bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts
Authors: Salehizadeh H. , Saka N.
Published: June 2008

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.
Nonlinear Effects in a Plain Journal Bearing: Part 2—Results
Authors: Braun M. J. , Choy F. K. , Hu Y.
Published: June 2008

Part 1 of this paper presented a numerical model that coupled the variable property Reynolds equation with a rotor dynamics model for the calculation of the nonlinear characteristics of a plain journal bearing working with a cryogenic fluid (LO2). Part 2 will present the numerical results yielded by the model that used (a) lubricant inlet temperature, (b) external load, (c) angular rotational speed, and (d) axial misalignment as input variables for the parametric study. The resulting pressure profiles and linear and nonlinear characteristics of the bearing are discussed and their inter-relationship is analyzed.
Non-Newtonian Elastohydrodynamic Lubrication of Point Contact
Authors: Kim Kyung Hoon , Sadeghi Farshid
Published: June 2008

A numerical solution to the problem of isothermal non-Newtonian elastohydrodynamic lubrication of rolling/sliding point contacts has been obtained. The multigrid technique is used to solve the simultaneous system of two-dimensional modified Reynolds and elasticity equations. The effects of various loads, speeds, and slide to roll ratios on the pressure distribution, film thickness, and friction force have been investigated. Results for the dimensionless load W = 4.6 × 10−6 and 1.1 × 10−6, and the dimensionless velocity U = 3 × 10−10 and 3 × 10−11 are presented. The results indicate that slide to roll ratio has negligible effect on the minimum film thickness, however, it significantly reduces the pressure spike.
Numerical Simulation of the Overrolling of a Surface Feature in an EHL Line Contact
Authors: Venner C. H. , Lubrecht A. A. , ten Napel W. E.
Published: June 2008

In this paper a Multigrid extension of a stationary solver is outlined for the EHL solution of a line contact under transient conditions. The solver is applied to calculate pressure and film thickness profiles at each time step when an indentation is moving through the contact, which results in an asymmetric pressure profile. The time-dependent results are compared with the stationary solutions. The pressure as a function of time is presented as well as the integrated pressure (over time) as a function of the spatial coordinate. These time-dependent pressures are used to compute the sub-surface stress field, which shows higher stresses below the trailing edge of the indentation. Therefore the risk of fatigue is higher below the trailing edge of the indentation, as is experimentally observed. The transient pressures can be used for a fundamental study of the emitted frequency spectrum of rolling bearings, as used in condition monitoring.
Further Results on the Friction of Ploughing in the Presence of Bulk Straining
Authors: Azarkhin A. , Richmond O.
Published: June 2008

Algorithms developed by the authors in previous work (Azarkhin and Richmond, 1990; Azarkhin and Richmond, 1991) have been used here to model friction due to ploughing of rigid, adhesionless, fully embedded asperities through the surface of a material undergoing bulk plane strain deformation. It is shown that the mean frictional stress is influenced by the intensity of the subsurface deformation and by the size of the contacting area relative to asperity dimensions.
Shear Strength and Tribological Properties of Stearic Acid Films—Part II: On Gold-Coated Glass
Authors: Timsit R. S. , Pelow C. V.
Published: June 2008

This paper reports measurements of the shear strength of dry and lubricated Au/Au, Al/Au and glass/Au couples from measurements of the frictional force during sliding of a hemispherical pin in contact with a flat side. The Au and Al surfaces are generated by vacuum deposition of thin metal films on glass. Shear strength is measured at a sliding speed of 60 μm s−1 and at contact stresses ranging from ~ 0.05 to 0.8 GPa. Lubrication is achieved by depositing a stearic acid on the slide. The shear strength of dry glass/Au sliding interfaces is found to increase linearly with contact stress but decreases slightly with increasing thickness of the gold film. The shear strength of dry Au/Au interfaces is larger than that of dry glass/Au. Stearic acid does not protect gold from mechanical wear during sliding because the acid is expelled from the gold/gold interface, even at the lowest compressive stresses used. These observations are interpreted in terms of the weak adhesion of stearic acid to gold. In contrast, stearic acid sustains mechanical shear in interfaces consisting of gold sliding on either bare glass or aluminum, to which the acid adheres. These observations suggest that a boundary lubricant film protects against mechanical wear if it adheres only to one of the contacting surfaces.
Traction in Thermal Elastohydrodynamic Lubrication of Rough Surfaces
Authors: Chang L.
Published: June 2008

This paper studies the traction behavior of elastohydrodynamically lubricated line contacts between two rough surfaces. The study uses a thermal micro-elastohydrodynamic-lubrication (micro-EHL) model and obtains traction coefficients for a wide range of operating conditions and for film parameters as small as 1.50. The simulation results suggest that the traction is generally insensitive to the roughness structure and magnitude as long as the contact maintains a full EHL film. The results also indicate clearly that the lubricant squeeze induced by the motion and interaction of rough surfaces significantly affects the numerical solutions to thermal micro-elastohydrodynamic lubrication.
Time Dependent Line EHD Lubrication Using the Multigrid/Multilevel Technique
Authors: Osborn K. F. , Sadeghi F.
Published: June 2008

A numerical solution of time dependent compressible elastohydrodynamic lubrication of line contacts has been obtained. The results show the effects of various operating parameters on the transient response behavior of a lubricated contact. The analysis models a startup situation where the surfaces are initially at rest and in contact. Then, with the contacts operating at a given load and speed, the analysis is run until the pressure and film thickness reach a steady-state condition. A multigrid/multilevel technique is used to simultaneously solve the time dependent Reynolds and elasticity equations. The effects of various loads and speeds have been investigated. Results are presented for nondimensional loads ranging from W = 2.0 × 10−5 to W = 2.3 × 10−4 and nondimensional speeds ranging from U = 1.0 × 10−12 to U = 1.0 × 10−10.
Simplified Contact Fatigue Life Prediction Model—Part II: New Model
Authors: Tallian T. E.
Published: June 2008

Part I of this two-part paper reviews eleven published models as a basis for the construction of a simplified, readily calculated engineering model encompassing the major life variables, based on explicit assumptions and derivations. Part II of the paper presents the new model. It uses the applied alternating shear stress field to define the critical stress as a function of depth, and computes life as crack propagation time through this field. The model defines surface defects as critical defects. Material fatigue susceptibility, fatigue limit stress and the defect severity distribution are the main endurance parameters. In addition to Hertz pressure, life-modifying variables are: interface traction, surface microgeometry and EHD film. The influence of the variables in the new model on life distribution and on load/life law are compared to the reviewed models and it is shown that the new model is capable of representing the influence of all major consensus parameters on life, by relationships that fall within the bounds of previously published behavior.
A Scanning Electron Microscope With Two Secondary Electron Detectors and Its Application to the Surface Topography Measurements of Magnetic Media
Authors: Tanaka K. , Nishimori K. , Maeda K. , Matsuda J. , Hotta M.
Published: June 2008

A scanning electron microscope (SEM) with two secondary electron detectors is applied for the surface topography measurement of magnetic media. The principle of gradient determination of the SEM is based on a relation that the difference in the square signals between the two detectors is linearly proportional to surface gradient. The great advantage of the instrument is the capability of relocation for profiling. It is extremely useful for the examination of wear process at a fixed position in a sequential manner during wear testing. This is demonstrated by two sample data of measurement on thin film rigid disks.
Formation of Lubricant Film in Rotary Sealing Contacts: Part I—Lubricant Film Modeling
Authors: Gabelli A. , Poll G.
Published: June 2008

The lubricant film developed in rotary lip seals is a vital element in achieving long-lasting seals with low friction. In this paper the basic principles controlling the development of a lubricant film in lip seals are studied using a micro-hydrodynamic model. This model takes into account the visco-elastic effects of the rubber on the development of the sealing pressure. Central to the model’s hypothesis is the assumption of the predominant action of the surface micro-geometry in the formation of the lubricant film. Optical observations of the contact area of a lip seal, using blue light induced fluorescence, supported this concept. Using this basic lubrication model, the minimum and average film thickness and shear stress are calculated for different loading conditions, material stiffnesses and statistical parameters characterizing the micro-geometry of the sealing surfaces. In the model the effect of the viscoelastic properties of the rubber on the dynamic response of the seal and resulting pressure is also considered. To support the predictions of the theory, a new experimental method for the determination of the film thickness in elastomeric contacts is applied. Comparison between experimental and theoretical results indicates the ability of the model to deal with effects previously excluded from the analysis. The correlation between measured film thicknesses and thicknesses predicted using the present model was found to be good for the full range of speeds tested.
A Numerical Model for the Contact of Layered Elastic Bodies With Real Rough Surfaces
Authors: Cole S. J. , Sayles R. S.
Published: June 2008

A numerical model for the two-dimensional dry, frictionless contact of two elastic bodies with real rough surfaces, where one body has a rigidly bonded surface layer, is presented. The model uses surface profile data directly recorded with a stylus measuring instrument and is suitable for use on a microcomputer. Verification of the accuracy of the model by reproduction of test case results is presented. Contact pressure distributions for layers of varying thickness and elastic modulus are presented.
The Mechanics of Crack Initiation at Hard Particles in Rolling Line Contacts
Authors: Salehizadeh H. , Saka N.
Published: June 2008

The mechanics of crack initiation in rolling contact bearings is investigated by considering the possibility of hard particle debonding from the surrounding softer matrix. The local elastoplastic stress and strain fields around a hard cylindrical particle located at the point of maximum shear stress below the Hertz contact are calculated by the finite element method. The calculations show that if the applied Hertz loading is sufficiently high, the matrix contiguous with the particle deforms plastically. Upon unloading tensile residual stresses will be set up normal to the particle-matrix interface. The particle-matrix interface debonds provided the stored elastic energy in and around the particle is larger than the work of adhesion, and the maximum residual radial stress is greater than the cohesive strength of the particle-matrix interface. The gradual softening of the martensitic matrix around non-metallic inclusions or carbides, which is known to occur after a large number of stress cycles in bearing steels, could result in a residual radial stress greater than the interfacial strength and cause particle-matrix debonding.
A Linear Theory of Vibrations Caused by Ball Bearings With Form Errors Operating at Moderate Speed
Authors: Yhland E.
Published: June 2008

A linear theoretical model is presented for the vibrations of a shaft bearing system caused by ball bearing geometrical imperfections. It is valid for low and medium speeds where ball centrifugal forces can be neglected. The excitation forces from each bearing are calculated and can serve as input to suitable rotor dynamics programs. Imperfections covered are radial and axial waviness of outer and inner rings, ball waviness and diameter distribution, nonuniform cage pocket distribution.
Simulation of Elastohydrodynamic Contacts Between Rough Surfaces
Authors: Kweh C. C. , Patching M. J. , Evans H. P. , Snidle R. W.
Published: June 2008

The paper describes the results of an elastohydrodynamic lubrication (EHL) analysis of an elliptical contact between a rough, stationary surface and a smooth, moving surface. The roughness consists of two-dimensional grooves/ridges aligned in a direction perpendicular to that of lubricant entrainment, and is sinusoidal in profile with two scales of wavelength and amplitude. The main feature of these results is the significant degree of asperity deformation and corresponding ripple in the pressure distribution. Also presented are preliminary results of a line contact EHL analysis in which profiles from real surfaces are used to simulate the lubrication of gear teeth at high temperatures. These results show significantly less proportional reduction of roughness due to asperity deformation.
Evaluation of Ultra-Low-Speed Jitter in Rolling Balls
Authors: Lovell M. R. , Khonsari M. M. , Marangoni R. D.
Published: June 2008

The frictional resistance generated by a ball bearing, when starting from rest, increases to a free rolling value in a finite amount of time instead of experiencing an instantaneous step increase. This is due to the complex ball dynamics involved. A change in the direction of rotation results in a reversal of the bearings dynamic torque characteristics. When a traversing process is continuously repeated, the friction torque of the bearing traces out hysteresis loops. This phenomenon is often described as ball jitter. An apparatus was built to study the ultra-low-speed hysteresis behavior found in jittering ball bearings. This behavior was first modeled by P. R. Dahl (1968). He found torque hysteresis loops to be characterized by the steady rolling friction torque, Ts, and the reversal torque slope, σ. A theoretical expression for Ts has been verified in previous research by Lovell et al. (1991), but no expression for σ has currently been determined at low speeds. Therefore, the experimental testing apparatus was canonically designed to incorporate three balls, rather than a full bearing. This was done in order that the characteristics of σ could be more readily determined, as many additional friction elements which occur in full bearings were eliminated. The effects of normal load, rotational rate, and lubrication regime on σ were all investigated using the testing apparatus. The experimental values obtained for the rest slope were coupled with previously determined values of Ts, so that empirical Dahl hysteresis curves could be generated. Excellent correlation was found to exist between the experimental jitter torque data and Dahl predicted dynamic torque behavior.
Analysis of Non-Newtonian Effects in Dynamically Loaded Finite Journal Bearings Including Mass Conserving Cavitation
Authors: Paranjpe R. S.
Published: June 2008

Non-Newtonian effects of multigrade engine oils in dynamically loaded crankshaft bearings are analyzed. The main focus of this work is on the shear-thinning effect. Viscoelastic effects are also considered over a limited range of the relaxation time. It has been shown that the same generalized Reynolds equation used in the Thermohydrodynamic (THD) analysis can be used for analyzing the shear-thinning effects as well. Consequently the shear thinning effect and the THD effect can be treated together. A mass conserving cavitation algorithm developed earlier for doing the THD analysis is used to solve the generalized Reynolds equation. Non-Newtonian shear-thinning significantly affects the power loss, film thickness, and oil flow of a multigrade oil as compared with a Newtonian oil. Over the range of relaxation times considered, no viscoelastic effects were discernible for crankshaft bearings lubricated with multigrade oils.
Tooth Thickness Effect on the Performance of Gas Labyrinth Seals
Authors: Rhode D. L. , Hibbs R. I.
Published: June 2008

A previously validated finite difference computer code was revised to allow the specification of upstream and downstream reservoir conditions as boundary conditions, whereas the domain extends only from the seal inlet to outlet plane. As a result of this special revision, the required execution CPU time is approximately only one hour on a VAX 8650 computer for three-cavity, straight-through seals. A parametric study focusing on tooth thickness showed that streamwise swirl development was only slightly higher for the thickest tooth. Further, for straight-through seals it was found that leakage is almost independent of tooth thickness and that the second cavity yields a definite increase in turbulence energy and turbulence length scale over the first cavity.
A Numerical Analysis for Piston Skirts in Mixed Lubrication: Part II—Deformation Considerations
Authors: Zhu Dong , Hu Yuan-Zhong , Cheng Herbert S. , Arai Takayuki , Hamai Kyugo
Published: June 2008

This paper presents a mathematical model for piston skirts in mixed lubrication. It takes into account the effects of surface waviness, roughness, piston skirt surface profile, bulk elastic deformation and thermal distortion of both piston skirts and cylinder bore on piston motion, lubrication and friction. The corresponding computer program developed can be used to calculate the entire piston trajectory and the hydrodynamic and contact friction forces as functions of crank angle under engine running conditions. Complete distributions of the oil film thickness and elastic deformation as well as the hydrodynamic and contact pressures can also be given at any crank angle if needed. This paper is the second part of a series of two papers. The first part (Basic Modeling), presented earlier by Zhu et al. (1991), gave the basic formulation and some preliminary results without bulk deformation considerations. In the present part, the three-dimensional finite element method is used to calculate so-called influence coefficient matrices. These matrices are repeatedly used to compute bulk elastic deformations of piston skirts. Results for 12 different cases are presented, and discussions are given focusing on the influences of elastic and thermal deformations on piston motion, lubrication and friction. An attempt to compare the calculated friction with experimental data is made, and agreement appears good for the two available cases. The computer program presented should be a useful tool for piston design and development.
Analysis of Lubrication Theory for the Power Law Fluid
Authors: Johnson M. W. , Mangkoesoebroto S.
Published: June 2008

A lubrication theory for the power law fluid is developed and analyzed. Only the infinite width gap is considered. Considered is flow between rigid walls of arbitrary shape under combined Couette and squeezing motion with a pressure gradient. Equations appropriate to a thin film are derived by asymptotic integration of the three-dimensional equations of fluid mechanics. Further integration of these equations yields an algebraic equation for the pressure gradient. Working out the details of the structure of this equation enables us to develop a numerical algorithm for its solution. To illustrate the theory, it is used to calculate the pressure distribution for a parabolic slider bearing and the pressure gradient and velocity distribution when the mass flux is prescribed. The latter results are compared with results obtained earlier by Dien and Elrod (1983).
A New Method for the Numerical Solution of the Reynolds Equation at Low Spacing
Authors: Zheming Zhao , Wenkang Shi
Published: June 2008

In this paper, an implicit scheme, based on the Patankar-Spalding method which is commonly utilized in numerical heat transfer and fluid flow problems, is developed for the numerical solution of the compressible Reynolds equation. The method has eliminated the numerical instability in pressure distribution in the high bearing number region. Some of the difficulties encountered by the different discretization approach when applied to slider geometries that have a discontinuous clearance slope, such as the tapered-flat slider, can be easily handled. Numerical results are presented and discussed.
Simulation and Identification of Nonstationary Heat Transfer in a Nonuniform Friction Contact
Authors: Bogatin O. , Chersky I. , Starostin N.
Published: June 2008

The results of numerical simulation of nonstationary thermal fields in cylindrical friction junctions are presented. On the basis of the marching method, a numerical algorithm which imposes no restrictions on the value of heat flow separation coefficient is constructed. Simulation results are given for different bearing designs both for the two and three-dimensional cases. Using the developed algorithm as a base, a method allowing for reconstruction of heat release and, hence, friction moment values from temperature measurements in the stationary unit element is suggested. Reliability of the results is proved by experiments.
Angular-Compliant Hydrodynamic Bearing Performance Under Dynamic Loads
Authors: Harnoy A. , Rachoor H.
Published: June 2008

The study is focused on a dynamically loaded composite bearing, consisting of a hydrodynamic journal bearing inside the internal race of a rolling-element bearing. In this combination, the hydrodynamic bearing has an angular-compliant sleeve with a restricted freedom of rotation around its axis. Under static loads, the improvement is primarily in a significant reduction of friction and wear during the starting and stopping. Under periodical loads, our analysis shows that the performance depends on two dimensionless design parameters. Below particular critical values of these parameters, the results show a considerable improvement, demonstrated by a reduction of the maximum eccentricity. However, above the critical values, the bearing becomes unstable. These results indicate the significance of incorporating this computer assisted computation for each design.
Compliant Foil Bearing Structural Stiffness Analysis—Part II: Experimental Investigation
Authors: Ku C.-P. Roger , Heshmat Hooshang
Published: June 2008

This paper describes the second part of an investigation into the mechanism of deformation of the corrugated foil (bump foil) strips used in compliant surface foil bearings. In the earlier work, a theoretical model was developed to predict the structural characteristics of bump foil strips under various loads, including the effects of the friction forces between the compliant elements, local interaction forces, load distribution profiles, and bump configurations. In the experiments described here in, two-dimensional deflections of bump foils were recorded via an optical tracking system for a wide range of operating conditions to verify the feasibility of the theoretical model. Test results corroborate the theoretical model for the linear regions of load and the deflection parameters. The effects of the bearing design parameters, such as bump configuration, load profile, and surface coating and lubricant, on the structural characteristics of the bump foil strip were investigated. In addition, the source and mechanism of nonlinear behavior of the bump foil strips under light load conditions were examined, and more effective methods of achieving both Coulomb damping and optimum structural compliance were investigated. An understanding of the analytical and semi-empirical relations resulting from this work offers designers the potential for enhancing the design of high-performance compliant foil bearings.
Contact Surface Temperature Models for Finite Bodies in Dry and Boundary Lubricated Sliding
Authors: Tian Xuefeng , Kennedy Francis E.
Published: June 2008

A model is proposed for use in determining the contact surface temperature in dry and boundary lubricated sliding systems. The model uses the concepts of small scale and large scale heat flow restrictions to divide the temperature increase in a sliding contact into two contributions, a nominal surface temperature rise and a local temperature rise. The model is particularly useful in studying the sliding surface temperature in bodies of finite thickness and in cases when the sliding contact area repeatedly sweeps over the same path on one of the contacting solids. Multiple heat sources within the real area of contact can be included, as can the effects of a cooling and/or lubricating fluid. Experiments were carried out to measure the contact surface temperature rise in several dry and boundary lubricated sliding systems. The experimental results were found to agree with the model.
Wildhaber-Novikov Circular Arc Gears: Elastohydrodynamics
Authors: Evans H. P. , Snidle R. W.
Published: June 2008

The paper describes an elastohydrodynamic lubrication (EHL) analysis of heavily loaded contacts between the teeth of Wildhaber-Novikov (W-N) circular arc gears. The contacts occurring in gears of this type are elliptical in shape with lubricant entrainment in the direction of the major axis of the contact. The results shown refer to a particular practical design and cover a range of operating conditions encountered in practice. Because of the high rolling velocity in W-N gears a relatively thick oil film is predicted over most of the contact. Severe thinning of the film occurs at the sides of the contact, however. Results of the full EHL analysis are compared with predictions using a published film thickness formula based upon analysis of moderately loaded elliptical contacts. It is suggested that the side-thinning effect is dependent upon the relative elastic deformation occurring in the contact.
Lubricating Grease Replenishment in an Elastohydrodynamic Point Contact
Authors: A˚stro¨m Henrik , O¨stensen Jan Ove , Ho¨glund Erik
Published: June 2008

A ball and disk apparatus was used to investigate the lubricant replenishment of an elastohydrodynamically lubricated point contact. This replenishment of the contact is crucial for building up a lubricating film. Whereas lubricating oil manages to achieve replenishment, lubricating grease appears not to achieve this, with lubricant starvation and a dramatic decrease in film thickness as a result. The distribution of grease around the contact was studied using normal and high-speed video. The movements of grease in the vicinity of the contact could be seen by adding molybdenum disulfide particles to the grease. A recording was then made, using highspeed video recording. The overall cavitation regions were studied using an ordinary video camera and grease without particles. On the basis of the results, possible lubricating grease replenishment mechanisms are discussed. The resulting film thickness was also compared with theoretical predictions using the Hamrock and Dowson starvation criterion, assuming negligible replenishment. The measured film thickness was larger than the predicted, which indicated that some replenishment occurs. In the case of an ordinary thrust ball bearing, replenishment was found to rely on the spin motion of the balls.
Frictionally Excited Thermoelastic Instability in Automotive Disk Brakes
Authors: Lee Kwangjin , Barber J. R.
Published: June 2008

Thermoelastic instability in automotive disk brake systems is investigated focusing on the effect of a finite disk thickness. A finite layer model with an antisymmetric mode of deformation can estimate the onset of instability observed in actual disk brake systems. Also some effects of system parameters on stability are found to agree well to experimental observations.
The Stress Field Induced by a General Elliptical Hertzian Contact
Authors: Sackfield A. , Hills D. A. , Nowell D.
Published: June 2008

Simple, concise formulas are given for the components of stress induced by a general elliptical Hertzian contact in terms of elementary functions. Explicit, readily evaluated formulas are given.
A Convex Decomposition Using Convex Hulls and Local Cause of Its Non-Convergence
Authors: Kim Yong Se , Wilde D. J.
Published: June 2008

To exploit convexity, a non-convex object can be represented by a boolean combination of convex components. A convex decomposition method of polyhedral objects uses convex hulls and set difference operations. This decomposition, however, may not converge. In this article, we formalize this decomposition method and find local cause of non-convergence.
Couette Dominance Used for Non-Newtonian Elastohydrodynamic Lubrication
Authors: Myllerup C. M. , Elsharkawy A. A. , Hamrock B. J.
Published: June 2008

The perturbational approach that assumes Couette dominance in non-Newtonian elastohydrodynamic lubrication analysis is discussed. The assumption is found valid for non-Newtonian fluid models exhibiting Newtonian properties at low shear strain rate. A general non-Newtonian fluid model which meets that requirement is incorporated into elastohydrodynamic lubrication analysis of line contacts by using the perturbational approach. In the case of a circular fluid model the results obtained from the perturbational approach are in good agreement with those obtained from the direct approach. However, a better convergence and the possibility of avoiding using stress boundary conditions at high shear stress can be achieved by using the perturbational approach. Results are presented for various values of the shape exponent in the general model, and it transpires that this also is an important parameter of the fluid model.
Molecular Dynamics Investigation of Two-Dimensional Atomic-Scale Friction
Authors: Kim D. E. , Suh N. P.
Published: June 2008

Molecular dynamics (MD) simulation studies of two-dimensional atomic-scale frictional force are presented. The motivation for this work is to gain insight into the effects of interatomic forces on the frictional phenomena. Instantaneous friction coefficients are calculated for an atom scanning across the surface of a two-dimensional Lennard-Jones type crystal in both static and dynamic modes. It is found that net frictional force can arise even in the absence of adhesive interaction between the scanning atom and the substrate. Furthermore, in the case of nondestructive sliding the frictional interaction leads to increase in the substrate temperature which can be calculated.
Differential Quadrature Solutions for Steady-State Incompressible and Compressible Lubrication Problems
Authors: Malik M. , Bert C. W.
Published: June 2008

This paper presents the very first application of the differential quadrature method to the solution of steady-state incompressible and compressible lubrication problems. It is shown that the differential quadrature method is a numerically accurate and computationally efficient technique which can compete against existing methods in use for the solution of lubrication problems.
Annular Honeycomb-Stator Turbulent Gas Seal Analysis Using a New Friction-Factor Model Based on Flat Plate Tests
Authors: Ha T. W. , Childs D. W.
Published: June 2008

A new empirical friction-factor model for honeycomb surfaces based on flat plate test results has been developed as a function of Mach number and dimensionless pressure and honeycomb geometry variables. A rotordynamic analysis for centered, turbulent-annular-honeycomb-stator seals has been developed incorporating the new empirical friction-factor model for honeycomb-stator surfaces. The results of the new analysis in predicting the rotordynamic and leakage characteristics have been compared to: (a) Moody’s friction-factor model analysis, and (b) experimental data for short (L/D = 1/6, 25.4 mm long) seal. The comparisons show that the new honeycomb friction-factor model greatly improves the predictions of leakage and rotordynamic coefficients compared to Moody’s friction-factor model, especially, for direct and cross-coupled stiffness.
Adiabatic Shear Localization in a Liquid Lubricant Under Pressure
Authors: Bair Scott , Qureshi Farrukh , Khonsari Michael
Published: June 2008

Experimental tests with a high-pressure flow visualization cell clearly reveal that the shear deformation in a lubricant film at elevated pressures can localize by a mechanism vastly different from previously reported mechanically-induced shear bands. Verification by numerical solution of the energy equation shows that for a stress-controlled experiment, provided that the Brinkman number is sufficiently large, the local temperature experiences a rapid rise. The rapid rise of temperature along with the local rate of shear favors an unstable temperature profile. The research provides valuable insight into the behavior of lubricants under extreme conditions since this phenomenon may be operating in the thermally dominated regime of EHD traction. Furthermore, the fact that the hot shear band is isolated from the metal boundaries by a cooler liquid, may confound recent attempts to infer the shear stress distribution in a concentrated contact from IR temperature measurement of the metal temperature distribution.
An Investigation of the Characteristics of Electromagnetic Bearings Using the Finite Element Method
Authors: Hsiao Foam-Zone , Lee An-Chen
Published: June 2008

The load capacity of EMBs with a restricted air gap is usually small in comparison with that of traditional ball bearings. One possible way to overcome this limitation is to increase the operation field strength of EMBs; however, this approach unavoidably involves nonlinear characteristics of EMBs. This paper investigates the nonlinear behavior of two commonly used types of EMBs by using the finite element method, in which the nonlinear relation of the B-H curve, the flux leakage, and the fringing effect are taken into account. The behavior of the EMBs under different bias currents and gap lengths is investigated, as are the effects of geometric parameters on the bearing characteristics. The results of the paper provide a useful guide for designing EMBs when using their nonlinear characteristics.
A Model of Piston Secondary Motion and Elastohydrodynamic Skirt Lubrication
Authors: Dursunkaya Zafer , Keribar Rifat , Ganapathy Venkatesh
Published: June 2008

A model of elastohydrodynamic lubrication of piston skirts in reciprocating engines was developed in the context of a simulation of piston secondary motions. The piston secondary dynamics, skirt lubrication and skirt elastic deformation problems are simultaneously solved in the calculation. The model can represent both conventional and two-piece articulated pistons and also includes a treatment of wristpin lubrication. Skirt deformations are calculated using a skirt compliance matrix derived from a finite element model of the piston. The model was exercised by calculating piston secondary motions and skirt deformations for a heavy-duty truck diesel piston at various operating conditions. Results show that peak skirt radial deformations can exceed the skirt-liner radial clearance and strongly depend on load. Articulated piston skirt deformations were shown to be significantly larger than those in conventional piston skirts. Consideration of skirt elastic deformations significantly affected (rigid piston) motion and skirt friction predictions, highlighting the importance of an elastohydrodynamic model.
Experimental Evaluation of Sector-Shaped Hydrodynamic Thrust Bearings Under Translation and Transverse Vibration
Authors: Wang Y. K. , Mote C. D.
Published: June 2008

The bearing load of a plane inclined sector-shaped hydrodynamic thrust bearing, under simultaneous translation and transverse vibration, is measured experimentally. The results are used to evaluate the lubrication theory solutions. Consequently, both the influences of the unsteady film inertia, measured by the squeeze Reynolds number Res, and the convective film inertia, measured by the modified Reynolds number Re*, on load amplitude and phase are investigated. It is found that the inertia-neglected lubrication solutions underestimate: (1) the oscillatory component of the bearing load by 6.5 percent at Res = 1.0 and by 1.4 percent at Re* = 1.0, and (2) the mean component of the bearing load by 0.7 percent at Res = 1.0 and by 2.0 percent at Re* = 1.0 Moreover, the fluid inertia induces an equivalent negative spring force component which shifts the phase of the bearing load by 9.5 deg at Res =1.0 and by 4 deg at Re* = 1.0 as compared to the lubrication theory predictions. Hence it can be an important consideration when designing bearings for vibration control purposes.
Inertia and Shear-Thinning Effects on Bearing Behavior With Impulsive Loads
Authors: Bou-Sai¨d Benyebka , Ehret Pascal
Published: June 2008

The study of bearings subjected to impulsive loads have previously showed that inertia effects and surface accelerations play an important role in the bearing response. Although the lubricant was considered Newtonian, this assumption is no longer valid with modern lubricant. In industrial applications, mineral lubricants are added to several long soluble chains of polymer in order to conserve optimum properties under different operating conditions. The addition of these polymers results in the drop of viscosity under high shear-rate, in the range of 10−6–10−8s−1. This study presents a continuation of previous works. It examines the influence of both effects, the decrease in viscosity and the fluid inertia, in a journal bearing under impulsive loads. Using the power-law model, the results show important differences in shaft responses compared to the Newtonian cases. Furthermore, in high shear-thinning effects, a reduction of lubricant capacity to absorb sudden dynamic loads is observed.
Full Film Lubrication of Strip Rolling
Authors: Sa Chung-Yeh , Wilson William R. D.
Published: June 2008

A mathematical model for liquid lubricated strip rolling in the full-film regime is developed. The model combines slab plasticity, hydrodynamic lubrication and thermal analyses to relate local and global condition to process variables and material properties. The predictions of the model are compared with experimental measurements of outlet speed ratio, roll separating force and roll torque in rolling 1100-H14 aluminum with a viscous mineral oil and 5P4E polyphenyl ether as lubricants. The excellent agreement which is obtained provides powerful support of the validity of the model.
An Analytical Approach to Elastic-Plastic Stress Analysis of Rolling Contact
Authors: Jiang Yanyao , Sehitoglu Huseyin
Published: June 2008

Based on a stress invariant hypothesis and a stress/strain relaxation procedure, an analytical approach is forwarded for approximate determination of residual stresses and strain accumulation in elastic-plastic stress analysis of rolling contact. For line rolling contact problems, the proposed method produces residual stress distributions in favorable agreement with the existing finite element findings. It constitutes a significant improvement over the Merwin-Johnson and the McDowell-Moyar methods established earlier. The proposed approach is employed to study combined rolling and sliding for selected materials, with special attention devoted to 1070 steel behavior. Normal load determines the subsurface residual stresses and the size of the subsurface plastic zone. On the other hand, the influence of tangential force penetrates to a depth of 0.3a, where a is the half width of the contact area, and has diminishing influence on the residual stresses beyond this thin layer. A two-surface plasticity model, commensurate with nonlinear kinematic hardening, is utilized in solution of incremental surface displacements with repeated rolling. It is demonstrated that a driven wheel undergoes greater plastic deformation than the driving wheel, suggesting that the driven wheel experiences enhanced fatigue damage. Furthermore, the calculated residual stresses are compared with the existing experimental data from the literature with exceptional agreements.
A Finite Length Plain Journal Bearing Theory
Authors: Capone G. , D’Agostino V. , Guida D.
Published: June 2008

This paper describes a theory for the approximated analytical determination of pressure distribution in the gap of a generic finite length journal bearing in isothermal laminar lubrication conditions as the position assumed by the journal axis varies in a reference frame fixed in the bearing. The same theory is used to set up lubricated finite length journal bearing models in order to obtain an analytical description of the fluid film force, which is characterized by considerable prediction accuracy in the whole field defining the length-diameter ratio. In order to assess the model’s prediction accuracy, the static characteristics of the journal bearing are analytically determined. The theoretical results, presented in the form of diagrams, are compared with the corresponding results obtained numerically.
Maintenance of Brine Transparency in Salinity Gradient Solar Ponds
Authors: Hull J. R.
Published: June 2008

Experience with maintenance of brine transparency during the more than eight years of operation of the 1000 m2 Research Salinity Gradient Solar Pond (RSGSP) at Argonne National Laboratory suggests that, in many sodium chloride brines, algal growth may be readily curtailed by minimizing the phosphate content of the brine. The addition of modest amounts of aluminum sulfate (<5 g m−2 yr−1) to precipitate soluble phosphate in the RSGSP has resulted in a reduction of the amount of chlorine used from 13 g m−2 yr−1 to 2.8 g m−2 yr−1, while still maintaining good transparency in the pond brine.
Heat Transfer to Unfrosted Wind Convectors: Mathematical Modeling and Comparison With Experimental Results
Authors: Finn D. P. , Monaghan P. F. , Oosthuizen P. H.
Published: June 2008

Wind convectors are an alternative air source evaporator system for heat pumps. This paper describes a mathematical model that calculates the heat transfer to wind convectors when forced convection conditions prevail and when wind convector surface frost and rainfall are absent. The mathematical model is validated and predicts heat transfer to within 8 percent of experimental data based on a root mean square difference estimation. Further simulation studies show that heat transfer to wind convectors is dominated by sensible convection and latent heat transfer, that longwave radiation contributes less than 5 percent of total heat transfer and that solar radiation can contribute up to 25 percent of total heat transfer under optimum conditions.
Prediction of Stochastic Blade Responses Using Measured Wind-Speed Data as Input to the Flap Code
Authors: Wright A. D. , Thresher R. W.
Published: June 2008

Accurately predicting wind turbine blade loads and response is important in predicting the fatigue life of wind turbines. The necessity of including turbulent wind effects in structural dynamics models has long been recognized. At SERI, the structural dynamics model, or FLAP (Force and Loads Analysis Program), is being modified to include turbulent wind fluctuations in predicting rotor blade forces and moments. The objective of this paper is to show FLAP code predictions compared to measured blade loads using actual anemometer array data and a curve-fitting routine to form series expansion coefficients as the turbulence input to FLAP. The predictions are performed for a three-bladed upwind field test turbine. An array of nine anemometers was located 0.8 rotor diameters (D) upwind of the turbine, and data from each anemometer are used in a least-squares curve-fitting routine to obtain a series expansion of the turbulence field over the rotor disk. Three 10-min data cases are used to compare FLAP predictions to measured results. Each case represents a different mean wind speed and turbulence intensity. The time series of coefficients in the expansion of the turbulent velocity field are input to the FLAP code. Time series of predicted flap-bending moments at two blade radial stations are obtained, and power spectra of the predictions are then compared to power spectra of the measured blade bending moments. Conclusions are then drawn about the FLAP code’s ability to predict the blade loads for these three data cases. Recommendations for future work are also made.
Buckling and Postbuckling of Electroconducting Elastic Plates in a Magnetic Field
Authors: Hasanyan Davresh , Librescu Liviu , Ambur Damodar R.
Published: June 2008

The basic equations of a fully nonlinear theory of electromagnetically conducting flat plates carrying an electric current and exposed to a magnetic field of arbitrary orientation are summarized. The relevant equations have been obtained by considering that both the elastic and electromagnetic media are homogeneous and isotropic. The geometrical nonlinearities are considered in the von-Ka´rma´n sense, and the soft ferromagnetic material of the plate is assumed to feature negligible hysteretic losses. Based on the electromagnetic and elastokinetic field equations, by using the standard averaging methods, the 3-D coupled problem is reduced to an equivalent 2-D one, appropriate to the theory of plates. Having in view that the elastic structures carrying an electric current are prone to buckling, by using the presently developed theory, the associated problems of buckling and post-buckling are investigated. In this context, the problem of the electrical current inducing the buckling instability of the plate, and its influence on the postbuckling behavior are analyzed. In the same context, the problem of the natural-frequencies electrical current interaction of flat plates, as influenced by a magnetic field is also addressed.