Engineering Commons^™

Effects Of Overload And Underload On Internal Strains/Stresses And Crack Closure During Fatigue-Crack Propagation, Soo Yeol Lee

Doctoral Dissertations

The overload and/or underload occurring during constant-amplitude fatiguecrack growth result in the retardation and/or acceleration in the crack-growth rate, making it difficult to predict the crack-propagation behavior and fatigue lifetime. Although there have been numerous investigations to account for these transient crackgrowth behavior, the phenomena are still not completely understood.

Neutron and X-ray diffraction, and electric-potential measurements were employed to investigate these transient crack-growth micromechanisms; gain a thorough understanding of the crack-tip deformation and fracture behaviors under applied loads; and establish a quantitative relationship between the crack-tip-driving force and crack-growth behavior. Five different fatigue-crack-growth experiments (i.e., fatigued, tensile overloaded, compressive …

Fundamental Mechanical-Behavior Studies Of Annealed And Nano-Particle-Strengthened Nickel-Based Alloys Using In-Situ Neutron-Diffraction Experiments, E-Wen Huang

Doctoral Dissertations

This dissertation addresses two issues concerning the fundamental mechanical behavior of the nickel-based superalloys: (1) the deformation mechanisms and (2) the nano-precipitate-strengthening effect. The precipitates are known to fortify the mechanical behavior of the metallic alloys. These precipitates can interact with the matrix upon the applied load. While the precipitation strengthening has been facilitated for many purposes, this research puts forward the mechanistic understanding.

The dissertation considers the thesis that Deformation Mechanisms and Nanoprecipitate Strengthening and their effects on the microstructure are central to the mechanical behavior of nickel-based superalloys.

The experimental methods employed in this research are in-situ neutrondiffraction …

Localized Deformation In Metallic Glasses At The Ambient Temperature, Shuangxi Song

Doctoral Dissertations

Metallic glasses have many unusual properties, such as extremely high strength and large elastic limit. However, they are also brittle, failing in a catastrophic manner, as a result of the formation of highly localized shear bands at room temperature. Such flow localization has been attributed to the influence of strain softening or local heating, or a combination of both, which leads to the local drop in viscosity and, finally, the runaway of the shear band.

In this thesis, a novel method was developed for in situ observation of the localized shear processes. The inhomogeneous deformation of metallic glasses at room …

Mechanical Behavior And The Role Of Deformation Twinning In Wrought Magnesium Alloys Investigated Using Neutron And Synchrotron X-Ray Diffraction, Liang Wu

Doctoral Dissertations

The mechanical behaviors and the associated deformation mechanisms with a focus on extension twinning under monotonic and cyclic loadings are investigated using neutron and synchrotron diffractions in the wrought magnesium alloys, ZK60A and AZ31B. It has been demonstrated that the extension twinning plays significant roles in the mechanical behaviors.

The significant tension-compression asymmetries and high anisotropies are observed. The tension-compression asymmetries are related to the twinning activation in one direction but not in the opposite direction. The high anisotropies are correlated with the initial texture distinction relative to the loading directions. The similar yielding stresses are noted irrespective of the …

Simpler Packaging, Tomiko Oden

Graphic Communication

This project explains how product packaging is become more "green", and thus more simple. Packaging needs to go beyond just simplifying materials and graphics - it needs to create a simpler process in order to reduce wasted time, energy, and resources.

Novel Design Of A Portosystemic Shunt Occluder, Tommy Lee Washington

Masters Theses

In some breeds of dog, specifically the Yorkshire Terrier, a genetic defect exists that causes a hepatic portosystemic shunt to form. A hepatic portosystemic shunt is a vessel that when present cause blood to bypass the liver, which is responsible for filtering waste from the digestive system and moving it out of the body. An implantable polymeric device was constructed that would slowly occlude the hepatic portosystemic shunt and force the blood to stop flowing through the bypassing vessel and flow through the vessel to the liver over 3-4 months time.

The portosystemic shunt occluder device consist of three polyoxymethylene …

Nucleation And Growth Behavior Of Tellurite-Based Glasses Suitable For Mid-Infrared Applications, Jonathan Massera

All Dissertations

Optical fibers transmitting in the 2-5 μm mid-infrared (MIR) spectral region are highly desirable for a variety of military and civilian applications including super-continuum generation, infrared countermeasures (IRCM), and MIR laser sources. These new applications in the mid-infrared require novel optical materials that transmit in this window and can be fabricated into fiber. As tellurite glasses are known to have good transparency in the (NIR) region, tellurite-based glasses are the material of choice for this study due to their high linear and nonlinear refractive index, their low glass transition temperature and the ability to form them into optical fiber.
This …

Production And Characterization Of Novel Shaped Fibers For Fluid Sorption And Transport, Lisa Fuller

All Dissertations

This work investigated the production and characterization of novel shaped fibers for fluid adsorption and transport. Shaped fibers such as Y, H, and octolobal, as well as conventional round fibers, were extruded using a research melt extruder. The fibers were extruded from 18 melt flow index (MFI) polypropylene (PP) and blends of 18 MFI PP and 400 MFI PP. Hydrophilic spin finish Bozzetto Favorol SF2 was applied to the surface of extruded fibers and hydrophilic polyester additive LB-100 was included in the blend of some H fibers to increase the hydrophilicity of the fiber surface. The geometric shape retention of …

Mechanical And Chemical Characterization Of Biological Composite Structures, Bonnie Zimmerman

All Theses

A better understanding of the bioresponse of naturally occurring systems will help
to optimize the engineering of synthetic biomaterials. The aim of this thesis was to
characterize the mechanical and chemical behavior of two distinct biological composite
systems, human teeth and wool fibers. These mechanical and chemical properties were
also studied as a function of natural structure and environmental conditions.
Human teeth are composite systems consisting primarily of hydroxylapatite and
protein. This project investigated how the use of clinical dental treatments and
procedures, such as whitening and etching, affects mechanical properties. Analysis of
nanoindentation with the Oliver-Pharr model provided elastic …

Investigation Of The Thermoelectric Behavior And Structure Formation Of (Pbte/Agsbte2)-Silver Chalcogenide Mixtures, Yisha Wang

All Theses

Sustainable energy research is currently on the forefront of scientific exploration and energy conservation and the development of new energy production techniques are both crucial for our long lasting stable future. Accordingly, thermoelectric materials will be a significant energy conservation and production source. The state-of -the-art thermoelectric materials can be used to collect the wasted heat and converted to power, which is the future for the green power generation.
PbTe is considered a state-of-the-art thermoelectric material, which has been extensively studied. It forms in the NaCl structure and it is a semiconductor with a room temperature gap value of 0.29 …

Synthesis And Evaluation Of Bioceramics For Orthopedics And Tissue Culture Applications, Hande Demirkiran

Material Science and Engineering Dissertations

Hydroxyapatite is the most well known phosphate in the biologically active phosphate ceramic family by virtue of its similarity to natural bone mineral. Among all bioglass compositions Bioglass®45S5 is one of the most bioactive glasses. This study initially started by adding different amounts (1, 2.5, 5, 10, and 25 wt. %) of Bioglass®45S5 to synthetic hydroxyapatite in order to improve the bioactivity of these bioceramics.The chemistries formed by sintering and their effect on different material properties including bioactivity were identified by using various techniques, such as powder and thin film x-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray …

Self Powered Sensing By Combining Novel Sensor Architectures With Energy Harvesting, Vishwas Bedekar

Material Science and Engineering Dissertations

Recent advancements in the field of wireless sensor networks have resulted in increasing demand for self-powering techniques that reduces the dependence on batteries. In order to address this problem, there has been significant effort on generating small electrical power locally by harvesting energy from freely available environmental sources such as mechanical vibrations, wind, and stray magnetic field. Further, there is need for inventing new sensing techniques to reduce the overall power consumption. The road for reaching the destination of self-powered sensor networks requires cooperative progress in reduction in sensor power consumption by developing new sensing mechanisms and local generation of …

Synthesis, Characterization And Potential Applications Of Fept Nanoparticles, Vikas Nandwana

Material Science and Engineering Dissertations

Monodisperse FePt nanoparticles with controlled size and geometry have drawn great attention in the last decade for fundamental scientific studies and for their potential applications in advanced materials and devices such as ultra-high-density magnetic recording media, exchange-coupled nanocomposite magnets, biomedicines and nanodevices. This dissertation focuses on the synthesis and characterization of FePt nanoparticles and their use in potential applications. The FePt nanoparticles of different size (2 to 16 nm) and shape (spherical, cubic, rod) were synthesized by a chemical solution method. The size and shape of these particles were controlled by adjusting reaction parameters. The as-synthesized FePt nanoparticles have chemically …

Tribological Performance Of Ashless Antiwear Additives Under Extreme Pressure Conditions, Bohoon Kim

Material Science and Engineering Dissertations

Zinc diakyl dithiophosphate (ZDDP) has been used in engine oil for several decades as an antiwear additive. However, ZDDP is the primary source of P, S and Zn in the exhaust, which results in frequent maintenance or replacement of exhaust gas treatment systems. The use of ashless additives is more desirable because of recent environmental regulations. The main goal of this research was to develop a fundamental understanding of how ashless compounds protect the tribological surface in comparison to ZDDP. X-ray absorption near edge structure spectroscopy (XANES) has been performed on tribo and thermal films in order to investigate the …

Design And Performance Of Load Bearing Shear Walls Made From Composite Rice Straw Blocks, Kevin Robert Camann

Master's Theses

Although rice straw and other grains have been used in building since pre-history, in the past two decades, there has been a move to utilize this rapidly renewable, locally available, agricultural byproduct as part of the sustainable construction movement. Up to this point, this has been done by simply stacking up the full straw bales. Stak Block, invented by Oryzatech, Inc., is a modular, interlocking block made of a composite of rice straw and binding agent that serves as an evolution in straw construction. This study investigates the feasibility of using these Stak Blocks as a structural system. The report …

Thermo-Mechanical Characterization Of Silicon Carbide-Silicon Carbide Composites At Elevated Temperatures Using A Unique Combustion Facility, Ted T. Kim

Theses and Dissertations

This research investigated four different types of CMCs in a simulated gas turbine engine hot section condition that involved the simultaneous application of a combustion environment and mechanical fatigue loading using a unique burner rig facility developed for this study at AFIT. Three of the materials were woven Melt-Infiltrated (MI) BN/SiC reinforced by Hi-Nicalon Type S (Hi-Nic-S), Sylramic (Syl) and Sylramic with insitu BN coating (Syl-iBN) fibers, respectively. They were made by the slurry cast method. The other CMC was MI Hi-Nic-S/BN/SiC made using the prepreg MI processing. Prepreg MI CMC and Sylramic-iBN fiber reinforced CMC showed better resistance to …

Mechanics Of Hydrogels And Biological Tissues, Jessica A. Zimberlin

Open Access Dissertations

The relationship between cells and their environment is one of dynamic reciprocity, whereby cells can influence their surrounding and the surroundings can influence the cells. One example of this relationship arises from the effect of the mechanical properties of an environment on a cell and of a cell on its environment. Inspired by this relationship, we investigate 1) the local environment of biological materials, both native and synthetic, and 2) the forces that cell sheets exert on surfaces. We do this by developing techniques that focus on local mechanical properties and experimental strategies that provide insight into intercellular mechanics. We …

Feasibility Of Ellipsometric Sensor Development For Use During Pecvd Siox Coated Polymer Product Manufacturing, Daniel Lynn Helms

Master's Theses

Polymeric materials have provided pathways to products that could not be manufactured otherwise. A new technology which merges the benefits of ceramics into these polymer products has created materials ideally suited to many different industries, like food packaging. Nano Scale Surface Systems, Inc. (NS3), a company which coats polymers with ceramic oxides like SiO2 through a process known as plasma enhanced chemical vapor deposition (PECVD), was interested in the feasibility of an in line measurement system for monitoring the deposited films on various polymer products. This project examined two different coated polymer products, polyethylene terephthalate (PET) beverage containers and biaxially …

Assessment Of Electrospinning As An In-House Fabrication Technique For Blood Vessel Mimic Cellular Scaffolding, Colby M. James

Master's Theses

Intravascular devices, such as stents, must be rigorously tested before they can be approved by the FDA. This includes bench top in vitro testing to determine biocompatibility, and animal model testing to ensure safety and efficacy. As an intermediate step, a blood vessel mimic (BVM) testing method has been developed that mimics the three dimensional structure of blood vessels using a perfusion bioreactor system, human derived endothelial cells, and a biocompatible polymer scaffold used to support growth of the blood vessel cells. The focus of this thesis was to find an in-house fabrication method capable of making cellular scaffolding for …

Exploring Earth-Building Technology For Liberia., Isaac Dompo Mayon

Electronic Theses and Dissertations

This paper discusses earth as a building material and the extent to which earth building technology has evolved over the years. In particular it addresses the adobe, compressed and rammed earth techniques of earth building as suitable techniques for Liberia consumption. In addition, the paper investigates the suitability of the Latosols soils of Liberia for earth building construction purposes using standardized earth building principles and requirements. A local Johnson City, Tennessee, earth sample found to have the same physical characteristics of the Latosols of Liberia was used to simulate Liberia soils to produce specimen blocks at different configurations of moisture …

Structure And Properties Of Nanoclay Reinforced Polymer Films, Fibers And Nonwovens, Raghavendra Ratnakar Hegde

Doctoral Dissertations

In this research, influence of different levels of Closite Na⁺ additives on the microstructure, morphology and mechanical properties of polymer products was studied. Importance was given to understand the additive level, extent of dispersion in matrix, change in microstructure and respective property observed in the end product. Polypropylene spunbond and meltblown web samples with various levels of Closite Na⁺ additives were produced and characterized. Injection molded polypropylene nanocomposite with 1 to 15 wt% nanoclay additives were also prepared and characterized for microstructure and mechanical properties.

Crystallization kinetics studies showed significant increase in crystallization rates on nylon 6 even …

Morphological Characterization Of Irradiated Ultra High Molecular Weight Polyethylene (Uhmwpe), Christopher Phillip Stephens

Doctoral Dissertations

Effects of radiation (gamma and proton) on Ultra High Molecular Weight Polyethylene (UHMWPE) is studied for prosthetic joints and for radiation shielding for manned space missions. The first section of the dissertation will cover gamma radiation effects on UHMWPE by means of solubility, hardness, three-phase model, crystallite thickness, and molecular mobility studies. The second part will cover proton radiation effects on UHMWPE by means of solubility, three-phase crystallite model, and crystallite thickness study. The combined studies of the gamma irradiated samples shows that chain scission occurs on the surface and crosslinking in the center. The combined studies of the proton …

Laser Machining Of Structural Ceramics: Computational And Experimental Analysis, Anoop Samant

Doctoral Dissertations

Outstanding mechanical and physical properties like high thermal resistance, high hardness and chemical stability have encouraged use of structural ceramics in several applications. The brittle and hard nature of these ceramics makes them difficult to machine using conventional techniques and damage caused to the surface while machining affects efficiency of components. Laser machining has recently emerged as a potential technique for attaining high material removal rates. Major focus of this work is to understand the material removal mechanisms during laser machining of structural ceramics such as alumina (Al₂O₃), silicon nitride (Si₃N₄), silicon …

A Study Of Helium Ion Induced Secondary Electron Production, Ranjan Ramachandra

Doctoral Dissertations

The scanning electron microscope (SEM) is a popular instrument used for imaging because of its high resolution images it can generate. However the new scanning helium ion scanning microscope (SHIM) can produce higher resolution and better contrast images than the conventional SEM. In both the microscopes secondary electron (SE) signal is the most widely used imaging mode because of their high yield efficiency and their high spatial resolution. In order to be able to properly evaluate the relative strengths and weaknesses of electron induced SE (eSE) and ion induced SE (iSE) imaging a detailed model able to quantify them is …

Development Of A Low Cost Handheld Microfluidic Phosphate Colorimeter For Water Quality Analysis, Sean C. Kaylor

Master's Theses

This thesis describes the design, fabrication, and testing process for a microfluidic phosphate colorimeter utilized for water quality analysis. The device can be powered by, and interfaced for data collection with, a common cell phone or laptop to dramatically reduce costs. Unlike commercially available colorimeters, this device does not require the user to measure or mix sample and reagent. A disposable poly(dimethylsiloxane) (PDMS) microfluid chip, powered by an absorption pumping mechanism, was used to draw water samples, mix the sample at a specific ratio with a molybdovanadate reagent, and load both fluids into an onboard cuvette for colorimetric analysis. A …

Short-Term Failure Analysis Of Aluminum Conducting Composite Core Transmission Lines, Brian Burks

Electronic Theses and Dissertations

Recently the inefficiency and lack of capabilities of electric energy transmission have been put in the global spotlight; a transmission line design known as the Aluminum Conducting Composite Core Trapezoidal Wire (ACCC/TW^TM) attempts to eliminate the deficiencies. The ACCC core is comprised of a new hybrid composite material. The most probable causes of short-term damage to the ACCC core were investigated through a series of finite element models. It was found that excessive bending was the most likely cause of short-term damage to the core. During bending of the ACCC core, stresses are concentrated at the interface in …

Morphology Of Ingaas Multilayer Nanostructure On Gaas High-Index Surfaces, Yanze Xie

Graduate Theses and Dissertations

This work aimed to explore nanostructure configuration by growing multiple layers of strained InGaAs on GaAs high index surface. The knowledge learned would help to achieve a comprehensive picture of strain-driven nanostructure evolution. Ordered arrays of InGaAs quantum dots were demonstrated on GaAs(311)B. The ordering patterns depended on the thickness of GaAs interlayer between InGaAs Quantum Dots (QDs). With an increased interfacial thickness, a transition from two dimensional (2D) lateral ordering to 1D dot chains was observed. InGaAs growth on GaAs(311)A and GaAs(331)A ended up with 1D quantum wires (QWRs). Straight InGaAs QWRs were uniformly distributed across the surfaces owing …

The Creation Of Micropatterns Through The Femtosecond Laser Ablation Of Diamond Materials, Matthew D. Parrish

Masters Theses

Laser systems that create nanometer and micrometer scale features on the surface of materials are important tools used by the scientific and industrial communities to develop novel applications and technology. The goal of the research presented in this thesis is to investigate the characteristics of a custom femtosecond micro and nano machining station that uses laser ablation to create features and to advance system capabilities. The improvements include programs that allow for a greater variety and complexity of features and patterns that are easily customized to specification. In this work, a titanium doped sapphire (Ti:S) laser oscillator and amplifier system …

High Permittivity And High Permeability Of Nanoparticles In Conducting Polymer Films, Matthew Wayne Fuller

Masters Theses

The purpose of this study is to synthesize a new material out of conducting polymers and magnetic nanoparticles that has high electric permittivity and high magnetic permeability. There is a strong desire in electronics for lighter, faster, cheaper and more bandwidth providing materials. There is also an interest with the military for materials that are light weight, have high electric permittivity and high magnetic permeability. A way to synthesize a material that meets those criteria is to use conducting polymers for their high permittivity properties and to disperse magnetic particles in the polymer for their high permeability properties. The synthesized …

Proton Irradiation Effects On Semiconductor Cdse/Zns Core/Shell Nanocrystals, Stephen Graham Charter

Graduate Theses and Dissertations

The absorbance and photoluminescence measurement of semiconductor CdSe/ZnS core shell nanocrystals were reviewed and investigated after they were exposed to proton irradiation. The CdSe/ZnS core shell nanocrystals of 3.2nm and 4.4nm were commercially purchased and investigated. These nanocrystals were embedded in UV resin. Proton irradiation of energy 2MeV was applied at doses from 3 x 1013 protons cm-2 to 1.47 x 1015 protons cm-2 for both nanocrystal sizes. Absorbance measurements were conducted at 300K. Results from absorbance measurements showed slight broadening of the first exciton peak of both samples but was most noticeable in the 3.2nm nanocrystal sample. UV resin …