The laser surface hardening process will enhance the hardness profile of automotive components and ensure better process control and predictability of quality as compared to the conventional hardening processes. A 2KW Nd-YAG laser system was used to harden the surface of alloy steel with various process parameters (laser power, focal spot diameter and beam velocity). The results (microhardness, microstructure change and residual stress distribution) were measured and analyzed with Vickers microhardness tester, optical/electron microscope and hole-drilling residual stress equipment. Statistical analyses of the experimental data were used for explaining the relationships between process parameters, microhardness and microstructure. General thermal hardening was applied in the research to show the influence of heating temperature and cooling method on microstructure and mechanical properties. Also, the results were compared with laser surface hardening process from microhardness, microstructure and residual stress to show the advantage of laser surface hardening. Through analysis of the results of the laser surface hardening experiments, a suitable laser power density and interaction time for optimum hardening was obtained. The presented laser surface hardening process can also be applied to other alloy steel surface hardening process.

In this work we studied properties of garnet scintillator layers (RxLu3-xAl5O12, RxY3-xAl5O12) doped by rare earth ions (Ce, Pr, Tb), orthosilicates (Y2SiO5; R = Ce, Tb) and influence of Sc codoping on Pr3+ and Tb3+ emissions. The Zr codoping on Ce3+ emission in orthosilicates was also studied. The samples were prepared by liquid phase epitaxy. The studied materials show high quantum efficiency and good chemical and mechanical stability. They represent ideal materials for 2D imaging devices. We studied optical absorption, excitation and emission spectra and scintillation properties (radiolunescence and photoelectron yield). The aim was to determine the properties of grown layers and their comparison to Czochralski grown single crystals. We looked for the impact of melt and growth conditions on measured layer properties. We also tried to determine optimal amount of dopants in layer. We used PbO - B2O3 and BaO - BaF2 - B2O3 fluxes. Using these fluxes, we succeeded in growing layers with less intrinsic defects in crystal lattice in comparison to single crystals. In grown layers of thickness from 1 to 30 µm higher dopant concentration was achieved than in single crystals.

No description available.

No description available.

Aux futurs collisionneurs linéaires et circulaires, la présence d’un halo autour du faisceau est susceptible de fortement limiter les performances, et peut également activer, voire endommager, les composants de l’accélérateur. Le halo doit par conséquent est contrôlé par un système de collimateurs efficace. Pour évaluer l’impact sur les expériences de physique des particules ainsi que les efficacités de collimation, une bonne compréhension des mécanismes physiques générateurs de halo est essentielle, pour par exemple prédire les distributions de probabilité de manière fiable. Pour ce faire, une investigation systématique ont été menée à l’Accelerator Test Facility (ATF) du KEK dans le cadre de cette thèse, d’abord à travers une analyse théorique des principales sources de halo dans ATF, puis moyennant le développement et l’implémentation de diagnostiques dédiés aux mesures du halo, dont les résultat sont ensuite présentés et comparés aux prédictions théoriques. Le halo produit par la diffusion des particules du faisceau sur les noyaux des molécules du gaz résiduel dans la chambre à vide (« Beam Gas Scattering » - BGS) est d’abord estimé analytiquement, avec certaines approximations, puis moyennant une simulation Monte-Carlo. Un nombre considérable de particules de halo BGS est prédit, ainsi qu’une dépendance dans la pression de gaz résiduel. Pour étudier la possible formation d’un halo par le mécanisme de diffusion intra-paquet à grand angle dit de « Touschek » en présence d’une dispersion optique résiduelle, le taux de cette diffusion a été estimé en fonction de plusieurs paramètres faisceau pertinents. Une simulation Monte-Carlo de la diffusion intra-faisceau à petit angle (IBS) et de « Touschek » est aussi en cours de développement. Pour tester les prédictions théoriques, les performances d’un détecteur de halo déjà existant basé sur un capteur diamant ont été améliorées moyennant une technique de repondération qui a permis d’en augmenter la gamme dynamique jusqu’à 10⁵. Afin de disposer d’un instrument complémentaire pour mesurer le halo, un moniteur YAG/OTR a aussi été conçu, construit et installé dans la ligne d’extraction d’ATF. Il a pu être montré que la gamme dynamique et la résolution de ce moniteur YAGOTR sont, respectivement, autour de 10⁵ et inférieure à 10 μm. Grâce aux diagnostiques développés pour mesurer le halo du faisceau d’ATF, les distributions transverses et en énergie ont pu être étudiées. L’accord satisfaisant obtenu entre les prédictions théoriques et les mesures, ainsi qu’une dépendance importante dans la pression de gaz résiduel, ont permis de montrer que la distribution verticale du halo est dominée par le mécanisme BGS. Par contre, la distribution horizontale est bien supérieure aux prédictions BGS, et est par ailleurs asymétrique. L’asymétrie observée peut être en partie reliée à la qualité du champ de l’élément pulsé servant à l’extraction du faisceau d’ATF, ainsi qu’à certaines aberrations dans le transport optique. La distribution de probabilité du halo en fonction de l’énergie a par ailleurs pu être mesurée, grâce à une technique nouvelle d’ajustement de la dispersion optique dans le plan vertical, et a été trouvée compatible qualitativement avec le mécanisme de diffusion « Touschek ». Un scénario plausible de génération du halo dans le plan horizontal a ainsi pu être suggéré. / At future linear and circular colliders, beam halo can strongly limit machine performances, cause as well component damage and activation, and should, therefore, be controlled by an efficient collimation system. To evaluate the impact on particle physics experiments and collimation efficiencies, a clear understanding of beam halo formation mechanisms is essential, e.g., to predict halo distribution reliably. For this purpose, systematic investigations have been carried out at the Accelerator Test Facility (ATF) of KEK. In this dissertation, the theoretical analysis of the primary halo sources at ATF and the development of dedicated halo diagnostics are presented. Measurements of beam halo at ATF are also described and compared with the theoretical predictions. Beam halo arising from Beam-Gas Scattering (BGS) in the damping ring was firstly estimated through analytical approximations and a Monte Carlo simulation. A considerable amount of halo particles generated by BGS and the corresponding vacuum dependence have been predicted. To explore the probability of beam halo formation from Touschek scattering in the presence of dispersion, the Touschek scattering rate was estimated with respect to relevant beam parameters. Furthermore, a Monte Carlo simulation of Intra-Beam Scattering (IBS) and Touschek scattering is under development. To probe the theoretical predictions, the performance of an already existing diamond sensor detector was optimized via a data rescaling technique to increase the dynamic range to 1×10⁵. For a complementary diagnostics of beam halo, a YAG/OTR monitor was also designed and installed in the extraction section of ATF2. The dynamic range and resolution of the YAG/OTR monitor have been shown to be around 1×10⁵ and less than 10 μm, respectively. Thanks to the halo monitors developed at ATF2, the transverse halo and momentum tail have been studied. Satisfactory agreement between numerical predictions and measurements as well as a significant vacuum dependence indicate that the BGS process dominates the vertical halo. On the other hand, the horizontal halo appeared to be higher than the prediction from BGS, and moreover asymmetric. The observed asymmetry was shown to be related to the quality of the extraction kicker field and optical aberration. Finally, the momentum tail was for the first time observed by implementing a novel scheme of vertical dispersion adjustment and was found to be qualitatively consistent with the presence of Touschek scattering. A possible scenario for horizontal beam halo formation from Touschek scattering was also suggested.

Die Arbeit beschäftigt sich mit der Umwandlung von ultrakurzen Laserpulsen in weiche Röntgenpulse. Dabei geht es hauptsächlich um die adaptive Pulsformung des Laserpulses und dessen Einfluss auf die generierte harmonische Strahlung / This work deals with the conversion of ultrashort laser pulses into soft x-ray radiation. Mainly, the effect of adaptive pulse shaping on the generated high-order harmonic radiation is investigated

Les études sur les procédés de soudage et sur la fiabilité des structures assemblées apparaissent actuellement comme un domaine de recherche actif, ouvert et complexe, car elles nécessitent de combiner de nombreuses connaissances dans différents domaines de la physique, de la mécanique et des procédés. La distribution des contraintes résiduelles joue un rôle important dans la vie des structures en favorisant la rupture par fatigue ou par fissuration. Ainsi, une meilleure compréhension des contraintes résiduelles évite l'utilisation de facteurs de sécurité plus élevés et, par conséquent permet de mieux optimiser le cycle de vie des structures soudées. A travers ce travail de thèse, nous nous sommes intéressés au soudage par laser d'un acier dual phase DP600, soudé en configuration par recouvrement, dont l'application est l'utilisation dans le domaine automobile. Cette thèse présente deux volets : un volet expérimental et un volet numérique.L'étude expérimentale nous a permis d'une part d'appréhender les conséquences métallurgiques et mécaniques du procédé laser sur l'acier DP600 et d'autre part d'utiliser et de valider les résultats numériques des modèles développés. L'étude numérique a eu pour objectif de prédire l'histoire thermique, métallurgique et l'évolution des caractéristiques mécaniques des tôles soudées par faisceau laser. Nous avons développé, sur un code de calcul par élémentsfinis Abaqus, trois modèles numériques. Le modèle thermomécanique, nous a permis de simuler la distribution spatio-temporelle de la température. Dans ce cas, le chargement appliqué est dépendant des paramètres du procédé etdes caractéristiques du faisceau laser et est associé à des conditions aux limites. Pour le modèle mécanique, nous avonsconsidéré un comportement élasto-plastique avec un chargement thermique transitoire, résultat du modèle thermique.Le deuxième modèle thermo-métallurgique nous a permis de simuler les phénomènes d'austénisation pendant la phase de chauffage (modèle de Waeckel) et de prendre en compte les fractions volumiques des phases martensitiques générées par les transformations de phases austénite-martensite lors du refroidissement (modèle de Koistinen-Marburger). Enfin, dans la dernière partie de simulation, nous avons réalisé le couplage thermo-metallo-mécanique. Les résultats obtenus dans la partie précédente, ont été implémentés dans deux modèles mécaniques : le modèle mécanique classique et le modèle mécanique avec prise en compte de la déformation liée aux effets de dilatation métallurgique. Cet effet a été intégré à travers le coefficient de dilatation thermique des phases ferritiques et martensitiques et des fractions volumiques obtenues à partir du modèle thermo-métallurgique. Les résultats ont montré que la répartition des contraintes résiduelles dans la zone de fusion et dans la zone affectée thermiquement sous l'effet de la déformation thermo-métallurgique donne des valeurs supérieures à celles estimées par le modèle élasto-plastique classique.

Made available in DSpace on 2014-06-11T19:28:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T19:57:14Z : No. of bitstreams: 1 lopes_am_me_araca.pdf: 932429 bytes, checksum: 58f57b4ef355fad92340a3819101663b (MD5) / A atividade antimicrobiana do laser Er:YAG foi avaliada sobre biofilme bacteriano constituído por Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 e 3 cepas de Fusobacterium nucleatum e sobre biofilme de microrganismos salivares. Os biofilmes foram submetidos à ação do laser a 1,2 W e 10 Hz por 5, 10, 15, 20, 30 e 60 s e fez-se a avaliação da microbiota residual em ágar sangue, em anaerobiose. O biofilme salivar se mostrou mais sensível nos primeiros tempos de irradiação. A redução microbiana em relação ao controle foi estatisticamente significativa entre todos os tempos testados. Avaliou-se também a ação do laser Er:YAG sobre 7 cepas de Fusobacterium nucleatum inoculadas sobre a superfície de corpos-de-prova (5mmX4mm) de dentes extraídos. Fez-se a aplicação do laser nos mesmos parâmetros físicos mencionados anteriormente, durante 15 s, levando à eliminação total do conteúdo séptico. O estudo avaliou também a irradiação do laser de Er:YAG durante tempos subinibitórios sobre a atividade hemolítica e susceptibilidade de 9 cepas de Fusobacterium nucleatum a amoxicilina, eritromicina, metronidazol e tetraciclina. Após a irradiação do laser, determinou-se a concentração inibitória mínima (CIM) para as drogas através do método de diluição em ágar. A ação do laser sobre a atividade hemolítica foi determinada em sangue humano. Verificou-se que o laser Er:YAG não afetou a atividade hemolítica de Fusobacterium nucleatum, que se mostrou α-hemolítica, tampouco a susceptibilidade a drogas dos isolados testados. / Antimicrobial activity of Er:YAG laser was evaluated on a bacterial biofilm constituted by Escherichia coli ATCC 8739, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and 3 strains of Fusobacterium nucleatum and on biofilm produced by salivary microorganisms. Biofilms were irradiated by Er:YAG laser, 1,2 W and 10 Hz, for 5, 10, 15, 20, 30, and 60 s and the evaluation of residual contamination was performed on blood agar, under anaerobiosis. It was verified that salivary biofilm showed to be more susceptibility to the Er:YAG laser in shorter periods of laser irradiation. Bacterial reduction was significative in all tested periods of irradiation. The activity of Er:YAG laser was also evaluated on 7 strains of Fusobacterium nucleatum inoculated on samples of human dentin (5mm X 4mm), obtained from extracted teeth. The laser was used following the same physical parameters, as previously described, for 15 s, leading to complete elimination of their septic content. The study also evaluated the effects of subinibitory irradiation of Er:YAG laser on bacterial susceptibility of 9 strains of Fusobacterium nucleatum to antimicrobial drugs (amoxicillin, erythromycin, metronidazole, tetracycline) and hemolysis. Thus, after laser irradiation, the minimal inhibitory concentration of antimicrobial drugs was determined by using an agar dilution method. The influence of laser on hemolysis was carried out on human blood. It was verified that Er:YAG laser did not produce any measurable effect on hemolytic activity and the microbial susceptibility to tested antimicrobial drugs.

Submitted by OTACILIO DONISETE FRANZINI null (otaciliodf@hotmail.com) on 2016-12-21T11:37:28Z No. of bitstreams: 1 APLICAÇÃO DE LASER PULSADO Nd YAG NA SOLDAGEM DO AÇO SUPER DUPLEX UNS S32750.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-22T12:59:13Z (GMT) No. of bitstreams: 1 franzini_od_me_ilha.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) / Made available in DSpace on 2016-12-22T12:59:13Z (GMT). No. of bitstreams: 1 franzini_od_me_ilha.pdf: 3133785 bytes, checksum: 7f73ce4a1615cca31edb63d392f368f2 (MD5) Previous issue date: 2016-12-13 / Os aços inoxidáveis Duplex e Super Duplex, 50% austenita e 50% ferrita, combinam as características mais desejáveis dos aços ferríticos e austeníticos, possuem excelente resistência mecânica e à corrosão para uma ampla variedade de meios, com expressiva resistência à corrosão em água do mar e outros ambientes contendo cloreto, devido a seu elevado nível de cromo, molibdênio, e nitrogênio. Quando soldado a região do metal de solda desses aços perdem suas características de resistência mecânica e à corrosão devido ao desbalanceamento das fases ferrita e austenita. No presente trabalho foi analisado a influência do processo de soldagem autógena a laser Pulsado Nd:YAG nas características mecânicas e microestruturais da junta soldada, variando a taxa de sobreposição dos pulsos de 40 a 90% em chapas de aço inoxidável Super Duplex UNS S32750 com 1,5 mm de espessura. Utilizou-se uma fonte laser pulsada Nd.YAG, United Winner 150A, com potência máxima de 150 W. A energia do pulso de soldagem foi fixada em 10J, potência de pico de 2 kW, largura temporal de 5 ms e frequência variando entre 1,5 e 9,0 Hz. Como gás de proteção utilizou-se argônio puro com vazão de 10 l/min. A caracterização microestrutural foi realizada através de microscopia ótica e microscopia eletrônica de varredura. Os resultados mostraram que o aumento da taxa de sobreposição da junta de 40% até 90% aumenta a resistência mecânica e a dureza do metal de solda. Em relação à microestrutura do metal de solda observou-se uma ferritização da mesma com pequena fração volumétrica de austenita nas regiões de contorno de grão. Não foi observada a presença de fases frágeis no metal de solda. / Duplex Stainless steels and Super Duplex 50% austenite and 50% ferrite, combine the most desirable traits of ferritic and austenitic steels possess excellent mechanical strength and corrosion resistance to a wide variety of ways, with substantial corrosion resistance in seawater and other environments containing chloride, due to its high level of chromium, molybdenum, and nitrogen. When welded to the weld metal region of these steels lose their mechanical strength features and corrosion due to the imbalance of the ferrite and austenite phases. In this paper we analyzed the influence of the welding process autogenous laser Pulsed Nd: YAG laser on the mechanical and microstructural features of the welded joint, by varying the overlap rate of pulses from 40 to 90% in stainless steel plates Super Duplex UNS S32750 with 1.5 mm thick. We used a pulsed laser source Nd.YAG, United Winner 150A, with maximum power of 150 W. The power of the welding pulse was set at 10 J, peak power of 2 kW, temporal width of 5 ms and frequency ranging from 1.5 and 9.0 Hz. As shielding gas used is pure argon with a flow rate of 10 l / min. Microstructural characterization was performed by optical microscopy and scanning electron microscopy. The results showed that increasing the overlap rate of 40% to 90% joint strength increases and the hardness of the weld metal. Regarding the welding ferritização observed a metal microstructure thereof with small volume fraction of the austenite grain boundary regions. It was observed the presence of brittle phases in the weld metal.

Orientador: Vicente Afonso Ventrella / Resumo: Os aços inoxidáveis Duplex e Super Duplex, 50% austenita e 50% ferrita, combinam as características mais desejáveis dos aços ferríticos e austeníticos, possuem excelente resistência mecânica e à corrosão para uma ampla variedade de meios, com expressiva resistência à corrosão em água do mar e outros ambientes contendo cloreto, devido a seu elevado nível de cromo, molibdênio, e nitrogênio. Quando soldado a região do metal de solda desses aços perdem suas características de resistência mecânica e à corrosão devido ao desbalanceamento das fases ferrita e austenita. No presente trabalho foi analisado a influência do processo de soldagem autógena a laser Pulsado Nd:YAG nas características mecânicas e microestruturais da junta soldada, variando a taxa de sobreposição dos pulsos de 40 a 90% em chapas de aço inoxidável Super Duplex UNS S32750 com 1,5 mm de espessura. Utilizou-se uma fonte laser pulsada Nd.YAG, United Winner 150A, com potência máxima de 150 W. A energia do pulso de soldagem foi fixada em 10J, potência de pico de 2 kW, largura temporal de 5 ms e frequência variando entre 1,5 e 9,0 Hz. Como gás de proteção utilizou-se argônio puro com vazão de 10 l/min. A caracterização microestrutural foi realizada através de microscopia ótica e microscopia eletrônica de varredura. Os resultados mostraram que o aumento da taxa de sobreposição da junta de 40% até 90% aumenta a resistência mecânica e a dureza do metal de solda. Em relação à microestrutura do metal de solda observou-se u... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre