bluuebunny/crossref_metadata_2025 huggingface dataset:
Glide Avalanche Prediction From Surface Topography
Authors: Marchon B. , Kuo D. , Lee S. , Gui J. , Rauch G. C.
Published: February 2008

As the head/disk spacing continues to decrease, the demand for thin film disks with glide capability below 20 nm becomes more pressing. As a consequence, the design of such media requires an ever increasing control of the surface topography to a nanometer level. This paper is an attempt to analytically predict the intrinsic glide capability of a textured disk, given the knowledge of its peak height distribution, as measured by a surface profilometer. This model also takes into account the long wavelength component of the topography, or waviness, by treating it as an independent variable leading to a broadening of the peak height distribution. This analysis also predicts relationships between various roughness parameters. Experimental data obtained on a total of 27 media surfaces of various types compare favorably to the theoretical predictions.
Evaluation of Dynamic Coefficients of a Two-Lobe Journal Bearing
Using an Electrical Analogy Approach
Authors: Prashad Har
Published: February 2008

A theoretical approach to evaluating capacitance, resistance, capacitive reactance, and impedance of the lower and upper lobes of a two-lobe elliptical hydrodynamic journal bearing under various operating conditions is developed. It is established that the change in capacitance and resistance with the change in eccentricity ratios is nonlinear. The capacitance and resistance, thus determined, are correlated with the dynamic coefficients of bearings using an electrical analogy. It is found that the stiffness and damping coefficients are higher for two-lobe bearings as compared to those of cylindrical bearings having identical dimensional parameters and operating under similar conditions. The analysis may have the potential to diagnose the stability regime of a bearing through the bearing’s electrical parameters. The electrical analogy may be a useful alternative to conventional techniques.
Ultrathin Perfluoropolyether Films—Influence of Anchoring and
Mobility of Polymers on the Tribological Properties
Authors: Ru¨he J. , Novotny V. , Clarke T. , Street G. B.
Published: February 2008

The tribological behavior of ultrathin films of hydroxyl terminated perfluoropolyethers attached to smooth silicon surfaces was studied in pin-on-disk experiments. The frictional properties of the films, which consisted of either physically adsorbed or chemically bonded polymer or a combination of both, was measured in sliding contact and lubricant loss was studied simultaneously by scanning microellipsometry. Prior to these experiments the kinetics of attachment of the polymer to silicon surfaces and the behavior of the polymer at high temperatures was investigated in order to obtain reproducible conditions for the deposition of the lubricant films and to rule out the occurrence of thermal degradation during film deposition. The tribological investigations showed that the lifetime of the surfaces with the attached boundary lubricant was strongly dependent on the mode of attachment of the polymer. The best tribological behavior was observed in films which contained both chemisorbed and physically adsorbed material.
Rheological and Physical Studies of Lubricating Greases Before and
After Use in Bearings
Authors: Mas Rémy , Magnin Albert
Published: February 2008

Lithium soap and calcium complex soap-based lubricating greases are studied when fresh and after use in roller and ball bearings. Examination of the rheological properties of these greases using rotating rheometers reveals changes that have occurred during use in the bearings. These modifications are not uniform throughout the hearing. Physical and chemical analyses enable these modifications in rheological properties to be linked to variations in composition or structure, depending on the type of grease and bearing. Several mechanisms involved in lubricating a bearing with a lubricating grease are confirmed or clarified.
Evaluation of Fretting Damage of Zircaloy Cladding Tubes
Authors: Vingsbo Olof , Massih Ali R. , Nilsson Stig
Published: February 2008

The work is part of the search for a technique to study the fretting properties of the cladding of fuel rods in nuclear reactors. The strategy is to compare the fretting scars of specimens tested in a near-full-scale, nonradioactive simulator (so called fuel assembly endurance test) with scars on specimens tested under well controlled conditions in the laboratory. By systematic variations of the laboratory testing parameters it has proved possible to achieve scars with the same type of damage characteristics as those from the fuel assembly endurance test. This makes it possible to estimate, by deduction, the parameters that cause fretting damage under actual service conditions in a reactor.
Thermal Analysis of a Medium-Carbon Steel Tribo-System and Its Application to Oxidational Wear
Authors: Lin Jen Fin , Chou Chau Chang , Yang Jeng Woei
Published: February 2008

Wear behavior of AISI 1045 carbon steel has been studied on a washer-on-disk wear machine at bulk disks temperatures of 25°C and 200°C. An analytical approach to the temperature solutions was developed in terms of a parabolic temperature polynomial for the frictional contact area; the maximum contact temperature Tc is thus obtained by using several measured temperatures as boundary conditions. The tribological properties of carbon steel in sliding contact were studied to investigate the oxidational wear rate associated with the tribo-chemical reaction arising on the worn surface due to frictional heating. A theoretical approach to predict the oxidational wear rate of this carbon steel at 25°C and 200°C was also established.
Roughness Effects on the Dynamic Coefficients of Ultra-Thin Gas Film in Magnetic Recording
Authors: Li Wang-Long , Weng Cheng-I , Hwang Chi-Chuan
Published: February 2008

The stiffness and damping coefficients of a slider gas bearing operating under arbitrary Knudsen number are calculated. A perfect gas is used as the lubricant, and its behavior is described by the modified average Reynolds equation proposed by Makino et al. (1993). The effects of molecular mean free-path on the roughness-induced flow factors are included. The effects of the nondimensional film thickness, Hs0, the surface characteristics, (γ1, γ2). the inverse Knudsen number, D0, the nondimensional frequency, Ω, and the modified bearing number, Λb, on the dynamic coefficients are discussed in this paper. As expected, the values of dynamic coefficients for various roughness orientations approach the smooth value as the ratio, Hs0, becomes greater and greater, and thus the roughness effect is getting smaller and smaller. The air film of two-sided longitudinal oriented roughness is stiffer than the other two-sided oriented cases. The effect on translational damping coefficients for various two-sided oriented roughnesses is reversed as D0 greater than some value, and this value is affected significantly by Λb. Transversely rough stationary case has the lowest critical value of Λb, at which the negative translational damping appears. The results show that the roughness effect and rarefaction effect on dynamic coefficients are significant, and they cannot be ignored for stability analysis.
Factored-lmplicit Finite Difference Solution of a Non-Newtonian Fluid Lubrication Equation for Three-Dimensional Bearings
Authors: White J. W.
Published: February 2008

A time dependent lubrication equation is developed for a non-Newtonian fluid whose shear stress is expressed in terms of instantaneous strain rate. By expanding the shear stress through a two function Taylor series, the stress/strain-rate relationship is linearized within the time interval (tn ≤ t ≤ tn+1) but accurate to O(Δt2). This produces a linear lubrication equation which is second-order time-accurate. The resulting finite difference form of the lubrication equation is then factored and split into two equations, each of which represents a sequence of one-dimensional systems of tri-diagonal scalar equations. A finite difference code based on this algorithm was written called VISQUSFLO which provides static and dynamic analysis of the head/disk interface of data storage systems. Numerical examples of a shear-thinning fluid are presented for clearances in the range of 25-50 nm for finite width slider bearings.
A Model for Elastohydrodynamic Film Failure in Contacts Between Rough Surfaces Having Transverse Finish
Authors: Evans H. P. , Snidle R. W.
Published: February 2008

The paper describes an elastohydrodynamic lubrication (EHL) model for collapse of the film in a contact of finite width between surfaces which have roughness aligned transverse to that of lubricant entrainment. The failure mechanism proposed is that of sideways leakage of the lubricant in the gaps that are present between the surfaces due to the valley features of the surface roughness. Under typical high temperature conditions with surfaces finished by conventional grinding, it is shown that the gap between the surfaces when lubricated is almost identical to that between the same dry surfaces in contact with the addition of a small land clearance equivalent to the nominal EHL film thickness. Analysis of idealized valley geometries leads to criteria for complete cavitation or significant loss of pressure between asperity contacts, but application of these criteria to a real contact suggests that scuffing occurs under conditions which are less severe than predicted by either of these simple failure models. Detailed analysis of leakage from the valley features in the transverse direction at the edges of a real elliptical contact shows that this can explain the complete loss of the film in a real contact, and this suggests a physical mechanism of scuffing.
Analysis of Thermal Effects in the Yield Phase of Hydrodynamic Lubricant Film in Plane Strain Forging
Authors: Bhatt V. K. , Sengupta D. K.
Published: February 2008

A thermal Reynolds equation, which takes into account viscosity variation across the lubricant film thickness due to shear energy dissipation within the film, has been developed. It also takes into account the effect of conduction and convection on heat transfer in the lubricant film. It indicates that the pressure gradients developed in a no-slip lubricated contact are increased with an increase in Peclet number. The use of the equation is illustrated by applying it in the film formation process in the yield phase of liquid lubricated plane strain forging. The analysis indicates that the Peclet number plays a dominant role infixing the lubricant film thickness in such contacts.
Abnormal Phenomena Appearing in EHL Contacts
Authors: Kaneta M. , Nishikawa H. , Kanada T. , Matsuda K.
Published: February 2008

In a previous paper the authors showed that when the surface velocity of a body having lower elastic modulus is faster than that of a body having higher elastic modulus, and when the radius of curvature of the former is larger than that of the latter, a deep conical depression (dimple) is produced in the contact surface. This dimple occurs in place of the flat plateau predicted by the point contact elastohydrodynamic lubrication (EHL) theory. In this paper, the effects of surface kinematic conditions on the formation of such abnormal phenomena, which cannot be predicted by the present EHL theory, are investigated under rolling/sliding conditions using the optical interferometry technique. Transient behavior of the dimple caused by a groove passing through the EHL conjunction is also discussed based on direct observations. It has been found that the dimple occurs when the lubricating oil in the contact area is composed of solidified and unsolidified parts, and the dimple itself corresponds to the solidified part. On the basis of this finding, it has been asserted that the establishment of a new EHL theory is needed.
A Study of the Oil-Lubricated Herringbone-Grooved Journal Bearing—Part 1: Numerical Analysis
Authors: Kang Kyungphil , Rhim Yoonchul , Sung Kiro
Published: February 2008

A numerical study of the oil-lubricated herringbone-grooved journal bearing is presented for the case of eight circular-profile grooves on the sleeve surface. The governing differential equation derived from the mass balance is solved by using the finite difference method. Some of the groove geometries are constrained because of the groove forming processes. Optimal values for various bearing parameters are obtained to maximize the radial force and to improve the stability characteristics. Results are compared with the plain and rectangular-profile grooved journal bearings. Radial force, attitude angle, stiffness and damping coefficients, and stability map are given for optimal configurations.
Polishing and Lapping Temperatures
Authors: Bulsara Vispi H. , Ahn Yoomin , Chandrasekar Srinivasan , Farris Thomas N.
Published: February 2008

Polishing is a finishing process in which a smooth work surface is produced by rubbing it against a polishing block with an abrasive slurry interspersed between them. A model has been developed to estimate the temperature rise of the work surface in polishing. In this model, the forces acting on an abrasive particle are derived from a mechanistic analysis of abrasive-workpiece contacts. The heat generated at a contact is taken as the product of the friction force and the relative sliding velocity between the abrasive and the work surface. For calculating the heat flux transferred into the workpiece, each of the abrasive-workpiece contacts is modeled as a hardness indentation of the work material by a conical indenter. The moving heat source analyses of Jaeger and Blok are then applied to estimate the fraction of the heat flux flowing into the workpiece, and the maximum and average temperature rise of the work surface. Calculations of the work surface temperature rise are made for the polishing of steel, soda-lime glass, and ceramics. These show that the work surface temperature rise in polishing is quite small, typically much less than 200°C, and substantially less than in grinding. The low values calculated for the work surface temperature rise are shown to be consistent with many observations pertaining to the mechanical state of polished surfaces. The effect of polishing process variables on the work surface temperature rise is analyzed.
An Experimental Investigation on the Static and Dynamic Characteristics of Journal Bearings Under the Influence of Twisting Misalignment
Authors: Arumugam P. , Swarnamani S. , Prabhu B. S.
Published: February 2008

The misalignment between the journal and the bearing in a rotor-bearing system may be due to manufacturing error, elastic deflection, thermal expansion etc. In the present work, the eight linearized stiffness and damping coefficients of the cylindrical and three lobe bearings are identified at different levels of bearing misalignment (twisting misalignment) and at different speeds of the rotor. The identification method used here needs FRFs (Frequency Response Functions) obtained by the measurements and the finite element method. The twisting misalignment changes the stiffness and damping coefficients in the vertical and horizontal directions. In the case of three lobe bearings, for 0.7 degree of misalignment, the stiffness in the vertical direction is increased by about 12 percent.
Relation of Dry-Friction to Surface Roughness
Authors: Bengisu M. T. , Akay A.
Published: February 2008

A formulation of friction force in the interface of a friction pair is developed considering the mechanical components arising from the elastic and plastic deformations of the asperities and the chemical components represented by the adhesive forces between local contact regions. The results relate the normal load and dry-friction force to the relative normal and tangential velocities of a friction pair as a function of asperity deformations and adhesive forces. It is shown that the important parameter in the relationship between normal load and the dry-friction force is the projection of the contact area in normal and tangential directions to the mean planes of contacting surfaces rather than the contact area itself. The two forms of dry-friction force derived from the statements of energy balance at the interface allow alternate approaches to modelling of the friction between interacting rough surfaces.
An Ultrathin Liquid Film Lubrication Theory—Calculation Method of Solvation Pressure and Its Application to the EHL Problem
Authors: Matsuoka Hiroshige , Kato Takahisa
Published: February 2008

This paper describes a new method for calculating the solvation pressure that acts between solid surfaces when the surfaces approach each other to within a very small distance in a liquid medium. Solvation pressure is calculated by solving the transformed Ornstein-Zernike equation for hard-spheres in a two-phase system with Perram’s method and using the Derjaguin approximation. Furthermore, the authors apply the new method to the elastohydrodynamic lubrication problem in which the film thickness is very small and solvation force and van der Waals force cannot be neglected. It will be shown that the calculation results agree well with experimental data. The results are then compared with two conventional solvation pressure models proposed so far, namely, Chan and Horn’s model, and, Jang and Tichy’s model. It is found that these two models neglect the elastic deformation of solid surface when obtaining the experimental parameter used in their models; thus they overestimate the solvation pressure resulting in the prediction of larger film thickness than the experiments.
Nanomechanical Properties of SiC Films Grown From C60 Precursors Using Atomic Force Microscopy
Authors: Morse K. , Weihs T. P. , Hamza A. V. , Balooch M. , Jiang Z. , Bogy D. B.
Published: February 2008

The mechanical properties of SiC films grown via C60 precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and diamond-tipped steel AFM cantilevers were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be 26 GPa by nanoindentation of the film with a Berkovich diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one half to one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of ~300 GPa is estimated for these SiC films.
The Effect of Disk Warpage/Skew on the Deflection and Vibration of a Flexible Disk Spinning Above a Baseplate and in Contact With a Point-Head
Authors: Wu R. Y. , Adams G. G.
Published: February 2008

A flexible disk, with small initial warpage/skew, is spinning in close proximity to a stationary baseplate. The partial differential equation for the disk deflection is coupled to the Reynolds equation of the stabilizing air-film. Disk warpage/skew produces a small change in the deflection which rotates with the disk. These deflections are obtained by linearizing the coupled equations about the axisymmetric configuration corresponding to a perfect disk. Numerical solutions are obtained and compared for different values of rotational speed and air-film thickness. The results show that among the three skewed/warped disks modeled, the skewed disk (i.e., the plane of the disk is skewed with respect to its axis of rotation) produces the largest deflection change (axial runout). With the effect of a point-contact head included, the existence of disk warpage/skew causes the head to produce a spatially-fixed harmonically varying force. The total disk motion is determined by superposition of the deflection pattern fixed on the disk and the space-fixed head-induced vibration. The disk pitch angle variation at the head is obtained and the results are compared for various values of the rotational speed and air-film thickness.
Wear Mechanisms of Multi-Layer Coated Cemented Carbide Cutting Tools
Authors: Cho S.-S. , Komvopoulos K.
Published: February 2008

Turning experiments were performed with cemented WC-Co cutting tools coated with two-layer and three-layer overcoats of TiC/Al2O3 and TiC/Al2O3/TiN, respectively. For comparison, uncoated WC-Co tools were also tested under similar cutting conditions. The predominant wear mechanisms of the various ceramic overcoats and cemented WC-Co were investigated using surface profilometry, scanning electron microscopy, and energy dispersive X-ray analysis. Representative results of the tool wear behavior are presented, and the significance of each ceramic layer on the overall tool wear resistance is interpreted in light of the identified dominant wear mechanisms. Delamination wear characterized by the propagation and linkage of surface, subsurface, and interfacial cracks, abrasion, surface plastic shearing, plucking of carbide grains, and dissolution/diffusion are shown to occur depending on the tool material. These wear processes are not mutually exclusive; they may occur simultaneously at different positions on the same tool surface. Based on nose wear data, correlations between wear lives of coated and uncoated tools and feedrate are established.
Imaging the Keyhole in PAW of Aluminum Alloys
Authors: Zheng B. , Wang H. J. , Wang Q. L. , Kovacevic R.
Published: February 2008

This paper presents a technique for front image sensing of the weld pool in variable polarity plasma arc welding of aluminum alloys, and describes the determination of the geometrical size of the keyhole for subsequent real-time feedback control of a full penetration weld. Image formation occurs when the arc light reflects off the concave mirror-like surface of the depressed keyhole weld pool, and passes through a band-pass filter onto the image sensor. The image of the visual keyhole (nominal keyhole) is a two-dimensional projected picture of the actual keyhole weld pool. The variation in area of the nominal keyhole is closely correlated with the variation of the bottom width of the weld bead.
Thermomechanical Analytical 3D Thermal/Stress Estimation Sidewall Grinding Model
Authors: Li Ya Yun , Kim Jongwon , Sun Yunquan , Yang Yanhua
Published: February 2008

A general three-dimensional thermal/stress grinding model, based on thermal and elastic/plastic classical analytical solutions, has been developed in this paper. The thermal model can predict the temperature distribution of surface and cylindrical external/internal creep-feed or conventional grinding for vertical or inclined sidewall surface grinding. This paper deals with a grinding burn problem that is widespread in the aerospace and automotive industries. The thermal model is compared with sidewall surface grinding experiments. The comparison of the temperature distribution results is expected. The general stress model has been developed, which combines both spherical and cylindrical coordinates. In addition, the 3D thermal/stress model is compared with four cases of external cylindrical grinding experiments. The residual stresses agree reasonably.
Layered-Manufacturing of Fiber-Reinforced Composites
Authors: Zak G. , Sela M. N. , Yevko V. , Park C. B. , Benhabib B.
Published: February 2008

In this paper, we present a rapid manufacturing process for the layered fabrication of polymer-based composite parts using short discontinuous fibers as reinforcements. This process uses a UV-laser-based system for the selective solidification of the composite liquid. The primary components of the prototype are: (1) fiber-resin mixing subsystem, (2) composite-liquid deposition subsystem, (3) liquid leveling subsystem, and (4) laser-light delivery subsystem. Axiomatic Design Theory was used to validate the design selected for the experimental embodiment of the process. Extensive microscopic examination of the layered composite parts verified that the prototype system can yield comparable layer quality, in terms of accuracy and uniformity, to that of pure-resin parts made by a photopolymer-based commercial system. Furthermore, mechanical testing of these composite specimens showed up to 60 percent improvement in modulus over the unreinforced layered specimens.
Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 3: Real-Time Estimation of Heat Sources
Authors: Fraser S. , Attia M. H. , Osman M. O. M.
Published: February 2008

Compensation of thermal deformation of machine tools requires real-time estimation of the heat input to the structure in order to fully describe its thermoelastic response. Available solutions of the inverse heat conduction problem IHCP are not suitable for real-time feedback control applications, since they are too slow and/or rely on future data to stabilize the solution. A new real-time IHCP solver is derived in the form of a convolution integral of the inverse thermal transfer function G−1(s) and the measured temperature difference at two points near the heat source. An expression for G−1(s) is derived for multi-dimensional structural components. To transform G−1(s) to the time domain, a special consideration is given to the treatment of its complex singularity functions. Analytical approach was followed to identify these functions and to determine their time-domain representation. Computer-simulation test cases were conducted using a finite element model of a three-dimensional structure. The random temperature measurement errors, which can lead to non-uniqueness and instability problems, have also been simulated. The test results showed that the computation time can significantly be improved to achieve a control cycle of less than one second, without compromising the accuracy and stability requirements.
Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 4: A Multi-Variable Closed-Loop Control System
Authors: Fraser S. , Attia M. H. , Osman M. O. M.
Published: February 2008

A multi-variable closed-loop control system is proposed to compensate for the thermal deformation of machine tool structures. The control system recognizes the fact the relative thermal displacement between the tool and workpiece is not accessible for direct measurement. Using the generalized thermoelastic transfer functions of the structure, which provide satisfactory input-output dynamic dependencies, the heat input to the structure and thermal displacements are estimated in real time. Artificial heating elements are used as the actuation mechanism of the control system, since they provide an economical solution for retrofitting existing conventional machine tools, and can also be combined with NC controllers to effect the desired compensation of the expansion and bending modes of deformation. Computer simulation test results indicated that even when the random temperature measurement and power actuation errors are taken in consideration, an accuracy of better than 2.5 μm and a control cycle of the order of 1 second are achievable.
An Evaluation of Ploughing Models for Orthogonal Machining
Authors: Waldorf D. J. , DeVor R. E. , Kapoor S. G.
Published: February 2008

An analytical comparison is made between two basic models of the flow of workpiece material around the edge of an orthogonal cutting tool during steady-state metal removal. Each has been the basis for assumptions in previous studies which attempt to model the machining process, but no direct comparison had been made to determine which, if either, is an appropriate model. One model assumes that a separation point exists on the rounded cutting edge while the other includes a stable build-up adhered to the edge and assumes a separation point at the outer extreme of the build-up. Theories of elastic-plastic deformation are employed to develop force predictions based on each model, and experiments are performed on 6061-T6 aluminum alloy to evaluate modeling success. The experiments utilize unusually large cutting edge radii to isolate the edge component of the total cutting forces. Results suggest that a material separation point on the tool itself does not exist and that the model that includes a stable build-up works better to describe the experimental observations.
Monitoring End-Mill Wear and Predicting Tool Failure Using Accelerometers
Authors: Roth J. T. , Pandit S. M.
Published: February 2008

Autoregressive models are fit to end-milling acceleration data and the Data Dependent Systems methodology is utilized to isolate the modal energies of the first and second multiples of the tooth pass frequency. The modal energies are shown to be closely linked to the wear curve and a detection scheme is developed that is capable of tracking the end-mill’s wear and providing an early warning of impending failure. Six life tests are conducted under varying conditions to demonstrate the capabilities of the detection scheme: standard cutting conditions, extreme cutting conditions, premature catastrophic failure and accelerometer placement. In all six cases, the detection scheme was able to provide a warning of impending failure several centimeters before the failure occurred.
Analysis of Acoustic Emission Signals in Machining
Authors: Bukkapatnam S. T. S. , Kumara S. R. T. , Lakhtakia A.
Published: February 2008

Acoustic emission (AE) signals are emerging as promising means for monitoring machining processes, but understanding their generation is presently a topic of active research; hence techniques to analyze them are not completely developed. In this paper, we present a novel methodology based on chaos theory, wavelets and neural networks, for analyzing AE signals. Our methodology involves a thorough signal characterization, followed by signal representation using wavelet packets, and state estimation using multilayer neural networks. Our methodology has yielded a compact signal representation, facilitating the extraction of a tight set of features for flank wear estimation.
Edge Trimming of Graphite/Epoxy with Diamond Abrasive Cutters
Authors: Colligan K. , Ramulu M.
Published: February 2008

The most common method currently employed in industry to trim composites is machining either with conventional fluted cutters or with diamond abrasive cutters. Although diamond abrasive machining is a common method for trimming composites, there is no research literature which addresses the use of this type of cutter. As a result, an experimental investigation was undertaken to establish the characteristics of the machined edges produced by diamond abrasive cutters in graphite/epoxy laminates. In addition, preliminary tests were performed to document the cutter forces produced by representative cutters with various grit sizes and feed rates. The machined edges produced were generally found to be free of delamination and characterized by regular grooving produced by the diamond grains. The surface finish was found to be inversely proportional to the grit number and was not affected by feed rate or cutting mode. Cutter forces were generally found to increase with material removal rate and the average side load was generally about 60 percent of the thrust forces.
Force Sensors Embedded in Surfaces for Manufacturing and Other Tribological Process Monitoring
Authors: Du H. , Klamecki B. E.
Published: February 2008

The measurement of tooling-workpiece interface forces is needed for process design, process modeling and analysis and process monitoring for control. One approach to measuring local interface loads with minimal disturbance of the surface and process is to embed sensors in the surface below the surface region of interest. Small piezoelectric sensing elements were cast into surfaces and their ability to measure loads applied normal to the surfaces was assessed. Sensor outputs were analyzed in terms of sensor depth below the surface, distance along the surface from the load location to the sensor location and sensor to sensor spacing. A mechanical model of the sensor-surface system was developed which predicted sensor output. The use of this sensing concept and type of sensor was demonstrated in strip drawing tests. Using temperature compensated sensors, workpiece holddown force was measured in tests during which drawbead penetration was varied.
State Space Modeling of Sheet Metal Assembly for Dimensional Control
Authors: Jin Jionghua , Shi Jianjun
Published: February 2008

In this paper, a state space modeling approach is developed for the dimensional control of sheet metal assembly processes. In this study, a 3-2-1 scheme is assumed for the sheet metal assembly. Several key concepts, such as tooling locating error, part accumulative error, and re-orientation error, are defined. The inherent relationships among these error components are developed. Those relationships finally lead to a state space model which describes the variation propagation throughout the assembly process. An observation equation is also developed to represent the relationship between the observation vector (the in-line OCMM measurement information) and the state vector (the part accumulative error). Potential usage of the developed model is discussed in the paper.
Analysis and Modeling of Surface Waviness Inspection with Light Reflection, Part 2: Back-Lighted Grid Method
Authors: Lee Ching-Chih
Published: February 2008

The back-lighted grid method for inspecting a reflective surface has been studied with analytical derivations and numerical modeling. The displacement of the image of a grid point due to surface waviness was found to be proportional to the surface slope along the viewing direction at the reflecting point and the distance between the grid and the reflecting point. The 2-D and 3-D numerical modeling was verified with analytical relations, and the 3-D modeling was then tested with the reflection from a profiled SMC (sheet molding compound) panel. The effects of short-term waviness, light box inclination, viewing angle, and surface waviness orientation are investigated. The reflection image patterns for typical surface features are predicted and characterized.
Analysis and Modeling of Surface Waviness Inspection with Light Reflection, Part 3: Light Intensity Distribution Method
Authors: Lee Ching-Chih
Published: February 2008

The light intensity distribution method for inspecting a reflective surface using a diffusing or retroreflective screen has been studied. Analytical derivations show that the angular light intensity in the screen projection is related to the surface curvature. Numerical modeling with light tracing and intensity accumulation is developed to simulate the D-Sight image formed by double reflection off a part surface with a retroreflective screen. The cone angle of a retroreflective screen is characterized experimentally. The numerical modeling is validated with an analytical solution and then tested by comparing the predicted with the photographed D-Sight images of a profiled SMC (sheet molding compound) panel. The characteristics of double reflection and the effects of eye-to-light distance, eye position relative to the light, angular dependence of intensity distribution inside a retroreflected cone, and surface waviness orientation on the image are investigated. The images of typical surface features are predicted.
On the Numerical Determination of Flow Factors
Authors: Peeken H. J. , Knoll G. , Riena¨cker A. , Lang J. , Scho¨nen R.
Published: February 2008

The paper focuses on the numerical determination of Patir and Cheng’s flow factors for general roughness patterns. Improved procedures for the generation of surface roughness and flow simulation are presented. It is shown that application of these techniques resolves differences to analytical solutions of Elrod and Tripp and reduces the scatter in the results to a reasonable degree. Flow factor charts are given for the ‘standard’ Gaussian/Peklenik roughness and for sintered surfaces with high skewness.
Numerical Simulation of the Effects of Three-Dimensional Roughness on Hydrodynamic Lubrication: Correlation Coefficients
Authors: Lunde L. , To̸nder K.
Published: February 2008

Numerical simulations of the lubrication of rough surfaces have been done using the Finite Element Method. Only pure pressure flow conditions have been considered. The correlation coefficient between pressure and height, pressure and height gradients etc. are presented for two different isotropic suifaces. For comparison, one slightly anisotropic surface and one surface with pure transverse roughness have also been investigated. The three-dimensional surface roughnesses have been produced numerically using Finite Impulse Response (FIR) filters and FFT. The only two significant correlations are between the pressure and the height gradient in x-direction and between the height and the pressure gradient in x-direction. The correlation coefficients can be used to apply better boundary conditions when analyzing the lubrication of a rough bearing, and how this can be done has been roughly explained.
Influence of Rolling Speed Upon Friction in Cold Rolling of Foils
Authors: Keife Hans , Jonsa¨ter Toste
Published: February 2008

A theoretical model for simulation of the cold rolling process is presented. A characteristic part comprises the coupling of the bulk plastic deformation and the local plastic deformation of the strip due to impression of roll surface asperities into the work material. The lubricant, which in this case is a liquid, is modeled as a Newtonian fluid. The shear stresses at the roll/strip interface will he a function of the real area of contact, the shear stresses from boundary lubrication and internal shearing in the lubricant film. Simulations have been carried out for rolling with different speeds. The result is a diagram that can be interpreted as a Stribeck curve for cold rolling. The mean friction coefficient in the roll bite decreases with increasing speed to a minimum value i.e., mixed film lubrication prevails. For higher speeds the friction coefficient increases (hydrodynamic lubrication). The influence of roll surface roughness, thickness reductions, and viscosities of lubricant upon the Stribeck curve is also studied. It is concluded that the model can be used to find optimal combination of process parameters for the cold rolling process.
Prediction of Ball Fatigue Life in a Ball/V-Ring Test Rig
Authors: Harris T. A.
Published: February 2008

Standard load and life ratings of ball bearings are based on fatigue failure of the bearing inner and outer raceway surfaces. The rating equations are derived from the mathematical and experimental work of Gustav Lundberg and Arvid Palmgren conducted in Sweden during the 1930s and 1940s; they considered the occurrence of subsurface-initiated, ball fatigue failure highly improbable. In modern ball bearings, this phenomenon occurs occasionally, creating the need for a life prediction means. Ball/v-ring rig fatigue endurance testing is a currently used method to screen ball materials and processing methods, particularly for aircraft applications. As a first step toward predicting ball fatigue life in bearings, the Lundberg-Palmgren and Ioannides-Harris life prediction methods were applied to ball/v-ring test data. The latter method predicted ball fatigue lives which correlated well with the measured ball lives. The Lundberg-Palmgren life prediction method modified using currently accepted material-life and lubrication-life factors did not yield satisfactory correlation.
Effects of Multiple Cracking on Crack Growth and Coalescence in Contact Fatigue
Authors: Kuo C. H. , Keer L. M. , Bujold M. P.
Published: February 2008

A three-dimensional fracture analysis is applied to investigate the interaction effects of multiple cracking on the crack growth in contact fatigue and to simulate the process of crack coalescence that leads to pitting failure. The rolling contact fatigue is simulated by a cyclic Hertzian contact loading moving across the surface of an elastic half-space containing several planar cracks. The body force method is applied to determine the three modes of stress intensity factors around the three-dimensional crack fronts. The fatigue crack propagation under contact loading is estimated based on the modified Paris law for mixed mode crack growth. For coplanar cracks, the growth rate increases significantly as the adjacent cracks are very close while parallel cracks appear to constrain the cracks from coalescing. A numerical simulation for the propagation of crack fronts versus contact cycles is shown to agree with the pitting cracks observed in gears.
Experimental Study of High Speed Sealing Capability of Single Stage Ferrofluidic Seals
Authors: Bonvouloir Jim
Published: February 2008

Several different configurations of single-stage ferrofluidic seals were tested on a spindle which was capable of operating at very high rotational speeds (up to 55 KRPM). A dimensionless number based on the ratio of magnetic force to centrifugal force was defined. It was discovered that this ratio is not a good predictor of high speed seal failure. Reynolds number was found to be a better predictor of seal failure; therefore an empirically derived model for predicting seal failure based on Reynolds number is proposed. The data herein may provide a basis for developing new theoretical models for ferrofluidic seal failures at high speed.
Eccentricity Effects on the Rotordynamic Coefficients of Plain Annular Seals: Theory Versus Experiment
Authors: Marquette O. R. , Childs D. W. , San Andres L.
Published: February 2008

Reliable high-speed data are presented for leakage and rotordynamic coefficients of a plain annular seal at centered and eccentric positions. A seal with L/D = 0.45 was tested, and measured results have good signal-to-noise ratios. The influence on rotordynamic coefficients of pressure drop, running speed, and static eccentricity was investigated. There is an excellent agreement between experimental and theoretical results in the centered position, even for direct inertia terms, which have not shown good agreement with predictions in past studies. However, the rotordynamic coefficients are more sensitive to changes in eccentricity than predicted. These results suggest that, in some cases, annular seals for pumps may need to be treated more like hydrodynamic bearings, with rotordynamic coefficients which are valid for small motion about a static equilibrium position versus the present eccentricity-independent coefficients.
Surface Roughness and Structural Inertia in a Mode-Based Mass-Conserving Elastohydrodynamic Lubrication Model
Authors: Boedo S. , Booker J. F.
Published: February 2008

Detailed formulations are presented for a mass-conserving, mode-based computational model which includes effects of structural inertia and surface roughness. Performance evaluation of a big end connecting rod hearing is shown to require only a few mode shapes, from which it is found that body forces arising from structural motion strongly influence film thickness history at operating engine speeds. Surface roughness effects on nominal film thickness are found to be small, even in assumed regions of partial lubrication.
Elastohydrodynamic Lubrication Model of Connecting Rod Big-End Bearings: Application to Real Engines
Authors: Ozasa Toshihiro , Noda Takashi , Konomi Toshiaki
Published: February 2008

This study presents an elastohydrodynamic (EHD) lubrication model of connecting rod big-end bearings developed taking into consideration the effects of inertia and oil holes. In this model, the effect of inertia, namely the body force, on load and deformation is practically and rationally expressed based on engine dynamics and a structural model of a connecting rod. A method of defining the deformation of bearings has been proposed to simplify numerical analysis. The effect of oil holes, namely an oil feed hole in a journal and an oil jet hole in a bearing, is considered as a boundary condition in the EHD lubrication theory. Calculations of oil flow rate and power loss are also included.
Debris Denting Effects on Elastohydrodynamic Lubricated Contacts
Authors: Xu Gang , Sadeghi Farshid , Cogdell J. David
Published: February 2008

A finite element model was developed to investigate the effects of a spherical debris on elastohydrodynamically lubricated rolling/sliding contacts. Three dimensional dent profiles were obtained using finite element method showing horseshoe shape material pile-up along the rolling direction. The dent profiles obtained from the finite element analysis (FEA) were compared with the experimental results. There is good qualitative agreement between FEA and experimental dent profiles. The FEA dent profiles were then used in a time dependent thermal elastohydrodynamic lubrication (EHL) point contact model to analyze the dent effects on the pressure, film thickness and temperature profiles. The presence of a dent in lubricated contacts generates high pressure spikes and increases the peak temperature. The internal stresses were calculated based on the pressure and traction data obtained from the EHL analysis. The results indicate that a dent created by a debris will cause the internal maximum Von Mises stress to occur near the surface, which contributes to surface initiated failures.
Magnetic Field Assisted Finishing of Ceramics—Part I: Thermal Model
Authors: Hou Zhen-Bing , Komanduri R.
Published: February 2008

A thermal model for magnetic field assisted polishing of ceramic balls/rollers is presented. The heat source at the area of contact between the balls and the abrasives where material removal takes place is approximated to a disk. The disk heat source is considered as a combination of a series of concentric circular ring heat sources with different radii. Each ring in turn is considered as a combination of a series of infinitely small arc segments and each arc segment as a point heat source. Jaeger’s classical moving heat source theory (Jaeger, 1942; Carslaw and Jaeger, 1959) is used in the development of the model, starting from an instantaneous point heat source, to obtain the general solution (transient and steady-state) of the moving circular ring heat source problem and finally the moving disc heat source problem. Due to the formation of fine scratches during polishing (on the order of a few micrometers long), the conditions are found to be largely transient in nature. Calculation of the minimum flash temperatures and minimum flash times during polishing enables the determination if adequate temperatures can be generated for chemo-mechanical polishing or not. This model is applied in Part II for magnetic float polishing (MFP) of ceramic balls and in Part III for magnetic abrasive finishing (MAF) of ceramic rollers.
Magnetic Field Assisted Finishing of Ceramics—Part II: On the Thermal Aspects of Magnetic Float Polishing (MFP) of Ceramic Balls
Authors: Hou Zhen-Bing , Komanduri R.
Published: February 2008

The thermal model developed in Part I of this three-part series is applied in this paper to magnetic float polishing (MFP) of ceramic (Si3N4) balls. Using this method, the flash temperatures, flash times, and temperature distribution at the interface between the balls and the shaft of the MFP apparatus are calculated. Examination of the polished surfaces (scratch lengths) of the balls showed that the length of most scratches during the final stage of polishing is <20 μm and most are formed under transient conditions. But because of the small area of contact and low load encountered in MFP, the results of the calculations under these conditions were found to be very close to the quasi-steady-state conditions. However, it is not possible to know a priori if the conditions are transient or quasi-steady state unless solutions are available for each case. The use of the general solution developed in Part I enables this determination. The minimum flash temperatures and minimum flash times that occur during polishing ensure the determination if adequate temperatures are generated for chemo-mechanical polishing to take place. Of course, the lengths of the scratches would be much longer and the corresponding flash duration longer during the semifinishing operation than during flnishing. The combined temperature and flash duration would determine the extent of chemo-mechanical action under these conditions. The flash temperatures and flash times required for chemo-mechanical action can be used as a basis for the optimization of polishing conditions in MFP.