bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastohydrodynamic Behavior of Rolling Elliptical Contacts: Part I: Pressure and Temperature Distributions
Authors: Mokhtar M. O. A. , Abdel Ghany A. A.
Published: October 2009

A two disk machine with a spherical disk mating a plain cylindrical one has been constructed to operate at different elliptical contact situations under various loads and rolling to sliding speeds. The disks axes can skew relative to each other so that various elliptical contacts could be tested. By the aid of specially modified evaporated transducers (Manganin band for pressure measurements and platinum band for temperature measurements), the elastohydrodynamic (EHD) pressure and temperature distributions could be accurately traced. Results, herein presented, confirmed that within the contact zone, the pressure distribution exhibits an almost Hertzian shape but with a second pressure peak (spike) near the trailing (exit) end of the oil film. The temperature has proven to display a distribution analogous to that described by the generated EHD pressure.
A New Fatigue Life Model for Rolling Bearings
Authors: Ioannides E. , Harris T. A.
Published: October 2009

This paper describes a novel model for the prediction of fatigue life in rolling bearings. Central to this model is the postulation of a statistical relationship between the probability of survival, the fatigue life, and a stress-related fatigue criterion level above a fatigue limit for an elementary volume of material in the bearing. Using this concept, the stress volume to fatigue and the fatigue life of the bearing can be calculated for different loads, material and operating conditions. Comparisons between experimentally obtained rolling bearing fatigue lives and lives predicted using this theory indicate its ability to account for phenomena hitherto excluded from fatigue life predictions. Furthermore, comparisons between experimentally obtained fatigue lives for other specimens used in structural fatigue tests and fatigue lives predicted using the new model show good agreement.
Surface and Subsurface Behavior of Selected Al-Cu Alloys in Sliding Wear
Authors: Caldwell S. G. , Wert J. J.
Published: October 2009

As materials are pushed to higher levels of performance, the nature of friction and wear phenomena occurring in sliding contact is of even greater importance in view of energy efficiency and maintained functional integrity. The present study investigated unlubricated sliding wear from the standpoint of transfer layer behavior. Microscopic studies of selected Al-4.5 Cu structures confirmed that asperity contact damage is very localized, as was the case for previously studied solid solutions. The subsurface region was found to consist of very fine crystallites lacking a stable, definable texture. Macroscopic wear testing was performed by three different methods using Cu-Al solid solutions. It was demonstrated that test multiplicity has the advantages of establishing machine-dependent results and also showing conditions for which a given parameter is rate controlling. Surface-sensitive tests using aluminum bronzes are dominated by surface oxide effects. The soft Cu2O component of films on low percentage solute alloys behaves as a solid lubricant. When tests are employed that produce more severe wear, bulk properties of the substrate predominate except for alloys with highly abrasive surface oxides. Results of this study have been found to be in good correlation with related transfer layer investigations.
Numerical Simulation of Dynamically Loaded Flexible Short Journal Bearings
Authors: van der Tempel L. , Moes H. , Bosma R.
Published: October 2009

A numerical method is proposed for calculating film thicknesses in flexible short journal bearings under dynamic load. The system of elastohydrodynamic integro-differential equations is discretized directly and solved by a 2-step Newton-Raphson method. The cavitation boundaries are located by a special discretization of the pressure. This type of condition puts practically no restrictions on the boundary alterations. The results for the con rod bearings of medium- and high-speed combustion engines are compared.
A Theoretical Model of Striated Film-Rupture Applied to the Cylinder-Plane
Authors: Fall C.
Published: October 2009

The author has previously presented a theoretical model of striated film-rupture consisting of a time-dependent linear perturbation analysis applied to the Reynolds equation. After review this model is applied to the cylinder-plane geometry for comparison with theoretical and experimental data due to Savage. Successful prediction of the number of striations for varying (ηU/T) and (R/h0) is achieved.
The Leading-Edge-Groove Tilting-Pad Thrust Bearing: Recent Developments
Authors: Mikula A. M.
Published: October 2009

This paper compares the leading edge groove and pressurized supply (flooded) lubricant supply methods, and analyzes their influence on the performance of equalizing tilting pad thrust bearings. This paper presents new experimental data on 6-shoe, 267 mm (10 1/2 in.) O.D. bearings, operating at shaft speeds up to 14000 rpm, with loads ranging up to 3.45 MPa (500 psi) for two different lubricants. The data presented details the power loss and babbitt temperature performance of two versions of the leading-edge-groove bearing design and contrasts the results with a pressurized supply bearing design.
Lubrication Theory at Arbitrary Knudsen Number
Authors: Gans R. F.
Published: October 2009

It is demonstrated that the slip flow Reynolds equations for ultra low clearance gas bearings can be derived from kinetic theory by an approximation scheme appropriate for arbitrary Knudsen numbers. Thus the usefulness of the slip flow Reynolds equation is extended to cases where it would not be expected to hold.
Transfer Lubrication for High Temperatures: A Review
Authors: Lancaster J. K.
Published: October 2009

Transfer lubrication is defined as lubrication provided by the continuous transfer of solid lubricant to sliding/rolling interfaces. The lubricant may either be incorporated within a self-lubricating composite or supplied from an auxiliary component. Both routes require similar research information on the factors influencing film formation, friction and wear, and film failure. This paper reviews what is known about these aspects for solid lubricants appropriate to high temperature applications (≥300°C). Areas are identified in which further research is needed.
Effect of Normal Stiffness in Loading System on Wear of Carbon Steel—Part 1: Severe-Mild Wear Transition
Authors: Chiou Y. C. , Kato K. , Kayaba T.
Published: October 2009

It is shown that the severe-mild wear transition and the wear rate of 0.45 percent carbon steel pair in dry friction is greatly influenced by the change of normal stiffness from 1 N/mm to 586000 N/mm in loading system. The wear rate increases with the increase of normal stiffness and the severe wear state is predominant under larger normal stiffness at low sliding velocity (0.25 m/s). However, the wear rate decreases with the increase of normal stiffness and the mild wear state is predominant under larger normal stiffness at high sliding velocity (1.57 m/s). This complicated wear behavior is explained by analyzing the effect of normal stiffness and normal load on wear rate-sliding velocity curve. It suggests that the increase of normal stiffness should physically mean the increase of normal load.
Thermohydrodynamic Analysis of Thrust-Bearing With Circular Pads Running on Bubbly Oil (BTHD-Theory)
Authors: Abdel-Latif Lotfie Ahmed , Peeken Heinz , Benner Joachim
Published: October 2009

This paper considers the steady-state bubble-thermohydrodynamic behavior of rigid circular pad thrust bearing and presents an iterative numerical scheme to solve the governing equations. The Reynolds equation, the energy equation of the oil film, and the heat conduction equation of the pad are converted by means of finite difference method and solved numerically. The air/gas bubbles included in the lubricant are assumed to be evenly dispersed. The variation in the oil density and viscosity due to bubble presence as well according to pressure differentials and temperature rise is considered. The surface tension of the bubbles is taken into account in the analysis. Typical graphs showing the influence of the bubble content on the most important design criteria of the bearing: load W, friction loss F, pressure center location Xp and temperature rise within the oil film are presented. The load carrying capacity, outlet temperature or friction loss does not change much with increasing bubble content. The pressure distributions predicted in earlier work by To̸nder [1–4] etc. is confirmed. The pressure center location, however, shifts more downstream, making the bearing more unstable for smaller loads.
Effect of Additive Molecular Structure on Friction Coefficient and Adsorption
Authors: Jahanmir S. , Beltzer M.
Published: October 2009

Experimental results on friction coefficients obtained with a number of model additives in a four ball test apparatus have confirmed a recently proposed model of boundary lubrication. The values of adsorption free energies, calculated from friction coefficient data, agreed very closely with the free energies of adsorption determined by contact potential difference measurements. In general, the ranking order of additives based on the free energy of adsorption was the same as the published literature. The friction coefficient data obtained here were in excellent agreement with the published data on the chain length effect, chain saturation and branching and polar end-group structure. The ranking order within each group of single chain compounds was explained by the chain dispersion interactions. In general, the greater the chain dispersion interaction, the lower the minimum friction coefficient (the friction coefficient at monolayer coverage).
Mechanical Behavior of Tribochemical Films Under a Cyclic Tangential Load in a Ball-Flat Contact
Authors: Tonck A. , Kapsa Ph. , Sabot J.
Published: October 2009

This paper describes an experimental investigation of some mechanical properties of four tribochemical films. Experiments have been performed for a contact between a 52100 steel flat covered with a film formed in boundary lubrication on a plane on plane tribometer. Measurements have shown that the tangential stiffness is reduced by the presence of film. The values of elastic shear modulus obtained for all films in the contact conditions are of the same order and similar to those of high molecular weight polymers. The study of contact degradation under cyclic microsliding have shown that the friction coefficient increase with the number of cycles, even for low amplitude microslidings (lower than 10 nm) when surface modifications are not yet observed. These results pointed out the existence of two types of films which present different friction and wear behaviors probably related to their plastic properties and to the boundary conditions.
Observation of Micro-Structure in Seized Portion and Mechanism of Seizure
Authors: Mishina Hiroshi , Sasada Tadashi
Published: October 2009

A pin-on-disk and a rod-in-bush apparatus were used to investigate the seizure mechanism of sliding components. Sliding was conducted in a dry condition in room air until the sliding components seized. X-ray micro analysis was made in the vertical section of the seized elements after the sliding system was stopped by the seizure. It was found that very high friction leading to seizure is the result of bonding of the rubbing elements by the transfer particles generated through the mutual transfer and growth process of wear particles. The particles are large and flattened and they form adhesive links between the rubbing components. Experimental results indicated that the seizure is not inherent to direct contact of the mating surfaces but is a result of the formation process of wear particles.
Wear in Ceramic/Ceramic and Ceramic/Metal Reciprocating Sliding Contact. Part 1
Authors: Aronov V. , Mesyef T.
Published: October 2009

This paper is the first of a series of two devoted to an investigation of wear mechanisms in ceramic/ceramic and ceramic/metal sliding contact tribological systems at high temperatures and exhaust gas environment. The first part presents results of the experiments carried out at room temperature and air environment. Scanning electron microscope, optical microscope and X-ray dispersion analysis were used for an identification of wear mechanisms. Surface geometry and morphology, friction coefficients and wear were determined as functions of sliding distance, nominal contact pressure, sliding velocity and mechanical properties of specimens (hardness and fracture toughness). The wear mechanism of ceramics rubbed against ceramics may be attributed to intensive plastic deformation of surfaces resulting in low cycle fatigue. The wear mechanism of ceramics rubbed against metals was polishing and surface fracture, while that of metals was adhesive transfer of material on to ceramic surfaces. Wear rates and friction coefficients were independent of mechanical properties of metallic samples.
On the Laminar Flow Characteristics of Conical Bearings. Part I—Analytical Approach
Authors: Kalita W. , Rodkiewicz Cz. M. , Kennedy J. S.
Published: October 2009

An analysis has been made of the characteristics of externally pressurized central recess conical bearings with nonconstant film thickness under the assumption of isothermal laminar flow of a viscous incompressible fluid. The flow in the narrow gaps that may be convergent, constant, or divergent has been approximately determined on the basis of the lubrication theory with convective inertia neglected except for that part which is due to rotation. The pressure distribution along the gap, the load capacity, and the torque of the bearings, were theoretically predicted. It was found that, while the gap is very narrow, both the load capacity and the torque for the convergent case decrease moderately, and for the divergent case increase significantly with respect to the constant gap bearing, provided with flow rate, rotational velocity and the film thickness at the outlet of the gap are the same.
The Convergence and Advantages of a Series Solution for Finite Hydrodynamic Bearings
Authors: Curzon A. E.
Published: October 2009

A series solution is available for the load capacity of a finite, rectangular, hydrodynamic bearing whose lubrication film is curved in one direction. It is shown that the even terms and the odd terms both converge uniformly. A given odd term is larger than the preceding even term so that errors due to truncation of the series are best estimated from the last odd term included in a partial sum. Advantages of the series solution over the standard two-dimensional numerical method are pointed out. They include smaller discretization errors, smaller computer storage requirements and less computer time.
Effect of a Surface Film on the Surface Temperature of a Rotating Cylinder
Authors: Gecim B. , Winer W. O.
Published: October 2009

Solution to the steady heat conduction problem of a rotating layered cylinder is presented. The governing differential equations (for the film and the substrate) are solved by using an integral transform technique. It is shown that the presence of a surface film measured in micrometers can substantially change the level of the surface temperature. The effect of the surface film on the surface temperature depends on: respective thermal properties of the film and the substrate; relative surface speed; heat source (contact) size; and surface film thickness. However, the range in which the effect of the film on the surface temperature is dependent on these parameters is limited. Outside this range (i.e., thin film/low speed or thick film/high speed) the surface temperature rise is determined by the thermal properties of the substrate, or by the properties of the film alone, respectively. Hence, outside this range, a further change in the film thickness does not influence the surface temperature rise. Dimensionless plots showing the change in surface temperature rise as a function of material thermal properties, surface speed, heat source size, and film thickness are presented. Behavior for specific material combinations are also presented. The present information can be utilized to predict the layer effect on the partition of heat between the layered cylinders.
Stokes Roughness Effects on Hydrodynamic Lubrication. Part I—Comparison Between Incompressible and Compressible Lubricating Films
Authors: Mitsuya Y. , Fukui S.
Published: October 2009

A perturbation method for the Navier-Stokes equations is presented for analyzing Stokes roughness effects on hydrodynamic lubrication in both incompressible and compressible films. The solution is obtained from direct numerical calculation by using an actual rough spacing, without applying the currently accepted assumption that the roughness height should be small. The roughness wavelength and height influences on flow rate, load carrying capacity and frictional force are clarified. Secondary quantities induced by Stokes effects are found to be proportional to wavenumber n squared for sufficiently large n values, so that the amount of the Stokes effect can be determined by the spacing to wavelength squared ratio. A significant difference between incompressible and compressible films is that Stokes roughness increases the flow resistance of and then enhances the load carrying capacity of incompressible films, while it inversely affects compressible films. The compressibility with respect to secondary pressure induced by the Stokes effects can be neglected for any compressibility number, no matter how large, as long as the local compressibility number, defined by the wavelength, is small.
A Numerical Study of Surface Roughness Effects on Ultra-Thin Gas Films
Authors: White J. W. , Raad P. E. , Tabrizi A. H. , Ketkar S. P. , Prabhu P. P.
Published: October 2009

A wedge bearing with transverse sinusoidal roughness pattern is studied numerically in order to predict the effect of surface roughness on compressible fluid films. A variable grid implicit finite difference scheme is used to provide steady-state solutions of the Reynolds equation over a bearing number range of five orders of magnitude. At a fixed bearing geometry and orientation, the bearing load is found to increase to a maximum as the bearing number increases, then to decrease and asymptotically approach a limiting value as the bearing number increases further. This is quite unlike the behavior of an incompressible fluid bearing. Analysis indicates that the maximum load occurs at a condition where pressure diffusion and Couette effects of the fluid film are of an equal order of magnitude. The increased emphasis of the pressure diffusion physics is due to the short length scales of the rough surfaces which “trigger” the higher derivative diffusion terms in the Reynolds equation. The criterion required for validity of an infinite bearing number solution with a rough surface is found to be much more restrictive than that of a smooth surface bearing. Last, the type of rough surface film clearance averages used in incompressible lubrication are shown to be incorrect for analysis of very thin gas films. It would appear that one application of this information would be the design of an artificially roughened surface for the take-off and landing of magnetic head sliders so as to minimize contact and wear of the magnetic media.
Hopf Bifurcation to Limit Cycles in Fluid Film Bearings
Authors: Hollis P. , Taylor D. L.
Published: October 2009

The nonlinear response of a cylindrical journal bearing operating close to the critical speed stability boundary is studied in this paper. Using linear stability theory, the value of the critical variable (usually speed) at the point of loss of stability is obtained and shown to agree with results of previous researchers. Using Hopf bifurcation analysis, parameters for determining the behavior close to this point are obtained. Analytically, these parameters prove that the system can exhibit stable limit cycles for speeds above the critical speed. Such supercritical limit cycles only exist for a narrow range of values of modified Sommerfeld number. In other cases, subcritical limit cycles are predicted. The results are supported by numerical simulation. The results show why it may be difficult to observe supercritical limit cycles in test rigs.
On the Stability of a Rigid Rotor in Finite Porous Journal Bearings With Slip
Authors: Chattopadhyay Ajit Kumar , Majumdar B. C.
Published: October 2009

This investigation deals with the stability characteristics of oil filled porous journal bearings of finite length and with velocity slip. The stability curves are drawn for different slip parameters, eccentricity ratios, slenderness ratios, and in the absence of any experimental data, the theoretical results for the solid bearings obtained by this analysis have been compared with the available results of solid bearing.
An Optimum Short Bearing Theory for the Elastohydrodynamic Solution of Journal Bearings
Authors: Goenka P. K. , Oh K. P.
Published: October 2009

An approximate method for solving the elastohydrodynamic (EHD) lubrication problem has been developed. The method is based on two assumptions: the separation of variable for pressure and a parabolic pressure distribution in the axial direction. To solve the governing equations, the Newton-Raphson method, in conjunction with Murty’s algorithm, is used. The finite-element and the finite-difference methods are then used to obtain approximate solutions. The rod bearing of a typical connecting rod is analyzed by the new method. The results are compared to the full EHD solution and the rigid bearing solution. Significant reduction in computation time is realized when compared to the full EHD solution.
Three Dimensional Shape Effect on Abrasive Wear
Authors: Kato K. , Hokkirigawa K. , Kayaba T. , Endo Y.
Published: October 2009

The three dimensional shape effect of asperity on abrasive wear was investigated with in-situ experiments in the scanning electron microscope. The geometry of model asperity was represented by attack angle and dihedral angle, where attack angle changed in 0∼90 deg and dihedral angle in 0∼180 deg. Wear modes of shearing, cutting, and wedge forming were observed and each mode was related to attack angle and dihedral angle by wear mode diagram. Wear rate in cutting mode increased with attack angle and was maximum at a certain dihedral angle.
Porosity Associated With Insoluble Carbides in VIM-VAR AISI M-50 Steel and Its Probable Effects on Rolling Contact Fatigue
Authors: Butterfield F. A. , McNelley T. R.
Published: October 2009

The influence on the heat treatment response and rolling contact fatigue behavior of thermomechanical processing (TMP) to refine grain and soluble carbide size was studied for VIM-VAR AISI M-50 steel. Material was processed by warm rolling and then given a final, hardening heat treatment. As-received material was also given the same final heat treatments to provide a comparison. Rolling contact fatigue testing indicates equivalence of the as-received (spheroidize-annealed) and TMP specimens evaluated. This is believed to result from inability of this TMP to refine insoluble carbides and also to the presence of porosity in both as-received and also the processed material. The porosity consists of voids at the ends of the insoluble carbides and does not appear to have been reported heretofore.
The Fretting Wear of Nitrogen-Bearing Austenitic Stainless Steel at Temperatures to 600°
Authors: Waterhouse R. B.
Published: October 2009

The fretting behavior of the nitrogen-bearing austenitic stainless steel, Nitronic 60, has been studied at 20, 400, 500, and 600°C in air. A spherical ended rider was vibrated against a flat specimen, both machined from the steel. Normal load was 3N, frequency 50Hz and peak-to-peak amplitude 40 μm. Coefficient of friction after 106 cycles showed a decrease as the temperature was increased, falling from 0.62 at 20°C to 0.10 at 600°C. Wear volume also dropped dramatically at 400° and above, with no measurable wear at 600°C. A smooth protective oxide was formed at 400, 500, and 600°C, typical of the glaze oxide previously found on nickel-based alloys. The oxide layer was approximately 10 μm thick and had the spinel structure. The electron diffraction pattern most closely resembled that of the spinel NiO, Cr2O3 but chemical tests showed that it contained iron. It is thought to be a mixed spinel containing all three metal ions.
Pressure Distribution Under a Ball Impacting a Thin Lubricant Layer
Authors: Safa M. M. A. , Gohar R.
Published: October 2009

A steel ball is dropped onto a glass plate covered by an oil droplet where impact occurs. A small manganin pressure transducer deposited on the plate and in the oil, enables pressure-time traces to be recorded at different points within the region of pressure. Their shapes are similar to those obtained under a steady ehl (elastohydrodynamic) rolling contact. Dimples are formed in each surface during the latter stages of the approach. These, together with the radial pressure distributions, are similar in shape to those obtained theoretically elsewhere. The nature of the pressure-time response suggest that no surface to surface contact occurs during the impact.
Predicting Microfracture in Ceramics Via a Microcontact Model
Authors: McCool J. I.
Published: October 2009

The point of view is taken that for ceramics, cone cracking on the microscale assumes the same role as plastic asperity deformation in metal materials, namely, as the agent causing stress raising micropits which precipitate surface fatigue. Empirical fracture data are interpreted in the context of published fracture mechanics analyses of cone cracking in static and sliding contact and used within the Greenwood-Williamson stochastic microcontact model to predict the relative likelihood of cone cracking when a rough flat ceramic contacts a smooth ceramic flat of the same material. The Greenwood-Williamson model is reviewed and its predictions are shown, for the steel and ceramic surfaces considered, to compare favorably to the more general anisotropic microcontact model ASPERSIM. A microfracture index analogous to the Greenwood-Williamson plasticity index, is shown to be a determinant of the ability of a surface to resist cone cracking.
Theory Versus Experiment for the Rotordynamic Coefficients of Annular Gas Seals: Part 2—Constant-Clearance and Convergent-Tapered Geometry
Authors: Nelson C. C. , Childs D. W. , Nicks C. , Elrod D.
Published: October 2009

An experimental test facility is used to measure the leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals will have significantly larger direct stiffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is prerotated.
Friction and Wear of Hot Pressed Silicon Nitride and Other Ceramics
Authors: Ishigaki H. , Kawaguchi I. , Iwasa M. , Toibana Y.
Published: October 2009

An investigation was conducted to determine the friction and wear characteristics of hot-pressed silicon nitride. Sliding produced wear debris and a damaged surface. The physical and crystallographic morphology of surfaces was compared with that of diamond ground surfaces. Wear tests were done with pin-on-disk apparatus at a load of 10N with various sliding speeds to 780 mm/s, and in four different environments which included in dry nitrogen, in air at humidities of 50 percent RH and 90 percent RH, and in distilled water. The results of the wear experiments indicated that residual α-silicon nitride was transformed into β-silicon nitride. Adsorbed water appeared to enhance plastic flow of the surface and reduced both the wear rate and friction. A second investigation was conducted to correlate the coefficient of friction with the fracture toughness of silicon nitride, silicon carbide, aluminum oxide and zirconium oxide. The friction experiments were done in reciprocating sliding, using spherical diamonds. Two tip radii, 0.005 mm and 0.1 mm were used over a range of load of 0.1 to 3N and a speed of 0.17 mm/s. The coefficient of friction was found to be inversely correlated with fracture toughness of all four ceramics in several conditions. Frictional anisotropy was also observed in the hot-pressed silicon nitride.
Dynamics of Gas-Lubricated Slider Bearings in Magnetic Recording Disk Files—Part I: Experimental Observation
Authors: Miu D. K. , Bogy D. B.
Published: October 2009

This two part paper presents the experimental observation and numerical simulation of the dynamic response of self-acting gas-lubricated slider bearings used to maintain the sub-micron spacings between the Read/Write transducers and the rotating disks in magnetic recording disk files. In this Part I, a novel laser Doppler interferometric technique is used to measure the transient motions of the R/W head as it encounters an artificially introduced crater-like surface imperfection and a sputtered rectangular step.
Sealing Effects of Squeeze Air Film
Authors: Takada H. , Kamigaichi S. , Miura H.
Published: October 2009

The sealing effects of squeeze air film were analyzed experimentally and theoretically. The air flow rate and the sealed pressure were measured in a squeeze face seal. The air flow rate can be expressed as the difference between the flow rate by the pumping and the flow rate by the leakage. The air flow rate by the pumping increases proportionally to the square of the vibration amplitude of the surface, as does the sealed pressure. The air flow rate by the leakage increases proportionally to the pressure difference between the vessel pressure and the ambient pressure. The experimental results showed good agreement with the theoretical results.
Misalignment in Thrust Bearings Including Thermal and Cavitation Effects
Authors: Heshmat H. , Pinkus Oscar
Published: October 2009

This paper offers an analysis and computer solutions for misaligned thrust faces, including thermal effects and proper cavitation boundary conditions. The geometries analyzed range from full 2π arcs to pads of 27 deg angular extent, for both parallel surfaces and standard tapered-land thrust bearings. It is shown that, except for parallel surfaces, no cavitation occurs in thrust bearings, even under severe misalignment; that the gain in hydrodynamic force versus a decrease in minimum film thickness is most favorable at low and moderate levels of misalignment; and that for high load capacity, small arcs (many pads) are preferred to large ones.
A Simple Approach to Evaluate Non-Newtonian Viscosity Effects in a Lubricating System
Authors: Bourgin Patrick , Francois Joseph-Marc
Published: October 2009

The working characteristics of a finite width slider bearing lubricated by a non-Newtonian fluid are computed. The analysis proposed here allows its performances to be evaluated by means of a pocket calculator. For that purpose, a computer code based on a finite element method is used. The program runs for different values of pertinent kinematical, geometrical and rheological parameters. The corresponding results are fitted by means of adequate analytical formulas, which are very easy to handle. The accuracy of these empirical formulas is investigated in several typical cases. The agreement with the numerical solution is proven to be satisfactory.
On the Dynamic Stability of the Spiral-Grooved Gas-Lubricated Thrust Bearing
Authors: Constantinescu V. N. , Galetuse S.
Published: October 2009

The dynamic stability of a blocked center inward pumping spiral grooved thrust bearing is investigated. For this purpose two methods are considered comparatively, namely a standard small perturbation one, and an extension of the method used previously to determine air-hammer phenomena in externally pressurized gas bearings. The first method gives a more detailed description of situations in which the film is stable or unstable, while the second one gives a limit for the speed (or compressibility parameter Λc) up to which the bearing is unconditionally stable. The second method is simpler and of practical interest since at higher speeds the critical mass furnished by the first method is of little practical interest (being too small).
Review of the Concept of Dynamic Coefficients for Fluid Film Journal Bearings
Authors: Lund J. W.
Published: October 2009

The development of the concept of spring and damping coefficients for journal bearings is briefly reviewed. Methods for computing the coefficients are described, and their use in rotor dynamics calculations (unbalance response, stability) is discussed. The limitations imposed by nonlinearities on the application of the coefficients is illustrated by examples.
Turbulent Two-Phase Flow in Face Shaft Seals
Authors: Beatty P. A. , Hughes W. F.
Published: October 2009

A general theory is presented for the calculation of leakage rates and quasi-static opening force for aligned face seals operating in a turbulent, two-phase flow regime. Here, the fluid is assumed to be a homogeneous mixture of liquid and vapor in thermodynamic equilibrium. Full account of inertial effects and heat generation due to viscous dissipation is made. Solution of the model governing differential equations is accomplished through the use of a fourth-order Runge-Kutta numerical integration scheme. Several numerical examples are presented. The calculation of mass leakage rates and opening force under choked and unchoked conditions are discussed and the phenomenon of all-liquid choked flow is explained. Opening force curves are generated as a function of gap height for some situations of interest and their relation to seal axial stiffness is examined.
A Pressure-Shear Plate Impact Experiment for Studying the Rheology of Lubricants at High Pressures and High Shearing Rates
Authors: Ramesh K. T. , Clifton R. J.
Published: October 2009

A new plate impact configuration is described for subjecting lubricants to simple shearing motion under uniform hydrostatic pressure. Thin layers (∼50 μm thick) of the lubricant are confined between two hard metallic plates which are subjected to impact by a parallel plate that is inclined relative to the direction of approach in order to induce both pressure and shear loading. Stress waves in the hard plates are monitored by laser interferometry; all measurements are made before unloading waves arrive from the periphery. For approximately one microsecond the compressed lubricant is subjected to a simple shearing motion and a continuous record of the shear stress and shear rate is obtained. Results presented for the lubricant 5P4E at pressures of 1-5 GPa and shear rates of approximately 9 × 105 s−1 show good agreement with available data on the dependence of the limiting shear stress on the confining pressure at lower pressures and lower shearing rates.
Magnetic Head-Media Interface Temperatures: Part 2—Application to Magnetic Tapes
Authors: Bhushan B.
Published: October 2009

An analytical model has been used to predict the interface temperature of a typical magnetic head-tape contact and of isolated (exposed) magnetic particles in contact with the head. Average and maximum interface temperatures for the assumed head-tape interface are about 7° and 10° C, respectively. If the exposed magnetic particles contact the head surface, the average and maximum temperture rises could be about 600° and 900° C, respectively. The duration of an asperity contact is about 2 to 4 μs and the thermal gradients perpendicular to the sliding surface are very large (a temperature drop of 90 percent in a depth of less than the radius of an asperity contact or a few micrometers). The predicted temperatures are compared with the temperatures previously measured using an infrared radiometric technique.
An Application of the Finite Element Method to the Thermohydrodynamic Analysis of a Thin Film Cylindrical Bore Bearing Running at High Sliding Speed
Authors: Gethin D. T.
Published: October 2009

A finite element model of the thermohydrodynamic behavior of a cylindrical bore bearing is presented. The predicted behavior is compared with experimental evidence where possible and favorable correlation is obtained. The analysis is extended to include thermoelastic behavior in both the shaft and bush and it is demonstrated that this mechanism can influence bearing behavior considerably.
Experimental Observation of Cavitating Squeeze-Film Dampers
Authors: Walton J. F. , Walowit J. A. , Zorzi E. S. , Schrand J.
Published: October 2009

This paper presents the results of an experimental investigation intended to observe cavitation in squeeze-film bearing dampers representative of those commonly found in aircraft gas turbine engines. Two different squeeze-film damper geometries were tested with both high-speed motion pictures and stroboscopic video recordings acquired at speeds up to 20,000 r/min. The results presented are limited to 8000 r/min due to the increased clarity of the photos acquired at the lower speeds and the similarity of trends at the higher speeds. Comparisons are also made with analysis formulated to handle the dynamics of the film rupture for the “short” damper case. The test results confirmed several of the commonly held “short” bearing assumptions (i.e., predominant axial flow and the effect of supply pressure and eccentricity on the cavitation zone). However, the test results demonstrated that significant flow reversals and film rupture were experienced in the feed/drain grooves in contradiction to the assumed boundary conditions. While agreement between analysis and test is of the right order of magnitude in predicting the cavitation zone shape and circumferential extent, current analyses do not adequately account for the observed variations in the boundaries and change in shape of the cavitation zone.
Stability of a Rigid Rotor in Finite Externally Pressurized Oil Journal Bearings With Slip
Authors: Chattopadhyay Ajit Kumar , Majumdar B. C. , Rao N. S.
Published: October 2009

A theoretical analysis has been carried out to determine the stability characteristics of externally pressurized porous oil journal bearings of finite length considering the tangential velocity slip at the bearing-film interface. The stability curves have been drawn for different slip parameters, eccentricity ratios, slenderness ratios, bearing speed parameters etc.
Temperatures at Interfacial Contact Spots: Dependence on Velocity and on Role Reversal of Two Materials in Sliding Contact
Authors: Kuhlmann-Wilsdorf D.
Published: October 2009

Based on the theory by Blok and Jaeger, simple equations have been obtained for the theoretical evaluation of flash temperatures, i.e., the temperatures of circular or elliptical contact spots between two homogeneous materials, when friction heat and/or Joule heat is evolved at the interface. The parameters appearing in the equations have been expressed in terms of experimental data, the coefficient of friction, known materials properties, and the ellipticity and number of contact spots. The equations are especially simple in the limiting cases of very high and of very low speeds, and were indeed known in these limits for circular, albeit not for elliptical contact spots. As an example, the flash temperatures of plastic contact spots on account of friction heat have been computed for (i) an electrical brush material sliding on copper, and (ii) a carbon steel sliding on itself. In these examples the dependence of the flash temperature on the velocity of the contact spots relative to either or both of the two sides has been investigated, wherein the effect of sliding rate on the flash temperature via the strain rate dependence of local hardness has been taken into consideration,- it is believed for the first time in any theoretical investigation of flash temperatures. In the high-speed case, in agreement with intuitive expectation, the numerical examples show that under otherwise same conditions and same macroscopic velocity, minimum flash temperature is attained when the spot moves relative to both sides. Typically, that minimum does not occur when the contact spot speed is one half of the relative speed on each of the two sides, however. Moreover, and somewhat unexpectedly, the results show that the previously neglected strain rate dependence of the hardness has a considerable effect.
An Inverse Solution to the Point Contact EHL Problem Under Heavy Loads
Authors: Hou K. P. , Zhu D. , Wen S. Z.
Published: October 2009

A set of computational results of the point contact EHL problem under heavily loaded condition is presented in this paper, and the numerical scheme for the inverse solution of the Reynolds Equation is developed. By using a deformation matrix to calculate the local elastic deformation and its inverse matrix to modify the pressure distribution, both the convergence and the stability of the numerical method are satisfactory. The examples of calculation adopted have been extended from Hamrock and Dowson’s cases into the operating region of heavy load. The results obtained have shown the effects of speed, load, and choice of materials on the film thickness, and have proved Hamrock and Dowson’s formulae for estimating film thicknesses to be accurate under heavily loaded condition.
The Influence of Certain Raceway Dent Geometries (3-D) on Contact Stresses and Rating Fatigue Life of Rolling Bearings
Authors: de Mul J. M. , Vree J. M. , Kuypers J. C.
Published: October 2009

With hard metal balls of 1 mm diameter, small indentations are pressed into the inner ring of a 6205 deep groove ball bearing in the middle of the track. Running the bearing over a short period of time, under a suitable load causes the dents to change shape. The deformed dent shape is theoretically transposed to a particular 7205B angular contact ball bearing geometry in the middle of its running track, and the possibility of theoretical 3-D analysis is explored. As a first step, pressure distributions in the ball-raceway contacts are calculated with a theoretical 3-D model, with due consideration of the indentations. This is followed by computation of subsurface stresses by means of another mathematical 3-D model. Finally, fatigue life is analyzed by integrating a fatigue (survival probability) function over the endangered volume in the inner ring, using a general 3-D model featuring a fatigue stress limit. As observed in experiments with similar dents, reported in the literature, the analysis predicts considerable reduction in fatigue life. Also, the maxima of fatigue stress and fatigue function are predicted in the experimentally observed region of initiation of failure.
Thermal Effects in Rolling/Sliding EHD Contacts: Part 1—Experimental Measurements of Surface Pressure and Temperature
Authors: Dow T. A. , Stockwell R. D. , Kannel J. W.
Published: October 2009

This paper discusses the results of a series of experiments to measure the pressure and temperature distribution between a pair of elastohydrodynamically lubricated (EHD) disks. Three lubricants have been studied: a synthetic paraffinic oil (XRM-109F), a polyphenyl ether (OS-124), and a traction fluid (Santotrac 50). Pressure and temperature readings throughout the contact are presented as three-dimensional plots. Simultaneous measurements of the EHD film thickness, and the tractive force between disks under slip conditions are also included. The variables are disk load and slip at a fixed surface speed. The highest temperatures were measured with the traction fluid which recorded a temperature rise of 50 degrees C through the contact.
Mechanisms of White Layer Generation With Reference to Machining and Deformation Processes
Authors: Griffiths B. J.
Published: October 2009

The term “white-layer” refers to hard layers of material which resist etching and appear featureless and white under the microscope. This paper presents some of the publications on white layer formed during machining and deformation processes. The mechanisms of white layer generation are discussed and to the three traditional mechanisms (usually associated with wear) of rapid heating and cooling, surface reaction and plastic deformation are added pressure, strain rate and cooling rate.
A Model for Run-In and Other Transitions in Sliding Friction
Authors: Blau Peter J.
Published: October 2009

The mathematical framework for a sliding friction model for run-in and other tribological transitions is presented. The semiempirical model was developed to portray the commonly observed shapes, durations, and variations in kinetic friction coefficient versus sliding time curves. Terms in the model involve material properties and physical interface conditions such as transfer, debris accumulation, and surface roughness. The forms of individual terms are adjustable through the use of systemspecific scaling parameters in order to provide enough modeling flexibility to treat a variety of possible tribological conditions. Effects of such conditions as lubrication efficiency loss over time, and temperature build-up can be incorporated by modification of appropriate terms. Illustrative plots using the framework with several combined contributions are compared with experimental data from previous work. The basic framework of the model can be further developed to incorporate sub-models for specific sliding friction contributions and, in so doing, reduce the number of empirical system parameters required to model actual tribosystem behavior.
Wear Reduction and Surface Layer Formation by a ZDDP Additive
Authors: Jahanmir Said
Published: October 2009

The results of wear tests and surface analyses confirmed that the wear behavior in the presence of ZDDP is controlled by chemically reacted surface films. Surface analysis by Auger microprobe showed that the reacted layer is composed of iron sulfide and zinc phosphate and that it extends to several hundred Å below the contact surface. It was found that the effectiveness of ZDDP in wear reduction was dependent on the test conditions. Under low loads and temperatures, it decreased wear by two orders of magnitude. However, at higher loads and temperatures, wear was increased by one order of magnitude. Scanning electron microscopy confirmed that at low loads, ZDDP changes the wear mechanism from plowing to a mild form of surface deformation, whereas at high loads plowing is changed to delamination of the surface layer. Surface analysis by Auger showed that higher loads and temperatures had resulted in reduction of sulfur content in the surface films. This reduction is attributed to changes in the reaction kinetics at higher contact temperatures caused by high contact loads and elevated oil temperatures. Since sulfides are usually harder than phosphates, the higher wear rate by delamination is explained by the loss of film strength due to reduction of sulfide content.
The Effects of Indent Residual Stresses on Mixed Mode Cyclic Crack Growth Driving Forces for Bearing Inner Rings
Authors: Bhargava V. , Rubin C. A. , Hahn G. T.
Published: October 2009

The residual stresses produced by plastic dents in a solid cylinder have been evaluated for overload, peak-contact-pressure-to-shear-strength ratios of poi/k = 3.5, and poi/k = 4. The effects of 2 sets of indent residual stresses on the cyclic crack growth driving forces generated by rolling contact at relative peak pressures of por/k = 0.5, 1.0 and 2.0, have been evaluated for 3 conditions. These are: (1) the slowly revolving ring, (2) the rapidly revolving ring with associated press fit and centrifugal stresses, and (3) the rapidly revolving ring with the superimposed circumferential compressive stresses arising from a carburized surface layer. The values of ΔKI ΔKII, and the combined mode, ΔKe, are calculated for 18 different rolling conditions, for small cracks with 8 different inclinations, 5 crack-face friction coefficients, and 21 locations in the dent region. The results show that the ΔK-values for a 2a=20μm long crack can exceed the Mode I threshold when the rim rotates slowly. Larger ΔK-values are obtained in the presence of press-fit and centrifugal stresses. However, the residual stresses of the carburized surface layer more than compensate for the press-fit and centrifugal stresses, reducing the ΔK-values below the levels obtained for the slowly rotating rim.