bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Effects of Homogeneous Reynolds Roughness in a Two-Dimensional Slider Bearing With Exponential Film Thickness
Authors: Phan-Thien N. , Atkinson J. D.
Published: November 2009

The effects of rough surfaces on the performance of a two-dimensional slider bearing with a mean exponential film thickness is investigated using the Reynolds equation, whose application requires the aspect ratio of the bearing to be large and the amplitude and the characteristic frequencies of the roughness to be considerably smaller than a representative film thickness (all are dimensionless). This problem has been previously considered by Sun using a straightforward perturbation approach; here, a formulation due to Keller is adopted and we make explicit use of h0/l<<1, where l is the bearing length and h0 is a representative film thickness. It is shown that neglecting terms of 0(h0/l), the load enhancement is maximum and positive for a transverse surface roughness; and it is minimum and negative for a parallel surface roughness. In these two extreme cases, both load enhancements depend on the statistics of the surface only through its mean square and are exactly predicted by Christensen’s theory.
Second Order Effects in Non-Newtonian Lubrication Theory. A General Perturbation Approach
Authors: Bourgin Patrick
Published: November 2009

This paper is a theoretical investigation into the problem of the isothermal laminar flow of a Rivlin-Ericksen fluid of complexity n between arbitrary two bidimensional surfaces separated by a small gap. Nonlinear viscosity effects and normal-stress effects have both been taken into account. It had been recently proved that the use of a method of resolution similar to that of Reynolds imposes to reduce the field of rheological models; a “generalized Reynolds equation,” available for Stokesian fluids was then derived. Returning now to the most general differential fluid, an analytic approximate solution has been searched under the form of perturbation expansions for the normal stress and velocity fields, respectively. The corresponding set of differential equations has been given. An example has been worked out in order to compare our approximate solution with an exact solution which exists in the considered particular case. At that occasion, a discussion is opened about the choice of adequate boundary conditions at the ends of the lubricant film.
Non-Newtonian Squeeze Film Between Two Plane Annuli
Authors: Elkouh A. F. , Nigro N. J. , Liou Y. S.
Published: November 2009

An analysis is presented for the laminar squeezing flow of an incompressible power-law fluid between parallel plane annuli. The results obtained are based on the thin-film approximation, and negligible fluid-inertia. Analytic expressions for the load capacity of the squeeze film and its thickness-time relation are presented.
Effects of Ultra-Clean and Centrifugal Filtration on Rolling-Element Bearing Life
Authors: Loewenthal S. H. , Moyer D. W. , Needelman W. M.
Published: November 2009

Fatigue tests were conducted on groups of 65-millimeter bore diameter deep-groove ball bearings in a MIL-L-23699 lubricant under two levels of filtration. In one test series, the oil cleanliness was maintained at an exceptionally high level (better than a class of “00” per NAS 1638) with a 3 micron absolute barrier filter. These tests were intended to determine the “upper limit” in bearing life under the strictest possible lubricant cleanliness conditions. In the tests using a centrifugal oil filter, contaminants of the type found in aircraft engine filters were injected into the filters’ supply line at 125 milligrams per bearing-hour. “Ultra-clean” lubrication produced bearing fatigue lives that were approximately twice that obtained in previous tests with contaminated oil using 3 micron absolute filtration and approximately three times that obtained with 49 micron filtration. It was also observed that the centrifugal oil filter had approximately the same effectiveness as a 30 micron absolute filter in preventing bearing surface damage.
Flange Loads Measurements in a Cylindrical Roller Bearing
Authors: Dow T. A. , Kannel J. W.
Published: November 2009

A method of measuring the forces between a roller and the guide flange in a turbine main shaft bearing has been developed. Experimental measurements of these forces were made for a nonpreloaded bearing with nominally balanced rollers and also intentionally unbalanced rollers. The bearing was radially loaded and measurements of the flange forces were made with the rollers, both in and out of the loaded region. Two different lubricants were studied, and significantly different flange forces were measured as a result of the change in viscosity. Using a MIL-L-23699 lubricant, edge loads in the range of 70–90 N (15–20 lb) were measured for both the balanced and the unbalanced rollers. However, when a light mineral oil (kerosene) was substituted for the higher viscosity military oil, higher edge loads (110–135 N) were measured for the unbalanced roller, but the end forces were reduced for the balanced roller.
A Unified Model for Rolling Contact Life Prediction
Authors: Tallian T. E.
Published: November 2009

Systematizing a ten-year development of engineering models for the prediction of rolling contact fatigue life distributions, a unified model is presented. Based on a crack growth rate relationship with local plastic strain and ductility, and on defect populations in the contact material and at the contact surfaces, the model predicts life of a defect, then generalizes to rolling body life. Subsurface and surface failure modes are considered; the effects of material matrix, defect severity, stress condition, surface traction, and asperity interactions are encompassed. The model includes crack initiation and propagation terms and allows for a finite minimum life. The model specializes to Lundberg-Palmgren theory.
The Effects of Artificially-Produced Defects on the Film Thickness Distribution in Sliding EHD Point Contacts
Authors: Cusano C. , Wedeven L. D.
Published: November 2009

The effects of artificially-produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact are investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, are held stationary at various locations within and in the vicinity of the contact region while the disk is rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.
Regimes of Traction in Concentrated Contact Lubrication
Authors: Bair S. , Winer W. O.
Published: November 2009

Experimental evidence is presented for the existence of three regimes of traction in concentrated contacts. Data were obtained in a rolling contact simulator by varying the lubricant, temperature, rolling speed, load and surface roughness at a fixed slide-to-roll ratio. In one regime, the traction is mainly governed by the limiting shear stress of the lubricant. At lower thicknesses (Λ < 1) the mixed regime is encountered and traction is increased due to asperity interaction. At higher film thicknesses, the lubricant pressure is distributed over a greater area than the Hertzian region resulting in a lower average pressure and reduced traction.
Effect of Surface Roughness on Elastohydrodynamic Line Contact
Authors: Majumdar B. C. , Hamrock B. J.
Published: November 2009

A numerical solution of an elastohydrodynamic lubrication (EHL) contact between two long, rough surface cylinders is obtained. A theoretical solution of pressure distribution, elastohydrodynamic load, and film thickness for given speeds and for lubricants with pressure-dependent viscosity, material properties of cylinders, and surface roughness parameters is made by simultaneous solution of an elasticity equation and the Reynolds equation for two partially lubricated rough surfaces. The pressure due to asperity contact is calculated by assuming a Gaussian distribution of surface irregularities. The elastic deformation is found from hydrodynamic and contact pressures by using plane strain analysis. The effect of surface roughness on EHL loads, speeds, and central film thicknesses is studied. The results indicate that for a constant central film thickness (1) increasing the surface roughness decreases the EHL load and (2) there is little variation in minimum film thickness as the surface roughness is increased.
Analysis of Starvation Effects on Hydrodynamic Lubrication in Nonconforming Contacts
Authors: Brewe D. E. , Hamrock B. J.
Published: November 2009

Numerical methods were used to determine the effects of lubricant starvation on the minimum film thickness under conditions of a hydrodynamic point contact. Starvation was effected by varying the fluid inlet level. The Reynolds boundary conditions were applied at the cavitation boundary and zero pressure was stipulated at the meniscus or inlet boundary. The analysis is considered valid for a range of speeds and loads for which thermal, piezoviscous, and deformation effects are negligible. It is applied to a wide range of geometries (i.e., from a ball-on-plate configuration to a ball in a conforming groove). Seventy-four cases were used to numerically determine a minimum-film-thickness equation as a function of the ratio of dimensionless load to dimensionless speed for varying degrees of starvation. From this, a film reduction factor was determined as a function of the fluid inlet level. Further, a starved fully flooded boundary was defined and an expression determining the onset of starvation was derived. As the degree of starvation was increased, the minimum film thickness decreased gradually until the fluid inlet level became critical. Reducing the fluid inlet level still further led to a sharp decrease in the minimum film thickness. An expression determining the critically starved fluid inlet level was derived. The changes in the inlet pressure buildup due to changing the available lubricant supply are presented in the form of three-dimensional isometric plots and also in the form of contour plots.
Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings
Authors: Li Chin-Hsiu
Published: November 2009

A general analysis and computational method is presented for calculating the unbalance and self-excited response of high-speed rotor-bearing systems. The analysis is applied to the calculation of the transient response of a rotor supported by two floating ring bearings. Included in the analysis are rotor gyroscopic moments as well as the flexibility of the shaft. Emphasis is placed on determining rotor whirl orbits as influenced by rotor unbalance, the phase angle of the unbalance masses, the clearances of the bearings, the viscosity of the lubricant, and the shock loads that the rotor may be subjected to. It is found that the rotor-bearing system normally operates in an unstable mode in the linear stability sense. However, the nonlinear forces developed by the fluid films of the floating ring bearing will bring the rotor-bearing system to whirl at a limit cycle well within the clearance circles. It is also shown that the rotor assembly will undergo a conical motion when the rotor and wheel configuration is asymmetrical.
Four Pad Tilting Pad Bearing Design and Application for Multistage Axial Compressors
Authors: Nicholas J. C. , Kirk R. G.
Published: November 2009

The advantages of operating multistage axial compressors on 4 pad tilting pad bearings are discussed and compared to other fixed bore and tilting pad bearing designs. These advantages include operation free of subsynchronous vibration and, with between pivot loading, placement of peak response speeds well outside of the operating speed range. Examples of analytical design studies of 3 actual rotor systems are presented and discussed to illustrate the design recommendations. Test stand results are also included for 3 axial compressors to help substantiate the analytical results.
An Evaluation of the Plane Strain Compression Test. II. Experimental Study of the Friction Test: Role of Transfer Layers in Boundary Lubrication
Authors: Delamare F. , De Vathaire M. , Kubie´ Jan
Published: November 2009

The Plane Strain Compression Test is used to measure the mean friction shear stress at the sheet-die interfaces. It is found that the shear-stress level is strongly influenced by transfer film formation on the dies. The thickness of these films, and their elementary chemical composition, have been determined by Auger Electron Spectroscopy and rugosimetry. The effect of contact mechanics and lubricant parameters on transfer film formation is discussed.
Effects of Amplitude of Oscillation on the Wear of Dry Bearings Containing PTFE
Authors: Lancaster J. K. , Bramham R. W. , Play D. , Waghorne R.
Published: November 2009

The friction coefficients and wear rates of two dry-bearing materials have been measured during oscillatory motion at different amplitudes. The materials were composites incorporating fabrics of interwoven PTFE and glass fibers and differed in the pitch of the glass fiber at the surface. The worn surfaces were examined by SEM, EPMA, and XPS. The results show that when the amplitude of oscillation becomes less than the glass fiber pitch, third-body debris films on the counterface become increasingly nonuniform and surface roughness increases. The resulting trend toward increased bearing liner wear, however, is small provided that the amplitude of oscillation remains constant. The relevance of the results to the operation of airframe dry bearings operating under active control is discussed.
Viscoplastic Lubrication of Asperities
Authors: Sheu S. , Wilson W. R. D.
Published: November 2009

Theoretical analyses for the lubrication of rigid wedge-shaped asperities by a viscoplastic liquid are developed. Two cases are considered in which wedge action and squeeze action are dominant. The results of the analyses are compared with previous experimental investigations of the factors influencing susceptibility to lubrication failure.
Theoretical Effects of Rigid Particle Additives in Noncyclic Squeeze Films
Authors: Sinha Prawal , Singh Chandan
Published: November 2009

The micropolar fluid theory, a possible non-Newtonian model for fluids with rigid particle additives in which the average molecular size may be comparable to the material characteristic length, is applied to a two-dimensional problem of squeeze film of a ball in a spherical seat and to some three-dimensional noncyclic squeeze film problems, assuming the characteristic coefficients to be constant, in an effort to study the effects of rigid particle additives for the three-dimensional micropolarity model. Increase in effective viscosity due to the presence of additives is established theoretically. It is also shown that the theoretical effects of the additives on three-dimensional lubrication are identical to the two-dimensional problems, at least qualitatively.
Effect of Surface Ellipticity on Dynamically Loaded Cylindrical Bearings
Authors: Goenka P. K. , Booker J. F.
Published: November 2009

The finite element formulation for regular cylindrical bearings is extended to include irregular (noncylindrical) bearing surfaces. The optimum bearing shape is sought for a specific duty cycle with a constant load and sinusoidal angular displacement. The optimization is done with a view to maximizing the minimum film thickness. For the purpose of optimization a one-dimensional cylindrical bearing is considered. The optimum among all elliptical shapes is found to combine a specifically elliptical sleeve and a perfectly circular journal. For this optimum noncylindrical bearing the absolute minimum film thickness is about a factor of 36 higher than that for the corresponding regular bearing. The absolute maximum pressure for the optimum bearing is about a factor of 5 lower than that for the regular bearing.
Effect of Biphase Lubricants on Dynamics of Rigid Rotors
Authors: Mukherjee A.
Published: November 2009

The dynamic behavior of rigid rotors as affected by the use of liquid-solid biphase lubricants in the supporting hydrodynamic bearings is studied theoretically. Two categories of dynamic behavior viz (a) unbalance response at low rotor speeds, and (b) half frequency whirl at high speeds, are studied. It is shown that the use of liquid-solid biphase lubricants causes considerable reduction in the size of journal orbit of an unbalanced rotor. The influence of particle size and dispersion concentration is studied. It is observed that an early reversal of journal surface velocity in the trailing half of crushing zone reduces the efficacy of the crushing action of the solid phase to some extent and results in periodic pulses applied by the solid phase on the journal. At higher journal speeds at which the operating point of the journal becomes unstable and the phenomenon of half-frequency whirl sets in, the use of biphase lubricants with small and medium-size particles causes a reduction in the size of whirl orbits. The journal, however, keeps whirling in a manner such that the whirl ratio crosses the value of + 1/2 twice in an orbit and thus the bearing loses its rotational load bearing capacity twice in an orbit. The use of large particles with heavy or medium weight rotors results in a significant qualitative change in the nature of whirl orbit. The journal center in such cases does not encircle the bearing center and the whirl ratio of + 1/2 is never reached. The liquid phase retains rotational load bearing capacity and shares the major part of rotor weight throughout.
A Comparison of Tilting Pad Thrust Bearing Lubricant Supply Methods
Authors: Mikula A. M. , Gregory R. S.
Published: November 2009

This paper compares three different lubricant supply methods—pressurized supply (flooded), spray feed, and leading edge distribution groove—and analyzes their influence on the performance of tilting pad, equalizing thrust bearings. The paper presents experimental data on 267 mm (10-1/2 in.) o.d. bearings, operating at shaft speeds up to 13,000 rpm with loads ranging up to 3.45 MPa (500 psi). The data presented demonstrate the effect each lubricant supply method has on bearing power loss and temperature. Conclusions are drawn, based upon the effectiveness of each design, to guide the potential user.
The Elastic Distortion of Rollers Under Combined Radial and Thrust Loads
Authors: So H. , Gohar R.
Published: November 2009

This paper describes an approximate analysis for finding the elastostatic radial and end face distortion, radial pressure distribution, and solid body rotation of a flat ended axially profiled bearing roller under combined radial and axial loading through the ribs. It is found that a small but significant end face bulge occurs at each roller end when there is radial loading only. Upon the addition of an axial load, this bulge becomes a small depression. The altered geometry there may become significant during bearing operation, as it affects roller skew, wear, and lubrication between the ribs and roller and faces.
Experimental Investigation of the Effect of System Rigidity on Wear and Friction-Induced Vibrations
Authors: Aronov V. , D’Souza A. F. , Kalpakjian S. , Shareef I.
Published: November 2009

This paper presents experimental data and a physical model of the effects of normal load and system rigidity on the friction and wear processes with water lubrication. The transition from mild to severe friction and wear was found to be independent of the system rigidity, but dependent on the normal load. As the normal load is increased further, it reaches another critical value, which depends on the system rigidity, at which high frequency self-excited vibrations are generated. These oscillations exhibit a coupling between the frictional and normal degrees of freedom. It is shown that mild wear rate increases with the normal load and also with the system rigidity.
Interactions Between Dynamic Normal and Frictional Forces During Unlubricated Sliding
Authors: Soom A. , Kim C.
Published: November 2009

The results of measurements showing large normal and frictional force oscillations during unlubricated smooth sliding between steel surfaces are presented. The measurements were made on a pin-on-disk type apparatus instrumented with piezoelectric force and acceleration transducers. Spectral analysis of the contact forces (including inertia forces) up to frequencies of 2 kHz indicate that the fluctuations have their major components in this frequency range. The force oscillations are primarily associated with normal and tangential contact vibrations which are excited by surface irregularities being swept through the contact region during sliding. Transfer function analyses between the normal and frictional forces show the frictional force fluctuations to be in phase with the normal force fluctuations, but related in magnitude by a ratio larger than the concurrently-measured (average) kinetic friction coefficient. This larger oscillatory (or AC) friction coefficient is indicative of fluctuations in the instantaneous coefficient of friction which are shown to occur in synchronism with the contact force oscillations.
Lubrication Mechanism of Solid Lubricants in Oils
Authors: Hisakado T. , Tsukizoe T. , Yoshikawa H.
Published: November 2009

Lubricating properties of machine oils containing such solid lubricants as (CF)n, MoS2, graphite, etc., were studied on a pin and disk machine by measuring an electric contact resistance and a friction force. After lubrication tests, solid lubricants films and transferred wear particles on worn surfaces have been observed by means of an XMA and an optical microscope. The wear mechanism of metals was analyzed considering a mean peak to peak distance and a mean depth of scratches on worn surfaces. The effects of particle size and concentration of (CF)n, and a suspending agent AD-6 on the friciton and wear process were also discussed. It was found that when the large number of (CF)n particles can penetrate into the interface in accordance with an oil flow, they show a good performance as a lubricant but solid lubricant films were not formed on worn surfaces besides graphite particles embedded on those of a copper disk.
The Normal Approach, Contact, and Rebound of Lubricated Cylinders
Authors: Chandra A. , Rogers R. J.
Published: November 2009

An algorithm has been developed to simulate the normal approach, contact, and rebound of lubricated cylinders. The detailed interaction between the lubricated cylinders is predicted, thus providing the pressure distribution, contact forces, and other variables useful in predicting rates of wear. The present technique improves on the existing elastohydrodynamic (EHD) models in the following areas: (1) during contact a solid-solid model is used; (2) a two-dimensional analysis is used to obtain the pressure distributions in both the circumferential and axial directions; (3) inertia effects are approximated; and (4) any specified load can be treated. The simulated results for the constant load case are compared with the results of Wada and Tsukijihara and a formula developed by Cameron. For sinusoidal loads the results are compared with experimental data from a cylinder and sleeve apparatus.
The Use of Line and Point Contacts in Determining Lubricant Rheology Under Low Slip Elastohydrodynamic Conditions
Authors: Heyes D. M. , Montrose C. J.
Published: November 2009

A theoretical study has been made of the elastohydrodynamic small strain behavior of lubricants in line and point contacts. The model for the lubricants is more realistic than those proposed to date and involves a reformulation of the Maxwell model in terms of a Volterra convolution integral equation. In addition to being more physically appealing, the approach can be easily generalized to describe coupled structural and shear relaxation of a nonexponential nature. The calculations predict that certain mineral oils change from exhibiting compressional viscoelastic to elastic behavior at maximum contact pressures and rolling speeds of order 0.5 GPa and 1.0 m/s.
Oil Leakage and Friction Forces of Reciprocating O-Ring Seals Considering Cavitation
Authors: Johannesson H. L.
Published: November 2009

This paper deals with the problem of calculating oil film thicknesses, oil leakage, and friction forces in seal situations like those occurring in hydraulic cylinders. A general scheme for the analysis is presented, covering both piston seals and piston rod seals. The theoretical model considers influence both from the seal itself and from surrounding parallel clearances. It also takes cavitation into account when this occurs. The validity of the model is limited to cases with well lubricated seal contacts, i.e., unbroken oil films. The analysis follows the inverse hydrodynamic theory and requires a known pressure distribution for each seal element. The pressure distributions are calculated with a method presented earlier by the author (at the 5th Leeds-Lyon Symposium on Tribology, September 1978). Calculated values of oil film thicknesses, leakage flows and friction forces are presented for different sealed pressures and different sliding velocities.
Linear Force Coefficients for Squeeze-Film Dampers
Authors: Szeri A. Z. , Raimondi A. A. , Giron-Duarte A.
Published: November 2009

This paper presents a simplifed analysis of viscous squeeze-film damper behavior. It makes use of the notation of averaged inertia and calculates linear velocity and inertia coeffcients. These coefficients are shown to be accurate at practical values of the length/diameter ratio and the gap Reynolds number of the viscous damper.
Transient Lubricating Films With Inertia
Authors: Elrod H. G. , Anwar I. , Colsher R.
Published: November 2009

This paper presents some new equations for the treatment of lubricating films when the effects of inertia cannot be neglected. These equations are necessarily more complicated than Reynolds equation, but reduce to the latter equation when the value of a certain inertia parameter is small. Transient, as well as steady-state operation, is considered via a generalized steam-function-pressure approach. The present paper deals with laminar, continuous films with the slider bearing used to illustrate the theory.
Thermohydrodynamic Analysis of Cooling Effect of Supply Oil in Circular Journal Bearing
Authors: Mitsui J. , Hori Y. , Tanaka M.
Published: November 2009

This paper deals with a theoretical and experimental investigation on the cooling effect of supply oil in a circular journal bearing. Bearing frictional torque, temperature distribution in the bearing bush as well as on the journal surface, eccentricity ratio, oil temperatures at the inlet and outlet, and oil flow rate were measured. A transparent plastic bearing was also used to observe the film flow near the oil groove as well as in the cavitation region. The mixing coefficient was introduced into the thermohydrodynamic analysis in order to determine the initial temperature distribution of the film just behind the inlet. The mixing coefficient was obtained experimentally and its value mainly ranges from 0.4 to 0.8.
Surface Roughness Effects in Hydrodynamic Lubrication: The Flow Factor Method
Authors: Tripp J. H.
Published: November 2009

The average flow model of Patir and Cheng [1, 2] for obtaining an average Reynolds equation in the presence of two dimensional surface roughness is extended and generalized. Expectation values of the flow factors appearing in the formalism are calculated by means of a perturbation expansion of the pressure in a nominal parallel film. Terms in the series are evaluated using the unperturbed Green function, which permits ensemble averaging to be performed directly on the solution. Calculations are carried to second order, which involves only two point correlation functions of the two rough surfaces. Perturbation results agree well with results of the earlier numerical simulation until surface contact becomes important when both approaches are inadequate. The theory displays the dependence of the flow factors on the roughness parameters in simple closed form, leading to improved understanding of the average flow method.
Overall Characteristics of Bearings Lubricated With Ferrofluids
Authors: Tipei N.
Published: November 2009

Using the results shown in some previous papers, the overall characteristics of bearings lubricated with ferrofluids are calculated. First, the load carrying capacity of infinitely long sliding and journal bearings is considered. The pressure center and the attitude angle are also determined. Then, similar characteristics of finite bearings are obtained. In both cases, the new boundary conditions and the actual film extent under magnetic stresses are taken into account. It is shown that friction forces are mainly affected by the change in viscosity due to magnetic particle suspensions, while magnetic stresses modify friction only under special conditions which usually are not met in lubrication. In addition, the flow rates and the side flow coefficients are calculated. It is shown that the lubricant leakage can be reduced and even avoided when proper measures are taken. For short bearings, diagrams are given for the film extent, the film boundaries, the load carrying capacity, and the attitude of the journal center.
Investigation of Friction and Wear of Dynamically Loaded Hydrodynamic Bearings With Abrasive Contaminants
Authors: Ronen A. , Malkin S.
Published: November 2009

A test system is described for investigating friction and wear of hydrodynamic bearings under cyclical dynamic loading conditions with contaminant abrasive particles in the oil supply. Dynamic loading on the test bearing is synchronized with the shaft rotation, so that the oil film thickness history can be determined from the measured shaft orbit for any point on the shaft and liner periphery. Either clean or contaminated oil can be supplied to the test bearing from two separate oil supply systems. Experimental results obtained for six shaft/liner bearing material combinations were similar to those previously obtained for static loading. The friction and wear behavior were found to depend on the relative hardnesses of the shaft and liner. A larger shaft-to-liner hardness ratio generally resulted in more shaft wear and less liner wear. This is attributed to an increased tendency for abrasive particles to partially embed in the liner and cut the shaft when the shaft is harder and/or the liner is softer. With partial embedding, high bearing friction indicative of continuing abrasion persists after changing from contaminated to clean oil.
A Numerical Solution for Layered Solid Contact Problems With Application to Bearings
Authors: Chiu Y. P. , Hartnett M. J.
Published: November 2009

Presented herein is a method of solution for three dimensional counterformal contact problems involving layered solids. Based on the generalized Boussinesq solution for a layered half space, displacement and stress coefficients are formulated for a uniformly distributed load applied over a rectangular area on the surface of a layered half space. A precise analytical solution has been developed to find the surface pressure, contact area, approach and subsurface stresses for contact of arbitrary surface shapes. Numerical results have been obtained for the indentation of a second order surface with a layered solid for the case the layer to substrate shear modulus ratio equal to 3, which simulates the contact of a steel rolling element with a steel bearing ring supported by aluminum substrate (or housing) in a transmission system.
Influence of Surface Roughness and Its Orientation on Partial Elastohydrodynamic Lubrication of Rollers
Authors: Prakash J. , Czichos H.
Published: November 2009

In this paper, a complete solution for a rough, isothermal elastohydrodynamic line contact operating in the partial lubrication regime is presented. The semianalytical EHD line contact model developed recently [12], is used in solving the coupled system of average Reynolds equation and the elasticity equation. The effects of various operating parameters and the roughness parameters are investigated with an emphasis on the outlet behavior. The results indicate that in the partial lubrication regime changes in the outlet may play an important role on the stability of elastohydrodynamic films.
On Isothermal Squeeze Films
Authors: Blech J. J.
Published: November 2009

It is shown that squeeze film damping cutoff frequencies can be computed directly from the lowest eigenvalue of the Helmholtz equation. A kinematic mode is proposed and analyzed for the computation of those frequencies and it is demonstrated that Griffin’s calculations may underestimate considerably those frequencies. New results are given for the squeeze film behavior between rectangular plates, annuli which are not necessarily thin and plate sectors.
Centrifugal Effects in Misaligned Hydrostatic Thrust Bearings
Authors: Safar Z. S.
Published: November 2009

An analysis is conducted and solutions are provided for the effect of centrifugal forces on hydrostatic misaligned thrust bearings. The results show that centrifugal forces reduce considerably the load capacity, the friction torque and increase the lubricant flow rate. It is found that the effect of centrifugal forces is decreased as tilting of the bearing is increased.
An Experimental Investigation of the Stability of Externally Pressurized Gas-Lubricated Porous Thrust Bearings
Authors: Chang H. S. , Wang Z. S. , Sun D. C.
Published: November 2009

The stability characteristics of the porous disk thrust bearing was studied experimentally and compared with a theoretical prediction [3]2. The discrepancy between them was found to be small in the low supply pressure region and large in the high supply pressure region. At instability the pressure in the plenum was found to oscillate in response to the oscillation of the upper thrust plate. Thus the plenum volume emerged as an important factor affecting stability. This finding, which appears to be the first ever reported, led to a preliminary theoretical investigation of the plenum volume effect. A satisfactory explanation of the observed stability characteristics was obtained by using a circuit analogy. In addition to the porous disk bearing, two other types of thrust bearings, viz, the plain disk with a porous insert and the plain disk with a recess and orifice restriction, were also included in the experimental study. The three types of bearings were compared with reference to their stability. Within the same range of the gas flow rate, the porous insert bearing displayed an equal or larger region of stable operation in comparison with the orifice bearing. Besides, the porous insert bearing exhibited a feature which could simplify its construction and make its application very attractive.
Suitability of radiochromic films for dosimetry of low energy X‐rays
Authors: Ebert Martin A , Asad Ali H , Siddiqui Salim A
Published: November 2009

This study examined the response characteristics of three commercially available radiochromic films when exposed to low energy (50 kVp) X‐rays. The aim was to evaluate the films for potential use in 2D dosimetry for a low‐kV intraoperative radiotherapy (IORT) device known as the ‘Intrabeam’. Dose‐response relationships were obtained for Gafchromic EBT, XR‐RV2, and XR‐QA film in water at several distances from the Intrabeam device. It was found that the dose rates from the source were excessive for use of the XR‐QA film, and that all three film types showed significant energy dependence within the limits of measurement uncertainty. Basic modeling of primary X‐ray spectra indicated large changes in the lower energy components with distance from the source, and it is hypothesized that the changes in film response are a result of changes in film energy response. This is in contrast to previous studies indicating less or negligible energy response. All films showed non‐linearity in response over the ranges examined. These results imply significant limitations for the use of these films for low‐kV dosimetry.

PACS number: 87.53.Bn
Evolution of X‐ray machine quality control acceptance indices
Authors: Ebisawa Maria Lucia Nana I , de Fatima A Magon Maria , Mascarenhas Yvone M
Published: November 2009

The quality assurance (QA) of radiographic images based on the operating conditions of X‐ray equipment is essential for good image quality, accurate medical diagnostics and for the prevention of health professionals and patients to unnecessary doses of ionizing radiation. This paper presents a historical analysis of 1,635 Quality Assurance Technical Reports of Health Institutions in the state of São Paulo, Brazil, over a seven‐year period. Based on acceptable limits for variations between nominal and measured parameters as the variable to determine the quality of X‐ray equipment operating conditions, a significant improvement was found in the percentage of acceptance of the overall parameters described in the QA technical reports over this period. As expected, we found a strong concentration in the categories of conventional and portable X‐ray equipment, which represent 72% and 84%, respectively, of the total number of equipments. A mechanical parameter such as half‐value layer (HVL), which is important not only for image quality but also for radiation protection, showed significant improvements. Again, only 58% of portable X‐ray equipment showed HVL values recommended for 80 kVp (above 2.3 mm Al), a percentage that improved to 76% in 2006. With regard to mammographers, which are newer machines, all the analyzed systems presented acceptable HVL values. Conventional X‐ray machines showed an increase of this conformity index from 89% in 2000 to 94% in 2006. All this improvement was attributed to the continuous and extensive enforcement of Regulation Act 453 in the state of São Paulo. The improvement in equipment quality control standards is expected to result in the improvement of diagnostic quality, as well as in the reduction of exam repetitions, and thereby reducing the patient's exposure to radiation.

PACS number: 87.57.C
Optimization of photon beam energy in aperture‐based inverse planning
Authors: St‐Hilaire Jason , Sévigny Caroline , Beaulieu Frédéric , Gingras Luc , Tremblay Daniel , Beaulieu Luc
Published: November 2009

Optimal choice of beam energy in radiation therapy is easy in many well‐documented cases, but less obvious in some others. Low‐energy beams may provide better conformity around the target than their high‐energy counterparts due to reduced lateral scatter, but they also contribute to overdosage of peripheral normal tissue. Beam energy was added as an optimization parameter in an automatic aperture‐based inverse planning system. We have investigated a total of six cases for two sites (prostate and lung), representative of deep‐seated and moderately deep‐seated tumors. For one case for each site, different numbers of beam incidences were considered. The other cases for each site were optimized using a fixed number of incidences. Four types of plans were optimized: 6 MV, 23 MV, and mixed energy plans with one or two energies per incidence. Each plan was scored with a dose‐volume cost function. Cost function values, number of segments, monitor units, dose‐volume parameters, and isodose distributions were compared. For the prostate and lung cases, energy mixing improved plans in terms of cost function values, with a more important reduction for a small number of beam incidences. Use of high energy allowed better peripheral tissue sparing, while keeping similar target coverage and sensitive structures avoidance. Low energy contribution to monitor units usually increased with the number of beam incidences. Thus, for deep‐seated and moderately deep‐seated tumors, energy optimization can produce interesting plans with less peripheral dose and monitor units than for low energy alone.

PACS numbers: 87.55.de, 87.55.dk, 87.56.N‐
Information technology resource management in radiation oncology*
Authors: Siochi R. Alfredo , Balter Peter , Bloch Charles D. , Bushe Harry S. , Mayo Charles S. , Curran Bruce H. , Feng Wenzheng , Kagadis George C. , Kirby Thomas H. , Stern Robin L.
Published: November 2009

The ever‐increasing data demands in a radiation oncology (RO) clinic require medical physicists to have a clearer understanding of information technology (IT) resource management issues. Clear lines of collaboration and communication among administrators, medical physicists, IT staff, equipment service engineers, and vendors need to be established. In order to develop a better understanding of the clinical needs and responsibilities of these various groups, an overview of the role of IT in RO is provided. This is followed by a list of IT‐related tasks and a resource map. The skill set and knowledge required to implement these tasks are described for the various RO professionals. Finally, various models for assessing one's IT resource needs are described. The exposition of ideas in this white paper is intended to be broad, in order to raise the level of awareness of the RO community; the details behind these concepts will not be given here and are best left to future task group reports.

PACS number: 87.52.Tr, 87.53.St, 87.53.Xd, 87.90.+y
Decline of the maple-dominated forest in southern Quebec: impact of natural stresses and forest management
Authors: Côté Benoît , Ouimet Rock
Published: November 2009

Forest decline was rather ubiquitous throughout the industrialized world in the 1980s. Maple decline was particularly severe in southern Quebec and large research programmes were put together to determine cause–effect relationships, as well as understand the mechanisms involved in forest decline. The present review of the causes of the decline of the maple-dominated forest in southern Quebec is heuristic in nature and not exhaustive in that we do not address the role of atmospheric pollution, a likely predisposing factor that has received wide scientific coverage over the last 15 years. Rather, we discuss the potential role of natural stresses and forest management practices on forest decline. The process of natural selection and forest succession and the trend toward monocultures of sugar maple in sugar bushes are emphasized as important predisposing factors of forest decline. Climatic stresses and insect defoliations appear to have been major triggering factors, whereas insects and pathogens were likely contributing (killing) factors. Changes in forest management practices that would favour tree species diversity and decrease the likelihood of physical injury, tree disease, and insect epidemics are suggested to increase tree vigour and, therefore, decrease the susceptibility of the maple forest to decline. The evolution in time and space of the last forest decline in southern Quebec, as well as its repercussions on forest monitoring and the regional economy are also reviewed.Key words: biodiversity, climatic extremes, forest decline, forest management, insect epidemics, maple.
Sequential accuracy testing plans for the applicability of existing tree volume equations
Authors: Wang Yue , LeMay Valerie M.
Published: November 2009

To determine whether an existing tree volume estimation equation is acceptable for application to a new species, a new region, or a local area, an accuracy test could be carried out. Three sequential accuracy testing plans (SATP) were developed, along with approximate operating characteristic and average sample number curves. These tests are extensions of fixed sample size accuracy tests using sequential probability ratio tests to obtain sequential sampling tests. Using Monte Carlo simulations with normally distributed error terms, the SATP procedures were shown to be reliable for classifying existing volume models as acceptable or not acceptable with achieved error probabilities (type I and type II error probabilities) that were lower than the nominal values specified prior to testing. Also, on average, the use of the SATP procedures resulted in a 40 to 50% reduction in the expected sample size compared with that required for an equally reliable fixed sample size procedure. A detailed example is given to illustrate the application of the SATP procedures.
Effects of aluminum on growth, polyamine metabolisms and inorganic ions in suspension cultures of red spruce (Picea rubens)
Authors: Minocha Rakesh , Shortle Walter C. , Coughlin Jr. Daniel J. , Minocha Subhash C.
Published: November 2009

The influence of age of red spruce (Picearubens Sarg.) cell suspensions on aluminum (Al) effects was studied by adding AlCl3 (0.2, 0.5, and 1.0 mM) to the media on each day of a 7-day culture period and analyzing for changes in total cell mass, polyamines, arginine decarboxylase activity, and inorganic ions after 24 h of incubation. The effective concentrations of monomeric Al in the medium were found to be approximately 0.09, 0.23, and 0.48 mM, respectively. All levels of Al inhibited growth and increased cellular putrescine levels and arginine decarboxylase activity. Spermidine and spermine levels were either slightly elevated or not affected by Al. Cellular content of Ca, Mg, Mn, and K decreased, while Al and P increased in Al-treated cells. Aluminum effects, in general, were dose dependent. Since the response to 24 h incubation with Al was generally independent of culture age, 3-day-old cultures were selected to further study short- and long-term (4 h to 11 days) effects of Al. Cellular putrescine levels remained elevated in the Al-treated cells for the entire duration of the experiment. There was a sharp dose-dependent increase in spermine levels by the 7th day of incubation. After the initial decrease, Al treatments for longer than 2 to 4 days did not cause consistent effects on Ca, Mn, and Mg levels. Potassium decreased and P and Al increased in a dose-dependent manner over the 11-day culture period.
Comparing branch biomass prediction equations for Abiesbaisamea
Authors: Lavigne M.B. , Luther J.E. , Franklin S.E. , Hunt Jr. E.R.
Published: November 2009

The use of sapwood cross-sectional area at breast height (S) was compared with the use of diameter at breast height (D) and total height (H) for predicting branch weight per tree (B). Data obtained by destructive sampling of 58 balsam fir (Abiesbalsamea (L.) Mill.) trees growing in western and northern Newfoundland were used to fit a simple linear and a nonlinear model using D2H and to fit a simple linear and two nonlinear models using S. Coefficients of determination and standard error of estimates were similar for all equations. There were large differences in estimates of branch weight per hectare between equations for 25 cruised stands. The relationship between B and leaf area was used to evaluate the accuracy of stand estimates. The allometric equation using S as the independent variable provided the most accurate estimates.
Survival and regeneration of dormant silver birch buds stored at super-low temperatures
Authors: Ryynänen Leena
Published: November 2009

Cryopreservation was developed for the storage of in vivo buds of silver birch (Betulapendula Roth). The principles of the optimized method were the use of buds already acclimated in nature and slow freezing with a cooling velocity of 10 °C/h down to a terminal temperature of −38 °C. After 24 h at this temperature the buds were immersed in liquid nitrogen at − 196 °C for 8 days, 6 months, or 12 months. After fast thawing, 5 min in a water bath at 37 °C, the buds were surface sterilized and cultured according to the normal laboratory routine. The buds were examined after 2 and 4 weeks of cultivation. There were no significant differences in survival and growth between the unfrozen controls and buds stored in liquid nitrogen for different times. The growth percentage of buds without a female catkin was double that of buds with a catkin. These results indicate that cryopreservation would be an ideal method for the ex situ gene conservation of birch and retention of the juvenility of adult genotypes.