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Abstract(s)
As juntas adesivas estão largamente difundidas na indústria nos dias de hoje substituindo em muitas situações as ligações mecânicas. Até há algumas décadas, um dos principais entraves à sua disseminação foi a falta de modelos que permitissem correctamente prever a resistência das juntas adesivas que resultava em estruturas fortemente sobredimensionadas, levando a um elevado custo de fabrico. Actualmente, técnicas de modelação como os modelos de dano coesivo (MDC) já demonstraram que é possível prever a resistência de juntas adesivas com precisão, como descrito no estudo de Carneiro [1]. As juntas adesivas são particularmente sensíveis a esforços de arrancamento, especialmente quando são usados adesivos mais frágeis como é o caso do Araldite® AV138. Para tentar melhorar a resistência de juntas em T, nesta dissertação é estudada a técnica de bi-adesivo. Esta técnica consiste na utilização de dois adesivos, colocando um adesivo mais dúctil nas extremidades da junta e um mais frágil na zona central. Para testar este método em juntas em T, nesta dissertação são usadas várias combinações dos adesivos Araldite® AV138, Araldite® 2015 e Sikaforce® 7752. Também são testados variados comprimentos do adesivo central, mantendo sempre a simetria da junta. Para avaliar estas combinações foi feito um estudo numérico usando a técnica de MDC, no software ABAQUS®, aplicando à junta um deslocamento de 6 mm e considerando um encastramento do aderente de base. Com o presente trabalho, foi inicialmente possível validar a técnica de MDC com resultados experimentais. O trabalho numérico que se seguiu mostrou que a resistência das juntas em T depende de forma significativa da combinação de adesivos usados, e que é possível atingir incrementos de resistência e energia dissipada significativos relativamente às juntas de adesivo único.
Adhesive joints are widely used in the industry today, replacing mechanical joints in many situations. Until a few decades ago, one of the main obstacles to its dissemination was the lack of models that could correctly predict the strength of adhesive joints, which resulted in strongly oversized structures, and leading to a high manufacturing cost. Currently, modeling techniques such as cohesive zone models (CZM) have already demonstrated that it is possible to accurately predict the strength of adhesive joints, as described in the study by Carneiro [1]. Adhesive joints are particularly sensitive to peel stresses, especially when more brittle adhesives such as Araldite® AV138 are used. To try to improve the strength of T joints, in this dissertation the bi-adhesive technique is studied. This technique consists of using two adhesives, placing a more ductile adhesive at the overlap ends and a brittle one in the central area. To test this method in T joints, in this dissertation, various combinations of the adhesives Araldite® AV138, Araldite® 2015 and Sikaforce® 7752 are used. Various lengths of the central adhesive are also tested, always keeping joint symmetry. To evaluate these combinations, a numerical study was carried out using the CZM technique, in the ABAQUS® software, applying a displacement of 6 mm to the joint and clamping the base adherend. With the present work, it was initially possible to validate the CZM technique with experimental results. The numerical work that followed showed that the strength of Tjoints significantly depends on the combination of adhesives used, and that it is possible to achieve significant increases in strength and dissipated energy relative to singleadhesive joints.
Adhesive joints are widely used in the industry today, replacing mechanical joints in many situations. Until a few decades ago, one of the main obstacles to its dissemination was the lack of models that could correctly predict the strength of adhesive joints, which resulted in strongly oversized structures, and leading to a high manufacturing cost. Currently, modeling techniques such as cohesive zone models (CZM) have already demonstrated that it is possible to accurately predict the strength of adhesive joints, as described in the study by Carneiro [1]. Adhesive joints are particularly sensitive to peel stresses, especially when more brittle adhesives such as Araldite® AV138 are used. To try to improve the strength of T joints, in this dissertation the bi-adhesive technique is studied. This technique consists of using two adhesives, placing a more ductile adhesive at the overlap ends and a brittle one in the central area. To test this method in T joints, in this dissertation, various combinations of the adhesives Araldite® AV138, Araldite® 2015 and Sikaforce® 7752 are used. Various lengths of the central adhesive are also tested, always keeping joint symmetry. To evaluate these combinations, a numerical study was carried out using the CZM technique, in the ABAQUS® software, applying a displacement of 6 mm to the joint and clamping the base adherend. With the present work, it was initially possible to validate the CZM technique with experimental results. The numerical work that followed showed that the strength of Tjoints significantly depends on the combination of adhesives used, and that it is possible to achieve significant increases in strength and dissipated energy relative to singleadhesive joints.
Description
Keywords
Juntas adesivas Juntas em T Adesivo estrutural Método de elementos finitos Biadesivo Modelos de dano coesivo Tenacidade à fractura Adhesive joints T-joints Structural adhesive Finite element method Bi-adhesive Cohesive zone models Fracture toughness