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Abstract(s)
A aplicação de adesivos estruturais vem ganhando cada vez mais espaço na indústria. Isso deve-se, sobretudo, ao facto de cada vez mais estudo serem feitos nesta área científica, o que permite chegar ao conhecimento de como se comportam estes componentes em certos meios e sob determinadas condições. Assim pode-se compreender porque é que os adesivos oferecem certas vantagens em relação aos métodos convencionais de união mecânica. Os substratos a ligar entre si, podem assumir diversas geometrias e serem de materiais distintos, dependendo da estrutura a ligar. Essas vantagens tornam os projetos de engenharia mais económicos e deixam as estruturas mais leves, ganhando tempo na assemblagem dos componentes. De entre os ramos de aplicação que mais utilizam estes tipos de ligação destacam-se a indústrias aeronáutica e automotiva. Essas indústrias investiram tempo e dinheiro para que estudos se fizessem na investigação dos adesivos e suas propriedades e, com isso, chegaram à conclusão que esta poderia ser uma solução viável para muitas aplicações nos seus respetivos ramos, quer na aeronáutica, automotiva e eletrónica. O objetivo principal desta tese centra-se no estudo numérico de juntas adesivas sujeitas a esforços de impacto. No desenvolvimento estão incluídos o planeamento do trabalho, a abordagem da metodologia numérica para a modelação dos modelos de dano coesivo ao impacto com recurso ao software ABAQUS®, assim como um estudo numérico paramétrico realizado sobre a influência na resistência das juntas adesivas das variáveis geométricas principais, como o comprimento de sobreposição (L0) e a espessura dos substratos (tp), e o estudo com alterações geométricas, como a introdução de chanfros interiores (θ) e exteriores () nos substratos, e a introdução de um fillet de adesivo (). São apresentados os gráficos com a distribuição das tensões normais y e das tensões de corte xy, assim como curvas P-, energia absorvida (Eabs) e carga máxima (Pmáx) para todas as juntas ensaiadas. Neste trabalho conclui-se que a resistência das juntas aumenta para adesivos rígidos, como é o caso dos adesivos Araldite® AV138 e Nagase® ChemtexXNR6852 E-2 e diminui para adesivos flexíveis, como é o caso do 3M® DP8005. Quando os parâmetros geométricos L0 e são incrementados, observa-se um aumento significativo da resistência da junta adesiva, tanto quanto a Pmáx como Eabs, uma vez que aumenta a área de secção resistente. Por sua vez, o incremento do parâmetro geométrico tp aumenta ligeiramente o valor de Pmáx suportada pelas juntas, mas diminui o valor de Eabs essencialmente devido ao aumento da rigidez dos substratos. Os paramentos θ e não trazem benefício à resistência das juntas, levando à perda da capacidade de suportar carga pela junta (Pmáx), bem como à perda da capacidade desta em absorver energia (Eabs), essencialmente devido à perda de rigidez quando θ e diminuem.
The application of structural adhesives has been increasing space in the industry. This is mainly due to the fact that more and more studies are being carried out in this scientific area, which makes it possible to get to know how these components behave in certain environments and under certain conditions. Thus, it can be understood why adhesives offer certain advantages over conventional mechanical bonding methods. The adherends to be joined together can assume different geometries and be of different materials, depending on the structure to be joined. These advantages make engineering projects more economical and make structures lighter, saving time in assembling components. Among the fields of application that most use these types of connections, the aeronautical and automotive industries stand out. These industries invested time and money for studies to be carried out in the investigation of adhesives and their properties and, with that, it was concluded that this could be a viable solution for many applications in their respective fields, whether in aeronautics, automotive and electronics. The main objective of this thesis focuses on the numerical study of adhesive joints subjected to impact loads. The development includes the planning of the work, the numerical methodology approach for modeling cohesive impact damage models using the ABAQUS® software, as well as a parametric numerical study carried out on the influence on the strength of the adhesive joints of the main variables, such as the overlap length (L0) and adherends thickness (tp), and the study of the geometrical changes, such as the introduction of inner (θ) and outer () chamfers on adherends, and the introduction of adhesive fillet (). Graphics with the distribution of y normal stresses and xy shear stresses are presented, as well as P- curves, absorbed energy (Eabs) and maximum load (Pmax ) for all joints tested. In this work, it was concluded that the strength of adhesive joints increases for stiff adhesives, as is the case of Araldite® AV138 and Nagase® ChemtexXNR6852 E-2 and decreases for flexible adhesives, as is the case of 3M® DP8005. When the geometric parameters L0 and are increased, a significant increase in the strength of the adhesive joint is observed, both in terms of Pmax and Eabs, because it increases the resistant sectional area. In turn, increasing the geometric parameter tp slightly increases the value of Pmax supported by the joints, but decreases the value of Eabs, essentially due to the increase in the stiffness of the adherends. The θ and parameters do not benefit the strength of the joints, leading to a loss of load-bearing capacity of the joint (Pmax), as well as a loss of its ability to absorb energy (Eabs), essentially due to the loss of stiffness when θ and decrease.
The application of structural adhesives has been increasing space in the industry. This is mainly due to the fact that more and more studies are being carried out in this scientific area, which makes it possible to get to know how these components behave in certain environments and under certain conditions. Thus, it can be understood why adhesives offer certain advantages over conventional mechanical bonding methods. The adherends to be joined together can assume different geometries and be of different materials, depending on the structure to be joined. These advantages make engineering projects more economical and make structures lighter, saving time in assembling components. Among the fields of application that most use these types of connections, the aeronautical and automotive industries stand out. These industries invested time and money for studies to be carried out in the investigation of adhesives and their properties and, with that, it was concluded that this could be a viable solution for many applications in their respective fields, whether in aeronautics, automotive and electronics. The main objective of this thesis focuses on the numerical study of adhesive joints subjected to impact loads. The development includes the planning of the work, the numerical methodology approach for modeling cohesive impact damage models using the ABAQUS® software, as well as a parametric numerical study carried out on the influence on the strength of the adhesive joints of the main variables, such as the overlap length (L0) and adherends thickness (tp), and the study of the geometrical changes, such as the introduction of inner (θ) and outer () chamfers on adherends, and the introduction of adhesive fillet (). Graphics with the distribution of y normal stresses and xy shear stresses are presented, as well as P- curves, absorbed energy (Eabs) and maximum load (Pmax ) for all joints tested. In this work, it was concluded that the strength of adhesive joints increases for stiff adhesives, as is the case of Araldite® AV138 and Nagase® ChemtexXNR6852 E-2 and decreases for flexible adhesives, as is the case of 3M® DP8005. When the geometric parameters L0 and are increased, a significant increase in the strength of the adhesive joint is observed, both in terms of Pmax and Eabs, because it increases the resistant sectional area. In turn, increasing the geometric parameter tp slightly increases the value of Pmax supported by the joints, but decreases the value of Eabs, essentially due to the increase in the stiffness of the adherends. The θ and parameters do not benefit the strength of the joints, leading to a loss of load-bearing capacity of the joint (Pmax), as well as a loss of its ability to absorb energy (Eabs), essentially due to the loss of stiffness when θ and decrease.
Description
Keywords
Ligações Adesivas Juntas Adesivas Tubulares Adesivos Estruturais Solicitações Estáticas e Dinâmicas Modelos CZM Métodos Numéricos Adhesive Bonds Tubular Adhesive Bonds Structural Adhesives Static and Dynamic Loadings CZM Models Numerical methods