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Title: Graphene Induced Formation of Nanostructures in Composites.
Creator: Shen, Chen, Zhai, Lei, Chen, Quanfang, Thomas, Jayan, Fang, Jiyu, Khondaker, Saiful, University of Central Florida
Abstract / Description: Graphene induced nanostructures in graphene-based composites and the performance of these composites have been explored in this study. For the metallic nanoparticles decorated graphene aerogels composites, the fabrication of hierarchically structured, reduced graphene oxide (rGO) aerogels with heavily metallic nanoparticles was realized. Higher loading of palladium nanoparticles in graphene aerogels leads to improved hydrogen gas sensing performance. For polymer derived ceramics (PDCs)...
Show moreGraphene induced nanostructures in graphene-based composites and the performance of these composites have been explored in this study. For the metallic nanoparticles decorated graphene aerogels composites, the fabrication of hierarchically structured, reduced graphene oxide (rGO) aerogels with heavily metallic nanoparticles was realized. Higher loading of palladium nanoparticles in graphene aerogels leads to improved hydrogen gas sensing performance. For polymer derived ceramics (PDCs) composites with anisotropic electrical properties, the fabrication of composites was realized by embedding anisotropic reduced graphene oxide aerogels (rGOAs) into the PDCs matrix. Raman spectroscopy and X-ray diffraction studies of PDCs composites with and without graphene indicate that graphene facilitates the transition from amorphous carbon to graphitic carbon in the PDCs. For composites composed of PDCs and edge functionalized graphene oxide (EFGO), bulk PDCs based composites with embedded graphene networks show high electrical conductivity, high thermal stability, and low thermal conductivity. For the study of poly(3-hexylthiophene) (P3HT) crystallization on graphitic substrates (i.e. carbon nanotubes, carbon fibers and graphene), different types of P3HT nanocrystals (i.e. nanowires, nanoribbons, and nanowalls) were observed. The type of nanocrystals grown from graphitic substrates depends on the curvature of graphitic substrates, the molecular weight of P3HT molecules, and the concentration of P3HT marginal solutions. Besides, both specific surface area and curvature of graphitic substrates have major effects on P3HT crystallization processes.
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Date Issued: 2018
Identifier: CFE0007095, ucf:51961
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007095

Title: Engaging and Enacting Writing in First-Year Composition: Re-Imagining Student Self-Efficacy in Writing.
Creator: Tripp, Mary, Wardle, Elizabeth, Pigg, Stacey, Scott, John, Slomp, David, University of Central Florida
Abstract / Description: According to educational theory, learning to write necessitates self-belief that one is capable of performing required tasks. This belief is called self-efficacy, a component of human agency. Students who enter First-Year Composition (FYC), are often unaware of the writing challenges that lie ahead, and many educational psychologists posit that self-efficacy beliefs are the most important factor in meeting these writing challenges. While socio-cognitive theory shapes views of self-efficacy in...
Show moreAccording to educational theory, learning to write necessitates self-belief that one is capable of performing required tasks. This belief is called self-efficacy, a component of human agency. Students who enter First-Year Composition (FYC), are often unaware of the writing challenges that lie ahead, and many educational psychologists posit that self-efficacy beliefs are the most important factor in meeting these writing challenges. While socio-cognitive theory shapes views of self-efficacy in education literature, to date, measures of self-efficacy in writing have focused only on the individual cognitive beliefs as they influence writing performance outcomes. However, current research in writing studies as well as posthuman theories of agency point to a broader, more contextually-bound view of agency for writing as emergent and enacted in socially constructed systems.This dissertation challenges the current view of self-efficacy as it is described in the educational literature as well as the ways in which self-efficacy in writing is measured, suggesting instead that self-efficacy beliefs and learning to write are deeply contextualized. In this dissertation, I examine student self-efficacy in writing using the lens of activity theory, not only as a set of stated individual beliefs but also as belief-in-action measured as images on writing maps, subtle shifts in language and talk about writing, as well as changes in writing practices. More importantly, I examine the agency that is constructed in the social system of FYC classrooms which may only later become internalized individual beliefs about abilities to write. My study suggests that self-efficacy beliefs are not bound by inside the head as belief about performing certain rules for writing, but instead self-efficacy beliefs about writing are emergent and enacted and bound to particular writing systems. Lingering feelings of agency forworking in particular systems can move with students to similar systems; however, strong beliefs about writing as fixed and rule-bound can actually hinder how much students learn in FYC. The evidence suggests that self-efficacy in writing may be better theorized as writing efficacy, emergent agency for writing that strengthens as participants become engaged in working toward the motives of a writing system.
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Date Issued: 2012
Identifier: CFE0004447, ucf:49336
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004447

Title: PREVENTION OF ENVIRONMENTALLY INDUCED DEGRADATION IN CARBON/EPOXY COMPOSITE MATERIAL VIA IMPLEMENTATION OF A POLYMER BASED COATING SYSTEM.
Creator: Tipton, Bradford, Sohn, Yongho, University of Central Florida
Abstract / Description: As the use of fiber reinforced plastics increases in such industries as aerospace, wind energy, and sporting goods, factors effecting long-term durability, such as environmental exposure, are of increasing interest. The primary objectives of this study were to examine the effects of extensive environmental exposure (specifically UV radiation and moisture) on carbon/epoxy composite laminate structures and to determine the relative effectiveness of polymer-based coatings at mitigating...
Show moreAs the use of fiber reinforced plastics increases in such industries as aerospace, wind energy, and sporting goods, factors effecting long-term durability, such as environmental exposure, are of increasing interest. The primary objectives of this study were to examine the effects of extensive environmental exposure (specifically UV radiation and moisture) on carbon/epoxy composite laminate structures and to determine the relative effectiveness of polymer-based coatings at mitigating degradation incurred due to such exposure. Carbon/epoxy composite specimens, both coated and uncoated, were subjected to accelerated weathering in which prolonged outdoor exposure was simulated by controlling the radiation wavelength (in the UV region), temperature, and humidity. Mechanical test data obtained for the uncoated specimens indicated a reduction in strength of approximately 6% after an environmental exposure duration of 750 hours. Test data revealed that no further degradation occurred with increased exposure duration. This reduction resulted from the erosion of the epoxy matrix in additional to the formation of matrix microcracks. The protective coatings evaluated were all epoxy based and included two different surfacing films applied during initial cure of the carbon/epoxy composite laminate and a chromate containing epoxy based paint primer applied after the cure was complete. Although the chromate primer performed well initially, degradation of the underlying substrate was detected with extended exposure durations. In contrast, the surfacing films provided superior protection against environmentally induced degradation. Although similar degradation attributes were identified in the surfacing film as observed in the uncoated composite, it is likely that this degradation was either confined within the surfacing film layer or only penetrated the very near surface of the carbon/epoxy substrate, as it did not result in a substantial reduction in mechanical strength.
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Date Issued: 2008
Identifier: CFE0002406, ucf:47731
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002406

Title: ANALYSIS OF KOLMOGOROV'S SUPERPOSITION THEOREM AND ITS IMPLEMENTATION IN APPLICATIONS WITH LOW AND HIGH DIMENSIONAL DATA.
Creator: Bryant, Donald, Li, Xin, University of Central Florida
Abstract / Description: In this dissertation, we analyze Kolmogorov's superposition theorem for high dimensions. Our main goal is to explore and demonstrate the feasibility of an accurate implementation of Kolmogorov's theorem. First, based on Lorentz's ideas, we provide a thorough discussion on the proof and its numerical implementation of the theorem in dimension two. We present computational experiments which prove the feasibility of the theorem in applications of low dimensions (namely, dimensions...
Show moreIn this dissertation, we analyze Kolmogorov's superposition theorem for high dimensions. Our main goal is to explore and demonstrate the feasibility of an accurate implementation of Kolmogorov's theorem. First, based on Lorentz's ideas, we provide a thorough discussion on the proof and its numerical implementation of the theorem in dimension two. We present computational experiments which prove the feasibility of the theorem in applications of low dimensions (namely, dimensions two and three). Next, we present high dimensional extensions with complete and detailed proofs and provide the implementation that aims at applications with high dimensionality. The amalgamation of these ideas is evidenced by applications in image (two dimensional) and video (three dimensional) representations, the content based image retrieval, video retrieval, de-noising and in-painting, and Bayesian prior estimation of high dimensional data from the fields of computer vision and image processing.
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Date Issued: 2008
Identifier: CFE0002236, ucf:47909
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002236

Title: Microstructual Characteristics of Magnesium Metal Matrix Composites.
Creator: Shin, Dongho, Sohn, Yongho, Coffey, Kevin, Suryanarayana, Challapalli, University of Central Florida
Abstract / Description: Magnesium (Mg) Metal matrix composites (MMCs) reinforced by ceramic reinforcements are being developed for a variety of applications in automotive and aerospace because of their strength-to-weight ratio. Reinforcement being considered includes SiC, Al2O3, Carbon fiber and B4C in order to improve the mechanical properties of MMCs. Microstructural and interfacial characteristics of MMCs can play a critical role in controlling the MMCs' mechanical properties. This study was carried out to...
Show moreMagnesium (Mg) Metal matrix composites (MMCs) reinforced by ceramic reinforcements are being developed for a variety of applications in automotive and aerospace because of their strength-to-weight ratio. Reinforcement being considered includes SiC, Al2O3, Carbon fiber and B4C in order to improve the mechanical properties of MMCs. Microstructural and interfacial characteristics of MMCs can play a critical role in controlling the MMCs' mechanical properties. This study was carried out to understand the microstructural and interfacial development between Mg-9wt.Al-1wt.Zn (AZ91) alloy matrix and several reinforcements including SiC, Al2O3, Carbon fibers and B4C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy was employed to investigate the microstructure and interfaces. Al increase in hardness due to the presence of reinforcements was also documented via Vicker's hardness measurements. Thermodynamic consideration based on Gibbs free energy was employed along with experimental results to describe the interfacial characteristics of MMCs. Reaction products from AZ91-SiC and AZ91-Al2O3 interfaces were identified as MgO, since the surface of SiC particles is typically covered with SiO2 and the MgO is the most thermodynamically stable phase in these systems. The AZ91-Carbon fiber interface consist of Al4C3 and this carbide phase is considered detrimental to the mechanical toughness of MMCs. The AZ91-B4C interface was observed to contain MgB2 and MgB2C2. In general, Vicker's hardness increased by 3X due to the presence of these reinforcements.
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Date Issued: 2012
Identifier: CFE0004441, ucf:49324
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004441

Title: WHAT IS COLLEGE-LEVEL WRITING? -THE COMMON GROUND FROM WHICH A NEW SECONDARY – POST SECONDARY COMPOSITION PARTNERSHIP CAN BE FORMED.
Creator: Berger, Nancy, Bell, Kathleen, University of Central Florida
Abstract / Description: In the Introduction to What is "College-Level" Writing?, editors Patrick Sullivan and Howard Tinberg state that the title asks "one of the most important questions in our profession" (xiii). However, even after 418 pages of essays written from the perspectives of high school teachers, college instructors, students, and administrators, the answer remains elusive because college-level writing does not, in fact, start in college - it starts in high school - where high school teachers believe...
Show moreIn the Introduction to What is "College-Level" Writing?, editors Patrick Sullivan and Howard Tinberg state that the title asks "one of the most important questions in our profession" (xiii). However, even after 418 pages of essays written from the perspectives of high school teachers, college instructors, students, and administrators, the answer remains elusive because college-level writing does not, in fact, start in college - it starts in high school - where high school teachers believe they are instilling in their college-bound students the writing skills required by post-secondary institutions. The students, meanwhile, show up in first-year composition classes to find not only have they not been prepared for college-level writing, they haven't the faintest idea what college-level writing is. Our students have more writing demands on them now than ever before -- both in and outside of academia -- what past CCCC president, Douglas D. Hesse, terms "obliged" and "self-sponsored" writing (349). The job market has gone global and careerism is a reality for the college graduates of today. Yet, college writing instruction represents the last chance students have to learn the rhetorical traditions behind the writing skills, along with the realization that without an understanding of process and purpose, the products they do produce will never reach full potential. It is this seemingly dichotomic relationship between the "global village" job market and the rhetorical tradition that has created the exigence for this research. This study examines twelfth grade English and first-year college composition instruction from the three perspectives comprising the College Writing Contact Zone rhetorical triangle (practitioners-professional organizations-textbooks). Following the model of analysis used by Patrick Sullivan and Howard Tinberg in What is "College-Level" Writing, essays and articles written by high school teachers and first-year composition instructors involved in the "what is college-level writing?" conversation are discussed, examining each for the common threads running throughout their different viewpoints. The curricula at both the 12th grade high school and first-year college levels is also researched, in light of the mandates instituted by the professional organizations of the discipline (the NCTE and CCCC). Specifically examined are the roles these respective professional organizations played in the evolution of 12th grade high school English classes and the first-year college composition course, as we know them today. Finally, the textbooks, which inform the curricula of 12th grade high school English and first-year college composition, are investigated in regards to scope and sequence, assumptions, and authorship. The learning theories driving the textbooks are then used to construct the definition of college-level writing from the perspective of textbook publishers. The answer to the "What is college-level writing?" question emerging from this research is not what one might expect. College-level writing, as an entity, does not exist because college-level writing is the result of college-level discourse literacy. Since first year college students must step outside their comfort zone into Pratt's contact zone, perhaps, "instead of asking how to make high school writing prepare students for college writing ,. . ." we should be asking what literacy looks like"(Thompson 80). Making students aware of the different discourse communities in existence at the college level (Hesse's self-sponsored and obliged) is the first step in their being able to learn what writing is considered appropriate within each discourse community. What is needed is a new paradigm in the form of a transitional composition class that cultivates students as critically thinking writers who are the experts of their own thoughts and ideas. Whether this class belongs in the twelfth grade curriculum or the first-year college curriculum needs to be determined, but its absence is the missing link responsible for the non-transference of writing skills from the high school to the college level, as well as the non-transference of writing skills beyond the first-year composition class within academia. Our high schools, recognizing the fact that all of their twelfth grade English students are not going on to college, teach the writing skills and reading analyses needed for post-secondary school life – whatever that may be. First-year composition instructors assign their essays and research papers expecting their students to already be well-versed in the self-sponsored and obliged discourses of the academy – but they are not. The contact zone is created and the conflict begins because students need to access those discourses if they are to start creating self-sponsored knowledge of their disciplines. It is this 'knowing,' this created knowledge, that transforms our students into writers; the writers for whom we are the stewards.
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Date Issued: 2007
Identifier: CFE0001878, ucf:47419
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001878

Title: FEASIBILITY STUDY OF LIGHTWEIGHT HIGH-STRENGTH HOLLOW CORE BALSA-FRP COMPOSITE BEAMS UNDER FLEXURE.
Creator: O'Neill, Kevin, Mackie, Kevin, University of Central Florida
Abstract / Description: The United States of AmericaÃ‚Â's Military, more specifically the Army, has since the late 1990Ã‚Â's had a vested interest in the development of super-lightweight, portable, short-span composite bridge and decking components to replace aging heavy metal-alloy machine driven modular systems. The following study looks at the feasibility of using balsa wood as the structural core material in fiber reinforced polymer (FRP) wrapped hollow-core composites...
Show moreThe United States of AmericaÃ‚Â's Military, more specifically the Army, has since the late 1990Ã‚Â's had a vested interest in the development of super-lightweight, portable, short-span composite bridge and decking components to replace aging heavy metal-alloy machine driven modular systems. The following study looks at the feasibility of using balsa wood as the structural core material in fiber reinforced polymer (FRP) wrapped hollow-core composites in short-span bridge applications. The balsa provides shear resistance and the FRP the flexural resistance, resulting in extremely high strength-to-weight and strength-to-depth ratios. Several scaled short span specimens were constructed and tested using a variety of fibers and resins. In addition, a calibrated finite element model (FEM) was developed using data acquired through testing. Of the 3 FRP-matrices tested (carbon-polyurethane, glass-polyurethane, and carbon-epoxy-resin), the carbon-epoxy-resin had the stiffest cross-section and highest ultimate load achieved, although the fiber did not have the highest elastic modulus and ultimate rupture strength of the constituent materials. The carbon-polyurethane fiber had the largest elastic modulus and ultimate strength, but due to construction difficulties did not perform as well as expected. The glass-polyurethane fiber had the lowest elastic modulus and ultimate load with high strain values and performed accordingly during specimen testing. Given the constraints of self-weight, section geometry, and deflection set forth for lightweight short-span portable bridging solutions, this study demonstrates that the balsa-FRP composite systems are viable solutions; in particular, when carbon fabric is paired with balsa cores.
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Date Issued: 2010
Identifier: CFE0002997, ucf:47931
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002997

$A modeling framework of brittle and ductile fractures coexistence in composites$

Title: A modeling framework of brittle and ductile fractures coexistence in composites.
Creator: Qiao, Yangyang, Bai, Yuanli, Gou, Jihua, Kassab, Alain, Gordon, Ali, An, Linan, University of Central Florida
Abstract / Description: In order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites ...
Show moreIn order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites (CMCs) according to their matrix materials.A set of mechanical experiments ranging from micro scale (single fiber composite and thin film composite) to macro scale (PMCs and MMCs) were conducted to fully understand the material behavior of composite materials. Loading conditions investigated includes uniaxial tension, three-point bending, uniaxial compression, simple shear, tension combined with shear, and compression combined with shear.For single fiber composite and thin-film composite, details of each composition are modelled. For the PMCs and MMCs which have plenty of reinforcements like fibers and particles, the details of the composition of structures cannot be modelled due to the current limitations of computing power. A mechanics framework of composite materials including elasticity, plasticity, failure initiation and post failure softening is proposed and applied to two types of composite materials.Uniaxial tension loading is applied to several single fiber composites and thin film composites. A surprising phenomenon, controllable and sequential fragmentation of the brittle fiber to produce uniformly sized rods along meters of polymer cladding, rather than the expected random or chaotic fragmentation, is observed with a necking propagation process. A combination of necking propagation model, fiber cracking model and interfacial model are proposed and applied to the finite element simulations. Good predictions of necking propagation and uniform fragmentation phenomenon are achieved. This modeling method of the micro-scale phenomenon reveals the physics inside composites in micro scale and helps the understanding of the process of nano fragmentation.Unidirectional carbon fiber composites were tested under multi-axial loading conditions including tensile/compression/shear loadings along and perpendicular to the fiber direction. Compression dominated tests showed a brittle fracture mode like local kicking/buckling, while tension dominated tests showed a fracture mode like delamination and fiber breakage. Simple shear tests with displacement control showed matrix material hardening and softening before total failure. The proposed modeling framework is successfully applied to the PMCs. A new parameter ? was introduced to represent different loading conditions of PMCs. Numerical simulations using finite element method well duplicated the anisotropic elasticity and plasticity of this material. Failure features like delamination was simulated using cohesive surface feature. It is also applied to carbon fiber composite laminates to further validate the proposed model.A round of experimental study on high volume fraction of metallic matrix nano composites was conducted, including uniaxial tension, uniaxial compression, and three-point bending. The example materials were two magnesium matrix composites reinforced with 10 and 15% vol. SiC particles (50nm size). Brittle fracture mode was exhibited under uniaxial tension and three-point bending, while shear dominated ductile fracture mode (up to 12% fracture strain) was observed under uniaxial compression. Transferring the Modified Mohr Coulomb (MMC) ductile fracture model to the stress based MMC model (sMMC), the proposed modeling framework is applied to this material. This model has been demonstrated to be capable of predicting the coexistence of brittle and ductile fracture modes under different loading conditions for MMCs. Numerical simulations using finite element method well duplicated the material strength, fracture initiation sites and crack propagation modes of the Mg/SiC nano composites with a good accuracy.
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Date Issued: 2018
Identifier: CFE0007078, ucf:51977
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007078

Title: Piezoresistive Behavior of Carbon Nanopaper Polymer Composites for Strain Sensing.
Creator: Beyrooti, Jayden, Kwok, Kawai, Gou, Jihua, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Carbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to...
Show moreCarbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to providing electrical heat actuation for the shape memory effect in polymers. This study focuses on strain sensing capabilities by developing a numerical model to predict piezoresistive behavior. The piezoresistive effect is a change in resistivity of a conductive network when a deformation is applied. This allows strain to be determined by simply measuring the electrical resistance. An equivalent resistor network can be formed to represent the fiber network. The proposed 2D model generates randomly oriented fibers inside a unit cell, determines their intersection points, and creates a mesh of the network for finite element analysis. Electrical conductivity is found for the initial and deformed fiber states by determining the current through the network for a known voltage. A piezoresistivity experimental study is conducted to investigate the strain sensing abilities of this material and validate model results. This simple model provides an initial framework that can be developed in future work. Despite its 2D nature, the model captures the governing mechanisms of piezoresistivity to a certain extent.
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Date Issued: 2019
Identifier: CFE0007788, ucf:52353
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007788

Title: Enhancing CNT Composites with Raman Spectroscopy.
Creator: Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Zhai, Lei, University of Central Florida
Abstract / Description: Carbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The...
Show moreCarbon Nanotubes (CNTs) have been the subject of intense research for their potential to improve a variety of material properties when developed as nano-composites. This research aims to address the challenges that limit the ability to transfer the outstanding nano-scale properties of CNTs to bulk nano-composites through Raman characterization.These studies relate the vibrational modes to microstructural characterization of CNT composites including stress, interface behavior, and defects. The formulation of a new fitting procedure using the pseudo-Voigt function is presented and shown to minimizethe uncertainty of characteristics within the Raman G and D doublet. Methods for optimization of manufacturing processes using the Raman characterization are presentedfor selected applications in a polymer multiwalled nanotube (MWNT) composite andlaser-sintered ceramic-MWNT composite. In the first application, the evolution of theMWNT microstructure throughout a functionalization and processing of the polymer-MWNT composite was monitored using the G peak position and D/G intensity ratio.Processing parameters for laser sintering of the ceramic-MWNT composites were optimized by obtaining maximum downshift in stress sensitive G-band peak position, whilekeeping disorder sensitive D/G integrated intensity ratio to a minimum. Advanced Raman techniques, utilizing multiple wavelengths, were used to show that higher excitationenergies are less sensitive to double resonance Raman effects. This reduces their ininfluence and allows the microstructural strain in CNT composites to be probed more accurately. The use of these techniques could be applied to optimize any processing parameters in the manufacturing of CNT composites to achieve enhanced properties.
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Date Issued: 2011
Identifier: CFE0004110, ucf:49098
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004110

Title: ON THE USE OF POLYURETHANE MATRIX CARBON FIBER COMPOSITES FOR STRENGTHENING CONCRETE STRUCTURES.
Creator: Haber, Zachary, Mackie, Kevin, University of Central Florida
Abstract / Description: Fiber-reinforced polymer (FRP) composite materials have effectively been used in numerous reinforced concrete civil infrastructure strengthening projects. Although a significant body of knowledge has been established for epoxy matrix carbon FRPs and epoxy adhesives, there is still a need to investigate other matrices and adhesive types. One such matrix/adhesive type yet to be heavily researched for infrastructure application is polyurethane. This thesis investigates use of polyurethane matrix...
Show moreFiber-reinforced polymer (FRP) composite materials have effectively been used in numerous reinforced concrete civil infrastructure strengthening projects. Although a significant body of knowledge has been established for epoxy matrix carbon FRPs and epoxy adhesives, there is still a need to investigate other matrices and adhesive types. One such matrix/adhesive type yet to be heavily researched for infrastructure application is polyurethane. This thesis investigates use of polyurethane matrix carbon fiber composites for strengthening reinforced concrete civil infrastructure. Investigations on mirco- and macro-mechanical composite performance, strengthened member flexural performance, and bond durability under environmental conditioning will be presented. Results indicate that polyurethane carbon composites could potentially be a viable option for strengthening concrete structures.
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Date Issued: 2010
Identifier: CFE0003073, ucf:48307
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003073

Title: PERCOLATION STUDY OF NANO-COMPOSITE CONDUCTIVITY USING MONTE CARLO SIMULATIONPERCOLATION.
Creator: Bai, Jing, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: A Monte Carlo model is developed for predicting electrical conductivity of carbon nanofiber composite materials. The conductive nanofibers are models as both 2D and 3D network of finite sites that are randomly distributed. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the percolation threshold. The effect of the nanofiber aspect ratio on the critical nanofiber volume rate is investigated in the current model, each of the...
Show moreA Monte Carlo model is developed for predicting electrical conductivity of carbon nanofiber composite materials. The conductive nanofibers are models as both 2D and 3D network of finite sites that are randomly distributed. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the percolation threshold. The effect of the nanofiber aspect ratio on the critical nanofiber volume rate is investigated in the current model, each of the nanofibers needs five independent geometrical parameters (i.e., three coordinates in space and two orientation angles) for its identification. There are three controlling parameters for each nanofiber, which includes the nanofiber length, the nanofiber diameter, and the nanofiber aspect ratio. The simulation results reveal a relationship between the fiber aspect ratio and the percolation threshold: the higher the aspect ratio, the lower the threshold. With the simulation results obtained from the Monte Carlo model, the effective electrical conductivity of the composite is then determined by assuming the conductivity is proportional to the ratio of the number of nanofibers forming the largest cluster to the total number of nanofibers. The numerical results indicate that as the volume rate reaches a critical value, the conductivity starts to rise sharply. These obtained simulation results agree fairly with experimental and numerical data published earlier by others. In addition, we investigate the convergence of the current percolation model. We also find the tunneling effect does not affect the critical volume rate greatly. We propose that the percolation model is not scalable as well.
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Date Issued: 2009
Identifier: CFE0002644, ucf:48230
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002644

Title: INTER-INSTITUTIONAL COMPARISON OF FACULTY PERCEPTIONS ON THE PURPOSE OF FRESHMAN YEAR COMPOSITION PROGRAMS.
Creator: Branciforte, Rosemarie, Kaplan, Jeffrey, University of Central Florida
Abstract / Description: The purpose of this study is an investigation of instructors' perceptions of composition learning objectives focusing on which should be taught and which should be emphasized. The researcher observed that instructors do not regard all course objectives in English Composition courses equally; emphasizing some and giving others brief consideration. From this observation, this study was developed to measure objectives as well as to examine principal reasons for the differences in perception....
Show moreThe purpose of this study is an investigation of instructors' perceptions of composition learning objectives focusing on which should be taught and which should be emphasized. The researcher observed that instructors do not regard all course objectives in English Composition courses equally; emphasizing some and giving others brief consideration. From this observation, this study was developed to measure objectives as well as to examine principal reasons for the differences in perception. Using an 18-question (16 content area and two demographic) survey based on content areas chosen to mirror general learning objectives in composition courses, along with six focused interviews, the researcher discovered some levels of agreement, some of disagreement, and some areas of neutrality. The researcher has established some connections and some disconnects between some of the general learning objectives from English Composition courses, which are intriguing and thought provoking. Since instructors deliver instruction using learning objectives as the goals to be achieved in the English Composition courses they teach, it is prudent to be concerned with how these objectives are perceived and implemented by the users. The data collected conclusively reflects instructors' perceptions of learning objectives are not all the same. As the researcher measured instructors' perceptions of English Composition learning objectives, the results demonstrate that there are stronger relationships with some of the learning objectives, and some objectives have no relationships; some objectives are well matched and others are not. The purpose of this study, understanding relationships between instructors' perceptions of learning objectives in FY English Composition courses, will provide us with research to help improve objectives and positively impact instruction.
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Date Issued: 2011
Identifier: CFE0003764, ucf:48742
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003764

Title: Carbon nanotube (CNT) metallic composite with focus on processing and the resultant properties.
Creator: Billah, Md Muktadir, Chen, Quanfang, Bai, Yuanli, An, Linan, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Metal-carbon nanotubes (CNTs) composites are the promising advanced materials that are being developed to take the advantage of the exceptional properties of CNTs. Because of the intrinsically strong in-plane atomic SP2 bonding CNTs offer high young's modulus (1.0(-)1.8 TPa), high tensile strength (30(-)200 GPa) and high elongation at break (10(-)30%). The thermal conductivity of individual single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are about 6000 W/m-K and...
Show moreMetal-carbon nanotubes (CNTs) composites are the promising advanced materials that are being developed to take the advantage of the exceptional properties of CNTs. Because of the intrinsically strong in-plane atomic SP2 bonding CNTs offer high young's modulus (1.0(-)1.8 TPa), high tensile strength (30(-)200 GPa) and high elongation at break (10(-)30%). The thermal conductivity of individual single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are about 6000 W/m-K and 3000 W/m-K, respectively. Therefore it is expected that by incorporation of CNTs in metal matrices multi-functional composites can be used ideally as thermal interface materials, light-weight high-strength structural materials, electric components, optical devices, electromagnetic absorption materials etc. However, so far results are far from satisfied for CNT composites, mainly due to the fact that there are two main key issues remained without good solutions for CNT composites: the poor uniformity in CNT dispersion and the weak interfacial bonding between CNTs and the matrices. In this study, MWCNTs were functionalized and coated with metals like Cu and Ni by electroless deposition methods prior to their application. Metal coatings result in strong interfacial bonding at CNT-metal interfaces and uniform dispersion. During metal coating processes CNTs are physically separated in electrolyte and after coating they get physically retain the separation by the coated metal layer that they are not allowed to aggregate to form bundles. Moreover, after metal coating, the resultant density of Ni-coated MWCNTs is close to that of molten metal matrix. This prevent separation of CNTs due to buoyancy effects and results in uniform dispersion. Metal coating on CNTs surfaces also allows to form strong interfacial bonding with the metal matrices.SnBi alloy has been identified as novel lead-free thermal interface material (TIM) for electronics packaging. However the thermal conductivity and the mechanical strength of pure SnBi alloy are not sufficient to withstand harsh environment imposed by powder electronics. Therefor how to increase the thermal conductivity and the mechanical strength of SnBi solders becomes important. In this study, MWCNTs have been added into SnBi alloy to form SnBi/CNT composite solders by different material processing methods. First, in sandwich method Cu-coated CNTs were added to the 70Sn-30Bi alloy and mixed mechanically. UTS was increased by 47.6% for 3 wt. % Cu/CNTs addition. Second. Ni-coated CNTs were added by sonication assisted melting method in fabricating 70Sn-30Bi solder. For 3 wt. % Ni-coated MWCNTs, equivalent to 0.6 wt. % pure MWCNTs, UTS and YS were increased by 88.8 % and 112.3% respectively. In addition the thermal conductivity was also increased by more than 70%. Ni-coated CNTs were also added to pure Al by powder metallurgy method. For 7 wt. % Ni/CNTs having diameter 30-50 nm, UTS and YS were increased by 92.7% and 101.6% respectively. For CNTs having diameter 8-15 nm, UTS and YS were increased by 108.9% and 128.2% respectively for 7 wt. % addition. All these results are first time obtained that are much greater than published data on CNT/metal composites. Results discussion and mechanism in reinforcement were also presented.
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Date Issued: 2017
Identifier: CFE0006567, ucf:51320
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006567

Title: Low Strain Rate Studies of Alumina Epoxy Composites using Piezospectroscopy.
Creator: Jones, Ashley, Raghavan, Seetha, Gordon, Ali, Vaidyanathan, Rajan, University of Central Florida
Abstract / Description: Particulate composites are widely used in many aerospace and military applications as energetic materials, armor materials or coatings and their behavior under dynamic loads have gained increasing significance. The addition of modifiers such as alumina nanoparticles generally facilitates the improvement of the mechanical strength to density ratio due to high specific area and particle rigidity. This allows for sufficient particle-matrix bonding and therefore improved stiffness and load...
Show moreParticulate composites are widely used in many aerospace and military applications as energetic materials, armor materials or coatings and their behavior under dynamic loads have gained increasing significance. The addition of modifiers such as alumina nanoparticles generally facilitates the improvement of the mechanical strength to density ratio due to high specific area and particle rigidity. This allows for sufficient particle-matrix bonding and therefore improved stiffness and load transfer in the composite. Photo-luminescent ?-alumina nanoparticles when embedded in an epoxy matrix allow for the added benefit of in situ measurements at low strain rates to provide stress-sensitive information using the particle piezospectroscopic (PS) property. To investigate the low strain rate behavior, cylindrical specimens of alumina-epoxy composites with varying volume fractions of alumina were fabricated using a casting process to ensure minimal surface finishing and reduced manufacturing time. The results illustrate the capability of alumina nanoparticles to act as diagnostic sensors to measure the stress-induced shifts of the spectral R-line peaks resulting from low compressive strain rates. The range of PS coefficients measured, -3.15 to -5.37 cm^-1/GPa for R1 and -2.62 to -5.39 cm^-1/GPa for R2, correlate well with static test results of similar volume fractions. Results reveal a general trend of increasing sensitivity of the PS coefficients with increasing strain rate when compared to similar materials under static conditions. In contrast to static results, at a given strain rate, the PS coefficients show varying degrees of sensitivity for each volume fraction. This information can be used to determine the time-dependent micro-scale stresses the nanoparticles sustain during composite loading. Additionally, this work facilitates failure prediction by monitoring upshifts in the PS information. Calibration of the in situ diagnostic stress sensing capabilities of varying volume fractions of alumina nanocomposites under quasi-static strain rates in this work sets the precedent for future studies at high strain rates.
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Date Issued: 2013
Identifier: CFE0005099, ucf:50728
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005099

Title: SILENT OUTSIDERS: SEARCHING FOR QUEER IDENTITY IN COMPOSITION READERS.
Creator: Duncan, Travis, Wallace, David, University of Central Florida
Abstract / Description: ABSTRACT This study searches twenty composition readers' table of contents for the degree of inclusivity of queer people and issues. Four means of erasure are labeled as possible erasing of queer identity: presuming heteronormativity, overt homophobia, perpetuating tokenism, and pathologizing queer identity. The presence of other differences are compared to the number of times that queer identity is referenced in the table of contents. The final portion of the analysis examines the two...
Show moreABSTRACT This study searches twenty composition readers' table of contents for the degree of inclusivity of queer people and issues. Four means of erasure are labeled as possible erasing of queer identity: presuming heteronormativity, overt homophobia, perpetuating tokenism, and pathologizing queer identity. The presence of other differences are compared to the number of times that queer identity is referenced in the table of contents. The final portion of the analysis examines the two most inclusive composition readers to understand more clearly how the readers present queer individuals and issues. In a sense, I want to explore the question of how often queer people are discussed or addressed and in what forms within these composition readers. My hope is to develop a means for instructors and students to investigate whether or not, and in what ways a composition reader prescribes presence for the queer individual.
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Date Issued: 2006
Identifier: CFE0001413, ucf:47051
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001413

Title: METHOD TO DISCRETIZE CONTINUOUS GRADIENT STRUCTURES AND CALCULATE THERMAL RESIDUAL STRESSES WITHIN LAYERED FUNCTIONALLY GRADED CERAMICS.
Creator: Neale, Ryan E, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Functionally graded materials (FGMs) are an advanced class of material which seeks to leverage the strengths of one material to mitigate the weaknesses of another. This allows for operation in extreme environments or conditions where materials properties must change at various locations within a structure. Fabrication of this advanced class of material is limited due to geometric, economic, and material constraints inherent in the various methods. For this reason, a model was developed to...
Show moreFunctionally graded materials (FGMs) are an advanced class of material which seeks to leverage the strengths of one material to mitigate the weaknesses of another. This allows for operation in extreme environments or conditions where materials properties must change at various locations within a structure. Fabrication of this advanced class of material is limited due to geometric, economic, and material constraints inherent in the various methods. For this reason, a model was developed to discretize continuous gradient curves to allow for the use of a step-wise approximations to such gradients. These alternative step-wise gradients would allow for the use of numerous manufacturing techniques which have improved composition control, cost of processing, cost of equipment, and equipment availability. One such technique, tape casting, was explored due to its robustness and ability to create layered ceramics. Since ceramics are inherently brittle materials, they serve to be strengthened by the thermal residual stresses that form in the creation of these step-wise graded composites. With models to calculate these residual stresses and determine step-wise approximations of various compositional gradients, the process of designing these layered ceramics can be significantly improved.
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Date Issued: 2019
Identifier: CFH2000530, ucf:45633
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000530

Title: Mechanical Properties and Thermal Residual Stresses of ZrB2-SiC Ceramic Composites for Hypersonic Vehicle Applications.
Creator: Stadelmann, Richard, Orlovskaya, Nina, Kumar, Ranganathan, Raghavan, Seetha, University of Central Florida
Abstract / Description: Ultra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB)...
Show moreUltra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB) fracture toughness were measured. In addition, in-situ bending experiments under a Raman microscope were performed to determine the piezo-spectroscopic coefficients of SiC Raman active peaks for calculation of thermal residual stresses. The results show that these materials are possible candidates for hypersonic air-breathing vehicles due to their high Young's modulus, ability to withstand high temperatures, and relatively low densities.
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Date Issued: 2013
Identifier: CFE0005060, ucf:49945
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005060

Title: Functional Scaffolding for Musical Composition: A New Approach in Computer-Assisted Music Composition.
Creator: Hoover, Amy, Stanley, Kenneth, Wu, Annie, Laviola II, Joseph, Anderson, Thaddeus, University of Central Florida
Abstract / Description: While it is important for systems intended to enhance musical creativity to define and explore musical ideas conceived by individual users, many limit musical freedom by focusing on maintaining musical structure, thereby impeding the user's freedom to explore his or her individual style. This dissertation presents a comprehensive body of work that introduces a new musical representation that allows users to explore a space of musical rules that are created from their own melodies. This...
Show moreWhile it is important for systems intended to enhance musical creativity to define and explore musical ideas conceived by individual users, many limit musical freedom by focusing on maintaining musical structure, thereby impeding the user's freedom to explore his or her individual style. This dissertation presents a comprehensive body of work that introduces a new musical representation that allows users to explore a space of musical rules that are created from their own melodies. This representation, called functional scaffolding for musical composition (FSMC), exploits a simple yet powerful property of multipart compositions: The pattern of notes and rhythms in different instrumental parts of the same song are functionally related. That is, in principle, one part can be expressed as a function of another. Music in FSMC is represented accordingly as a functional relationship between an existing human composition, or scaffold, and an additional generated voice. This relationship is encoded by a type of artificial neural network called a compositional pattern producing network (CPPN). A human user without any musical expertise can then explore how these additional generated voices should relate to the scaffold through an interactive evolutionary process akin to animal breeding. The utility of this insight is validated by two implementations of FSMC called NEAT Drummer and MaestroGenesis, that respectively help users tailor drum patterns and complete multipart arrangements from as little as a single original monophonic track. The five major contributions of this work address the overarching hypothesis in this dissertation that functional relationships alone, rather than specialized music theory, are sufficient for generating plausible additional voices. First, to validate FSMC and determine whether plausible generated voices result from the human-composed scaffold or intrinsic properties of the CPPN, drum patterns are created with NEAT Drummer to accompany several different polyphonic pieces. Extending the FSMC approach to generate pitched voices, the second contribution reinforces the importance of functional transformations through quality assessments that indicate that some partially FSMC-generated pieces are indistinguishable from those that are fully human. While the third contribution focuses on constructing and exploring a space of plausible voices with MaestroGenesis, the fourth presents results from a two-year study where students discuss their creative experience with the program. Finally, the fifth contribution is a plugin for MaestroGenesis called MaestroGenesis Voice (MG-V) that provides users a more natural way to incorporate MaestroGenesis in their creative endeavors by allowing scaffold creation through the human voice. Together, the chapters in this dissertation constitute a comprehensive approach to assisted music generation, enabling creativity without the need for musical expertise.
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Date Issued: 2014
Identifier: CFE0005350, ucf:50495
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005350

Title: FAILURE MODE IDENTIFICATIONS OF RC BEAMS EXTERNALLY STRENGTHENED WITH CARBON FIBER REINFORCED COMPOSITE.
Creator: O'Riordan-Adjah, Chris, Zhao, Lei, University of Central Florida
Abstract / Description: The application of carbon reinforced-fiber polymers (CFRP) to structures is a new development that is still under intense research. However, the rehabilitation or retrofit of damage reinforced concrete members by the external bonding of CFRP is becoming increasingly popular in the construction industry. The objective of the tests presented in this thesis is to study different CFRP designs on the reinforced concrete beams and compare their failure modes. The main goal is to determine the CFRP...
Show moreThe application of carbon reinforced-fiber polymers (CFRP) to structures is a new development that is still under intense research. However, the rehabilitation or retrofit of damage reinforced concrete members by the external bonding of CFRP is becoming increasingly popular in the construction industry. The objective of the tests presented in this thesis is to study different CFRP designs on the reinforced concrete beams and compare their failure modes. The main goal is to determine the CFRP design on the reinforced concrete beams that result in a progressive and gradual failure mode with enough warning before final failure. Different CFRP designs are investigated and compared with theoretical predictions. A retrofitting concept is also employed in this research. The retrofitting concept is the idea of strengthening cracked structures. The strengthening of the beams performed in the lab is carried out under sustained loads and on previously cracking the beams to simulate the realistic case that is usually faced in practice on the field. The RC beams are strengthened in flexure to double their flexural capacity by applying the adequate amounts of CFRP to the tension face of the beams. Due to the CFRP strengthening and increasing the strength capacity of the beams, different CFRP anchorage methods are employed to the beams for additional shear reinforcement to ensure flexural failure. The different CFRP anchorage methods will also be observed for their effectiveness during the debonding and propagation mechanism as well as evaluated for their progressive failure mode.
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Date Issued: 2004
Identifier: CFE0000288, ucf:46226
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000288

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asteroids (2)	+ -
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coating (2)	+ -
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