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Abstract(s)
Nos dias de hoje, o método de união com recurso a adesivos tem uma presença muito forte nas mais variadas indústrias, sobretudo na aeronáutica, indústria que impulsionou muito fortemente a utilização de juntas adesivas. Este método de união tem muitas vantagens relativamente a métodos mais tradicionais como a soldadura ou a ligação mecânica, entre as quais se destaca a facilidade da aplicação do adesivo, que permite a redução do tempo de fabrico e do custo, assim como uma redução de peso associado à estrutura final, ou o facto de este ser um método muito versátil, que permite a ligação entre diferentes materiais, o que muitas vezes não é possível com os outros métodos de ligação. O mercado de adesivos tem soluções para todos os tipos de ligação, nos quais se podem usar adesivos resistentes e frágeis, como é o caso do Araldite® AV138, ou adesivos menos resistentes, mas dúcteis, como o Araldite® 2015. Têm aparecido também adesivos de poliuretano como o Sikaforce® 7888, que combinam elevada resistência e ductilidade. Esta dissertação compara o desempenho dos três adesivos supracitados em juntas curvadas com substratos de um compósito de matriz epóxida reforçada a fibra de carbono, considerando a modificação dos parâmetros geométricos de comprimento de sobreposição (Lo), espessura dos aderentes (tp) e raio de curvatura dos aderentes (R). Para a previsão da resistência destas juntas foi utilizado o Método de Elementos Finitos (MEF) com o Modelo de Dano Coesivo (MDC), cuja análise recaiu sobre as tensões internas do adesivo, dano correspondente, resistência do adesivo e energia dissipada na rotura. O estudo numérico demonstrou grande influência do parâmetro geométrico tp no comportamento das ligações adesivas, sobretudo na resistência das juntas, onde se verificou que um aumento deste parâmetro provoca uma drástica queda de desempenho da ligação. Verificou-se também que maiores comprimentos de sobreposição causam um aumento global de todas as variáveis de estudo, demonstrando, no entanto, um comportamento logarítmico para todos os casos, o que indica que quanto mais se aumenta o Lo, o ganho de desempenho da junta é cada vez menor. Relativamente ao tipo de adesivo, as juntas unidas com o Sikaforce® 7888 demonstraram ter o melhor desempenho, seguidas de perto pelo adesivo Araldite® 2015. O adesivo AV138 demonstrou ter um desempenho relativamente inferior aos outros dois, com comportamentos muito constantes, independentemente da variação dos parâmetros de controlo.
Nowadays, the adhesive bonding method has a very strong presence in the most varied industries, especially in aeronautics, an industry that has strongly boosted the use of adhesive joints. This bonding method has many advantages over more traditional methods such as welding or mechanical bonding, among which the ease of application of the adhesive, which allows the reduction of the manufacturing time and cost, the reduction of weight associated with the final structure, or the fact that this is a very versatile method, which allows joining between different materials, which is often not possible with the other joining methods. The adhesives market has solutions for all types of bonding, in which strong and brittle adhesives can be used, such as the Araldite® AV138, or less strong but ductile adhesives such as the Araldite® 2015. Polyurethane adhesives have also appeared, such as the Sikaforce® 7888, which combine high strength and ductility. This dissertation compares the performance of the three above-mentioned adhesives in curved joints with adherends of a carbon fiber reinforced epoxy matrix composite, considering the modification of the following geometric parameters: overlap length (Lo), adherend thickness (tp) and adherends’ radius of curvature (R). For the prediction of the strength of these joints, the Finite Element Method (MEF) was used with Cohesive Zone Model (CZM), whose analysis was based on the internal stresses of the adhesive, corresponding damage, adhesive strength and energy dissipated at failure. The numerical study showed a great influence of the geometric parameter tp in the behavior of the adhesive joints, especially in the joint strength, where it was verified that an increase of this parameter causes a drastic decrease in the bond performance. It was also verified that larger overlap lengths cause an overall increase of all the study variables, nevertheless demonstrating a logarithmic behavior for all cases, which indicates that the more the Lo increases, the joint performance gain gets smaller. Regarding the type of adhesive, the joints bonded with the Sikaforce® 7888 showed the best performance, closely followed by the Araldite® 2015. The AV138 adhesive demonstrated to perform relatively inferior to the other two, with very constant behaviors, regardless of the variation of the control parameters.
Nowadays, the adhesive bonding method has a very strong presence in the most varied industries, especially in aeronautics, an industry that has strongly boosted the use of adhesive joints. This bonding method has many advantages over more traditional methods such as welding or mechanical bonding, among which the ease of application of the adhesive, which allows the reduction of the manufacturing time and cost, the reduction of weight associated with the final structure, or the fact that this is a very versatile method, which allows joining between different materials, which is often not possible with the other joining methods. The adhesives market has solutions for all types of bonding, in which strong and brittle adhesives can be used, such as the Araldite® AV138, or less strong but ductile adhesives such as the Araldite® 2015. Polyurethane adhesives have also appeared, such as the Sikaforce® 7888, which combine high strength and ductility. This dissertation compares the performance of the three above-mentioned adhesives in curved joints with adherends of a carbon fiber reinforced epoxy matrix composite, considering the modification of the following geometric parameters: overlap length (Lo), adherend thickness (tp) and adherends’ radius of curvature (R). For the prediction of the strength of these joints, the Finite Element Method (MEF) was used with Cohesive Zone Model (CZM), whose analysis was based on the internal stresses of the adhesive, corresponding damage, adhesive strength and energy dissipated at failure. The numerical study showed a great influence of the geometric parameter tp in the behavior of the adhesive joints, especially in the joint strength, where it was verified that an increase of this parameter causes a drastic decrease in the bond performance. It was also verified that larger overlap lengths cause an overall increase of all the study variables, nevertheless demonstrating a logarithmic behavior for all cases, which indicates that the more the Lo increases, the joint performance gain gets smaller. Regarding the type of adhesive, the joints bonded with the Sikaforce® 7888 showed the best performance, closely followed by the Araldite® 2015. The AV138 adhesive demonstrated to perform relatively inferior to the other two, with very constant behaviors, regardless of the variation of the control parameters.
Description
Keywords
Juntas adesivas Juntas curvadas Material compósito reforçado a fibras de carbono Adesivos estruturais Método de Elementos Finitos Modelos de Dano Coesivo Adhesive joints Curved joints Composite material reinforced with carbon fibers Structural adhesives Finite Element Method Cohesive Zone Models