bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonsynchronous Motion of Squeeze Film Damper Systems
Authors: Li Xuehai , Taylor Dean L.
Published: October 2009

The nonsynchronous motion of a rigid rotor-squeeze film damper system was investigated. This research classifies the phenomenon of the system with perfectly preloaded centering springs, reveals its existence conditions, and analyzes the system’s topological structures associated with the phenomenon. When the centering springs of the system do not perfectly balance the gravity load, a unidirectional gravitational residual is resulted. This research also studied the effect of the gravitational residual on the system’s behavior and the degree of stability for the various topological structures of the corresponding autonomous system. It shows that the residual improves the performance of the system because it either suppresses the nonsynchronous orbit of the system or changes it into various subharmonic orbits. This research shows that though the squeeze film damper system is inherently stable, it can have some undesirable nonsynchronous behavior for a wide range of system parameters.
The Role of Hard Layers in Lubricated and Dry Sliding
Authors: Komvopoulos K. , Saka N. , Suh N. P.
Published: October 2009

Lubricated and dry experiments on titanium and steel surfaces with and without TiN sputtered coatings of various thicknesses have been conducted. The significance of the layer thickness, interfacial “friction”, magnitudes of normal and tangential surface tractions, and the mechanical properties of the layer and of the substrate (e.g., elastic modulus and hardness) are critically examined. The conditions under which the deformation mode at the solid-solid contacts is elastic or plastic are addressed in light of the experimental evidence and a finite element analysis. It is shown that surfaces with very low friction, especially for unlubricated sliding, and practically zero wear rates can be obtained in both lubricated and dry sliding by coating the surfaces with sufficiently thick TiN layers. Removal of the protective TiN layer resulted in plowing, severe damage, and delamination.
Magnetic Head-Media Interface Temperatures: Part 1—Analysis
Authors: Bhushan B.
Published: October 2009

A “generalized” thermal analysis is described to estimate the flash temperature during sliding when both surfaces are of more or less equal roughness or one surface is substantially smoother than the other. High- and low-speed cases are considered. The basic model includes surface-topography statistics, frictional conditions, and mechanical and thermal parameters. Temperature history during the life of an individual asperity contact is calculated, from which average temperatures of an asperity contact are calculated. Thermal interaction of neighboring asperity contacts is considered. Then, an analysis is presented to show how individual asperity temperatures should be averaged. Temperature variations perpendicular to the sliding surfaces are also analyzed. Throughout the analysis, closed-form equations are developed, which can be conveniently used in the design of any sliding interface.
Elastohydrodynamic Lubrication of Piston Skirts
Authors: Oh K. P. , Li C. H. , Goenka P. K.
Published: October 2009

The elastohydrodynamic lubrication of an automotive piston was analyzed. The important effects of thermal and pressure distortions were demonstrated by analyzing two piston skirts which have different axial profiles but are otherwise identical. Results show that a significant reduction in friction can be realized.
The Effect of the EHD Pressure Spike on Rolling Bearing Fatigue
Authors: Houpert L. , Ioannides E. , Kuypers J. C. , Tripp J.
Published: October 2009

A recently proposed fatigue life model for rolling bearings has been applied to the study of lifetime reduction under conditions conducive to microspalling. The presence of a spike in the EHD pressure distribution produces large shear stresses localized very close to the surface which may account for early failure. This paper describes a parametric study of the effect of such spikes. Accurate stress fields in the volume are calculated for simulated pressure spikes of different height, width and position relative to a Hertzian pressure distribution, as well as for different lubricant traction coefficients and film thicknesses. Despite the high stress concentrations in the surface layers, reductions in life predicted by the model are modest. Typically, the pressure spike may halve the life, with the implication that subsurface fatigue still dominates. In corroboration of this prediction, preliminary experimental work designed to reproduce microspalling conditions shows that microindents due to overrolling particles are a much more common form of surface damage than microspalling.
Thermal Effects in Rolling/Sliding Contacts: Part 3—Approximate Method for Prediction of Mid-Film Temperature and Sliding Traction
Authors: Sadeghi Farshid , Dow Thomas A. , Johnson Richard R.
Published: October 2009

An approximate method for mid-film temperature and traction force in elastohydrodynamic (EHD) lubrication of sliding contacts is obtained. The results are obtained at the point of maximum pressure where the pressure gradient is zero. The results indicate excellent correlation exists between this approximate method and results of a previous paper by the authors [1].
Statistical Analysis of Wear Rate Data
Authors: Lhymn C.
Published: October 2009

The wear rate data of glass fiber reinforced polyethylene terephthalate (PET) has been analyzed statistically using the wear lifetime model together with the two-parameter Weibull distribution function. The specific wear rate versus normal load curve has been given a theoretical explanation, the empirical model being derived from the concepts of crack propagation and delamination physics.
Wear Analysis and Life Estimation of the XHP Series Rock Bit Bearing System
Authors: Wang Yi-Ling , Wang Zi-Shan
Published: October 2009

In this paper we will give a wear analysis and a life estimation of the XHP series Rock bit bearing system with the three-body abrasive wear equation developed by the authors. The result of the estimation indicates that it is possible to increase the service life by about eighty-six percent due to using the mechanical seal instead of the O-ring rubber seal.
Sliding Friction and Boundary Lubrication of Snow
Authors: Glenne B.
Published: October 2009

To understand the basic facets of snow tribology, it is necessary to consider dry, wet, compaction, and impact resistances. These mechanisms and their aggregate effect are reviewed and modeled for cold and warm snow temperatures with due consideration of snow moisture and wet lubrication.
The Interior Stress Field Caused by Tangential Loading of a Rectangular Patch on an Elastic Half Space
Authors: Ahmadi N. , Keer L. M. , Mura T. , Vithoontien V.
Published: October 2009

A solution is obtained for the tangential loading on a rectangular patch. The solution gives the internal stress field in terms of elementary functions and is a form analogous to the solution for vertical load developed by Love.
Combined Effects of Thermal and Non-Newtonian Character of Lubricant on Pressure, Film Profile, Temperature Rise, and Shear Stress in E.H.L.
Authors: Wang S. H. , Zhang H. H.
Published: October 2009

A derivation of the lubrication equation suitable for nonlinear rheological model is presented. Full numerical solutions coupling the lubrication equation with film shape equation and energy equation are obtained to reveal the combined influence of thermal and non-Newtonian character of lubricant on elasto-hydrodynamic lubrication. Results show that the minimum film thickness is influenced only slightly in general. Nevertheless, the spikes of pressure and temperature rise, and the coefficient of friction are strongly affected by the rheological character of lubricant. It is concluded that both the temperature rise and non-Newtonian character of the oil film should be considered in E.H.L. analysis in order to obtain reliable results.
A Model for the Influence of Pressure on the Bulk Modulus and the Influence of Temperature on the Solidification Pressure for Liquid Lubricants
Authors: Jacobson Bo O. , Vinet Pascal
Published: October 2009

Two pressure chambers, for compression experiments with liquids from zero to 2.2 GPa pressure, are described. The experimentally measured compressions are then compared to theoretical values given by an isothermal model of equation of state recently introduced for solids. The model describes the pressure and bulk modulus as a function of compression for different types of lubricants with a very high accuracy up to the pressure limit of the high pressure chamber used (2.2 GPa). In addition, the influence of temperature on static solidification pressure was found to be a simple function of the thermal expansion of the fluid.
The Distribution of Microcontact Area, Load, Pressure, and Flash Temperature Under the Greenwood-Williamson Model
Authors: McCool J. I.
Published: October 2009

Microcontact models provide average values of the random interfacial load, area and pressure between rough contacting surfaces. They do not provide a measure of the variability about that average. Events of tribological importance, however, are likely to be dependent on extreme rather than average behavior conditions. In this paper Monte Carlo simulation is used to determine the 75th and 90th percentiles of three dimensionless random variables as a function of the dimensionless separation of two contacting rough surfaces. These values may be used to determine the corresponding percentiles under the Greenwood-Williamson microcontact model of the distributions of 1) real contact area fraction, 2) the radius of the microcontact area, 3) microcontact load, 4) the maximum microcontact pressure and 5) the asperity flash temperature under low speed sliding conditions. A numerical example illustrates the computations.
On the Geometrical Imperfections in Cylindrical Roller Bearings
Authors: Gupta P. K.
Published: October 2009

Computer simulations of the dynamics performance of roller bearings, as obtained by the computer code ADORE, are used to model the infuence of race out-of-roundness, race taper and centrality of land on partly crowned rollers. Both oil and solid lubricated high-speed roller bearings are considered and the overall performance parameters, such as, bearing life, heat generation, cage interactions and race flange wear due to roller skew and tilt, are correlated to the magnitude of the various geometrical imperfections. Thus the strength of computer modeling approach to optimization of geometrical tolerances in cylindrical roller bearings is demonstrated.
Experimental Investigation of Externally Pressurized Bearings Under High Knudsen Number Conditions
Authors: Fukui S. , Kaneko R.
Published: October 2009

The characteristics of the externally pressurized bearings under high Knudsen number conditions were investigated experimentally by the use of surface restriction bearings in a medium vacuum on the order of 0.1 kPa (10−3 atm.). The experimental results agreed well with the numerical results calculated from a generalized lubrication equation based on the Boltzmann equation. Therefore, it would appear that this generalized lubrication equation is valid even when flows are categorized into transition flow or free molecular flow.
Stability of a Rigid Rotor Supported on Flexible Oil Journal Bearings
Authors: Majumdar B. C. , Brewe D. E. , Khonsari M. M.
Published: October 2009

This investigation deals with the stability characteristics of oil journal bearings, including the effect of elastic distortions in the bearing liner. Graphical results are presented for (1) steady-state load, (2) stiffness and damping coefficients, and (3) the stability. These results are given for various slenderness ratios, eccentricity ratios, and elasticity parameters. The lubricant is first assumed to be isoviscous. The analysis is then extended to the case of a pressure-dependent viscosity. It has been found that stability decreases with increase of the elasticity parameter of the bearing liner for heavily loaded bearings.
A Theoretical and Experimental Study of EHL Lubricated With Grease
Authors: Wen Shi Zhu , Ying Tsi Neng
Published: October 2009

It is known that the apparent viscosity of grease varies with service time and that grease starvation is important in EHL. However, these effects were often ignored in the research of EHL lubricated with grease. This paper deals with the thixotropy of grease and determines which value of rheological parameters can be used in numerical analysis. The starved boundary position and its cause are also discussed and observed experimentally. A steady starved boundary of grease was adopted in computing the film shape. Since in both calculation and experiment the thixororpy and grease starvation were considered, the numerical solution was quite consistent with the experimental data. This paper explains why even though the apparent viscosity of grease is always larger than that of its base oil, the film thickness of EHL lubricated with grease is equal to or lower than that with the oil alone.
Static Friction Coefficient Model for Metallic Rough Surfaces
Authors: Chang W. R. , Etsion I. , Bogy D. B.
Published: October 2009

The friction force required to shear interface bonds of contacting metallic rough surfaces is calculated, taking into account the prestress condition of contacting asperities. The surfaces are modeled by a collection of spherical asperities with Gaussian height distribution. Previous analyses for adhesion force and contact load of such surfaces are used to obtain the static friction coefficient. It is shown that this coefficient is affected by material properties and surface topography, and that it actually depends on the external loading contrary to the classical law of friction.
Static and Dynamic Characteristics of Rolling-Pad Journal Bearings in Super-Laminar Flow Regime
Authors: Mikami Makoto , Kumagai Mikio , Uno Shuetsu , Hashimoto Hiromu
Published: October 2009

Static and dynamic characteristics of load-on-type rolling-pad journal bearings with six pads have been studied theoretically and experimentally by considering the effects of both turbulence and viscous heat generation in the oil film. By concurrently solving a turbulent lubrication equation and an adiabatic energy equation, pressure and temperature distributions, load capacity, and friction force are obtained. Moreover, the linearlized spring and damping coefficients of oil film are calculated under the assumption of small displacements of the journal center. It is found that the load capacity and the friction force considerably increase due to turbulence, and the effects of heat generated under turbulent conditions are more pronounced than those under laminar conditions. Also clarified are that bearing characteristics are improved by preloading the lower-side two pads located before and after the lowest pad, and that the curvature radius of the pad insignificantly affects the characteristics. The experimental results on static characteristics agree well with the theoretical results.
Thermoelastic Instability in Elliptic Contact Between Two Sliding Surfaces
Authors: Johnson R. R. , Dow T. A. , Zhang Y. Y.
Published: October 2009

The scuffing failure of a sliding contact is a complicated process, involving physics, chemistry, and mechanical science. No comprehensive theory has yet been formulated; the published work consists of studying each aspect independently. The objective of this paper is to present a thermoelastic instability theory of scuffing for elliptic contact between sliding surfaces. From this analylsis, the condition for which instability occurs is obtained. The approximate equation includes the effects of load, speed, coefficient of friction and material properties and can be used as an estimate to prevent scuffing failure. The results calculated from this equation are shown to provide satisfactory agreement with available experimental data.
Thermal Effects in Externally Pressurized Conical Bearings With Variable Viscosity
Authors: Kennedy J. S. , Sinha Prawal , Rodkiewicz Cz. M.
Published: October 2009

The influence of varying slider temperature on the characteristics of a conical bearing with constant film thickness rotating with a uniform angular velocity is examined. The fluid is considered to be incompressible and the viscosity is assumed to vary exponentially with temperature. The governing system of coupled partial differential equations in conical coordinates is solved numerically using finite difference method to yield the various bearing characteristics. The results show that maintaining the slider at temperature lower than that of the pad causes an increase in the load capacity of the bearing.
Ways to Improve the Drilling Effectiveness of Rock Bits by a Tribological Method
Authors: Wang Yi-Ling , Luo Hong
Published: October 2009

Wear tests on the main bearings of 8.5 inch XHP 3 rock bits were performed, from which it is concluded that the way to improve the drilling effectiveness for the rock bits is to set drilling pressure and rotary speed properly, and to develop a new type of grease for rock bits which can bear a higher temperature than conventional grease. In addition, it is also shown that an inexpensive copper alloy can take the place of expensive Ag85Mn15 as an anti-wear material in the bearing, so that the production cost for the rock bits can be reduced.
Sliding Contact Stress Field Due to a Spherical Indenter on a Layered Elastic Half-Space
Authors: O’Sullivan T. C. , King R. B.
Published: October 2009

The quasi-static sliding contact stress field due to a spherical indenter on an elastic half-space with a single layer is studied. The contact problem is solved using a least-squares iterative approach and the stress field in the layer and substrate is determined using the Papkovich-Neuber potentials. The resulting stresses are discussed for different values of the layer stiffness relative to the substrate and also for different values of the friction coefficient.
Analysis of Ultra-Thin Gas Film Lubrication Based on Linearized Boltzmann Equation: First Report—Derivation of a Generalized Lubrication Equation Including Thermal Creep Flow
Authors: Fukui S. , Kaneko R.
Published: October 2009

A generalized Reynolds-type lubrication equation valid for arbitrary Knudsen numbers, defined as the ratio of the molecular mean free path to the film thickness, is derived from a linearized Boltzmann equation by semi-numerically calculating the flow rates of fundamental flows in the lubrication film: Poiseuille flow, Couette flow, and thermal creep flow. Numerical analysis of the equation for high Knudsen numbers reveals three principal results. First, Burgdorfer’s modified Reynolds equation featuring the first-order velocity slip boundary condition overestimates load carrying capacities, while the approximation equation including both the first- and second-order velocity slip boundary condition underestimates them. Second, since the flow rate of the Couette flow, which is independent of Knudsen numbers, becomes dominant as the bearing number increases, all the lubrication equation results tend toward the same asymptotic value for an infinite bearing number. Third, a new kind of load carrying capacity caused by thermal creep flow occurs if temperature gradients at the boundaries exist in the flow direction.
A Face Seal With Circumferential Pumping Grooves and Rayleigh-Steps
Authors: Ikeuchi K. , Mori H. , Nishida T.
Published: October 2009

This paper presents an analysis of a new noncontacting pumping seal. A hydrodynamic lubricating film is maintained due to Rayleigh-steps. If the low pressure side of the seal is filled with a fluid, the fluid can be pumped into the high pressure side by pumping grooves until the shaft speed reaches a limit value. The experimental results confirm the theoretical predictions for lubrication and sealing performance. Due to the high pumping ability in addition to the high stiffness of its hydrodynamic film, the seal can operate without wear and leakage for a high pressure fluid.
Analysis of Eccentric Annular Incompressible Seals: Part 2—Effects of Eccentricity on Rotordynamic Coefficients
Authors: Nelson C. C. , Nguyen D. T.
Published: October 2009

In Part 1 of this paper, a new analysis procedure is presented which solves for the flow variables of an annular pressure seal in which the rotor has a large static displacement (eccentricity) from the centered position. This part of the paper (Part 2) incorporates the solutions from Part 1 to investigate the effect of eccentricity on the rotordynamic coefficients. The analysis begins with a set of governing equations based on a turbulent bulk-flow model and Moody’s friction factor equation. Perturbations of the flow variables yields a set of zeroth- and first-order equations. After integration of the zeroth-order equations by means of the method described in Part 1, the resulting zeroth-order flow variables are used as input in the solution of the first-order equations. Further integration of the first order pressures yields the eccentric rotordynamic coefficients. The results from this procedure compare very well with available experimental data, and are clearly more accurate than the predictions based on a Finite Element model.
Analysis of Crack Propagation in Roller Bearings Using the Boundary Integral Equation Method—A Mixed-Mode Loading Problem
Authors: Ghosn L. J.
Published: October 2009

Crack propagation in a rotating inner raceway of a high-speed roller bearing is analyzed using the boundary integral method. The model consists of an edge plate under plane strain condition upon which varying Hertzian stress fields are superimposed. A multidomain boundary integral equation using quadratic elements was written to determine the stress intensity factors KI and KII at the crack tip for various roller positions. The multidomain formulation allows the two faces of the crack to be modeled in two different subregions making it possible to analyze crack closure when the roller is positioned on or close to the crack line. KI and KII stress intensity factors along any direction were computed. These calculations permit determination of crack growth direction along which the average KI times the alternating KI is maximum.
A Thermohydrodynamic Analysis of Journal Bearings Lubricated by a Non-Newtonian Fluid
Authors: Kacou A. , Rajagopal K. R. , Szeri A. Z.
Published: October 2009

Our earlier work on the flow of a non-Newtonian fluid of the differential type in a journal bearing is extended here to include nonisothermal operations and temperature dependent viscosity. We show that for the type of lubricant investigated, even a slight departure from Newtonian behavior renders the bearing performance relatively insensitive to changes in lubricant temperature. But whether this change in lubricant behavior actually results in improved load capacity depends on the value and the sign of the material parameters.
The Influence of Longitudinal and Transverse Roughness on the Elastohydrodynamic Lubrication of Circular Contacts
Authors: Lubrecht A. A. , Ten Napel W. E. , Bosma R.
Published: October 2009

The effect of longitudinal and transverse roughness on the elastohydrodynamic lubrication of circular contacts was investigated numerically for two different lubricating conditions. The influence of the amplitude and the wavelength of the roughness texture was also studied. The results are compared with predictions from the flow factor method.
Analysis of Heavily Loaded Tilted Pads Thrust Bearings With Large Dimensions Under TEHD Conditions
Authors: Abdel-Latif L. A.
Published: October 2009

Huge thrust bearings with centrally pivoted and tilted pads operating under heavy loads are analzyed using the (thermoelastohydrodynamic) TEHD-theory. The Reynolds equation, the energy equation of the oil film, and the heat conduction equation of the bearing, all are coupled with the deflection equation and solved simultaneously in order to determine the bearing characteristic values. The first three equations are transformed by means of finite difference method and the last equation is solved using the method of Ritz-Galerkin. Based on successive approximation method a new iterative scheme is presented to apply the heavy load incrementally which provides a successful convergence of the equation system. In order to find the equilibrium state of the pad, another iterative scheme based on a controlled change of the pad tilts is applied. The tilts are changed as a function of the offset of the hydrodynamic resultant force from the pivot location. It is proved that the new scheme is quite efficient in successful convergence of the equation system and in saving CPU time.
Effect of Dynamic Loading on Wear of Steel in Boundary Lubricated Sliding Contact
Authors: Aronov V. , Mesyef T.
Published: October 2009

This paper describes the results of an experimental and theoretical investigation of wear of steel under forced oscillations of applied load in boundary lubricated sliding contact. A special pin-on-disk type wear apparatus, which enabled continuous control of the dynamic loading parameters (mean load, amplitude and frequency of the load oscillations and sliding velocity), has been used in the experimental investigation. Wear rates and surface roughness were measured for various combinations of static and dynamic loading parameters. A wear equation which related wear to the parameters of dynamic loading has been derived. It has been shown both by experimental investigation and theoretical analysis that wear is an increasing function of the mean value of the applied load, amplitude of the load oscillation, and a ratio of the frequency of load oscillation to the sliding velocity.
Transient Response of Floating Ring Liquid Seals
Authors: Kirk R. G.
Published: October 2009

The design and analysis of pressure balanced seals are important to the designers and users of turbomachinery which require floating element seals. The design objective for compressor seals differs from that of the engineered pump seal but the common factor includes the ability to predict the dynamic response of the floating ring seal relative to the rotor shaft. Steady-state calculations can be used to study possible operating conditions for compressor designs, but they do not include accurate account of rotor shaft response and ring spin torque. In addition, engineered pump seal applications are such that the ring is expected to track shaft movement during start-up and shut-down transients when reduced pressures and leakage produce laminar flow sealing conditions. The analysis presented in this paper gives the designer the ability to evaluate seal ring dynamic transient response, including friction stick-slip on the axial sealing face and the ring spin torque interaction with the antirotation element. The analysis results presented in this paper were obtained from a personal computer program written specifically for seal transient analysis.
Sliding Contact Between Dissimilar Elastic Bodies
Authors: Sackfield A. , Hills D. A.
Published: October 2009

An analysis is presented of the stresses induced by sliding between two bodies having different elastic constants. It is assumed that the bodies are plane (i.e., two dimensional), are symmetrical with respect to a line perpendicular to the plane of contact, and are smooth and continuous. It is shown that a careful choice of profile leads to a better load carrying capacity than for a Hertzian contact, but that the severity of the stresses induced is greater than for uncoupled sliding, i.e., where the bodies have similar elastic constants.
A New Hydrodynamic Gas Bearing Concept
Authors: Eusepi M. W. , Wilcock D. F.
Published: October 2009

Difficulty in attaining and controlling a desirable level of damping in foil bearings, and in designing them for large shaft diameters, led to the concept of the Hydroflex™ bearing. In this concept, each of a number of rigid shoes is supported on a compound post and beam flexure, and the radial motion of the pad is damped by a Coulomb friction damper. In this fashion, the tolerance of the foil to shaft growth (centrifugal and thermal) and to misalignment is retained with the added advantages of a larger and controlled level of damping plus the ready availability of conventional gas bearing theory for design. The feasibility of the Hydroflex™ design approach was demonstrated on a simple test rotor with a 3.5-in. (89-mm) Hydroflex™ bearing at speeds up to 30,000 r/min.
Nonuniform Temperature in Non-Newtonian Compressible Fluid Film Lubrication of Rollers
Authors: Prasad Dhaneshwar , Singh Punyatma , Sinha Prawal
Published: October 2009

A theoretical analysis of heavily loaded rigid cylindrical roller bearings lubricated by a thin compressible fluid film, considering cavitation, is presented. The lubricating fluid is assumed to follow the non-Newtonian power law model and the consistency as well as density varies exponentially with pressure and temperature. The modified Reynolds and energy equations (adiabatic case) for a compressible power law fluid are obtained and are solved simultaneously. It is observed that the compressible fluid film pressure is comparatively higher than the incompressible one whereas this trend is reversed in case of temperature. Moreover, consistency and density variations, especially in the pressure peak region, are quite significant.
Lubrication Capacity of Gears of Circular-Arc Tooth-Profile
Authors: Attia Awny Y. , El-Bahloul Ahmed M. M.
Published: October 2009

The paper presents the results of an experimental investigation carried out at Mansoura University Laboratories aiming at studying the effect of change of speed, oil viscosity, and helix angle on the load carrying capacity of the oil film. A three pairs of test gears of 6 DP, 91.5 mm pitch diameter with 22.3, 33.6 and 42.25 deg helix angles were run in power circulating test rig at 100 to 3000 r.p.m. speeds and transmitting tooth load ranging from 185 to 1090 Kp. The test gears were lubricated with oils of 200, 462, and 653 cSt at 40°C kinematic viscosities. The oil film thicknesses between contacting teeth were measured by measuring the changes in capacitance between test gears and transferred to linear dimensions by calibration curves drawn by knowing the changes in capacitance through the gaps between teeth of values known through the amount of backlash. The experimental results show that; Oil film thickness decreases with tooth load, while increases with speed and viscosity of the lubricant. Oil film thickness versus helix angle give an inversed parabola for the smallest and medium tooth loads, while oil film thickness decreases with increasing the helix angle under increased tooth loads. Load carrying capacity increases with speeds and viscosity of the lubricant while decreases with increasing the helix angle.
An Alternate Solution of the Deformation of a Cylinder Between Two Flat Plates
Authors: Zantopulos H.
Published: October 2009

Using the method of conformal mapping, an alternate solution is obtained for the line contact deformation of a cylinder loaded between two flat plates. In this method, the elastic deformation of two half spaces, assuming an elliptical pressure distribution across the width of contact, does not have to be calculated relative to an arbitrarily selected stationary reference point.
Experimental Results for Labyrinth Gas Seals With Honeycomb Stators: Comparisons to Smooth-Stator Seals and Theoretical Predictions
Authors: Hawkins Larry , Childs Dara , Hale Keith
Published: October 2009

Experimental measurements are presented for the rotordynamic stiffness and damping coefficients of a teeth-on-rotor labyrinth seal with a honeycomb stator. Inlet circumferential velocity, inlet pressure, rotor speed, and seal clearance are primary variables. Results are compared to (a) data for teeth-on-rotor labyrinth seals with smooth stators, and (b) analytical predictions from a two-control-volume compressible flow model. The experimental results show that the honeycomb-stator configuration is more stable than the smooth-stator configuration at low rotor speeds. At high rotor speeds, the stator surface does not affect stability. The theoretical model predicts the cross-coupled stiffness of the honeycomb-stator seal correctly within 25 percent of measured values. The model provides accurate predictions of direct damping for large clearance seals; however, the model predictions and test results diverge with increasing running speed. Overall, the model does not perform as well for low clearance seals as for high clearance seals.
Theoretical Approach to Turbulent Lubrication Problems Including Surface Roughness Effects
Authors: Hashimoto H. , Wada S.
Published: October 2009

A new theoretical approach to turbulent lubrication problems including the surface roughness effects is described. On the basis of a logarithmic velocity distribution law in the turbulent boundary layers, the resistance laws for pressure and shear flows in the lubricant film are formulated separately in both cases of smooth and homogeneous rough surfaces. Moreover, combining the bulk flow concept proposed by Hirs with the formulated resistance laws, the generalized turbulent lubrication equation including the surface roughness effects is derived. Some numerical results for the modified turbulence coefficients are presented in the graphic form for different values of relative roughness, and the effects of surface roughness on the turbulent lubrication characteristics are generally discussed.
An Experimental Study of Thermoelastic Effects in Scuffing Failure of Sliding Lubricated Contacts
Authors: Rhatigan J. L. , Johnson R. R. , Dow T. A.
Published: October 2009

The thermoelastic instability theory of scuffing failure in elliptic contact between two sliding surfaces, developed by Johnson, Dow, and Zhang, was tested experimentally on a disk machine. The theoretical model predicts a boundary, beyond which scuffing failure is expected to occur, that depends upon contact load, sliding speed, coefficient of friction, geometrical parameters, and thermal and material properties of the contact surfaces. Experiments were performed using three contact lubricants of different viscosity, and two steels with different thermal and material properties. Results correlate with the model in the regime of high calculated specific film thickness (λ≥4) and for the two steels tested. The model as stated fails to predict scuffing failure in a regime of low calculated specific film thickness (λ≤1.3). The experimental results did not answer the question of whether there is a difference in the scuffing boundaries of the two steels tested. A time dependency to failure was observed in the regime of high specific film thickness and some indication of moving ‘hot spots’ was observed.
Discretization Pressure-Wear Theory for Bodies in Sliding Contact
Authors: Marshek K. M. , Chen H. H.
Published: October 2009

A theory is presented for studying contact pressure and wear distributions for bodies in sliding contact. This theory can be used in designing machine elements for improved wear resistance and failure prediction. A point force-displacement influence function and a profile function are employed in conjunction with a discretization method, an automatic mesh generation technique and a discretized wear equation to determine the instantaneous contact pressure distribution and the corresponding worn surface profile for a given sliding distance. The theory is implemented in a computer program and is applied to a simple unlubricated sliding contact and adhesive wear problem. The results show that a higher pressure will exist at the leading edge of the sliding block and thus there results a higher wear at the leading edge of the sliding block than the trailing edge. This study also shows the sliding contact wear of a copper sphere on a steel plane. As expected, instantaneous contact radius increases as the sliding contact continues (for the same normal load) and therefore results in a smaller pressure within the contact region.
The Steady-State Characteristics of a Hydrostatic Thrust Bearing With a Floating Disk
Authors: Harada M. , Tsukazaki J.
Published: October 2009

To reduce the frictional power loss of hydrostatic thrust bearings, the hydrostatic thrust bearing with a floating disk shaped in a simplified configuration is proposed. And the load capacity and the frictional torque are experimentally investigated in laminar and superlaminar regimes. Following results can be obtained: (1) The disk floats at a certain stable position for given shaft rotational speed and rotates at nearly half rotational speed of the shaft. (2) The frictional torque of this type of the bearing is less than half of a conventional hydrostatic thrust bearing with the same surface configuration as the floating disk.
On Dynamic Gear Tooth Loading Due to Coupled Torsional-Lateral Vibrations in a Geared Rotor-Hydrodynamic Bearing System
Authors: Kishor B. , Gupta S. K.
Published: October 2009

This paper is an attempt to provide an estimation of dynamic gear tooth loading due to coupled torsional-lateral vibrations in a geared rotor-hydrodynamic bearing system. The effects of mass unbalance and geometrical eccentricity of the pinion and the combined effects of manufacturing errors and profile modifications of gear teeth have been considered. Gear mesh compliance and damping at gear teeth are also included in the analysis. Journal lateral motions in the oil film spaces of hydrodynamic bearings are shown to be associated with variations in the angular velocity ratio of meshing gears and with dynamic loading of gear teeth. The journal center is observed to trace trajectories of limited amplitudes under stable operating conditions.
Fully Developed Sliding of Rough Surfaces
Authors: Liu C. , Paul B.
Published: October 2009

Given the contact region between two bodies, the normal pressure distribution over the contact region, and the coefficient of friction, we seek to find all combinations of tangential forces and twisting moment (about the normal to the contact surface) for which fully developed sliding impends. As part of the solution we must determine the distribution of the surface tractions (shear stresses) and the location of the instantaneous center (IC) of the impending motion. New closed form solutions of the stated problem are found for circular contact patches with pressure distributions corresponding to (a): a flat stamp; and (b): elastic spheroids with Hertzian pressure distributions. For contact regions other than circular, no closed form solutions are known. We have developed numerical procedures to solve for arbitrary contact patches, with arbitrary distributions of normal pressure, and present carpet plots of tangential force components (Fx, Fy) and IC coordinates for the following cases: flat ellipsoidal stamps; ellipsoidal indenters (Hertzian pressure); and a non-Hertzian, nonelliptical contact of a rail and wheel. Level curves of twisting moment Mz versus tangential force components are provided. Given any two of the three quantities (Fx, Fy, Mz), the algorithms and the plots in this paper make it possible and convenient to find the remaining force or moment which will cause gross sliding to impend, for virtually arbitrary contact regions and arbitrary pressure distributions.
Solution of the Lubrication Problem and Calculation of the Friction Force on the Piston Rings
Authors: Miltsios G. K. , Patterson D. J. , Papanastasiou T. C.
Published: October 2009

The Finite Element (FEM) is applied to solve the governing equations of lubrication of the piston rings and to calculate the friction force on each ring. The ring is assumed to have a circular profile in the direction of motion. This profile changes with time because tilting of the ring with the engine cycle is taken into account. In the circumferential direction, the ring is assumed to be a perfect circle and the bore cross-section is assumed elliptic. Mixed lubrication is considered when the oil film thickness becomes smaller than a certain value which depends upon the roughness of the surfaces in contact. The friction coefficient for this lubrication is taken as a function of the oil film thickness and the surface roughness. The predictions of the friction force are compared with experimental friction data for the same engine.
An Efficient and Accurate Formulation of the Surface-Deflection Matrix in Elastohydrodynamic Point Contacts
Authors: Chang L.
Published: October 2009

This paper presents a new method for formulating the surface-deflection matrix in elastohydrodynamic point contacts. This method evaluates the integrand of the deflection integral at an integration point in each of the rectangular elements and thus avoids generating lengthy and complex mathematical expressions. The new method is shown to be significantly more efficient than the conventional methods of pressure interpolation. Furthermore, it yields accurate surface-deflection results with relatively few grid points.
Measurements of and Relation Between the Adhesion and Friction of Two Surfaces Separated by Molecularly Thin Liquid Films
Authors: Homola A. M. , Israelachvili J. N. , Gee M. L. , McGuiggan P. M.
Published: October 2009

A new technique is described for sliding (shearing) two molecularly smooth surfaces laterally past each other in liquids while monitoring their exact contact area, the normal and transverse forces, and the surface separation. First, we show that the elastic deformations of two initially curved surfaces in adhesive contact are the same under static and dynamic (i.e., sliding) conditions. Detailed results are then presented of how the shear properties of thin films of water and a simple nonpolar liquid are “quantized” with the number of layers. Results with water as the intervening liquid, as well as the effects of humidity on sliding in air, reveal that more complex mechanisms are operating than with simple liquids which appear to be related to the complex “hydration” forces between two surfaces in water or in aqueous salt solutions. The results suggest a close correlation between the static forces and shear properties of very thin liquid films, and the molecular structure of the liquids confined within such films.
Determination of Creep Force, Moment, and Work Distribution in Rolling Contact With Slip
Authors: Wang Bor-Tsuen , Fries Robert H.
Published: October 2009

Investigators interested in the wear of wheels and rails frequently use a wear model that postulates wear is proportional to the work done in the contact patch. Most investigators compute the work using the rigid body motions of the wheel and the total creepage at the contact patch. Such an approach gives an overall or integrated measure of the wear in the contact patch. In previous wheel/rail wear work, we have assumed the wear to be distributed parabolically across the contact patch. In order to check this assumption and to permit refinement of our wear modeling technique, we desired to know the distribution of work within the contact patch. In order to compute the work distribution within the contact patch, we must be able to compute the distributions of both the creep force and the creepage. This paper describes a method of computing lateral and longitudinal creep force and creep moment distributions within the contact patch for combined rolling and slip conditions. It also describes the computations of creep distributions within the contact patch. The work distribution is computed from the dot product of force and creepage. The method uses Kalker’s simplified theory to determine the force and creepage distributions. The actual computations are made using a modification of Kalker’s program FASTSIM. A by-product of the work is the determination of the adhesion and slip regions for arbitrary creepage conditions.
Induced Chromosomal Proximity and Gene Fusions in Prostate Cancer
Authors: Mani Ram-Shankar , Tomlins Scott A. , Callahan Kaitlin , Ghosh Aparna , Nyati Mukesh K. , Varambally Sooryanarayana , Palanisamy Nallasivam , Chinnaiyan Arul M.
Published: October 2009

Androgen signaling facilitates the formation of an oncogenic fusion gene in prostate cancer cells.
Clean the Air, Heat the Planet?
Authors: Arneth Almut , Unger Nadine , Kulmala Markku , Andreae Meinrat O.
Published: October 2009

Measures to control emissions of air pollutants may have unintended climatic consequences.
Hot, Flat, Crowded—And Preparing for the Worst
Authors: Inman Mason
Published: October 2009

In a clarion call to other developing nations, Bangladesh is girding itself against the hazards of a warmer world
Peptide Microarray-Based Identification of
Mycobacterium tuberculosis
Epitope Binding to HLA-DRB1*0101, DRB1*1501, and DRB1*0401
Authors: Gaseitsiwe Simani , Valentini Davide , Mahdavifar Shahnaz , Reilly Marie , Ehrnst Anneka , Maeurer Markus
Published: October 2009

A more effective vaccine against
Mycobacterium tuberculosis
is needed, and a number of
M. tuberculosis
vaccine candidates are currently in preclinical or clinical phase I and II studies. One of the strategies to select
M. tuberculosis
(protein) targets to elicit a CD8
+
or CD4
+
T-cell response is to gauge the binding of candidate peptides to major histocompatibility complex (MHC) class I or class II molecules, a prerequisite for successful peptide presentation and to expand antigen-specific T cells. We scanned 61 proteins from the
M. tuberculosis
proteome for potential MHC class II-presented epitopes that could serve as targets for CD4
+
T-cell responses. We constructed a peptide microarray consisting of 7,466 unique peptides derived from 61
M. tuberculosis
proteins. The peptides were 15-mers overlapping by 12 amino acids. Soluble recombinant DRB1*0101 (DR1), DRB1*1501 (DR2), and DRB1*0401 (DR4) monomers were used to gauge binding to individual peptide species. Out of 7,466 peptides, 1,282, 674, and 1,854 peptides formed stable complexes with HLA-DR1, -DR2, and -DR4, respectively. Five hundred forty-four peptides bound to all three MHC class II molecules, 609 bound to only two, and 756 bound to only a single MHC class II molecule. This allowed us to rank
M. tuberculosis
proteins by epitope density.
M. tuberculosis
proteins contained “hot spots,” i.e., regions with enriched MHC class II binding epitopes. Two hundred twenty-two peptides that formed MHC class II-peptide complexes had previously been described as exclusively recognized by IgG in sera from patients with active pulmonary tuberculosis, but not in sera from healthy individuals, suggesting that these peptides serve as B-cell and CD4
+
T-cell epitopes. This work helps to identify not only
M. tuberculosis
peptides with immunogenic potential, but also the most immunogenic proteins. This information is useful for vaccine design and the development of future tools to explore immune responses to
M. tuberculosis
.
Denmark14-230 Clone as an Increasing Cause of Pneumococcal Infection in Portugal within a Background of Diverse Serotype 19A Lineages
Authors: Aguiar Sandra I. , Pinto Francisco R. , Nunes Sónia , Serrano Isa , Melo-Cristino José , Sá-Leão Raquel , Ramirez Mário , de Lencastre Hermínia
Published: October 2009

Pneumococci of serotype 19A are increasingly found to be the cause of infection in various geographic regions. We have characterized the serotype 19A isolates (n= 288) found among pneumococci responsible for infections (n= 1,925) and pneumococci recovered from asymptomatic carriers (n= 1,973) in Portugal between 2001 and 2006. We show that despite the existence of serotype 19A clones that have a greater potential to cause invasive disease or an enhanced colonization capacity, the lineage that is increasing as a cause of infection in Portugal is a multiresistant clone that is competent at both. The expanding Denmark14-230 clone found in Portugal is disseminated in other Mediterranean countries, where it is also increasingly responsible for invasive infections in both children and adults. The lineages driving the rise of serotype 19A infections in Asia and the United States (sequence type 320 [ST320] and ST199) are either absent or account for only a small proportion of isolates in Portugal. These data highlight the importance of locally circulating clones with the ability to compete in the nasopharyngeal niche in the emergence of the serotype 19A lineages which are an increasing cause of infection in various geographic regions.