Дисертації з теми "Composts collectifs"
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1
Kohli, Alice. "Effets de composts autoproduits et d'un biochar sur le transfert d'éléments trace dans des légumes de jardins familiaux modérément contaminés." Thesis, Rennes, Agrocampus Ouest, 2022. http://www.theses.fr/2022NSARD098.
Анотація:
Les jardins familiaux ont souvent été installés sur des sols urbains sans évaluation préalable du risque sanitaire. Le diagnostic de contamination du sol par des éléments trace comme le plomb (Pb) peut compromettre la poursuite du jardinage. Pour éviter un changement d’usage, l’apport au sol de compost industriel peut être efficace mais le potentiel des composts autoproduits par les jardiniers eux-mêmes doit être évalué. Ce travail de thèse a eu pour premier objectif d’analyser les pratiques de compostage dans les jardins familiaux et sélectionner des composts autoproduits différents en termes de propriétés biochimiques et de contenu en éléments trace. Les pratiques de compostage et la qualité des composts sont très variables. Les composts autoproduits au jardin (domestiques)sont généralement pauvres en matière organique et parfois contaminéscontrairement aux composts autoproduits en pied d’immeuble ou en restauration (collectifs) également utilisés au jardin. Le second objectif a été d’évaluer le risque sanitaire potentiel lié à la consommation de légumes de jardins familiaux modérément contaminés en Pb (100-200 mg.kg-1) amendés avec des composts autoproduits. Pour tenter d’améliorer la remédiation, du biochar a aussi été introduit. Une alimentation composée essentiellement des légumes autoproduits au jardin ne présenterait pas de risque sanitaire mais l’apport de composts autoproduits à une dose élevée (10-20 kg.m-2) a pu augmenter la biodisponibilité de As dans des sols de jardins familiaux. L’apport combiné d’un compost autoproduit et d’un biochar a toutefois limité les transferts de As et de Pb tout en augmentant la biomasse des légumes autoproduitsFor some time, allotment gardens have often been established on urban soils without prior health risk assessment. Soil analysis revealing contamination by trace elements such as lead (Pb) may now compromise the practice of gardening. To prevent a restriction or change of soil use, the introduction of industrial compost to the soil can be efficient, but the potential of composts self-produced by the gardeners themselves must be evaluated. The first objective of this thesis was to analyze composting practices in allotment gardens and select self-produced composts with different biochemical properties and trace element content. The composting practices and the quality of these composts are very variable. Composts self-produced in the garden (home composts) are generally poor in organic matter and sometimes contaminated,contrary to composts self-produced at the foot of buildings or in restoration (community composts) also used in gardens. The second objective was to assess the potential health risk of consuming vegetables from allotment gardens moderately contaminated with Pb (100 - 200 mg.kg-1) amended with self-produced composts. In an attempt to improve remediation, biochar was also introduced into the soil. A diet composed essentially of self-produced vegetables in the garden would not present a health risk, but the addition of self-produced composts at a high dose (10-20 kg.m-2) could increase the bioavailability of As in allotment garden soils. In contrast, the combined addition of self-produced compost and biochar limited the transfer of both As and Pb while simultaneously increasing the biomass of self-produced vegetables
2
Harrison, James A. "Turning compost : a collection of 40 poems." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/7832.
Анотація:
Turning Compost is a collection of forty poems, two of which, Seven Kakhaiku and Tres Troubled Triolets, are multiple poems intended to be read as units. The poems have been ordered so that there is a flow of connected or contrasting ideas from poem to poem, therefore it is recommended that they be read in the order presented. The themes covered by the poems are varied, but principal amongst them are memory, nature, dreams and symbols, family and friends, and the search for meaning; they appear in roughly that order. Death, and its challenges to meaning, is a theme which recurs throughout the collection, something which is reflected in the collection's title which is borrowed from one of the poems. Included is one poem, Pig People, which was written specifically for children. The poems are written in a variety of forms, evincing the poet's conscious rejection of stylistic consistency as a goal in developing his voice.
3
Taliani, Alexandra R. "An Annotated Catalog of the Music of Eusebia Simpson Hunkins in the Music and Dance Library Special Collections Room and the Mahn Center for Archives and Special Collections of Ohio University." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1587141633610687.
4
Demchyna, O. I., I. Yu Yevchuk, and R. Y. Musiy. "Nanostructed Organic-inorganic Composite for Application in Fuel Cells and Solar Collectors." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35382.
Анотація:
The paper describes the synthesis of nanostructed organic-inorganic composites using sol-gel technique.
The presence of sulfocontaining monomer (3-sulfopropyl acrylate potassium salt) in obtained
comonomer provides its proton conductive properties. Proton conductivity depending on temperature was
determined by means of impedance spectrometry. Nanostructed organic-inorganic composites have been
applied for obtaining thermoabsorbing coatings for solar collectors.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35382
5
Morel, Matthieu. "Composants pour la grille." Phd thesis, Université de Nice Sophia-Antipolis, 2006. http://tel.archives-ouvertes.fr/tel-00263646.
Анотація:
L'objectif de cette thèse est de faciliter la conception et le déploiement d'applications distribuées sur la Grille, en utilisant une approche orientée composants. Les problématiques du calcul sur grilles abordées dans notre proposition sont : la complexité de conception, le déploiement, la flexibilité et la performance. Nous proposons et justifions un modèle de composants et son implantation. Le modèle proposé repose sur le modèle de composants Fractal et sur le modèle des objets actifs. Il bénéficie d'une part, de la structure hiérarchique et de la définition précise du modèle Fractal, et d'autre part, de l'identification des composants comme activités configurables. Nous proposons un modèle de déploiement et nous spécifions un ensemble de primitives pour les communications collectives, grâce à la définition d'interfaces collectives. Les interfaces collectives permettent de gérer la distribution des données, le parallélisme et la synchronisation des invocations.Nous avons développé une implantation du modèle proposé avec l'intergiciel de grille ProActive. Le framework de composants bénéficie ainsi des fonctionnalités sous-jacentes offertes par l'intergiciel ProActive. Nous démontrons la capacité de passage à l'échelle et l'efficacité de notre framework en déployant sur plusieurs centaines de machines des applications intensives en termes de calcul et de communications. Nous mettons à profit les interfaces collectives pour développer une application SPMD à base de composants, dont nous évaluons les performances.
6
Nakamura, Yasuyuki. "Static and dynamic properties of collective phenomena in systems composed of formal neurons." Kyoto University, 1995. http://hdl.handle.net/2433/160765.
Анотація:
本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第6036号
工博第1433号
新制||工||988(附属図書館)
UT51-95-D355
京都大学大学院工学研究科数理工学専攻
(主査)教授 宗像 豊哲, 教授 片山 徹, 教授 足立 紀彦
学位規則第4条第1項該当
7
Ganapathy, Visvanathan 1957. "Structural analysis of stretched membrane reflector modules using advanced composites." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276569.
Анотація:
The concept of achieving low cost (≈ $20/m²) and ultra low weight (5 kg/m²) for heliostats is explored theoretically and experimentally. The objective of this work is to significantly improve the cost and performance of the structure under concern, without sacrificing strength and efficiency. The focus is on an innovative design of stretched-membrane heliostats. A reflective membrane of thin film is supported by a taut fishnet structural membrane consisting of graphite fiber-polymer matrix composite. The reflective and structural membranes are attached to a ring frame made of wood. The nonlinear problem of stress-strain analysis is formulated and solved using the finite-element code NASTRAN. The analysis is done for loads which include the initial stretching of the film and structural membrane and the pressure load due to wind. The scope of the present work is limited to analyzing the structural deformation behavior of flat-plate heliostats and partial extension to parabolic and semi-hemispherical dish reflectors.
8
Gao, Qian. "Microstructure and fracture toughness of the in-situ NiAl-Ni??3Al intermetallic composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22204.pdf.
9
Contreras, Maria Elena. "Paradoja: concerto for orchestra [score]." Diss., Temple University Libraries, 2008. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/969.
Анотація:
Music CompositionD.M.A.
Paradoja: Concerto for Orchestra consists of three contrasting movements: slow, fast, slow (Paradoja = "paradox," Sp.). These movements are framed by a motif that opens and closes each of them, and connects them all. This framing motif is based on an alternation between a rhythmical pattern in the bass drum, and a melody sung by a boy mezzo-soprano, both over a string pedal. The first movement, Lamentos (Sorrows), is dramatic in character; it goes from simple to complex in its orchestration, harmony, texture, dynamics and tempo changes. The second movement, Algarabía (Tangle), reflects a festive affection; it presents a contrast to the first in character, tempo and spirit. The third movement, Sosiego (Serenity) provides a peaceful ending to the piece; it is lighter than the other two movements in texture and orchestration. The general harmonic language of Paradoja: Concerto for Orchestra is non-tonal yet centric, with surface references to functional harmony. However, the pitch content varies from movement to movement. The first movement is highly chromatic and based in the twelve-tone collection. The melodies are created by a combination of small pitch-class sets and sometimes are broken down and distributed among different instruments. Harmony is the result of the juxtaposition and counterpoint of these melodies, which vertically reiterate the same cells or creates new sets. The second movement is based on smaller collections than the first, and it is less chromatic. Contrast is often created by changing the collections or simply transposing them. The third movement is the most homophonic and the least chromatic of all three. It is based on a combination and juxtaposition of diatonic and non-diatonic collections that interact with each other. Paradoja: Concerto for Orchestra is examined in two broad categories. The first is a structural analysis, which includes details of form and pitch selection such as pitch collections, set classes and motives. The second is a stylistic analysis, which includes aspects of style such as rhythm, orchestration. The conclusion refers to the influence of historical models and aspects of the compositional process. Both the structural and stylistic analyses demonstrate how I have tried to merge diverse stylistic music elements to obtain a new personal idiom.
Temple University--Theses
10
Goward, Gillian Ruth. "Physical characterization of tin composite oxides and related anode materials for lithium ion batteries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0028/NQ51198.pdf.
11
Alajmi, Faleh. "Water sorption of flowable composites." Master's thesis, Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/367584.
Анотація:
Oral BiologyM.S.
ABSTRACT Objectives: Flowable composites are characterized by lower filler loading and a greater proportion of diluent monomers in their formulation. These composites were traditionally created by retaining the same small particle size of the conventional hybrid composites, but reducing the filler content and allowing the increased resin to reduce the viscosity of the mixture However, their various mechanical properties such as flexural strength and wear resistance have been reported to be generally inferior compared to those of the conventional composites. Dental restorative materials are in continuous contact with fluids and saliva in the patient’s mouth. Consequently, the water sorption and solubility of these materials are of considerable importance. Resin based materials demonstrate water sorption in the oral cavity, which is the amount of water absorbed by the material on the surface and into the body while the restoration is in service. The water intrusion in the dental material can lead in a deterioration of the physical/mechanical properties, decreasing the life of resin composites. Water uptake can promote breakdown causing a filler-matrix debonding. Water sorption affects the physical and mechanical properties of resin composite such as dimensional change, decrease in surface hardness and wear resistance, filler leaching, change in color stability, reduction in elastic modulus, and an increase in creep and a reduction in ultimate strength, fracture strength, fracture toughness, and flexural strength. In addition, penetration of water into the composite may cause release of unreacted monomers (solubility) which may stimulate the growth of bacteria and promote allergic reactions. The effect of water sorption on conventional composites has been extensively studied and reviewed in the dental literature. However , there are no published studies on the water sorption of flowable composites. Water sorption increases as the amount of resin matrix increases and filler content decreases, since the filler particles do not absorb water. Thus, it is of utmost importance to study the water sorption of flowable composite. Hence the aim of this study was to evaluate and compare water sorption and solubility values of different light-activated flowable composite materials in solutions with varying pH values. And, since water filled porosities in the flowable composites may form small incubation chambers, a second related objective was to compare and correlate water sorption values of the various flowables to their ability to form Streptococcus mutans and Streptococcus sanguis single species biofilms in/on their surfaces. Methods: In this study, water sorption and solubility tests were performed according to the ISO standards (International Organization for Standardization specification 4049:07-2009- Dentistry- Polymer Based Restorative Materials [available at http://www.iso.org/iso/home/store.htm]). Three disc-shaped specimens of each flowable composite were made in a jig consisting of a Teflon mold (15 mm in diameter by 1 mm in thickness) compressed between 2 glass slabs with mylar strips used as separating sheets. The flowable resin was inserted in the Teflon mold in a single increment. All specimens were cured with a light-emitting diode curing unit. According to the ISO standard, discs were weighted every day for 35 days using the same balance, with a repeatability of 0.1 mg, until a constant mass (M1) was obtained. Once a constant M1 was obtained, the volume (V) was then calculated in cubic millimeters as follow: V =π(d/2)2h, where π=3.14; d is the mean diameter of the specimen; and h is the mean thickness of the specimen. After M1 was achieved, each flowable composite resin group of 3 discs was placed into buffers of pH = 4.0,5.5 and 7.0. After 24 hrs, specimens were wiped free of excess buffer with absorbent paper and weighed. This cycle was repeated at one week , one month, and six months. When a constant mass was achieved it was designated M2. Mass gain (Mg) was defined as follows: (M2 –M1). Per cent mass gain (%Mg) was defined as follows: (M2-M1/M1). Finally, the specimens were reconditioned to constant mass, once again following the above-mentioned procedure. This constant mass was recorded as M3. Water sorption (Wsp) was calculated in micrograms per cubic millimeter for each of the specimens by using the following equation provided by ISO 4049 standard: Wsp=(M2-M3)/V, where M2 is the mass of the specimens in micrograms after immersion in buffer for 30 days; M3 is the reconditioned mass of the specimen, in micrograms; and V is the volume of the specimen in cubic millimeters. Water solubility (Wsl) was calculated in micrograms per cubic millimeter for each of the specimens, using the following equation, provided by ISO 4049 standard: Wsl=(M1-M3)/V, where M1 is the conditioned mass of the specimen in micrograms before immersion in buffer; M3 is the reconditioned mass of each specimen in micrograms, and V is the volume of the specimen in cubic millimeters. For biofilm experiments, flowable discs were prepared as described above. Each disc was then sectioned into three equal portions using high speed and low speed handpieces , a diamond bur, and sandpaper discs, such that the three samples of each flowable had the same mass to within 0.3 mg. The samples were sterilized by dipping in 1.2% sodium hypochlorite (Chlorox), followed by rinsing with sterile distilled water, and then conditioning to a constant mass as described above, inside a desiccator that was wiped with 1.2 % Chlorox. Biofilm experiments were conducted as follows: three equal mass specimens of each flowable composite were placed in a series of wells of a sterile culture disc. Then sterile BHI broth (2 ml) was added to each well. One well served as control and no growing bacteria were added to it. To the other specimens was added 40 μl log phase S. mutans or S. sanguis cells. The culture dishes were then placed on a rotator at 37C for six hrs. Biofilm formation was measured by staining attached cells with crystal violet, destaining with 30% acetic acid, and measuring the satin spectrophotometically. Results: The pH of the solution influenced the % mass gain, as all samples gained more mass at pH 4.0 as compared to pH 5.5 and 7.0. The flowable resin SureFill showed the least % mass gain at each pH. However, there was no statistical difference in % mass gain based on pH of storage buffer for any of the flowable composites (P=.05) . Time had a significant influence on the % mass gain for the first week for all samples, with minor gains thereafter, and became steady after 1 month. Surefill showed the least water sorption when stored in buffer for 30 days, however it was not significant compared to the other flowables (P= 0.05). Filtek showed the least water solubility, but is not significant compared to the other flowables (P=0.05). The highest significant values (P< 0.05) for water sorption and solubility were observed for Virtuoso. Two trials indicated that strains of S. mutans and S. sanguis form biofilm readily on the surface of the composites, with S. sanguis having a higher predilection to form biofilm on all composites (Figure 6). However, no correlation was found between water sorption and solubility values of the flowable composites and biofilm formation. Conclusions: Within the limitations of this study the following is concluded: Time and storage conditions are important to the % mass gain due to water, with all flowable composites showing more mass gain at low PH. Due to its hydrophilic nature, as well as to the filler characteristics, the flowable composite Virtuoso exhibited significantly higher values of water sorption and water solubility than the other flowable composites that were tested. All flowable composites formed S. sanguis and S. mutans single species biofilm on their surfaces, with S. sanguis forming higher concentrations of biofilm on all samples. There was no clear correlation to water sorption and biofilm formation characteristics of the composites.
Temple University--Theses
12
Freihofer, Gregory J. "Enhancing CNT-composites with Raman spectroscopy." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4763.
Анотація:
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 formulation of a new fitting procedure using the pseudo-Voigt function is presented and shown to minimize the uncertainty of characteristics within the Raman G and D doublet. Methods for optimization of manufacturing processes using the Raman characterization are presented for selected applications in a polymer multiwalled nanotube (MWNT) composite and laser-sintered ceramic-MWNT composite. In the first application, the evolution of the MWNT 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, while keeping disorder sensitive D/G integrated intensity ratio to a minimum. Advanced Raman techniques, utilizing multiple wavelengths, were used to show that higher excitation energies are less sensitive to double resonance Raman effects. This reduces their influence 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.ID: 030646203; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.A.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 84-94).
M.S.A.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Aerospace Engineering; Space System Design and Engineering Track
13
Contreras, Maria Elena. "Paradoja [dissertation]." Diss., Temple University Libraries, 2008. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/926.
Анотація:
Music CompositionD.M.A.
Paradoja: Concerto for Orchestra consists of three contrasting movements: slow, fast, slow (Paradoja = "paradox," Sp.). These movements are framed by a motif that opens and closes each of them, and connects them all. This framing motif is based on an alternation between a rhythmical pattern in the bass drum, and a melody sung by a boy mezzo-soprano, both over a string pedal. The first movement, Lamentos (Sorrows), is dramatic in character; it goes from simple to complex in its orchestration, harmony, texture, dynamics and tempo changes. The second movement, Algarabía (Tangle), reflects a festive affection; it presents a contrast to the first in character, tempo and spirit. The third movement, Sosiego (Serenity) provides a peaceful ending to the piece; it is lighter than the other two movements in texture and orchestration. The general harmonic language of Paradoja: Concerto for Orchestra is non-tonal yet centric, with surface references to functional harmony. However, the pitch content varies from movement to movement. The first movement is highly chromatic and based in the twelve-tone collection. The melodies are created by a combination of small pitch-class sets and sometimes are broken down and distributed among different instruments. Harmony is the result of the juxtaposition and counterpoint of these melodies, which vertically reiterate the same cells or creates new sets. The second movement is based on smaller collections than the first, and it is less chromatic. Contrast is often created by changing the collections or simply transposing them. The third movement is the most homophonic and the least chromatic of all three. It is based on a combination and juxtaposition of diatonic and non-diatonic collections that interact with each other. Paradoja: Concerto for Orchestra is examined in two broad categories. The first is a structural analysis, which includes details of form and pitch selection such as pitch collections, set classes and motives. The second is a stylistic analysis, which includes aspects of style such as rhythm, orchestration. The conclusion refers to the influence of historical models and aspects of the compositional process. Both the structural and stylistic analyses demonstrate how I have tried to merge diverse stylistic music elements to obtain a new personal idiom.
Temple University--Theses
14
Dumpson, Donald. "FOUR SCHOLARS' ENGAGEMENT OF WORKS BY CLASSICAL COMPOSERS OF AFRICAN DESCENT: A COLLECTIVE CASE STUDY." Diss., Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/261236.
Анотація:
Music EducationPh.D.
The purpose of this research was to investigate ways classical composers of African descent have been included in the mainstream academic canon. I examined the insights of four scholars who have been committed to including classical composers of African descent throughout their music careers. The initial research questions of this study were: 1) How do participants describe their frameworks for making the commitment to include classical composers of African descent throughout their careers? 2) What have been the challenges and benefits associated with their commitment? 3) What might contemporary scholars view as strategies for integrating classical composers of African descent into the mainstream academic canon? Four musicians, who have contributed to the scholarship related to classical works by composers of African descent in very different ways, participated in this qualitative collective case study: Dr. Ysaye Maria Barnwell, a composer and performer; Dr. Dominique-Rene de Lerma, musicologist; Dr. Anthony Thomas Leach, educator, conductor, and organist; and Mr. Hannibal Lokumbe, composer, trumpeter, and visionary. Through two in-depth interviews with each of the four scholars, a related question emerged: How have the participants contributed to the inclusion of classical composers of African descent throughout professional careers and personal lives? I transcribed the interviews, returned them to the participants for member checks, and prepared final, revised transcripts based on their feedback for analysis. I examined the interview data to obtain a collective representation related to the research questions. I analyzed the data for emerging codes, categories, and themes until details considered substantive to the research emerged. Themes that emerged focused on the need to identify the importance of seeing the contributions for classical composers of African descent from an Afrocentric as well as a Eurocentric perspective; the impact of the Civil Rights Movement on how each participant engaged the music throughout their lives; the importance of informal and formal education and the roles family, community, and school played in their relationship with the music they shared; and, the significance of creating access to their works through publications and professional associations.
Temple University--Theses
15
Sun, Ying. "Mechanical properties of carbon nanotube/metal composites." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4611.
Анотація:
Carbon nanotubes (CNTs) have captured a great deal of attention worldwide since their discovery in 1991. CNTs are considered to be the stiffest and strongest material due to their perfect atomic arrangement and intrinsic strong in-plane sp[super]2--sp[super]2 covalent bonds between carbon atoms. In addition to mechanical properties, CNTs have also shown exceptional chemical, electrical and thermal properties. All these aspects make CNTs promising candidates in the development of novel multi-functional nanocomposites. Utilizing CNTs as fillers to develop advanced nanocomposites still remains a challenge, due to the lack of fundamental understanding of both material processing at the nanometer scale and the resultant material properties. In this work, a new model was developed to investigate the amount of control specific parameters have on the mechanical properties of CNT composites. The new theory can be used to guide the development of advanced composites using carbon nanotubes, as well as other nano-fibers, with any matrices (ceramic, metal, or polymer). Our study has shown that the varying effect based on changes in CNT dimensions and concentration fit the model predictions very well. Metallic CNT composites using both single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT), have been developed through a novel electrochemical co-deposition process. Copper and nickel matrix composites were developed by using pulse-reverse electrochemical co-deposition. Uniaxial tensile test results showed that a more than 300% increase in strength compared to that of the pure metal had been achieved. For example, the ultimate tensile strength of Ni/CNTs composites reached as high as about 2GPa. These are best experimental results ever reported within this field.; The mechanical results are mainly attributed to the good interfacial bonding between the CNTs and the metal matrices and good dispersion of carbon nanotubes within the matrices. Experimental results have also shown that the strength is inversely dependent on the diameter of carbon nanotubes. In addition to the mechanical strength, carbon nanotube reinforced metallic composites are excellent multifunctional materials in terms of electrical and thermal conduction. The electrical resistivity of carbon nanotube/copper composites produces electrical resistivity of about 1.0~1.2 x10[super]-6ohm-cm, which is about 40% less than the pure copper. The reduced electrical resistivity is also attributed to the good interfacial bonding between carbon nanotubes and metal matrices, realized by the electrochemical co-deposition.ID: 028916756; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 95-105).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
16
Shin, Dongho. "Microstructual Characteristics of Magnesium Metal Matrix Composites." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5494.
Анотація:
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 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.ID: 031001275; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Yongho Sohn.; Title from PDF title page (viewed February 22, 2013).; Thesis (M.S.M.S.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 49-51).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
17
Song, Young-Kyu. "Phase equilibria in the Ni-Si-Mg system and fracture toughness of selected in-situ intermetallic composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60567.pdf.
18
Tsoi, Marvin S. "Modeling of thermal properties of fiber glass polyester resin composite under thermal degradation condition." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4711.
Анотація:
Composites, though used in a variety of applications from chairs and office supplies to structures of U.S. Navy ships and aircrafts, are not all designed to hold up to extreme heat flux and high temperature. Fiber-reinforced polymeric composites (FRPC) have been proven to provide the much needed physical and mechanical properties under fire exposure. FRPC notable features are its combination of high specific tensile strength, low weight, along with good corrosion and fatigue resistance. However FRPC are susceptible to thermal degradation and decomposition, which yields flammable gas, and are thus highly combustible. This property restricts polymeric material usage. This study developed a numerical model that simulated the degradation rate and temperature profiles of a fiber-reinforced polyester resin composite exposed to a constant heat flux and hydrocarbon fire in a cone calorimeter. A numerical model is an essential tool because it gives the composite designer the ability to predict results in a time and cost efficient manner. The goal of this thesis is to develop a numerical model to simulate a zonal-layer polyester resin and fiber-glass mat composite and then validate the model with experimental results from a cone calorimeter. By inputting the thermal properties of the layered composite of alternating polymer and polymer-infused glass fiber mat layers, the numerical model is one step closer to representing the experimental data from the cone calorimeter test. The final results are achieved through adding a simulated heat flux from the pilot ignition of the degraded gas of the polyester resin. The results can be coupled into a mechanical model, which may be separately constructed for future study on the mechanical strength of composites under fire conditions.ID: 030646184; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 53-54).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids Track
19
Chaplin-Kyzer, Abigail. "Searching for Songs of the People: The Ideology of the Composers' Collective and Its Musical Implications." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157558/.
Анотація:
The Composers' Collective, founded by leftist composers in 1932 New York City, sought to create proletarian music that avoided the "bourgeois" traditions of the past and functioned as a vehicle to engage Americans in political dialogue. The Collective aimed to understand how the modern composer became isolated from his public, and discussions on the relationship between music and society pervade the radical writings of Marc Blitzstein, Charles Seeger, and Elie Siegmeister, three of the organization's most vocal members. This new proletarian music juxtaposed revolutionary text with avant-garde musical idioms that were incorporated in increasingly greater quantities; thus, composers progressively acclimated the listener to the dissonance of modern music, a distinctive sound that the Collective hoped would become associated with revolutionary ideals. The mass songs of the two Workers' Song Books published by the Collective, illustrate the transitional phase of the musical implementation of their ideology. In contrast, a case study of the song "Chinaman! Laundryman!" by Ruth Crawford Seeger, a fringe member of the Collective, suggests that this song belongs within the final stage of proletarian music, where the text and highly modernist music seamlessly interact to create what Charles Seeger called an "art-product of the highest type."
20
TRAETTEBERG, OLA. "Le mode collectif de l'onde de densite de spin dans les composes (tmtsf)#2(asf#6)#1##x(sbf#6)#x." Paris 11, 1993. http://www.theses.fr/1993PA112141.
Анотація:
Nous avons etudie l'effet sur le diagramme de phase et sur le transport du mode collectif de l'onde de densite de spin (ods) en fonction du desordre dans des alliages de conducteurs organiques: (tmtsf)#2(asf#6)#1##x(sbf#6)#x, ou la concentration x varie de 0 a 1. L'effet du desordre sur les proprietes a une particule et le diagramme de phase est faible mais sensible. L'effet sur l'accrochage de l'ods est grand, ce qui est observe dans le champ seuil pour la conductivite non lineaire et dans la constante dielectrique statique. La relaxation dielectrique montre une distribution de temps de relaxation. L'amortissement du mouvement de l'ods depend aussi du desordre, et l'on decrit cette diffusion des excitations ods par les defauts. A basse temperature la conductivite non lineaire est decrite par un effet tunnel quantique. Le desordre augmente le champ caracteristique pour l'effet tunnel
21
Tenery, Daeri. "IMAGING AND SPECTROSCOPY OF CONDUCTING POLYMER-FULLERENE COMPOSITE MATERIALS." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3241.
Анотація:
Since the development and optical study of conjugated (conducting) polymers it has become apparent that chain conformation and aggregation at the molecular scale result in complex heterogeneous nanostructured bulk materials for which a detailed insight into morphological, spectroscopic as well as optoelectronic properties and mechanisms is overwhelmingly difficult to obtain. Nanoparticles composed of the conjugated polymer poly (MEH-PPV) and nanocomposite nanoparticles consisting of MEH-PPV doped with 1-(3-methoxycarbonylpropyl)-1-phenyl-C61 (PCBM) were prepared as model systems to study these materials at the length scale of one to a few domains. The MEH-PPV and PCBM doped nanoparticles were analyzed by single imaging/particle spectroscopy (SPS) and revealed molecular scale information on the structure-property relationships of these composite materials. The data obtained from SPS were investigated in terms of spectral difference between doped and undoped nanoparticles. The doped nanoparticles are blue shifted by approximately 5-10 nm, have an additional blue shoulder, and show different vibronic structure than the undoped nanoparticles. Specifically, relative intensity of the 0-1 transition is lower than for the undoped nanoparticles. These data are indicative of differences in molecular order between both nanoparticle systems, detected at the molecular scale. In addition, the effect of electrical fields present in devices on the interfacial charge transfer properties was evaluated. Furthermore, these nanoparticles were incorporated into the lipid nanotubes to study the diffusion process of the single MEH-PPV nanoparticles inside the lipid nanotubes. Our data shows a clear proof of concept that diffusion of nanoparticles inside the hollow lipid nanotubes can be studied on a single particle basis, which will allow us to study diffusion processes quantitatively and mechanistically within the framework of developing a biocompatible drug and gene delivery platform.Ph.D.
Department of Chemistry
Sciences
Chemistry PhD
22
Gibson, Jason. "Nano-Particles in Multi-Scale Composites and Ballistic Applications." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5745.
Анотація:
Carbon nanotubes, graphene and nano sized core shell rubber particles have all been extensively researched for their capability to improve mechanical properties of thermoset resins. However, there has been a lack of research on their evaluation for energy absorption in high velocity impact scenarios, and the fundamental mechanics of their failure mechanisms during highly dynamic stress transfer through the matrix. This fundamental research is essential for laying the foundation for improvement in ballistic performance in composite armor. In hard armor applications, energy absorption is largely accomplished through delamination between plies of the composite laminate. This energy absorption is accomplished through two mechanisms. The first being the elongation of the fiber reinforcement contained in the resin matrix, and the second is the propagation of the crack in between the discreet fabric plies. This research aims to fundamentally study the energy absorption characteristics of various nano-particles as reinforcements in thermoset resin for high velocity impact applications. Multiple morphologies will be evaluated through use of platelet, tubular and spherical shaped nano-particles. Evaluations of the effect on stress transfer through the matrix due to the combination of nano sized and micro scale particles of milled fiber is conducted. Three different nano-particles are utilized, specifically, multi-walled carbon nanotubes, graphene, and core shell rubber particles. The difference in surface area, aspect ratio and molecular structure between the tube, platelet and spherical nano-particles causes energy absorption through different failure mechanisms. This changes the impact performance of composite panels enhanced with the nano-particle fillers. Composite panels made through the use of dispersing the various nano-particles in a non-contact planetary mixer, are evaluated through various dynamic and static testing, including unnotched cantilever beam impact, mixed mode fracture toughness, split-Hopkinson bar, and ballistic V50 testing. The unnotched cantilever beam testing showed that the addition of milled fiber degraded the impact resistance of the samples. Addition of graphene nano platelets unilaterally degraded impact resistance through the unnotched cantilever beam testing. 1.5% loading of MWCNT showed the greatest increase in impact resistance, with a 43% increase over baseline. Determining the critical load for mixed mode interlaminar shear testing can be difficult for composite panels that bend without breaking. An iterative technique of optimizing the coefficient of determination, R2, in linear regression is developed for objectively determining the point of non-linearity for critical load. This allows for a mathematical method of determination; thereby eliminating any subjective decision of choosing where the data becomes non-linear. The core shell rubber nano particles showed the greatest strain energy release rate with an exponential improvement over the baseline results. Synergistic effects between nano and micro sized particles in the resin matrix during transfer of the stress wave were created and evaluated. Loadings of 1% milled carbon fiber enhanced the V50 ballistic performance of both carbon nanotube and core shell rubber particles in the resin matrix. However, the addition of milled carbon fiber degrades the impact resistance of all nano-particle enhanced resin matrices. Therefore, benefits gained from the addition of micro-sized particles in combination with nano-sized particles, are only seen in high energy impact scenarios with micro second durations. Loadings of 1% core shell rubber particles and 1% milled carbon fiber have an improvement of 8% in V50 ballistic performance over the baseline epoxy sample for 44 mag single wad cutter gas check projectiles. Loadings of 1% multi-walled carbon nanotubes with 1% milled carbon fiber have an improvement of 7.3% in V50 ballistic performance over the baseline epoxy sample. The failure mechanism of the various nano-particle enhanced resin matrices during the ballistic event is discussed through the use of scanning electron microscope images and Raman spectroscopy of the panels after failure. The Raman spectroscopy data shows a Raman shift for the fibers that had an enhancement in the V50 performance through the use of nano-particles. The Raman band for Kevlar centered at 1,649 cm-1 stemming from the stretching of the C==O bond of the fiber shows to be more sensitive to the residual axial strain, while the Raman band centered at 1,611 cm-1 stemming from the C-C phenyl ring is minimally affected for the CSR enhanced panels due to the failure mechanism of the CSR particles during crack propagation.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
23
Hofmeister, Clara. "Development of Nitrogen Concentration During Cryomilling of Aluminum Composites." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5791.
Анотація:
The ideal properties of a structural material are light weight with extensive strength and ductility. A composite with high strength and tailorable ductility was developed consisting of nanocrystalline AA5083, boron carbide and coarser grained AA5083. The microstructure was determined through optical microscopy and transmission electron microscopy. A technique was developed to determine the nitrogen concentration of an AA5083 composite from secondary ion mass spectrometry utilizing a nitrogen ion-implanted standard. Aluminum nitride and amorphous nitrogen-rich dispersoids were found in the nanocrystalline aluminum grain boundaries. Nitrogen concentration increased as a function of cryomilling time up to 72hours. A greater nitrogen concentration resulted in an enhanced thermal stability of the nanocrystalline aluminum phase and a resultant increase in hardness. The distribution of the nitrogen-rich dispersoids may be estimated considering their size and the concentration of nitrogen in the composite. Contributions to strength and ductility from the Orowan relation can be more accurately modeled with the quantified nitrogen concentration.M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering; Accelerated BS to MS
24
Pinapati, Kishore. "VARIATION OF GEOTECHNICAL STRENGTH PROPERTIES WITH AGE OF LANDFILLS ACCEPTING BIOSOLIDS." Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3992.
Анотація:
The solid portion of waste disposal, known as Municipal Solid Waste (MSW) can be landfilled. Landfilling has proved to be a safe, sanitary and economical method of disposal. A by-product from wastewater treatment plants called biosolids is sometimes co-disposed along with MSW in landfills. Recent work at the University of Central Florida has focused on the behavior of the mixture of MSW and biosolids. As an increased amount of waste accumulates in these landfills, it creates a new problem – the geotechnical stability of landfills. In current literature, classical geotechnical testing methods have been followed to find the strength properties of these landfill materials. Furthermore, geotechnical methods of slope stability analyses have been employed to determine the stability of landfill slopes. As these materials have a high organic content, their strength properties may potentially change with time because of the decay of the organic materials. In the present work, an attempt is made to monitor the change in the geotechnical strength properties of the landfill materials as a function of time. Direct shear tests used for soil testing, with some modifications, were performed on cured compost samples of MSW mixed with biosolids. Geotechnical strength properties of these cured samples were compared to those of an artificially prepared mixture of MSW and biosolids, from the published literature. In addition, direct shear tests are also performed to find the interface properties of a geonet with the cured samples to check the role of a geonet in reinforcing the landfill slopes. A slope stability analysis software SLOPE/W is used to analyze the stability of the landfills. Cohesion is observed to decrease with time while the friction angle increases with time. Stability (the factor of safety against failure) of landfill slopes increases with time due to increased effective stresses and increased friction angle, as the organic material decays. This may result in additional subsidence but an increase in the effective shear strength with time. Based on the interface test results and subsequent slope stability analyses, it is found that the inclusion of a geonet improves the slope stability of a landfill. This could be a potential benefit to the landfill as reinforcement if properly placed. Based on the slope stability analysis on landfills with different slopes, it is concluded that the slope stability of a landfill is improved by keeping the slopes less steep.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering
25
LIU, XIAOXIAO. "A Preliminary Study on Water Collection Ability of Nanofibers Derived from Electrospun Polymers." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1573050761831223.
26
amini, manesh navid. "HEAT TRANSFER IN MULTI-LAYER ENERGETIC NANOFILM ON COMPOSITES SUBSTRATE." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3191.
Анотація:
The main purpose of this work is the physical understanding and the numerical description of the reaction of the dense metastable intermolecular composition (MIC). Energy density of MIC is much higher than conventional energetic material; therefore, MIC finds more applications in the propellant and explosive system. The physical model includes the speed of propagation and rate of reaction, and the relationship between the layer thickness, heat rate, and length of the flame based on physical model. In Part I of this thesis, a one-dimensional model based on Weihs was developed for 20 pairs of a multi-layer of aluminum and copper oxide. This problem was solved using an assumed value of constant atomic diffusion in Arrhenius' equation to obtain the velocity of self- propagation. Using the maximum and minimum measured velocities in a similar configuration, the activation energy was computed and was found to be significantly different. When the velocity was used to obtain a linear temperature profile, the margin of error was significant as well. Therefore, this method was seen to have severe shortcomings. In Part II of this thesis, adiabatic unit cell of one layer of aluminum and copper oxide in an ideal reaction was considered. Temperature profile based on chemical heat generation and phase transformation of reactants has been calculated. This model confirmed the highest possible temperature during reaction of 2920 C ± 5% obtained in the literature, however, the model was unable to provide other important flame characteristics. In Part III, a two-dimensional model was developed introducing the flame at the interface. A black box theory has been used to simplify some of the characteristics of the flame, ignoring diffusion characteristics. Using this model, the length of flame was calculated using the measured value of the speed of propagation of the flame. Measuring some of the characteristics of the flame was the main goal of Part III of this thesis. Controllable environment was created for the multilayer thin film of aluminum and copper oxide to eliminate the number of effective variables that affect the speed of propagation. Transformable heat of reaction was used to control the speed of propagation. In addition, a MIC sample was designed and fabricated to measure the speed of propagation with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on variable substrate up to 65 m/s. The flame length was also calculated for different speeds of propagation over different substrates. The temperature distribution on the substrate was calculated numerically. Significant improvements have been made in Part III; however, this model does not provide concentration profiles. For future work, a more complete two-dimensional physical model will be developed for self-propagation reaction of multilayer thin film of aluminum and copper oxide based on thermal transport and atomic diffusion. This two-dimensional model includes the reaction rate, speed of propagation and the temperature profile. Since this model relies on a number of physical variables that are as yet unknown, further work is warranted in this area to carry out a thorough computational study.M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering MSME
27
Bai, Jing. "PERCOLATION STUDY OF NANO-COMPOSITE CONDUCTIVITY USING MONTE CARLO SIMULATIONPERCOLATION." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4168.
Анотація:
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 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.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
28
Amini, Manesh Navid. "Heat transfer in multi-layer energetic nanofilm on composites substrate." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4587.
Анотація:
Numerical model was also used to estimate three major variables for a range of 30-60 m/s. In fact, the maximum combustion flame temperature that corresponds to flame speed along with the length of the flame, density of the product behind the flame, and maximum penetration depth in steady reaction, were calculated. These studies will aid in the design of nEM multilayer thin film. As further numerical and experimental results are obtained for different nEM thicknesses, a unified model involving various parameters can be developed.; The main purpose of this work is to find a physical and numerical description related to the reaction of the multilayer nano energetic material (nEM) in dense film. Energy density of nEM is much higher than the conventional energetic material; therefore, nEM finds more applications in propulsions, thermal batteries, material synthesis, nano igniters, waste disposals, and power generations. The reaction model of a multilayer nEM in a dense film of aluminum and copper oxide deposits on a composite substrate of silica/silicon is studied and solved in different stages. The two main interests in this study are propagation speed and maximum temperature of the reaction. In order to relate speed of reaction and maximum flame temperature a number of other variables such as heat loss, the product porosity, and the reaction length should be estimated. The main aim of this study is to introduce a numerical model which estimates and relates these values in multilayer nEM in a dense film. The following is a summary of the execution steps to achieve this goal. In Part I of this thesis, flame front speed and the reaction heat loss were the main targets. The time-of-flight technique has been developed to measure the speed of flame front with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on multilayer nEM over different substrate material up to 65 m/s. A controllable environment (composite silicon\silica) was created for a multilayer standard thin film of aluminum and copper oxide to control the reaction heat loss through the substrate. A number of experimental results show that as the thickness of silica decreases, the reaction is completely quenched. Reaction is not in self-sustaining mode if the silica thickness is less than 200 nm. It is also observed that by increasing silica's thickness in substrate, the quenching effect is progressively diminished.; The speed of reaction seems to be constant at slightly more than 40 m/s for a silica layer with thickness greater than 500 nm. This would be the maximum heat penetration depth within the silica substrate, so the flame length was calculated based on the measured speed. In Part II, a numerical analysis of the thermal transport of the reacting film deposited on the substrate was combined with a hybrid approach in which a traditional two-dimensional black box theory was used, in conjunction with the sandwich model, to estimate the maximum flame temperature. The appropriate heat flux of the heat sources is responsible for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is based on the previous author's work. This work highlights two important findings. One, there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon\silica. Secondly, by increasing the substrate thickness, the quenching effect is progressively diminished at given speed. These results also show that the average speed and quenching of flames depend on the thickness of the silica substrate and can be controlled by a careful choice of the substrate. In Part III, a numerical model was developed based on the moving heat source for multilayer thin film of aluminum and copper oxide over composite substrate of silicon\silica. The maximum combustion flame temperature corresponding to the speed of flame front is the main target of this model. Composite substrate was used as a mechanism to control the heat loss during the reaction. Thickness of the substrate, the length of flame front, and the density of the product were utilized for the standard multilayer thin film with 43 m/s flame front speed. The calculated heat penetration depth in this case was compared to the experimental result for the same flame front speed.ID: 030422800; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 140-149).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
29
Long, Xiang. "Numerical study on reinforcement mechanism of copper/carbon nanotubes composite." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5409.
Анотація:
Because of its high stiffness, carbon nanotubes (CNTs) are considered as one of the widely used reinforcement materials in the metal matrix composites. In this thesis, finite element (FE) models were built in Ls-Dyna3D to simulate Copper/CNTs composite deformation and fracture, and to explore CNTs reinforcement mechanisms. Several possible mechanisms were discussed. Deformation and failure of Cu/CNT composites were studied numerically using unit cell FE models, which consist of both metal matrix and CNTs. The simulation results have been verified by existing experiment data reported by Chen's group. The matrix material was modeled as elasto-plastic ductile solids. The CNTs material properties were taken from literature results using molecular dynamics simulation. FE simulations have showed that CNTs deformation exceeds material elastic limit, which means that CNTs plasticity should be taken into account as well. 2D unit cell models were developed using axial symmetric elements with suitable boundary conditions. Several mechanisms are found to affect CNTs reinforcement prediction. The first one is the boundary condition imposed in the models. The CNTs significantly affect the plastic flow of copper during plastic deformation, which is one important reinforcement mechanism. The second reinforcement mechanism is found to be the hardening zone of Cu matrix around CNTs, which is introduced by mismatch of coefficient of thermal expansion (CTE). A round of parametric studies was performed to investigate the effects of several modeling parameters in the FE simulations; these parameters include the volume fraction of CNTs, aspect ratio of CNTs, the size of hardening zone, and the residual plastic strain in the zone. A tool combining Matlab and Ls-Dyna was developed to automatically build 2D unit cell models and automatically post-process simulation results. Picking up suitable parameters, 2D unit cell model results well predict the experimental results from Chen's group. It should be noted that the interface between Cu and CNTs was assumed to be perfect in FE simulations since no CNTs debonding was observed in the experiments. Also, a 3D unit cell model using tetrahedral elements (with element numbers up to one million) was tentatively developed to obtain more accurate results. The purpose was to explore the interface properties of Cu/CNTs, the effect of CNTs orientation distribution, and the other reinforcement mechanism coming from geometry necessary dislocation (GND) since the size of Cu matrix is divided into nano scales by CNTs. 3D unit models are also used to verify the 2D unit cell one, which is a simplified and effective approach. Very interesting results was observed in this part of study. Further works are needed to overcome the difficulties in 3D modeling and the limitation of current CPU speed.ID: 031001326; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Yuanli Bai.; Title from PDF title page (viewed April 8, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 59-66).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermofluids
30
Jones, Ashley. "Low Strain Rate Studies of Alumina Epoxy Composites using Piezospectroscopy." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5957.
Анотація:
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 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.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Mechanical Systems
31
Hegg, Meredith Michelle. "Exact Relations and Links for Fiber-Reinforced Elastic Composites." Diss., Temple University Libraries, 2012. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/164322.
Анотація:
MathematicsPh.D.
Predicting the effective elastic properties of a composite material based on the elastic properties of the constituent materials is extremely difficult, even when the microstructure is known. However, there are cases where certain properties in constituents always carry over to a composite, regardless of the microstructure of the composite. We call such instances exact relations. The general theory of exact relations allows us to find all of these instances in a wide variety of contexts including elasticity, conductivity, and piezoelectricity. We combine this theory with ideas from representation theory to find all exact relations for fiber-reinforced polycrystalline composites. We further extend these ideas to the concept of links. When two composites have the same microstructure but different constituent materials, their effective tensors may be related. We use the theory of exact relations to find such relations, which we call links. In this work we describe a special set of links between elasticity tensors of fiber-reinforced polycrystalline composites. These links allow us to generalize certain results from specific examples to generate new information about this widely-used class of composites. In particular, we apply the link to obtain information about composites made from two transversely isotropic materials and polycrystals made from one orthotropic material.
Temple University--Theses
32
Zhao, Yao. "STUDY ON METAL-NANOCARBON COMPOSITES: PROCESSING, CHARACTERIZATION, AND PROPERTIES." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/595185.
Анотація:
Mechanical EngineeringPh.D.
Introduction of nanocarbons, such as graphene and carbon nanotubes, to metal matrices, may enhance the electrical and thermal transport, mechanical properties and some other properties of the composite materials. However, uniform distribution of the nanocarbon phase in the matrix material and manufacturing the composites in large scale can be challenging using traditional mixing methods. In this study, a facile method to fabricate metal-nanocarbon composites was developed. Firstly, copper (Cu)-polydopamine (PDA) composite was fabricated by coating Cu powders with the bioinspired PDA polymer, which was then converted to a graphite-like structure during the subsequent sintering. In terms of the properties, compared to the pure Cu sample, the Cu-PDA composite showed increased electrical and thermal conductivity, higher microindentation hardness, and enhanced wear resistance. These findings suggest the inclusion of nanocarbon phase converted from PDA can simultaneously improve the electrical, thermal, and mechanical properties of sintered Cu materials. Effect of sintering temperature and coating time (carbon content) on the microstructure and properties of the composites were discussed. Secondly, aluminum (Al)-copper nanoparticles (CuNP)-PDA composite was fabricated with a new method, to improve the sintering behavior of Al for serving as feedstock materials of additive manufacturing (AM). CuNPs were synthesized by directly reducing Cu ions in the aqueous solution. With the assistance of the PDA coating, the CuNPs can be better attached to the Al powder surfaces. The composite samples showed better sintering behavior by exhibiting higher electrical conductivities and mechanical properties, which may be due to local nanosized alloying phases generation after sintering. These findings illustrated that the composite powders could be a good candidate feedstock material for AM. The structural characterizations of the metal nanocarbon powders and the composites were performed with SEM, TEM, XRD and Raman spectroscopy. With the help of these techniques, the formation of the targeted structures in the composite was studied, including graphite-like structures of cPDA and nano alloying phases in Al-CuNP-PDA composites. Apart from the composite materials fabrication, a novel and facile manufacturing method based on metal powders was also developed. In this study, a new type of Cu- binder paste was formed, which not only can be utilized with direct ink/paste printing but also can be casted into a soft silicone rubber mold. Three-dimensional (3D) metal parts can then be subsequently obtained after sintering. Comparing to other additive manufacturing methods that involve high energy laser or electron beams, this new approach does not require expensive facilities, and it is less time-consuming. Moreover, the silicone rubber molds can be easily removed and reused. In summary, the composite powders fabricated in this study can be utilized as feedstock materials for additive manufacturing of metals and alloys. The new soft-mold casting could be used as an alternative method to manufacture 3D metal components. Therefore, the materials and the processing methods developed in the current study could have broad applications in various metal industries.
Temple University--Theses
33
Vermelle, Marie-Christine. "Collectif de travail et identites professionnelles. Le cas des ouvriers et techniciens d'un service de fabrication de composants de pointe." Lille 1, 1989. http://www.theses.fr/1989LIL12008.
Анотація:
Partant des theses qui, rompant avec le paradigme techniciste, mettent au centre des transformations du travail et de la production, l'effet d'integration en amont de l'activite dans l'etude et la conception des produits, cette recherche analyse les rapports au travail et a la formation des salaries, concus comme constitutifs de leurs identites professionnelles. La construction de ces identites s'appuie sur une analyse approfondie du travail (par observation directe et entretiens) dans un service assurant le transfert recherche-developpement-production de composants electroniques de pointe, par la meme, au coeur des mutations en cours, dans la branche electronique comme dans l'entreprise, observables dans le mouvement de substitution des activites de conception et d'etudes, assurees par les ingenieurs et techniciens, a la fabrication materielle (menacee de disparition et ou externalisation). Reposant sur la mise en relation des modes de mobilisation salariale construits par l'organisation du travail et elabores par les responsables ainsi que des strategies individuelles et collectives d'amenagement des situations de travail par les salaries eux-memes, la production sociale de ces identites professionnelles fait eclater les modalites traditionnelles d'attribution de la qualification (le diplome, la fonction, la categorie professionnelle)Occupational identities are building by workers according to learning and activity. They are arising from work organisation, wich give their skills and jobs to workers and from individual and collective means of learning, training and knowledge of the occupational world, what are enlarging on labour. In a research about a work group in wich we have organisation and living of jobs investigated - with direct observation and interviews - we displayed identities were resulted by speculation into formal and informal work or learnings organisation
34
Reilly, Barry M. Lugg Elizabeth T. "Teacher compensation and student achievement the relationship between salaries & benefits and ISAT & PSAE composite scores /." Normal, Ill. : Illinois State University, 2007. http://proquest.umi.com/pqdweb?index=0&did=1441197951&SrchMode=2&sid=6&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1216233095&clientId=43838.
Анотація:
Thesis (Ed. D.)--Illinois State University, 2007.Title from title page screen, viewed on July 16, 2008. Dissertation Committee: Elizabeth Lugg (chair), Joseph M. Pacha, Zeng Lin, Neil Sappington. Includes bibliographical references (leaves 163-170) and abstract. Also available in print.
35
Tipton, Bradford. "PREVENTION OF ENVIRONMENTALLY INDUCED DEGRADATION IN CARBON/EPOXY COMPOSITE MATERIAL VIA IMPLEMENTATION OF A POLYMER BASED COATI." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4226.
Анотація:
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 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.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
36
Kerr, Brittany. "Strengthening Potential of Single-Walled Carbon Nanotubes in Phenolic Resin Composites." Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2219.
Анотація:
Strengthening potential of single-walled carbon nanotubes (SWCNTs) in a phenolic resin composite was evaluated by characterization of purified and phenyl sulfonated SWCNTs, investigation of the load transfer capability of the purified SWCNTs, and characterization of the composites. Purified and phenyl sulfonated SWCNTs, as well as their composites, were examined by Raman spectroscopy, thermogravimetric analysis, scanning electron microscopy equipped with energy dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and ultra violet-visible spectrometry. Fabrication of the SWCNT/phenolic resin composite was performed by first dispersing the SWCNTs in ethylene glycol and then homogenizing the mixture with phenolic resin. The ethylene glycol was then evaporated from the mixture and the SWCNT/phenolic resin composite was cured at 200°C for 1 hour. The dispersion of SWCNTs in the phenolic resin was reduced with higher SWCNT concentrations. Load was transferred from the phenolic resin to the purified SWCNTs. This demonstrated the potential to strengthen phenolic resin composite with SWCNT reinforcement. The load transfer efficiency in total tension (0.8%) decreased with an increase in SWCNT concentration, while in total compression (-0.8%), the load transfer efficiency remained constant. At very low strain (± 0.2%), the load transfer efficiency remained constant regardless of SWCNT concentration in both tension and compression. Characterization of the phenyl sulfonated SWCNTs indicated that calcium was introduced as a contaminant that interfered with functionalization of the SWCNTs. The use of contaminated phenyl sulfonated SWCNTs resulted in macroscopic inhomogeneity within the composite.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
37
Pai, Anil. "DEVELOPMENT OF TITANIUM NITRIDE/MOLYBDENUM DISULPHIDE COMPOSITE TRIBOLOGICAL COATINGS FOR CRYOCOOLERS." Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2886.
Анотація:
Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler is being developed at University of Central Florida. The cryocooler will be used for storage and transport of hydrogen in spaceport and space vehicle application. One part in development of the cryocooler is to reduce the friction and wear between mating parts thus increasing its efficiency. Tribological coatings having extremely high hardness, ultra-low coefficient of friction, and high durability at temperatures lower than 60 K are being developed to reduce friction and wear between the mating parts of the cryocooler thus improving its efficiency. Nitrides of high-melting-point metals (e.g. TiN, ZrN) and diamond-like-carbon (DLC) are potential candidates for cryogenic applications as these coatings have shown good friction behavior and wear resistance at cryogenic temperatures. These coatings are known to have coefficient of friction less than 0.1 at room temperature. However, cryogenic environment leads to increase in the coefficient of friction. It is expected that a composite consisting of a base layer of a hard coating covered with layer having an ultra-low coefficient of friction would provide better performance. Extremely hard and extremely low friction coatings of titanium nitride, molybdenum disulphide, TiN/MoS2 bilayer coatings, DLC and DLC/MoS2 bilayer coatings have been chosen for this application. TiN film was deposited by reactive DC magnetron sputtering system from a titanium target and MoS2 film was deposited by RF magnetron sputtering using a MoS2 target. Microwave assisted chemical vapor deposition (MWCVD) technique was used for preparation of DLC coatings. These composite coatings contain a solid lubricating phase and a hard ceramic matrix phase as distinctly segregated phases. These are envisioned as having the desired combination of lubricity and structural integrity. Extremely hard coatings of TiN and DLC were chosen to provide good wear resistance and MoS2 was chosen as the lubricating phase as it provides excellent solid lubricating properties due to its lamellar crystal structure. This thesis presents preparation; characterization (SEM and XRD), microhardness and tribological measurements carried out on TiN and TiN/MoS2 coatings on aluminum and glass substrate at room temperature. It also presents initial development in preparation of DLC coatings.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
38
Draper, Robert. "Novel Nanostructures and Processes for Enhanced Catalysis of Composite Solid Propellants." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5929.
Анотація:
The purpose of this study is to examine the burning behaviour of composite solid propellants (CSP)
in the presence of nanoscale, heterogenous catalysts. The study targets the decomposition of am-
monium perchlorate (AP) as a key component in the burning profile of these propellants, and seeks
to identify parameters of AP decomposition reaction that can be affected by catalytic additives.
The decomposition behavior of AP was studied in the presence of titanium dioxide nanoparticles
in varying configurations, surface conditions, dopants, morphology, and synthesis parameters with
the AP crystals. The catalytic nanoparticles were found to enhance the decomposition rate of the
ammonium perchlorate, and promote an accelerated burning rate of CSP propellants containing
the additives. Furthermore, different configurations were shown to have varying degrees of effec-
tiveness in promoting the decomposition behaviour.
To study the effect of the catalyst's configuration in the bulk propellant, controlled dispersion con-
ditions of the nanoparticle catalysts were created and studied using differential scanning calorime-
try, as well as model propellant strand burning. The catalysts were shown to promote the greatest
enthalpy of reaction, as well as the highest burn rate, when the AP crystals were recrystalized
around the nanoparticle additives. This is in contrast to the lowest enthalpy condition, which cor-
responded to catalysts being dispersed upon the AP crystal surface using bio-molecule templates.
Additionally, a method of facile, visible light nanoparticle tracking was developed to study the
effect of mixing and settling parameters on the nano-catalysts. To accomplish this, the titania
nanoparticles were doped with fluorescent europium molecules to track the dispersion of the cat-
alysts in the propellant binder. This method was shown to succesfully allow for dispersion and
agglomeration monitoring without affecting the catalytic effect of the TiO2 nanoparticles.M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
39
Navale, Kunal. "FINITE ELEMENT SIMULATION OF REPAIR OF DELAMINATED COMPOSITE STRUCTURES USING PIEZOELECTRIC LAYERS." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3119.
Анотація:
Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
40
Carro, Rodolphe Valentin. "HIGH PRESSURE TESTING OF COMPOSITE SOLID ROCKET PROPELLANT MIXTURES: BURNER FACILITY CHARACTERIZATION." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3204.
Анотація:
Much Research on composite solid propellants has been performed over the past few decades and much progress has been made, yet many of the fundamental processes are still unknown, and the development of new propellants remains highly empirical. Ways to enhance the performance of solid propellants for rocket and other applications continue to be explored experimentally, including the effects of various additives and the impact of fuel and oxidizer particle sizes on burning behavior. One established method to measure the burning rate of composite propellant mixtures in a controlled laboratory setting is to use a constant-volume pressure vessel, or strand burner. To provide high-pressure burn rate data at pressures up to 360 atm, the authors have installed, characterized and improved a strand burner facility at the University of Central Florida. Details on the facility and its improvements, the measurement procedures, and the data reduction and interpretation are presented. Two common HTPB/AP propellant mixtures were tested in the original strand burner. The resulting burn rates were compared to data from the literature with good agreement, thus validating the facility and related test techniques, the data acquisition, data reduction and interpretation. After more than 380 successful recordings, an upgraded version of the strand burner, was added to the facility. The details of Strand Burner II, its improvements over Strand Burner I, and its characterization study are presented.M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering MSME
41
McKee, James. "Development and Characterization of Nanoparticlee Enhancements in Pyrolysis-Derived High Temperature Composites." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6320.
Анотація:
Thermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because they are not capable of supporting larger structures. The limitations of polymer reinforced composites have limited their entry into these applications, except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These materials have been successfully demonstrated their utility in extreme environments, such as spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited their use to similarly high performance applications where the costs are justifiable.
Previous work by others with "fuzzy fiber" composites have shown that aligned carbon nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To this end vertically aligned CNTs were studied for their potential use, but found to be difficult to process with current conventional techniques. A composite material comprised of basalt, a relatively new reinforcing fiber, and phenolic, which has been used in high-temperature applications with great success was made to attempt to create a new material for these applications. To further improve upon the favorable properties of the resulting composite, the composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel technique was also developed to promote in-situ carbon nanotube growth of the resulting basalt-carbon composite without using a monolithic piece of cured phenolic resin in place of the standard aromatic hydrocarbon-catalyst precursor. The in-situ growth of carbon nanotubes (CNTs) was explored as their thermal stability and effectiveness in improving performance has been previously demonstrated when used as a resin additive.
The specimens were examined with SEM, EDS, and TGA to determine the effects of both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the parameters of CVD processing. Additional testing would also show that the growth behavior of the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is a threshold temperature necessary to facilitate the availability of catalysts from within the basalt fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the newly formed composite with a high degree of thermal stability, making the new materials potentially usable in applications such as turbines, in addition to large-scale thermal protection systems.M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
42
O'Neill, Kevin. "FEASIBILITY STUDY OF LIGHTWEIGHT HIGH-STRENGTH HOLLOW CORE BALSA-FRP COMPOSITE BEAMS UNDER FLEXURE." Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3109.
Анотація:
The United States of America s Military, more specifically the Army, has since the late 1990 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.M.S.C.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering MS
43
Haber, Zachary. "ON THE USE OF POLYURETHANE MATRIX CARBON FIBER COMPOSITES FOR STRENGTHENING CONCRETE STRUCTURES." Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4105.
Анотація:
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 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.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering MS
44
Anderson, Jordan. "Electrochemical Studies of Nanoscale Composite Materials as Electrodes in Direct Alcohol Fuel Cells." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5104.
Анотація:
Polymer electrolyte membrane fuel cells (PEMFCs) have recently acquired much attention as alternatives to combustion engines for power conversion. The primary interest in fuel cell technology is the possibility of 60% power conversion efficiency as compared to the 30% maximum theoretical efficiency limited to combustion engines and turbines. Although originally conceived to work with hydrogen as a fuel, difficulties relating to hydrogen storage have prompted much effort in using other fuels. Small organic molecules such as alcohols and formic acid have shown promise as alternatives to hydrogen in PEMFCs due to their higher stability at ambient conditions. The drawbacks for using these fuels in PEMFCs are related to their incomplete oxidation mechanisms, which lead to the production of carbon monoxide (CO). When carbon monoxide is released in fuel cells it binds strongly to the platinum anode thus limiting the adsorption and subsequent oxidation of more fuel. In order to promote the complete oxidation of fuels and limit poisoning due to CO, various metal and metal oxide catalysts have been used. Motivated by promising results seen in fuel cell catalysis, this research project is focused on the design and fabrication of novel platinum-composite catalysts for the electrooxidation of methanol, ethanol and formic acid. Various Pt-composites were fabricated including Pt-Au, Pt-Ru, Pt-Pd and Pt-CeO2 catalysts. Electrochemical techniques were used to determine the catalytic ability of each novel composite toward the electrooxidation of methanol, ethanol and formic acid. This study indicates that the novel composites all have higher catalytic ability than bare Pt electrodes. The increase in catalytic ability is mostly attributed to the increase in CO poison tolerance and promotion of the complete oxidation mechanism of methanol, ethanol and formic acid. Formulations including bi- and tri-composite catalysts were fabricated and in many cases show the highest catalytic oxidation, suggesting tertiary catalytic effects. The combination of bi-metallic composites with ceria also showed highly increased catalytic oxidation ability. The following dissertation expounds on the relationship between composite material and the electrooxidation of methanol, ethanol and formic acid. The full electrochemical and material characterization of each composite electrode is provided.Ph.D.
Doctorate
Chemistry
Sciences
Chemistry
45
Slade, Robert Arthur. "Failure Analysis of Impact-Damaged Metallic Poles Repaired With Fiber Reinforced Polymer Composites." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5505.
Анотація:
Metallic utility poles, light poles, and mast arms are intermittently damaged by vehicle collision. In many cases the vehicular impact does not cause immediate failure of the structure, but induces localized damage that may result in failure under extreme service loadings or can promote degradation and corrosion within the damaged region. Replacement of these poles is costly and often involves prolonged lane closures, service interruption, and temporary loss of functionality. Therefore, an in situ repair of these structures is required. This thesis examines the failure modes of damaged metallic poles reinforced with externally-bonded fiber reinforced polymer (FRP) composites. Several FRP repair systems were selected for comparison, and a set of medium and full-scale tests were conducted to identify the critical failure modes. The material properties of each component of the repair were experimentally determined, and then combined into a numerical model capable of predicting global response. Four possible failure modes are discussed: yielding of the unreinforced substrate, tensile rupture of the FRP, compressive buckling of the FRP, and debonding of the FRP from the substrate. It was found that simple linear, bilinear, and trilinear stress-strain relationships accurately describe the response of the composite and substrate components, whereas a more complex bond-slip relationship is required to characterize debonding. These constitutive properties were then incorporated into MSC.Marc, a versatile nonlinear finite element program. The output of the FEM analysis showed good agreement with the results of the experimental bond-slip tests.ID: 031001508; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Kevin R. Mackie.; Title from PDF title page (viewed August 5, 2013).; Thesis (M.S.)--University of Central Florida, 2012.; Includes bibliographical references (p. 101-103).
M.S.
Masters
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering; Structural and Geotechical Engineering
46
Robert, Kévin. "Vers la fabrication collective de micro-supercondensateurs à électrodes interdigitées à base de nitrure de vanadium déposé en technologie couche mince." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I082/document.
Анотація:
Les objets mobiles connectés prennent une place prépondérante dans notre vie de tous les jours mais l’autonomie énergétique est à ce jour limitée. Ainsi, le développement de dispositifs de stockage d’énergie performants et miniaturisés est un domaine en pleine expansion. Les performances de ces systèmes dépendent des matériaux dont sont constituées leurs électrodes et de l’électrolyte utilisé. Cette thèse est consacrée à la fabrication de micro-supercondensateurs à électrodes interdigitées composées de films minces de nitrure de vanadium (VN) déposé par pulvérisation cathodique. La modulation des paramètres de dépôt a permis de densifier les dépôts afin d’augmenter la conductivité électrique ou, au contraire, de rendre poreuses les couches minces pour favoriser la capacité surfacique. La caractérisation operando par spectroscopie d’absorption X d’un film mince de VN cyclé en milieu aqueux KOH couplée à des analyses de surface (XPS / TOF-SIMS) montre que la capacité élevée du VN est due à l’oxyde de vanadium présent en surface du film. Des micro-supercondensateurs rapportant des performances à l’état de l’art en topologie interdigitée ou face / face ont été fabriqués en utilisant les films de VN optimisés dont nous avons fait varier l’épaisseur pour augmenter les densités d’énergie surfacique. Le dépôt de VN par ALD a été également mis au point dans le cadre de cette thèse afin de pouvoir assurer la formation de couches minces sur des substrats 3D de haute surface spécifique. Enfin, différents liquides ioniques ont été utilisés comme électrolytes afin de faire cycler des électrodes de VN, le but étant la formation d’électrolyte solide basé sur la technologie ionogelsThe mobile connected devices have a prominent place in our everyday life but energy autonomy is limited. Thus, the development of efficient and miniaturized energy storage devices is an expanding field. The performance of these systems depends on the used electrode materials and the electrolyte. This thesis is focused on the fabrication of micro-supercapacitors with interdigitated electrodes composed of sputtered vanadium nitride (VN) thin films. The modulation of the deposition parameters allows densifying the thin films in order to increase their electrical conductivity or, on the contrary, leads to the synthesis of porous thin films to increase the surface capacitance. X-ray absorption spectroscopy of VN thin films tested in aqueous KOH in operando configuration coupled with surfaces analyses (XPS/ ToF-SIMS) show that the high capacitance of the VN is due to the presence of thin layer of vanadium oxide at the VN surface. Micro-supercapacitors reporting state-of-art performance in interdigitated or face/face topologies were fabricated using optimized VN films: the film thickness was varied to increase the energy density. The Atomic Layer Deposition of VN layers was also achieved in the frame of this study in order to ensure the formation of thin layers on high specific surface area 3D substrates. Finally, different ionic liquids have been tested as electrolyte, the purpose being solid electrolyte formation based on ionogels technology
47
Abourezq, Ibraheem. "VOIDS IN SONIC FILLTM RESTORATIONS COMPARED TO TRADITIONAL INCREMENTALLY-FILLED COMPOSITE RESTORATIONS." Master's thesis, Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/282233.
Анотація:
Oral BiologyM.S.
SonicFillTM is a new composite resin and delivery system designed to provide rapid filling of cavity preparations by decreasing viscosity through application of sonic energy. However, it may produce unwanted air voids in the final restoration due to the short filling time. Air voids compromise long-term performance by providing weak foci, discontinuity at cavosurface margins and at internal cavity walls, and potential crack propagation. This study assessed the locations, sizes, and numbers of voids in SonicFill restorations compared with traditional composite resin restorations in a set of extracted molars with mesio-occlusal-distal (MOD) cavity preparations. Fifty noncarious intact extracted third molars were collected randomly from a large collection of discarded anonymous tooth specimens. Standardized MOD cavity preparations were cut, and teeth were assigned randomly to one of two groups (n = 25). The first group was restored with SonicFill composite in two steps. The second group was restored with Herculite UltraTM using an multiple increment layering technique (1-2 mm per layer). Cross-sectional images of the filling were taken by digital microscope. A total of 196 voids were found in the 50 specimens: 97 in SonicFill restorations and 99 in conventional restorations. Mean number of voids in SonicFill restorations was 3.88 versus 3.96 for conventional restorations. Mean percentage of void area in SonicFill restorations was 0.588% versus 0.508% for conventional restorations. Unpaired t tests for these differences indicated no statistically significant differences (p =.931 and p =.629, respectively). One-way ANOVA tests for mean void count and mean void area percentage differences by three location zones for conventional and SonicFill restorations also indicated no significant differences among the groups. The bulk-fill SonicFill system does not result in increased or decreased numbers or ii area of voids within Class II MOD restorations compared with a conventional composite resin layering system.
Temple University--Theses
48
Uribe, Restrepo Catalina. "Process-dependent microstructure and severe plastic deformation in SiCp?? reinforced aluminum metal matrix composites." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4712.
Анотація:
Discontinuously reinforced MMCs with optimized microstructure are sought after for exceptional high strain rate behavior. The microstructure evolution of a stir-cast A359 aluminum composite reinforced with 30 vol.% SiCsubscript p] after isothermal anneal, successive hot-rolling, and high strain rate deformation has been investigated. Quantitative microstructural analysis was carried out for the as-cast, annealed (470??C, 538??C and 570??C) and successively hot rolled specimens (64, 75, 88, and 96% rolling reductions). Selected composites were also examined after high strain rate deformation. X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy were employed for microstructural characterization. The strength and ductility of the A359 Al alloys, and the composite, were greatly influenced by the brittle eutectic silicon phase and its morphology. Lamellar eutectic silicon spheroidized with isothermal anneal and successive hot rolling with a corresponding decrease in hardness. The hot rolling process also considerably decreased the SiC particle size (approximately 20% after 96% reduction) by breaking-up the hard SiC particles. However, this break-up of particles increased the homogeneity of SiCsubscript p] size distribution. Successive hot rolling also healed voids due to solidification shrinkage, incomplete infiltration of molten Al and defects originating from fractured particles. Four selected specimens of composites were examined after high strain rate deformation. Fractography and metallographic analysis for the craters, voids, and relevant regions affected by the high velocity impact were carried out. The deposition of impact residuals was frequently observed on the exposed fracture surfaces. These residuals were typically observed as "molten-and-solidified" as a consequence of excessive heat generated during and after the damage.; Particularly in regions of entry and exit of impact, intermixing of residuals and composite constituents were observed, demonstrating that the Al matrix of the composite also had melted. In all samples examined, cracks were observed to propagate through the eutectic Si network while a small number of broken reinforcement particles were observed. A slight variation in failure mechanisms was observed (e.g., radial, fragmentation, petalling) corresponding to the variation in ductility against high strain rate deformation. In selected specimens, parallel sub-cracks at the exit were observed at 45?? and 30??. These sub-cracks were again filled with intermixed constituents from projectile residuals and composites. This observation suggests that the melting of composite constituents that leads to intermixing occured after the crack propagation and other damage.ID: 030646232; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; On t.p. "p??" is subscript.; Thesis (M.S.M.S.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 86-88).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
49
DeMarco, James P. Jr. "Mechanical characterization and numerical simulation of a light-weight aluminum A359 metal-matrix composite." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4933.
Анотація:
Aluminum metal-matrix composites (MMCs) are well positioned to replace steel in numerous manufactured structural components, due to their high strength-to-weight and stiffness ratios. For example, research is currently being conducted in the use of such materials in the construction of tank entry doors, which are currently made of steel and are dangerously heavy for military personnel to lift and close. However, the manufacture of aluminum MMCs is inefficient in many cases due to the loss of material through edge cracking during the hot rolling process which is applied to reduce thick billets of as-cast material to usable sheets. In the current work, mechanical characterization and numerical modeling of as-cast aluminum A359-SiCsubscript p]-30% is employed to determine the properties of the composite and identify their dependence on strain rate and temperature conditions. Tensile and torsion tests were performed at a variety of strain rates and temperatures. Data obtained from tensile tests were used to calibrate the parameters of a material model for the composite. The material model was implemented in the ANSYS finite element software suite, and simulations were performed to test the ability of the model to capture the mechanical response of the composite under simulated tension and torsion tests. A temperature- and strain rate-dependent damage model extended the constitutive model to capture the dependence of material failure on testing or service conditions. Several trends in the mechanical response were identified through analysis of the dependence of experimentally-obtained material properties on temperature and strain rate. The numerical model was found to adequately capture strain rate and temperature dependence of the stress-strain curves in most cases.; Ductility modeling allowed prediction of stress and strain conditions which would lead to rupture, as well as identification of areas of a solid model which are most likely to fail under a given set of environmental and load conditions.ID: 030423478; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 113-118).
M.S.
Masters
Mechanical, Materials, and Aerospace Engineering
Engineering and Computer Science
50
Olka, Michael. "FLEXURAL MECHANICAL DURABILITY OF CONCRETE BEAMS STRENGTHENED BY EXTERNALLY BONDED CARBON FIBER REINFORCED POLYMER SHEETS." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3120.
Анотація:
About 77,600 bridges throughout the United States in the Federal Highway Association (FHWA) bridge database are listed as structurally deficient. This has created a need to either replace or strengthen bridges quickly and efficiently. Due to high costs for total replacement of deficient bridges, strengthening of existing bridges is a more economical alternative. A technique that has been developing over the past two decades is the strengthening of bridges using carbon fiber reinforced polymer (CFRP) sheets. The CFRP sheets are attached to the bottom of the bridge girders using structural adhesives so that the CFRP becomes an integral part of the bridge and carries a portion of the flexural loading. The CFRP sheets allow for an increase in the capacity of the bridge with minimal increase in the weight of the structure due to CFRP having a low density. Because the CFRP is expected to be an integral component and carry some of the long-term loading it is important to understand the long-term durability of the composite section. This thesis is part of a larger project, in which the long-term durability of the CFRP composite on concrete beams is investigated experimentally. The CFRP strengthened beams are exposed to fatigue testing and thermal-humidity cycling followed by failure testing. The testing scheme for this experiment allows for the investigation of the individual effects of fatigue and thermal-humidity loading as well as to explore the effects from combined fatigue and thermal-humidity loading. The investigation of the combined effects is a unique aspect of this experiment that has not been performed in prior studies. Results indicate that a polyurethane-based adhesive could provide a more durable bond for the CFRP-concrete interface than possible with epoxy-based adhesives.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering MS