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Advisor(s)
Abstract(s)
As ligações adesivas são um método de união cada vez mais utilizado na conceção de estruturas mecânicas, porque esta técnica apresenta vantagens significativas em comparação com as ligações tradicionais. Entre as vantagens, destacam-se a redução de peso e possibilidade de unir diferentes materiais, incluindo compósitos, sem danificar as estruturas a ligar. Os adesivos comerciais variam desde resistentes e frágeis a menos resistentes e dúcteis. Existem adesivos, como os poliuretanos, que combinam elevada resistência e ductilidade. Entre as diferentes configurações de junta disponíveis para o projetista encontram-se as juntas tubulares que apresentam atualmente algumas aplicações industriais mas que ainda carecem de estudo aprofundado, como existe por exemplo para as juntas de sobreposição simples. O objetivo desta dissertação é comparar o desempenho à tração de juntas adesivas tubulares de alumínio (AW6082-T651) ligadas com três adesivos (Araldite® AV138, Araldite® 2015 e SikaForce® 7752), considerando a variação dos parâmetros geométricos principais e alterações geométricas que potencialmente promovam o aumento de resistência, através de um estudo numérico pelo Método de Elementos Finitos realizado no ABAQUS®. O parâmetro principal a estudar é o comprimento de sobreposição (L0). As alterações geométricas consistem na criação de chanfro interior, de chanfro exterior, na adição de um filete de adesivo e na combinação de alterações geométricas, nomeadamente entre um chanfro interior e um filete de adesivo. A análise numérica consistiu na utilização de modelos de dano coesivo (MDC) modelação da camada de adesivo. Para o efeito, foi realizada uma validação inicial da técnica numérica com dados experimentais obtidos de trabalhos anteriores. No presente trabalho foram estudadas as tensões de arrancamento e de corte em regime elástico e testada a capacidade do método MDC na previsão de resistência das juntas. No estudo paramétrico numérico em juntas adesivas tubulares verificou-se que existe um aumento significativo de força máxima (Pmáx) com o aumento de L0. Na análise dos parâmetros geométricos observou-se que, genericamente, as juntas adesivas com o adesivo Araldite® 2015 obtiveram os resultados de Pmáx mais elevados. O estudo de alterações geométricas mostrou que a combinação de alterações geométricas, nomeadamente entre um chanfro interior e um filete de adesivo, permitiu uma redução significativa das concentrações de tensões e consequentemente o aumento do Pmáx.
Adhesive joints are an increasingly used joining method in the design of mechanical structures, because this technique has significant advantages compared to traditional joints. Among the advantages, the reduction in weight and the possibility of joining different materials, including composites, without damaging the structures to be bonded can be highlighted. Commercial adhesives range from strong and brittle to less strong and ductile. There are adhesives, such as polyurethanes, that combine high strength and ductility. Among the different joint configurations available to the designer are tubular joints, which currently have some industrial applications but still need a deep study, as it exists for example for single-lap joints. The objective of this thesis is to compare the tensile performance of aluminium tubular adhesive joints (AW6082-T651) joined with three adhesives (Araldite® AV138, Araldite® 2015 and SikaForce® 7752), considering the variation of the main geometric parameters and geometric changes that potentially promote a strength improvement, through a numerical study by the Finite Element Method carried out in ABAQUS®. The main parameter to be studied is the overlap length (L0). The geometric changes consist of creating an inner chamfer, an outer chamfer, adding an adhesive fillet and combining geometric changes, namely between an internal chamfer and an adhesive fillet. The numerical analysis consisted of using cohesive zone models (CZM) to model the adhesive layer. For this purpose, an initial validation of the numerical technique was carried out with experimental data obtained from previous works. In the present work, peel and shear stresses in the elastic regime were studied and the ability of CZM to predict the joint strength was tested. In the numerical parametric study on tubular adhesive joints, it was verified that there is a significant increase in the maximum load (Pmáx) with the increase of L0. In the analysis of the geometric parameters, it was observed that, generally, the adhesive joints with the adhesive Araldite® 2015 obtained the highest Pmáx results. The study of geometric changes showed that the combination of geometric changes, namely between an inner chamfer and an adhesive fillet, enabled a significant reduction in stress concentrations and, consequently, an increase in Pmáx.
Adhesive joints are an increasingly used joining method in the design of mechanical structures, because this technique has significant advantages compared to traditional joints. Among the advantages, the reduction in weight and the possibility of joining different materials, including composites, without damaging the structures to be bonded can be highlighted. Commercial adhesives range from strong and brittle to less strong and ductile. There are adhesives, such as polyurethanes, that combine high strength and ductility. Among the different joint configurations available to the designer are tubular joints, which currently have some industrial applications but still need a deep study, as it exists for example for single-lap joints. The objective of this thesis is to compare the tensile performance of aluminium tubular adhesive joints (AW6082-T651) joined with three adhesives (Araldite® AV138, Araldite® 2015 and SikaForce® 7752), considering the variation of the main geometric parameters and geometric changes that potentially promote a strength improvement, through a numerical study by the Finite Element Method carried out in ABAQUS®. The main parameter to be studied is the overlap length (L0). The geometric changes consist of creating an inner chamfer, an outer chamfer, adding an adhesive fillet and combining geometric changes, namely between an internal chamfer and an adhesive fillet. The numerical analysis consisted of using cohesive zone models (CZM) to model the adhesive layer. For this purpose, an initial validation of the numerical technique was carried out with experimental data obtained from previous works. In the present work, peel and shear stresses in the elastic regime were studied and the ability of CZM to predict the joint strength was tested. In the numerical parametric study on tubular adhesive joints, it was verified that there is a significant increase in the maximum load (Pmáx) with the increase of L0. In the analysis of the geometric parameters, it was observed that, generally, the adhesive joints with the adhesive Araldite® 2015 obtained the highest Pmáx results. The study of geometric changes showed that the combination of geometric changes, namely between an inner chamfer and an adhesive fillet, enabled a significant reduction in stress concentrations and, consequently, an increase in Pmáx.
Description
Keywords
Ligações adesivas Junta adesiva tubular Adesivo estrutural Método de elementos finitos Modelo de dano coesivo Previsão de resistência Otimização da junta Adhesive joints Tubular adhesive joint Structural adhesive Finite element method Cohesive zone models Strength prediction Joint optimization