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Abstract(s)
O método de união com ligações adesivas está cada vez mais a ser utilizado na conceção de estruturas mecânicas, por causa das vantagens significativas desta técnica em comparação com as ligações tradicionais. De facto, as juntas com ligação adesiva estão sob investigação intensa há bastante tempo. Entre as vantagens, destaca-se a redução de peso e possibilidade de unir diferentes materiais, incluindo compósitos, sem danificar as estruturas a ligar. Os adesivos comerciais variam desde resistentes e frágeis (por exemplo, Araldite® AV138) a menos resistentes e dúcteis (por exemplo, Araldite® 2015).
Uma nova família de adesivos de poliuretano combina elevada resistência e ductilidade (por exemplo, Sikaforce® 7752).
Esta dissertação compara o desempenho à tração dos três adesivos supracitados, em juntas tubulares de alumínio (AW6082-T651), considerando a variação dos parâmetros geométricos principais e alteração geométrica das mesmas. Os parâmetros principais são o comprimento de sobreposição (LO) e a espessura dos tubos interior e exterior (tSI e tSE, respetivamente). As alterações geométricas consistem na consideração da existência de um chanfro exterior dos aderentes, chanfro interior dos aderentes e na adição de um filete de adesivo nas extremidades de LO. A análise numérica de modelos de dano coesivo (MDC) foi realizada para analisar as tensões de arrancamento (σy) e as de corte (τxy) na camada adesiva e para avaliar a capacidade MDC na previsão da resistência da junta.
O estudo paramétrico numérico em juntas adesivas tubulares demonstra que não se dão alterações significativas na resistência das mesmas relativamente à aplicação de chanfro externo ou interno dos aderentes ou de filete de adesivo. Por outro lado, verifica-se um acréscimo considerável de Pmáx com o aumento de LO, sendo que as juntas com o Araldite® 2015 são as que apresentam a resistência mais elevada. As juntas adesivas com menor resistência são as que utilizam o SikaForce® 7752. Estes resultados repetem-se considerando a variação crescente de tSI e tSI-tSE. O aumento do valor de tSE provoca um aumento considerável de Pmáx para o Araldite® 2015 mas que estabiliza rapidamente para valores de tSE reduzidos. Relativamente ao Araldite® AV135 não se observam melhorias na resistência das juntas e, no que toca às do SikaForce® 7752, conclui-se que o aumento de tSE prejudica o seu desempenho, uma vez que ocorre uma redução gradual de Pmáx.
Bonding with adhesives is increasingly being used in the design of mechanical structures, because of the significant advantages of this technique compared to traditional joints. In fact, adhesive bonded joints have been under intense investigation for quite some time. Among the advantages, it is worth mentioning the weight reduction and the possibility of joining different materials, including composites, without damaging the structures to be connected. Commercial adhesives range from strong and brittle (for example, Araldite® AV138) to less strong and ductile (for example, Araldite® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g. Sikaforce® 7752). This dissertation compares the tensile performance of the three above-mentioned adhesives on aluminum tubular joints (AW6082-T651), considering the variation of the main geometric parameters and their geometric alteration. The main parameters are the overlap length (LO) and the thickness of the inner and outer tubes (tSI and tSE, respectively). The geometric changes consist on the consideration of the existence of na outer chamfer of the adherends, inner chamfer of the adherends and the addition of a fillet of adhesive at the ends of LO. The numerical analysis by cohesive zone models (CZM) was performed to analyze peel (σy) and shear stresses (τxy) in the adhesive layer and to evaluate the CZM capacity in the joint strength prediction. A numerical parametric study of tubular adhesive joints demonstrates that there are no significant changes in their strength relative to the application of external or internal chamfers of adherends or adhesive fillets. On the other hand, there is a considerable increase of Pmáx with the increase of LO, and the joints with Araldite® 2015 are those with the highest strength. The less strong adhesive joints are those using SikaForce® 7752. These results are repeated considering the increasing variation of tSI and tSI-tSE. Increasing the tSE value causes a considerable increase in Pmáx for the Araldite® 2015 but which stabilizes rapidly at reduced tSE values. Concerning the Araldite® AV138, there is no strength improvement of the joints and, as regards to the SikaForce® 7752, it is concluded that the increase of tSE reduces its performance, since a gradual reduction of Pmáx occurs.
Bonding with adhesives is increasingly being used in the design of mechanical structures, because of the significant advantages of this technique compared to traditional joints. In fact, adhesive bonded joints have been under intense investigation for quite some time. Among the advantages, it is worth mentioning the weight reduction and the possibility of joining different materials, including composites, without damaging the structures to be connected. Commercial adhesives range from strong and brittle (for example, Araldite® AV138) to less strong and ductile (for example, Araldite® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g. Sikaforce® 7752). This dissertation compares the tensile performance of the three above-mentioned adhesives on aluminum tubular joints (AW6082-T651), considering the variation of the main geometric parameters and their geometric alteration. The main parameters are the overlap length (LO) and the thickness of the inner and outer tubes (tSI and tSE, respectively). The geometric changes consist on the consideration of the existence of na outer chamfer of the adherends, inner chamfer of the adherends and the addition of a fillet of adhesive at the ends of LO. The numerical analysis by cohesive zone models (CZM) was performed to analyze peel (σy) and shear stresses (τxy) in the adhesive layer and to evaluate the CZM capacity in the joint strength prediction. A numerical parametric study of tubular adhesive joints demonstrates that there are no significant changes in their strength relative to the application of external or internal chamfers of adherends or adhesive fillets. On the other hand, there is a considerable increase of Pmáx with the increase of LO, and the joints with Araldite® 2015 are those with the highest strength. The less strong adhesive joints are those using SikaForce® 7752. These results are repeated considering the increasing variation of tSI and tSI-tSE. Increasing the tSE value causes a considerable increase in Pmáx for the Araldite® 2015 but which stabilizes rapidly at reduced tSE values. Concerning the Araldite® AV138, there is no strength improvement of the joints and, as regards to the SikaForce® 7752, it is concluded that the increase of tSE reduces its performance, since a gradual reduction of Pmáx occurs.
Description
Keywords
Epóxido Poliuretano Juntas adesivas tubulares Método de Elementos Finitos Modelos de Dano Coesivo Parâmetros geométricos Epoxy Polyurethane Tubular adhesive joints Finite Element Method Cohesive Zone Models Geometric parameters