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Advisor(s)
Abstract(s)
As ligações adesivas são, cada vez mais, uma alternativa utilizada em aplicações de engenharia. De facto, estas ligações apresentam várias vantagens em relação a outros métodos de ligação mais convencionais. A melhor distribuição de tensões, o baixo peso, a possibilidade de unir materiais dissimilares, o fácil atravancamento e a resistência à corrosão são algumas das características das ligações adesivas que as tornam tão úteis. A possibilidade de automatização e o custo não muito elevado tornam-nas viáveis. Apesar de bem conhecidas as propriedades dos adesivos, as juntas adesivas são influenciadas por vários outros parâmetros. Em função das muitas variáveis existentes, os comportamentos de juntas adesivas variam muito e são por vezes imprevisíveis. A crescente utilização deste tipo de ligação torna necessária a existência de ferramentas que auxiliem o seu projeto. O Método de Elementos Finitos, combinado com critérios ou modelos de dano, tem-se revelado eficaz na simulação e previsão do comportamento de juntas adesivas, possibilitando a redução de tempo de projeto e dos custos. Entre os critérios ou modelos de dano associados ao Método de Elementos Finitos, os modelos de dano coesivo revelam bastante eficácia, combinando parâmetros de resistência e tenacidade para prever o desempenho de juntas adesivas. O principal objetivo desta dissertação é o estudo da influência dos parâmetros coesivos na previsão do comportamento e da resistência de juntas de sobreposição simples solicitadas ao impacto. A influência dos parâmetros coesivos foi estudada fazendo variar cada um destes parâmetros mantendo os restantes inalterados. Este estudo conta com os adesivos Araldite® AV138 (elevada rigidez) e Nagase Chemtex® XNR6852 E-2 (elevada tenacidade), para tentar compreender esta influência utilizando adesivos com diferentes propriedades. Os parâmetros coesivos estudados apresentam uma notória influência no comportamento dos adesivos e, consequentemente, na previsão de resistência de juntas adesivas.
Adhesive bonds are increasingly becoming an alternative to engineering applications. In fact, these bonds have several advantages over more conventional joining methods. The improved stress distribution, low weight, the ability to bond dissimilar materials and the resistance to corrosion are some of the characteristics of the adhesive bonds that make them so useful. The possibility of automation and the moderate cost make them viable. Although the properties of the adhesives are well known, adhesive joints are influenced by several other parameters. Due to many variables, the behaviour of adhesive joints widely varies and sometimes it is unpredictable. The increasing use of this type of joining requires suitable tools to support the design process. The Finite Element Method, combined with damage criteria, has proven to be an effective way to simulate and predict the behaviour of adhesive joints, making it possible to reduce design time and costs. Among the damage criteria or models associated with the Finite Element Method, cohesive zone models (CZM) are highly effective, combining strength and toughness parameters to predict the performance of adhesive joints. The main purpose of this work is to study the influence of the cohesive parameters in predicting the behaviour and strength of single-lap joints subjected to impact loads. The influence of the cohesive parameters was studied by varying each of these parameters while keeping the remaining ones. Araldite® AV138 (high stiffness) and Nagase Chemtex® XNR6852 E-2 (high toughness) are the chosen adhesives in order to try to understand this influence using adhesives with different properties. The cohesive parameters studied have a significant influence on the behaviour of the adhesives and, consequently, on the strength prediction of adhesive joints.
Adhesive bonds are increasingly becoming an alternative to engineering applications. In fact, these bonds have several advantages over more conventional joining methods. The improved stress distribution, low weight, the ability to bond dissimilar materials and the resistance to corrosion are some of the characteristics of the adhesive bonds that make them so useful. The possibility of automation and the moderate cost make them viable. Although the properties of the adhesives are well known, adhesive joints are influenced by several other parameters. Due to many variables, the behaviour of adhesive joints widely varies and sometimes it is unpredictable. The increasing use of this type of joining requires suitable tools to support the design process. The Finite Element Method, combined with damage criteria, has proven to be an effective way to simulate and predict the behaviour of adhesive joints, making it possible to reduce design time and costs. Among the damage criteria or models associated with the Finite Element Method, cohesive zone models (CZM) are highly effective, combining strength and toughness parameters to predict the performance of adhesive joints. The main purpose of this work is to study the influence of the cohesive parameters in predicting the behaviour and strength of single-lap joints subjected to impact loads. The influence of the cohesive parameters was studied by varying each of these parameters while keeping the remaining ones. Araldite® AV138 (high stiffness) and Nagase Chemtex® XNR6852 E-2 (high toughness) are the chosen adhesives in order to try to understand this influence using adhesives with different properties. The cohesive parameters studied have a significant influence on the behaviour of the adhesives and, consequently, on the strength prediction of adhesive joints.
Description
Keywords
Método de Elementos Finitos Impacto Modelos de dano coesivo Junta de sobreposição simples Finite Element Method Impact Cohesive Zone Models Single-lap Joint