bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analytical and Computational Investigation of High-Rate
Rheometry
Authors: Feng R. , Ramesh K. T. , Douglas A. S.
Published: February 2008

This paper examines a class of experimental techniques used to develop constitutive models for lubricants, by simulating the shearing of a thin lubricant layer while accounting for transient phenomena. The complete transient thermal problem with fully nonlinear constitutive relations is solved, and heat conduction is accounted for both in the lubricant layer and into the walls. Numerical simulations are used to examine the shear stress history, the velocity profile, and the temperature profile as functions of time. As a particular example, the high-rate torsional Kolsky bar rheometer (Feng and Ramesh, 1993) is simulated. The computations indicate that the Kolsky bar experiments, which are able to examine the time-histories of the stresses and of the motion, can he used to obtain material properties for lubricants at high shear rates. A full numerical analysis may be required to properly interpret some of the data available from the Kolsky bar experiments, since at longer times (greater than that associated with the peak shear stress) the thermal softening may dominate the response and the velocity field may become strongly inhomogeneous. The numerical simulations are performed using both rate-dependent and limiting stress constitutive laws, and the effects of the layer thickness and the rise time of the relative velocities are examined. The simulations show that the film thickness and the rise time of the relative velocities can have strong effects on the character of the solution when the transient phenomena are included in the analysis. The computations also demonstrate that highly inhomogeneous and even localized flows may occur within rheometers as a result of transient effects. The development of these flows depends on the layer thickness, the rise-time of the boundary velocity, the thermal boundary conditions, and the constitutive behavior of the lubricant.
Prediction of Equivalent Radial Loads for Tapered Roller
Bearings
Authors: Bailey Ted E. , Frayer Robert W.
Published: February 2008

Calculating the fatigue life of a tapered roller bearing has become a rather straightforward exercise thanks to the accumulation of rolling contact fatigue data and the subsequent development of formulation relating applied loading to bearing fatigue life. An integral part of the prediction process is to define an equivalent radial load (EQRL) by combining a bearing’s applied radial and thrust loading into a single entity. This paper reviews currently accepted formulation and offers a potentially more accurate alternative method for estimating the EQRL of a tapered roller bearing than does the current AFBMA standard.
Antiwear and Extreme-Pressure Action of Copper(II) Complex With Alkyl Phosphonic Acid Mono Alkyl Ester
Authors: Xiong Ren-Gen , Wang Hong , Zuo Jing-Lin , Liu Cai-Ming , You Xiao-Zeng , Dong Jun-Xiu , Zhang Pei
Published: February 2008

The copper(II) complex with alkylphosphonic acid monoalkyl ester (CuAMP) was synthesized, and its structure shown to be laminar on the basis of fast atom bombardment mass spectroscopy (FABMS). The extreme-pressure, antiwear and antiseizure performance of CuAMP was assessed using a four-ball machine. The results showed that CuAMP exhibits better extreme-pressure and antiwear properties than tricresyl phosphate. Based on the results of surface analysis, the antiwear action mechanism of CuAMP is discussed.
Squeeze Film Force Modeling for Large Amplitude Motion Using an
Elliptical Velocity Profile
Authors: Han Yingke , Rogers R. J.
Published: February 2008

With the aim of seeking a more reasonable solution for the squeeze film force for large amplitude motion with low viscosity fluids, an elliptical velocity profile and the corresponding squeeze film force equations are derived for a two dimensional rectangular plate model using three different approximation methods. Through comparisons with existing theoretical studies which use parabolic velocity profiles for moderate to large Reynolds numbers, it is shown that the squeeze film model using the elliptical profile may be closer to reality. The force level of the dominant temporal inertia component using the elliptical profile (with either the iterative or the energy methods) is between that obtained using the traditional parabolic profile with the momentum method and that obtained with either the iterative or the energy methods.
Friction Model of Thin Solid Film Lubrication
Authors: Zhang Xianhua , Kato Koji
Published: February 2008

Based upon previous results for thin solid film lubrication, a contact model has been proposed which can describe the physical essence of the steady-state friction condition. By using this contact model, a theoretical calculation method has been established. Good agreement between theoretical results and experimental results obtained for tribo-coatings shows that this theory can be used for practical application to obtain and maintain good solid lubrication.
Effects of CO2 Laser Surface Hardening in the Unlubricated Wear of Ductile Cast Iron Against Alumina
Authors: Papaphilippou C. , Vardavoulias M. , Jeandin M.
Published: February 2008

The microstructure of a ferrito-pearlitic ductile cast iron has been modified by CO2 laser surface hardening. Analysis of the laser-processed surfaces showed a dramatic increase in microhardness. Dry sliding wear of laser-treated specimens against an alumina counterbody has been investigated by “ball-on-disk” testing. The evolution of the wear coefficient, as well as metallographic observations, revealed an oxidational wear mechanism. The wear resistance of the laser-treated samples was significantly enhanced. The laser-treated cast iron has a better resistance to abrasion and plastic deformation. The improvement of the wear resistance was due to the fine and homogeneous microstructure produced after laser-treatment. Wear plots showing the evolution of wear coefficient with normal load, sliding velocity, and humidity have been established. The wear of the laser-treated cast iron is not influenced by the variation of operating conditions (normal load, sliding velocity, and relative humidity).
Evaluations of Diamond-Like-Carbon Film Optical Constants and Their Effects on Flying Height Determination
Authors: Li Yufeng , Menon Aric , Goglia Peter
Published: February 2008

The accuracy in flying height determination of a film coated magnetic slider relies on the availability of accurate optical property values of each film. In view of this, the index of refraction and coefficient of extinction of carbon and underlayer films, as used on a magnetic slider, was evaluated in this study. Various thicknesses of carbon and underlayer films were coated on Al2O3-TiC substrates, and their optical properties were determined by using a variable angle spectroscopic ellipsometer at multiple angles of incidence and two optical models via reasonable range and least square methods. Then the effects of the carbon and underlayer films on flying height measurement were assessed. It was found that the optical properties of the underlayer film are strongly thickness and wavelength dependent. Therefore, the flying height measurement errors caused by incorrect treatment of the films are functions of film thickness and light wavelength.
An Implicit Multidomain Spectral Collocation Method for the Simulation of Gas Bearings Between Textured Surfaces
Authors: Kuria Isaac M. , Raad Peter E.
Published: February 2008

This work presents an implicit, multidomain, Chebyshev spectral collocation method for the solution of the compressible Reynolds equation of lubrication for a self-acting air bearing supporting a taper-flat slider. The method maintains second-order accuracy in time and exponential accuracy in space. Multiple domains are introduced to allow for the distribution of additional collocation points in the boundary layer regions without increasing the number of collocation points everywhere else in the computational domain. Multiple domains are also used to resolve individual sinusoidal roughness waves, demonstrating the method’s utility in resolving geometric and/or flow features in the interior of the computational domain. The ordinary differential equations governing the slider’s two degrees of freedom are integrated in time by the use of a fourth-order Adams-Bashforth method which allows for accurate and efficient coupling with the fluid dynamics of the gas bearing. The strength of the multidomain pseudospectral method in resolving problems with important geometric features and boundary layers is demonstrated by numerical experiments for sliders possessing different taper lengths and surface textures.
The Effect of Disk Roughness on the Wear of Contact Recording Heads
Authors: Suk M.
Published: February 2008

In conventional disk files, the slider is supported by an air-bearing when the disk is rotating at its designed speed. With the continued reduction of magnetic spacing in order to increase the areal density, a natural extension of the traditional recording system is contact recording. We investigate the wear of the contact recording head designed for such a class of rigid magnetic disk files where the read/write element carrying slider is intended to remain in continuous contact during every phase of the disk drive operation. In particular, we study the effect of disk roughness and load on the wear rate of the recording head. It is observed that the wear rate is proportional to initial interfacial load, however the observation cannot be extrapolated beyond the loads studied in the paper. The experimental observations agree well with expectations for a system where an abrasive wear model applies. We also show that the wear rate is predominantly governed by the existence of isolated asperities that lie well outside of three standard deviations of the disk surface roughness.
Thin Spacing Analysis for Head-Tape Interface
Authors: Sakai Kazuo , Nagawa Yasumasa , Okuyama Koetsu , Terayama Takao
Published: February 2008

Very thin head-tape spacing, combining contact and floating conditions, is investigated for high density magnetic recording. A generalized lubrication equation, based on a linearized Boltzmann equation, is coupled with the tape deformation equation for analysis. Tape-surface roughness is also taken into account in the lubrication equation. The average flow model is adopted to analyzing tape-surface roughness. For very thin spacing conditions, it is found that the spacing based on the linearized Boltzmann equation is smaller than that based on first-order slip flow, and larger than that based on second-order slip flow. It is also found that considering tape-surface roughness reduces the calculated minimum spacing. Analytical results agreed with the experimental ones.
Self-Excited Oscillations in Sliding With a Constant Friction Coefficient—A Simple Model
Authors: Adams G. G.
Published: February 2008

The sliding of two surfaces with respect to each other involves many interacting phenomena. In this paper a simple model is presented for the dynamic interaction of two sliding surfaces. This model consists of a beam on elastic foundation acted upon by a series of moving linear springs, where the springs represent the asperities on one of the surfaces. The coefficient of friction is constant. Although a nominally steady-state solution exists, an analysis of the dynamic problem indicates that the steady solution is dynamically unstable for any finite speed. Eigenvalues with positive real parts give rise to self-excited motion which continues to increase with time. These self-excited oscillations can lead either to partial loss-of-contact or to stick-slip. The mechanism responsible for the instability is a result of the interaction of certain complex modes of vibration (which result from the moving springs) with the friction force of the moving springs. It is expected that these vibrations play a role in the behavior of sliding members with dry friction.
Discrete Nature of Ultrathin Lubrication Film Between Mica Surfaces
Authors: Matsuoka Hiroshige , Kato Takahisa
Published: February 2008

A new apparatus which can measure force and separation between surfaces accurately is developed. Ultrathin fluid lubrication film thickness between mica surfaces is measured using this apparatus. Octamethylcyclotetrasiloxane (OMCTS) is used as a lubricant. As a result of the experiment, it is found that when the film thickness is more than about 10 nm (ten times as large as the molecular diameter of OMCTS), there is good agreement with the conventional continuum fluid lubrication theory (EHL theory). In case of film thickness less than 10 nm, however, it deviates from the theoretical prediction and discretization of film thickness is observed. It is considered that this phenomenon is due to the solvation force (structural force), and that the molecular effect cannot be neglected in such an ultrathin lubrication phenomenon as in this experiment.
Magnetic Bearing Design for Reduced Power Consumption
Authors: Maslen E. H. , Allaire P. E. , Noh M. D. , Sortore C. K.
Published: February 2008

Magnetic bearings have relatively low power consumption compared to fluid film and rolling element bearings. They are now candidates for supporting gas turbines and aeropropulsion engines. This paper describes the design and construction of permanent magnet biased, actively controlled magnetic bearings for a flexible rotor. The rotor was originally supported in fluid film bearings consuming as much as 3000 watts of power. For the magnetic bearing, both permanent magnets and electromagnets are used in a configuration which effectively provides the necessary fluxes in the appropriate air gaps to support the rotor. The theoretical development related to the bearing design is presented along with some experimental performance results. The results include measurements of power consumption, load capacity, bearing linearized coefficients, and the dynamic response of the rotor. The measured total power consumption, excluding shaft losses, was 210 watts in the permanent magnet biased bearing.
Analytical, Numerical, and Experimental Investigation of the Flow Structure in a Flooded Ball Bearing
Authors: Fruman Daniel H. , Benmansour Ibtissem , Nouar Che´rif , Bidot Thierry , Vanel Jean-Marc
Published: February 2008

Using an order of magnitude estimate of the leading terms in the equations of motion, the three-dimensional flow in a flooded ball bearing is reduced to the investigation of two-dimensional flow problems in a series of bearing cross sections. Combining, through appropriate compatibility conditions, the individual analytical solutions for the spaces confined between the cage and the inner wall of the rings, the halls and the rings and the balls and the cage’s holes, a very simple analytical model is derived. It allows the computation, in the laminar regime, of the flow rate, the pressure drop, and the velocity profile in different cross sections of the confined spaces. The results of the analytical model are confirmed by those obtained using a CFD code and extended to the turbulent regime. The analytical and numerical results are compared to those obtained from flow visualizations and velocity measurements conducted in a specially designed large scale model of a ball bearing. The agreement is very satisfactory.
Computed Effects of Rotor-Induced Swirl on Brush Seal Performance—Part 1: Leakage Analysis
Authors: Sharatchandra M. C. , Rhode D. L.
Published: February 2008

This paper presents a numerical study of the effects of rotor induced swirl velocity on the performance of brush seals. Such effects have been studied experimentally by Ferguson (1988), but this paper is apparently the first to obtain an enhanced understanding from the detailed flowfield distributions. The analysis involves the solution of the full Navier-Stokes equations in a two-dimensional, idealized configuration using a strongly conservative finite volume method developed by the authors in conjunction with the QUICK differencing scheme. The present computations have demonstrated excellent agreement with measurements for the similar flow across tube banks. An enhanced understanding of decreasing leakage with increasing shaft speed was obtained in terms of the various flow features. Specifically, the cause and effect relationship of certain interactions between the axial and tangential flows was identified. Computer-drawn pathlines show how increased leakage resistance results from large rotor-induced lateral motion of leakage fluid particles. In addition, a first-order streamwise periodic boundary condition treatment which facilitates numerical convergence has been proposed for essentially any flow which is streamwise periodic in two orthogonal directions.
Computed Effects of Rotor-Induced Swirl on Brush Seal Performance—Part 2: Bristle Force Analysis
Authors: Sharatchandra M. C. , Rhode D. L.
Published: February 2008

This paper analytically investigates the aerodynamic bristle force distributions in brush seals used in aircraft gas turbine engines. These forces are responsible for the onset of bristle tip lift-off from the rotor surface which significantly affects brush seal performance. In order to provide an enhanced understanding of the mechanisms governing the bristle force distributions, a full Navier-Stokes flow simulation is performed in a streamwise periodic module of bristles corresponding to the staggered square configuration. As is the case with a companion paper (Sharatchandra and Rhode, 1996), this study has the novel feature of considering the combined effects of axial (leakage) and tangential (swirl) flows. Specifically, the effects of intra-bristle spacing and bristle inclination angle are explored. The results indicate that the lifting bristle force increases with reduced intra-bristle spacing and increased inclination angle. It was also observed that increases in the axial or tangential flow rates increased the force component in the normal as well as the flow direction.
Thermohydrodynamic Analysis of Submerged Oil Journal Bearings Considering Surface Roughness Effects
Authors: Ramesh J. , Majumdar B. C. , Rao N. S.
Published: February 2008

A theoretical study of a submerged oil journal bearing is made considering surface roughness and thermal effects. The total load-supporting ability under such condition is due to the thermohydrodynamic as well as the asperity contact pressure. The effect of surface roughness and viscosity-temperature dependency on hydrodynamic pressure has been found by solving the average Reynolds equation, energy equation and heat conduction equations simultaneously. The cavitation model of Jacobsson-Floberg has been modified to take the surface roughness effects into consideration. A parametric study of steady-state behavior has been carried out. Finally, the isothermal, thermohydrodynamic, and contact loads for a model bearing have been calculated, assuming the surface height distribution as Gaussian.
Study on the Adhesion Force of Lubricants—Adhesion Force Characteristics Under Boundary Lubrication
Authors: Kobayashi A. , Unno N. , Yonemoto T.
Published: February 2008

The mechanisms that generate adhesion forces in liquid lubricants are studied under various experimental conditions. These forces occur between two surfaces when they are detached in the normal direction under static boundary lubrication conditions. The adhesion force is not influenced by the speed at which the upper specimen is pulled up, but is influenced by the viscosity of the lubricant. The adhesion force under boundary lubrication is much greater than that under hydrodynamic lubrication, and it is closely related to the compressibility of the lubricant.
Influence of an Inlet Oil Meniscus Geometry on Parameters of a Point Elastohydrodynamic Contact
Authors: Kudish I. I. , Panovko M. Ya.
Published: February 2008

In the present paper an isothermal elastohydrodynamic problem for a lightly loaded lubricated point contact of elastic bodies is formulated and studied numerically. Mathematical formulation of the problem is based on a steady nonlinear system of integrodifferential equations: Reynolds’ equation, equations of elasticity, boundary conditions for pressure, and the equilibrium condition. Nonlinearity of the problem is caused by nonlinearity of the Reynolds equation and the boundary conditions for pressure describing a free boundary. The inlet contact boundary is considered to be known and located close to the center of the contact. In order to determine the location of the free boundary (exit boundary of the contact region) the problem is formulated as a problem of complementarity by Kostreva (1984a) and Oh (1984). The dimensionless system of equations and inequalities for the elastohydrodynamic lubrication (EHL) problem is solved using the Newton-Raphson method. The inlet boundary of a contact region is considered to have a complex irregular shape (the inlet oil meniscus has some deep notches) which is taken into account while deriving the finite-difference equations. The effect of the shape and location of the inlet oil meniscus on the lubrication film thickness, pressure, gap, sliding and rolling frictional and subsurface stress distributions are considered. Some numerical results are presented for pressure, gap, frictional and subsurface stress distributions in EHL contact. These numerical results show that variations in the inlet meniscus shape and location may cause significant qualitative and quantitative changes in distributions of parameters of a lubricated contact. For instance, the maximum values of pressure may change by 20 percent, and for rolling frictional stress by 100 percent and even more.
On the Mechanism of Multi-Valued Friction in Unsteady Sliding Line Contacts Operating in the Regime of Mixed-Film Lubrication
Authors: Zhai Xuejun , Needham G. , Chang L.
Published: February 2008

Systematic analyses are presented to reveal the mechanism of multi-valued friction behavior in lubricated sliding contacts with time-varying velocities. The analyses are based on the theoretical results generated by a mixed-film friction model developed in this paper for line contacts. The model, which integrates theories of transient elastohydrodynamics and asperity contact mechanics, is validated by comparing its results with published experimental data. The results and the subsequent analyses disclose that strong multi-valued friction behavior can only be generated in the mixed-film lubrication regime with simultaneous presence of significant asperity contacts and hydrodynamic squeeze. Principal factors which influence the magnitude of dynamic friction are investigated in the paper. Being instructive to the design of tribocontacts in precise-motion control systems, the analyses suggest means to minimize the undesirable multi-valued friction behavior through proper selection of system parameters.
Analysis of Oil-Film Pressure Distribution in Porous Journal Bearings Under Hydrodynamic Lubrication Conditions Using an Improved Boundary Condition
Authors: Kaneko Satoru , Hashimoto Yuji , I Hiroki
Published: February 2008

Pressure distributions in the oil film of a porous journal bearing are investigated theoretically and experimentally under hydrodynamic lubrication conditions. The circumferential boundary condition for the oil-film pressure is obtained by applying an integral momentum equation to the oil-film region in the bearing clearance. The oil-film pressure distributions are numerically solved using this momentum equation and taking into consideration the balance between oil fed into the clearance and that lost from it. The present analysis shows the occurrence of a negative film pressure before the trailing end of the oil-film region. The experimental results confirm the existence of this negative film pressure. Furthermore, the angular position of the trailing end of the oil-film region obtained in the present analysis moves toward the downstream region, yielding better agreement with the measured and calculated film regions than was found in our previous analysis based on the quasi-Reynolds boundary condition.
Angled Injection—Hydrostatic Bearings Analysis and Comparison to Test Results
Authors: San Andres Luis , Childs Dara
Published: February 2008

Hydrostatic/hydrodynamic (hybrid) journal bearings handling process liquids have limited dynamic stability characteristics and their application as support elements to high speed flexible rotating systems is severely restricted. Measurements on water hybrid bearings with angled orifice injection have demonstrated improved rotordynamic performance with virtual elimination of cross-coupled stiffness coefficients and null or negative whirl frequency ratios. A bulk-flow model for prediction of the static performance and force coefficients of hybrid bearings with angled orifice injection is advanced. The analysis reveals that the fluid momentum exchange at the orifice discharge produces a pressure rise in the hydrostatic recess which retards the shear flow induced by journal rotation, and thus, reduces cross-coupling forces. The predictions from the model are compared with experimental measurements for a 45 deg angled orifice injection, 5 recess, water hydrostatic bearing operating at 10.2, 17.4, and 24.6 krpm and with supply pressures of 4, 5.5 and 7 MPa. The correlations include recess pressures, flow rates, and rotordynamic force coefficients at the journal centered position. An application example for a liquid oxygen hybrid bearing also demonstrates the advantages of tangential orifice injection on the rotordynamic coefficients and stability indicator for forward whirl motions, and without performance degradation on direct stiffness and damping coefficients.
General Microhardness Indentation Theory for Multilayer Contacts
Authors: Engel Peter A. , Yang Qian
Published: February 2008

A refined method for interpreting the Vickers composite microhardness measurement for multilayer materials having layers of arbitrary plating thickness is first presented. The position of an “effective substrate” is found using the concept of the “plastic boundary,” and the depth-wise deformation of each layer is considered in a double-iterative procedure which converges fast. This computational method is then extended from pyramidal indenters to conical and spherical indenters (e.g., Meyer’s). For its confirmation, experimental investigations are carried out for two configurations of Cu/Ni/Au sandwiches, using different diameter spherical indenters and spherical tipped cones, through and well above the microhardness load range. The general rules for composite action are established.
Steady-State Analysis of Mechanical Seals With Two Flexibly Mounted Rotors
Authors: Wileman J. , Green I.
Published: February 2008

The dynamic behavior of a mechanical face seal with two flexibly mounted rotors is investigated. The equations of motion are derived using linearized rotor dynamic coefficients to model the dynamic behavior of the fluid film. The equations are shown to be linear in the inertial reference with harmonic forcing functions which result from the initial misalignment of the flexible supports. A method for obtaining the steady-state response in the system is derived by transforming the equations of motion into reference frames which rotate with the shafts. The resulting equations contain constant forcing functions and can be readily solved for the magnitude of the steady-state response. The method presented allows a rapid determination of the steady-state misalignment of a seal without resorting to numerical modeling.
Rotary Lip Seal Operation With an Ingested Meniscus
Authors: Salant R. F.
Published: February 2008

Previous numerical simulations and experimental observations have shown that the meniscus in a rotary lip seal will be ingested into the sealing zone when the shaft speed exceeds a critical value. The present numerical analysis shows that once the meniscus is ingested, multiple equilibrium operating points exist, so the steady-state operating characteristics of the seal will depend on the history of the seal as well as on the steady-state operating conditions and seal properties. The analysis also shows that if the meniscus moves too close to the liquid-side of the seal, asperity contact between the lip and the shaft will occur.
Micro-Inertia Effects in Laminar Thin-Film Flow Past a Sinusoidal Boundary
Authors: Hu Jin , Leutheusser Hans J.
Published: February 2008

Micro-inertia effects of surface roughness on hydrodynamic lubrication are analyzed in the light of similitude principles, viz. a newly conceived reduced Reynolds number and the classical parameter of relative roughness. In particular, the dynamic properties of laminar sheet flow in a two-dimensional channel between a sinusoidal wall and a flat wall are studied. FEM solutions of the Navier-Stokes equation are compared with corresponding experimental findings. The latter are gathered in an especially designed laminar-flow wind tunnel. Conclusions are drawn concerning the roughness sensitivity of laminar thin-film flows.
Cracking Induced by Fretting of Aluminium Alloys
Authors: Zhou Z. R. , Vincent L.
Published: February 2008

Fretting-wear and fretting-fatigue loadings can both result in wear (material loss) and in crack nucleation and propagation (fatigue process). This paper deals with cracking induced by small amplitude displacements in the case of aeronautic aluminium alloys. The two sets of fretting maps are introduced: running condition fretting map is composed of partial slip (sticking), mixed fretting and gross sliding regime; material response fretting map is associated with two macro-degradation modes. Crack nucleation and propagation are analysed for every fretting regime. The mixed fretting regime appeared most detrimental with regards to fatigue cracking. Slip amplitude and normal load main effects discussed for fretting wear can be used to justify the fatigue limit decrease often obtained for fretting fatigue experiments.
A Statistical Model for Interpreting Hard Disk Drive Stiction Measurements
Authors: Meyer D. , Goglia P. , Menon A. K. , Li Y.
Published: February 2008

A statistical methodology is presented for predicting drive performance based on fundamental static friction (stiction) measurements. The technique allows the prediction of drive stiction and dynamic friction failures, based on component level spin-stand measurements. We discuss both the fundamental measurement of component stiction and the interpretation of the results as applied to an actual disk drive. The component measurements examine the effects of acceleration, filtering and sampling. It is shown that motor acceleration and the electronic configuration of the test stand affect the stiction measurement, but by proper electronic and mechanical designs this effect can be reduced to an insignificant quantity. The interpretation of component results considers incorporating the effect of multiple heads in a drive, and a statistical model is devised that accounts for both static and dynamic friction variation, along with motor/driver variations. One can predict the probability of a single drive failure or the failure rates of a population of drives, either new or after extensive field exposure. We show that a poorly characterized measurement compared to an arithmetic average of the available motor torque may predict drive failure rates in error by several orders of magnitude.
Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing
Authors: Goodwin M. J. , Ogrodnik P. J. , Roach M. P. , Fang Y.
Published: February 2008

This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.
On the Breakdown Under Contact Conditions of Reynolds Equation for Gas Lubricated Bearings
Authors: Anaya-Dufresne M. , Sinclair G. B.
Published: February 2008

For the analysis of gas lubricated bearings, Reynolds equation is available in a number of forms—the original version, first-order modified, second-order modified, one-and-a-half order modified, and Boltzmann-Reynolds. All of these variants are asymptotically examined for instances in which local contact occurs in a bearing. These asymptotics serve to identify the order of the respective singularities in pressures, and thus imply the possible consequences of using a particular version of Reynolds equation in the presence of contact.
On the Combined Effects of Lubricant Inertia and Viscous Dissipation in Long Bearings
Authors: Kim E. , Szeri A. Z.
Published: February 2008

We have demonstrated earlier that for laminar, isothermal flow of the lubricant in the non-cavitating film of long journal bearings, inertia has negligible effect on the load-carrying capacity and influences only the stability characteristics of the bearing. The question we pose in the present paper is: “will these conclusions remain valid for nonisothermal flow, or will lubricant inertia and dissipation interact and result in significant changes in bearing performance?” The results obtained here assert that the effect of lubricant inertia on load-carrying capacity remains negligible, irrespective of the rate of dissipation. The stability of the bearing is, however, affected by lubricant inertia. These results, although obtained here for long bearings and noncavitating films, are believed to be applicable to some practical bearing operations and suggest that for these, bearing load may be calculated from classical, i.e., noninertial theory.
Finite Element Approach to the Prediction of Foil Bearing Rotor Dynamic Coefficients
Authors: Peng J.-P. , Carpino M.
Published: February 2008

A finite element perturbation approach to the prediction of foil bearing stiffness and damping coefficients is presented. The fluid lubricant is modeled as a simple barotropic fluid which is described by the Reynolds equation. The structural model includes membrane, bending, and elastic foundation effects in a general geometry. The equivalent viscous damping of the Coulomb friction caused by the foil relative motion is included in the structural calculation. Bearing stiffness and damping coefficients are predicted for an air-lubricated foil bearing with a corrugated sub-foil. The effects of the bearing number, bearing compliance, sub-foil Coulomb friction, and foil membrane stiffness on the bearing dynamic coefficients are discussed.
Advancements in Cone-type Rotary Piercing Technology
Authors: Hayashi Chihiro , Akiyama Masayoshi , Yamakawa Tomio
Published: February 2008

A cone-type piercing mill was developed by the authors for materials with poor hot workability. This piercing mill is called “the super piercer” in Europe. It has a pair of cone-type main rolls supported at both ends with their roll axes inclined and crossed so as to enable piercing at high feed and cross angles. In order to ensure the best performance of the rotary piercing, disc rolls are adopted instead of plate guide shoes. The super piercer was put into practice at the small-diameter seamless tube plant operated in 1983. The recent progress in our research and development on the super piercer has resulted in the concept of “the new super piercer,” which allows expansion piercing. Namely, the development of the skewing technology for disc roll axes and its application to the cone-type piercing technology has realized remarkable increase in the expansion ratio. The new super piercer was adopted as the core technology of the new medium-diameter seamless tube plant operated in 1997. In this paper, studied in detail were the influences of the expansion ratio, feed and cross angles on the rotary forging effects, redundant shear deformations and power consumption.
Analysis of Circular Braiding Process, Part 1: Theoretical Investigation of Kinematics of the Circular Braiding Process
Authors: Zhang Q. , Beale D. , Broughton R. M.
Published: February 2008

Circular braiding is a manufacturing process for making circular braided fabrics. Relative sliding of yarns during their interlacing motion introduces friction which limits the density of the braided fabric. A kinematic analysis is presented in this paper. Yarns’ absolute motion, relative sliding motion and twist motion in the convergent zone are found to be important quantities in braid kinematics that impact the final braid structure. The straight yarn assumption, which ignores the effect of interyarn forces, is analyzed in detail for its validity in calculating the braid angle. In Part 2 of this paper series a mechanics model is proposed to determine the braid angle by considering interlacing forces and their effects on the braided structure.
Analysis of Circular Braiding Process, Part 2: Mechanics Analysis of the Circular Braiding Process and Experiment
Authors: Zhang Q. , Beale D. , Broughton R. M. , Adanur S.
Published: February 2008

The final structure of a braid is a consequence of force interactions among yarns in the convergent zone. In Part 1, the influence of friction forces on the final braided structure was discussed via kinematic analysis. A transformation from a 3-D cone to a 2-D plane was made for the mechanics analysis. A mechanics model is proposed in this paper to determine the braid angle by considering interlacing forces. Equilibrium equations for the braiding process are deduced. A Newton-Raphson method is used to solve the nonlinear algebraic equation set. Experiments have been conducted to produce braids at different machine speeds and with different tensions, and reveal that the mechanics model is potentially a better predictor of final braid structure than the kinematic analysis.
Three-Dimensional Finite Element Modelling of Forging of a Titanium Alloy Aerofoil Sectioned Blade
Authors: Hu Z. M. , Brooks J. W. , Dean T. A.
Published: February 2008

Analysis of the forging of aerofoil blades, particularly those for aeroengines, is a complex operation because of the complicated three-dimensional geometry and the non steady-state contact between the workpiece and the die surface. In this paper a three-dimensional analysis of the hot forging of a titanium compressor blade, currently being made and used commercially, using the finite element method is presented and validated by the results from hot-die forging tests. The process is modelled assuming isothermal conditions, the main interest being the mechanics of the deformation. Abaqus/Explicit FE software has been used for process simulation in which the complicated die form, assumed rigid, has been modelled using smoothed Bezier surfaces which enable die/workpiece contact phenomena to be handled effectively. Predicted strain patterns in sections of forging, using either 2-D or 3-D analysis are compared. It is shown that the experimental forging load and the overall flow pattern are predicted by the analysis with good accuracy.
Temperature Field Regulation in Thermal Cutting for Layered Manufacturing
Authors: Fourligkas N. , Doumanidis C.
Published: February 2008

A general thermal modeling and control methodology for thermal processing of layered materials for rapid prototyping technologies is established in this article. An analytical multivariable model of lumped temperature outputs generated by heat inputs on a surface grid is developed, based on Green’s function and state-space descriptions. The few independent parameters needed in such a linearized formulation are experimentally identified, and their time-variability reflects the heat transfer nonlinearities and process disturbances. A robust controller with thermal feedback is designed by pole placement methods, to obtain a specified dynamic temperature field yielding the desired material structure and properties. The regulated thermal processing is optimized in real time by proper heat source power modulation and torch guidance through a simulated annealing strategy. Its performance is tested on both the computer model and a laboratory station, using robotically guided plasma-arc cutting and infrared thermal sensing, in regulating the sensitized zone during blanking of an elementary contour pattern on stainless steel.
Machine Vision Monitoring for Automated Surface Finishing
Authors: Bradley C. , Kurada S.
Published: February 2008

A considerable amount of research has recently been performed on automated die and mold finishing systems. The research has tended to focus on the development of the finishing tool, the means of positioning and controlling the tool or efficient algorithms for moving the tool to achieve desired degrees of surface roughness. However, there has been relatively less effort to develop sensors suitable for providing the critical surface finish data necessary for any closed loop system. This paper presents two algorithms that, when coupled with machine vision hardware, are capable of providing surface texture information. The algorithms are developed and the results calibrated against a stylus profilometer. Tests have been conducted on mold cavity surfaces and the results evaluated against standard tactile means. The hardware has been incorporated with a computer controlled coordinate machine.
Materials Modelling and Laser Inspection for the 3D Lay-up of Dry Fiber Composite Preforms
Authors: Zhang Z. , Sarhadi M.
Published: February 2008

Resin Transfer Moulding (RTM) is playing an ever increasing role in the manufacturing of composite components in the aerospace industry. However, the high labor and tooling costs and long manufacturing lead-times involved in the manual lay-up of dry carbon fiber preforms are obstructing the wide spread use of this technology. Recent development of Non-Crimp Fabrics (NCF) and automation technology has resulted in an automated preform manufacturing process, of which folding of materials constitutes an important step. This paper presents a mathematical model for the prediction of the 3D shapes of folded NCF sheets, a laser inspection system for the dimensional measurement of ply folds, and the integration of the two techniques for on-line monitoring of an automated preform manufacturing system.
A Novel Device for Producing Three-Dimensional Objects
Authors: Young J. S. , Fox S. R. , Anseth K. S.
Published: February 2008

This work describes a novel device for producing three-dimensional objects that has been developed using a liquid crystal display as a programmable, dynamic mask and visible light to initiate photopolymerization. This device has the potential to produce three-dimensional objects of comparable quality to the existing commercial devices, but in significantly less time. Additionally, capital, maintenance and operating costs are expected to be substantially lower than those for laser-based systems. The reduction in time and expense could expand this technology into the realm of custom part production and further increase the accessibility and usefulness of solid freeform fabrication and rapid prototyping.
An Elastic Contact Model for the Prediction of Workpiece-Fixture Contact Forces in Clamping
Authors: Li B. , Melkote S. N.
Published: February 2008

The design and evaluation of machining fixture performance requires accurate knowledge of workpiece-fixture contact forces since they strongly impact workpiece accuracy during clamping and machining. This paper presents an elastic contact model for the prediction of workpiece-fixture contact forces due to clamping. The fixture and workpiece are considered to be elastic bodies in the vicinity of the contact region. The model is formulated as a constrained quadratic program by applying the principle of minimum total complementary energy. The model predicts the normal force, and the magnitude and direction of the tangential (friction) force at each workpiece-fixture contact due to clamping forces. Experimental verification of the model under different clamping loads shows good agreement between predicted and measured normal and tangential contact forces. The model can be used to analyze fixture performance in terms of the contact forces and contact region deformation.
Predict and Assure the Matchable Degree in Selective Assembly via PCI-based Tolerance
Authors: Zhang Yu , Fang X. Daniel
Published: February 2008

Selective assembly is a method to achieve high precision fit using low precision parts. The current practices in selective assembly lack a physical process model to guide the design and process of mating parts, consequently, selective assembly is often a nightmare for manufacturing people and historically an event to be avoided. Process capability indices (PCIs) are the widely accepted process parameters, functioning as a measure of process performance, such as process centering, process spread, process bias, etc. In this paper, the concept of PCI-based tolerance is proposed as an interface between quality requirements and statistical process control (SPC) parameters. An analytical model involving PCI-based tolerance is developed to predict and assure the matchable degree in selective assembly. A detailed case study of the fit of dry liners and cylinder blocks in a diesel engine is presented. As matchable degree and other process quality requirements can be assured at the stage of design by introducing PCI-based tolerance, the process of selective assembly can be improved significantly as an effective way to achieve precision assembly with economical manufacturing processes.
The Effect of Tool Flexibility on Back-Cutting in End Milled Surfaces
Authors: Melkote S. N. , Sutherland J. W. , King C.
Published: February 2008

End milled surface texture is inhomogeneous and often exhibits complex lay patterns. An important contributing factor to these surface characteristics is the back-cutting effect. This effect causes cutter tooth mark patterns on the surface in the forward and reverse tool feed directions. In this paper, the dependence of back-cutting on end mill flexibility and its influence on the slot floor surface texture are modeled and experimentally verified. It is shown that the extent to which tool flexibility affects back-cutting is determined by the resultant cutting force system and not the feed force alone. The variation in the amount of back-cutting typically observed across the width of a milled slot is also explained by this model. The model, although simple in form, yields reasonably good agreement with the measured surface profiles.