The main portion of my thesis focuses on a 2-dimensional second order heat transmission problem in domains with pre-fractal interfaces. My focus is on the numerical approximation of the solutions. Precisely, I€™m concerned to develop a suitable mesh refinement algorithm that could be adapted to our situation, by taking into account the regularity of the solutions and the geometry of irregular pre-fractal interfaces. I obtain an error estimate between the weak solution and the discrete solution, which indicates an optimal rate of convergence as in the classical case when the solution has H^2-regularity. In addition, numerical simulations are also included, which demonstrates the features of our heat transmission model. Another portion of my thesis focuses on the asymptotic analysis of singular boundary value problems with highly conductive layers of pre-fractal type. My models illustrate the problems of a lower- dimensional highly conductive material intruding into a higher- dimensional material with lower conductivity. I consider a 2D model of Sierpinski pre-fractal layers and 3D models of hierarchical layers. The main results consist in the so-called Mosco-convergence of certain energy functionals, which implies the strong convergence of the solutions and of the spectral resolutions as a byproduct in real applications.

With the growth in importance of the aluminium industry, has come increased demand to invest into the quality improvement of the different aluminium based hot extruded products. One of the main mechanisms, which can influence deformation at high temperature within the 6xxx aluminium, is linked to the presence of the AlFeSi intermetallic phases. These phases severely restrict hot workability when present as hard and brittle plate-like precipitates b-AlFeSi. Damage initiation occurs in these alloys by decohesion or fracture of these intermetallic inclusions. The understanding and modeling of the deformation and fracture behavior of aluminium alloys at room and at hot working temperature is very important for optimizing manufacturing processes such as extrusion. The ductility of 6xxx aluminium alloys can be directly related to chemical composition and to the microstructural evolution occurring during the heat treatment procedures preceding extrusion if proper physics based deformation and fracture models are used. In this thesis, room temperature and hot tensile tests are adopted to address the problem experimentally. The damage evolution mechanisms is defined at various temperatures and a micromechanics based model of the Gurson type considering several populations of cavities nucleated by different second phase particles groups is developed on the basis of the experimental observations. This model allows relating quantitatively microstructure and ductility at various temperatures strain rates and stress triaxialities. Finite element simulations based on an enhanced micromechanics-based model are used to validate the model. Finally, the effect of some key factors that determine the extrudability of aluminium is also discussed and a correlation between the ductility calculations in uniaxial tension and the maximum extrusion speed is developed for one defined profile.

Lic.-avh. (sammanfattning) Luleå : Luleå tekniska univ., 2005. / Härtill 4 uppsatser.

In this thesis we investigate theoretically various types of sculptured thin film (STF) envisioned as platforms for optical sensing. A STF consists of an array of parallel nanowires which can be grown on a substrate using vapour deposition techniques. Typically, each nanowire has a diameter in the range from ~ 10-300 nmwhile the film thickness is ~<1μm. Through careful control of the fabrication process, both the optical properties and the porosity of the STF can be tailored to order. These abilities make STFs promising for optical sensing applications, wherein it is envisaged that the material to be sensed infiltrates the void region in between the parallel nanowires and hence changes the optical properties of the STF. Various homogenization formalisms can be used to estimate the constitutive parameters of the infiltrated STFs. In this thesis two different homogenization formalisms were used: the Bruggeman formalism (extended and non–extended versions) and the strong-permittivityfluctuation theory (SPFT). These were used in investigations of the following optical–sensing scenarios: (i) Electromagnetic radiation emitted by a dipole source inside an infiltrated chiral STF. The effects of using the extended Bruggeman homogenization formalism, which takes into account the nonzero size of the component particles,were studied. (ii) Surface–plasmon– polariton waves on ametal–coated, infiltrated columnar thin film. The influences of using the extended SPFT formalism, which takes into account the nonzero size of the component particles and their statistical distributions, were explored. (iii) A metal-coated infiltrated chiral STF which supports both surface-plasmon-polariton waves and the circular Bragg phenomenon. The possibility of using in parallel both surface-plasmon-polariton waves and the circular Bragg phenomenon was investigated using the non–extended Bruggeman formalism. Our numerical studies revealed that the design performance parameters of the infiltrated STF are bode well for these optical–sensing scenarios. The use of inverse Bruggeman formalism was also investigated: this was found to be problematic in certain constitutive parameter regimes, but not those for optical–sensing scenarios considered in this thesis.

Not available / text

Diss. Östersund : Mittuniversitetet, 2008.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Submitted by AMELIA ALIK DE FREITAS ZUMBA null (amelia.zumba@novelis.com) on 2016-09-28T20:39:28Z No. of bitstreams: 1 Mestrado - v.final.docx: 10697220 bytes, checksum: 300f19fc7542fa3470679a32d14fa78c (MD5) / Rejected by Ana Paula Grisoto (grisotoana@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo as orientações abaixo: A versão final da dissertação/tese deve ser submetida no formato PDF (Portable Document Format). O arquivo PDF não deve estar protegido e a dissertação/tese deve estar em um único arquivo, inclusive os apêndices e anexos, se houver. Por favor, corrija o formato do arquivo e realize uma nova submissão. Agradecemos a compreensão. on 2016-09-29T18:34:10Z (GMT) / Submitted by AMELIA ALIK DE FREITAS ZUMBA null (amelia.zumba@novelis.com) on 2016-09-29T20:05:22Z No. of bitstreams: 1 Mestrado - v.final.pdf: 2498608 bytes, checksum: df0eee2f47b660e50ddb61b07e057fb8 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-09-30T16:44:59Z (GMT) No. of bitstreams: 1 zumba_aaf_me_guara.pdf: 2498608 bytes, checksum: df0eee2f47b660e50ddb61b07e057fb8 (MD5) / Made available in DSpace on 2016-09-30T16:44:59Z (GMT). No. of bitstreams: 1 zumba_aaf_me_guara.pdf: 2498608 bytes, checksum: df0eee2f47b660e50ddb61b07e057fb8 (MD5) Previous issue date: 2016-08-02 / Há uma crescente demanda pelo uso de materiais na indústria em geral, que consigam aliar sustentabilidade e performance, onde o alumínio enquadra-se nestes dois requisitos. A liga AA5182 apresenta propriedades importantes, tais como: baixa densidade, alta resistência mecânica e à corrosão, bem como boa conformabilidade. Neste estudo, foi realizada a definição de uma região crítica na qual foram realizados três testes, simulando diferentes ciclos de homogeneização desta liga, através da realização do ciclo de homogeneização em menores tempos que o ciclo original, antes do envio para a laminação a quente e avaliando características superficiais e microscópicas, para que não exista impacto negativo nos processos subsequentes. Após as análises comparativas realizadas, percebeu-se que o teste onde o patamar de aquecimento foi abaixo da temperatura de liquação de precipitados de magnésio apresentou melhor resultado, proporcionando a redução do tempo de ciclo sem o aparecimento de linhas pretas, oriundas da oxidação do magnésio, permitindo assim, a redução do tempo de ciclo de homogeneização. / There is a growing demand for the use of materials in the industry in general, they can combine sustainability and performance, where aluminum fits these two requirements. The alloy AA5182 has important properties such as: low density, high mechanical resistance and corrosion resistance as well as good formability. First of all, this study was conducted to define a critical region in which there were three tests, simulating different homogenization cycles of this alloy, by conducting the homogenization cycle times smaller than the original cycle, prior to shipment to the hot rolling and evaluating superficial and microscopic characteristics, so that there is no negative impact on subsequent processes. After that, comparative analyzes it was observed that the test where the heating level was below the magnesium precipitates liquation temperature showed better results, providing a reduction in the cycle time without the appearance of black streaks, derived from the magnesium oxidation, thus, reducing the homogenization cycle time.

The problem under consideration is that of obtaining a representation of the permeability of a porous medium which is heterogeneous and anisotropic from limited information. To solve this inverse problem we propose the use of two different pieces that work together. A simulated annealing algorithm is presented and coupled with an homogenization technique; together these solve the problem which was posed. Further, numerical simulation results are presented illustrating the use of the simulated annealing algorithm as well as a coupling with the homoginization technique. This study illustrates that the performance of the annealing algorithm is enhanced with usage of homogenization.

By Banach algebra we mean Banach space enriched with a multiplication operation. It is a mathematical structure that is used in the non-periodic homogenization of composite materials. The theory of classical homogenization studies materials assuming the periodicity of the structure. For real materials, the assumption of a periodicity is not enough and is replaced by the so-called an abstract hypothesis based on a concept composed mainly of the spectrum of Banach algebra and Sigma convergence. This theory was introduced in 2004.