bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastohydrodynamic Behavior of Elliptical Contacts Under Pure Rolling Situations
Authors: Mokhtar M. O. A. , Abdel Ghany A. A.
Published: October 2009

This part is a complimentary work to a previously published work on EHD lubrication behavior under pure sliding and combined rolling and sliding situations. In order to cover all aspects of EHD lubrication, the experimental work has been herein extended to present the results attained when two disks describe a pure rolling motion. A wide range of loads and speeds has been applied to the contacting disks under EHD regimes. The recorded pressure values and distribution confirm the existence of a second peak (spike) near the exit of the contact zone also under pure rolling situation. The spike has a value higher than maximum Hertzian pressure. A local constriction of oil film profile to identify the minimum EHD film thickness at trailing (exit) end of the film is observed to be nearby the location of the pressure spike. The results, compared to theoretical predictions, concluded that under pure rolling conditions, any increase in the applied load results in a corresponding increase in the developed pressure while a noticeable reduction in the minimum film thickness is recorded with decreasing rolling speeds.
Effects of Skew Unidirectional Striated Roughness on Hydrodynamic Lubrication: Part 2—Moving Roughness
Authors: To̸nder K.
Published: October 2009

The author’s work on the lubrication of unidirectional striated roughness at arbitrary angles to the direction of motion has been extended to the case of moving roughness. The previously derived equations are applied to plane inclined pad bearings and solved for various parameter values. The results bring out strong effects that may be useful for bearing design optimisation. As in the case of stationary roughness, the main effect is the generation of a crosswise shear flow component that may improve bearing cooling considerably, or blocked, may generate higher pressures. It is concluded that stationary roughness seems to be preferable to a moving roughness pattern, but that a bearing surface pair having a crossed groove orientation is probably the best.
Hydrodynamics of Wire-Drum Contact
Authors: Magnin A. , Piau J. M. , Frene J. , Bois D. , Godet M.
Published: October 2009

The hydrodynamics of a wire-drum contact is analyzed using theoretical techniques developed in foil bearing studies. Analytical solutions and numerical solutions are obtained. Results show that: when for a given minimum film thickness the wire tension increases, the pressure arc extent decreases and reaches a minimum for certain wire tension level; the pressure distribution is independent of wire tension for large values of tension; and the active pressure zone depends strongly on film thickness.
A Study of Hysteresis on Attitude-Eccentricity Loci in Journal Bearings
Authors: Nakai Manabu
Published: October 2009

In this paper, hysteresis in attitude-eccentricity loci under conditions of increasing and of decreasing bearing loads is theoretically and experimentally investigated in journal bearings. This hysteresis is explained by the difference in pressure distributions due to the changes in the pressure and position of cavities under these two conditions. The phenomenon of journal shift on the attitude-eccentricity locus is also explained. Experimental results are qualitatively related to the theoretical framework. In addition, some observations are made on the tensile stress in the lubricant as generated in these experiments.
Squeeze Film Flow of Elastic Fluids at Steady Motion and Dynamic Loads
Authors: Harnoy A.
Published: October 2009

The role of the elasticity of the fluid is investigated in a squeeze film flow, between two parallel coaxial disks. An analysis is done for elastic fluids of low Deborah numbers, where the stress relaxation process is a first order effect to the dominant zero order effect of the viscosity. The constitutive equation of the fluid does not consider the normal-stresses. The results, which show a reduction in the load capacity for a steady speed squeeze action, are consistent with previous experiments in oil-polymer solutions. An improvement in the lubrication performance at dynamic loads is predicted and unlike in Newtonian fluids, the acceleration of the upper disk has a significant effect.
On the Squeeze Effect of Lubricant Between Two Rough Surfaces
Authors: Marui E. , Kato S. , Matsubayashi T. , Kobayashi A. , Senda S. , Ozawa M.
Published: October 2009

The clarification of the squeezing mechanism of lubricant, which flows between rough surfaces, is quite important for the improvement of the dynamic characteristics of sliding elements, and for the elimination of stick-slip vibration. In the present study, the surface roughness effect on the squeezing mechanism is examined. In the first place, the approximate equation of squeeze flow is introduced for flat surfaces. Then, the approximate equation is extended to the case of rough surface. The calculation of lubricant squeezing by the extended equation agrees well with the experimental results in both cases of circular and rectangular surfaces. The squeeze coefficient is the criterion for the load carrying capacity of the contact surface due to the lubricant squeezing. Then, this coefficient is obtained as a function of surface topography and oil film thickness. The representative equation of the squeeze coefficient for the rectangular surface is the same as for the circular surface. The fundamental information is important to improve the dynamic characteristics of sliding elements.
Dynamic Characteristics of Hydrostatic Thrust Air Bearing With Actively Controlled Restrictor
Authors: Sato Yuichi , Maruta K. , Harada M.
Published: October 2009

The dynamic characteristics of a hydrostatic thrust air bearing with an actively controlled orifice restrictor are investigated theoretically and experimentally. Theoretical results show that the dynamic stiffness and damping coefficients can be increased simultaneously when the restrictor area is controlled with appropriate phase-lag to the change of air film thickness, that is, plate vibrations. Consequently stability of the bearing can be improved. Experimental results show fairly good agreement with theoretical ones.
Further Test Results of the Leading-Edge-Groove (LEG) Tilting Pad Thrust Bearing
Authors: Mikula A. M.
Published: October 2009

This paper compares the LEG and pressurized controlled flow lubricant supply methods and evaluates their influence on the babbitt temperature and bearing power loss performance of a tilting pad, equalizing thrust bearing. The paper also presents new experimental temperature data from bidirectional testing of a unidirectional LEG bearing. The experimental data presented is from a 267 mm (10.5 in.) O.D. bearing, operating at shaft speeds up to 13000 rpm with applied loads that produced mean unit pressures of up to 3.45 MPa (500 psi). Conclusions are drawn based upon these test data.
On the Geometrical Imperfections in Ball Bearings
Authors: Gupta P. K.
Published: October 2009

Computer simulations of dynamic bearing performance, as obtained by the computer code ADORE, are used to develop correlations between key performance parameters and geometrical imperfections in both oil and solid lubricated ball bearings. The influence of race out-of-roundness, variation in groove curvatures and the variation in ball size, is modeled in terms of the effects on bearing life, heat generation and cage stability characteristics. The results demonstate the significance of the computer modeling approach to optimization of geometrical tolerances in practical bearing design.
Debris Damage in Rolling Bearings and Its Effects on Fatigue Life
Authors: Sayles R. S. , Ioannides E.
Published: October 2009

Predictions of fatigue life from debris indented roller bearings are calculated by the methods described by Webster, Ioannides, and Sayles [9] and presented as a comparison to the actual fatigue history of the bearings. Research is also presented on the influence of debris type and geometry in relation to the formation of dents within nonconforming contacts. In particular, the concept of elastic conformity around entrained debris is studied in detail and it is shown that a critical debris aspect ratio may well exist which defines a boundary between debris that can damage the contact surfaces, and that which cannot.
Performance Analysis of a New Concept Viscous Pump
Authors: Etsion I. , Yaier R.
Published: October 2009

A new concept of a viscous pump is described and the pump performance is analyzed. A linear relation is found between the flow rate and discharge pressure. Optimization of the pump geometry for maximum flow rate is presented. The potential of the new pump is demonstrated by numerical examples for general and medical applications. Finally the effect of misalignment tolerances on pump performance is discussed. It is found that under the maximum possible misalignment flow rate is reduced by no more than 30 percent and discharge pressure by less than 54 percent.
Parameters Affecting Thermo-Meohanical Cracking in Coated Media Due to High-Speed Friction Load
Authors: Ju F. D. , Liu J. C.
Published: October 2009

This investigation considers the thermo-mechanical effects of an asperity traversing at a high speed over a semi-infinite medium with a thin, hard coated surface. The general analytical solution of the temperature field and the thermal stress state are obtained and expressed in Fourier transform space. The analysis emphasizes the heating effect of the friction force, which leads to the initiation of the thermo-mechanical cracking or “heat-checking,” in the coating layer, the substrate, or their interface. For hard coated layers, the initiation of a crack will occur either in the coating layer, the substrate or the interface depending on the relative properties of the coating and the substrate and their bonding strength.
Thermomechanical Cracking in the Vicinity of a Near-Surface Void Due to High-Speed Friction Load
Authors: Chen T. Y. , Ju F. D.
Published: October 2009

This paper discusses the temperature distribution and the stress state in the vicinity of a near-surface rectangular cavity. They occur when the solid is subjected to the Coulomb frictional loading of an asperity moving at moderately high speed. The finite difference method is employed to calculate both the temperature and stress fields. The energy balance method is applied at the corners of the rectangular cavity to resolve the problem of singularities in the temperature field there. The stress singularity at each corner is represented by a special element that is introduced representing the behavior of the known stress singularity at the corner and its surrounding vicinity. Results show that the thermal stress effect dominates the stress field and eventually leads to failure. When a defect, such as a cavity, exists, the stress state that determines the failure phenomenon is more severe and can be quantified depending on the location of the cavity. These results were determined through a numerical computation based on the material properties of Stellite III. However, the parametric effect of material variations including changes in both thermal and mechanical properties were also considered. The study of the cavity location also established the existence of a critical cavity location. This location is defined by the critical ligament thickness (thickness between the wear surface and the top edge of the cavity), at which the cavity-influenced thermal tensile stress reaches a maximum. This thickness is important to designers when cavities at coating/substrate interface are either unavoidable or are too expensive to control in fabrication.
Thermohydrodynamic Analysis of Solid-Liquid Lubricated Journal Bearings
Authors: Khonsari M. M. , Esfahanian V.
Published: October 2009

Thermohydrodynamic theory is extended to include the effect of solid particles in hydrodynamically lubricated journal bearings. Appropriate governing equations and boundary conditions are derived for the fluid flow and heat transfer processes taking place in a finite journal bearing. A general computer program is developed to numerically solve the governing equations. Results are provided for biphase lubricants containing oil with molybdenum disulfide and polytetrafluoroethylene particles. The computational results are in good agreement with experimental findings. The results indicate that the bearing temperature field is affected significantly by the presence of particles in oil. Moreover, it is found that inclusion of particles in the lubricant results in a higher coefficient of friction in the mid-range of the Sommerfeld number compared to that of the clean oil.
The Magnetohydrodynamic Squeeze Film
Authors: Hamza E. A.
Published: October 2009

The motion of an electrically conducting fluid film squeezed between two parallel disks in the presence of a magnetic field applied perpendicular to the disks is studied. Analytic solutions through use of a regular perturbation scheme are obtained. The results show that the electromagnetic forces increase the load carrying capacity considerably.
Surface Reactions of Extreme Pressure Additive on Steel Surface in Ceramics-Steel Couples
Authors: Tanita Y. , Honda F. , Nakajima K.
Published: October 2009

The behavior of zinc dithiophosphate (ZnDTP) is investigated for the antiwear properties in SiC-steel and Si3N4-steel sliding contact systems under boundary lubrication. Reaction products formed on the steel surfaces under the sliding contact differ in the chemical compositions and the thickness between these couples. These differences are specifically related to the physical properties of mating materials such as heat conductivity and friction coefficient. The reaction products are analyzed by SEM (scanning electron microscope), EPMA (electron probe microanalysis), AES (Auger electron spectroscope), and PAS (photoacoustic spectroscopy), and it is confirmed that iron phosphate for SiC-steel and iron phosphate and zinc sulfide (or some complex compound containing equal amounts of Zn and S in atomic ratio) for Si3N4-steel couple exist on the steel surface, respectively. An examination is conducted on steel-steel couple in comparison with ceramics-steel couples, and the atomic ratio (Zn:P:S) of the constituent elements of the reaction products coincides fairly with that of SiC-steel couple.
Tribological Properties of SiC Whisker Containing Silicon Nitride Composite
Authors: Ishigaki H. , Nagata R. , Iwasa M. , Tamari N. , Kondo I.
Published: October 2009

The friction and wear characteristics of SiC whisker containing composite silicon nitride were studied. Silicon nitride powder which contains densification aids of Y2O3 and La2O3 was mixed with silicon carbide whiskers (10, 20, and 30 wt percent) and then hot-pressed at a temperature of 1800° C. Wear experiments were carried out with a ring on block type apparatus at the sliding conditions of the sliding speed of 314 mm/sec and the load of 5 N and experimental results showed that the SiC whisker had an evident effect to reduce the wear rate of silicon nitride blocks. Silicon carbide whiskers are not dispersed isotropically, but they are oriented to the direction which is perpendicular to the pressure of hot-press sintering. Therefore, wear characteristics of the composite ceramics are anisotropic. The effect of SiC whisker on wear rate of silicon nitride is larger for the surface which is perpendicular to the direction of pressure of hot-press sintering that than that for the surface which is parallel to the pressure. Although SiC whiskers have no evident effect on friction coefficient of silicon nitride at the above sliding condition, even small contents of SiC whiskers, such as 10 wt percent, reduce considerably the coefficient of friction and show similar frictional characteristics to that of monolithic silicon carbide at the lower sliding speed of 10 mm/min.
The Effects of Current Leakage on Electroadhesion Forces in Rolling Friction and Magnetic Flux Density Distribution on the Surface of Rolling Element Bearings
Authors: Prashad Har
Published: October 2009

The present work deals with the investigations carried out on the various rolling element bearings after being operated under the influence of electric fields, and pure rolling friction on the roller bearing test machine. The significant magnetic flux density was detected on surfaces of the bearings lubricated with low-resistivity grease under the influence of electrical fields. No such phenomenon was observed either on bearings using high or low-resistivity greases under pure rolling friction or on bearings lubricated with high-resistivity grease under the influence of electrical fields. New bearing surfaces do not show significant magnetic flux density but it has been detected after long operation on different motor bearings, lubricated with low resistivity greases. The electroadhesion forces in the bearings using low-resistivity greases increase under the influence of electrical fields in contrast to those with high resistivity greases. Under pure rolling friction resistivity of greases do not affect the electroadhesion forces. The investigations reported in this paper along with the study of damaged/corrugated surfaces, and deterioration of the used greases [1, 2, 3], the leakage of current leading to failure of the noninsulated motor bearings can be established.
Analysis and Design of a Gas-Lubricated, Sectored, Floating Ring Seal
Authors: Shapiro W. , Lee C. , Jones H.
Published: October 2009

Helium buffered floating-ring seals used in cryogenic turbopumps are sujbect to large temperature variations, shaft centrifugal growth, and dynamic shaft excursions. To prevent dangerous contact friction over a wide range of operating conditions generally requires liberal clearances with consequent high leakage. Reduction of helium consumption translates into lower space vehicle helium storage requirements and thus increased payload. A hydrostatic sectored floating-ring seal is described with self-adjusting clearance capabilities that enables the seal to operate with small clearances over the operating range to minimize leakage.
The Effects of Fluid Inertia Forces on the Dynamic Behavior of Short Journal Bearings in Superlaminar Flow Regime
Authors: Hashimoto H. , Wada S. , Sumitomo M.
Published: October 2009

The effects of fluid inertia on the dynamic behavior of oil film journal bearings are theoretically investigated. The dynamic oil film forces considering the combined effects of turbulence and fluid inertia are analytically obtained under the short bearing assumption. Based on the linearized analysis, the whirl onset velocity for a balanced rigid rotor supported horizontally in the oil film journal bearings are determined initially in the case of the length-to-diameter ratio of λ = 0.5 for Reynolds numbers of Re = 2750, 4580, and 5500. Moreover, the nonlinear equations of motion for the rotor are solved by the improved Euler’s method, and the relations between the transient journal motion and the pressure distribution corresponding to the above Reynolds numbers are examined. It is found that the fluid inertia significantly affects the dynamic behavior of turbulent journal bearings under certain operating conditions.
In-Situ Nanoindentation Hardness Apparatus for Mechanical Characterization of Extremely Thin Films
Authors: Bhushan B. , Williams V. S. , Shack R. V.
Published: October 2009

A nanoindenter apparatus is developed to measure the microhardness and microviscoelastic properties (in compression) of extremely thin films. In-situ indentation measurements are made by polarization interferometer by monitoring the absolute motions of the sample and indenter. A linear actuator provides the load, and the indenter load is inferred from the position of the indenter measured by the interferometer and the stiffness of the indenter parallel spring guide. A personal computer and associated electronics provide the control for load and penetration. These allow the instrument to determine microhardness and characterize microviscoelastic creep and relaxation properties. The linear actuator and the sample parallel spring guide are supported by an air bearing stage which is translated at a constant speed to conduct scratch tests for adhesion measurements. Based on the data reported in the paper, we find that microhardness and microviscoelastic properties at extremely low loads (or penetrations) are load (or penetration) dependent.
A Full Numerical EHL Solution for Line Contacts Under Pure Rolling Condition With a Non-Newtonian Rheological Model
Authors: Wang S. H. , Hua D. Y. , Zhang H. H.
Published: October 2009

The rheological effects of lubricants and the surface deformation of disks are considered in the lubrication of line contacts. The lubrication equation for fluids obeying power law model has been derived. The lubrication equation and the elastic equation have been solved simultaneously within the contact zone by means of the Newton-tangent method. Pressure distributions and film profiles are obtained. The results of this paper show that with the increase of the power law exponent n, the oil film becomes thicker and the position of the cavitation point moves closer to the center of contact.
Static Characteristics of a Slot-Entry Gas Journal Bearing With Feeding Holes
Authors: Yoshimoto S.
Published: October 2009

This paper describes the static characteristics of a slot-entry gas journal bearing with feeding holes. Gas flow in this bearing is restricted first by inflow resistance when gas rapidly flows into the narrow gap of the slot region from isolated feeding holes, and then, restricted more by viscous resistance in the slot region. Therefore, the maximum load capacity and stiffness in this type of bearing can be easily obtained even in a very small bearing clearance of less than 10 μm because gas flow entering the journal can be restricted to a very small amount. Here, the static characteristics of this type of bearings are determined numerically by using the finite difference method. The validity of the theoretical predictions is confirmed by comparison with the experimental results.
Analysis of Viscous Pumps With Shrouded Rayleigh-Steps Using Compressible Fluid
Authors: Sato Yuichi , Ono Kyosuke , Moriguchi Naoki
Published: October 2009

The paper describes an analysis of viscous pumps with shrouded Rayleigh-steps using compressible fluids. The optimum pump geometry for the maximum flow rate is presented. Frictional torque is examined for the optimized pump geometry. Finally the characteristics of the pump proposed in this paper are compared with those of spiral groove viscous pumps which are frequently used. Consequently the viscous pump with Rayleigh-steps has greater flow rate and higher pressure difference.
The Role of Plastic Deformation in Wear of Thin Films
Authors: Tangena A. G. , Wijnhoven P. J. M. , Muijderman E. A.
Published: October 2009

The correlation between mechanical stresses and tribological behavior for thin films was studied. A noble metal layer was applied on different substrates. Depending on the thickness of the film and the mechanical properties of the substrate, the wear of the film in a pin-on-plate configuration changed. Using finite element calculations it was shown that the geometry of the system, the mechanical properties of the substrate and the contact load determined the mechanical deformations of the top layer. The calculated von Mises stress averaged over the contact area and the depth of the thin film correlated well with the wear measured. If this average von Mises stress was above the yield stress of the thin film, the wear increased enormously, indicating the importance of plastic deformation in the film. A relatively simple low cycle fatigue model using the Coffin-Manson relation gave a good description of the wear behavior as a function of the average von Mises stress.
Tilting Pad Thrust Bearing Tests—Influence of Pivot Location
Authors: Gardner W. W.
Published: October 2009

Test data are presented on the effect of circumferential pivot position on bearing temperature for two tilting pad thrust bearing designs. Pivots at 50, 60, 70, and 80 percent of the arc length were used. These tests follow earlier tests with a third design (pad support configuration), previously reported. The results indicate that pad temperatures decrease significantly as the pivot is advanced from the central (50 percent) position to at least the 70 percent position, and then tend to level, with some indications that a minimum is reached at about 75 percent.
Flash Temperature on the Asperity Scale and Scuffing
Authors: McCool J. I. , John J.
Published: October 2009

A simulation model is described for determining the distribution of asperity flash temperatures when rough surfaces undergo relative sliding. The asperities are assumed to deform elastically and to have coulomb friction at their tips. The spherical asperity model of Greenwood-Williamson is joined with the flash temperature approximation formulas developed by Kuhlmann-Wilsdorf. Two example applications illustrate the effect of sliding speed and material role reversal on mean flash temperature. The model is applied to scuffing tests on ground and polished roller specimens reported in the literature. The predicted flash temperature is found to vary inversely with the experimentally observed scuffing loads within each finish type. For the same rolling and sliding speeds, the ground specimens had a lower observed scuffing load and a higher predicted mean flash temperature than the smoother polished specimens.
Axisymmetric Solution of a Flexible Disk Rotating Near a Rigid Surface
Authors: Carpino M. , Domoto G. A.
Published: October 2009

A rotating flexible disk separated from a rigid flat surface by a gas film is addressed. The gas film between the disk and the plate is represented by an incompressible Reynolds equation. Inertial effects are included. The disk is treated as a membrane where the tension is found from the plane stress solution for a spinning disk. Two different methods for the axisymmetric solution of this system are developed. The first uses the method of matched asymptotic expansions. The second method is a mixed numerical/perturbation procedure.
A Thin Film Flow Rupture Model for Newtonian and Viscoelastic Fluids
Authors: Tichy J. A. , Ku C.-P.
Published: October 2009

The problem of specifying adequate boundary conditions in two-dimensional steady incompressible flow between a cylinder and a plane for Newtonian fluids has been studied for many years. Unfortunately, Newtonian boundary conditions cannot be readily transposed to the case of viscoelastic fluids. In the present paper we consider the case of the second-order Rivlin-Ericksen fluid in prescribing suitable boundary conditions. The crux of the issue is that there are at least three possible stresses to be considered: (1) the transverse normal stress σy, (2) the longitudinal normal stress σx, and (3) the mechanical pressure p. The former, σy, is constant across the film and this variable is the one which carries load and measured by an experimental “pressure” tap. In the process of developing the viscoelastic model, a Newtonian model is developed which uses the Birkhoff-Hays separation conditions, considers surface tension as the Coyne-Elrod model but invokes the thin film assumption. The equations of motion are satisfied along and across the separated interface. Variation of the transverse normal stress profile with a minimum film thickness ratio, a surface tension parameter and Deborah number is shown. An earlier paper [6] shows that inconsistencies arise in applying simple rupture models (Gumbel or Swift-Stieber) to viscoelastic fluids. A relatively complicated model of this type is necessary to portray the basic behavior of film rupture in viscoelastic fluids.
Theoretical Analysis of Pneumatic Instability of Externally Pressurized Porous Gas Journal Bearings Considering Velocity Slip
Authors: Majumder M. C. , Majumdar B. C.
Published: October 2009

An analysis based on first-order perturbation theory is presented for the determination of pneumatic instability of a rigid rotor supported on externally pressurized porous gas journal bearings considering velocity slip. The variation of threshold mass parameter with feeding parameter for various supply pressures and L/D ratios under slip and no slip conditions is shown. It has been observed that there is a little decrease in stability when slip is taken in the analysis.
On the Consistent Formulation and Approximation of EHL Theory
Authors: Verstappen R. , van Groesen E.
Published: October 2009

In this paper a quasi-variational formulation for the creeping flow of a lubricant between deformable surfaces is derived on the basis of a principle of virtual power. This physical principle states that the state of the lubricated system is such that any change of the deformation or of the flow increases the total power. The principle correctly produces the governing differential equations and boundary conditions. Performing the usual approximations that are based on the scaling of the problem directly into the power functional (and not into the differential expressions), an approximate variational formulation is obtained that contains only quantities for and at the deformed surface. In deriving the differential equations and boundary conditions from this approximate functional it is noted that the usual formulation is obtained provided the sliding speed of the surfaces vanishes at the cavitation boundary. When restricted to hydrodynamic lubrication, a true variational principle results; the functional correctly produces the Reynolds equation, but differs from the functional that is commonly derived solely from this equation. The quasi-variational formulation that is derived for EHL gives an alternative way to formulate finite element approximations. Furthermore it specifies the relevance of the contribution of centrifugal forces on the deformation.
The Analysis of Thermoelectric Signals in Metallic Sliding
Authors: Shen Jui-Hsieh , Ettles C. M. , Scarton H. A.
Published: October 2009

The thermoelectric signal from an Alumel pin sliding over a steel surface was recorded and analyzed. The load, speed and surface topography were varied and correlations were attempted of the voltage signal against several parameters. The average temperature of the whole contact was found to agree fairly consistently with the surface temperature rise models of Blok and Archard. Of the available methods of signal analysis, the power spectrum of the voltage signal was found to give the best understanding of the micro-mechanisms of sliding, particularly when compared against the power spectra of profilometer signals. The largest component of the temperature signal was found to be caused by wavelength components equal to the extent of the contact. The correlation distance β* of the test surfaces was much less than the contact extent and contributed negligibly to the voltage signal rise.
Equilibrium and Associated Load Distribution in Ball and Roller Bearings Loaded in Five Degrees of Freedom While Neglecting Friction—Part II: Application to Roller Bearings and Experimental Verification
Authors: de Mul J. M. , Vree J. M. , Maas D. A.
Published: October 2009

A new, general and consistent mathematical model of highly modular character is presented for calculation of the equilibrium and associated load distribution in rolling element bearings. The bearings may be loaded and displaced in five degrees of freedom. High speed rolling element loading is considered, internal friction is neglected, the material is assumed linearly elastic and the bearing rings are modelled as rigid except for local contact deformation. Either classical Hertzian contact analysis or modern non-Hertzian contact analysis of sophisticated or approximate character is used as applicable. The bearing stiffness matrix is computed analytically and used internally in the iterative bearing equilibrium calculation; its final values may be used for other purposes such as (rotor) dynamics analysis. In Part I, the general theory and application to ball bearings is presented. In Part II, application of the general theory to ro´ller bearings and an experimental verification are presented.
Lubricated Wear Behavior of Composition-Modulated Nickel-Copper Coatings
Authors: Ruff A. W. , Myshkin N. K.
Published: October 2009

A study has been conducted of the wear behavior of electrodeposited, composition-modulated, nickel-copper materials having two different layer spacings, 10 nm and 100 nm, under lubricated sliding conditions against type 52100 bearing steel. The materials were prepared as coatings on steel cylinders; a standard crossed-cylinder wear test geometry was used. Two lubricating liquids were used: pure paraffin oil, with and without the addition of oleic acid. Wear and friction coefficient data were obtained. Electrical measurements of the contact resistance were also made during sliding to further study the nature of the boundary lubrication film present.
Hertzian Contact of Ground Surfaces
Authors: Nowell D. , Hills D. A.
Published: October 2009

Line contact between two elastic cylinders, one having a rough surface modelled as a periodic waviness is considered. The effects of asperity tip radius and characteristic wavelength on the surface and subsurface stress states are found, and the conditions under which St. Venant’s principle may be invoked determined. The reduction in surface strength compared with smooth contact is quantified and is found to be very sensitive to the tip curvature of the asperities.
Hardness Effect on Three-Body Abrasive Wear Under Fluid Film Lubrication
Authors: Xuan J. L. , Hong I. T. , Fitch E. C.
Published: October 2009

Under fluid film lubrication, the particulate contaminants in the fluid cause three-body abrasive wear on critical surfaces. The wear not only depends on the hardness of the wearing surface (Hj), but also on the hardnesses of its opposing surface (Hb) and the involved abrasives (Ha). In this paper, the hardness effect, particularly the relationships among these three hardnesses, is studied, by exploring the interdependence between two hardness ratios: the ratio between two rubbing surfaces (Hb/Hj) and the ratio between the surface to be protected (usually the harder surface) and the abrasives (Hj/Ha). Three types of journal-bearing pairs (Hb/Hj = 0.75, 0.6, and 0.3) were tested, subjected to four abrasive particles (Hj/Ha ranges from 0.14 to 2.75). The wear linearly varies with the Hj/Ha value at each metal hardness ratio on log-log diagram. The empirical constants in the wear function are obtained. The critical hardness ratio and the wear coefficient are also analyzed.
Thermal Effects in Dynamically Loaded Flexible Journal Bearings
Authors: Moes H. , Ten Hoeve P. B. Y. , Van der Helm J.
Published: October 2009

A method of taking into account the thermal effects when simulating dynamically loaded, flexible, journal bearings on a computer will be introduced. The method is an extension of Van der Tempel’s model for a flexible, short journal bearing under severe dynamic duty, with partial circumferential supply grooves, cavitation and cavitation induced starvation. It incorporates the heat generation due to the viscous dissipation and the cooling due to the axial and circumferential flow of lubricant. The results for the film thicknesses, the lubricant flow, the viscous dissipation and the temperature distribution in two specific connecting-rod bearing configurations will be presented.
Simple Formulas for Performance Parameters Used in Elastohydrodynamically Lubricated Line Contacts
Authors: Pan Ping , Hamrock B. J.
Published: October 2009

The film thickness and pressure in elastohydrodynamically lubricated conjunctions have been evaluated numerically for a rather complete range of operating parameters (dimensionless load, speed, and materials parameters) normally experienced in practical applications. From the film thickness and pressure throughout the conjunction a number of performance parameters were evaluated. By curve fitting the data, formulas were obtained that allow easy evaluation of the amplitude and location of the pressure spike, the minimum and central film thicknesses, the value of ρeHe, and the center of pressure.
The Experimental Determination of Squeeze-Film Dynamic Coefficients Using the State Variable Filter Method of Parametric Identification
Authors: Ellis J. , Roberts J. B. , Ramli M. D.
Published: October 2009

The state variable filter method of parametric identification is applied in the determination of squeeze-film dynamic coefficients from forced excitation tests on an experimental rig. The experimental squeeze-film damper had a centralizing spring, a central circumferential oil feed groove, and no end seals. Forced excitation tests are recorded at various journal support system natural frequencies and at different journal eccentricities. From these tests, estimates of the direct squeeze-film damping, stiffness and inertial coefficients are derived and presented. These results are shown to be in good agreement with results recently obtained using an independent frequency domain technique. The experimental damping and inertial coefficients were found to be considerably larger than values predicted by conventional short-bearing theory, but relatively insensitive to the support system’s natural frequency (and the forcing frequency) for most of the range investigated. The fluid film stiffness coefficient values at low values of the system’s natural frequency agreed with results from static stiffness tests. Two geometrically identical journals were used, one of steel and one of a low-weight, magnesium alloy. The use of the low weight journal markedly reduced the scatter in the inertial and film stiffness coefficients.
The Relation Between the Friction of Lubricated Rough Surfaces and Apparent Normal Pressure
Authors: Lacey P. , Torrance A. A. , Fitzpatrick J. A.
Published: October 2009

Most previous studies of boundary lubrication have ignored the contribution of surface roughness to friction. However, recent work by Moalic et al. (1987) has shown that when asperity contacts can be modelled by a slip line field, there is a precise relation between the friction coefficient and the asperity slope. Here, it is shown that there is also a relation between the friction coefficient and the normal pressure for rough surfaces which can be predicted from a development of the slip line field model.
Hybrid Journal Bearings: Theoretical and Experimental Results
Authors: Bou-Said B. , Chaomleffel J. P.
Published: October 2009

The analysis of actual lubrication problems needs to take into account particularities in the flow coming from kinematic conditions and contact geometry. For hybrid journal bearings lubricated by low dynamic viscosity fluid, turbulence and pressure drops due to inertia forces in the recess outlets are phenomena which must be taken into account to compute their working characteristics. A global method of study of lubricated contacts in isothermal laminar or not laminar flow by finite element method is presented. It can solve a great number of lubrication problems. A new type of approximation element for lubrication (Hermitian type) is used because it offers the following advantages: The nonlinearities in lubrication which come from turbulence phenomena, geometrical discontinuities (pressure drops) or boundary conditions (recess pressure) require the derivation of unknown functions. Added interpolations are not necessary to determine these values because the nodal unknowns are the values of the function and its derivatives in the two directions. As the modified Reynolds equation is in Cartesian coordinates, in the case of closed geometries such as journal bearings, joining is done just by nodal identification which guarantees continuity of the pressure and of its derivatives. The validity of this numerical model is realized with an experimental study done with a three recess hybrid journal bearing for different kinematic and geometric configurations. In a general way, experimental and theoretical results are in good agreement.
On the Dynamics of a Tapered Roller Bearing
Authors: Gupta Pradeep K.
Published: October 2009

The general motion of a roller and the cage in a tapered roller bearing is modeled as a function of frictional behavior in the bearing and cage clearances. Roller skew is shown to increase with increasing friction. At relatively high friction and low cage pocket and guide land clearances, the roller tends to pivot in the cage pocket such that it is in steady contact on one side of the pocket while the contact is cyclic on the other side with the roller skew frequency equal to its angular velocity. Such a pivoting motion promotes a high-frequency whirl of the cage which is clearly seen both in the whirl orbit and the whirl velocity solutions. As the friction in the bearing reduces such a high-frequency whirl is completely eliminated. When the cage clearances are somewhat larger, nominal cage whirl, with an almost circular orbit and with whirl velocity equal to cage angular velocity, is produced at higher values of friction. Again the whirl gradually subsides as the friction in the bearing is reduced. The results demonstrate significance of the computer modeling approach to optimizing bearing design under prescribed frictional behavior and operating environment.
Annular Honeycomb Seals: Test Results for Leakage and Rotordynamic Coefficients; Comparisons to Labyrinth and Smooth Configurations
Authors: Childs D. , Elrod D. , Hale K.
Published: October 2009

Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals shows the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluids entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.
An Entrance Region Friction Factor Model Applied to Annular Seal Analysis: Theory Versus Experiment for Smooth and Honeycomb Seals
Authors: Elrod D. , Nelson C. , Childs D.
Published: October 2009

A friction factor model is developed for the entrance-region of a duct. The model is used in an annular gas seal analysis similar to Nelson’s (1984). Predictions of the analysis are compared to experimental results for a smooth-stator/smooth-rotor seal and three honeycomb-stator/smooth-rotor seals. The model predicts leakage and direct damping well. The model overpredicts the dependence of cross-coupled stiffness on fluid prerotation. The model predicts direct stiffness poorly.
The Effects of Fluid Inertia Forces on the Static Characteristics of Sector-Shaped, High-Speed Thrust Bearings in Turbulent Flow Regime
Authors: Hashimoto H.
Published: October 2009

This paper describes a study on the performance characteristics of sector-shaped, high-speed thrust bearings subjected to the effects of both turbulence and fluid inertia forces. The basic lubrication equations are derived by integrating the momentum and continuity equations in the polar coordinates including the full inertia terms throughout the film thickness; and a numerical calculation technique combining the control volume integration and the Newton-Raphson linearization method is applied to solve the equations. The static characteristics such as the load carrying capacity and the pressure center are calculated for various values of pad extent angle and inner-to-outer radius ratio of a pad. The theoretical results of the load carrying capacity are compared with the experimental results. It was found that the fluid inertia forces have significant effects on the static characteristics of the bearings. Good agreement was obtained between theoretical and experimental results.
Elastic-Plastic Finite Element Analysis of Indented Layered Media
Authors: Komvopoulos K.
Published: October 2009

The elastic-plastic contact problem of a layered half-space indented by a rigid surface is solved with the finite element method. The case of a layer stiffer and harder than the substrate is analyzed and solutions for the contact pressure, subsurface stresses and strains, and location, shape, and growth of the plastic zone are presented for various layer thicknesses and indentation depths. Finite element results for a halfspace having the substrate properties are also given for comparison purposes. Differences between the elastic and elastic-plastic solutions are discussed and the significance of critical parameters such as the layer thickness, mechanical properties of layer and substrate materials, indentation depth, and interfacial friction on the threshold of plasticity, contact pressure distribution, and growth of the plastic zone are examined. Additionally, the mechanisms of layer decohesion and subsurface crack initiation are interpreted in light of the results obtained in this study.
A Theory of Liquid-Solid Lubrication in Elastohydrodynamic Regime
Authors: Khonsari M. M. , Wang S. H. , Qi Y. L.
Published: October 2009

A theoretical study of the effectiveness of solid particles dispersed in oil in the elastohydrodynamic line contact is presented. The analysis includes the variation of the viscosity and density of the lubricant as a function of pressure. The deformation of solid particles and that of the bounding surfaces are taken into consideration. Results are presented for the variation of the film thickness and the load carrying capacity as a function of the particle size, concentration, and properties of various types of particles.
Role of Mechanical Properties and Surface Texture in the Real Area of Contact of Magnetic Rigid Disks
Authors: Bhushan B. , Doerner M. F.
Published: October 2009

The analysis of real area of contact for particulate and thin-film rigid disks is presented. The mechanical properties (hardness and modulus) of the disk structure are measured by a nanoindentation apparatus and the surface texture is measured by a three-dimensional noncontact optical profiler. For typical rigid disks selected for this study, we find that most contacts are elastic; the same observation was made by Bhushan (1984) for flexible media. In the case of elastic contacts, the real area of contact is governed by the effective elastic modulus of the disk structure and its surface summit distribution. Typical values for the fractional real area of contact, number of contacts per unit area, mean asperity diameter, and mean real pressure for a thin-film disk are calculated to be of the order of 5 × 10−5, 20/mm2, 1μm, and 200 MPa, respectively.
An Analysis of the Steady State and Dynamic Characteristics of a Spherical Hydrodynamic Journal Bearing
Authors: Leung P. S. , Craighead I. A. , Wilkinson T. S.
Published: October 2009

With recent developments in N. C. manufacturing processes it is relatively straightforward to produce a journal bearing with spherical surfaces. Such a bearing offers two main advantages over a conventional bearing: it can tolerate much larger misalignment and it can resist axial forces. In this paper, the steady state performance of a spherical journal bearing is studied by using a finite bearing theory. The dynamic characteristics of the bearing are represented by eight displacement and velocity force coefficients and the boundary of bearing stability is determined. The effect of superlaminar flow upon the bearing performance is also studied, and typical bearing design charts are provided. In comparison, the behavior of the spherical journal bearing is found to be similar to that of an equivalent cylindrical bearing.