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Abstract(s)
A utilização de juntas adesivas em aplicações industriais tem vindo a aumentar, em substituição dos métodos tradicionais tais como a soldadura, brasagem e ligações aparafusadas e rebitadas. Este facto deve-se às vantagens que estas oferecem, como o facto de serem mais leves, comportarem-se bem sob cargas cíclicas ou de fadiga, permitirem a ligação de materiais diferentes e apresentarem menores concentrações de tensões. De modo a aumentar a confiança no projeto de estruturas adesivas, é importante conseguir prever com precisão a sua resistência mecânica e respetivas propriedades de fratura (taxa crítica de libertação de energia de deformação à tração, GIC, e corte, GIIC). Estas propriedades estão diretamente relacionadas com a Mecânica da Fratura e são estimadas através de uma análise energética. Para este efeito, distinguem-se três tipos de modelos: modelos que necessitam da medição do comprimento de fenda durante a propagação do dano, modelos que utilizam um comprimento de fenda equivalente e métodos baseados no integral J. Como na maioria dos casos as solicitações ocorrem em modo misto (combinação de tração com corte), é de grande importância a perceção da fratura nestas condições, nomeadamente das taxas de libertação de energia relativamente a diferentes critérios ou envelopes de fratura. Esta comparação permite, por exemplo, averiguar qual o melhor critério energético de rotura a utilizar em modelos numéricos baseados em Modelos de Dano Coesivo.
Neste trabalho é realizado um estudo experimental e um numérico utilizando o ensaio Single-Leg Bending (SLB) em provetes colados com três tipos de adesivos, de forma a estudar e comparar as suas propriedades de fratura. Para tal, são aplicados alguns modelos de redução da taxa de libertação de energia de deformação à tração, GI, e corte, GII, enquadrados nos modelos que necessitam da medição do comprimento de fenda e nos modelos que utilizam um comprimento de fenda equivalente. Numa fase posterior, procedeu-se à análise e comparação dos resultados adquiridos durante a fase experimental de GI e GII de cada adesivo. A discussão de resultados foi também feita através da análise dos valores obtidos em diversos envelopes de fratura, no sentido de averiguar qual o critério de rotura mais adequado a considerar para cada adesivo. Em geral, foi obtida uma concordância bastante boa entre métodos de determinação de GI e GII. Nos ensaios numéricos foi possível retratar o comportamento verificado nos ensaios experimentais, tendo sido validados os critérios de propagação escolhidos através da análise dos resultados experimentais.
The use of adhesive joints in industrial applications has been increasing, replacing traditional methods such as welding, brazing and bolted and riveted joints. This is due to the advantages they offer, such as the fact that they are lighter, behave well under cyclic loads or fatigue, enable the connection of different materials and have lower stress concentrations. To increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their mechanical strength and corresponding fracture properties (critical strain energy release rate in tension, GIC, and shear, GIIC). These properties are directly related to Fracture Mechanics and are estimated through an energetic analysis. To this end, there are three types of models: models that require the measurement of crack length during propagation of the damage, models that use an equivalent crack length and methods based on the J integral. As in most cases loads induce mixed mode (combination of tension with shear), it is of great importance the perception of fracture in these conditions, especially in the energy release rates for different criteria or fracture envelopes. This comparison allows, for example, to find out which is the best energetic criterion of failure to use in numerical models based on cohesive zone models. This work presents an experimental and numerical study using the Single-Leg Bending (SLB) test on specimens bonded with three types of adhesive, in order to study and compare their fracture properties. For this purpose, some data reduction methods were applied to estimate the strain energy release rate in tension, GI, and shear, GII, within the scope of the models that require the measurement of crack length and models using an equivalent crack length. At a later stage, the analysis and comparison of results obtained during the experimental phase of GI and GII of each adhesive were addressed. The discussion of results was also done by the analysis of the values obtained in several fracture envelopes, to ascertain which criteria are more appropriate for each adhesive. Overall, a very good agreement it was obtained between methods for the determination of GI and GII. In the numerical simulations it was possible to reproduce the observed behavior of the experimental tests, with a positive validation of the chosen propagation criteria have been validated propagation criteria obtained from the experimental results.
The use of adhesive joints in industrial applications has been increasing, replacing traditional methods such as welding, brazing and bolted and riveted joints. This is due to the advantages they offer, such as the fact that they are lighter, behave well under cyclic loads or fatigue, enable the connection of different materials and have lower stress concentrations. To increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their mechanical strength and corresponding fracture properties (critical strain energy release rate in tension, GIC, and shear, GIIC). These properties are directly related to Fracture Mechanics and are estimated through an energetic analysis. To this end, there are three types of models: models that require the measurement of crack length during propagation of the damage, models that use an equivalent crack length and methods based on the J integral. As in most cases loads induce mixed mode (combination of tension with shear), it is of great importance the perception of fracture in these conditions, especially in the energy release rates for different criteria or fracture envelopes. This comparison allows, for example, to find out which is the best energetic criterion of failure to use in numerical models based on cohesive zone models. This work presents an experimental and numerical study using the Single-Leg Bending (SLB) test on specimens bonded with three types of adhesive, in order to study and compare their fracture properties. For this purpose, some data reduction methods were applied to estimate the strain energy release rate in tension, GI, and shear, GII, within the scope of the models that require the measurement of crack length and models using an equivalent crack length. At a later stage, the analysis and comparison of results obtained during the experimental phase of GI and GII of each adhesive were addressed. The discussion of results was also done by the analysis of the values obtained in several fracture envelopes, to ascertain which criteria are more appropriate for each adhesive. Overall, a very good agreement it was obtained between methods for the determination of GI and GII. In the numerical simulations it was possible to reproduce the observed behavior of the experimental tests, with a positive validation of the chosen propagation criteria have been validated propagation criteria obtained from the experimental results.
Description
Keywords
Single-Leg Bending Ligação adesiva Mecânica da fratura Tenacidade à fratura Envelope de fratura Método de Elementos Finitos Modelo de dano coesivo Single-Leg Bending Adhesive joint Fracture mechanics Fracture toughness Fracture envelope Finite Element Method Cohesive zone models