| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 7.51 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
As ligações adesivas têm cada vez mais preponderância na conceção de estruturas
mecânicas, devido às vantagens significativas desta técnica em comparação com as
ligações tradicionais. O facto de as ligações adesivas terem uma boa relação
desempenho-peso, bem como a boa capacidade de unir diferentes materiais sem
danificar as estruturas a ligar, são vantagens destacadas deste tipo de ligações. Os
adesivos comerciais variam desde resistentes e frágeis (por exemplo o Araldite® AV138)
a menos resistentes e dúcteis (por exemplo o Araldite® 2015). Uma nova família de
adesivos de poliuretano combina elevada resistência e ductilidade (por exemplo o
Sikaforce® 7752).
A presente dissertação compara o desempenho à tração dos três adesivos supracitados,
em juntas tubulares de alumínio (AW6082-T651), em função de diferentes
comprimentos de sobreposição (LO). Nesta comparação, é efetuada uma análise
analítica cujos resultados são, numa fase posterior, comparados com uma análise
numérica por meio de modelos de dano coesivo (MDC) e com a resistência da junta
obtida experimentalmente. A análise analítica foi realizada por intermédio de três
modelos analíticos, a partir de uma formulação mais simples e direta, na qual são
analisadas as tensões de arrancamento (σy) e as de corte (τxy), e posteriormente
utilizados critérios da mecânica dos meios contínuos para inferir a resistência das juntas.
Este estudo permitiu verificar que os métodos analíticos preveem um comportamento
ligeiramente diferente, em termos de distribuições de tensões de corte, relativamente
aos obtidos numericamente. No entanto, as previsões da resistência obtidas
analiticamente, aplicando os critérios da mecânica dos meios contínuos, são
semelhantes aos resultados obtidos pelo MEF, mas distintas dos resultados obtidos
experimentalmente
Adhesive joints are increasingly prevalent in the design of mechanical structures, due to the significant advantages of this technique compared to traditional joints. The fact that adhesive joints have a good performance-to-weight ratio, as well as the good ability to join different materials without damaging the structures to be bonded, are outstanding advantages of this type of joints. Commercial adhesives range from strong and brittle (e.g., the Araldite® AV138) to less strong and ductile (e.g., the Araldite® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g., the Sikaforce® 7752). This dissertation compares the tensile performance of the three above mentioned adhesives, in aluminum tubular joints (AW6082-T651), as a function of different overlap lengths (LO). In this comparison, an analytical analysis is carried out, the results of which are, at a later stage, compared with a numerical analysis using cohesive zone models (CZM) and with the experimentally obtained joint strength. The analytical analysis was carried out using three analytical methods, from a simpler and more direct formulation, in which peel (σy) and shear stresses (τxy) are analyzed, and subsequently continuum mechanics criteria are used to infer the joint strength. This study allowed to verify that the analytical methods predict a slightly different behavior, in terms of shear stress distributions, compared to those obtained numerically. However, the strength predictions obtained analytically, applying the continuum mechanics criteria, are similar to the results obtained by FEM, but distinct from the results obtained experimentally
Adhesive joints are increasingly prevalent in the design of mechanical structures, due to the significant advantages of this technique compared to traditional joints. The fact that adhesive joints have a good performance-to-weight ratio, as well as the good ability to join different materials without damaging the structures to be bonded, are outstanding advantages of this type of joints. Commercial adhesives range from strong and brittle (e.g., the Araldite® AV138) to less strong and ductile (e.g., the Araldite® 2015). A new family of polyurethane adhesives combines high strength and ductility (e.g., the Sikaforce® 7752). This dissertation compares the tensile performance of the three above mentioned adhesives, in aluminum tubular joints (AW6082-T651), as a function of different overlap lengths (LO). In this comparison, an analytical analysis is carried out, the results of which are, at a later stage, compared with a numerical analysis using cohesive zone models (CZM) and with the experimentally obtained joint strength. The analytical analysis was carried out using three analytical methods, from a simpler and more direct formulation, in which peel (σy) and shear stresses (τxy) are analyzed, and subsequently continuum mechanics criteria are used to infer the joint strength. This study allowed to verify that the analytical methods predict a slightly different behavior, in terms of shear stress distributions, compared to those obtained numerically. However, the strength predictions obtained analytically, applying the continuum mechanics criteria, are similar to the results obtained by FEM, but distinct from the results obtained experimentally
Description
Keywords
Juntas adesivas tubulares Adesivos estruturais Métodos analíticos Métodos numéricos Distribuição de tensões Mecânica dos meios contínuos Tubular adhesive joints Structural adhesives Analytical methods Numerical methods Stress distribution Continuum mechanics