bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Fixed Rotor Tilt on the Rotordynamic Coefficients of Incompressible Flow Annular Seals
Authors: Scharrer J. K. , Rubin N. , Nelson C. C.
Published: June 2008

The basic equations are derived for incompressible flow in an annular seal with large rotor tilt. The flow is assumed to be completely turbulent in the axial and circumferential directions with no separation, and is modeled by Moody’s friction factor equation. Linearized zeroth and first-order perturbation equations are developed for small motion about an arbitrary position by an expansion in the eccentricity ratio. The zeroth-order continuity and momentum equations are solved using a Fast Fourier technique, yielding the axial and circumferential velocity components and the pressure distribution. The first-order equations are integrated to satisfy the boundary conditions and yield the perturbation pressure distribution. This resultant pressure distribution is integrated along and around the seal to yield the force developed by the seal and the corresponding dynamic coefficients. Results of a parametric study show that the detrimental effects of a tilted rotor are small.
Finite Element Analysis of Grooved Gas Thrust Bearings and Grooved Gas Face Seals
Authors: Bonneau D. , Huitric J. , Tournerie B.
Published: June 2008

A finite element method enabling the Reynolds equation solution for any face geometry of gas thrust bearing or of gas seal is presented. Difficulties due to thickness discontinuities are reduced by integration by parts of the terms involving derivatives. The weak form of the finite element Reynolds equation is then solved and the nonlinearity of the equation leads to the use of Newton-Raphson procedure. The process is fast convergent. The problem of oscillating solution is solved by the use of an upwind procedure. Some numerical examples show the accuracy and efficiency of the procedures. It is shown that the developed finite element program provides a numerical tool, more efficient than the method used until now, for the grooved gas seals design.
The Effect of Journal Misalignment on the Operation of a Turbulent Flow Hydrostatic Bearing
Authors: San Andres Luis
Published: June 2008

An analysis for calculation of the dynamic force and moment response in turbulent flow, orifice compensated hydrostatic journal bearings is presented. The fully developed flow of a barotropic liquid is described by variable properties, bulk-flow equations and local turbulent friction factors based on bearing surface condition. Bearing load and moments and, dynamic force and moment coefficients are calculated for perturbations in journal center displacements and misaligned journal axis rotations. Numerical results for the effect of static misalignment angles in the plane of the eccentricity vector are presented for a water lubricated hydrostatic bearing. The predictions show that journal axis misalignment causes a reduction in load capacity due to loss in film thickness, increases the flow rate and produces significant restoring moments (couples). Force and moment coefficients due to dynamic journal axis rotations are also discussed.
Numerical Simulation of Dynamic Loading in Hard Disk Drives
Authors: Jeong T. G. , Bogy D. B.
Published: June 2008

The dynamic loading process in hard disk drives is simulated numerically. The effects of the slider’s loading velocity and initial pitch and roll on its dynamics during loading, as well as on slider-disk contacts, are studied by using the dynamic loading simulator. The air bearing forces due to the squeezing and shearing flows are calculated and their contributions to the dynamics of the slider during loading are investigated. Slider-disk contacts are considered in the numerical simulation through generalized impulse-momentum equations. Slider-disk contact criteria are obtained from the numerical simulation, and they are compared with those obtained from a previous experimental parameter study.
Precision in Mechanical Testing of Magnetic Recording Thin-Film Disks
Authors: Bowen A. J.
Published: June 2008

A sensitive mechanical test for magnetic recording thin film disks is described. A model that explains the increased sensitivity is correlated to different heads and test methods. A major improvement in test precision is possible due to the reuse of test heads when water vapor is used to highlight the slightest wear to the disk.
Pole Tip Recession Measurements on Thin Film Heads Using Optical Profilometry With Phase Correction and Atomic Force Microscopy
Authors: Smallen Martin , Lee Jerry J. K.
Published: June 2008

Pole tip recession in magnetic recording thin film heads contributes to spacing loss, which leads to a degradation in the readback signal. As manufacturers improve the performance of magnetic recording devices, this recession will become more significant to the performance of future products. Pole tip recession can be measured by several techniques, including stylus profilometry, optical profilometry, and atomic force microscopy. Stylus profilometry is generally not used since it has several problems in this application. In this study, good correlation was found between optical profilometry and atomic force microscopy measurements, provided that the optical measurements were corrected for phase shift. This is necessary because of the dissimilar materials in the thin film head. There are several methods for making this correction. One method is an analytical correction using known optical constants for the head materials. These constants should be well characterized as the measurements are quite sensitive to them. Overcoating the head with a thin film provides two other methods for getting around the material differences problem. However, these methods require an optimum film thickness. The film must be thick enough so that it behaves as a substrate, but not so thick that it fails to replicate the head. PACS numbers: 85.70.Kh, 06.90. + v, 42.72. + h, 78.65.Pi
Correlation Between Contact Start/Stop and Constant Speed Drag Testing in Magnetic Head-Disk Tribology
Authors: Ganapathi S. K. , Talke F. E.
Published: June 2008

A model to establish the correlation between wear in constant speed drag testing and contact start/stop testing is developed. The model is based on the Archard wear equation and uses the quasi-steady Kita-Kogure-Mitsuya model for the transition of a slider from sliding to flying to calculate the velocity dependent contact force between the slider and disk during start/stop. Experimental results for the wear of a zirconia overcoated disk are obtained for both start/stop and constant speed drag testing as a function of the number of repeated cycles using optical profilometry. The correlation between predictions and experimental data shows good agreement for up to at least 10,000 cycles of sliding.
Tribology of Ion Bombarded Silicon for Micromechanical Applications
Authors: Gupta B. K. , Chevallier Jacques , Bhushan Bharat
Published: June 2008

Silicon is used in the fabrication of microelectromechanical systems (MEMS). The friction and wear characteristics are of major design concern for any mechanical device requiring relative motion. In the present investigations we have studied the influence of ion bombardment on the microstructure, crystallinity, composition, microhardness, friction, and wear behavior. The ion bombardment modifies the elastic/plastic deformation characteristics and crack nucleation that occurs during the indentation. C+ bombarded monocrystalline and polycrystalline Si exhibit very low coefficient of friction (0.025–0.05) and wear factors (10−7 mm3/N m) while slid against 52100 steel and alumina in dry and moist air and dry nitrogen atmospheres. Ion bombardment resulted in the formation of an amorphized layer that consists of SiC, C, and Si. We have shown that the improvements in friction and wear are because of the formation of SiC and not because of amorphization alone.
Tribological Characteristics of Liquid Lubricant on Magnetic Disks Treated by Far-UV Radiation
Authors: Tian Hong , Matsudaira Takeo
Published: June 2008

In this paper, we have shown that a perfluoropolyether lubricant after far-UV irradiation treatment proposed by Saperstein and Lin (1990) was strongly bonded to disk surfaces without depletion from disks rotating at 6000 rpm in a 50°C temperature environment. Nonbonded lubricant (mobile lubricant) on disk surfaces or on the top of the UV-fixed lubricant was easily depleted from rotating disks. Depletion data of the mobile lubricant agreed well with predictions of an inter-slip model. It has been demonstrated experimentally that the mobile lubricant on disk surfaces was simply displaced from the contact or the sliding regions. After a long period of head contact, the lubricant was built up at the head/disk interface due to migration of the mobile lubricant around the contact regions. By contrast, no such build-up was observed for disks with the UV-fixed lubricant. Consequently, long-term stiction was observed for disks with only mobile lubricant, while no stiction was observed for disks with the UV-fixed lubricant. The UV-treated disks also adsorbed less water at high relative humidities compared with the nontreated disks.
The Effect of Small Normal Loads on the Static Friction Coefficient for Very Smooth Surfaces
Authors: Etsion I. , Amit M.
Published: June 2008

The effect of normal loading on the static friction coefficient between smooth metallic surfaces is experimentally investigated. Normal loads in the range of 10−3N to 0.3N were applied to small diameter samples made of three different aluminum alloys and contacting a nickel coated surface. The tests were done under controlled humidity and clean air conditions. A dramatic increase in the static friction coefficient was observed as the normal load was reduced to its lower level. This behavior is attributed to the role played by adhesion forces which are more pronounced at small normal loads and smooth surfaces and is in agreement with recent theoretical analyses.
The Contact Between Rough Surfaces With Longitudinal Texture—Part I: Average Contact Pressure and Real Contact Area
Authors: Aramaki Hirotoshi , Cheng Herbert S. , Chung Yip-Wah
Published: June 2008

This paper describes a model to study the contact between two purely longitudinally rough surfaces based on the parabolic indentor problem in elasticity. Rough surfaces are characterized with three parameters: rms roughness, autocorrelation length, and bearing area. Problems encountered by conventional roughness models are treated here. It is shown that the average contact pressure and real contact area obtained from this model agree very well with a computationally more intensive model developed by Lee (1989), up to the bulk yielding pressure.
The Contact Between Rough Surfaces With Longitudinal Texture—Part II: Flash Temperature
Authors: Aramaki Hirotoshi , Cheng Herbert S. , Chung Yip-Wah
Published: June 2008

This paper deals with the distribution of asperity temperatures in the nominal contact area for purely longitudinal rough surfaces. It was found that the size of the largest asperity is proportional to the bearing length, from which we deduced a logarithmic relationship between the cumulative number of asperities and the asperity size. Combining these results with the roughness model developed in Part I of this series, we calculated the distribution of asperity temperatures and the effect of asperity interactions. These results are in reasonably good agreement with another model based on direct numerical analysis. The major advantage of our model is its faster speed in obtaining these results.
Prediction of Failure Transitions in Sliding Contacts by a Thermomechanical Wear Model
Authors: Yang Jinseung , Cowan Richard S. , Winer Ward O.
Published: June 2008

A wear equation in general form is offered by which the transition between mild wear and severe wear is identified. This wear criteria equation is governed by three nondimensional parameters: Fo, CT, and Gt, which are measures of time, material property dependence on temperature, and thermal stress intensity, respectively. From this equation, wear maps are constructed. Along with results from Hertzian contact theory, the wear criteria equation and wear map can be used for design guidance. As an example, AISI 52100 steel is examined by comparing calculated data, based on a thermomechanical wear model, with experimental results of sliding contacts. The critical temperatures at which thermomechanical wear can occur are also calculated.
On the Pressure Rippling and Roughness Deformation in Elastohydrodynamic Lubrication of Rough Surfaces
Authors: Chang L. , Webster M. N. , Jackson A.
Published: June 2008

The objective of this paper is to conduct a qualitative analysis on the effects of lubricant shear thinning, lubricant shear heating and the roughness-induced transients on the pressure rippling and roughness deformation that occurs under elastohydrodynamic lubrication (EHL) conditions. To facilitate the analysis, the numerical solutions to an example problem of EHL line contact between a perfectly smooth surface and a sinusoidal rough surface are presented. This micro-EHL problem is first solved using the conventional model of a Newtonian lubricant and a stationary rough surface under isothermal conditions. It is then solved by including the non-Newtonian effects, the roughness-induced transients and the thermal effects in sequence, so that the changes in the results brought about by each of these elements can be clearly observed and then analyzed. The analysis, which is not limited to the model problem solved in this paper, suggests that misleading results of large pressure rippling and flattened surface roughness are obtained using the Newtonian lubricant models under steady-state, isothermal conditions. Much less micro-deformation of the surface roughness is actually produced because the magnitude of the pressure ripples is greatly limited by either the lubricant non-Newtonian shear thinning and shear heating or the roughness-induced transients.
The Normal Approach and Stick-Slip Phenomena at the Interface of Two Rough Bodies
Authors: Lance B. J. , Sadeghi F.
Published: June 2008

A solution for the dry rolling/sliding contact of rough bodies under an applied normal load has been obtained. Both the deflection of the asperities and the bulk material are considered. The conservation of volume approach was used to model elastic-plastic deformation of the asperities. The bulk material was allowed to deform elastically. The stick-slip phenomen of the rolling contact has also been investigated, including asperity deformation and wear as a function of time. The contact width between the two rough cylinders is shown to be approximately 20 percent larger than the width predicted for smooth surfaces by the Hertz equations for the same loading conditions. Similarly, the maximum surface pressure on the bulk material decreases approximately 25 percent when rough surfaces are considered.
Spalling Life Model With Relaxed Distribution Constraints, for Rough Hertz Line Contacts
Authors: Tallian T. E.
Published: June 2008

A Hertz contact spalling fatigue life model is constructed without the constraints of a two-parameter Weibull life distribution. The model is based on the time of crack propagation following a simple Paris law, through the Hertzian alternating shear stress field, from populations of surface defects with depth (severity) distributed according to the Greenwood-Williamson asperity model, to the depth of the maximum alternating shear stress. The life distribution shows moderate deviations from the Weibull form, with the dispersion strongly dependent on the contact parameters. The 90 percent survival quantile is obtained as a function of: Hertz pressure, EHD film ratio, asperity traction coefficient, asperity height, slope and spectrum width, fatigue limit stress and stress concentration factor. This model provides insights into the interrelationship of life with its parameters, not available from models adhering to the power law constraints required to produce a Weibull life distribution. No unbridgeable contradictions emerge between the present formulation and published engineering models.
A Fast Model for Pressure Profile in Rough EHL Line Contacts
Authors: Ai Xiaolan , Cheng Herbert S.
Published: June 2008

A fast calculation model for the pressure distribution in EHL line contacts between rough surfaces is presented. Comparison between the results obtained from the model calculation and numerical simulation shows that, under heavily loaded conditions, the present model gives very accurate predictions of the pressure distribution for both deterministic and random transverse surface roughness. Since the model is based on the superposition of pressure fluctuations, the applications of this model are restricted to heavily loaded contacts.
Influence of Contact Temperature on Contact Fatigue Failure Forms: Part 1—Contact Temperature Analysis of Rolling-Sliding Contact Specimen
Authors: Chen Long-Qing
Published: June 2008

Under rolling-sliding contact, specimens have different failure forms, such as pitting and spalling etc. The surface roughness of specimen in contact has a strong influence on the failure form. The elevated contact temperature produced by a rougher surface is one of the key factors in producing changes in failure form. According to the results of the test and the analysis, the following viewpoint is suggested to explain the influence of the roughness on failure forms: the rougher contact surface produces elevated contact temperature; the elevated contact temperature causes the material yield strength over local areas to reduce transiently thus resulting in a plastic deformation layer, and have the change of failure form. The present study includes two parts: in the first part, the analysis of contact temperature distribution is carried out; in the second part, the results of the test and analysis are discussed.
Influence of Contact Temperature on Contact Fatigue Failure Forms: Part 2—The Test and Analysis
Authors: Chen Long-Qing
Published: June 2008

The surface roughness of contacting parts have a strong influence on the failure form of contact fatigue. Pitting failure is liable to occur on the contact parts with rougher surface. The present test shows that a plastic deformation layer (PDL) will generally occur beneath the race surface of the parts which fail in pitting; and the near-surface cracks will initiate in the plastic deformation layer, these cracks grow gradually and finally result in fatigue failure where the depth of the fatigue pit are 0.1–0.2 mm. According to the author’s analysis of contact temperature and contact stresses, the present paper suggests: when the race surface of rolling specimen is rough, the contact temperature rise reduces the transient yield strength of the metal below the maximum contact shear stress at this position, thereby, resulting in a plastic deformation layer.
Kinematics of an Elastic Sphere Rolling on a Plane and Between Two Planes
Authors: Kingsbury E.
Published: June 2008

A sphere rolling between a stationary and a spinning plane traces out a spiral path, even under quasistatic conditions. Published theory suggests that radial creep due to pivot produces the spiral path. We show experimentally a component of the sphere’s angular velocity not considered in the published analysis, raising questions about pivot in producing the spiral. We give a general expression for the sphere angular velocity vector which accommodates a linear, circular or spiral path, pivot or no pivot, and one or two planes in contact. We show that a sphere can roll in a circle on one or between two plane without pivot, but not between a stationary and a spinning plane. We show that a circumferential component of angular velocity results in a spiral path. A symmetry argument suggests that the spiral might be due to elastic deformation in the planes rather than to pivot, but the question is still open.
Multilevel Solution of the Elastohydrodynamic Lubrication of Concentrated Contacts in Spiroid Gears
Authors: Changhua Huang , Shizhu Wen , Ping Huang
Published: June 2008

This paper presents a new method for analyzing the lubrication performance of spiroid gears, which combines the elastohydrodynamic lubrication analysis with LTCA. The LTCA provides the geometry of teeth surfaces at the vicinity of contact point, normal load, lubricant entrainment velocity, etc. Multilevel techniques are used to solve the elastohydrodynamic lubrication of concentrated contacts with high ellipticity ratio under heavy load in spiroid gears. Finally, a pair of spiroid gears used in aircraft is analyzed. Some interesting new conclusions are presented.
Sliding Wear Calculation in Spur Gears
Authors: Wu Shifeng , Cheng H. S.
Published: June 2008

In gear applications where precipitous tooth failure mode such as scoring or scuffing has been avoided, “normal” wear becomes a life-determining factor. In this paper, sliding wear in spur gears, including the considerations of gear dynamics and rough-elastohydrodynamic lubrication, is analyzed. Formulas for equivalent wear rate and tooth wear profile along the line of action are derived. Results show that most materials are removed from both the addendum and dedendum tooth surfaces, and that the highest wear occurs at the beginning of an engagement. This high wear region corresponds to the root of the driving (pinion) teeth and the tip of the driven (gear) teeth. These analytical results correlate well with the practical evidences in AGMA documentation.
Observations of Shear Localization in Liquid Lubricants Under Pressure
Authors: Bair S. , Qureshi F. , Winer W. O.
Published: June 2008

A High Pressure Flow Visualization Cell has been designed and constructed to perform a fundamental investigation of the deformation behavior of liquid lubricants under lubricated concentrated contact conditions. A pressure of 0.3 GPa and a shear stress between parallel plates of about 25 MPa has been demonstrated. Time averaged velocity profiles show no continuous slip either in the bulk or at walls. Localized slip at shear bands inclined to the walls was demonstrated to occur during nonlinear shear response. The number of shear bands increases with shear rate (and shear stress) from as few as one at the onset of non-Newtonian flow until the shear region is essentially filled with bands with a spatial periodicity of 7 μm. Bands are typically inclined 19 deg off the solid surfaces in a direction which reduces the compressive normal stress due to shear on the plane of the band.
Lubrication With Binary Mixtures: Liquid-Liquid Emulsion in an EHL Conjunction
Authors: Wang S. H. , Al-Sharif A. , Rajagopal K. R. , Szeri A. Z.
Published: June 2008

Oil-in-water and water-in-oil emulsions are often employed as lubricants. In many applications of emulsion lubricants both the deformation of the bounding solid surfaces and the pressure dependence of the viscosity of the lubricant contribute essentially to performance, thus defining lubrication in the elastohydrodynamic (EHD) mode. In this paper we investigate lubrication with liquid-liquid binary mixtures of two Newtonian fluids in an EHD conjunction, and discuss the effect of varying the parameters of the problem on pressure, film thickness and volume fraction distribution. The basic theory of lubrication with liquid-liquid mixtures is contained in an earlier publication (Al-Sharif et al., 1992), here we use the theory to study an important application.
Lubrication With Emulsion in Cold Rolling
Authors: Wang S. H. , Szeri A. Z. , Rajagopal K. R.
Published: June 2008

Petroleum oil-in-water emulsion, where water is the continuous phase, is often employed under circumstances where the high heat capacity of water is beneficial while the poor lubricating properties of an oil-in-water emulsion can be tolerated. Usage includes cold-rolling but also some hot rolling applications. However, emulsions do not exhibit Newtonian behavior even when their individual components themselves are Newtonian, thus classical lubrication theory is not valid for these applications. In this paper we employ the extended Reynolds equations of Al-Sharif et al., derived for binary mixture lubricants, to study strip-rolling lubricated with oil-in-water emulsion. We are able to predict several experimentally observed phenomena such as oil-pooling, enhancement of oil-pooling with increased strip yield stress and with increased roller speed.
Experimental and Numerical Analyses of Effect of Thermal Stability of Lubricants on Heatstreaks in Cold Rolling of Stainless Steel
Authors: Yamamoto H. , Shiraishi T. , Ataka M. , Iwasaki Y.
Published: June 2008

The numerical analysis model of temperature in a roll and a rolled material was first derived by solving the equations of heat conduction. Next, the occurrence limits of heatstreaks for reduction in thickness and interface temperature in a roll bite were evaluated experimentally and numerically in cold rolling experiments of stainless steel (SUS430) with two kinds of lubricants. Also, the thermal stability of two lubricants was measured by thermal balance experiments. Consequently, the limit of interface temperature due to heatstreaks calculated numerically is almost constant in a lubricant, which suggests that an outbreak of heatstreaks is mostly dependent on the thermal stability of lubricant. Also, larger quantity of synthetic ester is considered to give higher heatstreak resistance in cold rolling of stainless steel.
Effect of Out-of-Roundness on the Performance of a Diesel Engine Connecting-Rod Bearing
Authors: Vijayaraghavan D. , Brewe D. E. , Keith T. G.
Published: June 2008

In this paper, the dynamic performance of the Ruston and Hornsby VEB diesel engine connecting-rod bearing with circular and out-of-round profiles is analyzed. The effect of cavitation is considered by using a cavitation algorithm, which mimics JFO boundary conditions. The effect of mass inertia is accounted for by solving coupled nonlinear equations of motion. The journal profiles considered are circular, elliptical, semi elliptical and three lobe epicycloid. The predicted journal trajectory and other performance parameters for one complete load cycle are presented for all of the out-of-round profiles and are also compared with the predictions for the circular bearing.
Limitations of the Short Bearing Approximation in Dynamically Loaded Narrow Hydrodynamic Bearings
Authors: Rezvani M. A. , Hahn E. J.
Published: June 2008

Transient solutions are still widely used for evaluating the vibrational behavior of rotor bearing systems containing dynamically loaded journal bearings with large unbalance, or noncircular orbit type squeeze film dampers, such as dampers without centralizing springs. For parametric design studies, such transient analyses need rapid means for evaluating the motion dependent fluid film forces and for narrow bearings or dampers (aspect ratios less than 0.5) the short bearing approximation (SBA) to the Reynolds equation has generally been assumed. Comparisons with exact numerical solutions under conditions of static loading and pure squeezing show that the SBA pressure profile predictions are significantly in error for aspect ratios as low as 0.25 at eccentricities around 0.9, whereas the optimal parabolic axial profile approximation (MSBA), while retaining all the rapid calculation features of the SBA, is accurate to within 1 percent under the same conditions and to within 3 percent for aspect ratios around 1.0. Using the MSBA as a yardstick under transient solution conditions, the SBA, while satisfactory for aspect ratios of 0.05, was found to be inadequate in predicting transient and steady state orbits and transmitted forces at aspect ratios of 0.5. At these aspect ratios, jump speeds and instability threshold speeds were also found to be erroneously predicted, with speed overestimates of 30 percent possible for practical unbalance situations. In view of the vastly improved accuracy obtainable by the MSBA, its use is to be preferred to the SBA under dynamic loading conditions for aspect ratios around 0.5, and probably around 0.25 or lower.
A Thermo-Elasto-Hydrodynamic Study of Journal Bearing With Controlled Deflection
Authors: Freund N. O. , Tieu A. K.
Published: June 2008

A thermo-elasto-hydrodynamic study of a specially modified journal bearing is included. A numerical simulation is carried out by the finite element method, coupling the deflection of the bearing housing and the pressure derived from the Reynolds equation. In turn, this is coupled through its temperature dependent viscosity terms to the energy equation. Elastic effects are treated in three dimensions. Thermal effects are considered in three dimensions in both the lubricating film and bearing housing with convection specified on the housing boundaries. The bearing is specially modified with an undercut on the bearing housing. It will be demonstrated that by design an appropriate deflection of the undercut can be achieved to improve the load capacity.
Simulation of Tape Floating Behavior in VTR
Authors: Itoh Jun , Ebihara Takeshi , Kubota Yuji , Takahashi Atsushi
Published: June 2008

An efficient method for numerical simulation of tape floating behavior in VTR has been developed. Parameter survey examples for tape floating height control in some drum-guide tape systems have been shown. The spacing between a drum and a tape is one of the most important topics regarding the tape/head interface problem for a VTR. The spacing is caused by air film lubrication and can be determined by using the Reynolds equation for air and the elastic equation for a tape. Each equation is discretized, using the finite element method, and solved by the Newton-Raphson method. The results, calculated by the present method, show good agreement with experimental results. The authors also investigated tape floating behavior for several drum-guide tape systems, which are intended to decrease tape/drum spacing, especially in the head entrance region, as follows; (1) Guidepost twist effect; (2) Difference between a rotary drum configuration and a rotary center drum configuration; (3) A new groove location for tape floating height equalization.
Scaling Criteria for Slider Miniaturization Using the Generalized Reynolds Equation
Authors: Crone R. M. , Peck P. R. , Jhon M. S. , Karis T. E.
Published: June 2008

The current trend in the magnetic storage industry is the reduction of the slider size and the height at which the slider flies over a rigid disk. Lower flying heights are achieved by miniaturizing sliders and reducing the normal load. In this paper, force scaling criteria are determined for 3370 and 3370K sliders that are dynamically loaded or operated in contact start/stop mode. Two forms of the generalized Reynolds equation (the first-order and continued fraction formulations) are incorporated into the analysis. The new scaling equation relates the steady-state flying height to design and operating parameters such as the disk velocity, normal load, ambient pressure, and the shape and dimension of the slider rail. The resulting quadratic equation contains two slider design dependent parameters which are calculated from two full scale numerical solutions to the generalized Reynolds equation for the slider design of interest. The new scaling equation accurately fits numerical and experimental results over an extremely wide range of ambient pressures, normal loads, disk velocities, and slider size reduction. The utility of the scaling equation is that it can rapidly and accurately predict the load required to obtain a desired flying height at a given disk velocity for any slider geometry. The scaling analysis also has the ability to qualitatively account for surface roughness effects. The equation could be applied to the design of contact recording devices, if surface roughness effects could be quantitatively incorporated into the analysis.
Wear Characteristics of Carbon-Coated Magnetic Rigid Disks With Well-Defined Surface Texture
Authors: Tanaka Hideaki , Shiota Katsuhiko , Gomi Kenichi , Miyake Yoshihiko
Published: June 2008

Wear characteristics are described for carbon-coated magnetic rigid disks with well-defined surface textures. Concentric circular hills with uniform height (ca. 80 nm) are produced on a disk surface using a photo-lithography technique, to control the apparent area of contact with a slider. Wear depth on the order of nanometers of the carbon overcoat is evaluated from the decrease in hill height after a drag test. Wear depth increases proportionally with the increase in average contact pressure, which is calculated from the load and apparent area of contact between the disk and slider. Lubricant diminishes wear of the carbon overcoat approximately 50 percent compared with that of an unlubricated overcoat.
Analysis of a Laminate Disk Rotating Near a Flat Plate
Authors: Carpino M.
Published: June 2008

A laminate disk which is rotated at high speed in close proximity to a rigid flat plate is analyzed in this paper. A thin gas film separates the disk from the rigid plate when the disk is rotating. Since the disk is composed of different materials, when it is rotated at high speeds, differences in stresses occur between the layers which produce an internal moment in the disk. This moment causes a flat static disk to deflect. The governing equations for this system are presented and solved. An approach is presented which can be used to quickly approximate the magnitude of the laminate structure effects in such a system.
On the Lubrication Theory: A Mechanism Responsible for Generation of the Parallel Bearing Load Capacity
Authors: Rodkiewicz C. M. , Sinha Prawal
Published: June 2008

Parallel sliding load support has been a subject of numerous theoretical and experimental investigations. Postulated mathematical models suffer from restricting assumptions. The present analysis evaluates the several models that have appeared and provides an orderly analysis which elaborates on the mechanism that may be responsible for the fluid generated lifting force. The governing continuity, momentum and energy equations for a Newtonian fluid, which are coupled, via temperature dependent density and viscosity are solved simultaneously using the finite difference method, to yield various bearing characteristics. The results indicate that the consideration for the foreregion pressure together with the density variation, may lead to a useful load support with a reduced friction, even for parallel sliding.
A Transition-Turbulent Lubrication Theory Using Mixing Length Concept
Authors: Kosasih P. B. , Tieu A. K.
Published: June 2008

This paper applies the recently introduced Reynolds stress expression (Tieu and Kosasih, 1992) in the transition-turbulent lubrication analysis. The Reynolds stress is modeled using the mixing length expression which is able to account for the effect of local shear stress gradient, and it can be extended to apply in the transition regime. This theory is then used to determine three-dimensional velocity distributions between parallel plates. From the results, a set of coefficients covering transition-turbulent regime used in conjunction with the modified Reynolds equation is presented. It is shown that the resulting coefficients agree well with results of Elrod and Ng (1967) in the fully turbulent regime while differences are shown in the transition regime. Pressure distributions and load carrying capacity of superlaminar journal bearing are compared with available experimental data.
Contact Simulation of Three-Dimensional Rough Surfaces Using Moving Grid Method
Authors: Ren Ning , Lee Si C.
Published: June 2008

A new method for simulating dry contacts of three-dimensional rough surfaces has been developed. The present work is based upon Moving Grid Method (MGM) which greatly reduces the required computer memory size. One of the major difficulties in simulating contact problems is the huge requirement in computer Random Access Memory (RAM). The total number of nodes (N) to represent a typical three dimensional roughness topography can easily be in the order of tens of thousands. To store the corresponding deformation matrix based on conventional matrix method requires memory size in the order of N2. The computational time necessary to construct such a matrix is also proportional to N2. Thus a reasonable solution for the three dimensional contact problem can be difficult to obtain. In Moving Grid Method, the required storage space for the deformation matrix is reduced to the order of N. The computing time to construct the matrix is also proportional to N. The contact simulation solutions which include the asperity pressure distributions and the corresponding deformed surface profiles were calculated. The digitized surface profiles were used in the simulations. The 3-D results were compared with an existing 2-D model and the comparison showed excellent agreement.
Variations in Contact Stress Distribution of Real Rough Surfaces During Running-In
Authors: Liang Xian , Kaiyuan Ji , Yongqing Ju , Darong Chen
Published: June 2008

A numerical model for the elastic contact of three-dimensional real rough surfaces has been developed and applied to the study of the variations in contact stress distribution in running-in process. The specimens for calculation and experiment are washers with nominally flat grinding surfaces. The stresses of real contact between specimens at each stage of running-in are calculated and the contact stress distributions are given. It is shown that the contact stress distribution is in an exponential form which could be characterized by one dimensionless parameter: λ, the index of contact stress distribution. The proportion of plastic deformation β may be expressed as a function of λ. The results of the present work confirm the reasonableness of the early opinion that the running-in process can be considered as a gradual increase in the elastic component of deformation of the contact area and a decrease in the proportion of plastic deformation.
Strength and Adhesion of Thin Aluminum Oxide Film Deposited on Iron Surface
Authors: Nakanishi M. , Okuya H. , Nakajima K.
Published: June 2008

The strength of deposited film and the adhesion between the film and the substrate were investigated with deposited aluminum oxide film on iron surface by scratching the surface with a diamond cone. Two types of samples were examined, one with oxide film deposited after cleaning the substrate surface by sputter etching, the other with the film deposited without any sputter etching. It was found that a law similar to Meyers’ for indentation hardness holds between the load and scratch width on the sample examined. These results suggest that by analyzing the scratch data the adhesion strength of the film to the substrate can be estimated together with the hardness of the film itself. Analyses by EPMA (electron probe X-ray microanalyzer) and AES (Auger electron spectroscopy) were conducted to correlate the results obtained by the scratch tests and friction experiments, and it was confirmed that (i) adhesion is improved by sputter etching prior to the deposition of the film; (ii) adhesion decreases considerably due to the progress of oxidation in the vicinity of the interface, which depends markedly on the oxygen concentration in the oxide film; and (iii) there is an optimum thickness of the three-component layer (Fe, Al, and O) formed by atomic mixing at the interface for maximizing the adhesion.
Finely Striated Lip-Seal Surfaces: Part 1—General Effects
Authors: To̸nder K.
Published: June 2008

The work presented previously by To̸nder and Salant (1992) is extended and generalized. In that work it was shown that the fine, axially oriented striations found on some lip-seals, under certain conditions, could lead to the total suppression of leakage through a fully lubricated seal. In the present work the behavior of the lubricant annulus is studied, as are the conditions required for leakage suppression. If the latter are met, it is shown that when a certain parameter—here called the seal number—is increased, the lubricant annulus width will shrink. This will lead to a reduction of the friction force. It is further shown that the striated roughness will also generate a radial force or load capacity. This effect does not involve local cavitation.
FE Analysis and LDA Measurement of the Dynamic Rotor/Stator Contact in a Ring-Type Ultrasonic Motor
Authors: Maeno Takashi , Bogy David B.
Published: June 2008

We study the dynamic contact characteristics between the rotor and stator of a ring-type ultrasonic motor by measurement and simulation. First, we measure the tangential and normal velocities and displacements of the rotor/stator interface using a LDA (laser Doppler anemometer). It is especially suitable for our measurement since it directly measures the velocity with high precision. Next, we solve the dynamic contact problem of the rotor/stator interface by use of finite element analysis taking into consideration inertial effects and replacing the ring by an equivalent straight model of the rotor/stator. The calculated tangential and normal displacements and velocities of the rotor/stator are in good agreement with the measured ones. The effect of inertia was studied by changing the density of the rotor in the calculation. When the rotor’s density is decreased to produce smaller natural frequencies, the velocity fluctuation and the frictional loss increase.
Thin Fluid Film Squeezed With Inertia Between Two Parallel Plane Surfaces
Authors: Yang Seung-Man , Leal L. Gary
Published: June 2008

The present study is concerned with estimating the inertial effects on the draining of thin fluid layer between two parallel plane boundaries. In particular, we consider the case in which an initially stationary object with a circular plane lower surface begins suddenly moving under the action of a constant applied force toward a parallel plane wall when the inertia of the object and that of the intervening fluid in the gap are not negligible. The method of solution is a matched asymptotic expansion involving characterization of the solution by different characteristic time scales in different parts of the solution domain in the limit of small but finite Reynolds number based on the gap height. The asymptotic solution is presented for the time-dependent motion of the object and the fluid in the thin film including a proper description of the effects of both the inertia of the object and the inertia of the fluid.
The Rheology of Lubricants at High Shear Rates
Authors: Feng R. , Ramesh K. T.
Published: June 2008

A modified torsional Kolsky bar is used to shear a thin annular layer of lubricant held between concentric cylinders. The shear rates obtained range from 4 × 103 to 4 × 104 s−1; the duration of the shear pulse is about 400 microseconds. The shear stress history and the corresponding shear-rate history are deduced using standard torsional Kolsky bar techniques. This experimental technique provides the capability of measuring the shear stresses sustained by fluids at very high shear rates, while the short test duration ensures a minimal rise in temperature due to the associated shear heating. Results are presented for a synthetic lubricant (5P4E) and a mineral oil (HVI650). The lubricants are both observed to be rate-sensitive over the entire range of shear rates examined; the rate-dependence of the shear response is strongly non-Newtonian at high shear rates. Softening during the test is observed for both materials; this softening appears to be largely driven by a thermal mechanism.
On the Indentation of a Transversely Isotropic Half-Space With Application to Thin Solid Lubricant Films
Authors: Ovaert T. C.
Published: June 2008

In this investigation, the contact between a model rigid ellipsoidal asperity and the surface of an oriented solid lubricant film has been simulated using an analysis developed previously for contact of a transversely isotropic half-space. In this case, unlike most previous work, the plane of isotropy is oriented normal to the plane of contact, instead of parallel. Under this condition, the contact patch is of a general elliptical form, depending on the shape and orientation of the model asperity and on the elastic constants of the solid lubricants. Several applicable material compositions are examined using the analysis, and the influence of asperity shape and elastic constants in relation to friction and potential design of solid lubricant formulations is discussed.
Surface Crack Initiation Under Contact Fatigue: Experimental Observation and Contact Analysis
Authors: Cheng W. , Cheng H. S. , Keer L. M. , Ai X.
Published: June 2008

An experimental study of surface crack initiation was performed by means of a transverse furrow manufactured by the electric discharge machining (EDM) method. Since there is no built-up edge and plastic zone associated with an EDM furrow, the associated stress analysis is relatively simple and provides a reliable means of comparison with experiment. The test results showed that the crack initiation life was not sensitive to the size of the furrow. This phenomenon was explained by means of a micro-elastohydrodynamic lubrication (MEHL) analysis. The calculated results indicated that the pressure peak, Pmax, near the furrow was not sensitive to the depth and width of the furrow, and Pmax could be estimated from the Hertzian contact pressure P0. The more heavily loaded tests showed a newly deformed plastic zone (bump) near the furrow. Two methods were used for the contact simulation. The elastic-plastic contact analysis was selected for the case when a bump was present; otherwise, the MEHL analysis was used. The stress analysis illustrates that the value and the location of the maximum Mises stress was influenced by the friction coefficient and the geometry of the deformed surface profile.
An Average Reynolds Equation for Non-Newtonian Fluids in EHL Line Contacts
Authors: Hughes G. D. , Bush A. W.
Published: June 2008

A closed-form of Reynolds equation is found for non-Newtonian inelastic fluids with a general constitutive equation by assuming that Couette flow dominates Pouiseuille flow. The roughness effects of the bearing surfaces are incorporated into the flow factors of an average Reynolds equation obtained by the technique of two scale analysis.
Turbulence Measurements of High Shear Flow Fields in a Turbomachine Seal Configuration
Authors: Morrison G. L. , DeOtte R. E. , Thames H. D.
Published: June 2008

The mean velocity and Reynolds stress tensor throughout a whirling annular seal are presented. The data were collected with a three-dimensional laser Doppler velocimeter using phase averaging. Two axial flow conditions (Re = 12,000 and 24,000) were studied at one shaft speed (Ta = 6,600). The eccentricity and whirl ratios were 50 percent and 100 percent, respectively. There is a region of high axial momentum at the inlet on the pressure side of the clearance that migrates around the seal to the suction side at the exit. The normalized axial momentum in this region is higher in the low Reynolds number case due to an axial recirculation zone that occurs on the suction side of the rotor at the inlet. The recirculation zone does not occur in the high Reynolds number case. At both Reynolds numbers there is a recirculation zone on the rotor surface in the pressure side of the inlet. This recirculation zone extends from 20 to 200 deg past the rotor zenith in the tangential direction, and is one third of a clearance wide radially. The high Reynolds number circulation zone is 1.5 mean clearances long, while the low Reynolds number zone extends two mean clearances downstream. When compared to previous studies, it is apparent that the tangential momentum is no greater for a seal with whirl than for one without if other parameters are constant. Areas of high tangential momentum occur in the clearance where the axial momentum is low. Average exit plane tangential velocities in the low Reynolds number case are 1.5 times greater than those in the other flow case. These results are in general agreement with predictions made by other investigators.