O novo contexto de formação nas instituições de ensino superior

Recentemente o ensino superior politécnico viu reconhecida uma das suas mais justas e ambicionadas aspirações, a faculdade deste subsistema de ensino conferir o grau de Doutor. Retirada a limitação meramente institucional, a ministração de ciclos de estudo de doutoramento passa a estar dependente da existência de ambientes próprios de investigação de elevada qualidade, designadamente considerando os resultados da avaliação das unidades de Investigação e Desenvolvimento, regularmente realizada pela Fundação para a Ciência e a Tecnologia, e a integração alargada dos docentes desse ciclo de estudos em unidades com classificação mínima de Muito Bom na área científica correspondente. Todas as instituições universitárias ou politécnicas, desde que tenham capacidade científica, poderão ministrar cursos de doutoramento.info:eu-repo/semantics/publishedVersio

Plasticity induced crack closure: a sensitivity analysis

Plasticity induced crack closure (PICC) is closely linked to the monotonic and reversed plastic deformation occurring at the crack tip. The objective of the paper is to identify the different physical and numerical parameters affecting PICC, and develop a sensitivity analysis to quantify their relative importance. The main parameters affecting PICC are the load parameters, the yield stress, the size of finite elements and the numerical parameter considered to quantify PICC. The numerical predictions should be independent of numerical parameters, therefore further work is required to optimize the numerical modelsFCT e FEDE

Residual stresses analysis in plasma dressed welded joints

The presence of residual stresses in a structure influences his behaviour. Fatigue strength of welded joints is significantly influenced by the presence of residual stresses, of flaws and notch sharpness at the weld toe. Plasma dressing at the weld toe is frequently used to remove flaws and to lessen the notch sharpness at the weld toe. With this re-melt, the stress field in the weld toe is also profoundly modified. The Finite Element Method (FEM) proves to be effective to simulate the stress fields generated by welding. The simplified two-dimensional models (2D) are efficient in this estimation. This paper presents a 2D finite element model to predict the residual stresses generated by Plasma dressing at the weld toe of a T-joint. The welded T-joints are made in St 52-3 steel, are obtained by covered electrode process and improved with plasma dressing. The analysis was developed with the MSC.Marc finite element code. The estimated stress field is validated with experimental stress results obtained using X-ray diffractio

A parameter for quantitative analysis of plasticity induced crack closure

Numerical models have been successfully developed to predict plasticity induced crack closure (PICC). However, despite the large research effort a full understanding of the links between physical parameters, residual plastic wake and PICC has not been achieved yet. The plastic extension of material behind crack tip, Dyp, obtained by the integration of vertical plastic deformation perpendicularly to crack flank, is proposed here to quantify the residual plastic field. The values of Dyp and PICC were obtained numerically in a M(T) specimen using the finite element method. An excellent correlation was found between PICC and Dyp which indicates that this parameter controls the phenomenon, and can be used to quantify the effect of physical parameters. An empirical model was developed to predict PICC assuming that the residual plastic field is a set of vertical plastic wedges, that the linear superposition principle applies and that the influence of a particular wedge exponentially decreases with distance to crack tip. The model was applied successfully to predict PICC for different residual plastic fields which provided an additional validation of Dyp as the parameter controlling PICC.info:eu-repo/semantics/publishedVersio

Simulation of crack growth in T-welded joints: residual stress field effect

In this article, a three-dimensional finite element model is used to predict the growth of cracks at the weld toe of a T-joint. The model is developed using the MSC Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law and the stress intensity factors are obtained by the virtual crack closure technique. The influence of residual stresses generated by plastic deformation at the weld toe on the crack propagation speed is analyzed. The existence of residual compression stress fields causes a delay in crack growth. The obtained results are compared with the integration solutions of the Paris-Erdogan law using the stress intensity factor computed through the Mk factor proposed by Bowness and Lee, included in BS 7910 standard.info:eu-repo/semantics/publishedVersio

Retrofitting of Welded Structures by TIG and Plasma Dressing

Due to economic and environmental constrains, the currently trend is to use the welded structures beyond their design lives. The predominant cause of in service failure of these aged structures is the fatigue of the welded joints. The use of improvement techniques in welded joints, as a repair technique, has been suggested by several authors. TIG dressing is one of the most promising of these repair techniques. However, the effectiveness of TIG remelting is closely linked to the depth of the repaired crack. The use of strain gauges can be effective to detect the presence of fatigue cracks in their initial phase of propagation, however their effectiveness in inspection programs on jobsite needs to be proven. Some TIG variants associated to recent technological innovations of fusion arc welding, are appointed to improve the penetration and the sustainability of the remelting process. In this article are presented some results of the work developed by the authors in the last years, relevant to assess the efficiency of sustainable repair, by TIG and plasma dressing, of welded structures. Relevance is given to the repair, complete or defective, of deep cracks, as well as the possible advantage of using TIG variants.info:eu-repo/semantics/publishedVersio

Análise da ruína das lâminas de corte do descascador de toros da CELTEJO

No âmbito do processo industrial da Celtejo, Empresa de Celulose do Tejo, S.A., foi identificada uma quebra no desempenho do descascador que opera no parque de madeiras da sua unidade industrial. Esta quebra de desempenho verificava-se devido à ocorrência de um desgaste excessivo das suas lâminas de corte, obrigando à sua substituição regular e prematura. Tais quebras de desempenho tinham como implicação direta um incremento dos custos associados à operação e à manutenção do equipamento, bem como aos materiais e recursos humanos associados a essas operações, assim como às perdas de produção daí resultantes. A administração da Celtejo lançou o repto ao IPCB, no sentido de analisar a origem do desgaste dos componentes do descascador, bem como apresentar eventuais propostas de soluções com vista a minimizar o seu desgaste precoce. O presente trabalho constitui um estudo preliminar do problema, tendo sido desenvolvido, com supervisão, pelos alunos Francisco Vicente Granada Reis Pio e Paulo Alexandre Costa dos Santos através do seu trabalho “Ensaio metalográfico e microdureza dos microconstituintes do aço Hardox 500”, submetido para avaliação no âmbito da Unidade Curricular de Caracterização Mecânica dos Materiais do 2.º ano curricular da licenciatura em Engenharia Industrial.info:eu-repo/semantics/publishedVersio

Effect of crack propagation on crack tip fields

Crack closure influences fatigue crack growth rate and must be included in the design ofcomponents. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, whichbecomes residual as the crack propagates. The objective here is to study numerically the effect of crackpropagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked tothe hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident,which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of squareelements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantifiedand compared with literature models. Finally, the removal of material at the first node behind crack tip withload cycling was observed for plane strain state and some hardening models in plane stress state

Soluciones innovadoras para el aprendizaje en línea de la Mecánica de Materiales en Ingeniería

Los desafíos de los recursos de aprendizaje digital se extienden mucho más allá de las plataformas convencionales de enseñanza-aprendizaje en línea como Moodle o Blackboard. Al estar la primera más orientada a momentos de aprendizaje asincrónico y la segunda a clases sincrónicas, estas dos plataformas están diseñadas para un proceso de enseñanza-aprendizaje controlado por el docente. Dado que la Educación Superior es un espacio que permite aumentar la autonomía de los estudiantes para aplicar sus conocimientos y habilidades a nuevas situaciones, es importante fomentar esta misma autonomía en los estudiantes a partir de soluciones atractivas e innovadoras.info:eu-repo/semantics/publishedVersio

Caraterização mecânica do aço S 355 a temperatura elevada

No presente trabalho pretende-se efetuar a caracterização mecânica do aço S 355 AR, EN 10025-4, a alta temperatura. A avaliação rigorosa da variação da tensão de cedência, do módulo de Young, do módulo de encruamento, do calor específico e do coeficiente de dilatação térmica, com a temperatura é essêncial na simulação numérica da distorção e das tensões residuais induzidas por campos térmicos. Embora esta informação esteja disponível em alguns códigos estruturais, como o Eurocódigo 3 parte 1.2, ela não inclui o efeito da composição química e da microestrutura. O aço S 355 AR é um material bastante utilizado em estruturas soldadas, onde a avaliação de distorções e tensões residuais é um problema usual. A caracterização mecânica do aço S 355 AR, EN 10025-4, foi obtida através de ensaios de tração isotérmicos realizados a temperaturas até 600 °C, por Calorimetria Exploratória Diferencial (DSC) realizada até à temperatura de 950 °C e por Análise Termomecânica (TMA) conduzida até aos 1350 °C. Os resultados obtidos diferem significativamente dos valores apresentados na parte 1.2 do Eurocódigo 3, para um aço ferrítico genérico.ABSTRACT: The present work aims to assess the mechanical characterization of S 355 AR steel, EN 10025-4, at high temperatures. The precise evaluation of the variation of yield stress, Young module, hardening module, specific heat and coefficient of thermal expansion, with the temperature is a key problem in numerical simulation of the distortion and the residual stresses induced by thermal fields. Although this information are available in some of the structural codes, like Eurocode 3 part 1.2, it does not include the effect of chemical composition and microstructure. The S 355 AR steel is a material commonly used in welded structures, where the evaluation of distortion and residual stresses is an usual issue. The mechanical characterization of the S 355 AR steel, EN 10025-4, were obtained by tensile tests conducted at temperatures up to 600 °C, by Differential Scanning Calorimetry (DSC) at temperatures up to 950 °C and by Thermomechanical analysis (TMA) conducted up to 1350 °C. The obtained results differ significantly from the values presented in Eurocode 3 part 1.2 for a general steel.info:eu-repo/semantics/publishedVersio