bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Approach to Finite Journal Bearings Lubricated With Ferrofluid
Authors: Sorge Francesco
Published: October 2009

Several cases of cylindrical bearings lubricated with ferrofluid are examined by means of a finite-difference numerical procedure. The subregion of cavitation is determined by imposing mass conservation across the “rupture” and “reformation” boundaries of the complete film. The examined cases refer to bearings confined by sealing rings formed by the lubricant itself, for which there is no need of external supply. In each case the most significant parameters are calculated and it is possible to see that the use of these bearings is favorable when speeds are low, clearances large, and loads light, because in such conditions the magnetic effects are comparable with the pure hydrodynamic ones and the load capacity results appreciably higher.
Corrosive Wear of Cast Iron in Sulphuric Acid
Authors: Yahagi Y. , Mizutani Y.
Published: October 2009

The wear rate of cast iron and the corrosion potential (Ecorr) and current (Icorr) were measured in sulphuric acid in order to study the mechanism of corrosive wear of cast iron. The corrosive wear rate of cast iron was found to reach a maximum at around 35 wt. percent sulphuric acid concentration and increase with load and acid temperature. The increment of corrosion current, i.e., the dissolution rate of Fe ion, due to friction (ΔIcorr) was found to correlate with the corrosive wear of cast iron. It has been concluded that the combined action of the changed properties and profile of corroded rubbing surfaces and the mechanical destruction due to wear causes the drastic corrosive wear, which is much greater than the wear seen with either one alone.
Relating Profile Instrument Measurements to the Functional Performance of Rough Surfaces
Authors: McCool J. I.
Published: October 2009

An easily programmed method is proposed for translating the rms height (Rq) and rms slope (Δq) determined using a profile measuring instrument, into more readily interpreted measures of functional severity such as the density of plastic contacts or the mean real contact pressure. The method involves estimation from the ratio Rq/Δq, of the exponent k of an assumed power function relation between the profile spectrum and the spatial frequency. Having estimated k, the mean square curvature is computed analytically and used together with Rq and Δq to determine the three input variables needed for the Greenwood-Williamson (GW) microcontact model. The GW model is then used to compute, as a function of the separation of two rough surfaces, the contact density, the plastic contact density, the mean load per unit area and the mean load per unit of real contact area. The mean square curvature estimated in this manner is compared to the directly measured mean square curvature for 12 distinct surface types. The values compared quite favorably (within 25 percent) for three of the specimens which included a bearing ball and the ground inner ring rolling path of a cylindrical roller bearing. The discrepancies exceeded a factor of 3 for three other specimens. The microcontact model output computed using both measured and estimated mean square curvature values showed that some output variables, e.g., plastic contact density, are more discrepant than the estimated and measured curvature values. Other output variables of the microcontact model, in particular, the mean real pressure, attenuate the discrepancies. The mean real pressures computed using the calculated and measured curvatures, were within 30 percent for all but three specimens. The maximum discrepancy observed was 55 percent. The results are sufficiently encouraging and the methodology so easy to apply, to commend the practice of routinely supplementing profile measurement data with microcontact model output.
Effect of a Rough Translating Surface on Gas Film Lubrication: A Numerical and Analytical Study
Authors: White J. W. , Raad P. E.
Published: October 2009

A thin gas film wide wedge bearing with rough translating surface is studied both numerically and analytically. The fluctuating inlet flow area causes a symmetric wave to be generated from the inlet boundary which travels at half the translating surface velocity, possesses a wavelength half that of the surface roughness, and which decays in amplitude in the direction of motion. Since the wave is out of phase with the surface roughness, it has essentially no influence on the load. The load generated varies monotonically with gas bearing number and at a finite bearing number is less than the load developed with the rough stationary surface bearing.
An Application of Short Bearing Theory to Dynamic Characteristic Problems of Turbulent Journal Bearings
Authors: Hashimoto Hiromu , Wada Sanae , Ito Jin-ichi
Published: October 2009

The dynamic characteristic problems of turbulent journal bearings are theoretically analyzed. The oil film forces considering the turbulent effects are analytically obtained under the short bearing assumption. The linearized stability analysis is developed for a perfectly rigid rotor supported horizontally in the two identical aligned oil film journal bearings and the whirl onset velocities for rotor-bearing systems are determined for various Reynolds numbers. In addition, the nonlinear equations of motion for rotor-bearing systems are solved by the improved Euler’s method and the journal center trajectories are examined for both cases with and without out-of-balance forces. The results obtained from the short bearing theory are compared with those from the finite bearing theory for the length-to-diameter ratio λ = 0.25 and 0.5. It is found that the turbulence has significant effects on the dynamic behavior of rotor-bearing systems and the short bearing theory has an advantage of reducing a computation time required for the calculation of journal center trajectories with an acceptable accuracy.
Analysis of the Large Plastic Deformation Involved in Wear Processes Using the Finite Element Method With an Updated Lagrangian Formulation
Authors: Ohmae Nobuo
Published: October 2009

Large plastic deformation caused by friction for high purity copper was investigated using the finite element method with an updated Lagrangian formulation. The phenomenological background of this large plastic deformation was studied with a scanning electron microscope, and the nucleation of voids similar to those obtained for copper rolled to over 50 percent reduction was observed. Void nucleation was found to correlate with the agglomeration of over-saturated vacancies formed under high plastic strains. The computer-simulation analyzed such heavy deformation with an equivalent stress greater than the tensile strength and with an equivalent plastic strain of 0.44. Crack propagation was discussed by computing the J-integrals.
A New Lubricity Evaluation Method for Metal Forming by a Compression-Twist Type Friction Testing Machine
Authors: Kawai Nozomu , Dohda Kuniaki
Published: October 2009

A new compression-twist type friction testing machine has been developed to simulate the frictional conditions prevailing in metal forming. Twin indenter tools with different sliding length were used and mineral oils were tested under frictional sliding between mild steel and a tool steel. New indexes of boundary lubricity, oil-film strength, and anti-galling ability are proposed to evaluate lubricant performance.
The Effect of Solid Film Lubricants on the Stability of Rolling Element Bearings
Authors: Kannel J. W. , Merriman T. L.
Published: October 2009

A technique has been developed for modeling solid films in rolling element bearings. For a given bearing geometry an effective viscosity can be calculated for a solid film as a function of the film shear modulus and ball-race friction coefficient. The calculated effective viscosity can subsequently be used as an input to a numerical model of cage motion and stability. Results from a sample calculation of effective viscosity and prediction of cage stability for a turbopump bearing are presented for films of molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE).
Piezoviscous-Rigid Rolling and Sliding Traction Forces, Application: The Rolling Element–Cage Pocket Contact
Authors: Houpert L.
Published: October 2009

Piezoviscous Rigid (PVR) film thicknesses, rolling and sliding traction forces formulas for the line and point contact case have been derived. They have been used to study the Rolling Element (R.E.)–cage pocket contact mechanism. As the R.E. gets closer to the cage web, the lubrication regime change gradually from the PVR regime to Piezoviscous Elastic (PVE or EHD) regime when steel cages are used. If plastic cages are used, the lubrication regime moves from the Isoviscous Elastic (IVE) regime to EHD regime. For the conditions simulated herein, the transition occurs at typical film thickness values of the order of 0.5 micrometers and substantially large loads can be calculated in the R.E.–steel cage contact. They can be of the order of 100 N at the transition. In many circumstances, the PVR regime prevails and the braking moment due to hydrodynamic traction in the contact can be easily calculated. A tight osculation between the R.E. and the cage pocket will increase significantly the load and braking moment on the R.E. Starvation effects are also estimated and cause a reduction of the load, but not of the braking moment.
Tribological Design Decisions Using Computerized Databases
Authors: Tallian T. E.
Published: October 2009

Tribological knowledge is widely scattered and inconvenient of access for practicing engineers. This results in suboptimal utilization of tribological knowledge in many engineering decisions. As a remedy, ASME has embarked on a project to create a comprehensive tribology database system accessible by desktop computer. Since tribological design methodology is as important as hard data in generating optimal engineering decisions, an artificial intelligence (AI) based expert system is projected to serve as a methodology guide for the database user. This paper describes the content and structure concept of the tribology database system “entry module,” which is to comprise this expert system.
Calculating Rotordynamic Coefficients of Seals by Finite-Difference Techniques
Authors: Dietzen F. J. , Nordmann R.
Published: October 2009

For modelling the turbulent flow in a seal the Navier-Stokes equations in connection with a turbulence model (k-ε-model) are solved by a finite-difference method. A motion of the shaft around the centered position is assumed. After calculating the corresponding flow field and the pressure distribution, the rotordynamic coefficients of the seal can be determined. These coefficients are compared with results obtained by using the bulk flow theory of Childs [1] and with experimental results.
A Fully Coupled Variable Properties Thermohydraulic Model for a Cryogenic Hydrostatic Journal Bearing
Authors: Braun M. J. , Wheeler R. L. , Hendricks R. C.
Published: October 2009

The goal set forth here is to continue the work started by Braun et al. [11] and present an integrated analysis of the behavior of the two row, 20 staggered pockets, hydrostatic cryogenic bearing used by the turbopumps of the space shuttle main engine (SSME). The variable properties Reynolds equation is fully coupled with the 2-D fluid film energy equation [η = η(P, T)]. The 3-D equations of the shaft and bushing model the boundary conditions of the fluid film energy equation. The effects of shaft eccentricity, angular velocity and inertia pressure drops at pocket edge are incorporated in the model. Their effects on the bearing fluid properties, load carrying capacity, mass flow, pressure, velocity and temperature form the ultimate object of this paper.
Recess Volume Fluid Compressibility Effect on the Dynamic Characteristics of Multirecess Hydrostatic Journal Bearings With Journal Rotation
Authors: Ghosh M. K. , Viswanath N. S.
Published: October 2009

An analysis using finite difference method and small amplitude perturbation technique has been presented to evaluate the frequency dependent stiffness and damping coefficients of multirecess hydrostatic journal bearings including the effect of shaft rotation that results in hybrid operation. Recess volume fluid compressibility effect that results in the frequency dependent dynamic coefficients have been taken into account. Results for direct and cross stiffness coefficients, direct and cross damping coefficients are presented for a capillary compensated bearing with deep recesses. Frequency effects are shown in terms of dimensionless squeeze number (σ) for various recess volume parameters (γ) for different eccentricity ratios (ε0) and dimensionless speed parameter (Λ). It has been found that the dynamic coefficients are very drastically altered within a very useful range of frequency parameter (σ) and recess volume parameter (γ) resulting in increased direct stiffness coefficient and a substantially decreased direct damping coefficients. Journal speed parameter (Λ) results in substantial magnitude of cross stiffness and cross damping parameters. However, the cross damping coefficient is usually small in comparison to direct damping coefficient.
Multigrid, an Alternative Method of Solution for Two-Dimensional Elastohydrodynamically Lubricated Point Contact Calculations
Authors: Lubrecht A. A. , ten Napel W. E. , Bosma R.
Published: October 2009

Detailed and accurate film thickness and pressure profiles have been calculated for point contacts at moderate and high loads, using a multigrid method. The influence of the compressibility of the lubricant and of the number of nodal points on the calculated minimum film thickness and maximum spike pressure have been examined. The required computing time is two orders of magnitude less, compared with the calculations using “classical” iterative methods.
Influence of Surface Waviness and Roughness on the Normal Pressure Distribution in the Hertzian Contact
Authors: Seabra J. , Berthe D.
Published: October 2009

Contact stresses are one of the most important parameters in the analysis of a contact problem found for instance, in the design of gears and roller bearings. In this work the influence of geometrical surface imperfections on the normal pressure distribution in the contact is studied. A variational formulation based on the principle of complementary virtual work is used to solve the normal contact problem. The normal contact between two elastic half-spaces is considered, as the contact surface is small when compared to the dimensions of the contacting bodies. Results are presented to determine the influence of surface roughness, wavelength, and amplitude on the normal pressure distribution.
A Numerical Solution for the Contact Problem Involving Bodies With Cylindrical Surface Considering Cylinder Effect
Authors: Chiu Y. P. , Hartnett M. J.
Published: October 2009

Presented here is a method of solution for three-dimensional contact involving cylindrical bodies without using the half-space assumption. The solution involves the numerical iterative technique to determine the contact pressure in various cells discretizing a prescribed area on the cylindrical surface, sufficiently large to cover the contact. The iteration is carried out using the flexibility matrix which is the radial deflections at various cell centers due to a uniformly distributed unit load acting in a small cell on the cylindrical surfaces. Numerical results have been obtained for (1) the closely conformed contact of a journal and a shaft and (2) the low conformity contact between a roller and a raceway. The results consist of contact pressure distribution, as well as elastic approach between the two bodies in contact.
Heat Partition and Transient Temperature Distribution in Layered Concentrated Contacts. Part II—Dimensionless Relationships and Numerical Results
Authors: Rashid M. , Seireg A.
Published: October 2009

The computer-based model described in Part I is utilized in this paper to develop dimensionless relationships for lubricated unlayered contacts and dry layered contacts. Because of the recent interest in tribological surface coating these relationships can be used to provide parametric evaluations of heat partition and temperature rise in the contacts under different coating parameters and operating conditions.
Frictional Properties of a Surface Covered With Soft Metal Surface Film (Surface Topography and Frictional Properties)
Authors: Kato Shinobu , Marui Etsuo , Tachi Kiyoo
Published: October 2009

The friction between a real engineering surface composed of many micro-asperities and a surface covered with soft metal film is discussed. First, the frictional coefficient shows a remarkable load dependency, when a hard single protuberance with a small radius of curvature is slid on a soft metal surface. This load dependence originates from the ploughing effect induced by the cooperation of contact pressure and shearing resistance of the soft metal film deforming on the protuberance surface. Based on this result, the effect of the real engineering surface topography on the frictional properties is studied.
Parameters Affecting the Kinetic Friction of Ice
Authors: Akkok M. , Ettles C. M. McC. , Calabrese S. J.
Published: October 2009

A study of the mechanics of ice friction was performed in which various theoretical models were compared to experimental results. Analytical models indicate that ice friction is affected by load, speed, ambient temperature, and thermal properties of the counterface material. All four parameters were varied and the results compared to analytical models with additional study using regression analysis. Conclusions indicate that under some conditions the friction of ice is subject to a thermal control mechanism.
Analysis of the Rolling Contact Residual Stresses and Cyclic Plastic Deformation of SAE 52100 Steel Ball Bearings
Authors: Hahn G. T. , Bhargava V. , Rubin C. A. , Chen Q. , Kim K.
Published: October 2009

Measurements of the cyclic stress-strain hysteresis loop shapes of hardened, HRC-62, SAE 52100 bearing steel, derived from torsion tests are presented. These are reduced to 3-parameter, elastic-linear-kinematic hardening-plastic (ELKP) representations. The ELKP behavior and properties of the steel are employed in an elastic-plastic finite element model of two dimensional, rolling contact. The distortion of the rim and the distribution and magnitude of the residual stresses and cyclic plasticity for repeated contacts at a Hertzian pressure of p0 = 3636 MPa (528 ksi), are calculated. The results are compared with the residual stresses and other features observed in the inner raceway of SAE 52100 steel, deep grooved ball bearings. The calculations predict the modest residual stresses observed in the early life: N ≲ 106 contacts. The much higher levels of residual stress that develop in later life: 108 ≲ N ≲ 1010, are shown to be connected with metallurgical changes and an attending volume expansion that are cyclic strain induced. The origins of these stresses and their effect on bearing life are discussed.
Highly Accurate Formulas for Rapid Calculation of the Key Geometrical Parameters of Elliptic Hertzian Contacts
Authors: Markho P. H.
Published: October 2009

The ellipticity ratio (κ), the complete elliptic intergrals of the first and second kinds (F and E, respectively), and the effective radius ratio (γ) for an elliptic Hertzian contact are related by a transcendental equation whose solution (or uncoupling) one would rather prefer to avoid. In this paper the currently available empirical formulas [1–3] relating each of κ, F, and E, separately, to γ are reappraised in terms of their quality of fit, then the work leading to new, more accurate, formulas is described. Two sets of such formulas are proposed which reduce the relative errors of fit, compared to the best currently available formulas, by up to well over two orders of magnitude for the range 1 ≤ γ ≤ 100. The paper ends with a brief discussion of the way the new equations presented here may also be utilized in the case of γ < 1, and of the implications of the new formulas with respect to simplified calculations of contact stresses and deformations, such as those proposed by Hamrock and Brewe [3].
Stability of Finite Orthogonally-Displaced Pressure Dam Bearings
Authors: Mehta N. P. , Singh Ajeet
Published: October 2009

During assembly, if the centers of the two halves of an elliptical pressure dam bearing are displaced horizontally, the bearing so obtained is termed orthogonally-displaced pressure dam bearing. The present paper describes the dynamic behavior of this bearing.
A Comparison of Identification Methods for Estimating Squeeze-Film Damper Coefficients
Authors: Ellis J. , Roberts J. B. , Hosseini Sianaki A.
Published: October 2009

The problem of identifying the dynamic coefficients relating to inertia, damping, and stiffness, in a single degree of freedom model of squeeze-film behavior, is discussed. It is demonstrated that two methods—referred to as “invariant imbedding” and “state variable filter”—are applicable, and that both yield a recursive scheme for sequentially estimating all three coefficients. The methods are compared through an analysis of simulated data, where the coefficient values are known a-priori. This is followed by a presentation of some typical results obtained from experimental tests, using both transient and forced response data. The comparisons indicate that the state variable filter method is much superior, with respect to both computational efficiency and accuracy.
Analysis of Tilting Pad Journal Bearings With Heat Transfer Effects
Authors: Knight J. D. , Barrett L. E.
Published: October 2009

An approximate solution technique for tilting pad journal bearings is presented. The method makes use of approximations to the axial pressure profile and the temperature profiles and includes heat transfer between the film and its boundaries. A second order profile is assumed to represent the temperature distribution across the film. The classical Reynolds equation is applied, using the viscosity based on the cross-film average of temperature. The transfer of heat in the pads is modeled as purely radial conduction, and the journal surface temperature is given by a circumferential average of the film temperatures. Results of calculations are presented for a sample case representative of an industrial compressor or turbine bearing and are compared to isothermal results. The dynamic characteristics in this case are found to vary by 10 to 35 percent for a change in lubricant inlet temperature of 28°C. Temperature distributions in the lubricant and on the surfaces of the pads are given.
Study of Conical Whirl Instability of Self-Acting Porous Gas Journal Bearings Considering Tangential Velocity Slip
Authors: Guha S. K. , Rao N. S. , Majumdar B. C.
Published: October 2009

The purpose of the present work is to study theoretically the conical whirl instability of unloaded self-acting porous gas journal bearings considering the tangential velocity slip at the bearing-film interface. The hydrodynamic pressure developed in the bearing clearance due to angular displacements of the journal at the midplane of the bearing is obtained by the simultaneous solution of equation of continuity in the porous medium and the modified Reynolds equations, satisfying the appropriate boundary conditions. With the help of the dynamic tilting stiffness and damping coefficients, stability characteristic is obtained. The effects of various parameters on conical stability parameter have been investigated for a nongyroscopic system.
Accurate Measurement of Gas-Lubricated Slider Bearing Separation Using Visible Laser Interferometry
Authors: Ohkubo T. , Kishigami J.
Published: October 2009

This paper outlines an optical method utilizing laser interferometry for measuring the static and dynamic characteristics of self-acting gas-lubricated slider bearings. The method achieves a high accuracy of down to 1–2 nanometers and a wide frequency range of more than 100 kHz by suppressing the adverse effect of undesirable interference patterns through the adoption of optics which permit the laser beam to be focused into a fairly small cavity. Experimental results derived from this method in an ambient helium atmosphere confirm that the modified Reynolds equation can be applied to the prediction of slider flying characteristics within an experimental range of spacing down to 0.025 μm and a corresponding Knudsen number as high as 8. Furthermore, experiments designed to measure slider transient motion as it travels across rectangular grooves or bumps indicate that the measurement system achieves a higher response performance than do conventional systems.
Rolling Bearing Life Prediction. Corrections for Material and Operating Conditions. Part I: General Model and Basic Life
Authors: Tallian T. E.
Published: October 2009

Computer based rolling bearing analysis programs exist which provide models for load and stress distribution, EHD conditions, heat balance and fatigue life prediction for rolling bearings and machine assemblies comprising such bearings. Fatigue life prediction is generally based on the ANSI standard. This two-part paper offers correction factors for refining the life prediction by modeling effects of material and operating variables. The corrections can be applied to the ANSI-predicted life of a complete bearing or to predicted lives of stressed volume elements in the bearing, with subsequent summation over the stressed volumes. Formulations are presented with a view to their incorporation into dynamic bearing analysis computer programs. This first part of the paper comprises the general model, basic life calculation and the nomenclature for both parts of the paper.
Effect of Surface Roughness on the Point Contact EHL
Authors: Zhu D. , Cheng H. S.
Published: October 2009

In this paper a full numerical solution for the partial elastohydrodynamic lubrication in elliptical contacts is presented, and the procedure of computation is briefly described. The average Reynolds equation developed by Patir and Cheng, the elasticity equation, and the pressure-viscosity relationship are solved simultaneously. The asperity contacts are also taken into account by using the model contributed by Greenwood and Tripp. The distribution of surface irregularities is assumed to be Gaussian. The effects of various roughness parameters on the film thickness are investigated. Special attention is given to the surface pattern parameter and hydrodynamic roughness parameter.
Thermal Instability of Sliding and Oscillations Due to Frictional Heating Effect
Authors: Maksimov I. L.
Published: October 2009

The stability of sliding has been studied, taking into account frictional heating effect and friction coefficient dependence upon the interface temperature and sliding velocity. The collective—thermal and mechanical—sliding instability has been found to exist; instability emergence conditions and dynamics (both in linear and nonlinear stages) have been determined. It is shown that both the threshold and the dynamics of thermofrictional instability differ qualitatively from the analogous characteristics of “stick-slip” phenomenon. Namely, the oscillational instability behavior due to the energy exchange between thermal and mechanical modes has been found to occur under certain initial conditions; the velocities range has been determined for which collective sliding instability may occur whereas the stick-slips would be not possible. The nonlinear analysis of instability evolution has been carried out for pairs with the negative thermal-frictional sliding characteristics, the final stage of sliding dynamics has been described. It is found that stable thermofrictional oscillations can occur on the nonlinear stage of sliding instability development; the oscillations frequency and amplitude have been determined. The possibility has been discussed of the experimental observation of new dynamical sliding phenomena at low temperatures.
Stability of a Rigid Rotor Supported by Aerostatic Journal Bearings With Circular Slot Restrictors (On the Double-Row Admission Bearing)
Authors: Yoshimoto S. , Anno Y. , Ohashi T.
Published: October 2009

This paper discusses the stability of a rigid rotor supported by double-row admission journal bearings with circular slot restrictors. In the theoretical analysis, the energy loss at the outlet of the slot is taken into account because the gas flow is subject to a rapid change in direction, and here, the energy loss coefficient is determined experimentally. It is found that a better agreement between the theoretical and experimental results for the threshold of instability can be obtained by considering the energy loss. Furthermore, in this paper, it is shown experimentally that an aerostatic journal bearing with circular slot restrictors has higher stiffness and higher stability than a conventional point source bearing with inherently compensated feeding holes.
Thermal Contact Simulation in 2-D and 3-D Mechanisms
Authors: Colin F. , Floquet A. , Play D.
Published: October 2009

Thermal simulation of complex mechanism performance is based on the simultaneous use of analytical methods for simple shaped moving parts and numerical techniques (Finite Element Method) of the others. The method presented called Hybrid method, uses these two techniques for 2-D and 3-D cases. A particular formulation of analytical results insures the compatibility with the Finite Element Method. Large CPU time savings are obtained when compared to a pure numerical analysis.
Pressure Spikes in Elastohydrodynamically Lubricated Conjunctions
Authors: Hamrock B. J. , Pan Ping , Lee Rong-Tsong
Published: October 2009

The film thickness, pressure, and flow in elastohydrodynamically lubricated conjunctions were calculated for a line contact. The main focus of the study was to get a better understanding of why a pressure spike exists in elastohydrodynamically lubricated conjunctions. Various combinations of viscous or isoviscous and compressible or incompressible situations were studied for a wide range of loads. The basic parameters were pressure, pressure gradient, film shape, and flow. It was found that the major factor causing the pressure spike to occur was the viscosity.
The Line Contact Between Two Cylinders—Some Experiments and Theoretical Predictions
Authors: de Mul J. M. , van Engelenburg H.
Published: October 2009

Experiments are presented in which various combinations of two (almost) straight cylinders with circular cross-section are pressed together while their axes remain basically parallel. Results are compared with theoretical predictions from a half space model; from this half space model extended with adjustments for the finite dimensions of the cylinders in contact; and from an infinite cylinder model from literature. Frictional effects are not considered and the material is assumed to be linear-elastic. Agreement in the approach of the center lines of the cylinders under load is found to exist more or less between the experimental results and the theoretical predictions by the models. The behaviour of the models is discussed, and reasonable to good agreement is demonstrated for the extended half space model using an integral depth adjustment of 3/4 of the diameter of each cylinder in contact. A possible way to further improve this model is indicated.
A Preliminary Analysis of Subsurface Crack Branching Under a Surface Compressive Load
Authors: Miller G. R.
Published: October 2009

This paper presents the results of a preliminary analysis of the branching behavior of a horizontal subsurface crack subjected to a moving compressive surface load. The purpose of the analysis is to provide some fundamental understanding concerning the behavior of subsurface contact fatigue cracks, including the onset of pitting or delamination. The analysis is approximate inasmuch as the traction-free boundary condition at the surface is only partially satisfied, and the history dependent effects arising from crack face friction are not included. The results show that mode I branching crack growth is possible even though the stress field is largely compressive. Nevertheless, based on a simple competing failure mode model the results indicate that within the limits of the analysis, nonbranching mode II growth is likely to be the dominant mode of propagation.
Radial Flow Between Axisymmetric Nonparallel Plates of Small Slope
Authors: Gans R. F. , Johnson A. G. , Malanoski S. B.
Published: October 2009

We have measured the separation and central pressure of a slightly concave axially symmetric pressurized bearing as a function of lubricant (air) mass flux and bearing load. We find that a mean face slope of 1.6 × 10−3 makes a dramatic difference in the behavior of the bearing, reducing the central pressure by more than a factor of two and eliminating the need for overpressures to start the system. We have also explored the behavior of the system analytically and find excellent agreement between theory and experiment.
A Fast Method for Calculating Dynamic Coefficients of Finite Width Journal Bearings With Quasi Reynolds Boundary Condition
Authors: Kato T. , Hori Y.
Published: October 2009

This paper presents a fast method for calculating the dynamic coefficients of the finite width journal bearings under quasi Reynolds boundary condition in which the trailing boundary line is given by a straight line and the continuity of bulk flow across this line is ensured. Calculated linear stiffness and damping coefficients agree well with the data of Lund and Thomsen [1]. The time required by this calculation with HITAC M682H is only 0.1–0.3 seconds (about 1/100 of the time required by the ordinary FDM), which suggests the possibility of real time journal bearing designs without using the database of the dynamic coefficients.
New Models in the Theory of the Hydrodynamic Lubrication of Rough Surfaces
Authors: Bayada G. , Chambat M.
Published: October 2009

Recent advances in mathematical analysis of problems described by several small parameters equations are used to revisit the general roughness problem. In this paper, we put forward a new qualitative study of a thin film flow with a rapidly varying gap. Using an asymptotic analysis of the three-dimensional Stokes system we obtain a family of new generalized Reynolds equations. We are led to distinguish three different cases in which the periodic roughness wavelength is on the order of, greater or shorter than the mean thickness of the gap.
Nonlinear Identification of a Squeeze-Film Damper
Authors: Stanway R. , Mottershead J. E. , Firoozian R.
Published: October 2009

In this paper the authors describe an experimental study to identify the damping laws associated with a squeeze-film vibration damper. This is achieved by using a nonlinear filtering algorithm to process displacement responses of the damper ring to synchronous excitation and thus to estimate the parameters in an nth-power velocity model. The experimental facility is described in detail and a representative selection of results is included. The identified models are validated through the prediction of damper-ring orbits and comparison with observed responses.
The Effect of Fluid Inertia on the Operating Characteristics of a Journal Bearing
Authors: You H. I. , Lu S. S.
Published: October 2009

The load capacity, attitude angle, and lubricant flow rate are computed using a modified Reynolds equation combined with the modified Coyne-Elrod boundary conditions. It was found that the pressure is decreased and the rupture point is shifted further downstream as the Reynolds number is increased or the surface tension parameter is decreased. Under a light loading condition, and a low surface tension parameter, a continuous film is approached.
Film Thickness Calculations in Elastohydrodynamically Lubricated Circular Contacts, Using a Multigrid Method
Authors: Lubrecht A. A. , Venner C. H. , ten Napel W. E. , Bosma R.
Published: October 2009

Minimum, central and average film thicknesses have been calculated for the isothermal E.H.L. point contact case, for a variety of load, rolling speed, and material parameters. The equations governing this problem were solved using a Multigrid method. This technique offers the possibility to work with a very fine grid, obtaining detailed and accurate solutions, at the cost of moderate cpu times and storage requirements, on medium size computers. Computations for low loads, requiring a large inlet zone, have been carried out using local grid refinements. The fluid in these calculations is assumed to be compressible and its viscosity-pressure behavior is described by either the Roelands equation, or the Barus equation. The ratio between the calculated minimum film thickness and the central value varied with the parameters governing the problem, but for low loads, a value of 3/4 was obtained. The film thickness behavior at these low loads can be accurately described in terms of the minimum film thickness. For higher loads, however, a description based on a film thickness, averaged over the Hertzian contact, is more appropriate to be compared with the asymptotic solution (Ertel, Grubin).
Effects of Ambient Gases on Friction and Interfacial Resistance
Authors: Chang Y.-J. , Kuhlmann-Wilsdorf D.
Published: October 2009

As is well known, ambient atmospheres can greatly affect the friction and wear behavior of metals sliding on each other, as well as the electric contact resistance between the metals. In order to better understand the mechanisms of those effects of ambient atmospheres, the coefficient of friction and the electric contact resistance have been studied for bundles of 50 micrometer thick copper wires, sliding on a polished copper surface in a specialized apparatus, called the hoop apparatus. The ambient gas was cycled between laboratory air and carbon dioxide, and between laboratory air and argon, respectively. The results indicate a reversible build-up and removal of surface films whose nature as well as speed of formation and removal depends on the gas present. Fiber bundles are used in order to eliminate the constriction resistance, so that the contact resistance is directly proportional to the specific film resistivity. The following properties were found to be affected by the ambient gases. (i) The average level of the contact resistance. (ii) The amplitude of the electric “noise.” (iii) The coefficient of friction. (iv) The difference between the static and the dynamic coefficients of friction in stick-slip motion. The results were found to be consistent with previous measurements in which the mechanism of forming wear particles was deduced from a wear chip analysis. Correspondingly they were interpreted in terms of the same wear model. This led to a further advance in the understanding of the interfacial processes accompanying sliding in this sample/substrate combination.
Friction Coefficients Measured at Lubricated Planar Contacts During Start-Up
Authors: Gassenfeit E. H. , Soom A.
Published: October 2009

Measurements of instantaneous coefficients of friction and associated motions during start-up at a planar contact are presented for four different lubrication conditions. The various patterns of transient behavior are discussed. Difficulties in interpreting static friction coefficients during rapidly applied tangential loads are described in relation to the motion data. It is shown that a molybdenum disulphide grease yields a friction characteristic that is quite different from either dry or boundary lubricated conditions in the presence of liquid lubricants. Transition distances from a static or maximum initial friction to kinetic conditions are examined and found to be considerably longer than had been previously found for concentrated contacts. Some suggestions regarding future studies of unsteady friction behavior are made.
Analysis of Thrust Bearings Operating in Turbulent Regime
Authors: Harada M. , Aoki H.
Published: October 2009

This paper relates to the turbulent motion in the lubricant fluid film with centrifugal effects and the lubrication theory for thrust bearings operating in turbulent regime. Using Prandtl’s mixing-length theory, three-dimensional turbulent velocity distributions, including pressure gradients and centrifugal effects, are calculated, and the cross-coupling of nonplanar flow of the lubricant fluid film is discussed. From these results, turbulent lubrication equations with centrifugal effects are derived. Applying these lubrication equations to a sectorial inclined thrust bearing, the steady-state characteristics and the dynamic ones are calculated.
On the Stability and Uniqueness of Elastohydrodynamic Lubrication Solutions
Authors: Glander D. W. , Bissett E. J.
Published: October 2009

It was suggested in [1] that solutions of the line contact problem of elastohydrodynamic lubrication (EHL) are unstable in a certain parameter regime, and that both stable and unstable solutions can coexist in another regime. The author also suggested that these regimes limit the applicability of the standard model equations. In this work, the present authors repeat this calculation using the highly accurate solutions described in our previous work [3]. In all cases we have considered, we find no evidence of instability or multiplicity of solutions. We conclude that the existence of regions of instability or multiplicity were based on numerical artifacts and that considerations of stability or multiplicity do not limit the applicability of the standard model equations of EHL.
An Experimental Investigation on the Rotating Journal Surface Temperature Distribution in a Full Circular Bearing
Authors: Andrisano A. O.
Published: October 2009

A method is described for measuring the rotating shaft surface temperature in a full circular bearing. The experimental measurements related to a journal bearing with a unitary length/diameter ratio, are reported. Contrary to the commonly held assumption, the shaft surface temperature is found to remain not quite constant, but to fluctuate during the journal revolution; the value of the temperature in the revolution appears to be maximum about the minimum film thickness. Typical surface temperature distribution scope traces, circumferential variation amplitudes of the surface temperature and increases in the mean revolution value of the journal surface temperature with respect to that of the inlet lubricant oil, are plotted versus shaft speed, lubricant viscosity and bearing load. The journal speed and lubricant viscosity appear to significantly affect the rotating shaft surface temperature as well as its fluctuation in the revolution; the effect of the bearing load is less influential.
Sliding Behavior of Alumina/Nickel and Alumina/Nickel Aluminide Couples at Room and Elevated Temperature
Authors: Blau Peter J. , DeVore Charles E.
Published: October 2009

Nickel aluminide alloys are ordered intermetallic compounds which show promise for elevated temperature applications, some of which involve sliding contact. The present investigation was conducted to develop an initial understanding of the unlubricated sliding behavior of a nickel aluminide alloy at room and elevated temperatures. In particular, the variations in the friction coefficient and the wear track morphology during the break-in stage and subsequent transitions were studied. Pin-on-disk experiments were conducted at room temperature and at 650° C (923° K) in air using fixed 9.5 mm diameter polycrystalline alumina balls as the pin material. To provide a comparison in behavior, nickel (Ni-200) disks were tested under the same conditions. The sliding friction coefficient of alumina on nickel aluminide was considerably higher than that for alumina on nickel at room temperature, but it was only slightly higher at 650° C. The wear was similar for both materials at room temperature, but the nickel aluminide exhibited relatively mild wear at 650° C, displaying less severe surface damage than the nickel. Work on identifying key friction and wear mechanisms and on evaluating the temperature limitations for future applications will continue.
Investigation of a Flexible Disk Rotating Near a Rigid Surface
Authors: Carpino M. , Domoto G. A.
Published: October 2009

A flexible disk rotating in close proximity to a flat rigid surface has been studied experimentally and theoretically. A bump is located on the surface to create a non-axisymmetric disturbance. The gas film between the disk and the rigid surface is represented by an incompressible Reynolds equation with inertial effects included. The general equations of a disk including both membrane and bending effects with displacement dependent tension distributions are presented. Numerical results are developed where the effects of displacement on the tension distributions and of bending in the disk are not included.
The Performance of Ball Bearings With Silicon Nitride Ceramic Balls in High Speed Spindles for Machine Tools
Authors: Aramaki Hirotoshi , Shoda Yoshio , Morishita Yuka , Sawamoto Takeshi
Published: October 2009

Two types of angular contact ball bearings for machine tools having steel rings and silicon nitride balls were tested and the temperature rise was compared with that of conventional steel ball bearings with grease lubrication and oil-air lubrication as well. Experimental results indicated that the temperature rise of silicon nitride ball bearings was much lower than that of steel ball bearings at high speeds. Calculations made using a computer demonstrated that the reduction of gyroscopic moments and centrifugal forces acting on balls because of the low density of silicon nitride resulted in about 30 to 50 percent less frictional loss at high speeds even with low-cost lubrication such as grease or oil-air.
The Influence of Crack Face Friction and Trapped Fluid on Surface Initiated Rolling Contact Fatigue Cracks
Authors: Bower A. F.
Published: October 2009

A two-dimensional model of a surface initiated rolling contact fatigue crack has been developed. The model takes into account the effects of frictional locking between the faces of the crack, and the influence of fluid pressure acting on the crack faces. The model has been used to investigate three possible mechanisms for propagating the cracks: mode II crack growth due to the cyclic shear stresses caused by repeated rolling contact; crack growth due to fluid forced into the crack by the load; and crack growth due to fluid trapped inside the crack. The predictions of the theory are compared with the behaviour of contact fatigue cracks.
Gas Lubrication of a Ringless Piston in an Internal Combustion Engine Under Dynamic Loading
Authors: Mourelatos Z. P.
Published: October 2009

A theoretical model is presented to solve the transient, two-dimensional, compressible Reynolds equation for a gas bearing. The Newton-Raphson method is used on the governing nonlinear Reynolds equaion while the Galerkin’s method is employed to solve the resulting linear equations for the correction term. The numerical solution of the pressure distribution of an infinitely long, plane-wedge, slider bearing compares very well with the analytical (exact) solution. This theoretical model is then used to calculate the trajectory of a ringless piston within the cylinder of an I. C. engine under a given dynamic loading. The flexible polyhedron unconstrained minimization method is used to find the equilibrium position of the piston within the cylinder for each crankangle. It was found that a 40 mm long ringless piston can support a uniform side load of about 50 Newtons at 2000 r/min running on a gas film. However, the same piston can sustain a nonuniform side load with a much higher peak value (three to five times the uniform load) which lasts approximately 20 to 30 degrees of crankangle only. The sustainable side load by gas lubrication is much lower than the peak piston side load of conventional internal combustion engines.