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Abstract(s)
As juntas adesivas têm vindo a ser aplicadas em diversas áreas, devido às vantagens que estas apresentam relativamente às ligações mecânicas convencionais. O aumento da resistência, a redução de peso e a facilidade de fabrico são algumas das vantagens que esta técnica apresenta. Com a evolução na aplicação de materiais compósitos, nomeadamente no setor aeronáutico e automóvel, a técnica de ligação adesiva tem assumido um papel fundamental como meio de ligação, visto que permite a ligação de materiais dissimilares, permitindo assim a construção de estruturas híbridas (materiais metálicos + compósito). A natureza do adesivo torna-se um fator fundamental dependendo do tipo de solicitações que a junta estará sujeita. Os adesivos comerciais podem variar desde rígidos e frágeis (como é o caso do Araldite® AV138) a adesivos flexíveis e dúcteis (como por exemplo o Araldite® 2015 e o Sikaforce® 7752). Esta dissertação tem como objetivo o estudo paramétrico de juntas adesivas tubulares de sobreposição simples quanto ao seu desempenho à tração com os adesivos supracitados e diferentes comprimentos de sobreposição (LO) pelo Método de Elementos Finitos eXtendido (MEFX), com ajuda da ferramenta de simulação/software ABAQUS®. O objetivo fundamental é avaliar a capacidade de previsão de resistência do MEFX, pela comparação com os respetivos resultados experimentais. É também efetuada uma comparação dos resultados obtidos com Modelos de Dano Coesivo (MDC). O estudo paramétrico numérico permite também avaliar de forma crítica o comportamento dos adesivos estudados neste tipo de junta, a distribuição de tensões de arrancamento (σy) e de corte (τxy) para LO=20 e 40 mm e a energia dissipada (Ediss) durante as simulações até a rotura. Concluiu-se que, com uma escolha correta dos critérios de iniciação e propagação de dano, o MEFX é um método viável e preciso para a previsão de resistência de juntas tubulares. Observou-se que, para juntas com LO pequenos (20 mm), o adesivo rígido e frágil (Araldite® AV138) apresenta melhores resultados de força máxima (Pmáx), quando comparado com adesivos dúcteis, mas menos resistentes. Por outro lado, o adesivo Araldite® 2015 (adesivo epóxido dúctil) apresenta o melhor comportamento dos três adesivos para LO maiores (40 mm). O adesivo poliuretano (Sikaforce® 7752) revelou ter o Pmáx inferior em ambas situações estudadas. Isto acontece devido à sua baixa resistência.
Adhesive joints have been applied in several areas due to their advantages over conventional mechanical joints. Increased strength, reduced weight and ease of fabrication are some of the advantages of this technique. With the evolution in the application of composite materials, namely in the aeronautical and automotive sectors, the adhesive bonding technique has assumed a fundamental role as a bonding technique, since it allows the bonding of dissimilar materials, thus allowing the construction of hybrid structures (metallic materials + composite). The nature of the adhesive becomes a key factor depending on the type of loads the joint will be subjected to. Commercial adhesives can range from stiff and brittle (such as the Araldite® AV138) to flexible and ductile adhesives (such as the Araldite® 2015 and Sikaforce® 7752). This dissertation aims at the parametric study of single-lap tubular adhesive joints regarding their tensile performance with the above-mentioned adhesives and different overlap lengths (LO) by the eXtended Finite Element Method (XFEM) with the help of the simulation/ABAQUS® software. The main objective is to evaluate the strength prediction abilities of the XFEM, by comparison with the respective experimental results. a comparison of the results obtained with Cohesive Zone Models (CZM) is also carried out. The parametric numerical study also allows a critical evaluation of the behavior of the adhesives studied in this type of joint, the distribution of peel (σy) and shear stresses (τxy) for LO=20 and 40 mm and the dissipated energy (Ediss) during the simulations until failure. It was concluded that, with a correct choice of damage initiation and propagation criteria, the XFEM is a viable and accurate method for the strength prediction of tubular joints. It was observed that, for joints with small LO (20 mm), the stiff and brittle adhesive (Araldite® AV138) presents better maximum load (Pmax) results when compared to ductile adhesives, although less resistant. On the other hand, the Araldite® 2015 (ductile epoxy adhesive) shows the best behavior of the three adhesives for the largest LO (40 mm). The polyurethane adhesive (Sikaforce® 7752) was found to have the lowest Pmax in both situations studied. This is due to its low resistance.
Adhesive joints have been applied in several areas due to their advantages over conventional mechanical joints. Increased strength, reduced weight and ease of fabrication are some of the advantages of this technique. With the evolution in the application of composite materials, namely in the aeronautical and automotive sectors, the adhesive bonding technique has assumed a fundamental role as a bonding technique, since it allows the bonding of dissimilar materials, thus allowing the construction of hybrid structures (metallic materials + composite). The nature of the adhesive becomes a key factor depending on the type of loads the joint will be subjected to. Commercial adhesives can range from stiff and brittle (such as the Araldite® AV138) to flexible and ductile adhesives (such as the Araldite® 2015 and Sikaforce® 7752). This dissertation aims at the parametric study of single-lap tubular adhesive joints regarding their tensile performance with the above-mentioned adhesives and different overlap lengths (LO) by the eXtended Finite Element Method (XFEM) with the help of the simulation/ABAQUS® software. The main objective is to evaluate the strength prediction abilities of the XFEM, by comparison with the respective experimental results. a comparison of the results obtained with Cohesive Zone Models (CZM) is also carried out. The parametric numerical study also allows a critical evaluation of the behavior of the adhesives studied in this type of joint, the distribution of peel (σy) and shear stresses (τxy) for LO=20 and 40 mm and the dissipated energy (Ediss) during the simulations until failure. It was concluded that, with a correct choice of damage initiation and propagation criteria, the XFEM is a viable and accurate method for the strength prediction of tubular joints. It was observed that, for joints with small LO (20 mm), the stiff and brittle adhesive (Araldite® AV138) presents better maximum load (Pmax) results when compared to ductile adhesives, although less resistant. On the other hand, the Araldite® 2015 (ductile epoxy adhesive) shows the best behavior of the three adhesives for the largest LO (40 mm). The polyurethane adhesive (Sikaforce® 7752) was found to have the lowest Pmax in both situations studied. This is due to its low resistance.
Description
Keywords
Juntas adesivas Adesivo Estrutural Epóxido Poliuretano Previsão de resistência Método de Elementos Finitos eXtendido Modelo de Dano Coesivo Energia dissipada Adhesive joints Structure adhesive Expoxy Polyurethane Strenght prediction eXtended Finite Element Method Cohesive Zone Model Dissipated Energy