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Abstract(s)
As juntas adesivas constituem uma boa alternativa às ligações soldadas e aparafusadas, uma vez que permitem evitar alguns problemas a estas associados. As juntas adesivas apresentam várias vantagens, tais como uma distribuição de tensões mais uniforme quando comparada com ligações soldadas ou aparafusadas, amortecimento de vibrações, possibilidade de ligações entre materiais diferentes, projeto mais flexível, acabamentos com contornos regulares, contacto contínuo entre componentes, peso e custo reduzidos, entre outros. As juntas adesivas podem ser solicitadas a vários esforços. Contudo, estão maioritariamente solicitadas a esforços de corte e arrancamento. Assim, é importante compreender o comportamento das juntas nestas solicitações, e o conhecimento de alguns parâmetros tais como o módulo de elasticidade longitudinal (E), a tensão de corte (τ), o módulo de corte (G), a taxa crítica de libertação de energia à tração de corte (GIc e GIIc, respetivamente), entre outros. Adicionalmente, a modificação de adesivos é também muito usada com o objetivo de alterar o adesivo quer a nível de propriedades mecânicas, como a nível de processo de cura e aspeto. A modificação de adesivos pode ocorrer recorrendo a diferentes reforços como partículas ou fibras. Este trabalho visa a estudar um adesivo recentemente lançado para o mercado, e que carece de caracterização para facilitar a previsão da resistência das respetivas juntas. Adicionalmente, o adesivo foi também estudado com a adição de microfibras de vidro em quatro percentagens mássicas diferentes (0 phr (phr - per hundred resin), 15 phr, 35 phr e 55 phr). Isto visa a compreender o comportamento do adesivo com a adição de microfibras de vidro e qual o impacto nas suas propriedades. São realizados cinco ensaios para caracterizar o adesivo: ensaios à tração de provetes de adesivo maciço, ensaios ao corte com geométrica block shear (BS), ensaios Double-Cantilever Beam (DCB), ensaios End-Notched Flexure (ENF) e ensaios em modo misto com a geometria de junta de sobreposição simples (JSS). Realizando os ensaios referidos são determinadas as propriedades mecânicas e de fratura à tração e ao corte. Os resultados, na sua grande maioria, foram de encontro com os disponibilizados pelo fabricante, com a exceção do ensaio BS. A adição de microfibras de vidro revelou no geral um aumento da rigidez e das propriedades de fratura, mas uma redução da resistência mecânica.
Adhesive joints are a good alternative to welded and fastened joints, as they avoid some problems associated with them. Adhesive joints have several advantages, such as a more uniform stress distribution when compared to welded or bolted joints, vibration dampening, possibility of joining different materials, more flexible design, finishing with regular contours, continuous contact between components, weight and reduced cost, among others. Adhesive joints can be loaded under various efforts. However, they are mostly loaded to shear and peel loadings. Thus, it is important to understand the behavior of the joints under these loadings, and the knowledge of some parameters such as the longitudinal elastic modulus (E), the shear stress (τ), the shear modulus (G), the critical strain energy release rate under tension and shear (GIc and GIIc, respectively), among others. Additionally, the modification of adhesives is also widely used in order to change the adhesive both in terms of mechanical properties, as well as in terms of the curing process and appearance. The modification of adhesives can take place using different reinforcements such as particles or fibers. This work aims to study an adhesive recently launched on the market, which still requires characterization to facilitate the prediction of the strength of the respective joints. Additionally, the adhesive was also studied with the addition of glass microfibers in four different mass percentages (0 phr (phr - per hundred resin), 15 phr, 35 phr and 55 phr). This aims to understand the behavior of the adhesive with the addition of glass microfibers and the impact on its properties. Five tests are carried out to characterize the adhesive: tensile tests of bulk adhesive specimens, shear tests with block shear (BS) geometry, Double-Cantilever Beam (DCB) tests, End-Notched Flexure (ENF) tests and mixed mode tests with single-lap joints (SLJ). Carrying out the aforementioned tests, the mechanical and fracture properties under tension and shear are determined. The results were mostly in line with those provided by the manufacturer, with the exception of the BS test. The addition of glass microfibers revealed overall an increase in the stiffness and fracture properties but a reduction of the mechanical strength.
Adhesive joints are a good alternative to welded and fastened joints, as they avoid some problems associated with them. Adhesive joints have several advantages, such as a more uniform stress distribution when compared to welded or bolted joints, vibration dampening, possibility of joining different materials, more flexible design, finishing with regular contours, continuous contact between components, weight and reduced cost, among others. Adhesive joints can be loaded under various efforts. However, they are mostly loaded to shear and peel loadings. Thus, it is important to understand the behavior of the joints under these loadings, and the knowledge of some parameters such as the longitudinal elastic modulus (E), the shear stress (τ), the shear modulus (G), the critical strain energy release rate under tension and shear (GIc and GIIc, respectively), among others. Additionally, the modification of adhesives is also widely used in order to change the adhesive both in terms of mechanical properties, as well as in terms of the curing process and appearance. The modification of adhesives can take place using different reinforcements such as particles or fibers. This work aims to study an adhesive recently launched on the market, which still requires characterization to facilitate the prediction of the strength of the respective joints. Additionally, the adhesive was also studied with the addition of glass microfibers in four different mass percentages (0 phr (phr - per hundred resin), 15 phr, 35 phr and 55 phr). This aims to understand the behavior of the adhesive with the addition of glass microfibers and the impact on its properties. Five tests are carried out to characterize the adhesive: tensile tests of bulk adhesive specimens, shear tests with block shear (BS) geometry, Double-Cantilever Beam (DCB) tests, End-Notched Flexure (ENF) tests and mixed mode tests with single-lap joints (SLJ). Carrying out the aforementioned tests, the mechanical and fracture properties under tension and shear are determined. The results were mostly in line with those provided by the manufacturer, with the exception of the BS test. The addition of glass microfibers revealed overall an increase in the stiffness and fracture properties but a reduction of the mechanical strength.
Description
Keywords
Juntas adesivas Aditivação de adesivos Propriedades mecânicas Propriedades de Fratura Propriedades em modo misto Microfibras Adhesive joints Adhesive additivation Mechanical properties Fracture properties Mixed mode properties Microfibers