bluuebunny/crossref_metadata_2025 huggingface dataset:
Load Distribution of Metal Timing Belts
Authors: Zhang Weiming , Koyama Tomio
Published: July 2002

Metal timing belt (perforation metal belt) is a new element of mechanical transmission and its application is increasing in many fields of industry in recent years. However, there has been almost no research on metal timing belt, especially its strength. In this paper, as a basic study on the strength of the metal timing belt, the distribution of the belt tension and the tooth load in metal timing belts is theoretically analyzed under the assumption that the belt pitch equals the pulley pitch. The tension distribution and the load distribution are the most important factors that influence the strength of the metal timing belt, similar to the traditional rubber timing belt which has been researched in detail by one of authors. Also experiments measuring the tension distribution have been carried out. Measured results agree well with calculations.
Bending and Extension of Thin-Walled Composite Beams of Open Cross-Sectional Geometry
Authors: Rand O.
Published: July 2002

A theoretical model for bending and extension of composite beams of open thin-walled geometry is devised. The model is based on a detailed description of the out-of-plane warping and may handle generic open cross-sectional geometries and arbitrary layup configurations. In view of the potential of composite beams to produce useful structural couplings, the analysis is focused on the ability to predict the coupling mechanisms, and draw lines of similarities and differences between such beams and similar thin-walled beams of closed cross sections. [S0021-8936(00)01204-6]
Study of Wet Friction Material Test Under Severe Thermal and Mechanical Loading (“Bump Test”)
Authors: Zhao Wenping , Zagrodzki Przemyslaw
Published: July 2002

One of the fatigue tests used for friction materials is the so called “bump test”. In this test, one of the reaction disks in a pack of disks has machined bumps across the contact surface. These bumps generate locally high contact pressure and temperature. In this way, severe contact conditions like that arising in service can be reproduced. The major difficulty in utilizing the “bump test” is estimation of the local pressure and temperature. In this paper, a model is developed and experimental verification of thermoelastic contact is presented. The model represents a multi-surface contact problem for a pack of disks. Due to the presence of bumps, contact surfaces are not conforming. To solve this strongly nonlinear contact problem, a robust finite element code is used. The model also includes thermal effects generated by frictional heating. The coupled elastic contact and thermal problems are solved sequentially. Contact pressure at interfaces is measured in static conditions (without sliding) using pressure sensitive film. Good agreement between the model and the measurement is observed in sense of contact length and magnitude of pressure. In order to verify the full thermoelastic model, the transient temperature inside one of the disks is measured by thermocouples. The results agree with model predictions. The study shows that the local contact pressure is an order of magnitude higher than nominal pressure. Also temperatures are much higher than that predicted for uniform contact conditions. The developed model helps to understand complex thermoelastic effects accompanying the test and to control the test parameters.
Thickness Deformation of Constrained Layer Damping: An Experimental and Theoretical Evaluation
Authors: Huang Peter Y. H. , Reinhall Per G. , Shen I. Y. , Yellin Jessica M.
Published: July 2002

This paper presents a study of thickness deformation of the viscoelastic material in constrained layer damping (CLD) treatments. The first goal of the study is to demonstrate the feasibility of using direct measurement to investigate thickness deformation in CLD treatments. The experimental setup consisted of a constrained layer beam cantilevered to a shaker, an accelerometer mounted at the cantilevered end, and two laser vibrometers that simultaneously measured the responses of the base beam and the constraining layer, respectively, at the free end. A spectrum analyzer calculated frequency response functions (FRFs) between the accelerometer inputs and the vibrometer outputs. Measured FRFs of the base beam and the constraining layer were compared to detect thickness deformation. Experimental results showed that direct measurements can detect thickness deformation as low as 0.5 percent. The second goal is to evaluate the accuracy of a mathematical model developed by Miles and Reinhall [7] that accounts for thickness deformation. FRFs were calculated by using the method of distributed transfer functions by Yang and Tan [13]. Comparison of the numerical results with the experimental measurements indicated that consideration of thickness deformation can improve the accuracy of existing constrained layer damping models when the viscoelastic layer is thick.
Reduced-Order Nonlinear Dynamic Model of Coupled Shaft-Torsional and Blade-Bending Vibrations in Rotors
Authors: Al-Bedoor B. O.
Published: July 2002

In this study, a reduced-order nonlinear dynamic model for shaft-disk-blade unit is developed. The multibody dynamic approach with the small deformation theory for both blade-bending and shaft-torsional deformations is adopted. The equations of motion are developed using Lagrange’s equation in conjunction with the assumed modes method (AMM) for approximating the blade transverse deflection. The model showed strong coupling between the blade bending and shaft torsional vibrations in the form of inertial nonlinearity, modal coupling, stiffening, softening, and parametric excitations. The model is suitable for extensive parametric studies for predesign stage purposes as well as for diagnostics of rotor malfunctions, when blade and shaft torsional vibration interaction is suspected.
Temperature Measurements in a Heavy Duty Gas Turbine Using Radiation Thermometry Technique: Error Evaluation
Authors: De Lucia M. , De Sabato R. , Nava P. , Cioncolini S.
Published: July 2002

This paper describes a technique for the analysis of temperature measurement data obtained by using a radiation thermometer in a heavy duty gas turbine (PGT2 from Nuovo Pignone GE). The main sources of error are shown and analyzed and their influence on measurements and techniques used to correct data read. Success in significant error elimination in acquisition results in a more realistic and correct description of target temperature distribution
Precision Laser Deburring and Acoustic Emission Feedback
Authors: Lee Seoung Hwan , Dornfeld David A.
Published: July 2002

Sensor feedback for process control is one of the essential elements in an automated deburring procedure. This paper presents the implementation of acoustic emission (AE), which has been developed as a feedback sensing technique for precision (mechanical) deburring, in a precision laser deburring process. AE signals were sampled during laser machining/deburring under various experimental conditions and analyzed using several signal processing methods including AE rms and spectral analysis. The results, such as the sensitivity of AE signals to different laser cutting depths, edge detection capability and the frequency analysis show a clear correlation between physical process parameters and the AE signals. A subsequent control strategy for deburring automation is also briefly discussed.
Neural Networks Based Active Vibration Control of Flexible Linkage Mechanisms
Authors: Song Y. M. , Zhang C. , Yu Y. Q.
Published: July 2002

An investigation is presented into the neural networks based active vibration control of flexible linkage mechanisms. A smart mechanism featuring piezoceramic actuators and strain gauge sensors is designed. A nonlinear adaptive control strategy named Neural Networks based Direct Self-Tuning Control (NNBDSC) is employed to suppress the elastodynamic responses of the smart mechanism. To improve the initial robustness of the NNBDSC, the Dynamic Recurrent Neural Network (DRNN) controllers are designed off-line to approximate the inverse dynamics of the smart mechanism. Through on-line control, the strain crest of the flexible link is reduced 60 percent or so and the dynamic performance of the smart mechanism is improved significantly.
Simple Shear Testing of Parallel-Fibered Planar Soft Tissues
Authors: Gardiner John C. , Weiss Jeffrey A.
Published: July 2002

The simple shear test may provide unique information regarding the material response of parallel-fibered soft tissues because it allows the elimination of the dominant fiber material response from the overall stresses. However, inhomogeneities in the strain field due to clamping and free edge effects have not been documented. The finite element method was used to study finite simple shear of simulated ligament material parallel to the fiber direction. The effects of aspect ratio, clamping prestrain, and bulk modulus were assessed using a transversely isotropic, hyperelastic material model. For certain geometries, there was a central area of uniform strain. An aspect ratio of 1:2 for the fiber to cross-fiber directions provided the largest region of uniform strain. The deformation was nearly isochoric for all bulk moduli indicating this test may be useful for isolating solid viscoelasticity from interstitial flow effects. Results suggest this test can be used to characterize the matrix properties for the type of materials examined in this study, and that planar measurements will suffice to characterize the strain. The test configuration may be useful for the study of matrix, fiber-matrix, and fiber-fiber material response in other types of parallel-fibered transversely isotropic soft tissues.
A Microcontact Approach for Ultrasonic Wire Bonding in Microelectronics
Authors: Jeng Yeau-Ren , Horng Jeng-Haur
Published: July 2002

Wire bonding is a popular joining technique in microelectronic interconnect. In this study, the effects of applied load, surface roughness, welding power and welding time on bonding strength were investigated using an ultrasonic bonding machine and a pull tester. In order to relate bonding strength to contact phenomena, the asperity model was used to compute real contact area and flash temperature between the wire and the pad. The experimental results show that a decrease in load or ultrasonic power produces a larger weldable range in which the combination of operation parameters allow the wire and pad to be welded. Regardless of roughness and applied loads, the bond strength increases to a maximum with increases in the welding time, and then decreases to fracture between wire and pad. The theoretical results and experimental observations indicate that bond strength curves can be divided into three periods. The contact temperature plays an important role in bonding strength in the initial period, and surface roughness is the dominant factor in the final period. The maximum bonding strength point occurs in the initial period for different loads and surface roughness values. Our results show that bond strength of ultrasonic wire bonding can be explained based on the input energy per real contact area.
Near-Net-Shape Forming of Ceramic Powder Under Cold Combination Pressing and Pressureless Sintering
Authors: Kim H. G. , Lee H. M. , Kim K. T.
Published: July 2002

Near-net-shape forming of zirconia powder was investigated under the combination of cold die and isostatic pressing and pressureless sintering. A combination pressing technique, i.e., die compaction under cold isostatic pressing, allowed the forming of a complex shaped ceramic powder body with better dimensional control than that achieved by cold isostatic pressing and more uniform density distribution than that by die pressing. The constitutive models proposed by Kim and co-workers were implemented into a finite element program (ABAQUS) to simulate densification of ceramic powder under cold compaction and pressureless sintering. Finite element calculations were compared with experimental data for density distribution and deformation of zirconia powder compacts under cold combination pressing and pressureless sintering. Finite element results agreed well with experimental data.
Precision Temperature Control of High-Throughput Fluid Flows: Theoretical and Experimental Analysis
Authors: Lawton Kevin M. , Patterson Steven R. , Keanini Russell G.
Published: July 2002

A precision method for attenuating temperature variations in a high-throughput control fluid stream is described and analyzed. In contrast to earlier investigations, the present study emphasizes heat transfer analysis of the constituent control device and derives theoretical descriptions of system responses to time-varying fluid temperatures. Experiments demonstrate that the technique provides: (1) frequency-dependent attenuation which is several orders of magnitude greater than that obtained via a perfect mixing volume; (2) attenuation, over two decades of disturbance frequency, that reduces in-flow temperature variations by factors ranging from 10 to ≈104; (3) asymptotic attenuation greater than three orders of magnitude for spectral components having periods less than the device thermal equilibrium time; and (4) attenuation which is fully consistent with theoretical predictions. The model developed provides design criteria for tailoring system performance. In particular, it is shown that for a given control stream flow rate, the magnitude of maximal attenuation can be adjusted by varying the thermal resistance between the flow and attenuating medium, while the range of frequencies maximally attenuated can be adjusted by varying the product of thermal resistance and attenuating medium heat capacity. The analysis and design are general and should prove useful in the design and analysis of other high-throughput precision temperature control systems.
Effect of Environmental Phase Characteristics on the Discharge of a Thermal Storage System
Authors: Hall Carsie A. , Mackie Calvin , Perkins Judy A.
Published: July 2002

The discharge of a thermal energy storage system, which is modeled as a one-dimensional slab of pure, molten material, is investigated semi-analytically. With the molten material initially at its fusion temperature, double-sided freezing is induced from convective and radiative cooling on one side, and convective cooling on the other, resulting in two coalescing freeze fronts. The effects of cyclic solar flux, cyclic sky temperature, and cyclic fluid temperature on the freeze front progression of one side of the slab and freeze time for entire slab are examined. On applying the quasi-steady approximation for the temperature distribution in each developing solid region, a pseudo-transcendental equation for the temperature of the surface exposed to convection and radiation is derived and solved at discrete time intervals by the Newton-Raphson method. Excellent agreement is obtained with previously published results for freezing caused by convective and radiative cooling only on one side, while the other side remains adiabatic. It is shown that low frequency (high period) cycling of the sky and fluid one temperatures increase the freeze time up to greater than 40% when the solar flux profile is constant or non-cyclic and when surface radiative heat loss is neglected.
A New Mechanism Explaining High Frequency Chatter Vibration Involving Tool Tip X-Y Looping in Fine Boring
Authors: Edhi Evita , Hoshi Tetsutaro
Published: July 2002

Chatter occurring at more than 10,000 Hz frequency was found in fine boring operation, and causing reduced tool life. To identify the mechanism for the onset of high frequency chatter, cutting tests and structural dynamics examination of the boring tool have been performed. Experimental study has revealed that the regenerative effect, the penetration effect, and the X-Y looping of the tool tip are three relevant characteristics in the onset of the chatter. Those findings are included in a new chatter model of which validity is evaluated by computational analysis of energy supplied and dissipated in the vibrating system.
Enhancing Small-Channel Convective Boiling Performance Using a Microporous Surface Coating
Authors: Ammerman C. N. , You S. M.
Published: July 2002

Performance characteristics are experimentally determined for enhanced convective boiling of FC-87 in a horizontal, small-cross-sectional-area, single-channel heater. The channel tested has a square cross section with a side length of 2 mm and a heated length of 8 cm. The heated surface of the channel is tested both with, and without, a microporous surface coating. Although few studies have been performed to quantify the effects of internal porous coatings on flow boiling, their application in this area is promising. The coating is shown to provide increases in both heat transfer coefficient and critical heat flux. Convective boiling curves are generated for mass fluxes from 500 to 5000 kg/m2s and for inlet subcooling levels ranging from 2 to 31°C.
Total Strain Fields of the Antero-Inferior Shoulder Capsule Under Subluxation: A Stereoradiogrammetric Study
Authors: Malicky David M. , Soslowsky Louis J. , Kuhn John E. , Bey Michael J. , Mouro Cameron M. , Raz Jonathan A. , Liu Changying A.
Published: July 2002

The antero-inferior capsule (AIC) is the primary restraint to antero-inferior glenohumeral dislocation. This study utilizes a biomechanical model to determine the total strain field of the AIC in a subluxed shoulder. Strains were calculated from two capsule states: a nominal strain state set by inflation and a strained state set by subluxation. Marker coordinates on the AIC were reconstructed from stereoradiographs and strain fields calculated. Peak strain on the glenoid side of the AIC was significantly greater than the humeral side and strain fields were highly variable. This study reports an accurate method for measuring planar strains in a three-dimensional membrane.
Effective Models for Prediction of Springback In Flanging
Authors: Song Nan , Qian Dong , Cao Jian , Liu Wing Kam , Li Shaofan
Published: July 2002

A study on the prediction of springback angle is presented, with focus on the straight flanging operation. The objective of this work is to evaluate the reliability of different methods of prediction. An experiment of straight flanging operation is conducted. Major prediction approaches such as analytical model, numerical simulation using the Finite Element Method (FEM) and the Meshfree Method using the Reproducing Kernel Particle Methods (RKPM) are discussed. A set of sample problems is computed and comparisons are made with the experiment. The numerical analysis shows that the prediction from the 3D meshfree contact code matches well with the data from the FEM 2D solid model. A material property described by the kinematic hardening law provides a better prediction of springback than the isotropic hardening law.
Wake–Wake Interaction and Its Potential for Clocking in a Transonic High-Pressure Turbine
Authors: Hummel Frank
Published: July 2002

Two-dimensional unsteady Navier–Stokes calculations of a transonic single-stage high-pressure turbine were carried out with emphasis on the flow field behind the rotor. Detailed validation of the numerical procedure with experimental data showed excellent agreement in both time-averaged and time-resolved flow quantities. The numerical timestep as well as the grid resolution allowed the prediction of the Ka´rma´n vortex streets of both stator and rotor. Therefore, the influence of the vorticity shed from the stator on the vortex street of the rotor is detectable. It was found that certain vortices in the rotor wake are enhanced while others are diminished by passing stator wake segments. A schematic of this process is presented. In the relative frame of reference, the rotor is operating in a transonic flow field with shocks at the suction side trailing edge. These shocks interact with both rotor and stator wakes. It was found that a shock modulation occurs in time and space due to the stator wake passing. In the absolute frame of reference behind the rotor, a 50-percent variation in shock strength is observed according to the circumferential or clocking position. Furthermore, a substantial weakening of the rotor suction side trailing edge shock in flow direction is detected in an unsteady flow simulation when compared to a steady-state calculation, which is caused by convection of upstream stator wake segments. The physics of the aforementioned unsteady phenomena as well as their influence on design are discussed.
Kinematic Clearance Sensitivity Analysis of Spatial Structures With Revolute Joints (*)
Authors: Innocenti Carlo
Published: July 2002

The paper presents a new method to assess the influence of joint clearances in spatial structures that are composed of links connected by revolute joints. The method allows assessment of the amount by which joint clearances affect the rigid-body position of a generic link of the structure when an external load is exerted on the link. Unlike other procedures, the proposed method relies on the clearance-free idealization of the structure under investigation. An example shows application of the proposed method to the analysis of the structure derived from a multi-loop manipulator by freezing its actuators.
Compressor Discharge Brush Seal for Gas Turbine Model 7EA
Authors: Ingistov Steve
Published: July 2002

Single-shaft, heavy-duty industrial gas turbines are extremely sensitive to compressed air bypassing at compressor discharge plane. This plane represents the highest pressure location in entire gas turbine unit (GTU). Standard method to minimize compressed air leakage is labyrinth seal that is integral part of the cylindrical element here called "inner barrel." The inner barrel is also the part of compressor discharge diffuser. This paper describes the efforts related to conversion of standard labyrinth seal into the hybrid seal that is combination of labyrinth and brush seals.
Vortex Dynamics of the Stator Wake-Rotor Cascade Interaction
Authors: Swirydczuk Jerzy
Published: July 2002

The behavior of turbine stator wakes moving with the flow through a rotor cascade is studied. The stator wake is modeled as a series of active vortices forming part of a von Karman vortex street, the motion of which is determined with the aid of the vortex dynamics theory. The study has recognized basic mechanisms and patterns of the wake-cascade interaction. In particular, it revealed that the course of the interaction depends on initial distribution of the vortices in the wake when it approaches the rotor cascade.
Design for Fixturability (DFF) Methodology for Commodity Parts: A Case Study With Connecting Rod Designs
Authors: Qureshi Khurshid A. , Saitou Kazuhiro
Published: July 2002

This paper presents a methodology called ‘Design for Fixturability’ (DFF). This methodology enables designers to perform manufacturability analysis of their product designs upfront into the design process. The DFF approach provides a mapping between parametric representation of a part design and fixturing capability of a facility and presents a methodology to evaluate the design with respect to the fixturing capabilities. The methodology is applicable to the mass-production commodity parts and part families, which typically require dedicated manufacturing facilities. A prototype DFF system for connecting rods of an automotive engine is developed. The system enables the designers to design the connecting rods by considering the fixturing (datums) capabilities of existing manufacturing facilities during the concept design stage, when design parameters are still not frozen. The DFF system analyzes the design with respect to fixturing capabilities of facilities and generates suggestions for the designer, to modify his design if required.
Modeling of Digital-Displacement Pump-Motors and Their Application as Hydraulic Drives for Nonuniform Loads
Authors: Ehsan Md. , Rampen W. H. S. , Salter S. H.
Published: July 2002

The digital-displacement pump-motor is a hybrid device, which combines reciprocating hydraulics with micro-processor control, creating a highly integrated machine capable of producing variable flow and power. It is based on the conventional hydraulic piston pump but with actively controlled poppet valves for each cylinder. This allows enabling or disabling on a stroke-by-stroke basis in any desired sequence. Time-domain modeling of the pump-motor system predicts the performance under variable-demand, variable-speed at different control-modes. The advantages of this approach over conventional techniques lie with both the response speed and the inherent energy efficiency. [S0022-0434(00)00801-7]
Effect of Elastic Accommodation on Diffusion-Controlled Cavity Growth in Metals
Authors: Mohan R. , Zhang J. , Brust F. W.
Published: July 2002

The effect of elastic accommodation on the grain boundary diffusion-controlled void growth was analyzed using an axisymmetric unit cell model. An incremental form of the virtual work principle was used to formulate the boundary value problem involving grain boundary diffusion. The model accounts for material elasticity and void interaction effects. Analyses are performed for initially spherical voids spaced periodically along the grain boundary. The results of the analyses on void growth rates agree well with the Hull-Rimmer model after the initial transient time. During the elastic transient, void growth rates can be several orders of magnitude higher than the steady state growth rate. Though the elastic transient time may occupy a small portion of the total rupture time, in metallic components experiencing cyclic loading conditions with short hold times, elasticity effects may be important. [S0094-4289(00)00903-8]
Decomposition Techniques for the Efficient Analysis of Area-Array Packages
Authors: Deshpande Anand M. , Subbarayan Ganesh
Published: July 2002

The goals of the present paper are to develop and demonstrate an efficient technique for the design/analysis of electronic packages through a novel decomposition procedure. The ultimate utility of these techniques is to enable quick and accurate design decisions at system-level, during package development by enabling one to develop a reusable library of modules in a manner analogous to the object-oriented programming paradigm of modern computer science. The methodology allows simultaneous design as well as domain decomposition and is based on a nonlinear optimization procedure that ensures the approximate satisfaction of the principle of virtual work. The developed procedure is demonstrated on a 5×5 hypothetical arrayed package. It is shown that with the use of the decomposed solution methodology, approximately 350 percent improvement in computational efficiency is achieved at an accuracy loss of only 6 percent. A windows-based graphical program founded on an artificial neural network model for predicting life given shear and axial deformation of solder joints was also developed. This neural network encapsulates the results of finite element analyses and predicts life for a given loading in a fraction of a second. [S1043-7398(00)00201-2]
Thermomechanical Fatigue Testing and Analysis of Solder Alloys
Authors: Palmer M. A. , Redmond P. E. , Messler, R. W.
Published: July 2002

Thermomechanical fatigue (TMF) is one of the most common causes of failure in solder joints. TMF occurs due to the introduction of stresses arising from thermal expansion mismatch during thermal cycling caused by either internal heating from power dissipation, the external environment, or both. Due to its complicated nature including partial compliance of joints, evolution of microstructure, and multiple deformation mechanisms, testing a material’s resistance to TMF is not straightforward. A method developed at Rensselaer, based on an apparatus designed at North Carolina State University, allows the direct measurement of each stress-strain cycle during thermal cycling. Through further analysis, using spreadsheet macros, it is possible to consider the energy absorbed by the joint on a per cycle basis. The interpretation of such data as well as the cumulative energy absorption can provide insight into the failure process. The behavior of three alloys, eutectic Sn–Bi, Sn–Pb, and Sn–Ag, will be presented. These data will be compared with that generated by other methods. A comparison of the behavior of these alloys, as well as the apparatus design, test method, interpretation, and possible enhancements is discussed. [S1043-7398(00)01201-9]
Experimental Study of Turbulent Asymmetric Flow in a Flat Duct Symmetric Sudden Expansion
Authors: Aloui F. , Souhar M.
Published: July 2002

This work presents an experimental study of recirculating flows downstream of a flat duct sudden expansion. Results of measurements of average and RMS quantities of the pressure P and the axial velocity U exhibit the asymmetry of the flow behind the sudden expansion as in the two-dimensional case. [S0098-2202(00)01401-2]
Evaluation of Blade Passage Analysis Using Coarse Grids
Authors: Miner Steven M.
Published: July 2002

This paper presents the results of a study using coarse grids to analyze the flow in the impellers of an axial flow pump and a mixed flow pump. A commercial CFD code (FLOTRAN) is used to solve the 3-D Reynolds Averaged Navier Stokes equations in a rotating cylindrical coordinate system. The standard k−ε turbulence model is used. The meshes for this study use 22,000 nodes and 40,000 nodes for the axial flow impeller, and 26,000 nodes for the mixed flow impeller. Both models are run on a SPARCstation 20. This is in contrast to typical analyses using in excess of 100,000 nodes. The smaller mesh size has advantages in the design environment. Stage design parameters for the axial flow impeller are, rotational speed 870 rpm, flow coefficient ϕ=0.13, head coefficient ψ=0.06, and specific speed 2.97 (8101 US). For the mixed flow impeller the parameters are, rotational speed 890 rpm, flow coefficient ϕ=0.116, head coefficient ψ=0.094, and specific speed 2.01 (5475 US). Evaluation of the models is based on a comparison of circumferentially averaged results to measured data for the same impeller. Comparisons to measured data include axial and tangential velocities, static pressure, and total pressure. A comparison between the coarse and fine meshes for the axial flow impeller is included. Results of this study show that the computational results closely match the shapes and magnitudes of the measured profiles, indicating that coarse CFD models can be used to accurately predict performance. [S0098-2202(00)02202-1]
Enhanced Natural Convection in a Vertical Rectangular Cavity on Account of the Mixing of Two Pure Gases
Authors: Campo Antonio , Zamora Blas
Published: July 2002

[S0022-1481(00)00901-4]
Static Friction and Initiation of Slip at Magnetic Head-Disk Interfaces
Authors: Wang S. , Komvopoulos K.
Published: July 2002

The apparent friction force and electric contact resistance at the magnetic head-disk interface were measured simultaneously for textured and untextured disks lubricated with perfluoropolyether films of different thicknesses. The initial stick time, representing the time between the application of a driving torque and the initiation of interfacial slip, was determined based on the initial rise of the apparent friction force and the abrupt increase of the electric contact resistance. Relatively thin lubricant films yielded very short initial stick times and low static friction coefficients. However, for a film thickness comparable to the equivalent surface roughness, relatively long initial stick times and high static friction coefficients were observed. The peak value of the apparent friction coefficient was low for thin lubricant films and increased gradually with the film thickness. The variations of the initial stick time, static friction coefficient, and peak friction coefficient with the lubricant film thickness and surface roughness are interpreted in the context of a new physical model of the lubricated interface. The model accounts for the lubricant coverage, effective shear area, saturation of interfacial cavities, limited meniscus effects, and the increase of the critical shear stress of thin liquid films due to the solid-like behavior exhibited at a state of increased molecular ordering. [S0742-4787(00)03101-5]
Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 2—Straight-Channel Diffuser
Authors: Deniz S. , Greitzer E. M. , Cumpsty N. A.
Published: July 2002

This is Part 2 of an examination of the influence of inlet flow conditions on the performance and operating range of centrifugal compressor vaned diffusers. The paper describes tests of a straight-channel type diffuser, sometimes called a wedge-vane diffuser, and compares the results with those from the discrete-passage diffusers described in Part 1. Effects of diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity on diffuser pressure recovery and operating range are addressed. The straight-channel diffuser investigated has 30 vanes and was designed for the same aerodynamic duty as the discrete-passage diffuser described in Part 1. The ranges of the overall pressure recovery coefficients were 0.50–0.78 for the straight-channel diffuser and 0.50–0.70 for the discrete-passage diffuser, except when the diffuser was choked. In other words, the maximum pressure recovery of the straight-channel diffuser was found to be roughly 10 percent higher than that of the discrete-passage diffuser investigated. The two types of diffuser showed similar behavior regarding the dependence of pressure recovery on diffuser inlet flow angle and the insensitivity of the performance to inlet flow field axial distortion and Mach number. The operating range of the straight-channel diffuser, as for the discrete-passage diffusers, was limited by the onset of rotating stall at a fixed momentum-averaged flow angle into the diffuser, which was for the straight-channel diffuser, αcrit=70±0.5 deg. The background, nomenclature, and description of the facility and method are all given in Part 1. [S0889-504X(00)00201-4]
Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage
Authors: Radomsky R. W. , Thole K. A.
Published: July 2002

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20 percent turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser-Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane midspan. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels. [S0889-504X(00)02302-3]
Investigations of Stochastic Layers in Nonlinear Dynamics
Authors: Luo Albert C. J. , Han Ray P. S.
Published: July 2002

The onset of a new resonance in the stochastic layer is predicted numerically through the maximum and minimum energy spectra when the energy jump in the spectra occurs. The incremental energy approach among all the established, analytic approaches gives the best prediction of the onset of resonance in the stochastic layer compared to numerical investigation. The stochastic layers in the periodically-driven pendulum are discussed as another example. Illustrations of stochastic layers in the twin-well Duffing oscillator and the periodically-driven pendulum are given through the Poincare´ mapping sections. [S0739-3717(00)00701-7]
Methionine by X-ray Photoelectron Spectroscopy
Authors: Brizzolara Robert A.
Published: July 2002

Methionine is one of the 20 amino acids, and one of the two sulfur-containing amino acids. Observations of chemical shifts in various constituents of methionine are important in determining its interaction with a surface in a thin film. As such, spectra of bulk films of methionine, as in this work, serve as a baseline for the thin film studies. In this work, an aqueous solution prepared from methionine powder was poured into a recessed sample holder and allowed to dry. This formed a block of methionine approximately 1/4 in. thick. The spectra were acquired at liquid nitrogen temperature. The atomic concentrations measured with XPS agree well with those expected for methionine, assuming the small amount of excess carbon and oxygen is due to adventitious material. Predominantly zwitterionic character is observed in the O 1s and N 1s spectra. A small amount of either neutral species or condensed polypeptide is also observed.
Etching of (Ba,Sr)TiO3 film by chlorine plasma
Authors: Shibano Teruo , Takenaga Takashi , Nakamura Keisuke , Oomori Tatsuo
Published: July 2002

Experimental studies of the etching of (Ba,Sr)TiO3 (BST) have been performed in Ar/halogen and Cl2 plasmas. In spite of the poor volatility of halogenated barium and strontium, some chemical enhancement of the etching reaction was observed in the etching of BST with halogen-containing plasmas. An investigation of the etching of BaOx, SrOx, TiOx, and BaxSryOz films with Cl2 plasma showed that the chemical enhancement in BST etching was related to the existence of titanium in BST films. The chemical reactivity of titanium with chlorine seemed to enhance the etching of BST. In the x-ray photoelectron spectroscopy analysis of the BST surfaces etched with Cl2 plasma, we found that barium- and strontium-rich surfaces were formed during the etching and that etching residues consisting of barium and strontium were observed after the BST films were etched off.
Etching of xerogel in high-density fluorocarbon plasmas
Authors: Standaert T. E. F. M. , Joseph E. A. , Oehrlein G. S. , Jain A. , Gill W. N. , Wayner P. C. , Plawsky J. L.
Published: July 2002

The etching of various xerogel films has been studied in high-density fluorocarbon plasmas. The xerogel etch rate is in part enhanced by the porosity. In discharges resulting in low surface polymerization, such as CF4 or oxygen-rich fluorocarbon plasmas, an additional enhancement up to 60% is observed. When the polymerization of the discharge is increased, this additional enhancement disappears and the xerogel etch rate becomes more suppressed. The suppression is more pronounced for xerogel films with a higher porosity and a larger pore size. X-ray photoelectron spectroscopy analysis on partially etched samples shows that the suppression in etch rate is accompanied by an increasing amount of fluorocarbon material at the xerogel surface, especially in the pores of the xerogel structure. Finally, a 30% porous xerogel film was patterned using CHF3 as an etching gas. Slight bowing of the sidewalls was observed.
Calculation of Evaporated Film Thickness Distribution on Nonplanar Surfaces for Variable Angle Vapor Incidence
Authors: Wasik C. A. , Gniewek J. J.
Published: July 2002

Equations which express evaporated film thickness ratios at various locations on nonplanar surfaces as a function of the substrate tilt angle are derived. The dependence of these ratios on the angle between the plane-normal and the direction of a uniform, unidirectional vapor stream is determined, as is the integrated effect of rotation of the plane about a normal. The conditions for improved coverage of step edges and on the plane between steps are indicated.
Theory of the Field Effect in Amorphous Covalent Semiconductor Films
Authors: Barbe D. F.
Published: July 2002

The Cohen–Fritzsche–Ovshinsky model for amorphous covalently bonded semiconductors is used to calculate the electrical characteristics of a field-effect structure utilizing an amorphous covalent film as the semiconductor. The effect of surface states on the semiconductor is considered. The analysis shows that the band bending is exponentially dependent on distance from the surface. The modulation of the surface conductance as a function of transverse field, geometry, and surface-state density is calculated. These calculations indicate that the field effect should be measurable for surface-state densities up to 1.5×1014 cm−2 (eV)−1. The results of these calculations should be used in the design of field-effect experiments in order to achieve the maximum sensitivity.
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Films Prepared by Electron-Beam Evaporation of Hot-Pressed Al2O3 in Oxygen Ambient
Authors: Hoffman Dorothy , Leibowitz Don
Published: July 2002

This paper describes the deposition as well as the electrical and physical evaluation of Al2O3 films on silicon substrates prepared by reactively evaporating Al2O3 in an oxygen ambient. The Al2O3 was evaporated using an electron-beam gun. Several ambient parameters were varied in order to obtain their effects on film properties. Variations in the substrates preheating, in temperature of the substrates during evaporation, and rates of evaporation were made. Measurement of MOS capacitance vs voltage provided data concerning the interface properties between oxide and silicon as well as conduction of the Al2O3 with applied bias conditions. These measurements indicated that mobile charge manifested by offset voltage in the C-V plots could be reduced below 7×1011 e/cm2 either by post heat treatments or deposition on heated substrates. The dielectric constant of these films at 100 kHz ranged between 7.6 and 7.8. Ellipsometry measurements show that the index of refraction varies from 1.72 to 1.55 as the deposition parameters were altered. X-ray analysis indicates that these films are fundamentally amorphous or are finely grained polycrystalline. Etching of the films in buffered HF suggests some degree of porosity. It may be generally concluded that the films produced by electron-beam evaporation were oxygen deficient and less dense than bulk. This result suggests that the Al2O3 source dissociates during the electron-beam evaporation. Obtaining stoichiometric Al2O3 onto silicon substrates requires the confinement of the evaporant and the reactive ambient in a chamber below the substrate.
A Review of the Electrical and Optical Properties of III–V Compound Semiconductor Films
Authors: Wieder H. H.
Published: July 2002

In recent years a better understanding has become available of the origin and characteristic electrical and optical properties of intermetallic semiconducting III–V compounds. This is due to the strong feedback coupling between fundamental research concerned with their electronic band structure and applied research concerned with the synthesis, growth, and technological applications of these compounds in bulk, thin film, and epitaxial layers. The charge carrier transport phenomena and the spectral response of films and layers will be described and compared to corresponding properties of bulk crystalline compounds. Particular emphasis will be placed on the narrow bandgap semiconductors InSb and InAs and on the indirect bandgap alloy GaP. It will be shown that the electrical and galvanomagnetic coefficients of III–V compound films are strongly dependent and their optical parameters are only weakly dependent on crystalline order. Electrical and optical properties exhibit a strong dependence on the type, size, and distribution of inhomogeneities. The properties and applications of spatially ordered inhomogeneities will be described with specific reference to InSb films.
Preparation of Alloy Deposits by Continuous Electron Beam Evaporation from a Single Rod-Fed Source
Authors: Nimmagadda R. , Raghuram A. C. , Bunshah R. F.
Published: July 2002

A theoretical model is presented for the evaporation of an alloy of the desired composition from a single rod-fed electron beam heated vapor source. Experimental work on deposition of a Ni—20Cr alloy from such a source confirms the proposed model. At high evaporation temperatures, the times necessary for the pool to assume steady state composition are small, about 15 min, thus making the process economically attractive.
Control of Resistivity, Microstructure, and Stress in Electron Beam Evaporated Tungsten Films
Authors: Sinha A. K. , Smith T. E. , Sheng T. T. , Axelrod N. N.
Published: July 2002

We have investigated the capability of the electron beam evaporation technique for producing thin W films having properties suitable for application as first-level metallization in refractory MOS (RMOS) devices. The apparatus consisted of a sputter-ion pumped 18-in. diam UHV station, 6-kW e gun, and a quartz crystal rate monitor. The evaporation process employs low background pressures (1−3×10−7 Torr), substrate heating (200–700 °C), a preevaporation step, and evaporation at rates of 100–500 Å/min. Maximum throughput is 16 1(14)-in. diam silicon slices per run. Using substrate temperatures of 500–700 °C, we have been able to produce mechanically stable, adherent films having a resistivity of 7–8 μΩ cm and a sheet resistance of ∼ 0.08 Ω/□ (for 9000-Å film). “Cold”-deposited films (> 1000 Å thick) having a high resistivity of 40–50 μΩ cm can be annealed at 1000 °C to resistivity of 10–15 μΩ cm. The films are single-phase bcc W with a small grain size of 0.1–0.2 μ. Low resistivity films (deposited above 550 °C) are associated with a large degree of microstructural perfection, and have small tensile stresses (3−7×109dyn cm−2). The films possess, excellent high-resolution etchability, and were found to be compatible with MOS structures provided care is exercised during the deposition.
Study of Adsorption and Nucleation of Cadmium on Tungsten and Germanium by a Molecular Beam Technique
Authors: Voorhoeve R. J. H. , Wagner R. S. , Carides J. N.
Published: July 2002

Polycrystalline tungsten, and several germanium single crystal faces, such as (111), (110), (211), etc., were bombarded with a calibrated cadmium beam of thermal energy. Various adsorption states were revealed by continuously monitoring cadmium evaporated from the substrate. Multilayer adsorption was found to precede growth of bulk cadmium for both types of substrate. The extent of this adsorption is 3–4 monolayers on tungsten and 2 monolayers on germanium (111). The heat of adsorption varies from 27 to 51 kcal/mole for tungsten, and is 25–32 kcal/mole for germanium. The nucleation of bulk cadmium has been studied with the same technique. Monitoring the evaporated cadmium during deposition allowed determination of the critical adatom coverage at which nucleation of bulk cadmium occurred. The nucleation kinetics shows critical behavior on germanium substrates but not on clean tungsten.
Electron Emission Studies from GaSe Surfaces
Authors: Williams R. H. , McEvoy A. J.
Published: July 2002

Photoelectric emission, LEED, and Auger electron spectroscopy studies have been carried out on GaSe single crystals cleaved in ultrahigh vacuum. The LEED measurements indicate the two-dimensional periodicity of the surface atoms to be the same as that of the bulk. The photoelectric threshold occurs at 5.4 eV, and the energy distribution of photoelectrons locates two maxima, separated by 1.3 eV, in the valence band density of states. These results are discussed in terms of the calculated band structure. A good cleavage face is found to be extremely inert to chemisorbed contamination, but poor cleavages are more reactive, and adsorption causes a low-energy peak in the energy distribution curves.