Metallic honeycomb structures are being studied for use as thermal protection systems for hypersonic vehicles and as structural panels in other aerospace applications. One potential concern is the growth of fatigue cracks in the thin face-sheets used for these structures. To address this concern, the fatigue behavior of thin aluminum base alloy sheets ranging from 30 m to 250 m in thickness was investigated. The effect of material roll direction was also considered at 30 m. In all cases, the fatigue crack growth rates were found to be one to two orders of magnitude higher than that of the same material of greater thickness. In addition to data for fatigue crack growth rate, data are also presented for the effect of thickness on the fracture toughness of these materials.

Orientador: Vicente Afonso Ventrella / Resumo: O presente trabalho estudou o processo de soldagem laser Nd:YAG pulsado aplicado em lâminas finas da liga de titânio Ti-6Al-4V, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química, petroquímica e alimentícia. Variou-se a energia de pulso de 1,0 J a 2,00 J, com incrementos de 0,25 J com a velocidade de soldagem de (ν) taxa de repeticao (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio com vazão de 10 l/min. Os ensaios realizados para a pesquisa foram: análise macrográfica, ensaio de tração e fractografia, ensaio de microdureza e caracterização microestrutural. Para revelação dos detalhes no metal de solda foi utilizado um ataque químico com o reagente Kroll. As medidas de geometria (largura do cordão, largura de união e profundidade) dos cordões de solda, bem como a microestrutura, foram realizadas através de imagens obtidas pelo Microscópio Óptico Neophot 21 e editadas utilizando o software ImageJ. O ensaio de tração foi realizado através de uma Máquina Universal de Ensaios, além do ensaio de microdureza, que foi realizado na escala Vickers. Os resultados obtidos mostraram que o controle da energia do pulso é de fundamental importância para a geração de juntas soldadas adequadas, em processo de soldagem por laser de lâminas finas. Também, os parâmetros geométricos aumentaram em função do aumento da energia de pulso e houve maior formaç... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work studied the pulsed Nd: YAG laser welding process applied in thin films of the titanium alloy Ti-6Al-4V, used in the coating of sensors that work in the corrosive environment of the sugar-alcohol, chemical, petrochemical and food industry. The pulse energy was varied from 1.0 J to 2.00 J, with increments of 0.25 J with welding speed (ν) and repetition rate (Rr) fixed in 525 mm / min and 39 Hz respectively and time width of 4 ms. An argon gas protection was used with a flow rate of 10 l / min. The tests carried out for the research were: macrographic analysis, tensile and fracture tests, microhardness test and microstructural characterization. A chemical attack with the Kroll reagent was used to reveal details on the weld bead. Measurements based on bead width, union width and depth of the fusion zone as well as the microstructure were performed using images obtained by the Neophot 21 Optical Microscope and edited using the ImageJ software. The tensile test was performed through a Universal Testing Machine, in addition to the microhardness test, which was performed on the Vickers scale. Results showed that the control of the pulse energy is of fundamental importance for the generation of suitable welded joints, in process of laser welding of thin slides. Also, geometric parameters increased as a function of the increase in pulse energy and there was more formation of the α 'phase (martensite) according to the highest peak energy used. Besides that, microhardnes... (Complete abstract click electronic access below) / Mestre

Resumo: O presente trabalho estudou a influência da energia do pulso de soldagem, no caso processo laser de Nd:YAG operando no modo pulsado, na soldagem de duas lâminas finas com 100 μm de Hastelloy C-276, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química petroquímica e alimentícia. Utilizou-se energia de pulso de 1,0 Joule a 2,25 Joules, com incremento de 0,25 Joules com a velocidade de soldagem de (ν) taxa de repetição (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio. Foram realizadas análises macrográficas e micrográficas das juntas soldadas, através de secções transversais das mesmas e ensaios de microdureza Vickers e ensaio de tração. Os resultados obtidos mostraram que o controle da energia do pulso, em processo de soldagem por laser de lâminas finas é de fundamental importância para a geração de juntas soldadas livres de descontinuidades. Os parâmetros geométricos da junta soldada, tais como largura do cordão, largura de união e profundidade do cordão, aumentaram em função do aumento da energia do pulso. O processo mostrou-se muito sensível à formação de porosidade e à presença de gap entre as lâminas / Abstract: This work measured experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser welding to examine the influence of the pulse energy in two thin foil welding with 100 μm thickness, employed to cover sensors that work in corrosive environment of the sugar and alcohol industry,chemical petrochemistry and nourishing. The pulse energy was varied from 1,0 to 2,25 J at an increment of 0.25 J and an increment of 0.25 Joules with a welding speed and(ν) repetition rate (Rr) fixed 525mm/min and 39Hz respectively and 4 ms pulse duration. The specimens were laser-welded in an argon atmosphere. The welds were analyzed by macroscopic and microscopic observations using optical microscopy and micro hardness and tensile test. The results indicated that pulse energy control, in laser welding of thin foils, is of considerable importance for weld quality since it can generate discontinuities free weld joints. The geometric parameters of the welded joints like bead width, connection width and bead depth increased with the pulse energy increasing. The process showed very sensitive to porosity formation and gap between couple / Orientador: Ruis Camargo Tokimatsu / Coorientador: Vicente Afonso Ventrella / Banca: Alessandro Roger Rodrigues / Banca: Ricardo Cury Ibrahim / Mestre

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2011Bitstream added on 2014-06-13T19:35:03Z : No. of bitstreams: 1 munekata_rm_me_ilha.pdf: 4705141 bytes, checksum: 56254cadfa4c90cb796f3b90671140ee (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho estudou a influência da energia do pulso de soldagem, no caso processo laser de Nd:YAG operando no modo pulsado, na soldagem de duas lâminas finas com 100 μm de Hastelloy C-276, utilizado no revestimento de sensores que trabalham em ambiente corrosivo da indústria sucroalcooleira, química petroquímica e alimentícia. Utilizou-se energia de pulso de 1,0 Joule a 2,25 Joules, com incremento de 0,25 Joules com a velocidade de soldagem de (ν) taxa de repetição (Rr) fixas de 525mm/min e 39Hz respectivamente e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio. Foram realizadas análises macrográficas e micrográficas das juntas soldadas, através de secções transversais das mesmas e ensaios de microdureza Vickers e ensaio de tração. Os resultados obtidos mostraram que o controle da energia do pulso, em processo de soldagem por laser de lâminas finas é de fundamental importância para a geração de juntas soldadas livres de descontinuidades. Os parâmetros geométricos da junta soldada, tais como largura do cordão, largura de união e profundidade do cordão, aumentaram em função do aumento da energia do pulso. O processo mostrou-se muito sensível à formação de porosidade e à presença de gap entre as lâminas / This work measured experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser welding to examine the influence of the pulse energy in two thin foil welding with 100 μm thickness, employed to cover sensors that work in corrosive environment of the sugar and alcohol industry,chemical petrochemistry and nourishing. The pulse energy was varied from 1,0 to 2,25 J at an increment of 0.25 J and an increment of 0.25 Joules with a welding speed and(ν) repetition rate (Rr) fixed 525mm/min and 39Hz respectively and 4 ms pulse duration. The specimens were laser-welded in an argon atmosphere. The welds were analyzed by macroscopic and microscopic observations using optical microscopy and micro hardness and tensile test. The results indicated that pulse energy control, in laser welding of thin foils, is of considerable importance for weld quality since it can generate discontinuities free weld joints. The geometric parameters of the welded joints like bead width, connection width and bead depth increased with the pulse energy increasing. The process showed very sensitive to porosity formation and gap between couple

Nickel based superalloys are currently being investigated for high temperature applications in advanced steam power plant operating at temperatures of 700˚C and above. Three nickel-based superalloys Inconel 617, Inconel 625 and Nimonic 263 alloys, which are of primary interest for boiler technology components such as furnace walls, superheater tubes, header and steam pipes, etc and for steam turbine technology components such as HP &IP cylinders, rotor forgings, casing and valve chest, blading, etc., have been evaluated for long and short term creep performance. Creep deformation processes occurring at high temperatures and stresses lead to the evolution of microstructures in the form of precipitation, precipitate coarsening and recovery effects. The deterioration in mechanical properties as a result of this microstructural change has been evaluated by hardness testing. This work discusses the microstructural evolution occurring in alloys in samples that have been creep exposed at a series of temperatures from 650°C to 775°C and for durations from 1000 to 45,000 hours using advanced FEGSEM, TEM, XRD and phase extraction techniques. The fractions and morphology of different phases, their locations during exposure to higher temperatures and probable creep fracture mechanism in these alloys are illustrated and discussed.