Villechaise B.
Published: June 2008

To study the thermoelastic behavior of coatings a two-dimensional model of a finite thickness layered medium submitted to a moving heat flux was presented in a previous paper (Leroy, Floquet, and Villechaise, 1989). The influence of thin coatings with variable properties or thicknesses on the temperature and stress fields is studied here. These results show that important stresses occur in a coating whose properties differ from those of the substrate, even for low temperature rises.
On Friction of Ploughing by Rigid Asperities in the Presence of Straining—Upper Bound Method
Authors: Azarkhin A. , Richmond O.
Published: June 2008

Upper bound applications traditionally assume that a rigid/perfectly-plastic material moves by rigid blocks, creating discontinuities of velocity at the interfaces between the blocks. In the present version, the elements (blocks) are plastically deformable and there are no velocity discontinuities between adjacent sides. Since this modification incorporates major features of finite element representation employing arbitrary cells, it allows the use of many parameters for minimization, thus achieving high accuracy. On the other hand, it retains the advantage of upper bound techniques in that the incremental procedure for loading is not necessary, and the results for steady processes are obtained directly. Some energy statements for combined loading are derived and a technique for calculating the ploughing force is presented. Examples for a single fully embedded rigid pyramid and a periodic array of asperities ploughing through the rigid/perfectly plastic material in the presence of subsurface straining are given. The friction factor decreased as the rate of subsurface straining increased, as the pyramid angle of the asperities increased, and as the distance between asperities increased.
Thermal Elastohydrodynamic Lubrication of Rough Surfaces
Authors: Sadeghi F. , Sui Ping C.
Published: June 2008

A numerical solution to the problem of thermal and compressible elastohydrodynamic (EHD) lubrication of rolling/sliding rough surfaces was obtained by neglecting the transient effects. The technique involves the simultaneous solution of thermal Reynolds and modified elasticity equations using the Newton-Raphson technique, and the energy equation using the control volume finite element method. The effects of various loads, amplitude of asperity, and radius of curvature of asperity have been investigated. Results have been presented for moderate dimensionless load of W = 9.03 × 10−5 to heavy load of W = 2.3 × 10−4 at the speed of U* = 9.2 × 10−11. The results indicate that surface roughness significantly affect the pressure, temperature, and traction in EHD lubrication.
Cavitation and Air Entrainment Effects on the Response of Squeeze Film Supported Rotors
Authors: Zeidan F. , Vance J.
Published: June 2008

This paper analyzes the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors. The fluid film force coefficients are obtained from experimental measurements corresponding to a wide spectrum of operating conditions. These conditions include regimes in which air entrainment effects are dominant. Other conditions where vapor cavitation and fluid inertial effects are dominant are included for comparison. The effects of air entrainment are shown to produce a nonlinear response representative of a softening spring effect not previously known to exist in squeeze film dampers.
On Stick-Slip and the Velocity Dependence of Friction at Low Speeds
Authors: Gao C. , Kuhlmann-Wilsdorf D.
Published: June 2008

Stick-slip is commonly ascribed to a difference between the static and dynamic coefficients of friction or at the least a strong negative slope of the friction/velocity curve at very small relative speeds. Other types of variable sliding have been ascribed to irregularities in local friction coefficients, to the excitation of resonance frequencies in oscillatory systems, and to local heating at contact spots. In the course of ongoing studies of metal-metal friction and contact resistance in the hoop apparatus, stick-slip, smooth sliding, somewhat disturbed harmonic oscillations, and a novel type of sliding dubbed “negative stick slip” have been examined. The coefficient of friction (μ) is again found to drop with decreasing ambient pressure, and the velocity dependence of μ determined directly from smooth sliding in vacuum shows an unexpected steep rise at low velocities. Both of these observations are in contradiction with the adhesive model of wear. Negative stick-slip suggests a still more complex μ(νrel) dependence which, however, appears to be compatible with the measurements. At any rate, negative stick-slip cannot be explained by any previously proposed models.
A Procedure for Evaluating the Friction Properties of Hertzian Contacts Under Reciprocating Sliding Motion
Authors: Othman M. O. , Seireg A.
Published: June 2008

The study reported in this paper presents an empirical procedure for evaluating the frictional properties in Hertzian contacts subjected to sinusoidal sliding motion. It utilizes the friction induced lateral vibration of a rod to evaluate the parameters of the frictional function using a gradient search which minimize the error between the analytical response and the friction-induced experimental vibrations. The use of sinusoidal sliding motion at the resonant frequencies of the vibrating rod is found to considerably minimize the effect of external vibrations on the experimental results.
Additional Test Results for Round-Hole-Pattern Damper Seals: Leakage, Friction Factors, and Rotordynamic Force Coefficients
Authors: Childs D. W. , Nolan S. A. , Kilgore J. J.
Published: June 2008

Test results are presented for round-hole-pattern damper seals at Reynolds numbers on the order of 90,000 to 250,000. The seals have roughened stators; Cr/R = 0.0075 and L/D = 1/2. The fluid CBrF3 entering the test seals has no intentional prerotation, i.e., the fluid is injected radially into the apparatus. There is no tangential injection; and no “slinger” is provided upstream of the seals. Test results consist of leakage rates, axial pressure gradients, friction factors, and rotordynamic-force coefficients. The hole-pattern-stator seals leak approximately one third less than smooth seals at the same clearances, have approximately the same damping performance, and about 20 percent lower stiffness values. Unlike earlier tests (Childs and Kim, 1986), variations in hole depth to radial clearance ratios h/Cr showed no clear optimum with respect to damping. Increasing the ratio of hole area to surface area from 0.27 to 0.34 to 0.42 showed no damping change, in moving from 0.27 to 0.34, but a substantial drop in moving from 0.34 to 0.42. Measured friction factors showed serious deviations from the assumed Blasius friction-factor model for wall-shear stress for some stators, particularly in regard to speed dependency. Despite these deviations, theoretical predictions based on measured friction factors are generally reasonable. Direct stiffness predictions are generally within 20 percent. Damping predictions are generally within 5 percent.
Stratified Two-Phase Flow in Annular Seals
Authors: Beatty P. A. , Hughes W. F.
Published: June 2008

A new mathematical theory for the analysis of leakage rate behavior of annular shaft seals operating in the two-phase regime is presented which is based on the stratified flow of the boiling liquid and vapor phases. The flow is presumed to be axisymmetric, steady, and so rapid as to be turbulent. A set of governing equations for film-averaged liquid and vapor properties is developed. The streams are assumed to be adiabatic and moving at different average velocities. Effects of heat generation due to viscous dissipation and of interfacial mass transfer are accounted for fully. The methods of calculation for leakage under choked and unchoked conditions are explained. Many numerical results of leakage rate calculations for cryogenic oxygen are presented and are compared to corresponding results from a homogeneous-equilibrium flow model. Parametric studies show that leakage is fairly insensitive to the arrangement of the liquid and vapor phases within the seal.
Thermoelastic Contact Between a Rolling Rigid Indenter and a Damaged Elastic Body
Authors: Goshima T. , Keer L. M.
Published: June 2008

The two-dimensional thermoelastic contact problem of a rolling, rigid cylinder on an elastic half space containing a surface-breaking crack is solved using complex variable techniques. The effects of heat generation and friction between the cylinder and half space and of friction and heat transfer on the faces of the crack are considered. The problem is reduced to a pair of singular integral equations which are solved numerically. Numerical results are obtained when the loading is a Hertzian distributed heat input. By consideration of combinations of parameters, stress intensity factors for which the crack is likely to grow are shown.
Micro-EHL in Lubricated Concentrated Contacts
Authors: Schipper D. J. , Vroegop P. H. , de Gee A. W. J. , Bosma R.
Published: June 2008

In sliding friction experiments, performed with lubricated concentrated contacts macroscopically operating in the lubricants’ liquid-state regime, the existence of micro-EHL has been shown. With the measuring method used, the lubricants’ limiting shear stress τ1 or the ratio of the limiting shear stress with pressure, τ1/p, can easily be obtained.
Variational Formulations and Finite Element Algorithms for Cavitation Problems
Authors: Bayada G. , Chambat M. , El Alaoui M.
Published: June 2008

In this paper gaseous cavitation in steady-state and transient lubrication problems is considered. Both conventional numerical procedures, associated with the Reynolds cavitation model, and a new finite element analysis for implementation of the Jakobson-Floberg model are presented. Applications to circumferentially supplied bearings and to seals are given.
Dynamic Behavior of Unbalanced Rigid Shaft Supported on Turbulent Journal Bearings—Theory and Experiment
Authors: Hashimoto H. , Wada S.
Published: June 2008

In this paper, the combined effects of turbulence and fluid film inertia on the dynamic behavior of an unbalanced rigid shaft supported horizontally on two identical aligned short journal bearings are investigated theoretically and experimentally. Utilizing analytical expressions for the dynamic fluid film force components considering the effects of turbulence and fluid film inertia, the nonlinear equations of motion for the rotor-bearing systems are solved by the improved Euler’s forward integration method. The journal center trajectories with unbalance eccentricity ratio of εμ = 0, 0.1 and 0.2 are examined theoretically for Reynolds number of Re = 2750, 4580, and 5500, and the theoretical results are compared with experimental results. From the theoretical and experimental results, it was found that the fluid film inertia improves the stability of unbalanced rigid shaft under certain operating conditions.
The Optimum Groove Geometry for Spiral Groove Viscous Pumps
Authors: Sato Yuichi , Ono Kyosuke , Iwama Akihiko
Published: June 2008

The optimum geometries of disk and cylindrical sprial groove viscous pumps to provide the maximum pressure or flow rate are investigated theoretically. The geometrical design parameters, such as the groove angle, groove to ridge clearance ratio, groove width ratio and ridge clearance ratio, are considered as functions of meridional coordinate. Results are obtained from the solution of a differential equation for the smoothed overall pressure distribution of a spiral groove viscous pump. It is found that outflow rate increases with the increase of groove to ridge clearance ratio λ, and that for each value of λ there exist “optimum” values of groove angle and groove width ratio, which give a maximum outflow rate. However, the increase of λ decreases the ridge clearance.
The Viscous Behavior of Polymer Modified Lubricating Oils Over a Broad Range of Temperature and Shear Rate
Authors: Wu C. S. Peter , Melodick T. , Lin S. C. , Duda J. L. , Klaus E. E.
Published: June 2008

A high-shear capillary viscometer was used to determine the viscosity of mineral oil lubricants containing an olefin copolymer up to shear rates of a million reciprocal seconds. Comprehensive measurements were conducted for a range of polymer concentrations from 1–3 wt percent polymer and a temperature range of 38–120° C. The experimental technique utilizes a theoretical analysis procedure to handle the complications associated with viscous heating, the influence of pressure on the viscosity, and the excess pressure drop which occur at the entrance and exit of the capillary. The viscosity of the polymer solutions is determined over the complete range of shear rate starting from the lower Newtonian limit, through the shear-thinning region, and finally, the Newtonian behavior at high shear rates. It is shown that the standard ASTM plot for viscosity-temperature behavior can be used to correlate the viscous behavior for a given polymer concentration over this broad range of shear rates and shear stresses.
Determination of Cone Bore Growth Due to Microstructural Changes
Authors: Neu R. W. , Sehitoglu Huseyin
Published: June 2008

A finite element analysis is used to model cone bore growth in a railroad bearing. Factors which influence the growth and profile of the cone include (a) the initial interference fit between the cone and axle journal, (b) the axial restraint from the torqued cap screws, and (c) a microstructural change in the cone. The primary microstructural change is a transformation of retained austenite to martensite, resulting in a volume expansion. In the model transformation of retained austenite occurred under the raceway of the cone where high contact stresses are located. The analysis shows that the bore profile becomes concave, which in turn does not allow for uniform interface forces between the cone and axle journal. It is shown that with sufficient microstructural change, the initial interference fit is overcome along part of the cone/journal contact, producing a gap between the cone and axle journal. Increasing the initial interference fit reduces the possibility of this gap from developing.
Analysis of Cylindrical Journal Bearing With Viscoelastic Bush
Authors: Zhang Z. , Jiang X.
Published: June 2008

Stationarily loaded cylindrical journal bearings with viscoelastic deformable bearing bush is analyzed in this paper. FEM is used to calculate the deformation of bush induced by the pressure of the oil film, which is in its turn influenced by this deformation causing an increment of the oil film thickness. The simultaneous solution of distributions of oil film pressure and thickness is used to obtain the static performances of the bearing. In the analysis of dynamic behavior of the system under small harmonic vibrations, the effect of linear viscoelastic dynamic deformation of bush is taken into consideration. The frequency method is used to obtain the distributions of the derivatives of complex amplitudes of dynamic pressure increment in the oil film with respect to amplitudes of variation of journal eccentricity and attitude angle, and the simultaneously coexisting distributions of derivatives of dynamic deformation amplitudes with respect to the same, wherefrom the linear dynamic coefficients of the viscoelastically supported oil film are obtained. Unbalance response properties and stability threshold speeds of the rotor-bearing system are calculated. Numerical results enable conclusions to be made that suitable viscoelastic property of the bush will effectively improve the dynamic behavior, both in unbalance response and stability.
Observation of Wall Slip in Elastohydrodynamic Lubrication
Authors: Kaneta M. , Nishikawa H. , Kameishi K.
Published: June 2008

A new experimental technique using optical interferometry has been developed to obtain a direct indication of non-Newtonian response of an oil film under conditions of elastohydrodynamic (EHD) lubrication. A glass disk or a steel ball has been driven by a stepping motor so that crescent-shaped thick oil films with undulation in thickness along the direction of motion have been generated. The experiments have been carried out under pure rolling and pure sliding conditions. It has been found that the oil in an EHD contact behaves like a solid and slips at or near the contact surfaces.
Fatigue Failure of Gears of Circular-Arc Tooth-Profile
Authors: Attia Awny Y. , El-Bahloul Ahmed M. M.
Published: June 2008

The paper embodies results and analysis of an experimental investigation carried out to study fatigue failures of a relatively new type of gearing having teeth of circular-arc profiles. Twenty-one pairs of gears having different helix angles but of the same overlap ratio were tested in a power circulating gear test rig lubricated by oils of different viscosities, running at different speeds and transmitting power exerting constant normal tooth load of 21 KN. Results show that fatigue crack was initiated on the tooth surface at the start of the zone of single contact and propagated to the tooth back till part of or all the tooth was broken. Curves representing fatigue life and its changes with helix angle, oil viscosity and speed are presented and discussed.
Approximate Analysis of Penetration of a Cylindrical Roller Into a Thin Elastic Coating
Authors: Gwo Tsung-Ju , Lardner Thomas J.
Published: June 2008

An approximate analytical solution to the problem of two-dimensional indentation of a frictionless cylinder into a thin elastic coating bonded to a rigid substrate has been obtained using the approach introduced by Matthewson for axisymmetric indentation. We show by comparing the results of the approximate solution to the exact solutions and to finite element calculations that the approximate solution is accurate for a/h> 2. The advantage of this approach is that the results are expressed in closed form and the accuracy of the approximate solution improves with increasing values of a/h. For a/h>2, for a given load, the theory overestimates the value of a/h compared to the exact solution by less than 10 percent. In many experimental studies and in preliminary design, it is convenient to have closed-form solutions exhibiting the dependence of the parameters.
Wear Process Description Based on Acoustic Emission
Authors: Klamecki B. E. , Hanchi J.
Published: June 2008

Since acoustic emissions are generated by fundamental mechanical processes, they can provide insight into the basic processes which determine friction and wear behavior. Descriptions of acoustic emission generated by plastic deformation and fracture were developed, and wear tests were performed, during which acoustic emission activity was measured. This work demonstrates that acoustic emissions can be used to track the wear process in terms of the energy dissipation mechanisms acting. The results show that acoustic emission count rate and amplitude distribution correspond to wear rate and that the amplitude distribution also indicates the active processes contributing to wear.
A Circular Non-Newtonian Fluid Model: Part I—Used in Elastohydrodynamic Lubrication
Authors: Lee Rong-Tsong , Hamrock B. J.
Published: June 2008

A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. Results show that the calculation of the central and minimum film thicknesses from the classical Reynolds equation is still valid for pure rolling conditions. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied. Such parameters as the pressure profile, the film shape, the coefficient of friction, the dimensionless shear stress at surface a, and the velocitiy contour in the conjunction were considered.
A Circular Non-Newtonian Fluid Model: Part II—Used in Microelastohydrodynamic Lubrication
Authors: Lee Rong-Tsong , Hamrock B. J.
Published: June 2008

A circular non-Newtonian fluid model and system approach is used in this paper to study the effect of a stationary surface irregularity where the film shape has been modified in the conjunctions of line contacts. A modified transient Reynolds equation is developed in this paper and is used to study the effect of a moving surface irregularity in the problem of microelastohydrodynamic lubrication. Lubrication performance factors such as pressure and film profiles were studied for both a stationary and a moving surface irregularity in a lubricated conjunction. The shear stress and traction coefficient for various height of the surface irregularity were also studied for a stationary surface irregularity. Results show that the film shape obtained from full-film elastohydrodynamic lubrication theory still gave a good prediction except when the surface irregularity occurred at inlet (Xp = − 1.0), but it failed to explain the high pressure and film fluctuations around the surface irregularity which was in the Hertzian contact zone. A bump or a groove occurring in the outlet around (Xp = 1.0) significantly affected the location of the outlet boundary, and the depth of the nip film thickness in the outlet caused by the surface irregularity profoundly affected the pressure spike for both a stationary and a moving surface irregularity.
Analysis of a Hydrodynamic Bearing Under Transverse Vibration of an Axially Moving Band
Authors: Tan C. A. , Mote C. D.
Published: June 2008

This paper presents a mathematical model of the flow and pressure developed in a hydrodynamic guide bearing film under transverse vibration of a translating band. The guide bearing is commonly used in band and circular sawing systems. The perturbed pressure is derived in the frequency domain based on a linearized, incompressible fluid film model. Unsteady fluid inertia, caused by the high frequency vibration modes of the flexible band, is included in the model. The perturbed pressure is generated by two mechanisms, one caused by the band convection, and the other by the band transverse vibration. Moreover, the pressure generations are governed by fluid impedance functions, which characterize the viscous diffusion across the film. Results for both the transient and steady state responses of the film are presented and discussed. It is shown that the pressure component caused by the band convection, which has not been considered in the literature, is important at low frequency. The pressure component caused by the band transverse vibration is dominant at high frequency.
Modal Analysis of Elastohydrodynamic Lubrication: A Connecting Rod Application
Authors: Kumar A. , Goenka P. K. , Booker J. F.
Published: June 2008

A method for performing transient elastohydrodynamic lubrication (EHD) analysis of journal bearings using the concept of modeshapes was developed earlier. This method was referred to as the modal EHD analysis method. In the present work, the method is applied to an engine bearing geometry and load. The numerical algorithm is found to be stable and robust, as long as the modeshapes are carefully chosen; some modeshapes do cause numerical instabilities. The results from the new method are compared to those from an available EHD analysis, DEHD. Modal EHD analysis results with only 8 modeshapes compared well with those from DEHD, both for film thickness and for pressure. The new method was found to take an order of magnitude less time than DEHD for analyzing the connecting-rod bearing.
Grinding Temperatures for Magnetic Ceramics and Steel
Authors: Chandrasekar S. , Farris T. N. , Bhushan B.
Published: June 2008

Grinding temperatures are measured using an infrared sensor in ferrite and steel. For reference purposes, temperatures are also measured in a reduced model for grinding which consists of a single diamond grain sliding across the workpiece surface at high speed. The results include temperature as a function of sliding velocity, rate of temperature decay as the grain moves away from contact, and histograms of the frequency that grains on the grinding wheel attain a given temperature. It is found that temperature measurements can be used to detect out-of-roundness in the wheel. Finally, a simplified two-dimensional model based on a heat flux moving with constant velocity gives reasonably good agreement with experiment.
Starting Pressure Boundary Conditions for Perturbed Reynolds Equation
Authors: Zhang Y.
Published: June 2008

The perturbation method is often used when calculating the oil film stiffness and damping coefficients of journal bearings. The oil pressure is divided into two parts, steady-state pressure and dynamic pressures. Proper boundary conditions are needed in solving the differential equations for the pressures. The paper presents a new pressure starting boundary condition, which is based on oil continuity condition, for those dynamic pressure terms. Then the film stiffness and damping coefficients, the critical mass and angular speed are computed by using two starting pressure conditions, Δp (θ10) = 0 and θp (θ10) ≠ 0 (θp (θ10) is the starting boundary value of the perturbed pressure terms). Significant differences of the results of these parameters between the two conditions are found. The paper also presents a method of how to determine the starting pressure boundary in numerical computation.
A Finite Volume Analysis of the Thermohydrodynamic Performance of Finite Journal Bearings
Authors: Han T. , Paranjpe R. S.
Published: June 2008

A rigorous thermohydrodynamic (THD) analysis of finite journal bearings has been developed. THD analysis not only allows a more accurate prediction of the bearing performance characteristics, but it also provides the temperature distribution in the bearing. It involves the simultaneous solution of the Reynolds and energy equations and can handle a wide variety of flow situations, including reverse flow, recirculating flow, and cavitation. The overall numerical scheme is based on a fully conservative finite-volume formulation. The calculated results are compared with the published literature. The qualitative agreement is good. Sample calculations for a typical automotive bearing show that the oil supply pressure and supply configuration significantly affect the bearing performance.
Interaction Force Between Thin Film Disk Media and Elastic Solids Investigated by Atomic Force Microscope
Authors: Miyamoto T. , Kaneko R. , Ando Y.
Published: June 2008

Atomic force microscopy is used to investigate the interaction force between the sharp tips of various elastic solids and four different samples. The samples are: thin film disk media coated with functional liquid lubricant having diol end groups, unlubricated disk media, a single-crystal silicon wafer, and Au evaporated onto single-crystal silicon. Relationships between the interaction and static friction force of disk media and a taper flat type head slider are examined. The interaction force between a disk medium coated with a functional liquid lubricant greater than 11.0 nm thick and tungsten tips with radii of 5 μm-100 μm is caused by the functional liquid lubricant meniscus, as pointed out by McFarlane and Tabor. However, at a thickness of several nanometers, the interaction force has a lower value than that for lubricant thicknesses above 11.0 nm. The interaction force has a minimum value of 0.4 μN at the functional liquid lubricant thickness of 2.0 nm. Mean interaction forces of the tungsten, Al2O3 − TiC and Si3N4 tips on a disk medium coated with a 2.0-nm-thick functional liquid lubricant are less than 0.1 times those for an unlubricated disk medium. Interaction forces of the SiC tip show very low values, even when the disk medium is unlubricated. Static friction force between a thin-film disk medium and a head or sphere is dependent on the interaction force between the medium and a tip that is made of the same material as the head or sphere. The use of an atomic force microscope (AFM), may allow the surface structure to be more thoroughly analyzed.
Visco-Elastohydrodynamic (VEHD) Lubrication in Radial Lip Seals: Part 1—Steady-State Dynamic Viscoelastic Seal Behavior
Authors: Stakenborg M. J. L. , van Leeuwen H. J. , ten Hagen E. A. M.
Published: June 2008

In general, most analyses of radial lip seal behavior assume a static deformation state in the seal lip. Nevertheless, a dynamic excitation of the seal lip always occurs in practice, due to unroundness of the shaft or motions of the shaft center. In this first part of a two part paper the influence of dynamic excitation on the occurrence of clearances in a dry seal-shaft contact is studied, taking into account viscoelasticity and inertia of the seal material. The ultimate goal is to determine whether viscoelastic seal behavior can result in a continuous fluid film or not. First, attention is paid to the mechanical behavior of synthetic rubber under an oscillating load. The seal elastomer shows a glass transition, resulting in a strong increase in stiffness with frequency. Next, a FEM analysis of the seal-shaft contact under dynamic conditions is presented. The steady-state response of the seal is represented by a transfer function approach. It is shown that clearances develop due to viscous and inertial seal material behavior. In practice, these clearances are filled with fluid. Due to entrainment and squeeze effects a fluid film is generated. This phenomenon is designated visco-elastohydrodynamic (VEHD) lubrication, and is subject of Part 2.
Visco-Elastohydrodynamic (VEHD) Lubrication in Radial Lip Seals: Part 2—Fluid Film Formation
Authors: van Leeuwen H. J. , Stakenborg M. J. L.
Published: June 2008

It is shown in Part 1 of this work (Stakenborg et al., 1990) that dynamic excitation of a radial lip seal will result in nonuniform clearances, due to viscous and inertial seal material behavior. These clearances are filled with fluid. Due to entrainment effects in a converging part of the clearance, fluid pressures will develop, which are sufficiently high to overcome the radial preload. These fluid pressures are excellently described by short bearing theory. The viscous and inertial effects can lead to a type of full film lubrication which is designated visco-elastohydrodynamic (VEHD) lubrication. VEHD lubrication addresses the (apparent) parallel fluid film lubrication problem in radial lip seals. At present, it is the only macro-hydrodynamic theory that results in calculated fluid film thicknesses, friction torques and leakage rates that are in agreement with experimental data. A novel feature of VEHD lubrication is the increase of frictional torque with decreasing viscosity under conditions of full film lubrication and low viscosity values, hitherto believed to be mixed lubrication.
A Numerical Simulation of the Head-Disk Assembly in Magnetic Hard Disk Files: Part I—Component Models
Authors: Ruiz O. J. , Bogy D. B.
Published: June 2008

In previous papers the dynamics of air bearing sliders used to carry the read/write transducers in magnetic hard disk files has been studied. These studies are useful in evaluating the steady flying and stability of sliders subjected to various disturbances. They are particularly useful in finding the natural frequencies of the air bearings. However, in hard disk drives the sliders are attached to suspensions, which are highly specialized structures that connect the sliders to the positioning actuators. These suspensions have to be relatively stiff in lateral translation, but very flexible in pitch and roll. This latter feature is accomplished by the gimbal or flexure that connects the slider to the end of the suspension. The suspension-gimbal structure has its own natural frequencies, which can be excited by disturbances such as track seeking and impacting the actuator against the crash stop. In order to study the effect of these structures on the head-disk spacing it is necessary to include them in the numerical simulator. In this two part study such a simulator is developed. In Part I the component parts and their interfaces are modeled. In Part II the numerical simulation of the coupled system is accomplished and the numerical results of several sample simulations are presented and discussed.
A Numerical Simulation of the Head-Disk Assembly in Magnetic Hard Disk Files: Part II—Solution of the Coupled System
Authors: Ruiz O. J. , Bogy D. B.
Published: June 2008

This paper is a continuation of Part I, which considers numerical models for the various components of the HDA. Here the solvers are coupled and the resulting numerical simulator is used to study the slider-disk spacing variation that occurs when a slider passes a bump on the disk. The results are compared with a simpler simulator and it is found that new information is obtained here that illustrates the role of suspension resonances in slider-disk spacing. We also study slider-disk spacing variations due to track accessing for both linear and rotary actuators. Finally we conduct a similar study for the problem of actuator crash stop. Of particular interest is the way in which the spacing variation depends on steady flying height. Low flying sliders have stiffer air bearings, which excite more suspension resonances. On the other hand, these sliders have less spacing change during track accessing and crash stop compared to higher flying sliders.
Tribological Studies on Bearing Balls of Different Composition Using Certain Heterocyclic Compounds as Potential E.P. Additives
Authors: Singh T. , Verma V. K.
Published: June 2008

Tribological studies on 12.7 mm dia steel bearing ball specimens of different composition have been carried out in a “4-ball machine” using certain potentially active heterocyclic compounds-paraffin oil admixtures. EP efficiency of these additives has been compared to a commercial sulphur-phosphorus additive. 2-Phenyl-3-phenylimino-5-p-methoxyphenylimino-1,2,4-thiadiazolidine has been found to be quite effective in the lubrication of bearing balls of different compositions. The topography and surface chemistry of the used bearing ball specimens have been examined using Scanning Electron Microscopy and Scanning Auger Electron Spectroscopy techniques respectively. Employing a suitable additive, the costlier alloy steel balls can be replaced by cheaper low carbon and chromium balls.
Experimental Investigation of Mechanism of Lubrication in Porous Journal Bearings: Part 1—Observation of Oil Flow in Porous Matrix
Authors: Kaneko S. , Obara S.
Published: June 2008

The oil flow in the porous matrix is experimentally investigated to explicate the mechanism of lubrication in the porous journal bearings. To visualize the flow in the porous matrix, a simplified model is used for the test bearing, whose matrix is composed of packed glass spheres having small uniform diameter. A dye-injection method is used for visualization. It is observed that there exists a circulation of oil through the porous matrix and this flow contributes to the lubrication in the porous bearings. The flow pattern is dependent on the lubrication conditions. Under hydrodynamic lubrication conditions, the oil in the porous matrix flows away from the position of the load line towards the unloaded region. However under boundary lubrication conditions, when the oil feed pressure is negligibly small, most of the oil in the porous matrix flows toward the region where the oil film pressure would take the minimum.
Application of Porous Materials to Annular Plain Seals: Part 2—Dynamic Characteristics
Authors: Kaneko S.
Published: June 2008

For improving the dynamic performance of the annular plain seals employed in pumps, porous materials are applied to the seal surface by insertion into the inlet part of the seal. The linear stiffness and damping coefficients of the seal film are calculated in the laminar-flow regime, assuming the mass effect of the fluid to be negligibly small. Numerical results show that the annular plain seals with the porous materials have larger main stiffness terms and smaller cross-coupled stiffness terms and main damping terms than the conventional ones with the solid surfaces. This tendency is more marked with increasing the axial length of the porous matrix applied to the seal surface. The larger main stiffness terms for “the porous seal” yield larger radial reaction force acting on a rotor as a consequence of small whirling motion of shaft about a centered position, which would contribute to rotor stability.
Tribological Reaction Generated on Ceramic – Steel Couples Under Boundary Lubrication
Authors: Tanita Y. , Mine T. , Nakajima K.
Published: June 2008

The effect of ZnDTP on Al2O3, Si3C, and Si3N4 surface was investigated with ceramic-steel couples under lubricated conditions. Metal transfer to the ceramic surfaces was found to increase with load and surface roughness, depending on the kind of ceramic. P, S, and Zn as atomic constituent elements of ZnDTP were measured on the ceramic surface in all three types of ceramic-steel couple. The amount of each of these elements deposited increased as the Fe content transferred onto the surfaces increased. Measurements of hardness and fracture toughness were conducted on SiC and Si3N4 in SiC - and Si3N4-steel couples with and without additive to determine changes in mechanical properties of the ceramic surfaces. Further investigations were conducted to determine the effect of the gases, O2 and N2, on friction and wear properties of the Si3N4-steel couple. Saturation of the lubricant oil with O2 and N2 was found to cause an increase of the wear rate at about 100 N in this couple.
Short Bearing Theory Prediction of Inertial Turbulent Journal Orbits
Authors: Capone G. , Russo M.
Published: June 2008

The proposed method enables a straightforward solution of the nonlinear equations of the cylindrical motion of rotors on journal bearings in conditions of unsteady nonlaminar hydrodynamic lubrication taking into account the inertia forces of the fluid particles. The analysis is restricted to the case of rigid supports and rigid symmetrical rotor adopting the short bearing theory. Some meaningful examples of predicted journal orbits are reported for balanced and unbalanced rotors.
The Accuracy of Short Bearing Theory in Presence of Cavitation
Authors: Prata A. T. , Ferreira R. T. S.
Published: June 2008

The accuracy of the short bearing approximation in presence of cavitation is tested for bearing aspect ratios (length/diameter) ranging from 0.1 to 1, and for eccentricity to clearance ratios from 0 to 1. Results for short bearings are obtained via the method of matched asymptotic expansion of [3]. These results are compared to those for finite bearings, which are calculated by numerical integration of the Reynolds equation utilizing boundary fitted coordinates that accommodate to the cavitation boundary. Except for very high eccentricities, the short bearing theory was shown to be accurate in predicting the load, within ten percent, for bearing aspect ratios up to 0.5. For large aspect ratios the short bearing theory overpredicts the load.
Tappet Rotation and Friction Reduction in a Center Pivot Rocker Arm Contact
Authors: Willermet P. A. , Pieprzak J. M. , Dailey D. P.
Published: June 2008

The instantaneous tappet rotation velocity and instantaneous friction torque were measured simultaneously for the CVH center pivot rocker arm geometry. The measurements were made in a cam/tappet friction apparatus equipped with a laser reflectance tappet rotation monitor capable of following rapid changes in tappet rotation velocity. The data showed that more rapid tappet rotation resulted in lower friction. The effect was greatest in the region of maximum cam lift. Several tappets were modified to produce higher rotation rates than production tappets. The best results were obtained with tappets incorporating an internal squeeze film bearing to reduce resistance to rotation. The data were analyzed to elucidate the cause for the friction reduction effect. The analysis showed that most important effect was the partial rolling motion between the surfaces, rather than enhancement of the oil film thickness. A model based on that conclusion agreed reasonably well with the experimental data.
Hydrodynamic Analysis of a Slider Gas Bearing Including the Gas Inertia Effect
Authors: Mourelatos Z. P.
Published: June 2008

A computationally efficient analysis is presented to calculate both the steady and unsteady compressible flow of an ideal gas in an infinitely wide slider bearing with the gas inertia effect included. In this analysis, the velocity profile across the film is assumed to be parabolic, and the gas pressure and density across the film are assumed constant. The results of the present approximate analysis for the steady-state case compare very well with the results from the open literature, experiments and a detailed Finite-Element analysis. It was found that both the pressure and velocity distributions in the slider bearing may be very much in error if the gas inertia effect is not considered. Comparing the results from the time-dependent analysis with the results from the steady-state analysis, it was concluded that (1) the pressure distribution does not change, (2) the flow through the slider bearing entrance may change considerably.