bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Model of Solid Waste Technology Assessment
Authors: Eslami-Nejad Parham , Saboohi Y.
Published: April 2008

Review of waste management models indicate that optimization models based on the chain of waste flow are developed and applied in waste management systems. These models do represent the flow of material through few stages and they lack an integrated approach that may include the flow of material from the point of waste generation in different sectors till the end point at the land fill. It is also argued that the existing models do rarely consider the interrelated issues of economics, environment and social aspects. This conclusion has been followed by the development of an integrated multi stage and multi period dynamic model of waste flow based on quasi dynamic optimization techniques. The model has then been applied to study the development of solid waste flow system in a limited district as a case study. The results of the case study reveal that the distributed separation, processing and transformation waste technologies at the source point in different sectors do have considerable impact on the economical and environmental impact of waste flow system. The results show that inclusion of distributed waste processing systems in the model, as an option, leads to reduced total discounted costs of the whole system and the emission of pollutants is decreased.
Intelligent Sensor Modeling and Data Fusion via Neural Network and Maximum Likelihood Estimation
Authors: Kumar Manish , Garg Devendra P. , Zachery Randy A.
Published: April 2008

The major thrust of this paper is to develop a sensor model based on a probabilistic approach that could accurately provide information about individual sensor’s uncertainties and limitations. The sensor model aims to provide a most informative likelihood function that can be used to obtain a statistical and probabilistic estimate of uncertainties and errors due to some environmental parameters or parameters of any feature extraction algorithm used in estimation based on sensor’s outputs. This paper makes use of a neural network that has been trained with the help of a novel technique that obtains training signal from a maximum likelihood estimator. The proposed technique was applied to model stereo-vision sensors and Infra-Red (IR) proximity sensor, and information from these sensors were fused in a Bayesian framework to obtain a three-dimensional occupancy profile of objects in robotic workspace. The capability of the proposed technique in accurately obtaining three-dimensional occupancy profile and efficiently removing individual sensor uncertainties was demonstrated and validated via experiments carried out in the Robotics and Manufacturing Automation (RAMA) Laboratory at Duke University.
A Dynamical State Space Representation and Performance Analysis of a Feedback Controlled Rotary Left Ventricular Assist Device
Authors: Ferreira Antonio , Chen Shaohui , Galati David G. , Simaan Marwan A. , Antaki James F.
Published: April 2008

The Left Ventricular Assist Device (LVAD) is a mechanical device that can assist an ailing natural heart in performing its functions. The latest generation of such devices is a rotary-type pump which is generally much smaller, lighter, and quieter than the conventional pulsatile-type pump. The rotary-type pumps are controlled by varying the rotor (impeller) speed. If the patient is in a health care facility, the pump speed can be adjusted manually by a trained clinician. However, an important challenge facing the increased use of these LVADs, is the desire to allow the patient to return home. The development of an appropriate patient adaptive feedback speed controller for the pump is therefore crucial to meet this challenge. In addition to being able to adapt to changes in the patient’s daily activities by automatically regulating the pump speed, the controller must also be able to prevent the occurrence of suction. In this paper we will discuss the theoretical and practical issues associated with the development of such a controller. As a flrst step, we will present a state-space mathematical model, based on a nonlinear equivalent circuit flow model, which represents the interaction of the pump with the left ventricle of the heart. The associated state space model is a 5-dimensional vector of time varying nonlinear difierential equations. The time variation occurs over 4 consecutive intervals representing the contraction, ejection, relaxation, and fllling phases of the left ventricle. The pump in the model is represented by a nonlinear equation which relates the pump rotational speed and the pump flow to the pressure difierence across the pump. Using this model, we will discuss a gradient based feedback controller which increases the pump speed to meet the patient requirements up to the point where suction may occur. At that point the controller will maintain a constant pump speed keeping the gradient of the minimum pump flow at zero. Simulation results using the model equipped with the feedback controller are presented for two cases representing two levels of patient activities. Performance of the controller for noisy measurements of pump blood flow is also investigated. Our results show that such a feedback controller performs very well and is fairly robust against measurements noise.
Minimizing Stress Concentrations in Laminated Composites by Genetic Algorithm
Authors: Cho H. K. , Rowlands R. E.
Published: April 2008

Design optimizations using a genetic algorithm (GA) are well suited for problems having many design variables and local optimum design points. Concomitant with recent manufacturing advances, the concept is utilized here to minimize the tensile stress concentration in a perforated laminated composite by orientating the fibers locally both within the plies and from ply-to-ply. The current optimization approach is advantageously conducted in conjunction with FEA. The geometry is discretized into general 3D solid 20-node isoparametric layered composite elements of our own design. Solid, rather than plate, elements enable one to reliably account for features such as stress variations within and between individual plies. A parallel computing scheme is implemented between the FEA and GA optimization. Design optimization variables are local fiber directions within discrete finite elements and within respective plies of the laminate. Since fiber orientations are optimized locally within individual plies, the technique provides more than just a favorable stacking sequence of various rectilinearly orthotropic plies having different fiber orientations.
Reversible Electrowetting of Liquid-Metal Droplet
Authors: Wan Zhiliang , Zeng Hongjun , Feinerman Alan
Published: April 2008

In this paper, we study in detail the electrowetting behavior of a liquid-metal droplet (mercury) on top of a dielectric insulating layer experimentally. 74° of the contact angle change (from 141° to 67°) is achieved by applying a voltage of 180V to a mercury droplet on a Parylene surface. By using a very thin Teflon AF coating, low contact angle hysteresis (2°) and highly reversible electro-wetting are reported. The dynamic responses of the droplet to a voltage stair and a voltage pulse are video-captured and analyzed by using a high-speed camera. The electrowetting has very fast rise/fall time, which is suitable for application in MEMS devices. By using a high-k material as the insulating layer along with a thin Teflon AF coating, a very large contact angle change of 40° (from 150° to 110°) is achieved with only 30V. Saturation of the electrowetting behavior is also observed and discussed. Applications of the electrowetting effect of a liquid-metal droplet in MEMS devices are discussed.
Elastic Properties of Composites Based on Tree Root Fibers
Authors: Remillat C.
Published: April 2008

The in plane mechanical properties of composites based on fibres which shape is that of a tree root has been investigated. The number of fibrils as well as the angle between them have been shown to influence significantly the effective properties of the composite. It can be shown that there is an optimal number of fibrils and an optimal angle for which the stiffness of the material is maximum
An Analytical-Thermal Modeling Approach for Predicting Forces, Stresses and Temperatures in Machining With Worn Tools
Authors: Karpat Yigit , O¨zel Tugrul
Published: April 2008

In this paper, predictive modeling of cutting and ploughing forces, stress distributions on tool faces and temperature distributions in the presence of tool flank wear are presented. The analytical and thermal modeling of orthogonal cutting that is introduced in Karpat, Zeren and O¨zel [3] extended for worn tool case in order to study the effect of flank wear on the predictions. Work material constitutive model based formulations of tool forces and stress distributions at tool rake and worn flank faces are utilized in calculating non-uniform heat intensities and heat partition ratios induced by shearing, tool-chip interface friction and tool flank face-workpiece interface contacts. In order to model forces and stress distributions under the flank wear zone, a force model from Waldorf [4] is adapted. Model is tested and validated for temperature and force predictions in machining of AISI 1045 steel and AL 6061-T6 aluminum.
Finite Element Modeling of Stresses Induced by High Speed Machining With Round Edge Cutting Tools
Authors: O¨zel Tugrul , Zeren Erol
Published: April 2008

High speed machining (HSM) produces parts with substantially higher fatigue strength; increased subsurface micro-hardness and plastic deformation, mostly due to the ploughing of the cutting tool associated with residual stresses, and can have far more superior surface properties than surfaces generated by grinding and polishing. In this paper, a dynamics explicit Arbitrary Lagrangian Eulerian (ALE) based Finite Element Method (FEM) modeling is employed. FEM techniques such as adaptive meshing, explicit dynamics and fully coupled thermal-stress analysis are combined to realistically simulate high speed machining with an orthogonal cutting model. The Johnson-Cook model is used to describe the work material behavior. A detailed friction modeling at the tool-chip and tool-work interfaces is also carried. Work material flow around the round edge-cutting tool is successfully simulated without implementing a chip separation criterion and without the use of a remeshing scheme. Finite Element modeling of stresses and resultant surface properties induced by round edge cutting tools is performed as case studies for high speed machining of AISI 1045 and AISI 4340 steels, and Ti6Al4V titanium alloy.
Performance Evaluation of Unstitched, Stitched and Z-Pinned Textile Composites Under Static Loading
Authors: Bolick Ronnie L. , Kelkar Ajit D. , Taylor Jeremy A. , Tate Jitendra S.
Published: April 2008

Advances in conventional tape laminates and textile composites provide aircraft manufacturers important technology, but the industry lacks the confidence to use these composites to manufacture wing and fuselage structures due to high cost and low damage tolerance. In order to overcome the high cost and to improve the damage tolerance of composites, researchers have developed new through-the-thickness reinforcement techniques, such as stitching through the thickness. This reinforcement technique can be used to join the skin, stiffeners, ribs and spars to form an integral structure. The structures are typically more damage tolerant, contain fewer fasteners and are less expensive to manufacture than conventional composite or metallic structures. Furthermore, stitching reduces the manufacturing time and labor compared to drilling holes for fasteners, and may eliminate the problems of fatigue and/or corrosion from galvanic reactions with metal fasteners. Woven composites with through the thickness reinforcements such as stitching have good properties not only in mutually orthogonal directions but also in the transverse direction and more balanced properties than traditional tape laminates. They are also expected to have better fatigue and impact resistance due to the interlacing. Another benefit is reduced manufacturing cost by reducing part count. Because of these potential benefits, these composites are being considered for various applications including primary/secondary components for aerospace structures. The objective of this effort is to develop experimental tools for comparing the performance of these composites reinforced by stitching to unstitched composites. Identification of damage mechanisms and forces available to grow damage is essential for identifying the primary parameters that determine performance. Accurate determination of the driving forces will require extensive manufacturing and experimentation. However, once the reinforcement techniques are well understood, it is anticipated that simplified experiments can be developed that could be used routinely by designers to evaluate the effects of the reinforcements on damage tolerance. This paper specifically addresses the performance evaluation of stitched low cost manufactured composites subjected to static loading. Static tension and compression testing was conducted to determine the Ultimate Tensile and Compressive Strengths, Young’s Moduli and Poisson’s Ratio. Two different stitch patterns or stitch densities were used for comparison. The first density was five rows of stitching per inch of width, with eight stitches per inch over the entire length. The second density was three rows of stitching per inch of width, with four stitches per inch over the entire length.
Polymer Shrink Film Lab Experiment
Authors: Dues Joseph Francis
Published: April 2008

Polymers have many unique properties that make them ideally suited for everyday products and applications. One of these applications is heat activated shrink film. Shrink film is commonly used for packaging and temporarily insulating windows. Shrink film contains cross links between its polymer chains that are stretched when the film is manufactured. The application of heat allows the polymer chains to move and the cross links between the polymer chains to contract causing the film to shrink. This lab experiment investigates the shrinkage of polymer film that is commonly used to insulate windows. The experiment is performed in an Introduction to Materials class for freshman mechanical engineering technology students. Students first measure the change in length of strips of the film when the film is free from constraints to determine the maximum possible change in length. Then they put the film in a frame and measure the forces generated by the film as it shrinks. The results of the experiment are that the students are able to observe the macroscopic effects of the nanoscale cross links between the polymer molecules in the window film. This experiment provided an opportunity to investigate a unique aspect of the properties of polymers beyond the typical material properties such as tensile strength, elongation and stiffness.
Adaptive Setup Planning of Prismatic Parts by Tool Accessibility Examination
Authors: Cai Ningxu , Wang Lihui , Feng Hsi-Yung
Published: April 2008

Setup planning for machining a part is to determine the number and sequence of setups (including machining features grouping in setups) and the part orientation of each setup. Tool accessibility plays a key role in this process. An adaptive setup planning approach for different types of multi-axis machine tools is proposed in this paper by investigating Tool Access Directions (TADs) of machining features, Tool Orientation Spaces (TOSs) of machine tools, and Primary Locating Directions (PLDs) of workpieces. In our approach, feasible TADs of a machining feature are predefined based on feature geometry and best practice knowledge, and denoted by unit vectors; The TOS of a machine tool is generated according to its configuration through kinematic analysis, and represented by a unit spherical surface patch; Primary locating directions and their priorities of a workpiece are determined based on the surface areas and the surface accuracy grades of non-machining surfaces. Starting from a 3-axis based machining feature grouping, setups for a 3-, 4- (or 3-axis with indexing table), or 5-axis machine can be achieved effectively by tool accessibility examination. A so-generated setup plan can provide not only the best coverage of machining features but the optimal orientation for each setup. Prismatic parts are considered in the proof-of-concept phase. Algorithms introduced here are implemented in MATLAB, and a case study is used to show the results.
Analysis of the Non-Linear Behavior of ECLIPSE Actuators
Authors: Webber Kyle G. , Lynch Christopher S.
Published: April 2008

This work discusses the development and characterization of rectangular shaped Epoxy Composite Laminated Piezoelectric Stress-Enhanced actuators (ECLIPSE). ECLIPSE actuators are unimorph type d31 actuators that are manufactured with a lead zirconate titanate (PZT) plate sandwiched between unidirectional Kevlar 49/epoxy composite layers with dissimilar coefficients of thermal expansion in orthogonal directions. Cooling the actuator from an elevated curing temperature resulted in a residual stress gradient through the actuator, a compressive stress on the brittle piezoelectric plate, and a large out-of-plane deformation. Extended classical lamination theory (ECLT) is used to model the residual stress state and curvature of the actuator. The model results are compared to the classical lamination theory. The ECLT was developed by Hyer to explain the non-linear behavior of unsymmetric cross-ply laminates [1-3]. Three actuator layups were fabricated and characterized: [90/PZT/90/0], [90/90/PZT/90/0/0], and [90/90/90/PZT/90/0/0/0]. It is shown that geometric non-linearity is important to consider when modeling ECLIPSE actuators.
The Reduction of Deformation Energy and Increase in Workability of Metals Through an Applied Electric Current
Authors: Perkins Timothy A. , Roth John T.
Published: April 2008

Many manufacturing processes (e.g., forging, rolling, extrusion, and sheet metal) rely on the application of heat to reduce the forces associated with fabricating parts. However, due to the negative implications associated with hot working, another more efficient means of applying energy is desired. This paper investigates the changes in the material properties of various metals (aluminum, copper, iron, and titanium based alloys) in response to electricity flow. Theory involving electromigration, and, more specifically, electroplasticity, is examined and the implications thereof are analyzed. It is shown that, using electrical current, the flow stresses in a material are reduced, resulting in a lower specific energy for open-die forging. It is also shown that an applied electrical current can increase the forgeability of materials, allowing greater deformation prior to cracking. Additionally, elastic recovery is shown to decrease when using electricity during deformation. Finally, For most materials, these effects were dependent on strain rate.
Direct Freeform Fabrication Technique for Bio-Manufacturing of Pre-Seeded, Spatially Heterogeneous, Anatomically-Shaped Alginate Hydrogel Implants
Authors: Cohen Daniel L. , Malone Evan , Lipson Hod , Bonassar Lawrence J.
Published: April 2008

A major challenge in orthopaedic tissue engineering is the generation of cell-seeded implants with structures that mimic native tissue, both in terms of anatomic geometries and intratissue cell distributions. By combining the strengths of injection molding tissue engineering with those of Solid Freeform Fabrication (SFF), three-dimensional pre-seeded implants were fabricated without custom-tooling, enabling efficient production of patient-specific implants. The incorporation of SFF technology also enables the fabrication of geometrically complex, multiple-material implants with spatially heterogeneous cell distributions that could not otherwise be produced. Using a custom-built robotic SFF platform and gel deposition tools, alginate hydrogel was used with calcium sulfate as a crosslinking agent to produce pre-seeded living implants of arbitrary geometries. The process was determined to be sterile and viable at 94±5%. The GAG production was found to be about half that of a similarly molded samples. The compressive elastic modulus was determined to be 1.462±0.113 kPa.
Conventional and Auxetic SMA Cellular Structures
Authors: Hassan Mohd R. , Scarpa F. , Mohammed N. A. , Ancrenaz Y.
Published: April 2008

This work illustrates the manufacturing and tensile testing of a novel concept of honeycomb structures with hexagonal and auxetic (negative Poisson’s ratio) topology, made of shape memory alloy (SMA) core material. The honeycombs are manufactured using Nitinol ribbons having 6.40 mm of width and 0.2 mm of thickness. The ribbons were inserted in a special dye using cyanoacrilate to bond the longitudinal strips of the unit cells. The ribbons were subjected to tensile test at room temperature (martensite finish) and austenite finish temperature. Tensile tests at room temperature were performed on the honeycomb. The stress-strain curve obtained from the test on a single ribbon at room temperature was then used to develop nonlinear Finite Element beam elements using a commercial code. The beam elements were then used to model the honeycomb samples under tensile loading. Good agreement is observed between numerical nonlinear simulations and the experimental results.
Near-Nash Strategies in Competitive Multi-Team Target Assignment
Authors: Galati David G. , Simaan Marwan A.
Published: April 2008

While the Nash equilibrium represents an important strategy concept for non-cooperative scenarios such as military combat, it is often difficult to justify its use in scenarios in which its computation is unfeasible or its existence cannot be guaranteed. To justify the use of Nash-like strategies in such applications, we extend the concept of a Nash equilibrium to encompass a definition of near-Nash strategies. We then employ this definition in an efficient algorithm designed to calculate target assignment strategies in the Multi-Team Dynamic Weapon Target Assignment problem. Using this approach we demonstrate that our concept of near-Nash strategies generates results similar to those produced using the exact Nash strategies.
Analytical and Numerical Investigation of the Strain Rate Field in the Secondary Shear Zone
Authors: Tounsi N.
Published: April 2008

The use of analytical modeling of continuous chip formation in conjunction with orthogonal cutting experiments is proposed in the open literature to identify the material coefficients of constitutive equation within the practical range of stress, strain, strain rate, and temperature encountered in metal cutting. However, most of these approaches do not provide reliable material coefficients since they use average value of the physical quantities in the primary and/or secondary shear zones. The average value of the effective stress, effective strain, effective strain rate and temperature are not very sensitive to the variation of the cutting conditions. The use of distributions of the physical quantities, rather than average values, is believed to provide well-conditioned information for the identification procedure of the constitutive law. An investigation of the primary shear zone has been published elsewhere. The secondary shear zone, characterized by higher temperature compared to the primary shear zone, is being tackled in this paper. An original analytical approach is proposed to investigate the strain rate field in the secondary shear zone for continuous chip formation processes. Based on the distribution of the flow velocity in the primary shear zone and the shape of the secondary shear zone, the field of flow velocity in the secondary shear zone is determined to respect the different boundary conditions. The ability of this approach to predict the velocity and the strain rate fields is assessed by comparing it to the results of numerical simulation of chip formation using DEFORM3D in the case of AISI 1045 steel.
Adaptive Hot-Spot Cooling of Integrated Circuits Using Digital Microfluidics
Authors: Paik Phil , Pamula Vamsee K. , Chakrabarty Krishnendu
Published: April 2008

Thermal management is becoming an increasingly important issue in integrated circuit (IC) design. The ability to cool ICs is quickly reaching a limit with today’s package-level solutions. While a number of novel cooling methods have been introduced, many of which are microfluidic approaches, these methods are unable to adaptively address the uneven thermal profiles and hot-spots generated in high performance ICs. In this paper, we present a droplet-based digital microfluidic cooling system for ICs that can adaptively cool hot-spots through real-time reprogrammable flow. This paper characterizes the effectiveness of microliter-sized droplets for cooling by determining the heat transfer coefficient of a droplet shuttling back and forth in an open system over a hot-spot at various speeds. Cooling is found to be significantly enhanced at higher flow rates of droplets. In order to further enhance cooling, the effect of varying droplet aspect ratio (width/height) in a confined system was also studied.
An Empirical Study of Boss/Seat Materials and Geometries for Ultra Low-Leakage MEMS Micro-Valves
Authors: Lynch Bernard A. , Jamieson Brian G. , Roman Patrick A. , Zakrzwski Charles M.
Published: April 2008

We report work on the testing and characterization of the sealing properties of various micro-valve seat/boss interfaces. Using a custom test set-up, we have measured helium leak rates for a variety of boss materials and seat geometries. The seat geometries are micro-machined in silicon, and an orifice is DRIE etched through the chip. The test fixture allows for leak-tight edge sealing of seat chips against a viton o-ring, independent of the force used to seal the boss against the seat. Bosses are sealed against the various seat chips with forces up to 400 mN by using a precision micrometer to deflect a small spring that is coupled to the boss chip. Soft metals, such as copper and gold, and polymers such as polydimethylsiloxane (PDMS) and parylene-c, coated on silicon boss chips have been tested on hard silicon seats. In all cases, leak rates were determined as a function of sealing pressure. Seat geometries include a concentric o-ring configuration, and a silicon knife-edge. Both seats have orifice diameters varying from 60 to 110 μm. Experimental results indicate that practical MEMS-scale forces (up to several hundred mN) are sufficient to cause deformation of the soft materials coating the bosses given the small loading area, which can improve sealing capacity but not repeatability. However, uneven loading of the boss prevented a tight seal across the entire seat, which is reflected in the leak rates detected. Soft boss-materials, like PDMS, however, have shown promising results for obtaining ultra-low leak rates. Leak rates as low as 1 × 10−4 atm·cc/sec were obtained on knife-edge seats with 110 μm diameter orifices.
Micro Thin Film Sensor Embedded in Metal Structures for In-Situ Process Monitoring During Ultrasonic Welding
Authors: Cheng Xudong , Li Xiaochun
Published: April 2008

The objective of this research is to develop an effective method, i.e., ultrasonic metal welding (USMW), to embed micro thin film sensors for metal tooling, and use micro thin film thermocouple study the heat generation during USMW. A complete understanding of the fundamental mechanisms of USMW does not yet exist, and the function of heat generation on weld formation is especially in argument due to the lack of the method to measure the temperature at the welding interface. Continuing on the previous preliminary study [1] which proved that thin film sensors can survive ultrasonic welding process, significant advances were made to improve sensor reliability as well as sensor fabrication effectiveness. These include the development of a new approach for batch production of the sensor units, improvement of the adhesion between metal encapsulating layers for the sensor, as well as the adhesion between the sensing layer and the dielectric layer. Welding experiments are conducted using a series of welding parameter settings with the in-situ data acquisition of temperature 50 μm away from the welding interface. Attempts are then made to correlate the heat generation to welding parameters. With the mechanical testing of the weld strength, the possibility of using heat generation as a weld strength indicator is explored.
Robust Fault Detection Based on Nonlinear Analytic Redundancy Techniques With Applications to Robotics
Authors: Halder Bibhrajit , Sarkar Nilanjan
Published: April 2008

A new approach to sensor and actuator fault detection in the presence of model uncertainty and disturbances, and its application to a wheeled mobile robot (WMR) are presented in this paper. Robust fault detection is important because of the universal existence of model uncertainties and process disturbances in most systems. This paper proposes a new approach, called robust nonlinear analytic redundancy (RNLAR) technique, to sensor and actuator fault detection for input-affine nonlinear multivariable dynamic systems in the presence of model-plant-mismatch and process disturbance. The proposed RNLAR can be used to design primary residual vectors (PRV) for nonlinear systems to detect sensor fault that are completely insensitive to both the model-plant-mismatch and process disturbance. It is shown that the PRV for actuator fault cannot be made completely insensitive to these factors. In order to overcome this problem, a nonlinear PRV design method to detect actuator faults is proposed where the PRVs are highly sensitive to the actuator faults and less sensitive to model-plant-mismatch and process disturbance. The proposed robust fault detection methodology is applied to a WMR and the simulation results are presented to demonstrate the effectiveness of this new approach.
A UAV Trajectory Planning Algorithm for Simultaneous Search and Track
Authors: Tisdale John , Hedrick J. Karl
Published: April 2008

This paper considers trajectories for an unmanned aerial vehicle (UAV) that must search an area while tracking a target. The UAV has a constrained turn rate and a constant velocity; it is assumed that there are certain areas of interest that have a higher search value than others. An algorithm is presented that seeks to maximize the value of the area searched while still maintaining the track. The problem is discretized in both time and the control; the motion of the UAV is constrained to the reachability graph, a subset of the forward reachable set. At each revisit, the target path is estimated for the next revisit. A heuristic method is used to determine the best UAV path, because the target path is not known a priori. Feasible paths are found by examining the terminating vertices of the reachability graph. A cooperative implementation, for a team of UAVs patrolling the same region, is developed. Simulation indicates the feasibility of the method for a real-time implementation. Trajectories for example scenarios are presented and discussed.
Mechanical Reliability Evaluation of Chip Scale Power Package
Authors: Ghosh Kaushik , McCluskey F. Patrick , Temple Victor A. K.
Published: April 2008

ThinPak™ is a highly volumetrically efficient technology for packaging high power semiconductor devices for a wide range of applications. Its elimination of wirebonds lowers thermal and electrical resistivity and impedance, while its two sided solder attach enhances cooling, thus promising improved performance and reliability. In this study, the thermomechanical durability of the ThinPak™ module was investigated using physics-of-failure modeling and accelerated thermal cycle testing. Post-test analysis of samples indicated that failure occurred first in the eutectic solder used to attach the ThinPak™ to the DBC substrate. The high lead solder in the ThinPak™ itself was very robust against failure. Viscoplastic stress analysis combined with Coffin-Manson damage modeling was used to quantify creep-fatigue accumulation. The failure criterion of a 20% increase in forward voltage drop was used in conjunction with stress analysis to assess the time to failure at the DBC/ThinPak™ interface. The calibrated constants for the fatigue ductility and exponent were then used to assess the life of the assembly for different temperature loading conditions.
Internet-Based Bilateral Teleoperation Based on Wave Variable With Semi-Adaptive Predictor and Direct Drift Control
Authors: Ching Ho , Book Wayne J.
Published: April 2008

In a conventional bilateral teleoperation, transmission delay over the internet can potentially cause instability. One of the more robust methods of dealing with this problem is the wave variable. Wave variable guarantees teleoperation stability even under varying transmission delay at the cost of poor transient performance. Adding a predictor on the master side can reduce this undesirable side-effect, but that would require a slave model. Inaccurate slave model used in the predictor as well as variations in transmission delay, both of which are likely under realistic situations, can result in steady state errors. A direct drift control algorithm is used to drive this error to zero regardless of the source of error. A semi-adaptive predictor that can distinguish between free space and rigid contact environment is also used to provide a more accurate force feedback on the master side. This research presents the experimental results and evaluations of the previously mentioned wave variable based methods under realistic operation environment using real master and slave.
An EFEA Formulation for Computing Structural Response of Complex Structures
Authors: Vlahopoulos Nick , Wang Aimin , Wu Kuangcheng
Published: April 2008

This paper presents a validation case study for an Energy Finite Element Analysis (EFEA) formulation through comparison to test data. The EFEA comprises a simulation tool for computing the structural response of a complex structure and the amount of the radiated power. When the forcing function originates from an external flow, then the EFEA can be used for computing the vibration and the noise created due to the external flow excitation. In the past the EFEA has been used for computing the flow induced vibration for a large scale vehicle. The EFEA formulation presented in this paper can account for periodic stiffeners, for partial fluid loading effects on the outer part of the structure, and for internal compartments filled with heavy fluid. The new developments are validated by computing the vibration induced on a 1/8 scale structure representative of an advanced hull concept, and by comparing the simulation results to the test data.
International Community Based Senior Design Projects: Santa Clara University and Universidad Centro Americana
Authors: Hight Tim , Gonzalez Jorge , Sa´nchez Ismael
Published: April 2008

As part of an initiative to promote community based engineering education, Santa Clara University engineering students undertook two ambitious senior design projects during the 2004-2005 school year that have direct impact on communities in El Salvador. The two projects were coordinated through our sister school, Universidad Centro Americana, in San Salvador, and also involved other local and international partners. The first project consisted of the design, purchase, and installation of a 3 kW solar powered water pumping system for Isla Zacatillo off the southwest coast of El Salvador. The new system replaces a standard electrical system that was dependent on an expensive undersea power connection to the mainland. The new system promises higher reliability and independence while also promoting sustainable energy and water solutions. The second project involved the design and construction of a prototype Human Powered Utility Vehicle (HPUV) for use in rural transportation of goods and people. The team faced a number of challenges in order to improve upon existing designs. The primary goals were to create a design that was robust, reliable, highly functional, and inexpensive. The paper will discuss the planning and logistics involved in accomplishing these international senior design projects, the challenging communication issues, the benefits to students and faculty beyond those of a conventional engineering design project, the impacts on the local society, and the final results of the projects.
Function-Based Design of a Spacecraft Power System Diagnostics Testbed
Authors: Hutcheson Ryan S. , Tumer Irem Y.
Published: April 2008

NASA’s Ames Research center is currently designing a testbed to validate and compare potential Integrated System Health Management (ISHM) technologies. The proposed testbed represents a typical power system for a spacecraft and includes components such as a fuel cell, solar cells and redundant batteries. To fulfill design requirements, the testbed must be capable of hosting a wide variety of ISHM technologies including those developed by NASA as well as those developed in the aerospace industry abroad. An internal fault injection subsystem must be built into the system to provide a common interface for evaluating these different ISHM technologies. Additionally, to ensure robust operation of the testbed, the capability to detect and manage external faults must also be present. In order to develop a set of requirements for the internal fault injection subsystems as well as predict external faults, a comprehensive set of potential failures must be identified for all of the components of the testbed. To best aid the development of the testbed, these failures needed to be identified as early as the conceptual design phase, where little is known about the actual components that would comprise the finished system. This paper demonstrates the use a function-based failure mode identification method to identify the potential failures of the testbed during the conceptual design phase. Using this approach, designers can explore the potential failure modes at the functional design stage, before a form or solution has been determined. A function-failure database is used to associate the failures of components from previous design efforts to the testbed based on common functionality. The result is a list of potential failure modes and associated failure rates, which are used to improve the design of the testbed as well as provide a framework for the fault injection subsystem.
Adhesion Energy of Single Wall Carbon Nanotube-Polyethylene Composite: Effect of Magnetic Field
Authors: Al-Haik M. S. , Hussaini M. Y. , Garmestani H.
Published: April 2008

In this paper, we investigate the adhesion energy at the interface between single wall carbon nanotubes and polyethylene matrix with and without an external magnetic field. The carbon nanotubes are of two different chiralities — armchair (10,10), and zigzag (10,0), and the external high magnetic field is of 25 Tesla intensity. The study employs molecular dynamics simulations and concludes that the magnetic field decreases the interfacial adhesion energy although it increases the individual potential energies of the nanotubes, the polyethylene, and the composite.
Characterization of LIGA Microsystems Using Digital Image Correlation Technique and SEM Imaging
Authors: Jin Helena (Huiqing) , Lu Wei-Yang , Chames Jeff , Yang Nancy
Published: April 2008

A new experimental technique was developed to characterize the mechanical properties of LIGA (an acronym from German words for lithography, electroplating, and molding) materials. An advanced imaging capability, scanning electron microscopy (SEM), with an integrated loading stage allows the acquisition of in situ microstructural images at the micro scale during loading. The load is measured directly from a load cell, and the displacement field is calculated from the SEM images based on the digital image correlation (DIC) technique. The DIC technique is a full-field deformation measurement technique which obtains displacement fields by comparing random speckle patterns on the specimen surface before and after deformation. The random speckle patterns are typically generated by applying a thin layer of material with high contrast to a specimen surface. Alternatively, DIC can also be applied using the microstructural features of a surface as texture patterns for correlation. DIC technique is ideally suited to characterize the deformation field of MEMS structures without the need to generate a random speckle pattern, which can be very challenging on the micro and nanoscale. In this paper, the technique is experimentally demonstrated on a LIGA specimen. The digital images showing LIGA surface features acquired during the loading can serve as random patterns for the DIC method. Therefore, full-field displacement and strain can be obtained directly on the specimen and the errors incurred by the testing system can be eliminated.
Compact Miniature Heat Exchangers With Advanced Foam-Like Structure
Authors: Wexler Eugene M. , Tuchinsky Lev J. , Ibrahim Sharly , Milligan Lance J.
Published: April 2008

Experimental study has been carried out to investigate convective heat transfer properties of air-cooled foam-like miniature heat exchangers, fabricated using innovative polycapillary materials technology. Practically important results with regard to heat transfer and hydraulic resistance were established and compared for heat exchangers with different structure.
Transfer Function Analysis of Atomic Force Microscope Cantilevers
Authors: Rubio-Sierra F. J. , Vazquez R. , Stark R. W.
Published: April 2008

Current methods to study atomic force microscope (AFM) cantilever dynamics use model simplification or are based on the non-trivial solution of the equation of motion. As an alternative method, transfer function analysis gives a more complete description of system dynamics. In this work a transfer function study of two different AFM configurations, the point force and base driven cantilever, is presented. Exact analytical expressions of the infinite dimensional transfer function are derived for cantilever deflection and slope along the cantilever. Frequency response and transfer function infinite product expansion are obtained for the case where system outputs are set at the free end of the cantilever. The frequency response reflects the full complexity of cantilever dynamics affected by the presence of an infinite number of poles and zeros. An analytical expression for all the zeros and poles of the system is obtained. From the frequency response and pole-zero investigations it is shown how cantilever actuation and output measurement affect AFM operation and cantilever dynamics modelling. Transfer function analysis of AFM cantilevers opens the possibility of model based AFM operation to increase imaging and manipulation performance.
CFD Investigation of Gear Pump Mixing
Authors: Strasser Wayne
Published: April 2008

A moving-deforming grid study was carried out using a commercial CFD solver, Fluent® 6.2.16, in order to quantify the level of mixing of a lower viscosity additive (at a mass concentration below 10%) into a higher viscosity process fluid for a large-scale metering gear pump configuration typical in plastics manufacturing. Second order upwinding and bounded central differencing schemes were used to reduce numerical diffusion. A maximum solver progression rate of 0.0003 revolutions per timestep was required for an accurate solution. Fluid properties, additive feed arrangement, pump scale, and pump speed were systematically studied for their effects on mixing. For each additive feed arrangement studied, the additive was fed in individual stream(s) into the pump intake. Pump intake additive variability, in terms of coefficient of variation (COV), was > 300% for all cases. The model indicated that the pump discharge additive COV ranged from 32% for a single centerline additive feed stream to 3.9% for multiple additive feed streams. It was found that viscous heating and thermal/shear-thinning characteristics in the process fluid slightly improved mixing, reducing the outlet COV to 2.3% for the multiple feed stream case. The outlet COV fell to 1.4% for a half-scale arrangement with similar physics. Lastly, it was found that if the smaller unit’s speed were halved, the outlet COV was reduced to 1.1%.
Cyclic Mechanical Durability of Sn3.0Ag0.5Cu Pb-Free Solder Alloy
Authors: Cuddalorepatta Gayatri , Dasgupta Abhijit
Published: April 2008

The isothermal mechanical durability properties of a hypoeutectic, Sn3.0Ag0.5Cu solder are presented and compared to that of near-eutectic Sn3.9Ag0.6Cu and of baseline eutectic Sn37Pb solder. Cyclic mechanical tests are performed at room temperature at various load levels, using a custom-built thermo-mechanical-microscale (TMM) test system. Both the SnAgCu solders are found to outperform the baseline Sn37Pb, with near-eutectic Sn3.9Ag0.6Cu having the best durability. These trends are found to be in agreement with similar results available in the literature for thermal cycling durability. Fatigue results are presented in terms of both cyclic strain range and cyclic work dissipation. The effect of microstructural coarsening resulting from long-term aging at room temperature is investigated by conducting similar tests at room temperature, on the aged samples. The durability of the hypoeutectic SnAgCu solder reduced on aging, with the drop being more significant for damage curves based on cyclic work dissipation, than on cyclic inelastic strain range.
Mathematical Modelling of Magneto-Hydrodynamic Dampers With Time-Varying Fluid Properties
Authors: Letelier Mario F. , Siginer Dennis A. , Rouliez Jean-Paul , Corral Omar F.
Published: April 2008

The fluid dynamics of dampers is investigated for the case where the damping fluid flows through passages in which a magnetic field is applied. This is a specific case of a new and promising field of applications that has emerged through the design of devices that take advantage of some properties of the so-called electrorheological fluids and magnetorheological fluids (ERF and MRF). These fluids are created when a base fluid is seed with very small dielectric or iron particles, so that it reacts to electric or magnetic fields by developing some non-Newtonian characteristics, most prominently a yield stress, viscosity change, and also viscoelasticity. These fluid properties can be controlled through control of the electric or magnetic fields’ strength. In this paper, a typical damping load is modeled and related to the required flow of a MRF inside the damper. To this end the fluid is modeled as a Bingham fluid with time-varying yield-stress. The analysis here developed makes it possible to determine the magnetic field variation necessary in order to achieve a specific displacement of the damper’s piston. The flow equations are analytically solved for any time-history of the dimensionless fluid’s yield-stress. Main results are some simplified relationships that correlate damping load and magnetic field time-variations. These results aim at providing analytical tools that may facilitate dampers’ design.