bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis and Testing for Rotordynamic Coefficients of Turbulent Annular Seals With Different, Directionally-Homogeneous Surface-Roughness Treatment for Rotor and Stator Elements
Authors: Childs D. W. , Kim Chang-Ho
Published: October 2009

A combined analytical-computational method is developed to calculate the transient pressure field and dynamic coefficients for high-pressure annular seal configurations which may be used in interstage and neck-ring seals of multistage centrifugal pumps. The solution procedure applies to constant-clearance or convergent-tapered geometries which may have different (but directionally-homogeneous) surface-roughness treatments on the stator or rotor seal elements. It applies in particular so-called “damper-seals” which employ smooth rotors and deliberately-roughened stator elements to enhance rotor stability. Hirs’ turbulent lubrication equations are modified slightly to account for different surface-roughness conditions on the rotor and stator. A perturbation analysis is employed in the eccentricity ratio to develop zeroth and first order perturbation equations. The zeroth-order equations define both the leakage and the development of circumferential flow due to shear forces at the rotor and stator surfaces. The first-order equations define perturbations in the pressure and axial and circumferential velocity fields due to small relative motion between the seal rotor and stator. The solution applies for small motion about a centered position and does not employ linearization with respect to either the taper angle or the degree of swirl, i.e., the difference between the circumferential velocity at the given axial position and the asymptotic circumferential-velocity solution. Test results for four different surface-roughness confirm the predicted net damping increase for “damper seals.” A round-hole-pattern stator yielded the highest net damping and lowest leakage of all seals tested. The seals are substantially stiffer than predicted, but the theory does an adequate job of predicting net damping.
Rotordynamic Coefficients for Compressible Flow in Tapered Annular Seals
Authors: Nelson C. C.
Published: October 2009

Derivation of the governing equations for compressible flow in a tapered annular seal is based on Hirs’ turbulent bulk-flow model. Zeroth and first-order perturbation equations are developed by an expansion in the eccentricity ratio. These equations are numerically integrated to obtain the leakage, and the direct and cross-coupled stiffness and damping coefficients. Seal parameters similar to the Space Shuttle Main Engine High Pressure Oxidizer Turbopump are used to demonstrate output from the analysis procedure. The effects of preswirl and seal taper are shown for three different length-to-diameter ratios. Generally the results indicate that prerotating the fluid significantly increases the cross-coupled stiffness but has little effect on the other coefficients, and increasing the convergent taper increases the direct stiffness while decreasing the direct damping and cross-coupled stiffness.
A Zero-Leakage Film Riding Face Seal
Authors: Lipschitz A.
Published: October 2009

A new [1] zero-leakage film riding mechanical face seal is presented. The seal serves as a static-contacting seal while the machine shaft is in stand-still and turns into a film riding dynamic seal by lifting off the rotor surface to a few micro-meters gap once motion has begun. The dynamic sealing as well as lifting capabilities stem from inter-connected hydro-dynamic bearings which are circumferentially distributed around the annular stator face. Approximate calculations together with preliminary experimental results are shown and analyzed.
Elastohydrodynamic Behavior of Rolling Elliptical Contacts: Part II: Oil Film Thickness and Contact Profile
Authors: Mokhtar M. O. A. , Abdel-Ghany A. A.
Published: October 2009

A spherically crowned circular disk in contact with a mating plain cylindrical one has been used in a two disk machine to conduct elastohydrodynamic (EHD) investigations with the contact zone describing elliptical shape. The oil film thickness variation has been accurately measured and herein presented under several contact situations with disks running with either pure rolling or combined rolling and sliding motion. Results confirmed that the introduction of a percentage slip over a rolling contact by either changing disks relative speed or skewing disks axes relative to each other, would affect the resultant oil film thickness by reducing it. However, the contact profile retained its shape with a mean oil film passage followed by a reduction at the trailing exit end. Compared with previous EHD theoretical and experimental findings, the present results come in line with previous predictions and confirm the importance of adopting thermal solutions in solving EHD situations.
Stability of Squeeze Film Damped Multi-Mass Flexible Rotor Bearing Systems
Authors: McLean L. J. , Hahn E. J.
Published: October 2009

A technique is presented for investigating the stability of and the degree of damping in the circular synchronous orbit equilibrium solutions pertaining to radially symmetric multi-mass flexible rotor bearing systems. It involves the analysis of appropriate linearized perturbation equations about the equilibrium solutions and is applicable to systems with several squeeze film dampers. For a system with a single damper, stability threshold maps, independent of unbalance distribution, may be found in terms of the same damper parameters and operating conditions as the equilibrium solutions, thereby allowing for damper design and performance monitoring. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows the utility of zero frequency stability maps for delineating multiple solution possibilities and that for low (in this case of the order of 0.06 or lower) bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system.
Measurements and Interpretations of Sliding Wear Damage in Metals
Authors: Blau P. J.
Published: October 2009

Research on sliding friction and wear of metals has involved studies of subsurface microstructural deformation. This paper considers the difficulties of measuring deformation and analyzing the implications of such studies on several bases: (1) defining the physical extent of sliding-induced deformation, (2) making appropriate measurements of deformation for complex tribological conditions, and (3) correlating microstructural wear damage with the measurable friction forces on sliding contacts. Data for unlubricated block-on-ring tests of Cu and 1020 steel on 4619 steel are used to demonstrate limitations and correlations possible with metallographic studies in tribology.
An Experimental Investigation Into the Thermohydrodynamic Behavior of a High Speed Cylindrical Bore Journal Bearing
Authors: Gethin D. T. , Medwell J. O.
Published: October 2009

A description of the design of a high speed journal bearing test apparatus and some results recorded from a cylindrical bore bush fed by two axial grooves are presented. These highlight the complex temperature patterns which are generated in the bush. To compliment this detailed information, the variation of load capacity, bush torque reaction, leakage, and bulk outlet temperature with speed are presented also. The work suggests that Taylor’s criterion may be applied broadly to determine the onset of non laminar flow in bearings. It also provides supportive evidence concerning the applicability of design procedures used in the transitional flow regime.
Head-Wear Measurements by Autoradiography of the Worn Magnetic Tapes
Authors: Bhushan B. , Nelson G. W. , Wacks M. E.
Published: October 2009

The transfer of wear debris of a nickel-zinc ferrite head to a magnetic tape was measured by autoradiography of the tape after it was worn against the irradiated ferrite head. Ferrite deposits on the tape were observed only after 5000 passes. Dots or specks on the autoradiograph of the tapes of about 200 micrometers in diameter, caused by particles of ferrite about 1 μm in diameter and mass of about 10−11 g, were measured. The average amount of ferrite deposited on the tape after 20,000 passes was about 0.6 nanogram per square centimeter; some areas showed uniform deposits of ferrite concentration of 10–20 ng/cm2. Based on our estimates of total head wear, only a small fraction (about 0.6 percent) of the total ferrite wear debris was transferred to the tape, about 0.2 percent was transferred to the tape-drive component surfaces, and the rest, we conclude, was airborne.
Measurement of Local Microscopic Wear
Authors: Dunaevsky V. V.
Published: October 2009

A method for determining a linear wear comparable to a surface roughness height is described here. The method allows estimation of the wear by results of profilometry of the worn surface only. The formulas presented provide wear evaluation for surfaces modeled by Gaussian random fields. The method simplifies the technology of precise wear measurements, improves their accuracy, and increases the availability of profilometrical ways of wear analysis.
A Kinematic Model for Mechanical Seals With Antirotation Locks or Positive Drive Devices
Authors: Green I. , Etsion I.
Published: October 2009

A kinematic model of mechanical face seals is presented. Two basic seal arrangements are considered: a flexibly mounted stator with antirotation locks, and a flexibly mounted rotor with positive drive devices. The equation of kinematic constraint is derived and presented in a simple form for all the possible types of antirotation or positive drive mechanisms found in practical seals. This simple form is then used to derive the dynamic moments acting on the flexibly mounted element of the seal.
Pumping Action of Aligned Smooth Face Seals Due to Axial Vibrations-Experiment
Authors: Kaneta M. , Fukahori M.
Published: October 2009

The mechanism of pumping action caused by axially vibrating one of the seal faces with continuous parallel film thickness is clarified experimentally. The results obtained in the experiment confirm the theory developed in a previous investigation [11]. The fundamental design principles of mechanical seals are also described from the viewpoint of this pumping phenomenon.
On the Laminar Flow Characteristics of Conical Bearings. Part II—Experimental Verification
Authors: Kalita W. , Yegani N. , Rodkiewicz Cz. M. , Kennedy J. S.
Published: October 2009

The laminar flow characteristics of the externally pressurized central recess conical bearings with narrow gaps, predicted theoretically in Part I of this paper, have been verified experimentally. Two main effects on the performance of conical bearings have been investigated, namely: the effect of nonconstant film thickness along the gap of the bearing and the effect of rotation. It was found that experimental pressure distributions and load capacity of the constant and divergent gap bearings were in close agreement with the theoretical data for the low rotational velocities however, with the increased rotation, the experimental values were higher than theoretically predicted. The experimental values of pressure, load capacity, and the torque of convergent gap bearings were found higher than theoretical.
Fluid Inertia Effects on the Load Capacity of Spherical Spiral Groove Bearings
Authors: Sato Yuichi
Published: October 2009

The effects of centrifugal force on the load capacity of inwardly and outwardly spherical spiral groove bearings, operated in laminar regime and lubricated with incompressible fluid, have been investigated. The narrow groove theory has been generalized to include the centrifugal effect of lubricant. The analysis demonstrates that the fluid inertia force reduces the load capacity of an inwardly pumping bearing, whereas it increases the load capacity of an outwardly pumping bearing. The theoretical results are compared with the experimental ones.
The Accuracy of Short Bearing Theory for Newtonian Lubricants
Authors: Buckholz R. H. , Hwang B.
Published: October 2009

The accuracy of the short bearing approximation is analyzed in this discussion. The results apply to Newtonian lubricants, and they can also be extended to non-Newtonian power-law lubricants. Reynolds’ lubrication equation is first solved by applying a regular perturbation expansion in pressure to the π film journal bearing; after this, a matched asymptotic expansion is applied to linear slider bearings. Approximate solutions are then compared with numerical solutions, to estimate the accuracy of the short bearing approximation. Finally, the accuracy of fluid film pressures predicted via short bearing theory is shown to depend upon three factors: the bearing aspect ratio, eccentricity ratio, and the partial-arc extent. Ocvirk’s short bearing series approximation—for finite bearing aspect ratio—is shown to become singular in the limit as the eccentricity ratio approaches unity. The one term π film Ocvirk solution is shown to be a nonconservative approximation to the journal bearing load capacity. A method to extend the accuracy of the short bearing approximation for partial-arcs and slider bearings is then presented.
Effects of Power—Law, Non-Newtonian Lubricants on Load Capacity and Friction for Plane Slider Bearings
Authors: Buckholz R. H.
Published: October 2009

The lubrication of a conventional, finite width plane bearing, using a power-law, non-Newtonian lubricant, is studied. The basic assumptions in this analysis are: thin fluid-film, no thermal effects, and a modified Reynolds’ equation for small bearing aspect ratios. Results from this study include bearing pressure, load, and friction formulas. Similar results for the not-so-small bearing aspect ratios are found via an Euler-Lagrange equation. This Euler-Lagrange equation is derived from the optimization integral for the modified Reynolds’ equation. Approximate solutions to the modified Reynolds’ equation and to the Euler-Lagrange equation are contrasted with numerical solutions for the modified Reynolds equation. Bearing aspect ratios in the range 0.1 to 0.6, clearance ratios in the range 1.2 to 4.0, and non-Newtonian power-law index in the range 0.4 to 1.0 are considered.
The Thermal Control of Friction at High Sliding Speeds
Authors: Ettles C. M. McC.
Published: October 2009

It is proposed that thermal effects govern friction in high speed unlubricated contact. The general principle can be found from a manipulation of Blok’s flash temperature theory to give the coefficient of friction as a dependent parameter. The principal factors controlling friction, provided the conditions are sufficiently severe, appear to be the decomposition temperature, hardness and thermal properties of the materials. The same mechanism appears from a numerical model of thermal effects in sliding. The model is compared with several sets of experimental results in different configurations.
Wear Mechanism of Ceramics and Surface Topography
Authors: Hisakado T.
Published: October 2009

Assuming that harder asperities sliding on a flat surface were semicylindrical with the hemispherical ends, whose surface consisted of a series of spherical micro-asperities, effects of the number of contact points n, total area Sp of the cross-sections of grooves ploughed by harder asperities and depth of plastic zone on the coefficient of friction and wear for ceramics were theoretically analyzed. To verify theory, wear tests with various ceramic pins and a Si3N4 disk were carried out at a sliding speed of 1.63 m/s and under load of 0.98 N with no lubrication. The sizes of wear scratches on the worn surfaces were measured by means of a Talysurf and SEM photographs. The wear rates of the pins and Si3N4 disks increased with an increase in the mean cross-sectional area Sp/n of the scratches. This trend agreed with the theoretical results, which also showed that the Sp values were proportional to the wear rates. Theory also indicated the existence of a new criterion applicable to estimation of the wear rate.
Performance Characteristics of Finite Width Journal Bearings Under the Separation Boundary Condition
Authors: Nakai M. , Kazamaki T. , Hatake T.
Published: October 2009

The separation boundary condition is considered to be comparatively exact in the physical consideration of the supposition. The calculated performance characteristics applied to infinite width journal bearings are related to experimental results to some extent. However, performance characteristics applied to finite width journal bearings, which might be able to explain the experimental results more precisely, have been unknown. The present paper describes the application of the separation boundary condition to finite width journal bearings, and calculation results of some performance characteristics. The results are related to well-known experimental results in several respects.
A Thermohydrodynamic Solution of Pivoted Thrust Pads: Part II—Static Loading
Authors: Jeng M. C. , Zhou G. R. , Szeri A. Z.
Published: October 2009

This is Part II, of a three-part sequence of papers on pivoted thrust pads. In this paper we apply the thermohydrodynamic theory of Part I to statically loaded, sector shaped pivoted thrust pads. The film shape is arbitrary and pad deformation can be specified once the geometry of the pad and the geometry of its support system are known. Presently we assume spherical crowning of the pad: crowning presents us with an opportunity to discuss film cavitation and its effects. Spherical-crowning is advantageous to employ, because it can be represented by a single parameter and because it yields the approximate shape of a loaded pivoted pad.
Analysis of Thermal Effects in Hydrodynamic Bearings
Authors: Boncompain R. , Fillon M. , Frene J.
Published: October 2009

A general THD theory and a comparison between theoretical and experimental results are presented. The generalized Reynolds equation, the energy equation in the film, and the heat transfer equation in the bush and the shaft are solved simultaneously. The cavitation in the film, the lubricant recirculation, and the reversed flow at the inlet are taken into account. In addition, the thermoelastic deformations are also calculated in order to define the film thickness. Good agreement is found between experimental data and theoretical results which include thermoelastic displacements of both the shaft and the bush.
Study of Conical Whirl Instability of Externally Pressurized Porous Oil Journal Bearings With Tangential Velocity Slip
Authors: Guha S. K.
Published: October 2009

In the present paper, an attempt has been made to study theoretically the conical whirl instability of unloaded hydrostatic porous oil journal bearings with tangential velocity slip on the bearing film interface. The effect of various parameters on stability has also been investigated.
Stability Analysis of Finite Offset-Halves Pressure Dam Bearing
Authors: Mehta N. P. , Singh A.
Published: October 2009

Cylindrical pressure dam bearings are manufactured in two halves. During assembly, intentionally or accidentally, the centers of two halves may get displaced. This paper analytically analyzes the dynamic behavior of a cylindrical pressure dam bearing having centers of both halves displaced. Hence the bearing is termed as offset-halves pressure dam bearing. It has been observed that stability of a cylindrical pressure dam bearing can be increased many times by displacing the centers of two halves. The bearing so obtained is even superior to elliptical and half-elliptical pressure dam bearings in stability. A simple and inexpensive method of increasing stability of cylindrical pressure dam bearings has been analytically analyzed in this paper.
Operating Aspects of an Oil Pumping Ring Seal
Authors: Smith P. J. , Keith T. G.
Published: October 2009

Past analyses have left several unanswered questions regarding the operation of a pumping ring seal. This paper addresses some of these unresolved problems. In particular, treatment of the film-ring interfacial boundary condition and the return portion of the pumping cycle are numerically investigated. Further, a simple model is proposed to determine whether or not the seal operates fully flooded.
Plowing Friction in Dry and Lubricated Metal Sliding
Authors: Komvopoulos K. , Saka N. , Suh N. P.
Published: October 2009

Experimental evidence for plowing under dry and lubricated sliding conditions is presented and analytical expressions for the coefficient of friction due to plowing are obtained. The theoretical friction coefficient was found to be a function of the sharpness of the hard asperities, the interfacial “friction” conditions and the shape of the plastic zone. The agreement between theoretical and experimental friction coefficients from lubricated sliding and cutting experiments was remarkably good. The discrepancy between theory and experiment in the case of dry sliding between like metals was shown to be due to plastic deformation of the asperities. Consequently, a different model for plowing was proposed for the case of dry sliding between like metals which produced estimates for the coefficient of friction in fair agreement with the experimental results.
Effect of Normal Stiffness in Loading System on Wear of Carbon Steel—Part 2: Dynamic Normal Load and Effective Sliding Distance
Authors: Chiou Y. C. , Kato K.
Published: October 2009

In order to explain the effect of normal stiffness in the loading system on wear, the mean dynamic normal load and the effective sliding distance were determined from the record of dynamic normal load. The mean dynamic normal load was approximately constant at normal stiffnesses smaller than 10 N/mm and increased markedly at normal stiffnesses larger than 103 N/mm. The effective sliding distance was approximately equal to the apparent sliding distance at normal stiffnesses smaller than 10 N/mm and decreased markedly at normal stiffnesses larger than 103 N/mm. The effective wear rate was newly defined in terms of the effective sliding distance. The change of effective wear rate with the change of sliding velocity was linearly correlated to the change of mean dynamic normal load under each normal load and normal stiffness.
Wear Behavior of Laser Surface-Hardened Gray and Ductile Cast Irons: Part 1—Sliding Wear
Authors: Molian P. A. , Baldwin Mark
Published: October 2009

The influence of laser surface transformation hardening on the sliding wear characteristics and mechanisms of ASTM class-40 gray and 80-55-06 ductile cast irons was investigated. A 1.2 kw, continuous wave, CO2 gas laser was employed to scan the beam successively across the surfaces of cast irons to generate hardened and tempered layers with various case depths. A pin-on-disk wear test system was then used to study the wear behavior as functions of case depth, microstructure, hardness, and surface roughness. As expected, a dramatic improvement in resistance to scuffing and sliding wear was obtained. However, the most significant result was the occurrence of negligible oxidational wear for a load range that increased with an increase in case depth. Resistance to mild and severe wear, mild-to-severe wear transition load, and frictional heating were increased with an increase in case depth. Analysis of worn surfaces and wear debris revealed that negligible oxidational wear in laser-hardened irons is due to two mechanisms: oxidation and adhesion of oxide to the substrate. In contrast, the mild oxidational wear of untreated irons occurs through the formation of loose oxide debris. The mechanisms of severe wear were plastic deformation, delamination, and adhesion; the rate process was controlled by adhesion for laser hardened irons and delamination for untreated irons.
A Thermal Hydrodynamic Lubrication Analysis for Hydrostatic Extrusion of a Work Hardening Metal
Authors: Mahdavian S. M.
Published: October 2009

The thermal hydrodynamic lubrication theory is extended to hydrostatic extrusion of a strain hardening metal. The effects of viscous heating in both inlet and work zones, and surface temperature of work zones are included. The results are compared with previous theoretical models. It indicates that thermal strain hardening effects play an important role in determining hydrostatic extrusion for high reduction of area and high strength metals.
The Application of a Deuteron Stripping Reaction to Investigate Extreme-Pressure Films
Authors: Azouz A. , Rowson D. M. , Quinn T. F. J.
Published: October 2009

Extreme-pressure (EP) additives containing sulphur have been tested using a fourball machine and the structure and thickness of the surface films which formed during wear tests have been studied using conventional methods of physical analysis. A nuclear technique based on a deuteron-proton stripping reaction, was employed to give complementary information (unobtainable by more usual techniques) which produced a better understanding of the structure and formation of such EP films.
Internal Stresses and Their Influence on Material Stresses in Hertzian Contacts—Calculations With Different Stress Hypotheses
Authors: Broszeit E. , Zwirlein O.
Published: October 2009

Using idealized assumptions, the stress condition in the semi-infinite body of the Hertzian contact region can be calculated for various geometries as a function of the surface pressure (normal force), the friction (tangential force at the surface), and the residual stresses in the material. Equivalent stresses can be formed from the coordinate stresses using various stress hypotheses (distortion energy hypothesis, shear stress hypothesis, and alternating shear stress hypothesis). The effects of friction, residual stresses, and contact geometry on the location and magnitude of the equivalent stresses appearing in the material have been investigated, the stress hypotheses being evaluated in terms of the extent to which they take account of these effects in an appropriate form. These investigations show clearly that the distortion energy hypothesis is the best representation of the extent of material stress in the case of dynamically loaded rolling elements. The shear stress hypothesis can be considered as a good approximation whereas the alternating shear stress hypothesis is only capable of providing useful conclusions to a limited extent.
Elastic Stresses Below Asperities in Lubricated Contacts
Authors: Ioannides E. , Kuijpers J. C.
Published: October 2009

The presence of contacting asperities in lubricated rolling bearings modifies the subsurface stress field strongly in the neighborhood of the surface and, to a lesser extent, at larger depths where the maxima of the shear or von Mises stress of a smooth Hertzian contact normally exist. The near surface stresses are of importance because they may result in micropitting, a mode of surface distress which leads to the eventual fatigue failure of the contacting surfaces. A mathematical method is presented in this paper which allows the statistical calculation of important parameters (maximum von Mises stress or maximum shear stress amplitude) of the stress fields generated under elastically deforming asperities during their passage through a lubricated contact. The asperities themselves are modelled using estimates of the surface spectral moments obtained from single-profile trace measurements. The method is applicable to both isotropic and anisotropic rough surfaces. Moreover, the important effect of the shear surface tractions, including tractions over the asperities, is contained in the analysis. Computed examples are presented for different surface textures and film thicknesses in the case of a deep groove ball bearing. Finally, a qualitative attempt is made to correlate features of these stress fields with the presence of surface pitting, and the limitations of the analysis are discussed.
Calculation of the Dynamic Coefficients of a Journal Bearing, Using a Variational Approach
Authors: Klit P. , Lund J. W.
Published: October 2009

The dynamic bearing coefficients are obtained from a solution to the variational equivalent of Reynolds equation. A perturbation method is applied to find the individual dynamic coefficients. The Finite Element Method is used in the numerical evaluation of the equations. The flow is assumed to be laminar, the lubricant is Newtonian. Allowance is made for viscosity-temperature dependency in circumferential and axial directions.
Ball Bearing Response to Cage Unbalance
Authors: Gupta P. K. , Dill J. F. , Artuso J. W. , Forster N. H.
Published: October 2009

Motion of the cage in a high-speed angular contact ball bearing is experimentally investigated as a function of prescribed unbalance, up to operating speeds corresponding to three million DN. The predictions of cage motion made by the recently developed computer model, ADORE, are validated in the light of the experimental data. It is shown the cage whirl velocity is essentially equal to its angular velocity at all levels of unbalance and over a wide range of operating conditions. For the inner race guided turbine engine bearing, the cage/race interaction takes place directly opposite to the location of the unbalance and the severity of the interaction increases with the level of unbalance and the operating speed. ADORE predictions, over the entire range of unbalance and bearing operating conditions, are in very good agreement with the experimental observations.
Lubricant and Additive Effects on Spur Gear Fatigue Life
Authors: Townsend D. P. , Zaretsky E. V. , Scibbe H. W.
Published: October 2009

Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided into four batches each of which had a different additive content. Lubricants tested with a phosphorous-type load carrying additive showed a statistically significant improvement in life over lubricants without this type additive. The presence of sulphur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt percent sulfur and 0.1 wt percent phosphorus EP additives in the lubricant had reactive films that were 200 to 400 Å (0.8 to 1.6 μin) thick.
The Significance of Oxide Layers in Boundary Lubrication
Authors: Komvopoulos K. , Saka N. , Suh N. P.
Published: October 2009

Analytical and experimental studies were conducted on oxidized and nonoxidized pure aluminum, OFHC copper, and electroplated chromium to investigate the role of surface oxide layers in boundary lubrication. The effects of the thickness of the oxide layers, the elastic moduli of the oxide and the metal, and the normal surface traction have been addressed. In addition, several possible failure mechanisms of both thin and thick oxide films have been proposed. The experimental results have shown that low coefficients of friction, about 0.1 or less, and especially low wear can be obtained in boundary-lubricated sliding if the metal surfaces are protected from plastic deformation by sufficiently thick oxide layers. Scanning electron microscopy has shown that when the oxide layers are not ruptured, the wear of the surfaces is negligibly small. In this case, the oxide-oxide contacts deform primarily elastically and the predominant friction mechanism is the shear of the lubricant film. Based on this evidence, a theoretical model for friction was proposed and the agreement between theoretical and experimental coefficients of friction was reasonably good. Disruption of the oxide layers during sliding, however, was found to result in plastic deformation and plowing of the surfaces.
Wear Mechanism of Ceramic Materials in Dry Rolling Friction
Authors: Kim S. S. , Kato K. , Hokkirigawa K. , Abe´ H.
Published: October 2009

Wear tests in dry rolling contact were carried out at room temperature on five ceramic materials, such as silicon nitride, silicon carbide, cermet, titania, and alumina. The results showed that wear rate of silicon nitride was smaller than any of the other ceramic materials and bearing steel. Observations of worn surface and wear debris revealed that ceramic materials have two types of wear, one related to real contact area and another related to Hertzian contact area. It was also found that brittle fracture dominates the wear process of ceramic materials in dry rolling contact. Based on the experimental results, wear rate of ceramic materials was expressed with a new nondimensional parameter.
The Elasto-Hydrodynamic Lubrication of Soft, Highly Deformed Contacts Under Conditions of Nonuniform Motion
Authors: Hooke C. J.
Published: October 2009

A method is described for the calculation of the film thicknesses in soft, highly deformed contacts for situations where the entrainment velocity is not constant. Two particular results are presented. It is shown that, where there is a rapid reversal of motion, the steady state analysis remains acceptable. However, for a contact reciprocating with a sinusoidal motion, it does not, and here the minimum film thickness occurs at the end of the stroke. The minimum film thickness lies at the end of the contact furthermost from the area swept during the stroke and can only be determined by a dynamic analysis.
Multigrid, An Alternative Method for Calculating Film Thickness and Pressure Profiles in Elastohydrodynamically Lubricated Line Contacts
Authors: Lubrecht A. A. , ten Napel W. E. , Bosma R.
Published: October 2009

Film thickness and pressure profiles have been calculated for line contacts at moderate and high loads, using a Multigrid method. Influence of the compressibility of the lubricant on the minimum film thickness and on the pressure spike has been examined. The required computing time is an order of magnitude less than when using the previous methods.
The Elastohydrodynamic Problem Expressed in Terms of Extended Variational Formulation
Authors: Strozzi Antonio
Published: October 2009

The elastohydrodynamic problem is revisited in terms of an extended variational formulation, where the corresponding functional exhibits minimum properties in the solution neighborhood. Such features are exploited in the development of a relaxation-type solver. The numerical results indicate that the convergence rate of the proposed relaxation scheme becomes increasingly poor as the solution of the elastohydrodynamic problem is approached. A polyalgorithm based on a combination between relaxation-type and Newton-type schemes is proposed. The numerical experiments referred to various sealing profiles of increasing foundation compliance show that the proposed procedure is particularly advantageous in the case of soft lubricated contacts.
Viscoelastic Parameters of 5P4E as a Function of Pressure and Temperature by Light Scattering Technique
Authors: Bezot P. , Hesse-Bezot C. , Berthe D. , Dalmaz G. , Vergne P.
Published: October 2009

Measurements of viscoelastic parameters as a function of pressure and temperature are reported for the m-bis (m-phenoxy phenoxy) benzene. Infinite frequency shear modulus is compared with the limiting shear strength data obtained from the literature under the same pressure and temperature conditions.
The Formulation of the Mixed Lubrication Problem as a Generalized Nonlinear Complementarity Problem
Authors: Oh Kong Ping
Published: October 2009

The mixed-lubrication problem is formulated as a nonlinear generalized complementarity problem in which the pressure acting on the load-bearing surface is taken as the unknown, and the lubricant flow and the gap between the surfaces are taken as its complements. An iterative method was developed to find the solution, which satisfies the complementarity condition that at each point on the load-bearing surface, the pressure or at least one of its complements, is zero at all times. Moreover, the pressure and its complements satisfy non-negativity constraints. The solution intrinsically decomposes the load-bearing surface into three distinct subregions: solid-to-solid contact, hydrodynamically lubricated contact, and no contact (or cavitation). It is shown that the mixed-lubrication formulation degenerates into the special cases of hydrodynamic or solid-to-solid contacts under appropriate load and speed conditions. A journal bearing with elastic support is analyzed to illustrate the method of solution. The transition of the lubrication mode from pure hydrodynamic contact to mixed contact is demonstrated.
Mobility and Impedance Tensor Methods for Full and Partial-Arc Journal Bearings
Authors: Moes H. , Sikkes E. G. , Bosma R.
Published: October 2009

Mobility and impedance tensors are introduced for full journal bearings. These tensors may replace the well known mobility and impedance vectors. Since tensors apply to arbitrary systems of reference, coordinates rotating with the sleeve, i.e. fixed coordinates, will be introduced and will henceforth replace the unidirectional system in current use. As a consequence, the restriction to full journal bearing applications which was necessary up to now may be withdrawn. The mobility- and impedance methods, as derived for full journal bearings, from now on apply equally well to partial-arc bearings. The mobility- and impedance tensor descriptions, needed in applications of the methods, can be derived in a straightforward manner form the generally applied vector descriptions for full journal bearings. Descriptions for partial-arc bearings will also be presented.
An Experimental Investigation on the Temperature Distribution in Circular Journal Bearings
Authors: Mitsui Junichi , Hori Yukio , Tanaka Masato
Published: October 2009

The temperature distributions in full circular bearings were measured in a test rig. The effects of journal speed, lubricant viscosity, and clearance ratio on the maximum bearing temperature and its location were discussed. The results were compared with the theoretical analysis by the present authors and good agreement was obtained over the wide range of operating conditions. The maximum bearing temperature is found to increase considerably with the increase of speed or lubricant viscosity and also with the decrease of clearance ratio. Its angular position is found to vary with speed and clearance ratio. These phenomena can be explained by the characteristics of maximum film temperature in the oil film.
Theoretical Modeling of the Vapor Cavitation in Dynamically Loaded Journal Bearings
Authors: Brewe D. E.
Published: October 2009

A theoretical investigation is made of the evolution of a vapor bubble for a submerged journal bearing under dynamically loaded conditions. The solution to the Reynolds equation is determined numerically using a control volume method (Elrod algorithm). This method conserves mass throughout the computational domain including the liquid-vapor interface which may or may not be in motion relative to the minimum film line. An ADI (Alternating Direction Implicit) method is used to effect the time march. Excellent agreement was found with the experimental work of Jakobsson and Floberg for stationary cavitation. Predictions of bubble life for nonstationary cavitation compare reasonably well with that measured by Jacobson and Hamrock using high-speed photography. A comparison study was performed to determine some of the consequences of applying a nonconservative theory to a dynamic problem. A complete dynamic cycle of a journal whirling in a circular path was chosen for the basis of comparison. Significant differences were observed in the load components near the end of the cycle. In each case, onset of cavitation was observed followed by bubble growth and subsequent collapse. More complete details of this phenomena are illustrated with the use of perspective graphic plots depicting the associated pressure distribution and region of cavitation with position and motion of the journal within the housing.
The Effect of Journal Bearing Misalignment on Load and Cavitation for Non-Newtonian Lubricants
Authors: Buckholz R. H. , Lin J. F.
Published: October 2009

An analysis for hydrodynamic, non-Newtonian lubrication of misaligned journal bearings is given. The hydrodynamic load-carrying capacity for partial arc journal bearings lubricated by power-law, non-Newtonian fluids is calculated for small valves of the bearing aspect ratios. These results are compared with: numerical solutions to the non-Newtonian modified Reynolds equation, with Ocvirk’s experimental results for misaligned bearings, and with other numerical simulations. The cavitation (i.e., film rupture) boundary location is calculated using the Reynolds’ free-surface, boundary condition.
Time-Varying Behavior of a Statically Indeterminate Shafting System in a Hydrodynamic Journal Bearing
Authors: Karni Z. H. , Parsons M. G. , Mourelatos Z. P.
Published: October 2009

A new direct iterative method for obtaining the time-varying behavior of a statically indeterminate shafting system within one of its hydrodynamic journal bearings is described. A modified Newmark’s method is used to step in time. At each integration time step an optimization technique iterates between the shafting system and the oil film analyses until an equilibrium is achieved. The three-dimensional shafting system structural analysis and the two-dimensional oil film hydrodynamic analysis utilize the finite element method. The “hourglass control” method is employed for the construction of the oil film fluidity matrix. A numerical example illustrates the method.
The Rotor Dynamic Coefficients of Coned-Face Mechanical Seals With Inward or Outward Flow
Authors: Green I.
Published: October 2009

The linearized fluid film dynamic coefficients, i.e., stiffness and damping, of flexibly-mounted rotor noncontacting mechanical face seals are found. The coefficients are derived from a previous study where the flexibly mounted element was the stator. The two cases of inward and outward flows, both having converging gaps in the direction of flow, are analyzed for the two mounting configurations, and it is found that the later case possesses higher angular stiffness.
Comparison of Hirs’ Equation With Moody’s Equation for Determining Rotordynamic Coefficients of Annular Pressure Seals
Authors: Nelson C. C. , Nguyen D. T.
Published: October 2009

The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs’ equation, assumes the friction factor is a function of Reynolds number only. The second, Moody’s equation, approximates Moody’s diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs’ constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals (e/2H0 = 0.05) Moody’s equation predicts 44 percent greater direct stiffness, 35 percent greater cross-coupled stiffness, 19 percent smaller cross-coupled damping, 59 percent smaller cross-coupled inertia, and nominally the same direct damping and direct inertia.
Determination of Squeeze-Film Dynamic Coefficients From Experimental Transient Data
Authors: Ramli M. D. , Roberts J. B. , Ellis J.
Published: October 2009

A technique for obtaining estimates of the direct damping and inertial coefficients of a squeeze-film bearing is described. This involves applying parametric identification and optimization techniques to digitized, free-decay experimental displacement records. The experimentally obtained coefficients, derived by this technique, were found to be significantly higher in magnitude (in some cases by a factor of about 10) than the corresponding values derived from conventional short-bearing theory, and to be virtually independent of the frequency of vibration.
Application of the k-ε Turbulence Model to the Squeeze Film Damper
Authors: Ku Chiao-Ping , Tichy John A.
Published: October 2009

The one-dimensional squeeze film damper is modeled for high speed flow by using the two-equation (k-ε) turbulent transport model. The assumption is made that the fluid flow at each local region of the squeeze film damper has similar behavior to inertialess flow in a channel at comparable Reynolds number. Using the k-ε model, the inertialess channel flow case is solved. Based on this result, correlations are obtained for the mean velocity, inertia and viscous terms of the integrated momentum equation for the squeeze film damper. It is found that turbulence increases the magnitude of the fluid pressure and the tangential force, while fluid inertia causes a shift on the pressure creating a significant radial force. In applications, turbulence may be a beneficial effect, increasing the principal damping force; while inertia may be detrimental increasing the cross-coupling forces.
Parallel Sliding Load Support in the Mixed Friction Regime. Part 1—The Experimental Data
Authors: Lebeck A. O.
Published: October 2009

When two parallel surfaces slide parallel to each other in the presence of a liquid, classical lubrication theory shows that no load carrying ability of the lubricant should result. In experiment after experiment it has been clearly demonstrated that a large and useful load carrying capability often does develop in such situations. Since the successful operation of a significant fraction of sliding bearings and face seals may depend upon this phenomenon, a better understanding would be very useful for bearing and seal design. In this paper much of the known data on parallel sliding experiments are reviewed and compared. Seals as well as bearings are included in this data base. A wide range of conditions and viscosities are included. Some recent work on parallel sliding in water is examined. A comparison of parallel sliding to tilted sliding is also made. It is shown that a strong load support mechanism is present in all of the experimental results. The experiments clearly show that as speed is increased the bearing surfaces are lifted up such that asperity contact and friction are reduced. While explanations are often given for individual sets of experiments, the pervasiveness of this behavior suggests that perhaps there is some mechanism common to all parallel sliding which is not well understood. A mixed friction model is developed and used to explain some of the results. Conclusions are reached concerning several characteristics of parallel sliding. The paper concludes that given the importance of this phenomenon, careful evaluation of the various possible load support mechanisms should be made so that an effective direction for further research can be established.
The Effect of Lubricant Inertia Near the Leading Edge of a Plane Slider Bearing
Authors: Buckholz R. H.
Published: October 2009

The influence of fluid inertia on a plane slider bearing that operates at a 0(1) modified Reynolds number is examined in this study. The flow is laminar, and the Reynolds number—based on the slider velocity, lubricant kinematic viscosity, and leading-edge slider height—can be as high as 1000. Our major conclusion is that the primary effect of fluid inertia is to raise the pressure boundary condition near the bearing leading-edge. Lubrication theory is used to determine the pressure in the fluid film in the region downstream of the bearing entry. The leading-edge pressure increase caused by convective inertia is determined by a mass-flux balance between the flow near the leading-edge, and the flow through the bearing gap, which is determined by lubrication theory. Analytical results are obtained both for the convective-inertia pressure at the bearing entrance and for the pressure under the slider bearing. Results are compared to other numerical calculations and to analytical results, where the fluid inertia terms were kept throughout the bearing gap.