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Advisor(s)
Abstract(s)
A utilização de ligações adesivas no âmbito das construções mecânicas tem vindo a aumentar significativamente ao longo da mais recente evolução industrial. O desempenho de uma junta adesiva varia consoante a sua configuração e parâmetros geométricos. Para avaliar o desempenho e a resistência deste tipo de ligação em função das propriedades do adesivo, são normalmente utilizadas metodologias numéricas baseadas no Método de Elementos Finitos (MEF). Em aplicações reais, muitas vezes as juntas adesivas são sujeitas a carregamentos dinâmicos, mais especificamente de impacto. No entanto, estes carregamentos ainda não se encontram suficientemente documentados na literatura, o que leva à necessidade do seu estudo e da validação de técnicas que consigam prever o comportamento das juntas a este tipo de carregamento. A presente dissertação avalia o efeito do comprimento de sobreposição na resistência de juntas de sobreposição simples (JSS) e juntas de sobreposição dupla (JSD), quando solicitadas ao impacto, através de ensaios experimentais e de modelos de dano coesivo (MDC). As juntas foram submetidas a um drop test e validadas através do modelo numérico, pela análise de tensões e de dano, prevendo a resistência das juntas em função do comprimento de sobreposição. De forma a avaliar o contributo das propriedades do adesivo, foram testados dois tipos de adesivo diferentes, o Araldite® AV138 e o Sikaforce® 7752, mantendo constantes os aderentes de compósito, o préimpregnado Seal® Texipreg HS 160 RM. Concluiu-se que o aumento do comprimento de sobreposição proporciona o aumento da resistência das juntas, principalmente nas que possuem um adesivo mais flexível, o Sikaforce® 7752, uma vez que este tipo de adesivo impede concentrações de tensões significativas e, sendo um adesivo dúctil, tem a capacidade de absorver os picos de tensão. Por outro lado, o adesivo Araldite® AV138, sendo mais rígido, concentra mais tensões nas juntas, impedindo um aumento significativo da resistência das mesmas com o aumento do comprimento de sobreposição. Verificou-se, ainda, que os MDC são capazes de prever a resistência das juntas ao impacto com boa precisão.
The use of adhesive joints in the field of mechanical constructions has been significantly increasing over the most recent industrial evolution. The performance of an adhesive joint varies depending on its configuration and geometrical parameters. To evaluate the performance and strength of this type of joint as a function of the adhesive properties, numerical methodologies based on the Finite Element Method (FEM) are normally used. In real applications, adhesive joints are often subjected to dynamic loading, more specifically impact. However, these loads are not yet sufficiently documented in the literature, which leads to the need for their study and the validation of techniques that can predict the behaviour of the joints for this type of loading. The present thesis evaluates the effect of the overlap length on the strength of singlelap joints (SLJ) and double-lap joints (DLJ), when impact loaded, through experimental tests and cohesive zone models (CZM). The joints were subjected to a drop test and validated through the numerical model, by the analysis of stresses and damage, predicting the joints’ strength as a function of the overlap length. In order to evaluate the contribution of the adhesive properties, two different types of adhesive were tested, Araldite® AV138 and Sikaforce® 7752, keeping constant the composite adherends, the pre-impregnated Seal® Texipreg HS 160 RM. It was concluded that the increase in the overlap length increases the joint strength, especially in those with a more flexible adhesive, Sikaforce® 7752, since this type of adhesive prevents significant stress concentrations and, being a ductile adhesive, has the ability to absorb peak stresses. On the other hand, the adhesive Araldite® AV138, being stiffer, concentrates more stresses in the joints, preventing a significant strength improvement with the increase in the overlap length. It was also found that the CZM are able to predict the impact joints’ strength with good precision.
The use of adhesive joints in the field of mechanical constructions has been significantly increasing over the most recent industrial evolution. The performance of an adhesive joint varies depending on its configuration and geometrical parameters. To evaluate the performance and strength of this type of joint as a function of the adhesive properties, numerical methodologies based on the Finite Element Method (FEM) are normally used. In real applications, adhesive joints are often subjected to dynamic loading, more specifically impact. However, these loads are not yet sufficiently documented in the literature, which leads to the need for their study and the validation of techniques that can predict the behaviour of the joints for this type of loading. The present thesis evaluates the effect of the overlap length on the strength of singlelap joints (SLJ) and double-lap joints (DLJ), when impact loaded, through experimental tests and cohesive zone models (CZM). The joints were subjected to a drop test and validated through the numerical model, by the analysis of stresses and damage, predicting the joints’ strength as a function of the overlap length. In order to evaluate the contribution of the adhesive properties, two different types of adhesive were tested, Araldite® AV138 and Sikaforce® 7752, keeping constant the composite adherends, the pre-impregnated Seal® Texipreg HS 160 RM. It was concluded that the increase in the overlap length increases the joint strength, especially in those with a more flexible adhesive, Sikaforce® 7752, since this type of adhesive prevents significant stress concentrations and, being a ductile adhesive, has the ability to absorb peak stresses. On the other hand, the adhesive Araldite® AV138, being stiffer, concentrates more stresses in the joints, preventing a significant strength improvement with the increase in the overlap length. It was also found that the CZM are able to predict the impact joints’ strength with good precision.
Description
Keywords
Previsão de resistência Método de Elementos Finitos Junta de sobreposição simples Junta de sobreposição dupla Ensaios de impacto Modelos de dano coesivo Drop test Strength prediction Finite Element Method Single-lap joint Double-lap joint Impact tests Cohesive zone models