La durabilité des composants mécaniques en général et leur résistance à la corrosion en particulier ont une importance primordiale dans l’industrie moderne, qu’elle concerne la production d’énergie, les produits chimiques, le transport, les machines, les matériels médicaux, ou même les composants électroniques. Pour des pièces obtenues par usinage, il est donc nécessaire d’améliorer leur durée de vie et de réduire le risque de défaillance prématurée en améliorant leur intégrité de surface. Ainsi, une compréhension de l’effet du procédé sur l’intégrité de surface induite par usinage et ses conséquences au niveau de sa résistance à la corrosion sont les clés pour relever ces défis.Cette thèse traite le cas particulier de l’usinage de finition du cuivre Cu-c2 et son impact sur la résistance à la corrosion. D’abord, une étude expérimentale comparative du tournage et de la coupe orthogonale est effectuée. Ensuite, vu sa simplicité, la coupe orthogonale fait l’objet de la suite de l’étude. Un modèle numérique est développé pour la prédiction de l’intégrité de surface induite par la coupe. Il utilise une nouvelle loi constitutive du Cu-c2 tenant en compte les transformations microstructurales et l’état des contraintes dans le matériau. Enfin, les résultats issus des études expérimentales ainsi que des simulations numériques concernant l’intégrité de surface sont statistiquement traités dans une analyse multi-physique, dans la perspective d’établir le lien entre la résistance à la corrosion, l’intégrité des surfaces et la physique de la coupe. / The functional performance and life of mechanical components in general and their corrosion resistance in particular are of prime importance in the modern industry, as far as energy production, transportation, machines, medical and even electronic components are concerned. In the case of machined components, it is essential to improve their life and to reduce the premature failure by improving their surface integrity. So, a comprehension of the effect of the machining process mechanics on surface integrity and its consequences on corrosion resistance are essential.This thesis deals with the particular case of finishing machining of oxygen free high conductivity copper (OFHC) and its impact on the surface integrity and corrosion resistance. Firstly, a comparative experimental study between turning and orthogonal cutting is performed. Then, due to its simplicity, orthogonal cutting makes the object of the pursuit of the study. A numerical model is developed to predict the surface integrity induced by the cutting process. It uses a new constitutive model for OFHC copper taking into account microstructural transformations and the state of stress in the work material. Finally, the results issued from experimental studies and the numerical simulations are statistically treated in a multi-physical analysis with the objective of establishing the relationship between corrosion resistance, surface integrity and cutting physics.

PhD thesis - Faculty of Science / The main aim of this thesis has been to study the way in which Fe(III) and Co(II) incorporation into Si-MCM-41 synthesis gels affects the properties of the unmodified material. Another aim was to investigate the influence of these hetero-atoms on the dispersion and particle size distribution as well as the catalytic activity of supported Au nanoparticles in the CO oxidation reaction. Si-MCM-41 has been successfully synthesized in this work using mixtures containing CTAB as a structure-directing agent (SDA) and water-glass as a SiO2 source. Replacement of water-glass with pre-calcined Si-MCM-41 for SiO2 source in the secondary synthesis step has produced Si-MCM-41 with improved structural properties (XRD, HRTEM and Raman spectroscopy), including restructured and more crystalline pore walls (Raman spectroscopy). The conventional shortcomings of Si-MCM-41 as a support for catalyticallyactive (transition) metal components such as low hydrothermal stability, low PZC, lack of cation exchange capacity and no reducibility have been partially addressed by modification with Fe(III) and Co(II). The premodification was achieved both during framework synthesis and after synthesis by the incipient wetness impregnation (IWI) method. As opposed to the one-pot synthesis of metal-containing derivatives, the IWI method gave materials with high metal loadings and maximal retention of the properties of pristine Si-MCM-41. On the other hand, metal incorporation during synthesis to a loading of ~8.8 wt% using aqueous solutions of metal precursors showed some collapse of the mesostructure. Consequently methods were sought to incorporate this amount of metal (and up to double, i.e., 16 wt%) with maximal retention of the MCM-41 characteristics. These methods included (i) using Si-MCM-41 as a SiO2 source, (ii) dissolving the metal precursors in an acid solution before inclusion into the synthesis gel, and (iii) using freshly precipitated alkali slurries of the metal precursors. The first method produced a highly ordered 16wt% Fe-MCM-41 material with excellent reducibility (TPR showed three well-resolved peaks) and pore-wall structure (Raman spectroscopy). Like the aqueous route, the acid-mediated metal incorporation route did not produce ordered materials at metal contents of ~16 wt%. The base precipitate route produced highly ordered composite materials up to 16 wt% metal content, with characteristics similar to those of Si-MCM-41 (XRD, BET and HRTEM), although some metal phases were observed as a separate phase on the SiO2 surface. Thus, metal-containing MCM-41 materials could be obtained with conservation of MCM-41 mesoporosity. Raman spectroscopic studies have shown that the effect of transition metal incorporation in MCM-41-type materials is to strengthen the pore walls (shift of Si-O-Si peaks to higher frequencies), while TPR studies revealed that the essentially neutral framework of Si-MCM-41 could be rendered reducible by transition metal incorporation. Gold-containing mesoporous nanocomposites were prepared by both direct synthesis and post-synthetically. Catalysts prepared by direct hydrothermal synthesis were always accompanied by formation of large Au particles because of the need to calcine the materials at 500 oC in order to remove the occluded surfactant template. The presence of transition metal components in Me-MCM-41 (Me = Fe and Co) has been found to play a significant role in the particle size distribution and also the dispersion of Au nanoparticles when these materials were used as supports. In general, a base metal-containing support was found to produce smaller Au nanoparticles than the corresponding siliceous support. It has been proposed that the transition metal components serve as anchoring or nucleation sites for the Au nanoparticles, which are likely to sinter during calcination. The anchoring sites thus retard the surface mobility of Au at calcination temperatures above their TTammann. The use of the Au/Me-MCM-41 materials as catalysts in the CO oxidation reaction has led to the following observations: (i) catalyst on metal-containing supports showed better activity than those on Si-MCM-41, probably due to the induced reducibility in metal-MCM-41, (ii) catalysts prepared by direct synthesis showed inferior activity owing to large Au particles, (iii) increasing Au content improves the catalytic performance, (iv) increasing the Fe content of the support at constant Au improves the catalytic performance, and (v) changing the base metal component of the support from Fe to Co led to a significant improvement in catalytic activity. The similarity of the apparent activation energies (Ea) for the 5 wt% Au-containing 5 wt% Fe- and 5 wt% Co-MCM-41 suggested that the difference in catalytic activity is associated with the number of active sites possessed by each catalyst system. The observed order of catalytic activity of these 5 wt% Au-containing systems in terms of the support type is: Co-MCM-41 > Fe-MCM-41 > Si-MCM-41. This was further supported by the average Au particle size, which, in terms of the support, followed the order Co-MCM-41 < Fe-MCM-41 < Si-MCM-41. Thus, metal-support interactions between Au and MCM-41 have been enhanced by introducing Fe(III) and Co(II), which also induced framework charge, ion exchange capacity (IEC) and reducibility in the neutral siliceous support.

La tenue résiduelle à l'impact basse vitesse est un critère dimensionnant des structures composites minces pour l'aéronautique. La majorité des travaux réalisés jusqu'ici porte sur l'analyse du comportement en zone courante. Ce travail élargit le domaine d'étude aux zones de variation d'épaisseur. L'objectif est d'étudier la tolérance aux dommages d'impact d'un stratifié comportant une zone de reprise de plis (ZRP) dans le cadre d'un dialogue essai/ calcul, en menant en parallèle une campagne d'essais expérimentaux et l'adaptation d'un modèle numérique de l'endommagement des composites.Le volet expérimental étudie successivement l'impact, la compression et la fatigue à R=-l après impact (CAI et FAI) d'éprouvettes comportant une ZRP. L'analyse des essais d'impact a permis d'identifier la résistance à l'impact et le mécanisme d'endommagement des éprouvettes. Ensuite, un outillage d'essai adapté à la géométrie des éprouvettes a été conçu pour les essais de CAI et de FAI. Les essais de compression montrent une tenue résiduelle statique après impact similaire à celle des éprouvettes sans perte de plis. Les essais de fatigue menés à 60 070 de la tenue résiduelle statique montrent une propagation des délaminages d'impact (en dessous du BVID) qui mène à la rupture des éprouvettes pour un nombre de cycles relativement faible. Alors que la tolérance aux dommages d'impact des ZRP sous chargement statique est comparable à celle des zones courantes lisses, on constate une forte vulnérabilité de ces zones sous chargement de fatigue.Le volet numérique a permis de tester l'approche DPM (Discrete Ply Model), développé lors de travaux précédents, sur une configuration particulière. Un maillage spécifique a été réalisé pour tenir compte des discontinuités de la ZRP. Au niveau de la loi matériau, une formulation unifiée de la rupture de fibres en traction/compression a été implémentée. Les résultats de la simulation d'impact sont en bonne corrélation avec les données expérimentales. Le modèle est capable de prédire la réponse globale de l'éprouvette ainsi que l'étendu des dommages internes. La modélisation de la CAI a permis de confirmer les mécanismes de rupture identifiés lors des essais. Ces résultats numériques sont remarquables puisqu' aucune modélisation locale particulière n'a été faite pour les arrêts de plis. L'approche DPM s'est révélée suffisamment robuste et bien adaptée à la modélisation de l'endommagement des stratifiés unidirectionnels. / The residual strength after low velocity impact is a sizing criterion of thin composite structures in aeronautics. The majority of work on the subject is focused on the analysis of plain laminates. This study expands the field of interest to tapered area. The objective is to study the impact damage tolerance of a laminate with ply drop-off using an experiment/ modelling dialogue: on one hand carrying experimental test campaign and on other hand adapting numerical modelling of composite damage. The experimental part successively examines the impact, compression and fatigue R=-l after impact (CAI and FAI) of specimens with ply drop-off. Analysis of the impact results has enabled the identification of impact resistance and damage mechanism. Then, a testing tool for CAI and FAI was specially designed to suit the geometry of the specimens. Compression tests show a static residual strength after impact similar to plain laminates. Fatigue tests carried at 60% of CAI strength show a propagation of impact delamination (below B VID). Failure of specimens occurs after a relatively small number of cycles. While the impact damage tolerance of tapered laminates is comparable to plain laminates under static loading, high vulnerability is observed under fatigue loading. The numerical part allowed to test the Discrete Ply Model (DPM), developed in previous works, on a particular configuration. A specific meshing was realized to account for the discontinuities in the ply drop-off area. Regarding the material law, a unified formulation of the fiber breakage in tension/ compression is implemented. Impact simulation results correlated well with the experimental data. The model is able to predict the overall response of the specimen and internal damage. The modeling of the CAI enabled to confirm the failure mechanisms identified during tests. These numerical results are remarkable since no particular local modeling has been realized for the ply drop-off area. DPM approach has proven robust enough and well suited to damage modeling of unidirectional laminates.

Made available in DSpace on 2016-04-25T19:20:57Z (GMT). No. of bitstreams: 1 Monica Bartolomei.pdf: 427391 bytes, checksum: 75b2ab791f9fc0424681a1ac5c373ba4 (MD5) Previous issue date: 2008-11-27 / This work has as its objective studying the subject of resilience when referring to persons with great suffering, living traumatic situations and of loss, such as in the case of terminal illnesses. Thus, studies were developed to research in literature the understanding of faith as a factor of resilience in the treatment of cancer. In order to meet the criteria of scope and ethical pleading, the research based itself on the analysis of what the health professionals think on the role of spirituality in the recovery of patients. The proximity between the reality of the practice of certain professional categories and the studies which associate patients with cancer to resilience is patent. Churchmen, psychologists and medical doctors were interviewed so as to allow the theoretic referential to fit in, obtained through bibliographic research into professional experience, found in the field of research, and thus to conclude the work. In this way one can see the perfect attuning between the experience of churchmen when exploring the subjects of terminality, of faith and their relation to illness and the capacity to overcome by certain individuals. The aspect of faith as an element, pure and simple, for curing was widely examined, having received extremely varying contributions, from the total release from the illness, against all medical prognoses, to strongly pragmatic positions, which refuse to accept any influence whatsoever of faith in the course of the evolution of the facts. Principally, churchmen and psychologists are in agreement when approaching the meaning of the traumatic event and the stimulus of resilience, over which the influence of the cultural and religious roots of the patient are exerted, perfectly in line with the theoretic basis, proposing fighting adversity by building a feeling of coherence, which it its self makes suffering manageable / Este trabalho objetiva estudar o tema resiliência no que se refere a pessoas com grande sofrimento, vivendo situações traumáticas e de perda, como é o caso de doenças terminais. Assim, foram desenvolvidos estudos de modo a pesquisar na literatura, o entendimento da fé como fator de resiliência no tratamento do câncer. Para atender a critérios de abrangência e postulados éticos, a pesquisa baseou-se na análise do que pensam os profissionais da saúde sobre o papel da espiritualidade na recuperação dos pacientes. Fica patente a proximidade entre a realidade da prática de algumas categorias profissionais e os estudos que associam pacientes com câncer à resiliência. Foram entrevistados Religiosos, Psicólogos e Médicos, de modo a permitir adequar o referencial teórico, obtido na pesquisa bibliográfica com a vivência profissional, encontrada na pesquisa de campo, e assim concluir o trabalho. Pode-se desta forma observar a perfeita sintonia entre a experiência dos religiosos quando explorados os temas da terminalidade, da fé e sua relação com a doença e a capacidade de superação de certos indivíduos. O aspecto da fé como elemento puro e simples de cura foi amplamente examinado, tendo recebido contribuições bastante divergentes, desde a total liberação da doença, contrariando prognósticos médicos, até posições bastante pragmáticas, que se recusam a aceitar qualquer influência da fé no curso de evolução dos fatos. São concordes principalmente religiosos e psicólogos quando abordam o sentido do evento traumático e o estímulo da resiliência, sobre a qual exercem influência as raízes culturais e religiosas do paciente, o que se afina perfeitamente com a base teórica, que propõe combater a adversidade construindo um sentido de coerência que torne o sofrimento administrável. Houve completa unanimidade de todos entrevistados, quanto ao papel que a fé desempenha na convivência com a doença. Para os médicos, tudo se confunde e assim fé, espiritualidade e religião são encaradas como fundamentos de utilidade para desencadear mecanismos de proteção, de amparo e de fortalecimento no lidar com a problemática da doença. Se todos vamos morrer, a verdadeira questão não deve consistir no fim em si, mas como viver até o desfecho. Talvez nisso resida a maior contribuição desta pesquisa

Os ânions inorgânicos nitrato (NO3-) e nitrito (NO2-) por muito tempo foram considerados produtos finais inertes do metabolismo do óxido nítrico (NO) e constituintes indesejáveis da dieta. Entretanto, é crescente o interesse das potenciais reações que podem se processar em meio fisiológico e, que envolvem especialmente o íon nitrito mediadas por complexos de metais de transição. Ferro-heme presente em proteínas como a mioglobina podem formar complexos porfirínicos com NO, gerando espécies que podem atuar principalmente como catalisadores em diversas vias biológicos importantes. Complexos com NOx coordenado a ferro-heme estão envolvidos tanto no processo da cura da carne (pigmentação da carne), como em processos redox, nos quais são capazes de oxidar substratos indiretamente pela produção de espécies reativas ou diretamente por reações de transferência de átomo de oxigênio (TAO). Os lipídeos, constituintes celulares fundamentais na composição de membranas e lipoproteínas, podem servir como substratos para essas reações e, sua oxidação pode ocasionar danos ao organismo. Tióis, importantes antioxidantes e constituintes de proteínas, também podem participar desse tipo de reações e, conseqüentemente gerar danos ao organismo. Considerando que o mecanismo e os parâmetros cinéticos e termodinâmicos destas reações ainda não foram completamente estabelecidos para explicar a vasta funcionalidade destes complexos, o presente projeto de pesquisa visa proporcionar um melhor conhecimento das reações redox envolvendo NOx e mediadas por porfirinas de ferro em alimentos e sistemas biológicos. / For long time, the anions nitrate (NO3-) and nitrite (NO2-) were considered inert end products of nitric oxide (NO) metabolism and undesirable constituents of the diet. Currently, there is an increasing interest for potential reactions which may occur in physiological conditions involving specially the nitrite ion and mediated by transition metal complexes. Heme NOx iron complexes are involved in meat curing process (meat pigmentation) and are able to oxidize substrates indirectly generating reactive species or directly by oxygen atom transfer reactions (OAT). Lipids, fundamental cellular constituents of membranes and lipoproteins, and thiols, important antioxidants and protein constituents, may serve as substrates to OAT and their oxidation may promote damage to the organism Considering that the mechanism and kinetic and thermodinamic parameters of these reaction have not yet been fully elucidated to explain the varied functionality of these complexes, the present research project aim to bring a better understanding of redox reactions involving NOx mediated by iron porphyrins in foods and biological systems. Thiols, important antioxidants and protein constituents, may serve as substrates to OAT and their oxidation may promote damage to the organism. The present work aims to bring a better understanding of the mechanism, kinetic and thermodynamic parameters of the reaction involving nitrite mediated by iron-porphyrins in food and biological systems.

Landbased Studies Foundation and Bachelor degrees (FD and BSc) are generally taught in specialist FE landbased colleges, with teachers typically teaching both FE (Ofqual RQF Levels 0–3) and HE (Ofqual RQF Levels 4–6). Such teachers are designated in the literature as being HE in FE (Higher Education in Further Education) or CBHE (College Based Higher Education) teachers. Using a single case study landbased college, this study adopts a qualitative, naturalistic methodology using intensive interviewing and classroom observations of six Animal, Equine and Veterinary Nursing Studies HE in FE teachers. Characterised as an under-represented group within UK education research, these teachers teach both HE and FE within a small, UK landbased college. The study examines the nature of HE teacher pedagogic practice enactments, and factors which enable and constrain them within an FE college environment. Conceived within a interpretivist socio-constructivist framework, this study is influenced by the anti-dualist social philosophy of Practice Theory (PT) whereby people, places and material objects all contribute to how practice is enacted. Rather than considering material artefacts to be merely background objects and a college being simply an inert container where teaching takes place, a sensitivity to Practice Theory considers the FE context, material aspects and teacher pedagogic practices as a whole, rather than from one or other side of the structure versus agency divide. Within this study a particular variant of Practice Theory, Practice Architectures (PA) (Kemmis and Grootenboer, 2008), has been used to sensitise the study. The study adopts a Constructivist Grounded Theory (CGT) approach as a means of exploring a neglected and under-theorised area of Post-Compulsory education. The CGT methodology influenced and guided the research design and interpretive data iv analysis. Using purposive sampling of teacher participants, theoretical sampling, and the iterative cycles of constant comparison associated with Grounded Theory (GT), the data was used to construct four key categories. From these categories three main theoretical themes were identified from the data; Surveillance and Control, Teacher Identity and Agency, and Pedagogic Risk Aversion. The interpretive analysis suggests that HE pedagogic practice enactments are influenced and constrained by the college as a site, by its management, and by the wider neoliberal landscape of surveillance and auditing, as well as by the teachers themselves, the HE students, and material, non-human physical spaces and artefacts. The resultant HE pedagogic practice enactments are risk averse, tending towards instrumentalism and teacher-centeredness. The final CGT theoretically accounts for the HE practice enactments of the HE in FE teachers at the college and is discussed in relation to HE in FE literature, and to a number of pertinent theories within and beyond education. The CGT contributes to an enhanced understanding of HE teacher pedagogic practice enactments, and has potential for generalisability beyond the specific college. The original contributions to knowledge consists of: devising a novel methodology whereby PT/PA and CGT are articulated; adding to the body of literature for HE in FE pedagogy; and adding to the pauce corpus of literature for landbased education.

No description available.

Estágio realizado na empresa Traterme Tratamentos Térmicos, Lda. - e orientado pelo Eng. J. Alexandre Silva / Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2012

Les mécanismes de la réaction de spallation ne sont pas encore parfaitement compris, parce qu'il est difficile de séparer expérimentalement les effets respectifs des différentes étapes de la réaction. Afin de comprendre ces mécanismes, nous avons mis au point un dispositif expérimental permettant d'effectuer des mesures exclusives. Le système de détection des particules légères chargées est plus spécialement détaillé. <br /> Afin de valider notre dispositif expérimental, nous avons comparé nos résultats préliminaires sur le système 56Fe+p à 1 GeV/u avec des mesures inclusives obtenues auparavant sur le spectromètre FRS du GSI. La comparaison des sections efficaces différentielles en charge montre un accord raisonnable. Cependant, notre dispositif a permis d'étendre les mesures précédentes aux charges Z=1 et Z=2, importantes pour les études relatives aux dommages des matériaux. Compte tenu des barres d'erreurs que nous avons obtenues, l'évolution des vitesses moyennes longitudinales avec la masse du résidu de spallation est comparable à celle observée au FRS. Ces premiers résultats, même s'ils restent préliminaires, permettent de valider notre dispositif expérimental. Il est maintenant possible d'envisager d'exploiter les points forts des mesures exclusives réalisées, à savoir les corrélations entre les différents observables mesurées. Enfin, les problèmes expérimentaux soulevés lors de l'analyse effectuée pourront être pris en compte lors des expériences, afin notamment de mieux définir les programmes de mesure nécessaires aux étalonnages des détecteurs.

Ce travail de thèse a pour but l'élaboration et la caractérisation microstructurale / magnétique de systèmes multicouches Fe/Mn présentant un couplage d'échange anisotrope. La caractérisation structurale a été effectuée par microscopie électronique en transmission, ce qui a permis d'identifier les structures α-Fe et α-Mn ainsi que l'évolution de la rugosité aux interfaces avec la température de dépôt. Les analyses en sonde atomique tomographique ont permis d'obtenir une analyse locale des interfaces. Les profils linéaires de concentration obtenus ont révélé une asymétrie des interfaces Fe/Mn et Mn/Fe avec la formation de mélange Fe-Mn à concentration modulée aux interfaces, ainsi qu'une augmentation de la largeur de l'interface Fe/Mn avec la température de dépôt. Les mesures de spectroscopie Mössbauer ont permis d'identifier l'environnement local des atomes de Fe. Les zones riches en Fe sont ferromagnétiques avec une distribution de champ hyperfin reflétant la composition modulée, et les zones riches en Mn sont antiferromagnétiques avec une température de Néel sensiblement proche de celle du α-Mn. La caractérisation magnétique a été effectuée dans un premier lieu par magnétométrie à SQUID, ce qui a permis de déterminer l'évolution de l'aimantation globale des échantillons, le champ de d'échange et le champ coercitif. Par ailleurs, les profils d'aimantation en profondeur ont été obtenus par réflectométrie de neutrons polarisés, ce qui a permis d'identifier deux types de couches de Fe, ainsi que l'influence de la température d'élaboration sur le champ coercitif.