Os processos de conformação de chapas metálicas são largamente usados na fabricação de produtos em diversas áreas, desde partes aeronáuticas a utensílios domésticos, devido a sua alta produtividade, confiabilidade e baixo custo de produção. Para se atingir tais qualidades, o desenvolvimento de um produto conformado deve levar em consideração os fatores metalúrgicos da chapa a ser usada. As chapas são geralmente produzidas por laminação a frio, o que as levam ter propriedades mecânicas distintas em relação à direção de laminação. Para modelar esta anisotropia, vários critérios de escoamento foram propostos. A fim de verificar a influência do critério de escoamento na distribuição de deformação no produto conformado, este trabalho teve como objetivo implementar os critérios de Hill (1979) e de Barlat et al. (1993) em um programa acadêmico que modela o processo de conformação de chapas via o método dos elementos finitos. O critério de Hill (1979) foi implementado e apresentou bons resultados, em acordo com a literatura. O critério de Barlat et al. (1993) foi deduzido em sua formulação para elementos finitos, embora não implementado. Com o critério de Hill (1979) foi possível analisar a distribuição da deformação para várias superfícies de escoamento, alterando-se apenas o valor de um parâmetro da função de escoamento. / The sheet metal forming processes are widely used in the manufacturing of products in several areas, from aviation to household utensils, due to its high productivity, reliability and low cost of production. To achieve these qualities, the design of a product made by sheet metal forming should take into consideration the metallurgical factors of the blank to be used. The blank is usually cold-rolled, which leads to different mechanical properties in the rolled and transverse directions. To take into account this anisotropy, several yield criteria were proposed. To check the influence of the yield criterion in the strain distribution of the final product, this study focused on the implementation of the yield criteria of Hill (1979) and Barlat et al. (1993) in an academic computer program that modeled the sheet metal forming process by the finite element method. The Hill (1979) criterion was implemented and had good results, in accordance with the literature. The Barlat et al. (1993) criterion was formulated for a finite element method analysis, though not implemented. By using Hill\'s non-quadratic yield criterion it was possible to analyze the strain distribution for various yield surfaces, changing only the value of one parameter of the yield function.

Entre os processos de fabricação mecânicos atuais destacam-se os processos de conformação de chapas metálicas devido à sua produtividade e confiabilidade e a seus baixos custos de produção, baixo consumo de material e produtos nos formatos bem próximos dos esperados nas fases de projeto. Isto só é possível se todas as variáveis do projeto e do processo estiverem conforme as especificações prévias, exigidas principalmente em setores da indústria tais como o aeronáutico e o automobilístico. Um recurso útil para se alcançar estas expectativas é o estudo da estricção e da conformabilidade em chapas metálicas, representadas em diagramas de limite de conformação (DLC), os quais, aliados à análise numérica através do Método dos Elementos Finitos, permitem predições a respeito das variáveis de projeto. Este trabalho tem como objetivos rever e aplicar conceitos relativos a estes aspectos. O objetivo principal deste trabalho é de dispor uma metodologia de avaliação e otimização para o processo de estampagem, utilizando-se elementos finitos e DLC. Uma modificação no método de Marciniak-Kuczynski é utilizada para a obtenção do DLC. Busca-se com isto uma contribuição para a redução de custos em aplicações industriais com o uso desta metodologia através da diminuição das fases de tentativas e erros em projeto e reforma de estampos (try-outs). / Nowadays, sheet metal forming processes have an important role amongst the mechanical manufacturing processes, because they are characterized by high productivity and reliability at low cost, low material waste and near net shapes from design. This is achieved by controlling the design and process parameters according to initial constraints. This scenario is common at aeronautic and at automobilistic productions . These results are obtained by studies of necking and formability in sheet metals and by the use of forming limit diagrams (FLD) and finite element numerical analysis to predict design parameters. This work reviews these concepts and presents a methodology for optimization of deep drawing processes, by using finite element method and FLD. A modification of the Marciniak-Kuczynski method has been introduced to obtain the FLD. Once this methodology has been performed, it can be possible to reduce try-outs in sheet metal dies and costs reduction can also be obtained.

Com a evolução dos processos de fabricação, aumenta o emprego de topografias engenheiradas com o objetivo de aumentar o desempenho dessas superfícies sob vários aspectos. Apesar do bom desempenho comprovado em algumas aplicações, existem outras em que o desempenho é questionável, como, em condições não lubrificadas e com elevadas pressões de contato. Neste cenário de dúvidas sobre a utilização de superfícies engenheiradas, o presente trabalho objetiva contribuir com as discussões por meio de um estudo do efeito de topografias anisotrópicas na transferência de material e resistência ao movimento em condições de deslizamento a seco com deformação plástica micro e macroscópica. O método utilizado contempla ensaios tribológicos que consistem, basicamente, em deslizar um material sobre superfícies engenheiradas de outro material com maior dureza, em duas condições de deformação plástica: i/ localizada no pico das asperezas em contato (ensaio pino-sobre-disco) e ii/ volumétrica (ensaio de compressão do anel). Os resultados permitiram concluir que os mecanismos de desgaste podem ser reproduzidos nos dois ensaios. Com deformação plástica microscópica (pino-sobre-disco) constatou-se que: i/ os vales e cavidades da topografia atuam de forma a evitar o contato das partículas de desgaste com o corpo em deslizamento; e ii/ os maiores valores do coeficiente de atrito foram obtidos com a superfície com maior quantidade de cavidades, a mesma condição topográfica que apresentou maior área com transferência de material. Com deformações plásticas macroscópicas (ensaio de compressão do anel) constatou-se que os vales da topografia da ferramenta atuaram como bloqueios para o deslizamento do anel conformado, o que resultou num aumento do coeficiente de atrito e redução da transferência de material. / The evolution of manufacturing progresses increases the use of engineered surfaces, seeking the improvement of the overall performance of these surfaces. Despite the enhanced performance under some circumstances, uncertainties still exist in conditions such as unlubricated and high contact pressure conditions. This work aims contributing to these discussions by studding the effect of anisotropic topographies on the material transfer and resistance to movement under dry sliding conditions including micro and macroscopic plastic deformation. The method consisted of tribological tests by sliding a material against engineered surfaces of higher hardness. Tests were conducted under two plastic deformation conditions: i/ localized on surface asperities contact (pin-on-disc test) and ii/ volumetric (ring test). Results allowed concluding that wear mechanisms can be reproduced on both tests. Under microscopic plastic deformation (pin-on-disc test) it was possible to verify that: i/ grooves and cavities have contributed to avoid the contact between wear debris and sliding body; and ii/ the higher friction coefficient was obtained when testing the surface with high amount of cavities, a condition that presented the larger area of material transfer. Under macroscopic deformation (ring test), grooves from tool topography played the role of blocking the ring material sliding, increasing friction coefficient and decreasing material transfer.

Em anos recentes, os processos de conformação de chapas automotivas têm sido drasticamente modificados. A utilização de equipamentos de medição metrológicos óticos sem contato e respectivos softwares baseados em fotogrametria, bem como o uso de programas de simulação de estampagem baseados no Método dos Elementos Finitos (FEM), estão se tornando uma rotina no desenvolvimento de ferramentais de estampagem, visto que a confiabilidade, precisão de resultados e facilidade de uso em relação à topologia superficial do ferramental, representou um grande salto tecnológico. Entretanto, por maior que tenha sido o avanço, persistem ainda problemas relacionados ao custo benefício quanto à adoção de certas técnicas e a possibilidade de utilizar ambos os sistemas de forma a um complementar o outro. Neste sentido, o objetivo desta tese é analisar o processo de conformação de chapas utilizando simulação computacional e engenharia reversa como ferramentas integradas no desenvolvimento e construção de estampos automotivos. São descritos casos industriais, cujos resultados demonstram que novas técnicas podem ser aplicadas na definição e modelagem do processo de estampagem de chapas metálicas, utilizando a metrologia ótica, engenharia reversa e a simulação computacional baseada no Método dos Elementos Finitos. / In recently years, sheet metal forming processes used in automotive industry have been drastically modified. The use of non-contact measurement devices based on optical metrology and respective software based on photogrammetry, and the use of stamping simulation programs based on Finite Element Method (FEM), are becoming a routine in the development of tools for stamping, visa that reliability, accuracy of results and ease of use, in relation to the tooling surface topology, was a major technology leap. However, although this advancement, there are still remaining problems related to the cost benefit of the adoption of certain techniques, and the possibility of the use of both systems, in order to complement one another. In this sense, the aims of this thesis is to analyze the sheet metal forming process using computer simulation and reverse engineering as integrated tools in design and construction of automotive dies. Industry cases are described, whose results show that new techniques can be applied in definition and modeling of stamping metal sheets process, using optical metrology, reverse engineering and computer simulation based on Finite Element Method.

Os processos de conformação de chapas metálicas são largamente usados na fabricação de produtos em diversas áreas, desde partes aeronáuticas a utensílios domésticos, devido a sua alta produtividade, confiabilidade e baixo custo de produção. Para se atingir tais qualidades, o desenvolvimento de um produto conformado deve levar em consideração os fatores metalúrgicos da chapa a ser usada. As chapas são geralmente produzidas por laminação a frio, o que as levam ter propriedades mecânicas distintas em relação à direção de laminação. Para modelar esta anisotropia, vários critérios de escoamento foram propostos. A fim de verificar a influência do critério de escoamento na distribuição de deformação no produto conformado, este trabalho teve como objetivo implementar os critérios de Hill (1979) e de Barlat et al. (1993) em um programa acadêmico que modela o processo de conformação de chapas via o método dos elementos finitos. O critério de Hill (1979) foi implementado e apresentou bons resultados, em acordo com a literatura. O critério de Barlat et al. (1993) foi deduzido em sua formulação para elementos finitos, embora não implementado. Com o critério de Hill (1979) foi possível analisar a distribuição da deformação para várias superfícies de escoamento, alterando-se apenas o valor de um parâmetro da função de escoamento. / The sheet metal forming processes are widely used in the manufacturing of products in several areas, from aviation to household utensils, due to its high productivity, reliability and low cost of production. To achieve these qualities, the design of a product made by sheet metal forming should take into consideration the metallurgical factors of the blank to be used. The blank is usually cold-rolled, which leads to different mechanical properties in the rolled and transverse directions. To take into account this anisotropy, several yield criteria were proposed. To check the influence of the yield criterion in the strain distribution of the final product, this study focused on the implementation of the yield criteria of Hill (1979) and Barlat et al. (1993) in an academic computer program that modeled the sheet metal forming process by the finite element method. The Hill (1979) criterion was implemented and had good results, in accordance with the literature. The Barlat et al. (1993) criterion was formulated for a finite element method analysis, though not implemented. By using Hill\'s non-quadratic yield criterion it was possible to analyze the strain distribution for various yield surfaces, changing only the value of one parameter of the yield function.

Cette thèse met l'accent sur la recherche scientifique pour développer une classe de procédés à hautesvitesses de déformation des tôles métalliques en alliages d'aluminium et en acier à haute résistance (AHR).Ces technologies emploient une impulsion de pression de courte durée qui propulse la tôle dans une matrice.Ces procédés sont généralement décrits comme procédés de formage par impulsion de pression (PPF). Letravail proposé dans ce mémoire de thèse a permis de surmonter trois obstacles pour l'utilisation desprocédés PPF et la fabrication à moindre coût de structures légères. Le premier obstacle a été le manque decorrélation entre formabilité et vitesses de déformation qui se développent lors d’un procédé PPF. Nous avonsproposé d’analyser la formabilité et la rupture des tôles, et de caractériser les vitesses de déformation et leurl'hétérogénéité pendant le procédé PPF. Le deuxième obstacle a été le manque de lois constitutives validéespour les métaux déformés par le procédé PPF. Nous avons étudié la microstructure et l'évolution despropriétés mécaniques durant le procédé PPF. Le troisième obstacle est le manque de modèles de formabilitéprédictifs validés pour le procédé PPF. Nous avons utilisé la méthode Marciniak-Kuczynski pour la prédictionde la formabilité de l’alliage AA5182 et de l’acier DP600 sous un large éventail de vitesses de déformation etsous différentes directions de ces vitesses. La combinaison de ces résultats de recherche permet une plusgrande capacité prédictive pour concevoir et développer des procédés PPF pour composants d’automobiledésirés à partir d'aluminium et d’acier AHR. / This thesis focuses on scientific investigation to develop and enable a class of high strain ratesheet metal forming of aluminum alloys and advanced high strength steel (AHSS). These technologiesemploy a short duration pressure‐pulse to drive sheet metal into single‐sided dies, and can generally bedescribed as pulse pressure forming (PPF) processes. The work under this thesis has overcome threetechnical barriers to using PPF processing for more cost effective lightweight vehicles. The first technicalbarrier was the lack of understanding of the interrelationship between formability and measured strainrates that develop during PPF processing. The work under this thesis investigated the formability andfracture of sheet metals during PPF, and characterized the strain rate and the strain rate heterogeneity.The second technical barrier was the lack of a validated constitutive model for lightweight materialsduring PPF processing. The work under this thesis investigated the microstructure and mechanicalproperty evolution in metals during PPF. The third technical barrier was the lack of validated andpredictive formability models for PPF processes. The work under this thesis used the Marciniak andKuczynski method of formability prediction to predict the formability of both aluminum alloy AA5182and AHSS alloy DP600 across a wide range of strain rates and strain rate directions. The combination ofthese research results permits a more predictive capacity to design and develop PPF manufacturingprocesses for a desired automotive component made from aluminum alloys and AHSS.

Esta dissertação tem como objetivo modelar numericamente a manufatura de painéis aeronáuticos de ligas AA7XXX com dupla curvatura variáveis sem reforçadores por meio do processo de conformação por fluência com envelhecimento (CFE). A fundamentação dos fenômenos processo CFE foram estudadas com ensaios de tração à quente, fluência e microscopia eletrônica de transmissão (MET) em amostras de AA7050. Utilizou-se a liga AA7010 e ensaios de fluência da literatura para a aplicação de modelos uniaxiais tanto simplificados quanto unificados para predição do comportamento de fluência com envelhecimento. Um modelo uniaxial unificado foi implementado programa de método dos elementos finitos MSC.Marc por meio de uma sub-rotina codificada em FORTRAN. Em seguida, construiu-se uma metodologia para se simular a fabricação de um revestimento feito de AA7475. Comparou-se a geometria obtida com a de um experimento real. Os resultados da modelagem uniaxial mostram que o modelo obtido é 46% mais exato que o modelo da literatura utilizado como referência e podem ser melhorados caso a influência do envelhecimento na fluência seja mais adequadamente quantificado. O método de simulação do processo CFE se mostrou aderente ao comportamento do material e pode ser mais exato conforme se melhore a modelagem do material. / This dissertation aims to model numerically the manufacture of aircraft wing panels with double variable curvature and without stringers by creep age forming (CAF) process. The phenomena fundamentals were studied using AA7050 alloy samples through hot tensile, creep tests and transmission electron microscopy (TEM).The modeling of creep behavior under uniaxial and aging condition was performed using both simplified and unified models and compared with literature data for the alloy AA7010. A unified model was implemented in MSC.Marc finite elements method program through a subroutine coded in FORTRAN. Then, it was built a methodology to simulate an AA7475 panel forming. The obtained geometry was compared with a real experiment. The uniaxial modeling results show that the obtained simplified model is 46% more exact that the literature model, utilized as reference. These results can be improved if the ageing influence on creep is better quantified. The simulation method has described the material behavior, but there are limitations due to the power law material model.

Dentre os principais problemas que ocorrem na estampagem de chapas metálicas estão a fratura, e estricção (necking) e o enrugamento (wrinkling). Este último pode fazer com que a peça fabricada seja rejeitada por problemas que vão desde motivos estéticos até dificuldades de montagem destas peças e desgaste excessivo da ferramenta. Diversos pesquisadores tem estudado o problema de instabilidade à compressão que origina o fenômeno de enrugamento. Pretende-se estudar os principais métodos para predição do enrugamento, a saber, a teoria da bifurcação, a introdução de uma falha induzida e a aplicação do indicador proposto por Nordlund e Häggblad (coeficiente NH). O método escolhido será implementado junto a um programa de análise por elementos finitos de modo a obter diagramas limite de estabilidade, para então ser aplicado a peças mais genéricas. O procedimento é aplicado a peças de geometria relevante para serem ensaiadas experimentalmente de modo a validar as simulações numéricas propostas. / Among the main problems in sheet metal forming processes are the fracture, the necking and the wrinkling behavior of the material. The last one can produce rejected parts due difficulties in the assembly of these parts or excessive wear of the tooling. Many researchers have been studied the problem of the compression instability phenomenon that origins the wrinkling behavior. The objective of this work is the study of the main available methods to the wrinkling prediction, as the bifurcation theory, the induced defect and an indicator proposed by Nordlund and Häggblad (NH coefficient). The more suitable method is implemented into a finite element analysis software in order to obtain the stability limit diagrams that can be used in the design of generic shape parts. Experimental studies will be done in parts subjected to compressive forming loads in order to validate the numerical simulations.

The sheet metal forming process basically involves the shaping of sheet metal of various thickness and material properties into the desired contours. This metal forming process has been extensively used by the automotive industry to manufacture both car panels and parts. Over the years numerous investigations have been conducted on various aspects of the manufacturing process with varied success. In recent years the requirements on the sheet metal forming industry have headed towards improved stability in the forming process while lowering environmental burdens. Therefore the overall aim of this research was to identify a technique for developing lubricant formulations that are insensitive to the sheet metal forming process. Due to the expense of running experiments on production presses and to improve time efficiency of the process the evaluation procedure was required to be performed in a laboratory. Preliminary investigations in the friction/lubricant system identified several laboratory tests capable of measuring lubricant performance and their interaction with process variables. However, little was found on the correlation between laboratory tests and production performance of lubricants. Therefore the focus of the research switched to identifying links between the performance of lubricants in a production environment and laboratory tests. To reduce the influence of external parameters all significant process variables were identified and included in the correlation study to ensure that lubricant formulations could be desensitised to all significant variables. The significant process variables were found to be sensitive to die position, for instance: contact pressure, blank coating of the strips and surface roughness of the dies were found significant for the flat areas of the die while no variables affected friction when polished drawbeads were used. The next phase was to identify the interaction between the significant variables and the main lubricant ingredient groups. Only the fatty material ingredient group (responsible for the formation of boundary lubricant regimes) was found to significantly influence friction with no interaction between the ingredient groups. The influence of varying this ingredient group was then investigated in a production part and compared to laboratory results. The correlation between production performance and laboratory tests was found to be test dependant. With both the Flat Face Friction test and the Drawbead Simulator unaffected by changes in the lubricant formulation, while the Flat Bottom Cup test showing similar results as the production trial. It is believed that the lack of correlation between the friction tests and the production performance of the lubricant is due to the absence of bulk plastic deformation of the strip. For this reason the Ohio State University (OSU) friction test was incorporated in the lubricant evaluation procedure along with a Flat Bottom Cup test. Finally, it is strongly believed that if the lubricant evaluation procedure highlighted in this research is followed then lubricant formulations can be developed confidently in the laboratory.

This thesis addresses the problem of damage at elevated temperature with a view to analysing transverse cracking during the continuous casting of microalloyed steels. Based on the results of a previous project undertaken at the University of Liège to simulate the continuous casting process at the macroscopic level, the present research aims at studying the damage growth using a finite element mesoscopic approach that models the grains structure of the material. The developments are done at the mesoscopic scale using information from both the microscopic and macroscopic levels. In order to determine the constitutive laws governing the damage process at the mesoscopic scale, the physical mechanisms leading to the apparition of cracks during steel continuous casting are first investigated. It is acknowledged that in the studied temperature range (800 to 1200 °C), the austenitic grain boundary is a favourable place for cracks to initiate and propagate. The mechanisms of voids nucleation, growth and coalescence are established, the cavities evolving under diffusion and creep deformations. Having identified the damage mechanisms occurring under continuous casting conditions, a numerical approach for the modelling of these phenomena at the grain scale is proposed. The mesoscopic model, which is implemented in the Lagrangian finite element code LAGAMINE developed at the University of Liège, is built on the basis of a 2D mesoscopic cell representative of the material. The finite element discretization comprises solid elements inside the grains and interface elements on the grains boundaries. An elastic-viscous-plastic law of Norton-Hoff type, which represents the thermo-mechanical behaviour of the material, is associated to the solid elements for the modelling of the grains; and a damage law accounting for cavitation and sliding is linked to the interface elements for the modelling of the damage growth at the grains boundaries. The transfer between the macroscopic and mesoscopic scales is realised by imposing the stress, strain and temperature fields, collected during the parent macroscopic simulation, as boundary conditions on the mesosopic cell. Macroscopic experiments, analytical computations and finite element simulations, as well as literature review and microscopic analyses, are used to define the parameters of the material laws. The experimental results and the identification methodology leading to the definition of the set of parameters specific to the studied steel are described. Finally, the influence of oscillation marks and process defects on cracks formation during the industrial process of continuous casting is analysed. The results are compared with in-situ observations and cracking risk indicators computed by the macroscopic model.