Mechanical Engineering Commons^™

Fabrication And Characterization Of Novel Electrodes For Solid Oxide Fuel Cell For Efficient Energy Conversion, Yu Chen

Theses and Dissertations

Solid oxide fuel cells (SOFCs) have been considered as one of the most promising technologies for future energy conversion since they can in principle be operated with fuels ranging from H2 to any hydrocarbon fuel. However, the system cost and coking (when using hydrocarbon as fuel) issues for the state-of-art electrode materials/designs often limit their further application. The objective of this Ph.D dissertation is aiming at overcoming these problems and accelerating SOFC commercialization. One approach to cost reduction is lowering the SOFC operating temperature to below 800 or even 600 oC, so that inexpensive materials can be used and quick …

Cost Avoidance Analysis Of Military Aircraft Components Utilizing Condition-Based Maintenance Practices, Erin Ballentine

Theses and Dissertations

This research involves two major case studies. Both look at the current maintenance practices done by the United States Army and propose a solution for improvement utilizing condition-based maintenance (CBM) practices. Each study details a cost avoidance that can be earned by implementing the solutions and the resulting benefits that can be experienced. Case Study I is a return on investment (ROI) that analyzes the benefits of the implementation of elastomeric wedges as vibration control on the Apache (AH-64D) aircraft. Analysis of the material and operational costs shows that the use of self-adhering elastomeric trailing edge wedges on the Apache …

Low Reynolds Number Turbulence: Mechanisms And Applications, Wei Zhao

Theses and Dissertations

Turbulence, as one of "the most important unsolved classical problem in physics" (R. Feynman, 1932), has been investigated for more than 130 years. Conventionally, turbulence is believed to be a phenomenon of high Reynolds numbers (Re). However, we find that turbulence can also be achieved at low Re by proper external forcing, either in macroflows or in microflows. In macroflows, the characteristics of high Re turbulence can be achieved in confined flows, when the bulk flow Re is around 400, by external forcing at its optimal frequency (Wang 2003; Wang 2006). Interestingly, the optimal narrow band of frequency is fixed …

Behavior Of Piezoelectric Wafer Active Sensor In Various Media, Tuncay Kamas

Theses and Dissertations

The dissertation addresses structural health monitoring (SHM) techniques using ultrasonic waves generated by piezoelectric wafer active sensors (PWAS) with an emphasis on the development of theoretical models of standing harmonic waves and guided waves. The focal objective of the research is to extend the theoretical study of electro-mechanical coupled PWAS as a resonator/transducer that interacts with standing and traveling waves in various media through electro-mechanical impedance spectroscopy (EMIS) method and guided wave propagation. The analytical models are developed and the coupled field finite element analysis (CF-FEA) models are simulated and verified with experiments. The dissertation is divided into two parts …

On The Development Of High Strain Rate Experiments For The Characterization Of Engineering Materials, Silas P. Mallon

Theses and Dissertations

In order to predict the damage accumulation and failure processes associated with highly dynamic events such as blast loading, shock wave loading, and ballistic impact loading, a commensurate understanding of the fundamental constitutive and fracture behavior of materials subjected to such high rate loading conditions is necessary. In this effort, high strain rate experimental facilities consisting of a shock tube apparatus and a torsional split Hopkinson bar apparatus have been designed, constructed, and subsequently used to investigate the mechanical properties of an array of engineering materials subjected to a variety of dynamic loading conditions. Designs for the experimental equipment utilized …

Applications Of Advanced Imaging Methods: Macro-Scale Studies Of Woven Composites And Micro-Scale Measurements On Heated Ic Packages, Siming Guo

Theses and Dissertations

As a representative advanced imaging technique, the digital image correlation (DIC) method has been well established and widely used for deformation measurements in experimental mechanics. This methodology, both 2D and 3D, provides qualitative and quantitative information regarding the specimen’s non-uniform deformation response. Its full-field capabilities and non-contacting approach are especially advantageous when applied to heterogeneous material systems such as fiber-reinforced composites and integrated chip (IC) packages. To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Stereo digital image …

Thermal Analysis Of High Pressure Micro Plasma Discharge, Mostafa Mobli

Theses and Dissertations

High pressure micro plasma discharge has been at the center of interest in recent years, because of their vast applications, ease of access and cost efficiency. This attributes to atmospheric discharges that are generated in ambient conditions and therefore can be readily applicable to everyday use. The absence of vacuum makes these high pressure discharges to be inexpensive to operate. Despite the ease of operation, the high pressure is a source of enhanced gas heating as the gas temperature cannot be controlled by diffusion alone. Gas heating is therefore an important factor when it comes to the simulation of high …

Plant-Biomimetic Hydrogel Actuators: Creating Movement In Hydrogels Through The Study Of Plants, Christen Rhodes

Theses and Dissertations

Plants are sessile organisms that have developed methods of movement to respond to environmental stimuli. Some of the approaches feature the unequal expansion of cells and controlling deformation direction through fibers under swelling and drying. Hydrogels are three dimensional polymer networks that have the capacity for large volume changes due their affinity for water and can be tough and/or stimuli-responsive. In this paper, three preliminary plant-biomimetic hydrogel actuator designs are discussed and tested from wet to dry. The first actuator design, termed a 1%-0.1% bilayer, features two layers of different swelling and drying rates due to differences in cross-linking density. …

Structural Health Monitoring Using Linear And Nonlinear Ultrasonic Guided Waves, Yanfeng Shen

Theses and Dissertations

The dissertation addresses Structural Health Monitoring (SHM) using linear and nonlinear ultrasonic guided waves, with an emphasis on the development of analytical and numerical models of guided wave propagation and interaction with linear and nonlinear structural damage.

An analytical model was developed based on the exact Lamb wave solution for the simulation of Lamb wave propagation and interaction with damage. The damage effects were inserted into the model using complex valued wave damage interaction coefficients (WDICs). The analytical procedure was coded as a framework into a MATLAB Graphical User Interface (GUI), and the software WaveFormRevealer (WFR) was developed as a …

Ultrasonics Transduction In Metallic And Composite Structures For Structural Health Monitoring Using Extensional And Shear Horizontal Piezoelectric Wafer Active Sensors, Ayman Kamal Abdelrahman

Theses and Dissertations

Structural health monitoring (SHM) is crucial for monitoring structures performance, detecting the initiation of flaws and damages, and predicting structural life span. The dissertation emphasizes on developing analytical and numerical models for ultrasonics transduction between piezoelectric wafer active sensors (PWAS), and metallic and composite structures.

The first objective of this research is studying the power and energy transduction between PWAS and structure for the aim of optimizing guided waves mode tuning and PWAS electromechanical (E/M) impedance for power-efficient SHM systems. Analytical models for power and energy were developed based on exact Lamb wave solution with application on multimodal Lamb wave …

Oxygen Flux And Dielectric Response Study Of Mixed Ionic-Electronic Conducting (Miec) Heterogeneous Functional Materials, Fazle Rabbi

Theses and Dissertations

Dense mixed ionic-electronic conducting (MIEC) membranes consisting of ionic conductive perovskite-type and/or fluorite-type oxides and high electronic conductive spinel type oxides, at elevated temperature can play a useful role in a number of energy conversion related systems including the solid oxide fuel cell (SOFC), oxygen separation and permeation membranes, partial oxidization membrane reactors for natural gas processing, high temperature electrolysis cells, and others. This study will investigate the impact of different heterogeneous characteristics of dual phase ionic and electronic conductive oxygen separation membranes on their transport mechanisms, in an attempt to develop a foundation for the rational design of such …

Investigation Of Thermal Performance Of Nanoparticle Enhanced Ionic Liquids (Neils) For Solar Collector Applications, Titan Chandra Paul

Theses and Dissertations

Concentrated Solar Power (CSP) is a prominent alternative energy technology, where mirrors or lenses are used to concentrate sunlight from a large area and stored in a collector filled with heat transfer fluid (HTF). The energy from this HTF is used to produce steam for power generation. CSP system requires high heat storage capacity and thermally stable HTF to reduce its operating cost. Having suitable thermophysical properties, ionic liquids (ILs) is considered as a potential HTF for the CSP applications; however thermophysical properties of ILs can be further enhanced by dispersing small volume percentages of nanoparticles. This liquid is called …

Dielectric Properties Of Composite Materials During Damage Accumulation And Fracture, Md. Rassel Raihan

Theses and Dissertations

Fiber reinforced polymer matrix composite materials have many unique properties and their high performance makes them available to use in many advanced technologies i.e. aerospace, microelectronics, and energy storage. There is a correlation that exists between the long term behavior of those materials under combined mechanical, thermal, and electrical fields, and the functional properties and characteristics of the composite materials that requires a fundamental understanding of the material state changes caused by deformation and damage accumulation. This will ultimately lead, for example, to the design and synthesis of optimal multifunctional material systems. Composite materials are heterogeneous and the complex morphology …

Performance And Durability Of Electrodes With Platinum Catalysts In Polymer Electrolyte Cells Prepared By Ultrasonic Spray Deposition, William A. Rigdon

Theses and Dissertations

Catalysts in the electrodes of polymer electrolyte cells serve a critical function in reactions which can be used to either generate electrical energy from chemical fuels or convert electrical energy into chemicals. For low temperature electrochemical fuel cells, platinum is often utilized for its exceptional catalytic activities towards hydrogen oxidation and oxygen reduction reactions of the anode and cathode, respectively. However, the limited supply of platinum and high demand result in prohibitive costs plaguing commercialization of this technology. Therefore, minimal amounts of the catalyst should be used to achieve the maximum output to reduce expenses. Electrochemical behavior is governed by …

Modeling Of Chemical-Mechanical Couplings In Solid Oxide Cells And Reliability Analysis, Xinfang Jin

Theses and Dissertations

Solid oxide fuel cell (SOFC) has been well demonstrated as a promising clean energy conversion technology. For practical applications, the SOFC systems should have both good electrochemical performance and high reliability. The SOFCs are usually operated under very aggressive conditions, e.g., high temperatures (600-1000oC) and extremely low oxygen partial pressures (anode electrode). These aggressive operating conditions could lead to a variety of material system degradations, imposing great challenges on meeting lifetime requirement of SOFC commercial applications. It is therefore essential to increase the understanding of fundamental SOFC degradation mechanisms.

The basic structure of SOFCs is a positive electrode-electrolyte-negative electrode (PEN) …

Material Synthesis And Fabrication Method Development For Intermediate Temperature Solid Oxide Fuel Cells, Hanping Ding

Theses and Dissertations

Solid oxide fuel cells (SOFCs) are operated in high temperature conditions (750-1000 oC). The high operating temperature in turn may lead to very complicated material degradation issues, significantly increasing the cost and reducing the durability of SOFC material systems. In order to widen material selections, reduce cost, and increase durability of SOFCs, there is a growing interest to develop intermediate temperature SOFCs (500-750 oC). However, lowering operating temperature will cause substantial increases of ohmic resistance of electrolyte and polarization resistance of electrodes. This dissertation aimed at developing high-performance intermediate-temperature SOFCs through the employment of a series of layered perovskite oxides …

Classification Of Low Velocity Impactors Using Spiral Sensing Of Acousto-Ultrasonic Waves, Chijioke Agbasi

Theses and Dissertations

The non-linear elastodynamics of a flat plate subjected to low velocity foreign body impacts is studied, resembling the space debris impacts on the space structure. The work is based on a central hypothesis that in addition to identifying the impact locations, the material properties of the foreign objects can also be classified using acousto-ultrasonic signals (AUS). Simultaneous localization of impact point and classification of impact object is quite challenging using existing state-of-the-art structural health monitoring (SHM) approaches. Available techniques seek to report the exact location of impact on the structure, however, the reported information is likely to have errors from …

Measuring The Effectiveness Of Education For Sustainable Development Interventions For Effecting Change In Knowledge, Attitude And Behaviors Toward Sustainable Development, Christopher Robin Wilson

Theses and Dissertations

The question addressed by this study is whether an intervention involving a brief, focused seminar providing Sustainability Fundamental education can affect change in sustainability-centric behavior via measured change in attitude toward sustainability and/or change knowledge of sustainability fundamentals.

This study focused on applying and extending lessons from a previous exploration of the relationships between sustainable behavior and both attitude toward sustainability and knowledge of sustainability. The test involved determining whether brief, science-based sustainability fundamentals seminars are an effective intervention for affecting the favorable sustainable behavior of practicing engineers, defined as professionals engaged in engineering post-completion of their formal studies, in …

Heat Transfer Enhancement By Three-Dimensional Surface Roughness Technique In Nuclear Fuel Rod Bundles, Kang Liu

Theses and Dissertations

DISS_abstract> This thesis investigate thermal characteristic of a single-phase nano-fluid in a single heater element loop tester and provides a comparison between heat transfer enhancement results achieved using water as a coolant and using nano-fluids with different volume percentage. The experimental investigation is performed on two simulated nuclear fuel rods with two different types of modified outer surfaces roughness. The fuel rod surfaces modified are termed as two-dimensional surface roughness (square transverse ribbed surface) and three-dimensional surface roughness (Diamond shaped blocks). The nano-fluid used are 0.5% and 2% ZnO-Deionized water based nano-fluid. The maximum heat transfer co-efficient enhancement achieved compared …