bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of True Dimensional Quality and Build Errors Using Coordinate Measurement Data
Authors: Gu R. J. , Barber G. C.
Published: February 2008

For manufacturing personnel there exist two major tasks: determination of the quality of the build, and locating build errors if the quality is inferior. To serve this purpose a coordinate measuring machine is employed to determine the actual locations of designated material points. Depending on the measuring coordinate frame chosen, the initial raw data, unfortunately, do not impartially represent the true deviations of all the measurement points. This paper shows a technique to overcome this inevitable drawback embedded in the CMMs and determine if the build has acceptable quality under specified tolerances. Also presented in this paper is a method to quantify the quality of the measurement points for easy identification of build errors. Numerical examples are given to demonstrate the feasibility of the technique.
Analysis and Modeling of Surface Waviness Inspection with Light Reflection, Part 1: Laser Beam Scanning Method
Authors: Lee Ching-Chih
Published: February 2008

The laser beam scanning method for inspecting a reflective surface has been studied with analytical derivations and numerical modeling. Specular reflection off the surface was assumed and mathematical relations consistent with analytic geometry were used to trace the laser beam and predict its screen projection. It was found that deviation of the screen projection is proportional to the surface slope along the projection direction at the reflecting point and the distance from the point to the screen. The 3-D modeling was validated with 2-D analytical relationship as a special case and was tested with a profiled SMC (sheet molding compound) panel. The screen projections of reflected laser scans off surfaces with typical features of interest are predicted and the effects of waviness orientation are investigated.
Flying Characteristics of the Transverse and Negative Pressure Contour (“TNP”) Slider Air Bearing
Authors: White J. W.
Published: February 2008

The TNP contour air bearing slider is composed of oversized transverse pressure contour (TPC) outer rails and a central negative pressure (NP) cavity. The NP cavity is separated from the TPC rails by an ambient pressure reservoir which serves two functions. First, it prevents direct hydrodynamic interaction between the various component air bearing surfaces and thus, eliminates pressure distortion and dilution, common causes of problems related to flying height and roll angle control. Second, the ambient reservoir allows the TPC rails and NP cavity to be configured and dimensioned independently so that they will track each other with a nearly constant force difference, resulting in a flying height that has significantly reduced sensitivity to altitude change. The multi-function TPC sections of the outside rails are able to overcome the effects of a changing radius and wide skew angle variation over the disk radius as well as a changing vacuum load and asymmetry of the NP cavity pressure, in order to provide a truly constant low flying height over the entire data surface. The combination of a high air bearing stiffness and a gradually developing cavity vacuum as disk velocity increases produces a rapid slider take-off from the disk surface. Dynamic stability of the TNP slider air bearing is enhanced by the unusual combination of a high air bearing stiffness and high air film damping in each of the three slider excursion modes. Finally, the TNP slider experiences a reduced sensitivity of flying height to manufacturing and operational tolerances as compared to non-NP type sliders. The entire TNP slider air bearing is created by a two-etch process. A shallow etch creates the TPC sections and leading edge step. A deeper etch forms the NP cavity, ambient pressure reservoir, and outermost edge of each side rail.
Behavior of Cold-Rolling Oil-in-Water Emulsions: A Rheological Approach
Authors: Vergne P. , Kamel M. , Querry M.
Published: February 2008

The rheological behavior of oil-in-water emulsions has been studied as a function of oil concentration, shear strain rate, pressure and temperature. Results are discussed and correlated with several models which take into account the physical structure of emulsions. At low and medium shear rates and high concentrations, the emulsion’s behavior is non-Newtonian while under high shear rates, it becomes Newtonian. At ambient pressure, the viscosity of emulsions is weak and less temperature dependent than the base oil. The difference between the base oil and emulsion’s viscosity is less pronounced at high pressure. These tendencies are summarized by estimating the film formation ability of these lubricants. The oil concentration is the dominant parameter: if at low concentration the emulsions film formation ability is very weak, the results obtained at high concentration show a significant increase. This last point should be helpful to explain previous observations related to oil concentration variations inside the contact.
The Boiling Interface in a Misaligned Two-Phase Mechanical Seal
Authors: Etsion I. , Pascovici M. D. , Burstein L.
Published: February 2008

The boiling interface in a misaligned two-phase mechanical seal is analyzed using a complete thermohydrodynamic approach that requires complex simultaneous iterative solutions of the nonaxisymmetric heat transfer and phase-change problems. It is shown that under certain operating conditions, characterized by a modified Sommerfeld number, several approximate solutions with various levels of simplification can be utilized to calculate the boiling radius.
Forces and Moments Due to Misalignment Vibrations in Annular Liquid Seals Using the Averaged Navier-Stokes Equations
Authors: Arghir Mihai , Freˆne Jean
Published: February 2008

This paper presents a method to calculate forces and moments in misaligned annular liquid seals operating in centered position and turbulent flow regimes. The method is based on the numerical integration of the perturbed averaged Navier-Stokes equations so it has the capacity to treat recirculating flows in seal grooves. Due to the analytic coordinate transformation used in deriving the perturbed flow equations, the approach is limited to smooth-rotor seals. The perturbed flow equations are cast in an appropriate form in order to obtain a single expression for eccentric and misaligned seals. The boundary conditions are obtained from the no-slip conditions and from the logarithmic law. Validations of the method are made using the experimental results of Kanemori and Iwatsubo (1994) for a straight seal. Comparisons with other theoretical predictions are also included. Forces and moments in a four-grooves labyrinth seal are discussed.
Central and Minimum Elastohydrodynamic Film Thickness at High Contact Pressure
Authors: Smeeth M. , Spikes H. A.
Published: February 2008

A new optical technique has been developed which is able to obtain accurate film thickness profiles across elastohydrodynamic (EHD) contacts. This has been used in conjunction with a high pressure EHD test rig to obtain both central and minimum EHD film thicknesses at high contact pressures up to 3.5 GPa. The results have been compared with the classical film thickness equations of Hamrock and Dowson and also with recent high pressure computations due to Venner. It is found that minimum film thickness falls more rapidly with applied load at high than at low contact pressures, with a film thickness/load exponent of −0.3. This confirms the findings of recent high pressure computational EHD modeling.
Measurements of Static Loading Versus Eccentricity in a Flexure-Pivot Tilting Pad Journal Bearing
Authors: Walton Nick V. , San Andres Luis
Published: February 2008

An experimental investigation examining the static loading characteristics of a four-pad, flexure-pivot tilting pad bearing is presented. Tests are conducted on a Fluid Film Bearing Element Test Rig for journal speeds ranging from 1800 to 4500 rpm, and applied static loads between pads to 1400 N. Results obtained from measurements of bearing eccentricities and bearing pad temperatures were compared to numerical predictions. Bearing power losses were also estimated using a simple thermal model for the bearing assembly. Comparisons between theory and experimental results indicate good correlation for measured eccentricities over the tested range of applied static loads and journal speeds. Negligible displacements in the direction orthogonal to the applied load verified the expected behavior of the test bearing over the range of operating conditions. Thermal analysis of the hearing system lead to good prediction of the bearing power losses, and indicated that the majority of the mechanical energy is transferred via convection.
A Nonlinear Model for Structural Vibrations in Rolling Element Bearings: Part II—Simulation and Results
Authors: Datta J. , Farhang K.
Published: February 2008

This is the second of two companions papers. In the first paper, “A Nonlinear Model for Structural Vibrations in Rolling Element Bearings: Part I—Derivation of Governing Equations,” equations governing the vibrational response of rolling element bearings were developed. The mathematical formulations are utilized in this paper to study a number of effects on bearing structural vibrations. These include the effects of relative size of roller and inner and outer races, and inertias of inner and outer race assemblies, i.e., inertia of the races plus the components of an external system to which the inner and outer races are attached; the load acting on the bearing, its magnitude and nature (i.e., whether linear, rotational etc.). The studies are made under constant operating conditions (speed, lubrication) and the results obtained are discussed.
Point Contact EHL Based on Optically Measured Three-Dimensional Rough Surfaces
Authors: Zhu Dong , Ai Xiaolan
Published: February 2008

This paper presents a numerical solution for the elastohydrodynamic lubrication in point contacts, using optically measured three-dimensional rough surface profiles as input data. The multi-grid computer program originally developed by Ai and Cheng (1993, 1994) is modified, so that both contacting surfaces can be three-dimensional measured rough surfaces moving at different velocities. Many different engineering surfaces are measured and analyzed in the present study, demonstrating that the numerical analysis is practical for real surfaces of bearings, cams, gears and other components, as long as a significant EHL film still exists. In addition, discussions are given in this paper for the effects of three-dimensional rough surface topography, which is related to machining process. It appears that, for the circular contact cases analyzed, surface roughness texture and orientation do not have a significant effect on the average film thickness, but they do affect the maximum pressure peak height and asperity deformation in the contact zone considerably.
Transient Thermoelastohydrodynamic Study of Tilting-Pad Journal Bearings—Comparison Between Experimental Data and Theoretical Results
Authors: Monmousseau P. , Fillon M. , Freˆne J.
Published: February 2008

The aim of this paper is to study the increase in temperature of an unloaded tilting-pad journal bearing during rapid start-up. First, an analysis is carried out to choose an appropriate time step and grid refinement to minimize numerical errors. Then, the transient THD and TEHD theoretical models are developed to show the influence of solid bearing deformations. Experimental tests are realized on a four-shoe tilting-pad journal bearing. The temperatures at the shaft and pad surfaces, at the half thickness and the back of the pads are compared for both theoretical and experimental investigations. Good agreement is found between the theoretical results and the experimental data, especially when the variation of the operating bearing clearance is taken into account.
Effects of Foil Bending Rigidity on Spacing Height Characteristics of Hydrostatic Porous Foil Bearings for Web Handling Processes
Authors: Hashimoto H.
Published: February 2008

In this paper, the effects of foil bending rigidity on the spacing height characteristics of hydrostatic foil bearings with a hollow porous shaft for web handling processes are analyzed by the finite width bearing theory. In the analysis, in order to save computation time and to improve the convergence of solutions, the two-dimensional modified Reynolds equation considering the added flow through porous shaft is reduced to an ordinary differential equation based on the weighted residual method. The reduced Reynolds equation and elastic equation for the foil are discretized by the finite difference method and solved numerically by the iterative technique. The numerical solutions for the pressure and film thickness distributions between foil and shaft are obtained for a wide range of bearing width-to-diameter ratio under various combinations of foil bending rigidity and foil wrap angle, and the spacing height characteristics of the foil bearings are examined theoretically.
CFD Based Design Techniques for Thermal Prediction in a Generic Two-Axial Groove Hydrodynamic Journal Bearing
Authors: Keogh P. S. , Gomiciaga R. , Khonsari M. M.
Published: February 2008

There are many physical parameters that influence the thermal condition of a hydrodynamic journal bearing. This remains the case even when appropriate nondimensionalization procedures have been applied. However, two dimensionless parameters are particularly useful, since they embody lubricant shearing, convection, conduction and viscosity temperature variation. In this paper, these parameters are varied to obtain design charts for the maximum bearing shell and journal temperatures. Computational fluid dynamics (CFD) techniques are used in this process. They are applied to a generic two-axial groove circular bearing having a section of journal that extends beyond the width of the shell. The results demonstrate the usefulness of the charts through example design studies.
Tribochemical Study of Hydrogenated Carbon Coatings With Different Hydrogen Content Levels in Ultra High Vacuum
Authors: Yun Xiaohan , Bogy David B. , Bhatia C. Singh
Published: February 2008

Hydrogenated carbon films (CHx) with different hydrogen content percentages have been examined. Drag tests on CHx coated disks, using 50 percent Al2O3/TiC sliders, with and without carbon coating on the slider air bearing surfaces (ABS), were conducted in an ultra high vacuum chamber equipped with a mass spectrometer. Mass fragments of lubricant released from the head disk interfaces were recorded in real time along with friction measurements. The results show that a higher hydrogen content in the carbon overcoat can improve wear durability by reducing the friction coefficient and affecting the chemical reactions between the sliders and the lubricant. A carbon overcoat on the slider ABS can protect Z-dol lubricant from catalytic reaction with the Al2O3 in the slider material. The wear durability at the head disk interface is controlled by combined mechanical and chemical factors, which are defined by the atomic structures of the contacting surfaces.
A Mixed-Lubrication Study of Journal Bearing Conformal Contacts
Authors: Wang Qian (Jane) , Shi Fanghui , Lee Si C.
Published: February 2008

Numerical analyses of finite journal bearings operating with large eccentricity ratios were conducted to better understand the mixed lubrication phenomena in conformal contacts. The average Reynolds equation derived by Patir and Cheng was utilized in the lubrication analysis. The influence function, calculated numerically using the finite element method, was employed to compute the bearing deformation. The effects of bearing surface roughness were incorporated in the present analysis for the calculations of the asperity contact pressure and the asperity contact area. The numerical solutions of the hydrodynamic and asperity contact pressures, lubricant film thickness, and asperity contact area were evaluated based on a simulated bearing-journal geometry. The calculations revealed that the asperity contact pressure may vary significantly along both the width and the circumferential directions. It was also shown that the asperity contacts and the lubricant film thickness were strongly dependent on the bearing width, asperity orientation, and operating conditions.
FEM Simulation of Friction Testing Method Based on Combined Forward
Rod-Backward Can Extrusion
Authors: Nakamura Tamotsu , Bay Niels , Zhang Zhi-Liang
Published: February 2008

A new friction testing method by combined forward rod-backward can extrusion is proposed in order to evaluate frictional characteristics of lubricants in forging processes. By this method the friction coefficient μ and the friction factor m can be estimated along the container wall and the conical die surface in the forward rod extrusion using theoretical calibration diagrams representing the relationship between the punch travel, the forward rod extrusion length and form without requirements of measuring the forming forces and the flow stress of the workpiece. The theoretical calibration curves are obtained by rigid-plastic FEM simulations in a combined forward rod-backward can extrusion process for a reduction in area Rb, = 25, 50 and 70 percent in the backward can extrusion. It is confirmed that the friction factor mp on the punch nose in the backward can extrusion has almost no influence on the calibration curves. The optimum initial height/diameter ratio of the workpiece is 1.0–1.1. The influence of the workhardening index on the calibration curves is insignificant in the range 0.1 ≤ n ≤ 0.5. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants. They confirm the analysis resulting in reasonable values for the friction coefficient and the friction factor.
Experimental and Theoretical Analysis of Magnetic Head-Disk Interface Equilibrium in the “Rupture” Regime of the Starved-Liquid Bearing
Authors: Streator J. L.
Published: February 2008

Previous friction measurements in the magnetic head-disk interface (HDI) indicated some anomalous friction force behavior with low sliding speeds (.25 mm/s to 0.25 m/s) and lubricant film thicknesses in the range of 20–80 nm, showing decreasing friction force with increasing apparent shear rate. The physical explanation for such behavior has not yet been established. Possible explanations for such behavior have included dramatic shear thinning, interfacial slip and partial loss of contact with the lubricant film due to slider tipping. In the present study, we investigate the possibility of slider tipping as an explanation for the decreasing friction force with increasing sliding speed. Measurements with an optical probe indicate that slider tipping does not occur for the conditions tested. Numerical analysis of slider equilibrium also supports this conclusion.
An Optimum Design of the Transverse Pressure Contour Slider for Enhanced Flying Characteristics
Authors: Yoon Sang-Joon , Choi Dong-Hoon
Published: February 2008

This paper proposes a design method for determining the configuration of a TPC slider by using an optimization technique in order to meet the desired flying characteristics over the entire recording band. The desired flying characteristics considered in this study are to minimize the variation in flying height from a target value, to maintain the pitch angle as large as possible, to keep the roll angle as small as possible, and to keep the outside rail to fly lower than the inside rail. The design variables selected are left-side step width, pad width, right-side step width, side step depth, front taper height, and pivot offset in the transverse direction of the slider. The sequential quadratic programming (SQP) method in Automated Design Synthesis (ADS) is used to efficiently find the optimum design variables which simultaneously meet all the desired flying characteristics. To validate the suggested design method, a computer program is developed and applied to the configuration design of two TPC slider models positioned by a rotary actuator. The optimum configurations of each slider model are automatically obtained for three different target flying heights with the same predefined skew angle range without any difficulty. This shows the effectiveness of the proposed design method in comparison with the conventional one based on the parametric study.
The Effect of Interfacial Shear Strength on the Performance of Coated Surfaces in Repeated Sliding
Authors: Kapoor A. , Williams J. A.
Published: February 2008

When hard rough surfaces slide repeatedly on softer half-spaces, systems of protective residual stresses may be developed in the near surface layers of the softer material which enable loads sufficiently large to cause plastic deformation in the early cycles of loading to be accommodated purely elastically in the later stages of component life. This is the process of shakedown and limits on the intensity of the allowable Hertzian pressures consistent with the eventual cessation of plastic deformation for uniform half-spaces are now well established. In this paper, we produce shakedown maps for coated or treated surfaces, choosing principally to carry out the numerical calculations on a system which models the behavior of ceramic coatings on steel substrates. In addition to the relative hardnesses of coating and the substrate, important system parameters are shown to be the normalized thickness of the coating and the strength or integrity of the bond at the interface between the coating and substrate. It is quite possible for the production of a coating of less than the critical thickness, or one displaying poor adhesion, to reduce the shakedown performance to lower values than would be the case for an unprotected surface. Design curves are produced which illustrate how the improvement in shakedown performance of such coated surfaces varies with the normalized depth of coating and the strength of the interlayer bond.
Rotordynamic Coefficients of Circumferentially-Grooved Liquid Seals Using the Averaged Navier-Stokes Equations
Authors: Arghir Mihai , Freˆne Jean
Published: February 2008

The paper presents a method to calculate the rotordynamic coefficients of circumferentially-grooved liquid seals operating in centered position and turbulent flow regimes. The method is based on the integration of the averaged Navier-Stokes equations and uses a coordinate transformation proposed by Dietzen and Nordmann (1987). The effect of the coordinate transformation on the components of the stress tensor is included in the first order transport equations. To ensure grid independent solutions, numerical boundary conditions for the first-order velocities were formulated using the logarithmic law. The perturbation of the turbulent viscosity was also considered. A pressure recovery effect at the exit section was included in the first order mathematical model. The method is validated by calculations for straight and circumferentially-grooved seals. Comparisons with experimental and theoretical results show a good agreement for straight seals and for seals with few grooves, and a reasonable agreement for severe industrial cases (high Reynolds numbers and large number of grooves).
Plate-Impact Technique for Measuring Dynamic Friction at High Temperatures
Authors: Frutschy K. J. , Clifton R. J.
Published: February 2008

A new pressure-shear plate impact experiment is described for measuring the friction between two sliding surfaces at high temperature. Additionally, the techniques developed for this experiment extend the capability of the general pressure-shear experiment so that the shear strength of materials can be measured at high temperatures.
Magnetic Field Assisted Finishing of Ceramics—Part III: On the Thermal Aspects of Magnetic Abrasive Finishing (MAF) of Ceramic Rollers
Authors: Hou Zhen-Bing , Komanduri R.
Published: February 2008

Conditions during finishing of advanced ceramics by magnetic abrasive finishing (MAF) processes are found to be, by and large, transient. Consequently, the available quasi-steady-state solutions for the moving heat sources are not directly applicable for this case. Hence, the general solution for a moving disk heat source, developed in Part I of this three-part series, is applied to determine the minimum flash temperatures and flash times generated at the contact points between the workmaterial (Si3N4 roller) and the abrasive (Cr2O3)). Since chemo-mechanical action between the abrasive—the workmaterial—the environment depends on both the thermodynamics and kinetics of the process, it is important to determine the flash temperatures as well as flash times during polishing. These were determined as a function of the polishing pressure and the rotational speed of the work material in this investigation. Thermodynamic considerations (not covered in this paper) indicate that even the minimum flash temperatures generated under the conditions of lower pressure, lower sliding velocity, and transient state would be adequate to initiate chemo-mechanical action, and experimental results confirmed the formation of chemo-mechanical reaction products during polishing (Bhagavatula and Komanduri, 1996).
A 3-D Model for a Multilayered Body Loaded Normally and Tangentially Against a Rigid Body: Application to Specific Coatings
Authors: Plumet S. , Dubourg M.-C.
Published: February 2008

Coatings are increasingly used to improve the mechanical and tribological behavior of surfaces. It is necessary to develop models to guide the initial choice of coating/substrate combinations that can withstand the applied loads. A three-dimensional model of an elastic multilayered body, loaded both normally and tangentially against an elliptical rigid body (partial sliding, rolling/sliding conditions), is presented here. This model is based on linear elasticity theory, integral transforms, Fast Fourier Transform, and unilateral contact analysis with friction. Normal and tangential contact conditions between the two bodies are first determined and then used to calculate the multilayered body stress field. One application is given here: The influence of the mechanical properties of coating and substrate, as well as coating thickness, is studied on contact conditions, internal stresses, and potential failure mechanisms.
A New Principle in Contact Mechanics
Authors: Ja¨ger J.
Published: February 2008

Two nonrotating elastic half-planes in quasi-static contact without coupling of the normal and tangential surface stresses are analyzed in this paper. It is proved that the tangential traction under constant normal forces and increasing tangential forces is equal to the difference between the actual normal pressure and the pressure for a smaller contact area, multiplied by the coefficient of friction. Every stick area corresponds to a contact area (or a configuration of multiple contact areas) that is smaller than the present contact area. In the same way as the contact area develops with increasing pressure, the stick area recedes with increasing tangential traction. General loading scenarios are solved by superposition of oblique increments under constant angles. As an example, this principle is applied to a rigid surface of the form Akxk, in contact on 0 ≤ x ≤ a and with a corner at x = 0, indenting an elastic half-plane.
Finite Element System Approach to EHL of Elliptical Contacts: Part I—Isothermal Circular Non-Newtonian Formulation
Authors: Hsiao Hsing-Sen S. , Hamrock Bernard J. , Tripp John H.
Published: February 2008

The column continuity equation is used in formulating a modified Reynolds equation for elastohydrodynamic lubrication of elliptical contacts. A finite element method (FEM), here the Galerkin weighting method with isoparametric Q9 elements, is used to discretize the weak form of the Reynolds equation. In addition to the nodal pressures and the offset film thickness, the locations of the two-dimensional irregular free boundary are explicitly solved for by simultaneously forcing the essential and the natural Reynolds boundary conditions. Newton-Raphson’s iterations with a user-friendly yet efficient meshless scheme (i.e., automatic meshing-remeshing) are finally applied to solve these equations. A decoupled circular non-Newtonian fluid model is adapted in a way to illustrate the implementation of this new solution method. Extensive results will be given in Part II.
Waviness Amplitude Reduction in EHL Line Contacts Under Rolling-Sliding
Authors: Lubrecht A. A. , Graille D. , Venner C. H. , Greenwood J. A.
Published: February 2008

Due to technological pressures the lubricant film thickness in EHD contacts has decreased over the years and will continue to do so for the foreseeable future. On the other hand, financial constraints cause the surface roughness in these contacts to decrease very slowly, or might even cause an increase. As a result, the ratio of film thickness to composite roughness will continue to decrease. The question that remains to be answered is to what extent this decrease will affect the contact performance. A third development makes this question even more acute, the request of increased reliability. As a consequence, the problem of the detailed understanding of the elastohydrodynamic lubrication with rough surfaces is as urgent as ever. Recent work has shown that the features inside the contact deform, and that the level of deformation is a function of the wavelength of the feature and the contact operating conditions, including slip. This last aspect of the problem, which has not been addressed previously, forms the central topic of the current paper. Instead of studying the deformation of a real roughness profile, the deformation of its sinusoidal Fourier components is investigated.
A Rapid Boundary-Element Method for Modeling Viscous Flow Within Asymptotically-Thin Gaps
Authors: Kelmanson M. A.
Published: February 2008

A new boundary-element method is presented for the rapid and accurate solution of viscous-flow boundary-value problems in which the inherent geometry has a high aspect ratio, R ≫ 1, As such, the method is particularly suited to the investigation of steady flow within thin-gap bearings of arbitrary geometry, in which the spatial dimension in one direction is an order of magnitude greater than that in a perpendicular direction. Our theory predicts that the new method is O(R2) times faster than, and requires O(R−1) the storage of, existing boundary-element techniques with equivalent computational mesh resolution. The new method is applied to the test problem of steady 2-D viscous flow within an exponential-profile slider bearing, and results obtained provide convincing evidence to support the theory in that, as R → ∞, the thin-film solution is recovered. The new method, which brings problems which were hitherto computationally restrictive within reach of modest computational platforms, is intended to provide the basis of a fast and accurate solver which can incorporate random surface roughness.
Effects of Average Lubricant Velocity and Sliding Velocity on Friction Behavior in Mild Steel Sheet Forming
Authors: Dohda Kuniaki , Wang Zhrgang
Published: February 2008

A series of experiments was carried out using a rolling-type tribometer to investigate the frictional dependence on the average velocity of the lubricant V at the contact zone inlet and the relative sliding velocity ΔV between the roll and workpiece during deformation. Experiments using mild steel strips with a dull surface of 0.63 fxm Ra showed that the friction coefficient decreases with increasing forming velocity, especially at high forming velocity. This variation in the friction coefficient may be due to the increase in ΔV derived from the increase of the forming velocity, because the friction coefficient decreases with increasing ΔV but varies little with increasing V. It was also confirmed that an increase of ΔV or a decrease in V promotes flattening of the workpiece asperities.
Grease Lubrication in Fretting
Authors: Zhou Z. R. , Kapsa Ph. , Vincent L.
Published: February 2008

This paper concerns an experimental investigation of fretting behavior using grease lubrication for ball (ball bearing steel) -flat (low alloyed steel) contact. The influences of the imposed displacement amplitude, contact geometry, pressure, and frequency are emphasized. In order to better understand the effect of grease lubrication at the interface, a glass counterface was used to visualize the contact; sliding tests were used to identify the effect of a large displacement amplitude. Dynamic loading analysis, in combination with subsequent metallographic examinations, have shown that fretting damage depends strongly upon fretting conditions and upon grease durability. Lubrication conditions and palliative effect in fretting are discussed. Results have shown an important effect of normal force, displacement amplitude, and frequency of motion on the lubricating effect of grease. The separation of grease into two phases in the contact during friction, creating bubbles, appears to be an important phenomenon.
Analysis of Surface Tractions in Complex Fretting Fatigue Cycles Using Quadratic Programming
Authors: Nowell D. , Dai D. N.
Published: February 2008

Real fretting fatigue cycles often involve complex loading where the fretting force may vary with a different phase or frequency to the other loads on the components. Analysis of the contact tractions in such cases can be difficult. Here we present a quadratic programming technique which enables the shear tractions to be determined in a relatively straightforward manner. A number of sample load histories are investigated and it is shown that the shear traction cycle rapidly shakes down to a steady state. Further, the results are relatively insensitive to the manner in which loading is commenced.
Ultra-Thin Gas Squeeze Film Characteristics for Infinitely Large Squeeze Number
Authors: Li Wang-Long
Published: February 2008

In this study, the characteristics of ultra-thin gas films are analyzed asymptotically for infinite squeeze number using the molecular gas film lubrication equation with coupled roughness and rarefaction effects taken into consideration. The governing equation of the internal region was obtained by a time averaged technique, and the boundary conditions were obtained numerically from the matching conditions near the boundaries. Two new functions, H and H−1 were proposed for deriving the matching equation near the boundary. Finally, the characteristics of squeeze film bearings with infinite width were analyzed for various roughness parameters (Peklenik number, standard deviations of the composite roughness, and roughness orientation angles), rarefaction parameter (Knudsen number), and operation conditions (excursion ratio).
Compressible Narrow Groove Analysis—Part 1: Derivation
Authors: Pan Coda H. T.
Published: February 2008

The technique of High-Resolution Modeling of Thin Films is combined with a two-scale analysis to formulate the Compressible Narrow Groove Analysis. The data bank of Fukui and Kaneko (1990) is emulated in the form of an empirical formula to treat the state of arbitrary rarefaction of the gas film. Due to its transcendental character, the compressible fine-scale solution is treated on the fly as a part of the global-scale computation. Derivations for the Compressible Narrow Groove Analysis are presented here. In a companion paper (Pan, 1998), the Compressible Narrow Groove Analysis is used to compute the pressure field of a spherical device operating in both the pressurizing and evacuating modes.
Compressible Narrow Groove Analysis—Part 2: Computation of Pressure Field in a Spherical Device Rotating in Either Direction
Authors: Pan Coda H. T.
Published: February 2008

Compressible Narrow Groove Analysis, as derived in a companion paper (Pan, 1998), is a model implementation of Thin Film High-Resolution Modeling for gas films. This paper describes the numerical procedure to compute the pressure field in a centered spherical device, which has general design features originally intended for a high performance gas bearing gyroscope (Keating and Pan, 1968). The number of groove patterns is varied to bring out the significance of the local compressibility number. Increased local compressibility, associated with reduced number of groove patterns, causes successive degradation of the pressurization capacity until it is entirely suppressed at 32 groove patterns. Further study is made with reversed rotation to create a high vacuum state in the gas film concurrent with a large compressibility number. The evacuation operation (with reversed rotation) is relatively insensitive to the number of groove patterns, but is highly dependent on the accommodation coefficient. Experience in preparing these examples lends evidence to the robustness of Thin Film High-Resolution Modeling. Trouble free iterative computations are routinely performed for the local Knudsen number in excess of 109 and the effective local compressibility number larger than 100.
Effect of Stress State of Different Tin Films on Their Tribological Behavior
Authors: Daming Zhuang , Jiajun Liu , Baoliang Zhu , Zhong-Rong Zhou , Vincent Leo , Kapsa Philippe
Published: February 2008

Titanium nitride films were deposited by the methods of ion beam enhanced deposition (IBED), plasma chemical vapor deposition (PCVD) and ion plating (IP). X-ray diffraction analysis was employed to determine the internal stress state of TiN film and 52100 steel substrate at both sides of the interface. The effect of stress state on their bonding strength and tribological behavior was analyzed systematically, their wear and failure mechanisms were discussed in detail as well.
Experimental Evaluation of Stiffness and Damping of Slider-Air Bearings in Hard Disk Drives
Authors: Zeng Q. H. , Bogy D. B.
Published: February 2008

The system identification method was applied to experimentally investigate the dynamic characteristics of slider-air bearings in hard disk drives. The transient responses of sliders were measured, and the modal frequencies and damping ratios that are directly related to the stiffness and damping of the bearings were obtained by data processing and parameter identification. The dynamic property of a particular advanced air bearing (AAB) slider was measured and compared with simulation results. It was found that, contrary to usual perception, the suspension assembly significantly affects the dynamic characteristics of the air bearings. Contacts between the load beam and the flexure may introduce a larger damping and nonlinear property. The preliminary results also show that the proposed method is robust for experimentally evaluating the dynamic properties of slider-air bearings.
In-Situ Measurement of Near-Surface Fretting Contact Temperatures in an Aluminum Alloy
Authors: Szolwinski M. P. , Harish G. , Farris T. N. , Sakagami Takahide
Published: February 2008

Fretting is the tribological phenomenon observed in nominally-clamped components which experience vibratory loads or oscillations. Associated with fretting contacts are regions of small-amplitude relative motion or microslip that occurs at the edges of contact. A newly-available infrared technology capable of resolving temperatures fields finely, both spatially and temporally, is used to characterize the near-surface conditions associated with fretting contact between an aluminum alloy cylinder and flat. Both frictional heating due to interfacial slip and the coupled-thermoelastic effect arising from strains in the material induce these temperatures. The experimental results provide insight into not only the magnitude and distribution of near-surface temperatures, but also the nature of the contact stress field and the mechanics of partial slip fretting contacts. Comparisons of the measured temperature fields are made with those predicted by considering both conduction of the frictional heat flux and coupled-thermoelastic theory.
Numerical Analysis of Herringbone-Grooved Gas-Lubricated Journal Bearings Using a Multigrid Technique
Authors: Kobayashi Takuji
Published: February 2008

In this paper, a multigrid technique is applied to the compressible Reynolds equation discretized by the divergence formulation in order to analyze both static and dynamic characteristics of herringbone-grooved gas-lubricated journal bearings. The developed code demonstrates quicker convergence than an optimized successive over-relaxation scheme, and the dominance in numerical efficiency is especially remarkable at higher values of bearing number where slow convergence is generally observed. Comparisons between the present nonlinear orbit solutions and previously published experimental results show reasonable agreement in both steady-state and dynamic stability performances.
Journal Asymmetric Heating—Part II: Alteration of Rotor Dynamic Properties
Authors: Larsson Bjo¨rn
Published: February 2008

An approximation of heat conduction dynamics in a rotating shaft is presented for use in the rotor dynamic analysis of multiple hydrodynamic bearings to predict alteration of vibrations due to shaft bows. The interactions form a closed-loop system. Initial unbalance gives a vibration, which results in an asymmetrical temperature distribution on the surface of the journal. Heat conduction in the shaft results in a bow. The new bow changes the unbalance and thus the vibration of the rotor. The loop is thus closed. The approximation of heat conduction is in the form of an ordinary differential equation. The coefficients in this equation result from a curve-fitting to the solution of a nonstationary partial differential equation. The result opens the way for stability analysis, transient analysis, and evaluation of actual mass unbalance response (including fully developed bows).
Wear Studies of Tungsten Carbide Cutting Tools Using Micro-Beam Techniques
Authors: Nickel J. , Shuaib A. N. , Allam I. M.
Published: February 2008

Particle accelerator based μ-PIXE and μ-RBS techniques along with optical microscopy, SEM and EDS were employed to examine the worn faces of uncoated tungsten carbide inserts used for cutting free machining steel. The study is concentrated on the deposited manganese sulfide onto the rake and flank faces of the tool tips, and on the changes in the tool matrix composition arising from the prevailing wear mechanisms. The manganese and iron distributions on the worn faces of the tool tips showed a very good reproducibility for similar cutting conditions. Evidence of the decomposition of tungsten carbide in the crater and the diffusion and/or oxidation of the freed tungsten is presented. The strength of the μ-PIXE and μ-RBS versus conventional techniques is demonstrated by the ability of the former techniques to resolve the structure and the composition of deposited layers in three dimensions.
A New Approach to Calculation of Contact Characteristics
Authors: Chekina O. G. , Keer L. M.
Published: February 2008

A new method of calculation of contact characteristics for rough surfaces is proposed based on integral relations that express the normal contact stress as an explicit function of the surface shape. To produce calculations by this method, a region having a simple shape should be chosen first, where the contact is supposed to be nominally complete. An iterative procedure with regard to the shape is applied within the load-free surface portion, and allows the normal stresses, surface displacement and the real area of contact to be determined. The method is applicable to rough bodies of arbitrary shape for which the half-space formulation and equivalent roughness concepts apply; the real contact area should lie within the initially chosen contact region and can include a system of unconnected contact spots. Both 2D and 3D cases are considered in the present work. The 2D analysis is based on known integral relations for nonperiodic and periodic contact problems. In the 3D case, new analytical relations are obtained and their properties are analyzed. An iteration algorithm based on these relations and its efficient numerical implementation are described. Application of the method to the contact of real rough surfaces is discussed.
Air Film Thickness Estimation in Web Handling Processes
Authors: Hashimoto Hiromu
Published: February 2008

In this paper, in order to estimate an air film thickness between moving web and guide roller (web spacing height), an air film thickness formula was derived based on the finite width compressible foil bearing theory. In the derivation of the air film thickness formula, the two-dimensional Reynolds equation and foil equilibrium equation were discretized by the finite difference method and solved iteratively to obtain the pressure and air film thickness distributions for various parameters. Based on the numerical results, the simplified convenience formula for the estimation of air film thickness between web and guide roller was obtained. On the other hand, the air film thickness between web and guide roller was measured by an optical sensor, and the experimental results were compared with the calculated results. Moreover, the variation of air film thickness between two layers in web winding processes was analyzed by making use of the air film thickness formula derived above. From the theoretical and experimental results obtained, the effects of air film thickness on the web transporting systems were clarified.
Lundberg-Palmgren Fatigue Theory: Considerations of Failure Stress and Stressed Volume
Authors: Harris T. A. , Yu Wei Kuei
Published: February 2008

Load ratings and fatigue life prediction of rolling bearings is based on the Lundberg-Palmgren theory first published in Sweden in 1947. The basic equation of this theory includes the stressed volume of material in the bearing raceway subsurfaces as a major parameter. This volume of material is simplistically determined to have a nearly rectangular subsurface cross-sectional area bounded by the length of the maximum contact area ellipse and the depth at which the maximum failure-causing stress occurs. The latter stress is assumed to be effective over this area. In fact, a distribution of stress occurs, and in this investigation it is demonstrated that the subsurface volume with a potential for fatigue cracking is substantially different from that used by Lundberg and Palmgren. This difference in volume, particularly in the presence of surface shear stresses, can have a profound effect on the method and prediction of bearing fatigue lives.
A Numerical Solution of a Surface Crack Under Cyclic Hydraulic Pressure Loading
Authors: Xu Z.-Q. , Hsia K. J.
Published: February 2008

Material degradation and failure in rolling contact components are often associated with surface crack initiation and propagation under repeated contact loading. In the presence of lubricating fluid, the hydraulic pressure in the fluid film between the contacting surfaces may play an important role in the crack growth process. This paper presents a method to model the effect of hydraulic pressure loading on surface crack growth. The governing equations of the coupled viscous fluid/cracked solid problem are obtained, which are nonlinear integral and differential equations. The fluid is assumed to be Newtonian and incompressible. The cracked solid is considered to be linearly elastic. Pressure loading history is prescribed at the crack mouth. Finite difference methods are used to solve the governing equations. For each time step, Newton-Raphson iteration method is used to search for the root of the nonlinear equations. Both transient and steady-state pressure distributions under cyclic pressure loading are obtained using this method. A few numerical examples are given to demonstrate the reliability and effectiveness of the solution method. The solution shows that there exists a characteristic time, which determines whether pressure fluctuations at the crack mouth can be transmitted deep into the crack. The steady-state pressure distribution exhibits a phase delay from the applied cyclic loading.