| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 5.9 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
Atualmente, as ligações adesivas têm vindo a ser utilizadas em várias áreas, com mais frequência nos últimos anos. Estas ligações apresentam vantagens em relação a outros métodos como a soldadura. As vantagens que se destacam são obviamente a redução significativa do peso, bem como a redução de concentração de tensões. Para a previsão da resistência das juntas, recorre-se frequentemente a técnicas da Mecânica da Fratura. A tenacidade à tração (GIC) e ao corte (GIIC) são dois dos parâmetros mais importantes para a previsão do comportamento da junta. Em relação aos adesivos, estes dividem se em dois grupos, os frágeis e os dúcteis. O Método de Elementos Finitos (MEF) tem vindo a ser usado nas últimas décadas, pois este método é bastante mais rápido na análise da resistência da junta. Mais recentemente, surgiu o Método de Elementos Finitos Extendido (MEFX), que também pode ser utilizado para prever o comportamento das juntas, carecendo, no entanto, da validação para este efeito.
Esta dissertação tem como principal objetivo a previsão do comportamento de juntas em degrau usando o MEFX, com diferentes comprimentos de sobreposição (LO). Para análise foram usados três adesivos, Araldite® AV138, Araldite® 2015 e Sikaforce® 7752, cujas propriedades são bastante diferentes. Para comparação deste trabalho numérico, foram usados os dados experimentais da dissertação de Silva [1]. As tensões de corte e arrancamento dos adesivos foram analisadas, o que possibilita uma análise do comportamento dos diferentes adesivos em diferentes condições. Para a análise usaram-se diferentes critérios de iniciação de dano usando as tensões e deformações.
Também se considerou a análise da lei de dano, nomeadamente as leis linear e exponencial de propagação de dano. O MEFX revelou ser adequado para previsão da resistência das juntas utilizando os critérios QUADS e MAXS, onde apresenta resultados bastante precisos.
Currently, adhesive bonds have been used in several areas, more frequently in recente years. These joints have advantages over other methods such as welding. The advantages that stand out are the significant reduction of weight as well as the reduction of stress concentrations. For the joint strength prediction, Fracture Mechanics techniques are often used. The tensile (GIC) and shear toughness (GIIC) are two of the most important parameters to predict the joint behaviour. In relation to adhesives, these are divided into two groups, brittle and ductile. The Finite Element Method (FEM) has been used in the last decades, because this method is much faster in the analysis of the joint strength. More recently, the Extended Finite Element Method (XFEM) has emerged, which can also be used to predict the joint behaviour, however, lacking validation for this purpose. This dissertation has as main objective the prediction of the behaviour of step joints using the XFEM, with different overlap lengths (LO). Three adhesives, Araldite® AV138, Araldite® 2015 and Sikaforce® 7752, whose properties are quite different, were used in the analysis. To compare this numerical work, the experimental data of Silva [1] was used. Peel and shear stresses of the adhesives were analysed, which allows an analysis of the behaviour of the different adhesives under different conditions. For the analysis, different damage initiation criteria were used using stresses and strains. The damage law shape was also evaluated, namely the linear and exponential damage propagation laws. The XFEM was found to be adequate to predict the joint strength using the QUADS and MAXS criteria, where it presents fairly accurate results.
Currently, adhesive bonds have been used in several areas, more frequently in recente years. These joints have advantages over other methods such as welding. The advantages that stand out are the significant reduction of weight as well as the reduction of stress concentrations. For the joint strength prediction, Fracture Mechanics techniques are often used. The tensile (GIC) and shear toughness (GIIC) are two of the most important parameters to predict the joint behaviour. In relation to adhesives, these are divided into two groups, brittle and ductile. The Finite Element Method (FEM) has been used in the last decades, because this method is much faster in the analysis of the joint strength. More recently, the Extended Finite Element Method (XFEM) has emerged, which can also be used to predict the joint behaviour, however, lacking validation for this purpose. This dissertation has as main objective the prediction of the behaviour of step joints using the XFEM, with different overlap lengths (LO). Three adhesives, Araldite® AV138, Araldite® 2015 and Sikaforce® 7752, whose properties are quite different, were used in the analysis. To compare this numerical work, the experimental data of Silva [1] was used. Peel and shear stresses of the adhesives were analysed, which allows an analysis of the behaviour of the different adhesives under different conditions. For the analysis, different damage initiation criteria were used using stresses and strains. The damage law shape was also evaluated, namely the linear and exponential damage propagation laws. The XFEM was found to be adequate to predict the joint strength using the QUADS and MAXS criteria, where it presents fairly accurate results.
Description
Keywords
Método de Elementos Finitos Método de Elementos Finitos Extendido Junta adesiva Junta em degrau Adesivo estrutural Finite Element Method Extended Finite Element Method Adhesive joint Step joint Structural Adhesive