Digital Commons Network^™

Fiber Optic Guided Wave Sensors For Structural Health Monitoring, Erik Frankforter

Theses and Dissertations

Risks and costs associated with aging infrastructure have been mounting, presenting a clear need for innovative damage monitoring solutions. One of the more powerful damage monitoring approaches involves using ultrasonic guided waves which propagate through a structure and carry damage-related information to permanently bonded sensors. Ultrasonic fiber-optic sensors are one of the most promising technologies for this application: they are immune to electromagnetic interference, present no ignition hazard, and transmit their data over tens of kilometers. However, before they can be widely employed, several limitations need to be overcome: poor sensitivity, unidirectional sensing, and loss of ultrasonic functionality due to …

Promotional Effect Of Molten Carbonates On Proton Conductivity And Oxygen Reduction Reaction – An Experimental And Computational Study, Xiaolei Xiong

Theses and Dissertations

Recent research of Solid oxide fuel cells (SOFCs) is aimed to lower the operating temperature to an intermediate temperature (IT) range of 500 to 700^oC, while maintaining a proper performance. This Ph.D. research project investigates the promotional effects of alkaline carbonate eutectics on the proton conductivity of proton conducting electrolytes and cathodic ORR reactivity in SOFCs by both experimental and computational methods. The ionic conductivity of the MC-BZY composite above 500^oC increases with the higher loading of MC. The sample exhibited nearly a factor of two higher conductivity in H₂-containing atmosphere than in air. …

Numerical Analysis Of Phase Change, Heat Transfer And Fluid Flow Within Miniature Heat Pipes, Mehdi Famouri

Theses and Dissertations

Heat pipes with broad applications in thermal systems have the ability to provide effective heat transport with minimal losses in over reasonable distances due to their passive nature. Their exceptional flexibility, simple fabrication, and easy control, not to mention, all without any external pumping power make them especially attractive in electronics cooling. Heat pipe development is motivated to overcome the need to presumably manage thermal dissipation in progressively compressed and higher-density microelectronic components, while preserving the components temperatures to specification.

Computation of flow and heat transfer in a heat pipe is complicated by the strong coupling among the velocity, pressure …

On The Microstructural Behavior Of Pure Magnesium Under Various Strain Rates, Peter Malchow

Theses and Dissertations

An investigation into the localized microstructural response of pure magnesium under both quasi-static and dynamic loading is presented in the form of several experimental works. The meso-scale events were examined using Digital Image Correlation techniques, which provide a methodology for mapping the in-situ full-field material strain behavior.

Firstly, an analysis of the grain boundary activity specifically under dynamic conditions at high magnification is discussed. An area of interest in the region of multiple grain boundaries and triple junctions is selected for characterizing the evolution of the strain and local rotation. This is followed by a study experimentally verifying the causes …

Computational Wave Field Modeling Using Sequential Mapping Of Poly-Crepitus Green’S Function In Anisotropic Media, Sajan Shrestha

Theses and Dissertations

In this thesis, a meshless semi-analytical computational method is presented to compute the ultrasonic wave field in the generalized anisotropic material while understanding the physics of wave propagation in detail. To understand the wave-damage interaction in an anisotropic material, it is neither feasible nor cost-effective to perform multiple experiments in the laboratory. Hence, recently the computational nondestructive evaluation (CNDE) received much attention to performing the NDE experiments in a virtual environment. In this thesis, a fundamental framework is constructed to perform the CNDE experiment of a thick composite specimen in a Pulse-Echo (PE) mode. To achieve the target, the following …

Multi-Axis Multi-Material Fused Filament Fabrication With Continuous Fiber Reinforcement, Wout De Backer

Theses and Dissertations

Additive Manufacturing (AM) has become a well-recognized method of manufacturing and has steadily become more accessible as it allows designers to prototype ideas, products and structures unconceivable with subtractive manufacturing techniques for both consumer grade and industrial grade applications. Commonly used thermoplastics for 3D printing have properties that may not be sufficient to comply with the application’s certification requirements, or their performance is less than desirable for aerospace and other high performance applications. Additionally, additively manufactured parts have reduced mechanical properties in the build direction of the print, and are generally weaker than their equivalent injection-molded parts. Furthermore, Computer Aided …

Instability In Nonequilibrium And Nonthermal Plasma Discharges, Rajib Mahamud

Theses and Dissertations

Microplasma, or plasma in micron scale interelectrode separation, is an effective way to attain nonthermal plasma operation at atmospheric and higher pressure. However, the small size causes the effect of other operating parameters to be crucial in stable operation and make the microplasma discharge system to be susceptible to instabilities. The two major instabilities that are commonly observed are the instability in the negative differential resistance (NDR) region and the Striations or the ionization waves. The physics and reaction kinetics of NDR instability for high pressure system is not well understood. This study pursues both experimental characterization and development of …

Non-Destructive Evaluation Of Composites: Predictive Ultrasonic Guided-Waves Modeling, Non-Destructive Material Characterization, And The Application To Aerospace Structures, Darun Barazanchy

Theses and Dissertations

To predict guided wave dispersion curves, it is common to use different solution approaches depending on the material type (isotropic or anisotropic) of the medium in which the wave propagates. The two different solution methods are defined in different domains, frequency-phase velocity domain for isotropic materials and wavenumber-phase velocity domain for anisotropic materials. This may lead to difficulties and unsatisfying results when predicting the dispersion curves for hybrid laminates which contain both isotropic and anisotropic materials. Therefore, a unified formulation defined in the wavenumber-phase velocity domain to accomodate both isotropic and anisotropic materials, as well as hybrid combinations, is desired. …

Progressive Failure Analysis Of Composite Materials Using The Puck Failure Criteria, Karan Kodagali

Theses and Dissertations

Fiber reinforced composites have been used in various engineering structures and applications especially in naval, automotive, aeronautical and sports industries. These composite materials generally exhibit brittle damage behavior. The anisotropy in the material and different kinds of failure mechanisms make it difficult to accurately characterize the behavior of composite materials. The present work aims to verify and apply the Puck Failure Criteria using the commercially available finite element package ABAQUS by writing a user-material subroutine in FORTRAN. The model is implemented with different post failure degradation schemes.

In the present work, the progressive failure on composite materials in analyzed using …

Enhanced Dropwise Condensation Via Wettability Contrast Mechanism, Mohammad Alwazzan

Theses and Dissertations

Condensation heat transfer performance can be improved by many methods including the most common used method, which is by increasing the droplet removal rate of the condensing surface. Commonly, this approached can be achieved by promoting a dropwise condensation mode in which super/hydrophobic coatings can be applied on the entire condenser surface to reduce the surface wettability degree. In this dissertation, two main approaches were adapted to enhance the condensation heat transfer performance of the condensing surface via wettability contrast mechanism. Three approaches of investigation were performed to better understand such dropwise condensation promoter methods.

In the first part, alternative …

Experimental And Numerical Investigation Of Pressure Drop In Silicon Carbide Fuel Rod For Application In Pressurized Water Reactors, Ahmed Musafi Abir

Theses and Dissertations

Spacer grids are used in pressurized water reactors (PWRs) fuel assemblies which enhances heat transfer from fuel rods. However, there remain regions of low turbulence in between the spacer grids which contributes to lower heat transfer. To enhance turbulence in these regions surface roughness is applied on the fuel rod walls. Meyer et al [1] used empirical correlations to predict heat transfer and friction factor for artificially roughened fuel rod bundles at high performance light water reactors (LWRs). At present, several types of materials are being used for fuel rod cladding including zircaloy, uranium oxide, etc. But researchers are actively …

Nondestructive Evaluation And Health Monitoring Of Adhesively Bonded Composite Structures, William Walker Roth

Theses and Dissertations

As the growth of fiber reinforced composite materials continues in many industries, structural designers will have to look to new methods of joining components. In order to take full advantage of composite materials, such as increased stiffness, decreased weight, tailored material properties and increased fatigue life, mechanical fasteners will need to be replaced by adhesive bonding or welding, when possible. Mechanical fasteners require the drilling of holes, which damages the laminate and becomes the source of further fatigue damage. Also, an increase in laminate thickness or inclusion of other features is required for the material to withstand the bearing stress …

A Comprehensive Evaluation Of Hybrid Wetting Configurations On Dropwise Condensation, Karim Khazal Egab

Theses and Dissertations

The heat transfer during condensation on a surface depends on the pattern design of the surface, which can highly influence hydrophobic/hydrophilic wettability. In this study hybrid pattern designs were studied. The relationship between the droplet dynamic and the hybrid pattern design can alter the drainage rates, droplet departure frequencies, and the condensation heat transfer rates. Therefore, two series of hybrid patterned surfaces have been designed, developed, and tested during condensation of water vapor on horizontal copper tubes, and compared to complete dropwise and complete filmwise condensation samples. This is to investigate the design that provides the maximum improvement in the …