bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Measurement of Surface Topography and Friction Force by a Single-Head Lateral Force Microscope
Authors: Lu C.-J. , Jiang Zhaoguo , Bogy D. B. , Miyamoto T.
Published: February 2008

Although friction force measurements using one sensor to detect both the normal deflection and rotation angle of a scanning probe are convenient and popular, the critical issues regarding the calibration of the instruments have not been fully studied. A Lateral Force Microscope (LFM), modified from the Point Contact Microscope (PCM), is used to simultaneously measure the surface topography and friction force. An optical head is used to measure the normal bending deflection and rotation angle of the cantilever that carries the diamond tip. Emphasis is put on the development of reliable calibration procedures for obtaining the normal deflection and rotation sensitivities of the optical head as well as the spring constants in the bending and torsion modes. The friction loop, which is essential for friction measurements, is investigated in detail. The LFM is used to measure a two-phase composite to show its ability to distinguish different materials on a surface. Wear tests on a single-crystal silicon <100> surface show different friction coefficient regimes, depending on the applied load. For small loads, there is no wear and the friction coefficient is constant. For larger loads, the friction coefficient and wear depth increase with normal load.
A Transient Thermohydrodynamic Analysis Including Mass Conserving Cavitation for Dynamically Loaded Journal Bearings
Authors: Paranjpe Rohit S. , Han Taeyoung
Published: February 2008

A comprehensive transient thermohydrodynamic analysis for dynamically loaded journal bearings such as engine crankshaft bearings has been developed. A key element in this analysis is consideration of different time scales for the oil film, journal and bushing. Another important element of this analysis is consideration of moving grids in the oil film. Mass conserving cavitation is included via the Elrod cavitation algorithm. The 3-D energy equation is solved without any simplification in the oil film or the bushing. The journal is treated as a lumped thermal element. We found that the time scales for thermal transients in the oil film are of the same order as the period of the dynamic loading (one engine cycle for a crankshaft bearing); consequently, thermal transients in the oil film were considered. However, the time scales for thermal transients in the journal and bushing are several orders of magnitude greater than those for the oil film. Consequently, these elements were treated as if they were in quasi-steady state over one loading cycle. Results from this analysis are presented for an engine crankshaft main bearing under sinusoidal loading. Oil film temperatures are found to vary considerably over time and space.
The Effects of Three-Dimensional Pad Deformations on Tilting-Pad Journal Bearings Under Dynamic Loading
Authors: Desbordes H. , Fillon M. , Freˆne J. , Chan Hew Wai C.
Published: February 2008

Pad distortions are generally not taken into account for the dynamic study of tilting-pad journal bearings. The objective of this paper is both to show the influence of the three-dimensional (3-D) pad deformations due to the pressure field on the bearing response and to analyse the bearing behavior for various unbalance eccentricities. Similar orbits are obtained using 2-D or 3-D pad deformations; however, due to the axial profile of the film thickness, the minimum film thickness obtained with the 3-D model is about 40 percent lower than the one obtained with the 2-D model for the greatest unbalance eccentricity. The maximum pressure is decreased by about 16 percent when the 3-D model is used but that value is nearly similar to the one obtained without deformation. The dynamic behavior of the bearing is largely modified when the dynamic load is greater than the static load.
Axial Oil Film Rupture in High Speed Bearings Due to the Effect of the Centrifugal Force
Authors: Koeneke Carlos E. , Tanaka Masato , Motoi Hisayuki
Published: February 2008

The two-dimensional steady-state Navier-Stokes equation and the continuity equation are applied to the lubricating film assumed to be concentric in journal bearings operating at very high speeds. The equations are numerically solved for the pressure variation in the axial direction and also across the film thickness with the centrifugal force being considered to act on the lubricant film due to high rotational speed of the journal. Linked with a new cavitation model proposed, the lubricant film is theoretically found to rupture near the journal surface toward the bearing end. This axial film rupture (AFR) is shown to reduce the driving torque of the inner film of floating bush bearings at very high shaft speeds, and some phenomena observed in the operation of floating bush bearings can be explained with this model.
Prediction of Cavitation in Journal Bearings Using a Boundary Element Method
Authors: Yu Qiulin , Keith Theo G.
Published: February 2008

In this paper, a boundary element cavitation algorithm is utilized to predict cavitation in journal bearings with axially variable clearance. Film rupture and reformation boundary conditions, obtained from the JFO theory, are directly combined with the generalized boundary integral equation which is derived from Elrod’s universal differential equation. The two boundaries are simulated by two confluent interpolation polynomials: The governing equation is transformed into an undetermined boundary problem. The procedure effectively eliminates the phenomenon of solution oscillation experienced by finite difference cavitation algorithms and caused by unadaptable grid shape and density. It also eliminates the discontinuous derivative of the fractional film content. The results for aligned and misaligned journal bearings are compared with those obtained using the finite difference method. Tapered, barrel, and hourglass Journal bearings are also analyzed. The computational results demonstrate the effects of the journal geometric parameters on journal bearing performance.
A Numerical Elastoplastic Model for Rough Contact
Authors: Mayeur C. , Sainsot P. , Flamand L.
Published: February 2008

Pressure distributions due to surface roughness in contact induce high stresses just beneath the surface. These stresses can bring on crack initiation and micro-pitting. A purely elastic contact model to account for these effects is restrictive because stress fields often exceed the yield strength of the material. Plastic flow occurs and modifies the surface shape and material properties (work hardening). This paper presents a numerical model for elastoplastic rough contact. It allows the determination of real pressures and permanent surface displacements (flattening of asperities) as well as residual stress and plastic strains useful in fatigue analysis). The material is assumed to obey the Von-Mises yield criterion with linear kinematic hardening. Real surface profiles obtained from a measurement can be considered. In addition, simplified methods have been used to treat cyclic loading. Thus the ability of a rough surface to reach an elastic shakedown state can be investigated, even for a three-dimensional contact found, for instance, in roller bearings.
Empirical Prediction of the Shear Layer Thickness in Lubricating Films
Authors: Wang N. Z. , Seireg A.
Published: February 2008

A computational procedure has been presented by Wang and Seireg (1993) for the thermohydrodynamic analysis of fluid film bearings with the assumption of a central heat generation (shear) zone and the consideration of the thermal expansion across the film. This paper presents a dimensionless relationship for predicting the thickness of the shear layer in lubricating films, which is developed based on the extensive experimental data for the journal bearing reported by Ezzat (1971) and Seireg and Ezzat (1973). The relationship which was found to be a function of Sommerfeld and Peclet numbers is then applied to evaluate the pressure distribution for other cases of journal and slider bearings. The results show excellent correlation with the experimental results in all the investigated conditions.
A Non-Newtonian TEHL Analysis of Tilting-Pad Bearings Subjected to Inlet Pressure Build-Up
Authors: Rodkiewicz C. M. , Yang P.
Published: February 2008

The characteristics of the infinitely wide tilting pad bearings operating under thermal elastohydrodynamic lubrication (TEHL) condition were investigated theoretically. The power-law rheological model was chosen to describe the non-Newtonian flow of the lubricant. An iterative procedure was developed to determine the shear stresses as well as the equivalent viscosity within the oil film. The analysis considers, simultaneously or individually, the following affecting factors: generation and transfer of heat, elastic and thermo-elastic deformations of bearing components due to pressure and temperature, and the inlet pressure build-up. The results were presented and discussed in terms of the applicable non-dimensional parameters.
The Influence of Elastic Deformation of the Roll and the Sheet in a Hydrodynamically Lubricated Cold Rolling Process
Authors: Lugt P. M. , ten Napel W. E.
Published: February 2008

A model has been developed for simulating hydrodynamic lubrication in cold rolling. Both Roelands’ and Barus’ viscosity-pressure relations have been applied. Thermal effects regarding heat development caused by plastic deformation as well as work hardening have been included. Furthermore, elastic deformation of the surfaces has fully been incorporated in the model, i.e., elastic deformation of both the strip and the rolls. The governing equations have been solved numerically throughout the entire contact i.e. inlet, work and outlet zone using a very dense grid. Multigrid techniques have been used to solve the equations. It will be shown here that roll flattening has a significant effect on film thickness. However, elastic deformation of the strip material in the inlet region even has a more pronounced effect on film thickness and thus on several process conditions. Furthermore, it is shown that the choice of the viscosity-pressure parameter is limited. Higher values of this parameter cause excessive shear stresses on the strip surface.
Eccentric Operation and Blade-Loss Simulation of a Rigid Rotor Supported by an Improved Squeeze Film Damper
Authors: Zhao J. Y. , Hahn E. J.
Published: February 2008

This paper outlines an improved squeeze film damper which reduces significantly the dependence of the stiffness of conventional squeeze film dampers on the vibration amplitudes. This improved damper consists of a conventional squeeze film damper with a flexibility supported outer ring. This secondary flexible support is considered to be massless, and to have a constant stiffness and damping. Assuming the short bearing approximation and the ‘π’ film cavitation model, the performances of this damper in preventing bistable operation and sub-synchronous and nonsynchronous motions are theoretically demonstrated for a rigid rotor supported on a squeeze film damper. Blade-loss simulations are carried out numerically.
Elevated Temperature Wear Maps of X40 and Mar-M247 Alloys
Authors: Saito Yoshiyuki , Mino Kazuaki
Published: February 2008

Self-mated wear tests of X40 (Cobalt-base alloy) and Mar-M247 (Nickel base alloy) were conducted under unlubricated sliding conditions using a pin-on-disk tester. Wear maps were constructed for both alloys over the temperature range of room temperature to 1173 K at relatively low sliding speed. Microstructural and chemical information has been obtained by using various microscopies, an X-ray diffractometer, and an X-ray photo-electron spectroscopy. They show that the wear resistance of X40 is superior to that of Mar-M247 at room temperature due to the lower concentration of metallic state elements and higher concentration of Cr2O3 and Co (OH)2 at the surface of X40. The degradation in the wear resistance of X40 at about 500 K was attributed to the decrease in Cr2O3 and Co(OH)2 concentrations at the surface.
On the Tribological Behavior and Surface Analysis of a Sliding PSZ Ceramic-Steel Pair
Authors: Wang Fu-Xing , Cheng Yin-Qian , Guan De-Hui
Published: February 2008

Using a ring-on-block wear test machine, friction and wear tests were carried out on a PSZ (partially stabilized zirconia) ceramic-steel pair under the lubrication conditions of paraffin oil and paraffin oil with 0.5 percent ZDDP additive. Surface analysis techniques of XPS and AES were used to analyze the rubbing surfaces. The test results showed that the PSZ ceramic-steel pair possesses very good tribological behavior. The wear resistance of the pair was increased when ZDDP was added to the paraffin oil lubricant. Surface analysis showed that the increased wear resistance could be attributed to the formation of a surface reaction film containing the elements Zn, P, and S on the rubbing surfaces.
Some Exact Solutions of Reynolds Equation
Authors: Anaya-Dufresne M. , Sinclair G. B.
Published: February 2008

In order to check the numerical analysis of Reynolds equation for gas lubricated bearings, it is desirable to have available exact analytical solutions. This note outlines the construction of some exact, two-dimensional, transient solutions for this purpose.
An Extended Three-Control-Volume Theory for Circumferentially-Grooved Liquid Seals
Authors: Marquette O. R. , Childs D. W.
Published: February 2008

Circumferentially-grooved seals are used in centrifugal pumps to reduce leakage flow. They can also have a significant impact on pump rotordynamic characteristics. Florjancic (1990) developed an analysis for leakage and rotordynamic coefficients, using a partition of the seal into three control volumes. This paper presents a new theory, based on an extension of Florjancic’s work (1990) for circumferentially-grooved liquid seals. The current theory differs from Florjancic’s analysis in the retention of transfer momentum terms and the introduction of diverging flow in the through-flow section within a seal groove. Validation of the new analysis is achieved through a comparison with existing experimental data taken from Kilgore (1988), and Florjancic (1990). Theoretical results are reasonable and consistent; i.e., a modification in the seal parameters induces a correct evolution of the rotordynamic coefficients. Direct and cross-coupled stiffness coefficients are slightly underpredicted, whereas the direct damping coefficient is underpredicted within 40 percent. Leakage flow predictions are very good.
Elastohydrodynamic Model of the Rotary Lip Seal
Authors: Salant R. F.
Published: February 2008

A model of the non-leaking equilibrium behavior of the lip seal has been developed. It consists of an elastohydrodynamic model of the lubricating film and a simplified model of the meniscus on the air-side of the seal. The model predicts the location of the meniscus, the film thickness and pressure distributions, and the locations of cavitation regions. It also predicts the maximum pressure that can be sealed with zero leakage, and the maximum speed, above which the meniscus is ingested into the sealing zone.
On the Accuracy of Rolling Bearing Fatigue Life Prediction
Authors: Harris T. A. , McCool J. I.
Published: February 2008

Ball and roller bearings are designed to meet endurance requirements basically determined according to the Standard fatigue life calculation method. This method is based on the Lundberg-Palmgren fatigue life theory as modified by reliability, material, and lubrication factors. As application load and spied requirements have increased, the Lundberg-Palmgren method has resulted in bearings of increased size, adding unnecessarily to the size and weight of mechanisms. This is a critical design situation for weight and size-sensitive components such as aircraft gas turbine engines and helicopter power transmissions. The bearing life prediction method developed by Ioannides and Harris recognizes the existence of a fatigue limit stress. If the stresses an operating bearing experiences do not exceed the limit stress, the bearing can achieve infinite life. In any case, the method tends to predict longer lives than the Lundberg-Palmgren method. This paper evaluates the life prediction accuracies of the Lundberg-Palmgren and Ioannides-Harris methods by comparing lives calculated according to these methods and to those actually experienced in 62 different applications. As a result of the investigation, the Ioannides-Harris method is shown to more accurately predict bearing fatigue endurance.
Effects of Cone/Axle Rubbing Due to Roller Bearing Seizure on the Thermomechanical Behavior of a Railroad Axle
Authors: Wang Hao , Conry T. F. , Cusano C.
Published: February 2008

A thermomechanical analysis of a railroad axle with a 6 1/2 × 12 tapered roller bearing assembly is conducted to determine the effects of a loose cone rubbing on the axle. For this analysis, it is assumed that the bearing elements have seized or jammed and the smallest resistance torque is due to the friction at the loose cone-axle interface. Temperature-dependent material properties are used as well as a coefficient of friction obtained by means of a pin-on-disk apparatus over a range of temperatures up to 1000° C. For initial radial clearances between cone and axle varying from 0.05 to 5.0 mm and an initial ambient temperature of 25°C, the thermomechanical degradation of the axle is examined as a function of time. The times required for plastic collapse of the axle to occur are determined for the various clearances. For the conditions considered, this collapse takes place in less than three minutes.
Spectral Analysis of Two-Dimensional Contact Problems
Authors: Ju Y. , Farris T. N.
Published: February 2008

Contact problems can be converted into the spatial frequency domain using Fast Fourier Transform (FFT) techniques. Spectral analysis is used to develop an algebraic relationship between the surface displacement and the contact pressure. This relationship can be used to find the contact pressure or displacement for the contact of smooth surfaces or the complete contact of rough surfaces. In addition to providing rapid, robust solutions to contact problems, the algebraic relationship contains details of the relationship between surface displacement and contact pressure on different length scales. In particular, it is shown that the frequency composition of pressure is similar to that for slope of the surface displacement. Thus, the high frequency content of the surface profile gives rise to high localized contact pressure, in some cases singular pressure for complete contact. However, measurement limitations always lead to the omission of certain high frequency components of the surface profile. Assuming that the high frequency content of the surface profile obeys a power law, spectral analysis is also used to estimate partial contact parameters. This result relates the exponent of the power law to the contact pressure and implied surface integrity. It is concluded that spectral analysis can be combined with the FFT to provide a useful technique for classifying rough surface contacts.
Scale Effects of Elastic-Plastic Behavior of Microscopic Asperity Contacts
Authors: Polonsky I. A. , Keer L. M.
Published: February 2008

Scale effects of elastic-plastic asperity microcontact behavior are studied theoretically using a new simulation method developed by the authors. Contact plastic deformation is described in terms of discrete dislocations, which allows the model to be made scale-sensitive. The present work deals with two-dimensional asperity microcontacts. It is found that when asperity size decreases and becomes comparable to the characteristic microstructural length, contact plastic deformation becomes increasingly difficult, and finally impossible. The effect of a simultaneous decrease in the asperity size and the microstructural length is also studied.
On the Dynamic Thermal State in a Hydrodynamic Bearing With a Whirling Journal Using CFD Techniques
Authors: Tucker P. G. , Keogh P. S.
Published: February 2008

A thermohydrodynamic analysis, based on computational fluid dynamics (CFD) techniques, that accounts for conduction in the rotating and orbiting shaft of a hydrodynamic bearing is presented. No restrictions apply to the circumferential or axial variation of journal/shaft temperature. Dynamic cavitation effects are also introduced, such that pressures in the cavitation region are predicted rather than set. The model predictions are validated against analytical and published experimental results. For the case of a centrally located synchronous forward circular whirl orbit, it is demonstrated that the journal does not behave as a circumferentially isothermal element and that significant steady temperature differentials across the journal may occur.
The Effect of Surface Roughness on the Head-Tape Interface
Authors: Wu Y. , Talke F. E.
Published: February 2008

The effect of tape surface roughness on the head-tape interface is investigated for typical head contours using tapes with different surface roughness characteristics. Intensity-based monochromatic interferometry is used to obtain the asperity compliance curves for tapes of different roughness by relating contact pressure to the spacing between the head and the tape. A parabolic model and the Greenwood-Williamson model for contact between rough surfaces are used to “curve fit” experimental results for contact pressure versus spacing, and numerical calculations for the head-tape spacing of a cylindrical head with and without transverse slots are presented for two tapes with different roughness characteristics. The numerical calculations for the head-tape spacing are compared with experimental measurements showing excellent agreement between numerical and experimental results. It is concluded that the head-tape spacing for high recording density applications is limited by tape surface roughness.
Ultrathin Liquid Lubrication of Magnetic Head–Rigid Disk Interface for Near-Contact Recording: Part II—Shear Thinning and Thermal Thinning
Authors: Hsiao Hsing-Sen S. , Bhushan Bharat , Hamrock Bernard J.
Published: February 2008

The Carreau shear thinning equation and the modified Roelands thermal thinning equation are combined by using the generalized master curve approach to construct a new thermal non-Newtonian rheology model. The Newton-Raphson method is then used to curve-fit existing experimental data for two perfluoropolyethers to this new model. The thermophysical properties thus found are then used to calculate thermal and shear thinning correction factors for the ultrathin liquid lubrication of magnetic head-rigid disk interfaces. The results of rheology modeling show excellent fits of the widely ranging raw data with the new thermal non-Newtonian model. The results of hydrodynamic analysis indicate that the friction force-isothermal Newtonian shear stress curve for these interfaces is simply a lubricant characteristic curve of thermal-shear thinning.
Dynamic Characteristics of Hard Disk Drive Spindle Motors—Comparison Between Ball Bearings and Hydrodynamic Bearings
Authors: Ku C.-P. Roger
Published: February 2008

Recently, many computer hard disk drive companies and spindle motor manufacturers have been looking for a substitute for ball bearings to continue making dramatic progress in increasing the capacity of data storage systems. In this paper, the frequency-forced responses of hard disk drive spindle motors supported by both ball bearings and liquid-lubricated spiral groove hearings (SGBs) were studied experimentally. It is found that both shaft rigidity and disk flexibility have great effects on the natural frequency of the spindle motor conical (rocking) mode. The high damping capacity of the SGB is able to suppress the vibration amplitudes of both motor rocking mode and the flexible disk modes. But at a very low frequency range, the SGB motors displayed a large amplitude in the axial direction vibration test. With an adequate bearing design, the SGB motors have proven their superior dynamic characteristics.
Numerical Simulations of Slider Interaction With Multiple Asperity Using Hertzian Contact Model
Authors: Cha Ellis , Bogy D. B.
Published: February 2008

A numerical simulation of slider-disk contact in a magnetic hard disk drive is studied using the Hertzian contact model. The slider-disk contact is caused by flying height fluctuation due to disk runout for very low flying sliders. The rough disk topography is generated numerically by combining a sinusoidal waviness and a Gaussian roughness. For each asperity contact, the radius of curvature is calculated from the disk topography, and the radius is used to calculate the contact force using the Hertzian contact model. The slider’s response to a single asperity calculated using the Hertzian contact model agrees well with the result obtained using the impulse-momentum based contact model. The simulation results of slider-disk contact including suspension dynamics are calculated with and without friction for a “nano-slider.”
Pole Tip Recession: Investigation of Factors Affecting Its Measurement and Its Variation With Contact Start-Stop and Constant Speed Drag Testing
Authors: Nadimpalli Chandrasekhar , Talke Frank E. , Smallen Martin , Lee Jerry J. K.
Published: February 2008

Optical interferometry and contact mode atomic force microscopy are used to investigate the various factors that influence the measurement of pole tip recession. These factors include: (a) effect of dissimilar materials on optical interferometry results, (b) size and location of the air bearing surface used as the reference area, (c) the effect of slider crown, (d) the magnification of the objective used in optical interferometry and (e) the dependence of the AFM measurements on slider materials and scan direction of the AFM tip. The possibility of determining a local value of pole tip recession is examined wherein the sputtered alumina, rather than the Al2O3-TiC surface, is used as the reference surface. Finally, the effect of contact start/stop (CSS) and constant speed drag testing on pole tip recession is investigated by measuring the change in pole tip recession as a function of the number of start/stop and constant speed drag cycles.
Numerical Simulation of Head-Disk Impacts During Dynamic Loading Processes
Authors: Jeong Tae Gun , Bogy D. B.
Published: February 2008

In order to estimate the contact stress and deformation at the instant of head-disk impact during dynamic loading, Hertz’s impact theory is implemented in a dynamic loading numerical simulator. By using a finite difference model for the air bearing, a finite element model for the slider-flexure-suspension system, and Hertz’s contact model of head-disk impact, we obtain estimates of contact stress, area and time through simulation of the dynamic loading process. With our choice of the material properties and geometric configurations, the duration of sliding contact is about 7 μs, the maximum width of contact is about 10 μm, and the maximum contact stress is about 620 MPa. This is below the yield stresses of the chosen media.
Accurate Real Area of Contact Measurements on Polyurethane
Authors: Hendriks C. P. , Visscher M.
Published: February 2008

Theoretical models describing the contact of rough surfaces have been developed for at least three decades. Experimental verification, however, has not been straightforward up till now, since current measurements suffer from large inaccuracies, often 100 percent or worse. In this paper a new method, based on autofocus techniques, is applied with an accuracy better than 15 percent. Measurements are presented for the contact of a rough polyurethane specimen in contact with a smooth glass plate. It was not yet possible to conclude whether the real area of contact is proportional to the contact load, but the results show the forming of contact agglomerations, which becomes significant at 10 percent real area of contact. Asperity interaction appears to be important, even at low loads. However, one or both of these facts are often not considered in present contact models, questioning their reliability.
A Correlation Between Low Cycle Fatigue Properties and Scuffing Properties of 4340 Steel
Authors: Kim Kitae , Ludema Kenneth C.
Published: February 2008

A correlation is demonstrated between the low-cycle fatigue properties and the scuff resisting properties of 4340 steel. Low cycle fatigue properties were estimated from measured tensile properties for specimens with a wide range of hardness. Scuff resistance was measured in sliding tests using white mineral oil as the lubricant.
Tribological Behavior of Cubic Boron Nitride Film Sliding Against Diamond
Authors: Watanabe Shuichi , Miyake Shojiro , Murakawa Masao
Published: February 2008

Cubic boron nitride (c-BN) film was deposited onto a silicon substrate by means of a magnetically enhanced plasma ion plating method utilizing a hot cathode plasma discharge in parallel magnetic field. In this study, the friction and wear behaviors of the c-BN film, particularly when it came into sliding contact with diamond, were investigated using a reciprocating tribometer in an applied normal load range of 0.1 ~ 4.9 N. The results showed that the friction coefficient of the c-BN film sliding against the diamond indenter tended to decrease as the load increased, and was very low, exhibiting values of 0.03 ~ 0.065 at the maximum load of 4.9 N. Furthermore, the study confirmed that the friction coefficient of annealed c-BN film was lower than that of as-deposited c-BN film throughout the whole load range. Judging from the results of comparable investigations in which c-BN film came into contact with other materials such as c-BN compact, SiC and stainless steel, the wear performance and peeling resistance of the c-BN film proved to be significantly better in the case of contact with diamond.
Dust Generation From Rolling-Sliding Elements of Combined Stainless Steel and Silicon Nitride
Authors: Miyake S.
Published: February 2008

To select tribological materials for use in clean environments, dust-generation properties from rolling-sliding elements made of silicon nitride ceramics and stainless steel were investigated. The rolling-sliding testing apparatus was used to investigate dust-generation properties of basic rolling-sliding elements. The number of dust particles generated increases rapidly with the percentage of sliding, or with what is called sliding rate in the rolling-sliding tests. Compared with pure martensitic stainless steel (440C) and silicon nitride (Si3N4), the combination of stainless steel and silicon nitride generates the least amount of dust PFPE grease lubrication drastically reduces the number of dust particles larger than 0.1 μm diameter. Dust generation increases with friction and wear volume. The generated dust volume is about 1/200 to 1/300 of the wear volume of a specimen without lubricant. This indicates that the dust particles were formed mainly by sliding.
Thermal Non-Newtonian EHL Analysis of Rib-Roller End Contact in Tapered Roller Bearings
Authors: Jiang Xiaofei , Wong Pat Lam , Zhang Zhiming
Published: February 2008

An EHL approach to the rib-roller end contact in tapered roller bearings has been achieved by taking into account the non-Newtonian behavior of lubricants and thermal effects and with full consideration of the peculiar geometrical and kinematic conditions. Two kinds of geometrical configurations of rib and roller end were investigated: tapered rib/spherical roller end and spherical rib/spherical roller end. Optimal ratios of curvature radius of roller end to rib face were deduced. The film thickness, friction torque, lubricant temperature, and surface temperature at various speeds and loads were calculated.
Model-Based Investigation of Friction During Start-Up of Hydrodynamic Journal Bearings
Authors: Harnoy A.
Published: February 2008

An analysis is developed for the time-variable friction during the start-up of a rotor system. The analysis is based on a dynamic friction model that has been developed from the theory of unsteady lubrication and can describe the observed friction characteristics. The model reduces to the Stribeck curve of friction versus steady velocity, and shows hysteresis curves in oscillating velocity. The “Dahl effect” of a presliding displacement before the breakaway is also included. The results indicate that the friction characteristics and energy friction losses, during the start-up, depend on a set of dimensionless parameters that represent the bearing as well as the dynamic system. The study shows that appropriate design and operation can prevent stick-slip friction and minimize wear during start-up.
A Method of Friction Torque Measurement for a Hydrodynamic Thrust Bearing
Authors: Da˛browski Leszek , Wasilczuk Michał
Published: February 2008

Measurements of thrust bearing friction torque are difficult because of the small values of the friction force in comparison with the axial load. Another problem of a thrust bearing test rig design is the necessity of accommodation of the axial load so that it does not interact with the frictional forces. Separation of fluid drag in the housing from torque in the bearing itself is also important. An analysis of a design in which the above-mentioned problems have been solved is presented. Theoretical analysis and calibration of the torque meter proved that the effect of axial load was successfully compensated for. Example of the results obtained due to the torque meter illustrate the application of the new design.
The Importance of Traction in Web Handling
Authors: Ducotey K. S. , Good J. K.
Published: February 2008

An experimental study shows that the traction coefficient of friction (μT) is a function of the predicted air film height, the roller and film surface roughness, and the static coefficient of friction between the web and roller. The traction coefficient shows a noticeable decrease as the air film height becomes greater than the equivalent root mean square roughness of the web and roller and also becomes less dependent on the static coefficient of friction.
Inertia Effects on Film Rupture in Hydrodynamic Lubrication
Authors: Ota Terukazu , Yoshikawa Hiroyuki , Hamasuna Makoto , Motohashi Takeshi , Oi Soshu
Published: February 2008

A perturbation analysis was made to study the effect of inertia on the film rupture in hydrodynamic lubrication using a modified Reynolds equation. A simplified boundary condition at film rupture proposed by Ota (1987) was employed. The theory was extended to investigate the wave number of the film rupture surface and to investigate the effect of gas bubbles included in the lubricant. Numerical calculations were carried out for a cylinder-plane bearing and are compared with previous experimental and numerical data. The effects of inertia on film rupture characteristics are clarified and the present numerical results are found to be in good agreement with earlier experimental data.
Measurement of Oil Film Journal Bearing Damping Coefficients—An Extension of the Selected Orbit Technique
Authors: Parkins D. W.
Published: February 2008

This paper describes a novel experimental procedure for measuring the four velocity or damping coefficients of an Oil Film Journal Bearing from imposed dynamic orbits. All four damping coefficients are derived from one imposed journal center dynamic orbit and, therefore, may be regarded as being obtained at the same time. The method requires the production of a “figure of eight” shaped orbit and utilizes the “cross-over” point therein. Coefficients are initially evaluated in a coordinate system which is chosen to align with the designated parts of the measured orbit. Each coefficient is then separately evaluated from single values of instantaneous imposed force and resulting journal center velocity. Coefficients are then converted into any other desired axes system. All the benefits of the original selected orbit technique are retained. The presented method places much less severe demands on experimental procedure. An available example illustrates the technique. A realistic uncertainty analysis for this example is included. Indications are provided which show how the orbit features may be adjusted to substantially reduce uncertainty.
A High Performance Journal Bearing With Controlled Elastic Deflection
Authors: Tieu A. K. , Freund N. O.
Published: February 2008

A thermo-elasto-hydrodynamic analysis of an undercut journal bearing is presented whereby elastic deflection is introduced in a certain area of the bearing surface. The hydrodynamic pressure is computed from the generalized Reynolds equation, which takes into account thermal effects on viscosity. This is accomplished by solving the full energy equation for temperature. The elastic deflection is obtained from the elasticity equation. This study is then complemented with an elasto-hydrodynamic analysis of the full bearing. The controlled elastic deflection increases the bearing load carrying capacity and reduces friction.
Journal Orbits and Their Stability for Rigid Unbalanced Rotors
Authors: Brancati Renato , Rocca Ernesto , Russo Michele , Russo Riccardo
Published: February 2008

With reference to a rigid symmetrical unbalanced rotor on lubricated journal bearings and adopting the short bearing theory, synchronous orbits and orbits with a 1/2 component described by the journal are determined as approximated solutions of the system of non-linear motion equations. The method also makes it possible to evaluate the stability of the above solutions and thus of the journal orbital motion. For different values of dimensionless unbalance of the rotor, examples of orbits thus obtained are given and, in the modified Sommerfeld number-stability parameter plane, the stability areas of the solutions are identified, in particular, the area of stability of the small synchronous orbits corresponding to the stable operating condition of the rotor-bearings system.
Finite Element Analysis of Rolling Contact for Nonlinear Kinematic Hardening Bearing Steel
Authors: Howell M. , Hahn G. T. , Rubin C. A. , McDowell D. L.
Published: February 2008

A Mroz image point, two surface, nonlinear-kinematic-hardening-plastic (MNKP) representation of bearing steel is inserted into a finite element model of 2-dimensional, line contact for pure rolling. The calculations are compared with previous results for the same contact pressure derived for elastic-linear-kinematic-hardening-plastic (ELKP) behavior. The residual stress, deformation, and the connection between continuing cyclic deformation, etching bands, and cracks are analyzed. Unlike the ELKP constitutive properties, the MNKP behavior displays a distinct transient region which results in higher residual stresses.
Effect of Humidity on the Friction and Wear Properties of Sn
Authors: Imada Y. , Nakajima K.
Published: February 2008

Variation in friction and wear properties with relative humidity was obtained with an Sn pin sample on a Cu disk at a constant speed (0.4 m/s), load (6.4 N), and sliding distance (5 km), using a pin-on-disk apparatus. The influence of atmosphere on the tribological properties was investigated, including moisture ranging from 4% to 95 percent relative humidity (RH). It was found that the wear loss of the pin sample is very large at low humidity of around 5 percent RH, but it decreases and reaches saturation at about 50 percent RH. Factors characterizing the friction and wear at 50 percent RH were examined along with surface analysis of the disk. The results showed that the extensive transfer of Sn from pin to disk occurs during sliding and that the friction and wear behavior is determined by the friction and wear of an Sn sliding on Sn. An examination was carried out with an Sn pin sample on a stainless steel disk in comparison with an Sn-Cu couple. It was concluded that the friction and wear behavior is determined by the properties of the film transferred to the disk surface.
Friction, Temperature, and Wear Analysis for Ceramic Coated Brake
Disks
Authors: Watremez M. , Bricout J. P. , Marguet B. , Oudin J.
Published: February 2008

Coating adherence, friction coefficient, surface temperature, and wear mass loss are determined for a set of scale reduced steel brake disks on which NiCr cement based coatings and low conductivity subcoatings are plasma sprayed. The related pads are made of either sintered iron copper or sintered aluminum titanate. It is mainly shown that NiCr-Cr3C2 cermet coating on the disk, coupled with sintered aluminum titanate pad, leads to good damage resistance and stable friction coefficient in the simulation of high speed train braking. Low conductivity sublayers are also involved and it is found that temperatures in disc or pad may be also controlled.
Realistic Braking Operation Simulation of Ventilated Disk
Brakes
Authors: Floquet A. , Dubourg M.-C.
Published: February 2008

A three-dimensional numerical method for the prediction of transient temperatures reached during realistic braking operations in a ventilated disk brake assembly is presented in this paper. This Layered FFT-FEM numerical method (Fast Fourier Transform-Finite Element Method) takes advantage of the high Peclet number “skin effect” to decouple the moving boundary contact problem from the spatially periodic but non-axisymmetric cooling associated with the vents. The first problem is modeled according to the FFT-FEM method developed previously by the authors. This technique succeeded in using high Peclet numbers for axisymmetric moving solids submitted to general loading conditions. No numerical convergence problems are encountered and short computer time is required. The second problem is modeled according to traditional three-dimensional finite element techniques. The Layered FFT-FEM results are compared with analytical results. A braking operation is simulated for an industrial ventilated disk brake.
Experimental Study of Freely Alignable Journal Bearings—Part 1:
Static Characteristics
Authors: Tieu A. K. , Qiu Z. L.
Published: February 2008

The characteristics of two misaligned journal bearings were experimentally studied. A bearing test rig was developed. The experimental journal was freely alignable in two possibly misaligned journal bearings. In Part 1, the static characteristics, such as the distributions of oil film thickness and the pressure and temperature of two misaligned bearings, are measured; the relationships of eccentricity, attitude angle, and side flow to the Sommerfeld number are experimentally determined. In Part 2, the traditional harmonic excitation method is extended to estimate the sixteen dynamic force coefficients of two misaligned journal bearings. Sixteen force coefficients of two circular journal bearings, each with two axial grooves, are estimated and the threshold stable speeds are predicted. Various experimental errors and the uncertainty of the estimated coefficients are analyzed.
The Influence of Temperature on Failure Development in Steels Under
Transition to Seizure
Authors: Rapoport L.
Published: February 2008

Seizure phenomena in pin-on-disk tests have been studied for “soft” and “hard” steel specimens. Differences in competing and dominant wear mechanisms under steady state friction have been preserved for “soft” and “hard” specimens in the region of transition to seizure or galling. Severe wear was observed for “soft” specimens under all loads tested, while adhesion and splitting off of wear particle conglomerates (microseizure) were identified for “hard” specimens. The contact temperature, calculated in accordance with the temperature model of plastically deformed contact spots (Kuhlmann-Wilsdorf), has appeared to be low for “soft” specimens and not sufficient for adhesion interaction. The effect of oxide films on the friction of “hard” specimens has been estimated in accordance with the temperature model for a coated semi-infinite body (Tian and Kennedy). The insulated oxide films on the surface of “hard” specimens create the “skin effect” and lead, therefore, to raising the temperature up to the temperature of adhesion interaction. Temperature instability of hard surfaces has been demonstrated to result from the “skin effect” and from a disturbance in equilibrium of formation and failure of oxide films. It has been shown that for “soft” specimens the prime cause of transition to seizure was the mechanical interlocking between the wear particles and the soft disk surface combined with mechanical instability, while for “hard” specimens the cause was temperature instability. A more realistic temperature model of the contact has been considered, which takes into account some competing wear mechanisms (oxidational wear, ploughing, delamination) and the effect of wear particles.
Experimental Study of Thermal Effects in Tilting-Pad Journal Bearings
at High Operating Speeds
Authors: Bouchoule C. , Fillon M. , Nicolas D. , Barresi F.
Published: February 2008

In this work, a test machine, experimental results and the comparison between theoretical TEHD results and experimental data are presented. The tested bearings are located in two speed increasing and reduction gearboxes (back-to-back test bed). The shaft is driven by a 1 MW motor. The bearing diameter and the bearing length are equal to 160 mm. The rotational speed varies from 2700 rpm (22 m/s) to 11,880 rpm (100 m/s). The applied load is up to 88,000 N. Temperatures in the bearing (film/pad interface, oil, pad and housing), power losses and oil flow are measured. The influence of the bearing design and of the pivot position on the pad is analyzed.
Tribological Behavior of Amorphous Carbon Nitride Overcoats for
Magnetic Thin-Film Rigid Disks
Authors: Cutiongco Eric C. , Li Dong , Chung Yip-Wah , Bhatia C. Singh
Published: February 2008

Amorphous carbon nitride coatings of thickness of 5 and 30 nm were deposited onto 65 and 95 mm magnetic thin-film rigid disks surfaces using single-cathode and dual-cathode magnetron sputtering systems containing nitrogen-argon plasmas. Under optimum deposition conditions, amorphous carbon nitride coatings can be synthesized on ultrasmooth thin-film disks with no significant pinholes at thickness down to 5 nm, with hardness 22–28 GPa (compared to 7–12 GPa for amorphous carbon), and r.m.s. roughness as low as 0.25 nm. These amorphous carbon nitride coatings were shown to have better contact-start-stop performance and three-to-four times better pin-on-disk contact durability compared with amorphous carbon overcoats under identical testing conditions. Amorphous carbon nitride appears to be a promising candidate overcoat material for replacing amorphous carbon in the next-generation magnetic thin-film rigid disk systems.
On the Generalization of Thermohydrodynamic Analyses for Journal
Bearings
Authors: Khonsari M. M. , Jang J. Y. , Fillon M.
Published: February 2008

The results of extensive amount of thermohydrodynamic simulations are presented in the form of design charts for journal bearings. These charts enable one to evaluate the maximum temperature and an effective hearing temperature. Numerous examples are presented that show the applicability of these charts in predicting bearing performance parameters.
Generalized Boundary Interactions for Powder Lubricated Couette Flows
Authors: McKeague K. T. , Khonsari M. M.
Published: February 2008

Application of grain flow theories to powder lubrication of hydrodynamic bearings requires careful consideration of slip of the flow velocity at the boundaries together with appropriate formulation of the fluctuation (thermal) velocity conditions at the boundaries. Generalized boundary conditions that can be applied to a wide variety of surface and grain material characteristics are developed for a Couette flow configuration. The equations account for both the energy loss at the boundary due to inelastic grain-wall collisions and the energy supplied by the boundary due to collisional momentum supply. The predictions of the model are compared to a number of published results that are based on direct computer simulation of grain-grain collisions. The model’s flexibility is demonstrated by simulating the effects of unequal surface roughnesses.