bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of a Groove on the Behavior of a Squeeze Film Between a Grooved and a Plain Rotating Annular Disk
Authors: Razzzaque M. Mahbubur , Kato Takahisa
Published: February 2008

A model simulating the squeezing process of an annular disk rotating against a grooved counterpart has been developed. Grooving effects are incorporated using the narrow groove assumption. Disks are considered impermeable, rigid, perfectly aligned, and smooth. It is assumed that the fluid film is isothermal and obeys Reynolds equation. The governing equations derived from the model are solved numerically. The effects of groove geometry, orientation and applied load on film thickness, transmitted torque, speed, squeeze time, and viscous power dissipation have been calculated and analyzed. It has been found that angular orientation significantly affects the squeezing process. Squeeze time and power dissipation are less for grooves with angular orientation in the range 40–60 deg.
Analysis of an Aerodynamic Compliant Foil Thrust Bearing: Method for a Rapid Design
Authors: Iordanoff I.
Published: February 2008

A very simple design method for an aerodynamic compliant foil thrust bearing is presented in this paper. It is based on 3D modeling (called: complete direct calculation) of the elastoaerodynamic problem. In this approach, the structural analysis has been simplified. This enables the calculation to be carried out faster. However this model, based on the resolution of the Reynolds equation, only gives the performance of a thrust bearing for a given geometric profile. An efficient method for solving the inverse problem for predicting the desired bearing performance parameters is presented. The complete direct calculation is only used to improve the profile geometry thus found. Finally, the proposed method has been applied for the design of a 80 mm outer diameter 40 mm inner diameter thrust bearing operating between 20,000 and 50,000 rpm. It is shown that the thrust bearing designed by this approach has a high load capacity (300 kPa) at a speed of 50,000 rpm. It is also shown that the predicted performance of the bearing agrees well with the complete direct calculation.
Effect of Frequency Excitation on Force Coefficients of Spiral Groove Gas Seals
Authors: Zirkelback Nicole , San Andre´s Luis
Published: February 2008

An analysis for compressible fluid spiral groove thrust bearings (SGTBs) and face seals (SGFSs) is presented. Zeroth- and first-order equations rendering the static and dynamic performance of SGFSs, respectively, are solved using the finite element method with a successive approximation scheme. Comparison of the present isothermal compressible fluid model for static and dynamic SGTB and SGFS performance validates previous narrow groove theory, finite difference, and finite element analyses. A discussion follows to indicate the importance of using a small number of grooves to prevent instabilities from negative damping in SGTBs and SGFSs when pressurization is lost. Force coefficients are shown to reach asymptotic limits as the axial excitation frequency increases.
Mixed-Film Lubrication Theory and Tension Effects on Metal Rolling Processes
Authors: Qiu Z. L , Yuen W. Y. D. , Tieu A. K.
Published: February 2008

A cold rolling model, based on Wilson and Chang’s asperity flattening model and von Mises homogenous deformation model, for mixed film lubrication is developed. A more rigorous average Reynolds equation is used to calculate the hydrodynamic pressure. The variations of the yield stress with strain are considered in the model. An efficient iteration procedure is developed to solve the contact area, film thickness, and hydrodynamic pressure. The model is more practical with fewer assumptions, and converges quickly. It is applicable to a wider range of rolling regimes, particularly at high rolling speed. The calculation results agree well with the literature as well as with measured data from a rolling mill.
Analysis of High Pressure Liquid Seal Ring Distortion and Stability Using Finite Element Methods
Authors: Baheti S. K. , Kirk R. G.
Published: February 2008

The evaluation of floating bushing ring oil seals is of great importance for designs of high pressure centrifugal compressors. This is a result of their enhanced damping capacity at low speeds and their strong destabilizing action at speeds in excess of twice the compressor first critical speed. Accurate prediction of oil seal leakage and exit temperature is very important from the standpoint of the pump and cooler selection for the seal oil console. The previous research has performed thermohydrodynamic (THD) analysis of bushing seal rings with various geometries. The current work is to evaluate the influence of the mechanical deformation on the thermohydrodynamic analysis of the bushing seal ring. The finite element method is used to predict the mechanical deformation of the bushing seal ring due to oil pressure and to solve the nonlinear and coupled Reynolds and energy equations for the pressure and temperature distributions, respectively. The perturbation technique is used to evaluate the stiffness and damping coefficients of the oil seals. Eigenvalue analysis is performed to study the dynamic stability of the compressor rotor. Results comparing the seal leakage, seal oil outlet temperatures, stiffness and damping coefficients, growth factors and damped natural frequencies from the THD analyses with and without the influence of the mechanical deformation of the bushing seal ring are presented. The results indicate that under high pressure conditions the influence of the mechanical deformation of the bushing seal ring on the seal performance is very significant.
Study of Tribochemical Processes on Hard Disks Using Photoemission Electron Microscopy
Authors: Anders Simone , Stammler Thomas , Fong Walton , Chen Chao-Yuan , Bogy David B. , Bhatia C. Singh , Sto¨hr Joachim
Published: February 2008

The interface between hard disk and slider involves mechanical and tribochemical processes between the hard carbon overcoat of the disk, the lubricant, and the carbon coated or uncoated slider surface. These processes have been studied by two related X-ray techniques—Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy and Photoemission Electron Microscopy (PEEM) using X-rays. NEXAFS allows studying the elemented composition and chemical bonding in a material, whereas PEEM combines this ability with imaging of the sample. Lubricated and unlubricated disks were worn under various conditions using carbon coated and uncoated sliders. The wear tracks on the hard disks were investigated using PEEM to find chemical and elemental changes caused by the wear. Local NEXAFS spectra taken in wear tracks using the PEEM microscope show no chemical changes on unlubricated disks, just a reduction of the hard carbon overcoat thickness. On lubricated disks remarkable chemical modifications of the lubricants caused by the wear are observed if the disks failed the wear tests. The chemical changes are manifested in a formation of various new carbon-oxygen (mostly carboxylic) bonds in the wear tracks and in a strong reduction of the amount of fluorine and carbon. The chemical modifications were only found inside the wear tracks and are clearly caused by the wear. It was found that lubricant degradation is not solely a mechanical process of molecule scission but accompanied by oxidation reactions. The chemical changes were strongly correlated to the tribological behavior of the disks: the worse the disks performed in the wear tests, the stronger were the chemical modifications.
Defects of the Classic Formulation of a Nonsteady EHL Problem for a Journal Bearing. New Problem Formulation
Authors: Kudish Ilya I. , Kelley Frank , Mikrut Daniel
Published: February 2008

A nonsteady problem for an elastohydrodynamically lubricated (EHL) journal bearing is considered. It is shown that under certain circumstances contact pressure and shaft normal velocity are discontinuous functions of time. The initial normal velocity of the shaft has a certain value which is predetermined by the shaft initial position and applied load. Therefore, the EHL solution cannot accommodate any different initial normal velocity of the shaft. These defects pertain to any nonsteady EHL problem in the “classic” formulation. The main goal of this paper is to propose a modified formulation of the EHL problem free from the above defects. For purely squeezed lubrication film an analytical and numerical analysis of a dynamic bearing response to abrupt changes in external load is performed based on the classic and “modified” problem formulations leading to discontinuous and smooth solutions, respectively.
Study of Hybrid Lubrication at the Tooth Contact of a Wormgear Transmission: Part 1—Formulation and Analysis
Authors: Yuan Qin , Sun D. C. , Brewe D. E.
Published: February 2008

The paper presents a lubrication analysis for the tooth contact of a proposed wormgear transmission. The information needed for the lubrication analysis has been mostly obtained from a previously published wormgear analysis. The information includes the geometry of the clearance between the meshing surfaces, the velocity of the worm surface relative to the gear surface, and the normal force acting on a gear tooth as it moves through the meshing zone. The lubrication analysis is carried out after a design of the oil supply configuration is made, that consists of a single transverse oil recess and a capillary tube flow restrictor. Under the predetermined normal force, the lubrication analysis is aimed at obtaining the needed supply pressure to separate the meshing surfaces by a minimum oil film thickness, which is prescribed to insure the establishment of fluid film lubrication at the contact. The lubrication analysis considers (1) the hybrid lubrication effect (combined hydrostatic action and hydrodynamic wedge and squeeze actions), (2) the temperature rise in the oil film flow and the restrictor flow, and (3) the pressure and temperature dependence of oil properties. Part I describes the formulation of the oil film flow problem (in discrete form) and the restrictor flow problem (in analytical form). The two problems are coupled through the conditions of flow continuity and energy balance in the oil recess.
Study of Hybrid Lubrication at the Tooth Contact of a Wormgear Transmission: Part 2—Results and Discussion
Authors: Yuan Qin , Sun D. C. , Brewe D. E.
Published: February 2008

Part 2 begins by describing the numerical solution procedures of the hybrid lubrication problem. Results of the computation are then presented that include the detailed pressure and temperature distribution in the oil film, the required supply pressure for maintaining the prescribed minimum oil film thickness, the fluid friction acting on the worm coil surface, the mass flow rate of supply oil, and the power loss associated with the restrictor flow. The feasibility of the hydrostatically lubricated wormgear transmission is discussed in light of these results.
Partial Hydrodynamic Lubrication With Large Fractional Contact Areas
Authors: Wilson W. R. D. , Marsault N.
Published: February 2008

An alternative average Reynolds equation for use under conditions of large fractional contact area is proposed. The flow factors for this form of the equation are calculated for a variety of longitudinal surfaces and the results are shown to be relatively insensitive to the initial height distribution. Pressure and shear flow factors for the Christensen height distribution and a variety of Peklenik surface pattern parameters are also derived from the work of Patir and Cheng, Lo and Tripp. These are represented by semi-empirical equations over the full range of contact conditions. The implications of the results, with respect to the lubrication of metal forming processes, is discussed.
Elastic Contact and Friction Between Sliders and Circumferentially Textured Disks—Part I: Analytical Model
Authors: Tanaka K. , Kusumi T.
Published: February 2008

This series of three papers presents an experimental and numerical analysis of the friction between a head slider and a thin-film rigid disk with circumferential surface texture, under various humidities. In Part I, we develop a model of a cylindrical contact of a slider rail with strong anisotropic asperities under dry conditions. This model predicts that the real contact pressure is primarily determined by the height distribution and geometry of asperities on the disk, whereas it is very weakly dependent on the surface curvature of the rail. The result of the latter calculation suggests that the frictional coefficient is insensitive to variation in the head contact angle due to head pitching motion.
Kinetic Meniscus Model for Prediction of Rest Stiction
Authors: Bhushan B. , Kotwal C. A. , Chilamakuri S. K.
Published: February 2008

The time dependence of static friction is an important aspect of tribological studies whereby the static friction increases with an increase in the time of stationary contact (rest static friction or rest stiction). This effect is commonly observed in computer disk drives especially at high humidities, in which the static friction increases rapidly with an increase in rest time between some head slider and the disk surfaces. For the first time, a comprehensive kinetic meniscus model is proposed to explain this phenomenon, both for a single asperity and multiple asperity contacts at a liquid mediated interface. It is found that the static friction increases up to a certain equilibrium time with a power law relationship after which it remains constant. The equilibrium time is dependent on the liquid film thickness, the liquid viscosity and the contact geometry. The model developed is applied to a rough textured disk, a polished disk and a super smooth disk. To study the effect of the scan size on the meniscus force, the static friction is calculated by using roughness parameters obtained from measurements at different scan sizes.
Synthesis of Coatings With Hardness Exceeding 40 GPa by Magnetron Sputtering
Authors: Wu Mei-Ling , Yang Zunde , Chung Yip-Wah , Wong Ming-Show , Sproul William D.
Published: February 2008

Single- and dual-cathode DC magnetron sputtering was used to produce TiB2 coatings and CNx/ZrN multilayers, respectively, with hardness exceeding 40 GPa. The composition, structure, topography, and mechanical properties were determined by various techniques, including Auger electron spectroscopy, X-ray diffraction, high-resolution electron microscopy, atomic force microscopy, and nanoindentation. An optimum combination of the sputtering pressure and substrate bias results in the production of ultrasmooth TiB2 coatings with hardness up to 50 GPa and excellent wetting properties. The rationale for studying the CNx/ZrN system is that ZrN(111) provides excellent lattice match to the hypothetical β-C3N4(0001) face (β-C3N4 was predicted to have mechanical properties comparable to diamond). Using a dual-cathode sputtering system, we produced crystalline multilayers of CNx/ZrN with bilayer thickness of 1–2 nm. Using various combinations of nitrogen partial pressure, target powers, and substrate bias, we found that the hardness of these coatings correlates very strongly with the occurrence of (111) texture of ZrN, consistent with the lattice-match strategy. Even with a ZrN volume fraction of 70 percent, such multilayer coatings have been synthesized with hardness in the 50 GPa regime.
Experimental and Theoretical Investigation on Rolling Contact Fatigue of 52100 and M50 Steels Under EHL or Micro-EHL Conditions
Authors: Ne´lias D. , Dumont M.-L. , Couhier F. , Dudragne G. , Flamand L.
Published: February 2008

The purpose of this investigation is to clarify the role of roughness on rolling contact fatigue. Tests have been carried out on a two-disk machine, for two rolling bearing steels (52100 and M50), two surface roughnesses corresponding to EHL and micro-EHL conditions (two different surface finishing), three normal loadings (1.5, 2.5 and 3.5 GPa), and under pure rolling or rolling plus sliding conditions. No surface damage has been observed up to 50 106 cycles for tests with smooth specimens. Tests with rough specimens have produced a typical surface damage, called here surface distress, made of a large population of asperity-scale micro-cracks and micro-spalls. The paper describes the surface distress observed, such as micro-cracks and micro-spalls. Surface damages obtained are different for tests under pure rolling conditions and tests under rolling plus sliding conditions. Therefore, the role of the friction direction is underlined. A link is made between our experimental observations and calculations that have been carried out using a transient EHL model. The influence of an indent in a line contact, simulating a micro-spall, is studied. Surface pressure and associated sub-surface stress field are analyzed versus the sliding direction.
A Possible Mechanism for Rail Dark Spot Defects
Authors: Kaneta M. , Matsuda K. , Murakami K. , Nishikawa H.
Published: February 2008

Rail dark spot defect, also termed squat failure or shelling, which is a kind of rolling contact fatigue failure and occurs frequently on running surfaces of railway rails carrying high speed traffic, is one of the most dangerous rail failures. The dark spot crack is characterized by a principal crack propagating in the direction of traffic and a second crack growing in the direction opposite to traffic. By using a newly developed two-disk machine, the authors have succeeded in reproducing very similar dark spot cracks to those which appear in actual rails. It is found that the dark spot defects are caused by frequent repetitions of dry and wet runnings, and that the traction force plays an important role for the occurrence of the cracks. The principal crack may occur from a tiny pit formed a posteriori on the contacting surface and after that, the second crack is formed by cracks branched from the extended principal crack. It has also been proved experimentally that water is capable of entering the tip of the crack. Furthermore, a possible mechanism for the dark spot cracking has been proposed on the basis of the fracture mechanics approach.
Transient Thermoelastohydrodynamic Study of Tilting-Pad Journal Bearings—Application to Bearing Seizure
Authors: Monmousseau P. , Fillon M. , Freˆne J.
Published: February 2008

Nowadays, tilting-pad journal bearings are used under more and more severely demanding operating conditions. Three limits of safe operation were defined (Leopard, 1976): the hydrodynamic limit, the mechanical limit and the thermal limit. The purpose of this study is to determine the hydrodynamic limit of safe operation during start-up for a tilting-pad journal bearing. During start-up, the rapid increase of the temperature in the bearing solids leads to the thermal expansion of both the pads and the shaft. The operating bearing clearance decreases and, when it tends toward zero, seizure occurs. The evolution of the main characteristics (temperature, pressure, film thickness and displacements) versus time is analyzed in the case when a seizure occurs.
Micro-Patterning of Silicon by Frictional Interaction and Chemical Reaction
Authors: Kim Dae-Eun , Yi Jae-Joon
Published: February 2008

In this paper a novel and economical method of generating three-dimensional micro-patterns on single crystal silicon without the need for a mask is presented. The technique is based on the fundamental understanding of frictional interaction at light loads. Micro-patterning is done through a two-step process that comprises mechanical scribing and chemical etching. The basic idea is to induce micro-plastic deformation along a prescribed track through frictional interaction between the tool and the workpiece. Then, by exposing the surface to a chemical under controlled conditions, preferential chemical reaction is induced along the track to form hillocks about 5 μm wide and 1 μm high. This method of micro-machining may be used for making patterns in micro-electro-mechanical systems (MEMS) at low cost. Furthermore, this process demonstrates how microtribological processes can be utilized in the fabrication of micro-structures.
Lubrication by Diamond and Diamondlike Carbon Coatings
Authors: Miyoshi Kazuhisa
Published: February 2008

Regardless of environment (ultrahigh vacuum, humid air, dry nitrogen, or water), ion-beam-deposited diamondlike carbon (DLC) and nitrogen-ion-implanted, chemical-vapor-deposited (CVD) diamond films had low steady-state coefficients of friction (<0.1) and low wear rates (≤ 10−6 mm3/N·m). These films can be used as effective wear-resistant, self-lubricating coatings regardless of environment. On the other hand, as-deposited, fine-grain CVD diamond films; polished, coarse-grain CVD diamond films; and polished and then fluorinated, coarse-grain CVD diamond films can be used as effective wear-resistant, self-lubricating coatings in humid air, in dry nitrogen, and in water, but they had a high coefficient of friction and a high wear rate in ultrahigh vacuum. The polished, coarse-grain CVD diamond film revealed an extremely low wear rate, far less than 10−10 mm3/N·m, in water.
Dent Initiated Spall Formation in EHL Rolling/Sliding Contact
Authors: Xu Gang , Sadeghi Farshid , Hoeprich Michael R.
Published: February 2008

Dents in elasto-hydrodynamic lubricated (EHL) contacts will initiate spalls and shorten the fatigue life significantly. Experimental results are provided from a ball-on-rod rolling contact fatigue tester with the rod predented with a single large dent. The results indicate that the spall usually initiated at the trailing edge of the dent on the driving surface. These cracks and spalls can also be created in the absence of lubricant. Based on the accumulated plastic strain and damage mechanics concept, a line contact spall initiation model was developed to investigate the dent effects on spall initiation and propagation. The near surface volume of the contact solid was divided into many small metal cells and for each cell the damage law was applied to determine whether the cell is undergoing damage or not. If the cell on the surface is damaged, then it is removed from the surface and a spall will be formed. If the damaged cell occurs below the surface, then a subsurface void is generated, this void could grow to the surface depending on the running conditions. The spall will further modify the surface geometry and initiate a new spall, hence, the spall will propagate. The results indicate that the location of spall initiation depends on the EHL and dent condition. Spalls can initiate at either the leading or trailing edge of the dent depending on the surface traction.
Equations for Time-Dependent Wear and Induced Concentration Profiles in Particle-Filled Polymer Composites
Authors: Han Sung Won , Blanchet Thierry A.
Published: February 2008

A time-dependent description of the sliding wear behavior of hard particle-filled polymer composites is developed. The description is based upon the accumulation of wear-resistant filler particles in the surface region, and development of wear-induced subsurface concentration profiles. Descriptive expressions for wear volume and induced filler volume fraction profile are functions of sliding distance as well as composite characteristics such as filler and matrix bulk volume fractions and specific wear rates. An experimental demonstration validates filler surface accumulation phenomenon as a basis for this model of time-dependent polymer composite wear. The demonstration also supports the feasibility of engineering composite materials with near-surface graded volume fraction profiles, resisting run-in wear contributions at the onset of sliding. Model predictions of steady-state volume fraction profile may guide design of such graded composite bearing surfaces.
Tool Surface Topographies for Controlling Friction and Wear in Metal-Forming Processes
Authors: Sheu Simon , Hector Louis G. , Richmond Owen
Published: February 2008

A conceptual framework is introduced for the design of tool surface topographies in bulk metal forming processes. The objective of the design is to control friction to desired levels while minimizing wear of the workpiece and tool surfaces and adhesive metal transfer between the workpiece and tool. Central to the design framework are the tool/workpiece interface properties of lubricant retention and interface permeability. Lubricant retention refers to the capacity of an interface to retain lubricant rather than freely channel it to the exterior of the tool/workpiece conjunction. Permeability refers to the capacity to distribute lubricant to all areas within the conjunction. These properties lead to the concept of two-scale surface topography consisting of a fine scale background of interconnected channels on which is superimposed an array of coarser-scale cavities. Control of friction and wear is achieved by designing the tool surface topographies at these two scales to address the unique tribological conditions of specific bulk metal forming processes. The coarser scale is designed to ensure adequate supply of lubricant within the conjunction. The finer scale is designed to ensure adequate delivery of lubricant to all parts of the conjunction where nascent workpiece surface is being formed. The design concepts are illustrated with results from laboratory experiments using the rolling process as an example, and comparing the performance of various roll surface topographies under similar processing conditions. A two-scale surface topography consisting of hemispherical cavities distributed across a background surface of finer scale, interconnected channels was shown to reduce friction compared to a single-scale ground finish, but not as much as a single-scale coarse topography consisting of densely-packed cavities produced by an electrical discharge treatment. On the other hand, the smoother cross-sections of the cavities, especially when elongated in the direction of greatest relative motion, produced significantly less wear than either of the single-scale tool surface treatments. It is concluded that two-scale engineering of tool surface topographies based upon the concepts of lubricant retention and interface permeability can provide a broad basis for achieving desired levels of interface friction while minimizing workpiece surface wear and adhesive material transfer in many metal-forming processes.
Some Advanced Air-Bearing Design Issues for Proximity Recording
Authors: Bogy David B. , Lu Sha , O’Hara Matthew A. , Zhang Shuyu
Published: February 2008

In magnetic hard disk drives the minimum spacing between the air-bearing slider and disk has been reduced to under 50 nm, and some drives now employ so-called proximity sliders that are designed to operate at some level of interference between the slider and the peak asperities on the disk. This ultra-low flying condition brings into play some new interface phenomena and accentuates some of the well known ones as well. In this paper, we consider some air-bearing design issues related to proximity recording. First, we examine the effects of shear flow in the bearing, which is usually neglected, and we show that for high-pitch proximity slider designs the effect is not negligible. Next, we note that such low spacing also tends to accelerate particle accumulation at the trailing edges of the slider. In an effort to address this problem, a model is developed for calculating forces on particles in the air bearing. Including this in the CML air bearing design code we show that designs can be created that eject most of the particles from the sides rather than trapping them at the trailing edge. Finally, we investigate the performance of proximity sliders with regard to their sensitivity to altitude changes. We include altitude sensitivity as an objective in the design optimization scheme and demonstrate that it can yield air-bearing design with performance much less sensitive to changes in altitude.
Experimental Verification of Subcritical Whirl Bifurcation of a Rotor Supported on a Fluid Film Bearing
Authors: Deepak J. C. , Noah S. T.
Published: February 2008

The paper presents the results of the experiments that were conducted on a short fluid film bearing with a simple single disk rotor. The behavior of the journal was analyzed as a function of the rotor system parameters such as the load, speed, and imbalance mass. It was verified that the journal bearing can lose stability through either a subcritical or a supercritical bifurcation. In the supercritical bifurcation, the expected gradual increase in the amplitude of the limit cycle was observed, while in the subcritical bifurcation there was a sudden jump to a large limit cycle. In the case of a subcritical bifurcation, it was also observed that the journal bearing became unstable below the rotor threshold speed of instability, following a small perturbation applied to the rotor. Demarcations were made for the stable regions of operation (regions where the rotor is stable below the threshold speed of instability) for the journal bearing based on the obtained experimental results. Experiments were also performed to analyze the effects of imbalance of the rotor on the threshold speed of instability. It was observed that the flexible unbalanced rotor had a lower threshold speed of instability. The limitations of the linear theory of fluid film bearings in predicting these phenomena are discussed.
An Investigation of a Squeeze Film Between Two Plane Annuli
Authors: Usha R. , Sridharan Rukmani
Published: February 2008

An analysis of a laminar squeeze flow of an incompressible Newtonian fluid between parallel plane annuli is presented. The local and convective inertia of the flow are considered in the investigation. The solution is obtained as a power series in a single nondimensional parameter (squeeze Reynolds number) S, for small values of S. Expressions for the pressure and load capacity are given and are compared with those based on the assumption of inertialess flow. As applications, the constant velocity squeezing state and the case when the walls perform reciprocating harmonic oscillations with finite amplitude are considered. The changes in load capacity with the changes in the parameters that govern the motion have been investigated.
Non-Newtonian Lubrication With the Second-Order Fluid
Authors: Sawyer W. G. , Tichy J. A.
Published: February 2008

In certain applications where the lubricant is subjected to rapidly changing conditions along its flowing path (such as an elastohydrodynamic contact), the inherently time dependent nature of the lubricant may be significant. The simplest type of model to correctly account for such time dependence is the second-order fluid, which is a systematic small departure from Newtonian behavior, involving higher order rate-of-rate-of strain tensors. As in a companion paper using the Maxwell model, the formalities of applying such a model to thin film flow are emphasized. Using a regular perturbation in the Deborah number, with the conventional lubrication solution as the leading term, a solution can be obtained. Viscoelasticity may raise or lower pressure depending on the nature of edge boundary conditions.
Structural Component Development of Three-Layer Cylinders for Superconducting Generators, Part 2: Development of Three-Layer Welding Techniques to Extend Axial Length and Evaluation of the Welds
Authors: Suzuki Nobuhisa , Murakami Toshiaki , Shibuya Junichi , Furukawa Yasuhiro , Asai Satoru , Ohshima Shizuo
Published: February 2008

The warm damper is one of the multi-cylindrical rotor components, which is located at the outermost position in a rotor of the superconducting generator. The main function of the warm damper, in addition to bear rotor torque, is to shut off the magnetic fields of the armature. While maximum stresses in the warm damper are caused by electromagnetic forces in the event of a short-circuit fault, which cause large bending stresses, so it is required to have high conductivity and sufficient strength against bending stresses. A promising design for it is a three-layer cylindrical structure composed of a highly conductive Cu-Cr cylinder sandwiched between inner and outer stiffeners made of a high-strength nonmagnetic material (A286). To realize this structure, it is necessary first to select a suitable layer bonding method and then to research and develop the procedures to construct this large structure. The previous paper described selection of diffusion bonding as the suitable layer bonding method. The first step to fabricate this large structure was to prove the structural integrity of a diffusion-bonded mock-up model, which was 885 mm in diameter and 2800 mm in axial length [1]. This paper is a study on circumferential three-layer welding to extend the axial length allowing for the fabrication of a ever larger structure. Two A286/Cu-Cr/A286 three-layer rings, 625.5 mm in O.D. and 300 mm in axial length, were prepared by diffusion bonding the layers of each rings simultaneously by HIP. Then, the axial ends of their three-layers were butt welded with the filler wires, which were selected for each layers in advance. Subsequently, in accordance with the results of a study on the condition for aging treatment following diffusion bonding (800°C × 4 h) to obtain the proper mechanical properties of the alloy A286, which is a material for the major load bearing component, the rings were age-treated at 700°C for 10 h. The tensile test results of the welded joint and weld metal specimens cut out from the welded rings proved that both alloys A286 and Cu-Cr welded components had adequate mechanical properties. That is these properties were equivalent to those of the base metals, with no reductions of layer bonding strength due to weld heat input.
A Numerical and Experimental Investigation of Neural Network-Based Intelligent Control of Molding Processes
Authors: Demirci H. H. , Coulter John P. , Gu¨c¸eri S. I.
Published: February 2008

The current investigation focused on the development of intelligent injection molding processes by utilizing a neural network based control unit. In this study, the emphasis was on the control of flow front progression during injection molding processes. The progression of a flow front into a mold, cavity is crucial since it dictates the locations of possible air voids and weld lines. It is desired that the flow front progresses towards the vent locations and that weld lines coincide with locations where their quality decreasing influence has a minimum impact on the overall part performance. The intelligent control scheme developed is based on a neural network that was trained with data obtained from a first-principles based process model rather than actual molding experimentation. The control strategy was developed such that one can specify a desired flow progression scheme and the controller will take corrective actions during the molding process to realize this scheme. This is done by controlling the inlet flow rate at various inlet gate locations. Experiments were conducted with a 2-D, complex shaped, mold cavity to test the performance of the control unit during actual injection molding processes. The mold had two inlet gates and three different desired flow progression schemes were considered. In all cases, the first principles model/neural network based control unit was able to steer the flow front along the corresponding desired flow progression path.
Four Dimensional Holospectrum—A New Method for Analyzing Force Distributions
Authors: Du R. , Chen Yue-Dong , Chen Yubao
Published: February 2008

In this paper, a new method, called four dimensional (4D) holospectrum, is introduced for analyzing force distributions. First, it is shown that the dynamics of a three dimensional force can be represented by the holospectrum, which consists of a series of ellipses in a three dimensional space with each ellipse representing the frequency characteristics of the force at a concerned frequency. An ellipse can be described by its normal vector, major axis, minor axis, eccentric ratio, area, and inclination angle. The formula of calculating these quantities are derived next. 4D holospectrum reveals the dynamic characteristics of a three dimensional force such as phase and spatial correlation that cannot be accessed otherwise. As demonstrated by the experimental tests on a spindle, 4D holospectrum adds a new dimension for force analysis and is very valuable for on-line monitoring and diagnosis as well as design.
Tribology in Cold Metal Forming
Authors: Wilson W. R. D.
Published: February 2008

The tribological aspects of cold metal forming processes is reviewed. Special attention is paid to rolling and stamping operations as these are typical of bulk forming and sheet forming processes, respectively, and are the most important commercial processes. It is shown that a better understanding of tribological fundamentals, as applied to cold metal forming, can result in better lubrication systems and process models.
A Method for Extracting and Thickening a Mid-Surface of a 3D Thin Object Represented in NURBS
Authors: Fischer A. , Wang K. K.
Published: February 2008

In analyses of manufacturing processes such as injection molding of plastics or die casting of metals, the geometry of a typical 3D thin-walled structure is usually represented by an aggregation of mid-surfaces. This geometric simplification associated with assigned part thicknesses significantly reduces the computational complexity in engineering analysis (e.g., flow and solidification simulations). On the other hand, it complicates data transfer from and back to any CAD/CAM system in which objects are not represented by their mid-surfaces. As a part of an overall effort to develop a feature-based system for concurrent design and manufacturing of complex thin parts, a new algorithm has been developed for representing both the objects and their mid-surfaces. This algorithm can extract a mid-surface representation from a complex 3D thin object and then reconstruct the object from the modified mid-surface according to the analysis results. The objects consist of sculptured features with tubular topology and are represented by NURBS. The proposed method is based on offsetting techniques and deals directly with the control polygons of the object boundaries and of the mid-surfaces. The algorithms are based on offsetting techniques since there is a high correlation between medial surfaces and offset surfaces. In the case of swept features, simplification is achieved by using 2D rather than 3D techniques.
Overview and Perspectives on Japanese Manufacturing Strategies and Production Practices in Machinery Industry
Authors: Lee Jay
Published: February 2008

Japan has been a world leader in manufacturing in the past several decades. Undoubtedly, this leadership will persist well into the 21st century. It is, therefore, very important to understand the status of Japan’s manufacturing technologies as well as its projected manufacturing strategies for the future, especially, those technologies which would generate substantial impact on the manufacturing industries in the next five years. This paper gives an overview and perspectives on Japanese manufacturing strategies and production practices in machinery industry.
About the Orthogonal Parameterization of Sculptured Part Surfaces and Initial Tool Surfaces
Authors: Radzevitch S. P. , Goodman E. D.
Published: February 2008

In the domain of multi-axis NC machining of sculptured surface parts, the use of orthogonal parameterizations of part and tool surfaces is convenient because it simplifies the transformation of coordinate systems. Using the so-called “differential-geometric method of sculptured surface NC machining,” developed by one of the authors, many parameterizations of part and tool surfaces are easily shown not to be orthogonal. To transform nonorthogonal part and tool surface parameterizations into orthogonal ones, the Jacobian of the transformation may be used. In cases when the Jacobian of the transformation is not known, it is possible to use differential equations for isogonal trajectories on the surfaces (choosing an orthogonal case), or a special kinematic method for obtaining sculptured surface equations. Influences of coordinate system transformations (translations and rotations along and about axes through the origin) on example part and tool surface parameterizations for four types of general helicoidal surfaces are described. The results mentioned above simplify the analytical description of the multi-axis NC machining process, and may be useful for writing NC toolpath generation software.
Geometrical Modeling of Surface Generation Through Wrapping
Authors: Oancea N. , Oancea V. G.
Published: February 2008

A number of methods exist for determining profiles of cutting tools that work by wrapping. Most of these methods are based on the envelope theory and almost inevitably require cumbersome analytical formulations not always easy to resolve. This work presents a new method for studying conjugated surfaces associated with rolling axodes. Originally devised in an analytical form in a previous work of the first author, a purely numerical method is developed here based on a theorem which we call “the theorem of the minimal distance.” The advantage is twofold: first, geometrical modeling of tool profile calculation is possible even for profiles which cannot be described analytically; second, a very useful tool is provided for the inverse problem—starting from the measured cutting edges profiles, one can calculate the effectively generated surface on the workpiece. Several examples are shown for rack, shaper, and rotational cutters.
A Perspective on Material Handling Engineering: History and New Challenges
Authors: Pence Ira W.
Published: February 2008

It is especially appropriate to consider the status of material handling at this time, as the Material Handling Engineering Division of the ASME marks the 75th Anniversary of its founding. Seventy-five years is a long time, and those of us actively engaged in research, development, and application owe a great debt to those who have gone before, like Jim Allred, Irv Footlik, Walter O’Mally, Ralph Sims, Howard Zollinger, and the like. It would be inappropriate to try to review the current status without reviewing how we got here.
Deadlock Prevention in Manufacturing Systems With AGV Systems: Banker’s Algorithm Approach
Authors: Kim Chang Wan , Tanchoco J. M. A. , Koo Pyung-Hoi
Published: February 2008

An important issue in the operational control of an automated job shop is the prevention and resolution of shop deadlocks. In this paper, we discuss the problems and solutions of deadlocks in manufacturing systems with automated guided vehicle systems, describe a banker’s algorithm for the control of material flow in job shops, and present the results of simulation experiments to compare the performance of several deadlock handling methods.
Phase Change in a Misaligned Mechanical Face Seal
Authors: Etsion I. , Pascovici M. D.
Published: February 2008

The combination of phase change, coning, and face misalignment in mechanical seals is studied. The seal performance is calculated using an implicit analytical solution of the thermohydrodynamic problem. It is found that phase change can be detrimental to the seal’s angular stiffness. It is also found that the boiling interface is practically axisymmetric, even at moderate face misalignment. Thus, future analyses of phase change with misalignment can be considerably simplified.
Reductions in Wear Rate of Carbon Samples Sliding Against Wavy Copper
Surfaces
Authors: Lin Jau-Wen , Bryant M. D.
Published: February 2008

Wear rates (μgm/s) versus rotor speed for carbon samples sliding against smooth and wavy copper rotors (250 μm thick copper sheets were attached to smooth and wavy steel and polycarbonate backings) were identical at some speeds, but at other speeds wear rates for the wavy rotors were almost half those of the smooth rotors. Slider vibrations (periodic, with period set by rotation) perpendicular to the sliding surface were measured and Fourier analyzed. Comparison of vibration spectral amplitudes to spectral amplitudes derived from surface profiles identified vibration modes dynamically enhanced by surface waviness on the wavy rotor. At speeds where wear rates on the wavy rotor were most reduced, amplitudes of certain modes in the vibration spectrum were most enhanced. For all these cases, the product of mode number times speed was nearly constant, suggesting resonance. Contact forces and contact voltage drop (due to a mA current flowing from slider to rotor) were measured and plotted versus time during all experiments. Friction coefficients rapidly varied between 0.1 and 0.4, but averaged 0.2. Traces of friction coefficient versus time for both wavy and smooth rotors were similar, even when wear rates plunged on the wavy rotor. There were no large jumps in the contact voltage drop data, suggesting that the slider never disconnected from any of the rotors. Photoelastic visualizations (Bryant and Lin, 1993) of slider-rotor interfaces revealed concentrated contact on the smooth rotors, but none on the wavy rotors. The absence (induced by vibration) of concentrated contact may have caused differences in wear rates. Appreciable reductions (up to 50 percent) in wear rate are possible by adding small surface waves to a rotor that induce micro-vibrations of the slider-spring-rotor contact system. The effect appears most pronounced at resonance.
A Two-Component Mixed Friction Model for a Lubricated Line
Contact
Authors: Polycarpou A. A. , Soom A.
Published: February 2008

A two-component, two-dimensional friction model for a lubricated line contact, operating in boundary and mixed lubrication regimes, is developed. The friction is explicitly decomposed into the solid and the fluid shear components. The solid component is due to the asperity interactions and the fluid shear arises from the lubricant present at the interface. The friction model includes the sliding velocity, the instantaneous separation of the sliding bodies, normal to the sliding direction, the normal load and fluid properties. The model is based on unsteady friction experiments carried out under constant normal loads and time-varying sliding velocities. The model is applied to quasi-steady sliding, unsteady continuous and intermittent sliding, including sticking and momentary reversals of motion. In each case it becomes possible to track the instantaneous fluid shear and solid friction components.
Hardness of Thin-Film Media: Scratch Experiments and Finite Element
Simulations
Authors: Kral E. R. , Komvopoulos K. , Bogy D. B.
Published: February 2008

Experiments and finite element simulations are presented pertaining to the effective hardness and the mechanics of indentation and sliding contact on elastic-plastic layered media. Hardness measurements obtained from scratch experiments are presented for thin-film rigid disks with 30 nm carbon overcoats. Reproducible results are obtained for residual scratch depths greater than approximately 8 nm. A simple force balance model is used to calculate the effective hardness of the layered medium. Hardness values for the surface layer are calculated by fitting a relationship between the hardness, scratch geometry, and layer thickness to the experimental data. The experimental results are compared with three-dimensional finite element simulations of a rigid spherical indenter sliding over a half-space with a stiffer and harder surface layer. The finite element results are used to verify the hardness model applied to the experimental data and to provide insight into the observed experimental behavior in the context of the associated elastic-plastic deformation characteristics of the layered medium.
An Analysis of Powder Lubricated Slider Bearings
Authors: McKeague K. T. , Khonsari M. M.
Published: February 2008

A theory for predicting the behavior of powder lubricated slider bearings based on the collisional characteristics of the grain particles and their interactions at the boundaries is presented. General boundary conditions that account for the effects of powder slippage are applied to the slider bearing configuration. Theoretical predictions are presented with comparison to published experimental measurements. An extensive parametric study is also conducted to illustrate the behavior of the flow and the response of the bearing's load-carrying capacity and friction factor to changes in various powder material and boundary parameters.