bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of MHS Materials in Large Strains
Authors: Yu T. X. , Karagiozova D. , Gao Z. Y.
Published: April 2008

Different from conventional metal foams, the mixed open/closed cell characteristic of the sintered metallic hollow sphere (MHS) materials offers excellent specific stiffness and energy absorption capacity. Based on our experimental study on two types of MHS specimens we reported before, a theoretical model is presented here to predict the mechanical behavior of the MHS materials in large strains (i.e. in the plateau phase). It is anticipated that the HCP packing configuration dominates in the actual MHS material structure, so that this configuration is taken in the idealized model. Based on the hypothesis of a periodic repeatability of a representative block, the large deformation of hollow spheres compressed by rigid balls is numerically simulated to identify the characteristics of deformation mechanism. Then, a rigid-plastic analysis is adopted to model this large deformation mechanism and to predict the stress-strain behavior of the representative block. Thus, the variation of the stress with strain is obtained for the idealized material of certain relative density, resulting in a relationship between the average stress in large strains (i.e. the plateau stress) and the relative density of the actual material. The predicted stresses are found in good agreement with the experimentally measured characteristic stresses of the two types of MHS materials.
Micro-Machined Temperature Sensor Arrays for Studying Micro-Scale Features in Film Boiling
Authors: Ahn H. S. , Sinha N. , Banerjee D.
Published: April 2008

In this study we report the design, fabrication and testing of a surface micro-machined array of temperature sensors for studying micro-scale features in film boiling. The fabrication steps involved deposition by metal evaporation and “lift-off” process. The thermocouple junction sizes were less than 50μm wide and 100-250nm thick. Wire bonding techniques were explored for packaging. An apparatus for boiling experiments was constructed to test the micro-machined temperature sensors. The apparatus consists of a viewing chamber containing a metal block (copper block covered with a steel jacket) in which cartridge heaters and thermocouples are embedded. A silicon wafer with the surface micro-machined thermocouple arrays was clamped on top of this metal block. Surface temperatures were measured, during boiling experiments with PF-5060 as the working liquid, using the surface micro-machined thermocouple. Since the micro-machined thermocouples have very low characteristic time constant, temperature measurements can be performed with better accuracy, spatial resolution and temporal precision, than standard thermocouples.
Fluid Flow Resistance in a Simple Cubic Packed Bed
Authors: Choi C. C.-C. , Lee S. H.-K.
Published: April 2008

Motivated by its frequent appearance in practical applications, scientists and engineers have been putting much efforts to pursue the ability to predict fluid flow behavior in sphere packed bed, in particular the fluid-solid interaction therein. The network model has recently been used to predict the fluid flow behavior in a sphere packed bed for a smaller length-scale domain of interest. The major questions for this approach are the representation of the irregular void space as a three dimensional network and the assignment of the flow resistance values. The application of Deluanay Cell to discretize the void space helps retain the geometrical and topological information without any empirical data fitting in. However, the calculation of the flow resistance within the Delaunay cell is still a question to be solved due to its highly irregular topology. The objective of this study is to solve for the flow resistance between the pores in a simple cubic retaining all the geometrical information. And then to correlate the flow resistance with different values of Reynolds number such that the application of network model could extend outside the creeping flow regime. The results has been validated against experimental correlation and then correlated with Reynolds number with a correlation factor larger than 0.9.
Shape Memory Alloy Actuator Arrays Using Thermoelectric Devices for Dual Sensing and Actuation
Authors: Odhner Lael , Asada H. Harry
Published: April 2008

A sensor-less control method for locally heating and cooling Shape Memory Alloy (SMA) actuators using an array of thermoelectric devices (TED) for both temperature measurement and actuation is presented in this paper. Each SMA wire is divided into many segments whose thermal state is controlled independently and selectively for generating a desired displacement of the SMA wire. In lieu of dedicated temperature sensors, each TED used to heat and cool the SMA wires can also be used to monitor the local temperature difference across each device via the Seebeck effect. A pulse width-modulated control system is implemented to drive the thermoelectric device and sample the Seebeck voltage of each TED between pulses. Least-squares system identification is employed to fit an auto-regressive/exogenous input model to the measured temperature of the SMA wires using the Seebeck voltage and the ambient temperature as inputs. A feedback controller is presented which, using this model, is able to control the temperature of the shape memory alloy wires to within 3 °C over a target temperature range between 30 °C and 80 °C.
An Experimental Investigation of a Micro Injection Molded Mechanical Device
Authors: Tom Alan M. , Angelov Aleksandar K. , Coulter John P.
Published: April 2008

The primary objective of this study, through a scientific experimental investigation, was to determine optimum injection molding processing parameters on semi-crystalline materials HDPE and POM focusing on mechanical properties, obtained thru the use of a nano-indenter, of micro gears being manufactured on non-heated and heated mold bases. A secondary objective was to initiate a similar experimental study using amorphous COC material. Taguchi’s method utilizing an L-9 orthogonal array was used to determine the effects of Tnoz, Tmold, Pinj, Vinj, Ppack, and tpack injection molding processing parameters. A nano-indenter was used to determine investigated mechanical properties on final injection molded parts that included stiffness (S), reduced modulus (Er), and hardness (H). Results showed HDPE, POM and COC, heated mold experiments exhibiting increases in mechanical properties S, Er, and H, on the order of 1.2–4.0 times those of non-heated molding trials. Decreases in optimum molding conditions for Tnoz, Pinj, and Ppack was also observed for heated molding trials. The highest mold temperatures and injection pressures tested did not produce greatest optimum molding conditions. However, largest packing times tested produced optimum molding conditions.
Dynamic Response of Normal and Osteoporotic Trabecular Bone by Vibration Analysis
Authors: Tawackoli Wafa , Gunaratne Gemunu , Hussain Fazle , Liebschner Michael
Published: April 2008

Osteoporosis afflicts about 200 million people worldwide; and osteoporotic fractures are in the millions annually in the US alone and cost tens of billions of dollars [1]. Characterization of bone quality in osteoporotic patients is important with respect to monitoring treatment efficacy, though currently quite limited. While some technical hurdles in developing a noninvasive diagnostic tool using low frequency vibration have been overcome, changes in the frequency response signal of bone have not been investigated at the various bone organizational levels. Our principal hypothesis is that the vibrational modes of bone tissue change significantly with the deterioration of bone micro-architecture and that these modes can be captured by noninvasive sensors.
T-Cobot: Transformable Collaborative Robot
Authors: Wannasuphoprasit Witaya , Chanphat Supaphon
Published: April 2008

Recently, the emerging research between human and robotic device has been adapted to many applications. Collaborative Robot or Cobot is one of promising candidates because it is inherently passive and intrinsically safe. Cobot’s joints are coupled together by CVTs (continuous variable transmissions). The cobot’s endpoint direction can be controlled by adjusting transmission ratios of these CVTs. Former cobots developed in recent years have constant joint-to-joint distances. Some will be reviewed. In this paper, we propose a novel transformable cobot called T-Cobot which has ability to expand the joint distances. We describe the design and construction of the T-Cobot Prototype. In addition, the kinematics of the T Cobot is proposed.
Extracting Engineering Principles From a Hovercraft Design Project for Engineering Sophomores
Authors: Coates Cameron W.
Published: April 2008

The design of a hovercraft involves complex principles derived from fluid mechanics, mechanics of materials, thermodynamics and mechanical design. This work seeks to extract the fundamental principles from these subjects and implement them in the design and construction of a hovercraft. The challenge is to maintain a level-appropriate engineering standard while enabling sophomores from different engineering majors understand and effectively apply these standards. In order to do this, we have to decide what parameters to ignore and what engineering approximations should be made. By examination of the underlying engineering assumptions, it is shown that this aspect engages the engineering students interest as they find opportunities to implement what they are currently learning or have recently learnt. Actual construction of the hovercraft allows the basic theories to be tested and improves understanding of their effectiveness by quantifying underlying engineering assumptions. Assessment methods indicate that this project provides excellent preparation for future design innovation.
Overview of Payload Vibration Isolation Systems
Authors: Caruntu Dumitru I. , Shove Christopher
Published: April 2008

This paper is an overview of recent spacecraft payload vibration isolation systems for further possible application to reusable launch vehicles sub-orbital missions. A summary of vibro-acoustic environment of Orbital Science and Kistler Aerospace’s small launch vehicles indicated a severe level of random vibrations, shock and acoustics that the payload must endure. The same level of random vibrations has been found for an entire family of sounding rockets: Black Brant, Orion, Nike-Orion, Taurus-Orion and Terrier-Orion. This paper also presents recent flight experiments designed to test either launch isolation or on-orbit isolation systems. While the on-orbit vibration isolation systems were active-passive systems, which lately used smart structures and new control algorithms including adaptive neural network-based, launch isolation systems evolved from passive to active-passive systems which were lately tested during the VALPE-2 experiment. Launch active-passive systems provided a vibration reduction 10 to 1 versus up to 5 to 1 provided by passive systems. Also, on-orbit active-passive systems provided a vibration reduction of about 10 to 1. Suborbital missions became very important due to the growing number of research projects dedicated to remote sensing of high resolution and effects of microgravity. The number of orbital and especially suborbital reusable launch missions is estimated to increase considerably in the near future as vehicles develop. The actual tendency is to reduce payload weight and mission costs, and to improve the payload environment. This requires more efficient vibration isolation systems that will guarantee payload safety and better operational performance for reusable launch vehicles.
Nano-Chemo-Mechanical Sensor Array Platform for High Throughput Selective Coating Material Search
Authors: Lim Si-Hyung “Shawn” , Raorane Digvijay , Satyanarayana Srinath , Majumdar Arunava
Published: April 2008

Microcantilever (MC) sensors can detect the presence of chemical vapors at very low concentrations based on the surface stress changes generated by the interactions between probe and target molecules on their surfaces [1-2]. The magnitude of the surface stress change depends on the type of interaction taking place which include hydrogen bonding, electrostatic, van der Waals forces, etc. Pinnaduwage et al [2] demonstrated detection of explosive materials at ultra low concentrations (10-30 ppt) using single MC AFM tip coated with a thiol (-SH) self assembled monolayer (SAM). They were able to get highly sensitive and reproducible signals from their MC sensor while detecting chemicals like PETN, RDX, etc. However, they did not demonstrate the specificity of the coating material to explosive materials. Most types of chemical sensors (metal oxide, conductive polymer, carbon nano tube or belt sensors) are known to respond to interfering chemical agents in a similar manner as the target. Bietsch et al [3] used a set of MC’s (1D array) coated with different types of polymers as chemical sensing layers to try and identify unique deflection signatures for each target chemical. The performance of such sensors is expected to degrade during long term usage as the binding force between the polymer coating and the silicon cantilever structure is weak. Furthermore, polymer coating layers are in general not selective to specific target vapors since they have limited chemical and structural information due to the simple repetition of same chemical structure. To increase the selectivity for a particular target vapor, it is necessary to develop coating materials, which have enough chemical/structural information and long term stability specifically for that target. To expedite the screening process for testing several coating materials in parallel, we need a high throughput sensor array platform.
Nanoscale Rapid Melting and Crystallization of Amorphous Silicon Thin Films
Authors: Chimmalgi A. , Hwang D. J. , Griogoropoulos C. P.
Published: April 2008

Nanostructuring of thin films is gaining widespread importance owing to ever-increasing applications in a variety of fields. The current study details nanosecond laser-based rapid melting and crystallization of thin amorphous silicon (a-Si) films at the nanoscale. Two different near-field processing schemes were employed. In the first scheme, local field enhancement in the near-field of a SPM probe tip irradiated with nanosecond laser pulses was utilized. As a second approach, the laser beam was spatially confined by a cantilevered near field scanning microscope tip (NSOM) fiber tip. Details of various modification regimes produced as a result of the rapid a-Si melting and crystallization transformations that critically depend on the input laser fluence are presented. At one extreme corresponding to relatively high applied fluence, ablation area surrounded by a narrow melt region was observed. At the other extreme, where the incident laser energy density is much lower, single nanostructures with a lateral dimension of ~90 nm were defined. The ability to induce nucleation and produce single semiconductor nanostructures in a controlled fashion may be crucial in the field of nano-opto-electronics.
Validating GPS Based Measurements for Vehicle Control
Authors: Rock Kirstin L. , Beiker Sven A. , Laws Shad , Gerdes J. Christian
Published: April 2008

The increasingly widespread use of the Global Positioning System (GPS) in determining the location of vehicles raises the possibility of using the information provided by GPS for vehicle control purposes. The use of a multi-antenna GPS system provides the ability to measure not only position and velocity, but vehicle heading and sideslip as well. This paper presents a validation of a GPS based system with an automotive grade two-axis optical sensor. The results show excellent agreement between the two sensor systems, confirming the accuracy of the GPS based system even in highly dynamic situations. Although any GPS based system is subject to dropouts from driving under trees and bridges, cornering stiffness estimates obtained when GPS is available enable construction of a vehicle state observer for use in the absence of GPS.
Wireless Sensor Networks for Machinery Monitoring
Authors: Sundararajan V. , Redfern Andrew , Schneider Michael , Wright Paul , Evans James
Published: April 2008

Wireless sensor networks (WSNs) are currently been actively investigated in the research community on account of their unprecedented spatial density of sensors, local computational plus storage capacity, and potential for distributed and fault-tolerant monitoring. Today, they are mainly deployed for environmental monitoring - e.g. for “smart building” control, water quality monitoring, and botanical studies. In the future, it is clear they have a huge potential for industrial applications such as machinery monitoring, shop instrumentation, and process control. Wireless sensor nodes can be mounted on various parts of machinery and plant to promote early fault detection and analysis. Their small size and autonomy enables their placement in locations that are usually difficult to access. In addition, it is also possible, with minimal changes to the machine configuration, to deploy sensors on the machinery after it has been installed. The sensor nodes cannot only monitor their own output but also collaborate with neighboring nodes to determine the health of the overall machines and provide early warnings of potential failure. We study, in this paper, the benefits of using wireless sensor networks in machine tools and plant equipment. We discuss the uses of these networks and the issues that must be addressed in order for these implementations to be successful. We also present two case studies for machinery and machine too monitoring.
Improvement of the Dynamic Behavior of a Fan Using Finite Element Method
Authors: Parausanu Ioan , Sorohan Stefan , Gheorghiu Horia , Hadar Anton , Caruntu Dumitru I.
Published: April 2008

The first part of this article presents a dynamic analysis of the fan of a generator connected by rigid coupling to a diesel engine. The purpose of this analysis is to correlate the main components of the fan’s frequency response spectrum with the ones of the excitation source, i.e., the diesel engine. The second part describes a finite element analysis of the fan in order to find the best design solution.
Control of Cylindrical Shell Panels With Input Shaping and Phase Shift of Shape Memory Ring Segments
Authors: DeHaven J. G. , Tzou H. S.
Published: April 2008

The purpose of this study is to investigate the control effect from shape memory alloy (SMA) ring segments placed at the desired positions along the length of a cylindrical shell panel. Equations of motion for an elastic cylindrical shell panel are defined first and then used with the assumed mode shape functions for the appropriate boundary conditions in a free vibration analysis. The results from this are used with the generic shell sensing equation to determine the spatial strain distribution. From this, optimal placement of ring segments for each given mnth mode is determined. Through use of the modal expansion method, the open-loop control force induced by the SMA ring segments applied to a cylindrical shell panel is determined next. This evaluation shows that only the odd modes in the circumferential direction can be controlled. Longitudinal modes are controlled via placing a varying number, depending on the mode, of ring segments along the length of the cylindrical shell panel. To predict control effects of the SMA ring segments, the modal participation factor response is determined for an external harmonic excitation applied to the shell along with SMA control force induced to eliminate the unwanted effects. The results show that with proper choice of waveform function for the applied temperature to the SMA ring segments and minor modifications to frequency and phase, the SMA ring segments can control unwanted external vibration.
Simulation of Mechanical Properties of Woven Fabric Laminated Composite Plates at Given Damage State
Authors: Lua Jim , Yu Wenbin , Mohan Ram , Sankar Jagannathan
Published: April 2008

Composite ship structures are subjected to both the low and high velocity impact during their service life. The dynamic impact can generate fiber, matrix and/or delamination damage inside a woven fabric composite laminate, which may significantly reduce its stiffness and strength. Both the structural mechanics and fracture mechanics based models cannot fully capture the impact damage evolution due to coexistence of continuum and discrete damage. The stress and strain at the element level cannot be directly used to predict the constituent damage and the resulting mechanism driven stiffness degradation. In this paper, a hybrid discrete and continuum damage model is developed and numerically implemented within the LS-DYNA environment via a user-defined material model. The continuum damage progression and its associated stiffness degradation are predicted based on the constituent stress/strain and their associated failure criteria while the delamination damage is numerically captured via a cohesive interface model.
Development of Carbon-Nanotube-Based Nanocomposite Strain Sensor
Authors: Pham Giang T. , Park Young-Bin , Wang Ben
Published: April 2008

This paper presents the development of carbon-nanotube-based, polymer composite films that can be used as high-sensitivity strain sensors. The films were fabricated via either melt processing or solution casting of thermoplastic polymer matrices containing low concentrations of multi-walled carbon nanotubes. The electrical resistivities of the films were measured in situ using laboratory-designed fixtures and data acquisition system. The measured resistivities were correlated with the applied strains to evaluate the sensitivity of the nanocomposite film sensor. Various types of loading mode, including tension and flexure were considered. The paper suggests that conductive network formation, thus strain sensitivity of the conductive films, can be tailored by controlling nanotube loading, degree of nanotube dispersion, and film fabrication process. The developed sensors exhibited a wide range of sensitivity, the upper limit showing nearly an order of magnitude increase compared to conventional strain gages. Military and industrial applications of the sensitivity-tunable strain sensors are presented.
High Performance Heat Storage and Dissipation Technology
Authors: Park Chanwoo , Kim Kwang J. , Gottschlich Joseph , Leland Quinn
Published: April 2008

High power solid state laser systems operating in a pulse mode dissipate the transient and excessively large waste heat from the laser diode arrays and gain material. The heat storage option using Phase Change Materials (PCMs) has been considered to manage such peak heat loads not relying on oversized systems for real-time cooling. However, the PCM heat storage systems suffer from the low heat storage densities and poor thermal conductivities of the conventional PCMs, consequently requiring large PCM volumes housed in thermal conductors such as aluminum or graphite foams. We developed a high performance metal hydride heat storage system for efficient and passive acquisition, storage, transport and dissipation of the transient, high heat flux heat from the high power solid state laser systems. The greater volumetric heat storage capacity of metal hydrides than the conventional PCMs can be translated into very compact systems with shorter heat transfer paths and therefore less thermal resistance. Other exclusive properties of the metal hydride materials consist of fast thermal response and active cooling capability required for the precision temperature control and transient high heat flux cooling. This paper discusses the operating principle and heat storage performance results of the metal hydride heat storage system through system analysis and prototype testing. The results revealed the superior heat storage performance of the metal hydride system to a conventional PCM system in terms of temperature excursion and system volume requirement.
High Knudsen Number Physical Vapor Deporition: Predicting Deposition Rates and Uniformity
Authors: Malhotra Chetan P. , Mahajan Roop L. , Sampath W. S.
Published: April 2008

Although the analogy between thermal radiation and collisionless molecular flow has been known since the experiments of Knudsen in the early 20th century, it has not been exploited for mainstream analysis of physical vapor deposition processes. With the availability of commercial finite element and computational fluid dynamics software having built-in cavity radiation solvers with features such as automatic surface definition, meshing and view factor calculation, the analysis of thermal radiation problems has become a straightforward procedure. A direct result of this is the ease with which high vacuum deposition processes can be analyzed via the radiation-molecular flow analogy. There are several advantages of using the analogy as opposed to analytical and Monte-Carlo methods which have been traditionally employed for analyzing PVD processes. These include the ease of handling complex geometries and reduced computing times due to the replacement of the probabilistic calculations in Monte Carlo simulations with a deterministic one. In this paper, we demonstrate the use of a commercial finite element software, ABAQUS, for predicting deposition profiles from planar as well as tube sources and compare them with those presented in thin-film literature. We also compare the prediction of flow rates through long tubes with those calculated analytically by Knudsen. The predictions are in good agreement with the analytical and experimental data thus establishing the validity of the method in analyzing real-life deposition and molecular flow problems. Finally, we employ ABAQUS for predicting the thickness variation in an actual thin-film deposition setup and compare the results with experimental measurements.
Studies on Onset of Ratcheting in Pipe Bends and Effect of Thickness on Strain Accumulation
Authors: Shanmuga Sundaram K. , Thanigaiyarasu G. , Palaniswamy Manoj Kumar
Published: April 2008

This paper intends to provide an overview of various possibilities of ratcheting in pipelines subjected to cyclic thermal and mechanical loadings. The present work deals with review on results from the studies of research papers providing experimental data and analytical study on ratcheting. There has been no well-defined material model and analysis procedure to predict this phenomenon accurately. An analysis carried out on 2-inch NPS SS304 pipe bends with different thickness (Schedule 40 and Schedule 80) using ABAQUS, non-linear FEA software to predict the strain accumulation and their influences on ratcheting failure is presented. The results and their inferences are included.
Analysis of Heat Affected Zone During Short Pulse Laser Irradiation of Tumors
Authors: Pal Gopalendu , Mitra Kunal , Grace Michael S.
Published: April 2008

The objective of this study is to analyze the heat-affected zone in tissue phantoms containing inhomogeneities and skin tumors in live anaesthetized rats when irradiated with a focused beam from a short pulse laser source. Tumors are simulated with the inhomogeneities embedded inside the tissue phantoms with different combinations of optical and thermo-physical properties with respect to the base tissue matrix. Experiments are also performed on anaesthetized rats with tumorogenic agent injected below and on the skin. The experiments performed demonstrate that short-pulsed laser heating results in a higher peak temperature rise with a lower heat affected zone compared to a continuous wave source. Hyperbolic non-Fourier heat conduction formulation is used to study axial and radial temperature distributions in tissue medium. Experimentally measured temperature profiles match extremely well with the prediction from the non-Fourier model than the Fourier formulation, particularly for time less than the relaxation time of tissues.
The Performance of the Cold Crucible Melting of Refractory Materials
Authors: Min B. T. , Song J. H. , Chung S. H.
Published: April 2008

To investigate the performance of a cold crucible employed for the melting of refractory material, which has a very high melting temperature of about 3000 K, a computational analysis of the coupled electro-magnetic field, heat transfer, and fluid flow is carried out. Governing differential equations, basic numerical methods, computational model, and the results of the simulation of cold crucible melting are discussed. Computational Analyses were performed for the melting of corium, which is a mixture of UO2 and ZrO2, and pure zirconia. By comparing the analysis results with the experimental data, it is shown that the proposed computational model reasonably predicts the fundamental characteristics of a cold crucible melting.
Model Based Spur Gear Failure Prediction Using Gear Diagnosis
Authors: Choi Sukhwan , Li C. James
Published: April 2008

Gears are common mechanical components used in power transmissions and frequently responsible for transmission failures. Since the crack size is not directly measurable while gear is in service, there is difficulty in predicting residual life of gears in service. The aim of this study is to present a prognostic methodology to predict the residual life of a cracked spur gear that is in service utilizing 2D FEM/fracture mechanics based failure model. The previously developed gear diagnostic algorithms and artificial neural network were employed to estimate crack size from measured gear vibration. The predicted results were validated with experimental data. Experimental results showed that the method had an averaged error of 12.94% in its estimate of remaining life.
Analysis of Lateral Track Strength for High Speed Rail
Authors: Chrismer Steven M.
Published: April 2008

Recently the FRA has proposed a reduction in the maximum allowable net axle lateral load limit from the current 50 percent of static vertical axle load (NAL/V limit = 50%) to less than 40 percent depending, in part, on the basis of FRA’s lateral track strength model, TREDA. Such a reduction could indirectly result in limiting the maximum speed of high speed passenger trains to the equivalent of 7 inches (178 mm) cant deficiency. This paper reports on the author’s investigation of selected assumptions and calculations made in TREDA. Improvements to the model are recommended and a revised NAL/V relationship is proposed, derived from an independent analysis of the driving and resisting forces. Finally, a vehicle dynamic analysis is performed to determine how the author’s proposed revised NAL/V limit would affect 9-inch (229 mm) cant deficiency operation as the high speed rail industry is now considering.
Packaging of In-Plane Thermal Microactuators for BioMEMS Applications
Authors: Panchawagh Hrishikesh V. , Faheem Faheem F. , Herrmann Cari F. , Serrell David B. , Finch Dudley S. , Mahajan Roop L.
Published: April 2008

This paper addresses two issues related to in-plane, electro-thermal actuators for BioMEMS applications. First, in order to protect the actuator from biological debris and particulates, a packaging technique using a flip-chip bonded polysilicon cap is demonstrated. The encapsulated actuator transmits motion outside the package via a piston, which moves through a small clearance. The second issue addressed is the reduction in efficiency of the thermal actuator in liquids. By coating the packaged actuator with a thin conformal hydrophobic layer via an atomic layer deposition (ALD) process, the liquid is prevented from entering the encapsulation. This avoids direct contact between the actuator and the surrounding liquid thereby improving its efficiency. The unpackaged and packaged actuators were tested in both air and de-ionized water. Although the packaging resulted in a reduction in the performance of the thermal actuator in air, the actuation efficiency in water was significantly improved due to the isolation of the hot arms from the liquid. This packaging technique is also applicable to other MEMS devices and in-plane actuators such as electrostatic comb drives for engineering as well as biological applications.
Thermal Reliability Design and Optimization for Multilayer Composite Electronic Boards
Authors: Khalilollahi Amir , Warley Russell L. , Onipede Oladipo
Published: April 2008

Boards made of composites are susceptible of structural failure or irreversible damage under thermally raised stresses. A thermal/structural finite element model is integrated in this study to enable the predictions of the temperature and stress distribution of vertically clamped parallel circuit boards that include series of symmetrically mounted heated electronic modules (chips). The board is modeled as a thin plate containing four heated flush rectangular areas that represent the electronic modules. The finite element model should be to able to accept the convection heat transfer on the board surface, heat generation in the modules, and directional conduction inside the board. A detailed 3-D CFD model is incorporated to predict the conjugate heat transfer coefficients that strongly affect the temperature distribution in the board and modules. Structural analyses are performed by a FE model that uses the heat transfer coefficients mentioned above, and structural elements capable of handling orthotropic material properties. The stress fields are obtained and studied for the models possessing two and there laminates with different fiber orientations, and inter-fiber angles. Appreciable differences in values of max stress intensity were observed as the fiber orientation and inter-fiber angle changed. The angular parameters in this study were guided by experimental design (DOE) concepts leading to a metamodel of the stress intensity in the board. The optimum design variables found by the equations of the metamodel.
Characterization of a Liquid-Vapor Phase-Change Actuator
Authors: Whalen S. A. , Bahr D. F. , Richards C. D. , Richards R. F.
Published: April 2008

Factors affecting the efficiency of liquid-vapor phase-change actuators during dynamic operation are explored. To do this, a model actuator was specifically designed so that actuator geometry, material properties and operation could be easily varied in order to parametrically study their effects on actuator efficiency. A numerical model was developed so that the detailed energy budget within the device could be elucidated. It was found that device efficiency was maximized when the energy input into the actuator was equal to the energy required to dry out the evaporator. Membrane thermal mass and compliance, as well as the thickness of the evaporating liquid layer were also found to have a large impact on efficiency. In contrast, membrane thermal conductivity was found to have a minimal effect on efficiency for dynamic operation. Based on the parameter study, a liquid-vapor phase-change membrane actuator fabricated with a 10.3μm thick wicking structure and a 200nm thick 3mm-square silicon nitride actuation membrane was shown to demonstrate improved performance characteristics. The actuator generated peak pressures and deflections of 123kPa and 167μm when actuated with a 14.3mJ heating pulse for a thermal efficiency of 0.15%.
Analysis of the Evaporation Process in a High Heat Flux Flat Plate Heat Pipe
Authors: Carbajal Gerardo , Sobhan C. B. , Peterson G. P.
Published: April 2008

A numerical analysis of the evaporation process in a flat plate heat pipe (FPHP) is presented. Three different heat flux configurations were applied at the evaporator section: parabolic, linear and constant; and three different wick thicknesses were evaluated. A two-dimensional explicit Finite Difference Model was used to conduct the transient computational analysis of the heat pipe. The results indicate that the vaporization rate was more intense at the evaporator for the parabolic heat flux distribution, than for either the linear or constant heat flux distributions. The velocity field is nearly identical to the shape of the input heat flux distribution. The maximum Mach number for all the cases analyzed was low, indicating that the incompressible flow assumption in the vapor was valid. The modeling results also indicated that the thickness of the heat pipe wick was a significant factor in the determination of the overall thermal resistance, with the resulting temperature drop proportional to the thickness of the wick. Typical distributions of the field variables, particularly the temperature in the wall, and the temperature, velocity and pressure in the wick and the vapor core of the flat plate heat pipe are also presented and discussed.
Semiactive Control of Hunting Stability in Rail Vehicles
Authors: Ahmadian Mehdi , Mohan Anant
Published: April 2008

This paper discusses a methodology for improving hunting behavior in rail vehicles by semiactive control of suspension elements. This methodology focuses on increasing the critical velocity of hunting beyond the operational speed range. Earlier studies have shown that the critical velocity is most sensitive to the primary longitudinal stiffness, KPX. A higher primary longitudinal stiffness can significantly increase the critical hunting velocity of the rail vehicle. But, having high values of KPX is largely undesirable, since that would make the wheelset suspension very rigid. Any disturbance to the wheels due to imperfections in the rails will result in a forcing function in the equations of motion, thereby facilitating the transfer of the recurrent wheelset oscillations to the car body, leading to a poorer ride quality. As an alternative to using sustained high values of KPX throughout the ride, a semiactive approach has been attempted, whereby, a nominal value of KPX was assumed for the majority of the simulation time. On a need basis, this value was made to increase for limited portions of the oscillatory cycle. As an initial approach, the value of KPX was made to be a function of the wheelset lateral excursion. A moderate value of KPX was assumed for the duration of time that the wheelset lateral excursions were below a preset threshold value. Whenever the lateral displacement exceeded this threshold limit, the value of KPX was increased to 10 times the original value. It was thought that this approach would raise the critical hunting velocity, and drive the oscillations down towards the center. But simulation showed that this strategy barely improved the critical velocity. A subsequent approach was to make the value of KPX a function of the wheelset yaw displacement instead. This approach yielded a significant improvement in the critical velocity.
Numerical Simulation of Fluid Flow in Microchannels With Superhydrophobic Walls
Authors: Salamon Todd , Lee Wonsuck , Krupenkin Tom , Hodes Marc , Kolodner Paul , Enright Ryan , Salinger Andrew
Published: April 2008

The three-dimensional flow of a Newtonian fluid in a microchannel with superhydrophobic walls is computed using a finite element analysis. Calculations of the fully-developed laminar flow of water under a pressure gradient of 1 psi/cm in an 80 μm high channel with superhydrophobic upper and lower surfaces containing a 2 μm pitch array of 0.2 μm square posts shows a 40 percent flow enhancement relative to the smooth, non-patterned surface case, and an apparent slip length of 5.4 μm. A sharp gradient is observed in the axial velocity field within 0.5 μm of the post surface and normal to the post center. The calculated axial velocity field away from the superhydrophobic surface agrees well with the analytical solution for two-dimensional channel flow with Navier’s slip condition applying at the channel wall. Mesh refinement studies indicate the important role that adequate resolution of the sharp gradient in the velocity field adjacent to the post surface plays in obtaining accurate flow enhancement predictions. Decreasing the relative contact area of the fluid with the solid portion of the channel surface, either by increasing the post-to-post spacing or decreasing the post size, results in a monotonic increase in the flow enhancement. Wetting of the fluid into the post structure is shown to dramatically decrease the calculated flow enhancement. Calculations of the flow enhancement for fixed surface properties and varying channel heights result in apparent slip lengths that agree to within 1 percent, suggesting that the macroscopic flow behavior is adequately characterized in terms of an apparent slip model, with the magnitude of the slip length a function of the post size, post spacing and wetting behavior that characterize the local flow field.
High Reliability Flip Chip Using Low CTE Laminate Substrates
Authors: Copeland D. Scott , Rahim M. Kaysar , Suhling Jeffrey C. , Tian Guoyun , Lall Pradeep , Jaeger Richard C. , Vasoya Kris
Published: April 2008

In this work, we report on our efforts to develop high reliability flip chip on laminate assemblies for deployment in harsh thermal cycling environments characteristic of ground and aerospace vehicles (e.g. −55 to 150 °C). Reliability enhancement has been achieved through the use of a novel low expansion, high stiffness, and relatively low cost laminate substrate material that virtually eliminates CTE mismatches between the silicon die and top layer PCB interconnect. The utilized laminate features a sandwich construction that contains standard FR-406 outer layers surrounding a low expansion high thermal conductivity carbon fiber-reinforced composite core (STABLCOR®). Through both experimental testing and modeling, we have demonstrated that robust flip chip assemblies can be produced that illustrate ultra-high solder joint reliability during thermal cycling and extremely low die stresses. Liquid to liquid thermal shock testing has been performed on test assemblies incorporating daisy chain test die, and piezoresistive test chips have been used to characterize temperature dependent die stresses. In both sets of experiments, results obtained using the hybrid PCB laminate with FR-406 outer layers and carbon fiber core have been compared to those obtained with more traditional glass-epoxy laminate substrates including FR-406 and NELCO 4000-13. Nonlinear finite element modeling results for the low expansion flip chip on laminate assemblies have been correlated with the experimental data. Unconstrained thermal expansion measurements have also been performed on the hybrid laminate materials using strain gages to demonstrate their low CTE characteristics. Other experimental testing has demonstrated that the new laminate successfully passes toxicity, flammability, and vacuum stability testing as required for pressurized and un-pressurized space applications.
Analysis of Sewage Sludge Treatment Process Using Taguchi Method
Authors: Hwang Joon , Kang Woo-Jung
Published: April 2008

This paper presents the experimental analysis of sewage sludge drying process using Taguchi method to know the characteristics and optimize drying process parameters. There have been attempt to perform the sewage sludge disposal such as simple reclaiming, dumping in the sea, incineration. Currently, these methods are restricted by national or international government regulations. The drying process is adopted as effective method for sewage sludge treatment, however sewage sludge makes difficult to treat with large volume at the real drying process plant because of its own complicated physical, chemical, and thermal properties. To treat the sewage sludge in view of environmental friendly and cost effective way, it is necessary to control the volume and weight of sewage sludge. It is not only reduces the delivery expenses and improve the re-usability, but also prevents several shift environmental pollution from nocuous sewage sludge. In this study, sewage sludge drying process parameter was modeled and evaluated with Taguchi method. From these research results the process parameters can be optimized to satisfy the desired qualities of particle diameter and moisture content of dried sewage sludge, and also provided to achieve the economic process operation.
Numerical Analysis for the Breaking Characteristic of Fuse-Link
Authors: Shanshan Zheng , Qi Lin
Published: April 2008

Fuses are widely used in many fields. In this paper the breaking processes of low voltage fuse-links of different styles have been simulated in using the FEM. The temperature distribution along the fuse-links has been analyzed numerically at constant over-current operation. The breaking performance has also been studied by comparing the breaking capacity of the different kinds of fuse-links. The results show that, under the same power load condition, the tin-dot welded in the vital position can regulate its temperature rising ratio for a threadlike fuse-link, and delays or accelerates the breaking due to the diameter of the tin-dot. The paper also presents a group of data that help optimize the design of the tin-dot fuse-link so as to meet the protecting demand in a practical circuit.
Immunology Based Multi-Robot Collaboration for Countermine Operations
Authors: Nair Adarsh G. , Agarwal Sanjeev , Krishnamurthy K.
Published: April 2008

Past studies have shown that mechanisms employed by biological systems can motivate development of algorithms for coordination of distributed systems. In this study, an immune system based collaboration is established between heterogeneous robots to perform countermine operations. Heterogeneity of the robots is defined based on their capabilities to detect and/or mark location of mines, and diffuse them. Concepts related to an immune system like clonal expansion, primary and secondary response, immune memory and antigen specificity are exploited in this study. The developed methodology is validated by simulation studies using MATLAB.
Dynamic Response Modeling of Piezoelectric Ultrasonic Motors
Authors: Dabney James B. , Harman Thomas L. , Aswatharanayan Charanya , Randolph-Gips Mary , Ghorbel Fathi H. , Chakkungal Joseph J.
Published: April 2008

Piezoelectric ultrasonic motors (PUMs) fill a unique niche in mechatronic actuators. The motors are lightweight, simple, and reliable, containing a single moving part that provides the function of motor, transmission, and brake. They are ideal for a variety of robotic applications as well as commercial and medical applications. In order to exploit PUMs fully, computationally efficient models of dynamic response, capturing all important dynamics, are needed. This paper describes the experimental characterization of the dynamic response of a typical commercial PUM (Shinsei USR-30) using an inertial load and evaluation of three classes of dynamic models: second-order predictive (physics-based) models, algebraic (curve fitting) descriptive models, and neural network approximation.