bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Investigation of the Steady-State Response of a Mechanical Seal With Two Flexibly Mounted Rotors
Authors: Wileman J. , Green I.
Published: February 2008

A parametric analysis is performed to investigate the steady-state dynamic response of a mechanical seal with two flexibly mounted rotors. The effect of changing various inertia, support, and fluid film properties is examined. Short rotors are shown to benefit from gyroscopic aligning moments and to exhibit their maximum steady-state misalignment when one of the shaft speeds is zero. Long rotors experience misaligning gyroscopic moments, but if only one of the two rotors is long then aligning moments from the short rotor can be transmitted through the fluid and counteract the detrimental gyroscopic effect in the long rotor. In this case rotors which corotate are shown to have a higher steady-state misalignment than those which counterrotate because of the reduction of the hydrodynamic moments, thus leading to increased leakage and a higher probability of face contact.
On the Scuffing Failure of Hydrodynamic Bearings in the Presence of an Abrasive Contaminant
Authors: Khonsari M. M. , Pascovici M. D. , Kucinschi B. V.
Published: February 2008

The presence of rigid particulate contamination in hydrodynamic bearings is known to lead to considerable damage resulting in failure. This paper presents a model for evaluating the flash temperature between a fixed, rigid particle embedded into the bearing over-layer while in contact with the slider. Scuffing is assumed to occur if the flash temperature exceeds a certain critical value. The model provides a convenient procedure for estimating an appropriate filter size. Examples are provided to illustrate the utility of the model.
Flying Stiction, Lubricant Pick-Up and Carbon-Overcoat Wear of Magnetic Heads
Authors: Gao Chao , Dai Peihua , Vu Vinh
Published: February 2008

Flying stiction, a high static friction force resulting from a magnetic head seeking/flying over a disk surface, has posed a new challenge in magnetic-disk tribology for low flying heights (˜30 nm or less), as demanded by high recording densities. Two types of magnetic heads were used in this study. A more than 10-fold increase in flying stiction force was observed for the carbon coated heads after a 24 hours of seeking/flying over the disk surface. Using Time of Flight Secondary Ion Mass Spectroscopy and a scanning micro-ellipsometer, we found that the lubricant pickup during seeking/flying operation was responsible for the observed 10-fold increase of the flying stiction force. A nearly exponential dependence of flying stiction force on lubricant amount picked up on the air bearing surface (ABS) of the magnetic heads was found. For 24 hours of seeking/flying time, the lubricant accumulated on the ABS surfaces can be up to 1.5 nm, comparable to the lubricant thickness on the disk surfaces. The lubricant amount was found quite uniformly distributed over the ABS surface of the head. Wear on the carbon overcoat of the magnetic heads was also measured, and was equivalent to approximately 1 nm carbon loss for a 24-hour seeking/flying period. The wear rate of the carbon overcoat was very fast for short periods of seeking time (˜2 hours) and slowed down to near-zero as lubricant built up on the ABS surface, indicating that the lubricant on the head protected carbon wear. The wear of carbon overcoat strongly suggests that intermittent physical contacts between the disk surface and head ABS occurred during seeking/flying operations.
Rheological Models for Stick-Slip Behavior
Authors: Jang Siyoul , Tichy John
Published: February 2008

Stick-slip is a complex phenomenon which has been studied by researchers from many points of view. A variety of engineering factors, such as surface roughness, may contribute to this behavior. However, recent studies from basic science have shown that molecularly smooth surfaces separated by a film also exhibit stick-slip. Thus, the process may be intrinsically film-induced due to transitions between solid-like and fluid-like behavior. The authors of such studies often state that this kind of response indicates the futility of trying to describe such behavior from a continuum perspective. A purpose of this paper is to refute that point of view. Other studies, both experimental and theoretical, have indicated that continuum rheological models may be valid for films of molecular (nanometer) scale. Various rheological models which can predict stick-slip are proposed in this paper. Calculated results are similar to those of experiment.
Dynamic Stability and Spacing Modulation of Sub-25 nm Fly Height Sliders
Authors: Hu Yong , Bogy David B.
Published: February 2008

Designing a reliable sub-25 nm spacing head/disk interface for today’s magnetic hard disk drives demands a greater dynamic stability and a smaller spacing modulation. An air bearing dynamic simulator with multiple features is developed to investigate the dynamic characteristics of three shaped-rail negative pressure sub-25 nm fly height sliders. Various simulations including air bearing stiffness, impulse response, surface roughness induced spacing modulation, bump response, and track seeking dynamics are performed. The results indicate that the roughness induced spacing modulation decreases with the increase of the air bearing stiffness and the decrease of the slider size. The suspension dynamics is integrated into the air bearing dynamics simulation for the track accessing motion by modal analysis. It is concluded that the fly height modulation during a track accessing event is attributed to many factors such as the effective skew angle, the seeking velocity, and the roll motion caused by the inertia of the moving head. The extent of the roll motion effect depends on the air bearing roll stiffness and the level of the inertia force of the moving head. Larger roll stiffness and smaller inertia force produce a smoother track accessing performance.
Stability of Sliding in a System Excited by a Rough Moving Surface
Authors: Berger E. J. , Krousgrill C. M. , Sadeghi F.
Published: February 2008

A two-degree-of-freedom translational system has been developed to study the influence of normal force oscillations on the stability of the steady sliding position. Excited by a small, periodic surface roughness, the normal and tangential motion are coupled through a velocity-dependent friction law. The linearized system has been examined using the first-order averaging technique of Krylov and Boguliubov. In addition to the primary forced resonance, a 2:1 parametric resonance and a 1/2 sub-harmonic resonance have been encountered. Arising from velocity-dependent coupling of the normal and tangential modes and the periodic normal force variations, the parametric resonance has been found to produce locally unstable responses in some cases. Conditions for the stability of the local response based upon local friction curve slope, static normal force, system damping, and surface velocity have been derived for a broad range of frequency.
Flying Height Measurement on Al2O3 Film of a Magnetic Slider
Authors: Li Yufeng
Published: February 2008

Flying height has been successfully measured on the Al2O3film of a magnetic slider by using a specially developed ellipsometer, a reflectometer, and an intensity based interferometric flying height tester. The accuracy of the measured flying height values has been verified with a profilometer. It is found that, under certain conditions, the flying height value generated by the currently used methodology in the hard disk drive industry is misleading in the sense that it can be significantly different from both the true gap and the minimum flying heights. Therefore, it is proposed that the flying height measurement methodology reported in this study be used by the hard disk drive industry to correctly measure the gap and minimum flying heights.
Development and Optimization of Carbide-Reinforced Tools and Application to Hot Rolling of Stainless Steel
Authors: Tsubouchi Kenji , Akiyama Masayoshi , Okuyama Tsutomu
Published: February 2008

A new design philosophy was tried out on a carbide-reinforced tool for hot working of stainless steel. The carbide particle in the micro structure of the new tool was selected so as to meet the relatively large optimum size. Attention has been focused, in the conventional tool, on the enlargement of the area fraction of fine carbide particles on the surface. The tool was made by a plasma transferred arc process, and it was found in the laboratory that an optimum mixture ratio of NbC and AISI316L powder realizes the best performance against wear and galling. It was also found that coating of the new tool material on the mother metal of moderate strength, toughness, and ductility ensures the longevity of the tool. The new tool was subjected to hot rolling of a stainless-steel seamless tube by a plug mill to verify the high performance.
Survey of Experimental Data for Fixed Geometry Hydrodynamic Journal Bearings
Authors: Swanson E. E. , Kirk R. G.
Published: February 2008

An extensive survey of the experimental research on the static and/or dynamic characteristics of fixed geometry, hydrodynamic journal bearings, available in English, in the open literature is presented. The type(s) of bearing, size of bearing(s) and range of parameters measured in each work are reported for slightly over 100 published experimental works. In addition, some general observations about the available experimental data sets are made. This annotated survey is intended to help the analytical community by providing an extensive list of sources of experimental data for use in analysis verification. It is intended to help the experimental community by highlighting the shortcomings of the available literature, as well as by providing a list of sources for appropriate data to help with current and future test rig debugging.
Thermohydrodynamic Design Charts for Slider Bearings
Authors: Jang J. Y. , Khonsari M. M.
Published: February 2008

Thermohydrodynamic Design Charts are developed for slider bearings that enable one to rapidly determine a conservative estimate for the bearing maximum temperature and a pertinent mean temperature from which all of the bearing performance parameters are computed. A number of examples are presented which illustrate the utility of the design charts.
Frictional Analysis of MoS2 Coated Ball Bearings: A Three-Dimensional Finite Element Analysis
Authors: Lovell M. R. , Khonsari M. M. , Marangoni R. D.
Published: February 2008

A brief review of finite element contact and friction theory is presented for low-speed bearing operations. A three-dimensional finite element model is developed to realistically characterize the friction experienced by a coated ball bearing element. The finite elements results, which are obtained for various normal loads and ball materials, are verified using Hertzian contact theory and previous experimental tests performed by the authors. From the results, general trends for the frictional behavior of coated bearing surfaces are established and implications to the field of controls, as applied to precision positioning and tracking instruments are discussed.
Tribo-Electromagnetic Phenomena of Hydrogenated Carbon Films—Tribo-Electrons, -Ions, -Photons, and -Charging
Authors: Nakayama Keiji , Bou-Said Benyebka , Ikeda Hiroshi
Published: February 2008

Triboemission of negatively charged particles and positively charged particles, tribo-charging and friction coefficient were measured simultaneously using a frictional system with diamond sliding on hydrogenated carbon films in ambient air. The hydrogen content of the carbon films varied from 0 to 43 at. percent. All the carbon films tested emitted both negatively and positively charged particles during sliding. For films with hydrogen content of from 0 to 15 at. percent, neither tribo-charging nor tribo-photons were observed; beyond 15 at. percent hydrogen content, tribo-charging and tribo-photons were observed. With increasing hydrogen content, the emission intensity of the negatively and positively charged particles, photons and tribo-charging increased. It is concluded that a micro-plasma state is formed at the frictional contacts of diamonds sliding on hydrogenated carbon films.
Surface Roughness Effects in High-Speed Hydrodynamic Journal Bearings
Authors: Hashimoto H.
Published: February 2008

This paper describes an applicability of modified Reynolds equation considering the combined effects of turbulence and surface roughness, which was derived by Hashimoto and Wada (1989), to high-speed journal bearing analysis by comparing the theoretical results with experimental ones. In the numerical analysis of modified Reynolds equation, the nonlinear simultaneous equations for the turbulent correction coefficients are greatly simplified to save computation time with a satisfactory accuracy under the assumption that the shear flow is superior to the pressure flow in the lubricant films. The numerical results of Sommerfeld number and attitude angle are compared with the experimental results to confirm the applicability of the modified Reynolds equation in the case of two types of bearings with different relative roughness heights. Good agreement was obtained between theoretical and experimental results.
Derivation of Hydrodynamic Bearing Coefficients Using the Minimum Square Method
Authors: Mu¨ller-Karger Carmen M. , Granados Andre´s L.
Published: February 2008

A linear analysis of the parameters for the orbital transient response of journal-bearing systems is made with the purpose of computing the bearing dynamic coefficients using the minimum square method. The journal-bearing response is obtained from a nonlinear simulation that includes a transient solution of the Reynolds equation. The minimum square method permits the adjustment of coefficients with only one orbit and does not need prior linearization of the response. Therefore it was found to be advantageous compared with the more traditional experimental method of using a frequency domain method with two orbital responses. Three different Sommerfeld numbers were analyzed. Comparisons between the eight adjusted coefficients and the linear coefficients obtained from perturbations of the Reynolds equation about the equilibrium position permit the establishment of the ranges where the bearings behave linearly.
The Influence of Humidity on the Fretting Wear of Steel Surfaces Using Thin Layer Activation
Authors: De Baets P. , Kalacska G. , Strijckmans K.
Published: February 2008

It is generally known that the humidity in the surrounding atmosphere influences wear processes in general. For fretting wear several authors examined the influence of humidity on the wear scar morphology and the composition of the wear debris. No agreement between the different results has been found, yet. In the present study, a distinction is made between running-in and steady-state fretting wear. Especially for the running-in stage, the influence of the humidity in ambient air on the friction and wear behavior and material transfer of steel surfaces subjected to contact vibrations has been investigated. The fretting experiments were conducted with a spherical against a flat specimen under gross-slip regime. The fretting wear and accompanying material transfer between the contacting specimens quantitatively are measured with Thin Layer Activation method. It has been observed that high ambient humidity has a beneficial influence on the running-in fretting wear of steel surfaces. It has also been found that the results of several authors concerning the influence of humidity on the fretting wear of steel have to be treated with great care, as classical wear measuring techniques can give erroneous wear results.
Performance Analysis of Grease-Lubricated Journal Bearings Including Thermal Effects
Authors: Jang J. Y. , Khonsari M. M.
Published: February 2008

A detailed analysis of the flow characteristics and lubrication effectiveness of grease in journal bearings is presented. Based on the ideal Bingham plastic model, the appropriate governing equations are developed which effectively handle the formation of a floating core as well as a core which may attach itself to either the shaft or the stationary bushing. The formulation and numerical solutions presented pertain to three-dimensional flows in finite journal bearings. Moreover, an extensive amount of computational results are presented, which take thermal effects into account according to the thermohydrodynamic theory.
Dynamics of Machine Tool Spindle/Bearing Systems Under Thermal Growth
Authors: Jorgensen Bert R. , Shin Yung C.
Published: February 2008

Increased use of high-speed machining creates the need to predict spindle/bearing performance at high speeds. Spindle dynamic response is a function of the nonlinear bearing stiffness. At high speeds, thermal expansion can play an important role in bearing stiffness. A complete bearing load-deflection analysis including thermal expansion is derived and is coupled with an analysis of spindle dynamic response. Steady-state temperature distribution is found from heat generation at the contact point and from a quasi three-dimensional heat transfer model. Numerical solutions give a good prediction of thermal growth and heat generation in the bearing. Predicted high-speed spindle frequencies show good agreement with experimentation. The effects of loading condition and bearing material type on bearing stiffness are also shown.
Flow-Induced Vibration of Tubes in Cross-Flow
Authors: Chen S. S. , Cai Y. , Zhu S.
Published: February 2008

This paper presents an unsteady-flow theory for flow-induced vibration of tubes in cross-flow. It includes a general description of motion-dependent fluid forces, characteristics of fluid-force coefficients, and mathematical models. Detailed results are presented for the constrained mode in the lift direction for various tube arrangements.
ULSLEA: A Limit Equilibrium Procedure to Determine the Ultimate Limit State Loading Capacities of Template-Type Platforms
Authors: Bea R. G. , Mortazavi M. M.
Published: February 2008

During the past three decades, an immense amount of effort has been devoted to development of sophisticated computer programs to enable the assessment of storm wind, wave, and current loadings and the ultimate limit state capacity characteristics of conventional, pile-supported, template-type offshore platforms (Billington et al, 1993; Frieze, 1993; Hellan et al., 1993, 1994). These programs require high degrees of expertise to operate properly, are expensive to purchase and maintain, and require large amounts of manpower and time to complete the analyses. Due to the sophistication of these programs, experience has shown that it is easy to make mistakes that are difficult to detect and that can have significant influences on the results. This paper summarizes the second phase of development and verification of simplified procedures to evaluate environmental loadings and ultimate limit state lateral loading capacities of template-type platforms. Reasonable simplifications and high degrees of user friendliness have been employed in development of the software to reduce the engineering effort, expertise, and costs associated with the analyses. The computer program that has been developed to perform the simplified analyses has been identified as ULSLEA (ultimate limit state limit equilibrium analyses) (Mortazavi and Bea, 1994).
Reliability of Welded Structures Containing Fatigue
Cracks
Authors: Lanning D. , Shen M.-H. H.
Published: February 2008

This study investigates the reliability of a cracked fillet welded T-joint typically found in offshore structures. A formulation for the aspect ratio (a/c) of a propagating semi-elliptical fatigue crack located at the toe of the weld is developed using Newman and Raju’s stress intensity factor for a cracked flat plate in conjunction with a weld magnification factor. The reliability in terms of fatigue lifetime is then calculated using the aspect ratio and Paris’s law of crack propagation with both fracture toughness and elastic-plastic failure criteria. The variation in crack aspect ratio in the T-joint is compared to that in a cracked flat plate, and examples are provided of reliability calculations for tension and bending loads.
An Atlas of the Wave-Energy Resource in Europe
Authors: Pontes M. T. , Athanassoulis G. A. , Barstow S. , Cavaleri L. , Holmes B. , Mollison D. , Oliveira-Pires H.
Published: February 2008

An atlas of the European offshore wave energy resource, being developed within the scope of a European R&D program, includes the characterization of the offshore resource for the Atlantic and Mediterranean coasts of Europe in addition to providing wave-energy and wave-climate statistics that are of interest to other users of the ocean. The wave data used for compiling the Atlas come from the numerical wind-wave model WAM, implemented in the routine operation of the European Centre for Medium Range Weather Forecasts (ECMWF), in addition to directional wave measurements from the Norwegian offshore waters.
Static Rolling Bearing Models in a C.A.D. Environment for the Study of Complex Mechanisms: Part I—Rolling Bearing Model
Authors: Bourdon A. , Rigal J. F. , Play D.
Published: February 2008

This paper, the first of two companion papers, proposes a general methodology for accurate modeling of the nonlinear behavior of ball and roller bearings. The models give stiffness matrices which can be introduced into standard finite element models of complex mechanical systems, with the aim of predicting mechanical behavior and load and strain distributions. In the case of an “isolated” ball bearing, the results obtained with the proposed approach are compared to results from the literature. Applications are implemented to evaluate the influence of external loadings on the stiffness matrices of tapered roller bearings mounted in a rigid mechanical environment.
Role of Inclusions, Surface Roughness and Operating Conditions on Rolling Contact Fatigue
Authors: Ne´lias D. , Dumont M. L , Champiot F. , Vincent A. , Girodin D. , Fouge´res R. , Flamand L.
Published: February 2008

Tests have been performed on a two-disk machine in order to evaluate the role of inclusions, surface roughness and operating conditions on rolling contact fatigue of AISI 52100 and M50 bearing steels. Important parameters—such as nature and location of inclusions, small and large wavelengths of surface roughness, normal loading or sliding conditions—on crack initiation and propagation stages have been identified. The operating conditions have been selected to encompass typical jet engine applications. Tests have been carried out up to 4.2 GPa, for two different surface finishes. Surface distress and sub-surface damage which could result in catastrophic failure have been observed. Indeed, surface initiated deep spalling (observed at 3.5 GPa for unpolished surfaces and under rolling plus sliding conditions) as well as sub-surface initiated deep spalling (at 4.2 GPa for polished specimens) have been observed. Sub-surface micro-cracks were detected early and followed during some interrupted tests by the means of an ultrasonic echographic device. Results of our experiments are analyzed and discussed in relation to the rolling contact fatigue theories.
Analysis of Traction Curve in Linear Region Considering Volume Viscoelasticity
Authors: Yoshimura Narihiko , Umemoto Noboru , Nakahara Tsunamitsu
Published: February 2008

Measurements of the gradient in the linear region of traction curve, where the effects of heat generation and nonlinearity of shear viscosity can be neglected were made for two kinds of synthetic oils, DOP and 5P4E, using a traction tester improved to a precision less than 0.01 percent in slip ratio. The measured results were compared with the theoretical results based on a viscoelastic model for shear stress and on an elastic model for compressibility using primary data of the rheological properties which were obtained not by means of traction test; they were markedly less than the theoretical results under low speed for both oils and also under high speed for DOP. A new analysis of the traction was performed considering volume viscoelasticity for compressibility which relates shear viscoelasticity under high pressure. The theoretical results agree fairly with the measured results.
Effects of Structural Vibrations on the Film Thickness in an EHL Circular Contact
Authors: Wijnant Y. H. , Venner C. H. , Larsson R. , Eriksson P.
Published: February 2008

In elastohydrodynamic lubrication (EHL), one generally imposes force balance, i.e., the contact force resulting from the pressure in the contact is equal to the applied load. When studying the effect of structural vibrations, this force balance equation obviously does not hold and the more general equation of motion is required. In Wijnant and Venner (1996), an EHL contact model was introduced that incorporates both squeeze and entraining motion as well as the equation of motion. It was shown numerically that due to a small initial deviation or initial velocity, the rolling element starts an oscillatory motion around the equilibrium position. This motion is slightly damped because of the viscous losses in the lubricant. Moreover, it was shown that these oscillations cause film thickness modulations with a wavelength, directly related to the dimensionless frequency Ω. This paper compares results from experiments that were carried out on a ball and disk apparatus with results obtained with the EHL contact model. In this experiment, the applied load was rapidly increased by impacting a wedge between the base and the ball holder. This results in an increase of the contact area and, as a result of inertia forces of the ball, disk and supports, and oscillatory motion of the contacting bodies. Modulations in the film thickness which result from these oscillations, are clearly visible. The contact model was tailored to this experiment and a qualitatively close agreement has been found.
Thermal Modeling and Effects From Debris Particles in Sliding/Rolling EHD Line Contacts—A Possible Local Scuffing Mode
Authors: Nikas G. K. , loannides E. , Sayles R. S.
Published: February 2008

The damage caused by debris particles in concentrated contacts has been studied extensively in the past, both theoretically and experimentally. Most of the theoretical studies, in which the damage on the surfaces was calculated in the form of dents, were performed isothermally. It is known that sliding asperity contacts, which resemble third body contacts, reach high local temperatures that can affect local material properties which, in turn, will affect the way damage is generated on the surfaces of machine elements. In the present work the heat transfer of lubricated, rolling/sliding line contacts in the presence of a ductile spherical particle is modeled. The particle is assumed to be significantly softer than the counterfaces that squash it. The local flash temperatures due to the combined sliding and squashing of a debris particle are calculated. It is found that high temperatures caused from small and soft particles are rather the rule than the exception.
Friction and Wear Characteristics of Aluminum Alloy Impregnated Carbon Composite
Authors: Goto Hozumi , Omori Shunji
Published: February 2008

Pin-on-disk unidirectional sliding friction and wear experiments for an aluminum alloy impregnated carbon composite in contact with a bearing steel were carried out at various levels of contact load in wet and dry air. The aluminum alloy impregnated carbon composite exhibits better friction and wear characteristics than the matrix materials, aluminum alloy and graphite in wet air. The coefficient of friction and wear rate decrease, especially at high loads in wet air. Graphite, together with metallic and oxidative wear particles, adheres to the disk sliding surface of the bearing steel, resulting in the formation of compacted, uniform surface films. The films prevent metal-to-metal contact, achieving a good sliding friction and wear condition.
CFD Comparison to 3D Laser Anemometer and Rotordynamic Force Measurements for Grooved Liquid Annular Seals
Authors: Moore J. Jeffrey , Palazzolo Alan B.
Published: February 2008

A pressure-based computational fluid dynamics (CFD) code is employed to calculate the flow field and rotordynamic forces in a whirling, grooved liquid annular seal. To validate the capabilities of the CFD code for this class of problems, comparisons of basic fluid dynamic parameters are made to three-dimensional laser Doppler anemometer (LDA) measurements for a spinning, centered grooved seal. Predictions are made using both a standard and low Reynolds number κ-ε turbulence model. Comparisons show good overall agreement of the axial and radial velocities in the through flow jet, shear layer, and recirculation zone. The tangential swirl velocity is slightly under-predicted as the flow passes through the seal. By generating an eccentric three-dimensional, body fitted mesh of the geometry, a quasi-steady solution may be obtained in the whirling reference frame allowing the net reaction force to be calculated for different whirl frequency ratios, yielding the rotordynamic force coefficients. Comparisons are made to the rotordynamic force measurements for a grooved liquid annular seal. The CFD predictions show improved stiffness prediction over traditional multi-control volume, bulk flow methods over a wide range of operating conditions. In cases where the flow conditions at the seal inlet are unknown, a two-dimensional, axisymmetric CFD analysis may be employed to efficiently calculate these boundary conditions by including the upstream region loading to the seal. This approach is also demonstrated in this study.
Frequency Effects on the TEHD Behavior of a Tilting-Pad Journal Bearing Under Dynamic Loading
Authors: Monmousseau P. , Fillon M.
Published: February 2008

In this paper, a theoretical nonlinear analysis of a tilting-pad journal bearing is presented when both a dynamic load and a static load are applied. This analysis is performed under TEHD regime which takes into account both thermal behavior and elastic deformations of the bearing. A comparison between numerical maximum journal amplitudes and experimental data in the case of synchronous dynamic loading is carried out in order to justify the TEHD analysis. The influence of the dynamic loading frequency, which can occur because of vibrations in a turbomachinery, will be studied at a constant rotational speed (15,000 rpm) and for a low (200 N) and a high (2652 N) rotating load and for a periodic dynamic load. It will be shown that, for a critical frequency, the amplitude of the shaft orbit is maximum and this changes the behavior of the tilting-pad journal bearing. It is apparent that the application of the dynamic load generates a thermal transient regime. The increase in the maximum bearing temperature is larger for high dynamic loading response. Consequently, the behavior of the bearing is mainly modified during the first few seconds when the loading frequency is near the critical frequency.
An Experimental Study of Transient Thermal Effects in a Plain Journal Bearing
Authors: Kucinschi B. , Fillon M.
Published: February 2008

The present study deals with the experimental determination of temperature distribution in a plain, steadily loaded journal bearing, during transient thermal periods such as start-up or slow changing in velocity. A number of chromel-alumel thermocouples, placed circumferentially in the median section of the bearing, are used in order to carry out the measurements. The temperature at film-shaft interface is also measured by means of a chromel-alumel thermocouple and a mercury transmitter. The effects of journal speed and load on bearing temperature and fluid friction torque are analyzed. The bearing temperature increases considerably with the increase of rotational speed. In addition, for slight bearing loads the bearing temperatures are greater than for higher loads, due to the oil recirculation. The fluid friction torque increases at start-up and afterwards tends to decrease because of the temperature rise which decreases the oil viscosity.
The Physical Effects of Intra-Drive Particulate Contamination on the Head-Disk Interface in Magnetic Hard Disk Drives
Authors: Altshuler Kenneth J. , Harrison Joshua C. , Ackerman Evelyn
Published: February 2008

The physical damage at the Head-Disk Interface (HDI), caused by common ceramic particles found in the manufacturing environments of the heads and disks in hard magnetic disk drives, is reported. The need for this study arises from industry wide reliability problems due to particulate induced damage at the HDL The intent of this study is to characterize the head/disk damage caused by 1 μm diamond, 1–2 pm Tie particles, 0.2–1 μm alumina particles, the alumina and TiC grains sintered to make Al-TiC (the slider body), and sputtered alumina. These particles were introduced to the HDI in over thirty disk drives. The drives were then made to perform magnetic recording and retrieval operations for known data sequences, with the resultant reading errors tabulated. After the functional testing, the drives were opened and resulting damage was examined with a number of surface characterization tools. This study confirms that the severity of problems with the read-back signal, caused by particle damage, has an inverse relationship with the magnetic track width. In addition, the harshness of physical damage to the HDI has a positive relationship with particle hardness. Finally, particle shape and size can be contributing factors in damaging the HDL.
A Transducer for Simultaneously Measuring Forces Normal to and Parallel to Surfaces
Authors: Hao S. , Klamecki B. E. , Ramalingam S.
Published: February 2008

A transducer for measuring interface loads was fabricated, characterized, and demonstrated by measuring coefficient of friction. It is composed of a segmented body supported on normal force and shear force piezoelectric sensors. The transducer can measure forces normal to and parallel to its surface simultaneously. It is suitable for inclusion into tribological interfaces for characterization of friction in laboratory apparatus or monitoring of forces in machines for machine and process control.
Experimental Force Coefficients for a Two-Bladed Labyrinth Seal and a Four-Pocket Damper Seal
Authors: Ransom David , Li Jiming , Andre´s Luis San , Vance John
Published: February 2008

Experiments are presented to identify the stiffness and damping force coefficients of a two-blade, teeth on stator labyrinth seal with diverging clearance and its modified version as a four-pocket gas damper seal. The seals were tested without journal rotation and at rotor speeds of 1500 rpm and 3000 rpm for seal supply to ambient pressure ratios ranging from 1 to 3. Calibrated impact loads excite a flexibly supported housing holding rigidly the test seal. The impact loads and seal displacement and acceleration time responses are measured and recorded as frequency spectra. The instrumental variable filter method is used to identify the seal dynamic force coefficients from the measured transfer functions over a frequency range. The experiments demonstrate the four pocket gas damper seal has large (positive) direct damping coefficients and relatively small (negative) direct stiffness coefficients. The two bladed labyrinth seal exhibits positive direct stiffness and negative damping force coefficients. The leakage performance of both seals is nearly identical. The four pocket damper seal clearly outperforms the labyrinth seal in terms of rotordynamic forces. Both seals show a minimal amount of cross-coupling force effects, well within the experimental uncertainty.
Flattening of Random Rough Surfaces in Metal-Forming Processes
Authors: Sutcliffe M. P. F.
Published: February 2008

Flattening of random rough surfaces on a workpiece undergoing bulk deformation has beenanalyzed using a model of the surface consisting of just two wavelength components. Asperities are flattened at a rate which depends on the ratio of the initial r.m.s. amplitudes of the long and short wavelength components. The flattening behavior of the long wavelength asperities only becomes important when the amplitude of the long wavelength asperitiesis much greater than that of the shorter wavelength asperities. The surface modification was investigated experimentally by cold rolling of aluminium strips. The power spectral density of the roughness was used to extract appropriate amplitudes for the short and longwavelength components of roughness. The change in roughness amplitudes showed excellent agreement with theory.
Deformation of Rough Line Contacts
Authors: Gelinck E. R. M. , Schipper D. J.
Published: February 2008

The influence of surface roughness on the bulk deformation of line contacts is studied. The model of Greenwood and Tripp (1967) will be extended to line contacts. It is found that the central pressure is a very good parameter to characterize the pressure distribution of rough line contacts. Function fits of the central pressure, the effective half width, the real area of contact, and the number of contacts are made. Comparison is made with the work of Lo (1969) and Greenwood et al. (1984).
The Influence of Heat Generation In the Contact Zone on Bearing Fatigue Behavior
Authors: Bo¨hmer H.-Ju¨rgen , Lo¨sche Thomas , Ebert Franz-Josef , Streit Edgar
Published: February 2008

The material behavior of the standard bearing steel SAE 52100 and the heat resistant bearing steels M50, M50 NiL, and Cronidur 30 as a function of the operational temperature has been investigated. The reduction in rolling contact fatigue strength due to a temperature rise was found to be significantly higher than the reduction of hardness. The mechanism of heat generation due to the bearing operation induces a temperature distribution, which makes it necessary to distinguish between the temperature ruling the subsurface fatigue processes and a higher temperature dominating the surface originated damage initiation.
Some Insights Into Micro-EHL Pressures
Authors: Fang N. , Chang L. , Johnston G. J.
Published: February 2008

An analytical model is developed in this paper which relates the major component of micro-EHL pressure responses to lubricant properties, roughness geometry, contact load, velocity, and slide-to-roll ratio. Analyses are then conducted showing the effects of system parameters on this micro-EHL pressure. For a Newtonian lubricant with an exponential pressure-viscosity law, this pressure would be large unless the contact practically operates right at pure rolling. The magnitude of the pressure rippling is largely independent of the slide-to-roll ratio, and smaller wavelength components of the surface roughness generate larger micro-EHL pressures. With less dramatic pressure-viscosity enhancement such as the two-slope model, the micro-EHL pressure is generally smaller and sensitive to the slide-to-roll ratio, larger with higher sliding in the contact. Furthermore, this pressure-viscosity model yields a micro-EHL pressure that becomes vanishingly small corresponding to sufficiently small wavelength components of the roughness. For a shear-thinning non-Newtonian lubricant, such as the Eyring model, with an exponential pressure-viscosity law, substantially less micro-EHL pressure rippling is generally developed than its Newtonian counterpart. While the pressure rippling is insensitive of the slide-to-roll ratio like its Newtonian counterpart, it vanishes corresponding to sufficiently small wavelength components of the roughness. The analyses revealed that a key factor resulting in a smaller micro-EHL pressure with the two-slope model or the Eyring model is the lower viscosity or shear-thinned effective viscosity in the loaded region of the contact. Since EHL traction is proportional to this viscosity, contacts lubricated with oils exhibiting higher traction behavior would develop larger micro-EHL pressures and thus would be more vulnerable to fatigue failure.
A Mixed Elastohydrodynamic Lubrication Model With Asperity Contact
Authors: Jiang Xiaofei , Hua D. Y. , Cheng H. S. , Ai Xiaolan , Lee Si C.
Published: February 2008

Most machine elements, such as gears and bearings, are operated in the mixed lubrication region. To evaluate lubrication performance for these tribological components, a contact model in mixed elastohydrodynamic lubrication is presented. This model deals with the EHL problem in the very thin film region where the film is not thick enough to separate the asperity contact of rough surface. The macro contact area is then divided into the lubricated area and the micro asperity contact areas by the contacted rough surfaces. In the case when asperity to asperity contact is present, Reynolds equation is only valid in the lubricated areas. Asperity contact pressure is determined by the interaction of two mating surfaces. The applied load is carried out by the lubricant film and the contacted asperities. FFT techniques are utilized to calculate the surface displacement (forward problem) by convolution and the asperity contact pressure (inverse problem) by deconvolution for non-periodic surfaces. With the successful implementation of FFT and multigrid methods, the lubricated contact problem can be solved within hours on a PC for the grids as large as one million nodes. This capability enables us to simulate random rough surfaces in a dense mesh. The load ratio, contact area ratio and average gap are introduced to characterize the performance of mixed lubrication with asperity contacts. Discussions are given regarding the asperity orientation as well as the effect of rolling-sliding condition. Numerical results of real rough topography are illustrated with effects of velocity parameter on load ratio, contact ratio, and average gap.
Lubrication Model of an Artificial Hip Joint: Pressure Profile Versus Inclination Angle of the Acetabular Cup
Authors: Meyer Donna M. , Tichy John A.
Published: February 2008

Formulation of a three-dimensional, quasi-static lubrication model of an artificial hip joint is proposed which includes the inclination angle of the acetabular cup. This is performed by deriving a transformed Reynolds equation accounting for this cup tilt angle. The numerical simulation also addresses mass conservation at the location of film rupture. A 3-D spherical representation of the articulating surfaces of the hip prosthesis is mapped onto a cartesian coordinate system of the entire geometry of the “ball and socket” joint. Results include the lubricating fluid pressure distributions for various inclination angles of the acetabular cup demonstrating that the greatest pressures occur for large eccentricities in the upward vertical direction.
An Optimization Method for Design of Subambient Pressure Shaped Rail Sliders
Authors: Choi Dong-Hoon , Kang Tae-Sik
Published: February 2008

This study proposes a design methodology for determining configurations of subamient pressure shaped rail sliders by using a nonlinear programming technique in order to meet the desired flying characteristics over the entire recording band. The desired flying characteristics considered in this study are to minimize the variation in flying height from a target value, to keep the pitch angle within a suitable range, and to ensure that the outside rail flies lower than the inside rail even with the roll distribution due to manufacturing process. The design variables selected are recess depth, geometry of the air bearing surface, and pivot location in the transverse direction of the slider. The method of feasible directions in Automated Design Synthesis (ADS) is utilized to automatically find the optimum design variables which simultaneously meet all the desired flying characteristics. To validate the suggested design methodology, a computer program is developed and applied to a 30 percent/15 nm twin rail slider and a 30 percent/15 nm tri-rail slider. Simulation results for both sliders demonstrated the effectiveness of the proposed design methodology by showing that the flying characteristics of the optimally designed sliders are enhanced in comparison with those of the initial ones.
Computer Analysis of Bouncing Vibration and Tracking Characteristics of a Point Contact Slider Model Over Random Disk Surfaces
Authors: Ono Kyosuke , Takahashi Kan , Iida Kohei
Published: February 2008

This study is a computational analysis of the bouncing vibration of a point contact slider model over computer generated random disk surfaces and the design conditions of slider to disk interface parameters necessary for contact recording. The Gaussian random surface of a disk with various standard deviations and frequency characteristics is generated by using a modified midpoint displacement algorithm. From the calculated results of bouncing vibration of a slider for various parameter values, it was found that the decrease in contact stiffness and increase in slider load can significantly reduce the bouncing vibration as well as the increase in contact damping and the smoothness of the surface. It was also found that the bouncing vibration spectrum of a contact slider over a simulated disk surface agreed closely with the experimental results presented in a previous study by the authors. The maximum and rms values of the spacing and the contact force were examined for various design parameters. The design conditions of the contact pad to the disk interface were discussed in terms of tracking ability and wear durability for slider loads of 0.5 mN and 5 mN.
Pseudospectral Orbit Simulation of Nonideal Gas-Lubricated Journal Bearings for Microfabricated Turbomachines
Authors: Piekos E. S. , Breuer K. S.
Published: February 2008

A journal bearing simulation tool developed to aid the design of the MIT microturbo-machine bearings is described. This tool uses an orbit method with a pseudospectral technique for treating the Reynolds equation. Comparison is made to various published data. Two types of stability chart are presented and their application to turbo-machine bearing design is discussed. Simulations of imbalance, noncircular geometry, and nonuniform pressures at the bearing ends are also demonstrated.
Thermal Characteristics of a Wet Clutch
Authors: Jang J. Y. , Khonsari M. M.
Published: February 2008

A comprehensive formulation of the governing equations, boundary conditions, and numerical solution technique is presented for modeling the thermal aspects of the engagement process in a wet clutch. The thermal model includes full consideration of the viscous heat dissipation in the fluid as well as heat transfer into the separator, friction material, and the core disk. Roughness, waviness, deformability and permeability of the friction material are taken into account. It is shown that very large temperatures develop in the fluid during the engagement process which takes place on the time scale of one second. It is also shown that thermal effects influence the engagement time and the torque behavior of a clutch and should be included in the analytical studies.