O presente trabalho visa apresentar informações que viabilizem a fabricação de componentes de rolamentos com limites superiores de resistência à fadiga, com a intenção de proporcionar uma vida útil maior ao rolamento, e, também, a otimização da fabricação das peças, dispensando em alguns casos o processo final e usual de retificação, o que implica uma redução de custos. As motivações deste estudo são a geração de altas tensões residuais compressivas no torneamento duro-seco a altas velocidades, a aplicação do RMB como técnica de medição das tensões residuais em aço 100CrMn6 e a otimização da qualidade/custos na fabricação de rolamentos. Para atingir essas metas, será estudada a influência dos parâmetros da usinagem (velocidade de corte (Vc), avanço (a), penetração (p) e desgaste da ferramenta (VB)) na geração das tensões residuais superficiais (sR) e sobre as forças de torneamento (Fc, Fa, Fp), em anéis internos de rolamentos cônicos de aço DIN 100CrMn6 endurecidos termicamente, procurando-se estabelecer uma correlação entre o desgaste da ferramenta e os referidos esforços e tensões residuais. Na etapa experimental, será utilizado um planejamento fatorial completo para executar os ensaios e medições projetadas. No ensaio de torneamento, serão medidas as forças de corte utilizando-se, para isso, um dinamômetro piezoelétrico. Em seguida, serão efetuadas medições de rugosidade. Também será realizado o estudo da microestrutura através da análise metalográfica. As tensões residuais serão medidas utilizando-se o método do furo-cego com extensometria elétrica, e as medidas das alterações microestruturais superficiais serão realizadas pela técnica do Ruído Magnético de Barkhausen (RMB). Serão correlacionados os valores de tensão residual obtidos pela técnica do furo com o RMB. / The present work presents information for the manufacturing of ball bearings components with higher limits of resistance to fatigue, enabling a longer useful life and also the optimization of the production of the pieces, making the usual and final process of grinding unnecessary, which would result in a costs reduction. The motivations of this study are the generation of compressive high residual stress in the hard-dry turning at high speeds, the application of the MBN as technique of measurement of the residual stress in steel 100CrMn6, and the optimization of the quality/costs in the manufacturing of ball bearings. In order to achieve these purpose, the work will study the influence of the machining parameters (cutting speed (Vc), feed rate (a), depth of cut (p), and wear of tool (VB)) in the generation of the superficial residual tensions and also the turning forces (Fc, Fa, Fp), in internal conical rings of ball bearings of steel 100CrMn6 thermally hardened, seeking to find a correlation between the stress of the tool and the referred efforts. In the experimental phase, a complete factorial planning will be used to perform the tests and measurements projected. In the turning tests, the cutting forces will be measured using a piezoelectric dynamometer. After that, measurements of superficial roughness will be performed. Also, the study of the microstructure will be made through the metallographic analysis. The residual tensions will be measured using the strain gage hole-drilling method and the measurement of the superficial microestrutural alterations will be carried out using the technical of the magnetic Barkhausen noise (MBN). The values of residual tension obtained by the hole-drilling will be correlated with the RMB.

O presente trabalho, realizado junto ao Grupo de Novos Materiais e Dispositivos (GNMD), no Laboratório de Microeletrônica do Departamento de Sistemas Eletrônicos da Escola Politécnica da USP, visou determinar algumas das propriedades termo-mecânicas de materiais depositados pela técnica de plasma enhanced chemical vapor deposition (PECVD) que são importantes para o desenvolvimento de sistemas microeletromecânicos (MEMS). O módulo de elasticidade, a tensão mecânica residual, o coeficiente de expansão térmica e a condutividade térmica de filmes finos de carbeto de silício amorfo hidrogenado (a-SiC:H) e de oxinitreto de silício (SiOxNy) foram estudados. Medidas de nanoindentação e ressonância de cantilevers foram utilizadas para a obtenção do módulo de elasticidade e os resultados obtidos foram similares (75 e 91 GPa) pelos dois métodos e compatíveis com valores encontrados na literatura. Além disso, obteve-se o módulo de elasticidade de filmes de cromo (285 GPa). A tensão mecânica residual dos filmes utilizados neste trabalho foi medida através da curvatura do substrato induzida pela deposição dos filmes e pela deformação de cantilevers. O valor médio da tensão mecânica, obtido pela curvatura do substrato, variou de -69 MPa até -1750 MPa, mostrando grande dependência das condições de deposição dos filmes. O método que utiliza a deformação de cantilevers possibilitou a obtenção do gradiente de tensão mecânica, que também mostrou uma dependência das condições de deposição, sendo sempre o a-SiC:H quase estequiométrico o menos tensionado. O coeficiente de expansão térmica foi medido utilizando a técnica do gradiente de temperatura e o valor obtido foi similar a valores reportados na literatura para o carbeto de silício cristalino. Para um a-SiC:H quase estequiométrico foi obtido um coeficiente de expansão térmica de 3,41 m/oC, enquanto para um a-SiC:H rico em carbono o valor foi de 4,36 m/oC. Também foi verificado que a variação da resistência do cromo em função da temperatura é pequena, não permitindo sua utilização como sensor de temperatura e inviabilizando a obtenção da condutividade térmica dos filmes estudados. Além disso, foram apresentados trabalhos promissores, mostrando o potencial dos materiais estudados para o desenvolvimento de MEMS. Nesses trabalhos, demonstrou-se a viabilidade de integrar microestruturas atuadas termicamente e guias de onda ópticos, utilizando os materiais estudados neste trabalho. Foram fabricados chaves ópticas, portas lógicas ópticas, fontes de luz integradas e acoplamento das fontes de luz com guias de onda. / This work, realized at the New Materials and Devices Group (GNMD) at the Microelectronics Laboratory of the Department of Electronic Systems of the Polytechnic School of the University of São Paulo, focused at the determination of thermo-mechanical properties of materials deposited by plasma enhanced chemical vapor deposition (PECVD) that are important for the development of microelectromechanical systems (MEMS). The Youngs modulus, the residual stress, the coefficient of thermal expansion and the thermal conductivity of amorphous hydrogenated silicon carbide (a-SiC:H) and silicon oxynitride (SiOxNy) thin films were studied. Nanoindentation and the resonance of cantilevers were used to obtain the Youngs modulus. The results were similar (75 and 91 GPa) with both methods and compatible with literature values. Further, the Youngs modulus of chromium films was also obtained (285 GPa). The residual stress of thin films was obtained through the substrate curvature induced by the film deposition and through the deformation of cantilever beams. The residual stress, obtained through the substrate curvature, varied between -69 MPa and -1750 MPa, showing great dependence on the deposition conditions of these materials. The deformation of cantilevers allowed the determination of the stress gradient and it was also affected by the deposition conditions. In all stress measurements the near stoichiometry a-SiC:H film was less stressed. The coefficient of thermal expansion was measured using the temperature gradient technique and the obtain values were similar to those reported in the literature for crystalline silicon carbide. For a near stoichiometry a-SiC:H film, a value of 3.41 m/oC was obtained, while a carbon rich film showed a thermal expansion coefficient of 4.36 m/oC. It was also verified that the variation of the chromium resistance as a function of temperature is small. This did not allow the utilization of chromium as a temperature sensor, which prevented the obtention of the thermal conductivity of the studied films. Also, some promising works were presented, showing potential applications of the studied materials for the development of MEMS. In these works, the viability of integration of thermal actuated microstructures and optical waveguides was demonstrated. In these works, optical switches, optical logic gates, integrated light sources and coupling of integrated light sources with optical waveguides were presented.

The optimisation of compressor stage aerofoil and fan blade design remains an important area of titanium alloy research and development for aerospace gas turbines. Such research has important implications for critical and sensitive component integrity and efficiency. In particular, a better understanding of how deformation twinning interacts with microstructural features in titanium alloys is required, because such twinning facilitates plastic deformation at a higher strain rate than dislocations. To investigate this behaviour, commercial purity titanium and the titanium alloy Ti–6Al–4V were subjected to ballistic impact testing at room temperature with a high strain rate of 10³s⁻¹. In addition, a detailed analysis was conducted of three manufacturing processes of Ti–6Al–4V (wt. %) that are likely to cause deformation twinning: metallic shot peening, laser shock peening and deep cold rolling. The results presented in this thesis have furthered the understanding of the role of deformation twinning in the plastic deformation of α-phase titanium. Key findings of the research include the characterisation of deformation twinning types and the conditions that favour certain deformation twinning types. From the analysis of the ballistic testing of commercial purity titanium, the first definitive evidence for the existence of {112‾4} twinning as a rare deformation twinning mode at room temperature in coarse-grained commercial purity titanium is presented. In addition, the ballistic testing results of the Ti–6Al–4V alloy highlighted very different deformation twinning characteristics. Commercial purity titanium deformed plastically by a combination of {101‾2} and {112‾1} tensilve twinning and {112‾4} and {112‾2} compression twinning modes. By contrast, the deformation twinning of Ti–6Al–4V was limited to only the {101‾2} and {112‾1} tensile twinning modes. The two tensile deformation twinning types have very different morphologies in equiaxed fine grained Ti–6Al–4V. {112‾1} deformation twins span multiple grain boundaries and {101‾2} deformation twins reorient entire grains to a twinned orientation. This observation provides evidence for whole grain twinning of equiaxed fine grained Ti–6Al–4V by {101‾2} twinning. Grain boundary interactions between various deformation twinning types and alpha phase grain boundaries in commercial purity titanium and Ti–6Al–4V are reported and analysed. In commercial purity titanium {101‾2} as well as other deformation twinning types were observed interacting across alpha phase boundaries and higher angle alpha phase grain boundaries. The analyses of the manufacturing processes of Ti–6Al–4V highlight the very different dislocation and deformation twinning structures in surfaces processed by these techniques. A notable feature of material processed by laser shock peening is the almost complete absence of deformation twinning, contrasting with the frequent observation of extensive deformation twinning observed in the material processed by metallic shot peening and deep cold rolling. Therefore, the findings suggest that there is a strain rate limit above which deformation twinning is suppressed. The implications of this research are that a better understanding of the conditions that that favour certain deformation twinning types or propagation behaviours will enable more accurate plasticity modelling and better alloy design. This is important for the design and the manufacturing of titanium components and the high strain rate deformation to which titanium components in aerospace gas turbines can be subjected because of bird strike, foreign object debris ingestion or fan blade failures.

Les verres métalliques massifs à base de zirconium, développés depuis la fin des années 80, présentent des propriétés mécaniques très intéressantes. Ils peuvent être envisagés pour de multiples applications y compris à des températures élevées et il est donc intéressant d’étudier leur résistance à l’oxydation dans de telles conditions. L’objectif fondamental de cette étude consiste à mieux comprendre le rôle de divers paramètre thermodynamiques et chimiques sur le comportement à l’oxydation des verres métalliques à base de zirconium à des températures intermédiaires sous air sec, à déterminer les contraintes résiduelles au sein de la couche d’oxyde formée, en comparaison avec des alliages amorphe cristallisés après un traitement de recuit. La cinétique d’oxydation de ces verres et la structure cristalline de la couche d’oxyde ZrO2 dépend de la température et de la durée d’oxydation : pour des durées courtes d’oxydation et pour une température légèrement inférieure à Tg, la cinétique d’évolution est parabolique alors que si l’échantillon est oxydé à T > Tg, la loi cinétique peut être décomposée en deux parties. Les mêmes alliages cristallisés après un traitement de recuit, s’oxydent selon une loi parabolique quelque soit la température. Pour des durées d’oxydation longues à une température proche de Tg, les lois cinétiques deviennent plus complexes et la cristallisation du verre métallique pouvant avoir lieu au cours des essais d’oxydation. De même la structure cristalline des couches d’oxyde dépend de la température d’oxydation. Ainsi, pour T < Tg, la couche d’oxyde des alliages amorphes est uniquement constituée de la zircone tétragonale alors que pour ces mêmes alliages portés à une température T > Tg et pour les alliages cristallisés, on observe de la zircone monoclinique. Les mécanismes d’oxydation dépendent de la température d’oxydation. Pour les températures où les alliages restent vitreux, la formation de l’oxyde est due à la fois à la diffusion des ions d’oxygène vers l’intérieur mais également à la diffusion des ions de zirconium vers l’extérieur de la couche. En revanche, pour les alliages en cours de cristallisation, la diffusion des ions de zirconium est progressivement freinée jusqu’à devenue nulle lorsque la cristallisation est totale, l’oxydation étant alors uniquement contrôlée par la diffusion interne des ions d’oxygène.Les contraintes résiduelles correspondantes au sein de couches d’oxyde sont de compression, aussi bien pour les alliages amorphes que pour les alliages cristallisés, et qu’elles augmentent linéairement avec l’épaisseur de la couche. Les contraintes de croissance lors de l’oxydation et résiduelle après l’oxydation sont fortement influencées par le changement de phase de la zircone. / The Zr-based bulk metallic glasses, developed since the late 1980s, have very interesting mechanical properties, which can be considered for many applications including working under oxidizing atmosphere conditions at high temperatures. It is therefore interesting to study their oxidation resistance and to characterize the oxide scale formed on alloys’ surface. The fundamental objective of this thesis is to enhance the understanding of the role of various thermodynamic and chemistry parameters on the oxidation behaviour of the Zr-based bulk metallic glasses at high temperature under dry air, to determine the residual stresses in the oxide layer, in comparison with their crystalline alloys with the same chemical composition after an annealing treatment. The oxidation kinetics of these glasses and the crystalline structure of oxide scale ZrO2 depend on the temperature and the oxidation duration: for short periods of oxidation or at a temperature below Tg, the kinetics follows a parabolic law, whereas, if the sample is oxidized at T > Tg, the kinetics can be divided into two parts. The crystalline counterparts are oxidized by a parabolic rule whatever the temperature; for long oxidation duration at a temperature close to Tg, the kinetics becomes more complex because of the crystallisation of the glasses during the oxidation tests. Also the crystalline structure of the oxide layers depends on the oxidation temperature: the oxide layer consists only in tetragonal Zirconia at T < Tg, while monoclinic Zirconia was formed at higher temperature. The mechanism of the formation of the oxide scale is due to both the interior diffusion of Oxygen ions and the external diffusion of Zirconium ions. However the diffusion of Zirconium ions slows gradually during the crystallisation process of the glass matrix. When the crystallisation is completed, the formation of Zirconia is controlled by only the internal diffusion of oxygen ions. The corresponding residual stresses existing in the oxide layer are compressive, both for the metallic glass and counterpart, and they increase linearly with the thickness of the oxide layer. The growth and residual stresses are strongly influenced by the phase transition of Zirconia during oxidation process.

Cette thèse étudie les effets du processus de brunissage à bille assisté par vibrations ultrasoniques sur l'intégrité de surface des surfaces usinées par fraisage hémisphérique. Compte tenu de l'inexistence d'outils commerciaux capables de réaliser ce processus, l'étude débute par la conception et la caractérisation d'un prototype capable de l'exécuter. Par la suite, une analyse expérimentale est menée, en utilisant le procédé sur les surfaces de deux alliages d'intérêt industriel et aéronautique, AISI 1038 et Ti- 6Al-4V. Pour cela, un plan d'expériences est élaboré à base d'une matrice orthogonale Taguchi. Cinq facteurs sont inclus dans le modèle : la précharge, le nombre de passes, la vitesse d'avance, la stratégie de brunissage et la texture initiale de la surface préalablement usinée. Les résultats sont évalués en termes de texture finale, de contrainte résiduelle et de dureté, pour identifier et comprendre l'impact de ce procédé et des paramètres opératoires sur l'intégrité de surface, pour définir les meilleurs paramètres à appliquer pour chaque matériau, et pour évaluer les effets positifs provoqués par l'introduction de vibrations comme moyen d'assistance. Pour cela, la notion d'intégrité de surface est rappelée, voire redéfinie dans le cas de la texture de surface. En effet, les critères classiquement utilisés se révèlent inaptes à caractériser les surfaces obtenues, et une nouvelle méthodologie d'analyse des topologies de surface est proposée. Les résultats obtenus suite à la réalisation du plan d'expériences révèlent que la texture initiale est le paramètre prépondérant. Les résultats de la topologie de surface montrent que les vibrations peuvent améliorer la rugosité et la texture des surfaces dans la mesure où l'état de surface initial est suffisamment fin. Ensuite, seule la précharge et le nombre de passes influencent le résultat, avec, dans tous les cas, un couple de valeurs limites à partir desquelles les surfaces sont endommagées. Les résultats des contraintes résiduelles montrent que tous les paramètres influent sur le résultat final, en particulier la stratégie de brunissage, avec laquelle la direction préférentielle du tenseur de la contrainte superficielle peut être modifiée. Enfin, le brunissage montre une modification positive de la dureté à des couches d'environ 0,5 mm en appliquant le processus assisté avec vibrations. Nous concluons que les paramètres de processus optimaux sont différents en fonction de l'objectif d'optimisation, et que certaines combinaisons peuvent être utiles en fonction de ces objectifs. / This dissertation is an experimental research project into the mechanical effects of the ultrasonic vibration-assisted ball burnishing process on the surface integrity of surfaces machined through ball-end milling. Due to the lack of commercial tools able to perform this process, the study includes firstly the design and characterisation of a prototype to that effect. An experimental analysis is then undertaken, applying the process to AISI 1038 and Ti-6Al-4V surfaces of high industrial and aeronautical value. The experimental campaign is designed based on a Taguchi orthogonal array that includes five factors, namely: preload, number of passes, feed velocity, strategy and initial surface texture. Results are analysed in terms of topological characteristics, residual stress and hardness, in order to identify and understand the impact of process parameters on surface integrity, to define the best parameters for performing the process and to assess the positive effects caused by the introduction of vibrations as a means of assistance. Results reveal that the initial texture is the most influential parameter on all outcomes. Texture results show that the vibrations can enhance the roughness and texture results, as long as they have sufficient low initial amplitude. Furthermore, only the preload and number of passes influence the results, with a pair of values being found in all cases that serve a threshold from which further plastic strain is detrimental for the final surface topology. In terms of residual stress, all parameters are influential in the results, especially the burnishing strategy, through which a certain component of the residual stress tensor can be adequately reinforced. Finally, the burnishing operation proves to modify the hardness of deep layers down to 0.5 mm, applying the vibration-assisted process. The main conclusion is that the optimal parameters for performing the process are different with regards to the optimisation objective. Some useful combinations are proposed for performing the process depending on the desired target.

Nesse trabalho foram realizados experimentos para determinar as tensões residuais introduzidas no Aço A36, que é uma liga de baixo carbono e que é muito utilizado em vários setores da produção industrial, quando esta é submetida à soldagem do tipo MIG (Metal Gas Inert). A escolha desse tipo de soldagem foi para manter constantes os parâmetros que pudessem influenciar nos resultados. Nessa análise foi verificada a distribuição das tensões residuais na zona termicamente afetada, a distribuição da tensão em relação a profundidade. Para isso usamos uma remoção eletrolítica e um corte transversal pelo processo de eletroerosão. Nesse trabalho foi usado o método do sen2&#61561;, devido a sua facilidade para a análise dos dados do Programa PSD. O resultado das mediadas realizadas na região do cordão de solda, zona termicamente afetada (ZTA) e metal base próxima da ZTA, mostrou uma variação da distribuição da tensão em relação à profundidade do material e na distância do ponto de soldagem. No ponto de soldagem um aumento da tensão em relação à profundidade do material. Os fatores que influenciaram na introdução dessas tensões no processo de soldagem, foram causados pelo gradiente de temperatura, pelo resfriamento heterogêneo do material e também pelo resfriamento rápido da superfície / In this work experiments were conducted to determine the residual stresses introduced in the A36 steel, which is an alloy of low carbon, which is widely used in various sectors of industrial production, when it is subjected to welding-type MIG (Metal Inert Gas). The choice of this type of welding was to keep constant the parameters that could influence the results. In this analysis we detected the distribution of residual stresses in the heat affected zone, the stress distribution over the depth. For this we use an electrolytic removal and a cross section through the process of spark erosion. In this study we used the method of sen2&#61561;, due to its ease to the analysis of data from the PSD. The result showed a variation of stress distribution for the depth of the material and the distance from the point of welding. The welding point ran a rise in tension over the depth of the material. Factors influencing the introduction of these stresses in the welding process were caused by the temperature gradient by cooling the heterogeneous material and also by the rapid cooling of the surface

Ce mémoire présente une méthode visant à mettre en évidence l’influence de l’intégrité de surface obtenue en tournage, sur la fatigue de l’acier 15-5PH. Le travail réalisé consiste à développer des moyens d’obtention de surfaces à intégrités maitrisées, puis à réaliser des essais de fatigue pour observer l’influence des paramètres d’intégrité. Les procédés de tournage et de galetage sont utilisés pour obtenir des lots d’éprouvettes possédant différentes intégrités de surfaces. Ces éprouvettes sont ensuite toutes caractérisées, en rugosité et contraintes résiduelles, de manières non destructives. Certaines éprouvettes font l’objet d’analyses complémentaires pour caractériser l’état de la matière sous la surface. Ces analyses permettent de constituer des lots d’éprouvettes possédant des caractéristiques de surfaces très proches. Toutefois, il a été mis en évidence une très grande sensibilité de l’intégrité de surface générée, vis-à-vis du diamètre de la pièce usinée, ce qui se traduit par une dispersion importante des intégrités de surface obtenues. Les lots constitués sont ensuite testés en fatigue sur une machine de flexion rotative (R = -1) selon la méthode Staircase. Cette méthode permet de déterminer la limite d’endurance avec 50 % de probabilité de rupture pour un nombre de cycles donné. Les résultats sont ensuite confrontés aux intégrités de surface des lots pour déterminer les caractéristiques les plus influentes. Une comparaison des données expérimentales est réalisée avec les modèles de la littérature. Il est montré que ces modèles ne parviennent pas à décrire de manière satisfaisante le comportement en fatigue vis à vis de la rugosité ou du niveau de contraintes résiduelles. L’analyse de ces résultats montre que le profil de contraintes résiduelles, dans le cas du 15-5PH, est la caractéristique la plus influente sur la tenue en fatigue. La rugosité n’apparait pas comme un facteur d’influence notable, à l’exception des cas où les contraintes résiduelles ont un niveau très faible. Des pistes d’améliorations sont enfin suggérées pour améliorer la prise en compte de l’intégrité de surface dans le cadre d’un dimensionnement en fatigue. / This thesis aims to show a method to highlight the influence of surface integrity obtained by turning on the fatigue of a 15-5PH steel. Several ways are developped to obtain desired surface integrities, then fatigue test are performed to observe the influence of surface integrity parameters'. Turning and ball burnishing were used to achieve specimens with differents surface integrities. Theses samples are then fully characterized in term of surface roughness and residual stresses, in a non-destructive way. Some specimens are subject to further analysis to characterize the state of the material under the surfaece. These analyses are used to create batches of specimens with very close surfaces characteristics. However, it has been shown a high sensitivity of the generated surface integrity, with respect to the workpiece diameter, which result in a significant dispersion of surface integrities obtained. Batches are then tested on a rotating bending test machine (Stress ration R=-1) thanks to the Staircase method, in order to determine the fatigue limit at two billion cycle with a 50% failure probability. The results are then compared with the surface integrities in order to determine the most influencial parameter. A comparison of the experimental datas with models in the literature is performed. It is shown that models are unable to describe the fatigue behavior with respect to the roughness or the residual stress state. The results analysis shows that residual stresses profile, in the case of 15-5PH steel, is the most influencial parameter on the fatigue life. Roughness does not appears as a factor of major influence, except in cases where residual stresses have a very low level. Prospects for improvement are finaly suggested in order to improve the consideration of surface integrity during the fatigue design of parts.

Les travaux effectués au cours de cette thèse ont pour objectif d’étudier et de modéliser une opération de soudage multipasse d’un acier à haute limite d’élasticité utilisé en construction navale. Dans ce cadre il s’agit de prédire les conséquences métallurgiques et mécaniques du procédé et tout particulièrement la répartition et l’intensité des contraintes résiduelles post- soudage nécessaires pour analyser l’intégrité de la structure navale en service. Deux maquettes représentatives d’un joint d’angle en Té ont permis de caractériser l’évolution des cycles thermiques, de la microstructure et des contraintes résiduelles (estimées par les méthodes du contour et du trou profond) après chaque passe de soudage. La suite de l’étude concerne la caractérisation et la modélisation du comportement thermo-métallurgique et thermo- mécanique des différentes phases apparaissant au cours du soudage. La dernière partie porte sur l’implémentation des modèles retenus dans le code de calcul élément finis Abaqus à l’aide de sous-programmes spécifiques. Une étape de transition d’échelle a permis de décrire le comportement thermomécanique multiphasé de cet acier. Des calculs préliminaires ont été conduits pour valider l’implémentation des modèles sur des cas simples. Différents couplages ont été réalisés, soit une analyse thermique puis thermo-métallurgique, pour estimer la dureté après chaque passe et enfin métallurgique-mécanique pour prédire les contraintes résiduelles pour le procédé de soudage multipasse. Les résultats des calculs éléments finis ont été discutés et comparés aux résultats expérimentaux obtenus dans la première partie de cette étude. / This thesis aims at studying and modeling a multipass welding operation of a high strength steel used in shipbuilding. In this framework, work focus on predicting the metallurgical and mechanical consequences of the process and, in particular, the residual stress distribution after welding. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Two welding mock-ups which are representative of a T- joint were used to characterize the evolution of thermal cycles, microstructure and residual stresses (measured by contour method and deep hole drilling) after each welding pass. Metallurgical and mechanical behaviors were thoroughly characterized in order to feed numerical models with reliable constitutive equations. The last part deals with the implementation of the models in the finite element calculation code Abaqus using specific subroutines. A scale transition procedure has been added to describe the thermomechanical multiphase behavior of the steel. Preliminary calculations were carried out for simple cases to validate the implementation of models. Different numerical couplings were made. First a thermal analysis then a thermo-metallurgical analysis, to estimate the hardness after each welding pass. Finally, a metallurgical-mechanical analysis is achieved for the prediction of residual stresses due to multipass welding. The results of the finite element calculations were discussed and compared with the experimental results obtained in the first part of this work.

Oil Jet Cavitation Peening in Air (OPA) is capable of inducing compressive residual stress in standard aerospace materials. This paper demonstrates the process capabilities of OPA on Al 2024-T3. Specifically, changes in the workpiece residual stress, microhardness, mass loss and surface roughness are investigated as a function of the control parameters for the system. Additionally, the paper identifies a method to monitor the process in situ through the use of high frequency acoustic emission sensors. The results indicate the OPA process is capable of generating residual stresses comparable to those of standard shot peening, up to 60% of the yield strength of the material, at similar depths, around 300 µm. Finally, the acoustic emission signal may be utilized to monitor the process, specifically in predicting the microhardness and mass loss of the system.

<p>The aim of this thesis is to investigate how material surfaces are affected by various surface treatments and how this relates to the adhesion of the coating. The materials that were studied were WC-Co and Cermets and the surface treatments used were polishing, grinding with coarser and finer abrasive grains, and finally wet blasting and dry blasting. Focus was on deformations and residual stresses in the surface, surface roughness and cracks. The test methods used for examining the samples included surface roughness measurements, residual stress measurements, adhesion tests using Rockwell indentation and SEM images of the surface and the cross section.<br /><br />The results concluded that polishing gives very good adhesion. Additionally, the adhesion for ground surfaces was good for WC-Co but very poor for Cermets. Furthermore, it was observed that finer abrasive grains did not result in better adhesion. In fact, the coarser grains gave slightly better results. Finally, it was concluded that wet blasting has a clear advantage over dry blasting and results in much better adhesion, especially for the Cermets. The results for the WC-Co were a bit inconsistent and so further research is required.</p>