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Advisor(s)
Abstract(s)
A utilização de estruturas sandwich tem possibilitado uma melhoria das propriedades de estruturas mecânicas, como resistência e rigidez à flexão e, ao mesmo tempo, uma redução do peso através da combinação de materiais. De facto, ao utilizar um núcleo flexível de elevada espessura entre peles finas de alta rigidez e resistência, é possível obter componentes leves e resistentes, com aplicações na indústria aeronáutica, aeroespacial e outras. Uma vez que estas estruturas apresentam elevada responsabilidade, é necessária a existência de métodos de previsão de resistência que consigam reproduzir o seu comportamento mecânico em serviço, para tornar o seu projeto mais expedito e reduzir a necessidade de realização de ensaios experimentais, com a consequente redução de custos. No presente trabalho realizou-se um estudo ao comportamento de estruturas sandwich nos ensaios de flexão em três e quatro pontos. Este estudo consistiu na realização de ensaios experimentais, dos quais foram obtidos os gráficos de forçadeslocamento, e depois comparados com os gráficos obtidos através dos modelos numéricos, realizados no programa Abaqus®. Para tal foram fabricadas duas configurações de estruturas sandwich. Os materiais utilizados para as faces foram préimpregnados de fibra de carbono HS 160 REM e de fibra de vidro EE 330 ET445. Como núcleo utilizou-se espuma de PMI e, para ligar as faces ao núcleo, usou-se o adesivo SikaForce®-7710 L100. A diferença entra estas estruturas está na direção da camada de fibra de vidro, já que numa das configurações a camada de fibra de vidro está a ±45˚, na outra está a 0˚/90˚. As camadas de fibra de carbono são unidirecionais e dispostas a 0˚ e 90˚. Nos modelos numéricos utilizaram-se critérios e modelos para simular o comportamento real dos materiais. No adesivo fez-se uso do modelo de dano coesivo, no núcleo empregou-se o modelo de crushable foam e nas faces o critério de Tsai-Wu. No ensaio experimental, os valores obtidos mostram que entre as duas configurações ensaiadas não há uma diferença muito significativa ao alterar a direção de uma camada interior da face. Numericamente. Foi possível reproduzir com precisão os ensaios experimentais.
The use of sandwich structures has enabled an improvement in the properties of mechanical structures, such as flexural strength and stiffness, and at the same time, a reduction in weight through the combination of materials. In fact, by using a flexible core of high thickness between thin skins of high rigidity and resistance, it is possible to obtain light and resistant components, with applications in the aeronautical, aerospace, and other industries. Since these structures have a high responsibility, it is necessary to have resistance prediction methods that can reproduce their mechanical behavior in service, to make your project more expeditious and reduce the need to carry out experimental tests, with the consequent reduction of costs. In the present work, a study was carried out on the behavior of sandwich structures in the three- and four-point bending tests. This study consisted of carrying out experimental tests, from which the load-displacement curves were obtained, and then compared with those obtained through numerical models, carried out in the Abaqus® program. For this purpose, two configurations of sandwich structures were manufactured. The materials used for the faces were carbon fiber HS 160 REM and glass fiber EE 330 ET445 pre-pregs. As core, PMI foam was used and, to bond the faces to the core, the SikaForce®-7710 L100 adhesive was used. The difference between these structures is in the direction of the fiberglass layer, since in one of the configurations the fiberglass layer is at ±45˚, in the other it is at 0˚/90˚. The carbon fiber layers are unidirectional and arranged at 0˚ and 90˚. In the numerical models, criteria and models were used to simulate the real behavior of the materials. For the adhesive, cohesive zone models were used, the crushable foam model was used for the core and the Tsai-Wu criterion for the faces. In the experimental test, the obtained values show that between the two configurations tested there is not a very significant difference when changing the direction of an inner layer of the face. Numerically, it was possible to accurately reproduce the experimental tests.
The use of sandwich structures has enabled an improvement in the properties of mechanical structures, such as flexural strength and stiffness, and at the same time, a reduction in weight through the combination of materials. In fact, by using a flexible core of high thickness between thin skins of high rigidity and resistance, it is possible to obtain light and resistant components, with applications in the aeronautical, aerospace, and other industries. Since these structures have a high responsibility, it is necessary to have resistance prediction methods that can reproduce their mechanical behavior in service, to make your project more expeditious and reduce the need to carry out experimental tests, with the consequent reduction of costs. In the present work, a study was carried out on the behavior of sandwich structures in the three- and four-point bending tests. This study consisted of carrying out experimental tests, from which the load-displacement curves were obtained, and then compared with those obtained through numerical models, carried out in the Abaqus® program. For this purpose, two configurations of sandwich structures were manufactured. The materials used for the faces were carbon fiber HS 160 REM and glass fiber EE 330 ET445 pre-pregs. As core, PMI foam was used and, to bond the faces to the core, the SikaForce®-7710 L100 adhesive was used. The difference between these structures is in the direction of the fiberglass layer, since in one of the configurations the fiberglass layer is at ±45˚, in the other it is at 0˚/90˚. The carbon fiber layers are unidirectional and arranged at 0˚ and 90˚. In the numerical models, criteria and models were used to simulate the real behavior of the materials. For the adhesive, cohesive zone models were used, the crushable foam model was used for the core and the Tsai-Wu criterion for the faces. In the experimental test, the obtained values show that between the two configurations tested there is not a very significant difference when changing the direction of an inner layer of the face. Numerically, it was possible to accurately reproduce the experimental tests.
Description
Keywords
Estruturas sandwich Material compósito Espuma de PMI Modelação numérica Modelos de dano coesivo Flexão em 3 pontos Flexão em 4 pontos Sandwich structures Composite material PMI foam Numerical modeling Cohesive zone models 3-point flexure 4-point flexure