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Authors
Abstract(s)
A tecnologia de ligação por adesivos estruturais tem vindo a ser utilizada ao longo de várias décadas, permitindo solucionar diversos problemas associados a técnicas chamadas "tradicionais" de ligação, como a soldadura, a rebitagem ou a ligação aparafusada. Esta é uma alternativa viável para substituir as ligações mecânicas, devido a diversos fatores como o menor peso estrutural, menor custo de fabricação e capacidade de união de diferentes materiais. O crescente recurso a materiais compósitos em diversas indústrias, nomeadamente a aeronáutica e naval, levaram ao consequente aumento da aplicação de ligações adesivas,
por serem indicadas como forma de união destes materiais, onde é de enaltecer a sua elevada resistência à fadiga.
Uma junta adesiva está maioritariamente sujeita a esforços de corte e arrancamento e portanto o conhecimento dos módulos de elasticidade à tração (E) ou corte (G) do adesivo, e ainda as resistências máximas à tração e ao corte, não é suficiente quando se pretende prever o comportamento da mesma. Na verdade, torna-se necessário abranger na análise a plastificação progressiva verificada nas juntas adesivas antes da rotura, sendo necessário o conhecimento de parâmetros tais como a taxa crítica de libertação de energia de deformação à tração (GIc) e corte (GIIc).
Este trabalho pretende estudar um adesivo estrutural recentemente lançado no mercado, carecendo portanto da sua caracterização, para facilitar a previsão da resistência de estruturas adesivas ligadas com o mesmo. São 4 os ensaios a realizar: ensaios à tração de provetes em bruto, ensaios ao corte com a geometria Thick Adherend Shear Test (TAST), ensaios Double-Cantilever Beam (DCB) e ensaios End-Notched Flexure (ENF). Com a realização dos ensaios referidos, serão determinadas as propriedades mecânicas e de fratura à tração e ao corte, e serão fornecidos os parâmetros para a previsão da resistência de juntas adesivas com este adesivo por uma variedade de métodos, desde métodos analíticos mais expeditos até aos métodos numéricos mais avançados existentes atualmente.
Os resultados foram de encontro aos disponibilizados pelo fabricante, sempre que estes se encontravam disponíveis, obtendo-se discrepâncias bastante reduzidas nos diversos parâmetros determinados.
Bonding by structural adhesives has been used for several decades, allowing to solve various problems related to the "traditional" joining techniques, such as welding, riveting or bolting. This is a viable alternative to replace mechanical joints, due to several factors such as less structural weight, lower manufacturing cost and possibility to join different materials. The increasing use of composite materials in various fields of engineering, including aerospace and shipbuilding, led to the consequent increase in the application of adhesive joints, since these are suited to join these materials, on account of their high fatigue strength. An adhesive joint is mainly subjected to shear and peel forces. Thus, the knowledge of the tensile (E) or shear (G) moduli of the adhesive, and yet its maximum tensile and shear strength, is not enough to predict the joint behaviour. In fact, the analysis needs to account for the progressive plasticization observed in the adhesive joints before failure, being required to estimate parameters such as the critical strain energy release rate in tension (GIc) and shear (GIIc). This work aims to study a structural adhesive recently launched in the market, thus lacking proper characterization, to ease the strength prediction of bonded structures with this adhesive. With this purpose, 4 tests should be performed: tensile testing to bulk specimens, shear testing with Thick Adherend Shear Tests (TAST), and Double-Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests. These tests will enable the estimation of the mechanical and fracture properties of the adhesive in tension and shear. The parameters to predict the strength of adhesive joints with this adhesive by various methods will be provided, ranging from the easy to apply analytical methods to the most advanced numerical methods available nowadays. The obtained results were in close agreement with the data provided by the manufacturer, with small deviations in the estimated parameters.
Bonding by structural adhesives has been used for several decades, allowing to solve various problems related to the "traditional" joining techniques, such as welding, riveting or bolting. This is a viable alternative to replace mechanical joints, due to several factors such as less structural weight, lower manufacturing cost and possibility to join different materials. The increasing use of composite materials in various fields of engineering, including aerospace and shipbuilding, led to the consequent increase in the application of adhesive joints, since these are suited to join these materials, on account of their high fatigue strength. An adhesive joint is mainly subjected to shear and peel forces. Thus, the knowledge of the tensile (E) or shear (G) moduli of the adhesive, and yet its maximum tensile and shear strength, is not enough to predict the joint behaviour. In fact, the analysis needs to account for the progressive plasticization observed in the adhesive joints before failure, being required to estimate parameters such as the critical strain energy release rate in tension (GIc) and shear (GIIc). This work aims to study a structural adhesive recently launched in the market, thus lacking proper characterization, to ease the strength prediction of bonded structures with this adhesive. With this purpose, 4 tests should be performed: tensile testing to bulk specimens, shear testing with Thick Adherend Shear Tests (TAST), and Double-Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests. These tests will enable the estimation of the mechanical and fracture properties of the adhesive in tension and shear. The parameters to predict the strength of adhesive joints with this adhesive by various methods will be provided, ranging from the easy to apply analytical methods to the most advanced numerical methods available nowadays. The obtained results were in close agreement with the data provided by the manufacturer, with small deviations in the estimated parameters.
Description
Keywords
Adesivo estrutural Ductilidade Tenacidade Bulk Thick Adherend Shear Test Double- Cantilever Beam End-Notched Flexure Structural adhesive Ductility Fracture toughness