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Abstract(s)
A utilização de ligações adesivas tem vindo a despertar bastante interesse por parte da comunidade científica. Constata-se que, ao longo dos anos, as ligações adesivas têm vindo a substituir as ligações mecânicas, permitindo combater problemas a elas associadas. As suas vantagens técnicas relacionadas com o desempenho, produtividade e custo têm vindo a despertar interesse pelas indústrias. Atualmente, este tipo de ligações está associado a aplicações estruturais, sendo aplicadas nas mais variadas áreas. Dos vários tipos de juntas existentes, as juntas em degrau apresentam a vantagem de diminuir os gradientes de tensão ao longo da zona de ligação, embora os degraus exteriores ainda se encontrem com níveis de tensões superiores aos degraus na zona interior da ligação. Uma possível maneira de reduzir este gradiente de tensões consiste na combinação deste tipo de junta com a utilização de dois adesivos, o que já provou conseguir reduzir os picos de tensões em juntas convencionais. Esta dissertação consiste no estudo experimental e numérico de juntas adesivas em degrau compostas por dois adesivos em substratos de alumínio, para vários comprimentos de sobreposição. A parte experimental do estudo consistiu no fabrico, ensaio e análise dos resultados obtidos das juntas mistas. A análise dos resultados experimentais encontra-se sob a forma de curvas P-δ, modos de rotura, resistência de juntas, energias de rotura e comparação de resultados com juntas de adesivo único. A parte numérica do estudo consistiu na aplicação do Método de Elementos Finitos através dos modelos de dano coesivo com lei triangular na previsão do comportamento das ligações. O estudo numérico consiste na explicação das condições da análise numérica e no modelo de dano utilizado, na determinação das propriedades de dano, na análise de tensões das juntas, no estudo da variável de dano, na previsão do comportamento das juntas (curvas P-δ, modos de rotura, resistência das juntas, energias de rotura) e na comparação de resultados com juntas de adesivo único. Na parte final desta dissertação também se encontra um pequeno estudo numérico para outras configurações de adesivos não estudados no trabalho experimental. Foi possível concluir que, de uma maneira geral, os modelos de dano coesivo apresentaram previsões bastante precisas. De uma maneira geral não se conseguiu obter um aumento de resistência significativo com esta técnica, mas por outro lado, obtiveram-se aumentos de energia dissipada significativos.
The use of adhesive bonds has attracted considerable interest from the scientific community. It has been noted that, over the years, adhesive bonding has been replacing mechanical bonding, allowing tackling the associated problems. Its technical advantages related to performance, productivity and cost have been attracting the industrial interest. Currently, this type of joint is associated with structural applications, being applied in the most varied areas. Of the various types of joints available, step joints have the advantage of decreasing stress gradients along the bond length, although the outer steps still encounter stress levels above the steps in the inner zone of the joint. One possible way to reduce this stress gradient is to combine this type of joint with the use of two adhesives, which has proven to reduce stress peaks in conventional joints. This dissertation consists of the experimental and numerical study of step adhesive joints composed of two adhesives on aluminium adherents, for various overlap lengths. The experimental part of the study consisted in the manufacture, testing and analysis of the results obtained from the mixed joints. The analysis of the experimental results is in the form of P-δ curves, failure modes, joint strength, maximum breaking energies and comparison of results with single adhesive joints. The numerical part of the study consisted in the application of the Finite Element Method through the models of cohesive damage with triangular law in the prediction of the behaviour of the bonds. The numerical study consists of the explanation of the conditions of the numerical analysis and the damage model used, in the determination of the damage properties, in the analysis of joint stresses, in the study of the damage variable, in the prediction of joint behaviour (P-δ curves, failure modes, joint strength, failure energies) and in the comparison of results with joints with a single adhesive. In the final part of this dissertation, there is also a small numerical study for other adhesive configurations not studied in the experimental work. It was possible to conclude that, in general, the cohesive zone models presented precise predictions. In general, no significant increase in strength was achieved with this technique but, on the other hand, significant dissipated energy increases were obtained.
The use of adhesive bonds has attracted considerable interest from the scientific community. It has been noted that, over the years, adhesive bonding has been replacing mechanical bonding, allowing tackling the associated problems. Its technical advantages related to performance, productivity and cost have been attracting the industrial interest. Currently, this type of joint is associated with structural applications, being applied in the most varied areas. Of the various types of joints available, step joints have the advantage of decreasing stress gradients along the bond length, although the outer steps still encounter stress levels above the steps in the inner zone of the joint. One possible way to reduce this stress gradient is to combine this type of joint with the use of two adhesives, which has proven to reduce stress peaks in conventional joints. This dissertation consists of the experimental and numerical study of step adhesive joints composed of two adhesives on aluminium adherents, for various overlap lengths. The experimental part of the study consisted in the manufacture, testing and analysis of the results obtained from the mixed joints. The analysis of the experimental results is in the form of P-δ curves, failure modes, joint strength, maximum breaking energies and comparison of results with single adhesive joints. The numerical part of the study consisted in the application of the Finite Element Method through the models of cohesive damage with triangular law in the prediction of the behaviour of the bonds. The numerical study consists of the explanation of the conditions of the numerical analysis and the damage model used, in the determination of the damage properties, in the analysis of joint stresses, in the study of the damage variable, in the prediction of joint behaviour (P-δ curves, failure modes, joint strength, failure energies) and in the comparison of results with joints with a single adhesive. In the final part of this dissertation, there is also a small numerical study for other adhesive configurations not studied in the experimental work. It was possible to conclude that, in general, the cohesive zone models presented precise predictions. In general, no significant increase in strength was achieved with this technique but, on the other hand, significant dissipated energy increases were obtained.
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Keywords
Método de Elementos Finitos Modelo de dano coesivo Junta em degrau Junta mista Jjunta com dois adesivos Junta adesiva Adesivo estrutural Ensaios mecânicos Finite Element Method Cohesive Zone Modelling Stepped-lap joint Mixed joint Joints with two adhesives Adhesive joint Structural adhesive Mechanical tests