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Selective excitation through tapered silica fibers of fluorescent two-photon polymerized structures

CORREA, Daniel S.; TRIBUZI, Vinicius; CARDOSO, Marcos Roberto; MISOGUTI , Lino; MENDONCA, Cleber Renato
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.11%
Two-photon polymerization has emerged as a powerful tool to design complex three-dimensional microstructures for applications ranging from biology to nanophotonics. To broaden the application spectrum of such microstructures, different materials have been incorporated to the polymers, aiming at specific applications. In this paper we report the fabrication of microstructures containing rhodamine 610, which display strong fluorescence upon one- and two-photon excitation. The latter increases light-penetration depth and spatial selectivity of luminescence. We also demonstrate that by using silica submicrometric wires we were able to select individual microstructures to be excited, which could be explored for designing microstructure-based optical circuits.; FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; CAPES from Brazil; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Air Force Office of Scientific Research (AFOSR) [FA9550-07-1-0374]; U.S. Air Force Office of Scientific Research (AFOSR)

Indirect doping of microstructures fabricated by two-photon polymerization with gold nanoparticles

Tribuzi, Vinicius; Correa, Daniel Souza; Avansi, Waldir, Jr.; Ribeiro, Caue; Longo, Elson; Mendonça, Cleber Renato
Fonte: OPTICAL SOC AMER; WASHINGTON Publicador: OPTICAL SOC AMER; WASHINGTON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.11%
Nanoplasmonics and metamaterials sciences are rapidly growing due to their contributions to photonic devices fabrication with applications ranging from biomedicine to photovoltaic cells. Noble metal nanoparticles incorporated into polymer matrix have great potential for such applications due to their distinctive optical properties. However, methods to indirectly incorporate metal nanoparticles into polymeric microstructures are still on demand. Here we report on the fabrication of two-photon polymerized microstructures doped with gold nanoparticles through an indirect doping process, so they do not interfere in the two-photon polymerization (2PP) process. Such microstructures present a strong emission, arising from gold nanoparticles fluorescence. The microstructures produced are potential candidates for nanoplasmonics and metamaterials devices applications and the nanoparticles production method can be applied in many samples, heated simultaneously, opening the possibility for large scale processes. (C) 2012 Optical Society of America; FAPESP; FAPESP; CNPq; CNPq; CAPES from Brazil; CAPES from Brazil

Fabricação de microestruturas com múltiplas dopagens via fotopolimerização por absorção de dois fótons; Fabrication of multi-doped microstructures by two-photon absorption photopolymerization

Otuka, Adriano José Galvani
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 23/03/2012 PT
Relevância na Pesquisa
37.28%
Microestruturas poliméricas dopadas despertam grande interesse nas áreas de óptica, fotônica e biologia, pois viabilizam a produção de dispositivos com propriedades específicas. Contudo, a dopagem de microestruturas com mais de um dopante é pouco explorada na literatura. Nesse contexto, o presente trabalho propõe o desenvolvimento de uma metodologia para fabricar microestruturas poliméricas com múltiplas dopagens, através de fotopolimerização por absorção de dois fótons. Esta técnica de microfabricação faz uso de um feixe laser pulsado (Ti:safira, 780 nm, 100 fs) que é focalizado, através de lentes de microscópio, no volume de uma resina polimérica contendo fotoiniciador composto orgânico responsável por iniciar o processo de polimerização. A intensidade dos pulsos de femtossegundos é alta o bastante para que processos não lineares absorcivos, nesse caso absorção de dois fótons, ocorram apenas no volume focal, induzindo a polimerização apenas ao seu redor. Como dopantes utilizamos os corantes fluorescentes Rodamina e Fluoresceína. Para averiguar a eficácia do sistema de fabricação desenvolvido, produzimos estruturas com apenas um dopante, e as caracterizamos utilizando microscopia óptica e eletrônica. Microestruturas contendo mais de um dopante...

Fabricação de microestruturas dopadas com nanofios de ZnO via fotopolimerização por absorção de dois fótons; Fabrication of microstructures doped with ZnO nanowires by two-photon absorption polymerization

Rodriguez, Ruben Dario Fonseca
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 24/07/2012 PT
Relevância na Pesquisa
37.18%
No presente trabalho produzimos microestruturas, através da técnica de fotopolimerização via absorção de dois fótons, dopadas com nanofios de ZnO, um material que vem sendo amplamente explorado devido as suas interessantes propriedades ópticas e elétricas. Para a fabricação das microestruturas, utilizamos um oscilador laser de Ti:safira que produz pulsos de aproximadamente 100 fs em 800 nm. A intensidade dos pulsos de femtossegundos é alta o suficiente para induzir a absorção¬ de dois fótons em torno do volume focal, localizando a polimerização a esta região. Portanto, através da varredura do feixe na resina polimérica fabrica-se a estrutura desejada. Neste trabalho, desenvolvemos uma metodologia para introduzir nanofios de ZnO às microestruturas fabricadas, a partir da mistura do pó de nanofios de ZnO à resina acrílica. A resina utilizada é uma combinação de duas resinas, o etoxilated(6)trimethylolpropane triacrylate (SR-499) e tris(2-hydroxy ethyl)isocyanurate triacrylate (SR-368). Como fotoiniciador utilizamos o Lucirin TPO-L (2,4,6-trimetilbenzoiletoxifenil phosphine oxide). As microestruturas produzidas foram caracterizadas pelas técnicas de microscopia óptica, microscopia eletrônica de varredura...

Fabricação de microestruturas poliméricas opticamente ativas integradas com nanofibras de vidro; Fabrication of optically active polymeric microstructures integrated with glass nanofibers

Gomes, Vinicius Tribuzi Rodrigues Pinheiro
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 19/04/2013 PT
Relevância na Pesquisa
27.24%
Este trabalho demonstra o uso da fotopolimerização via absorção de dois fótons na produção de microestruturas dopadas com compostos orgânicos e nanopartículas de Au. A capacidade de produção de microestruturas com propriedades variadas é extremamente relevante, pois viabiliza o desenvolvimento de uma nova geração de dispositivos ópticos. Além disso, realizamos a conexão entre as microestruturas fabricadas e fontes de excitação, por meio de nanofibras de vidro. A integração entre essas estruturas, e destas com meios externos de excitação e detecção, é um passo essencial para o desenvolvimento de microcircuitos fotônicos, que podem representar uma nova revolução tecnológica, a exemplo do que foram os microcircuitos eletrônicos. Exploramos as possibilidades de dopagem da resina usando: (i) um composto fluorescente, (ii) um composto com birrefringência fotoinduzida e (iii) nanopartículas de ouro. Microestruturas contendo Rodamina B apresentaram boa integridade estrutural e fluorescência, tendo sido usadas para demonstrar a conexão dos microelementos com meios externos de excitação. Através de nanofibras e de micromanipuladores, comprovamos a capacidade de excitação seletiva de microestruturas através do guiamento da luz de um laser de Ar+. Estruturas birrefringentes foram obtidas pela dopagem com o azopolímero HEMA-DR13. Montamos um aparato que permite a observação da dinâmica de indução de birrefringência nas microestruturas...

Fabricação de microambientes para crescimento celular utilizando polimerização via absorção de dois fótons; Fabrication of micro-environments to study cell growth by two-photon absorption polymerization

Salas, Oriana Ines Avila
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 25/11/2013 PT
Relevância na Pesquisa
27.11%
Neste trabalho, demonstramos a fabricação de microambientes tridimensionais para investigar o crescimento celular. Inicialmente, desenvolvemos um sistema de microfabricação que utiliza fotopolimerização via absorção de dois fótons, com o qual se pode fabricar um conjunto de microestruturas com formas e espaçamentos pré-determinados. Este sistema de fabricação utiliza pulsos de femtossegundos, provenientes de um laser de Ti:safira operando em 790 nm. A intensidade destes pulsos é alta o bastante para induzir a absorção de dois fótons no fotoiniciador, o qual é responsável por promover a polimerização em uma resina acrílica. A natureza não linear da absorção de dois fótons confina a excitação ao volume focal, permitindo a fabricação de estruturas tridimensionais com alta resolução espacial. Para a obtenção dos microambientes, foi necessário o desenvolvimento de um sistema opto-mecânico de movimentação, tanto do feixe quando do substrato da amostra. Com esta técnica, fabricamos microambientes compostos de estruturas com diferentes formas (paralelepípedos, cilindros e cones) e espaçamentos, os quais foram caracterizados através de microscopia óptica e eletrônica. Para demonstrar a viabilidade destes microambientes para a investigação do crescimento celular...

Caracterização estrutural de granitoides sintectônicos em ambiente de transcorrência

Schnorr, Evelin Roberta
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
Relevância na Pesquisa
27.11%
Os Granitoides Arroio Divisa (GAD), localizados no distrito de Quitéria, município de São Jerônimo, RS, representam uma associação de rochas predominantemente granodioríticas, foliadas, com enclaves microgranulares máficos e diques sinplutônicos, intrusivas no Complexo Arroio dos Ratos (CAR). Suas estruturas sugerem posicionamento em zona de cisalhamento dúctil correlacionada ao Cinturão de Cisalhamento Sul-brasileiro (CCSb), de idade neoproterozoica. Detalhamento estrutural foi desenvolvido em duas zonas, uma de baixa e outra de alta deformação, a fim de esclarecer as estruturas, as relações com as encaixantes e determinar as condições tectono-termais a que estavam submetidos os GAD quando do seu posicionamento. As principais estruturas observadas em escala de afloramento, na zona de mais baixa deformação, são uma foliação de origem magmático-deformacional, marcada pela orientação de feldspatos e biotitas, com componente milonítica de intensidade variável e mesma orientação. Na zona de mais alta deformação, predomina uma forte foliação milonítica, de direção e mergulho paralelos à foliação ígnea, aqui subordinada. As foliações, em ambas as zonas, possuem direção preferencial ENE-WSW, com mergulhos que variam de médio a predominantemente alto ângulos e lineações tipicamente de baixo caimento para WSW. As microestruturas geradas durante a cristalização indicam concomitante deformação atuante durante o seu posicionamento...

An overview of the microstructures present in high-speed steel - Carbides crystallography

Serna, M. M.; Jesus, E. R B; Galego, E.; Martinez, L. G.; Corrêa, H. P S; Rossi, J. L.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 48-52
ENG
Relevância na Pesquisa
36.87%
The aim of the work was to prepare an overview about the microstructures present in high-speed steel, focused on the crystallography of the carbides. High-speed steels are currently obtained by casting, powder metallurgy and more recently spray forming. High-speed steels have a high hardness resulting from a microstructure, which consists of a steel matrix (martensite and ferrite), in which embedded carbides of different crystal structure, chemical composition, morphology and size, exist. These carbides are commonly named MxC, where M represents one or more metallic atoms. These carbides can be identified by X-ray diffraction considering M as a unique metallic atom. In this work, it is discussed, in basis of the first principles of physics crystallography, the validation of this identification when it is considered that other atoms in the structure are substitutional. Further, it is discussed some requirements for data acquisition that allows the Rietveld refinement to be applied on carbide crystallography and phase amount determination.

Indirect doping of microstructures fabricated by two-photon polymerization with gold nanoparticles

Tribuzi, Vinicius; Corrêa, Daniel Souza; Avansi Junior, Waldir; Ribeiro, Caue; Longo, Elson; Mendonça, Cleber Renato
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 21107-21113
ENG
Relevância na Pesquisa
27.11%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Nanoplasmonics and metamaterials sciences are rapidly growing due to their contributions to photonic devices fabrication with applications ranging from biomedicine to photovoltaic cells. Noble metal nanoparticles incorporated into polymer matrix have great potential for such applications due to their distinctive optical properties. However, methods to indirectly incorporate metal nanoparticles into polymeric microstructures are still on demand. Here we report on the fabrication of two-photon polymerized microstructures doped with gold nanoparticles through an indirect doping process, so they do not interfere in the two-photon polymerization (2PP) process. Such microstructures present a strong emission, arising from gold nanoparticles fluorescence. The microstructures produced are potential candidates for nanoplasmonics and metamaterials devices applications and the nanoparticles production method can be applied in many samples, heated simultaneously, opening the possibility for large scale processes.

Quantification of the microstructures of hypoeutectic white cast iron using mathematical morphology and an artificial neural network

Victor Hugo C. de Albuquerque; João Manuel Ribeiro da Silva Tavares; Paulo César Cortez
Fonte: Universidade do Porto Publicador: Universidade do Porto
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.11%
This paper describes an automatic system for segmentation and quantification of the microstructures of white cast iron. Mathematical morphology algorithms are used to segment the microstructures in the input images, which are later identified and quantified by an artificial neuronal network. A new computational system was developed because ordinary software could not segment the microstructures of this cast iron correctly, which is composed of cementite, pearlite and ledeburite. For validation purpose, 30 samples were analyzed. The microstructures of the material in analysis were adequately segmented and quantified, which did not happen when we used ordinary commercial software. Therefore, the proposed system offers researchers, engineers, specialists and others, a valuable and competent tool for automatic and efficient microstructural analysis from images.

Study on microstructures and work hardening behavior of ferrite-martensite dual-phase steels with high-content martensite

Zuo,Xiurong; Chen,Yunbo; Wang,Miaohui
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2012 EN
Relevância na Pesquisa
36.87%
A kind of medium-carbon low-alloy dual-phase steels with high-content martensite produced by intercritical annealing at 785-830 ºC for 10-50 minutes were studied in aspect of microstructures and work hardening behavior using SEM and tensile testing machine. The experimental results showed that the work hardening of the studied steels obeyed the two-stage work hardening mechanism, whose work hardening exponent of the first stage was higher than that of the second stage. The work hardening exponent increased with increasing the intercritical annealing temperature and time. For series A steel intercritically annealed at 785 ºC with starting microstructure of ferrite plus pearlite, austenite nucleated at the pearlite colonies, so the holding time of only 50 minutes can increase the work hardening exponent obviously. For series B steel with starting microstructure of martensite, austenite nucleated at lath interfaces, lath colony boundaries of primary martensite and carbides, accelerating the formation of austenite, so holding time for 30 minutes made the work hardening exponent increase obviously. High work hardening rate during initial plastic deformation (<0.5% strain) was observed.

Rapid Constructions of Microstructures for Optical Fiber Sensors Using a Commercial CO2 Laser System

Irawan, Rudi; Chuan, Tjin Swee; Meng, Tay Chia; Ming, Tan Khay
Fonte: Bentham Open Publicador: Bentham Open
Tipo: Artigo de Revista Científica
Publicado em 27/06/2008 EN
Relevância na Pesquisa
27.18%
Exposing an optical fiber core to the measurand surrounding the fiber is often used to enhance the sensitivity of an optical fiber sensor. This paper reports on the rapid fabrication of microstructures in an optical fiber using a CO2 laser system which help exposing the optical fiber core to the measurand. The direct-write CO2 laser system used is originally designed for engraving the polymeric material. Fabrications of microstructures such as in-fiber microhole, D-shaped fiber, in-fiber microchannel, side-sliced fiber and tapered fiber were attempted. The microstructures in the fibers were examined using a SEM and an optical microscope. Quality of microstructures shown by the SEM images and promising results from fluorescence sensor tests using in-fiber microchannels of 100μm width, 210μm depth and 10mm length show the prospect of this method for use in optical fiber sensor development. The direct-write CO2 laser system is a flexible and fast machining tool for fabricating microstructures in an optical fiber, and can possibly be a replacement of the time consuming chemical etching and polishing methods used for microstructure fabrications of optical the fiber sensors reported in other literatures.

In-Situ Roughening of Polymeric Microstructures

Shadpour, Hamed; Allbritton, Nancy L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/2010 EN
Relevância na Pesquisa
27.18%
A method to perform in-situ roughening of arrays of microstructures weakly adherent to an underlying substrate was presented. SU8, 1002F, and polydimethylsiloxane (PDMS) microstructures were roughened by polishing with a particle slurry. The roughness and the percentage of dislodged or damaged microstructures was evaluated as a function of the roughening time for both SU8 and 1002F structures. A maximal RMS roughness of 7-18 nm for the surfaces was obtained within 15 to 30 s of polishing with the slurry. This represented a 4-9 fold increase in surface roughness relative to that of the native surface. Less than 0.8% of the microstructures on the array were removed or damage after 5 min of polishing. Native and roughened arrays were assessed for their ability to support fibronectin adhesion and cell attachment and growth. The quantity of adherent fibronectin was increased on roughened arrays by two-fold over that on native arrays. Cell adhesion to the roughened surfaces was also increased compared to native surfaces. Surface roughening with the particle slurry also improved the ability to stamp molecules onto the substrate during microcontact printing. Roughening both the PDMS stamp and substrate resulted in up to a 20-fold improvement in the transfer of BSA-Alexa Fluor 647 from the stamp to the substrate. Thus roughening of micron-scale surfaces with a particle slurry increased the adhesion of biomolecules as well as cells to microstructures with little to no damage to large scale arrays of the structures.

Using femtosecond laser to fabricate highly precise interior three-dimensional microstructures in polymeric flow chip

Lee, Chia-Yu; Chang, Ting-Chou; Wang, Shau-Chun; Chien, Chih-Wei; Cheng, Chung-Wei
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
Publicado em 18/10/2010 EN
Relevância na Pesquisa
27.18%
This paper reports using femtosecond laser marker to fabricate the three-dimensional interior microstructures in one closed flow channel of plastic substrate. Strip-like slots in the dimensions of 800 μm×400 μm×65 μm were ablated with pulse Ti:sapphire laser at 800 nm (pulse duration of ∼120 fs with 1 kHz repetition rate) on acrylic slide. After ablation, defocused beams were used to finish the surface of microstructures. Having finally polished with sonication, the laser fabricated structures are highly precise with the arithmetic roughness of 1.5 and 4.5 nm. Fabricating such highly precise microstructures cannot be accomplished with nanosecond laser marking or other mechanical drilling methods. In addition, since laser ablation can directly engrave interior microstructures in one closed chip, glue smearing problems to damage molded microstructures possibly to occur during the chip sealing procedures can be avoided too.

Benchtop fabrication of PDMS microstructures by an unconventional photolithographic method

Hwang, Chang Mo; Sim, Woo Young; Lee, Seung Hwan; Foudeh, Amir M; Bae, Hojae; Lee, Sang-Hoon; Khademhosseini, Ali
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.24%
Poly(dimethylsiloxane) (PDMS) microstructures have been widely used in bio-microelectromechanical systems (bio-MEMS) for various types of analytical, diagnostic and therapeutic applications. However, PDMS-based soft lithographic techniques still use conventional microfabrication processes to generate a master mold, which requires access to clean room facilities and costly equipment. With the increasing use of these systems in various fields, the development of benchtop systems for fabricating microdevices is emerging as an important challenge in their widespread use. Here we demonstrate a simple, low-cost and rapid method to fabricate PDMS microstructures by using micropatterned poly(ethylene glycol) diacrylate (PEGDA) master molds. In this method, PEGDA microstructures were patterned on a glass substrate by photolithography under ambient conditions and by using simple tools. The resulting PEGDA structures were subsequently used to generate PDMS microstructures by standard molding in a reproducible and repeatable manner. The thickness of the PEGDA microstructures was controllable from 15 to 300 μm by using commonly available spacer materials. We also demonstrate the use of this method to fabricate microfluidic channels capable of generating concentration gradients. In addition...

Spatiotemporal Characterization of Extracellular Matrix Microstructures in Engineered Tissue: A Whole-Field Spectroscopic Imaging Approach

Xu, Zhengbin; Ozcelikkale, Altug; Kim, Young L.; Han, Bumsoo
Fonte: American Society of Mechanical Engineers Publicador: American Society of Mechanical Engineers
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.18%
Quality and functionality of engineered tissues are closely related to the microstructures and integrity of their extracellular matrix (ECM). However, currently available methods for characterizing ECM structures are often labor-intensive, destructive, and limited to a small fraction of the total area. These methods are also inappropriate for assessing temporal variations in ECM structures. In this study, to overcome these limitations and challenges, we propose an elastic light scattering approach to spatiotemporally assess ECM microstructures in a relatively large area in a nondestructive manner. To demonstrate its feasibility, we analyze spectroscopic imaging data obtained from acellular collagen scaffolds and dermal equivalents as model ECM structures. For spatial characterization, acellular scaffolds are examined after a freeze/thaw process mimicking a cryopreservation procedure to quantify freezing-induced structural changes in the collagen matrix. We further analyze spatial and temporal changes in ECM structures during cell-driven compaction in dermal equivalents. The results show that spectral dependence of light elastically backscattered from engineered tissue is sensitively associated with alterations in ECM microstructures. In particular...

Computation and Simulation of the Effect of Microstructures on Material Properties

Carter, W. Craig
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 1514395 bytes; application/pdf
EN_US
Relevância na Pesquisa
37.18%
Methods for and computed results of including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) ferroelectric materials for actuator devices; 2) coarse-graining of atomistic data for simulations of microstructural evolution during processing; 3) periodic and non-periodic photonic composites; and 4) re-chargeable battery microstructures.; Singapore-MIT Alliance (SMA)

Numerical Modelling of Ice Microstructures; Numerische Modellierung von Mikrostrukturen in Eis

Rößiger, Jens
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
36.87%
Accurate modelling of ice mechanical behaviour under natural conditions is important for climate reconstruction and prediction, as well as for other scientific questions. It influences estimates of sea level changes and interpretation of past climate variations or signals recorded in ice cores. Better insight into the behaviour and constitutive equations of ice is imperative to improve modelling of glaciers and ice sheets. The aim of this thesis was to develop numerical models to simulate the microstructural behaviour of ice, as observed in nature and experiments. Numerical simulations were carried out with the numerical modelling platform "Elle", for which many new routines and algorithms were developed and implemented in this project. In a first series of models static grain growth and simultaneous grain-size reduction by rotational recrystallization was investigated. Well-established theory for static grain growth predicts a linear increase of the grain area with time for ice. The growth rate is then determined by the growth parameter k, which is commonly assumed to be a temperature and material-dependent constant. However, the simulations show that k also depends on the microstructure and can thus vary as the microstructure evolves. Experiments that start with non-equilibrium microstructures potentially yield growth parameters (k and the growth exponent...

Numerical simulation of deformation microstructures and folds in polar ice and ductile rocks

Llorens Verde, Maria Gema
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
EN
Relevância na Pesquisa
37.11%
This thesis contains 8 manuscripts for peer-reviewed journals (4 published, 2 submitted, 2 to be submitted within 4 weeks) that present studies of deformation microstructures and folds in polar ice and ductile anisotropic rocks by means of numerical simulations. It is organized in four different parts that focus: (1) Viscoplastic deformation of polycrystalline polar ice in simple and pure shear coupled with dynamic recrystallisation simulating microstructure evolution and formation of folds; (2) Folding and unfolding of single and multilayers in pure and simple shear; (3) Influence of anisotropy degree and type on rotation of rigid bodies (porphyroclasts and porphyroblasts); and (4) Analysis of the effects of dynamic recrystallisation on the rheology and microstructures of partially molten rocks. The first part (chapters 2, 3 and 4) contains three manuscripts analysing the influence of dynamic recrystallisation on deformation of pure polar ice. A full-field viscoplastic code (FFT) that fully reproduces the ice crystal’s mechanical anisotropy is coupled with dynamic recrystallisation processes to perform a series of numerical simulations in pure (chapter 2) and in simple shear (chapter 3 and 4). The results show that dynamic recrystallisation (DRX) has remarkable effects on the developed ice microstructures...

NUMERICAL PREDICTION OF EFFECTIVE ELASTIC PROPERTIES AND EFFECTIVE THERMAL EXPANSION COEFFICIENT FOR POROUS YSZ MICROSTRUCTURES IN SOLID OXIDE FUEL CELLS

Shakrawar, Sangeeta
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
27.18%
Solid oxide fuel cells represent a potentially important application for ceramic materials. There are, however, some significant issues which can affect the reliability and durability of the cell. Mechanical failure owing to stress is one of the critical factors which can affect the stability and working life of the fuel cell stacks. These stresses generate in Solid Oxide Fuel Cells (SOFCs) owing to mechanical forces and change in temperature during fabrication, assembly and operating conditions. There can be chances of cell delamination and micro-cracks in cell electrodes if these stresses are too high. The elastic properties and thermal expansion coefficient play a vital role to improve cell stability and performance. These properties depend on the types of materials and geometries of the composites. In this research, a numerical framework to predict the effective elastic properties and the effective thermal expansion coefficient for porous Yttria-Stabilized Zirconia (YSZ) electrode microstructures in a Solid Oxide Fuel Cell is presented. The electrodes of Solid Oxide Fuel Cells are discretized as porous microstructures that are formed by randomly distributed and overlapping spheres with particle size distributions that match those of actual ceramic powder. Three-dimensional (3D) microstructures of YSZ-pore are formed with a porosity ranging from 25% to 40%. The technique involves the construction of the YSZ-pores microstructures based on measurable starting parameters and subsequent numerical prediction of effective elastic properties and effective thermal expansion coefficient. Three domain sizes are considered for the generation of YSZ-pore microstructures. The method of prediction of effective Young’s modulus (Eeff)...