Please use this identifier to cite or link to this item: http://hdl.handle.net/10316/29559
DC FieldValueLanguage
dc.contributor.advisorFernandes, José Valdemar Bidarra-
dc.contributor.advisorSantos, Abel Dias dos-
dc.contributor.authorReis, Luís Carlos Duarte dos-
dc.date.accessioned2015-09-28T16:28:16Z-
dc.date.available2015-09-28T16:28:16Z-
dc.date.issued2016-04-18-
dc.date.submitted2015-09-28-
dc.identifier.citationREIS, Luís Carlos Duarte dos - Constitutive parameters identification of metal sheets using circular bulge tests. Coimbra : [s.n.], 2016. Tese de doutoramento. Disponível na WWW: http://hdl.handle.net/10316/29559-
dc.identifier.urihttp://hdl.handle.net/10316/29559-
dc.descriptionTese de doutoramento em Engenharia Mecânica, na especialidade de Produção Tecnologica, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbrapt
dc.description.abstractO ensaio de expansão biaxial sob pressão hidráulica continua a ser hoje em dia uma ferramenta importante de caracterização do comportamento plástico de chapas metálicas quando sujeitas a grandes deformações plásticas. A informação retirada deste ensaio não só faculta dados adicionais aos da curva tensão-deformação em tração, mas também desempenha um papel importante como informação necessária para a identificação dos parâmetros dos critérios de plasticidade mais avançados. Este trabalho foi realizado recorrendo a simulações numéricas do ensaio de expansão biaxial em matriz circular, com recurso ao programa DD3IMP. Tem como objetivo contribuir para a determinação da curva tensão-deformação de chapas metálicas em tração biaxial, de modo simples e preciso. Durante o ensaio foram analisadas a geometria e outras variáveis do ensaio, tais como, a evolução de pressão, o raio de curvatura e as trajetórias de tensão e de deformação no pólo da calote. Isto permitiu delinear algumas recomendações, de modo a melhorar o procedimento tradicional experimental de determinação da curva de encruamento, e desenvolver novos métodos diretos e inversos com o intuito de simplificar a sua avaliação. O procedimento tradicional de obtenção da curva de encruamento do ensaio de expansão biaxial em matriz circular não toma em consideração a anisotropia do material. Neste estudo analisam-se em pormenor algumas questões, tais como a geometria da calote esférica e as trajetórias de tensão e de deformação no pólo, de modo a compreender as relações entre as diferentes variáveis do ensaio em função da anisotropia do material e para diferentes comportamentos de encruamento. Isto permite uma compreensão aprofundada sobre a precisão na determinação do raio de curvatura e na espessura da chapa no pólo da calote esférica durante o ensaio, com impacto na determinação experimental da curva de encruamento do material. Foram propostos modelos analíticos para que descrevem a evolução do raio de curvatura e da espessura de chapa em função da altura de pólo. Estes modelos são baseados numa ampla análise de comportamentos de materiais, ou seja, para diferentes valores de tensão limite de elasticidade, coeficiente de encruamento, anisotropia, e também para diferentes valores de espessura inicial da chapa e geometrias circulares de matriz. As variáveis analisadas, respeitantes à geometria da matriz, são o raio da matriz e o raio de concordância da matriz. A validação dos modelos analíticos propostos foi realizada com resultados gerados numericamente e experimentais; neste último caso, foram utilizados os existentes na literatura, para várias geometrias de matriz, e os obtidos no âmbito da presente tese, com uma geometria de matriz específica. Esta formulação mostra-se adequada para simplificar a determinação experimental da curva de encruamento recorrendo ao ensaio de expansão biaxial sob pressão hidráulica. Nomeadamente, é possível evitar o procedimento experimental complexo para determinar os valores de tensão e de deformação durante o ensaio, que requer dispositivos específicos para a análise do raio de curvatura e da espessura da chapa no pólo da calote. Por fim, os presentes resultados também mostram que é possível sobrepor as curvas da evolução da pressão em função da altura de pólo e este conhecimento foi utilizado de modo a conceber uma estratégia de análise inversa para identificar os parâmetros da lei encruamento de Swift, baseada no ensaio de expansão biaxial. A sobreposição das curvas de pressão em função da altura de pólo é possível de obter com a utilização de fatores de multiplicação para a pressão e para a altura de pólo, no caso de materiais com o mesmo coeficiente de encruamento independentemente dos restantes parâmetros da lei de encruamento de Swift, da anisotropia e da espessura inicial da chapa. Além disso, a análise da evolução da pressão durante o ensaio mostrou que os valores desses fatores são sensíveis aos parâmetros da lei de Swift e à espessura inicial da chapa, sendo apenas ligeiramente dependentes da anisotropia do material. A metodologia proposta consiste em definir a melhor sobreposição entre os resultados experimentais e de referência, obtidos numericamente para materiais isotrópicos com diferentes valores de coeficiente de encruamento. Esta metodologia foi validada utilizando resultados gerados numericamente e resultados experimentais. Ela permite simplificar o procedimento experimental e não está exposta a erros relacionados com a determinação experimental da deformação no pólo da calote e a utilização da teoria de membrana na avaliação da tensão a partir da análise do raio de curvatura, que é normalmente a principal fonte de erro. The hydraulic bulge test remains nowadays an important tool for characterizing the behaviour of sheet materials submitted to large plastic deformation. Data from this test, not only provides additional information to the tensile stress-strain curve, but also plays an important role as input information when identifying the parameters of the current most advanced yield criteria. The circular hydraulic bulge test is studied by means of finite element simulations, using the in-house code DD3IMP. This work aims to contribute to the easy and accurate evaluation of stress-strain curve of sheet metals in biaxial tension. The geometry and other variables of the test, such as pressure evolution during the test, radius of curvature, strain and stress paths at the pole of the cap, were analysed. This allows to make recommendations in order to improve the traditional experimental procedure for determining the hardening curve, but also the development of new direct and inverse methodologies for simplifying its evaluation. The traditional procedure for obtaining the hardening curve from the circular bulge test does not takes into account the anisotropy of the material. This study analyses in detail issues such as the geometry of the spherical cap and the stress and strain paths at the pole, in order to understand the relationships between different variables of the test as a function of the anisotropy and for different hardening behaviours of the material. This allows the in-depth understanding about the accuracy of the assessment of thickness and radius of curvature at the pole of the spherical cap during the test, with repercussions on the experimental determination of the hardening curve of the material. Analytical models for the radius of curvature and the sheet thickness evolutions with the pole bulge height were proposed. These models are based in an extensive analysis of material Abstract vi behaviours, i.e. different values of yield stress, hardening coefficient, anisotropy, and also different values of initial sheet thickness and geometry of the circular bulge test. The geometric variables analysed are the bulge die radius and the fillet radius of the die. The validation of the proposed analytical models is performed with numerically generated and experimental results; in the latter case, results from literature, with various die geometries, and those obtained in the framework of this thesis, with a specific die geometry, were used. This formulation shows to be appropriate for simplifying the experimental assessment of the hardening curve from the hydraulic bulge test. Namely, it is possible to avoid the complex experimental procedure to determine the stress and strain values during the test, which requires specific devices for evaluating the radius of curvature and the sheet thickness at the pole of the cap. Finally, the current results also showed that it is possible to overlap the curves concerning the evolution of the pressure with the pole height, and this insight was explored in order to build an inverse strategy for identifying the parameters of the Swift hardening law, from the bulge test. The overlapping of these curves can be accomplished by using multiplying factors for the pressure and the pole height, in case of materials with the same hardening coefficient regardless of the remaining parameters of the Swift law, anisotropy and initial thickness of the sheet. Moreover, analysis of the pressure evolution during the test has shown that the values of these factors are sensitive to the parameters of Swift law and the initial sheet thickness, being only slightly dependent of the anisotropy of the material. The proposed methodology consists on choosing the best overlap between the experimental and reference results, numerically obtained for isotropic materials with various values of the hardening coefficient. It was validated using numerical generated and experimental results. The methodology allows simplifying the experimental procedure and additionally is not exposed to experimental errors related to the experimental evaluation of strain at the pole of the bulge and the use of membrane theory approach for assessment of the stress from the radius of curvature, which is usually the major source of error.pt
dc.description.abstractThe hydraulic bulge test remains nowadays an important tool for characterizing the behaviour of sheet materials submitted to large plastic deformation. Data from this test, not only provides additional information to the tensile stress vs. strain curve, but also plays an important role as input information for identifying the parameters of the current most advanced yield criteria. The circular hydraulic bulge test is studied by means of finite element simulations, using the in-house code DD3IMP. This work aims to contribute to the easy and accurate evaluation of stress vs. strain curve of sheet metals in biaxial tension. Variables of the test, such as pressure evolution during the test, geometry of the cap, including radius of curvature and sheet thickness, strain and stress paths at the pole of the cap, were analysed. This allows to make recommendations in order to improve the traditional experimental procedure for determining the stress vs. strain curve, but also to develop new direct and inverse methodologies for simplifying its evaluation. The traditional procedure for obtaining the stress vs. strain curve from the circular bulge test does not takes into account the anisotropy of the material. The detailed analysis of issues such as the geometry of the spherical cap and the stress and strain paths at the pole, allowed to understand the relationships between such variables of the test, the sheet anisotropy and the different hardening behaviours of the material. The in-depth understanding of these relationships has repercussions on the experimental evaluation of the stress vs. strain curve of materials when using the bulge test, for which recommendations are made. Analytical models for the radius of curvature and the sheet thickness evolutions with the pole bulge height were proposed. These models are based in an extensive analysis of material behaviours, i.e. different values of yield stress, hardening coefficient, anisotropy, and also different values of initial sheet thickness and geometry of the circular bulge test. The analysed geometric variables include the bulge die radius and the fillet radius of the die. The validation of the proposed analytical models is performed both by numerically generated results and experimental results; in the latter case, results were considered not only from literature, having various die geometries, but also from an experimental equipment in the framework of this thesis, having a specific die geometry. This formulation shows to be appropriate for simplifying the experimental assessment of the hardening curve from the hydraulic bulge test. Namely, it is possible to avoid the complex experimental procedure to determine the stress and strain values during the test, which requires specific devices for evaluating the radius of curvature and the sheet thickness at the pole of the cap. Finally, the current results also showed that it is possible to overlap the curves concerning the evolution of the pressure with the pole height, and this insight was explored in order to build an inverse strategy for identifying the parameters of the Swift hardening law, from the bulge test. The overlapping of these curves can be accomplished by using multiplying factors for the pressure and the pole height, which in case of materials with the same hardening coefficient it is independent of the remaining parameters of the Swift law, anisotropy and initial thickness of the sheet. Moreover, the analysis of the pressure evolution during the test has shown that corresponding values of these factors are sensitive to the parameters of Swift law and the initial sheet thickness, being only slightly dependent of the anisotropy of the material. The proposed methodology consisted on choosing the best overlap between the experimental and reference results, which were numerically obtained for isotropic materials with various values of the hardening coefficient. Validation was performed using numerical generated results and experimental results. The methodology allows simplifying the experimental procedure and in addition is not exposed to experimental errors related to the experimental evaluation of strain at the pole and the use of membrane theory approach, for assessment of the stress from the radius of curvature, which is usually the major source of error.pt
dc.description.sponsorshipFCT - Pest-C/EME/UI0285/2013pt
dc.language.isoengpt
dc.rightsopenAccesspt
dc.subjectLei de encruamentopt
dc.subjectEnsaio de expansão biaxial sob pressão hidráulicapt
dc.subjectChapas metálicas isotrópicas e anisotrópicaspt
dc.subjectModelaçãopt
dc.subjectAnálise inversapt
dc.subjectTeoria da membranapt
dc.subjectSimulação numéricapt
dc.subjectHardening lawpt
dc.subjectHydraulic bulge testpt
dc.subjectIsotropic and anisotropic metal sheetpt
dc.subjectModellingpt
dc.subjectInverse analysispt
dc.subjectMembrane theorypt
dc.subjectNumerical simulationpt
dc.titleConstitutive Parameters Identification of Metal Sheets using Circular Bulge Testspt
dc.typedoctoralThesispt
dc.peerreviewedyespt
dc.date.embargo2016-04-18*
dc.identifier.tid101514140pt
uc.rechabilitacaoestrangeiranopt
uc.date.periodoEmbargo0pt
uc.controloAutoridadeSim-
item.grantfulltextopen-
item.languageiso639-1en-
item.fulltextCom Texto completo-
crisitem.advisor.deptFaculdade de Ciências e Tecnologia, Universidade de Coimbra-
crisitem.advisor.parentdeptUniversidade de Coimbra-
crisitem.advisor.researchunitCentre for Mechanical Engineering-
crisitem.advisor.orcid0000-0003-3692-585X-
Appears in Collections:FCTUC Eng.Mecânica - Teses de Doutoramento
Files in This Item:
File Description SizeFormat
Constitutive Parameters Identification of Metal Sheets using Circular Bulge Tests.pdf6.37 MBAdobe PDFView/Open
Show simple item record

Page view(s) 50

365
checked on Oct 21, 2020

Download(s) 50

397
checked on Oct 21, 2020

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.