bluuebunny/crossref_metadata_2025 huggingface dataset:
Damping in Vibration Transfer Through Deep-Groove Ball Bearings
Authors: Mitsuya Yasunaga , Sawai Hidekazu , Shimizu Masaki , Aono Yasushi
Published: February 2008

Damping characteristics in vibration transfer through deep-groove ball bearings were measured precisely using a single ball bearing (equivalent to the 6200 type) and the compliance transfer function resulting from the impulses applied to the bearing. To eliminate uncertainties caused by bearing assembly and preloading, a monolithic-type ball bearing was specially fabricated by unifying its inner ring with a shaft, and its outer ring with a rotor. This structure enables preloading without the need for any solid contact using an externally pressurized air bearing. Experimental damping ratios were found to range from two to four percent and damping coefficients 0.15-0.35 Ns/mm. Damping was found to decrease with an increasing preload, and to be larger for a larger clearance and for a larger ball number. The decreases in damping resulting from superimposing the tilting mode vibration upon the lateral mode and from an increasing clearance indicated more ball rolling motion rather than slipping motion to be the cause of decreased damping. Also, the bearing rotation effect is found to be small. Addition of grease hardly provided any additional damping during rotation.
A Physically Based Model for Endurance Limit of Bearing Steels
Authors: Lamagnere P. , Fougeres R. , Lormand G. , Vincent A. , Girodin D. , Dudragne G. , Vergne F.
Published: February 2008

Available models are not suitable for calculating the load rating of bearings when an infinite life is required. This paper presents a new model that has been developed from a detailed analysis of the damage mechanism responsible for failure of bearings operating under EHD pure rolling conditions. It is based on the comparison between the local shear stress concentration built up around inhomogeneities present in steels and the microyield stress of the martensitic matrix. The predictions of this model are in good agreement with some literature data concerning the fatigue limit of bearing steels. Finally, the influence of material parameters and operating conditions on the endurance limit of bearings is investigated.
Some Observations on Scuffing in Tapered Roller Bearings
Authors: Zantopulos Harry
Published: February 2008

Tests were run on tapered roller bearings under severe operating conditions to promote the incidence of scuffing. This resulted in varying degrees of scuffing damage on the cone (inner race) ribs and/or spherical roller ends of some of the bearings. These were then examined using both the optical microscope and the scanning electron microscope (SEM). In addition, metallographic examinations were conducted on some of the damaged areas. On the basis of these observations, a qualitative model for the onset of scuffing is outlined. The quantitative data obtained from these tests was then analyzed in terms of Blok’s critical temperature criterion and also the scuffing criterion of the form WVx = constant.
A Finite Element Analysis of Crack Initiation and Propagation in a Notched Disk Submitted to Rolling Contact Fatigue
Authors: Bordi V. , Dorier Ch. , Villechaise B.
Published: February 2008

A finite element model has been developed to predict crack initiation and propagation in a notched disk submitted to rolling contact fatigue. The aim of this study is to validate the model with experimental results obtained by tests carried out on a two-disk machine. First, a three-dimensional finite element analysis is performed. A unidimensional equivalent damage stress is calculated by applying a plastic criterion in an attempt to estimate the damage location and the time necessary to initiate cracks from the notches. Then a two-dimensional calculation based on linear fracture mechanics is conducted to determine mixed mode stress intensity factors at the tip of a crack initiated from the notch. Several crack growth criteria are used to evaluate crack growth direction and rate. Numerical results are in good agreement with experimental ones.
EHD Film Thickness in Non-Steady State Contacts
Authors: Sugimura J. , Jones W. R. , Spikes H. A.
Published: February 2008

This paper describes a study of EHD film thickness in non-steady state contact conditions. A modification of ultrathin film interferometry is employed which is able to measure both central film thickness and film thickness profiles 50 times a second. Film thickness with two perfluoropolyethers and two mineral base oils are investigated in a number of different types of non-steady state motion, including acceleration/deceleration, stop/start and reciprocation. The results demonstrate a range of transient behaviors of EHD film whose thicknesses deviate from those in steady state conditions.
Elastohydrodynamic Analysis of the Sealing Performance of Rotary Shaft Helix Lip Seals—Part 1
Authors: Liming Lou , Yamamoto Kazutoshi , Ikeuchi Ken
Published: February 2008

Based upon EHD theory, the sealing performance of a rotary shaft helix lip seal has been analyzed numerically using a complete hydrodynamic lubrication model. In order to verify the analytical method, several experiments are carried out under different operating conditions. After verification by the experimental results, the analytical method is used to calculate the sealing limit and the optimum seal radial load. The effects of the boundary pressure of sump side upon the pumping rate of a seal are discussed.
Wear of Physical Vapor Deposition TiN Coatings Sliding Against Cr-Steel and WC Counterbodies
Authors: Wu Kee-Rong , Bayer Raymond G. , Engel Peter A. , Sun D. C.
Published: February 2008

Cutting tools are often coated with titanium nitride (TiN) for its good wear resistance. The method of coating by physical vapor deposition (PVD) has many superior features over other methods of deposition. Among the parameters affecting the wear resistance of PVD TiN coatings, the most crucial ones are the deposition temperature and the coating thickness. This paper presents an experimental investigation of the wear characteristics of PVD TiN coatings produced at two deposition temperatures (around 220°C and 371°C) and for a range of coating thicknesses (0.48 μm to 3.25 μm). A ball-on-flat configuration was used in the study. The flat specimen, made of M2 tool steel coated with TiN, was slid against a 52100 chromium steel (Cr-steel) or a tungsten carbide (WC) ball, dry. These two counterbody materials were chosen because of their different properties. The wear volume was measured and wear scar examined with a 3-D optical profilometer. The worn surfaces and debris were analyzed with scanning Auger microscopy (SAM) and an electron probe microanalyzer (EPMA). Quantitative data were obtained for the wear volume and coefficient of friction (COF) as functions of the sliding cycles. In the case of TiN versus Cr-steel, the presence of transferred wear debris on the flattened ball surface and iron oxide in the wear tracks of the coating surface was a major factor controlling the wear behavior. In the case of TiN versus WC, no transferred layers were observed; instead, the presence of flake type debris from the coating in the wear tracks appeared to be the controlling factor. It was concluded that deposition temperature, coating thickness, and counterface influenced wear behavior. For the lower deposition temperature, wear was significantly reduced by thinner coatings. However, for the higher deposition temperature, wear reduction was only obtained with the Cr-steel counterface.
Load-Dependency of Friction Coefficient Between Silicon-Oxides and Diamond Under Ultra-Low Contact Load
Authors: Yokohata Toru , Kato Koji , Miyamoto Takanori , Kaneko Reizo
Published: February 2008

The load-dependency of the friction coefficient under a contact load in the order of sub-micronewtons was revealed. The frictional force was measured experimentally with a diamond tip of 0.1 μm radius on silicon-oxide surfaces in a laboratory atmosphere. The frictional force was obtained even under a certain amount of negative external force. The contact load was regarded as the sum of the external force and the attractive force between two surfaces, the latter being estimated from an elastic contact theory which took into account the van-der-Waals force. The friction coefficient, as the ratio of the frictional force to the contact load (not to the external force), was plotted against the contact load. Below 0.4 μN in the contact load, the friction coefficient increased in inverse proportion to the decrease in contact load. Above 0.4 μN in the contact load, the friction coefficient was stable at about 0.1. We discussed this load-dependency, and derived a hypothesis that the real area of contact should include some part of the attractive region around the repulsive region at the contact point when the contribution of the attractive force is not negligible to the contact load.
“Internal Variables” Effects in Punch Friction Characterization
Authors: Hsu Tze-Chi , Liu Chi-Chia
Published: February 2008

Despite the complexity and importance of friction, most current simulations of metal-forming processes use relatively simple friction models such as the Amontons-Coulomb constant friction coefficient. It has been pointed out that simple models are not capable of capturing the influence of process variables such as geometry, speed, and surface topography on friction. A realistic friction model should include the internal variables such as lubricant film thickness, tooling roughness, and workpiece roughness. In the present research, the punch friction tests which use a tensile strip experiment to simulate the stretching of sheet over a punch corner radius in a typical draw die are used to measure the effects of internal variables on friction in various stretching conditions. The measured friction coefficients increase with lower stretching speed and decrease if lubricant is applied at the interface between workpiece and cylindrical pin. Theoretical friction modeling, which includes the different lubrication regimes range from thick film, thin film, mixed regime and boundary regime, are presented. Numerical methods have been used to solve the governing differential equations with the known initial boundary conditions obtained from the experiments. The theoretical prediction shows the same trend as the experimental measurements.
Spacing Modulation of Magnetic Head Due to Topographical Feature of Disk Surface
Authors: Suzuki Shoji
Published: February 2008

To achieve high recording density, the combination of low flying head and smooth disk surface is very desirable. Although high stiction associated with the smooth surface can be avoided by zone texturing or ramp load, stable flying condition must be assured by a smooth disk surface. Disk topography is an important factor in the flying stability of the head. In this work, read back signal modulation analysis was incorporated to characterize the disk topography. By increasing the writing frequency up to 25 MHz, high resolution was demonstrated in the fly height range between 15 nm to 50 nm. This resolution is sufficient to evaluate today’s low flying heads. A subambient pressure design which is typical for an MR head and a proximity head design for an inductive head were evaluated over very smooth aluminum disks. The effect of various disk clamping forces was also investigated. Relationship between disk waviness and flying stability of heads was studied.
Simultaneous Three-Wavelength Interferometry for Head/Tape Spacing Measurement
Authors: Baugh E. , Swenson J. , Talke F. E.
Published: February 2008

Instrumentation for the simultaneous acquisition of three monochromatic interference patterns for the measurement of head/tape spacing in magnetic tape drives is described. An algorithm to process the three images using a weighted average method into a map of the head/tape spacing and an estimated contact pressure map is presented. Both experimental evidence and Monte-Carlo simulation indicate that the three-wavelength technique is an improvement over standard monochromatic techniques. Sample one- and two-dimensional measurements are given.
Frequency Domain Characterization of Take-Up Reel Air-Entrainment in Low-Tension and High-Speed Tape Transport
Authors: Mathur P. D. , Messner W. C.
Published: February 2008

Air entrainment in tape spooling is important because it affects the tape stacking quality and the dynamics for which the transport controller must be designed. Accurate estimates of the air film thickness between the layers of tape are difficult to obtain by direct measurement. In this paper, a new frequency domain method is presented where the length of the entrained air film is estimated by determining the spring constant of the unsupported tape span. Using multi-input single-output (MISO) frequency based system identification, the resonant frequency of the system associated with the longitudinal mode of the tape is derived. These data are compared to predictions from the well known nip height equation. The utility of these equations is discussed.
Maximum Load Capacity Profiles for Gas Thrust Bearings Working Under High Compressibility Number Conditions
Authors: Iordanoff I.
Published: February 2008

To meet the requirements of new commercial equipment, performances of air thrust bearings always have to be improved. This work is concerned with the research of the converging profile that will give high load capacities. When compressibility effects increase (when the compressibility number Λ is over 50), a one-dimensional study shows that the best bearing is a composite bearing, i.e., one in which the leading portion has a constant slope followed by a surface parallel to the runner. For each compressibility number, entrance film thickness H1 and the transition angle θ1 define the best profile. In a two-dimensional study, for compressibility numbers from 10 to 1000, comparison in term of load capacity is made between tapered and composite profiles. It outlines the better load capacity of the composite bearings and confirms the good results obtained by Heshmat (1983) and Gray (1981) with such profiles.
An Experimental Study of Thrust Pad Flutter
Authors: Gardner W. W.
Published: February 2008

Tilting pad thrust bearings are commonly used on both the active and inactive (loaded and unloaded) sides of thrust collars of turbomachinery rotors. Fatigue failure of temperature sensor leadwires to the inactive side thrust pads and abnormal wear at contact points of these thrust pads, in several field applications, led to an investigation as to the cause. Since these problems occurred only on “unloaded” thrust bearings, flutter (vibration) of these inactive side thrust pads was suspected. Tests were run in the laboratory on a double thrust bearing under conditions simulating a turbomachine application. Pad flutter was found at two distinct conditions; low oil flows (as suspected), and also at high oil flows. The paper presents the results of these tests with data on the influence of the parameters studied, and the findings with respect to elimination of this flutter.
On the Choice of Element for Solving Lubrication Problems
Authors: Turaga Ram , Sekhar A. S. , Majumdar B. C.
Published: February 2008

This study deals with the stability characteristics of journal bearings using the finite element method. Two different elements, a 3-node linear triangle and a 6-node quadratic triangle, have been used. The results show a significant difference in (1) stiffness and damping coefficients and (2) stability characteristics at high eccentricity ratios due to the use of the two different elements.
Simulations of Air Slider Bearings With Realistic Gas-Surface Scattering
Authors: Wenski T. E. , Olson T. , Rettner C. T. , Garcia Alejandro L.
Published: February 2008

We have calculated the pressure distribution for an infinitely wide plane slider air bearing by using a particle-based direct simulation Monte Carlo method. These simulations include a sophisticated gas-surface scattering model and take measured accommodation coefficients as inputs. Our results are in good agreement with the molecular gas lubrication theory of Fukui and Kaneko for both glass and disk-drive surfaces.
An Enhanced Dynamic Model in Turning Including the Effect of Ploughing Forces
Authors: Shawky A. M. , Elbestawi M. A.
Published: February 2008

In this paper computer simulation of cutting process dynamics in turning, using a mechanistic cutting force model, is significantly enhanced by incorporating a dynamic ploughing force model. The ploughing forces are decomposed into static and dynamic components. The effect of tool feed on increasing the clearance face contact is described mechanistically. The ploughing model is developed for the complex geometry of a multi-edge cutting tool and the effect of integrated tool/workpiece vibrations is considered. The cutting process damping is predicted by tracking the dynamic ploughed volume resulting from the interaction with machined surface undulations. The model has been used through computer simulations to predict the cutting forces and machined surface errors. The results clearly demonstrate the effect of including the ploughing model on the process dynamics. The theoretical predictions show a good agreement with the experimental results.
Design and Machining of Globoidal Index Cams
Authors: Tsay Der Min , Lin Bor Jeng
Published: February 2008

A simple, yet useful approach to the geometry design and machining of globoidal index cams and roller-follower turrets is developed. From the machining point of view of the globoidal cam by an end mill, the side surface geometry can be easily defined as the swept surface by the tool path. By using the analytical cam surface formulation, the pressure angle, the contact forces, and the torques between the cam and the turret can be investigated. In the machining process, to avoid undercutting, principal curvatures are analyzed. To demonstrate the usefulness and effectiveness of the procedure, two numerical examples of the globoidal index cams are presented along with the 3D computer printouts and the photography of machined samples.
Forming Mechanism of Planetary Conical Rolling
Authors: Mori T. , Saito Y.
Published: February 2008

This research deals with the development of a new process for tube ironing. The process of tube ironing is done without sliding friction which is the main cause for galling and breakage in conventional ironing. In this process a number of rollers rotate around the cone while revolving around their respective axis. The process Planetary Conical Rolling is termed PCR. This process has the following advantages: (1) rollers are supported by a shaft being free of lateral force, (2) the diameter of the shaft is almost the same as the inner diameter of the product, (3) high rigidity of the shaft results in high accuracy of products, (4) rollers inclination does not allow slide between roller and material in the radial direction. Experiments are conducted on two types of processes, i.e., forward and backward process, and two aluminum materials, i.e., A1050 and A5052 with different rotation, feed rate and so on. The results show this process can produce thickness reduction larger than 0.89 with mirror-finished outer surface.
Effects of Microcracks in CVD Coating Layers on Cemented Carbide and Cermet Substrates on Residual Stress and Transverse Rupture Strength
Authors: Katayama Sakae , Hashimura Masayuki
Published: February 2008

Microcracks were mechanically induced in the CVD coating layers on two types of cemented carbides with different thermal expansion coefficients, and one type of cermet. The microcracks were found to have beneficial effects on residual stress, transverse rupture strength, and chipping resistance during interrupted cutting. Residual stress in the coating on cemented carbide is tensile. Tensile residual stress decreases with increasing microcrack width and decreasing microcrack distance. Induction of 20 μm-distant and 0.025 μm-wide cracks relieves tensile residual stress by about 0.5 GPa, increases transverse rupture strength by about 0.70 GPa, and almost doubles the chipping resistance. Residual stress in the coating on cermet is compressive. Microcracks in the coating layer do not change residual stress or transverse rupture strength.
Current Trends in High-Speed Machining
Authors: Smith S. , Tlusty J.
Published: February 2008

The focus of the majority of high-speed machining research has been directed toward improving metal removal rates. Tool materials capable of withstanding high cutting speeds have become available (silicon nitride for cast iron, solid carbide for aluminum, and superabrasives for hardened steels), and the focus of research has shifted to maximizing the cutting performance of the machine tool. Measurement of cutting performance, chatter avoidance, structural design, tool retention, and axis control have become important research topics. The purpose of this paper is to provide an overview of the state of the art in high-speed machining and to provide our view of the emerging research areas.
Application of Computational Machining Method to Discontinuous Chip Formation
Authors: Obikawa T. , Sasahara H. , Shirakashi T. , Usui E.
Published: February 2008

A finite element modeling is developed to simulate and visualize the discontinuous chip formation in the orthogonal cutting of 60 percent Cu-40 percent Zn brasses. A ductile fracture criterion expressed as a function of strain, strain rate and hydrostatic pressure is applied to the crack growth from the tool tip to the chip free surface in the segmentation of discontinuous chips. Chip shape and the inclination of fracture surface produced in computational machining are in good agreement with those in actual machining. The visualization of the computational machining processes clarifies the mechanism of discontinuous chip formation. The influences of chip segmentation upon the residual stress and strain in the machined layer are also clarified quantitatively.
Influence of Process Parameters on the Ironing of Deep-Drawn Cups
Authors: Chang Der-Form , Wang Jyhwen E.
Published: February 2008

An analytical model for the ironing of deep-drawn cups is developed using the slab method. Inhomogeneous deformation of the drawn cup is taken into consideration. Elastic recovery after a cup being ironed is also modeled. Predictions on punch load and frictional force at the punch-cup interface show excellent agreements with experimental measurements. Influence of die semi-angle, ironing reduction ratio and friction on the process is investigated. With this model, new process parameters for ironing can be designed and analyzed before actual die tryout.
Higher-Order Approximation in Accuracy Computations of Machine Tools and Robots
Authors: Portman V. T. , Weill R. D. , Shuster V. G.
Published: February 2008

Second and higher-order approximations for machine accuracy calculations are necessary when the precision of the error estimation obtained on the basis of the first order approximations is poor or when first order approximations are not influencing the output accuracy of the machine. This latter case is widely present in the calculations of the functional accuracy of machines, in particular when estimating the machine tool set-up errors or when calculating the influence of machine setting displacements. In the case of machining operations, the second order approximation for the normal position error of the real surface relative to the nominal one is shown to depend on the second fundamental form of the nominal surface. As a real world application, the setting of a grinding machine for a crowned conic surface grinding operation is calculated.
Principal Curvature Alignment Technique for Machining Complex Surfaces
Authors: Bedi S. , Gravelle S. , Chen Y. H.
Published: February 2008

Machining complex three dimensional surfaces is a challenging task. This paper presents two methods of machining these surfaces on a 4 and 5 axis machine, using a toroidal shaped cutter. The methods propose to align the principal axis of curvature of the machining surface with that of the machined surface in order to increase the volume of material removed. The increase in material removal at a point reduces the scallop height. Thus, fewer passes are required to achieve the same surface finish.
Life-Cycle Planning of Cutting Fluids—A Review
Authors: Sheng P. S. , Oberwalleney S.
Published: February 2008

With the recent emergence of environmental management standards and regulations for metalworking industries, effective management of cutting fluids in machining facilities has become an issue of increased significance. This paper reviews the basic components, performance and health effects, and post-processing options for nonwater-miscible and water-mixed cutting fluids currently practiced. The basic components of non-water-miscible and water-mixed fluids are introduced. Time-based degradation mechanisms for cutting fluid performance including liquid contamination, solid contamination, acidity/alkalinity, corrosion resistance, emulsion stability and bacteriological effects are examined. These degradation mechanisms are related to possible human health effects. Recycling effectiveness for different techniques such as sedimentation, magnetic separation, skimming, barrier filtration and centrifugation are also examined. Disposal pre-treatment options for cutting fluids are discussed. Finally, three case examples of cutting fluid management at a research facility, automotive supplier and grinding shop are presented.
Milestone Developments in Welding and Joining Processes
Authors: Kannatey-Asibu E.
Published: February 2008

Welding, like other major manufacturing processes such as casting, metal forming, and material removal, has its roots in ancient times, though not necessarily in the various forms as we know them today. It therefore has a long history, with thousands of articles having been published on various aspects of the welding process over the years. However, there have been periodic reviews of the literature in the past, that summarize significant developments in the field. Thus, due to constraints on page limit, and to avoid unnecessary repetition of what is already well reviewed in the literature, this article will reference the key literature reviews on the subject, providing brief summaries where appropriate. The bulk of the article will then be devoted to more recent developments in the field. Due to the breadth of material to be covered, this review is designed to be more of a summary of key developments rather than a critique of a specific field.
Effect of Intermittent Contact on the Stability of Thermoelastic
Sliding Contact
Authors: Ruiz Ayala Jose R. , Lee Kwangjin , Rahman Mujibur , Barber J. R.
Published: February 2008

In many sliding systems, the sliding surfaces are not coextensive, so that points on one surface experience alternating periods of contact and separation. This intermittent process can be expected to influence the sliding speed at which the system is susceptible to frictionally-induced thermoelastic instability (TEI). This question is explored in the context of a simple system consisting of a rotating thin-walled cylinder whose end face slides against a rigid surface. The results show that at low Fourier number—i.e., when the frequency of the process is high compared with the thermal transient of the system—only the time-averaged frictional heat input is important and the critical speed is an inverse linear function of the proportion of time in sliding contact. At higher Fourier number, lower critical speeds are obtained, but the dependence on Fourier number is relatively weak.
Finite Element Modeling of Engagement of Rough and Grooved Wet
Clutches
Authors: Berger E. J. , Sadeghi F. , Krousgrill C. M.
Published: February 2008

A finite element model has been developed to investigate the engagement of rough, grooved, paper-based permeable wet clutches. The finite element (Galerkin) approach was used to discretize the modified Reynolds and force balance equations, and the solution domain geometry was described using an isoparametric formulation. Surface roughness effects were modeled via the Patir and Cheng (1978) average flow model, while asperity load sharing was calculated using the Greenwood and Williamson (1966) approach. The finite element model developed, was used to investigate the effects of applied load, friction material permeability, and groove size on the engagement characteristics of wet clutches (i.e., torque, pressure, engagement time, and film thickness). The results indicate that the applied load, friction material permeability, and groove width significantly influence the engagement characteristics. Higher facing pressures increase peak torque and decrease engagement time. Higher permeability of the friction material significantly decreases engagement time but dramatically increases peak torque. Wider grooves decrease the peak torque and increase the engagement time. Groove depth does not significantly affect engagement characteristics for this model.
Rolling/Sliding of a Vibrating Elastic Body on an Elastic
Substrate
Authors: Spector A. A. , Batra R. C.
Published: February 2008

The rolling/sliding in the presence of friction of a vibrating elastic body on an elastic substrate is studied. It is shown that the longitudinal components of the velocity of the center of mass of the body and of the resultant frictional force are not affected by the vibration process. However, the normal vibration of the body influences the slip velocities and the distribution of frictional forces. For the problem of a harmonically oscillating long cylinder rolling/sliding on the flat surface of an elastic substrate, the time histories of the width of the contact zone and the length of adhesion subzone are computed. It is shown that the local frictional forces and slip velocities oscillate, and that the set of admissible values of the external frictional forces and moments providing the rolling/sliding regime is smaller under conditions of normal vibrations than that when the cylinder does not vibrate.
Numerical Analysis of the Influence of Waviness on the Film Thickness
of a Circular EHL Contact
Authors: Venner C. H. , Lubrecht A. A.
Published: February 2008

Surface roughness and/or surface imperfections are well known to significantly affect the performance of concentrated contacts. Any deviation from the smooth surface will act as a stress raiser for itself (bump) or of its neighborhood (dent), and will therefore reduce the fatigue life of the component it is part of. These imperfections can also act as initiation sites of other types of contact failure such as scuffing, when contact conditions such as load, speed and film thickness become more and more severe. With the help of increasing computer speeds and more efficient numerical techniques, a theoretical analysis of the failure of concentrated contacts becomes possible. The full answer will involve many aspects of the contact, including the generation of heat, thermal response of the lubricant and solids, non-Newtonian as well as surface chemistry effects. This paper concentrates on the way the lubricant film thickness is affected by waviness and tries to identify the locations and the conditions where the film thickness is minimal. The lubrication of nonsmooth surfaces is a transient two-dimensional problem, which will be treated without any geometrical simplification. More precisely, this paper focuses on the influence of rolling speed and the slide-to-roll ratio on the film thickness separating a smooth surface and one with transverse waviness.
A Global Approach of Thermal Effects Including Pad Deformations in
Tilting-Pad Journal Bearings Submitted to Unbalance Load
Authors: Fillon M. , Desbordes H. , Frêne J. , Chan Hew Wai C.
Published: February 2008

The purpose of this paper is to study the response of a tilting-pad journal bearing submitted to an unbalance load. A pseudo-time transient analysis has been developed taking into account the effective viscosity of the lubricant, the thermal expansion of bearing elements, and the elastic pad deformations. At each time interval, and for each pad, an effective temperature of the film is deduced from an energy balance. First, a comparison between theoretical results and experimental data is presented for a four-shoe tilting-pad journal bearing subjected to a static load. Second, the influence of the thermal and pad flexibility effects on the journal center orbit, on the minimum film thickness and on the maximum pressure is studied for various unbalance loads. Both the viscosity variation and the operating clearances due to elastic and thermal deformations of the bearing elements have a great influence on the behavior of the bearing.
Turbulent Flow, Flexure-Pivot Hybrid Bearings for Cryogenic
Applications
Authors: San Andres Luis
Published: February 2008

The thermal analysis of flexure-pivot tilting-pad hybrid (combination hydrostatic-hydrodynamic) bearings for cryogenic turbopumps is presented. The advantages of this type of bearing for high speed operation are discussed. Turbulent bulk-flow, variable properties, momentum and energy transport equations of motion govern the flow in the bearing pads. Zeroth-order equations for the flow field at a journal equilibrium position render the bearing flow rate, load capacity, drag torque, and temperature rise. First-order equations for perturbed flow fields due to small amplitude journal motions provide rotordynamic force coefficients. A method to determine the tilting-pad moment coefficients from the force displacement coefficients is outlined. Numerical predictions correlate well with experimental measurements for tilting-pad hydrodynamic bearings. The design of a liquid oxygen, flexure-pad hybrid bearing shows a reduced whirl frequency ratio and without loss in load capacity or reduction in direct stiffness and damping coefficients.
Thermohydrodynamic Analysis of Tilting-Pad Journal Bearings Operating
in Turbulent Flow Regime
Authors: Bouard L. , Fillon M. , Frêne J.
Published: February 2008

A thermohydrodynamic analysis of tilting-pad bearing in turbulent flow regime is presented. Two tilting-pad journal bearings are studied. A local analysis of thermal turbulent phenomena is shown. The theoretical prediction of the maximum temperature decreases when the flow regime becomes nonlaminar and the decrease corresponding to higher power losses is explained using the velocity component profiles and the local heat flux in the film.
The Oscillating Fluid Mechanics Method (OFMM) for Studying Oil Film
Oscillation and Dynamic Characteristics of Journal Bearings
Authors: Zuoyi Chen , Yongzhong Sun
Published: February 2008

A new method to study oil film oscillation and to determine the unstable rotational speed and rotordynamic coefficients of bearings is presented. Differences between the new method called the Oscillating Fluid Mechanics Method (OFMM) and the previous method (quasi-steady state method) are discussed. Insufficiencies of the previous method are analyzed. The theory and calculational procedure of OFMM are given. Calculated results show that this new method provides significantly improved predictions.
Ball Bearing Dynamic Analysis Using Computer Methods—Part I:
Analysis
Authors: Meeks Crawford R. , Tran Long
Published: February 2008

An analytical ball bearing dynamics model was developed that rigorously models all of the significant kinematic, structural, and dynamic effects. The model can analyze bearings of any material combination for the races, balls and ball cage. This model analyzes the stresses and deflections of the loaded elements due to (1) preload, (2) external axial, radial and moment loads, (3) centrifugal and gyroscopic ball loads. A rigorous six-degree-of-freedom model of ball cage motions was developed to analyze ball and cage dynamics. The ball cage equations of motion were written in a rotating coordinate system, which greatly simplifies the equations, resulting in a highly efficient, but rigorous, model of bearing dynamics. A computer program was developed, incorporating the algorithms, to solve the multiple simultaneous quasi-static ball-to-race load equations using modified Newton-Raphson methods. The Lawrence Livermore Ode package (LSODA) is employed for numerical integration of the dynamic equations of motion. This method assures convergence, while controlling the accuracy of the calculations as a function of computer run time and automatically selects the appropriate integration method for stiff and non-stiff system of ODE. The program analyzes ball and cage motions in time domain, wear life, fatigue life, lubricant film effects, ball-to-cage forces, torque noise and many other bearing parameters.
The Effects of Surface Texture on EHL Point Contacts
Authors: Ai Xiaolan , Cheng Herbert S.
Published: February 2008

The effect of surface texture on EHL point contact is studied numerically by using the multigrid method. Numerical simulations have been performed for waviness and random roughness with three different orientations, transverse, oblique and longitudinal. Results reveal a strong domination of unidirectional Couette flow in the EHL conjunction. The geometrical variations at inlet of the contact are transported downstream throughout the EHL conjunction. As a consequence, the oblique surface roughness striations are largely distorted, forming nearly longitudinal wavy passages. Results show that the oblique roughness induces local three dimensional EHL pressure fluctuations. The maximum pressure is higher than that of the transverse roughness. For sinusoidal waviness, oblique orientation gives the smallest minimum film thickness as compared with those of longitudinal and transverse waviness.
The Characteristics of Elastically Contacting Ideal Rough
Surfaces
Authors: Yongsheng Leng , Guiping Yang , Yan Huang , Linqing Zheng
Published: February 2008

The analysis of the elastic contact of ideal rough surfaces is presented in this paper. The rough asperities are assumed to be spherical with the same vertical height and spatial distance. The mutual influence of asperities is considered. Numerical results show that for the same load, the contact area is less than the Hertzian prediction, while the pressure distribution is still of a Hertzian type, but is increased to some extent. We find that the asperity interaction is associated with a parameter, called the “loading level,” which combines the surface texture, mechanical properties, and the nominal mean pressure. Of significant importance is the discovery of the variation of the reference plane position with the contact load. In the classical theory of rough contact (Greenwood and Williamson, 1966), the reference plane was in fact assumed to be in the mean line position. We prove that the location of the reference plane is determined by the number of contacting asperities and the loading level, thus making the analysis of the contact of rough surfaces somewhat complex.
Side-Pull and Stiffness of Magnetic Bearing Radial Flux Return
Paths
Authors: Knospe C. R. , Stephens L. S.
Published: February 2008

Certain magnetic bearing designs, both radial and axial, contain a cylindrical radial flux return path. The magnetic flux in this path produces a radial negative stiffness and, if the journal is displaced, a side-pull force. In this paper, closed-form solutions are found for both of these properties by determining the magnetomotive force in the eccentric gap. This is achieved by solving the Dirichlet boundary value problem in the eccentric annulus. A conformal transformation to bipolar coordinates is utilized which results in a much simpler boundary value problem than if the physical coordinates are used. An example problem is presented which indicates the significance of these two properties.
The Synthesis of Planar RR and Spatial CC Chains and the Equation of a Triangle
Authors: McCarthy J. M.
Published: February 2008

This paper formulates the planar and spatial versions of an equation that determines one vertex of a triangle in terms of the other two vertices and their interior angles. The fact that a slight modification of Sandor and Erdman’s standard form equation for the design of RR chains yields this planar triangle equation is the basis for identifying the equivalent equation for a spatial triangle as the standard form equation for CC chains. The simultaneous solution of two of the planar equations yields an analytical expression of Burmester’s relationship between the fixed pivot of an RR chain and the relative position poles of its floating link. A similar solution of simultaneous spatial triangle equations yields Roth’s generalization of this insight, specifically, the fixed axis of a CC chain views two relative screw axes in one-half the dual crank rotation angle. These results provide the foundation for generalizing planar linkage synthesis techniques based on complex numbers to the synthesis of spatial linkages.
Terrain Adaptive Vehicles
Authors: Waldron K. J.
Published: February 2008

Research on walking vehicles and variable configuration wheeled vehicles is reviewed. The central feature of the vehicles discussed is terrain adaptive capability. The principal elements of the technical problems of coordination and control are discussed for each vehicle type. Examples of each vehicle type are discussed and an extensive reference list is provided. Although the article is primarily a review article, it contains a new discussion of the coordination problem of robotic mechanisms.
Knowledge-Based Systems for Design
Authors: Dixon J. R.
Published: February 2008

Knowledge-based systems are a special class of computer programs that purport to perform, or to assist humans in performing, specified intellectual tasks. This paper describes how knowledge-based programs are special; that is, how they differ from other computer programs. A structure for understanding the use of knowledge-based programs in engineering design is presented, together with an example. The role of knowledge-based systems in design research is discussed.
Applied Theory of Gearing: State of the Art
Authors: Litvin F. L.
Published: February 2008

The contents of the paper cover: a brief history of some concepts of the theory of gearing, and new developments in this area, (i) theory of enveloping curves and surfaces, (ii) simulation of meshing and contact of gear tooth surfaces, (iii) basic kinematic relations as the key to the determination of direct relations between the curvatures of contacting surfaces, and avoidance of singularities, (iv) transfer from line contact of tooth surfaces to point contact, and (v) design and manufacturing of gears with compensated transmission errors caused by misalignment.
Optimum Design and Control of Active Constrained Layer Damping
Authors: Baz A. , Ro J.
Published: February 2008

Conventional Passive Constrained Layer Damping (PCLD) treatments with viscoelastic cores are provided with built-in sensing and actuation capabilities to actively control and enhance their vibration damping characteristics. The design parameters and control gains of the resulting Active Constrained Layer Damping (ACLD) treatments are optimally selected, in this paper, for fully-treated beams using rational design procedures. The optimal thickness and shear modulus of the passive visco-elastic core are determined first to maximize the modal damping ratios and minimize the total weight of the damping treatment. The control gains of the ACLD are then selected using optimal control theory to minimize a weighted sum of the vibrational and control energies. The theoretical performance of beams treated with the optimally selected ACLD treatment is determined at different excitation frequencies and operating temperatures. Comparisons are made with the performance of beams treated with optimal PCLD treatments and untreated beams which are controlled only by conventional Active Controllers (AC). The results obtained emphasize the potential of the optimally designed ACLD as an effective means for providing broad-band attenuation capabilities over wide range or operating temperatures as compared to PCLD treatments.
Lyapunov Stability, Semistability, and Asymptotic Stability of Matrix Second-Order Systems
Authors: Bernstein D. S. , Bhat S. P.
Published: February 2008

Necessary and sufficient conditions for Lyapunov stability, semistability and asymptotic stability of matrix second-order systems are given in terms of the coefficient matrices. Necessary and sufficient conditions for Lyapunov stability and instability in the absence of viscous damping are also given. These are used to derive several known stability and instability criteria as well as a few new ones. In addition, examples are given to illustrate the stability conditions.
Eddy Current Effects on the Design of Rotor-Magnetic Bearing Systems
Authors: Kim C. , Palazzolo A. B. , Kascak A. , Brown G.
Published: February 2008

The recent growth of magnetic bearing applications in the chemical, utility and aerospace industries requires more accurate design tools to insure reliable and effective operation as components of the overall rotor bearing system. This paper provides a novel approach for simulating a flexible rotor suspended in magnetic bearings, accounting for eddy current effects. The manuscript discusses some magnetic bearing fundamentals, leading up to the new methods for modeling. Test results show very good correlation with theory and confirm the importance of considering eddy current effects. Surface conductivity and frequency dependent permeability effects on the B field in the magnet gaps are shown to be very significant on overall system stability. The results in the manuscript should be very useful to the design or test rotor dynamicist.
Active and Semi-Active Vibration Isolation
Authors: Karnopp D.
Published: February 2008

In the five decades since the founding of the ASME Design Engineering Division, the important problem of vibration isolation has been attacked first through the design of passive spring-damper suspensions and later by the use of active and semi-active elements. This paper reviews the historical development of theoretical concepts necessary for the design of isolation systems and indicates how control theory began to influence vibration isolation in the last half of this period. Practical active and semi-active suspensions have only recently become possible with the advent of powerful but relatively inexpensive signal processors. To illustrate these developments for engineers who have not been intimately involved with active systems, only simple vibrational system models will be discussed, although some modern hardware will be shown which is now being applied to complex systems. Instead of attempting to review the many theoretical concepts which have been proposed for active systems, this article will focus on a relatively simple idea with which the author has been associated over the past thirty years; namely the “skyhook” damper. This idea came through purely theoretical studies but is now used in combination with other concepts in production suspension systems. Two quite different application areas will be discussed. The first involves stable platforms to provide extreme isolation for delicate manufacturing operations against seismic inputs and the second involves automotive suspensions. Although similar concepts are found in these two application areas, the widely varying requirements result in very different suspension hardware. The special case of the semi-active damper, which requires very little control power and is presently reaching production, will also be discussed.
Decomposition and Representation Methods in Mechanical Design
Authors: Kusiak A. , Larson N.
Published: February 2008

The broad interest in concurrent engineering has inspired research in the area of decomposition in mechanical design. Much of the research reported in the literature falls into one of three categories: (1) product decomposition, (2) problem decomposition, or (3) process decomposition. This paper provides a detailed discussion of the typology of decomposition in mechanical design. Related work is described and examples are provided to illustrate the need for decomposition of products, problems, and processes in design. Representation techniques and methodologies for decomposition are outlined. Finally, future research issues in decomposition in mechanical design are identified.