bluuebunny/crossref_metadata_2025 huggingface dataset:
Wetting of Compacted Nanoclay Powder by Epoxy Resin
Authors: Aktas Levent , Hamidi Youssef K. , Altan M. Cengiz
Published: April 2008

Spreading behavior and advancing contact angle of a low viscosity epoxy resin on three commercially available nanoclays — Cloisite® Na+, Cloisite® 15A and Cloisite® 25A — at 52°C is investigated. In addition, effect of temperature on spreading dynamics of epoxy on Cloisite® Na+ is analyzed at 33, 52 and 77°C. For wetting experiments, nanoclay powder is compressed into 12.7mm diameter disk shaped compacts under 20MPa pressure. The surface topologies of the compacts are analyzed by scanning electron microscopy (SEM), where as energy dispersive x-ray analysis (EDXA) is utilized to quantify the chemical composition of the surface. An epoxy drop is placed on each of the compacts and spreading is monitored via a CCD camera equipped with a high magnification lens. Temporal evolution of the advancing contact angle as well as drop penetration into the nanoclay compact is determined using the drop profiles extracted from the sessile drop images. Spreading of epoxy on Cloisite® Na+ is observed to be 12-fold faster at 77°C compared to 33°C. Analogous to its spreading speed, rate of penetration of resin into the nanoclay compact increased 20-fold in the same temperature range. Behavior of different nanoclay types are assessed by repeating the wetting experiments on Cloisite® 15A and Cloisite® 25A compacts. Unlike Cloisite® Na+, which did not have a finite static contact angle, Cloisite® 15A and Cloisite® 25A yielded static contact angles of 59.2°and 40.1°, respectively. These differences are attributed to different surface energies as a result of different chemical compositions of the surfaces and dissimilar surface topologies.
Effect of Fiber Content on Void Morphology in Resin Transfer Molded E-Glass/Epoxy Composites
Authors: Hamidi Youssef K. , Dharmavaram Sudha , Aktas Levent , Altan M. Cengiz
Published: April 2008

Effect of fiber volume fraction on occurrence, morphology, and spatial distribution of microvoids in resin transfer molded E-glass/epoxy composites is investigated. Three disk-shaped center-gated composite parts containing 8, 12, and 16 layers of randomly-oriented, E-glass fiber perform are molded, yielding 13.5, 20.5 and 27.5% fiber volume fractions, respectively. Voids throughout these disk-shaped composites are evaluated by microscopic image analysis of samples obtained along the radius. Each identified void’s equivalent radius, area, and shape are determined at 200x magnification. Number of voids is found to decrease moderately with increasing fiber content. Void areal density decreased from 10.5 to 9.5 voids/mm2 as fiber content is increased from 13.5 to 27.5% fiber content. Similarly, void volume fraction decreased from 3.1 to 2.5%. Average void size is observed to remain similar at 53 to 55 μm when the fiber content is increased from 13.5 to 27.5%. Increasing fiber volume fraction from 13.5 to 27.5% lowers the contribution of irregularly-shaped voids from 40% of total voids down to 22.4%. Along the radial direction, combined effects of void formation by mechanical entrapment and void mobility are shown to yield a spatially complex void distribution. However, increasing fiber content is observed to affect the void formation mechanisms as more voids are able to move towards the exit vents during molding. These findings are believed to be applicable not only to resin transfer molding, but generally to liquid composite molding processes.
Application of Monte Carlo Simulations to Hydrated Nafion Stiffness Predictions
Authors: Weiland Lisa Mauck , Lada Emily K. , Smith Ralph C. , Leo Donald J.
Published: April 2008

Application of Rotational Isomeric State (RIS) theory to the prediction of Young’s modulus of a solvated ionomer is considered. RIS theory directly addresses polymer chain conformation as it relates to mechanical response trends. Successful adaptation of this methodology to the prediction of elastic moduli would thus provide a powerful tool for guiding ionomer fabrication. The Mark-Curro Monte Carlo methodology is applied to generate a statistically valid number of end-to-end chain lengths via RIS theory for a solvated Nafion case. The distribution of chain lengths is then fitted to a Probability Density Function by the Johnson Bounded distribution method. The fitting parameters, as they relate to the model predictions and physical structure of the polymer, are studied so that a means to extend RIS theory to the reliable prediction of ionomer stiffness may be identified.
Single-Phase Heat Transfer in Mems-Based Pin Fin Heat Sink
Authors: Kosar Ali , Peles Yoav
Published: April 2008

An experimental study has been performed on single-phase heat transfer of de-ionized water over a bank of shrouded micro pin fins 243-μm long with hydraulic diameter of 99.5-μm. Heat transfer coefficients and Nusselt numbers have been obtained over effective heat fluxes ranging from 3.8 to 167 W/cm2 and Reynolds numbers from 14 to 112. The results were used to derive the Nusselt numbers and total thermal resistances. It has been found that endwalls effects are significant at low Reynolds numbers and diminish at higher Reynolds numbers.
Transient Heat Conduction for Small Fourier Number
Authors: Sheyman Vladimir
Published: April 2008

In this paper, a specific transient heat conduction case for small Fourier number in comparison with the lumped-heat-capacity system is considered.
Fatigue Properties of Electro-Active Papers for Biomimetic Actuators
Authors: Shelton John , Craft William J. , Kim Jaehwan , Grant Jamil , Sankar Jag , Choi Sang H.
Published: April 2008

Cellulose-based Electro-Active Papers (EAPap) have been studied as potential actuators as a result of their low voltage operation, light weight, and low power consumption. In addition, they are bio-degradable and potentially inexpensive.1 The construction of many EAPap electromechanical actuators has been based on cellulose paper film coated with thin electrode layers. This EAPap actuator has shown a reversible and reproducible bending movement as well as longitudinal displacement under low voltage alternating current. However, the EAPap is a complex anisotropic material, which has not been extensively characterized and additional basic and design testing is required before developing EAPap application and devices. It is important to know the extended fatigue and elastic properties of EAPap materials, and this requires testing and evaluation. It has been known that the cellulose based EAPap has two distinct elastic constants connected by a bifurcation point along the stress strain diagram.2 The initial Young’s modulus of EAPap is in the range of 5-8GPa, - quite high compared to other polymer materials.3 Since these materials are anisotropic, elastic properties also differ as a function of orientation. These materials are sensitive to humidity and temperature. Fatigue tests conducted and described in this paper identify critical properties of this under-analyzed class of materials to provide a measure of its fatigue capabilities. Mechanical strain of EAPap materials has been evaluated, and it appears to follow closely a linear creep model as confirmed by low frequency cyclic (fatigue) loading. The creep parameter has also been determined to be a function of temperature and load level for all the EAPap materials tested.
Numerical Simulation of Turbulent Flows in Ribbed Pipes
Authors: Vijiapurapu Sowjanya , Cui Jie
Published: April 2008

The Reynolds averaged Navier-Stokes (RANS) equations were solved along with three turbulence models, namely κ-ε, κ-ω, and Reynolds stress models (RSM), to study the fully developed turbulent flows in circular pipes roughened by repeated square ribs. The spacing between the ribs was varied to form three representative types of surface roughness; d–type, intermediate, and k–type. Solutions of these flows at two Reynolds numbers were obtained using the commercial computational fluid dynamics (CFD) software Fluent. The numerical results were validated against experimental measurements and other numerical data published in literature. Extensive investigation of effects of rib spacing and Reynolds number on the pressure and friction resistance, flow and turbulence distribution was presented. The performance of three turbulence models was also compared and discussed.
Evaluation of Tool Wear Suppressive Ability of Lubricants Usein in Minimum Quantity Lubrication Application in High Speed Machining of Cast Aluminum Alloys
Authors: Bardetsky Alexander , Attia Helmi , Elbestawi Mohamed
Published: April 2008

The disadvantages of conventional metalworking fluids such as disposal problems, health problems and economic factors have led to the development of strategies to reduce their amount in metalworking. Recently, Minimum Quantity Lubrication (MQL) technology was developed and it seems to be a suitable alternative for economically and environmentally compatible production. It combines the functionality of lubrication with an extremely low consumption of lubricant and has a potential to replace metalworking fluids application in machining operations. The MQL lubricants are formulated with two major groups of additives; anti-wear (AW) additives and extreme pressure (EP) additives. When such lubricants are applied to the cutting zone, protective layers are formed on the interacting surfaces of the workpiece and the cutting tool. These layers prevent direct contact between the tool and chip surfaces, and, therefore reduce friction forces and tool wear. In order to utilize MQL to its full potential, it is essential to select appropriate lubricant composition for particular work material and machining parameters. The experimental study of different compositions of MQL lubricants is reported. The effectiveness of the lubricants are determined in terms of their ability to protect the cutting tool in high speed machining of cast aluminum alloys, which are widely used in automotive industry. The main objective of this research is to quantitatively evaluate the ability of lubricant’s additive composition to reduce the tool wear. This is reached through the comparison between the tool wear rate measured during the machining of aluminum cast alloy with the application of MQL, and the tool wear rate obtained in dry machining of the same alloy. Two kinds of the lubricants are evaluated; vegetable and synthetic. The content of AW and EP additives in each kind of lubricant was varied on three levels in order to capture the effect of the lubricant’s composition on tool wear. The result of the MQL lubricants evaluation is discussed and the recommendations for optimal lubricant composition are made.
Development of a Variable Dynamic Automotive Suspension Model Using Virtual Test Bed
Authors: Brewer Thomas , Rocheleau David
Published: April 2008

This paper is concerned with the development of a fully dynamic automotive suspension model in Virtual Test Bed (VTB), a dynamic system simulation environment developed by the University of South Carolina Department of Electrical Engineering for modeling multi-technical dynamic systems. VTB is normally used to prototype large scale electrical systems, but as shown in this paper, it can also be used to accurately simulate dynamic mechanical devices. Mathematical equations governing vehicle dynamic motion were developed and converted into C++ code. This code was then converted into a VTB model using Microsoft C++. A model of a full car passive suspension system was developed in VTB around this model, in which all dimensions, spring and damper constants, and vehicle path can be changed easily, without recoding the model itself. The model was then compared to a previously validated model created in Matlab Simulink. The results of this comparison, as well as validation with experimental data from a quarter-car suspension system, showed that VTB is a valid platform for modeling dynamic mechanical systems, and could be used to model active vehicle suspension as well.
A Fracture Mechanics Approach to the Prediction of Tool Wear in Dry High Speed Machining of Aluminum Cast Alloys: Part 1 — Model Development
Authors: Bardetsky Alexander , Attia Helmi , Elbestawi Mohamed
Published: April 2008

The analysis of the mechanism of cutting tool wear in high speed machining of cast aluminum alloys is conducted in this research work. The result of analysis indicates that the interaction between the hard silicon constituencies of the alloy and the surface of the cutting tool is the most detrimental to tool life. The wear of the cutting tool in such interactions, governed by fatigue wear mechanism, is directly proportional to silicon content of the alloy, silicon grain size and to the tool’s loading conditions. In order to predict the tool wear in machining aluminum cast alloys, a new wear model is developed. The fracture mechanics approach in wear rate estimation is implemented in this model. As an input data for the tool wear modeling, the normal and tangential stresses, acting on the flank of cutting tool are used. The fracture mechanics analysis of the subsurface crack propagation in the cobalt binder of cemented carbide cutting tool material is performed using a finite element (FE) model of the tool-workpiece sliding contact. The real microstructure of cemented carbide is incorporated in the FE model of tool-workpiece contact, and elastic-plastic properties of cobalt, defined by continuum theory of crystal plasticity are introduced in the model by UMAT subroutine of the ABAQUS® FE software. The crack propagation rate, determined from FE modeling, is used then in the model of cutting tool wear, developed in this work. This model is capable to predict the wear rate of cutting tool, base on the microstructural characteristics of the cutting tool and workpiece material and the tool’s loading conditions. The model can be used for cutting tool life assessment and management in high speed machining of Al-Si alloys in an industrial setting.
Ring Microgyroscope Modeling and Performance Evaluation
Authors: Esmaeili Mehdi , Durali Mohammad , Jalili Nader
Published: April 2008

This paper discusses the effects of substrate motions on the performance of a microgyroscope modeled as a ring structure. Using Extended Hamilton’s Principle, the equations of motion are derived. The natural frequency equation and response of gyroscope are then extracted in closed-form for the case where substrate undergoes normal rotation. The Galerkin approximation is used for discretizing the partial differential equations of motion into ordinary differential equations. In these equations, the effects of angular accelerations, centripetal and coriolis accelerations are well apparent. The response of the system to different inputs is studied and the system sensitivity to input parameter changes is examined. Finally, the sources of error in the measurement of input rotational rate are recognized. The study demonstrates the importance of errors caused by cross axes inputs on the gyroscope output measurements.
Large Eddy Simulation of Unsteady Flow Around a Door Mirror Model and Prediction of Resulting Far-Field Sound
Authors: Wang Hong , Kato Chisachi , Yamade Yoshinobu , Guo Yang
Published: April 2008

Unsteady flow and resulting far-field sound are numerically investigated for a door mirror model in this paper. The flow field is solved by Large Eddy Simulation (LES) with the dynamic Smagorinsky model while the surface pressure fluctuations obtained by LES are used to predict the far-field sound based on the acoustic analogy. For the prediction of the far-field sound, Curle’s equation is used under the assumption that the characteristic length of the door mirror model is much smaller than the wavelength of the sound. Comparisons between the predicted and measured data are presented in terms of the time-averaged and fluctuating surface pressure distributions as well as the far-field sound spectrum. Reasonably good agreements have been obtained between the predicted and the measured data. Investigation of the effects of the mesh resolution also shows that improved results can be obtained efficiently if the mesh resolution is increased along the stream-wise direction within the separation region and wake region.
Effect of Operating Variables With Heat Treatment and Their Interactions on Wear Behavior of High Carbon Steels in Dry Sliding
Authors: Younis Aimen M. , Akbar Ahmed A.
Published: April 2008

The present study deals with the wear data analysis of high carbon steels to investigate the relationship between the operating variables and the heat treatment. The steel selected was 1095 in the AISI standard which is equivalent to C105W1 in the German standard. The wear studies were carried out by using pin on disc apparatus at room temperature in dry sliding. The wear data were carried out based on an experimental design (24 factorial design ) following by analysis of variance method (ANOVA) to examine the main effect of sliding velocity, normal load, sliding distance, heat treatment, and their interactions on wear behavior. The results show that severe deformation of annealed and quenched 1095 steels on the contact surface was responsible for high wear loss at high normal loads and low sliding velocities. At high normal load and low sliding velocity, severe wear by oxidative-metallic was main mechanism and at low normal load for the same sliding velocity, mild wear by oxidative was main mechanism. The ANOVA results show that the operating variables have more significant effect on wear loss than that of heat treatment.
Surface Enhacement of Large Dies and Moulds by Ball-Burnishing
Authors: Lo´pez de Lacalle L. Norberto , Lamikiz Aitzol , Mun˜oa Julen
Published: April 2008

In this paper the use of the ball burnishing process to improve the final quality of form tools (moulds and dies) is studied. This process changes the roughness of the previously ball-end milled surfaces, achieving the finishing requirements for plastic injection moulds and stamping dies. Ball burnishing can be easily applied in the same machining centres as those used for milling. In this way, both lead times and production costs can be dramatically reduced. In this paper the use of the ball burnishing process to improve the final quality of form tools (moulds and dies) is studied. This process changes the roughness of the previously ball-end milled surfaces, achieving the finishing requirements for plastic injection moulds and stamping dies. Ball burnishing can be easily applied in the same machining centres as those used for milling, as is shown in the three industrial examples. In this way, both lead times and production costs can be dramatically reduced. Both the burnishing system and its main parameters are taken into account, considering their influence on finishing. Examples of different materials, machined surfaces, and three industrial applications are explained, two on GGG70L and the last one in GS60. Final roughness are measured.
Gas Turbine Combustor: Modelling and Optimization
Authors: Ganesan V. , Kumar V. Jyothish
Published: April 2008

Present work is concerned with the flow field analysis inside an annular gas turbine combustor both under non-reacting and reacting conditions. Three-dimensional gas turbine combustor of 20-degree sector has been modeled using the pre-processor GAMBIT. Flow through the combustor has been simulated using FLUENT code by solving the appropriate governing equations viz., conservation of mass, momentum and energy. RNG κ-ε turbulence model is used for physical modeling. Initially prediffuser optimization has been carried out with respect to angle, length and contours. Flow through holes is modeled using porous jump boundary condition as well as modeling real holes themselves to study the efficacy of real hole modeling. Total pressure loss has been calculated to evaluate the cold flow as well as hot flow losses. Combustion has been modeled using the Probability Density Function (PDF) approach. Temperature and species concentrations are predicted.
Study of Turbulence Models in Flows Through Adverse Pressure Gradient System
Authors: Karunakaran E. , Ganesan V.
Published: April 2008

This paper is concerned with the study of performance of popular turbulence models used in the CFD analysis. Turbulence models considered for evaluation include the eddy viscosity models and the Reynolds stress model. The recent k-ε-v2-f model recommended for a flow with separation is also studied. Evaluation of the turbulence models in the present study focuses on a three-dimensional flow field development with adverse pressure gradient and flows that simulate wall-bounded turbulence. Numerical calculations are performed using SIMPLE based algorithm. Nowadays, decelerating flow in a diffuser is assessed by numerical simulations and the validation is done with experimental results. A comparison of the numerical results and the experimental data are presented. The main objective of the comparison is to obtain information on how well the numerical simulations representing the flow field with the standard turbulence models, are able to reproduce the experimental data.
Development of Optical Diagnostics for Multiphase Flow Velocity Measurements
Authors: Opalski Anthony B. , Wernet Mark P.
Published: April 2008

The NASA Glenn Research Center Two-Phase Flow Facility (TΦFFy) project is conducting a robust technology program to develop enabling products for advanced life support and power conversion systems. Future system safety and reliability will be enhanced by addressing focused microgravity fluid physics issues associated with flow boiling and multi-phase system stability. The project includes both normal gravity testing and reduced gravity aircraft flight campaigns. The development of novel compact heat exchanger designs for use in reduced gravity operations requires advanced quantitative planar velocimetry diagnostics in order to verify system performance. The development of a comprehensive package of non-intrusive and non-invasive optical diagnostics to provide phasic velocity information throughout the range of flow boiling regimes in both gravity and microgravity-based test rigs is discussed. The application of both point-based probe techniques and planar-based imaging techniques to obtain phasic velocity information is analyzed. The application of planar and stereo imaging techniques to multiple flow regimes is presented. Extensions of liquid film thickness and local void fraction measurement techniques are examined to evaluate their potential to provide velocity information for interfacial waves and global void interface tracking. The extension of development efforts applied to ground-based test rigs into aircraft-based microgravity rigs is also presented.
Solution Structures for Imposing Boundary Conditions in Mesh Free Analysis of Heat Conduction Problems
Authors: Gu Linxia , Kumar Ashok V.
Published: April 2008

One of the main advantages of meshless methods is that it eliminates the mesh generation, but it is still necessary to place nodes with controlled spacing variation on the boundary and within the domain. However, due to lack of connectivity between nodes it is more difficult to interpolate the field variables and impose boundary conditions. In this paper, a mesh free method is presented for analysis using a structured grid that does not conform to the geometry of the domain. The geometry of the domain is independent of the structured grid and is represented using implicit equations. The implicit equations of the boundaries can be used to construct solution structures that satisfy boundary conditions exactly even though the nodes of the grid are not on the boundaries of the domain. The solution structures are constructed using the implicit equations of the boundary together with a piece-wise interpolation over the structured grid. The implicit equations are also used to construct step function of solid such that its value is equal to unity inside the solid and zero outside. The step function of the solid is used for volume integrations needed for the analysis. The traditional weak form for Poisson’s equation is modified by using this solution structure to eliminate the surface integration terms. The accuracy and implementation of the present mesh free method is illustrated for two-dimensional heat conduction problems governed by Poisson’s equation. Satisfactory results are obtained when compared with analytical results and results from commercial finite element software.
Numerical Modeling of Buoyancy Induced Convection in Finned Heat Sinks in Presence of Unheated and Heated Shrouds
Authors: Bahga S. S. , Bhattacharya A. , Mahajan Roop L.
Published: April 2008

This paper investigates the effects of the presence of unheated and heated shrouds on the thermal performance of longitudinal finned heat sinks. A comprehensive numerical study was conducted to determine the impact of the shroud clearance from the tip of the fins and shroud heating. The first part of the study deals with the effects of an unheated shroud on finned heat sinks of different fin height, fin pitch and length in an attempt to cover a wide range of geometry. The numerical results reveal an optimum clearance for maximum heat transfer. For all heat sinks studied the unheated shroud improved the performance by as much as 15% until the shroud was very close when the performance decreased by as much as 10%. In the second part of the paper, the effects of heating of the shroud were considered. In these numerical runs, an isothermal boundary condition was imposed on the shroud. For the heating levels considered, it was found that heating of the shrouds can increase or lower the thermal performance of the heat sink depending on the heat sink geometry and shroud clearance. Finally, the numerical results also revealed a systematic dependence of the normalized Nusselt number on the Rayleigh number for a given heat sink geometry.
Automated Sample Preparation System for Rapid Biological Threat Detection
Authors: Stachowiak Jeanne C. , Shugard Erin E. , Caton Pamela , Mosier Bruce P. , Renzi Ron , Davalos Rafael V. , McGraw Gregory J. , Simmons Blake A. , Vandernoot Victoria A. , Haroldsen Brent A.
Published: April 2008

Rapid, automated sample preparation of bacterial cells and spores is required for threat analysis by remotely deployed chemical and biological warning systems. Sandia is designing, building, and testing an automated front-end sample preparation system based on miniature and microfluidic components, with the goal of concentrating bacterial species collected from the air, harvesting and solubilizing proteins from them, and delivering them to Sandia’s MicroChemLab capillary gel electrophoresis system1,2 for analysis (Fig. 1). Miniature, motorized valves and pumps control flow between system components connected by fused silica capillaries (Fig. 4). Sample processing modules include concentration by dielectrophoresis in an array of insulating posts or by mechanical filtration; heat-activated chemical lysis; mechanical filtration; removal of chemical lysis agents by size exclusion chromatography (SEC); and in-capillary fluorescent labeling.
Fluorescent Melting Curve Analysis Compatible With a Flowing Polymerase Chain Reactor
Authors: Dalton Tara M. , Kinahan David J. , Davies Mark R.
Published: April 2008

A primary tool for analysing PCR product is the Fluorescent Melting Curve Analysis (FMCA). The temperature at which a double helix DNA strand denatures depends both on its length and base pair composition. Accurate measurement of this melting temperature using fluorescence allows estimations be made regarding DNA product length and composition. Current progress in development of PCR thermal cyclers has been primarily aimed at micro-channel based flowing devices. This paper addresses the challenges associated with performing FMCA analysis which is compatible with the output from a flowing PCR thermocycler. Two PCR products of significantly different lengths and base pair composition are compared using space domain FMCA. Results allow for differentiation of the PCR product, and compare favourably with results from a commercial thermal cycler. The successful application of FMCA within a channel shows its potential for use in high throughput flow based total analysis systems (μTAS).
Experimental Investigations of Oscillatory Fluctuation in an Ammonia-Water Mixture Turbine System
Authors: Amano Yoshiharu , Kawanishi Keisuke , Hashizume Takumi
Published: April 2008

This paper reports results from experimental investigations of the dynamics of an ammonia-water mixture turbine system. The mixture turbine system features Kalina Cycle technology [1]. The working fluid is an ammonia-water mixture (AWM), which enhances the power production recovered from the low-temperature heat source [2], [3]. The Kalina Cycle is superior to the Rankine Cycle for a low temperature heat source [4], [5]. The ammonia-water mixture turbine system has distillation-condensation processes. The subsystem produces ammonia-rich vapor and a lean solution at the separator, and the vapor and the solution converge at the condenser. The mass balance of ammonia and water is maintained by a level control at the separator and reservoirs at the condensers. Since the ammonia mass fraction in the cycle has a high sensitivity to the evaporation/condensation pressure and vapor flow rate in the cycle, the pressure change gives rise to a flow rate change and then level changes in the separators and reservoirs and vice versa. From the experimental investigation of the ammonia-water mixture turbine system, it was observed that the sensitivity of the evaporating flow rate and solution liquid density in the cycle is very high, and those sensitivity factors are affected by the ammonia-mass fraction. This paper presents the experimental results of a study on the dynamics of the distillation process of the ammonia-water mixture turbine system and uses the results of investigation to explain the mechanism of the unstable fluctuation in the system.
Numerical and Experimental Analysis of a Nonlinear Vibrating MEMS
Authors: Braghin Francesco , Leo Elisabetta , Resta Ferruccio
Published: April 2008

When significantly displacing a proof mass, the nonlinear hardening characteristic of the supporting beams becomes visible. Thus, the resonance peak of the structure is no longer vertical but bends towards the higher frequencies. This property is useful to easily synchronise sense and drive resonances thus increasing the sensibility of the MEMS gyroscope. Through a test structure designed to investigate the high deformation range of the supporting beams, its nonlinear vibrations were investigated both experimentally and numerically. It is shown that a simple nonlinear lumped parameter model could be sufficient to schematise the system and that a semi-analytical integration method allows to quickly determine both stable and unstable branches of the system’s dynamic response and to design the supporting structure.
Optical and Electrical Methods to Measure the Dynamic Behavior of a MEMS Gyroscope Sensor
Authors: Cigada Alfredo , Leo Elisabetta , Vanali Marcello
Published: April 2008

A full characterization of the mechanical parameters for vibrating MEMS sensors is required before integrating the mechanical and the electronic part. This is to verify that the main design specifications are fulfilled before sensors are available on the market. The main goal is to accurately establish the well-working devices in the shortest time. In this paper the electrical method based on the measurement of the GND current is used to satisfy this purpose. To check the validity of the achieved results through this method a comparison is done with those obtained through the widely used optical method based on vibration measurements through by means of a Laser Doppler Vibrometer (LDV).
A Novel Glucose Sensor Based on Deflection of a Thin Membrane
Authors: Mariserla Sandeep , Leseman Zayd , Mackin Thomas J.
Published: April 2008

A novel glucose sensor based on the deflection of a thin membrane is proposed in the article. The sensor consists of a glucose-sensitive hydrogel layer which exhibits swelling when immersed in a glucose-containing solution. A detailed overview of the fabrication procedure and preliminary experimental results for real-time glucose monitoring using our prototype devices will be presented.
The Effects of DC Current on the Tensile Properties of Metals
Authors: Ross Carl , Roth John T.
Published: April 2008

When fabricating parts, deformation is commonly conducted in a “warm” or “hot” state in order to reduce the total energy required to form the metal. However, there are several negative effects associated with this method of energy reduction (e.g., high tool/die adhesions, environmental reactivity, etc.) Hence, another more efficient method of reducing the total deformation energy would be very beneficial. This paper examines an alternative means of reducing the energy by applying an electrical current and also determines how the material’s tensile properties are affected while the current is present. Also investigated are the influences of strain rate and cold work on the electrical effects. The stress-strain curves indicate that, when current flows through a metallic specimen, the energy required to cause deformation is greatly decreased; demonstrating that electricity provides a viable alternative to increasing the workpiece temperature. However, the effect of the electricity diminishes with increasing strain rates.
A Transient Model of Induced Natural Circulation Thermal Cycling for Hydrogen Isotope Separation
Authors: Shadday Martin A. , Heung Leung Kit
Published: April 2008

The property of selective temperature dependence of adsorption and desorption of hydrogen isotopes by palladium is used for isotope separation. A proposal to use natural circulation of nitrogen to alternately heat and cool a packed bed of palladium coated beads is under active investigation, and a device consisting of two interlocking natural convection loops is being designed. A transient numerical model of the device has been developed to aid the design process. It is a one-dimensional finite-difference model, using the Boussinesq approximation. The thermal inertia of the pipe walls and other heat structures as well as the heater control logic is included in the model. Two system configurations were modelled and results are compared.
Control System Design for Full Range Operation of a Narrow Commuter Vehicle
Authors: Kidane S. , Alexander L. , Rajamani R. , Starr P. , Donath M.
Published: April 2008

One way of addressing the traffic congestion problem is by efficiently utilizing the existing highway infrastructure. Narrow commuter vehicles can be part of this solution if they can be designed to be safe, stable and easy to operate. In this paper the design of a control system that ensures the tilt stability of a narrow tilting vehicle from start up to highway speed without requiring any learned skill from the driver and without affecting the handling of the vehicle is presented. This proposed control scheme constitutes of two different controllers. For low speed operation of the vehicle a new and improved Direct Tilt Control system is designed that results in minimal transient torque requirement and zero steady state torque requirement. For higher operating speed of the vehicle a Steering Tilt Control based control law is designed to ensure tilt stability of the vehicle. Finally a new method of integrating these two control schemes that guarantees smooth switchover between the controllers is proposed. The performance of the compound control system is evaluated by simulations carried out for different vehicle operating conditions. Preliminary results on direct tilt control are presented.
Numerical Modeling of Radiative Heat Transfer in Pool Fire Simulations
Authors: Krishnamoorthy G. , Borodai S. , Rawat R. , Spinti J. , Smith P. J.
Published: April 2008

Different approaches to modeling radiative heat transfer in Large Eddy Simulations (LES) of a 38 cm diameter methane pool fire are compared. The P-1 radiation model and the discrete ordinates method are spatially decomposed to solve the radiative transport equation (RTE) on parallel computers. The radiative properties are obtained in the form of mean absorption coefficients from total emissivity data or of spectral absorption coefficients extracted from a narrow band model (RADCAL). The predictions are compared with experimental data. The different approaches are able to predict total radiative heat loss fractions with only a moderate loss of accuracy. However, only the discrete ordinates method is able to qualitatively predict the distributions of the radiative heat flux vectors in regions away from the fire. Results obtained from the calculations performed with the gray property model are very close to those obtained with non-gray calculations. Employing the P-1 radiation model with the gray property model provides adequate coupling between the hydrodynamics and radiative heat transfer while decreasing computational time by about 20% compared to the discrete ordinates method in moderate size grids. The computational savings associated with the P-1 model can become significant in LES calculations that are performed on large computational grids (employing hundreds to thousands of processors) to resolve structures on the scale of the pool diameter. Such resolution is necessary to capture both the large structures on the scale of the pool fire and the smaller regions of air engulfments and visible flame structures that are pivotal to characterizing soot location and temperature.
Metallic Glass Surface Patterning by Micro-Molding
Authors: Bardt Jeffrey , Mauntler Nathan , Bourne Gerald , Schmitz Tony L. , Ziegert John C. , Sawyer W. Gregory
Published: April 2008

The micro-molding of bulk amorphous metal to create sub-micrometer to sub-millimeter surface features was investigated. The goal was to demonstrate the reproduction of such features in a metallic material from a master. The bulk metallic glass material was embossed between the glass transition and crystallization temperatures. Silicon wafers patterned by deep reactive ion etching were used as masters. The patterns were designed to test the effects and interactions of aspect ratios, geometry, and spatial proximity. In addition to these patterns, a master was developed to mold two-dimensional channel geometries. Comparisons between the replicated features and the molds are provided.
Numerical and Experimental Study on Micro-Electrical Discharge Micromachining Characteristics on Molybdenum
Authors: Allen Phil , Chen Xiaolin , Kim Dave
Published: April 2008

Electrical discharge micromachining (micro-EDM) is an ideal process for obtaining burr-free machined micron-size apertures. Molybdenum is one of the most attractive high energy and power aperture materials due to its mechanical and physical properties, mainly its high melting temperature and relatively high thermal conductivity. In this paper, fundamental machining characteristics for micro-EDM of molybdenum were investigated both numerically and experimentally. A thermo-numerical model was created to simulate a single spark discharge process. Experimental crater size is investigated using scanning electron microscopy and optical evaluation methods. The effects of important EDM parameters such as the pulse duration on crater shape, temperature distribution, tool wear percentage, and eroded volume were studied. Correlations between numerical and experimental data are also discussed. The model effectively estimates the size of single spark craters in molybdenum. The results show that the developed thermo-numerical model can be an effective tool in predicting the size of a crater formed by a single spark discharge in the micro-EDM process.
Sensor Based Failure Analysis of Rolling Element Bearings
Authors: Midturi Swaminadham
Published: April 2008

Failure-free operation of rolling element bearings is essential for the safe and reliable operation of rotating industrial equipment, especially of the type high-energy aircraft engines. However, improper installation and maintenance, large variations in applied loads, and cycle time initiate functional defects to reduce the service life of bearing elements severely. In-service condition monitoring of bearings by permanently mounted sensors offers excellent potential to reduce the risk of failures and avoid premature failure of bearings and the rotor system. This paper presents the results from a study on experimental investigation of bearing defect identification by sensor-based condition monitoring methods. Vibration spectra from a direct mount accelerometer are analyzed to interpret and classify bearing defects. Sensor locations on the bearing are selected for enhanced sensitivity and minimum loss in the signal transmission path. Signal processing methods such as Fast Fourier Transform and statistical Kurtosis and skewness parameters are applied to characterize the dynamic spectra due to bearing defects in outer race, inner race, and cage elements of a test bearing. Unlike the previous research, this study analyzes the dynamic spectra of a test bearing to identify the spectral differences due to varying loads. The results are presented in simple and easy to understand format for the maintenance and engineering staff to affect repairs to bearing assemblies.
Mechanism to Harvest the Potential Energy in the Ocean Waves
Authors: Viggiani Pedro , Valencia Guillermo
Published: April 2008

In this paper the design of an oscillating-arm mechanism with a ratchet link to a power shaft, is presented. This device is an original idea of the authors and it might make possible to harvest the potential energy of the ocean waves. This mechanism is formed by an arm (bar) linked to a rotating shaft in one of its ends, through a ratchet union, while in the other end it has a linked floating body in contact with the waves. The shaft is supported by bearings located on fixed supports, and it moves a load. The ratchet union connects the arm with the shaft when the arm is moving down, therefore this is the power generation step. More weight might be added on a pin located in the end of the arm, near to the floating body, in order to increase the moment on the shaft. This mechanism could operate in an individual or in a group way, over one shaft, to increase the power output. In this paper are presented the equations involved and a general design procedure that, given some particular parameters as input, it is capable to dimension the device and also estimate its performance for those conditions.
Toward the Fabrication of Hierarchically-Structured Porous Polymers for Tissue Engineering Scaffords
Authors: Wang Hai , Li Wei
Published: April 2008

Hierarchically-structured porous polymers play an important role in scaffold-based tissue engineering. However, the fabrication of these polymers presents a significant challenge because of the requirements of controllable pore size, distribution and interconnectivity. In this work, we report on a novel porous polymer fabrication method using high-intensity focused ultrasound (HIFU). The measurements of both spatial and temporal temperature field are reported for biocompatible PMMA (polymethyl methacrylate) samples insonated with a 1.1 MHz/3.3 MHz HIFU transducer. The acoustic power and insonation duration were both varied. The results have shown that HIFU has a dramatic heating effect on polymers: the temperature increasing rate can exceed 20°C/second and the final temperature can be higher than 120°C. This rapid, localized heating effect is exploited to foam CO2 saturated PMMA samples selectively and generate hierarchical microstructures. The created microstructures were characterized using the scanning electron microscopy (SEM). The results have shown that the amount and rate of acoustic energy dissipation during the HIFU insonation directly affect the polymer foaming process. Preliminary theoretical modeling of the acoustic field and heat transfer behavior in the porous polymers are also presented.
Study on Ultrasonic Cavitation Based Solidification Processing and Nanoparticle Feeding for High Volume Fabrication of Aluminum Matrix Nanocomposites
Authors: Yang Yong , Li Xiaochun
Published: April 2008

Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. It would be advantageous to produce low-cost as-cast bulk lightweight components of aluminum based MMNCs. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten aluminum. In this paper, a high power ultrasonic probe is used to disperse nano-size SiC particles in aluminum alloy A356. Experiment results show that the ultrasonic cavitation based dispersion of naoparticles in molten aluminum alloy is effective. The uniform nano particle dispersion resulted in significantly improved mechanical properties. Various nanopartilce feeding techniques were investigated and experimental results are presented.
Success Achieved Using High Performance VHB™ Tapes in a Harsh Outdoor Application
Authors: Bailey Nancy , Hwang S. Jimmy
Published: April 2008

The Qualcomm OmniTRACS™ Antenna Communications Unit (ACU) is a mobile transceiver which when installed on trucks allows two-way communication between drivers and fleet logistic centers. A global positioning device (GPS) inside the ACU shows controllers the geographical location of the truck and its cargo. The ACU is deployed in frequently harsh, inhospitable regions of the world and as such must operate reliably when exposed to diverse climatic conditions such as high humidity encountered in the Amazon River basin, extreme heat typical of deserts in the American southwest and while operating in northern Alaska where the terrain is rugged and winter temperatures reach −40C.
Effect of Alloying, Heat Treatment and Carbon Content on White Layer Formation in Machining of Steels
Authors: Han Sangil , Melkote Shreyes N.
Published: April 2008

This paper describes an experimental investigation of the role of alloying, carbon content, and heat treatment on white layer formation in machining of steels. This is carried out by machining steels that differ in alloying, heat treatment and carbon content, via orthogonal cutting tests performed with low CBN content tools. The thickness of white layer produced in AISI 1045 and AISI 4340 annealed steels are compared to determine the effect of alloying on white layer formation. The effect of heat treatment on white layer formation is investigated by machining annealed and hardened AISI 4340 steels. The effect of carbon content on white layer formation is investigated by cutting AISI 52100 and AISI 4340 steels of the same hardness (53 HRC). Since 52100 steel has almost twice the amount of carbon and less number of alloying elements than AISI 4340 steel, an approximate understanding of the effect of carbon content on white layer formation can be inferred. The results of the study show that alloying, heat treatment, and carbon content influence white layer formation. The possible roles of the maximum workpiece surface temperature, effective plastic strain and stress on white layer formation in the different steels are also analyzed via finite element simulations performed in a commercially available code.