Dans le cadre des opérations de perçage, les billettes en acier subissent un réchauffage de la température ambiante à une température d’environ 1250°C. Au cours de ce réchauffage, le gradient de température dans les billettes entraîne la détérioration de la santé axiale de celles-ci et est à l’origine de l’apparition de défauts sur le tube formé. Une méthodologie d’analyse des mécanismes à l’origine de ces défauts a été mise en place. Elle se base sur la caractérisation de la santé axiale par essais rhéologiques permettant d’établir des indicateurs de ductilité et par des examens métallurgiques identifiant les défauts internes.L'étude de la sollicitation thermomécanique induite par le réchauffage du produit est analysée à l’aide de simulations numériques par éléments finis et les zones de sollicitations critiques associées au procédé sont identifiées. La caractérisation des anomalies observées sur les billettes est ensuite faite à partir d’essais de fissuration et de simulations numériques X-FeM. L’implémentation d’un critère de rupture en contrainte dans la simulation du cycle de chauffe a permis de définir les valeurs de gradient thermique limite et les courbes de chauffe optimales. Les analyses montrent que les conditions de chauffe en début de cycle thermique ont une forte influence sur la santé axiale des billettes. Les résultats de ces travaux conduisent à des solutions concrètes pour l’amélioration de la productivité. / As part of the piercing operations, billets undergo a reheating process from room temperature to a temperature of about 1250°C. During this heating, the thermal gradient in the billet leads to a deterioration of the axial health and is responsible of the initiation ofdefects on the formed tube.A methodology for the analysis of the mechanisms at the origin of these defects has been established. It is based on first, the characterization of the axial health with hot rheological tests to establish some indicators of ductility and second, on metallurgical analyses to identify the internal defects.Then finite element simulations have been performed to study the thermo-mechanical loadings induced by heating. Critical solicitation zones of the product during the processes have been identified.Finally a characterization of the observed defects into the billets has been led coupling cracks growth tests and X-FeM numerical simulations. The implementation of the experimental stress failure criterion, in the simulation of the heating cycle allows to obtain good values of thermal gradient boundary curves and leads to optimal heating curves.The analysis shows that the conditions at the beginning of the reheating process have a strong influence on the axial health of the billets. The results of these studies lead to friendly industrial solutions for improving productivity.

Made available in DSpace on 2014-08-20T13:48:07Z (GMT). No. of bitstreams: 1 Bento Selau da Silva Junior_Tese.pdf: 16249436 bytes, checksum: 84ea1994e54232bb233d34e45b2e1140 (MD5) Previous issue date: 2013-03-27 / This thesis has the objective to describe how a group of blind people explains its graduation in higher education, identifying the factors associated with this conclusion, in the light of L. S. Vygotski s studies. Methodologically, the thesis consisted in a qualitative study, assuming the form of case studies. The research counted on the participation of nine blind people based on the following criteria: being blind and being higher education egresses. The instruments to collect data were the interview and the document analysis. The collected data were worked out through the discursive textual analysis. The theoretical framework brought information pertaining to the participation of blind students in higher education; definition of terms blind and disability; social movements influence on the blind; inclusion of disabled people in higher education; the presence of obstacles for the blind to attend higher education; and the role of professors who work with visually impaired students.It included the presentation of psychological-pedagogical propositions about blindness, arising from investigations developed by Vygotski in the context of his defectology, which resulted in a reorganization of the texts of Tome V of his Collected Works, so that, it would be possible to understand his proposals around the theme.Other concepts of Cultural-Historical theory which were considered as fundamental to this work were also discussed:consciousness, will and subjectivity, besides the terms overcome and overcoming that appear in the author set of defectology. The findings of the research were organized into four emerging categories: Quality of basic education attended , Difficulties found , External facilitator factors and Internal facilitator factors . Such findings indicated that the quality of learning and educational inclusion in basic education influenced the path of the blind through higher education. The difficulties found during attendance at higher education above all, in the selection process for university entrance the need to work/being employed during the study period, difficulties relating to the relationship to some teachers, the lack of technological instrumental and adaptation of materials in resource rooms, interferedin the subjects route through higher education.The assistance received outside the university and the support of some teachers, were facilitator factors. The basic education living of the blind, the difficulties and the facilitator factors, were not, however, decisive for the completion of higher education; the main factors identified in the data and interpreted with the support of the studies developed by Vygotski, were the internal (subjective): consciousness and will. It was defended the thesis that the consciousness about the discrepancies between the lived and the expected reality, generated the wish to complete higher education, that is to say, factors connected to the subjectivity of the students, leading the group of blind which was studied, to achieve this goal. / Esta tese teve como objetivo descrever como um grupo de cegos explica a sua conclusão da educação superior, identificando os fatores associados a essa conclusão, à luz dos estudos de L. S. Vygotski. Metodologicamente a tese constituiuse em um estudo de natureza qualitativa, assumindo a forma de estudos de casos. A pesquisa contou com a participação de nove sujeitos, selecionados com base nos seguintes critérios: serem cegos e egressos da educação superior. Os instrumentos para a coleta de dados foram a entrevista e a análise documental. Os dados coletados foram trabalhados por meio da análise textual discursiva. O referencial teórico trouxe informações atinentes à participação de cegos na educação superior; definição dos termos cego e deficiência; influência dos movimentos sociais em prol dos cegos; inclusão de deficientes na educação superior; presença de obstáculos para a frequência à educação superior por cegos; e ao papel dos professores universitários que trabalham com deficientes visuais. Incluiu a apresentação das proposições psicológico-pedagógicas sobre a cegueira, oriundas das investigações desenvolvidas por Vygotski no âmbito de sua defectologia, o que implicou em uma reorganização dos textos do Tomo V de suas Obras Escogidas, para que se pudesse entender melhor as suas propostas em torno da temática. Foram discutidos, ainda, outros conceitos, da teoria histórico-cultural, que se mostraram fundamentais para este trabalho: tomada de consciência, vontade e subjetividade, além dos termos superar e superação, que aparecem no conjunto da defectologia do autor. Os achados da pesquisa foram organizados em quatro categorias emergentes: Qualidade da educação básica cursada , Dificuldades encontradas , Fatores facilitadores externos e Fatores facilitadores internos . Os resultados indicaram que a qualidade da aprendizagem e da inclusão educacional na educação básica influenciaram a trajetória dos cegos pela educação superior. As dificuldades encontradas durante a frequência à educação superior sobretudo no processo de seleção para a entrada na universidade , a necessidade de trabalhar/estar empregado durante o período de estudo, as dificuldades relativas à relação com alguns professores, a falta do instrumental tecnológico e de adaptação de materiais, nas salas de recursos, interferiram no percurso dos sujeitos pelo ensino superior. Foram fatores facilitadores o auxílio recebido fora da universidade e o apoio de alguns professores. As vivências dos cegos na educação básica, as dificuldades e os fatores facilitadores não se constituíram, todavia, em determinantes para a conclusão do ensino superior; os principais fatores identificados nos dados e interpretados com apoio nos estudos de Vygotski foram os internos (subjetivos): a tomada de consciência e a vontade. Defendeu-se a tese de que a tomada de consciência sobre as discrepâncias entre a realidade vivida e a esperada gerou a vontade de concluir a educação superior, isto é, fatores ligados à subjetividade dos estudantes, levando o grupo de cegos estudados à consecução desse objetivo.