bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Simulations of Frontal Impact Crash Sensing Tests
Authors: Lin Chin-Hsu , Neal Mark O. , Wang J. T.
Published: June 2008

An extensive study of using non-linear finite element analyses to aid in calibrating an airbag crash sensing system using multiple sensors is presented. Details that are crucial for using a single vehicle model to simulate multiple testing conditions were identified and incorporated in a chosen vehicle model. The vehicle model was then used to simulate a set of no-deployment and all-deployment calibration events. The simulation results were compared with test data to identify Finite Element Analysis compatible (FEA-compatible) measures. These measures could be used to develop a new generation of FEA-compatible crash sensing algorithms.
Analysis of the Machining Process Using a Thermo-Elastic-Viscoplastic Finite Element Model
Authors: Balihodzic N. , Kishawy H. A. , Rogers R. J.
Published: June 2008

A plane-strain thermo-elasto-viscoplastic finite element model has been developed and used to simulate orthogonal machining. Simulations of cutting 304L stainless steel have been carried out using sharp, chamfered, and honed ceramic tools. Employing a combined thermal and mechanical stress analysis with temperature-dependent physical properties, the finite element model is used to investigate the effect of process parameters, tool geometry and edge preparation on the machining process. Stress and strain distributions within the chip and the elastic tool are presented. In addition, trends in the cutting and thrust forces, contact stress distributions and the plastic deformation beneath the machined surface are studied.
Mechanics and Dynamics of Serrated End Mills
Authors: Merdol S. Doruk , Altintas Yusuf
Published: June 2008

Mechanics and dynamics of serrated milling cutters are presented in the article. The serrated flute design knots are fitted to a cubic spline, which is then projected on helical flutes. Cutting edge geometry at any point along the serrated flute is represented by its immersion angle and tangent vectors in radial, tangential and helix directions. The chip thickness removed by each cutting edge point is determined by using previously proposed exact kinematics of dynamic milling. The cutting forces are evaluated by orthogonal to oblique cutting mechanics transformation. The experimentally proven model is able to predict the cutting forces and chatter stability lobes in time domain.
Analysis of Tension Effect on Chatter Stability in Machining
Authors: Chiou Richard Y. , Lu Lin
Published: June 2008

This paper presents an analysis of the effect of tension on machining stability. It studies the mechanism of a self-excited vibration process by applying a tension force in the axial direction in a turning operation. This research investigates the tension effect on machining stability and develops a comprehensive model for the simulation of stability resulting from the axial tension force in machining, particularly for those applications in cutting long, slender, or thin materials. In addition, a new tension-fixturing technology is introduced to maximize stability and minimize undesirable chatter vibration in machining. The research can lead to a better understanding of stability and control of the cutting processes. It also can improve the traditional clamping method and provide important information in the design of the machine tool system, as well as in the planning, optimization, and production control for cutting processes. Following the theoretical analysis, an experimental study on chatter boundary illustrates the tension effect on machining stability. A comparison between the predicted and experimentally measured stability boundary, over a range of cutting conditions, shows favorable agreement.
Finite Element Model of THOR Dummy Lower Leg
Authors: Zhou Qing , Yu Hailing , Medri Marisol B. , DiMasi Frank
Published: June 2008

THOR is a next generation crash test dummy incorporating additional advanced instrumentation and improved biofidelity than the Hybrid III dummy. This paper describes the development and validation of a finite element model of the lower leg assembly of the THOR 50th percentile male. The lower leg assembly has one translational degree-of-freedom in the axial direction along the tibia, and three rotational degrees-of-freedom in the ankle area with respect to its knee joint. It also includes a representation of the Achilles tendon load path. Modeling approaches used to simulate these features are discussed. Material properties of individual deformable components and articulated joints, as well as overall dynamic model performance, are calibrated using results of physical tests that mimic the loading environments experienced by the lower leg and foot in typical vehicle crashes. The model provides a computational tool for studying lower extremity injuries, including that of foot and ankle, which have gained increasing attention in recent years.
Packaging of Single Mode Laser Diodes
Authors: Bo̸rgesen Peter , Kondos Pericles A. , Yamunan Vinu
Published: June 2008

From a manufacturing perspective optoelectronics packaging is often quite immature and significant optimization still possible. This may, however, require some understanding of the optics as well as of the mechanical and thermal design, materials, and process issues. This is certainly the case for single mode laser diode packaging, where optical alignment and coupling plays a dominant role. Referring to a couple of current generic packages for illustration the present work offers a discussion of some of the manufacturing issues involved and potentials for improvements. This includes alternatives in terms of package design and contents, optical alignment and coupling schemes, and the use of laser welding, soldering, and adhesives.
The Effects of Defects and Acoustic Impedance Mismatch on Heat Conduction in SiGe Based Superlattices
Authors: Huxtable Scott T. , Abramson Alexis R. , Majumdar Arun , Shakouri Ali , Croke Edward T. , Ahn Channing C.
Published: June 2008

The cross-plane thermal conductivity of four Si/Ge, Si/Si0.4Ge0.6, and Si0.9Ge0.1/Si0.1Ge0.9 superlattices was measured using the 3ω technique. All four superlattices were found to have thermal conductivity values between 1.8 and 3.5 W/m-K, which are below the values of typical SixGe1−x alloys. The growth quality of these superlattices was evaluated qualitatively through the use of x-ray diffraction and transmission electron microscopy. These studies indicated that the superlattices contained a relatively high density of dislocations. The low thermal conductivity values are presumed to be due in large part to these dislocations.
Cyclic Mechanical Durability of Sn-3.9Ag-0.6Cu and Sn-3.5Ag Lead-Free Solder Alloys
Authors: Zhang Qian , Dasgupta Abhijit , Haswell Peter
Published: June 2008

The isothermal mechanical durability properties of two lead-free solder alloys, Sn3.5Ag and Sn3.9Ag0.6Cu, are presented and compared to that of the baseline eutectic Sn37Pb solder. Cyclic mechanical tests are performed at room temperature at various strain-rates and load levels, using a thermo-mechanical-microstructural (TMM) test system developed by the authors. The data is analyzed using standard power-law durability models based on work and inelastic strain range. The Sn3.9Ag0.6Cu lead-free alloy is found to be most durable, followed by the Sn3.5Ag solder and finally the baseline Sn37Pb eutectic alloy, under the test conditions investigated. However, tests at high load levels show a greater difference in durability than tests at low load levels. This trend is the opposite of that reported in the literature for thermal cycling durability. A hypothesis is put forward to explain the observed differences between mechanical cycling and thermal cycling, based on the energy-partitioning damage model.
Lead-Free Flip Chip Assembly
Authors: Gopakumar Sunil , Poyyapakkam Vinodh , Blass Dan , Borgesen Peter , Srihari K.
Published: June 2008

It is well established that Pb free alloys tend to solder less readily than Sn/Pb. It is not clear that this is always a major problem, but two factors combine to make it more of a concern for flip chip than for other applications. Not surprisingly, wetting and spreading appears to become less effective as the solder volume is reduced and a larger fraction of it is near the surface. At the same time assembly yields tend to become more sensitive to this. The present paper addresses the assembly of flip chips with Sn/Ag/Cu bumps onto Ni/Au and OSP coated copper pads on organic substrates. Soldering defects observed included incomplete wetting and collapse, as well as poor self centering. The sensitivity to fluxes, reflow profiles, and substrate pads were investigated and potential consequences for assembly yields calculated numerically.
An Analytical Dishing and Step Height Reduction Model for Chemical Mechanical Planarization (CMP)
Authors: Fu Guanghui , Chandra Abhijit
Published: June 2008

An analytical model for dishing and step height reduction in chemical mechanical planarization (CMP) of copper is presented. The model is based on the assumption that at the feature scale, high areas on the wafer experience higher pressure than low areas. The slurry is assumed to be Prestonian. The model delineates how dishing and step height reduction depend on slurry properties (selectivity and Preston’s constants), pad characteristics (stiffness and bending ability), polishing conditions (pressure, relative velocity and overpolishing) and wafer surface geometry (linewidth, pitch and pattern density). Model predictions are in good agreement with existing experimental observations. The present model facilitates understanding of the CMP process at the feature scale. Based on the proposed model, design avenues for decreasing dishing and increasing the speed of step height reduction may be explored through modification of appropriate parameters for slurry, pad and polishing conditions. The proposed model may also be used as a design tool for pattern layout to optimize the performance of the CMP process.
A Physical Model for Predicting Annular Film Flow Droplet Entrainment in Heat Transfer Systems
Authors: Holowach M. J. , Hochreiter L. E. , Cheung F. B.
Published: June 2008

The ability to accurately predict droplet entrainment in annular two-phase flow is required to effectively calculate the interfacial mass, momentum, and energy transfer, which characterizes nuclear reactor safety, system design, analysis, and performance. Most annular flow entrainment models in the open literature are formulated in terms of dimensionless groups, which do not directly account for interfacial instabilities. However, many researchers agree that there is a clear presence of interfacial instability phenomena having a direct impact on droplet entrainment. The present study proposes a model for droplet entrainment, based on the underlying physics of droplet entrainment from co-current upward annular film flow that is characteristic to Light Water Reactor (LWR) safety analysis. The model is developed based on force balance and a stability analysis that can be implemented into a transient three-field (continuous liquid, droplet, and vapor) two-phase heat transfer and fluid flow analysis computer code.
Development of MEMS Microchannel Heat Sinks for Micro/Nano Spacecraft Thermal Control
Authors: Paris Anthony D. , Birur Gajanana C. , Green Amanda A.
Published: June 2008

MEMS-based microchannel heat sinks are being investigated at the Jet Propulsion Laboratory (JPL) for use in micro/nano spacecraft thermal control. The current stage of development focuses on the integration of microchannel heat sinks into spacecraft pumped cooling loops. Two microchannel heat sinks, adapted from a Stanford University Microfluidics Laboratory design, were fabricated at JPL and tested for thermal and hydraulic performance in a single-phase pumped cooling loop. The first microchannel heat sink design was demonstrated to remove heat fluxes of up to 25 W/cm2 with a maximum device temperature of less than 80 °C. Both the original and redesigned heat sinks where shown to meet hydraulic performance criteria requiring less than 1 psi pressure drop with water as the working fluid. It was concluded that the design methodology developed for this project produces microchannel heat sink devices capable of high heat flux removal in future micro/nano spacecraft thermal control architecture.
Suppression of Stress Relaxation in MEMS Multilayer Film Microstructures by Use of ALD Nanocoatings
Authors: Zhang Yanhang , Dunn Martin L. , Elam Jeffrey W. , George Steven M.
Published: June 2008

We study the suppression of stress relaxation in MEMS multilayer film microstructures by the use of alumina nanocoatings realized by atomic layer deposition (ALD). Gold (0.5 μm thick) / polysilicon (1.5 or 3.5 μm thick) beam and plate microstructures were fabricated by the MUMPs surface micromachining process. The microstructures were then coated on both sides with a 40 nm thick amorphous Al2O3 layer by ALD. The beam and plate microstructures were initially thermal cycled between room temperature and 190°C tostabilize the gold microstructure. After the initial thermal cycles, the microstructures were cooled from 190°C to 120°C and held at 120°C for about 2000 hours (three months). We measured, using an interferometric microscope with a custom-built temperature chamber, full-field deformed shapes (and from these determined the average curvatures in x- and y- directions) of the microstructures during the initial thermal cycles, during the cooling process from 190 °C to 120 °C, and during the isothermal hold. Measurements were made on both coated and uncoated microstructures to assess the influence of the coating. We find that while the 40 nm thick coating has a small effect on the thermoelastic response of the microstructure, it significantly reduces the extent of stress relaxation during the isothermal hold. We modeled the curvature evolution with time assuming the stress relaxation mechanism is power-law creep in the gold, ε˙ = Aσn, and that the polysilicon and alumina deform elastically. The simple model describes the observed behavior reasonably well for the uncoated microstructures (when the power-law parameters are fit using the measured curvature), however, for the coated microstructures, the model predicts a decrease in the stress relaxation, but nowhere near the magnitude observed. This suggests that not only is the stress state in the gold film altered by the nanoscale coating, but also the fundamental deformation mechanisms are altered.
Development of a Monitoring System for Near Burner Slag Formation
Authors: Tan C. K. , Wilcox S. J. , Ward J.
Published: June 2008

A series of experiments on two different coals at a range of burner conditions have been conducted to investigate the behaviour of pf coal combustion on a 150kW pulverised fuel (pf) coal burner with a simulated eyebrow (a growth of slag in the near burner region). The simulation of a burner eyebrow was achieved by inserting an annulus of refractory material immediately in front of the face of the original burner quarl. Results obtained from monitoring the infrared (IR) radiation and sound emitted by the flame were processed into a number of features which were then used to train and test a self organising map neural network. Results obtained from the neural network demonstrated a classification success, never lower than 99.3%, indicate that it is not only possible to detect the presence of an eyebrow by monitoring the flame, but it is also possible to give an indication as to its size, over a reasonably large range of conditions.
A Nano-Scale Multi-Asperity Contact and Friction Model
Authors: Adams George G. , Mu¨ftu¨ Sinan , Azhar Nazif Mohd
Published: June 2008

As surfaces become smoother and loading forces decrease in applications such as MEMS and NEMS devices, the asperity contacts which comprise the real contact area will continue to decrease into the nano scale regime. Thus it becomes important to understand how the material and topographical properties of surfaces contribute to measured friction forces at this nano scale. We have incorporated the single asperity nano contact model of Hurtado and Kim into a multi-asperity model for contact and friction which includes the effect of asperity adhesion forces using the Maugis-Dugdale model. Our model spans the range from nano-scale to micro-scale to macro-scale contacts. We have identified three key dimensionless parameters representing combinations of surface roughness measures, Burgers vector length, surface energy, and elastic modulus. Results are given for the normal and friction forces vs. separation, and for the friction coefficient vs. normal force for various values of these key parameters.
Micro-Electrostatic Vibration-to-Electricity Converters
Authors: Roundy Shad , Wright Paul K. , Pister Kristofer S. J.
Published: June 2008

Advances in low power VLSI design, along with the potentially low duty cycle of wireless sensor nodes open up the possibility of powering small wireless computing devices from scavenged ambient power. Low level vibrations occurring in typical household, office, and manufacturing environments are considered as a possible power source for wireless sensor nodes. This work focuses on the design of electrostatic vibration-to-electricity converters using MEMS fabrications technology. Detailed models of three different design concepts are developed. The three design concepts are evaluated and compared based on simulations and practical considerations. A formal optimization of the preferred design concept is performed, and a final design is produced using the optimal design parameters. Simulations of the optimized design show that an output power density of 116 μW/cm3 is possible from input vibrations of 2.25 m/s2 at 120 Hz. Test devices have been designed for a Deep Reactive Ion Etching (DRIE) process that etches MEMS structures into the top layer of a Silicon On Insulator (SOI) wafer. The devices are currently being fabricated.
Effect of Particle Size on Pipeline Flow of Solid-Liquid Slurry With Fixed Particle Size Distribution
Authors: Skudarnov P. V. , Daas M. , Lin C. X. , Ebadian M. A. , Gibbons P. W. , Erian F. F. , Rinker M. W.
Published: June 2008

The transport properties of solid-liquid slurries having the same well-defined particle size distribution but different median particle sizes have been studied in a 22-mm I.D. horizontal pipeline flow loop. The solid-liquid slurries were glass beads-water mixtures. The particle size distribution of solids was Rosin-Rammler with median diameters of 50 mm and 250 mm. The relationship between the pressure drop in the straight horizontal sections of the flow loop and the mean slurry velocity was determined for different solids volume concentrations varying from 4.5 to 25% and mean slurry velocity ranging from 0.5 to 2.5 m/s. Critical deposition velocity was measured from visual observations. An existing empirical model of Wasp et al. that predicts the pressure gradient for a single-species slurry flow in a horizontal pipeline was used to describe the pressure drop data. The Oroskar-Turian correlation for critical velocity was used for comparison with the measured critical velocities.
Numerical Simulation of Natural Gas Combustion Process Using a One-Step and a Two-Step Reaction
Authors: Nieckele Angela O. , Naccache Moˆnica F. , Gomes Marcos S. P. , Carneiro Joa˜o N. E. , Isnard Andre´ Augusto , Serfaty Ricardo
Published: June 2008

The work evaluates the combustion of natural gas in a cylindrical furnace. The Generalized Finite Rate Reaction Model was selected for predicting the reactions. Two situations were considered. In the first case the combustion of the fuel was predicted by a single global reaction, and in the second case a two-step reaction was considered for predicting the combustion process. The conservation equations of mass, momentum, energy and chemical species were solved by the finite volume procedure, with the commercial software FLUENT. The turbulent flow was modeled by employing the two differential equation κ–ε model. The solutions obtained with the two reaction models, for the temperature and species concentration fields, were compared among them and against experimental data available in the literature. It was observed that the two-step reaction model represents better the physical phenomena, showing a better agreement with the experimental data.
Analysis of Intermittent Sprays
Authors: Jawad Badih A.
Published: June 2008

The purpose of this study is to gain further insight into the atomization mechanism, the variation over time in droplet size distribution and spray penetration. This is done based on effect of chamber pressure, injection pressure, and type of fuel. A laser diffraction method is used to determine droplet mean diameters, single injection with synchronized time mechanism allowed the time dependent studies. Obscuration signals are obtained through a digital oscilloscope from which arrival time of spray can be measured. The spray penetration correlation obtained is compared to other correlations obtained from other techniques used in the literature.
Implementing Approximate Boundary Conditions for Finite-Volume Time-Domain Electromagnetic Code
Authors: Camberos Jose´ A.
Published: June 2008

In addition to the governing equations, a properly posed mathematical problem requires a statement of the solution bounds and boundary conditions. Numerical methods applied to solve the governing equations must also implement proper solution bounds and boundary conditions. In developing a finite-volume, time-domain solver for electromagnetic computations, the author implemented a variety of approximate boundary conditions formulated to mimic reflecting metallic boundaries and truncated solution-domain (outer) boundaries. These approximate boundary conditions are presented and discussed in context of selected results for predicting the radar-cross section of various shapes (with analytic solutions available for comparison).
Numerical Simulations of the Pulsed Inductive Thruster
Authors: Mikellides Pavlos G.
Published: June 2008

Numerical modeling of the Pulsed Inductive Thruster exercising the magnetohydrodynamic code, MACH2 aims to provide bilateral validation of the thruster’s measured performance and the code’s capability of capturing the pertinent physical processes. Computed impulse values demonstrate excellent correlation to the experimental data for a range of energy levels and helium propellant-mass values. The effects of the vacuum tank wall and mass-injection scheme were investigated to show trivial changes in the overall performance.
High Power Electromagnetic Thrusters for Spacecraft Propulsion
Authors: LaPointe Michael R. , Gilland James H. , Mikellides Pavlos G.
Published: June 2008

High power electromagnetic plasma thrusters are being developed as primary in-space propulsion systems for future robotic and piloted space missions. Electromagnetic thrusters effectively process megawatts of electrical power, providing a wide range of specific impulse values to meet a variety of in-space propulsion requirements. Potential applications for high power thrusters include the orbit raising and maneuvering of large space platforms, lunar and planetary cargo transport, piloted planetary missions, asteroid rendezvous and sample return, and robotic deep space exploration. The NASA Glenn Research Center is developing MW-class magnetoplasmady-namic (MPD) thrusters and pulsed inductive thrusters (PIT) to support these diverse mission requirements. This paper provides an overview of the current GRC research program, describes the operating principles, challenges, and status of each technology, and outlines plans for further development.
Exploring the Limits of System Integration With Smart Dust
Authors: Warneke Brett A. , Pister Kristofer S. J.
Published: June 2008

The Smart Dust project aims to explore the limits of system integration by packing an autonomous sensing, computing, and communication node into a cubic millimeter mote that will form the basis of massive distributed sensor networks, thus demonstrating that a complete system can be integrated into 1 mm3. Effectively exploring this space requires new approaches to design that emphasize energy and volume constraints over all others. To this end a 16 mm3 autonomous solar-powered sensor node with bi-directional optical communication has been demonstrated, with smaller nodes forthcoming. System integration limits will shrink even further as carbon nanotube technology matures.
Design Consideration, Process and Mechanical Modeling, and Tolerance Analysis of MEMS-Based Mechanical System-on-a-Chip (SOAC) for Nanomanufacturing
Authors: O’Neil Chad B. , Malshe Ajay P. , Virwani Kumar , Schmidt William F.
Published: June 2008

In this paper the authors describe the design considerations including force and tolerance analysis and mechanism and tip design, for a novel, dynamic scanning probe microscopy tip directly insertable into today’s existing atomic force microscopy tools. This tool is the first of its kind and is a major step in the field of nanomanufacturing enabling the use of nanomechanical machining operations for nanostructure top-down manufacturing. The application of this device is the nanomechanical drilling and milling of III-V semiconductor substrates for various applications such as nanovias for electrical interconnection of next generation electronic and photonic applications, as well as reservoirs and capillaries for nano-fluidics. Results to date indicate that device performance parameters allow a normal drilling force of 25 μN, tangential drilling force of 35 μN, maximum rotational speed of 100,000 rpm, and minimum machined feature size of less than 200 nm. This device is currently being fabricated at Sandia National Laboratories, SUMMIT MEMS foundry and being packaged at the University of Arkansas, Fayetteville High Density Electronics Center (HiDEC).
A Micro Heat Engine for MEMS Power (Keynote Paper)
Authors: Richards C. D. , Bahr D. F. , Richards R. F.
Published: June 2008

Progress in the development of a micro heat engine is presented. The prototype micro heat engine is an external combustion engine, in which thermal power is converted to mechanical power through the use of a novel thermodynamic cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. The design, well suited to photolithography-based batch fabrication methods, is unlike any conventionally manufactured macro-scale engine. In this paper, the design, fabrication and preliminary testing of a working prototype are discussed. The operation of the engine and its key component, the piezoelectric membrane generator is presented. For the first time, the production of electrical power by a dynamic micro heat engine is demonstrated.
Numerical Simulation of Room Airflow Using Different Closure Models and Grid Generation Schemes
Authors: Singh Anupreet , Hosni Mohammad H. , Schwarz Walter R.
Published: June 2008

Proper distribution of conditioned air plays an important role in both human thermal comfort and indoor air quality. Experimental investigations of airflow and temperature distributions for typical indoor environmental conditions are essential but expensive and time consuming. Technological advances in computer hardware and development of computational software in recent years have made numerical simulations of such flow conditions possible. The objectives of this study were to: (1) Evaluate the applicability of a commercial software in conducting numerical simulations of indoor airflow conditions for both isothermal and non-isothermal conditions using different turbulence closure models, and (2) Determine the effects of different grid generation techniques on the numerical results. The computations were performed for a large rectangular geometry room. Conditioned air entered the room through a high sidewall grille located on one side of the wall and exited through a return located on the opposite side of wall. All walls and ceiling were insulated. The floor was heated at a constant heat rate. This paper presents velocity, temperature, and turbulent kinetic energy profiles at various cross-sections. Good agreements between the numerical simulation results and experimental data were achieved.
Utilization of Turkey Feather Fibers in Erosion Control Materials
Authors: George Brian R. , Bockarie Anne , McBride Holly
Published: June 2008

Currently, between two and four billion pounds of feathers are produced annually by the poultry processing industry. These feathers are usually converted to animal feed in an attempt to recycle it rather than dispose of them in landfills. However, this method can result in diseases being passed along to the ingestors of this feather meal. Until recently there was no method of removing the quill from feather, but a method of effectively stripping the feather fibers from the quill without damaging the fibers has been patented, and as a result research is being conducted to determine uses for these fibers. Current research has focused on creating nonwoven latex bonded fabrics containing turkey feather fibers for utilization as erosion control fabrics. These fabrics have been compared with currently available erosion control fabrics to determine their suitability for this particular purpose.
STM Studies on the Surface Structure of a New Carbon Fiber From Lyocell
Authors: Wu Qilin , Pan Ding
Published: June 2008

Rayon-based carbon fiber (RCF) and lyocell-based carbon fiber (LCF) were investigated through surface analysis by SEM and STM. SEM delineated much smoother surface of LCF, while RCF exhibited rough surface with obvious cracks and grooves, which undoubtedly lead to the tensile strength decrease of RCF. At 500nm×500nm area using STM, it was found that the surfaces of LCF are characterized by bulk structure with the area of about 150nm2. The bulk structure was constituted of smaller slug-like microstructures, each of which has a width of about 25 nm and length of 150 nm aligned at an angle of 45° to the fiber axis. The distance between two adjacent carbon atoms of LCF estimated by section analysis of STM revealed that hexagonal carbon rings did not form on the surface of LCF.
Effect of Nesting of Fiber Bundles on Micro Fracture of Laminated Woven Fabric Composite
Authors: Osada Toshiko , Nakai Asami , Hamada Hiroyuki
Published: June 2008

In laminated woven fabric composites, fiber bundles do not pack tightly because there are resin rich regions caused by crimp of fiber bundles. The fiber bundles in one layer are often fitted into the neighboring layer, which is called nesting. In this study, the effect of nesting by laminating on mechanical properties and micro fracture behavior of composites was investigated. Tensile testing of woven fabric composites with different number of layers and observation using optical microscopy were performed. With the increase of number of layers, nesting is more likely to occur, resulting in a decrease in thickness per layer increase in fiber volume fraction. This also lead to an increase in modulus and strength but a decrease in knee point stress. The locations at which cracks occurred were different in specimens with and without nesting.
Optimization of Optical Methodology for High-Digital Resolution Quantitative Evaluation of Reliability of Microelectronics and Packaging
Authors: Furlong Cosme , Pryputniewicz Ryszard J. , Yokum Jeffrey S.
Published: June 2008

Recent technological trends based on miniaturization of mechanical, electromechanical, and photonic devices to the microscopic scale have led to the development of microelectromechanical systems (MEMS). Effective development of MEMS components requires the synergism of advanced design, analysis, and fabrication methodologies, and also of quantitative metrology techniques for characterizing their performance, reliability, and integrity during the electronic packaging cycle. In this paper, we describe optoelectronic techniques for measuring, with sub-micrometer accuracy, shape and changes in states of deformation of MEMS structures. With the described optoelectronic techniques, it is possible to characterize MEMS components using the display and data modes. In the display mode, interferometric information related to shape and deformation is displayed at video frame rates, providing the capability for adjusting and setting experimental conditions. In the data mode, interferometric information related to shape and deformation is recorded as high-spatial and high-digital resolution images, which are further processed to provide quantitative 3D information. Furthermore, the quantitative 3D data are exported to computer-aided design (CAD) environments and utilized for analysis and optimization of MEMS structures. Capabilities of optoelectronic techniques are illustrated with representative applications demonstrating their applicability to provide indispensable quantitative information for the effective development and optimization of MEMS structures.
Effects of Void, Crack, and PCB Thickness on the Solder Joint Reliability of Wafer-Level Chip-Scale Package (WLCSP) Assemblies
Authors: Lau John , Zou Yida , Camerlo Sergio
Published: June 2008

The creep analyses of solder-bumped wafer-level chip-scale package (WLCSP) on printed circuit board (PCB) subjected to temperature cycling loading are presented. Emphasis is placed on the effects of PCB thickness on the solder joint reliability of the WLCSP assembly. Also, the effects of crack-length on the crack tip characteristics such as the J-integral in the WLCSP solder joint are studied by the fracture mechanics method. Finally, the effects of voids on the crack growth in the WLCSP solder joint are investigated.
Optimization of Multiple Head SMT Placement Machine: Model and Approaches
Authors: Zeng Youjiao , Yan Junqi , Jin Ye , Jiang Tao
Published: June 2008

In order to maximize the throughput rate of single multiple head surface mounted technology placement machine, the time taken for pick-and-place of components for each printed circuit board has to be minimized. This gives rise to two related essential problems, namely feeder assignment problem and pick-and-place sequence determination problem. In this paper, we introduce a model that simplifies problems. We regard all components during a pick-and-place cycle as a unit and give it a matching weight. In this way, we change multiple head machine problems into single head machine problems. The optimisation problem becomes two sub-problems: minimum weight matching problem and travelling salesman problem of these units. We presented algorithms to obtain near optimal solution and implement them as a computer program. We performed experiment on a real four head placement machine. The experimental results are presented to analyse their performance.
Optimization of Contact Dynamics for an RF MEMS Switch
Authors: Pryputniewicz Ryszard J. , Furlong Cosme , Pryputniewicz Emily J.
Published: June 2008

Functional operation of RF MEMS resistive switches depends on dynamic characteristics of the cantilever contacts. Characteristics of these contacts, in turn, depend on parameters defining their shape and dimensions, material properties, boundary conditions, and actuation voltages. In this paper, a simple analytical model is presented and used to develop an understanding of the switch behavior. In addition, uncertainties corresponding to this model are also determined to quantitatively show the influence that various parameters defining the cantilever contact have on its dynamics which, in turn, influences performance of the RF MEMS switch. This performance can be optimized with the objective of achieving resonance frequency within, e.g., 1% of the desired value while constraining the nominal dimensions and finding the optimum set of uncertainties in these dimensions. Analytical results correlate well with the preliminary experimental characterization of the contacts.
Determination of Glass Transition Temperature (Tg) of Adhesive-Based Optical Fiber Components by In-Situ Bragg Grating Strain Sensing
Authors: Broadwater Keita , Barker Donald , Yang Yubing
Published: June 2008

This paper presents an in-situ evaluation technique that can be used to measure the Tg of thin layers. The studies presented in this paper were conducted on fiber optic connectors, but the results can be applied in general to ferrule-based components that use epoxy adhesives. This paper demonstrates how a strain sensor can theoretically detect the glass transition response of the epoxy material using a simple mechanics of materials approach. Several experimental results are presented showing that there is adequate sensor discrimination to detect the glass transition region. The technique also clearly showed residual curing and small changes in the Tg of the epoxy as the ferrule samples were subjected to multiple thermal cycles. The experimental results also demonstrate that the measured Tg of the epoxy in thin layers is different that that measured in bulk samples.
Theoretical Evaluation of Convective Heat Transfer Coefficients in Conjugated Problems Using the Second Law of Thermodynamics
Authors: Shrivastava Devashish , Roemer Robert
Published: June 2008

The Tissue Convective Energy Balance Equation (TCEBE) is a recently derived, general bio-heat transfer equation from which a derivation of Pennes BHTE can be obtained. To accurately implement the TCEBE it is necessary to obtain expressions for the values of the overall heat transfer coefficients between the blood vessels and the tissue. One of the requisite steps in evaluating the overall heat transfer coefficients is to estimate convective heat transfer coefficients between the blood vessels and the tissue. To achieve this goal, a new technique is presented using the second law of thermodynamics to estimate convective heat transfer coefficients in conjugated problems at steady state. One dimensional results obtained are qualitatively similar to two dimensional results from the analytical solution for conjugated problems.
Investigation of Advanced CFD Methods and Their Application to Centrifugal Compressors
Authors: Hutchinson Bradley R. , Shi Feng , Sorokes James M. , Koch Jay M.
Published: June 2008

The past decade has seen considerable growth in the application of CFD to centrifugal compressors. As computational methods applicable to compressors have improved, and computing power has increased dramatically, so has the scope of application. Impellers, diffusers, return channels, inlets, volutes and other components are now routinely analyzed, sometimes simultaneously. With the expansion of CFD, the user is now faced with many choices in establishing the most effective and efficient way to perform a given analysis. Advice, guidance and reports as to the experiences of other practitioners are of considerable value. This paper aims to investigate and compare relevant computational factors such as mesh type and density, and CFD solver discretization scheme as applied to the impeller, vaneless diffuser and volute of a centrifugal compressor.
A New Approach to Predicting Centrifugal Compressor Sideload Pressure
Authors: Hardin James R.
Published: June 2008

This paper presents a new method of predicting pressure in a centrifugal compressor sideload. The method is compared with results from a CFD analysis and with test data points from five different sideloads. In all cases for which the sideload exit total pressure was known, the new method predicted the total pressure within 1 percent, usually within 0.5 percent. The new method is simple enough to use in unsophisticated prediction programs or spreadsheets or even hand calculations. Furthermore, the curvature factor developed for this method illustrates how sideload geometry affects sideload pressure.
A Parametric Study of Surge and Flow Instabilities in Gas Pipeline Compression Systems: The Effect of Pipe Parameters on Surge Margins
Authors: Albayrak K. , Burtaskiray D. , Eralp O. C. , Akyuzly K. M.
Published: June 2008

There is a need to understand the effect of coupling of the flow characteristics of a compressor with that of the pipeline and how this coupling effect the stability of the flow in a compression system. This study addresses such a need by carrying out a numerical simulation of the flow in the whole compression system including the compressor, the pipeline, and the other associated flow elements. A nonlinear, one-dimensional mathematical model is adopted for the present study. In this model, the gas flow inside the pipeline is assumed one-dimensional, viscous, and compressible. A parametric study is carried out using the proposed model, with air as the working fluid, to predict the surge margins for a subscale compression system and to study the effect of pipe length and diameter on these margins. Furthermore, the effect of these geometrical parameters on the amplitude and frequency of the flow oscillations are also established by numerical experimentation.
Current Status, Design and Performance Trends for the Regenerative Flow Compressors and Pumps
Authors: Raheel Mukarrum , Engeda Abraham
Published: June 2008

Regenerative flow compressors and pumps, hereafter called RFC/RFP have found many applications in industry; still they are the most neglected turbomachines in the family of dynamic compressors. The number of publications existing in literature is very small compared to the large number of papers about the centrifugal and axial turbocompressors. This paper gives a detail discussion of fundamentals and working principle of regenerative turbomachines. Regenerative compressors are compared with centrifugal compressors and the importance of regenerative turbomachines in low specific speed range is emphasized. The major findings of available literature on regenerative turbomachine are summarized. The current status, limitations and some of the challenges faced by RFC/RFP are assessed in context of performance improvement. The paper concludes with an overview of ongoing research and future directions to be followed for performance improvement of this neglected class of turbomachines.
Reducing the Deposition of Scale in the Evaporator of a Mechanical Vapour Recompression System for Concentration of Pulp Mill Effluents
Authors: Toma Peter , Miller Karl , Hoddenbagh J. Mark A.
Published: June 2008

A numerical model was developed, validated with the aid of pilot evaporator tests, and used to assess practical methods of minimizing scaling observed in a mechanical vapour recompression (MVR) plant at Millar’s Western’s Meadow Lake, Saskatchewan pulp mill. On average, 8,000 m3/day of effluent (approximately 7 m3/Bone Dry Tonne product) resulting from bleached-chemi-thermo-mechanical wood processing, are purified and the recovered water is returned to the plant while the effluent is concentrated to 75% TD&SS in a recovery boiler. The evaporators are used in the first stage of the feed concentration process. The system uses a heat pump principle: steam produced during the boiling of the falling liquid film is mechanically compressed and condensed on the outer surface of a vertical tube evaporator. Most of the condensation and compression heat is recovered. Reducing the rate of scale deposition and increasing the interval between two successive cleaning operations of vertical evaporators used in the MVR scheme was identified as an essential component of operation costs and given special attention. To assist the mill in assessing practical methods for achieving this goal an experimental pilot evaporator and a numerical model were developed and used first at the Alberta Research Council in Edmonton, Canada, and then at the mill location. The mill uses a different model for control and supervision of system parameters. The magnitude of the (critical) temperature difference (CTD) across the laminar sub-layer of boiling liquid film is calculated and is recommended in this paper to be used to quantify the fouling tendency. Further to recommendations resulting from previous experimental investigations [1,2] as well as in this study, the mill introduced additional process control parameters to reduce and maintain the temperature drop across the effluent boiling film to a maximum range of 2–4°C. In addition to CTD, the wall (top-bottom) axial temperature difference (ATD) has been identified as another criteria for assessing potential scale deposition during evaporation-concentration. Calculations and experimental measurements performed with the pilot evaporator [3] suggest that increasing the circulation rate of effluent pumped from the sump to feed the liquid film at the top of evaporator tubes has a positive effect on reducing the CTD and the ATD. During four months of laboratory investigations with a pilot evaporator, non-uniform liquid distribution among vertical evaporator tubes of the evaporator was observed and is discussed separately. This paper will present the model and mill observations and summarize the main results and suggested practical strategies for reducing the rate of scale deposition and improving the system economics.
Modeling Two-Point Wheel/Rail Contacts Using Constraint and Elastic-Force Approaches
Authors: Shabana Ahmed A. , Zaazaa Khaled E. , Escalona Jose´ L. , Sany Jalil R.
Published: June 2008

Two approaches are commonly used for solving the problem of wheel/rail contact in railroad dynamics. The first is the elastic approach in which the wheel is assumed to have six degrees of freedom with respect to the rail. The normal contact forces are defined using Hertz’s contact theory or in terms of assumed stiffness and damping coefficients. The second approach is the constraint approach in which nonlinear kinematic contact constraint equations are introduced, leading to a model in which the wheel has five degrees of freedom with respect to the rail. It is the objective of this investigation to present a new formulation for the wheel/rail contact problem based on the elastic force approach. Crucial to the success of any elastic force formulation for wheel/rail contact problem is the accurate prediction of the location of the contact points. To this end, features of multibody formulations that allow introducing arbitrary differential equations are exploited in this investigation in order to obtain a good estimate of the rail arc length traveled by the wheel set. In the formulation presented in this paper, four surface parameters are used to describe the wheel and the rail surfaces each with arbitrary geometry. In order to determine the location of the points of contact between the wheel and the rail, a first order differential equation for the rail arc length is introduced and is integrated simultaneously with the multibody equations of motion of the wheel/rail system. The method presented in this paper allows for multiple points of contact between the wheel and the rail by using an optimized search for all possible contact points. The normal contact forces are calculated and used with non-linear expressions for the creepages to determine the creep forces. The paper also discusses two different procedures for the analysis of the two-point contact in the wheel/rail interaction. Numerical results obtained using the elastic force model are presented and compared with the results obtained using the constraint approach.