Simulação do comportamento não linear de materiais quase-frágeis via elementos finitos com fissura embebida

Latest revision as of 11:07, 14 June 2017

Abstract

A combined constitutive model based on the Continuum Damage Mechanics is presented to represent the nonlinear behavior of quasi-brittle materials, which present different response when subjected to tension or compression. The constitutive model is a composition of two simple and specific models designed to treat each type of behavior. The combined model is able to deal with alternating load (tensioncompression), involving formation, closure and reopening of cracks. To model the compressive behavior, a degradation criterion based on the second invariant of the deviatoric part of the effective stress tensor (Von Mises or J2 criterion) is used. To simulate cracking, a damage model with degradation criterion based on the strain energy associated to the positive part the effective stress tensor is adopted. The combination of the models is made on the basis of the effective stresses. The model is able to represent the formation of discontinuities in the displacement field (strong discontinuities) for quasi-brittle materials. The region of strain localization (fracture process zone) is described by a softening law which establishes dissipation energy compatible with the fracture energy. The continuous region is described by the J2 damage model, with parameters adjusted to describe the compressive nonlinear behavior in compression. Some basic tests are performed to assess the ability of the model to represent the main aspects of the behavior of quasi-brittle materials. The ability of the model to predict the ductile behavior of reinforced concrete beams is also studied by comparing the numerical results with experimental ones.

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 == Abstract ==
-No presente trabalho desenvolve-se um modelo constitutivo baseado na mecânica do dano contínuo para representar o comportamento de materiais que apresentam diferentes respostas quando solicitados à tração ou à compressão. Obtém-se uma representação constitutiva através da composição de modelos simples e específicos para tratar cada tipo de solicitação. O modelo combinado é capaz inclusive de lidar com carregamentos alternados (tração e compressão), envolvendo fechamento e reabertura de fissuras existentes. Para modelar o comportamento em compressão emprega-se o modelo constitutivo que tem como critério de degradação o segundo invariante do tensor de tensão desviador (critério de Von Mises ou J2). Para simular o aparecimento de fissuras de tração, usa-se o modelo de daño com critério de degradação baseado na energia de deformação da parte positiva do tensor de tensões efetivas. A integração dos modelos é feita com base em tensões efetivas. O modelo é apto para representar a formaçãao de descontinuidades no campo de deslocamento (descontinuidades fortes) em materiais quase-frágeis. Nesse caso, a região de localização de deformação (zona de proceso da fratura) pode ser descrita pelo modelo de dano combinado, com lei de abrandamento de tensões (softening) exponencial, que estabelece dissipaçãao compatível com a energia de fratura. A região contínua pode ser descrita pelo modelo de dano J2, com parâmetros ajustados com base no comportamento não linear à compressão. Para a validação do modelo proposto, analisam-se alguns testes básicos, focando a capacidade do modelo em representar os principais aspectos do comportamento de materiais quase-frágeis. Summary A combined constitutive model based on the Continuum Damage Mechanics is presented to represent the nonlinear behavior of quasi-brittle materials, which present different response when subjected to tension or compression. The constitutive model is a composition of two simple and specific models designed to treat each type of behavior. The combined model is able to deal with alternating load (tensioncompression), involving formation, closure and reopening of cracks. To model the compressive behavior, a degradation criterion based on the second invariant of the deviatoric part of the effective stress tensor (Von Mises or J2 criterion) is used. To simulate cracking, a damage model with degradation criterion based on the strain energy associated to the positive part the effective stress tensor is adopted. The combination of the models is made on the basis of the effective stresses. The model is able to represent the formation of discontinuities in the displacement field (strong discontinuities) for quasi-brittle materials. The region of strain localization (fracture process zone) is described by a softening law which establishes dissipation energy compatible with the fracture energy. The continuous region is described by the J2 damage model, with parameters adjusted to describe the compressive nonlinear behavior in compression. Some basic tests are performed to assess the ability of the model to represent the main aspects of the behavior of quasi-brittle materials. The ability of the model to predict the ductile behavior of reinforced concrete beams is also studied by comparing the numerical results with experimental ones.
+A combined constitutive model based on the Continuum Damage Mechanics is presented to represent the nonlinear behavior of quasi-brittle materials, which present different response when subjected to tension or compression. The constitutive model is a composition of two simple and specific models designed to treat each type of behavior. The combined model is able to deal with alternating load (tensioncompression), involving formation, closure and reopening of cracks. To model the compressive behavior, a degradation criterion based on the second invariant of the deviatoric part of the effective stress tensor (Von Mises or J2 criterion) is used. To simulate cracking, a damage model with degradation criterion based on the strain energy associated to the positive part the effective stress tensor is adopted. The combination of the models is made on the basis of the effective stresses. The model is able to represent the formation of discontinuities in the displacement field (strong discontinuities) for quasi-brittle materials. The region of strain localization (fracture process zone) is described by a softening law which establishes dissipation energy compatible with the fracture energy. The continuous region is described by the J2 damage model, with parameters adjusted to describe the compressive nonlinear behavior in compression. Some basic tests are performed to assess the ability of the model to represent the main aspects of the behavior of quasi-brittle materials. The ability of the model to predict the ductile behavior of reinforced concrete beams is also studied by comparing the numerical results with experimental ones.
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