Coupling of material, process, and performance models is an important step towards a fully integrated material-process-performance design of structural components. In this research, alternative approaches for introducing the effects of manufacturing and material microstructure in plasticity constitutive models are studied, and a cyberinfrastructure framework is developed for coupled process-performance simulation and optimization of energy absorbing components made of magnesium alloys. The resulting mixed boundary/initial value problem is solved using nonlinear finite element analysis whereas the optimization problem is decomposed into a hierarchical multilevel system and solved using the analytical target cascading methodology. The developed framework is demonstrated on process-performance optimization of a sheetormed, energy-absorbing component using both classical and microstructure-based plasticity models. Sheetorming responses such as springback, thinning, and rupture are modeled and used as manufacturing process attributes whereas weight, mean crush force, and maximum crush force are used as performance attributes. The simulation and optimization results show that the manufacturing effects can have a considerable impact on design of energy absorbing components as well as the optimum values of process and product design variables.

With the increased focus on reducing carbon emissions in today’s society, several industries have to overcome new challenges, where especially the automotive industry is under a lot of scrutiny to deliver improved and more environmentally friendly products. To meet the demands from customers and optimize vehicles aerodynamically, new cars often contain complex body geometries, together with advanced materials that are introduced to reduce the total vehicle weight. With the introduction of the complex body components and advanced materials,one area in the automotive industry that has to overcome these challenges is manufacturing engineering, and in particular the departments working with the sheet metal forming process. In this process complex body component geometries can lead to non-linear strain paths and stretch bending load cases, and newly introduced advanced materials can be prone to exhibit behaviour of edge cracks not observed in conventional sheet metals. This thesis takes it onset in the challenges seen in industry today with predicting failure of the three complex load cases: Non-Linear Strain Paths, Stretch-Bending,and Edge Cracks. Through Finite Element simulation attempts are made to accurately predict failure caused by aforementioned load cases in industrial components or experimental setups in an effort to develop post-processing methods that are applicable to all cases.

Bending deformation characteristics of monolithic, bi-layer and tri-layer laminate sheet materials are studied using Analytical and FE models in this work. The analytical model, based on advanced theory of pure bending considers von Mises yielding, Ludwik hardening law and Bauschinger effect for various laminate constituent thickness ratios. The principal stresses and strains through the thickness and, change in relative thickness at specified bend curvatures are obtained as a function of increasing curvature during bending. Additionally, 2D and 3D finite element (FE) based models for bending are developed to overcome simplifications of the analytical models such as the effect of specimen width on strain distribution. Further, to experimentally assess and validate bending characteristics from the analytical models, a new experimental bend test-jig that is closer to pure bending is developed. The experimental set-up is an open concept design that allows access to the tensile surface as well as through-thickness region for recording and analyzing strains using an online strain mapping system based on digital image correction (DIC) method. Experimental bending is carried out on annealed AA2024 monolithic aluminum alloy sheet and Steel/Aluminum (SS400/AA1050) bi-layer laminate sheet at different thickness ratios. The model and experiments are studied in terms of stress and strain distribution as a function of relative thickness for different clad to matrix thickness ratios. Further the case of simultaneous bending and stretching over small radius bending is analyzed for limit strain prediction using an existing limit strain criterion based on major strain acceleration. An angular stretch bend test is used to subject an hour-glass shaped AA20240-O aluminum sheet specimen to simultaneous stretching and bending deformation while continuously imaging the critical tensile surface region using an optical camera. The strain development in the critical region is subsequently analyzed using digital image correlation (DIC) method. The effect of DIC parameters such as facet size, facet step, and effect of curve fitting procedures on limit strain are studied. An average limit strain of 0.2 is obtained for AA2024 for a facet size of 9x9 pixels, a facet step of 5 pixels and by applying a 5th order polynomial curve fit to the strain data. The results obtained are comparable with a limit strain of the material. The results are compared with a commercially available tri-layer laminate sheet material Alclad 2024 that has 80 μm thin layer of soft AA1100 on both surfaces of harder AA2024 core material. An improved stretch bendability limit strain of 0.24 for Alclad 2024 tri-layer specimen was predicted by utilizing the major strain acceleration criterion. The thin AA1100 protective layer produced a positive effect on the stretch bendability of Alclad 2024 when compared with monolithic AA2024 specimen. / Thesis / Doctor of Philosophy (PhD)

No description available.

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.

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.

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.