bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Thermohydrodynamic Squeeze Films
Authors: Rohde S. M. , Ezzat H. A.
Published: November 2010

This paper presents an analysis of the thermohydrodynamic performance of squeeze films. The mathematical model consists of a 3-dimensional Reynolds equation, a 3-dimensional time dependent energy equation, and a 3-dimensional time dependent heat conduction equation. The system of equations is solved numerically. Fluid film pressure and temperature distributions and the temperature distribution in the solids are presented. Fluid film velocity profiles as a function of time are also shown. The load-time characteristics for different operative conditions are studied. It is shown that a thermohydrodynamic squeeze-film parameter can give rise to a phenomenon which radically changes the fluid film performance.
A Theory of Hydrodynamic Friction Forces in Starved Point Contact Considering Cavitation
Authors: Chiu Y. P.
Published: November 2010

Expressions for the hydrodynamic friction forces between two rigid bodies each having two principal radii of curvature have been found using an exponential pressure-viscosity assumptions. The rolling friction forces are presented graphically in terms of a dimensionless meniscus distance. These formulas are applicable to the computation of the rolling friction in a ball-race contact and in a ball-cage contact with a variable degree of starvation. In particular, the rolling friction forces can be predicted as a function of the usual speed-viscosity parameter and the thickness of the inlet fluid layer far upstream of the inlet.
Contact Stresses Between an Elastic Cylinder and a Layered Elastic Solid
Authors: Gupta P. K. , Walowit J. A.
Published: November 2010

The generalized plane strain problem of the contact of layered elastic solids is reduced to an integral equation using Green’s function approach. Approximate numerical solutions are obtained by replacing the integral equation by a matrix inversion when the trapezoidal rule is used to represent the integral. Results for determining the actual contact pressure at the center of the contact zone and size of contact zone for a wide range of layer thicknesses are presented for two most practical cases, (i) when the indenter is rigid, and (ii) when the indenter is elastic having a modulus of elasticity equal to that of the substrate of the indented body. When the layer is softer than the substrate it is found that the actual contact pressure distribution is very closely determined by a weighted sum of elliptic and parabolic functions. For a substrate softer than the layer the pressures substantially deviate from an elliptical or parabolic behavior, for the cases when the layer thickness is finite. The analysis checks with the Hertzian solution in the extreme cases when the layer thickness either tends to zero or approaches infinity.
Piston Ring Lubrication and Cylinder Bore Wear Analyses, Part II—Theory Verification
Authors: Ting L. L. , Mayer J. E.
Published: November 2010

Based on the analytical method presented in the previous paper (Part I), comparisons of predicted wear curves along the major and minor side-thrust sides of the cylinder bore are made with the measured ones obtained from several truck engines for various vehicle mileages. The agreement was found to be good. This indicates the analytical model developed in Part I is relevant and suitable for predicting the severity of piston-ring bore contact for varying engine operating and lubrication conditions. From this, the necessary parameter changes may be found such that the wear rate of the cylinder bore may be reduced. Wear factor data, however, must be available in order to make quantitative predictions of wear. The model ultimately may be useful also in the design optimization of engine components. Since the method is general, it also can be applied to other reciprocating piston devices, such as gas compressor, Rankine cycle engine, or Stirling engine.
Performance of High-Speed Ball Bearings With Lead and Lead-Alloy-Plated Retainers in Liquid Hydrogen at 1.2 Million DN
Authors: Brewe D. E. , Scibbe H. W. , Wisander D. W.
Published: November 2010

Forty-millimeter-bore ball bearings with lead and lead-alloy-coated retainers were operated in liquid hydrogen at 30000 rpm under a thrust load of 1780 Newtons (400 lb). Bearing lives were compared using different (1) lead- and lead-alloy coatings, (2) coating thicknesses, (3) substrate materials, (4) retainer locating surfaces, and (5) plating techniques. Longer bearing run times were achieved using retainers with a lead-tin-copper alloy coating electroplated onto a leaded-bronze material (22.5 hr) and an aluminum-bronze alloy (19.3 hr). Thirty percent of the bearings tested achieved the desired objective of 10 hours. All of the lead-alloy coated retainers exceeded this objective. A coating thickness of at least 36 microns (0.0014 in.) was used for all bearings exceeding the 10-hour goal.
Elastohydrodynamic Film Thickness Model for Heavily Loaded Contacts
Authors: Loewenthal S. H. , Parker R. J. , Zaretsky E. V.
Published: November 2010

An empirical elastohydrodynamic (EHD) film thickness formula for predicting the minimum film thickness occurring within heavily loaded contacts (maximum Hertz stresses above 1.04 × 109 N/m2 (150,000 psi)) was developed. The formula was based upon X-ray film thickness measurements made with synthetic paraffinic, fluorocarbon, Type II ester and polyphenyl ether fluids covering a wide range of test conditions. Comparisons were made between predictions from an isothermal EHD theory and the test data. The deduced relationship was found to adequately reflect the high-load dependence exhibited by the measured data. The effects of contact geometry, material and lubricant properties on the form of the empirical model are also discussed.
Comparison Between Predicted and Measured Axial Pressure Distribution Between Cylinders
Authors: Kannel J. W.
Published: November 2010

A technique for observing two-dimensional variations of pressures using a Manganin pressure transducer is presented. Comparisons are made between pressure predictions using a straightforward analytical tool for pressure analysis and experimental observations. These comparisons are made for the case of a roller with a cylindrical central region with a dub-off edge radius in both aligned as well as misaligned contact with a flat cylinder. Reasonable agreement is shown between theory and experiment. In addition, the theory has been found to be capable of isolating stress risers such as occur at sharp curvature changes between bodies in contact.
Parametric Study of the Lubrication of Thrust Loaded 120-MM Bore Ball Bearings to 3 Million DN
Authors: Signer H. , Bamberger E. N. , Zaretsky E. V.
Published: November 2010

A parametric study was performed with 120-mm bore angular-contact ball bearings under varying thrust loads, bearing and lubricant temperatures, and cooling and lubricant flow rates. Contact angles were nominally 20 and 24 deg with bearing speeds to 3 million DN. Endurance tests were run at 3 million DN and a temperature of 492 K (425 deg F) with 10 bearings having a nominal 24-deg contact angle at a thrust load of 22241 N (5000 lb). Bearing operating temperature, differences in temperatures between the inner and outer races, and bearing power consumption can be tuned to any desirable operating requirement by varying 4 parameters. These parameters are outer-race cooling, inner-race cooling, lubricant flow to the inner race, and oil inlet temperature. Preliminary endurance tests at 3 million DN and 492 K (425 deg F) indicate that long-term bearing operation can be achieved with a high degree of reliability.
On the Failure of Lubrication Theory in Squeezing Flows
Authors: Jones A. F. , Wilson S. D. R.
Published: November 2010

The problem is the motion of a film of liquid squeezed between a fixed and a uniformly moving plane. The case when the squeeze Reynolds number R is small is reconsidered in order to point out defects in the conventional lubrication theory which may have practical importance. The effects of initial conditions and large R are then examined.
Inertia, Convection, and Dissipation Effects in the Thermally Boosted Oil Lubricated Sliding Thrust Bearing
Authors: Rodkiewicz C. M. , Hinds J. C. , Dayson C.
Published: November 2010

The influence of inertia terms and the effects of convection and dissipation on the characteristics of an infinitely wide cooled slider bearing are examined. The lubricant is assumed to be incompressible and the variation of viscosity with temperature is taken into account. The nondimensionalized governing equations, transformed in terms of the stream function, are solved numerically. The results verify that inclusion of the inertia terms causes an increase in the dimensionless load capacity of the bearing. Retention of the convective terms in the energy equation results in a larger dimensionless load capacity. The dissipation terms when included yield a smaller dimensionless capacity.
The Influence of Fluid Inertia on the Dynamic Properties of Journal Bearings
Authors: Reinhardt E. , Lund J. W.
Published: November 2010

Based on a first-order perturbation solution in a modified Reynolds number an analysis is presented to determine the effect of the fluid film inertial forces on the dynamic properties of a journal bearing. The corrections to the regular amplitude and velocity coefficients are found to be small, but the accompanying acceleration coefficients which may correspond to a virtual mass of several times the mass of the journal itself, could become significant for short rotors. Numerical results are given in graphical form with dimensionless coefficients as functions of the operating eccentricity ratio.
The Viscous Lubrication of Rolling and Sliding Rigid Cylinders
Authors: Carlson Stephen F. , Winer Ward O.
Published: November 2010

The general viscous lubrication of rolling and sliding rigid cylinders is examined. The flow is assumed isothermal and the fluid rheology is assumed completely defined by its compressibility as a function of pressure and by its viscosity as a function of pressure and shear stress. A general problem formulation and a general solution technique are developed. The solution technique is based on the iterative solution of a discrete representation of the problem formulation. These results are specialized for a viscosity function of the form μ=μ0eβp(1+a2(kτ)2)(1+(kτ)2)−1 Typical solutions are obtained and discussed. A dimensionless survey of design parameters is presented for the above viscosity function with (a) = 0.0. The use of such nonlinear general viscous fluids results in a significant loss of load capacity.
A Thermal Elastohydrodynamic Inlet Zone Analysis
Authors: Murch L. E. , Wilson W. R. D.
Published: November 2010

An equation which takes account of the effects of viscous heating is used in place of the conventional Reynolds equation in a Grubin style analysis of the elastohydrodynamic inlet zone. The analysis indicates that viscous heating in the inlet zone can result in substantial reduction in the lubricant film thickness. The results of the analysis are expressed in a simple equation which will be useful for the design of elastohydrodynamically lubricated contacts under conditions where viscous heating is important.
Transient Ball Motion and Skid in Ball Bearings
Authors: Gupta P. K.
Published: November 2010

The generalized differential equations of motion of the ball in an angular contact ball bearing operating under elastohydrodynamic traction conditions are formulated and integrated with prescribed initial conditions. A complete transient and steady state motion is thus obtained to predict the amount of skid and resulting wear rates for a set of given operating conditions. The analysis provides an up-to-date design tool in predicting skid and ball motion as a whole in ball bearings operating under arbitrary ball-race traction characteristics.
Study of Lubricant Jet Flow Phenomena in Spur Gears
Authors: Akin L. S. , Mross J. J. , Townsend D. P.
Published: November 2010

Lubricant jet flow impingement and penetration depth into a gear tooth space were measured at 4920 and 2560 using a 8.89-cm- (3.5-in.) pitch dia 8 pitch spur gear at oil pressures from 7 × 104 to 41 × 104 N/m2 (10 psi to 60 psi). A high speed motion picture camera was used with xenon and high speed stroboscopic lights to slow down and stop the motion of the oil jet so that the impingement depth could be determined. An analytical model was developed for the vectorial impingement depth and for the impingement depth with tooth space windage effects included. The windage effects on the oil jet were small for oil drop size greater than 0.0076 cm (0.003 in.). The analytical impingement depth compared favorably with experimental results above an oil jet pressure of 7 × 104 N/m2 (10 psi). Some of this oil jet penetrates further into the tooth space after impingement. Much of this post impingement oil is thrown out of the tooth space without further contacting the gear teeth.
Molecular Degradation of Lubricants in Sliding Elastohydrodynamic Contacts
Authors: Walker D. L. , Sanborn D. M. , Winer W. O.
Published: November 2010

The extent of lubricant degradation in a sliding elastohydrodynamic contact has been investigated. The lubricant was subjected to peak Hertz pressures of approximately 109 N/m2 and average shear rates of 106 to 107 s−1. Hydrocarbon lubricants, bulk polymers and polymer containing hydrocarbon solutions were examined. Small samples (10−8m3) of test lubricant were extracted from the entrance and exit regions of the EHD contact. These samples were then analyzed to determine alterations in the molecular weight distribution. In addition, a microcapillary viscometer was developed to determine viscosity changes. Degradation resulting in up to a 70 percent viscosity loss was found in fluids which had molecular weights of over 1000. High degrees of correlation were found between molecular weight loss, viscosity loss and the energy dissipated in the contact.
A Thermoelastohydrodynamic Analysis of a Finite Slider Bearing
Authors: Rohde S. M. , Oh Kong Ping
Published: November 2010

The thermoelastohydrodynamic (TEHD) behavior of a finite inclined-plane slider bearing is studied. The fluid film momentum, continuity, and energy equations are coupled to the heat conduction equations and the elasticity equations of the solid, and solved numerically. The elastic and thermal distortions of the solid as well as the variation of fluid properties with temperature are considered in the analysis. Several models for the bearing solids are treated.
High Shear Stress Behavior of Some Representative Lubricants
Authors: Jakobsen J. , Winer W. O.
Published: November 2010

Shear stress independent behavior was observed for representative, synthetic, nonblended lubricants to about 4.8 × 106 N/m2 (700 psi) shear stress in high pressure viscometric measurements. This shear stress is of the same magnitude as the shear stress in sliding elastohydrodynamic contacts. It is shown that dissipation heating is the only mechanism of importance in the generation of the deviations from constant viscosity as measured with capillary tube viscometric methods. The Newtonian end corrections for the capillary tubes were found to be constant for the nonblended, liquid lubricants. Newtonian behavior will be expected of the fluids in a high shear lubrication situation. Shear induced, nonliquid behavior was found for the silicone lubricant at about 106 N/m2 and for the polymer-blended mineral oil at about 104 N/m2 at a relatively low pressure level. The observations might provide a key to an understanding of the generation of the anomalous low elastohydrodynamic film thickness as found with these lubricants. The polymer-blended oil showed shear thinning effects. The apparent viscosity was found to increase (∼30 percent) with increasing shear stress in the range of the second Newtonian viscosity level.
Quasi-Static Analysis of Foil Journal Bearings for a Brayton Cycle Turboalternator
Authors: Eshel A.
Published: November 2010

A quasi-static analysis is presented for foil journal bearings designed for a NASA Brayton Cycle Turboalternator. Included in the analysis are effects of “slack” (due to flexural rigidity of the foil), of frictionally restrained extension of the foil-length in contact with cylindrical guides, of fluid inertia and compressibility, and of thermal expansion of rotor, foil and supporting structure. Comparisons are made with results of early experiments performed by Licht [1, 2] and recent data of Licht and Branger [6, 7]. Variations of film thickness, foil tension and bearing stiffness are presented graphically as functions of pertinent parameters for the case of operation in zero-gravity environment.
An Experimental Evaluation of the Stresses in Drilled Balls
Authors: Nypan L. J. , Coe H. H. , Scibbe H. W.
Published: November 2010

Stresses in dimensionally similar large models of 40-, 50- and 60-percent mass reduction cylindrically hollow “drilled” bearing balls were experimentally evaluated with flat strain gage rosettes. Dimensionless principal stress coefficients were calculated and were applied to estimate the bending stresses in the drilled balls of three series of full-scale bearing experiments. Stresses were highest when the applied load approached the edge of the hole, and ranged up to almost 620 × 106 N/m2 (90,000 psi) at the bore.
Impact of a Lubricated Surface by a Sphere
Authors: Conway H. D. , Lee H. C.
Published: November 2010

This paper presents an analysis of the impact between a sphere and a flat surface covered by an oil film. Pressure distributions are found as functions of time for oils whose viscosities are either constant or pressure-dependent. It is believed that the increase of oil viscosity with pressure is a main cause of the deep conical dents observed experimentally.
Rarefaction Effects of Gas-Lubricated Bearings in a Magnetic Recording Disk File
Authors: Tseng R. C.
Published: November 2010

The load versus spacing characteristics of a self-acting, gas-lubricated slider bearing similar to that used in a magnetic recording disk file have been investigated experimentally under sub-atmospheric ambient conditions. Interferometric techniques are used to measure the steady spacing between a rotating glass disk and the slider over a wide range of ambient pressures and disk speeds. For local Knudsen number less than 0.1, excellent agreement is found to exist between experimental data and numerical solutions of the Reynolds lubrication equation taking into account the velocity-slip boundary conditions. Effects of rarefaction on the bearing performance for a range of pertinent bearing parameters (i.e., bearing number and inlet-to-outlet ratio) are presented.
Squeeze Film Behavior in a Spherical Porous Bearing
Authors: Murti P. R. K.
Published: November 2010

The squeeze film behavior in a hemispherical porous bearing under a steady load is analyzed. A nonspinning spherical rotor moves vertically down toward the inner surface of the bearing squeezing the incompressible lubricant film in the gap between the rotor and the bearing. The analysis shows that the permeability of the bearing matrix and the wall thickness of the bearing adversely affect the load capacity and greatly reduce the time needed for the rotor to attain a given eccentricity. Also, unlike the case of an impermeable bearing, there exists the possibility of the rotor coming in actual contact with the bearing (ε = 1) in finite time. The results are presented in graphical and tabular forms.
Energy Integral Approach for MHD Hydrostatic Thrust Bearing
Authors: Kapur V. K. , Verma Kamlesh
Published: November 2010

An attempt has been made to investigate the bearing characteristics by energy integral approach (an approximate technique) and the results so obtained are compared with those of Krieger, Day and Hughes [1], for normalized flow rate and normalized load capacity.
The Contribution of Fluid Film Inertia to the Thermohydrodynamic Lubrication of Sector-Pad Thrust Bearings
Authors: Chen Chung-Moon , Dareing D. W.
Published: November 2010

This paper is concerned with the load carrying capacity of thermohydrodynamic lubricating films in sector pad thrust bearings; it combines the effects of the thermal wedge and fluid film inertia in one analysis. Particular emphasis is placed on fluid film inertia in a rotational fluid film analysis. The nonlinear partial differential equations are transformed into finite difference equations and a successive over-relaxation method is used to obtain numerical solutions to the equations using a digital computer. The convergence of iterations is accelerated by introducing a relaxation factor. The analysis shows that fluid film inertia significantly affects the loading capacity (or pressure distribution), and velocity profiles. Temperature variance caused by fluid film inertia is insignificant.
Theory of Thermoelastic Instability of Rotating Rings in Sliding Contact With Wear
Authors: Lebeck A. O.
Published: November 2010

The instability of two rings in rotating, sliding contact is examined. The configuration is typical of that of a mechanical face seal. Circumferentially varying friction heating at the seal interface may lead to an unstable thermoelastic distortion of the ring and uneven wear. Heat transfer equations are developed which include the effects of contact conductance and unsteady state heat transfer in one of the rings. Deflection equations, which include both thermal and mechanical loading, are developed and combined with a wear equation to form a mathematical model that predicts the limits for stable operation. It is shown that contact conductance, ring stiffness, thermal coefficient of expansion, sliding speed, friction, thermal conductivi¨ty, and geometry are important parameters in relation to stability. Stability conditions are established for several cases. The harmonic content of the uneven wear resulting from instability depends on the initial waviness of the ring and point of operation in the region of instability. It is shown that some seals are stable at all harmonics.
On the Heavily Loaded Elastohydrodynamic Contacts of Layered Solids
Authors: Gupta P. K.
Published: November 2010

An inlet zone analysis is presented for the elastohydrodynamic lubrication of heavily loaded contacts of layered elastic solids under isothermal and isoviscous conditions. An elastic layer of incompressible elastomeric material (with Poisson’s ratio, ν = 0.50) bonded to a rigid substrate is considered. Numerical results are presented in dimensionless form to describe the variation of nominal film thickness over a wide range of loads, layer thicknesses, and other operating variables.
Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part II—Ellipticity Parameter Results
Authors: Hamrock B. J. , Dowson D.
Published: November 2010

A numerical solution of the isothermal elastohydrodynamic problem for point contacts has been presented which reproduces all the essential features of the previously reported experimental observations based upon optical interferometry. In particular, the two “side lobes” in which minimum film thickness regions occur are shown to emerge in the theoretical solutions. The influence of the ellipticity parameter upon solutions to the point contact problem has been explored in the present paper. The ellipticity parameter (k) was varied from one (a ball on a plate) to eight (a configuration approaching line contact), and it has been shown that the minimum film thicknesses can be related to the well known line contact solutions by remarkably simple expressions involving either (k) or the effective radius of curvature ratio (Ry/Rx).
Bending Stresses in Spherically Hollow Ball Bearing and Fatigue Experiments
Authors: Nypan L. J. , Coe H. H. , Parker R. J.
Published: November 2010

Spherically hollow balls of 21.7, 50.0 and 56.5 percent mass reduction have been operated in ball bearings and in a 5-ball fatigue tester with differing outcomes. Available theoretical and experimental treatments of stresses in spherically hollow balls are reviewed and compared. Bending stresses are estimated for these spherically hollow balls to better understand the differences in ball bearing and fatigue test experience.
On the Mechanism of Lubricant Film Failure in Sliding Concentrated Steel Contacts
Authors: Begelinger A. , de Gee A. W. J.
Published: November 2010

The lubrication mechanism of fully submerged sliding point contacts of AISI 52100 steel has been studied as a function of surface roughness and oxygen content of the lubricant. Strong indications are found that, at relatively low values of normal load and sliding speed, a partial elastohydrodynamic lubricant film (incompletely) separates the surfaces. This film survives asperity contacts because newly formed contacts oxidize rapidly. Collapse of the lubricant film occurs if oxidation can no longer keep ahead of the formation of new asperity contacts. Increasing surface roughness and decreasing oxygen content of the lubricant both cause a reduction in load carrying capacity. Depending upon the value of the speed of sliding, collapse of the EHD film either leads to “incipient scuffing” or to severe wear (scoring). This effect is probably associated with a metallurgical transformation in the steel at a particular value of the conjunction temperature.
Static and Dynamic Performance of an Infinite Stiffness Hydrostatic Thrust Bearing
Authors: Tully N.
Published: November 2010

A novel form of variable hydrostatic restriction is proposed which will automatically achieve a high, infinite or negative static stiffness over a substantial load range. The restrictor is formed between the bearing body and a spring mounted conical plug. The steady state performance is analyzed and design curves presented which are valid for any cone angle from zero, i.e., fixed clearance, to 90 deg which is the normal diaphragm restrictor. The dynamic response to forced sinusoidal vibrations is examined in conventional vibration analysis form and it is found that the restrictor system may be designed to act as a vibration absorber.
Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part IV—Starvation Results
Authors: Hamrock B. J. , Dowson D.
Published: November 2010

Utilizing the theory and numerical procedure developed by the authors in an earlier publication the influence of lubricant starvation on minimum film thickness was investigated. This study of lubricant starvation was performed simply by moving the inlet boundary closer to the contact center. From the results it was found that for the range of conditions considered the value of dimensionless inlet distance at the boundary between fully flooded and starved conditions (m*) can be expressed simply as m*=1+3.06Rxb2Hc,F0.58 or m*=1+3.34Rxb2Hmin,F0.56 that is, for a dimensionless inlet distance (m) less than m*, starvation occurs, and for m ≥ m*, a fully flooded condition exists. Furthermore, it has been possible to express the central and minimum film thickness for a starved condition as Hc,S=Hc,Fm−1m*−10.29Hmin,S=Hmin,Fm−1m*−10.25 Contour plots of the pressure and film thickness in and around the contact are shown for the fully flooded and starved lubricant condition. From these contour plots it was observed that the pressure spike becomes suppressed and the film thickness decreases substantially as starvation increases.
An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing
Authors: Etsion I. , Fleming D. P.
Published: November 2010

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.
Thermally Induced Migration of Hydrocarbon Oil
Authors: Fote A. A. , Slade R. A. , Feuerstein S.
Published: November 2010

An investigation of the surface migration of thin films of hydrocarbon oil on metal substrates has been undertaken to determine the effect of temperature gradients on the distribution of lubricants in spacecraft mechanical assemblies. The results of experiments performed in air were discussed earlier. We now discuss the results of experiments performed under vacuum. The important role played by surface finishes is demonstrated. Mathematical models of these results are developed.
A Class of Maximum Load Capacity Sector Thrust Bearings
Authors: Gregory E. W. , Maday C. J.
Published: November 2010

A finite element method is used to determine the pressure distribution for a sector pad of a thrust bearing. The optimization technique known as pattern search is applied to the load capacity as a function of the pocket boundary and pocket depth. An optimum ratio of effective length to width is discovered and the optimum pocket geometry, associated two dimensional pressure distribution, power dissipation, center of pressure, and maximum load capacity are calculated for bearings of various curvature and degree of arc.
Turbulent Flows Near Steps in a Thin Channel With One Moving Wall
Authors: Salimonu D. O. , Kistler A. L. , Burton R. A.
Published: November 2010

Experimental measurements are reported for flow in a cylindrical annulus, with moving inner surface and a step on the stationary outer cylinder. This is related to bearing flows near steps. Strong effects of convected inertia are observed, and these are subdivided into three major classifications. Simplified analyses which include the major physical influences in each category are developed, and are shown to be in reasonable agreement with the measurements.
Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part III—Fully Flooded Results
Authors: Hamrock B. J. , Dowson D.
Published: November 2010

Utilizing the theory developed by the authors in an earlier publication, the influence of the ellipticity parameter, the dimensionless speed, load, and material parameters on minimum film thickness was investigated. The ellipticity parameter was varied from one (a ball on a plate configuration) to eight (a configuration approaching a line contact). The dimensionless speed parameter was varied over a range of nearly two orders of magnitude. The dimensionless load parameter was varied over a range of one order of magnitude. Conditions corresponding to the use of solid materials of bronze, steel, and silicon nitride and lubricants of paraffinic and naphthenic mineral oils were considered in obtaining the exponent in the dimensionless material parameter. Thirty-four different cases were used in obtaining the minimum film thickness formula given below as H¯min=3.63U0.68G0.49W−0.073(1−e−0.68k) A simplified expression for the ellipticity parameter was found where k=1.03RyRx0.64 Contour plots were also shown which indicate in detail the pressure spike and two side lobes in which the minimum film thickness occurs. These theoretical solutions of film thickness have all the essential features of the previously reported experimental observations based upon optical interferometry.
Surface Temperatures in Distributed Contacts. Application to Bearing Design
Authors: Floquet A. , Play D. , Godet M.
Published: November 2010

Two dimensional Fourier transform methods developed by Ling to calculate contact temperatures were applied to the case of a dry bearing operating with a plastic liner. Results show that uncertainties concerning heat distribution along the contact arc cause smaller differences in contact temperatures than some apparently minor design changes. The effect on temperature of various parameters such as liner position, liner thickness, types of motion and speed, and cooling conditions is given. The method proves to be valuable as a guide in the design of dry bearings.
A Method for Measuring Surface Temperature Between Rolling/Sliding Steel Cylinders
Authors: Kannel J. W. , Zugaro F. F. , Dow T. A.
Published: November 2010

A special bisignal transducer has been developed which allows pressure and temperature measurements to be made (essentially) simultaneously. With this technique, it is possible to locate the contact zone temperature relative to pressure and evaluate the relationship between heat generation and pressure. Temperature and pressure data obtained using a synthetic mineral oil as the lubricant have been obtained for rolling and rolling-sliding contact in a disk apparatus. The temperature rise through the contact zone has been shown to be on the order of 20–40 C.
Lubrication of High-Speed, Large Bore Tapered-Roller Bearings
Authors: Parker R. J. , Signer H. R.
Published: November 2010

The performance of 120.65-mm- (4.75-in.-) bore tapered-roller bearings was investigated at shaft speeds up to 15,000 rpm (1.81 × 106 DN). Temperature distribution and bearing heat generation were determined as a function of shaft speed, radial and thrust loads, lubricant flow rate, and lubricant inlet temperature. Lubricant was supplied either by jets or by a combination of holes through the cone directly to the cone-rib contact and jets at the roller small-end side. Cone-rib lubrication significantly improved high-speed tapered-roller bearing performance, yielding lower cone-face temperatures and lower power loss and allowing lower lubricant flow rates for a given speed condition. Bearing temperatures increased with increased shaft speed and decreased with increased lubricant flow rate. Bearing power loss increased with increased shaft speed and increased lubricant flow rate.
An Investigation Into the Influence of Fluid Viscoelasticity in a Squeeze Film Bearing
Authors: Tichy John A. , Winer Ward O.
Published: November 2010

This investigation concerns a prediction of the behavior of viscoelastic fluids in a parallel circular squeeze film with a constant approach velocity, and a comparison to experimental results. The squeeze film geometry has direct application to unsteady hydrodynamic lubrication. The analysis predicts that load capacity of a viscoelastic fluid may be increased due to normal stress effects or decreased due to a delayed response of shear stress to a change in shear rate. Ten tested fluids include Newtonian control fluids, silicone fluids, high molecular weight polymers in petroleum oils, and extremely high molecular weight polymers in water and glycerin. The experimental squeezing is accomplished by the free fall of a cylindrical steel rod along its axis toward a stationary opposing surface. Film thickness, velocity of approach and load are measured. The velocity of approach is essentially constant in the range of film thickness considered. The water-glycerin-polymer solutions exhibited load capacity increases up to 33 percent, while the petroleum-polymer and silicone fluids showed decreases to 23 percent. It appears that viscoelastic effects cannot account for the reported improved bearing performance of polymer-additive lubricants.
Wear Studies on Aircraft Brake Materials
Authors: Ho Ting Long
Published: November 2010

An investigation of both worn surfaces of friction pads and steel rotors which are being applied in current aircraft brakes has been carried out by employing an x-ray diffraction technique. It consists of the analysis of chemical element distribution in the surface layers. The wear particles were also examined by using the scanning electron microscope. The initiation and growth of surface cracks and the oxidation were emphasized in this investigation. A wear model was proposed for the current aircraft brake materials. Essentially this model proposed that cracks are formed in the surface layer of the break material due to the normal and fractional stresses. It is primarily surface temperature dependent.
The Wear of High Molecular Weight Polyethylene—Part I: The Wear of Isotropic Polyethylene Against Dry Stainless Steel in Unidirectional Motion
Authors: Atkinson J. R. , Brown K. J. , Dowson D.
Published: November 2010

The wear of surgical grade ultra-high molecular weight polyethylene against stainless steel has been studied for unidirectional motion. After a short wearing-in period, two distinct steady-state regions appear on the wear graphs. In the first section adhesion is the predominant wear mechanism and a transfer film of polymer builds up on the steel counterface. After a certain sliding distance, determined by the load, the adhesive mechanism is augmented by fatigue wear and the wear rate increases sharply and remains constant at the new value.
Calculation of Surface Deformation in Point Contact EHD
Authors: Biswas S. , Snidle R. W.
Published: November 2010

The paper describes three different numerical techniques for the accurate evaluation of the elastic deformation in elastohydrodynamic point contacts. The first method relies on a first order representation of the pressure distribution over triangular elements whereas the second and third methods use a second order method with rectangular elements. Comparison of results obtained using the numerical techniques described with known, exact values indicates that accuracies better than one percent can be expected when using the methods in the ehd problem.
Effect of Gas Bubbles on Behavior of Isothermal Michell Bearings
Authors: To̸nder Kristan
Published: November 2010

An account of an analysis of the effect of finely dispersed bubbles on the hydrodynamic lubrication of isoviscous straight pivot pads is presented. The bubble-effect is seen to shift the load center position, and more so for small tilts than for high ones. This is shown to establish two distinct operational modes for very realistic pivot positions, the one stable and the other unstable and representing the limit of stability of bubbly Michell bearings.
Wear–A Critical Synoptic View
Authors: Tabor David
Published: November 2010

This paper discusses critically some of the major processes that are likely to be involved in wear and to ask questions that might generate useful and creative responses. For simplicity wear processes are divided into three groups. The first type is that in which wear arises primarily from adhesion between the sliding surfaces; the second is that deriving primarily from nonadhesive processes; and the third is that very broad class in which there is interaction between the adhesive and nonadhesive processes to produce a type of wear that seems to have characteristics of its own. The paper deals with metals, polymers, and ceramics and concludes with the view that, on account of the complex interaction of various wear mechanisms, the constant challenge to predict the wear of any given system, based on material properties, is unlikely to be surmounted for many years to come.
Adhesive Wear of Polymers
Authors: Belyi V. A. , Sviridyonok A. I. , Smurugov V. A. , Nevzorov V. V.
Published: November 2010

Adhesive wear is a characteristic but inadequately studied type of wear of polymer materials. In local regions of real contact an intensive molecular (adhesive) interaction is observed under rubbing conditions, which is stronger than the bonds between individual elements in the supermolecular formations or in polymer molecules, leading to cohesive failure of the material. Wear products can escape from the contact region as gases or as solid substances, or they can form a “third body”, i.e., a transferred layer of one material is deposited on the surface of the other. The direction, mechanism, and character of the occurring processes are determined, first of all, by the structures of the interacting materials. To know the mechanism of adhesive wear enables one to predict dangerous failures of the surfaces under rubbing due to seizure, on the one hand, and to find ways of governing the frictional interaction and create efficient self-lubricated polymer-based materials on the other hand. One of the efficient ways of providing minimum wear in metal-polymer friction pairs is to govern the process of developing “friction polymers” and to use mixtures of polymers having different thermophysical properties as antifrictional materials.
Wear of Abrasives in Simulated Hot Grinding
Authors: Komanduri R. , Laverty W. H. , Shaw M. C.
Published: November 2010

Chemical interaction between the work material and the abrasive plays an important role in grinding. This will be more so in hot grinding. In this paper a novel experimental setup to study the wear and performance of various abrasives in hot grinding (up to ≈ 1000° C) is described. An oxy-acetylene torch under the work material is used as the heat soruce. Initial results on the performance of two commonly used abrasives, namely aluminum oxide and silicon carbide in simulated hot grinding of a cobalt base superalloy at 1000° C are presented using a scanning electron microscope. The results are compared with similar ones obtained at room temperature for the same combination of work material and abrasive. The results indicate that while silicon carbide wears more than aluminum oxide at room temperature, the reverse was found to be the case at high temperature. Also, the mode of wear and the nature of buildup were found to be different. In hot grinding, wear of aluminum oxide was found to involve the continuous release of micron sized crystallites while the formation of whiskers of silicon carbide was associated with the wear of silicon carbide. Buildup on aluminum oxide as metal was invariably found at room temperature while a uniform reaction product was present at high temperature.
The Analysis of Contact Stresses in Rolling Element Bearings
Authors: Hartnett M. J.
Published: November 2010

A numerical solution is presented which can be used to analyze the complete range of frictionless contact problems found in rolling element bearings. A three dimensional, linear elastic solution to the problem is developed by combining the Boussinesq force-displacement relationships for a half-space with a modified flexibility method. In this manner a stable system of linear algebraic equations in terms of the unknown surface pressures is formed, with no restrictions placed upon either contact symmetry or material connectivity. Several numerical examples of common but hitherto unsolved contact problems prevalent in rolling element bearing applications are also presented.
An Analysis of the Flow of a Viscoelastic Fluid Between Arbitrary Two-Dimensional Surfaces Subject to Normal High Frequency Oscillations
Authors: Tichy J. A. , Skinkle Mary Ellen
Published: November 2010

An analytic solution is presented for the flow of a viscoelastic fluid between arbitrary but sufficiently smooth two-dimensional surfaces, one of which is subjected to small high frequency oscillations normal to the other. The results are presented in terms of the complex viscosity parameters of linear viscoelasticity, and are valid for any simple viscoelastic fluid, provided the oscillation amplitude is sufficiently small. Fluid inertia effects are included although convective inertia terms are shown to be negligible through order-of-magnitude considerations. The resulting linearized equations of motion can be solved through conventional means by techniques established in earlier works. Solutions for the velocity field, pressure distribution, and load are presented in terms of the Reynolds and Deborah numbers. Two illustrative cases are demonstrated—the tapered thrust bearing and the partial journal bearing. Unusual resonance effects in pressure and load are exhibited as the oscillation frequency (or Reynolds number) is increased for a particular fluid.
Factors Influencing Power Loss of Tilting-Pad Thrust Bearings
Authors: Gregory R. S.
Published: November 2010

Several recent technical papers have discussed the advantages of various designs of thrust bearings by comparing the power losses of the different type bearings. However, great care must be exercised to ensure that the comparisons are fair. There are many external factors that influence loss, such as oil flowrate, clearance, supply temperature and so on. Unless compensation for these external factors is included in the analysis, the power loss comparisons may be misleading. This paper attempts to show both qualitatively and quantitatively the influence that various external factors have on bearing power loss. It has been determined experimentally that oil flowrate adjustment can vary power loss by as much as 150 percent. The choice of radial or tangential discharge can reduce power loss by 60 percent, while the actual size of the discharge can influence power loss by 50 percent. Varying the bearing end play has little effect on measured power loss.
Effect of Phosphorus on the Friction and Wear Characteristics of Cu-Sn-P Alloys
Authors: Taga Y. , Nakajima K.
Published: November 2010

The effects of phosphorus on the friction and wear characteristics of Cu-5 at. percent Sn-P alloys containing 1–5 at. percent P were studied using a pin on disc apparatus. The results showed that the decrease in both the coefficient of friction and the rate of wear became conspicuous with the increase in quantity of Cu3P coexisting in the matrix; its amount increases with the content of phosphorus. The structural changes in the surface of the specimen due to heating in a vacuum were observed by using Auger electron spectroscopy and X-ray photoelectron spectroscopy. It was seen that the surface concentration of phosphorus strongly increased after heating at 573K, whereas the diffusion of tin atoms was markedly retarded. It was concluded from these results that the behavior of phosphorus atoms in the surface during sliding played an important role in the friction and wear characteristics of Cu-Sn-P alloys.
Abrasion of WC-Co Alloys by Quartz
Authors: Larsen-Basse J. , Koyanagi E. T.
Published: November 2010

Cemented WC-Co composites were abraded by quartz abrasives in a three-body test. It was found that the quartz has an effective hardness as an abrasive of 1260–1320 kg/mm2 (12.36–12.94 GPa), which makes it a soft abrasive relative to most cemented carbides. Material is removed in abrasive wear by two mechanisms—cobalt extrusion and carbide fragmentation. The binder extrusion is rate-controlling and occurs due to repeated loading of the surface material in friction-generated shear. The cracking and fragmentation of the carbide grains is a secondary removal mechanism which depends upon the relaxation of compressive stresses in the carbide grains as the cobalt binder is extruded. The wear rate is directly related only to binder mean free path and it increases linearly with this parameter.
A Rheological Model for Elastohydrodynamic Contacts Based on Primary Laboratory Data
Authors: Bair Scott , Winer W. O.
Published: November 2010

A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: Low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature and, in one specific case where direct comparison could be made, good numerical agreement is shown.
Dynamics of Rolling-Element Bearings—Part III: Ball Bearing Analysis
Authors: Gupta P. K.
Published: November 2010

An analytical formulation for the generalized ball, cage, and race motion in a ball bearing is presented in terms of the classical differential equations of motion. Ball-race interaction is analyzed in detail and the resulting force and moment vectors are determined. The ball-cage and race-cage interactions are considered to be either hydrodynamic or metallic and a critical film thickness defines the transition between the two regimes. Simplified treatments for the drag and churning losses are also included to complete a rigorous analytical development for the real-time simulation of the dynamic performance of ball bearings.