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Abstract(s)
A utilização de juntas coladas em aplicações industriais tem vindo a aumentar nos
últimos anos, em detrimento dos métodos tradicionais de ligação tais como a soldadura,
brasagem, ligações aparafusadas e rebitadas. As juntas de sobreposição simples são o tipo
de juntas mais frequentemente utilizadas em aplicações industriais, porque são as mais
simples de fabricar. No entanto, a aplicação descentrada da carga neste tipo de junta
provoca efeitos de flexão que originam o aparecimento de tensões normais na direção da
espessura do adesivo (arrancamento), reduzindo assim a resistência da junta colada. De
uma maneira geral, existem dois tipos de métodos para reduzir as concentrações de
tensões. O primeiro é utilizar alterações no próprio material, otimizando as propriedades do
adesivo e do substrato, enquanto o segundo método envolve alterar a geometria da junta,
como por exemplo utilizando filetes de adesivo, chanfros nas extremidades dos substratos,
aplicar uma geometria ondulada ou dobrar os substratos na zona de sobreposição, ou ainda
utilizar rasgos nos substratos ao longo da sobreposição.
Neste trabalho é realizado um estudo experimental e numérico por Elementos
Finitos de duas alterações efetuadas à geometria de juntas de sobreposição simples, de
modo a aumentar a sua resistência comparativamente às juntas sem alteração geométrica.
A primeira condição efetuada foi a utilização de rasgos nas extremidades do comprimento
de sobreposição e a segunda foi a utilização de rasgos a meio do comprimento de
sobreposição. No final do estudo experimental, verificou-se que a resistência da ligação foi
significativamente melhorada com algumas das configurações testadas para cada alteração,
e foi possível estabelecer em ambos os casos a configuração ótima.
Numa fase posterior, procedeu-se à simulação numérica, que incluiu uma análise de
tensões e previsão do comportamento das juntas através de modelos de dano coesivo. A
análise permitiu obter os modos de rotura, as curvas força-deslocamento e a resistência das
juntas. Obteve-se uma concordância bastante boa com os resultados experimentais, o que
mostrou a adequabilidade do método de previsão proposto para estimar o comportamento
das juntas.
The use of bonded joints in industrial applications has been increasing in recent years over traditional joining methods such as welding, brazing, bolting and riveting. Single-lap joints are the most frequently used in industrial applications because they are the easiest to manufacture. However, the load eccentricity causes bending effects, which gives rise to normal stresses in the adhesive thickness (peel stresses), thereby reducing the strength of the bonded joint. Generally, two techniques are available to reduce stress concentrations. The first one involves changes in the material itself, by optimization of the adhesive and substrate properties, and the second one is accomplished by modifying the joint geometry, as for example applying adhesive fillet chamfers at the ends of the overlap, applying wavy or bend geometries at the overlapping regions, or even introducing slots between the overlap ends. This work consists on an experimental and numerical study (by Finite Elements) of two changes to the joint geometry in order to increase the strength of single-lap joints over the un-modified joints. The first change consisted on machining slots at the ends of the overlapping length, and in the second one, they consisted on machining slots were applied at the middle of the overlap length. At the end of the experimental study, it was found that the bond strength was significantly improved. At a later stage, a numerical simulation was performed to provide a stress analysis and to predict the joints behavior regarding the failure modes, load-displacement curves and joint strength.
The use of bonded joints in industrial applications has been increasing in recent years over traditional joining methods such as welding, brazing, bolting and riveting. Single-lap joints are the most frequently used in industrial applications because they are the easiest to manufacture. However, the load eccentricity causes bending effects, which gives rise to normal stresses in the adhesive thickness (peel stresses), thereby reducing the strength of the bonded joint. Generally, two techniques are available to reduce stress concentrations. The first one involves changes in the material itself, by optimization of the adhesive and substrate properties, and the second one is accomplished by modifying the joint geometry, as for example applying adhesive fillet chamfers at the ends of the overlap, applying wavy or bend geometries at the overlapping regions, or even introducing slots between the overlap ends. This work consists on an experimental and numerical study (by Finite Elements) of two changes to the joint geometry in order to increase the strength of single-lap joints over the un-modified joints. The first change consisted on machining slots at the ends of the overlapping length, and in the second one, they consisted on machining slots were applied at the middle of the overlap length. At the end of the experimental study, it was found that the bond strength was significantly improved. At a later stage, a numerical simulation was performed to provide a stress analysis and to predict the joints behavior regarding the failure modes, load-displacement curves and joint strength.
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Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto