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Abstract(s)
As ligações adesivas estão amplamente difundidas na indústria aeroespacial, aeronáutica e
automóvel. Quando comparadas com as ligações mecânicas convencionais, as ligações adesivas
envolvem um menor número de componentes, reduzem o peso final da estrutura, permitem ligar
materiais dissimilares, e resistem a solicitações e carregamentos exigentes com uma distribuição
do estado de tensões mais uniforme comparativamente aos métodos de ligação convencionais. A
afirmação industrial das juntas adesivas só tem sido possível devido ao desenvolvimento de
metodologias de previsão que permitam validar a sua utilização, de modo a contornar o paradigma
segundo o qual o sobredimensionamento das juntas adesivas resulta em estruturas mais pesadas
e dispendiosas, devido à inexistência de modelos materiais precisos e critérios de rotura
adequados. A técnica de dimensionamento mais difundida e validada designa-se por Modelos de
Dano Coesivo. No que diz respeito à área de investigação das juntas adesivas tubulares obtidas por
hidroformagem, e uma vez que este é um tópico emergente, existem poucos trabalhos de
investigação, em comparação com as geometrias tradicionais de sobreposição.
O objetivo principal do desenvolvimento numérico do trabalho consiste na análise numérica de
juntas adesivas tubulares hidroformadas solicitadas a esforços de tração, considerando a variação
de parâmetros materiais (tipo de adesivo e material do aderente) e geométricos. Para este efeito,
é realizada uma validação dos modelos coesivos através dos resultados experimentais e numéricos
recuperados de um trabalho de investigação anterior. De seguida, pretende-se avaliar
numericamente a resistência mecânica dos conjuntos, a plastificação máxima dos aderentes, a
ductilidade das juntas, a evolução da variável do dano para o instante da carga máxima e ainda a
distribuição das tensões de corte e arrancamento. Como complemento à análise numérica realizada
foi aplicado o Método de Taguchi para a definição de uma junta ótima, considerando a variação de
mais do que um fator de controlo, e verificação estatística da significância de cada parâmetro na
resistência e ductilidade das juntas. De seguida, foram abordadas as propostas de alterações
geométricas com o objetivo de concluir, face à geometria de base, se a variação de um dos
parâmetros se traduzia na melhoria das propriedades mecânicas da junta. Por fim, realizou-se uma
análise de mercado que procura validar a geometria ideal, e determinar se esta é passível de ser
implementada do ponto de vista económico e industrial. Para tal, foi projetado um molde que
permite obter os aderentes hidroformados, seguindo-se de uma análise dos custos de maquinagem
através do custo das matérias-primas, ferramentas e processos de fabrico.
A validação dos modelos de dano coesivo foi realizada com sucesso. Após realizar um estudo
numérico intensivo, optar pelos fatores de controlo mais significativos e analisar uma proposta de
aplicação a nível industrial, determinou-se que a geometria ótima utiliza o adesivo Araldite® AV138,
ângulo de filete adesivo igual a 15°, comprimento de sobreposição de 10 mm, diâmetro exterior do
aderente não hidroformado de 20 mm, ângulo do ressalto exterior de 45°, e espessura dos
aderentes de 2 mm. Esta configuração justifica o investimento requerido, uma vez que a proposta
garante a melhoria da resistência mecânica e ductilidade em 60 e 75%, respetivamente, quando
comparada com a geometria de referência.
Adhesive joints are widespread in the aerospace, aeronautics, and automotive industries. When compared to conventional mechanical joints, adhesive joints involve a smaller number of components, reduce the final weight of the structure, enable joining dissimilar materials, and resist the applied loadings with a more uniform stress state distribution compared to conventional joining methods. The industrial affirmation of adhesive joints has only been possible due to the development of predicting methodologies that allow validating their use, to circumvent the paradigm according to which the oversizing of adhesive joints results in heavier and more expensive structures, and due to the lack of accurate material models and appropriate failure criteria. The most widespread and validated design technique is called Cohesive Zone Models. Regarding the research area of tubular adhesive joints obtained by hydroforming, since this is an emerging topic, there are few research works compared to traditional overlap geometries. The main objective of this work consists of the numerical analysis of hydroformed tubular adhesive joints subjected to tensile loads, considering the variation of material parameters (type of adhesive and adherent material) and geometric parameters. For this purpose, a validation of cohesive models is carried out through experimental and numerical results retrieved from a previous research work. Next, the aim is to numerically evaluate the mechanical strength of the joints, the plasticization of the adherents, the ductility of the joints, the evolution of the damage variable at maximum load, and the distribution of shear and peel stresses. As a complement to the numerical analysis carried out, the Taguchi Method was applied to determine an optimal joint, considering the variation of more than one control factor, and to statistically verify the significance of each parameter in the strength and ductility of the joints. Then, proposals for geometric changes were addressed with the aim of concluding, in view of the base geometry, whether the variation of one of the parameters would translate into an improvement in the mechanical properties of the joint. Finally, a market analysis was carried out that seeks to validate the ideal geometry and determine if it is possible to be implemented from an economic and industrial point of view. To this end, a mold was designed to obtain hydroformed adherents, followed by an analysis of machining costs through the cost of raw materials, tools and manufacturing processes. Validation of the cohesive models was successfully performed. After carrying out an intensive numerical study, opting for the most significant control factors and analyzing an application proposal at an industrial level, it was determined that the optimal geometry uses the adhesive Araldite® AV138, adhesive fillet angle equal to 15°, overlap length of 10 mm, outside diameter of the non-hydroformed adherent of 20 mm, exterior joggle angle of 45°, and thickness of the adherents of 2 mm. This configuration justifies the required investment, since the proposal guarantees an improvement in mechanical strength and ductility by 60 and 75%, respectively, when compared to the reference geometry.
Adhesive joints are widespread in the aerospace, aeronautics, and automotive industries. When compared to conventional mechanical joints, adhesive joints involve a smaller number of components, reduce the final weight of the structure, enable joining dissimilar materials, and resist the applied loadings with a more uniform stress state distribution compared to conventional joining methods. The industrial affirmation of adhesive joints has only been possible due to the development of predicting methodologies that allow validating their use, to circumvent the paradigm according to which the oversizing of adhesive joints results in heavier and more expensive structures, and due to the lack of accurate material models and appropriate failure criteria. The most widespread and validated design technique is called Cohesive Zone Models. Regarding the research area of tubular adhesive joints obtained by hydroforming, since this is an emerging topic, there are few research works compared to traditional overlap geometries. The main objective of this work consists of the numerical analysis of hydroformed tubular adhesive joints subjected to tensile loads, considering the variation of material parameters (type of adhesive and adherent material) and geometric parameters. For this purpose, a validation of cohesive models is carried out through experimental and numerical results retrieved from a previous research work. Next, the aim is to numerically evaluate the mechanical strength of the joints, the plasticization of the adherents, the ductility of the joints, the evolution of the damage variable at maximum load, and the distribution of shear and peel stresses. As a complement to the numerical analysis carried out, the Taguchi Method was applied to determine an optimal joint, considering the variation of more than one control factor, and to statistically verify the significance of each parameter in the strength and ductility of the joints. Then, proposals for geometric changes were addressed with the aim of concluding, in view of the base geometry, whether the variation of one of the parameters would translate into an improvement in the mechanical properties of the joint. Finally, a market analysis was carried out that seeks to validate the ideal geometry and determine if it is possible to be implemented from an economic and industrial point of view. To this end, a mold was designed to obtain hydroformed adherents, followed by an analysis of machining costs through the cost of raw materials, tools and manufacturing processes. Validation of the cohesive models was successfully performed. After carrying out an intensive numerical study, opting for the most significant control factors and analyzing an application proposal at an industrial level, it was determined that the optimal geometry uses the adhesive Araldite® AV138, adhesive fillet angle equal to 15°, overlap length of 10 mm, outside diameter of the non-hydroformed adherent of 20 mm, exterior joggle angle of 45°, and thickness of the adherents of 2 mm. This configuration justifies the required investment, since the proposal guarantees an improvement in mechanical strength and ductility by 60 and 75%, respectively, when compared to the reference geometry.
Description
Keywords
Tubular adhesive joints Cohesive Zone Models Taguchi Method Geometric changes Market analysis