Dissertations / Theses on the topic 'Microstructure and Characterization'
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1
DeCost, Brian L. "Microstructure Representations: Applied Computer Vision Methods for Microstructure Characterization." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/764.
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Recent advances in computing power and automated microstructural image acquisition have opened the doors to data-driven quantitative microstructure analysis. Extraction of salient microstructure features is a crucial enabling component in this rapidly developing field of research; in the past decade the computer vision community has made enormous progress in this area, much of which has gone relatively unexplored by the quantitative microstructure analysis community. This dissertation explores applications of image texture recognition algorithms to engineer efficiently computable generic microstructure descriptors, enabling quantitative microstructure comparisons between and across a wide variety of materials systems. The literature review serves as a broad, high-level introduction for the materials scientist to some of the major themes in image recognition, along with some brief discussion of their relationship to contemporary microstructure science. After establishing that these image texture recognition algorithms can be effectively applied to classify diverse microstructure datasets, I begin to explore novel materials science applications. These include characterization and qualification of powder materials, exploratory analysis of large microstructure datasets, and extraction of quantitative relationships between materials processing and properties metadata and microstructural image features. The fusion of microstructure image analysis and contemporary machine vision techniques will facilitate development of robust autonomous microscopy systems, and may support quantitative engineering standards for complex hierarchical microstructure systems.
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Yamoah, Nana Kwame Gyan. "Microstructure Characterization of SUS444 Ferritic Stainless Steel." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23253.
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Redesigning heavy components with thinner components is one way to lower automotive weight and improve fuel efficiency. Therefore, replacing thick cast iron exhaust manifolds with thinner heat resistant stainless steel one is a prime example of this approach. Material for a thin exhaust manifold must tolerate cyclic thermal fatigue. In SUS 444, this characteristic is directly related to the influence of microstructure on high temperature strength and the stability of the microstructure at the high operating temperature range. The goal of this research is to identify the cause for the drastic difference in the stress-strain behavior between two potential manufacturer heat treatments that will serve as a simplified model case for high temperature cyclic fatigue. Transmission electron microscopy (TEM) based microstructure analyses of samples which have been aged at 750"C for 100 hours and then hot-tensile tested at 750"C with a strain rate of suggest continuous recrystallization as the mechanism responsible for the stable high temperature strength. The initial high temperature strength observed in the unaged sample was due to the precipitation of fine Laves phases which pinned down the motion of dislocations. As deformation progressed the strength increased until a critical precipitate size, volume fraction and dislocation density before Laves phases begun to rapidly coarsen and resulted in the abrupt decrease in strength. Microstructure evidence suggests the absence of precipitation strengthening effect in the aged samples could be a contributing factor to the decrease in peak strength between the aged samples and the unaged samples.Master of Science
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Song, Hyeyun. "Multi-scale Microstructure Characterization for Improved Understanding of Microstructure-Property Relationship in Additive Manufacturing." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480349872328654.
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Yu, Miao. "Separation mechanisms and microstructure characterization of zeolite membranes." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3256404.
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Pathange, Lakshmi Prasad. "Characterization of protein microstructure by various chromatographic techniques." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26851.
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Due to the rising health care costs and with the advent of biogenerics, there is a growing demand to develop new and reliable techniques to characterize proteins and biopharmaceuticals. In addition, characterization aids in understanding the intricate relationship between a protein's structure and its function. To address this challenge, two protein structural parameters, 1) amino acid surface area and 2) amino acid microstructure, were chosen to be investigated. Two chromatographic techniques, 1) ion exchange chromatography (IEC) and 2) immobilized metal affinity chromatography (IMAC), were used to characterize the above-mentioned protein structure parameters.
The model protein chosen for our work is T4 lysozyme. The protein consists of 164 amino acids with molecular weight ~ 18 kD. SYBYL 7.1 software was used to generate in silico point mutants. Two categories of protein variants (point mutants) were generated using site-directed protein mutagenesis. The goal for generating point mutants was to obtain mutants that vary in the two structural parameters. The first category point mutants vary in the surface accessibility of a surface accessible histidine residue. The second category point mutants predominantly vary in protein net charge and the amino acid microstructure. In total, seventeen point mutants were generated: 1) category I consists of seven variants that vary predominantly in their histidine surface accessibility, and were obtained by replacing a charged amino acid residue at different locations on the surface of the protein molecule, and 2) category II consists of ten variants that vary in both net charge and charge distribution were obtained by replacing charged and neutral amino acid residues at different locations (different microenvironments) on the protein surface.
PCR technique was used to generate the point mutants. Gene and protein sequencing were employed to confirm the veracity of point mutation. CD and Lysozyme activity assays were performed to determine whether or not the 3D structure of all the protein variants was intact. Zonal analysis was used to obtain the binding strength values of all seventeen variants in IMAC with copper as the immobilized metal ions, and gradient elution method was used to obtain the relative retention times (rRT) values of all the variants in IEC.
The seven lysozyme variants generated in category I each contains one surface histidine residue. In IMAC, there is a correlation between the surface accessibility of the lone surface histidine and the protein's binding strength with R²⁺= 0.76. In IEC, the correlation between the protein's microstructure, which predominantly consists the surface accessibility of the histidine residue, and the protein's retention times was R²⁺= 0.95. However, there were few outlier variants (e.g. variant K83H) which did not follow the correlations. The variations presented by few outlier variants can be attributed to the presence of intramolecular bonds, which restrict the mobility of the amino acid side chains and subsequently hinder the specific interaction between the amino acid residue and chromatographic media.
For category II variants, short and medium range charge perturbations around the sole histidine residue in T4 lysozyme were engineered within 15 Ã distance of histidine. There was a strong correlation (R²⁺ = 0.96) between the theoretical (DeltaDeltaGElec) values, calculated using simple Coulomb's law, and the experimental (DeltaDeltaGB) values, which were obtained by measuring the protein binding strength values using IMAC. Similar correlation (R²⁺= 0.93) was obtained between the change in net charge (-2 to +2 units) and the relative retention times in IEC. Similarly, there were few variants (e.g. S136K, R76D) that did not follow the trends. The deviations of the few outlier variants can be attributed to the presence of unique microstructure effects around the histidine residue. These microstructure effects were quantified in IMAC as (DeltaDeltaGMicro), and in IEC they were quantified by the change in rRT values.
In summary, all seventeen variants had different binding strengths and rRT values indicating the variation in the protein structure around the histidine residue. Our work reveals that it is possible to capture the microstructural effects of a protein through the combination of protein molecular modeling and simple chromatographic experiments.Ph. D.
6
Li, Linlin. "Microstructure characterization of polymers by modern NMR techniques." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353000762.
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Mosaliganti, Kishore Rao. "Microscopy Image Analysis Algorithms for Biological Microstructure Characterization." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211390127.
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Camesasca, Marco. "MULTISCALING ANALYSIS OF FLUIDIC SYSTEMS: MIXING AND MICROSTRUCTURE CHARACTERIZATION." online version, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1144350255.
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Yang, Xuan. "Three-dimensional Characterization of Inherent and Induced Sand Microstructure." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7557.
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In the last decade, a significant amount of research has been performed to characterize the microstructure of unsheared and sheared triaxial sand specimens to advance the understanding of the engineering behavior of soils. However, most of the research has been limited to two-dimensional (2-D) image analysis of section planes that resulted in loss of information regarding the skeleton of the soil (pore structure) and other attributes of the three-dimensional (3-D) microstructure. In this research, the 3-D microstructures of triaxial test specimens were, for the first time, characterized. A serial sectioning technique was developed for obtaining 3-D microstructure from 2-D sections of triaxial test specimens. The mosaic technique was used to get high-resolution large field of view images. Various 3-D characterization parameters were used to study the microstructures of the specimens.
To study the preparation method induced variation in soil microstructure, two specimens prepared with air pluviation and moist tamping methods were preserved with epoxy impregnation. A coupon was cut from the center of each specimen, and following a serial sectioning and image capture process, the 3-D structure was reconstructed. To study the evolution of structure during shearing tests, two additional specimens prepared to the same initial conditions with the same methods were subjected to axial compression loading under constant confining pressure up to an axial strain level of 14%. After shearing, the structure of these specimens were also preserved and analyzed following the same procedures as the unsheared specimens. The evolution of the pore structures was investigated accordingly.
It was found that generally, moist tamped specimens were initially less uniform but had a more isotropic structure than air pluviated specimens. The standard deviations of 2-D local void ratio and 3-D pore size in dilated regions of sheared air pluviated and moist-tamped specimens were found to be smaller than those of as-consolidated specimens at a given void ratio. Tortuosity decreased with increasing pore size. It was also evident that the soil structures evolved differently depending on the initial structure. Comparison between 2-D and 3-D results indicated that it is not sufficient to use 2-D section information for characterizing some microstructural features.
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Komulainen, M. (Miika). "Microstructure characterization of pulsed laser deposited metal oxide nanoparticles." Master's thesis, University of Oulu, 2016. http://jultika.oulu.fi/Record/nbnfioulu-201602111172.
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Abstract. In this thesis, the effects of pulsed laser deposition processing parameters on microstructure of tungsten trioxide thin films was studied. Samples were deposited at room temperature under three different background oxygen pressure levels using three different laser beam fluence. Some samples were post-annealed at temperatures between 400 and 600 °C, and the rest were left as deposited. Micro- and crystal structure of the samples were examined with X-ray diffraction, Raman spectroscope, atomic force microscope, and field emission scanning electron microscope. Results showed that the films were porous, constructed of nanoparticles and had a rough surface. In crystal structure studies, amorphous phase as well as crystalline monoclinic γ- ja ε-phases were found.
Value of background pressure and laser beam fluence were found to have significant effect on crystal structure, morphology, porosity, and thickness of the films. Effect of post-annealing temperature was non-linear and dependent on the as-deposited structure of the films. Before the post-annealing, the films were mostly amorphous and during the heating some of them remained amorphous, some crystallized into γ-phase, and some formed different mixtures of γ- and ε-phases. Grain sizes of the samples were studied with different methods, which gave somewhat different results, but it could be concluded that fluence of the laser was largely insignificant, and pressure and post-annealing temperature had more dominant effects.Pulssilaserkasvatettujen metallioksidinanopartikkeleiden mikrorakenteen karakterisointi. Tiivistelmä. Tässä työssä tutkittiin pulssilaserkasvatuksen parametrien vaikutusta volframitrioksidistaohutkalvojen mikrorakenteeseen. Näytteet kasvatettiin huonelämpötilassa kolmessa eri happipaineessa ja kolmella eri laserin intensiteetillä. Osa näytteistä jälkihehkutettiin 400–600 °C asteen lämpötilassa. Näytteiden mikro- ja kiderakennetta tutkittiin röntgendiffraktiolla, Raman spektroskopialla sekä atomivoima- ja elektronimikroskopian menetelmillä. Tuloksista kävi ilmi kalvojen huokoinen, nanopartikkeleista koostuva rakenne, pinnan karheus sekä eri faasien määräsuhteet. Amorfisen faasin lisäksi näytteistä löytyi kiteiset monokliiniset γ- ja ε-faasit.
Taustapaineen ja laserin intensiteetin muutosten havaittiin vaikuttavan voimakkaasti kalvojen huokoisuuteen, pinnan rakenteeseen ja kalvon paksuuteen. Paineen ja intensiteetin vaikutukset olivat vastakkaisia, mutta aina samanlaisia. Jälkihehkutuksen vaikutus oli epälineaarinen sekä riippuvainen hehkutuslämpötilasta, mutta myös hehkuttamattomasta kalvon rakenteesta. Ennen jälkihehkutusta kalvot olivat pääsääntöisesti amorfista faasia, mutta hehkutettaessa osa jäi pääosin amorfiseksi ja loput kiteytyivät melko puhtaaksi monokliiniseksi γ-faasiksi tai erilaiseksi yhdistelmäksi ε- ja γ-faaseja. Jälkihehkutettujen kalvojen raekokoja laskettiin röntgendiffraktion mittaustuloksista eri menetelmillä, joilla saatiin hieman eriäviä tuloksia, mutta kaikista kävi ilmi, että laserin intensiteetillä ei ollut merkittävää vaikutusta keskimääräiseen raekokoon toisin kuin lämpötilalla ja taustapaineella.
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Kulkarni, Raghav Shrikant. "Characterization of carbon fibers: coefficient of thermal expansion and microstructure." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3073.
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The focus of the research is to develop a consistent and repeatable method to
evaluate the coefficient of thermal expansion (CTE) of carbon fibers at high
temperatures. Accurate measurement of the CTE of carbon fibers is essential to
understand and develop optimal processing procedures as well as computational
simulations to predict properties and allowables for fiber-reinforced composites. The
mismatch between the coefficient of thermal expansion of the fiber and the matrix has a
profound impact on the development of residual stresses and the subsequent damage
initiation and progression, potentially diminishing the performance of composite
structures.
In situ transmission electron microscopy (TEM) is selected to perform the
experimental work on account of the high resolution and the capability of evaluating
both the longitudinal and transverse CTE. The orthotropy in the CTE is tested by
rotating the fibers through 45° about their axis. The method is validated by testing
standard tungsten filaments of known CTE. Additionally, the microstructure of the fibers
is studied in a field emission scanning electron microscope as well as through selected
area diffraction patterns in a TEM to observe presence of any potential orthotropy. The
pitch based P55 fiber revealed a cylindrically orthotropic microstructure, but the PAN
based IM7 and T1000 fibers did not reveal any orthotropy. Finite element models of
hexagonally arranged IM7 fibers in a 977 epoxy matrix are developed using PATRAN
and analyzed using the commercial FEA code ABAQUS 6.4. The fiber properties were
considered temperature independent where as the matrix properties were varied linearly
with temperature. The lamina properties evaluated from the finite element modeling are
in agreement with the experimental results in literature within 10% in the temperature
range of room temperature to the stress free temperature of the epoxy, however at
cryogenic temperatures the difference is greater. The residual stresses developed during
processing of the composite indicated a potential location for fiber matrix debonding to
be in the matrix dominant regions.
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Punurai, Wonsiri. "Cement-based materials' characterization using ultrasonic attenuation." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04042006-171125/.
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Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.Dr. Jennifer Michaels, Committee Member ; Dr. Jacek Jarzynski, Committee Member ; Dr. Jianmin Qu, Committee Member ; Dr. Laurence J. Jacobs, Committee Chair ; Dr. Kimberly E. Kurtis, Committee Co-Chair.
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G, Kelekanjeri V. Siva Kumar. "Non-destructive Electrical Characterization of Controlled Waspaloy Microstructures." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14561.
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In this research, controlled Waspaloy microstructures were produced with the objective of studying microstructural evolution in this alloy via electrically-based ac/dc non-destructive techniques. Correlations were developed between electrical measurements and alternate characterization techniques such as Ultra Small Angle X-ray Scattering (USAXS), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to gain a complete understanding of the microstructural transformations and the associated mechanisms. Three different sets of controlled microstructures were produced in this research. In Set I microstructures, matrix (gamma) grain sizes of 13, 52 and 89 micrometers were obtained after solution-treatments at 1045 and 176;C, 1090 and 176;C and 1145 and 176;C respectively. A vacancy stabilization treatment at 1045 and 176;C followed after which, the specimens were aged at 800 and 176;C for times ranging from 0.1 hrs to 100 hrs to vary the gamma prime precipitate size distribution. In Sets II and III, the solution-treatment was only conducted at 1145 and 176;C, with the stabilization treatment conducted only in Set II. Subsequently, aging experiments were conducted at 725 and 176;C (or 700 and 176;C in Set II), 800 and 176;C and 875 and 176;C for times up to 100 hrs.
DC four-point probe resistivity of specimens increased to a maximum upon initial aging from the solution-treated condition and showed a decreasing trend thereafter with successive aging. This, in addition to complementary evidence from SEM and USAXS, led to the conclusion that gamma prime nucleation-growth was complete by the time the resistivity maximum was observed. Resistivity variations that ensued upon successive aging after the maximum were attributed to microstructural/compositional changes due to gamma prime coarsening. The height of the maximum decreased drastically with increase in aging temperature from 725 and 176;C to 800 and 176;C, while the resistivity did not increase from the solution-treated condition upon aging at 875 and 176; C. Coarsening studies based on USAXS analysis indicated an LSW type volume diffusion mechanism of coarsening in Waspaloy, with an average coarsening rate constant of 3.25x10-29 [m3/sec] for Set I specimens aged at 800 and 176;C.
Analytical and Finite Element (FE) models of two-probe impedance and dc four-point probe resistivity methods were developed to gain insight into the measured response and the accurate determination of material properties.
AFM-based localized electrical examination of sub-grain Waspaloy microstructures was successfully conducted using electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM) and current-AFM (I-AFM) electrical modes. I-AFM experiments revealed that the conductivity of the gamma prime phase was lower than that of the gamma phase.
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Dickerson, Bryan Douglas Jr. "Characterization of Ferroelectric Films by Spectroscopic Ellipsometry." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/10148.
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Process dependent microstructural effects in ferroelectric SrBi2Ta2O9 (SBT) thin films were characterized and distinguished from material dependent optical properties using a systematic multi-layer modeling technique. Variable angle spectroscopic ellipsometry (VASE) models were developed by sequentially testing Bruggeman effective-media approximation (EMA) layers designed to simulate microstructural effects such as surface roughness, porosity, secondary phases, and substrate interaction. Cross-sectional analysis by atomic force microscopy (AFM), transmission and scanning electron microscopy (TEM) and (SEM) guided and confirmed the structure of multi-layer models for films produced by pulsed laser deposition (PLD), metal-organic chemical vapor decomposition (MOCVD), and metal-organic deposition (MOD). VASE was used to estimated the volume percentage of second phase Bi2O3 in SBT thin films made by MOD. Since Bi₂O₃ was 10 orders of magnitude more conductive than SBT, second phase Bi₂O₃ produced elevated leakage currents. Equivalent circuits and percolation theory were applied to predict leakage current based on Bi₂O₃ content and connectivity. The complex role of excess Bi2O3 in the crystallization of SBT was reviewed from a processing perspective. VASE helped clarify the nature of the interaction between SBT films and Si substrates. When SBT was deposited by MOD and annealed on Si substrates, the measured capacitance was reduced from that of SBT on Pt due mainly to the formation of amorphous SiO₂ near the SBT/Si interface. VASE showed that the thickness and roughness of the SiO₂ reaction layer increased with annealing temperature, in agreement with TEM measurements. Unlike PZT, SBT crystallization was not controlled by substrate interaction.Master of Science
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Gurumurthy, Ashok. "Simulation methodologies for multiphase three-dimensional microstructures." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52261.
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There is a need for simulation methodologies for multiphase three-dimensional microstructures that can be used in numerical simulations of material behavior or in exact computation of effective properties using microstructural correlation functions. Specifically, the methodology must be able to generate verifiably realistic microstructures, with complex morphology accurately represented.
Striving to address that need, the research presented here develops a general microstructure simulation toolbox for multiphase two- and three-dimensional microstructures consisting of one connected phase and one or more particulate phases. Previous work by other researchers has found successful solutions to a variety of special cases of the general problem, but most of them are intended for binary microstructures, and nearly all simulate only two-dimensional microstructures. The toolbox presented here attempts to exceed those limitations.
Its framework is a Metropolis stochastic-optimization routine running a simulated-anneal schedule, with particle position coordinates defining the configuration space and a range of forms available for the ﾓenergyﾔ? function. The toolbox allows several parameterizations of the microstructure, supplying all elementary properties (phase volume fractions, mean sizes, etc.) and some non-elementary properties (distributions of elementary properties, properties relating to inter-phase distances and morphology) of microstructures as possible parameters.
The toolbox is able, as one special case, to simulate realistic microstructures of uniaxially compacted mixtures of elemental Al-Ti-B powders and achieve basic microstructure-processing correlation. Statistical tests involving microstructural correlation functions bear out the realism. The toolbox is also able to generate virtual microstructures for the same system, for use in the design of experiments (which are in fact high-strain-rate impact simulations), and for evaluating hypotheses involving achievable material properties.
The Al-Ti-B powder compacts are potential advanced energetic materials that, when subjected to high-strain-rate impact (which may or may not constitute shock compression), explosively release heat by anaerobic reaction according as certain incompletely understood conditions are met or not. The study of those conditions and the mechanism of reaction initiation (carried out by a collaborator) is the specific application that the simulations in this work cater to.
To ensure realistic morphology in simulated Al-Ti-B microstructures, this work included reconstruction (carried out by montage serial sectioning) of large three-dimensional volumes of Al-Ti and Al-B binary compacts for two sets of powders that yielded actual 3 D Ti and B particle images. Accordingly, advancement of the experimental technique of montage serial sectioning and a quantitative characterization of the real powder microstructures also formed part of this research.
While only examples from Al-Ti-B powders are used throughout this work, it is clear that the methods will apply to other similar systems.
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Sears, Jasmine Soria, and Jasmine Soria Sears. "Characterization of Novel Plasmonic, Photonic, and Semiconductor Microstructures." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625672.
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The fields of telecommunications and optoelectronics are under constant pressure to shrink devices and reduce power consumption. Micro-scale photonic and plasmonic structures can trap light and enhance the brightness of active emitters; thus, these types of structures are promising avenues to accomplishing the goals of miniaturization and efficiency. A deeper understanding of specific structures is important in order to gauge their suitability for specific applications. In this dissertation, two types of microstructures are explored: one-dimensional silicon photonic crystals and self-assembled indium islands. This dissertation will provide novel characterization of these structures and a description of how to utilize or compensate for the observed features.
A photonic crystal can act as a tiny resonator for certain wavelengths, making it a promising structure for applications that require extremely small lasers. However, because of silicon’s indirect bandgap, a silicon photonic crystal cavity would require the addition of an active emitter to function as a light source. Attempts to incorporate erbium into these cavities, and the observation of an unusual coupling phenomenon, will be discussed.
Self-assembled indium islands are plasmonic structures that can be grown via molecular beam epitaxy. In theory, these islands should be pure indium nanoantennas on top of a smooth gallium arsenide substrate. In practice, the component materials are less segregated than predicted, giving rise to unexpected hollow dome shapes and a sub-surface indium layer. Although these features were not an intended result of indium island growth, they provide information regarding the island formation process and potentially contribute additional applications.
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Lieberman, Scott Ian. "Microstructural Characterization, Visualization, and Simulation of Ti-B Materials." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14578.
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Additions of boron in modified titanium alloys and Ti-B composites result in the in situ formation during high temperature processing of TiB reinforcement phases that improve the mechanical properties and wear resistance of unreinforced titanium alloys, while still utilizing the high strength-to-weight ratio and excellent corrosion resistance of titanium. Several boron-modified titanium alloys and Ti-B composites in a Ti-6Al-4V matrix have been investigated to determine the effect of processing parameters on the TiB reinforcement phases and resultant microstructures and mechanical properties. Using optical microscopy, scanning electron microscopy, conventional characterization techniques, and newly developed methodologies for three-dimensional visualization, the microstructures of these Ti-B materials have been studied. Observations included a similar anisotropic whisker morphology with roughly hexagonal cross-sections among all TiB phases; alignment of all TiB phases with extrusion, with the extent of alignment affected by thermomechanical processing parameters; brittle fracture behavior of TiB whiskers, with fracture down the length of whiskers not aligned in the tensile direction and across the width of whiskers aligned in the tensile direction; and discoveries of the anisotropic morphologies of the coarse primary TiB phase and the sub-micron precipitated TiB phase. It has been observed that extruded boron-modified alloys with compositions in the hypoeutectic regime of the quaternary system of titanium, alloying elements aluminum and vanadium, and boron, containing a unimodal size distribution of eutectic TiB whiskers, significantly improve the strength and stiffness compared to unreinforced Ti-6Al-4V alloy while also demonstrating tensile elongation to failure within the fracture-critical limits required for aerospace structural applications. Materials design methodologies have been developed using Ti-B materials, and they show promise for predicting the effects of processing parameters and the resultant microstructures and mechanical properties for boron-modified titanium alloys and Ti-B composites optimized for a variety of commercial and industrial applications.
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Delpouve, Héloïse. "Relation microstructure et épaisseur d’une interphase BN et ses propriétés mécaniques." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0197/document.
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L’utilisation des composites à matrice céramiques (CMC), et particulièrement les matériaux SiC/SiC, à la place des alliages métalliques dans les moteurs aéronautiques peut permettre de réduire leur consommation. Ils possèdent en effet des propriétés physiques et mécaniques très intéressantes à haute température : faible densité, résistance élevée aux chocs thermiques et rupture non-fragile. Dans ces matériaux, une fine couche est insérée entre les fibres et la matrice : l’interphase. Le nitrure de bore pyrolytique est le matériau d’interphase de choix pour les applications visées. La bibliographie souligne bien la nécessité et la difficulté de « contrôler » l’intensité des liaisons interfaciales fibres/matrice (F/M) grâce à l’interphase. Mais l’influence exacte de la cristallinité et de l’épaisseur des interphases de type BN sur son contrôle, et par conséquent sur le comportement mécanique final du CMC industriel est encore mal connue.Une première problématique abordée dans cette thèse est l’échelle du CMC de laboratoire à utiliser. En effet jusqu’ici, les matériaux modèles les plus couramment employés sont les mini- et les micro- composites 1D. Ils peuvent être élaborés facilement et rapidement par dépôt chimique en phase vapeur mais ne rendent pas compte de phénomènes inévitablement présents au sein du composite industriel. C’est pourquoi l’utilisation de nouveaux matériaux modèles 2D comme les « monostrates » comprenant un pli de tissu, l’interphase BN et une matrice de SiC dont la porosité peut être comblée par du Si comme dans le cas des CMC industriels est plus pertinente et est proposée. Cependant, de par la faible épaisseur des éprouvettes, les protocoles de caractérisation et de tests mécaniques ont dû être revus. Il s’agit notamment de caractériser la liaison F/M par deux paramètres : la contrainte de cisaillement de la liaison interfaciale (τi) et le module de cisaillement du matériau (G12).Pour la partie mécanique, des essais de traction monotone et cyclée dans l’axe des fibres du renfort (exploités à l’aide de modèles micromécaniques), des essais de cisaillement Iosipescu, ainsi que des essais de push out ont été mis au point et exploités. Des analyses de micro caractérisation par microscopie électronique (MEB, FIB-MEB, MET) ont été réalisées avant et après essais mécaniques avec des interphases de différentes configurations afin de relier les différences de microstructures et d’épaisseurs aux chemins de fissuration matricielle et aux comportements mécaniques macroscopiques des composites. La liaison F/M la plus forte est notamment obtenue quand le degré de cristallisation et l’anisotropie structurale du BN sont peu élevés, pourvu que l’épaisseur de l’interphase soit suffisanteThe use of ceramic matrix composites (CMC), and particularly SiC/SiC materials, in place of metal alloys in aircraft engines has the potential to reduce their fuel consumption. They have very interesting physical and mechanical properties at high temperatures: low density, high resistance to thermal shock and non- brittle failure. In these materials, a thin layer is inserted between the fibres and the matrix: the interphase. Pyrolytic boron nitride is the interphase material of choice to achieve the desired applications. The bibliography clearly highlights the need and difficulty of "controlling" the intensity of fibre/matrix interfacial bonds (F/M) thanks to the interphase. But the exact influence of the crystallinity and thickness of BN-type interphases on its control, and consequently on the final mechanical behaviour of the industrial CMC, is still insufficiently known.A first issue addressed in this thesis is the scale of the CMC to be used in the laboratory. Indeed, so far, the most commonly used model materials are 1D mini and micro composites. They can be easily and quickly prepared by chemical vapour deposition but do not account for phenomena inevitably present in the industrial composite. Therefore, the use of new 2D model materials such as "monostrates" comprising a single-ply woven, the BN interphase and a SiC matrix in which the porosity can be filled with Si as in the case of industrial CMCs is more relevant and is proposed. However, due to the thinness of the specimens, the characterization and mechanical testing protocols had to be reviewed. This involves characterizing the F/M bond by two parameters: the shear stress of the interfacial bond (τi) and the shear modulus of the material (G12).For the mechanical part, monotonic and cycled tensile tests in the fibre axis of the reinforcement (operated using micromechanical models), Iosipescu shear tests, as well as push-out tests were developed and used. Micro characterization analyses by electron microscopy (SEM, FIB-SEM, TEM) were performed before and after mechanical tests with interphases of different configurations in order to link the differences in microstructures and thicknesses to the matrix cracking paths and macroscopic mechanical behaviours of the composites. The strongest F/M bond is obtained notably when the degree of crystallization and structural anisotropy of the BN are low, provided that the interphase is thick enough
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Fletcher, Michelle Lynn. "Characterization of creep and microstructure of novel high-temperature magnesium alloys." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42230.
Full textAbstract:
The desire for fuel efficient, yet high performance, vehicles in the automotive industry has resulted in a high demand for light weight structural materials. Magnesium alloys are one of the lightest structural materials available to engineering designers. Wrought magnesium alloy bars, sections and tubes have been used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to below 100°C, since creep resistance begins to deteriorate above this temperature. Creep deformation in magnesium alloys has been generally contributed to grain boundary sliding and plastic deformation leading to inter-granular failure.
This research investigated the creep resistance of five wrought magnesium alloys (AE42, AJ32, AX30, EZ33 and ZE10) developed for elevated temperature automotive applications. Non-conventional techniques were utilized to study the creep resistance of these alloys on the micro and macro scale at temperatures ranging from 25°C to 175°C. Neutron diffraction techniques were utilized to measure alloy texture, total strain and elastic creep strain. Metallographic techniques were subsequently used to analyze microstructural constituents in each alloy. The alloy microstructure was then correlated to the alloy’s creep resistance.
The results indicate that the aluminum free magnesium alloys (i.e., EZ33 and ZE10) had higher creep resistance compared to aluminum containing alloys (i.e., AE42, AJ32 and AX30). For the aluminum containing alloys, twinning and formation of a large amount of the Mg₁₇Al₁₂ intermetallic compound likely contributed to a decreased creep resistance. Strontium and calcium were both seen to limit Mg₁₇Al₁₂ formation, thus improving creep resistance of the AJ32 and AX30 alloys with respect to the AE42 alloy, respectively. Both the EZ33 and ZE10 alloys contained nanoprecipitates uniformly dispersed throughout the matrix, possibly contributing to dispersion strengthening and improved creep resistance. The results of neutron diffraction studies suggest that the aluminum containing alloys have experienced unique lattice structure changes on different crystallographic planes. In contrast, the aluminum free alloys had very stable crystallographic lattice strains throughout the duration of creep testing.
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Khorashadizadeh, Anahita [Verfasser]. "Microstructure characterization of ultra-fine grained Cu-0.17wt%Zr / Anahita Khorashadizadeh." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1029489432/34.
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Bricker, Stephen. "Anomaly Detection and Microstructure Characterization in Fiber Reinforced Ceramic Matrix Composites." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1448880983.
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Suits, Frank. "Deposition and characterization of optically nonlinear thin films with novel microstructure." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184535.
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This work concerns the vacuum deposition of novel thin films that exhibit nonlinear optical effects due to their unusual microstructure. We discuss four different materials: 1) Tilted columns of aluminum-oxide 2) Gold particles in aluminum-oxide 3) Cadmium sulpho-selenide particles in aluminum-oxide 4) Silver particles in zinc-sulphide. We begin with a description of the vacuum system and some the techniques used to characterize the optical and structural properties of the films. This leads to our study of second-harmonic generation (SHG) in aluminum-oxide thin films deposited at an angle to the evaporant source. We show that SHG is very sensitive to the non-isotropic microstructure that results from such a deposition. and the behavior of the SHG signal with sample orientation provides insight to the symmetry properties of the microstructure. In a related study we show that AU/Al₂O₃ composite films produce a large SHG signal. We investigate the dependence of the strength of the SHG signal with fill-fraction of gold and show that it increases quadratically. in agreement with theory. The third material we discuss is cadmium sulpho-selenide doped aluminumoxide. We describe attempts at nucleating semiconductor crystallites in a variety of hosts through a process of co-deposition and subsequent annealing. We also deposit alternate layers of CdS-Se and Al₂O₃ with the semiconductor layer thin enough that interspersed crystallites form. This results in suspended. isolated crystallites similar to the doped-glass materials of interest to nonlinear optics. A waveguide of a CdS/Al₂O₃ "sandwich" demonstrates optical nonlinearity through a power-dependent prism coupling experiment, and the degree of nonlinearity is much greater than undoped glass, though less than doped glass. The final section of the dissertation is a theoretical description of nonlinear optical behavior in a novel composite material consisting of metal particles in a nonlinear dielectric host. We assume the enhanced field around the resonating particles drives the host locally nonlinear through either a Kerr-type or thermal nonlinearity. We calculate the change in optical properties of the medium due to this effect and show that for a system of silver in zinc-sulphide the nonlinearity can be significant.
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Groeber, Michael Anthony. "Development of an automated characterization-representation framework for the modeling of polycrystalline materials in 3D." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1187104216.
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楊曄 and Ye Yang. "Microstructure characterization of high Tc superconducting thin films and multilayer Josephson junctions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31220186.
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Shaikh, Vasim. "Mist and Microstructure Characterization in End Milling Aisi 1018 Steel Using Microlubrication." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc283858/.
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Flood cooling is primarily used to cool and lubricate the cutting tool and workpiece interface during a machining process. But the adverse health effects caused by the use of flood coolants are drawing manufacturers' attention to develop methods for controlling occupational exposure to cutting fluids. Microlubrication serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process. Microlubrication minimizes the exposure of metal working fluids to the machining operators leading to an economical, safer and healthy workplace environment. In this dissertation, a vegetable based lubricant is used to conduct mist, microstructure and wear analyses during end milling AISI 1018 steel using microlubrication. A two-flute solid carbide cutting tool was used with varying cutting speed and feed rate levels with a constant depth of cut. A full factorial experiment with Multivariate Analysis of Variance (MANOVA) was conducted and regression models were generated along with parameter optimization for the flank wear, aerosol mass concentration and the aerosol particle size. MANOVA indicated that the speed and feed variables main effects are significant, but the interaction of (speed*feed) was not significant at 95% confidence level. The model was able to predict 69.44%, 68.06% and 42.90% of the variation in the data for both the flank wear side 1 and 2 and aerosol mass concentration, respectively. An adequate signal-to-noise precision ratio more than 4 was obtained for the models, indicating adequate signal to use the model as a predictor for both the flank wear sides and aerosol mass concentration. The highest average mass concentration of 8.32 mg/m3 was realized using cutting speed of 80 Surface feet per minute (SFM) and a feed rate of 0.003 Inches per tooth (IPT). The lowest average mass concentration of 5.91 mg/m3 was realized using treatment 120 SFM and 0.005 IPT. The cutting performance under microlubrication is five times better in terms of tool life and two times better in terms of materials removal volume under low cutting speed and feed rate combination as compared to high cutting speed and feed rate combination. Abrasion was the dominant wear mechanism for all the cutting tools under consideration. Other than abrasion, sliding adhesive wear of the workpiece materials was also observed. The scanning electron microscope investigation of the used cutting tools revealed micro-fatigue cracks, welded micro-chips and unusual built-up edges on the cutting tools flank and rake side. Higher tool life was observed in the lowest cutting speed and feed rate combination. Transmission electron microscopy analysis at failure for the treatment 120 SFM and 0.005 IPT helped to quantify the dislocation densities. Electron backscatter diffraction (EBSD) identified 4 to 8 µm grain size growth on the machined surface due to residual stresses that are the driving force for the grain boundaries motion to reduce its overall energy resulting in the slight grain growth. EBSD also showed that (001) textured ferrite grains before machining exhibited randomly orientated grains after machining. The study shows that with a proper selection of the cutting parameters, it is possible to obtain higher tool life in end milling under microlubrication. But more scientific studies are needed to lower the mass concentration of the aerosol particles, below the recommended value of 5 mg/m3 established by Occupational Safety and Health Administration (OSHA).
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Mukherjee, Kunal Ph D. Massachusetts Institute of Technology. "Lattice-mismatched epitaxy of AlInP and characterization of its microstructure and luminescence." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/112386.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 178-183).
The synthesis of high-quality III-V ternary alloy semiconductors is vital to the success of major technologies such as LEDs, laser diodes, high-efficiency solar cells and power electronics. However, the epitaxy of ternary alloys can be complicated due to the dissimilar behavior of constituent atoms on the growth surface. Historically, lattice matching of the ternary alloy to a substrate is another important constraint that limits access to all but a few alloy fractions. A technologically important ternary alloy in which both surface kinetics and lattice matching is crucial is the wide band-gap AlxIn1-xP system. This alloy is commercially used at one specific composition, a random solid solution of Al0.5In0.5P lattice-matched to GaAs, as a high indirect band-gap cladding/barrier layer for the ubiquitous red LEDs and laser diodes. Little is known about AlxIn1-xP at other compositions and with non-random microstructures despite the potential benefit of gaining access to the highest direct band-gap semiconductor amongst all non-nitride III-V semiconductors. In this thesis, InyGa1-yAs compositionally graded buffers are used to bridge lattice mismatch, leading to the synthesis of AlxIn1-xP at a range of compositions with low threading dislocation densities (105-06/cm2) and low oxygen levels (2x1016/cm3). The high-quality of these films result in the first report of room-temperature yellow-green luminescence from AlxIn1-xP comparable in brightness to lattice-matched films. An accurate band-gap vs composition map of the AlxIn1-xP alloy space is created with Al0.43In0.57P identified as having the highest direct band-gap of 2.33 eV. The formation of non-random microstructures in AlxIn1-xP due to phase separation and atomic ordering is studied in detail. Phase separation into aluminum-rich and indium-rich domains is found to evolve from random compositional perturbations via a positive-feedback process limited by aluminum surface-diffusion. A reduction in band-gap by more than 200 meV is obtained by converting a random microstructure to a non-random one using growth temperature. Random/non-random interfaces are designed to use this large band-gap change to improve the efficiency of the first double-heterostructure yellow-green and amber AlxIn1-xP LEDs. Finally, we observe and explain how strain fields from an inhomogeneous distribution of misfit dislocations result in surface roughness and composition fluctuations in lattice-mismatched AlxIn1-xP LEDs. The results obtained in this work will be useful not only in providing control over nanometer-scale structures but also over wafer-scale features. This is crucial in transitioning novel lattice-mismatched devices from the lab to the marketplace.
by Kunal Mukherjee.
Ph. D.
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Gerislioglu, Selim. "Microstructure Characterization of Polymers and Polymer-Protein Bioconjugates by Hyphenated Mass Spectrometry." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1534269781343128.
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Velichko, Alexandra. "Quantitative 3D characterization of graphite morphologiesin cast iron using FIB microstructure tomography." Aachen Shaker, 2008. http://d-nb.info/992480035/04.
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Yang, Ye. "Microstructure characterization of high Tc superconducting thin films and multilayer Josephson junctions /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19471099.
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Mazinanian, Neda. "Influence of microstructure and proteins on the metal release of micron-sized stainless steel powder particles." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98082.
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Knowledge on metal release processes from stainless steel powder, which can be potentially inhaled at occupational settings, is essential within the framework of human health and environmental risk assessments. An in-depth knowledge concerning powder history, physical properties of particles (e.g. size, morphology, and active surface area) combined with their chemical properties (such as the chemical composition of the particles and their metal release behavior) is needed for better understanding of the interaction mechanisms between metal powders and humans. So far, limited in vitro and in vivo studies exist that assess the correlation between stainless steel surface properties, protein adsorption effects, and metal release processes. The aim of this study is to add information to fill this knowledge gap through in vitro investigations of protein-induced metal release (iron, nickel, chromium, and manganese) and induced surface changes of five differently sized and/or produced (water-atomized (WA) and gas-atomized (GA)) stainless steel powder particles (three austenitic: AISI 316L, 310B, and 304B; one martensitic: AISI 410L; and one ferritic: AISI 430L) after exposure up to one week into a phosphate buffer saline (PBS) solution of pH 7.2-7.4 containing either lysozyme (LYS) or bovine serum albumin (BSA). The results show that the outmost surface oxide composition of the powders strongly depends on the production method and particle size. Gas-atomized 316L powder particles (with spherical shapes) indicated a high relative manganese content in their surface oxide (more significant in the case of 316L particles sized <4µm), while no manganese compounds were detectable in the surface oxide of water-atomized powders (of irregular particle shapes). Although austenitic stainless steels should present non-magnetic properties, the investigation of magnetic properties indicated that differently sized gas-atomized 316L particles and water-atomized 304B were to some extent ferromagnetic suggesting the presence of ferrite. BSA induced a significant enrichment of chromium in the surface oxide of all investigated powders (especially for ferritic WA430L and austenitic WA316L), except in the case of 316L powders (<4µm) showing no significant change. Metal release studies illustrated that both proteins enhanced the amount of released metal, with a preferential iron release from water-atomized particles and manganese release from gas-atomized powders. BSA-containing medium induced the highest extent of metal release in comparison with other tested biological media (up to 35-fold increase in the case of ferritic 430L particles produced by water atomization). Comparison between the metal release behavior of particulate and massive stainless steel indicated a significantly higher extent of metal released from abraded stainless steel sheets compared with particles, which is most probably an effect of freshly abraded surfaces of the massive metal sheets, not true for the particles with aged surface oxides, along with the presence of higher relative chromium content in the surface oxide.
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Leung, Ming Yan. "Dynamic characterization of micro scale samples using the Hopkinson tensile bar technique /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MECH%202007%20LEUNG.
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Clay, Stephen Brett. "Characterization of Crazing Properties of Polycarbonate." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28648.
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The purpose of this study was to characterize the craze growth behavior of polycarbonate (PC) as a function of stress level, model the residual mechanical properties of PC at various craze levels and strain rates, and determine if the total surface area of crazing is the sole factor in residual properties or if the crazing stress plays a role. To obtain these goals, a new in-situ reflective imaging technique was developed to quantify the craze severity in transparent polymers.
To accomplish the goal of craze growth rate characterization, polycarbonate samples were placed under a creep load in a constant temperature, constant humidity environment. Using the new technique, the relative craze density was measured as a function of time under load at stresses of 40, 45, and 50 MPa. The craze growth rates were found to increase exponentially with stress level, and the times to 1% relative craze density were found to decrease exponentially with stress level. One exception to this behavior was found at a crazing stress of 50 MPa at which over half of the samples tested experienced delayed necking, indicating competitive mechanisms of crazing and shear yielding. The draw stress was found to be a lower bound below which delayed necking will not occur in a reasonable time frame.
The yield stress, elastic modulus, failure stress, and ductility were correlated to crazing stress, relative craze density, and strain rate using a Design of Experiments (DOE) approach. The yield stress was found to correlate only to the strain rate, appearing to be unaffected by the presence of crazes. No correlation was found between the elastic modulus and the experimental factors. The failure stress was found to decrease with an increase in relative craze density from 0 to 1%, increase with an increase in crazing stress from 40 to 45 MPa, and correlate to the interaction between the crazing stress and the strain rate. The ductility of polycarbonate was found to decrease significantly with an increase in relative craze density, a decrease in crazing stress, and an increase in strain rate.
The craze microstructure was correlated to the magnitude of stress during craze formation. The area of a typical craze formed at 40 MPa was measured to be more than 2.5 times larger than the area of a typical craze formed at 45 MPa. The fewer, but larger, crazes formed at the lower stress level were found to decrease the failure strength and ductility of polycarbonate more severely than the large number of smaller crazes formed at the higher stress level.Ph. D.
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Malfavon-Ochoa, Mario, and Mario Malfavon-Ochoa. "Characterization of Semiconductor Nanocrystal Assemblies as Components of Optoelectronic Devices." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625902.
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This dissertation presents new insight into the ability of small molecule passivated NCs to achieve intimate approach distances, despite being well passivated, while developing guiding principles in the area of ligand mediated microstructure control and the resulting macroscopic optical and electronic properties that close packing of high quality NCs enables.
NC ligand coverage will be characterized quantitatively through thermogravimetric analysis (TGA), and qualitatively by photoluminescence and electroluminescence, in the case of functional devices; illustrating the importance of practitioner dependent control of ligand coverage through variations in the dispersion precipitation purification procedure. A unique examination of the relative contribution of energy and charge transfer in NC LEDs will demonstrate the ability to achieve charge transfer, at a level competitive with energy transfer, to well passivated NCs at various wt% loading in a polymer matrix. The observation of potential dependent recombination zones within an active layer further suggest novel, NC surface passivation mediated control of blend microstructure during solution processing towards the development of a bi-continuous network.
Next, NC self-assembly and resulting microstructure dependent optical and electronic properties will be examined through electroluminescence and high-resolution transmission electron microscopy (TEM) micrographs of functional NC/polymer bulk heterojunction LEDs. The joint characterization of NC optical properties, and self-assembly microstructure provide a deeper understanding of the significant and inseparable effects of minimal changes in NC surface passivation on structure and function, and emphasize the potential to rely on strongly passivating ligands to control physical properties and processing parameters concurrently towards higher efficiency devices via low cost processing.
Finally, micro-contact printing of blazed transmission gratings, using stable dispersions of core and core/shell NCs will be shown to produce close packed assemblies of NCs forming near-wavelength luminescent superstructures separated in space. We show the dominant contribution of a two-monolayer thick sharp interface CdS shell to the diffraction efficiency, and necessarily the refractive index, of the NCs, independent of core size. Utilization of these gratings as in-coupling elements at various positions within a device architecture are also examined. These new observations were achieved by unprecedented control of NC architecture during dispersion processing, while maintaining high luminescence, made possible by optimized NC surface passivation. These studies enable the formation of new LED architectures, and new optoelectronic devices based on angle resolved, monochromatic fluorescence from diffraction gratings prepared from simple solution processing approaches. Further, the novel observation of angle amplified interfering fluorescence from these features is argued to be a result of long range radiative coupling and superradiance enabled by the monodispersity and high-quality NC surface passivation described herein.
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Alipour, A. "Characterization of Elastomer Nanocomposite Blends Based on NR/EPDM/Organoclay." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35610.
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Elastomer nanocomposites based on NR/EPDM/organoclay were prepared by two-roll mill to investi-gate the effect of different percentages of nanoclay (0, 1, 3, 5 & 7 Wt%) and different matrix compositions (100/0, 75/25, 50/50, 25/75 & 0/100) on the microstructure, mechanical properties and best applicability of the mathematical models. Results of X-ray diffraction showed that enlargement of the silicate layers, pene-tration of polymer chains into layers and formation of an intercalated and exfoliated structure which was confirmed by TEM analysis. Mechanical properties as well as heat build up of the samples improved by addition of nanoclay. Addition the compounds with EPDM leads to an increase in compression strength, modulus and compressin set and decrease in tensile and tear strength. The prepared samples receive more aging resistance by addition of more clay and EPDM.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35610
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Davut, Kemal. "Characterization Of Steel Microstructures By Magnetic Barekhausen Noise Technique." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12608103/index.pdf.
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This aim of this thesis is to examine the possibility of using Magnetic Barkhausen Noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels as well as annealed low carbon steels. To determine the average grain size by MBN, SAE 1010 steel consisting of dominantly ferrite was used. The specimens were slowly cooled in the furnace after austenitizing at different time and temperature variations. By metallographic examination the average ferrite grain size of specimens was determined. The magnetic parameters were measured by a commercial MBN system. With increasing ferrite grain size, the magnetic Barkhausen jumps caused by the microstructure were decreased due to the reduction in grain boundary density per unit volume. A clear relationship has been observed between average grain size and the magnetic Barkhausen noise signals. SAE 4140, 5140 and 1040 steels were used to characterize the microstructures of quenched and tempered specimens. After austenitizing and quenching identically, the specimens were tempered at various temperatures between 200oC and 600oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic and annealed steels.
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Rammal, Mohammad. "Structural and thermal characterization of AIN thin films and their integration in laser devices." Thesis, Nantes, 2019. http://www.theses.fr/2019NANT4021/document.
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Des couches minces de nitrure d'aluminium sont développées sur plusieurs substrats à l'aide d'une pulvérisation cathodique par magnétron à basse température (<200 ° C) afin d'assurer la gestion thermique des dispositifs laser. La caractérisation de la microstructure (DRX, Raman, SEM, TEM) montre un film d’AIN bien cristallisé à structure dense et en colonne lorsqu’il est déposé sur des substrats de silicium, de saphir et d’InP. Les films AlN sont orientés (002) avec Rocking curve (FWHM) de 1,8 ° sur silicium, 0,9 ° sur saphir et entre 2,5 ° et 3 ° sur InP avec de ridge pour une épaisseur de 2 μm. De plus, la mesure thermique utilisant la technique photothermique pulsée a donné une conductivité thermique de 175 W.m-1.K-1 pour une couche d’AlN de 3 μm d’épaisseur. Ces valeurs élevées de conductivité thermique ont fait de l’AlN un bon candidat pour remplacer les matériaux BCB et SiO2 possédant une conductivité thermique faible. Les couche d’AlN sont utilisées comme dissipateurs de chaleur afin d’éliminer rapidement une chaleur énorme sur une très petite surface, avec un flux de chalaur allant jusqu’à 1 kW.cm-2, pour une stratégie de gestion thermique efficace et une prévention des pannes système. Les films AlN sont intégrés dans un dispositif laser après un processus de gravure sèche utilisant un mélange de plasma BCl3/Cl2/Ar. La vitesse de gravure était d’environ 200 nm/min. La gravure de AlN a été étudiée expérimentalement et numériquement afin de montrer l’effet de divers paramètres et conditions. Il a été remarqué que l’ajout de gaz BCl3 au mélange de plasma facilite et améliore le processus de gravureAluminum nitride thin films are grown on several substrates by using DC magnetron sputtering at low temperature (<200°C) in order to ensure the thermal management of laser devices. The microstructure characterization (XRD, Raman, SEM, TEM) shows a well crystallized AlN films with dense and columnar structure when deposited on silicon, sapphire and InP substrates. AlN films are (002) oriented with Rocking curve (FWHM) of 1.8° on silicon, 0.9° on sapphire, and between 2.5° and 3° on ridged InP for thickness of 2 μm. Furthermore, the thermal measurement using pulsed photothermal technique, has given a thermal conductivity of 175 W.m-1.K-1 for an AlN layer of 3 μm thick. These high values of thermal conductivity has made AlN a good candidate replacing BCB and SiO2 materials possessing low thermal conductivity. AlN layers are used as heat spreaders in order to rapidly remove enormous heat on a very small surface, with heat flux up to 1 kW.cm-2, for an efficient thermal-management strategy and system failure prevention. AlN films are integrated in laser device following a dry etching process using BCl3/Cl2/Ar plasma mixture. The AlN etch rates were around 200 nm/min. The AlN etching was studied deeply, experimentally and numerically in order to show the effect of various parameters and conditions. It was noticed that the addition of BCl3 gas to the plasma mixture facilitates and improves the etching process
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Kyriakides, Steven Alan. "Characterization of Shear Strengths and Microstructures for Solid Rocket Motor Insulation Materials." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/35974.
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As advances in solid rocket technology push rocket motors to more extreme operating speeds and temperatures, it becomes increasingly important to have well-designed material systems capable of surviving these harsh conditions. One common component in these systems is the use of a fiber- and particle-reinforced EPDM insulation layer between the motor casing and the solid fuel to shield the casing from the temperatures of the burning fuel and from the high velocity of gas particles traveling within the motor. This work studies several insulation materials to determine which exhibits the highest shear strength after being charred. Double-notch shear test specimens of three materials, ARI-2718, ARI-2719, and ARI-2750, were charred and tested to measure the failure strength of each charred material. The ARI-2750 showed the highest shear strength when loaded along the material orientation, but the ARI-2719 was strongest when transversely loaded. The strength measurements for ARI-2750 were highly sensitive to loading direction, unlike ARI-2718 and ARI-2719. Extensive scanning electron microscopy to identify correlations between shear strength and microstructure revealed that the amount of fiber orientation and amount of residual matrix material may have significant impacts on charred shear strength in these materials.Master of Science
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Trivedi, Pankaj. "Characterization of dislocation structures and their influence on processing of al alloys." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Spring2005/p%5Ftrivedi%5F050305.pdf.
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Oualmakran, Mohamed. "Multi-scale behaviour of aggregated soils:Experimental characterization and Constitutive modelling." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/222938.
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Natural and other aggregated or structured soils present peculiar mechanical behaviour which differs, in some parts, from the behaviour of soils reconstituted in laboratory. This difference can be explained by a specific structure which gathers the particles arrangement and bonding. However, numerous constitutive models were originally based on the behaviour of reconstituted soils. Therefore, classical models should be extended in order to reproduce more complex features of behaviour linked to the soil structure. This work provides a general framework to describe and predict the behaviour of aggregated and reconstituted soils. A multi-scale study was performed to understand the effect of the structure and its evolution upon loading. From an experimental point of view, a preliminary review of literature has been completed by an experimental program carried out on a silty soil in which different structures have been generated by various compaction conditions. At the macro-scale, conventional mechanical tests evidence the overconsolidation effect induced by structure and the important compressibility during its degradation. At the micro-scale, the fabric evolution during the destructuration process (induced by saturation and loading) has been mainly quantified by the evolution of the pore size distribution. This characterisation has been done by Mercury Intrusion Porosimetry. The samples compacted on the dry side of optimum exhibit a double porosity characterized by a bimodal pore size distribution, by opposition to the samples compacted on wet side of optimum that show a single class of pores. The deformation induced by mechanical loading is related to the closure of the biggest pores and the pore size distribution of aggregated soils tends towards unimodal shape upon the destructuration process. A constitutive critical state model (ACMEG) has been extended, based on experimental observations, in order to reproduce the behaviours of aggregated and reconstituted soils. In this purpose, a structure variable has been introduced in the yield function and its evolution has been integrated in the hardening law. Explicit and implicit methods of integration have been discussed and implemented to reproduce stress-strain responses on geomechanical tests (oedometric, isotropic and triaxial compression tests). Finally, the model has been validated by comparison of model predictions with the experimental results.Doctorat en Sciences de l'ingénieur et technologie
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Berglund, Anders. "Characterization of factors interacting in CGI machining : machinability - material microstructure - material physical properties." Licentiate thesis, KTH, Production Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9258.
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The Swedish truck industry is forced to find new material solutions to achieve lighter engines with increased strength. Customers and new environmental regulations demand both higher specific power and more environmentally friendly trucks, and this places a rising pressure on the manufactures. This demand could be met by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This however exposes the engine to higher loads and material physical properties must therefore be enhanced.
Today, alloyed gray iron is the predominantly used engine material. This material cannot meet the requirements of tomorrow’s engines. Compacted Graphite Iron has good potential to be the replacement; it opens new design opportunities with its superior strength, which can lead to smaller, more efficient engines and additional power. The question is: how will manufacturing be affected?
The main goal of this thesis is to identify and investigate the main factors’ effect and their individual contributions on CGI machining. When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, then the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding is developed mainly through experimental analysis. No attempt has been made to optimize the material to be used as engine material in this thesis.
The thesis demonstrates the importance of having good casting process control. It also illustrates the microstructural properties’ effects on CGI machinability, and what new aspects of machining must be taken into account, compared to gray iron.
OPTIMA CGI
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Martin, Samuel R. "Experimental Characterization of the Effect of Microstructure on the Dynamic Behavior of SiC." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5024.
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For roughly fifteen years the military has sought to use the properties of ceramics for armor applications. Current high-performance ceramics have extremely high compressive strengths and low densities. One ceramic that has been shown to be highly resistant under ballistic impact is silicon carbide (SiC). It has been found that even within the silicon carbides, those manufactured by certain methods and those with certain microstructural properties have advantages over others. In order to understand the microstructural reasons behind variations in ballistic properties, plate impact tests were conducted on two sintered silicon carbides with slightly different microstructures.
Two variations of a silicon carbide with the trade name Hexoloy SA were obtained through Saint Gobain. Regular Hexoloy (RH) and Enhanced Hexoloy (EH) are pressureless sintered products having exactly the same chemistries. EH went through additional powder processing prior to sintering, producing a final product with a slightly different morphology than RH. Samples of each were characterized microstructurally including morphology, density, elastic wavespeeds, microhardness, fracture toughness, and flexure strength. The characterization revealed differences in porosity distribution and flexure strength. It was determined that the porosity distribution in EH had fewer large pores leading to an 18% increase in flexural strength over that for RH.
The focus of the mechanics of materials community concerning dynamic material behavior is to pin down what exactly is happening microstructurally during ballistic events. Several studies have been conducted where material properties of one ceramic type are varied and the dynamic behavior is tested and analyzed. Usually, from one variation to the next, several properties are different making it hard to isolate the effect of each. For this study, the only difference in the materials was porosity distribution.
Plate impact experiments were conducted at the Army Research Laboratory (ARL) using the gas gun facilities within the Impact Physics Branch. A VISAR was utilized to measure free surface velocities. Tests were performed on each material to determine the Hugoniot Elastic Limit (HEL) and spall strength. Spall strength was measured as a function of impact stress, and pulse duration.
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Lee, Soon Gi. "Quantitative Characterization of Processing-Microstructure-Properties Relationships in Pressure Die-Cast Mg Alloys." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11552.
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The central goal of this research is to quantitatively characterize the relationships between processing, microstructure, and mechanical properties of important high-pressure die-cast (HPDC) Mg-alloys. For this purpose, a new digital image processing technique for automatic detection and segmentation of gas and shrinkage pores in the cast microstructure is developed and it is applied to quantitatively characterize the effects of HPDC process parameters on the size distribution and spatial arrangement of porosity. To get better insights into detailed geometry and distribution of porosity and other microstructural features, an efficient and unbiased montage based serial sectioning technique is applied for reconstruction of three-dimensional microstructures. The quantitative microstructural data have been correlated to the HPDC process parameters and the mechanical properties. The analysis has led to hypothesis of formation of new type of shrinkage porosity called, gas induced shrinkage porosity that has been substantiated via simple heat transfer simulations. The presence of inverse surface macrosegregation has been also shown for the first time in the HPDC Mg-alloys. An image analysis based technique has been proposed for simulations of realistic virtual microstructures that have realistic complex pore morphologies. These virtual microstructures can be implemented in the object oriented finite elements framework to model the variability in the fracture sensitive mechanical properties of the HPDC alloys.
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Muwanguzi, Abraham Judah Bumalirivu, Andrey Karasev, Byaruhanga K. Joseph, and Jönsson G. Pär. "Characterization of chemical composition and microstructure of natural iron ore from Muko deposits." KTH, Tillämpad processmetallurgi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-123054.
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The study aimed at investigating the chemical composition and microstructure of raw iron ore from the deposits in Muko area (south-western Uganda). The quality of this iron ore was evaluated to establish its suitability to serve as a raw material for iron production. Samples were taken from the six hills of Muko ore deposits and tests carried out to establish their composition and properties. X-ray diffraction and scanning electron microscopy were employed in the investigation and chemical analysis performed to determine the compounds constituting the ore. The quality of this ore was compared to generalized world market standards and ores from other nations. It was found that Muko ore is a rich hematite grade with Fe content above 65%. It has little gangue (<6% SiO2 and 3-4% Al2O3) and low contents of the deleterious elements (P ~ 0.02% and S < 0.006%), which correspond to acceptable levels for commercial iron ores.QC 20130531
Sustainable Technology Development in the Lake Victoria Region
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Jordan, Aaron. "Microstructure characterization and corrosion properties of two recycled aluminium alloys AA5050 and AA6011." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/microstructure-characterization-and-corrosion-properties-of-two-recycled-aluminium-alloys-aa5050-and-aa6011(b2cd54d8-c3c4-4422-8af6-a3c3584de285).html.
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The influence of recycling on aluminium alloys and subsequent influence on the microstructure and corrosion performances have been investigated. The investigation was commenced by taking two block cast, recycled aluminium alloys (AA5050 and AA6011) and rolling them into 1mm gauge plate. In the case of AA6011, the plate was subjected to subsequent solution heat treatment and artificial aging steps, in order to attain certain temper specifications. To replicate the automotive paint bake industrial practice, a sample was subjected to a 2% tensile stretch followed by heat treatment for 30 minutes at 180˚C. Microstructural observations revealed Al-Fe-Mn-Si intermetallics to be the dominant secondary phase in both alloys. The size, distribution and composition of these were unaffected by artificial aging. Mg2Si was found in a coarse, localised form in both alloys also, albeit in much less amounts in AA5050. The presence of this phase was likely due to poor homogenisation during thermomechanical processing. HR-TEM of AA6011 revealed needle/rod shaped precipitates, aligning in the [001]Al lattice direction. This is consistent with β''/β' hardening precipitates consisting of magnesium and silicon. Circumstantial evidence was found for the copper-containing Q phase precipitate also. An additional, unidentified precipitate was observed, nucleating on the {111} habit plane of the aluminium matrix. The high iron content of AA6011 retarded the precipitation hardening response by capturing elements associated with hardening precipitates in the Al-Fe-Mn-Si intermetallics. Electrochemical corrosion experiments revealed the materials had a high susceptibility to localised corrosions, with the open circuit potential and breakdown potential possessing similar values. Atmospheric corrosion experiments showed that artificial aging had a large influence on the preferred corrosion mechanism. Non-heat treated samples showed susceptibility for pitting corrosion. This was particularly true for the -T4P temper, which showed large scale pitting. Heat treated samples saw an introduced susceptibility to intergranular corrosion. This was attributed to precipitation at grain boundaries, which would then form a microgalvanic couple with adjacent depleted zones. In the case of the -T8P temper, tensile stretching introduced defects into the sub-grain microstructure. This resulted in intergranular corrosion fronts of increased width, where grains with higher stored energy undergo preferential dissolution alongside the grain boundary attack. Overall, the detrimental effects of high iron content need to be overcome before AA5050 and AA6011 can be seriously considered for use in the automotive industry. However, the corrosion performance of AA6011-T8P is encouraging.
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Berglung, Anders. "Characterization of factors interacting in CGI machining : machinability - material microstructure - material physical properties /." Stockholm : Industriell teknik och management, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9258.
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Cuevas, Assunta Mariela. "Microstructure characterization of friction-stir processed nickel-aluminum bronze through orientation imaging microscopy." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FCuevas.
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Tampu, Iulian Emil. "Morphological characterization of neural tissue microstructure using the orientationally-averaged diffusion MRI signal." Thesis, Linköpings universitet, Avdelningen för medicinsk teknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-158153.
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Diffusion-weighted magnetic resonance imaging (dMRI) is a powerful tool for thecharacterisation of neural tissue microstructural features. The role of neural projectioncurvature on the diffusion signal was recently studied for three temporal regimes of the diffusion pulse sequence in search for a description of the different decay trends in the orientationally-averaged diffusion signal reported in in vivo human studies.This work experimentally investigates the effects of neural projection curvedness in one of these regimes, namely the short diffusion time regime. Multi-shell diffusion MRI acquisitions on fixed rat spinal cord were performed using a custom number of diffusion gradient directions on a vertical bore pre-clinical MRI scanner capable of generating 3000 mT/m. Diffusion was probed in three different q-values ranges [450, 970], [600, 1400] and [1500, 1750] mm-1 using diffusion pulse durations of 1.4,2 and 2.5ms, respectively. Noise correction was performed on the diffusion data and the orientationally-averaged signal was computed for each shell using a weighted mean. The signal from selected regions in the sample was then fitted to a power law. Results show that gray matter areas exhibit a signal reduction with variable decay trends in the range of diffusion sensitivity values used here. This suggests that gray matter microstructure features are pictured by the orientationally-averaged signal in the high diffusion sensitivity regime and, as theoretically suggested, neurite curvature might play a role in characterizing the signal decay. These preliminary results may prove useful in the development of models for the interpretation of the diffusion signal and the design of acquisition strategies that aim to study the high diffusion sensitivity regime.
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Gai, Fangyuan, and Fangyuan Gai. "Processing and Microstructural Characterization of Ultra-High Temperature Ceramics." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626334.
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Spark plasma sintering (SPS), also known as direct current sintering (DCS) is an advanced sintering technique that and uses a continuous pulsed direct current to rapidly process materials through Joule heating and offers significant advantages and versatility over conventional sintering methods. The technique features in energy saving owing to high heating rates and is very suitable for consolidation as well as diffusion bonding of electrical conductive advanced ceramic materials such as ultra high temperature ceramics (UHTCs). However, cooling rate in SPS also plays an important role as it directly influences the generation of residual stress especially for specimens consist of dissimilar phases such as composites and laminates primarily due to CTE mismatch. Therefore, in order to produce high quality materials, a zirconium diboride with addition of silicon carbide (ZrB2-SiC) ultra high temperature ceramic composite is selected to investigate the effect of cooling rate in SPS on microstructure and mechanical properties. After being densified at the target temperature, ZrB2-25vol%SiC specimens are cooled from 1800°C using controlled cooling rates of 10 °C/minute to ~225.5 °C/minute (free cooling). A time dependent finite element analysis (FEA) model is used to simulate the temperature gradients across the specimens at dwell times and during the cooling processes. The residual stress within the specimens are experimentally verified using X-ray diffraction (XRD) and Raman spectrometry, and found maximum residual stress within the specimen cooled at 225.5 °C/minute. Peak Hardness and moderate elastic modulus is found for specimen sintered at 1800 °C and cooled at 100 °C/minute, which make this temperature and cooling rate appropriate conditions for future fabrication of UHTCs with similar thermal and electrical properties. These materials are of great interest for their excellent high-temperature capabilities, wear and corrosion resistance, and are regarded as material candidates for engineering applications in extreme environments. Therefore, development of an effective joining technique is important since near-net shape fabrication is challenging, and joints formed by brazing or conventional solid-state diffusion bonding limit the mechanical strength and high temperature applications of the base materials. Using SPS we have rapidly and successfully joined ZrB2 to hafnium diboride (HfB2) at 1750 and 1800 °C within a minute through electric current assisted solid-state diffusion bonding. The electric current enables localized Joule heating as well as plastic deformation of the mating surface asperities, and enhances the elemental interdiffusion process at the HfB2/ZrB2 interfaces owing to electromigration, which leads to the formation of ZrxHf1-xB2 solid solution. A series of characterization and analytical techniques including scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (S/TEM) are employed to study the microstructure and chemical composition at of the HfB2/ZrB2 interfaces. Apart from enhanced diffusion as a result of electromigration, the applied electric current can also be use to promote plastic deformation in ZrB2, which does not go through gross plastic deformation due to its extremely high melting point and brittle nature even when elevated temperature and pressure are applied. Through “electroplastic effect” (an effect based on electromigration) the mobility and multiplication of the existing dislocations in ZrB2 is enhanced, and a “metal-like” primary recrystallization phenomenon in the ZrB2 is observed meaning the material has experienced a sufficient amount of plastic deformation and reached the critical dislocation density and configuration for nucleation of “strain-free” grains. The average grain size of the recrystallized grain is only ½ of its original value. These findings suggest great potentials in microstructural tailoring and grain refinement of conductive advanced ceramics using SPS, and provide promising ideas for future fabrications and applications.
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Lolla, Sri Venkata Tapasvi. "Understanding the Role of Initial Microstructure on Intercritically Reheated Heat Affected Zone Microstructure and Properties of Multi-Pass Welds." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397826410.
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Deshpande, Nishkamraj U. "Characterization of fracture path and its relationship with microstructure and fracture toughness of aluminum alloy 7050." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20210.
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