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Modelação numérica de juntas adesivas sujeitas ao impacto por modelos de dano coesivo
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Resumo(s)
Ao longo da evolução tecnológica e devido à necessidade de várias indústrias, as
ligações adesivas têm sido cada vez mais utilizadas. Este aumento da procura deve-se
às vantagens significativas que as juntas adesivas apresentam em relação aos métodos
convencionais tais como soldadura, ligações rebitadas e aparafusadas. As ligações
adesivas permitem a redução de concentrações de tensões, redução de peso e maior
facilidade de fabrico. Devido à utilização crescente destas juntas, é necessária a
existência de ferramentas que tornem possível a previsão da resistência dessas
mesmas ligações com um grau de precisão elevado. Neste domínio o Método de
Elementos Finitos (MEF) é capaz de prever o comportamento da junta. Por outro lado,
em muitos casos reais, as juntas adesivas são sujeitas a cargas dinâmicas, como por
exemplo impacto, pelo que se torna relevante a existência e validação de técnicas
numéricas de previsão de resistência nestas condições de carregamento.
Nesta tese é apresentado um estudo experimental e numérico pelo MEF de juntas de
sobreposição simples, fabricadas com um adesivo frágil e rígido (Araldite®️ AV138) e
outro de elevada flexibilidade e ductilidade (Sikaforce®️ 7752). Para a construção das
juntas foram considerados aderentes de compósito, denominado por plástico
reforçado a fibra de carbono (PRFC). Foram consideradas juntas adesivas com
diferentes comprimentos de sobreposição, submetidas a esforços de impacto, de
modo a avaliar o seu desempenho. No estudo experimental, utilizou-se uma máquina
de drop-test para submeter os provetes fabricados ao ensaio de impacto a uma
energia cinética de impacto pré-estabelecida. A análise numérica foi baseada no MEF e
em modelos de dano coesivo (MDC) e permitiu obter a distribuição de tensões na
camada adesiva, a resistência da junta e a energia absorvida. Com a comparação dos
valores numéricos aos obtidos experimentalmente é possível validar os estudos
numéricos para este tipo de solicitações dinâmicas. Para este caso de estudo a técnica
de MDC foi validada de forma positiva para o cálculo da resistência de juntas adesivas
ao impacto. Além disto, verificou-se a influência do adesivo em estudo e do
comprimento de sobreposição.
Throughout the technological evolution and due to the need of several industries, adhesive connections have been increasingly used. This increase in demand is due to the significant advantages that adhesive joints have over conventional methods such as welding, riveted and screwed connections. Adhesive connections allow the reduction of stress concentrations, weight reduction and greater ease of manufacture. Due to the increasing use of these joints, it is necessary to have tools that make it possible to predict the resistance of those same connections with a high degree of precision. In this domain the Finite Element Method (FEM) is able to predict the behaviour of the joint. On the other hand, in many real cases, adhesive joints are subjected to dynamic loads, such as impact, for which reason the existence and validation of numerical strength forecasting techniques in these loading conditions becomes relevant. This thesis presents an experimental and numerical study by the FEM of simple overlapping joints, manufactured with a brittle and rigid adhesive (Araldite®️ AV138) and another with high flexibility and ductility (Sikaforce®️ 7752). For the construction of the joints, composite adhesives were considered, known as carbon fiber reinforced plastic (CFRP). Adhesive joints with different lengths of overlap were considered, subjected to impact efforts, in order to evaluate their performance. In the experimental study, a drop-test machine was used to subject the manufactured specimens to the impact test to a pre-established impact kinetic energy. The numerical analysis was based on the FEM and cohesive damage models (CDM) and allowed to obtain the distribution of stresses in the adhesive layer, the resistance of the joint and the absorbed energy. By comparing the numerical values to those obtained experimentally, it is possible to validate the numerical studies for this type of dynamic loads. For this case study, the CDM technique was positively validated to calculate the resistance of adhesive joints to impact. In addition, the influence of the adhesive under study and the overlap length was verified.
Throughout the technological evolution and due to the need of several industries, adhesive connections have been increasingly used. This increase in demand is due to the significant advantages that adhesive joints have over conventional methods such as welding, riveted and screwed connections. Adhesive connections allow the reduction of stress concentrations, weight reduction and greater ease of manufacture. Due to the increasing use of these joints, it is necessary to have tools that make it possible to predict the resistance of those same connections with a high degree of precision. In this domain the Finite Element Method (FEM) is able to predict the behaviour of the joint. On the other hand, in many real cases, adhesive joints are subjected to dynamic loads, such as impact, for which reason the existence and validation of numerical strength forecasting techniques in these loading conditions becomes relevant. This thesis presents an experimental and numerical study by the FEM of simple overlapping joints, manufactured with a brittle and rigid adhesive (Araldite®️ AV138) and another with high flexibility and ductility (Sikaforce®️ 7752). For the construction of the joints, composite adhesives were considered, known as carbon fiber reinforced plastic (CFRP). Adhesive joints with different lengths of overlap were considered, subjected to impact efforts, in order to evaluate their performance. In the experimental study, a drop-test machine was used to subject the manufactured specimens to the impact test to a pre-established impact kinetic energy. The numerical analysis was based on the FEM and cohesive damage models (CDM) and allowed to obtain the distribution of stresses in the adhesive layer, the resistance of the joint and the absorbed energy. By comparing the numerical values to those obtained experimentally, it is possible to validate the numerical studies for this type of dynamic loads. For this case study, the CDM technique was positively validated to calculate the resistance of adhesive joints to impact. In addition, the influence of the adhesive under study and the overlap length was verified.
Descrição
Palavras-chave
Junta de sobreposição dupla adesivos estruturais junta adesiva Método de Elementos Finitos impacto ensaios experimentais Double-lap joint Structural adhesive Adhesive joint Finite element method Impact