bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of the Fiber-Matrix Interphase for Controlled Energy Absorption and Strength
Authors: Kissounko Denis A. , Danner Katherine M. , Deitzel Joseph M. , Gillespie John W.
Published: July 2010

Hybrid polysiloxane-based sizings with embedded silica and silica/latex nanoparticles were studied to improve Interfacial Shear Strength (IFSS) and energy absorption using the micro-droplet test method. The sizing mixture comprised of mixed polysiloxane with silica nanoparticles has been screened by varying one parameter at a time. The best mechanical performance was observed in the following concentration range: 1.0–2.0 wt% tetraethoxysilane (TES)/3-glycidoxypropyltrimethoxy silane (GPS) mixture, and 1.0–3.0 wt% Ludox® silica nanoparticles; 1.0–1.5 TES/GPS ratio, and 20 nm silica nanoparticles size. Increase of nanoparticles size leads to a decline in both strength and energy absorption, whereas chemical modification of nanoparticles surface has no significant effect compared to the baseline. The study also shows that the combination of hard (silica) and soft (latex) nanoparticles works best to maximize the strength and energy absorption. Hard particles increase surface roughness that increases interfacial strength and energy absorption during debonding whereas rubber particles contribute to improved energy absorption. Possible rational for such sizing composition/material property relationship will be discussed.
Low Power Electronics for Square-Wave Piezoactuator Driving
Authors: Biancuzzi G. , Lemke T. , Goldschmidtboeing F. , Ruthmann O. , Schrag H.-J. , Vodermayer B. , Schmid T. , Woias P.
Published: July 2010

The German Artificial Sphincter System (GASS) project aims at the development of an implantable sphincter prosthesis driven by a micropump. During the last few years the feasibility of the concept has been proven. At present our team’s effort is focused on the compliance to safety regulations and on a very low power consumption of the system as a whole. Therefore a low-voltage multilayer piezoactuator has been developed to reduce the driving voltage of the micropump from approximately 300 Vpp to 40 Vpp. Doing so, the driving voltage is within the limits set by the regulations for active implants. The operation of the micropump at lower voltages, achieved using multilayer piezoactuators, has already resulted in a much better power efficiency. Nevertheless, in order to further reduce power consumption, we have also developed an innovative driving technique that we are going to describe and compare to other driving systems. A direct switching circuit has been developed where the buffer capacitor of the step-up converter has been replaced by the equivalent capacitance of the actuator itself. This avoids the switching of the buffer capacitor to the actuator, which would result in a very low efficiency. Usually, a piezoactuator needs a bipolar voltage drive to achieve maximum displacement. In our concept, the voltage inversion across the actuator is done using an h-bridge circuit, allowing the employment of one step-up converter only. The charge stored in the actuator is then partially recovered by means of a step-down converter which stores back the energy at the battery voltage level. The power consumption measurements of our concept are compared to a conventional driving output stage and also with inductive charge recovery circuits. In particular, the main advantage, compared to the latter systems, consists in the small inductors needed for the power converter. Other charge recovery techniques require very big inductors in order to have a significant power reduction with the capacitive loads we use in our application. With our design we will be able to achieve approximately 55% reduction in power consumption compared to the simplest conventional driver and 15% reduction compared to a charge recovery driver.
Heavy Truck Roll Cage Effectiveness
Authors: Batzer Stephen A. , Enz Bruce E. , Herndon G. Grant , Thorbole Chandrashekhar K. , Hooker Robert , Parnell T. Kim , Ziejewski Mariusz
Published: July 2010

National accident statistics consistently show that the profession of Class VIII truck drivers is dangerous, and that their fatality rate is very high. One significant reason for this is the lack of rollover crashworthiness of many commercial truck designs. Analysis of numerous trucks that have been through rollovers shows that cab designs are typically designed to be durable, rather than strong, energy absorbing, and able to maintain shape under significant loading. In this current work, both destructive rollover testing and finite element analysis were performed with the objective being the determination of the effectiveness of conventional structural cab reinforcement for diminishing tractor cabin deformation. Intrusion into the tractor’s survival space can lead to mechanical injury (crush) and can also facilitate partial, or full, occupant ejection. The results of this testing show that the amount of structural deformation of the tractor cabin can be significantly reduced, and the amount of occupant survival space preserved using straightforward and cost effective techniques.
Liquid-Mediated Reversible Thermal Interface for Satellite Thermal Management
Authors: Cha Gilhwan , Ju Y. Sungtaek
Published: July 2010

Ability to establish and break thermal contacts in a reversible manner is important in a wide range of applications. These include active thermal conductance control for bolometers [1], pulsed thermoelectric cooling [2], chip scale atomic clocks, and thermal energy harvesting, and thermally reconfigurable networks for satellite thermal management [3]. The last is particularly interesting as it potentially has significant near- as well as long-term technical impact.
Fabrication of Polymeric and Polymeric Nano-Composite MEMS Structures
Authors: Li Daizong , Tumkor Serdar , Manoochehri Souran , Pochiraju Kishore
Published: July 2010

This paper presents methodologies for rapid prototyping of complex and functional polymeric MEMS structures using lithography steps only. In order to overcome stiffness and strength limitations of the polymeric structures, reinforcing nano-materials were added to enhance stiffness. A challenge in processing polymeric MEMS devices is achieving the release of the MEMS structure from the substrate. This paper presents several process sequences and photoresist combinations that produce freestanding polymeric MEMS structures. Negative photoresist (SU8) and positive photoresist (AZ4620) materials were used in spin coat, bake, exposure and selective development steps. This paper describes the experiments used for determining the optimal process parameters and the release performance. In addition, the paper also illustrates exposure control techniques that reduce process-induced defects such as heat–induced bubbles, degassing and overexposure.
Flow Induced Oscillation of a Set-In Circular Cylinder
Authors: Oviedo-Tolentino F. , Romero-Mendez R. , Hernandez-Guerrero A. , Luna J. M.
Published: July 2010

This work studies the fluid-structure interaction of a set-in, large aspect-ratio circular cylinder in cantilever subjected to a cross flow. Experiments were conducted in a water tunnel and observations were obtained using flow visualization techniques and direct observation of the deflection of the cylinder. The flow behavior was observed using dye injection. The experiments show that the dominant vibration of the cylinder is transversal to the flow direction, and that the first mode of vibration of the cylinder appears at a particular Reynolds number, which is a function of the mechanical properties of the cylinder. The deflection stops when the Reynolds number is increased. The peak deflection and frequency of oscillation, as a function of the Reynolds number, were also determined. The analysis shows a close relation between the frequency of oscillation and the frequency of appearance of a vortex shedding. For large deflections of the cylinder the flow structure is modified substantially, and the frequency at which vortex appears is different to the frequency that occurs for fixed cylinders.
Wheel Power Management Systems: Dynamics and Efficiency Evaluation
Authors: Andreev Alexandr F. , Kabanau Viachaslau I. , Vantsevich Vladimir V.
Published: July 2010

In recent years, leading automotive companies have been developing various wheel power management systems for controlling power distribution among the driving wheels of all-wheel drive vehicles. Such systems being successors of tank turn/steer mechanisms have inspired new designs of wheeled vehicle driveline systems. Modern wheel power management systems usually consist of planetary transmissions with controllable clutches. The proposed paper analyzes kinematics and dynamics of main types of these systems and then the impact of the systems on the vehicle energy loading, mechanical power loss and, finally, on vehicle energy efficiency. Results of analytical research of double differentials, and open differential with three-link planetary rows are presented in comparison with traditional open differential. Conditions for providing improved energy (i.e. fuel efficiency) are formulated and then analytical representation is given to mathematically link parameters of the wheel power management systems with vehicle tread and minimal turn radius. Hence, a design engineer can assign the optimal parameters of a wheel power management system that provides improved vehicle energy/fuel efficiency.
A Study on the Material Modeling of a Robot Polyurethane Stopper
Authors: Bang Kyukwon , Kim Taewung , Jeong Hyun-Yong
Published: July 2010

Polyurethane stoppers are used to protect heavy parts from damage in case of an unpredicted impact between parts in a robot. In order to evaluate the performance of a polyurethane stopper during impact, it was necessary to model the material behavior. Thus, the compression test, the tension test, the pure shear test, the torsion vibration test were conducted, and the hyperelastic material constants and viscoelastic material constants (Prony series parameters) were determined. Finite element simulations for the tests were conducted to check whether the material model adequately represented the material behavior. In addition, a finite element simulation for an impact between a part of a robot and a stopper was conducted to evaluate the performance of a stopper.
Investigation of Casimir and Van der Waals Forces for a Nonlinear Double-Clamped Beam Using Homotopy Perturbation Method
Authors: Mojahedi Mahdi , Moeenfard Hamid , Ahmadian Mohammad Taghi
Published: July 2010

In this study, static deflection and Instability of double-clamped nanobeams actuated by electrostatic field and intermolecular force, are investigated. The model accounts for the electric force nonlinearity of the excitation and for the fringing field effect. Effects of mid-plane stretching and axial loading are considered. Galerkin’s decomposition method is utilized to convert the nonlinear differential equation of motion to a nonlinear algebraic equation which is solved using the homotopy perturbation method. The effect of the design parameters such as axial load and mid-plane stretching on the static responses and pull-in instability is discussed. Results are in good agreement with presented in the literature.
Interface Effects in Strained Thin Films
Authors: Robison Andrew , Lei Lei , Ramarapu Sowmya , Koslowski Marisol
Published: July 2010

Crystalline films grown epitaxially on a substrate consisting of a different crystalline material are of considerable interest in optoelectronic devices and the semiconductor industry. The film and substrate have in general different lattice parameters. This lattice mismatch affects the quality of interfaces and can lead to very high densities of misfit dislocations. Here we study the evolution of these misfit dislocations in a single crystal thin film. In particular, we consider the motion of a dislocation gliding on its slip plane within the film and its interaction with multiple obstacles and sources. Our results show the effect of obstacles such as precipitates and other dislocations on the evolution of a threading dislocation in a metallic thin film. We also show that the material becomes harder as the film thickness decreases in excellent agreement with experiments.
Adaptive Trajectory Tracking Control of Nanopositioning Stage Under Dynamic Load Condition
Authors: Sheikh Sofla Mohammad , Rezaei Seyed Mehdi , Zareinejad Mohammad
Published: July 2010

Piezoelectric actuators (PEAs) are frequently used in a wide variety of micromanipulation systems. However their accuracy is limited due to hysteresis nonlinearity. Also investigation of the fundamental properties of the piezoceramics depicts that external mechanical loads cause inclination in hysteresis loop which can deteriorate tracking performance furthermore. A novel modeling and control approach is proposed in this paper, for precision trajectory tracking control of piezoelectric actuators under dynamic load condition. First the hysteresis nonlinear function based on Bouc-Wen hysteresis model is approximated by a Taylor series expansion. Then an adaptive trajectory tracking control is proposed based on the backstepping method using the developed mathematical model. The asymptotical stability in displacement tracking and robustness to the dynamic load disturbance can be provided using the proposed control approach. Experimental results are illustrated to verify the efficiency of the proposed method for practical applications.
Mechanical Properties of Microscale Graphitic Carbon Foam Ligaments and Nodes
Authors: Ganguli S. , Roy A. K. , Wheeler R.
Published: July 2010

Carbon foam is recognized as having the greatest potential to replacement for metal fins in thermal management systems such as heat exchangers, space radiators, and thermal protection systems [1–5]. Carbon foam refers to a broad class of materials that include reticulated glassy, carbon and graphitic foams that are generally open-cell or mostly open-cell. They can be tailored to have low or high thermal conductivity with a low coefficient of thermal expansion and density. These foams have high modulus but low compression and tensile strength. Among the carbon foams, the graphitic foam offers superior thermal management properties such as high thermal conductivity. Graphitic foams are made of a network of spheroidal shell segments. Each cell has thin, stretched ligaments in the walls that are joined at the nodes or junctions. The parallel arrangement of graphene planes in the ligaments confers highly anisotropic properties to the walls of the graphitic foams. The graphene planes tend to be oriented with the plane of the ligaments but become disrupted at the junctions (nodes) of the walls. Since conduction is highest along parallel graphene planes, the thermal conductivity is highest in the plane of the ligaments or struts, and much lower in the direction transverse to the plane of these ligaments. In a previous study [6] extensive mechanical and thermal property characterization of carbon foams from Kopper Inc. (L1) and POCO Graphite, Inc. (P1) were reported. These foams were graphitic ones that are expected to have high thermal conductivity. Figure 1 shows sections of light microscopy images of the three foams of four foams. The most important thing to notice is that the images were not at the same magnification. The large cells in the GrafTech foam have an average diameter of only ∼100 μm but have a bimodal distribution cells with many small closed-cells few micrometers in diameter. Changes in density in the GrafTech foam was accompanied by a change in the large cells’ diameter — larger diameter giving greater porosity and lower density without changing the smaller cells’ sizes that filled the solid phase between the larger bubbles. The POCO foam has a fairly uniform size cell distribution of a few hundred micrometers. The Koppers’ foams show larger cells yet with the left (“L” precursor) having a uniform size while the right-hand (“D” precursor) is a less uniform and lower porosity.
Shape Anisotropy Study of Nickel and Iron/Cobalt Nanoparticles
Authors: Vial Karine , Kumar Dhananjay
Published: July 2010

Shape anisotropy of Nickel and Iron/Cobalt nanoparticles embedded respectively in gold and Titanium/Nitride thin film matrix on a sapphire substrate has been study. The samples have been fabricated using a pulsed laser deposition. The measurements of magnetic moment per cm2 versus magnetic field at different temperatures (10 K and from 50 K to 300 K every 50 K) and with a magnetic field applied parallel to the sample or perpendicularly have been made in order to determine the coercivity of the material for these parameters. We also report our investigation on the magnetoresistance effect per cm2, where measurements have been lead for different temperatures (10 K, 100 K, 200 K, and 300 K) and two positions of the sample (parallel and perpendicular to the magnetic field). The comparison of the two cases, magnetic field parallel and magnetic field perpendicular to the sample, has shown that the difference of coercivity between them decreases when the temperature increases for all samples. For gold/nickel monolayer samples the difference varies from 120 Oe at 10 K to 6 Oe at 300 K for coercivities of about 200 Oe to 450 Oe at 10 K depending on the sample to coercivities of about 80 Oe to 150 Oe at 300K depending on the sample. For Titanium-Nitride/ Iron-Cobalt monolayer and trilayers samples the difference of coercivities varies between 10 Oe to 500 Oe depending on the temperature and the sample for coercivities between 30 Oe and 750 Oe. The difference in the percentage of magnetoresistance at 0 Oe is between 5 to 40% for Au/Ni sample and 0% to 10% for TiN/FeCo samples.
Comparing the Predictive Ability of T-Method and Cobb-Douglas Production Function for Warranty Data
Authors: DasNeogi Protyusha , Cudney Elizabeth , Adekpedjou Akim , Kestle Rodney
Published: July 2010

Predictive models are used in an attempt to anticipate future transitions, mitigate losses, and maximize economic gains. In today’s market, companies look for high reliability and quality of products due to great market competition. Hence warranty data is of considerable interest to companies. Warranty shows the ability of a system or component to perform its functions within a given customer usage. Many statistical and data mining methods are available to predict the warranty data. This study focuses on analyzing the predictive efficiency of the T-method and Cobb-Douglas production function on warranty data by comparing their prediction capability. The T-method, developed by Genichi Taguchi, is founded upon the fundamentals of the Taguchi System of Quality Engineering which is used to calculate an overall prediction based on signal-to-noise ratio. Using this method, the required parameters are calculated to obtain an overall estimate of the true value of the output for each signal member. The Cobb-Douglas production function is then applied on the same dataset. In economics, the Cobb-Douglas functional form of production function is widely used to represent the relationship of the output to inputs. The strength of the relationship is then assessed using the R-squared and adjusted R-squared values.
Axial Force Regulation in MEMS Resonant Sensors
Authors: Hassanpour Pezhman A. , Wong Chris T. , Nieva Patricia M. , Khajepour Amir
Published: July 2010

In this paper, a passive mechanism is proposed for regulating the axial forces due to thermal stresses induced in MEMS resonant sensors. It is shown that by using this mechanism, one can control the axial force or thermal stresses to be compressive or tensile, or zero. An analytical model and a finite element model are developed for this study. It is shown that the analytical model is a powerful tool to predict the overall response and/or optimize the design, while the finite element model can be used for fine tuning and obtaining more accurate results.
Gradient Interphases in Polymer Nanocomposites
Authors: Qiao Rui , Brinson L. Cate
Published: July 2010

As revealed by experimental data on ultrathin polymer films [1, 2], polymer mobility changes in a gradient fashion away from the polymer-surface interface. However, little is yet known on gradients in mechanical properties in polymer nanocomposites. In this work, we discuss a novel nanoindentation experimental approach to measure these properties in model nanocomposite systems, the associated modeling to extract realistic data (Figure1), and simulations of representative volume elements (RVE) of nanocomposites including interphase layers (Figure2).
Fabrication and Characterization of Suspended Single-Walled Carbon Nanotubes Composite Beams
Authors: Lee Dongjin , Cui Tianhong
Published: July 2010

We report the fabrication and characterization of single-walled carbon nanotube (SWCNT) multilayer micropatterns and suspended micro-beams prepared by layer-by-layer (LbL) assembly. The SWCNT multilayer is etched using oxygen plasma with the masking layer of the photoresist, resulting in the feature size of 2 μm. Furthermore, it is released by etching a sacrificial layer of oxide in the hydrofluoric acid vapor. I-V measurements reveal that the resistance of suspended beams decreases upon release due to the exposed surface, excluding the effects of substrate. A high Young’s modulus has been found on the range of 500–800 GPa due to the deviation of spring constants measured and the variation in thickness of beams. It is much higher than those of the other CNT-polymer composites due to the organized structure. Stiff CNT-polymer composite micropatterns and the suspended micro-beams may have potential applications for novel physical sensors, nano-switches, other M/NEMS devices, etc.
Numerical Simulation of Synthetic Microstructured Fibrillar Adhesive Pads
Authors: Safdari Masoud , Baniassadi Majid , Ghazavizadeh Akbar , Ruch David , Ahzi Said
Published: July 2010

Recently, the study, analysis and prototyping of biologically inspired adhesives pads have been subject of growing interest. These synthetic adhesives consist of rafts of tiny protruding fibers. The adhesion performance of these micro-engineered products is highly dependent on the geometrical and mechanical properties of microfibers and the surface they adhering to. Small fluctuations in these parameters can drastically change their adhesion performance. In this investigation, a more comprehensive mathematical model of a single micro-fiber with adhesion capability in contact with an uneven surface has been developed. To simulate realistic conditions, this analytical model could be extended to an array of micro-fibers. Using Monte Carlo techniques it was possible to study the behavior of an array of these micro-fibers under several degrees of uncertainty. The results deduced by this novel modeling approach are in good agreement with experimental measurements of adhesion performance in synthetic adhesive pads available in literature.
Effect of Conductivity and Environmental Pressure on Electro-Plasma Process (EPP)
Authors: Wahab M. A. , Liang Jiandong , Guo Shengmin
Published: July 2010

Electrolytic plasma process is an efficient surface modification method for metallic materials. With proper control of the process parameters Electro-Plasma Process (EPP) could generate unique surface morphology, which is suitable for effective cleaning of the metallic surfaces and inherently, good adhesion strength can be achieved for eventual coating the surfaces. Increasing input voltage beyond the conventional Faraday region of electrolysis, luminous discharge is observed on the surface of one of the electrodes. The electrode surface must be covered by layers of bubbles before the discharge could be set in. The discharge of energy is then taken place in an explosive way with localized high temperature. The combination of heat and kinetic impact could effectively remove the surface contaminants and could produce a unique surface morphology. In this paper, the conditions of process control parameters and the resultant surface conditions that could be achieved are studied. It has been found that elevated temperature is beneficial towards the plasma formation on electrodes; and the increase of temperature essentially increases the kinetic energy of electrons in the electrolytic solution and a high electrolyte temperature assists the boiling process and the chemical reactions that generate bubbles. The conductivity of the electrolytic solution could also affect the threshold voltage and the current density, but the total power input does not vary significantly with conductivity. Environmental pressure has been proved to be the single most critical important factor for Electro Plasma Process; and by increasing the pressure level the total breakdown energy tends to increase and more importantly, the resultant surfaces manifest that the energy consumed for surface modification increases with pressure.
Hybrid Method of Engineering Analysis: Combining Meshfree Method With Distance Fields and Collocation Technique
Authors: Tsukanov Igor , Posireddy Sudhir R.
Published: July 2010

Most of the modern engineering analysis methods (Finite Element, Finite Difference, Finite Volume, etc.) rely on space discretizations of the underlying geometric model. Such spatial meshes have to conform to the geometric model in order to approximate boundary conditions, construct basis functions with good local properties as well as perform numerical integration and visualization of the modeling results. Despite recent advances in automatic mesh generation, spatial meshing still remains difficult problem which often requires geometry simplification and feature removal. Conforming spatial mesh also restricts motions and variations of the geometry and breaks design-analysis cycle. In order to overcome difficulties and restrictions of the mesh-based methods, the alternative analysis methods have been proposed. We present a numerical technique for solving engineering analysis problems that combines meshfree method with distance fields, radial basis functions and collocation technique. The proposed approach enhances the collocation method with exact treatment of boundary conditions at all boundary points. It makes it possible to exclude boundary conditions from the collocation equations. This reduces the size of the algebraic system which results in faster solutions. On another hand, the boundary collocation points can be used to enforce the governing equation of the problem which enhances the solutions accuracy. Ability to use unstructured grids empowers the meshfree method with distance fields with higher level of geometric flexibility. In our presentation we demonstrate comparisons of the numerical results given by the combined approach with results delivered by the traditional collocation technique and meshfree method with distance fields.
Performance Evaluation of a Portable Restraint for a Motor Coach Occupant in a Rollover Accident
Authors: Thorbole Chandrashekhar K. , Batzer Stephen A. , Renfroe David A.
Published: July 2010

A quarter roll of a motor coach could result in fatal injuries to its occupants due to ejection and occupants striking each other and striking the bus interior. The best rational solution to prevent ejection and serious head injury is to restrain the occupants to their seats. This study addresses the dynamic performance of the portable restraint in a rollover accident and compares it to the conventional restraint. The biodynamic code MADYMO is used to analyze and compare the occupant kinematic with the portable restraint and the conventional restraint. The full scale bus rollover motion data with different ATD’s (Anthropomorphic test devices) placed at different locations on the bus shall be used to prescribe motion to this MADYMO model. This study demonstrates the success of the portable restraint in preventing ejections if the lateral belt used for securing the system to the seat does not slip. The study further demonstrates the possibility of improving the portable restraint performance using computational model.
Formation and Protection of Fe-Cr Oxide Spinel During the Oxidation Process of Stainless Steels in LBE Environment
Authors: Tan Taide , Chen Yitung
Published: July 2010

The formation of the spinel of magnetite and chrome oxide, is a very complex process, especially with the scale removal effect in flowing lead bismuth eutectic (LBE) nuclear coolant. This paper studied the formation and the protection of the spinel of magnetite and chrome oxide on stainless steel, in different environments at a mesoscopic level. The role of the alloying element has been analyzed. The formation of the spinel of magnetite and chrome oxide and the scale removal effect are simulated using a stochastic cellular automaton method. The protection of this spinel layer to the structural materials has been analyzed.
A Combined Approximation Based MATLAB Code for Dynamic Re-Analysis of Aerospace Structures
Authors: Afifi Hesham A. , Nikolaidis Efstratios , Afifi Emily K. , Gangadharan Sathya N.
Published: July 2010

Achieving a high strength-to-weight ratio is one of the most important goals in the design of aerospace structures. Designers are continuously striving to find the optimum solutions that will make aerospace vehicles simultaneously strong and light. During the design process, the structure experiences several changes to reach this goal. Any change to the geometry and/or material property directly influences the global stiffness of the structure. Modification of the applied loading or stiffness impacts the solution of displacements. Each design change requires the implicit analysis equation to be resolved. In large scale models with thousands of degrees of freedom, the cost and time of repeated reanalysis, even for a small change, is significant. A combined approximation approach (CA) was previously developed to provide an efficient and accurate reanalysis of large structures, even with great changes in the design. High quality results have also been obtained through utilizing the CA method for dynamic reanalysis. This approach involves the combination of local and global approximation methods including series expansion, reduced basis vector, matrix factorization, and Gram-Schmidt orthonormalization. In this study, a combined approximation based MATLAB code for dynamic reanalysis has been developed. Changes in both baseline design properties and excitation frequency range have been introduced. The response of the modified system is calculated as a function of these changes, directly via inversion of the dynamic stiffness matrix and approximately via combined approximation method. A reanalysis example of a simplified aircraft wing spar model using this code is presented. Both methods are compared for solution accuracy.
Towards Truly Multiscale Simulation of Fatigue Processes in Metallic Structures
Authors: Emery John M. , Bozek Jeffrey E. , Ingraffea Anthony R.
Published: July 2010

The fatigue resistance of metallic structures is inherently random due to environmental and boundary conditions, and microstructural geometry, including discontinuities, and material properties. A new methodology for fatigue life prediction is under development to account for these sources of randomness. One essential aspect of the methodology is the ability to perform truly multiscale simulations: simulations that directly link the boundary conditions on the structural length scale to the damage mechanisms of the microstructural length scale. This presentation compares and contrasts two multiscale methods suitable for fatigue life prediction. The first is a brute force method employing the widely-used multipoint constraint technique which couples a finite element model of the microstructure within the finite element model of the structural component. The second is a more subtle, modified multi-grid method which alternates analyses between the two finite element models while representing the evolving microstructural damage. Examples and comparisons are made for several geometries and preliminary validation is achieved with comparison to experimental tests conducted by the Northrop Grumman Corporation on a wing-panel structural geometry.
Modeling of a Multifunctional Pressure-Temperature Sensor
Authors: Sohi Ali Najafi , Shavezipur Mohammad , Nieva Patricia , Khajepour Amir
Published: July 2010

Development of new sensors with precise and innovative measurement mechanisms is a key in underpinning the competitiveness of industries like automotive, aviation, and power generation. Due to progresses made in micromachining technologies, fabrication of such sensors for multifunctional applications and their integration with readout circuits is easily achievable. In this paper a new multifunctional sensor for the simultaneous measurement of pressure and temperature is proposed and modeled. It uses membranes and beams as active bodies and capacitance measurement as readout system. The sensor can be fabricated with available CMOS-compatible foundry processes. The results of the finite element simulations are presented for pressures up to 1 MPa and temperature changes up to 250 °C.
Mechanical Property Characterization of Multiscale Carbon Fibers and Carbon Nanofibers Reinforced Polymer Matrix Composite
Authors: Hsiao Kuang-Ting , Ryals James , Wu Peter H. , Liu Ming C.
Published: July 2010

Multiscale polymeric composite laminate reinforced by carbon micro-fibers (CFs) and carbon nanofibers (CNFs) is fabricated via an in-house developed prepreg and vacuum bag/compression molding process. The multiscale fiber system is expected to form a multiscale fiber reinforcement network inside the composite. As a result, the mechanical properties of the prepreg-processed multiscale composite laminate are expected to be different from the traditional carbon fiber reinforced composite laminate. This CNFs modified multiscale composite laminate is tested for its mechanical strength with respect to various important properties for composite aerostructures. The effects of the CNFs in the matrix sensitive properties and in the carbon micro-fiber dominated properties of the multiscale composite are revealed.
Mechanical and Optimization Analyses for Novel Wound Composite Axial Impeller
Authors: Wang Jifeng , Li Qubo , Mu¨ller Norbert
Published: July 2010

A mechanical and optimal analyses procedure is developed to assess the stresses and deformations of Novel Wound Composite Axial-Impeller under loading conditions particular to centrifuge. This procedure is based on an analytical method and Finite Element Analysis (FEA, commercial software ANSYS) results. A low-cost, light-weight, high-performance, composite turbomachinery impeller from differently designed patterns will be evaluated. Such impellers can economically enable refrigeration plants using water as a refrigerant (R718). To create different complex patterns of impellers, MATLAB is used for creating the geometry of impellers, and CAD software UG is used to build three-dimensional impeller models. Available loading conditions are: radial body force due to high speed rotation about the cylindrical axis and fluid forces on each blade. Two-dimensional plane stress and three-dimensional stress finite element analysis are carried out using ANSYS to validate these analytical mechanical equations. The von Mises stress is investigated, and maximum stress and Tsai-Wu failure criteria are applied for composite material failure, and they generally show good agreement.
Wavelength and Coherence Independent Method of Optically Exciting Mechanical Resonance
Authors: Nielson Gregory N. , Phinney Leslie M. , Epp David S. , Wittwer Jonathan , Gupta Vipin , Resnick Paul , Krishnamoorthy Uma
Published: July 2010

We have developed and demonstrated a technique for optical excitation of mechanical resonance that does not require coherent, monochromatic, or time-varying light. Previous methods for optically exciting mechanical motion in microscale devices required monochromatic, coherent light or time varying light. This technology could allow sunlight (or other ambient light source) to drive a MEMS device. It could also be used to convert sunlight to mechanical energy and subsequently to electrical energy through piezoelectric or capacitive techniques, essentially a micromechanical analog to the photovoltaic cell. We have demonstrated this method of optical excitation of a MEMS cantilever using simple cantilever beam structures fabricated using Sandia National Laboratories’ SUMMiT V™ process. The bimorph structure was created with polysilicon and aluminum. The minimum power to induce resonance was 3.5–4 mW of optical power incident on the cantilever under a vacuum of less than 1 mTorr. Resonance was observed at 45.6 kHz (slightly less than the 48.5 kHz predicted by FEA).
Foil Definition for Optimizing the Shape of Microfabricated Columns for Capillary Electrochromatography
Authors: Sukas Sertan , Gardeniers J. G. E. Han
Published: July 2010

A novel design approach for optimizing the shape of the microfabricated pillar columns [1] for capillary electrochromatography (CEC) is presented. Applying this optimization approach, a new foil shape definition was introduced. Several design alternatives were evaluated starting from typical NACA 4-digit series symmetric airfoil definition. In order to avoid stagnant regions over the leading edge for NACA airfoil, the maximum thickness point was defined at the center of the chord. Then this shape was defined as the intersection of two parent circles to create the same geometry with simpler definition. As a final step of the optimization, a custom foil shape was obtained by fitting the 4th order polynomial, which was obtained from typical NACA 4-digit series, according to the defined boundary conditions. Microfluidic flow simulations were performed for electroosmotic flow (EOF) case for evaluating the performance of the foil definitions over other popular geometries (diamond and hexagon) from literature [2]. For electric field of 100 V/cm and same length and width, the custom foil shape yielded a plate height value of 2.76 μm, while 2.85 μm was obtained with hexagon as being the lowest value among other alternatives from the literature.
Finite Element Modeling of Setar, a Stringed Musical Instrument
Authors: Mansour Hossein , Kasaiezadeh Alireza , Arzanpour Siamak , Behzad Mehdi
Published: July 2010

This paper introduces a finite element model of Setar, a Persian long-necked lute. Setar is modeled as a transfer function between the imposed force on the bridge and the near-field resulted sound. Numerical modeling of stringed musical instruments is a computationally challenging task which has always been done with extreme simplifications. Phenomena such as fluid-structure interaction, composite structure, preload effect and infinite boundary are considered in this model. The cycle of Software used in here is CATIA, HyperMesh, Nastran, and HyperGraph. The frequency response between the force of string and generated sound in near field are obtained, taking into account the fluid inside and outside of the soundbox. This model is useful to predict the effect of modification in specific parts to the sound generated by the instrument. The numerical results have excellent agreement with the experimental ones. The modeling procedure can be extended to other musical instruments as well as less complicated problems such as passenger compartment of vehicles.
Material Mismatch Effect on the Fracture of a Bone-Nanocomposite Interface
Authors: Khandaker M. P. H. , Ilik Igor , Teske Timothy
Published: July 2010

In every case where dissimilar materials are bonded together and undergo a subsequent change of dimension due to change of temperature, particle size and types, stresses develop at the interface due to mismatch of material properties. The magnitude of the stresses can be very large and may have a significant influence on the life of each material in the bonded construct. The potential application of nanocomposite cement in biomedical industry requires evaluating the material mismatch effects on the fracture toughness of bone-nanocomposite interfaces. Three point bend tests were conduct in this study on bovine femoral cortical bone and composite cements (Cobalt HV bone cement with 36 μm and 27 nm MgO additives) bonded specimen to measure the material mismatch effect on the interface fracture toughness. Experimental results found that particles size has significant influence on the interface fracture toughness of the bone-composite cements.
An Experimental Investigation on the Bridge Effect in Sound Produced by Setar
Authors: Mansour Hossein , Arzanpour Siamak , Alghassi Hedayat , Behzad Mehdi
Published: July 2010

This study aims to evaluate the amount of energy transfers through the bridge in Setar, a Persian long-necked lute. Stringed musical instruments are among the most complicated acoustical systems. When the string is plucked, its vibration distributes into the entire vibrating system (i.e. body, string, air enclosure) and produces sound. The resultant sound consists of three parts: the first is the string’s direct sound; the second is that part of sound-box vibration being excited by string’s direct sound, and the third is the part of sound-box vibration being excited by string force passing through bridge. The last part believed to have the major share and the others have minor effect. For this research, a specific fixture has been made and a precise plucking machine is installed to hold and pluck the instrument uniformly. Also, a novel approach is utilized to evaluate the share of each abovementioned part in the output near-field sound produced by Setar.
On-Chip Young’s Modulus Characterization of the Effect of Phosphorus Heavy Doping on Polysilicon Thin Films
Authors: Bassiachvili E. , Nieva P. , Khajepour A.
Published: July 2010

Information on material properties of structural thin films for MEMS fabrication is very limited. The small information available in the literature suggests that the Young’s modulus of structural thin films such as polysilicon can change up to 30% with heavy doping at room temperature. Accurate knowledge of these variations is critical for proper design as well as operation of MEMS devices, especially for applications that require them to be exposed to harsh environmental conditions. In this paper, devices for the on-chip characterization of the Young’s modulus of polysilicon as a function of the doping concentration conditions are presented. Analytical modeling has been performed to predict the change in the devices’ pull-in voltage as a function of doping concentration. The devices were fabricated using the PolyMUMPs process on two different polysilicon layers on the same chip separated by a layer of oxide. The top layer devices are heavily doped while the bottom layer devices are left lightly doped. The lightly doped devices serve as a reference, allowing some account for fabrication uncertainties in order to ensure consistent results. Devices for measuring in-plane stresses, out-of-plane stress gradients and specially designed resistor structures that account for the effect of contact resistance have also been fabricated to monitor these quantities while testing. The devices will be tested using a customized vacuum chamber to study the effect of phosphorus concentration on these structures.
Study of Embrittled Friction-Stir-Welds
Authors: Wahab Muhammad A. , Taylor David , Meletis Efstathios
Published: July 2010

A reduction in mechanical properties has been observed in Friction-Stir-Welded (FSW) Aluminum panels. This reduction in strength has generally been attributed to Residual Oxide Defect (ROD). From NASA experience it was also found that certain processing parameters would yield these reduced mechanical properties. The strength of FSW Aluminum panels generally decreases with increasing tool travel rate, decreasing rotation speed, and offset of the weld seam to the retreating side of the FSW tool. The microstructure of welds exhibiting these strength reduction as well as welds that behaved as expected were examined to determine microstructural effects of processing parameters. Therefore the evolutions of microstructural properties are immensely important to understand and evaluate to avoid any catastrophic failures due to the defects arising from welding operations. Scanning Electron Microscopy shows that these weld conditions are accompanied by large precipitates along the grain boundary for both AA-2219 and AA-2195 FSW welded samples. Transmission Electron Microscopy (TEM) also shows the precipitates to be “theta particles (Al2Cu)” and intermetallics in the AA-2219; and T1 (Al2CuLi), and TB particles in the AA-2195. The large size and heavy distributions of these precipitates, especially on the advancing side of the weld seam may influence these properties. It is determined that the existence of ROD in the samples must be analyzed systematically and carefully through the evolutions of microstructures, if catastrophic failures are to be avoided during service conditions. A more complete understanding of this phenomenon is necessary to ensure consistent and predictable weld properties thereby reducing or eliminating the risk of unforeseen failures.
Tunable Band Gaps of Acoustic Waves in Two-Dimensional Phononic Crystals With Reticular Band Structures
Authors: Huang Zi-Gui , Hwang Yunn-Lin , Wang Pei-Yu , Mao Yen-Chieh
Published: July 2010

The excellent applications and researches of so-called photonic crystals raise the exciting researches of phononic crystals. By the analogy between photon and phonon, repetitive composite structures that are made up of different elastic materials can also prevent elastic waves of some certain frequencies from passing by, i.e., the frequency band gap features also exist in acoustic waves. In this paper, we present the results of the tunable band gaps of acoustic waves in two-dimensional phononic crystals with reticular band structures using the finite element method. Band gaps variations of the bulk modes due to different thickness and angles of reticular band structures are calculated and discussed. The results show that the total elastic band gaps for mixed polarization modes can be enlarged or reduced by adjusting the orientation of the reticular band structures. The phenomena of band gaps of elastic or acoustic waves can potentially be utilized for vibration-free, high-precision mechanical systems, and sound insulation.