bluuebunny/crossref_metadata_2025 huggingface dataset:
Limitations and Corrections of Optical Profilometry in Surface Characterization of Carbon Coated Magnetic Recording Disks
Authors: Li Yufeng , Talke F. E.
Published: June 2008

The thickness of a thin absorbing carbon step on a strongly absorbing magnetic layer is measured using contact stylus and noncontact optical profilometer instrumentation, The dependence of optical profilometer measurements on carbon film thickness and optical properties of both the magnetic layer and the carbon film is investigated, and the error in the optical measurement is evaluated as a function of the phase shift of the light reflected from the sample surface. A marked improvement in the accuracy of the step height measurement is obtained if account is taken of the phase shift of the light reflected from the carbon overcoat and the magnetic substrate, respectively. The measurement of surface roughness of thin films on strongly absorbing substrates is discussed and the use of a dual wavelength technique is proposed to enhance the accuracy of optical profilometry.
Analysis of a Low Speed Flexible Flat Land Thrust Bearing
Authors: Carpino M.
Published: June 2008

The problem of a flexible flat land thrust bearing is studied here. The bearing consists of a flexible circular plate running against a rigid flat surface. Point loads are applied to the plate at equally spaced locations causing deflection of the plate. The deflection of the plate creates the converging clearances necessary for hydrodynamic lubrication. The fluid film between the disk and the plate is treated as incompressible. Results are presented in terms of normalized variables enabling the design of a broad range of bearings based on this mechanism.
Generation of Submicrometer Particles in Dry Sliding Contact
Authors: Xuan J. L. , Cheng H. S. , Miller R. J.
Published: June 2008

The generation of submicrometer-sized particles during dry sliding between stainless steel surfaces is investigated by means of a laser spectrometer for particle counting and scanning tunnelling microscopy for asperity topography characterization. It has been found that, when the submicrometer wear increases with increasing sliding distance or with an initially rougher surface, the number of particles having a submicrometer size is a power function of that size. The two wear coefficients in the power function are determined empirically for the case of stainless steel contact. Different from the generation pattern of several-micrometer particles, the generation rate of submicrometer particles continuously increases until reaching the equilibrium surface condition. The asperity topography measurement shows the micrometer-sized asperities also have subasperities whose sizes are about one order of magnitude smaller. An asperity model similar to Archard’s is thus proposed for estimation of submicrometer wear. The dominant wear mechanisms are brittle fracture and plastic deformation combined with adhesion transfer. The asperity contact can be considered as a plastic-elastic deformation system with subasperities deformed plastically all the time and the micrometer asperities first deformed plastically and then deformed elastically because of the significant increase of microhardness on the soft surface in a metal pair. When the microhardness ratio between two rubbing surfaces reaches a stable value, the generation of submicrometer particles reaches the maximum rate and the wear grows steadily.
Approximate Analysis of Turbulent Hybrid Bearings. Static and Dynamic Performance for Centered Operation
Authors: San Andre´s Luis
Published: June 2008

An analytical study for the flow and dynamic force response in turbulent hybrid journal bearings is presented. Fluid inertia effects at the recess edges and film lands are included. For small amplitude motions about the centered position, the equations for the flow on the film lands and recesses are solved in close form by invoking the thin-land assumption. Predictions from the present simplified analytical theory agree well with full numerical predictions. The effect of recess pressure on the dynamic force response of a L02 hybrid bearing is discussed in detail.
Turbulent Hybrid Bearings With Fluid Inertia Effects
Authors: San Andre´s Luis
Published: June 2008

High speed hybrid bearings for cryogenic applications demand large levels of external pressurization to provide substantial load capacity. These conditions give rise to large film Reynolds numbers, and thus, cause the fluid flow within the bearing film to be turbulent and dominated by fluid inertia effects both at the recess edges and at the thin film lands. The analysis includes the effect of recess fluid compressibility and a model for the pressure rise within the recess region. Flow turbulence is simulated by friction factors dependent on the local Reynolds numbers and surface conditions. A perturbation method is used to calculate the zeroth and first flow fields and determine the bearing steady-state and dynamic force response. Comparison of results with existing experimental data shows the accuracy of the present full inertial-turbulent analysis. A roughened bearing surface is shown to improve considerably the stability characteristics of hybrid bearings operating at high speeds.
Measurement of Oil Film Thickness Between W-N Helical Gear Tooth Profiles Using Laser Transmission Method
Authors: Ji-Bin Yang , Yu-Lin Qi , Chen-Wen Chen
Published: June 2008

In this experiment, it was the first time that the center oil film thickness between W-N helical gear tooth profiles has been measured indirectly through measuring the change of gaps of a pair of unloaded involute spur gears mounted on the extended shafts of W-N gear box by means of laser transmission method. During the measurement of every time, it was calibrated separately, so that all errors could be eliminated completely except ones of measuring apparatus. The accuracy of this method has reached 0.1 μm (dynamic) and 0.01 μm (static), respectively. Measurement results were identical with theoretical ones. This method is also suitable for the measurement of center oil film thickness between tooth profiles and deformation of any cylindrical spur and helical gears.
An Experimental and Theoretical Study of Cavitation in a Finite Submerged Squeeze Film Damper
Authors: Ku Chiao-Ping , Tichy J. A.
Published: June 2008

In fluid film lubrication, pressure often seeks a level lower than the lubricant vapor pressure, in which case the liquid film ruptures and a vapor cavity is formed. The Jakobsson-Floberg-Olsson (JFO) model would seem to correctly predict the extent of the cavitation region in heavily loaded finite bearings and to specify proper pressure boundary conditions on the interface. However, this model is difficult to apply in practice, requiring extreme numerical effort in guessing the unknown cavity shape and checking flow balancing. In the present study, we propose a simplified model which agrees well with the JFO conditions, and provide supporting experiments. The ordinary differential equations for the distance of cavity boundary from the bearing centerline and the pressure profile at the bearing centerline are obtained by using the integral method. Compared to results obtained by the modified Elrod algorithm, considerable numerical work is saved and little accuracy is lost. Experiments are conducted with a submerged circular-centered orbit squeeze film damper bearing with both ends open. In the cavity the pressure is nearly constant and almost equal to the absolute zero pressure. Compared to the results predicted by the present model, agreement with experimental measurements of the centerline pressure profile, the size, and location of cavity is very good.
Stability Criterion for Spiral Grooved Thrust Gas Bearings
Authors: Constantinescu V. N. , Galetuse S.
Published: June 2008

A previous analysis of dynamic stability for a blocked center inward pumping spiral grooved thrust gas bearing is extended to two other types of similar bearings, namely annular thrust bearings with either inward or outward pumping. Both a numerical small perturbation analysis and an analytical procedure are used, the latter one being based on an approximate shape of the pressure distribution. The analysis provides a critical compressibility number up to which the bearings is unconditionally stable.
Reynolds Lubrication Theory: A Consideration of Boundary Conditions
Authors: Rubenchik V.
Published: June 2008

The pressure boundary condition at film edges, as formulated in the original Reynolds theory of lubrication, presents an approximation. The internal pressure in the film will normally differ from the external pressure. In this paper, a derivation which involves in-plane stresses and vorticity is presented. As a first-order correction, the boundary condition is formed based on the assumption that the in-plane vorticity on approaching the edges is zero. An advanced theory, resembling Reissner’s theory of plates, is also traced.
A Study of Elastohydrodynamic Lubrication of Rough Surfaces
Authors: Chang L. , Webster M. N.
Published: June 2008

This paper reports some results of rough-surface, elastohydrodynamically lubricated (EHD) contacts obtained using a previously developed transient EHD model. The surface roughness is modeled with sinusoidal functions of small wavelength compared to the contact zone. Results are presented showing how the operating conditions affect the film thickness, micro-deformation of the roughness, and the pressure perturbations due to motion and interaction of roughness within the contact. This preliminary work suggests that the entraining velocity and the slide-to-roll ratio are the most sensitive parameters influencing the lubrication process of rough-surface EHD contacts.
p-Version Incompressible Lubrication Finite Element Analysis of Large Width Bearings
Authors: Nguyen S. H.
Published: June 2008

This paper presents a p-version finite element formulation for incompressible lubrication analyses where the pressure field can be of any arbitrary polynomial of order p. The formulation ensures the C° continuity between mating element boundaries. Numerical examples are provided to demonstrate the simplicity of modeling and the accuracy of the formulation.
The Detection of Flash Temperatures in a Sliding Contact by the Method of Tribo-Induced Thermoluminescence
Authors: Suzuki S. , Kennedy F. E.
Published: June 2008

A method is presented for measuring short duration flash temperatures in sliding contacts. The method uses a photomultiplier to collect photons emitted by a hot contact spot. The method was used to measure flash temperatures at the contact between a spherical sapphire slider and a rapidly moving thin film magnetic disk. It was found that temperature flashes of over 1000° C, lasting less than 2 μs, can occur at the sliding interface.
A Fast Solution of the Dry Contact Problem and the Associated Sub-Surface Stress Field, Using Multilevel Techniques
Authors: Lubrecht A. A. , Ioannides E.
Published: June 2008

The most time-consuming routine in the present EHL and dry contact computations is the calculation of the elastic deformation integrals. Using Multilevel Multi-Integration (MLMI) these integrals can be computed in O(n log n) instead of O(n2) operations. This fast integration is applied to the dry contact problem. To make optimal use of this integration, it is also necessary to construct an efficient solver for the integral equation. This is again accomplished using multilevel techniques. The total complexity of the new dry contact solver is O (n log n) which gives a big reduction in computing time over “classical” solution methods, enabling the solution of contact problems on grids with so many points that a realistic modelling of the surface roughness lies within reach. The fast integration is then applied to compute the stress distribution below the surface. As an example, the stress distribution under a smooth surface with a bump in contact is calculated for both a 2-dimensional and for a 3-dimensional contact case, and for a 2-dimensional rough surface in contact
A Numerical Solution for Calculating Elastic Deformation in Elliptical-Contact EHL of Rough Surface
Authors: Lin Jen Fin , Chu Hsiaw Yeh
Published: June 2008

The analytical expressions are developed for elastic deformation provided the pressure function on a nine-node element of any nonequidistant rectangle is approximated by a biquadratic polynomial. Using the present scheme, the coefficients Aij showing in pressure solution are simply calculated once enough in the full iterations. The computational works are greatly reduced.
A Sliding Wear Model for Partial-EHL Contacts
Authors: Wu Shifeng , Cheng H. S.
Published: June 2008

A sliding wear model has been developed for partial-EHL contacts, in which both the thermal desorption wear mechanism at low asperity contact temperature and the oxidative wear mechanism at elevated asperity contact temperature are considered. To include micro-EHL effects, digitized actual surface roughness profiles are used in simulating two contacting rough surfaces, and in obtaining the asperity contact area and asperity contact temperature distributions within a Hertzian contact region. Wear measurements in a two-disk machine configuration have been made over a comprehensive range of slide-to-roll ratios. The experimental results show a continuous decrease in wear rate with the increase in slide-to-roll ratio when the slide-to-roll ratio is relatively small, and a drastic rise in wear rate when slide-to-roll ratio is further increased. The experimental wear rate curve as a function of slide-to-roll ratio verifies the model prediction. The drastic rise in wear rate with the increase in slide-to-roll ratio in the range of slide-to-roll ratio beyond unity seems to suggest that a transitional phenomenon exists in the relation between wear rate and slide-to-roll ratio.
A Comparison of the Fluid Models Effect on the Internal Stresses of Rough Surfaces
Authors: Sadeghi F.
Published: June 2008

A comparison between the effects of Newtonian, hyperbolic, and Eyring fluid models on the internal stresses in EHD lubrication of a smooth and rough stationary surface in contact with a moving smooth surface was obtained. The Newton-Raphson technique was used to solve the simultaneous system of Reynolds and modified elasticity equations. The elasticity equation was modified with the experimental surface measurements obtained from a typical bearing. The pressure and film thickness results obtained from the EHD solution were used to calculate the surface shear stress and the internal stresses. Results have been presented for the dimensionless loads of W = 1.3 × 10−4, 2.3 × 10−4 and speeds of U = 5.46 × 10−11, 1.092 × 10−10 for smooth and rough surface conditions. The results indicate that surface roughness of typical bearings do not significantly affect the depth at which the maximum shear stress occurs.
The Unlubricated Sliding Wear Behavior of Polyetheretherketone Against Smooth Mild-Steel Counterfaces
Authors: Ovaert T. C. , Cheng H. S.
Published: June 2008

In this investigation, the sliding wear of polyetheretherketone (PEEK) against smooth (polished) and slightly roughened mild-steel counterfaces was studied under dry, lightly-loaded conditions. In this counterface roughness regime, the wear rate of PEEK decreased to a relative minimum as roughness increased. The worn system of PEEK against polished steel was simulated using several contact models. The application of a numerical non-Hertzian elastic stress analysis yielded estimates of subsurface stresses, which were correlated with results of wear particle morphological studies. As counterface roughness increased, minor changes were observed in the wear mechanism. Wear particle morphology, however, displayed evidence of mechanical counterface interaction resulting in interfacial film formation and reduced wear.
Dynamic Characteristics of Externally Pressurized, Double-Pad, Circular Thrust Bearings With Membrane Restrictors
Authors: Wang C. , Cusano C.
Published: June 2008

The dynamic characteristics of externally pressurized, double-pad, circular thrust bearings with membrane variable flow compensation are analytically studied. Under static loads or load composed of a static and cyclic component, membrane compensation gives better overall performance characteristics than capillary (fixed flow) compensation. As the frequency increases, capillary compensation gives approximately the same performance as optimal membrane compensation when the bearing operates under pure cyclic loading
Effects of Ion Implantation Conditions on the Tribology of Ferrous Surfaces
Authors: Wei R. , Wilbur P. J. , Sampath W. S. , Williamson D. L. , Wang Li
Published: June 2008

The effects of implanted nitrogen ion dose and target surface temperature during implantation on the wear characteristics of iron (ferrite) and 304 stainless steel (austenite) have been studied systematically. Wear test results obtained using an oscillating pin-on-disk tester show that high dose rate, high dose implantation into these materials when they are being held at an elevated temperature (near 400°C) induce dramatic improvements in their wear characteristics. Surface and near-surface analysis techniques are used to demonstrate that implanted ion dose and surface temperature can be controlled to produce a desired microstructural state and thickness of the nitrogen-implanted layer. The most wear resistant surfaces are produced when γ’-Fe4N is formed in the ferrite and a concentrated solid solution of nitrogen is produced in the austenite. Implanted layer thicknesses greater than ~ 1 μm (an order of magnitude beyond the ballistic implantation depth) are observed in the austenite.
Thermoelastic Effects in Lubricated Rolling/Sliding Line Contacts
Authors: Sui P. C. , Sadeghi F.
Published: June 2008

A numerical model was developed to investigate the subsurface mechanical and thermal stresses in rolling/sliding machine elements operating under elasto-hydrodynamic (EHD) lubrication of line contacts. A thermal non-Newtonian EHD lubrication model was modified to include the thermoelastic displacement of the solids. The pressure, film thickness, and temperature distribution obtained from the model were used to calculate the subsurface mechanical and thermal stresses within the rolling/sliding machine elements. The thermoelastic effects on the magnitude and location of the maximum shear stresses are presented.
Scuffing Failure in Heavily Loaded Slow Speed Conformal Sliding Contacts
Authors: Shen M. C. , Cheng H. S. , Stair P. C.
Published: June 2008

Scuffing failure phenomenon is studied experimentally in heavily loaded slow speed conformal sliding contacts of two flat thrust washers in a regime close to boundary lubricated condition. Lubricants used are base oils of pure mineral oil and poly-α-olefin (PAO). Speed range is 0.76–33.0 cm/s. Material studied is hardened 52100 steel for both washers in contact. Scuffing threshold load at failure, friction, and surface bulk temperature are major data measured. The surface total temperature is determined with the measure bulk temperature in addition to the surface flash temperature calculated using Jaeger’s theory. Characteristic scuffing failure mechanisms are categorized in terms of various speed ranges. A simple model is proposed to predict scuffing failure based on theories in adsorption/desorption dominated lubricated wear and metal oxide formation kinetics. Good agreement is found between experimental data and theoretical prediction in terms of threshold load in certain speed range.
Effects of Lubrication Upon Plastic-Metal Contact
Authors: Marui Etsuo , Hasegawa Norihiko , Miyachi Reiji
Published: June 2008

It is important to examine the contact mechanics between metal surfaces for greater accuracy of guideway motion and for pre-estimates of contact rigidity and damping capacity of mechanical systems. In the present study, the contact of a hard steel ball and a soft duralumin surface is examined, and the effect of lubrication on the plastic contact mechanics is discussed. Frictional stress between contact surfaces plays an important role in the deformation of surfaces. The parameters, which define the state of contact, are estimated in the experiment, taking lubrication into consideration.
Seal-Rotordynamic-Coefficient Test Results for a Model SSME ATD-HPFTP Turbine Interstage Seal With and Without a Swirl Brake
Authors: Childs D. W. , Ramsey C.
Published: June 2008

Test results are presented and compared to theory for a model Space Shuttle Main Engine(SSME) Alternate Turbopump Development(ATD) High-Pressure Fuel Turbopump (HPFTP) with and without swirl brakes. Tests are conducted with supply pressures out to 18.3 bars and speeds out to 16,000 rpm. Seal back pressure is controlled to provide four pressure ratios at all supply pressures. Three inlet guide vanes are used to provide the following three fluid prerotation cases: (a) no pre-rotation, (b) moderate prerotation in the direction of rotation, and (c) high prerotation in the direction of rotation. Test results demonstrate the pronounced favorable influence of the swirl brake in reducing the seal destabilizing forces. Without the swirl brake, the cross-coupled stiffness k increases monotonically with increasing inlet tangential velocity. With the swirl brake, k tends to either be constant or decrease with increasing inlet tangential velocity. Direct damping either increases or remains relatively constant when the swirl brake is introduced. Direct stiffness is relatively unchanged. No measurable differences in leakage were detected for the seal with and without the swirl brake. Comparisons between Scharrer’s (1988) theory and measurements for the seal without a swirl brake indicate that the predictions can be used to provide design guidelines only. Specific predictions for rotordynamic coefficients should be treated cautiously, since systematic differences were observed between theory and experiment due to changes in running speed, supply pressure, and pressure ratio.
Fractal Model of Elastic-Plastic Contact Between Rough Surfaces
Authors: Majumdar A. , Bhushan B.
Published: June 2008

Roughness measurements by optical interferometry and scanning tunneling microscopy on a magnetic thin-film rigid disk surface have shown that its surface is fractal in nature. This leads to a scale-dependence of statistical parameters such as r.m.s height, slope and curvature, which are extensively used in classical models of contact between rough surfaces. Based on the scale-independent fractal roughness parameters, a new model of contact between isotropic rough surfaces is developed. The model predicts that all contact spots of area smaller than a critical area are in plastic contact. When the load is increased, these plastically deformed spots join to form elastic spots. Using a power-law relation for the fractal size-distribution of contact spots, the model shows that for elastic deformation, the load P and the real area of contact Ar are related as P~Ar(3−D)/2, where D is the fractal dimension of a surface profile which lies between 1 and 2. This result explains the origins of the area exponent which has been the focus of a number of experimental and theoretical studies. For plastic loading, the load and area are linearly related. The size-distribution of spots also suggests that the number of contact spots contributing to a certain fraction of the real area of contact remains independent of load although the spot sizes increase with load. The model shows that the load-area relation and the fraction of the real area of contact in elastic and plastic deformation are quite sensitive to the fractal roughness parameters.
Microscopic Studies of Flank Wear on Alumina Tools
Authors: Kim Sukyoung , Durham Delcie R.
Published: June 2008

The flank wear of alumina cutting tools in the machining of annealed steels, AISI 1045 and 4340, which were approximately the same hardness, was studied microscopically. The intent was to establish whether any chemical wear occurred in addition to the mechanical wear on the flank surface. While the hardness of the two steels was essentially the same, the chemistry and the carbide present in the microstructure differed. The flank wear morphology was studied and three regions within the wear land could be defined. The flank wear of the alumina tools, which increased with an increase of cutting speeds, was found to be strongly dependent upon the chemistry of the work material being machined. At the higher speeds, the flank wear when cutting AISI 1045 steel was approximately twice that of AISI 4340. It was observed that different wear mechanisms could be associated with the material being machined. The thermally activated chemical and mechanical wear processes were predominant in the AISI 1045 machining, but the chemical wear was not significant in machining AISI 4340. At lower temperatures, the mechanical wear predominated for both steels. The wear pattern consisted of three regions on the flank wear surface, which varied with cutting speed, cutting distance, and position within the wear land. The surface roughness on the worn tool was also related to these same test parameters. The flank wear appears to depend upon not only the workpiece, but also upon an interfacial oxide layer that forms during cutting. The physical and mechanical properties of the interfacial oxide depend upon its constituents, which relate back to workpiece composition and thermal conditions at the interface.
The Tribological Behavior of TiN Coatings Prepared by IBAD
Authors: Dillich S. A. , Kant R. A. , Sartwell B. D. , Sprague J. A. , Smidt F. A.
Published: June 2008

Ion Beam Assisted Deposition (IBAD) provides the ability to control the micro-structure, and therefore the properties of thin films and coatings. This paper describes the tribological properties of TiN coatings prepared by reactive IBAD using evaporation of Ti from an electron beam evaporator in a 10−3 to 10−4 Pa partial pressure of nitrogen and simultaneous bombardment with a directed beam of 0.5 keV Ar+ ions. Films prepared with an Ar+ to Ti atom arrival rate ratio of 0.1 were found to be soft (Knoop hardness of < 1000 with 5 gr load) while those prepared at an arrival rate ratio of 0.4 were hard (Knoop hardness of ~2000 at 5 gr load). Transmission electron microscopy of the films showed the soft films had significant porosity at the grain boundaries while the hard films had almost none. All films were highly adherent. The wear life during pin on disk testing was a complex function of film hardness, ductility and debris formation.
Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part II: Durability
Authors: Streator J. L. , Bhushan B. , Bogy D. B.
Published: June 2008

Several perfluoropolyether (PFPE) lubricants are evaluated in terms of their ability to maintain low friction and resist wear. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant. Dynamic friction measurements are presented for an IBM 3380-type slider in contact with 130 mm carbon-coated thin film disks. Disk surface run-in and disk durability are evaluated by monitoring the friction force during constant speed sliding. Disk run-in is presented as a function of lubricant thickness and sliding speed, while disk durability is determined for different disk topographies and lubricant thicknesses. It was found that lubricant viscosity was well correlated with the amount of disk run-in and the number of sliding cycles until disk failure. It is proposed that the greater wear durability of the less viscous lubricants can be attributed to their greater mobility on the disk surface.
The Composition of Surface Layers Formed in a Lubricated Cam/Tappet Contact
Authors: Willermet P. A. , Pieprzak J. M. , Dailey D. P. , Carter R. O. , Lindsay N. E. , Haack L. P. , deVries J. E.
Published: June 2008

The frictional behavior of two oils was measured in a cam/tappet friction apparatus using a direct acting bucket tappet geometry. One oil contained a soluble molybdenum friction modifier. The tappet was equipped with a removable friction disk, which allowed the frictional surface to be easily removed for surface characterization using surface profilometry, reflection infrared and XPS spectroscopies. The films consisted of varying amounts of inorganic phosphates, sulfates and sulfides with zinc, magnesium, and possibly molybdenum as cations. MoS2, expected because additives containing molybdenum and sulfur were present, was not detected. The detection limit was less than 0.1 atom percent Mo. The film formed by the friction modified oil was thinner, smoother and contained small amounts of molybdenum. While the smooth surface finish could reduce friction by improving microelastohydrodynamic lubrication, friction reduction could not be tied to any of the chemical structures detected in these experiments.
Rotordynamic Coefficients for Partially Tapered Annular Seals: Part I—Incompressible Flow
Authors: Scharrer J. K. , Nelson C. C.
Published: June 2008

The basic equations are derived for incompressible flow in an annular seal with a partially tapered clearance. The flow is assumed to be completely turbulent in the axial and circumferential directions with no separation, and is modeled by Hirs’ turbulent lubrication equations. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order continuity and momentum equations are solved exactly, yielding the axial and circumferential velocity components and the pressure distribution. The first-order equations are reduced to three ordinary, complex, differential equations in the axial coordinate Z. The equations are integrated to satisfy the boundary conditions and yield the perturbation pressure distribution. This resultant pressure distribution is integrated along and around the seal to yield the force developed by the seal and the corresponding dynamic coefficients. Since no component test data exist for this type of seal, the results of a parametric study on the effect of the taper length/total length ratio on the seal leakage and rotor-dynamic coefficients are presented.
Inertia and Turbulence Effects on Dynamic Characteristics and Stability of Rotor-Bearings Systems
Authors: Capone Giuseppe , Russo Michele , Russo Riccardo
Published: June 2008

The influence of turbulence and inertia of oil film on the dynamic characteristics and stability of rotor-bearings systems is theoretically analyzed for various Reynolds number values. The rotor is assumed to be rigid, symmetrical, balanced, and supported in two identical aligned journal bearings. The fluid film forces are evaluated under the short bearing assumption. Stiffness, damping, and acceleration coefficients, and the stability limit curves are reported versus modified Sommerfeld number for various Reynolds numbers and for radius-clearance ratio R/C = 500.
The Transition Between Mild and Severe Wear for Boundary-Lubricated Steels
Authors: Samuels B. , Richards M. N.
Published: June 2008

The wear of AISI-4340 steel under boundary lubrication has been measured in reciprocating sliding. As the hardness of martensitic specimens is reduced from 700 Hv to 250 Hv the wear passes through a transition from “mild” to “severe” wear. A two-component wear model, associating the wear mechanisms with sub-surface and surface plasticity controlled modes of asperity deformation, has been quantitatively fitted to the experimental data. Good agreement is found between the values of constants in the model obtained in this way, and other theoretical and experimental data in the literature. The model can also account for the results of increasing the applied load, by allowing for the effects of increased friction and plastic collapse and removal of the most severely deformed asperities.
Compressible Navier–Stokes Computations for Slider Air-Bearings
Authors: Henshaw W. D. , Reyna L. G. , Zufiria J. A.
Published: June 2008

Two-dimensional computations of the compressible Navier–Stokes equations are used to study the flow at the inlet and outlet of slider air-bearings operating under conditions typical of computer disk-storage devices. Inlet results show a pressure gain of several times the dynamic pressure of the incoming flow, with the actual value depending on the local Reynolds number. Although the outlet of the slider is characterized by a sudden pressure drop, the numerical results show that for sliders operating at small Mach numbers there is only a small temperature drop. The computations show the position of the separating streamline on the back surface of the slider, which is found to depend on the radius of curvature of the outlet corner. Results are also shown from calculations of the global flow underneath and around a two-dimensional slider.
Normal Vibrations and Friction Under Harmonic Loads: Part I—Hertzian Contacts
Authors: Hess D. P. , Soom A.
Published: June 2008

Nonlinear vibrations at a Hertzian contact are studied by the perturbation technique known as the method of multiple scales. The vibrations are excited by the dynamic component of an externally applied normal load. Solutions are obtained for both the average and instantaneous contact deflections. As a result of the nonlinear Hertzian stiffness, the average normal contact deflection during oscillations is smaller than the static deflection under the same average load. It is shown that this can result in a reduction of the average area of contact and, by implication, the average friction force in the presence of even small dynamic loads. The parametric dependence of the normal motion on the various contact parameters is investigated. It is shown that the maximum average friction reduction without contact loss is approximately ten percent.
Normal Vibrations and Friction Under Harmonic Loads: Part II—Rough Planar Contacts
Authors: Hess D. P. , Soom A.
Published: June 2008

Nonlinear normal contact vibrations, excited by the application of a dynamic normal load to the contact region formed between rough surfaces, are studied using the method of multiple scales. The planar rough surface is described by the Greenwood and Williamson model. The contact region behaves as a nonlinear spring in parallel with a viscous damper, and supports a rigid mass. It is shown that the average contact separation in the presence of dynamic loading is greater than the static separation under the same average load. In contrast to some previous results, this increase in average separation does not result in a significant change in the average friction force.
Elasto-Plastic Coupled Temperature-Displacement Finite Element Analysis of Two-Dimensional Rolling-Sliding Contact With a Translating Heat Source
Authors: Kulkarni S. M. , Rubin C. A. , Hahn G. T.
Published: June 2008

The present paper, describes a transient translating elasto-plastic thermo-mechanical finite element model to study 2-D frictional rolling contact. Frictional two-dimensional contact is simulated by repeatedly translating a non-uniform thermo-mechanical distribution across the surface of an elasto-plastic half space. The half space is represented by a two dimensional finite element mesh with appropriate boundaries. Calculations are for an elastic-perfectly plastic material and the selected thermo-physical properties are assumed to be temperature independent. The paper presents temperature variations, stress and plastic strain distributions and deformations. Residual tensile stresses are observed. The magnitude and depth of these stresses depends on 1) the temperature gradients and 2) the magnitudes of the normal and tangential tractions.
The Application of Scanning Tunneling Microscopy to Study Lubricant Distribution of Magnetic Thin Film Rigid Disk Surfaces
Authors: Sriram T. S. , Wahl K. J. , Chung Y.-W. , Bhushan B. , Rothschild W.
Published: June 2008

A special imaging mode of the scanning tunneling microscope (STM) based on charge trapping was used to probe the uniformity of lubricant distribution on magnetic thin film rigid disks at resolutions of better than 35 nm. Electron beam deposited STM tips were used to achieve this resolution. Coupons from untested rigid disks and those subjected to wear in dry helium and humid air were examined. We also examined coupons of an untested disk on which a scratch mark was made with a ferrite pin. It was found that the lubricant layer was nonuniform in the scratched region.
Wear and Lubrication as Observed on a Lap Table With Loose and Bonded Abrasive Grit
Authors: Abrahamson G. R. , Duwell E. J. , McDonald W. J.
Published: June 2008

Lapping machines are widely used for the planar grinding of both metals and ceramics. In principle, they resemble the many pin-on-disk machines that have been constructed for tribology studies. However, they generally have the advantage of rugged construction and a wide choice of operating speeds. Most lapping machines are used with loose abrasive grit, but covering the table with a bonded coated abrasive presents no serious problem. In this mode, two-body abrasion can be studied and compared with three-body abrasion using identical speeds and loads. The primary purpose of this study was to elucidate the role of lubricants in such operations.
A Finite Element Cavitation Algorithm: Application/Validation
Authors: Kumar A. , Booker J. F.
Published: June 2008

A mass-conserving simulation algorithm for cavitating hydrodynamic lubrication has been described elsewhere. The algorithm, which is particularly well adapted to finite element implementation, is outlined qualitatively and demonstrated quantitatively through bearing applications studied experimentally by others. Present simulation results and previous experimental data agree relatively closely for these applications, providing limited validations of the algorithm and suggesting new lines of investigation.
A Comparison Between the Thermomechanical Wear Model and Some Experimental Observations
Authors: Yang J. , Winer W. O.
Published: June 2008

A wear map is constructed from the thermomechanical wear theory. This wear map can be used as a wear criteria to predict the transition of wear of ceramics as well as some steels. Maximum principal stress theory and von Mises criteria are used as failure criteria to make the wear map. The theory is used to present wear maps with the coordinates of dimensionless Hertz pressure and a friction heating condition parameter, Gt which are shown to be related to the traditional PV product design criteria. These wear maps are compared with the experimental data of other researchers. Both data sets show good agreement in trend and magnitude.
Propagation of Semi-Elliptical Surface Cracks in Lubricated Rolling/Sliding Elliptical Contacts
Authors: Kaneta M. , Murakami Y.
Published: June 2008

In this paper the three-dimensional mixed mode stress intensity factors for semi-elliptical inclined cracks formed on elliptical Hertzian contact surfaces are calculated. This analysis accounts for both the frictional forces between the contact surfaces and between the crack faces, as well as including fluid pressure acting on the crack faces. Various factors affecting the crack growth are discussed and possible growth modes are investigated. In particular, the analytical results predict that the crack has a faster growth rate when the major axis of the contact ellipse is in the direction of motion of the load as compared to the minor axis being in the direction of motion of the load.
A High Speed Photography Study of Cavitation in a Dynamically Loaded Journal Bearing
Authors: Sun D. C. , Brewe D. E.
Published: June 2008

The earlier study made by Jacobson and Hamrock on the cavitation of liquid lubricant films in a dynamically loaded journal bearing was repeated with a quartz sleeve, which was more rigid than the Polymethylmethacrylate (PMMA) sleeve used previously. Various improvements of the test rig were made concomitantly so that the experimental errors could be better controlled and assessed. This paper describes the updated high-speed photography experiment and its results.
The Effects of Surface Roughening and Protective Film Formation on Scuff Initiation in Boundary Lubrication
Authors: Lee Young-ze , Ludema K. C.
Published: June 2008

The mechanisms of failure of lubricated steel surfaces were investigated. The focus was on two phenomena, namely, the effects of lubricant reactivity and the effects of sliding speed. Experiments were performed with the ball-on-flat and the cylinder-on-flat geometries in the manner of the methods used to develop the failure maps of the (OECD) IRG. Contact resistance and coefficient of friction were measured during the tests and surface roughness was measured frequently during the tests. Surface failure could not be predicted by using the ratio λ (the ratio of fluid film thickness to composite surface roughness) except when chemically inert lubricants are used. Even then the adverse influence of temperature rise on fluid film thickness does not adequately explain the low load carrying capacity of lubricated surfaces at high sliding speeds. There is a separate effect, namely, a quicker and more severe surface roughening at high speeds than at low speeds, which causes surface failure. The protective layers on sliding surfaces that form by chemical reaction with the lubricant were found to reduce the surface roughening and increase the load carrying capacity of surfaces to values of λ as low as 0.03.
An Investigation Into Laminar-to-Turbulent Transition in Tilting-Pad Bearings
Authors: Innes G. E. , Leutheusser H. J.
Published: June 2008

It has long been known that superlaminar flow occurs in lubrication fluid films above a critical speed. The consequence of the transition from laminar to superlaminar flow is an increase in power losses, with corresponding changes in heat generation and operating costs. While a formula exists to predict the onset of superlaminar flow for hydrodynamic journal bearings, there is no clear criterion for the transition in tilting-pad thrust bearings. The paper describes a detailed investigation, performed on a large-scale model of a single tilting-pad, to obtain fundamental information on the transition phenomenon. Based on this work a lower critical Reynolds number of laminar-to-turbulent transition is proposed.
Comparison of Lubricant Performance in an Oscillating Spacecraft Mechanism
Authors: Carre´ D. J. , Fleischauer P. D. , Kalogeras C. G. , Marten H. D.
Published: June 2008

A life test of lubricants for the R2 shaft bearings of a spacecraft oscillating scanner mechanism was performed under simulated orbital conditions. The lubricant originally used in the application, a chloroarylalkylsiloxane (CAS) oil, and a linear perfluoropolyalkylether (PFPE) oil failed in less than 2500 hr of operation. A poly-alpha-olefin (PAO) oil has been running for more than 11,000 hr without any indication of lubricant or system degradation. The performances of the oils are discussed in terms of the boundary lubrication conditions of the test.
Friction and Wear of Ceramics for Magnetic Recording Applications—Part II: Friction Measurements
Authors: Chandrasekar S. , Bhushan Bharat
Published: June 2008

Friction and wear experiments have been conducted under lightly loaded conditions (less than 0.1 MPa) on a number of single crystal and polycrystalline ceramics in sliding contact against magnetic thin-film hard disk and against themselves in order to compare their tribological behavior. The ceramics studied range from single crystal diamond and sapphire to polycrystalline engineering ceramics such as manganese-zinc ferrite, alumina-titanium carbide, and zirconia. The results are analyzed in the context of earlier work on the friction and wear of these ceramics under lightly loaded conditions which has been recently reviewed by Chandrasekar and Bhushan (1990).
Correlation of Scuffing Experiments With EHL Analysis of Rough Surfaces
Authors: Lee S. C. , Cheng H. S.
Published: June 2008

Scuffing experiments were conducted on a twin disk machine using straight mineral oil. The purpose of these experiments was to validate some existing scuffing theories based on the breakdown of lubrication film in concentrated partial ehl (elastohydrodynamic lubrication) contacts. The verify these scuffing theories, a model for solving the complete inlet half ehl solution to the line contact between two rough longitudinally ground surfaces was developed. This ehl contact model was based on a newly developed concept, “average gap.” The effect of surface roughness on lubrication was taken into account by simulating the contacts between many different pairs of rough surfaces. In order to solve for the ehl contact solutions of the two disks under scuffing conditions, the actual run-in surface profiles of the mating disks, digitized just prior to failure, were used. Finally the correlations were made between the scuffing theory and the experimental data.
Scuffing Theory Modeling and Experimental Correlations
Authors: Lee S. C. , Cheng H. S.
Published: June 2008

The scuffing behavior for contacts operating in the partial elastohydrodynamic lubrication regime is shown to be greatly affected by the asperity contact temperatures and the lubricant pressures inside the elastohydrodynamic lubrication conjunction. A scuffing model which takes into account the temperature and pressure effects for predicting the onset of scuffing failure has been developed. This model is based on the lubricant molecule physisorption theory and is capable of predicting the scuffing failures for general contact conditions including the boundary lubrication contacts and the elastohydrodynamic lubrication (ehl) contacts. A preliminary investigation into this model showed a good correlation existing between the theory and some scuffing experiment results conducted on a twin disk machine. However, more experimentation is necessary to further ascertain the validity of this new model. To validate the new scuffing theory, a method for calculating the asperity flash temperatures is formulated. The flash temperature calculations were performed using the actual digitized run-in surface profiles of the mating bodies. The necessary informations for calculating the flash temperatures such as, the real areas of contact and the asperity contact pressures were all determined using a recently developed rough surface contact simulation model.
Analysis of a Transversely Isotropic Half Space Under Normal and Tangential Loadings
Authors: Lin W. , Kuo C. H. , Keer L. M.
Published: June 2008

This paper analyzes the response of a transversely isotropic half space subjected to various distributions of normal and tangential contact stresses on its surface. Both the interior displacement and stress fields are given in closed form. Among them, rectangular patch solutions are constructed for application to solutions to non-Hertzian contact problems.
Convection and Dissipation Effects in Oil Lubricated Conical Bearings With Variable Viscosity
Authors: Sinha Prawal , Rodkiewicz C. M.
Published: June 2008

The influence of the inclusion of convection and dissipation terms in the energy equation, on the characteristics of a conical bearing with constant film thickness, rotating with a uniform angular velocity is examined. The slider temperature is taken to be an arbitrary constant, greater, equal or smaller, than the assumed constant temperature of the pad. The fluid is considered to be incompressible and the viscosity is assumed to vary exponentially with temperature. The governing system of coupled momentum and energy equations, in conical coordinates, is solved numerically using the finite difference method to yield the various bearing characteristics. The results show that the inclusion of dissipation function alone leads to an underestimation of load capacity and torque, whereas the inclusion of convection terms alone leads to an overestimation of the same.