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Resistência à tração de juntas compósitas em degrau: Análise experimental e numérica por modelos de dano coesivo
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Abstract(s)
O uso de ligações adesivas tem aumentado significativamente nos últimos anos e é nos
dias de hoje uma técnica de ligação predominante na indústria aeronáutica e automóvel.
Este tipo de ligação visa substituir os métodos tradicionais de fixação mecânicos na
união de estruturas. A melhoria ao longo dos anos dos vários modelos de previsão de
dano, nomeadamente através do Método de Elementos Finitos (MEF), tem contribuído
para o desenvolvimento desta técnica de ligação. Os Modelos de Dano Coesivo (MDC),
usados juntamente com o MEF, são uma ferramenta viável para a previsão de resistência
de juntas adesivas. Os MDC conciliam critérios da resistência dos materiais para a
iniciação do dano e conceitos da mecânica da fratura para a propagação da fenda. Deste
modo, existem vários fatores que condicionam o comportamento de uma junta adesiva,
bem como a necessidade de avaliar alguns desses principais fatores, tais como o tipo de
adesivo (frágil, dúctil ou uma combinação entre as duas propriedades) e geometria da
junta, mediante o comprimento de sobreposição (LO).
O trabalho realizado tem como principal objetivo avaliar de forma numérica e
experimental o desempenho mecânico de juntas adesivas em degrau submetidas a
esforços de tração, em função do comprimento de sobreposição (LO). Foram analisadas
juntas ligadas com três tipos de adesivos, o adesivo frágil Araldite® AV138, o adesivo
com características intermédias Araldite® 2015 e o adesivo dúctil Sikaforce® 7752. Para
concretizar estes objetivos, é efetuada uma análise experimental, na qual são testadas
diferentes configurações para os vários adesivos,sendo realizada a respetiva análise dos
resultados obtidos. Estes resultados experimentais são depois comparados com
resultados numéricos obtidos utilizando o software ABAQUS®, recorrendo a um módulo
integrado de MDC. Dos resultados numéricos obtidos é realizado um estudo das tensões
de arrancamento (σy) e de corte (τxy) na camada adesiva. No estudo por MDC, é também
avaliada a variável de dano SDEG (stiffness degradation) em função de LO, que permite
observar a degradação da camada adesiva desde o inico de aplicação da carga até à
rotura completa, apresentando-se depois comentários dos resultados obtidos. Com o
estudo em questão, percebe-se que o tipo de adesivo usado tem grande influência na
resistência das juntas, uma vez que o adesivo frágil apresenta melhor desempenho para
LO menores, enquanto para adesivos dúcteis são obtidas maiores capacidades de carga
para LO maiores, já que os adesivos dúcteis tem um maior capacidade de distribuição
das tensões que se desenvolvem ao longo do adesivo. De salientar que os MDC foram
uma ferramenta precisa na determinação do comportamento das diferentes juntas.
The use of adhesive bonds has increased significantly in recent years and is now a predominant bonding technique in the aeronautical and automotive industry. This type of bonding aims to replace the traditional mechanical joining methods in the union of structures. The improvement over the years of the various damage prediction models, namely through the Finite Element Method (FEM), has contributed to the development of this joining technique. Cohesive Zone Models (CZM), used together with the FEM, are a viable tool to predict the strength of adhesive joints. The CZM combines strength criteria for damage initiation and fracture mechanics concepts for crack propagation. Thus, there are several factors that condition the behavior of an adhesive joint, as well as the need to evaluate some of these main factors, such as the type of adhesive (brittle, ductile or a combination of the two properties) and joint geometry, through the overlap length (LO). The main objective of this study is to numerically and experimentally evaluate the mechanical performance of stepped-lap bonded joints submitted to tensile loads, as a function of LO. Bonded joints were analyzed with three types of adhesives, the brittle adhesive Araldite® AV138, the adhesive with intermediate characteristics Araldite® 2015 and the ductile adhesive Sikaforce® 7752. To achieve these goals, an experimental analysis is performed, in which the different configurations for the various adhesives are tested, and the respective analysis of the obtained results is performed. These experimental results are then compared with numerical results obtained using ABAQUS® software using an integrated CZM module. From the obtained numerical results, a study of peel (σy) and shear (τxy) stresses in the adhesive layer is performed. In the CZM study, the damage variable SDEG (stiffness degradation) as a function of LO is also evaluated, which allows to observe the degradation of the adhesive layer from the beginning of the application of the load until the complete rupture, and the comments of the obtained results are then presented. With the study in question, it is clear that the type of adhesive used has a major influence on the strength of the joints, since the brittle adhesive has better performance for smaller LO, while for ductile adhesives higher loading capacities for larger LO are obtained since ductile adhesives have a higher ability to distribute the stresses that develop along the adhesive. To be noted that the CZM were an accurate tool in determining the behavior of different joints.
The use of adhesive bonds has increased significantly in recent years and is now a predominant bonding technique in the aeronautical and automotive industry. This type of bonding aims to replace the traditional mechanical joining methods in the union of structures. The improvement over the years of the various damage prediction models, namely through the Finite Element Method (FEM), has contributed to the development of this joining technique. Cohesive Zone Models (CZM), used together with the FEM, are a viable tool to predict the strength of adhesive joints. The CZM combines strength criteria for damage initiation and fracture mechanics concepts for crack propagation. Thus, there are several factors that condition the behavior of an adhesive joint, as well as the need to evaluate some of these main factors, such as the type of adhesive (brittle, ductile or a combination of the two properties) and joint geometry, through the overlap length (LO). The main objective of this study is to numerically and experimentally evaluate the mechanical performance of stepped-lap bonded joints submitted to tensile loads, as a function of LO. Bonded joints were analyzed with three types of adhesives, the brittle adhesive Araldite® AV138, the adhesive with intermediate characteristics Araldite® 2015 and the ductile adhesive Sikaforce® 7752. To achieve these goals, an experimental analysis is performed, in which the different configurations for the various adhesives are tested, and the respective analysis of the obtained results is performed. These experimental results are then compared with numerical results obtained using ABAQUS® software using an integrated CZM module. From the obtained numerical results, a study of peel (σy) and shear (τxy) stresses in the adhesive layer is performed. In the CZM study, the damage variable SDEG (stiffness degradation) as a function of LO is also evaluated, which allows to observe the degradation of the adhesive layer from the beginning of the application of the load until the complete rupture, and the comments of the obtained results are then presented. With the study in question, it is clear that the type of adhesive used has a major influence on the strength of the joints, since the brittle adhesive has better performance for smaller LO, while for ductile adhesives higher loading capacities for larger LO are obtained since ductile adhesives have a higher ability to distribute the stresses that develop along the adhesive. To be noted that the CZM were an accurate tool in determining the behavior of different joints.
Description
Keywords
Método de elementos finitos Modelos de dano coesivo Mecânica da fratura Adesivo estrutural Juntas adesivas Juntas em degrau Ensaios mecânicos Finite element method Cohesive zone models Fracture mechanics Structural adhesive Adhesive joints Stepped-lap joint Mechanical tests