Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Restricted until October 2004. Includes bibliographical references.

Thesis (doctoral)--VTT Micronova, 2006. / Includes bibliographical references. Also available on the World Wide Web.

Carbon fibre reinforced polymer, or CFRP composite materials, play an increasingly important role in modern manufacturing. They are widely used in aerospace, and their use is currently spreading to other industries where high strength-to-weight ratios are required. However, machining of composites is still a challenging task and often hampered by poor quality. Despite the extensive research that was conducted on the machining of composite materials over the last few years, mechanical drilling still suffers from delamination, fibre pull-out and poor surface finish, whereas laser cutting produces microstructured defects and a taper problem. This thesis reports on the drilling of CFRP composites by demonstrating the possibility of drilling small diameter holes (i.e. 8mm) into 25.4mm thick carbon fibre reinforced polymer composites (CFRPs) using mechanical drilling and laser drilling as stand-alone processes and as a sequential combination. The research involved four main phases of experimental testing. The first part of Phase 1 involved!preliminary experiments of drilling thick CFRP to identify the most suitable drilling strategy. Three mechanical drilling strategies conducted in the same parameter by using a 2-flute uncoated WC twist drill that was assessed with respect to feasibility of drilling thick CFRP. The results showed that the single-step strategy was the most feasible strategy to drill thick CFRP compared to 2- and 4-peck drilling strategies. The second part of Phase 1 concerned the influence of speed-feed combinations on hole quality by utilising three twist drills with different materials and geometries in both an uncoated and coated condition. The results indicated that a significant increase in peel-up delamination was found with increasing feed rate. In contrast, using a constant feed rate but increasing the spindle speed seemed to reduce peel-up delamination. Furthermore, the hole entry for 2-flute uncoated WC drill bits was an uncommon study finding because most of the previous researchers experienced more damages at the hole exit and their investigation focused on the hole exit only. Currently, implementation of laser technology in cutting and drilling composites is becoming popular as an alternative solution. Various experiments were conducted with the goal of identifying the effects of machining parameters on key output measures (i.e. heat affected zone (HAZ), hole depth and other damages) in drilling of 25.4 mm thick CFRP by using a fibre laser. Phase 2 involved a number of machining parameters selected to identify the potential of a fibre laser in drilling thick CFRP composites (i.e. laser power, scanning speed, focal point plane position (FPP), assisted-gas type and gas pressure). The results proved that a fibre laser could penetrate thick CFRP to a 22mm depth only. Moreover, the spiral trepanning strategy was able to penetrate 80% out of the total thickness of the CFRP in continuous wave (CW) mode, whereas the modulated laser beam (i.e. laser pulse mode) can penetrate 67% only. This result was a major recorded breakthrough because previous research attempts cut up to 5mm only. Laser power proved to be the most influential factor for hole depth in laser drilling of thick CFRP when the spiral trepanning strategy was applied. Machining trials were conducted in Phase 3 by using a 16kW fibre laser in modulated pulsed laser mode. In this phase, laser power of more than 1kW was attempted to cut the whole thickness of CFRP composites in CW mode, but it was unsuccessful. However, a new parameter was discovered (i.e. the cooling time between passes in modulated pulsed mode), which proved a considerable reduction of HAZ when the higher cooling time was imposed. Finally, phase 4 involved the experiments of sequential laser-mechanical drilling. A 1kW fibre laser was selected as a pre-drilling or initial step and followed by mechanical drilling as the final step. The sequential drilling method successfully reduced thrust force and torque for mechanical drilling by an overall average of 61%, resulting in high productivity and decreasing the thermal and mechanical stresses in the cutting tool and, in turn, promoting higher tool life. The highest delamination factor (Fda) ratio was experienced by the sequential laser 8mm – mechanical 8mm for both tools (i.e. 2- and 3-flute uncoated tungsten carbide) and laser pre-drilling strategies (i.e. single- and double-side). Thus, a novel laser-mechanical sequential drilling technique was developed, evaluated and tested in the drilling of thick CFRP composites; this is the first time ever in drilling thick CFRP (i.e. 25.4mm).

Ce projet de recherche conjugue deux aspects complémentaires : le développement d’un montage de microscopie intégrant un système d'Optique Adaptative (OA) et l’étude de masses cancéreuses (Sphéroïdes Multicellulaires) sous pression mécanique.Ces deux axes seront mutuellement bénéfiques puisque l’implémentation de l’OA rendra possible l’imagerie et les mesures physiques au sein des sphéroïdes ; d’un autre côté, l’étude des sphéroïdes permettra de caractériser les aberrations induites par ce type d’échantillons et de mieux comprendre les exigences sur le système d’OA qu’imposent l’observation de ces échantillons ainsi que les limites de la microscopie optique dans les tissus biologiques. / This research project combines two complementary aspects: the development of an assembly incorporating an Adaptive Optics microscope system and the study of cancerous masses (multicellular spheroids) under mechanical pressure.These two axes are mutually beneficial since the implementation of the adaptive optics will enable imaging and physical measurements in spheroids; On the other hand, the study of spheroids will characterize the aberrations induced by this type of samples and understand the requirements of the adaptive optics system imposed by the observation of these samples as well as the limits of optical microscopy in biological tissues.

Le développement du marché des appareils de communication nomades, a nécessité l'intégration de composants passifs et actifs sur du silicium via des montages « hybrides ».Ceci a amené le LMP partenaire de l'entreprise STMicroelectronics à rechercher des solutions pour une intégration « monolithique ». Le silicium micro/mésoporeux est un candidat potentiel pour satisfaire les exigences de cette intégration. Ce travail traite de la réalisation de caissons profonds de silicium poreux sur silicium résistif de type P 30-50 Ω.cm et N 37-46Ω.cm. L'utilisation de l'acide acétique comme solvant industriellement compatible nous a permis de réaliser des structures micro/mésoporeuses. L'intégrité mécanique de nos échantillons a été étudiée via la mesure de la porosité en fonction de l'épaisseur. Ainsi des caissons poreux avec des épaisseurs de plus de 400 µm et 50 % de porosité ont été fabriqués.La réalisation d'une couche N⁺ sur du silicium type N 37-46 Ω.cm a permis la mise en œuvre de doubles couches composées d'une dizaine de micromètres de micro/mésoporeuse sur une couche de 200 µ.m de silicium macroporeux. Des changements importants ont été observés par addition d'une très faible quantité d'un tensioactif (triton X-I00®) a notre solution électrolytique et où des doubles couches ont été obtenues sur silicium type P 30-50 Ω.cm. / The rapid expansion of wireless devices caused a tremendous demand of the development of active and passive devices integration on silicon via « hybrid » systems. The search of a« monolithic » integration has led the LMP in partnership with STMicroelectronics to focus on this topic. Micro/Mesoporous silicon is a good candidate to fulfill the requirements to achieve this purpose. The present work deals with the realization of thick porous silicon layers on low doped P type (30-50 Ω.cm) and N type Si (37-46 Ω.cm). The use of a particular solution based on HF-H₂O and acetic acid allowed the implementation of micro/mesoporous Si structures. The mechanical integrity is studied via the porosity and the PS layer thickness.Thus layers with a thickness up to 400 µm have been implemented with a porosity of 50 % on P Type Si samples. Double layers with micro/mesoporous layer of tenth micrometers on a macroporous layer stack up to 200 µm have been realized on N-Type Si samples via the realization of an N⁺ layer by phosphorous implantation. Important changes occurred when a tiny amount of surfactant (triton X-I00®) has been introduced into our organic electrolyte and allowed the implementation of double layers on P type Si.

Aços de alta resistência e baixa liga (HSLA) tem sido amplamente empregados na indústria nos últimos anos, em especial na indústria automotiva, com a finalidade de reduzir peso dos produtos sem prejudicar características importantes como a resistência. O aço LNE 380 vem sendo aplicado na fabricação de peças mais robustas e que passam por processos de dobra. Dessa forma, esse estudo tem como objetivo principal determinar as deformações máximas causadas pelas tensões de tração em chapas do aço de alta resistência e baixa liga NBR 6656 LNE 380 submetidas ao processo de dobramento. Chapas de 6,35mm de espessura foram inicialmente analisadas por meio de ensaios de tração para verificar as propriedades mecânicas do aço. Os ensaios de tração apresentaram uma tensão de escoamento de 469±8MPa e tensão máxima de resistência de 539±3MPa. O ensaio de dobramento semiguiado foi utilizado para detectar o nível de deformação na região externa das chapas, ocasionado pelos esforços de tração durante o processo, bem como seu retorno elástico. No ensaio de dobramento utilizaram-se três raios de punçãovariando o deslocamento do mesmo para se obter diferentes raios de dobra. As máximas deformações relativa e verdadeira foram medidas na região externa da dobra, e posteriormente comparadas com resultados teóricos a fim de validar equações indicadas na bibliografia. Os valores teóricos variaram conforme o raio do punção, diferente do observado nos ensaios, onde a deformação permaneceu a mesma para todos os três raios utilizados. A maior deformação, calculada e medida, refere-se ao ensaio realizado com o menor raio de punção, assim como o maior Fator de Retorno Elástico. Verificou-se que no ensaio de dobramento, para o aço LNE 380, nas condições pré-definidas, a variação do raio do punção não interferiu de forma significativa nos resultados, uma vez que, as deformações e retorno elástico medido obteram valores próximos para diferentes raios. / High Strength Low Alloy (HSLA) steels have been widely used in the industry in the last years, especially in the automotive industry, in order to reduce weight products without impairing important characteristics such as strenght. The LNE 380 steel has been applied in the manufacture of more robust parts and that go through bending process. Therefore, this study has as main objective to determine the maximum deformation caused by the tensile stresses in sheets of High Strength Low Alloy steel NBR 6656 LNE 380 submitted to bending process. Sheets of 6,35mm thick were initially analyzed by tensile tests to verify the mechanical properties of the steel. The tensile tests showed a yield stress of 469±8 and maximum tensile strength of 539±3. The semi-guided bending test was used to detect the level of deformation in the external fibers of the sheets, caused by tensile stresses during the process, as well as their springback. Three punch radii were used in the bending test varying their displacement to achieve different bending radii. The maximum relative and true deformations were measured in the outer region of the bend, and subsequently compared with theoretical results in order to validate equations used in the bibliography. The theoretical values varied according to the punch radius that was different from those observed in the tests, where the deformation remained the same for all three radii used. The largest deformation calculated and measured refers to the test performed with the smallest punch radius, as well as the largest springback fator. It was observed that in the bending process, for the LNE 380 steel, under the pre-defined conditions, the variation of the punch radius did not interfein the results significally, since the values of deformation and springback measured were similar for different radii.

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Agradecemos a compreensão. on 2016-11-10T12:39:58Z (GMT) / Submitted by CAMILA PAIXÃO SANTOS (camila.paixao@yahoo.com.br) on 2016-11-11T18:37:20Z No. of bitstreams: 1 DEFESA_FINAL.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO null (luizaromanetto@hotmail.com) on 2016-11-16T19:53:18Z (GMT) No. of bitstreams: 1 santos_cp_me_guara.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) / Made available in DSpace on 2016-11-16T19:53:18Z (GMT). No. of bitstreams: 1 santos_cp_me_guara.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) Previous issue date: 2016-09-03 / Não recebi financiamento / Este trabalho apresenta e discute o uso do óxido de cério na fabricação de filmes espessos por “screen printing” para aplicações em sensores de gás. Nesse estudo o CeO2 puro foi obtido pelo método dos precursores poliméricos utilizando como resina precursora o citrato de céria. O “puff” – espuma resultante da primeira fase do tratamento térmico da resina- foi calcinado a 550, 600, 700 e 750°C. O pó foi caracterizado por termogravimetria (TG) e as propriedades estruturais, morfológicas foram avaliadas por difratometria de raios X (DRX), espectroscopia Raman, área de superfície por isotermas Brunauer, Emmett e Taller (BET) e microscopia eletrônica de varredura (MEV). A resposta sensora foi estudada em uma câmara de teste construída no Laboratório de Catálise e Superfícies do Instituto de Ciência de Tecnologia de Materiais (INTEMA) da Universidade de Mar del Plata. A TG mostrou a formação de óxido de cério a 550°C, temperatura relativamente baixa quando comparada com outros métodos. Mediante DRX todas as amostras mostraram picos correspondentes à fase pura de CeO2 o qual cristaliza em uma estrutura cúbica do tipo fluorita, entretanto, maiores temperaturas de calcinação mostraram aumento da cristalinidade e tamanho do cristalito. No espectro Raman, um forte pico em torno do 461 cm-1 foi detectado, atribuído às vibrações simétricas do Ce-O. A área de superfície BET dos pós foi de 301, 77 m2/g o que evidencia a formação de partículas muito pequenas e altamente reativas. As micrografias obtidas por MEV mostram a presença de diferentes tamanhos na forma de aglomerados. A caracterização da resposta sensora mostrou que o sensor fabricado a partir de pós de CeO2 puro apresenta um bom tempo de resposta, alcançando a melhor performance com temperatura de trabalho de 400 °C, tanto em atmosferas redutoras e oxidantes. A característica principal observada foi que os resultados são dependentes dos ciclos anteriores, a reprodutibilidade do sistema é garantida quando se apaga a “memória” do sistema, expondo-o ao vácuo. / This paper presents and discusses the use of cerium oxide in the production of thick films for "screen printing" for applications in gas sensors. In this study the pure CeO2 was obtained by the polymeric precursor method using as a precursor resin citrate ceria. The "puff" - resulting foam from the first stage of thermal treatment of the resin-calcined at 550, 600, 700 and 750 °C. The powder was characterized by thermogravimetry (TG) and structural, morphological were evaluated by X-ray diffraction (XRD), Raman spectroscopy, isothermal Brunauer surface area, Emmett and Taller (BET) and scanning electron microscopy (SEM) . The sensor response was studied in a test chamber built in the Laboratory of Catalysis and Surface Materials Technology Institute of Science (INTEMA), University of Mar del Plata. The thermogravimetry showed the formation of cerium oxide at 550° C, relatively low temperature compared with other methods. Upon XRD all samples showed peaks corresponding to pure CeO2 phase which crystallizes in a cubic fluorite type structure, however, higher calcination temperatures showed increased crystallinity and crystallite size. In the Raman spectrum, a strong peak around 461 cm-1 was detected, assigned to symmetric vibrations of the Ce-O. The BET surface area of the powders was 301, 77 m2 /g which shows the formation of very small and highly reactive particles. The SEM micrographs show the presence of different sizes in the form of agglomerates. The characterization of the sensor response showed that the sensors manufactured from pure CeO2 powder has a good response time, achieving better performance at 400 °C working temperature in both reducing and oxidizing atmospheres. The main feature observed was that the results are dependent on previous cycles, the system reproducibility is guaranteed when it deletes the "memory" of the system, exposing it to vacuum.

Aços de alta resistência e baixa liga (HSLA) tem sido amplamente empregados na indústria nos últimos anos, em especial na indústria automotiva, com a finalidade de reduzir peso dos produtos sem prejudicar características importantes como a resistência. O aço LNE 380 vem sendo aplicado na fabricação de peças mais robustas e que passam por processos de dobra. Dessa forma, esse estudo tem como objetivo principal determinar as deformações máximas causadas pelas tensões de tração em chapas do aço de alta resistência e baixa liga NBR 6656 LNE 380 submetidas ao processo de dobramento. Chapas de 6,35mm de espessura foram inicialmente analisadas por meio de ensaios de tração para verificar as propriedades mecânicas do aço. Os ensaios de tração apresentaram uma tensão de escoamento de 469±8MPa e tensão máxima de resistência de 539±3MPa. O ensaio de dobramento semiguiado foi utilizado para detectar o nível de deformação na região externa das chapas, ocasionado pelos esforços de tração durante o processo, bem como seu retorno elástico. No ensaio de dobramento utilizaram-se três raios de punçãovariando o deslocamento do mesmo para se obter diferentes raios de dobra. As máximas deformações relativa e verdadeira foram medidas na região externa da dobra, e posteriormente comparadas com resultados teóricos a fim de validar equações indicadas na bibliografia. Os valores teóricos variaram conforme o raio do punção, diferente do observado nos ensaios, onde a deformação permaneceu a mesma para todos os três raios utilizados. A maior deformação, calculada e medida, refere-se ao ensaio realizado com o menor raio de punção, assim como o maior Fator de Retorno Elástico. Verificou-se que no ensaio de dobramento, para o aço LNE 380, nas condições pré-definidas, a variação do raio do punção não interferiu de forma significativa nos resultados, uma vez que, as deformações e retorno elástico medido obteram valores próximos para diferentes raios. / High Strength Low Alloy (HSLA) steels have been widely used in the industry in the last years, especially in the automotive industry, in order to reduce weight products without impairing important characteristics such as strenght. The LNE 380 steel has been applied in the manufacture of more robust parts and that go through bending process. Therefore, this study has as main objective to determine the maximum deformation caused by the tensile stresses in sheets of High Strength Low Alloy steel NBR 6656 LNE 380 submitted to bending process. Sheets of 6,35mm thick were initially analyzed by tensile tests to verify the mechanical properties of the steel. The tensile tests showed a yield stress of 469±8 and maximum tensile strength of 539±3. The semi-guided bending test was used to detect the level of deformation in the external fibers of the sheets, caused by tensile stresses during the process, as well as their springback. Three punch radii were used in the bending test varying their displacement to achieve different bending radii. The maximum relative and true deformations were measured in the outer region of the bend, and subsequently compared with theoretical results in order to validate equations used in the bibliography. The theoretical values varied according to the punch radius that was different from those observed in the tests, where the deformation remained the same for all three radii used. The largest deformation calculated and measured refers to the test performed with the smallest punch radius, as well as the largest springback fator. It was observed that in the bending process, for the LNE 380 steel, under the pre-defined conditions, the variation of the punch radius did not interfein the results significally, since the values of deformation and springback measured were similar for different radii.

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2017-11-21T16:18:26Z No. of bitstreams: 2 Dissertação - José Henrique Faleiro - 2017.pdf: 5571418 bytes, checksum: f2f7b51d7be2c4a4b3934960f30f3bea (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-11-22T10:15:25Z (GMT) No. of bitstreams: 2 Dissertação - José Henrique Faleiro - 2017.pdf: 5571418 bytes, checksum: f2f7b51d7be2c4a4b3934960f30f3bea (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-11-22T10:15:25Z (GMT). No. of bitstreams: 2 Dissertação - José Henrique Faleiro - 2017.pdf: 5571418 bytes, checksum: f2f7b51d7be2c4a4b3934960f30f3bea (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-09-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / CHEMICAL STUDY OF Eugenia dysenterica DC. (MYRTACEAE) IN ASSOCIATION TO LEAF-CUTTING ANTS Atta laevigata CONTROL AND ALELOPATIC EFECT – The study described in this work contributed to the chemical and biological knowledge of species E. dysenterica, found especially in Cerrado and popularly known as “cagaita”. Species of Eugenia are also used in folk medicine for various diseases and biological activities have been reported for E. dysenterica such as, antiviral, fungicidal, cytotoxicity, among others activities. This work describes the isolation and structural identification of seven secondary metabolites presente in the ethanolic extract of flowers of E. dysenterica, as well as the biological evaluation of the ethanolic extracts of flowers, leaves, stems and seeds against leaf-cutting ants A. laevigata and evaluation of allelopathic effect. The study of flowers was carried out using chromatographic technics and the isolated compounds were identified by 1D and 2D NMR experiments. The chemical investigation of flowers extract, first time investigated, led to identified the compounds ethyl gallate, gallic acid, kaempferol, quercetin, myricetin, (-)- epicatechin and juglanin. The ethanolic extracts of E. dysenterica and the fractions obtained from the flower extract didn’t show significant results in the ingestion tests against the workers A. laevigata. The allelopathic assays performed with the crude ethanolic extracts of leaves, flowers, stems and seeds provided satisfactory results. The flowers and leaves extracts (2 mg/mL) showed the highest inhibition values, allowing the germination of less than 5% of seeds evaluated. / ESTUDO QUÍMICO DE Eugenia dysenterica DC. (MYRTACEAE) EM ASSOCIAÇÃO AO CONTROLE DE FORMIGAS CORTADEIRAS Atta laevigata E EFEITO ALELOPÁTICO – O estudo descrito neste trabalho contribui para o conhecimento químico e biológico da espécie E. dysenterica, encontrada especialmente em região de Cerrado e conhecida popularmente como “cagaita”. Espécies do gênero Eugenia são utilizadas na medicina popular para o tratamento de diversas doenças e E. dysenterica possui relatos de atividade antiviral, fungicida, citotóxica, entre outras. Este trabalho descreve o isolamento e identificação estrutural de sete metabólitos secundários presentes no extrato etanólico das flores de E. dysenterica, assim como a avaliação biológica dos extratos etanólicos das flores, folhas, galhos e sementes frente a formigas cortadeiras da espécie A. laevigata e avaliação do efeito alelopático. O estudo das flores foi realizado utilizando diferentes técnicas cromatográficas e os compostos isolados foram identificados por experimentos uni e bidimensionais de Ressonância Magnética Nuclear de 1H e 13C. A investigação química do extrato das flores, realizada pela primeira vez, levou a identificação dos compostos ácido gálico, galato de etila, quercetina, miricetina, kaempferol, (-)-epicatequina e a juglanina. Os extratos etanólicos de E. dysenterica e as frações obtidas do extrato das flores, não apresentaram resultados significativos nos ensaios por ingestão frente às operárias A. laevigata. Já os ensaios alelopáticos realizados com os extratos etanólicos brutos das folhas, flores, galhos e sementes forneceram resultados satisfatórios, sendo que os extratos das flores e folhas (2 mg/mL) apresentaram os maiores valores de inibição, permitindo a germinação de menos de 5% das sementes avaliadas.