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Evaluation of austenitic-ferritic stainless steel wires for orthodontic applications

ITMAN FILHO, A.; SILVA, R. V.; GOUVEA, C. A. R.; CASTELETTI, L. C.
Fonte: AMER SOC TESTING MATERIALS Publicador: AMER SOC TESTING MATERIALS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.36%
Several studies have shown that austenitic stainless steels are suitable for use in the final phases of orthodontic treatments, such as finishing and retention. These steels demonstrate appropriate mechanical properties, such as high ultimate tensile strength and good corrosion resistance. A new class of materials, the austenic-ferritic stainless steels, is substituting for austenitic stainless steels in several industrial applications where these properties are necessary. This work supports the hypothesis that orthodontic wires of austenic-ferritic stainless steels can replace austenitic stainless steels. The advantages are cost reduction and decrease of the nickel hypersensitivity effect in patients undergoing orthodontic treatments. The object of this study was to evaluate wires of austenitic-ferritic stainless steel SEW 410 Nr. 14517 (Cr26Ni6Mo3Cu3) produced by cold working through rolling and drawing processes. Tests were performed to evaluate the ultimate tensile strength, hardness, ductility, and formability. In accordance with technical standards the wires exhibited ultimate tensile strength and ductility suitable for orthodontic clinical applications. These austenitie-ferritic wires can be an alternative to substitute the common commercial wires of austenic stainless steels with the advantage of decreasing the nickel content.

Preparação, caracterização e avaliação da atividade catalítica de óxidos de lantanóides incorporados em sílica mesoporosa ordenada na degradação de compostos orgânicos poluentes via ozonização catalítica heterogênea; Preparation, characterization and evaluation of the catalytic activity of lanthanide oxides incorporated on ordered mesoporous silica for the degradation of organic pollutants via heterogeneous catalytic ozonation

Soeira, Luciana Serra
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/11/2012 PT
Relevância na Pesquisa
75.43%
Neste trabalho realizou-se a síntese e caracterização de materiais contendo óxidos de lantanóides incorporados em sílica mesoporosa ordenada, os quais foram utilizados como catalisadores no processo de ozonização de compostos orgânicos poluentes. Empregando-se o método de impregnação úmida, realizou-se a incorporação de óxido de cério e óxido de lantânio no suporte mesoporoso, do tipo SBA-15. Utilizaram-se diferentes precursores dos óxidos metálicos, a fim de verificar a influência que a fonte do cátion metálico exerça tanto nas características estruturais, texturais e morfológicas dos materiais quanto na atividade catalítica. A caracterização destes materiais mostrou que em todas as amostras não houve colapso da estrutura ordenada de mesoporos da SBA-15. Porém nos materiais incorporados observou-se a diminuição da área superficial específica e o volume de poro, devido à presença do CeO2 ou do La2O3 tanto na superfície do suporte quanto no interior dos mesoporos. Também foi possível identificar as fases cristalinas destes óxidos após a etapa de incorporação. Os catalisadores foram empregados na degradação de um azocorante, Preto Remazol B. Para todos os materiais verificou-se que a ozonização catalítica heterogênea proporcionou o aumento da mineralização em relação ao processo de ozonólise. Para os catalisadores que continham CeO2...

Caracterização físico-química de SiC sintetizado pelo processo Acheson a partir de diferentes fontes de SiO2; Physical-chemical characterization of SiC synthesized by Acheson process from different sources of SiO2

Silva, Mariane Capellari Leite da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/02/2015 PT
Relevância na Pesquisa
65.43%
Atualmente, há uma forte demanda por cerâmicas como materiais estruturais para substituição de metais e ligas de elevada dureza e para uso em ambientes hostis. Dentre as famílias das cerâmicas estruturais, o SiC se destaca devido ao seu conjunto de propriedades: alta resistência à oxidação/corrosão, elevada resistência à abrasão, elevada condutividade térmica, baixa massa específica, elevada dureza, boa resistência ao choque térmico e manutenção da maioria destas propriedades em temperaturas elevadas. O processo Acheson se caracteriza, industrialmente, como o principal processo de síntese do SiC, consistindo em dois eletrodos sólidos, conectados a pó de grafite compactado, circundados por uma mistura de sílica e coque, em que o aquecimento é realizado eletricamente entre temperaturas de 2200 a 2600 oC [SOMIYA, 1991]. A formação do SiC é dependente da pressão parcial dos gases, da temperatura, do tamanho de grão dos reagentes, das propriedades individuais de cada grão, assim como da área de contato e do grau de mistura entre SiO2 e C [LINDSTAD, 2002]. O SiC produzido pelo processo Acheson contém impurezas como Al, Fe, Ti, Na, provindas da matéria-prima, que durante a síntese têm seu comportamento influenciado pela variação de temperatura. Partículas metálicas ou carbetos dessas impurezas estão distribuídos na matriz de SiC...

Otimização da formulação e avaliação fisico-mecanica de biomateriais compositos para obturações odontologica; Formulation, optimization and physical-mechanical evaluation of dental resin-based restorative biomaterial

Raul Ernesto Lopez Palacio
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/12/1995 PT
Relevância na Pesquisa
75.43%
Este trabalho teve como objetivo principal a otimização da formulação e a caracterização de compósitos de matriz polimérica, reforçados com partículas de quartzo, para uso em odontologia com cura fotoquímica e química. Na otimização da formulação foi determinada a relação par iniciador-monômero, relação mistura iniciadora - carga e a distribuiçãodo tamanho das partículas de carga. No processo de avaliação foram determinadas as propriedades físico-mecânicas, segundo a metodologia descrita na norma I.S.O. 4049 (1), e a dependência dessas determinações com as condições experimentais. Realizou-se um estudo complementar para determinar a relação microestrutura-propriedades mecânicas fazendo uso da Microscopia Eletrônica de Varredura. Os resultados obtidos permitem afirmar que os compósitos obtidos cumprem com todos os requisitos fisico-mecânicos exigidospara ser utilizados como obturantes dentários. Além disto concluiu-se que os valores obtidos do comportamento mecânico dos compósitos são relativos, pois os mesmos dependem das condições experimentais. O estudo microestrutural demostrou que, além da dureza da carga, as variações no comportamento mecânico destes materiais com a porcentagem de carga dependem da interface monômero-carga formada no compósito.; This paper presents the characterization and evaluation of light and chemical cured composites. In the optimizationformulation a initiator-monomer relationship...

Simulação física do processo de soldagem por atrito com pino não consumível do aço inoxidável duplex UNS S32205; Physical simulation of UNS S32205 duplex stainless steel friction stir welding

Eduardo Bertoni da Fonseca
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/07/2013 PT
Relevância na Pesquisa
75.29%
Simulação física da soldagem por atrito com pino não consumível (SAPNC) foi realizada com o objetivo de se determinar as condições termomecânicas impostas ao material durante o processo, as quais são essenciais para o melhor entendimento da soldagem e para o desenvolvimento da simulação numérica da SAPNC. Por isso, ensaios de torção a quente foram realizados no aço inoxidável duplex (AID) UNS S32205 utilizando um simulador termomecânico Gleeble 3800®. Foi desenvolvido um sistema de resfriamento com nitrogênio líquido para se reproduzir, nos ensaios de torção, a história térmica medida durante a SAPNC do AID. Assim, foram reproduzidas as microestruturas da zona termomecanicamente afetada (ZTMA), tanto do lado de avanço quanto do lado de retrocesso, e da zona misturada (ZM) central. As microestruturas foram comparadas em termos de morfologia, de fração volumétrica, de tamanho de grão médio e de fração recristalizada de cada fase, por meio de microscopia óptica e difração de elétrons retroespalhados (EBSD). Além disso, foram analisados os mecanismos de amaciamento de cada fase durante a deformação a quente. Simulações numéricas do ensaio de torção foram realizadas para determinar a deformação verdadeira e a taxa de deformação em cada região simulada. A ZTMA foi simulada fisicamente a 1030 °C...

Nondestructive Characterization and Evaluation of Embrittlement Kinetics and Elastic Constants of Duplex Stainless Steel SAF 2205 for Different Aging Times at 425°C and 475°C

Vera Lúcia de Araújo Freitas; Paulo G. Normando; Victor Hugo C. de Albuquerque; Edgard de Macedo Silva; Antonio Almeida Silva; João Manuel R. S. Tavares
Fonte: Universidade do Porto Publicador: Universidade do Porto
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
75.38%
In this work, an experimental study was carried out to evaluate the potential of the ultrasonic technique, with ultrasonic velocity and attenuation measurements, to assess the heat aging effects on duplex stainless steel SAF 2205, at temperatures of 425 ºC and 475 ºC for time periods of 12 h, 24 h, 50 h, 100 h and 200 h, as well as in the as received state of the material. Velocity measurements were calculated for both longitudinal and transversal waves. The elastic constants, Young#8217;s modulus and shear modulus, of the material were computed from the relationship between longitudinal and transversal velocities. For the ultrasonic attenuation, only longitudinal waves were considered. Despite the large scatter measurements, both ultrasonic velocity and attenuation increased with the heat aging time, particularly at 475 ºC. Thus, it may be concluded that the technique used is promising and provides relevant contributions to an accurate characterization of materials and evaluation of their mechanical properties in a non-destructive manner.

Artifact level produced by different femoral head prostheses in CT imaging: diamond coated silicon nitride as total hip replacement material

Rodrigues, Simone; Paiva, José; De Francesco, Silvia; Amaral, Margarida I.; Oliveira, Filipe; Silva, Rui
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
75.4%
Commercial femoral head prostheses (cobalt–chromium alloy, yttria partially stabilized zirconia (Y-PSZ) and alumina) and new silicon nitride ceramic ones (nanocrystalline diamond coated and uncoated) were compared in terms of artifact level production by computed tomography (CT). Pelvis examination by CT allows the correct diagnosis of some pathologies (e.g. prostate and colon cancer) and the evaluation of the prosthesis-bone interface in post-operative joint surgery. Artifact quantification is rarely seen in literature despite having a great potential to grade biomaterials according to their imaging properties. Materials’ characteristics (density and effective atomic number), size and geometry of the prostheses can cause more or less artifact. A quantification procedure based on the calculation of four statistical parameters for the Hounsfield pixel values (mean, standard deviation, mean squared error and worst case error) is presented. CT sequential and helical scanning modes were performed. Results prove the artifact reproducibility and indicate that the cobalt–chromium and Y-PSZ are the most artifact-inducing materials, while alumina and silicon nitride (diamond coated and uncoated) ceramic ones present a low level of artifact. Considering the excellent biocompatibility and biotribological behaviour reported in earlier works...

A comparative study of high resolution cone beam X-ray tomography and synchrotron tomography applied to Fe- and Al-alloys

Kastner, Johann; Harrer, Bernhard; Requena, Guillermo; Brunke, Oliver
Fonte: Butterworth-Heinemann Publicador: Butterworth-Heinemann
Tipo: Artigo de Revista Científica
Publicado em /10/2010 EN
Relevância na Pesquisa
65.34%
X-ray computed tomography (XCT) has become a very important method for non-destructive 3D-characterization and evaluation of materials. Due to measurement speed and quality, XCT systems with cone beam geometry and matrix detectors have gained general acceptance. Continuous improvements in the quality and performance of X-ray tubes and XCT devices have led to cone beam CT systems that can now achieve spatial resolutions down to 1 μm and even below. However, the polychromatic nature of the source, limited photon flux and cone beam artefacts mean that there are limits to the quality of the CT-data achievable; these limits are particularly pronounced with materials of higher density like metals. Synchrotron radiation offers significant advantages by its monochromatic and parallel beam of high brilliance. These advantages usually cause fewer artefacts, improved contrast and resolution.

Multimodal optical studies of single and clustered colloidal quantum dots for the long-term optical property evaluation of quantum dot-based molecular imaging phantoms

Kang, HyeongGon; Clarke, Matthew L.; Lacerda, Silvia H. De Paoli; Karim, Alamgir; Pease, Leonard F.; Hwang, Jeeseong
Fonte: Optical Society of America Publicador: Optical Society of America
Tipo: Artigo de Revista Científica
Publicado em 09/05/2012 EN
Relevância na Pesquisa
75.35%
Understanding the optical properties of clustered quantum dots (QDs) is essential to the design of QD-based optical phantoms for molecular imaging. Single and clustered core/shell colloidal QDs of dimers, trimers, and tetramers are self-assembled, separated, and preferentially collected using electrospray differential mobility analysis (ES-DMA) with electrostatic deposition. Multimodal optical characterization and analysis of their dynamical photoluminescence (PL) properties enables the long-term evaluation of the physicochemical and optical properties of QDs in a single or a clustered state. A multimodal time-correlated spectroscopic confocal microscope capable of simultaneously measuring the time evolution of PL intensity fluctuation, PL lifetime, and emission spectra reveals the long-term dynamic optical properties of interacting QDs in individual dimeric clusters of QDs. This new method will benefit research into the quantitative interpretation of fluorescence intensity and lifetime results in QD-based molecular imaging techniques. The process of photooxidation leads to coupling of the QDs in a dimer, leading to unique optical properties when compared to an isolated QD. These results guide the design and evaluation of QD-based phantom materials for the validation of the PL measurements for quantitative molecular imaging of biological samples labeled with QD probes.

Ultrasonic nondestructive evaluation and imaging of defects in reinforced cementitious materials

Wang, Ji-yong, 1967-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 leaves; 7775811 bytes; 7775571 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
75.42%
Characterization of defect is one of the important objectives of nondestructive evaluation (NDE) for condition assessment of structures. Among many other NDE techniques, ultrasonic methods play a prominent role in the both quantitative and qualitative assessment of discontinuities in reinforced cementitious materials. Due to the heterogeneous nature of concrete, ultrasonic waves are highly scattered and attenuated, leading to the difficulty of concrete inspection using conventional ultrasonic techniques, including those that work well on relatively homogeneous materials such as metals. This thesis presents an advanced method for sizing and imaging of defects in reinforced cementitious materials. A two-dimensional, three-phase composite model of concrete is proposed to study the propagation and interaction behaviors of ultrasonic waves in concrete structures, and to gain a knowledge about wave diffraction with multiple cylindrical obstacles. The response of the modeled concrete structure to an incident ultrasonic pulse input signal (pulsed ultrasonic P-wave) is analytically investigated and simulated. A characteristic profile of the defect sizing as a function of focal depth is formulated via the synthetic focusing technique. A defect sizing parameter...

Mechanical characterization and in vivo operation of an implantable drug delivery MEMS device

Li, Yawen, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 137 p.
ENG
Relevância na Pesquisa
85.4%
The goal of this thesis was to advance an implantable drug delivery MEMS (MicroElectroMechanical Systems) device developed in our laboratory. This device was designed to locally deliver multiple substances in complex release profiles in order to maximize the effectiveness of drug therapies. It consists of an array of microreservoirs etched into a silicon substrate. Different types and dosages of drugs can be contained in these reservoirs capped by thin gold membranes. The drug release is achieved by the application of a small anodic potential on the gold membrane in a chloride containing medium (such as the body fluid). The gold membrane will corrode and disintegrate so that the drug contained within the reservoir is free to diffuse into the surrounding medium. Previous researchers have demonstrated in vitro and in vivo release of tracer molecules as well as a radiolabled chemotherapeutic agent (carmustine, or BCNU) from the device. However, systematic characterization of the mechanical and electrochemical behavior of gold membranes on the drug delivery device was necessary in order to achieve more reliable device performance and to demonstrate efficacy of BCNU delivered from the MEMS device against an experimental tumor model. A bulge test apparatus was constructed to characterize the mechanical properties of gold membranes. Uniform pressure was applied from underneath the gold membrane and the membrane deflection was measured using optical interferometry. Analyzing the deflection and pressure data allowed extraction of the elastic modulus and residual stress of the gold membrane.; (cont.) Gold membranes with in-plane sizes ranging from 20 to 200pim showed lower modulus (126-168 GPa) than bulk (111) single crystal gold (189 GPa). But their yield strength (317-351 MPa) was higher than the bulk value. An in situ experimental setup was constructed to observe the electrochemical disintegration process of the gold membranes. Real time images recorded from a CCD camera showed non-uniform corrosion occurring first around the membrane edges. Bulge tests on the corroded membranes indicated a gradual loss of mechanical integrity of the gold membranes due to corrosion. The gold membrane disintegration probably occurred by a combination of membrane thinning through active dissolution and accumulation of plastic deformation due to the transient formation of a passive film on top of the gold membrane in each voltammetry cycle. Dense gold membranes with reproducible opening behavior are critical to the success of large scale in vivo studies and future commercial applications. Defects in the gold membranes led to premature leakage of BCNU...

Preparo e avalia????o de comp??sitos contendo nova matriz inorg??nica monomodal submicrom??trica; Preparation and evaluation of new inorganic matrix composites containing submicron monomodal

VALENTE, Lisia Lorea
Fonte: Universidade Federal de Pelotas; Odontologia; Programa de P??s-Gradua????o em Odontologia; UFPel; BR Publicador: Universidade Federal de Pelotas; Odontologia; Programa de P??s-Gradua????o em Odontologia; UFPel; BR
Tipo: Dissertação
POR
Relevância na Pesquisa
65.38%
In this study dental composites containing a novel monomodal inorganic matrix based on submicron Ba-Al-Si glass particles (NanoFine NF180, Schott) were prepared and evaluated. Composites with particles of similar composition but micron-sized (UltraFine UF1.0, Schott) served as a reference. The study was carried out in two phases: (i) characterization of the inorganic particles, involving x-ray microanalysis and granulometry; (ii) preparation and characterization of micron and submicron composites involving analysis of the morphology of the composites and measurements of radiopacity, degree of C=C conversion, hardness, flexural strength and modulus, work-of-fracture, surface roughness and gloss before and after toothbrushing abrasion and compressive creep. The composites were formulated from the same co-monomer based on Bis-GMA, Bis-EMA8, UDMA and TEGDMA at a 7:7:5:1 (w/w) ratio, with photoinitiators added. A mass of 75% of micron and 78% of submicron particles were incorporated based on pilot studies. Quantitative data restricted to direct comparisons between the composites were analyzed using t-tests. Roughness and gloss data for the comparison between the composites before and after toothbrushing were submitted to Repeated Measures Analysis of Variance and Student-Newman-Keuls test (5%). Both inorganic systems showed narrow grain size range (175??30 and 1000??200nm)...

In situ synthesis and characterization of a hierarchically structured Al₂0₃/Al₃Ti composite; In situ synthesis and characterization of a hierarchically structured Al(2)0(3)/Al(3)Ti composite

Zhu, H.; Jiang, Y.; Song, J.; Li, J.; Munroe, P.; Xie, Z.
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
75.43%
A hierarchically structured α-Al₂O₃/Al₃Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO₂. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti₂O₃, and γ-Al₂O₃, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO₂ occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al₂O₃/Al₃Ti composites.; Heguo Zhu, Yaling Jiang, Jinzhu Song, Jianliang Li, Paul Munroe, Zonghan Xie

Physical simulation of investment casting of Mar-M247 Ni-based superalloy

Rahimian, Mehdi
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
75.33%
Mar-M247 is a Ni-based superalloy developed for high temperatures applications, such as advanced jet engines, where high strength and excellent creep resistance are required. Investment casting process has been widely used for fabrication of complex shape parts and is only commercially technique for fabrication of nozzle guide vanes (NGVs) known as a one of the most important structural parts of engines and gas turbines. Nevertheless, the development of NGVs is hindered by the complexity of investment casting process of complex shape parts. Therefore, there is high demand to find and apply a method to overcome those drawbacks. Physical simulation of investment can be a method to tackle these shortcomings. Physical simulation of investment casting was developed to mimic solidification of alloy during investment casting of new generation NGVs from Mar-M247 by high capability physical simulator machines. This tool, consisting of thermal model and melting/solidification experiments, is the exact reproduction of the thermal and mechanical history of full scale investment casting process in the laboratory scale. Initially, the Pro-Cast based thermal model was developed, validated and applied to predict local cooling rates at defined points of NGVs. Then...

Mechanical Properties and Microstructure of AZ31B Magnesium Alloy Processed by I-ECAP

GZYL, Michal; ROSOCHOWSKI, Andrzej; PESCI, Raphaël; OLEJNIK, Lech; YAKUSHINA, Evgenia; WOOD, Paul
Fonte: Springer Publicador: Springer
EN
Relevância na Pesquisa
95.36%
Incremental equal channel angular pressing (I-ECAP) is a severe plastic deformation process used to refine grain size of metals, which allows processing very long billets. As described in the current article, an AZ31B magnesium alloy was processed for the first time by three different routes of I-ECAP, namely, A, BC, and C, at 523 K (250 C). The structure of the material was homogenized and refined to ∼5 microns of the average grain size, irrespective of the route used. Mechanical properties of the I-ECAPed samples in tension and compression were investigated. Strong influence of the processing route on yield and fracture behavior of the material was established. It was found that texture controls the mechanical properties of AZ31B magnesium alloy subjected to I-ECAP. SEM and OM techniques were used to obtain microstructural images of the I-ECAPed samples subjected to tension and compression. Increased ductility after I-ECAP was attributed to twinning suppression and facilitation of slip on basal plane. Shear bands were revealed in the samples processed by I-ECAP and subjected to tension. Tension-compression yield stress asymmetry in the samples tested along extrusion direction was suppressed in the material processed by routes BC and C. This effect was attributed to textural development and microstructural homogenization. Twinning activities in fine- and coarse-grained samples have also been studied.

Assessment of FRP-confined concrete : understanding behavior and issues in nondestructive evaluation using radar; Assessment of fiber-reinforced plastic-confined concrete : understanding behavior and issues in nondestructive evaluation using radar

Ortega, Jose Alberto, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 237 p.; 13476446 bytes; 13476238 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
65.53%
Increase in the use of fiber-reinforced polymer (FRP) composite materials for strengthening and retrofitting of concrete columns and bridge piers has urged the development of' an effective non-destructive evaluation (NDE) methodology. Radar technologies have shown great potential for assessing the structural and material integrity of FRP-confined concrete systems. In developing such technology, an interdisciplinary approach must be pursued by integrating contributions of various engineering fields. Under this framework, this thesis aims at establishing fundamental knowledge in two particular research areas: the mechanics and damage behavior of FRP-confined concrete and the characterization of electromagnetic (EM) properties for concrete and FRP materials. Research on mechanics and damage behavior of FRP-confined concrete involved a thorough literature survey on the state-of-the-art understanding of the subject and the execution of an experimental program for load-deformation characterization of FRP-confined concrete cylindrical specimens subjected to monotonic axial compressive loads. Based on the experimental results and comparative studies with recent analytical models, the experimental program was extended to the characterization of specific damage levels using a volumetric deformation metric. Visual inspection of the concrete core of specimens previously loaded to levels close to ultimate failure revealed the existence of significant residual volumetric strains...

Lattice modeling of ultrasonic nondestructive evaluation of attenuating materials

Thomas, Anton F. (Anton Felipe), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 208 p.
ENG
Relevância na Pesquisa
65.37%
Theoretical predictions of specific strength and specific stiffness of nanocomposites make them attractive replacements for alloys and fiber reinforced composites in future generations of numerous structures. The reliable and safe utilization of nanocomposites will require their periodic characterization with nondestructive evaluation. When subjected to ultrasonic waves, nanocomposites often exhibit attenuation that is an order of magnitude higher than that of carbon fiber reinforced polymeric composites. Thus, an accurate model of ultrasonic wave propagation in nanocomposites as well as several other modem composites must include attenuation. Lattice modeling is a heuristic approach that consists of the discretization of solids into regularly spaced particles interconnected via nearest-neighbor interactions. For example, the mass-spring-lattice model (MSLM), a lattice model for the simulation and visualization of elastic wave propagation, has been used in favor of other finite-difference and finite-element methods due to its straightforward implementation of boundary conditions and relatively inexpensive explicit numerical integration. Its utility notwithstanding, MSLM discretization produces documented, yet previously unresolved and uncharacterized...

Design, Characterization, and Evaluation of a Surface Plasmon Resonance Sensor

Greenley, Michael
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Tese de Doutorado
Publicado em //2012
Relevância na Pesquisa
65.34%

Characterization of thin films, prominently including self-assembled monolayers is important to the understanding of interfacial events in both biological and manufactured systems. To facilitate such work, a surface plasmon resonance device, or SPR, was constructed, and tests were conducted to evaluate the performance of the system relative to current systems and mathematical models. First, relevant analytical equations are introduced to describe the behavior of the system. In subsequent chapters, the design of the device, its calibration, and operating procedure are explained. Finally, the system is tested against samples with known behaviors, and the experimental and analytical results are compared.

; Thesis

Evaluation of a pulse coding technique for speckle reduction and structure characterization

Rao, Navalgund; Abury, M.
Fonte: The Institute of Electrical and and Electronics Engineers Publicador: The Institute of Electrical and and Electronics Engineers
Tipo: Proceedings Formato: 651967 bytes; application/pdf
EN_US
Relevância na Pesquisa
65.41%
Pulse coding techniques have been used in the past primarily to improve signal to (electronic) noise ratio. However, the flexibility inherent in pulse coding can be exploited to solve several problems in medical imaging and nondestructive testing. We have experimentally examined its potential for two such problems: (i) speckle reduction with multispectral imaging and data averaging; (ii) structural characterization of scattering medium on a scale below the resolution of the imaging system. The ability to change the point spread function and the spectral content with frequency modulated pulse coding has been utilized. Water filled sponge with pore size much smaller than the resolution cell volume was used as a speckle generating medium. A non-focused transducer was driven with FM coded pulses. The pulse compression processing was carried out digitally on a computer. FM pulses with 143 different combinations of center frequency f0 and 6 dB bandwidth Δf were used. Normalized decorrelation factors were calculated to evaluate effectiveness for speckle averaging. Significant decorrelation was observed specially at lower Δf, indicating a potential for frequency diversity processing for speckle reduction. Point signal to noise ratio (SNRA) was also calculated on the envelope detected signal for structural characterization. SNRA showed significant increase from its high density limit value of 1.91 (fully developed speckle) at certain specific frequencies. Both simulation and theoretical considerations are used to show that this resonance effect is a signature of the underlying semiperiodic scattering structure of the medium (Refer to PDF file for exact formulas).; "Evaluation of a pulse coding technique for speckle reduction and structure characterization...

Characterization and evaluation of cocoa (Theobroma cacao L.) pod husk as a renewable energy source

Martínez-Ángel,J. Daniel; Villamizar-Gallardo,R. Amanda; Ortíz-Rodríguez,O. Orlando
Fonte: Colegio de Postgraduados Publicador: Colegio de Postgraduados
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2015 EN
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65.34%
In Colombia, the cocoa pod husk (CPH) is expected to reach 2 100 000 t year-1 in 2021 which is usually burned or left over for decomposing outdoors at the plantations without any environmental control. Therefore, this study evaluated the energetic potential of CPH obtained after the initial processing of this fruit (Theobroma cacao L.). Three biological materials were analyzed: clone CCN-51 (CPH1), clone ICS-39 (CPH2) and a hybrid (CPH3), which present high yield and number of fruits per tree. The samples were examined by using different characterization techniques for raw biomass and ashes; in addition to the ultimate, proximate and heating value analyses, different fouling indexes were determined in order to estimate the phenomena of solids formation inside the reactor when combustion or gasification is used as a thermochemical valorization process. The Colombian CPHs contain relatively homogeneous levels of C, H and O, but very heterogeneous ash contents (1.4 to 12.9 wt %). The three studied samples showed high content of K2O in ashes (67 to 74 wt %). The higher heating value (HHV) ranged from 15 395 to 16 670 kJ kg-1. Furthermore, the fouling index and the fusibility analysis suggest the appearance of agglomeration and sintering phenomena when CPH is used as a fuel. The gasification is proposed as the process with major possibilities for the energetic use of CPH. CPH1 sample seems to allow a more stable and flexible operation...