Orientador: Eugênio José Zoqui / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T19:24:03Z (GMT). No. of bitstreams: 1 Paula_LeandroCassiode_M.pdf: 11868477 bytes, checksum: 50ec26b022fc4e33bbc8a761b91efff5 (MD5) Previous issue date: 2014 / Resumo: A tecnologia de semissólidos normalmente utiliza ligas de alumínio de alto teor de silício como matéria-prima. Ligas contendo médio teor de silício, como a A355.0 (Al-5wt%Si-1,0wt%Cu-0,6wt%Fe-0,4wt%Mg) não são disseminadas para esta aplicação. Determinar se esta liga em particular pode ser utilizada como matéria-prima para estes processos é o principal objetivo deste estudo, para tanto foram produzidos lingotes utilizando refinador de grãos (Al - 5,0wt%Ti - 1,0wt%B) combinado a agitação eletromagnética durante o lingotamento estanque. Por meio das simulações do software Thermo-Calc® e ensaios de DSC e DTA, a temperatura de transição de sólido para líquido foi mapeada a fim de se obter o melhor comportamento semissólido e, consequentemente, a melhor temperatura de tixoconformação. As ligas foram submetidas a tratamentos térmicos de globularização nas condições de 0 s, 30 s, 60 s, 90 s e 120 s, para as frações sólidas de 45% e 60%, temperaturas de 595 °C e 575 °C, respectivamente, para avaliar a estabilidade do material na faixa semissólida. Foram realizadas as caracterizações em termos de micro e macroestrutura dos lingotes e das amostras reaquecidas. Em seguida, os ensaios de viscosidade foram realizados obedecendo às mesmas condições do tratamento térmico de globularização. Assim, em todas as condições estudadas, a liga A355.0 apresentou valores estáveis de tamanho de grão, tamanho de glóbulo, circularidade e viscosidade, tornando desnecessário o controle extremamente preciso desses parâmetros em processos industriais. Desta maneira, a liga A355.0 com refinador e agitação eletromagnética pode ser usada em tixoconformação / Abstract: The technology of semi-solid typically uses aluminum alloys of high-grade silicon as raw material. Alloys containing medium silicon content, such as A355.0 (Al-5wt%Si-1,0wt%Cu-0,6wt%Fe-0,4wt%Mg) are not disseminated for this application. Determining whether this alloy in particular can be used as raw material for these processes is the main objective of this study; therefore, ingots were produced using grain refiner (Al - 5,0wt%Ti - 1,0wt%B) combined with electromagnetic stirring during the tight casting. Through simulations of the Thermo-Calc® software and tests DSC and DTA, the transition temperature from solid to liquid was mapped in order to get the best semisolid behavior and, consequently, the best thixoforming temperature. The alloys were submitted to heat treatments globularization the conditions of 0 s, 30 s, 60 s, 90 s and 120 s, for solid fractions of 45% and 60%, temperature of 595 ° C and 575 ° C, respectively, to evaluate the stability of materials in semi-solid range. Characterizations were carried out in terms of micro and macrostructure of the ingots and of the reheated samples. Then the viscosity tests were carried out by following the same conditions of the heat treatment globularization. Under all conditions studied, the A355.0 alloy showed stable values of grain size, globule size, circularity and viscosity, making it unnecessary to control these parameters with extreme precision in industrial processes. Therefore, the A355.0 alloy with refiner and electromagnetic stirring can be used in thixoforming / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Eugênio José Zoqui / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T09:00:41Z (GMT). No. of bitstreams: 1 Torres_LuisVanderlei_D.pdf: 19771789 bytes, checksum: fa0a6d2df1dd36171457713c814fcafb (MD5) Previous issue date: 2013 / Resumo: Este trabalho tem como objetivo avaliar a tixoconformabilidade de ligas Al-Xwt%Si- 2,5wt%Cu abrangendo todas as etapas do processo: obtenção das ligas tixofundidas, caracterização microestrutural, caracterização do comportamento viscoso e processo de tixoforjamento em dois conjuntos de equipamentos diferentes, a saber, prensa excêntrica e prensa pneumática. As ligas Al-2,0wt%Si-2,5wt%Cu, Al-3,0wt%Si-2,5wt%Cu, Al-4,0wt%Si- 2,5wt%Cu, Al-5,0wt%Si-2,5wt%Cu e Al-7,0wt%Si-2,5wt%Cu foram produzidas via lingotamento estanque com agitação eletromagnética e com técnica de ultra-refino (adição do refinador Al-5,0wt%Ti-1,0wt%B). As ligas foram submetidas a tratamentos térmicos de globularização pelos tempos de 0s, 30s, 90s e 210s, para duas condições de frações sólidas, 45% e 60%; foram realizados ensaios de viscosidade sob as mesmas condições e ensaios de tixoforjamento com a fração sólida de 45% e com todos os tempos de tratamento. Por fim, foram avaliadas as propriedades mecânicas, via ensaios de tração, das peças tixoforjadas. Os tratamentos térmicos promovem a globularização das partículas de fase primária, de forma que os melhores resultados de viscosidade foram alcançados para ligas submetidas às frações sólidas de 45%: todas as ligas apresentaram resultados de viscosidade aparente na faixa de 106 (Pa.s), segundo a literatura, materiais que se encontram nesta faixa de viscosidade possuem o comportamento similar ao do vidro fundido e demonstram alta conformabilidade, mostrando-se viáveis ao processo de tixoconformação. As peças tixoforjadas apresentaram boa conformabilidade preenchendo toda a matriz e reproduzindo sua geometria. Apresentaram boas propriedades mecânicas através dos ensaios de tração e quando submetidas ao tratamento de solubilização apresentaram propriedades mecânicas superiores, ou seja, houve um aumento do limite de escoamento em todas as ligas em torno de 50MPa, aumento no alongamento em torno de 2 a 3 vezes e o aumento do limite de resistência a tração em todas as ligas em torno de 80MPa / Abstract: The goal of this work was to evaluate the thixoformability of Al-Xwt%Si-2,5wt%Cu alloys, including all the stages process: obtaining the thixocasting, characterization in terms of microstructural, characterization of the rheological behavior, and the thixoforging process in two different sets equipment, ie., eccentric press and pneumatic press. The Al-2,0wt%Si-2,5wt%Cu, Al-3,0wt%Si-2,5wt%Cu, Al-4,0wt%Si-2,5wt%Cu, Al-5,0wt%Si-2,5wt%Cu e Al-7,0wt%Si- 2,5wt%Cu alloys were produced by direct casting with electromagnetic stirring and by ultrarefining (addiction of Al-5,0wt%Ti-1,0wt%B). The alloys were submitted to re-heating treatment for 0s, 30s, 90s and 210s in two conditions of solid fraction, 45% and 60%; had been realized tests of viscosity under the same conditions and thixoforging tests with solid fraction of 45% and with all re-heating treatment times. Finally, had been the mechanical properties, by tensile tests, of the thixoforged pieces. Re-heating treatment times promote the solid phase particles globularization, from that the best results of viscosity been reached for alloys treated with solid fractions of 45%: all the alloys presented resulted of apparent viscosity of 106 (Pa.s), literature according to materials that if find in this index of viscosity possess the similar behavior the casting glass and demonstrate high conformability, revealing viable the process thixoforming. The thixoforged piece presented good conformability, total fulfilling of the matrix and reproducing geometry. Showed good mechanical properties by tensile tests and subjected to solubilization treatment had superior mechanical properties, ie, an increase in the yield strength in all alloys about 50MPa, elongation increased approximately 2 to 3 times and increasing the limit of tensile strength in all leagues around 80MPa / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Abstract Several numerical methods and algorithms, for solving the mathematical model of a continuous casting process, are presented, and theoretically studied, in this work. The numerical algorithms can be divided in to three different groups: the Schwarz type overlapping methods, the nonoverlapping Splitting iterative methods, and the Predictor-Corrector type nonoverlapping methods. These algorithms are all so-called parallel algorithms i.e., they are highly suitable for parallel computers. Multiplicative, additive Schwarz alternating method and two asynchronous domain decomposition methods, which appear to be a two-stage Schwarz alternating algorithms, are theoretically and numerically studied. Unique solvability of the fully implicit and semi-implicit finite difference schemes as well as monotone dependence of the solution on the right-hand side are proved. Geometric rate of convergence for the iterative methods is investigated. Splitting iterative methods for the sum of maximal monotone and single-valued monotone operators in a finite-dimensional space are studied. Convergence, rate of convergence and optimal iterative parameters are derived. A two-stage iterative method with inner iterations is analyzed in the case when both operators are linear, self-adjoint and positive definite. Several new finite-difference schemes for a nonlinear convection-diffusion problem are constructed and numerically studied. These schemes are constructed on the basis of non-overlapping domain decomposition and predictor-corrector approach. Different non-overlapping decompositions of a domain, with cross-points and angles, schemes with grid refinement in time in some subdomains, are used. All proposed algorithms are extensively numerically tested and are founded stable and accurate under natural assumptions for time and space grid steps. The advantages and disadvantages of the numerical methods are clearly seen in the numerical examples. All of the algorithms presented are quite easy and straight forward, from an implementation point of view. The speedups show that splitting iterative method can be parallelized better than multiplicative or additive Schwarz alternating method. The numerical examples show that the multidecomposition method is a very effective numerical method for solving the continuous casting problem. The idea of dividing the subdomains to smaller subdomains seems to be very beneficial and profitable. The advantages of multidecomposition methods over other methods is obvious. Multidecomposition methods are extremely quick, while being just as accurate as other methods. The numerical results for one processor seem to be very promising.

Both Elasmobranchii and Acipenseriformes have a spiral intestine, developed by the intestine folding inward and twisting upon itself. A comparative analysis of the digestive system of examples of Subclass Elasmobranchii (sharks and rays) to Order Acipenseriformes (sturgeon and paddlefish) was conducted through gross dissection and scanning electron microscopy (SEM) analysis. Urobatis jamaicensis, Acipenser baerii, and Polyodon spathula were used due to accessibility. Gross dissection analysis yielded that the acipenserids have a columnar spiral valve with 8 infoldings, and U. jamaicensis has a posterior spiral valve with 13 infoldings. SEM analysis showed angiogenesis, where visible, occurred inversely with age in all species. More venous vessels were present than arterial vessels in the outer layers of the intestine, the muscularis and serosa, while the majority of the arterioles were found in the mucosa and submucosa. The vascularization pattern of the spiral valve in U. jamaicensis showed a diamond branching pattern on the surface anteriorly and posteriorly with a lateral drainage system at the midsection. Only the lateral drainage system was found in A. baerii and P. spathula. The daughter arterioles and venules to the intraintestinal artery and intraintestinal vein coincided with the turns present in the spiral valve of each species. This study suggests A. baerii and P. spathula are sister taxa and do not share a direct common ancestor with U. jamaicensis based on similarities and differences between the spiral valve vasculature.

The goal of this diploma thesis is to on a practical example, with use of the quality system, describe the current state of input casting inspection in Tribotec Ltd. and output casting inspection of casting suppliers in this company and to suggest a new way of output casting inspection on Tribotec Ltd. with higher quality of spoilage rate survey of supplying casting already at the input inspection stage.

CO2 adsorption is considered as a promising strategy to decrease the amount of CO2 in the atmosphere and stop global warming. The goal of this project is to prepare a cellulose-based CO2 adsorbent with a good mass transfer. Monolithic adsorbent based on cellulose nanofibrils (CNF) was fabricated via freeze-casting. 0.1g or 0.5g cellulose acetate (CA) or 0.1g acetylated CNC (aCNC) was dipped into the crosslinked aerogel to increase its CO2 capacity. Acetylation of CNC was confirmed by Fourier transformed infrared spectroscopy (FT-IR) and the degree of substitution was determined to be 1.6 through titration. Scanning electron microscopy (SEM) images showed that monolithic structure was formed through freeze-casting and the structure was maintained after dipping. Compression test suggested that the mechanical properties of the aerogel increased with the increasing amount of dipped CA, while the CO2 capacity of the adsorbent decreased. Furthermore, the outstanding reinforcing effect of aCNC was noticed in the compression test, and the aerogel dipped with aCNC has the highest CO2 capacity with a value of 1.49 mmol/g.

Abstract In today's world, enormous amounts of data are being collected everyday. Thus, the problems of storing, handling, and utilizing the data are faced constantly. As the human mind itself can no longer interpret the vast datasets, methods for extracting useful and novel information from the data are needed and developed. These methods are collectively called knowledge discovery methods. In this thesis, a novel combination of feature selection and data modeling methods is presented in order to help with this task. This combination includes the methods of basic statistical analysis, linear correlation, self-organizing map, parallel coordinates, and k-means clustering. The presented method can be used, first, to select the most relevant features from even hundreds of them and, then, to model the complex inter-correlations within the selected ones. The capability to handle hundreds of features opens up the possibility to study more extensive processes instead of just looking at smaller parts of them. The results of k-nearest-neighbors study show that the presented feature selection procedure is valid and appropriate. A second advantage of the presented method is the possibility to use thousands of samples. Whereas the current rules of selecting appropriate limits for utilizing the methods are theoretically proved only for small sample sizes, especially in the case of linear correlation, this thesis gives the guidelines for feature selection with thousands of samples. A third positive aspect is the nature of the results: given that the outcome of the method is a set of conditional probabilities, the derived model is highly unrestrictive and rather easy to interpret. In order to test the presented method in practice, it was applied to study two different cases of steel manufacturing with hot strip rolling. In the first case, the conditional probabilities for different types of retentions were derived and, in the second case, the rolling conditions for the occurrence of wedge were revealed. The results of both of these studies show that steel manufacturing processes are indeed very complex and highly dependent on the various stages of the manufacturing. This was further confirmed by the fact that with studies of k-nearest-neighbors and C4.5, it was impossible to derive useful models concerning the datasets as a whole. It is believed that the reason for this lies in the nature of these two methods, meaning that they are unable to grasp such manifold inter-correlations in the data. On the contrary, the presented method of conditional probabilities allowed new knowledge to be gained of the studied processes, which will help to better understand these processes and to enhance them.

Conventional urea-based moulding compounds for investment casting patterns are manufactured using a slow “cooking” process. Nowadays in industrial processes the use of a faster process is highly recommended to increase throughput levels. At the same time, for quality control purposes, the requirements of an investment caster must be met. This study is therefore focused on: <ul><li> Finding the appropriate conventional process and conditions to prepare urea-based investment casting moulding compounds. </li><li> Optimising the composition variables to meet the mechanical, thermal, surface, flow and cost properties needed in investment casting. </li><li> Characterising the moulding compounds to meet the requirements of an investment caster by comparing them with an industrial, “cooked” urea-based compound. </li></ul> Polyvinyl alcohol (PVOH) and ethylene vinyl acetate (EVA) urea-based moulding compounds were prepared using a two-roll mill and a conventional extrusion processes respectively. It was possible to injection mould PVOH urea-based moulding compounds with a urea content of up to 90 wt % which had been compounded using a two-roll mill. Using the conventional extrusion process, it was also possible to compound and injection mould EVA urea-based moulding compounds containing up to 70 wt % urea. The effects on composition variables on the properties of the moulding compound were studied and compared to those of the existing “cooked” urea-based moulding compound (Benchmark). The mechanical properties were characterised using the three-point bending test and Charpy impact test. The thermal properties were determined using simultaneous differential thermal analysis and thermogravimetric analysis (SDTA/TGA) and differential scanning calorimeter (DSC). The thermo-mechanical and visco-elastic properties were determined using a dynamic mechanical analyser. A scanning electron microscope was used to study the surface texture of the mouldings. The EVA urea-based moulding compounds showed two endothermic melting peaks and multiple exothermic crystallisation peaks in the DSC curves. The peak at ca. 55 - 66°C corresponds to the melting of the wax/EVA blend, while the large peak at 130 - 132°C corresponds to the melting of the urea. The DSC heating curve of the PVOH urea-based moulding compounds showed two endothermic peaks. The small peak corresponds to the melting of the wax, while the large peak corresponds to the melting of the urea/PVOH blend. PVOH urea-based moulding compound had better mechanical properties than the industrial benchmark. The mechanical properties of the EVA urea-based compound were generally lower. The effect of the wax and polymer content on the mechanical properties was as follows: <ul><li> Increasing polymer content produced weaker but tougher moulding compounds. </li><li> Increasing wax content improved the strength and stiffness but gave compounds that were less tough. </li><li> Two-way Analysis of Variance (ANOVA) indicated significant polymer-wax interactions. </li></ul> The urea content determined the stiffness (elastic modulus) of the compounds. PVOH mouldings had superior stiffness compared with the EVA and cooked urea-based mouldings. The Dynamic mechanical analysis (DMA) results confirmed the result obtained from the modulus of elasticity determination in the three-point bending test. The impact strength increased with an increase in polymer content and reduced with an increase in wax content. The linear thermal expansion coefficient decreased as the urea content was increased. Measured values (100 to 156x10-6°C) were comparable to those of the benchmark. The cooked urea-based moulding compound had the lowest melt viscosity at 110°C, as indicated by its melt flow index (MFI). Fluidity increased with the polymer content. The thermo gravimetric analysis (TGA) results confirmed that both the PVOH and EVA urea-based moulding compounds decomposed readily and left less than 1 wt % ash after combustion. From the SEM results apparent surface roughness appeared to increase with wax content. The EVA urea-based moulding compound had an irregular surface texture. Based on the criteria of cost-effectiveness and environmental friendliness, the synthesis of PVOH urea-based patterns is preferable. The use of a conventional extrusion process to prepare PVOH urea-based patterns is recommended. / Thesis (PhD)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

Cette thèse s’inscrit dans le projet PRINCIPIA (PRocédés INdustriels de Coulée Innovants Pour l'Industrie Aéronautique) de l’ANR MATETPRO (Matériaux et Procédés pour des Produits Performants). L'objectif de ce projet est la promotion de nouveaux alliages aluminium-cuivre-lithium à destination de l'industrie aéronautique afin d'apporter une alternative aux composites. Cependant, ces alliages sont sujet à une importante porosité pour deux raisons : une forte solubilité à l'hydrogène et une facilité d'oxydation. Dans ce projet, le but de la thèse était d'établir un modèle de prédiction de la porosité à l'échelle du produit. La porosité se forme lors de la solidification de l’alliage à cause d'une plus faible solubilité de l'hydrogène dans le solide. La teneur en hydrogène dans la phase liquide va augmenter par ségrégation et provoquer la nucléation des pores. Il est donc nécessaire de prendre en compte la solidification dans la modélisation de la porosité. De plus, la composition locales modifie la cinétique de croissance des pores et la microstructure exerce une contrainte mécanique sur les pores qui modifie leur équilibre chimique. Après une première partie consacrée à améliorer les connaissances sur les phénomène de transport dans la coulée semi-continue d'aluminium, nous avons modélisé la formation de porosité en se basant sur les modèles disponibles. Le modèle a reproduit l'inhomogénéité de la porosité observée expérimentalement sur une plaque d'alliage aluminium-magnésium. L'analyse nous a montré que la limitation de la croissance par le temps de diffusion de l'hydrogène était responsable de ce profil particulier. La densité volumique des pores est critique pour la limitation de la croissance par la diffusion de l’hydrogène. En fonction de la densité, la croissance passe d'une croissance limitée à une croissance non limitée / This thesis is part of the project PRINCIPIA (PRocédés INdustriels de Coulée Innovants Pour l'Industrie Aéronautique) of the ANR MATEPRO (MATériaux Et PROcédés pour des produits performants). The goal of this project is the promotion of new aluminum-copper-lithium alloys for the aeronautic industry in order to propose an alternative to composite materials. Unfortunately, these alloys are highly sensitive to the appearance of porosity during the alloy creation process. It is due to a high hydrogen solubility and oxidation. Inside this project, my work was to establish a porosity model at the scale of the ingot. Porosity starts to develop during the solidification process due to a lower solubility of hydrogen in the solid phase. Hydrogen content in liquid phase increases by segregation and leads to pores' nucleation. Thus, it is necessary to take into account solidification for porosity-modeling purposes. It is even more important because the alloys' local composition alters the pores' growth and the microstructure modifies the chemical equilibrium by pinching effect.After a first part dedicated to general improvement of knowledge about transport phenomena in DC casting, the porosity formation model was developed based on model found in literature. The model was able to reproduce the inhomogeneity experimentally observed in an aluminum-magnesium ingot. This profile is explained by the hydrogen diffusion time which limits the pore growth. The pore density is critical for the growth limitation by hydrogen diffusion. Depending on the density, the growth switch from a non limited to a limited growth.

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