Engineering Commons^™

Multiple Channel Laser Beam Combination And Phasing Using Stimulated Brillouin Scattering In Optical Fibers, Brent W. Grime

Theses and Dissertations

Brightness scaling lasers using stimulated Brillouin scattering (SBS) in optical fibers is explored. A multiple-channel amplifier approach is used to increase the total power of a laser system while avoiding a significant burden on a single channel. The work explores two approaches utilizing both SBS beam cleanup and SBS piston error conjugation. A unique beam combiner that takes advantage of the SBS beam cleanup properties of a long, gradient-index multimode fiber was designed and tested. The beam combiner was developed to combine multiple-channel laser beams simultaneously with high input and output coupling efficiency. The design for the SBS beam combiner …

Thermal And X-Ray Analysis On The Origin Of Double Melting Phenomena Of Poly(L-Lactic Acid) Films, Xiaoyun Ling

Doctoral Dissertations

Thermal analysis is one of the most commonly used techniques to characterize the structure and properties of semicrystalline polymers. Unfortunately, the interpretation of thermal events is not always straightforward, but can be quite complicated. However, the complexity involved is often overlooked, leading to erroneous or, at least, questionable results and interpretations. In the present study we carry out an extensive investigation of the thermal behavior of poly(L-lactic acid), PLLA, films prepared under a wide range of crystallization conditions, including isothermal and non-isothermal crystallization from both the glassy state and the melt. The primary techniques used were differential scanning calorimetry (DSC), …

High-Temperature Low-Cycle-Fatigue And Crack-Growth Behaviors Of Three Superalloys: Hastelloy ® X, Haynes ® 230, And Haynes ® 188, Yulin Lu

Doctoral Dissertations

Extensive smooth-bar low-cycle-fatigue (LCF) and fatigue crack growth (FCG) experiments on three solid-solution-strengthened superalloys HASTELLOY X, HAYNES 230, and HAYNES 188 have been conducted at 816 and 927 C. Limited tests were run at 649 C, 871 C, and 982 C to study the temperature effect. The LCF tests were performed under a total-strain-range-control mode at Solar Turbines Inc., Metcut Research Inc., and The University of Tennessee (UT). The FCG tests were done under both the constant-load-range and constant-stress-intensity-factor-range modes at Westmoreland Testing Inc. and UT. Various hold times were imposed at the maximum strain or load in both the …

The Effect Of Ultrasonic Vibration On The Solidification Of Light Alloys, Xiaogang Jian

Doctoral Dissertations

This exposition presents the novel thermodynamical and microstructural modification to light alloys, such as aluminum alloys and magnesium alloys, by ultrasonic vibrations during their solidification processes. Ultrasonic vibration has proven to be effective in controlling columnar dendritic structure, reducing the size of equiaxed grains, and under some conditions, producing globular non-dendritic grains. Despite this, the solidification process under the effect of ultrasonic vibration was not clear. Not only was there no such research on how ultrasonic vibration affected its solidification thermodynamically, but also its effects on the as-cast microstructure, including the primary fcc phase, the eutectics, and the secondary phases, …

Experimental, Theoretical, And Device Application Development Of Nanoscale Focused Electron-Beam-Induced Deposition, Steven Jeffrey Randolph

Doctoral Dissertations

To elucidate the effects of beam heating in electron beam-induced deposition (EBID), a Monte-Carlo electron-solid interaction model has been employed to calculate the energy deposition profiles in bulk and nanostructured SiO₂. Using these profiles, a finite element model was used to predict the nanostructure tip temperatures for standard experimental EBID conditions. Depending on the beam energy, beam current, and nanostructure geometry, the heat generated can be substantial. This heat source can subsequently limit the EBID growth by thermally reducing the mean stay time of the precursor gas. Temperature dependent EBID growth experiments qualitatively verified the results of the …

Effect Of Hydrogenon On Mechanical Behavior Of A Zircaloy-4 Alloy, Elena Garlea

Masters Theses

Hydride formation is one of the main degradation mechanisms of zirconium alloys in hydrogen-rich environments. When sufficient hydrogen is present, zirconiumhydride precipitates can be formed. Cracking of the brittle hydrides near a crack tip can initiate the growth of a crack leading to the premature failure of the material. Hydride formation is believed to be enhanced by the presence of residual or applied stresses. Therefore, the increase in the stress field ahead of a crack tip may promote precipitation of additional hydrides. In order to verify these phenomena, the effect of internal stresses on the zirconium-hydride-precipitate formation, and in turn, …

The Development Of Qualification Standards For Cast Super Duplex Stainless Steel (2507 Wrought Equivalent), Vasudevan Hariharan

Masters Theses

The objective of the program is to determine the suitability of ASTM A923 “Standard Test methods for Detecting Detrimental Intermetallic Phase in Wrought Duplex Austenitic-Ferritic Stainless Steels” for 25 Cr Cast Super Duplex Stainless Steels (ASTM A890-5A).

Different tests were carried out on the materials procured from various steel foundries as stated in the ASTM A923. The foundries were designated as Foundry A, B, C and D. All the materials were foundry solution annealed. Materials from Foundry D were solution heat treated at The University of Tennessee also and then they were subjected to heat treatment schedule which was derived …

Synthesis, Microstructure, And Mechanical Behavior Of Fe-Cu Composites, Jin-Woo Jeon

Masters Theses

The synthesis, microstructure, and mechanical properties of ball-milled nanocrystalline (nc) Fe powder and immiscible Fe-Cu alloy composites are investigated in this thesis. Experimental approaches are described for the characterization of the grain size and hardness of nc Fe powders and the internal stress state of bulk Fe-Cu alloy composites are presented.

The grain size measurements of ball-milled Fe powders obtained from the XRD line broadening analysis (15 nm) and TEM observation (18 nm) showed good agreement between two results. From the nanoindentation tests, the hardness values of the ball-milled Fe powders were increased from 3.5 to 10.5 GPa as the …

An Experimental Evaluation Of The Constant Β Relating The Contact Stiffness To The Contact Area In Nanoindentation, Jeremy Harper Strader

Masters Theses

Measurements of mechanical properties by nanoindentation with triangular pyramidal indenters like the Berkovich rely heavily upon the relationship between the contact stiffness, S, the contact area, A, and the reduced elastic modulus, E_r . This relationship is often written in the form: S = 2βEr(A/π)1/2, where βis a constant that depends on the geometry of the indenter. Although the most common values for βused in experimental measurements are 1.000 and 1.034, various theoretical analyses have yielded values as small as 1.00 or as large as 1.2, depending on the assumptions made to model the deformation. Here the most appropriate …

Evaluation Of Textile Fabric Properties Utilized In Foam-In-Place Head Restraints, Rebecca Anne Pfeifer

Master's Theses and Doctoral Dissertations

The purpose of this research was to evaluate and compare the physical properties of knitted fabrics in bilaminate and trilaminate composite forms used in Foam-In-Place (FIP) manufacturing technology for automotive applications. Seven physical tests employed by the automotive industry to evaluate the physical properties of fabric were used. The factors tested were Elongation, Boardiness, Weight, Thickness, Stretch and Set, Breaking Radius, and Ravel. Each test was performed according to standard test methods established by American Society for Testing and Materials (ASTM) or Society of Automotive Engineers (SAE) or the specifications of tier-one automotive seat suppliers. Fabric samples consisted of three …

Integration Of Micro Nano And Bio Technologies With Layer -By -Layer Self -Assembly, Dinesh Shankar Kommireddy

Doctoral Dissertations

In the past decade, layer-by-layer (LbL) nanoassembly has been used as a tool for immobilization and surface modification of materials with applications in biology and physical sciences. Often, in such applications, LbL assembly is integrated with various techniques to form functional surface coatings and immobilized matrices. In this work, integration of LbL with microfabrication and microfluidics, and tissue engineering are explored. In an effort to integrate microfabrication with LbL nanoassembly, microchannels were fabricated using soft-lithography and the surface of these channels was used for the immobilization of materials using LbL and laminar flow patterning. Synthesis of poly(dimethyldiallyl ammonium chloride)/poly(styrene sulfonate) …

Development Of Palladium Nanowires, Chuanding Cheng

Doctoral Dissertations

Inherent limitations of traditional lithography have prompted the search for means of achieving self-assembly of nano-scale structures and networks for the next generation of electronic and photonic devices. The nanowire, the basic building block of a nanocircuit, has recently become the focus of intense research. Reports on nanowire synthesis and assembly have appeared in the scientific literature, which include Vapor-Liquid-Solid mechanism, template-based electrochemical fabrication, solvothermal or wet chemistry, and assembly by fluid alignment or microchannel networks. An ideal approach for practical application of nanowires would circumvent technical and economic constraints of templating. Here we report on the self-assembly of highly-ordered …

A Fe-Fd Hybrid Scheme For Solving Parabolic Two-Step Micro Heat Transport Equations In Irregularly Shaped Three Dimensional Double -Layered Thin Films Exposed To Ultrashort -Pulse Lasers, Brian R. Barron

Doctoral Dissertations

Multi-layer thin films are important components in many micro-electronic devices. These films are often used when a single film layer is insufficient to meet devices specifications. The continued reduction in component size has the side effect of increasing the thermal stress on these films and consequently the devices they comprise. Understanding the transfer of heat-energy at the micro-scale is important for thermal processing using a pulse-laser. Often, micro-voids may be found in processed devices. This is due to thermal expansion. Such defects may cause an amplification of neighboring defects resulting in severe damage and consequently the failure of the device. …

Rate Dependence And Short Term Creep Behavior Of Pmr-15 Neat Resin At 23 And 288°C, Candice M. Westberry

Theses and Dissertations

This research focuses on experimental investigation of rate-dependent behavior and short-term creep of PMR-15 neat resin at 23 and 288°C. Effect of loading rate on monotonic stress-strain behavior was explored in monotonic tests at constant stress rates of 0.75, 0.075, and 0.0075 MPa/s at 23 and 288°C. In addition, effect of prior stress rate on creep behavior was explored in creep tests preceded by uninterrupted loading to a target stress. At each temperature three creep tests were conducted for a given stress level, where loading rate was changed from test to test. Creep stress levels were 30 and 25 MPa …

Fatigue Behavior Of A Zirconium-Based Bulk Metallic Glass, William Hutchison Peter

Doctoral Dissertations

Although the mechanical behavior of Zr-based bulk metallic glasses (BMGs) has been studied, fatigue studies in controlled environments and testing conditions have not been adequately performed or understood. Early fatigue examinations of rectangular bar specimens tested in bending had resulted in fatigue strengths substantially lower than anticipated [1,2,3,4,5]. Preliminary work performed by Peter et al. and Wang et al. on uniaxial button-head specimens have yielded in very different fatigue behavior with fatigue-endurance limits comparable to conventional high-strength, crystalline alloys [6,7,8,9,10]. Between all S-N results studied, the fatigue-endurance limits for Zr-based BMGs have been observed to range from 150 MPa to …

The Mechanical And Electrochemical Properties Of Bulk Metallic Glasses, Mark Lee Morrison

Doctoral Dissertations

Bulk metallic glasses (BMGs) represent an emerging class of materials with an amorphous structure and a unique combination of properties. Some of these outstanding properties include exceptionally high strength, large elastic deformation, near-net-shape formability, and superplasticity. However, these materials are not commonly used in structural applications because of a lack of plasticity and a lack of clarity in terms of deformation and failure mechanisms. Furthermore, the electrochemical behavior of these materials with and without loading is not well defined. Thus, the objectives of this study were to define and model the electrochemical and mechanical behaviors of BMGs, in addition to …

Microstructural Evolution Of Tial-Intermetallic Alloys Containing W And B, Lan Huang

Masters Theses

The TiAl alloys have been considered as promising candidates for structural-materials applications at around 800⁰C. In this work, new TiAl alloys, containing tungsten (W) and boron (B), have been developed. Using the scanning-electron microscopy (SEM), electron-microprobe, and transmission-electron microscopy (TEM), the effects of W and B on the microstructural evolution of TiAl alloys, including the colony size and lamellar spacing, were analyzed. It is important to point out that fine uniform microstructures (with the colony size smaller than 50 mm) can be conveniently developed after Hot-Isostatic Pressing (HIP) the as-cast alloys at 1,250⁰C and 150 MPa …

Design, Fabrication, And Characterization Of An Electrostatically Actuated Microfluidic Valve, Ryan Dale Rivers

Master's Theses

Microfluidic device construction uses certain critical structures throughout many different applications. The valve structure remains one of the primary structures that present a barrier to miniaturization and portability. The extensive support devices required to power common microfluidic valves remove a significant amount of freedom from microfluidic device design. Moving to electrostatic methods of actuation could reduce the overall footprint of the microfluidic valve. This thesis covers three concept prototypes. Concept I presents an attempt at inlaying gold electrodes into polydimethylsiloxane substrates. Concept II attempts to use liquid silver injected into channels as electrode materials. Concept III uses aluminum sputtering to …

Determination Of The Constitutive Equations For 1080 Steel And Vascomax 300, Zachary A. Kennan

Theses and Dissertations

The objective of this research is to establish a better representation of the components utilized in a gouging event being considered in research leading to a better understanding of the Holloman High Speed Test Track. Gouging occurs when two metals are traveling at a slight incline to each other at velocities nearing 1.5 kilometers per second, and results in a structural failure of both the metals. The gouging process occurs at very high strain rates, which results in non-linear stress-strain relations. The coefficients that lead to the Johnson-Cook equations have been determined by the Split Hopkinson Bar test for 1080 …

High Temperature Chemical Degradation Of Pmr-15 Polymer Resins, Grant W. Robinson

Theses and Dissertations

PMR-15 is a polymer resin for glass and carbon reinforced composites used for high temperature, civilian and military aerospace applications. The harsh environments of PMR-15 applications lead to long term structural degradation and, in turn, impact the readiness capabilities of the system. This study investigated the thermal and oxidative degradation of PMR-15 neat resin powder through the use of thermal gravimetric analysis (TGA) in oxygen, argon and air at isothermal hold temperatures of 260, 288, 316, and 343 °C for 250 hours. The TGA measured the degradation by recording the change in neat resin powder mass versus time. The qualitative …

Nanostructured Composite Materials Based On Carbon Nanotubes And 3-D Photonic Crystals, Jing Chen

Dissertations

Carbon nanotubes (CNT) and in particular, single-wall carbon nanotubes (SWCNT) have been extensively studied, in large part, due to their unique one-dimensional crystalline structures and related electronic and optical properties. Various polymeric composite materials, which were based on carbon nanotubes, have been also developed in an attempt to combine the properties of polymer and CNT in a single film. Such composites were mainly formed by mixing carbon nanotubes within the polymer without special emphasis on the structure and thereby, the nanoscopic properties of the resultant material.

Photonic crystals belong to a class of man-made structures aimed at manipulating the propagation …

Thin Film Sputtering Of Gadolinium And Chromium-Doped Yttrium Aluminum Garnet, Yuepeng Deng

Doctoral Dissertations

Rare-earth and transition metal-doped yttrium aluminum garnet (Y₃A1₅O₁₂ or YAG) phosphors have been widely used because of very stable chemical, mechanical properties of YAG and subsequent high efficiency of doped YAG phosphors. However, to synthesize pure YAG materials by different approaches such as solid-state reaction, sol-gel, spray pyrolysis, co-precipitation, and combustion method. But nearly all of these techniques require high temperature (>1600C) and prolonged processing time.

In this work, rf magnetron reactive sputtering was used to synthesize YAG thin films at relatively low temperature and short processing period. An appropriate post heat treatment, 10 …

Fabrication And Characterization Of Nanoelectronic Devices For Electron Beam Lithography Applications, Xiaojing Yang

Doctoral Dissertations

Vertically aligned carbon nanofibers (VACNFs) have shown promise for use as field emission electron sources. Dual-gate field emission structures (triodes) have been fabricated and characterized. The electron beams can be successfully focused in these triodes. These studies show VACNF based field emission devices are promising for electron beam lithography applications. In this thesis, work is continued on triode device investigation. Methods to improve the device fabrication, to understand/optimize the device performance, and to repair defective triodes are presented.

Numerical simulation of the triode performance is included. Depth of field (DOF) of these triode structures is calculated by simulation and is …

Charge Transport Measurements Of Vertically Aligned Carbon Nanofiber, Lan Zhang

Doctoral Dissertations

Vertically aligned carbon nanofibers (VACNFs) have found a variety of electronic applications. To further realize these applications, a good understanding of the charge transport properties is essential. In this work, charge transport properties have been systematically measured for three types of VACNF forests with Ni as catalyst, namely VACNFs grown by direct current PECVD, and inductively coupled PECVD at both normal pressure (3.6 Torr) and low pressure (50 mTorr).

The structure and composition of these nanofibers have also been investigated in detail prior to the charge transport measurements. It has been found that the dc VACNF body consists of three …

Applying Particle Swarm Optimization To Dynamic Lot Sizing With Batch Ordering, Ahmad Hassan Sayed Aly

Archived Theses and Dissertations

No abstract provided.

Investigation Of A Phase Transition In Pure And Magnesia- And Titania-Substituted Hexacelsian, Melanie Jean Kirkham

Masters Theses

Hexacelsian, the hexagonal polymorph of BaAl_{2Si2O8, experiences a phase transition near 300ºC with an accompanying large volume change, which can lead to cracking and thermal shock, limiting the potential applications of hexacelsian. It has previously been reported that certain additions, including MgO and TiO2, can suppress the undesirable phase transition. Room-temperature neutron and high-temperature X-ray diffraction have been used to study the structure and thermal behavior of hexacelsian, both pure and substituted with varying amounts of MgO and TiO2. The diffraction data of the pure sample was refined using the}

P-3 space group. Attempting to refine the substituted sample …

Synthesis And Solution Characterization Of Water-Soluble Polyacrylamide And Its Applications In Oil Industries, Ghuwaya Humaid Alnuaimi

Theses

No abstract provided.

Fundamental Studies Of Stabilization Of Polyacrylonitrile Precursor, Stephen Alan White

Masters Theses

The purpose of this study was to examine the stabilization of polyacrylonitrile precursor. Currently, the stabilization of polyacrylonitrile is the limiting step in the production of carbon fibers because of its cost and time requirements. By furthering the understanding of the stabilization process, it may be possible to reduce the cost and time required, allowing the widespread use of carbon fiber in several industries to be achieved.

In this study, the effects of temperature, time, environment, and pressure on the stabilization of polyacrylonitrile were examined. Once fiber samples were heat treated, four experimental techniques were used to examine the samples. …

Carbon Nanotubes And Tungsten Oxide Nanorods: Synthesis And Applications, Bing Xiao

Electrical & Computer Engineering Theses & Dissertations

Synthesis and applications of two types of one-dimensional nanomaterials, carbon nanotubes (CNTs) and tungsten oxide nanorods, are investigated in this dissertation. Multi-walled CNTs have been successfully synthesized using two types of chemical vapor deposition (CVD) methods: microwave plasma enhanced CVD and atmospheric pressure thermal CVD. CNTs and their synthesis processes are characterized with various analysis techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical emission spectroscopy. Ultra-thin and high quality multi-walled CNTs are discovered in CNT films produced by MPCVD, which exhibit good field emission performance that is found to be dependent on the synthesis …

An Investigation Of A Simplified Gouging Model, Gregory S. Rickerd

Theses and Dissertations

Gouging is a type of structural failure that becomes important when two metals slide against each other at velocities in the range of 1.5 kilometers per second. A computer model has previously been used to model the development of gouging at the Holloman High Speed Test Track. This model has not been experimentally verified to be correct, due to the complexity of the model. This research develops a simplified model that can be experimentally verified. The computer program utilized in this research was studied to determine the most appropriate options to use in simulations. This was accomplished by modeling a …