bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological Flow Studies in Exact-Replica Atherosclerotic Carotid Bifurcations
Authors: Bale-Glickman J. , Selby K. , Saloner D. , Savas¸ O¨.
Published: May 2008

Some results from a series of physiological flow experiments in a model of an atherosclerotic carotid bifurcation are presented. The flow model exactly replicates the lumen of the plaque excised intact from a patient with severe carotid atherosclerosis. Flow visualization (FV) and particle image velocimetry (PIV) are employed as the tools for this study. The complex internal geometry of the diseased artery combined with the pulsatile input flows gives rise to complex flow patterns. The flow fields are highly three-dimensional and chaotic with details varying from cycle to cycle. These flow patterns also include internal jets, three-dimensional shear layers, numerous separation/recirculation zones and stagnation lines. The vorticity and streamline maps confirm this complex and three-dimensional nature of the flow. Planar streamline maps show the three-dimensional flow by the multiple sources/sinks throughout the model. Wall shear stresses (WSS) are estimated to range form about −7 Pa to 34 Pa at the stenotic neck over time with the peak at peak systolic. These WSS also exhibit chaotic behavior during pulsatile flow cycles.
Modeling the Effect of Surface Roughness on the Adhesion, Contact and Friction in Micro-Electro-Mechanical Systems (MEMS) Interfaces
Authors: Tayebi Noureddine , Polycarpou Andreas A.
Published: May 2008

It has been experimentally shown that surface texturing (roughening) decreases the effect of intermolecular adhesion forces that are significant in MEMS applications. These forces can hinder normal operation of sensors and actuators as well as micro-engines where they might increase friction, which could be catastrophic. In this paper, a model that predicts the effects of roughness, asymmetry, and flatness on the adhesion, contact, and friction forces in MEMS interfaces is presented. The three key parameters used to characterize the roughness the asymmetry and the flatness of a surface topography are the root-mean-square roughness (RMS), skewness and kurtosis, respectively. It is predicted that surfaces with high RMS, high kurtosis and positive skewness exhibit lower adhesion and static friction coefficient, even at extremely low external normal forces.
Dynamic Analysis of Sheet Deformation Using Spring-Mass-Beam Model
Authors: Yoshida Kazushi
Published: May 2008

Since sheet jamming occurs due to a collision between stacked sheets in the sheet stacking mechanism, it is necessary to establish a dynamic analytical method that can predict the behavior of both the leading and trailing edges of stacked sheet to avoid sheet jamming. We present one method of predicting the dynamic behavior of sheets and introduce a dynamic analysis of sheet deformation using a spring-mass-beam model, the Lagrange multiplier, and functions that express the configuration of the mechanism guide plates. From the Lagrange equation obtained through Hamilton’s principle, the equations of motion and constraints for each element can be determined. Resistance force due to air is also considered. The calculated and experimental results concur with each other and indicate that the proposed methods are useful in designing a time interval between sheets being stacked that prevents sheet jamming.
Sliding Mode Control of a Non-Collocated Flexible System
Authors: Frame Aimee M. , Book Wayne J.
Published: May 2008

A new control method is developed for position tracking control of a flexible, non-collocated system. The desired trajectory is specified for the free end of a flexible beam that moves along a horizontal track actuated by a linear motor. First, a system model is reformulated based on a pendulum with stiffness and dampening. Small angle approximations are used so that a linear model can be obtained. Next, variable structure control is chosen as the control method due to its seemingly robust nature. The sliding surface and feedback gains are designed using the developed model based on literature describing various variable structure control techniques. Simulations are then conducted to verify the control method and examine its robustness. Finally, the method is implemented on an actual system using a Kalman filter to estimate the states.
Three-Dimensional Forced Convection Flow in Plane Symmetric Sudden Expansion
Authors: Nie J. H. , Armaly B. F.
Published: May 2008

Simulations of three-dimensional flow and heat transfer in laminar incompressible forced convection in plane symmetric sudden expansion (backward-facing step in rectangular duct) are presented for different Reynolds numbers. The duct’s downstream (H) and upstream (h) heights are 0.04m and 0.02m, respectively, thus providing a step height (S) of 0.01m and an expansion ratio of 2. The duct’s width (W) is 0.08m, thus resulting in an aspect ratio of 4 before and 2 after the expansion, respectively. The incoming flow is considered to be isothermal, hydro-dynamically steady and fully developed. Uniform and constant heat flux is specified on the stepped walls, while the other walls are treated as adiabatic surfaces. The flow appears to be symmetric for the low Reynolds number range that is considered in this study (Re=150). A “jet-like” flow develops near the sidewall and its impingement on the stepped wall creates a swirling flow inside the primary recirculation region adjacent to the stepped wall, and that is responsible for creating a maximum in the Nusselt number distribution. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped wall does not coincide with the location of the outer edge of the primary recirculation region, especially in the region near the sidewall. Neither one of these boundary lines represents the reattachment region of the separated flow in the region adjacent to the sidewall. The maximum Nusselt number on the stepped wall is located inside the primary recirculation region and is not identical to the “jet-like” flow impingement point. The maximum friction coefficient on the stepped wall is located inside the primary recirculation region, and it is at the center of the duct for the Reynolds number range considered in this study. The minimum friction coefficient on the stepped wall is located at the impingement of the “jet-like” flow.
A New Cyclic Impact Test Instrument and Methodology for Hand-Struck Tools
Authors: Glancey J. L. , Popper P. , Mitch M. , Truitt P. , Nasr N. , Orgovan M. , Stevens J.
Published: May 2008

The use of hand-struck tools is still a necessary job function for technicians in several industries throughout the world. Despite the importance of these tools, evolving concerns regarding the detrimental effects of their long-term use continue to grow. Repetitive motion injuries, nerve damage of the hands and arms, and hearing loss are some of the problems that continue to afflict users of these types of tools. Although hammer-tool systems are relatively simple mechanical systems that have required very little improvement historically, the growing concerns associated with their use necessitate a thorough evaluation of current tool designs. In addition, the introduction of new and modified tools with improved performance characteristics will be essential to maintaining their long term, effective use in the workplace. Currently, no standard test methods exist to assess the performance characteristics of hand-struck tools. This makes evaluations and comparisons very difficult since performance characteristics are significantly influenced by the user of the tool. As a result, for the purposes of assessing the performance of current hammer-tool systems as well as evaluating alternate designs, a new testing device for hand-struck tools was developed. The device is designed to simulate the approximate cyclic kinematic motion of a user repeatedly hitting a tool with a conventional hammer. A computer controller automates the striking and return stroke actions, and the resulting impact velocity and force exerted by the hammer are adjustable and approximate the performance of a human. For the purpose of development, the testing device was designed to accept steel hand-struck chisels. As configured, a chisel is placed in the device and used to shear a standard, replaceable work piece. The key output of this test is the number of impacts needed to fail the standard piece. Other features integrated into the device include a load cell under the work piece to capture the force exerted during a hammer impact, measurement of the hammer velocity at impact, noise measurements, and an automatic counter to record the number of hammer impacts required to fail the work piece. Preliminary tests with standard, conventional chisels indicate the device is capable of failing a standard 6.5 mm steel drill rod work piece in the same number of hammer blows as an experienced chisel user. Subsequent work will focus on characterizing and improving the properties of hammer-chisel systems relevant to the detrimental effects associated with their long term use.
Design and Performance of Hand-Struck Tools Using High Performance Polymers
Authors: Glancey J. L. , Popper P. , Nasr T. , Truitt P. , Orgovan M. , O’Brian D.
Published: May 2008

One of the oldest tools in the world, the hand-struck chisel, has been improved with the addition of a polymer cap. The cap enhances the safety and ergonomic features without compromising chisel cutting performance. During the development of this new design, a lumped-parameter model was used to quantify force transmission characteristics, and select a suitable polymer-reinforced nylon (Minlon™). In addition, a finite element model together with laboratory and field tests were used to demonstrate that the addition of the polymer cap significantly reduces chisel vibration and noise. Additional long term tests confirmed the cutting effectiveness and durability of the capped chisel.
Fabrication and Preliminary Testing of a Novel Piezoelectrically Actuated Microvalve
Authors: Ayhan Fatih , Vipperman Jeffrey S. , Clark William , Thornton Jimmy , Gemmen Randall
Published: May 2008

This paper presents the fabrication and preliminary testing of a novel piezoelectric microvalve. Fabrication has three steps, which are the actuator fabrication, valve body fabrication and assembly of the microvalve. Fabricating an actuator involves cutting piezoelectric and brass beams, gluing the brass and piezoceramic beams into a trimorph sandwich structure, and curing them under pressure at elevated temperatures. Actuators are then wired either by using conductive epoxy or soldering. Valve body parts are constructed from single crystal silicon substrates using deep reactive ion etching (DRIE). DRIE is a subtractive process, whereby a mask is created on the surface of the stock, which will shield the parts that are not to be machined. Refinements in the actuator manufacturing process are made to increase the quality and decrease the fabrication time. Using a photonic probe, tip deflections of the actuators have been tested at various temperature and voltage levels. Currently, the valves are being assembled. Once assembled, multiple microvalves will undergo cold flow testing with air followed by extensive flow extensive flow testing at elevated temperatures with humidified hydrogen.
Characterization of a Radiantly Driven Multistage Knudsen Compressor
Authors: Young M. , Han Y. L. , Muntz E. P. , Shiflett G.
Published: May 2008

Knudsen Compressors are meso/micro scale gas compressors/pumps based on thermal transpiration or thermal creep. The design of radiantly driven Knudsen Compressors is discussed, along with a model that was developed to understand their performance. Experimental pumping performances for Knudsen Compressors with one, two, five, and fifteen stage, radiantly driven cascades are also discussed. Temperature measurements across the transpiration membranes, for various pressures of Nitrogen, were obtained and compared to those predicted by the performance model. The results agree with the model to within 15% consistently under predicting the measured hot side temperature of the transpiration membrane. The pump-down curves, steady-state maximum pressure differences, and maximum flow rates produced by a single stage Knudsen Compressor were obtained. A variety of configurations were studied at pressures from 500 mTorr to atmospheric pressure. The experimental results agreed with the performance model’s predictions to within 20%.
Heat Transfer Between Particulates and Surface in a Vibrofluidized Layer
Authors: Sheyman Vladimir , Rathod Mulchand S.
Published: May 2008

The apparatus, in which fluidization of the particulates is obtained by filtration of the gas in the upward direction through the layer of the particulates, is widely used in the industry for various types of processes. This gas serves as source of fluidized agent and the heat transfer carrier. In particular, the fluidized bed creates a favorable condition to carry out numerous heterogeneous processes. In spite of a significant advantage of this hydrodynamics regime, there are some drawbacks. The fluidization occurs only when sufficient filtration velocity of gases is achieved. In some cases when there is a significant difference in particulate sizes, this condition is not acceptable, and for a layer of fine particulates, such type of fluidization cannot be obtained at all. In the latter case, a combination of vibration and filtration of very small amount of gas through the layer is used, and the heat transfer to the solids occurs by conduction from the heating surface. In this paper, a set of differential equations for the heat and mass transfer are formulate and solved for variable and constant temperature of the heating surface. As a result, a relationship of the solid temperatures as a function of time is established. An experimental research also was performed. A comparison of the experimental research data and theoretical analysis shows that the deviation does not exceed 10%. The experimental research also shows that the main influence on the intensity of the mass transfer process has the amplitude of vibration and to the lesser extent the effects of frequency of vibration.
Design, Build, and Test of Modular Mobile Micro Robots
Authors: Sahin Ferat , Walter Wayne , Kreigbaum Kevin
Published: May 2008

This paper presents a novel architecture for a mobile micro robot design. The architecture will have hardware and software modularity. The modular architecture of the platform provides “plug-and-play” capability that will allow hardware and software subsystems to be easily swapped. This paper focuses on vertical hardware modularity in the sense that modules will not be identical to each other but have common connectivity. Our approach slices a robot into functional modules such as locomotion, control, sensors, communication, and actuation. Any mobile robot can be constructed by combining the above abstract modules. A sub-module is a piece of hardware, which accomplishes the functionality of an abstract module, i.e. a wireless communication sub-module for a communication module. The software architecture consists of abstract classes and their objects. The abstract classes are “robot”, “locomotion”, “control”, “communication”, “sensor”, and “actuators”. From these abstract classes, concrete classes are derived. The objects are going to be created from the concrete classes. For example, “wireless” can be a class inherited from “communication” class. Then, an instance of “wireless” class can be created as the communication module in the robot. The objects (tasks) are dynamically loaded into the robots so that the modular OS can run the tasks on the sub-module it has. The paper explores generations of micro robot designs with modular architecture.
A Case Study on Educating Engineers for Geographically-Dispersed Design Teams
Authors: Dannenhoffer John F. , Davidson Barry D. , Ingraffea Anthony R. , Zehnder Alan T. , Jones Scott L.
Published: May 2008

The mantra of industry today is to design products and processes using collaborative design teams. While the potential benefits of such a design philosophy are numerous and significant, many organizations find themselves falling short in the implementation. Sometimes these shortcomings are due to cultural and technical difficulties in the organization, but too frequently they are due to a lack of knowledge as to how to collaborate effectively. Described herein is an educational initiative by Syracuse and Cornell Universities to together teach collaborative design methodologies through a common two-semester, senior-level engineering design course. In the course, not only are the lectures taught to the two cohorts of students using at-a-distance technologies, but the students are teamed in cross-university teams to execute a series of 6-week design challenges, from preliminary through detailed thermal-structural design of the external skins of seconds-generation reusable launch vehicles. An Advanced Interactive Discovery Environment (AIDE), which is a computer-based infrastructure specifically designed for this course, is used to support both synchronous and asynchronous communications amongst the team members and with the faculty. Extensive surveys of the students, together with faculty observations, indicate that proper use of collaboration tools can facilitate effective geographically-dispersed design teams, making them as successful as local design teams.
Mechanical and Thermal Design of a Combustion-Based Thermionic Micro Power Generator
Authors: Zhang Chunbo , Najafi Khalil , Bernal Luis P. , Washabaugh Peter D.
Published: May 2008

This paper reports the mechanical and thermal design of a MEMS-fabricated micro power generator based on thermionic emission and catalytic combustion. Thermionic power generation results from electron emission from a hot emitter to a cold collector. Scaling analysis reveals that the miniaturization of a thermionic generator is favorable to output power density and efficiency, provided that excellent thermal isolation can be realized. However, there are stringent constrains on the thermal and mechanical properties of the micro device structure. Thermal and structural analyses have been performed and prototype structures have been designed and fabricated. SiO2 rings of thickness ~40–50μm surrounding the combustion chamber and emitter are used for thermal isolation. Excellent thermal behavior of the structures is shown both in finite element simulations and experiments. The simulations also show that the emitter bending under pressure and thermal stresses is less than 3μm.
High Precision Femtosecond Laser Micromachining for Rapid Manufacture of MEMS Devices
Authors: Bulusu A. , Joshi S. P. , Shiakolas P. S.
Published: May 2008

Laser assisted machining in the MEMS context is gaining recognition due to its versatility in application and its cost effectiveness compared to processes such as LIGA, chemical vapor deposition, electrical discharge machining etc. High thermal conductivity causes instant heat transfer to the surroundings leading to significant heat affected zones. Damage to the surroundings is further aggravated by high ablation thresholds for metals when excimer lasers are used. Ultrashort pulse lasers have been found to minimize thermal damage to the surroundings more than any other known laser. Peak power densities cause direct evaporation and plasma formation of the material. High-pressure shock waves at the machined surface transfer the particles away from the spot preventing material redeposition around the feature. In this paper, we explore the use of femtosecond lasers for rapid manufacturing of MEMS devices through laser micromachining of master molds that can be used in replication processes such as hot embossing and injection molding. The effect of various factors that affect the size and quality of the machined feature such as beam quality, length of beam path, beam waist, polarization, energy per pulse and focal length of the lens used is investigated. The effect of various materials along with the use of vacuum and inert gases on the quality of the cut is also This work aims at laying the foundation for the development of a comprehensive database on the effect of various factors that need to be considered in the design of a laser micromachining system for rapid manufacture of MEMS devices.
Design and Fabrication of Microtacks for Retinal Implant Applications
Authors: Cambron Scott , Keynton Robert , Franco Jose , Crain Mark , Shire Doug , Walsh Kevin , Naber John , Kaplan Henry , Rizzo Joseph
Published: May 2008

To adhere an artificial retinal implant onto the epiretinal surface of the eye, our group has designed retinal microtacks. The microtacks were fabricated using two different micromachining techniques: 1) deep reactive ion etching (DRIE) and 2) ultrahigh precision micromilling. The DRIE process consisted of machining a double-sided polished three-inch silicon wafer using ICP with the Bosch process. For the ultra-high precision micromilling technique, titanium foil was bonded to a silicon wafer and precision machined with a 150-μm end-mill using PMAC code interfaced to a machine motion controller. Due to fabrication limitations, the tip of the DRIE fabricated Si tack was chisel-shaped, whereas versatility of the micromilling technique allowed a partially conical, tapered tip to be added to the Ti tack, which created a sharper point. For the Si tacks, the average overall length and width were measured to be within 7% and 2%, respectively, of the design while the Ti tacks were found to be within 1% and 6%, respectively. Additionally, the grip width, stop thickness, and the tip taper angle of the Ti tacks were within 3%, 9%, and 4%, respectively, of the design.
Effects of Absolute Pressure on Fluid Slip in a Hydrophobic Microchannel
Authors: Tretheway Derek C. , Meinhart Carl D.
Published: May 2008

This work examines the effects of absolute pressure on fluid slip in a hydrophobic microchannel. Previous experiments with hydrophobic surfaces have indicated the presence of an apparent fluid slip. The mechanism responsible for the apparent fluid slip observed by Pit. et. al. (Phys. Rev. Lett., 85, 980–983), Zhu and Granick (Phys. Rev. Lett., 87, 096105), and Tretheway and Meinhart (Phys. of Fluids, 14, L9-L12) is unknown. Recently, Tyrell and Attard () have observed the presence of nanobubbles on a hydrophobic surface. Modeling these nanobubbles as a thin gas layer and solving for the velocity profile between two infinite parallel plates yields an apparent fluid slip consistent with the experimentally observed results. As the slip length is highly dependent on the nanobubble or gas layer thickness, increases in absolute pressure should decrease the bubble size and reduce the measured slip. This work explores the proposed mechanism by measuring velocity profiles and calculating slip lengths at varying absolute pressures.
Design and Fabrication of Electrostatically Actuated Synthetic Microjets
Authors: Roman Max , Aubry Nadine
Published: May 2008

The purpose of this paper is to design and fabricate efficient electrostatically actuated synthetic microjets. For this, special attention is given to the coupling between the electrostatic actuation, the solid deformation of the membrane, and the generated fluid flow. In particular, the motion of the membrane, which is critical in generating the jet flow, is studied using the energy method applied to the large displacement of plates, which, in turn, leads to a relation between the required voltage and the membrane deformation. The flow is then deduced. Finally, we present an efficient method to microfabricate such devices.
Laser Curing of Gold Nanoparticle Inks
Authors: Chung Jaewon , Ko Seunghwan , Bieri Nicole R. , Grigoropoulos Costas P. , Poulikakos Dimos
Published: May 2008

The concept of effective laser curing of nanoparticle suspensions (NPS) with a laser beam is presented in this paper. A toluene solvent is employed as the carrier of gold nanoparticles possessing a lower melting temperature than that of bulk gold. Using a modified drop-on-demand jetting system, the gold nanoparticle suspended solution is printed on a glass substrate and cured with laser irradiation. The laser energy coupling to the nanoparticles in conjunction with thermocapillary effects and the evaporation of the solvent are critical to the quality of the electrically conductive gold microlines. By employing a intensity-modulated double laser beam processing scheme, to optimize the curing process, it is demonstrated for the first time, that the gold nanoparticles could be sintered on a glass substrate to form a gold line of resistivity close to that of bulk gold. This is a noticeable result, compared to recently published microconductor manufacturing with nanoparticle suspensions with oven [1] or low power single laser beam [2] curing reporting resistivities four to five times higher than that of bulk gold. As a consequence, in addition to their scientific value, the current results demonstrate the potential of laser printing for use in the microelectronics manufacturing for the first time. It was also shown that the morphology of the gold line could be modified by appropriate design of the shape of the processing laser beam.
Bifurcation in Rotating Flow Due to Boundary Oscillation
Authors: Kovinskaya Svetlana I. , Amromin Eduard L.
Published: May 2008

Numerical analysis of viscous flow in narrow gaps between rotating disks gives several solutions for the same value of the Reynolds number. The non-uniqueness of solution can be considered as indication of the flow instability and close laminar-turbulent transition. Although the obtained solutions have the same boundary values of velocity components and their first derivatives, these solutions differ by the second derivative of the axial velocity. This second derivative is generally proportional to the axial component of the boundary acceleration. Consequently, the mentioned difference can be associated with disk oscillation/vibration and can exhibit the minimum stimulating acceleration as function of Reynolds number. Although the flow bifurcation can be associated with the laminar-turbulent transition, such analysis of viscous flow gives no information on principal flow modes that may appear due to this stimulation. These principal modes can be found in the framework of potential theory. According to many experimental and numerical researches, the flow between rotating disks is composed from a quite thin boundary layer and the practically inviscid core. The Reynolds-dependent time-averaged circumferential velocity in this core is smaller than the disk rotation speed. Possible modes of flow oscillations and their frequencies depend on the ratio of this circumferential velocity to the rotation speed.
IIST Passive Core Cooling on Pressurizer Top Break
Authors: Liu Tay-Jian , Lee Chien-Hsiung
Published: May 2008

Two experiments for small-break loss-of-coolant accident on pressurizer top were conducted at the INER Integral System Test (IIST) facility to investigate thermal-hydraulic behavior of a passive core cooling system (PCCS) in a Westinghouse pressurized water reactor (PWR). The test results are compared with the previous IIST tests under the same initial and boundary conditions for a power-operated relief valve (PORV) stuck-open incident. The objectives of this study are to understand of the key thermal-hydraulic phenomena associated with PCCS and to compare the effectiveness of accident management with or without PCCS. The break sizes were scaled down based on one and all three fully-opened PORVs. This paper identified the key phenomena commonly observed and the phenomena unique to a PWR with PCCS.
Refined Finite Element Analysis for the Low Frequency Characteristics of the Trachea-Bronchia
Authors: Al-Jumaily A. M. , Mago N.
Published: May 2008

Incorporating the properties of the surrounding medium, the low frequency characteristics of the trachea-bronchia are determined using a relatively accurate Finite Element Model (FEM). Focus is made on the effect of the branching angle and the embedding surroundings on these characteristics. It is concluded that the natural frequencies are significantly influenced by the surrounding medium elastance and are insignificantly affected by the branching angle within realistic values (30, 45 60 degree in plane and 45 degree in plane plus 45 degree out of plane branching angles investigated).
An Experimental Investigation of Liquid Jet Array and Single Phase Spray Impingement Cooling Using Polyalphaolefin
Authors: Sleiti Ahmad K. , Kapat J. S.
Published: May 2008

Experiments on triangular and rectangular array jet impingement and single phase spray cooling have been performed to determine the effect of both cooling techniques on heat transfer coefficient and the coolant mass flux required for a given cooling load. Experiments were performed with circular orifices and nozzles for different H/D values from 1.5 to 26 and Reynolds number range of 219 to 837, which is quite lower than the ranges used in widely used correlations. The coolant used was polyalphaolefin. For the custom fabricated orifices, commercial nozzles and conditions used in this study, both cooling techniques showed enhancement of heat transfer coefficient as H/D increases to a certain limit after which it starts to decrease. The heat transfer coefficient always increases with Reynolds number. In keeping with previous studies, single-phase spray cooling technique can provide the same heat transfer coefficient as jets at a slightly lower mass flux, but with a higher pressure head.
Thermal Modeling for Finish Hard Turning Using a New Tool
Authors: Chou Y. Kevin , Song Hui
Published: May 2008

This study develops an analytical thermal model for temperature predictions in finish hard turning by a new tool. Tool life in finish hard turning is limited by part surface quality, e.g., white layer formations (microstructural alterations). Thermal damage due to temperature rise at machined surfaces is the primary source of such surface degradation. Thus, a thermal model capable of machined surface temperature predictions will enable part surface damage assessment as well as thermal management strategy for process optimization. A mechanistic model that accounts for nonuniform uncut chip thickness across the cutting edge is employed to estimate three-component machining forces. Machining forces and cutting characteristics, i.e., shear angle and chip-tool contact, approximate the heat intensity and geometry of shear plane and rake face heat sources. Due to tool nose radius, the two heat sources are three dimensional in nature and are further discretized into small segments, each treated as an individual rectangular heat source. Individual small heat-source segments are then used to study temperature rise in machining, using modified moving oblique heat source (shear plane) and modified moving and stationary heat sources (rake face) developed by Komanduri and Hou [1,2]. Temperature rise due to all small heat-source segments is superimposed, with proper coordinate transformation, to obtain final temperature distributions due to overall heat sources. The thermal model can be applied to study machining parameter effects on machining temperatures. It is indicated that maximum machined-surface temperatures are adversely affected by increasing feed rate and cutting speed, but favorably by increasing depth of cut. Tool rake face temperatures increase with cutting speed and feed rate as well. However, rake face temperatures decrease with increased depth of cut at high feed rates, but, reversely at low feed. The model has also been tested to evaluate white layer formations in finish hard turning. Tool nose radius effects have been analyzed and the results show that the smaller the tool nose radius, the deeper the white layer under identical machining conditions. Experimental results show good agreement with analytical predictions.
Meshless Analyses of Fracture, Plasticity and Impact
Authors: Eskandarian A. , Chen Y. , Oskard M. , Lee J. D.
Published: May 2008

The governing equations for rate-independent large strain plasticity are formulated in the framework of meshless method. The numerical procedures, including return mapping algorithm, to obtain the solutions of boundary-value problems in computational plasticity are outlined. The crack growth process in elastic-plastic solid under plane strain conditions is analyzed. The large strain plastic response of material under high-speed impact is simulated. Numerical results are presented and discussed.
Optimal Rollover Prevention With Steer by Wire and Differential Braking
Authors: Carlson Christopher R. , Gerdes J. Christian
Published: May 2008

This paper uses Model Predictive Control theory to develop a framework for automobile stability control. The framework is then demonstrated with a roll mode controller which seeks to actively limit the peak roll angle of the vehicle while simultaneously tracking the driver’s yaw rate command. Initially, control law presented assumes knowledge of the complete input trajectory and acts as a benchmark for the best performance any controller could have on this system. This assumption is then relaxed by only assuming that the current driver steering command is available. Numerical simulations on a nonlinear vehicle model show that both control structures effectively track the driver intended yaw rate during extreme maneuvers while also limiting the peak roll angle. During ordinary driving, the controlled vehicle behaves identically to an ordinary vehicle. These preliminary results shows that for double lane change maneuvers, it is possible to limit roll angle while still closely tracking the driver’s intent.
Active Noise Control Using Phase-Compensated, Damped Resonant Filters
Authors: Bisnette Jesse B. , Vipperman Jeffrey S. , Budny Daniel D.
Published: May 2008

An active noise control device called active noise absorber (ANA), which is based upon damped, resonant filters is developed and demonstrated. It is similar to structural positive position feedback (PPF) control, with two exceptions: 1) acoustic transducers (microphone and speaker) can not be truly colocated, and 2) the acoustic actuator (loudspeaker) has significant dynamics. The speaker dynamics can affect performance and stability and must be compensated. While acoustic modal control approaches are typically not sought, there are a number of applications where controlling a few room modes is adequate. A model of a duct with speakers at each end is developed and used to demonstrate the control method, including the impact of the speaker dynamics. An all-pass filter is used to provide phase compensation and improve controller performance. A companion experimental study validated the simulation result and demonstrated nearly 10 dB of control in the first duct mode.
Viscoplastic Constitutive Properties and Reliability of Lead-Free Sn3.9Ag0.6Cu Solder
Authors: Zhang Qian , Dasgupta Abhijit , Haswell Peter
Published: May 2008

The viscoplastic constitutive properties of Sn3.9Ag0.6Cu lead-free alloy are presented and compared with baseline data from eutectic Sn63Pb37 solder. Steady-state creep models are obtained from creep and monotonic tests at three different temperatures for both solders. Based on steady-state creep results and creep test data, a transient creep model is developed for both Pb-free and Sb37Pb solders. One-dimensional incremental model of the test setup is developed to simulate constant-load creep, monotonic, and isothermal cyclic mechanical tests performed over various temperatures, strain rates and stresses using a thermo-mechanical-microstructural (TMM) test system, developed by the authors. By fitting simulation results to monotonic testing data, plastic models are also achieved. The devoloped viscoplastic constitutive models are evaluated in a two-dimensional nonlinear Finite element analysis of a PBGA352 package under a −55°C∼125°C thermal cycling environment. The viscoplastic behavior of Pb-free solder is compared with that of eutectic Sn37Pb solder.
Pulse-Width Modulation Control of a Pneumatic Positioning System
Authors: Qi Yufeng , Surgenor Brian
Published: May 2008

The paper describes an experimental investigation of pulse-width modulation (PWM) control of a pneumatic positioning system. PWM has been applied in the past to pneumatic positioning systems. But there are a number of different pneumatic circuit designs and PWM algorithms to choose from. This paper presents a new system design that is believed to be an improvement over previous pneumatic circuit and PWM algorithm designs. A single 3-position solenoid valve is used together with two manual flow control valves. The conventional PWM algorithm is modified with a dual switching gain to account for the valve characteristic. Test results indicate that the new system design can match the performance of previous designs. But careful consideration must be given to issues such as PWM carrier frequency and valve response times.
A New Method for the Convex Approximation of QFT Controller Bounds
Authors: May Douglas , Jayasuriya Suhada
Published: May 2008

This paper offers an enhancement to the method of automatic QFT loop shaping explored in the research of Chait et. al. [1] and Croulard et. al. [2]. An integral part of the method involves computing an appropriate convex approximation of a nonconvex 2-dimensional boundary. It is found in this paper that with some important limitations, the problem of finding the largest convex polygon that will fit inside a nonconvex polygon can be cast as a quadratic optimization problem. One limitation is that an origin must be selected within the nonconvex boundary to serve as a locus for the new convex shape, and hence the solution may not be unique. However, since the origin and a selected region around the origin will be guaranteed to be included in the new convex region, this method turns out to be even better suited for an automatic loop shaping method than an algorithm that solves the abstracted problem more rigorously.
A One-Dimensional Model for Cooling of Optical Fibers
Authors: Ghani M. Usman , Marin Ovidiu , Theriault Martin
Published: May 2008

This paper presents a one-dimensional model for the cooling of optical fibers. Heat transfer between the fiber, gas and wall, by conduction, convection, and radiation, are taken into account. The model offers advanced features such as multiple inlets and outlets. Six different pure gases or their mixtures may be used to study the effect of gas composition. The forced convection heat transfer coefficient is computed using the correlation for the forced convection in tubes and conduits. This correlation is then corrected to account for the enhanced heat transfer due to the motion of the fiber. This factor is determined from the limited experimental data available in the literature. The mathematical model consists of a system of ordinary differential equations and is solved using the LSODE solver. The model was used to study the effect of various operational parameters. The results show that at the typical conditions used in a commercial draw tower, Helium is the most effective cooling medium. A smaller diameter exchanger is more effective in cooling the fiber. More cooling is achieved if the incoming gas temperature is lower as well as if the cooler wall is kept at a lower temperature. The most critical factor is the fiber draw speed. At higher draw speeds, the residence time is low, which leads to shorter contact time for the fiber and gas to exchange heat. The effect of gas flow rate is not very significant, provided the flow regime is laminar. The turbulence flow regime is, in general, not desirable as it may cause vibrations, which is detrimental to fiber properties such as diameter and strength. Comparisons of the one-dimensional model results with the results of a two-dimensional model as well as simulations using Fluent, a commercial CFD package, are also presented. The results of these simulations may be used for an improved design of an exchanger, providing more efficient cooling of optical fiber. An improved design of exchanger will be the focus of future work in this area.
A Comparison Between Two Models That Predict the Elastic-Plastic Behavior of Particulate Metal Matrix Composites Under Multiaxial Fatigue Type Loading
Authors: Owolabi Gbadebo Moses , Singh Meera N. K.
Published: May 2008

This paper is an effort to first modify two cyclic plasticity models developed for homogeneous metals to address the heterogeneous nature of particulate metal matrix composites (PMMCs), and subsequently to evaluate the resulting relations both theoretically and experimentally. Specifically, using the original Mro´z model and the endochronic theory of plasticity as their bases, two sets of elastic-plastic constitutive relations are identified. These sets of relations account for the interaction in stress fields between adjacent particles in PMMCs. The behavior predicted by each model is compared with experimental results obtained from a series of uniaxial and biaxial (tension-torsion) tests performed on circular specimens made of the 6061/Al2O3/20p-T6 PMMCs with 20% volume fraction of particles. The materials are tested for a variety of applied monotonic and cyclic loading paths.
Effect of Temperature Dependent Properties and Particle Shape on Heat Transfer in Plasma Flow
Authors: Wen Yuemin , Jog Milind A.
Published: May 2008

In this paper, plasma flow over non-spherical particles has been investigated numerically. The conservation equations for mass, momentum, and energy are solved simultaneously using finite volume method. To body-fit the non-spherical particle surface, an adaptive orthogonal grid is generated. The flow field and the temperature distribution are calculated for oblate and prolate particle shapes. A number of particle surface temperatures and far field temperatures are considered and thermophysical property variation is fully accounted for in our model. The shapes are represented in terms of variations in the axis ratio which is defined as the ratio of axis along the flow direction to the axis perpendicular to the flow direction. For oblate shape, axis ratios from 0.4 (disk-like) to 1 (sphere) are used whereas for proate shape, axis ratios of 1 (sphere) to 1.6 (cylinder-like) are used. The computational model is first validated by comparison with results and correlations available in literature for constant property flow. Effects of flow Reynolds number, particle shape, surface and far field temperatures, and variable properties, on the flow field, temperature variations, drag coefficient, and Nusselt number are outlined.
Short Crack Growth Model in a Particulate Composite Using Nonlinear Elastic Fracture Mechanics
Authors: Zhang Ying , Chu Tsuchin , Mahajan Ajay
Published: May 2008

The fracture mechanics model for a long crack does not work very well with short-crack propagation when the initial crack length is less than 5.1 mm (0.2 inch). In order to investigate the short crack effect, a series of tests of particulate composite specimens with long and short cracks were performed and the results recorded on a video tape. This test data was analyzed to determine the fracture parameters. Two initial crack lengths, 2.5 mm (0.1 inches) and 7.6 mm (0.3 inches) were used in the crack propagation tests. Based on the principle of linear elastic fracture mechanics (LEFM), the stress intensity factor KI was obtained. The instantaneous time-dependent J-integral for 0.1 and 0.3 inch crack specimens was determined by the NEFM analytical approach. The crack growth behavior was also investigated in the form of J-integral resistance curves. The calculated J-integral was reversed to derive a new KI. The new KI was compared with the measured value obtained from LEFM analysis results to determine the feasibility of applying the linear fracture approach to the non-linear behavior of the material. The results showed that the KI computed from the J-integral increased by 24.5%, and was at the time prior to the peak load for the 0.1 inch crack. For the 0.3 inch crack, the acceptable range was from the onset of propagation to the 9% strain stage (yield strain for the material), where the increase of the new KI was within 15.6%.
Thermal Conductivity Measurements of Thin Aluminum Layers Using Steady State Joule Heating and Electrical Resistance Thermometry in Suspended Bridges
Authors: Reifenberg J. , England Voss R. , Rao P. , Schmitt W. , Yang Y. , Shojaei-Zadeh S. , Liu W. , Sadeghipour S. M. , Asheghi M.
Published: May 2008

Thin metallic film layers are extensively used as the constituents of the micro-devices. The reliability of these devices, therefore, strongly depends on the thermal behavior of such film layers. Aluminum thin film layers are of particular interest in this respect. The lateral thermal conductivity of the aluminum film layers is measured, using the steady state electrical Joule heating and electrical resistance thermometry technique. Aluminum suspended microbridges of identical thicknesses (500 nm) and variable widths (16 to 18 μm) and/or lengths (200 to 500 μm) are fabricated, using conventional microfabrication processes. The lateral thermal conductivity of the 500 nm thick Aluminum film layer was found to be k = 174 ± 13 Wm−1 K−1, at room temperature (300 K).
The Effects of Processing Conditions on the Thermal Conductivity of Polycrystalline Silicon Films
Authors: Graham Samuel , Olson Brandon , Wong Channy , Piekos Edward
Published: May 2008

Polycrystalline silicon has been a primary material used in development of mocroelectrical mechanical systems due to its attractive structural properties and compatibility with CMOS processing. Among its many applications, polysilicon is currently being employed in MEMS devices that require thermal dissipation or thermal management to ensure functionality (thermal actuators, microengines, etc.). In these applications, heat conduction in polycrystalline silicon becomes a primary factor in the design, performance, and reliability of thermal MEMS.