「兵役制度」為國民至軍隊服役制度，是保障國家安全之武裝力量，平時以法律規範，完成兵員補充、武裝組織、軍事訓練，使人民依法履行義務。「兵役制度」依國家安全環境考量，由戰略家與兵力規劃者權衡戰事，反覆檢視安全環境、戰略目標、可利用資源，從整體戰略來決定兵力結構，以合理有效訓練方式提升兵力水準，以支撐軍事戰略。 兩岸為創造有利之安全環境與挑戰內外競敵，不斷在軍事戰略思維實施調整。中共已賦予解放軍保障國家安全利益之任務與角色，並自1949年建政以來，持續運用針對性之軍事演習或武力展示威懾台灣，以達其政治目的，並於1985年大裁軍後，以量小質精、齊全、強大的軍兵種常規武裝力量，遂行立體作戰整備。台灣軍事戰略從「反攻大陸」－「攻守一體」－「防衛固守」－「防衛固守，有效嚇阻」－「有效嚇阻，防衛固守」，各階段戰略決策有所不同，依當時國防威脅逐年修正，台澎防衛作戰又將作戰區區分安全警戒區、主要戰鬥區、後方區域，以提高作戰層次與建軍備戰。台灣如何於獲得先進武器後，搭配組建優質兵力，以形成整體軍力優勢，為維護整體國防安全之碁石。為因應台海快速變化的戰爭型態，台灣之國防組織必須採「平戰一體」，才能因應未來戰事。然而，台灣目前國防設計則偏向平戰轉換，在國防體制上是「常後分立」，戰時才將後備動員轉換為戰力．台灣軍方較迷失動員人力「到召率」，認為到召率數提高，戰力便從而昇起，而因應台海戰爭發展迅速，如完全仰賴動員，戰事亦可能告敗結束。 / The “Conscription System” is a military service scheme ordinarily enforced by law，through which the citizens of a country are called up for obligatory military service.It is the basic formation of armed forces to safeguard the national security，so that supplement of military manpower，organization of armed services，arrangement of military training，and exertion of authority over the citizens for observance of the obligatory duties can be undertaken without hindrance .Based on the consideration of national circumstantial security，the blueprint of conscription system，including the size of military forces，strategic structure of armed forces，elevation of the standard of armaments to support the decided military strategy is entrusted to groups of military strategists and planners to formulate and decide after their repeated careful surveyals of the national security circumstances，strategic aims and national resources available.The opponents on opposite coasts of Taiwan Strait for creating environments，advantageous to their own potentials and challenging their hostiles，either extrinsic or intrinsic，unremittingly adjust and readjust their thoughts of military strategy to suit the alterations of situations.The Communist China has long since bestowed upon its “Liberation Army” the role and task of safeguarding national safety and benefits，and indeed since its accomplishment of civil administration in 1949，it persistently manipulates purposeful military maneuvers or military displays to threaten Taiwan to effectuate its political aims.On the side of Taiwan，the military strategy has been modified from “Restoration of Mainland” at the beginning to “Unification of Attack and Defensive Holdout” and then to “Defensive Holdout and Effective Deterrence” by the Department of Defense，year in，year out，based on the altering strategic situation at various stages.With respect to the Taiwan-Penghus Defense in case of war，the entire war theater is divided into safe surveillance zone，main or major combat zone and rear zone so as to elevate the orders of warfare and raise weapons for war. How to acquire modern weapons to incorporate the raising of a military force of high quality to create military supremacy，is the solution or cornerstone of safeguarding the overall safety of defense.To be able to cope with the war in the Taiwan strait，which， in general assumption，could change rapidly in pattern，the coustitution of national defense must be based on a conception of ‘war and peace alike” .Nevertheless，at present，the design of national defense inclines to be based on a theory of ‘peace and war switchover” .In the structure of defense，regulars and reservists are independent and individualized without intimate and close linkage，and in case of war，the reservists are then called up to form combatant units.The higher military echelons，owing to being bewildered by high summon or attending rate of the called－up reservists，are of the opinion that if the summon rate is raised，the combative strength is also elevated.Since the fashion of war of the Taiwan Strait could be swift，should meeting the enemy solely rely on mobilization of reservists，the war might end in defeat.

Le composite HexTOOL TM à base de la matrice bismaléimide renforcé par des fibres de carbone fait partie d’une famille de matériaux composites récemment utilisés pour des applications à haute température. Vu la part croissante de l’utilisation de ce matériau dans les domaines industriels, il est inconcevable de ne pas s’intéresser aux endommagements (fissuration et usure…), engendrés par des sollicitations de contact, en particulier vis-à-vis de matériaux métalliques. L’une des sources de ces endommagements est associée aux vibrations apparaissant lors de sollicitations de petits débattements (fretting).L’objectif de ce travail est de développer une méthodologie expérimentale, permettant d’expertiser le comportement à long terme en fretting du composite HexTOOL TM. Deux résultats essentiels sont mis en avant au cours de cette étude. Le premier concerne l’étude de l’endommagement de la matrice bismaléimide (BMI). Pour cela, les conditions d’amorçage et de propagation des fissures ainsi que l’usure ont été analysées en fonction des conditions de sollicitation locale. Le deuxième résultat est le développement d’une stratégie d’analyse de l’usure du composite HexTOOL TM. L’orientation locale des fibres a une influence notable sur le phénomène de l’usure du composite. Des essais effectués sous des niveaux de force normale et des conditions de température différentes ont mis en évidence une meilleure résistance à l’usure dans les zones où les fibres sont parallèles à la direction de glissement. En outre, des essais menés en fonction de la température ont montré l’influence de la matrice et du troisième corps sur la cinétique d’usure. / Carbon fibre/bismaleimide composite or HexTOOL TM is one of a family of composite materials recently developed for high temperature applications. Given the increasing use of this material in industrial fields, it is interesting to study damage (cracking and wear ...), caused by contact stresses, in particular in the contact with metallic materials. One source of this damage is associated to vibration occurring when a small displacement amplitude oscillatory motion is conducted (fretting). The objective of this work is to develop an experimental methodology, allowing the analyzing of the long-term behavior of composite HexTOOLTM under fretting conditions.Two main results are put ahead during this research. The first concerns the study of damage of the bismaleimide matrix. Two types of damage, depending on local stress conditions: the Cracking and Wear, were analyzed. These experimental data conditions were used for the fretting maps to better visualize the behavior of the composite matrix. The second result is the development of a wear analysis strategy of the composite HexTOOLTM. Influence of the local fibre orientation on the wear kinetics of composite is here presented. Tests performed under constant normal force and different temperature conditions show the best wear resistant performance of composite with parallel fibre orientation to the sliding direction. In addition, the influence of the matrix behaviour (viscous response) and the third body on the wear is shown.

Les systèmes de maintien situés sur les structures assemblages-combustibles des réacteurs nucléaires à eau sous pression (REP) sont constitués d'un empilement de lames qui agissent à la fois, comme élément accommodant les incompatibilités thermiques résultant des différences de coefficients de dilatation Acier, alliages de zirconium et principalement, comme système permettant de limiter les effets hydrodynamiques induits par le passage du fluide caloporteur à travers les assemblages. Actuellement, l'alliage 718 est le matériau constitutif de ces ressorts à lames. Il présente les performances en service nécessaires et suffisantes pour répondre aux sollicitations de ces systèmes ainsi qu'aux exigences des autorités de sûreté (dans les conditions actuelles de fonctionnement des REP). Or, dans le cadre de l'augmentation des performances générales des assemblages combustibles, l'emploi d'autres matériaux, dont les propriétés de relaxation sous flux neutronique sont supérieures à celles du 718, est envisagé par AREVA. Les matériaux étudiés sont principalement des superalliages base Ni, tels que les nuances 625+ et 725 qui à l'instar de l'alliage 718 durcissent par précipitation de phases secondaires, ainsi que des nuances d'alliage 718 riche en Molybdène. Cependant, bien que ces nouveaux matériaux présentent une relaxation sous flux neutronique améliorée, ils doivent répondre également à un cahier des charges strict, propre à leur utilisation en centrale : des propriétés mécaniques équivalentes, une bonne résistance à la corrosion sous contrainte (CSC) et une bonne résistance à la fragilisation par l'hydrogène (FPH) en milieu primaire de REP. Chacune de ces propriétés a été étudiée avec attention dans le double but de comparer ces matériaux entre eux et afin de cerner les paramètres clés contrôlant leur différence de comportement aussi bien en CSC qu'en FPH / Hold-down systems used in the fuel assembly of Nuclear Pressurized Water Reactor (PWR) are constituted by stiff springs. The role of the hold-down springs is to ensure the bond between the fuel assembly and the lower plate of the intern structure of the core, thus holding down the assembly on the bottom plate of the reactor, during all the exploitation and maintenance periods. Nowadays, alloy 718 is the constitutive material of these hold-down springs. Its properties in terms of mechanical behaviour, corrosion resistance… fill in the specifications required for such application in the present service conditions. However, in order to improve the common efficiency of fuel assemblies, the upgrading of their design as well as the use of new materials are advocated by the nuclear power plant company, AREVA. Though other Ni-base superalloys known for their good behaviour under neutronic radiation can be proposed as new materials, those superalloys must fill in all the application specifications in order to substitute alloy 718. So, sufficient mechanical properties, good resistance to Stress Corrosion Cracking (SCC) and good resistance to Hydrogen Embrittlement (HE) are also required to allow the replacement. All of these properties are carefully studied with the double aim to characterize and compare different superalloys, and to determine key parameters governing the SCC and HE behaviours of such alloys in primary water of PWR

Les procédés conventionnels de transformation thermique de la biomasse sont conçus pour la production d’huiles ou de gaz riches en CO, CO2, H2 et hydrocarbures légers à des fins énergétiques ou chimiques. Le pilote de pyrolyse rapide utilisé dans cette étude comporte un réacteur cyclone, chauffé à ses parois, et capable de mettre en oeuvre la pyroliquéfaction ou la pyrogazéification par le simple jeu des conditions opératoires. Les produits de réaction (charbon, huiles et gaz) sont récupérés et analysés. Les bilans de matière massiques et élémentaires (C, H, O) bouclent de façon très satisfaisante. Les basses températures de paroi et faibles débits de gaz vecteur favorisent la pyroliquéfaction. La production d’huiles augmente avec le débit de biomasse. La taille des particules a une faible influence sur les sélectivités en gaz, liquides et charbon. Un modèle de fonctionnement du cyclone est établi en tenant compte de l’hydrodynamique des phases gaz et solide ainsi que des lois de transferts de chaleur paroi-gaz et paroi-solides dans le cyclone. Ce modèle inclut également un schéma cinétique de pyrolyse rapide intégré dans un modèle de décomposition de la particule, ainsi qu’un modèle de craquage des vapeurs. Validé successivement sur la cellulose puis sur le bois, il permet de prédire les variations des sélectivités en fonction des conditions opératoires. Le modèle montre que les réactions de craquage se déroulent majoritairement dans une mince couche limite proche des parois chaudes. On propose deux lois générales (pyrogazéification et pyroliquéfaction) regroupant les différents paramètres opératoires contrôlant les performances du réacteur / The usual processes of biomass thermal upgrading are designed for the production of bio-oils or of gases rich in CO, CO2, H2 and light hydrocarbons for energy or chemical productions. The laboratory-scaled set-up used in this study includes a cyclone reactor, heated at its walls and able to carry out the fast pyroliquefaction or pyrogazeification by simply changing the operating conditions. The reaction products (charcoal, liquids and gases) are recovered and analyzed. The masses and elementary (C, H, O) balances closures are very accurate. Pyroliquefaction conditions are favoured by low walls temperatures and small carrier gas flowrates. The bio-oils fractions increase with the biomass flowrate. The particles size has only a weak influence on gas, liquids and charcoal selectivities. A model representing the cyclone behaviour is established by taking into account the hydrodynamics of the gases and solids, and the wall-gas and wall-solids heat transfer laws inside the cyclone. This general model includes also a model of particle decomposition (scheme of fast pyrolysis in competition with heat transfers) and a model of vapours cracking. Validated successively with cellulose and then with wood, it allows to predict the variations of the selectivities according to the operating conditions. The model shows that the cracking reactions occur mainly inside a thin boundary layer close to the hot walls. Two laws (pyrogazeification and pyroliquefaction) gathering the various operational parameters that control the performances of the reactor are finally proposed

Le procédé de craquage thermique est un procédé industriel sensible aux conditions de température et de pression. L’utilisation de réacteurs aux parois nervurées est une méthode permettant d’améliorer la sélectivité chimique du procédé en augmentant considérablement les transferts de chaleur. Cependant, cette méthode induit une augmentation des pertes de charge dans le réacteur, ce qui est dommageable pour le rendement chimique et doit être quantifié. En raison de la complexité de l’écoulement turbulent et de la cinétique chimique, le gain réel offert par ces géométries en termes de sélectivité chimique est toutefois mal connu et difficile à estimer, d’autant plus que des mesures expérimentales détaillées sont très rares et difficiles à mener. L’objectif de ce travail est double: d’une part évaluer le gain réel des parois nervurées sur le rendement chimique; d’autre part proposer de nouveaux designs de réacteurs offrant une sélectivité chimique optimale. Ceci est rendu possible par l’approche de simulation numérique aux grandes échelles (LES), qui est utilisée pour étudier l’écoulement réactif à l’intérieur de diverses géométries de réacteurs. Le code AVBP, qui résout les équations de Navier Stokes compressibles pour les écoulements turbulents, est utilisé pour simuler le procédé grâce à une méthodologie numérique adaptée. En particulier, les effets des pertes de charge et du transfert thermique sur la conversion chimique sont comparés pour un réacteur lisse et un réacteur nervuré afin de quantifier l’impact de la rugosité de paroi dans des conditions d’utilisation industrielles. Une méthodologie d’optimisation du design des réacteurs, basée sur plusieurs simulations numériques et les processus Gaussiens, est finalement mise au point et utilisée pour aboutir à un design de réacteur de craquage thermique innovant, maximisant le rendement chimique / Thermal cracking is an industrial process sensitive to both temperature and pressure operating conditions. The use of internally ribbed reactors is a passive method to enhance the chemical selectivity of the process, thanks to a significant increase of heat transfer. However, this method also induces an increase in pressure loss, which is damageable to the chemical yield and must be quantified. Because of the complexity of turbulence and chemical kinetics, and as detailed experimental measurements are difficult to conduct, the real advantage of such geometries in terms of selectivity is however poorly known and difficult to assess. This work aims both at evaluating the real benefits of internally ribbed reactors in terms of chemical yields and at proposing innovative and optimized reactor designs. This is made possible using the Large Eddy Simulation (LES) approach, which allows to study in detail the reactive flow inside several reactor geometries. The AVBP code, which solves the Navier-Stokes compressible equations for turbulent flows, is used in order to simulate thermal cracking thanks to a dedicated numerical methodology. In particular, the effect of pressure loss and heat transfer on chemical conversion is compared for both a smooth and a ribbed reactor in order to conclude about the impact of wall roughness in industrial operating conditions. An optimization methodology, based on series of LES and Gaussian process, is finally developed and an innovative reactor design for thermal cracking applications, which maximizes the chemical yield, is proposed

La corrosion sous contrainte (CSC) des alliages à base nickel est un des principaux phénomènes de dégradation des composants du circuit primaire des Réacteurs à Eau Pressurisée (REP). La compréhension de ce mécanisme de fissuration est un élément essentiel pour la prolongation de la durée d’exploitation des réacteurs.Des études antérieures ont permis d’établir un modèle de propagation de la CSC basé sur une oxydation sélective et dissymétrique du joint de grains en pointe de fissure qui s’accompagne d’une zone appauvrie en chrome. La cinétique de diffusion du chrome étant plus lente que celle de l’oxygène, il est supposé que la diffusion du chrome est une étape limitante de la propagation de la fissure. Si ces observations ont été validées dans la littérature, les hypothèses proposées sur l’origine de l’appauvrissement en chrome dans le grain sont encore sujettes à discussion. Comme la diffusion du chrome en volume dans les alliages base nickel à 350°C ne permet pas d’expliquer les ordres de grandeur des appauvrissements en chrome mesurés dans la littérature, il est supposé qu’il existerait un élément accélérateur de la diffusion du chrome dans l’alliage en pointe de fissure. Ainsi, deux hypothèses sont proposées dans ces travaux : la diffusion du chrome accélérée sous l’effet de la plasticité et la migration des joints de grains induite par la diffusion.L’objectif principal de la thèse a été de confronter les deux hypothèses énoncées au moyen d’essais expérimentaux et de modélisation afin de déterminer le mécanisme de formation de la zone appauvrie en chrome et d’identifier les paramètres favorisant cet appauvrissement.A cet effet, des essais de diffusion sous charge ont été réalisés dans le but d’étudier l’effet de la déformation plastique sur la diffusion du chrome. Les résultats ont permis d’établir une relation entre le coefficient de diffusion et la vitesse de déformation. Ainsi, une accélération de la diffusion en volume de l’ordre de 106 est observée à 350°C sous l’effet de plasticité. De même, des traitements thermiques visant à mettre en évidence la migration des joints de grains induite par la diffusion (DIGM) sont présentés dans ces travaux. Les caractérisations chimiques et microstructurales montrent que la DIGM est bien associée à la formation d’une zone appauvrie en chrome observée dans le sillage du joint de grains migrant. Pour finir, une discussion est proposée afin de relier ces hypothèses au modèle de propagation de la CSC. / Stress Corrosion Cracking (SCC) of nickel base alloys is one of the major degradation phenomena in the primary circuit of Pressurized Water Reactors (PWR). Understanding the SCC mechanism is a key issue for the extension of reactor lifetime.A SCC model based on a selective and asymmetrical oxidation of the grain boundary ahead of the crack tip has been proposed in previous studies. Adjacent to this oxide, a chromium-depleted area is observed exclusively in one of the two grains adjacent to the grain boundary. As oxygen transport is found to be faster than chromium diffusion in the alloy, the latter is assumed to be the rate-limiting step of crack propagation. Nevertheless, the mechanism responsible for chromium depletion is still under debate. Indeed, the lattice and the grain boundary diffusion coefficients of chromium in nickel-based alloys at 350°C are not high enough to explain the chromium depletion magnitudes measured in the literature. Accordingly, factors accelerating chromium diffusion in the alloy ahead of the SCC crack tip should exist. Thus, two assumptions have been proposed in this work: plasticity-enhanced chromium diffusion and diffusion-induced grain boundary migration (DIGM).The aim of this study is to confront these two assumptions by combining both experiments and modeling in order to explain chromium depleted areas observed at the SCC crack tip.Thus, diffusion tests under loading were performed in order to study the effect of plastic deformation on chromium diffusion. Plasticity-enhanced diffusion is evidenced. A relationship between the diffusion coefficient and strain rate has been established leading to a 106-fold increase of the diffusion coefficient at 350°C. In addition, thermal treatments and oxidation tests have shown that diffusion-induced grain boundary migration occurs in Ni-Cr alloys. DIGM leads to dissymmetric Cr-depleted areas, observed in the wake of the moving grain boundary.

Partindo das evidencias encontradas na literatura sobre o desenvolvimento do uso de ferramentas de percussão para quebra de frutos encapsulados, propomos um projeto focalizando não apenas quando as alterações motoras aparecem, mas também na relação dessa trajetoria de mudança com duas possíveis vias de influencia do nicho ecológico sobre a trajetoria de mudança comportamental que da origem ao uso de ferramentas de percussão para quebra de frutos encapsulados em macacos-prego (Sapajus libidinosus). Em primatas, os aspectos físicos e sociais (isto é, artefatos: martelos, bigornas e restos de cocos, e o comportamento dos coespecíficos) canalizam as oportunidades individuais de aprendizagem, permitindo maiores níveis de manipulação de objetos apropriados em contextos apropriados para o surgimento do uso de ferramentas e facilitando a exploração de várias fontes de forrageamento. Por tanto, procuramos determinar o papel de duas variáveis específicas de influência de nicho construídas: reuso dos artefatos e scrounging, no processo de desenvolvimento do repertório manipulativo em um grupo silvestre de macacos-prego (Sapajus libidinosus). Especificamente: 1) Como é a trajetória de mudança na atração e reutilização de artefatos relacionados ao craqueamento de noz (martelos, bigornas e cascas de nozes) e como isso se relaciona com o surgimento de ferramentas de percussão; E, 2) Como relaciona-se o scrounging, no contexto da quebra de frutos, com a emergencia de habilidades manipulativas adequadas para a quebra de frutos encapsulados. Propomos uma pesquisa de campo longitudinal de uma população de macacosprego livres no Brasil, através da observação naturalista. O resultados indicam que não só a idade está relacionada tanto com as mudanças na atração e reuso dos artefatos e com o scrounging, mas também que ambas variaveis estão relacionadas e podem estar em função das mudanças no repertorio manipulative exibido pelos individuos, de tal forma que não só os individuos mais velhos exibem maiores indices de reuso e menores indices de scrounging, como também os indices de variabilidade comportamental e proficiencia na quebra estão intimamente relacionados com os indices de reuso dos artefatos e scrounging / Based on the evidence found in the literature on the development of the use of percussion tools for encapsulated fruit breakage, we propose a project focusing not only \"when\" motor alterations appear, but also on the relation of this trajectory of change with two possible ways of influencing the ecological niche on the trajectory of behavioral change that gives origin to the use of percussion tools to crack nuts in capuchin-monkeys (Sapajus libidinosus). In primates, physical and social aspects (ie, artifacts: hammers, anvils and remains of coconuts, and co-specific behavior) channel individual learning opportunities, allowing greater levels of manipulation of appropriate objects in appropriate contexts for the emergence of use of tools and facilitating the exploration of various foraging sources. Therefore, we sought to determine the role of two niche-specific variables constructed: artifact reuse and scrounging, in the process of developing the manipulative repertoire in a wild group of monkey-prey (Sapajus libidinosus). Specifically: 1) How is the trajectory of change in the attraction and reuse of artifacts related to nut cracking (hammers, anvils and walnut shells) and how does this relate to the emergence of percussion behavior. And, 2) How scrounging is related, in the context of the fruit break, with the emergence of adequate manipulative skills for the breaking of encapsulated fruits. We propose a longitudinal field survey of a population of free monkey-natives in Brazil, through naturalistic observation. The results indicate that not only age is related both to changes in attraction and reuse of artifacts and to scrounging, but also that both variables are related and may be due to changes in the manipulative repertoire exhibited by individuals, such that not only do older individuals exhibit higher reuse rates and lower scrounging rates, but also the indices of behavioral variability and proficiency in the break are closely related to the artifact reuse indices and scrounging

This research focused on a comprehensive microstructural and mechanical property characterisation study of the Ni-Fe-Cr alloys 718 and 945X. The aim of the project was to better understand the relationship between performance and microstructure of existing (Alloy 718) and newly developed (Alloy 945X) high strength nickel alloys focusing on downhole applications. The main difference between the two alloys is that alloy 945X has lower Nb content than alloy 718, which may minimise the tendency to form delta when combined with correct processing. Previous studies have related the hydrogen embrittlement in alloy 718 with the collection of hydrogen by delta phase. Microstructural characterisation of the new alloy 945X after long term isothermal exposure up to 120 hours in the temperature range 650◦C to 900◦C was conducted with scanning electron microscopy (SEM), to generate a time-temperature-transformation (TTT) diagram. The TTT diagram was used as a road map for designing two isothermal heat treatments of alloy 945X on tensile specimens. Then, the effect of hydrogen charging on the tensile properties and microstructure of the 'as-received' and these two variant heat treatments was investigated. Fractographic analysis showed that, in the presence of hydrogen, intergranular fracture occurred for all the heat treatments, regardless the presence of delta phase at grain boundaries. There was no simple correlation between the volume fraction of delta-phase and susceptibility to hydrogen assisted embrittlement. Rather, it was demonstrated that the morphology and distribution of delta-phase along grain boundaries plays a key role and the other precipitate phases also have an influence through their effect on the ease of strain localisation. This study also examined the hydrogen embrittlement sensitivity of nickel alloy 718 given four different heat treatments to obtain various microstructural states. Each heat treatment leads to differences in the precipitate morphologies of γ', γ'' and delta phases. Material characterisation and fractography of the examined heat treatments were performed using a high resolution FEG-SEM. Three specimens of each condition were pre- charged with hydrogen and tensile properties were compared with those of non-charged specimens. It was observed that hydrogen embrittlement was associated with intergranular and transgranular microcrack formation, leading to an intergranular brittle fracture. delta phase may assist the intergranular crack propagation, and this was shown to be particularly true when this phase is coarse enough to produce crack initia- tion, but this is not the only factor determining embrittlement. Other microstructural features play a role, as does the strength of the material. Finally, the evolution of delta-(Ni3Nb) phase in alloy 718 from the early stages of precipitation, with a particular focus on identifying the grain boundary characteristics that favour precipitation of grain boundary delta phase was investigated. Results showed that delta phase was firstly formed on Σ3 boundaries after 5 hours at the examined temperature (800◦C). Increasing ageing time at 800◦C was observed to lead to an increase in size and precipitation of phases γ'-γ''-delta, an increase in fraction of the special CSL boundaries and an evolution in the morphology of twins and the growth of grains.

O objetivo deste trabalho é analisar e comparar o comportamento quanto à resistência à corrosão, permeabilidade de hidrogênio e sua relação com a susceptibilidade ao trincamento induzido por hidrogênio de aços ARBL, em ambientes contendo H2S, enfatizando a influência da microestrutura. Foram realizados tratamentos térmicos de normalização e têmpera (em água) de dois tipos de tubos API 5L X65 para aplicação sour service, obtendo-se três condições com diferentes microestruturas para cada tubo. Assim, as duas amostras tais como recebidas apresentavam microestruturas de: ferrita/perlita e, o outro, ferrita/ferrita acicular; após tratamento de normalização os dois tipos de amostras apresentaram microestrutura de ferrita/perlita; e, por último, os aços que passaram por têmpera constituíram-se de martensita. O eletrólito empregado foi a solução A (ácido acético contendo cloreto de sódio) da norma NACE TM0284-2011, saturado com H2S. Os materiais foram submetidos a: ensaios de polarização linear para determinação da Resistência de Polarização (Rp), ensaios de permeabilidade de hidrogênio - baseado na ASTM G148-2003 - e ensaios de resistência ao trincamento induzido por hidrogênio (HIC) segundo a norma NACE TM0284-2011; exames em microscópio óptico e eletrônico de varredura para caracterização microestrutural, da morfologia da corrosão e do trincamento. Após os ensaios de polarização linear, foi observada uma diferença pequena dos valores de Rp entre as diferentes amostras estudadas, entre 120 ?.cm2 e 210 ?.cm2; dentro desta faixa, as microestruturas de martensita (aços temperados) apresentaram a menor resistência à corrosão. Foi realizado o tratamento dos dados obtidos por polarização linear com a metodologia desenvolvida por Mansfeld (1973) para cálculo da taxa de corrosão, observando mudanças nos declives de Tafel evidenciando a formação de produtos de corrosão. Apesar da formação destes produtos a taxa de corrosão não foi afetada, já que estes produtos são dissolvidos na solução A, oferecendo uma baixa proteção contra à corrosão. Nos ensaios de permeabilidade de hidrogênio foi utilizada uma célula modificada tipo Devanathan-Stachurski, com a solução A, com injeção de H2S no lado de geração de hidrogênio e 0,2M NaOH no lado de detecção. Foi realizado o tratamento dos dados com o método tlag, calculando a difusividade aparente, concentração de hidrogênio no metal e quantidade de sítios de ancoramento de hidrogênio. Também foi utilizado um método de ajuste da curva experimental com a equação obtida a partir da segunda lei de Fick para calcular a difusividade aparente. Foram comparados os valores obtidos com os dois métodos, obtendo-se resultados similares de difusividade aparente. As amostras temperadas foram as que apresentaram menor difusividade aparente, maior concentração de hidrogênio e maior número de sítios de ancoramento. Após o ensaio de resistência ao trincamento induzido por hidrogênio os exames em microscópio óptico mostraram que as amostras de tubos API 5L X65 como recebidas e normalizadas não apresentaram trincamento, já as amostras que passaram por tratamento de têmpera apresentaram trincas. A realização dos ensaios e tratamento dos dados permitiram observar a relação entre a quantidade de interface e a taxa de corrosão: assim a microestrutura martensítica apresenta a maior taxa de corrosão devido a maior quantidade de interfaces. A difusividade de hidrogênio também é afetada por esta mesma microestrutura, por ter maior quantidade de interface e maior número de discordâncias, apresentando menor difusividade aparente, maior concentração de hidrogênio e maior quantidade de sítios de ancoramento, tem-se que a microestrutura de martensita apresenta maior susceptibilidade ao trincamento induzido por hidrogênio. A nucleação e propagação das trincas nesta microestrutura depende de vários mecanismos que atuam simultaneamente: (i) nucleação das microtrincas, (ii) formação de H2 nas microcavidades com aumento da pressão local e (iii) migração de átomos de hidrogênio até a ponta da trinca diminuindo a força coesiva do reticulado facilitando a propagação. No entanto, esta relação entre microestrutura e HIC não pode ser generalizada, pois a susceptibilidade ao trincamento depende tanto da quantidade de sítios de ancoramento, como de sua energia de ligação, localização microestrutural e tamanho destes sítios. Outro fator importante é a presença de regiões de pouca ductilidade onde as trincas nucleadas tenham maior facilidade para sua propagação. Este trabalho contribuiu para o melhor entendimento dos mecanismos que levam à fragilização e danos provocados pelo hidrogênio, mostrando a relação entre microestrutura, corrosão, difusão e trincamento. Permitiu ampliar o conhecimento sobre os testes utilizados para avaliar o desempenho de aços microligados para aplicações em ambientes severos. / Pipelines produced from High Strength Low Alloy steels (HSLA) are a safe and cheap way to transport large quantities of petroleum and gas. HSLA steels offers mechanical and economic advantages. When HSLA steels are exposed to environments containing hydrogen sulphide (H2S), the steel can corrode and generate atomic hydrogen in the surface wich can diffuse and trapped, leading loss of mechanical properties and subsequent failures. The infrastructure to transport oil and gas represent a high cost investment, in adittion, they must be free from degradation processes that can causes severe health and environmental impacts. For this reason, the development of materials with high performance in aggressive environments is required. The aim of this study is to analyze and compare the corrosion behavior, hydrogen permeability and its relation with the susceptibility to Hydrogen Induced Cracking (HIC) of HSLA steels in environments containing H2S, with emphasis on the influence of microstructure. Normalizing and quenching heat treatments were applied in two different API 5L X65 pipelines for sour service. Three conditions were obtained (as received, normalized and quenched). The as received has a microstructure of ferrite / pearlite and ferrite / acicular ferrite, respectively; the microstructure of normalized specimens consist of ferrite / pearlite and finally quenched steels presented a microstructure of martensite. Solution A (acetic acid containing sodium chloride), according to NACE TM0284-2011 standard and saturated with H2S was used. The materials were tested by linear polarization technique, hydrogen permeability and Hydrogen Induced Cracking test (HIC). HIC tests were performed according to NACE TM0284-2011 standard. Optical microscope and scanning electron microscope were used for microstructural, corrosion and cracking characterization. Rp values show a slight difference between the different samples studied (120 ?.cm2 e 210 ?.cm2); the martensite microstructure (quenched) showed the lower corrosion resistance. Mansfeld (1973) method was used to calculate the corrosion rates from polarization curves. The Tafel slopes are differents between samples making evident the formation of corrosion products. Despite the growth of those corrosion products, the corrosion rate was not affected, since these products are dissolved in the solution A, providing a low corrosion protection. A modified Devanathan-Stachurski cell was used for the hydrogen permeability tests. It was used the solution A, with injection of H2S in the charging cell, and 0.1M NaOH solution on the oxidation cell. The hydrogen effective diffusivity, sub-surface concentration of atomic hydrogen at the charging side and number of hydrogen-trap sites were calculate by tlag method. Moreover, the experimental data were fitted using an equation derived from Fick\'s second law, in order to determinate the diffusion coefficient. The diffusion coefficient obtained from both methods were compare showing similar results. The quenching samples showed the lower diffusion coefficient, higher hydrogen concentration and number of trap sites. The steels in the as received and normalized conditins did not show cracks in Hydrogen Induced Cracking test; in the other hand, quenched samples presents cracks. The results shoed the relationship between the amount of interface and the corrosion rate. Being the martensitic microstructure the one with the higher corrosion rate. The diffusion coefficient in the martensitic microstructure, is a result of the high amount of interfaces and high dislocation density, leading to a lower diffusion coefficient, higher hydrogen concentration and number of trap sites. In the Hydrogen induced Cracking test the martensitic microstructure has shown the lower resistance to crack. The nucleation and propagation of the cracks in martensite depend of mechanisms that may act simultaneously: (i) nucleation of micro-cracks in preferential sites, (ii) formation of H2 in micro-cavities, with increase the local pressure, and (iii) hydrogen migration to the tip of the crack, decreasing the cohesive force in the lattice. However, the relationship between microstructure and Hydrogen Induced Cracking can not be generalized, since the susceptibility to cracking depends of several factors, like number of trap sites, binding trap energy, microstructural distribution and trap sizes. In addition, the presence of regions of low ductility can result in easy cracks nucleation and propagation. This thesis contributed to the understanding of the mechanisms that lead to hydrogen embrittlement and hydrogen damage, showing the relationship between microstructure, corrosion rate, diffusion and cracking, I ncreasing the scientific knowledge about the standard tests actually used to evaluate the performance of microalloyed steels in sour environments.

Il est de plus en plus admis que l’effet d’échelle doit être pris en compte dans la conception des structures de Génie Civil. Pour le béton, ce problème est complexe car celui-ci ne possède pas d’adoucissement plastique, et sa rupture est due à la fissuration caractérisée par une grande zone de microfissuration (fracture process zone) qui dépend de la taille du granulat max d .Cette fissuration passe par un adoucissement sous la forme de microfissures et de glissement interparticules. Expérimentalement, l’effet d’échelle sur le béton est très souvent étudié à l’aide des corps d’épreuves homothétiques entaillés où l’on cherche à relier la résistance nominale ( oN )estimée à partir de la charge de rupture en flexion à une dimension caractéristique D. Ceci conduit à une diminution du ratio dmax/D avec l’augmentation de la taille de la structure. Parmi les objectifs de cette thèse est d’étudier expérimentalement l’impact de l’hétérogénéité ( dmax/D)supposé comme facteur fondamental de l’effet d’échelle. Trois coupures granulaires ont été testées sur trois tailles de poutres différentes en suivant le processus de fissuration par émission acoustique et la technique de corrélation d’images. Celles-ci permettent de suivre l’ouverture des fissures et identifient assez clairement la FPZ. Les résultats mettent en évidence une grande influence de la taille du granulat sur le comportement à la rupture du béton. Il existe une relation directe entre les paramètres de l’effet d’échelle obtenus par la loi de Bazant et la taille du granulat( dmax ). Le traitement des résultats d’une même taille avec différents granulométries dans le même diagramme conduit à la même loi d’effet d’échelle structurelle classique avec une valeur de transition identique. La modélisation du comportement mécanique est effectuée par la méthode d’éléments discrets (DEM). Le modèle de contact linéaire ne s’avère pas adéquat pour le mortier et le béton où le rapport compression / traction est très élevé. De ce fait, Il a été modifié pour prendre en compte la contribution des moments inter-granulaires. Les paramètres micromécaniques sont déterminés par des essais classiques avec une analyse inverse en utilisant l’algorithme de Levenberg-Marquardt. Les résultats montrent que cette approche est capable de reproduire le comportement à la fissuration locale du béton et de reproduire l’effet d’échelle et celui des granulats. Ensuite, un modèle d'adoucissement est développé afin de mieux reproduire la réponse post pic et le processus de fissuration. / It is now commonly understood that in the design of civil engineering structures, size effect must be taken into consideration. For concrete, this problem is complex because it does not exhibit plastic softening. The failure of concrete is generally preceded by propagation of cracks, characterized by alarge microcracking zone (fracture process zone or FPZ) which is proportional to the maximum aggregate size ( dmax ). This fracture process is accompanied by strain-softening in the form of microcracking and fractional slip.Experimentally, size effect in concrete is commonly studied by using geometrically similar notched beams where thenominal strength ( oN ) obtained from the bending failure loadis related to the characteristic dimension (D). This leads to adecrease in the ratio of dmax/D with an increase in the size of the structure. One of the objective of this thesis is to study experimentally the effect of heterogeneity ( dmax/D) size. This ratio is recognized as a fundamental factor causing the size effect. Three aggregate grading segments were tested on three different sizes of beams and the cracking process was investigated by acoustic emission and the image correlation technique. These methods make it possible to trace the crack.openings and identify distinctively the FPZ. The results demonstrate a significant influence of the aggregate size on the fracture behaviour of concrete. There is a direct relationship between the size effect parameters obtained by Bazant's law and maximum aggregate size ( dmax ). The results obtained from the specimen having the same size but made of concretes with different aggregate sizes produced the same classical size effect with identical transitional between LEFM and strength based laws. The mechanical behaviour is modelled by the Discrete Element Method (DEM). However, the linear contact model inserted in DEM is not suitable to satisfy the materials like mortar and concrete with high unconfined compressive strength to tensile strength ratio. As a result, the model is modified to take into account the contribution of interparticle moments. The micromechanical parameters are determined by conventional tests with inverse analysis using the Levenberg-Marquardt algorithm. The results showed that this approach is able to reproduce the local cracking behaviour of concrete as well as classical size effect and aggregate size effect. Then, a softening model is developed to better reproduce the post-peak response and the cracking process.