bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Geometry on Thermoelastic Instability in Disk Brakes and Clutches
Authors: Yi Yun-Bo , Du Shuqin , Barber J. R. , Fash J. W.
Published: February 2008

The finite element method is used to reduce the problem of thermoelastic instability (TEI) for a brake disk to an eigenvalue problem for the critical speed. Conditioning of the eigenvalue problem is improved by performing a preliminary Fourier decomposition of the resulting matrices. Results are also obtained for two-dimensional layer and three-dimensional strip geometries, to explore the effects of increasing geometric complexity on the critical speeds and the associated mode shapes. The hot spots are generally focal in shape for the three-dimensional models, though modes with several reversals through the width start to become dominant at small axial wavenumbers n, including a “thermal banding” mode corresponding to n = 0. The dominant wavelength (hot spot spacing) and critical speed are not greatly affected by the three-dimensional effects, being well predicted by the two-dimensional analysis except for banding modes. Also, the most significant deviation from the two-dimensional analysis can be approximated as a monotonic interpolation between the two-dimensional critical speeds for plane stress and plane strain as the width of the sliding surface is increased. This suggests that adequate algorithms for design against TEI could be developed based on the simpler two-dimensional analysis.
Thermal Behavior of Power Gearing Transmission, Numerical Prediction, and Influence of Design Parameters
Authors: Manin L , Play D.
Published: February 2008

Thermal behavior prediction of Power Gearing Transmissions during preliminary design becomes necessary in order to optimize all the parts of mechanical systems (lubrication, cooling device dimensioning, static and dynamic stress resistance, etc.). It also reduces prototype tests. The thermal network method is used to model each technological element as a thermal finite element and a nonlinear system of equations is obtained. Geometric discretization is adapted to the scale of phenomenological observation and result requirements. As assumptions have to be made for the modeling of convection heat transfer and oil flow, experimental verifications are made. The influence of gear parameters, the effect of time varying running conditions, and oil flow defaults are then studied and discussed.
Finite Element System Approach to EHL of Elliptical Contacts: Part II—Isothermal Results and Performance Formulas
Authors: Hsiao Hsing-Sen S. , Bordon Juan L , Hamrock Bernard J. , Tripp John H.
Published: February 2008

Extensive isothermal solutions for elastohydrodynamic lubrication (EHL) of elliptical contacts under pure rolling are obtained by using the newly developed finite element system approach. The Hamrock-Dowson type of performance formula is revisited with these close-to-Newtonian results. Additional solutions are also compared with those obtained by a multigrid technique. The current solutions show good agreement with their existing counterparts.
Development of a New Tool Material to Ensure High Performance in Hot Steel Rolling
Authors: Tsubouchi Kenji , Akiyama Masayoshi , Yamamoto Eiji , Mase Toshiro
Published: February 2008

A new structure design was presented to prolong the tool life for hot metal working. The tool surface deteriorates quickly when attacked under continuous severe sliding conditions by hot metal at a temperature above 1473 K. Observations were made on guide shoes used in seamless tube rolling to reach the conclusion that enlargement of the size and change in the structure of chromium carbide prolong the tool life. This is contrary to the structure design of high-speed steel for which small carbide is recommended. The validity of the new tool was verified both in laboratory tests and in the production line.
Heat Transfer and Roll Surface Temperature in the Hot Rolling of Aluminum Sheet
Authors: Yoneyama Takeshi , Asaoka Hiroshi , Kimura Hiroshi , Hoshino Ikuya , Kokubo Misao
Published: February 2008

Roll surface temperature in the arc of contact has been directly measured by a temperature sensor embedded on the roll surface during the hot rolling of aluminum sheet. Influences of the rolling parameters such as initial sheet temperature, reduction ratio, and lubrication condition on the roll surface temperature have been investigated. The roll surface temperature abnormally increases in the entrance part of the contacting arc when the rolled sheet seized on the roller with no lubricant. By comparison with the roll surface temperature simulated by one-dimensional finite difference method, the heat transfer coefficient between the roll and the sheet surfaces was estimated to be approximately 400 kW/m2K. A simulation of the abnormal increase in the roll surface temperature in the case of seizure has been performed by adding the heat generation in the surface layer of the sheet caused by friction on the boundary surface.
On the Frictional Characteristics of Ball Bearings Coated With Solid Lubricants
Authors: Lovell M. R. , Khonsari M. M.
Published: February 2008

The problem of a ball bearing in normal contact between two transversely isotropic coated substrates is investigated using the finite element method (FEM). A three-dimensional finite element model is developed that accurately determines the steady friction force in low-speed bearing systems containing soft layered solid lubricant films. Extensive numerical results, which are verified using Hertzian contact theory and laboratory experiments, are obtained at 540 operating conditions by varying coating material, coating thickness, normal load, ball material, and ball radius. Friction force results generated from the FEM are normalized by introducing the dimensionless transversely isotropic coating parameter, ξ. A numerical expression for the normalized friction force in coated ball bearings is determined by curvefitting the results of the 540 simulations performed. The relevance of such an expression, as related to the durability of low-speed bearings, is subsequently ascertained and discussed.
Models for Temperature-Kinetic Aspect of Friction and Wear in Oil Lubrication
Authors: Lin Jen Fin , Chou Chau Chang , Chen San Tong
Published: February 2008

Experiments were conducted using a gear-cam adapter to simulate line-contact lubrication and wear in a lubricant with various additive concentrations. In this study, the growth of an adsorption film and a chemical film in oil lubrication can be detected by the electrical contact resistance (ECR) apparatus of a wear testing machine. A constant current source was applied; the electrical voltage is thus obtained if the ECR is available. Roller wear rate and wear loss are formulated in terms of roller-lower specimen contact temperature and several relevant parameters. In addition, wear loss is also related to the rise of electrical voltage during the period of lubrication. The experimental data for wear rate and wear loss can be regressed by the models proposed for various additive concentrations. The roller’s wear rate can be predicted through the investigation of the combined effect of growth in electrical voltage and its commencement. For lowering wear rate, the optimum additive concentration in a lubricating oil is determined under various operating conditions.
Sliding Wear of Copper Against Alumina
Authors: Kailas Satish V. , Biswas S. K.
Published: February 2008

OFHC copper pins with 10 ppm oxygen were slid against alumina at a load of 50 N and sliding speeds of 0.1 ms−1 to 4.0 ms−1. The wear characteristics of copper were related to the strain rate response of copper under uniaxial compression between strain rates of 0.1 s−1 and 100 s−1 and temperatures in the range of 298 K to 673 K. It is seen that copper undergoes flow banding at strain rates of 1 s−1 up to a temperature of 523 K, which is the major instability in the region tested. These flow bands are regions of crack nucleation. The strain rates and temperatures existing in the subsurface of copper slid against alumina are estimated and superimposed on the strain rate response map of copper. The superposition shows that the subsurface of copper slid at low velocities is likely to exhibit flow band instability induced cracking. It is suggested that this is the reason for the observed high wear rate at low velocities. The subsurface deformation with increasing velocity becomes more homogeneous. This reduces the wear rate. At velocities >2 ms−1 there is homogeneous flow and extrusion of thin (10 μm) bands of material out of the trailing edge. This results in the gradual increase of wear rate with increasing velocity above 2.0 ms−1.
Derivation of Modified Reynolds Equation—A Porous Media Model
Authors: Li Wang-Long
Published: February 2008

In this study, a porous media model is developed which can be applied to thin film lubrication problems. The microstructure of bearing surfaces is modeled as porous layers attached to the impermeable substrate. The Brinkman-extended Darcy equations and Stokes’ equations are utilized to model the flow in the porous region and fluid film region, respectively. The stress jump boundary condition at the porous media/fluid film interface and effects of viscous shear are included in deriving the modified Reynolds equation. The present model can correct and modify a previous study based on the Darcy model with slip-fiow effects or another based on the Brinkman-extended Darcy model with stress continuity at the porous media/fluid film interface. In the results, the effects of material properties: viscosity ratio (αi2), thickness of porous layer (Δi), permeability (Ki), stress jump parameter (βi), on the velocity distributions, and performance of one-dimensional converging wedge problems are discussed.
Theoretical Investigation of Fluid Inertia Effects and Stability of Self-Acting Gas Journal Bearings
Authors: Belforte G. , Raparelli T. , Viktorov V.
Published: February 2008

The journal equation of motion and the complete Reynolds equation of compressible fluid film are numerically solved and a computer program is developed. The formulas are for externally pressurized bearings, but results are shown only for self-acting bearings. For certain cases, the validity of the theoretical results is verified by comparison with the experimental data available from the literature. Through intensive use of the program, journal center trajectories are obtained and effects of fluid inertia are investigated. New stability parameters are presented and stability diagrams are established for bearings with L/D = 0.25, 0.5, 1, 1.5, and 2. The rotor unbalance effects on bearing stability limits are illustrated for several cases.
Dynamically Loaded Finite Length Journal Bearings: Analytical Method of Solution
Authors: Hirani H. , Athre K. , Biswas S.
Published: February 2008

A closed-form pressure distribution, using a combination of short- and long-bearing approximations, is proposed for dynamically loaded journal bearings. The angles for start and finish of positive pressure curve are determined employing simple analytical equations. The mobility method, based on the suggested pressure distribution is easy to use, predicts results of acceptable accuracy and the execution time is comparable to that required for the short bearing approximation. This paper also provides a conceptually simple analytical method for evaluating angular location of the instantaneous maximum pressure using proposed closed form pressure distribution. Simple algebraic equations are derived to obtain the instantaneous maximum pressure in dynamically loaded bearings directly, without involving any iteration. To illustrate the validity of present study, a connecting rod big end bearing and two crankshaft main bearings are analyzed. The mobility components, minimum film thickness and maximum pressure are plotted over a load cycle and compared with established analytical and curve fit methods. The results are also compared with those obtained using finite element method.
Dynamic Analysis of the Rarefaction-Modified Reynolds Equation Considering Porosity of Thin Liquid Lubricant Film
Authors: Mitsuya Yasunaga , Deng Zhisheng , Ohka Masahiro
Published: February 2008

A rarefaction-modified Reynolds equation was derived to solve dynamic problems of a thin liquid lubricant film coated on a sliding surface. Applying the perturbation method, a calculation procedure based on FEM was formulated to obtain the stiffnesses and damping coefficients of gas lubricating films over a permeable liquid lubricant. Calculations were performed for a specified flying head slider. First, the effects of the permeability and porosity correction coefficients, which serve to increase the molecular mean free path, were presented focusing on landing on/off characteristics. Next, the effects of those on the stiffnesses and damping coefficients were demonstrated using the frequency domain. The results showed that the permeability and porosity correction coefficient increasingly had an influence on the landing on/off characteristics more in the higher velocity region, and that the permeability was effective in increasing the damping of lubricating films.
Characteristics of Liquid Lubricant Films at the Nano-Scale
Authors: Luo Jianbin , Huang Ping , Wen Shizhu , Li Lawrence K. Y.
Published: February 2008

Characteristics of a liquid lubricant film at the nanometer scale are discussed in the present paper. The variations of the film thickness in a central contact region between a glass disk and a super-polished steel ball with lubricant viscosity, rolling speed, substrate surface tension, running time, load, etc. have been investigated. Experimental results show that the variation of film thickness in the thin film lubrication (TFL) regime is largely different from that in the elastohydrodynamic lubrication (EHL) regime. The critical transition point from EHL to TFL is closely related to lubricant viscosity, surface energy of substrates, and so on. The film in TFL is much thicker than that calculated from the Hamrock-Dowson formula. An unusual behavior of the lubricant film has also been observed when the effect of the running time on the film thickness is considered. The time effect and the formation mechanism of the enhanced film in the running process have been discussed.
Numerical Analysis on Dynamic Characteristics of Cryogenic Hydrostatic Journal Bearing
Authors: Yoshikawa Hiroyuki , Ota Terukazu , Higashino Kazuyuki , Nakai Shunichiro
Published: February 2008

Dynamic characteristics of a two row staggered recess cryogenic hydrostatic journal bearing used in the liquid hydrogen turbopump of rocket engines for space transport systems are numerically analyzed. Effects of the rotational speed and the shaft eccentricity are studied in the analysis. Their effects on the stiffness and damping coefficients and the whirl frequency ratio are clarified. Moreover, effects of the orifice parameter, the distance between two recess rows, and the number of recesses on these dynamic characteristics are investigated.
THD Analysis in Tilting-Pad Journal Bearings Using Multiple Orifice Hybrid Lubrication
Authors: Santos I. F. , Nicoletti R.
Published: February 2008

Tilting pad journal bearings (TPJB) using multiple orifice hybrid lubrication are analyzed applying a thermohydrodynamic (THD) theory. Adiabatic boundary conditions are adopted, and a two-dimensional model is used to represent the fluid flow behavior in the bearing gap. The influence of operational conditions on the temperature distribution and on the bearing load capacity is discussed and compared to theoretical and experimental values for a conventional hydrodynamic case (without radial oil injection). To improve the cooling effects, as well as rotor attitudes, the best location for orifices is the area near the pad edges.
Effect of Pore Ensemble Statistics on Load Support of Mechanical Seals With Pore-Covered Faces
Authors: Burstein Leonid , Ingman Dov
Published: February 2008

A mathematical model was developed for predicting the performance of laser-textured seals with pores. A solution of the two-dimensional steady-state Reynolds equation was given for rectangular and exponential pores, as well as expressions for the hydrodynamic pressure distribution over the control cell and for the cell load support. The difference between the two pore shapes can be reduced from a factor of multiple times to 30 percent at most—if the pore volume is kept constant. It was also shown that the total hydrodynamically induced load-carrying capacity can be obtained with accuracy, even if the pore radius of the seal surface is assumed to vary over a wide interval about its mean value, as it does in reality. Diameters in an ensemble of over 4 · 104 pores were run at random for 500 seal faces. It was established for the first time that load support of an ensemble exceeds by 22 percent the one determined for N identical pores. The model for the entire pore population as an ensemble with size variation is more realistic, and substantiates the possibilities and advisability of pore size diversity, hitherto considered undesirable in the pore production process. In general, the pore ensemble is an essential aspect in exact determination of the load support and better insight into the tribologic behavior of pore-covered surfaces.
A Statistical Model on Drive-Level Stiction
Authors: Tang H. , Gui J.
Published: February 2008

We present a statistical model that correlates the drive-level stiction behavior, which involves multiple head-disk interfaces, to its constituentsrsquo; component-level stiction behavior. The model takes into account all types of component-level stiction events, namely fly stiction as well as normal stiction. The important conclusions from this study are as follows, (i) Drives with a large number of head-disk interfaces are significantly more immune to stiction induced spin failure than one might perceive. (ii) The stiction per interface measured in a drive is always lower than the component-level stiction and decreases with increasing number of head-disk interfaces.
Analysis of Bouncing Vibrations of a 2-DOF Tripad Contact Slider Model With Air Bearing Pads Over a Harmonic Wavy Disk Surface
Authors: Ono Kyosuke , Takahashi Kan
Published: February 2008

In this study, the authors numerically analyzed the bouncing vibrations of a two-degree-of-freedom (2-DOF) model of a tripad contact slider with air bearing pads over a harmonic wavy disk surface. The general features of bouncing vibrations were elucidated in regard to the modal characteristics of a 2-DOF vibration system and design parameters such as contact stiffness, contact damping, air hearing stiffness, the rear to front air bearing stiffness ratio, static contact force and the coefficient of friction. The design of a contact slider was discussed in terms of tracking ability and wear durability. In addition, two sample designs of a perfect contact slider with sufficient wear durability were also presented.
Contact Take-Off Characteristics of Proximity Recording Air Bearing Sliders in Magnetic Hard Disk Drives
Authors: Hu Yong
Published: February 2008

A partial contact air bearing model and Archard’s wear law are used to investigate the air bearing and wear characteristics of proximity recording sliders during a take-off process. The air bearing pitch torque, pitch and contact force are used to characterize the contact take-off process. In addition, the wear factor derived from the Archard’s wear law is employed to measure the take-off performance. The results indicate the existence of two distinct take-off stages: a period of rapidly increasing pitch preceding a relatively steady take-off event. The proper range of taper angle and step height, which produce a rapid initial pitch increase and steady subsequent take-off as well as less wear in the head/disk interface, are determined through simulation. While the simulation results demonstrate the negligible effect of crown height on the rate of the initial pitch increase, larger crown values are shown to yield higher pitch and smaller wear in the head/disk interface during the take-off process. In summary, the partial contact air bearing simulation and the wear factor calculation of the take-off process, developed in this study, offers a fast and accurate analytical tool to optimize ABS design for the fast take-off performance.
Design and Analysis of Slider’s Landing Pads for Fast Take-Off Performance in Magnetic Hard Disk Drives
Authors: Hu Yong
Published: February 2008

Exponential growth in both capacity and performance has been exhausting a lot of existing technologies in magnetic hard disk drive industry, one of them being laser zone texturing. Maintaining such a rapid growth requires innovative technologies. Adding landing pads to a slider’s air hearing surface (ABS) appears to be able to further stretch the glide/stiction envelope into the ultra-low glide and stiction regime. To materialize this new technology, the pad wear needs to be minimized, underlining the importance of the fast take-off air bearing characteristics. This paper analyzes the slider’s landing pad designs for fast take-off performance through the partial contact air bearing simulation of a take-off process. Two landing pad designs (3-pad and full texture) are created on a suhambient pressure ABS. The contact force and its center profiles as well as the evolution of the contact pressure contour are used to characterize the movement of the contact location during the take-off process. The effects of the absolute and relative pad heights as well as the rear pad location on both the transition of the contact location and the rate of contact force decrease are calculated. While raising leading pads delays the transition of the contact location from the leading pads to rear pad, distancing the rear pad from the trailing edge greatly facilitates the movement of the contact location from the rear pad to the trailing edge. A fully textured ABS with a reasonably low and uniform pad height as well as rear pads being well distanced from the trailing edge offers a fast take-off performance.
Thermal Response of a Magneto-Resistive Head When it Flies Over an Asperity
Authors: Zhang Shuyu , Bogy David B.
Published: February 2008

A two-dimensional model is developed for the heat transfer in a magneto-resistive (MR) head-air bearing system. Using this model, the MR head temperature response is studied for various cases. It is found that the temperature in the head depends on the current through it and the change is only significant within a small area around the MR transducer at the trailing edge. With a typical current value (say 13 mA), the MR head temperature is about 25°C higher than the ambient temperature. When the slider flies over an asperity without contact, the MR temperature fluctuation follows that of the air bearing spacing, which is caused by the cooling effect of the air bearing.
Nonvibrating Contact Potential Difference Probe Measurement of a Nanometer-Scale Lubricant on a Hard Disk
Authors: Yano D. , Korach C. , Streator J. , Danyluk S.
Published: February 2008

This paper reports on a feasibility study in the detection of nanometer thick lubricated regions on a hard disk by a novel use of a Kelvin probe. A nonvibrating Kelvin probe was constructed and used to measure the voltages between the copper surface of the probe and a hard disk partially-lubricated with a perfluoropolyether. The probe, constructed of a shielded 1.6 mm diameter gold-coated copper wire, was fixed above the hard disk and the probe voltage was obtained as a function of the speed of the disk and lubricant thickness. The probe generates an electrical signal as the interface between the lubricated and unlubricated regions is crossed. Results show that the probe can distinguish between regions on the hard disk that contain 3 and 10 nm thick lubricant films.
Free Vibration Analysis of PZT Glide Heads
Authors: Tsay Alex Y. , Ouyang Jin-Hui , Ku C.-P. Roger , Shen I. Y. , Kuo David
Published: February 2008

This paper studies natural frequencies and mode shapes of a glide head with a piezoelectric transducer (PZT) through calibrated experiments and a finite element analysis. In the experiments, the PZT transducer served as an actuator exciting the glide head from 100 kHz to 1.3 MHz, and a laser Doppler vibrometer (LDV) measured displacement of the glide head at the inner or outer rail. The natural frequencies were measured through PZT impedance and frequency response functions from PZT to LDV. In the finite element analysis, the glide head was meshed by brick elements. The finite element results show that there are two types of vibration modes: slider modes and PZT modes. Only the slider modes are important to glide head applications. Moreover, natural frequencies predicted from the finite element analysis agree well with the experimental results within 5% of error. Finally, the finite element analysis identifies four critical slider dimensions whose tolerance will significantly vary the natural frequencies: PZT bonding length, wing thickness, slider thickness, and air bearing recess depth.
Dynamics for Micromachined Mother Ship Negative Pressure Slider Bearings With an Integrated Microsuspension Mechanism in Proximity Magnetic Recording
Authors: Tagawa Norio , Mori Atsunobu , Kajitani Hiroshi , Hashimoto Masanobu
Published: February 2008

This paper describes head/disk interface dynamics for micromachined mother ship negative pressure slider bearings with an integrated microsuspension mechanism that we proposed, at steady-state flying in proximity magnetic recording. The authors first indicated the analytical model for air bearing dynamics of mother ship slider mechanisms, and the advantages of the mechanisms were discussed from the dynamics points of view, compared with conventional flying head slider mechanisms. Dynamic design considerations and optimization for micromachined mother ship negative pressure slider bearings with an integrated microsuspension mechanism were also investigated. Finite element simulation for the stiffness analysis of a microsuspension mechanism was carried out and the design optimization for low stiffness gimbals was studied. Furthermore, the effects of slider mass ratio and slider car film stiffness ratio of a secondary slider to a primary slider on mother shipslider dynamics were analyzed numerically. Considering those numerical simulationresults, system optimization for sliders as well as microsuspension gimbals was established to achieve head/disk interface reliability in high density proximity magnetic recording.
Evaluation of Perfluorinated Polyalkylether Grease Rheology on Disk Drive Bearing Performance
Authors: Prater Walter , Burns John , Stone Garvin , Ting Tom
Published: February 2008

A matrix of specially formulated greases composed of perfluorinated polyalkylether (PFPE) oil and telomers of polytetrafluoroethylene (PTFE) particulate thickener were tested. The PFPE greases were chosen for this evaluation because their oils have a very low vapor pressure and they will not volatilize in the disk drive. Base oil viscosity, PTFE particle size and percentage of oil content were varied. The rheological properties of complex viscosity, storage and loss moduli, and loss factor were measured. Percent oil was determined using thermal gravimetric analysis. The thickener’s PTFE particle sizes were measured and their shapes were imaged using scanning electron microscopy. Bearing low speed torque and bearing noise tests were performed to evaluate the effect of the grease on bearing performance. The head settle track misregistration (TMR) was measured on disk drives to measure the effect of bearing lubrication on the servo performance. Generally, greases with high base oil viscosity had the lowest complex viscosity. Greases with highest viscosity PFPE oils had the highest torque and lowest noise. Greases with large PTFE particles had high loss factors and exhibited high torque and noise levels. High PTFE thickener to PFPE oil ratio (thicker grease) causes the bearings to have fluctuations in torque and noise levels. Actuator bearings lubricated with greases having higher viscosity oil had lower head settle TMR.
Elastic Contact and Friction Between Sliders and Circumferentially Textured Disks—Part II: Meniscus Force
Authors: Tanaka K.
Published: February 2008

This series of three papers presents an experimental and numerical analysis of friction in a thin-film rigid disk with a circumferential surface texture, under various humidities. In Part II, we develop a theoretical formulation of the meniscus force of elliptical contact at isolated liquid bridges. This model predicts that the mean real pressure due to the meniscus force apparently decreases the net real contact pressure pr and increases the frictional coefficient. This effect becomes significant when the relative surface energy of the liquid 2γ/σ is comparable to pr, where σ is the standard deviation of asperity height distribution. When the disk is covered with lubricant and the liquid bridges are connected with each other, the solid noncontacting asperities play an important role in the formation of the meniscus force, and the relative lubricant thickness t/σ is the critical factor determining the friction.
Particle Trajectories Around a Flying Slider
Authors: Lin S. C. , Kuo T. C. , Chieng C. C.
Published: February 2008

The Eulerian-Lagrangian approach is employed to simulate droplet trajectories due to the large-velocity gradient between two solid surfaces: a stationery block (slider) and a rotating plane (disk). Sudden expansion after the extremely small spacing will trap the particles in the open spaces. The fluid phase flowfield is obtained by solving Navier-Stokes equations with slip boundary correction in the Eulerian approach, and the droplet trajectories are calculated by integrating equations of motion with slip correction in the Lagrangian approach. Because of the extremely small spacing and the droplet size, Brownian motion effectively increases the probability of slider-head collisions, especially for extremely small particles. This study demonstrates that the effect due to particle size is the dominant factor in determining the probability of particle-slider collision, especially for particle sizes comparable with the air mean free path and the flowfield immediately adjacent to the solid surfaces. The results also show that lowering the flying height of the slider and increasing the disk velocity attracts the particles toward the gap between the disk and the slider.
An Elliptic Elastic-Plastic Asperity Microcontact Model for Rough Surfaces
Authors: Horng Jeng Haur
Published: February 2008

An elastic-plastic microcontact model, that takes into account the directional nature of surface roughness, is proposed for elliptic contact spots between anisotropic rough surfaces. In addition, the plasticity index was modified to suit more general geometric contact shapes. This contact model, which expands the usefulness of the CEB model, is also utilized to determine the effect of effective radius ratio (γ) on microcontact behavior and to compare the results of this model and other models under different surface topographies. The results show that the elliptic contact model and circular contact model deviate considerably in regard to the separation (h), total real contact area (At), plastic area (Ap) and plasticity index (Ψ). The present model can be simplified to become other stochastic models.
Sliding Tractions on a Deformable Porous Layer
Authors: Ateshian Gerard A. , Wang Xiaodong
Published: February 2008

The problem of sliding surface tractions on a porous biphasic layer with viscous interstitial fluid is solved, which can serve as the basis for solving problems of elastohydrodynamic lubrication of deformable porous layers bonded to a rigid substrate. A general small strain solution is derived for a layer of arbitrary thickness, using Fourier transform methods. The applied tractions, consisting of two normal components and two shear components, have arbitrary distributions and are assumed to slide at a constant speed along the layer surface. It is found that the solution to this problem is dependent on five nondimensional parameters; one of these, Rh, is the ratio of the sliding speed to the characteristic speed of fluid flow within the porous layer; another, τf, controls the transition between Darcy-like and Navier-Stokes flow. Results are presented for various values of these parameters, particularly in relation to the flux of fluid relative to the solid phase along the tangential and normal directions to the layer surface. Discussion of these results and their potential effect on the analysis of elastohydrodynamic lubrication of deformable porous bearings is provided.
Frictional Response of Sliding Interfaces Subjected to Time Varying Normal Pressures
Authors: Prakash Vikas
Published: February 2008

In the present investigation a plate-impact pressure shear loading device is employed to study frictional characteristics of sliding interfaces subjected to step changes in normal pressure. The present experimental configuration represents a significant improvement over the conventional tribology experiments by allowing the control of interfacial tractions through the use of pressure-shear loading waves instead of manipulating actuator motion. Moreover, the experimental configuration allows critical frictional parameters such as the applied normal pressure, the interfacial slip resistance, and the interfacial slip velocity to be interpreted by using the framework of one-dimensional plane wave analysis. The experimental results, deduced from the response to step changes imposed on the normal pressure at the frictional interface, reinforce the importance of including frictional memory in the development of the rate-dependent state variable friction models. The scope of the above experiments include technologically important combinations of workpiece materials such as 4340VAR structural steel and a commercially available titanium alloy (Ti-6Al-4V), and tool materials such as tungsten based tool cermets (WC-Co alloys).
Analysis of Mechanical Seal Behavior During Transient Operation
Authors: Harp S. R. , Salant R. F.
Published: February 2008

A mathematical model that predicts the transient behavior of gas or liquid lubricated hydrostatic mechanical seals has been developed. The analysis includes an evaluation of the fluid, contact, and deformation mechanics of a mechanical seal subject to constant or varying rotational speed and sealed pressure. Squeeze film effects are included. For gas seals, slip at the walls is also taken into account. Results include predictions of film thickness distributions, contact forces, leakage rates, pressure distributions, heat generation rates, thermal deformation, and mechanical deformation.
A Mixed-TEHD Model for Journal-Bearing Conformal Contacts—Part I: Model Formulation and Approximation of Heat Transfer Considering Asperity Contact
Authors: Shi Fanghui , Wang Qian (Jane)
Published: February 2008

A mixed-TEHD (thermal elastohydrodynamic) model was developed for journal bearings working at large eccentricity ratios in order to facilitate a better understanding of mixed-lubrication phenomena for conformal-contact elements. The model consists of a mixed-lubrication process that considers the roughness effect and asperity contact, a thermal process for temperature analyses, and a thermal-elastic process for deformation calculations. In this model, the interactive journal, lubricant, and bearing were treated as an integrated system. Finite-element, finite-difference, and influence-function methods were utilized in the numerical process. The overall solution was achieved by the iteration method. Analyses of a simulated bearing-lubricant-journal system working under mixed-lubrication conditions were conducted, and the influence of the changes of lubricant flows as a result of the asperity contact on the system heat transfer and temperature distributions was numerically investigated.
A Mixed-TEHD Model for Journal-Bearing Conformal Contact—Part II: Contact, Film Thickness, and Performance Analyses
Authors: Wang Qian (Jane) , Shi Fanghui , Lee Si C.
Published: February 2008

Investigation of the mixed lubrication of journal-bearing conformal contacts is very important for failure prevention and design improvement. This paper studies the asperity contact in heavily loaded journal bearings with Lee and Ren’s asperity contact theory in a newly developed mixed-TEHD (Thermal Elasto-Hydro-Dynamic) model and analyzes the performance of simulated journal bearings under high eccentricity ratios. The effects of operating conditions, bearing structures, and thermal conditions on the contact severity were numerically investigated. The results indicate that the asperity contact pressure and the performance of journal bearings in the mixed lubrication are strongly affected by the geometric design and the thermal-elastic deformations. The heat transfer of the bearing-lubricant-journal system was also shown to play a role.
Analysis of Two-Phase Flow in Cryogenic Damper Seals—Part I: Theoretical Model
Authors: Arauz Grigory L. , San Andre´s Luis
Published: February 2008

Cryogenic fluid damper seals operating close to the liquid-vapor region (near the critical point or slightly sub-cooled) are likely to develop a two-phase flow region which affects the seal performance and reliability. An all-liquid, liquid-vapor, and all-vapor, i.e., a “continuous vaporization” bulk flow model is presented for prediction of the seal dynamic forced response. Continuity, momentum, and energy (enthalpy) transport equations govern the two-phase flow of a homogeneous saturated mixture in thermodynamic equilibrium. Static and dynamic force performance characteristics for the seal are obtained from a perturbation analysis of the governing equations. Theoretical predictions and comparisons to experimental measurements in a liquid and gaseous nitrogen seal are presented in Part II. The effects of two-phase flow regimes on the dynamic force coefficients and stability of an oxygen damper seal are also discussed.
Analysis of Two-Phase Flow in Cryogenic Damper Seals—Part II: Model Validation and Predictions
Authors: Arauz Grigory L. , San Andre´s Luis
Published: February 2008

Cryogenic fluid damper seals operating close to the liquid-vapor region (near the critical point or slightly sub-cooled) are likely to develop a two-phase flow region which affects the seal performance and reliability. An all-liquid, liquid-vapor, and all-vapor, i.e., a “continuous vaporization” bulk flow model for prediction of the seal dynamic forced response is given in Part I. The numerical method of solution of the flow equations is detailed here. Computed predictions for static seal characteristics, leakage and axial pressure drop, correlate well with existing measurements for a gaseous nitrogen seal and a liquid nitrogen seal with two-phase at the seal exit plane. The effects of two-phase flow regimes on the dynamic force coefficients and stability of an oxygen damper seal are discussed. Fluid compressibility effects, particularly for mixtures with low mass content of vapor, are of utmost importance. Under these conditions, an increase on seal direct stiffness and reduction of whirl frequency ratio are shown to occur.
Evaluation Technique of Head/Tape Contact Using Acoustic Emission
Authors: Matsuoka Kaoru , Taniguchi Koji , Ueno Yoshihiro
Published: February 2008

A new on-line methodology has been developed for both evaluation and analysis of head/tape interface phenomena. It uses the direct relationships between the power in the acoustic emission (AE) signal and wear, and between the power in the AE signal and the normal force acting on the magnetic head. The AE transducer is directly mounted onto the head assembly of a VCR mechanism in order to measure the head/tape contact behavior. This technique has been used to: (a) monitor the effect of relative humidity on head wear; (b) investigate the wear characteristics of Mn-Zn ferrite as a function of crystallographic orientation without direct measurement of the wear volume; and (c) evaluate tape abrasiveness. Explicit correlations were also obtained for the normal force acting on the magnetic head, the tape wrap angle around the head, and the reproduced signal flatness in terms of the tape transverse stress distribution. Moreover, the normal force as a function of the tape stress distribution is closely related to the longitudinal tape vibration at the head exit region.
Partial Contact Air Bearing Characteristics of Tripad Sliders for Proximity Recording
Authors: Hu Yong , Jones P. M. , Chang P. T. , Bogy David B.
Published: February 2008

Proximity recording introduces some new head/disk interface characteristics as compared to the conventional noncontact recording. The different design philosophy has led to several distinct partial contact tripad air bearing designs, including the shaped rail negative pressure and straight rail positive pressure tripad sliders. The impact of these new characteristics and design differences on the head/disk reliability needs to be thoroughly understood in order to ensure a successful proximity recording. This paper investigates the partial contact air bearing characteristics of three representative tripad slider designs. The contact stiffness is used as a measure of the air bearing compliance. Simulations of the fly height, contact force, altitude sensitivity, substrate waviness induced spacing and contact force modulations, contact take-off, track seeking and crash stop dynamics are performed for the three tripad slider designs. The results demonstrate that the negative pressure tripad sliders can be designed such that they can achieve both flat fly height and contact force profiles and, fast take-off, while still maintaining a small contact stiffness. However, the air bearing compliance and waviness following performance have to be compromised for the correct partial contact air bearing pitch stiffness.
Effect of Slider Burnish on Disk Damage During Dynamic Load/Unload
Authors: Suk M. , Gillis D.
Published: February 2008

Two of the most difficult issues to resolve in current design of head/disk interface in magnetic recording devices are stiction and durability problems. One method of overcoming these problems is by implementing a technology known as load/unload, where the system is designed so that the slider never touches the disk surface. One potential problem with this type of system is slider/disk contact induced disk defects. The objective of this paper is to show that the likelihood of disk scratches caused by head/disk contacts during the load/unload process can be significantly decreased by rounding the edges of the air-bearing surface. Using the resistance method, we observe that head/disk contacts burnish the corners of the slider and thereby decrease exponentially with load/unload cycles. A well burnished slider rarely causes any disk damage thus resulting in an interface with significantly higher reliability. A simple Hertzian contact stress analysis indicates that the contact stress at the head/disk interface can be greatly decreased by increasing the radius of curvature of the air-bearing surface edges.
Wear Resistance of Super Alloys at Elevated Temperatures
Authors: Lawen J. L. , Calabrese S. J. , Dinc O. S.
Published: February 2008

This paper provides the results of an extensive sliding wear testing program to evaluate wear resistance of several material couples currently used for high temperature applications such as ground based gas turbines and aircraft engines. Nickel and cobalt base superalloys and iron base stainless steels were tested in different combinations, and their wear rates compared to determine optimal wear resistance. The results show that an alloy’s wear resistance is highly dependent on operating temperature and its coupling with another material. The influences of friction, hardness, and oxide formation on the alloy’s wear resistance are also presented and discussed.
Three-Dimensional Molecular Dynamics Analysis of Atomic-Scale Indentation
Authors: Yan W. , Komvopoulos K.
Published: February 2008

The complete atomic-scale indentation cycle is analyzed using molecular dynamics simulations. A hysteresis is observed in the instantaneous normal force versus surface separation distance curve obtained with an atom or a rigid tip indenting and, subsequently, retracting from a dynamic face-centered-cubic substrate consisting of argon or copper. The generation of irreversible deformation in a Lennard-Jones solid is revealed in light of simulation results for indentation by a single atom. The direction of irreversible deformation is shown to coincide with that of macroscopic plastic flow. The compressive yield strength decreases with increasing substrate temperature and decreasing indentation speed. The phenomena of tip wetting by substrate atoms and connective neck formation, elongation, and rupture at the tip/substrate interface are elucidated by simulation results for the unloading process. It is shown that energy dissipation decreases as the substrate temperature increases and the energy consumed by irreversible deformation is always greater than that due to heating.
Effect of Visco-Elastic Property on Friction Characteristics of Paper-Based Friction Materials for Oil Immersed Clutches
Authors: Milayzaki Tomoyuki , Matsumoto Takayuki , Yamamoto Takashi
Published: February 2008

The friction characteristic of paper-based friction materials is one of the most important factors that influence the shifting performance of oil immersed clutches in automobile automatic transmissions. Visco-elasticity and porosity of the material are considered to be important properties that may control the friction characteristics of the material. In this study, the relationship between the friction characteristics and the visco-elasticity of a paper-based friction material is discussed. In order to vary the visco-elasticity while retaining the ingredients almost constant in a paper-based friction material, the formulation of the sample materials required changing the compression rate during the clutch plate bonding process and changing the volume percentage of resin. The properties of the sample materials such as porosity (pore diameter, pore diameter distribution, porosity percentage), and visco-elastic deformation in the compressive and the shearing directions, etc. were measured. In order to clarify the relationship between the friction and visco-elasticity of friction material, friction characteristics were measured. Friction characteristics of the sample materials were evaluated by a breaking-away test and continuous slip tests with a newly designed friction testing machine. From the experimental results, which showed that the lower the longitudinal modulus of the friction material, the higher the friction coefficient, it was found that friction characteristics of oil immersed paper-based friction materials are influenced by the visco-elasticity.
A Framework for Thermohydrodynamic Lubrication Analysis
Authors: Wilson William R. D.
Published: February 2008

Thermohydrodynamic lubrication is complicated by the multiplicity of heat transfer paths from the site of dissipation to the surroundings. This has impeded a general understanding of thermohydrodynamic phenomena. The method of lumped variables is applied to a simple slider bearing (as an example) to explore thermohydrodynamic lubrication. This approach leads to a better understanding of the interplay between the different modes of heat transfer and the influence of the associated temperature rises on performance, and how this can be captured by the use of appropriate non-dimensional measures. Such measures also allow the mapping of the problem into a set of regimes characterized by the relative importance of different heat transfer modes.