Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 165-173).

Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-08Bitstream added on 2014-06-13T19:14:23Z : No. of bitstreams: 1 silvajunior_g_me_guara.pdf: 2753248 bytes, checksum: 05b8f846d2550bb9618bdde67704e992 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A falha por fadiga é resultado de nucleação e propagação de trinca em consequência de um carregamento cíclico. Na indústria aeronáutica, em componentes como trens de pouso, a resistência à fadiga é um importante parâmetro a ser considerado em projeto, assim como resistência ao desgaste e à corrosão. O aço inox 15-5PH é aplicado em diversos componentes nos eixos estruturais do trem de pouso. A sua aplicação justifica-se devido a sua alta resistência mecânica e elevada resistência à corrosão. Contudo sua aplicação é restringida devido a sua baixa resistência ao desgaste, fazendo-se necessária a utilização de um tratamento superficial de endurecimento de superfície. O método de HVOF vem sendo considerado uma alternativa à eletrodeposição do cromo pela indústria aeronáutica, para aumento de resistência ao desgaste e à corrosão. Nesta pesquisa, é realizado o estudo do comportamento em fadiga do aço inoxidável 15-5PH tratado superficialmente em três condições: revestido com WC-13Co-4Cr, e WC-18Co por HVOF; e revestido com cromo eletrodepositado. O tratamento de shot peening foi aplicado com intuito de recuperar a resistência à fadiga nos materiais revestidos. Os ensaios de fadiga e a medida de tensões residuais proporcionam uma análise comparativa da resistência à fadiga dos revestimentos estudados. O presente trabalho tem como objetivo comparar a influência dos revestimentos WC-13Co-4Cr e WC-18Co, aplicados por HVOF, com revestimento de cromo eletrodepositado, na resistência à fadiga axial do aço inox 15-5PH, com intuito substituir o método de eletrodeposição do cromo pelo de HVOF. Os resultados mostram que o aço 15-5PH revestido com WC-13Co-4Cr por HVOF é o melhor sistema de revestimento a ser empregado considerando o desempenho em resistência à fadiga / Fatigue failure is result of a crack initiation and propagation, in consequence of a cyclical load. In aeronautical industry, components as landing gear, the fatigue strength is an important parameter to be considered in project, as well as the corrosion and wear resistance. The 15-5PH stainless steel is applied on carrying axles in landing gear. The reason for its application is due to high mechanical strength, and corrosion resistance. Nevertheless the application of 15-5PH it‟s restricted due to low wear resistance, becoming necessary a hardening surface treatment. The method of HVOF has been considering the alternative to chromium electroplated by the aircraft industry, in order to improve the wear and corrosion resistance. This research present an evaluation of fatigue strength of 15-5PH stainless steel in three main conditions of surface treatments: coated by HVOF with WC-13Co-4Cr, and WC-18Co; and coated with chromium electroplated. The shot peening treatment was applied in order to restore the fatigue strength on coated materials. The fatigue tests and residual stress measurement were carried out to obtain a comparative analysis among coated materials. The main propose of this research is compare the influence of WC-13Co-4Cr, WC-18Co coated by HVOF, with chromium electroplated, on the fatigue strength of 15-5PH, in order to replace the electroplating method by HVOF. The results show that 15-5PH coated with WC-13Co-4Cr by HVOF is the best coating system to be applied considering the fatigue strength performance

Laser cladding is a process that is used to improve the properties of a metal surface. The properties in question may include hardness, wear-, corrosion- and/or fatigue-resistance. The process involves fusing a thin layer of additional metal to the original surface, using a laser as the heat source. Unfortunately, residual stresses are generated due to the rapid and highly localised thermal expansion and contraction that occur during the heating-melting-solidification-cooling cycle. These residual stresses can have a detrimental effect on the final performance of the clad component, especially with respect to corrosion resistance. Detrimental tensile residual stresses can be mitigated through the use of post-processing techniques such as laser shock peening (LSP). LSP is a process that uses a pulsed laser to generate intense spots of recoil pressure on a surface, thereby introducing compressive residual stresses. Post weld heat treatment (PWHT) is another process that could be also used in laser cladding in order to relieve tensile residual stresses. In this work, laser cladding was carried out by depositing a clad layer of AISI grade 316L stainless steel on to either a S275 steel substrate or an AISI grade 316L stainless steel substrate, using different process parameters. The hardness and residual stresses in the overlay and substrate were assessed for each laser clad sample before and after being treated with LSP and PWHT. The corrosion rate and microstructure were also assessed in each case. The novelty of this work is two-fold. Firstly, to the author's knowledge, it is the first study that attempts to link process parameters to both the residual stresses and the corrosion performance of austenitic stainless steel overlays deposited by laser cladding. The second novel aspect is based on the application of both LSP and PWHT to the deposited overlay in order to investigate whether an improvement in the mechanical properties and the corrosion resistance can be realised. In this study, tensile residual stresses were generated in the clad layers. However, the magnitude of the residual stresses did not appear to be particularly sensitive to the deposition parameters. Indeed, it was found that the number of layers that is deposited is more important than the choice of process parameters. LSP was effective in reducing the tensile residual stresses and in fact it introduced compressive stresses to all the samples that were treated. In contrast, PWHT only led to satisfactory stress relief when the AISI grade 316L stainless steel was deposited on to a matching substrate material. This was related to the fact that a difference between the thermal expansion coefficients of the overlay and substrate led to the development of significant tensile residual stresses on cooling down after PWHT. The corrosion tests on the clad coupons led to the development of pits and cracks. However, after LSP only pits were found, without any sign of cracking, for the test durations that were investigated owing to the fact that compressive stresses were generated. Similar results were found after PWHT for the clad samples in which the overlay material matched the substrate material. However, signs of cracking were observed after PWHT in samples where AISI grade 316L stainless steel was deposited on to an S275 steel substrate due to tensile residual stresses remaining within the overlay. This result suggests that there may be little benefit in carrying out PWHT for components in which grade 316L stainless steel is deposited on to a steel substrate. In contrast, there appear to be clear benefits associated with carrying out LSP in order to mitigate the residual stresses and retard the onset of cracking.

The design and material properties of rails and projectiles are critical to the success of the Navy railgun. This thesis addresses the design, fabrication, and testing of a scalable square bore electromagnetic railgun. This railgun is designed to permit series augmented operation, and incorporates disposable rail liners to facilitate investigating the suitability of variousrail materials. A series of shots has demonstrated performance consistent with theoretical modeling, including significant performance enhancement as a result of both slotted rail geometry and augmentation over solid rail and un-augmented configurations. A capacitor based stored energy supply input of 35 kJ resulted in a measured velocity of 294 m/s for an 11.4 gram projectile. Suggestions are provided for future power supply configurations, rail materialsand surface treatments, and a variety of armature geometries.

<p>This study is concerned with investigating the effects of warm laser shock peening (wLSP) on the enhancement of mechanical performance of laser welded joints. A 3-D finite element model is presented which predicts the surface indentation geometry and in-depth compressive residual stresses generated by wLSP. To define the LSP pressure on the surface of the material, a 1-D confined plasma model is implemented to predict plasma pressure generated by laser-coating interaction in an oil confinement regime. Residual stresses predicted by the finite element model for wLSP reveal higher magnitude and depth of compressive residual stresses than room temperature laser shock peening. A novel dual laser wLSP experimental setup is developed for simultaneous heating of the sample, to a prescribed temperature, and to perform wLSP. The heating laser power is tuned to achieve a predefined temperature in the material through predictive analysis with a 3-D transient laser heating model.</p><p>Laser welded joints of AA6061-T6 and TZM alloy in bead-on-plate (BOP) and overlap configurations, created by laser welding with a high power fiber laser, were post processed with wLSP. To evaluate the strength of the welded joints pre- and post-processing, tensile testing and tensile-shear testing were carried out. To understand the failure modes in tensile-shear testing of the samples, a 3-D finite element model of the welded joint was developed with weld regions’ material strength properties defined through microhardness testing. The stress concentration regions predicted by the finite element model clearly explain the failure regions in the experimental tensile testing analysis. The tensile tests and tensile-shear tests carried out on wLSP processed AA6061-T6 samples demonstrate an enhancement in the joint strength by about 20% and ductility improvement of about 33% over as-welded samples. The BOP welds of TZM alloy processed with wLSP demonstrated an enhancement in strength by about 30% and lap welds demonstrated an increase in joint strength by 22%.<br></p><p></p>

Resumo: O tubo superior do garfo suspensão é um dos componentes de grande importância no conjunto de peças que compõe uma bicicleta, pois durante a operação é submetido a carregamentos cíclicos e caso falhe pode causar acidentes ao ciclista. Este componente é confeccionado por processo de usinagem a partir de um perfil tubular extrudado em liga de alumínio Al 6013-T6. Neste trabalho foi realizado um estudo sobre o comportamento em fadiga desta liga de alumínio submetida a diferentes condições de shot peening, objetivando aumentar a resistência à fadiga do material e conseqüentemente aumentar a vida útil/segurança do componente. Para ensaiar os corpos-de-prova em perfil tubular com geometria embasada nas dimensões do tubo superior, desenvolveu-se uma metodologia especifica de ensaio. Os ensaios mostraram que o processo de fabricação de rosca por conformação mecânica aumentou consideravelmente a resistência à fadiga dessa liga em relação ao processo de fabricação por usinagem convencional. Os efeitos de concentradores de tensão como filetes de rosca usinada e defeitos superficiais são extremamente prejudiciais para a vida em fadiga da liga Al 6013-T6. Os tratamentos de shot peening realizados pela empresa Zirtec induziram um perfil significativo de tensões residuais compressivas, porém, reduziram a vida em fadiga da liga Al 6013-T6 em perfil tubular. Esse efeito foi potencializado com intensidades Almen elevadas. O aumento na vida em fadiga ocorreu apenas nos corpos-de-prova que foram lixados na superfície interna. O shot peening com esfera de vidro e intensidade Almen intermediária apresentou a maior vida em fadiga. Os resultados deste trabalho estão sendo usados para providenciar melhorias na matéria prima e como base para novos ensaios com o tubo superior. / Abstract: The fork supension's steerer tube is one of component of great importance in a set that makes a bicycle, since during operation is subjected to cyclic loading and if fails may cause accident to the rider. This component is manufactured by machining processes from the extrusion tubular profile in aluminum alloy 6013-T6. This work carried out a study on the fatigue behavior of aluminum alloy subjected to different shot peening conditions, proposing to increase the fatigue strength and consequently to increase a useful life/safety of the component. To test tubular profile specimen with geometry based in steerer tube dimensions, has developed a specific methodology for testing. The tests showed that thread forming by manufacturing process, increase the fatigue strength of this aluminum alloy comparing the manufacturing process through conventional machining. The effects of concentration stress like machined thread and surface defects are extremely detrimental to fatigue life alloy AL 6013-T6. Shot peenig treatment carried out in Zirtec company induced a significant compressive residual stress profile, but decrease the fatigue life alloy Al 6013-T6 in tubular profile. This effect was strengthened with high Almen intensities. The fatigue life incresase ocurred only specimen that were polished on the inner surface. Shot peening using glass shot and intermediate Almen intensity had the greatest fatigue life. The results os this work are being used to provide improvements in primary material and as a basis for new test on the stereer tube. / Orientador: Herman Jacobus Cornelis Voorwald / Coorientador: Maria Odila Hilario Cioffi / Banca: Marcelo dos Santos Pereira / Banca: Carlos Angelo Nunes / Mestre

In this report, the feasibility of a massively parallel, nanoscale laser shock peening process is investigated. This report will give a fundamental background on laser shock peening processes in general. The background will include a description of the mechanisms associated with laser shock peening, and the theory behind laser shock peening. The experiments that were performed to develop a nanoscale laser shock peening process will also be described in detail. The problems associated with different experiments and the results will be presented. / text

Resumo: A falha por fadiga é resultado de nucleação e propagação de trinca em consequência de um carregamento cíclico. Na indústria aeronáutica, em componentes como trens de pouso, a resistência à fadiga é um importante parâmetro a ser considerado em projeto, assim como resistência ao desgaste e à corrosão. O aço inox 15-5PH é aplicado em diversos componentes nos eixos estruturais do trem de pouso. A sua aplicação justifica-se devido a sua alta resistência mecânica e elevada resistência à corrosão. Contudo sua aplicação é restringida devido a sua baixa resistência ao desgaste, fazendo-se necessária a utilização de um tratamento superficial de endurecimento de superfície. O método de HVOF vem sendo considerado uma alternativa à eletrodeposição do cromo pela indústria aeronáutica, para aumento de resistência ao desgaste e à corrosão. Nesta pesquisa, é realizado o estudo do comportamento em fadiga do aço inoxidável 15-5PH tratado superficialmente em três condições: revestido com WC-13Co-4Cr, e WC-18Co por HVOF; e revestido com cromo eletrodepositado. O tratamento de shot peening foi aplicado com intuito de recuperar a resistência à fadiga nos materiais revestidos. Os ensaios de fadiga e a medida de tensões residuais proporcionam uma análise comparativa da resistência à fadiga dos revestimentos estudados. O presente trabalho tem como objetivo comparar a influência dos revestimentos WC-13Co-4Cr e WC-18Co, aplicados por HVOF, com revestimento de cromo eletrodepositado, na resistência à fadiga axial do aço inox 15-5PH, com intuito substituir o método de eletrodeposição do cromo pelo de HVOF. Os resultados mostram que o aço 15-5PH revestido com WC-13Co-4Cr por HVOF é o melhor sistema de revestimento a ser empregado considerando o desempenho em resistência à fadiga / Abstract: Fatigue failure is result of a crack initiation and propagation, in consequence of a cyclical load. In aeronautical industry, components as landing gear, the fatigue strength is an important parameter to be considered in project, as well as the corrosion and wear resistance. The 15-5PH stainless steel is applied on carrying axles in landing gear. The reason for its application is due to high mechanical strength, and corrosion resistance. Nevertheless the application of 15-5PH it‟s restricted due to low wear resistance, becoming necessary a hardening surface treatment. The method of HVOF has been considering the alternative to chromium electroplated by the aircraft industry, in order to improve the wear and corrosion resistance. This research present an evaluation of fatigue strength of 15-5PH stainless steel in three main conditions of surface treatments: coated by HVOF with WC-13Co-4Cr, and WC-18Co; and coated with chromium electroplated. The shot peening treatment was applied in order to restore the fatigue strength on coated materials. The fatigue tests and residual stress measurement were carried out to obtain a comparative analysis among coated materials. The main propose of this research is compare the influence of WC-13Co-4Cr, WC-18Co coated by HVOF, with chromium electroplated, on the fatigue strength of 15-5PH, in order to replace the electroplating method by HVOF. The results show that 15-5PH coated with WC-13Co-4Cr by HVOF is the best coating system to be applied considering the fatigue strength performance / Orientador: Herman Jacobus Cornelis Voorwald / Coorientador: Maria Odila Hilario Cioffi / Banca: Carlos de Moura Neto / Banca: Midori Yoshikawa Costa / Mestre

Le procédé de grenaillage permet d’améliorer la durée de vie en fatigue des pièces mécaniques dans l’industrie. La mise en compression de la surface par les billes introduit un gradient de déformations inélastiques hétérogènes qui engendre un champ de contraintes résiduelles. Ce sont principalement ces contraintes résiduelles de compression qui sont à l’origine du gain de durée de vie. Les contraintes résiduelles générées évoluent lors des sollicitations thermomécaniques des composant mécaniques après grenaillage. La relaxation et la fatigue ont été étudiées à l’échelle des phases sur l’acier de type TRIP780, acier multiphasé (ferrite, bainite, austénite) possédant une phase austénitique résiduelle susceptible de se transformer en martensite sous un chargement thermomécanique. Pour cet acier, le gain de durée de vie dû au grenaillage est dépendant de la stabilité des contraintes résiduelles de compression dans les différentes phases au cours des chargements mécaniques généralement cyclique. Des essais de flexion cycliques ont été réalisés sur des éprouvettes planes afin de déterminer les durées de vie en fonction des conditions de grenaillage. Avec l’aide d’essais cycliques interrompus, l’évolution des profils de contraintes, de dosage de phase et des largeurs intégrales ont été caractérisée par diffraction des rayons X dans les phases ferritiques et austénitique montrant ainsi la relaxation des contraintes résiduelles en fonction du chargement mécanique appliqué (niveau des contraintes et nombre de cycles). A partir de ces différents résultats, des simulations utilisant la méthode des éléments finis ont été développées pour prédire la relaxation. Après génération numérique des champs de contraintes dans l’éprouvette (méthode thermique fictive), des modèles de comportement élastoplastiques globaux et par phases ont été proposés dans le cas de faibles nombres de cycle. Dans une dernière partie, un post-traitement global par critère de fatigue multiaxial de type Crossland intégrant les résultats sur la relaxation a été proposé. Les résultats ont alors été comparés aux courbes expérimentales de fatigue. / Shot peening process aim at enhancing life duration of mechanical parts in industry. Balls introduce a compressive state on the surface of the part by strain hardening the subsurface which must be accommodated by elastic strain. Compressive residual stresses are mainly the origin of the enhancing life duration. These residual stresses evolve during thermomechanical solicitations after shot-peening. Relaxation and life duration are studied at the phase scale in the TRIP780 steel – a multiphased steel (bainite, ferrite and austenite) owning a metastable austenitic phase which can transform in martensite under thermomechanical solicitations. In this steel, life duration gain depends on the compressive residual stresses stability in the different phases during cyclic loads. Bending test were carried out on thick samples to determine life duration in function of shot-peening conditions. With interrupted cyclic test, the evolution of the residual stress profile, phase partition and integral width were characterized by X-ray diffraction in ferritic and austenite phases showing the relaxation of residual stresses following the mechanical loads (loading level and number of cycle). With these experimental results, finite element simulations were carried out to forecast the relaxation. After residual stress numerical generation (fictive thermal method), global and by-phase comportment models were proposed in the case of the low number cycles. In the last part, a post-treatment by multiaxial fatigue criterion like Crossland one integrating relaxation results was proposed. The results were compared to the experimental fatigue curves.

Aços inoxidáveis são materiais usados em aplicações específicas onde uma boa resistência à corrosão, boa resistência à oxidação e boa resistência mecânica são requeridas. O processo de shot peening tem sido utilizado para melhorar as propriedades mecânicas de superfícies metálicas. Além disso, o processo de shot peening pode ter influência no comportamento eletroquímico do material, dependendo dos parâmetros de processos utilizados na aplicação do mesmo. Shot peening é um processo aplicado para acrescentar tensões residuais compressivas em superfícies metálicas com o objetivo de melhorar a resistência à fadiga, a resistência à corrosão sob tensão, e desgaste abrasivo. O objetivo deste trabalho é avaliar o efeito do processo de shot peening na morfologia da superfície, na resistência à corrosão e na resistência à oxidação do aço inoxidável ferrítico AISI 430. Na realização deste estudo foi definida a utilização de três condições de amostras, sendo a primeira amostra com a superfície no estado como recebido, a segunda amostra com superfície lixada e a terceira a amostra tratada com o processo de shot peening. Para avaliar influência do processo de shot peening na morfologia da superfície das amostras, foram realizados os ensaios de microscopia óptica, microscopia eletrônica de varredura (MEV), ensaio de perfilometria e avaliação da molhabilidade. Para avaliar a influência do shot peening no comportamento eletroquímico da superfície das amostras foram realizados, avaliação do potencial de circuito aberto (OCP), polarização potenciodinâmica e espectroscopia de impedância eletroquímica (EIE). Ensaio de oxidação por ganho de massa em alta temperatura foi realizado para analisar a influência do shot peening na resistência a oxidação e a análise de difração de raio-X foi realizada para avaliar as fases presentes. Os resultados obtidos demonstraram que as amostras de aço inox AISI430 tratadas com shot peening apresentaram um comportamento mais hidrofílico comparado com as amostras na condição como recebido e lixada. Além disso, o processo de shot peening, com os parâmetros de processo de aplicação usados neste estudo, alterou significativamente a morfologia da superfície reduzindo à resistência a oxidação e a resistência à corrosão das amostras de aço inoxidável AISI 430. / Stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. The shot peening process has been used in order to improve the metallic surfaces mechanical properties. Thus, the shot peening process might have influence in the electrochemical behavior of the material, depending of the defined process parameters. Shot peening is a process applied in order to add residual compression stresses in metallic surfaces with the intent of improving the fatigue life, stress corrosion cracking, and galling. The proposal of this study is to evaluate the effect of the shot peening process in the morphology of the surface, corrosion resistance and oxidation resistance of a ferritic stainless steel AISI430. In order to perform this study it was established the use of three samples conditions, being the first one with the surface in the original state condition (as received), the second one with the sanded surface and the third one treated through shot peening. In order to evaluate the influence of the shot peening in the morphology of surface of samples, there were submitted to optical microscopy, scanning electron microscopy (SEM), profilometry test and wettability test. In order to evaluate the effect of the shot peening process in the electrochemical behavior of the surface of samples, the tests such as open circuit potential monitoring (OCP), potentiodynamic polarization curves and electrochemical impedance spectroscopy were carried out. Oxidation test was carried out to analyze the influence of the shot peening in the oxidation resistance and the X-ray diffraction (XRD) was performed to evaluate the presented phases. The obtained results showed that the samples of stainless steel AISI 430 treated with shot peening had a more hydrophilic behavior compared with the samples in the original state condition and sanded surface. Beyond that, the shot peening process with the used process parameters of application in this study changed significantly the morphology of the surface reducing the oxidation resistance and corrosion resistance of the samples of stainless steel AISI430.