This study focuses on the effects of different constitutive models in sheet metal forming operations by considering the cylindrical and square cup drawing and V-bending simulations. Simulations are performed using eight different constitutive models / elastic plastic constitutive model with isotropic hardening, elastic plastic constitutive model with kinematic hardening, elastic plastic constitutive model with combined hardening, power law isotropic plasticity, piecewise linear isotropic plasticity, Barlatthree-parameter, cyclic elastoplastic and Hill&rsquo / 48 model.The numerical analyses are accomplished by using three different 1 mm thick sheet materials / St12 steel, Al-5182 aluminum and stainless steel 409 Ni. An explicit finite element code is used in the simulations. For square cup drawing, three different blank holder forces / 2 kN, 4 kN and 5 kN are considered for St12 steel, whereas only 5 kN blank holder force is applied for stainless steel 409 Ni and Al-5182 aluminum. A number of experiments are carried out and analytical calculations are utilized to evaluate the results of simulations. In cylindrical cup drawing, simulation results of different constitutive models show good agreement with analytical calculations for thickness strain and effective stress distributions. In square cup drawing, simulation results of all the models displayed good agreement with the experimental results for edge contour comparisons, although the distributions of effective stress vary for different models within the cup. The numerically and experimentally obtained springback amounts are also in good agreement. The simulation results obtained for piecewise linear isotropic plasticity and power law isotropic plasticity models show better agreement with the analytical solutions and experiments.

<p>A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles.</p><p>Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process.</p><p>The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step).</p><p>Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced.</p><p>Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena.</p> / QC 20100506

Bisherige Bemühungen zur Reduzierung der Rückfederung von Blechbauteilen begrenzten sich hauptsächlich auf die Gestaltung der letzten Formgebungsstufe. In der vorliegenden Arbeit wird ein innovativer Ansatz zur Erhöhung der Maßhaltigkeit durch die Modifikation der Vorziehstufe untersucht. Dabei wird auf Grundlage eines beispielhaften Industriebauteils ein Demonstrator mit einer offenen und einer geschlossenen Kontur entwickelt. Durch die Abbildung der Herstellungsmethode in der Simulation (FEM) lässt sich die Rückfederung beurteilen. Durch die Charakterisierung des Werkstoffverhaltens wird die Qualität der Simulation gesteigert, da die Materialkennwerte (Fließkurve & Grenzformänderungskurve) für die Simulation genauer spezifiziert werden können. Es erfolgt die Variation der Vorziehstufe hinsichtlich geometrischer (Radius & Grad der Vorziehstufe) und prozesstechnischer Parameter (Niederhalterkraft & Schließabstand), sodass nach der Auswertung der Rückfederungsergebnisse Gestaltunghinweise erarbeitet werden. Die Validierung der Simulationsergebnisse wird vorgenommen, indem die Bauteile real hergestellt werden. Dadurch ist es möglich, die Rückfederungen der Simulation und der realen Herstellungsmethode zu vergleichen und die Gestaltungshinweise zu bewerten. / Approaches to reduce springback of sheet metal parts are mainly focused on the last forming stage. This study deals with modifications made on the pre-drawing stage so that an increased dimensional accuracy results. A demonstrator with an open and a closed contour is developed based on an exemplary industrial part. The assessment of springback is conducted by incorporating the manufacturing method into simulation (FEM). To increase the quality of the simulation the characterization of materials is set and hence more information about material properties (flow curve and forming limit curve) is specified. Variations of geometric (radius & proportion of pre-drawing stage) and process parameters (blankholder force & closing distance) are made which purpose the development of design guidelines after evaluation. The simulation results are validated by producing real sheet metal parts. The design guidelines will be feasible/can be assessed if the comparison of the springback results converges between simulation and reality.

No description available.

A uniaxial High-Velocity Compaction (HVC) process for polymer powder using a cylindrical, hardened steel die and a new technique with relaxation assist was tested with a focus on the compactibility characteristics and surface morphology of the compacted materials using various heights of relaxation assist device with different compacting profiles. Relaxation assist device was presented as a new technique to reduce springback, pull-out phenomenon and to improve the compaction process. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomenon during the decompacting stage. In this study, polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. It was found that the relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). Experimental results for different compaction profiles were presented showing the effect of varying the opposite velocity during the decompacting stage and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists, and the influences of the relaxation assist device on the process characteristics. It was found that the relaxation assist improves the compaction of the polymer powder by locking the powder bed in the compacted form. In addition, the relative times of the compacting stage, decompacting stage and the reorganisation of the particles can be controlled by altering the height of the relaxation assist. It was found that the high-velocity compaction process is an interruption process and that the delay times between the pressure waves can be reduced by increasing the height of the relaxation assist device. Furthermore, the first gross instantaneous springback and the total elastic springback are reduced. Two bonding strain gauges and a high-speed video camera system were used to investigate the springback phenomenon during the compaction process. Scanning electron microscopy (SEM) and image computer board Camera (IC-PCI Imaging Technology) were used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. / QC 20100506

Orientador: Marcelo dos Santos Pereira / Resumo: O desenvolvimento dos aços avançados de alta resistência tem sido a principal estratégia por parte das siderúrgicas para atenderem às demandas das indústrias automobilísticas por um material que permita a redução de peso, diminuição do consumo de combustível e, simultaneamente, que possibilite uma melhora na resistência ao impacto e na segurança dos passageiros. Neste contexto, o aço bifásico apresenta grande potencial tecnológico de aplicação, principalmente em componentes estruturais, em virtude de suas propriedades mecânicas especiais, como alta resistência à tração, alta taxa de encruamento e muito boa ductilidade. No entanto, é necessário minimizar os problemas dimensionais provocados pelo efeito do retorno elástico (springback) durante a estampagem, assim como, as falhas durante o processamento. Este trabalho tem por objetivo caracterizar um aço bifásico da classe 1000 MPa (DP980), quanto à microestrutura e propriedades mecânicas. A caracterização microestrutural, por meio de técnicas de microscopia óptica e eletrônica de varredura, determinaram as fases presentes de maneira qualitativa e quantitativa, assim como suas morfologias, com o objetivo de correlacionar a microestrutura com as propriedades mecânicas. Evidenciou-se a presença de grãos alongados, acompanhando o sentido de laminação da chapa e uma fração volumétrica de martensita de 51,4%. As características em relação aos processos de estampagem foram estudadas por meio do ensaio de dobramento para determinar o r... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The development of advanced high strength steels (AHSS) has been the main strategy for steelmakers to meet the demands of the automotive industry for a material that reduces weight and fuel consumption, provides shock resistance and vehicle safety. Within this context, dual-phase steel (DP) shows great technological potential, mainly in structural parts, due to its special mechanical properties, such as high tensile strength, work hardening, and ductility. However, it is necessary to minimize the dimensional problems caused by springback during stamping, along with the processing failures. This work aims to characterize a 1000 MPa (DP980) dual-phase steel regarding its microstructure and mechanical properties. The microstructural characterization, through optical microscopy and scanning electron microscopy, determined the present phases in a qualitative and quantitative manner, as well as their morphologies, in order to correlate microstructure with mechanical properties. The presence of elongated grains, following the direction of lamination of the sheet, as well as a volumetric fraction of martensite of 51.4% were observed. Features of the stamping processes were examined through a bending test to determine the springback in samples submitted to bending punches with radii of 5 mm and 0.3 mm. The samples tested with the 5 mm radius punch show a strong springback in function of the high strength of the steel. With the 0.3 mm radius punch, the springback decreases significantl... (Complete abstract click electronic access below) / Doutor

No description available.

Este trabalho procura avaliar o retorno elástico em aços avançados de alta resistência utilizados em processo de dobramento. Para isso, foram usadas chapas de aço bifásico DP 600 e DP 800, ambas revestidas. Foram empregados dois métodos de medição a fim de abordar e avaliar o retorno elástico. O primeiro método abordado foi à conformação de tiras em U e o segundo método foi à realização do ensaio Dobramento Sob Tensão, aos quais possibilitaram a coleta de dados para aplicação em cálculo de coeficiente de atrito no processo de dobramento. Em ambas as avaliações foram utilizadas duas diferentes condições de lubrificação para o processo de dobramento, visando variar a condição de atrito no processo. A primeira foi à aplicação de um lubrificante em forma de pasta, de nome comercial Clarus Desmoldax DCP 35 e a segunda foi à aplicação em forma líquida, denominado Clarus Desmoldax DCP 35X. Para analisar o retorno elástico, foram utilizadas como critério de avaliação as medições de abertura da parede da tira conformada, permitindo desta forma considerar o atrito por intermédio da variação do tipo lubrificante. As análises realizadas nos corpos de prova conformados em formato U evidenciaram um retorno elástico menor para as amostras do aço DP 600, se comparadas com as amostras do aço DP 800. Não existiu relevância na variação dos lubrificantes quanto ao retorno elástico nas amostras de um mesmo tipo de aço. As análises realizadas nos corpos de prova submetidos ao ensaio de dobramento sob tensão, também evidenciaram um retorno elástico menor para as amostras do aço DP 600 se comparadas com as amostras do aço DP 800. Comparando as amostras com base nos dados coletados e aplicados ao cálculo de coeficiente de atrito, percebeu-se que as amostras que tiveram um retorno elástico menor, também possuíam coeficientes de atrito menor, constatando assim que quanto menor o coeficiente de atrito, menor é o retorno elástico. / This piece of work seeks to evaluate the springback effect on advanced high strength steel used in the bending process. For this, biphasic steel plates DP 600 and DP 800, both coated, were used. Two methods of measurement were used to approach and asses the springback effect. The first method approached was the conformation of strips in U and the second method was the preformance of the Bending Under Tension test, which enabled the data collect for the application in calculation of the friction coefficient in the bending process. In both assessments two different lubricant conditions for the bending process were used with the aim of varying the condition of friction in the process. The first one was the application of a paste lubricant, with the brand name Clarus Desmoldax DCP 35 and the second one was the application of a liquid lubricant, called Clarus Desmoldax DCP 35X. To analyze the springback effect the measurements of the opening of the wall of the conformed strip were used, thus allowing to consider the friction through the variation of the type of lubricant. The assessments carried out in the specimens in U shape showed a smaller springback effect for the steel samples DP 600 in comparison with the DP 800 ones. There was no relevance in the range of lubricants as the springback effect in the samples of the same type of steel. The analyzes carried out in the specimens subjected to bending under pressure test also showed a smaller springback effect for the steel samples DP 600 compared with the DP 800 ones. Comparing the samples based on the data collected and applied to the calculation of the friction coefficient, it was noticed that the samples that had a smaller springback effect also had lower friction coefficients, therefore verifying that the lower the friction coefficient is, the lower the springback effect.

Submitted by Érika Aparecida da Silva null (erikametais@gmail.com) on 2016-07-15T22:12:15Z No. of bitstreams: 1 Versão final.pdf: 12982211 bytes, checksum: 38bfd8e2bd40ff36d58029a14bf04fba (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-07-18T14:18:45Z (GMT) No. of bitstreams: 1 silva_ra_dr_guara.pdf: 12982211 bytes, checksum: 38bfd8e2bd40ff36d58029a14bf04fba (MD5) / Made available in DSpace on 2016-07-18T14:18:45Z (GMT). No. of bitstreams: 1 silva_ra_dr_guara.pdf: 12982211 bytes, checksum: 38bfd8e2bd40ff36d58029a14bf04fba (MD5) Previous issue date: 2016-07-11 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Diante da necessidade da produção de novos materiais para a indústria automotiva com melhores performances aliada à preocupação com as questões ambientais, visando a redução do consumo de combustíveis fósseis, surgiram, a partir da década de 1990, os aços avançados de alta resistência (AHSS), os quais conciliam uma pequena espessura da chapa e alta resistência mecânica. Porém, a produção em massa de componentes estruturais é limitada devido aos desafios na conformabilidade e união de chapas devido ao retorno elástico, conhecido como efeito springback. O presente trabalho avaliou 10 tipos de aços amplamente utilizados pela indústria automotiva, os quais estão agrupados em aços bifásicos, aços baixo carbono, aços endurecíveis após pintura e aços com interstícios livres. Todos esses materiais foram submetidos à caracterização mecânica e microestrutural por meio de determinação de composição química, ensaios de tração, ensaios de dureza e nanodureza, ensaios de dobramento de três pontos ao ar, análises de difração de elétrons retroespalhados (EBSD) e simulação de dobramento mecânico pelo método de elementos finitos (MEF) em software ABAQUS. Com os resultados provenientes do MEF, foi possível identificar as diferenças nos perfis anisotrópicos de cada material e correlacionar cada perfil com as características cristalográficas analisadas por meio de EBSD. Assim, foi possível compreender a variação no grau de springback com base na estrutura do retículo cristalino, uma vez que as diferenças estruturais do retículo cristalino são as responsáveis pelas diferentes respostas mecânicas. Concluiu-se que o modelo de encruamento isotrópico utilizado no MEF foi eficiente na determinação do perfil anisotrópico dos materiais, porém para uma perfeita acurácia na previsão e eliminação do springback, faz-se necessária a utilização do modelo de encruamento cinemático aliado ao uso de contrapunção nos ensaios experimentais. / In face of the need of the production of new materials for the automotive industry with better performance allied to the concern with environmental issues, aiming to reduce the consumption of fossil fuels, emerged from the decade of 1990, the advanced high-strength steels (AHSS), which reconcile a small sheet thickness and high mechanical resistance. However, the mass production of structural components is limited due to the challenges in conformability and union of sheets due to elastic return, known as springback effect. The present work has evaluated 10 types of steels are widely used in the automotive industry, which are grouped into biphasic steels, low carbon steels, bake hardening steels and interstitial free steels. All these materials were submitted to mechanical and microstructural characterization through determination of chemical composition, tensile tests, hardness Vickers tests and nanoindentation tests, sheet metal forming through three points bending in air, analyzes of electron backscatter diffraction (EBSD) and simulation of sheet metal forming by finite elements method (MEF) in ABAQUS software. With the results from the MEF, it was possible to identify the differences in anisotropic profiles of each material and correlate each profile with the crystallographic characteristics analyzed through EBSD. Thus, it was possible to understand the variation in degree of springback based on the structure of the crystal lattice, once the structural differences of crystal lattice are responsible for different mechanical responses. It was concluded that the model of isotropic hardening used in MEF was efficient in determining the anisotropic profile of materials, however for a perfect accuracy in prediction and elimination of springback, it is necessary to use a model of kinematic hardening allied to the use of counter-punch in experimental sheet metal forming. / 141827/2015-7 / CAPES: 99999.002440/2014-08

Este trabalho procura avaliar o retorno elástico em aços avançados de alta resistência utilizados em processo de dobramento. Para isso, foram usadas chapas de aço bifásico DP 600 e DP 800, ambas revestidas. Foram empregados dois métodos de medição a fim de abordar e avaliar o retorno elástico. O primeiro método abordado foi à conformação de tiras em U e o segundo método foi à realização do ensaio Dobramento Sob Tensão, aos quais possibilitaram a coleta de dados para aplicação em cálculo de coeficiente de atrito no processo de dobramento. Em ambas as avaliações foram utilizadas duas diferentes condições de lubrificação para o processo de dobramento, visando variar a condição de atrito no processo. A primeira foi à aplicação de um lubrificante em forma de pasta, de nome comercial Clarus Desmoldax DCP 35 e a segunda foi à aplicação em forma líquida, denominado Clarus Desmoldax DCP 35X. Para analisar o retorno elástico, foram utilizadas como critério de avaliação as medições de abertura da parede da tira conformada, permitindo desta forma considerar o atrito por intermédio da variação do tipo lubrificante. As análises realizadas nos corpos de prova conformados em formato U evidenciaram um retorno elástico menor para as amostras do aço DP 600, se comparadas com as amostras do aço DP 800. Não existiu relevância na variação dos lubrificantes quanto ao retorno elástico nas amostras de um mesmo tipo de aço. As análises realizadas nos corpos de prova submetidos ao ensaio de dobramento sob tensão, também evidenciaram um retorno elástico menor para as amostras do aço DP 600 se comparadas com as amostras do aço DP 800. Comparando as amostras com base nos dados coletados e aplicados ao cálculo de coeficiente de atrito, percebeu-se que as amostras que tiveram um retorno elástico menor, também possuíam coeficientes de atrito menor, constatando assim que quanto menor o coeficiente de atrito, menor é o retorno elástico. / This piece of work seeks to evaluate the springback effect on advanced high strength steel used in the bending process. For this, biphasic steel plates DP 600 and DP 800, both coated, were used. Two methods of measurement were used to approach and asses the springback effect. The first method approached was the conformation of strips in U and the second method was the preformance of the Bending Under Tension test, which enabled the data collect for the application in calculation of the friction coefficient in the bending process. In both assessments two different lubricant conditions for the bending process were used with the aim of varying the condition of friction in the process. The first one was the application of a paste lubricant, with the brand name Clarus Desmoldax DCP 35 and the second one was the application of a liquid lubricant, called Clarus Desmoldax DCP 35X. To analyze the springback effect the measurements of the opening of the wall of the conformed strip were used, thus allowing to consider the friction through the variation of the type of lubricant. The assessments carried out in the specimens in U shape showed a smaller springback effect for the steel samples DP 600 in comparison with the DP 800 ones. There was no relevance in the range of lubricants as the springback effect in the samples of the same type of steel. The analyzes carried out in the specimens subjected to bending under pressure test also showed a smaller springback effect for the steel samples DP 600 compared with the DP 800 ones. Comparing the samples based on the data collected and applied to the calculation of the friction coefficient, it was noticed that the samples that had a smaller springback effect also had lower friction coefficients, therefore verifying that the lower the friction coefficient is, the lower the springback effect.