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Abstract(s)
A constante investigação e desenvolvimento de novos materiais tem possibilitado avanços significativos em diversas indústrias que de outro modo não seriam possíveis. Também nesse sentido surgiu a utilização de estruturas sandwich, que permitem obter a melhor combinação de propriedades de diferentes materiais tendo em vista a finalidade de cada estrutura. Estas estruturas carecem de estudo aprofundado para obter as suas propriedades combinadas, algo que a nível da previsão do comportamento mecânico pode ser efetuado com recurso ao método de elementos finitos. Esta dissertação apresenta um estudo do comportamento de estruturas sandwich solicitadas à flexão em três e quatro pontos. Os resultados experimentais foram comparados com resultados numéricos obtidos pelo Método de Elementos Finitos com recurso ao software Abaqus®. Para o efeito foram estudadas três diferentes configurações de estruturas sandwich, nas quais se fez variar a espessura do núcleo e a configuração do laminado que compõe as peles. Os materiais utilizados foram espuma de poliuretano para o núcleo, pré-impregnados de fibra de carbono e matriz de resina epóxi para as peles e um adesivo bi-componente com base de poliuretano para fazer a ligação das peles ao núcleo. Os modelos numéricos foram baseados na utilização de um modelo crushable foam para a espuma, o critério de Tsai-Wu para as peles e modelos de dano coesivo para o adesivo. Com este trabalho foi possível concluir que, para as combinações de materiais estudados e com os modelos utilizados, é possível obter resultados numéricos bastante semelhantes aos resultados experimentais, com vantagens ao nível rapidez para a obtenção desses resultados, especialmente com a modelação em 2D, dado não ser necessário fazer a produção dos provetes para os ensaios mecânicos.
The constant research and development of new materials has enabled advances made in several industries that would not otherwise be possible. In this sense, the use of sandwich structures also emerges, which allows to obtain the best combination of different material properties, accounting for the end purpose of each structure. These structures require an in-depth study to obtain their combined properties, which can be done using the finite element method for the prediction of mechanical behaviour. This thesis presents a study of the behaviour of sandwich structures loaded under three and four-point bending. The experimental results were compared with the numerical results obtained by the Finite Element Method using the Abaqus® software. For this purpose, three different configurations of sandwich structures were studied, in which the core thickness and the configuration of the laminate that makes up the skins were varied. The materials used were polyurethane foam for the core, carbon fibre prepregs and epoxy resin matrix for the skins and a two-component polyurethane-based adhesive to make the skins bond to the core. The numerical models were based on the use of a crushable foam model for the foam, the Tsai-Wu criterion for the skins and cohesive zone models for the adhesive. With this work it was possible to conclude that, for the specifications of studied materials and with the models used, it is possible to obtain quite similar numerical predictions to the experimental results, with advantages in terms of speed to obtain the results, especially with a 2D modelling approach, given that it is not necessary to produce specimens for mechanical testing.
The constant research and development of new materials has enabled advances made in several industries that would not otherwise be possible. In this sense, the use of sandwich structures also emerges, which allows to obtain the best combination of different material properties, accounting for the end purpose of each structure. These structures require an in-depth study to obtain their combined properties, which can be done using the finite element method for the prediction of mechanical behaviour. This thesis presents a study of the behaviour of sandwich structures loaded under three and four-point bending. The experimental results were compared with the numerical results obtained by the Finite Element Method using the Abaqus® software. For this purpose, three different configurations of sandwich structures were studied, in which the core thickness and the configuration of the laminate that makes up the skins were varied. The materials used were polyurethane foam for the core, carbon fibre prepregs and epoxy resin matrix for the skins and a two-component polyurethane-based adhesive to make the skins bond to the core. The numerical models were based on the use of a crushable foam model for the foam, the Tsai-Wu criterion for the skins and cohesive zone models for the adhesive. With this work it was possible to conclude that, for the specifications of studied materials and with the models used, it is possible to obtain quite similar numerical predictions to the experimental results, with advantages in terms of speed to obtain the results, especially with a 2D modelling approach, given that it is not necessary to produce specimens for mechanical testing.
Description
Keywords
Estruturas sandwich Adesivo estrutural Análise de elementos finitos Ensaios mecânicos de estruturas sandwich Ensaios de flexão Crushable foam Critério de TsaiWu Modelos de dano coesivo Sandwich structures Structural adhesive Finite element analysis Mechanical tests to sandwich structures Flexure tests Crushable foam Tsai-Wu criterion Cohesive zone models