| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 7.45 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
As uniões com ligações adesivas são um método cada vez mais utilizado na projeção e fabrico de estruturas mecânicas, por causa das vantagens significativas desta técnica em comparação com as ligações tradicionais. 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 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 do comprimento de sobreposição (Cs). Esta comparação passa por elaborar uma análise numérica e um modelo físico criado e testado em laboratório. A análise numérica de modelos de dano coesivo (MDC) foi realizada para analisar as tensões de arrancamento (y) e as de corte (xy) na camada adesiva e para avaliar a capacidade MDC na previsão da resistência da junta. No final, verifica-se que, apesar de haver uma dispersão considerável de valores máximos de rotura dos provetes testados, consegue-se provar que os valores numericamente calculados descrevem a realidade de forma precisa. Também é de salientar que as tensões de rotura obtidas experimentalmente para as juntas com o SikaForce® 7752 são superiores às calculadas numericamente, porque se utilizou uma lei coesiva triangular para modelar um adesivo marcadamente dúctil. Assim sendo, pode-se afirmar que os MDC são uma boa ferramenta para dimensionar e prever o comportamento de juntas adesivas.
Adhesive bonded joints are an increasingly used method in the design and manufacture of mechanical structures, because of the significant advantages of this technique compared to traditional bonds. Benefits include weight reduction and the ability to join different materials, including composites, without damaging the structures to be bonded. Commercial adhesives range from strong and brittle (e.g. Araldite® AV138) to less strong and ductile (e.g. Araldite® 2015). A new family of polyurethane adhesives combines strength and ductility (e.g. SikaForce® 7752). This dissertation compares the tensile performance of the three abovementioned adhesives in aluminum tubular joints (AW6082-T651), considering the variation of the overlap length (Cs). This comparison involves elaborating a numerical analysis and a physical model created and tested in the laboratory. Numerical analysis of cohesive zone models (CZM) was performed to analyze peel (y) and shear stresses (xy) in the adhesive layer and to evaluate the CZM ability to predict joint strength. In the end, it appears that, although there is a considerable dispersion of maximum failure values of the tested specimens, it can be proved that the numerically calculated values accurately describe reality. It should also be noted that the experimentally obtained failure strengths for the joints with the SikaForce® 7752 are higher than those calculated numerically, because a triangular cohesive law was used to model a markedly ductile adhesive. Therefore, it can be said that CZM is a good tool for design and predicting the behavior of adhesive joints.
Adhesive bonded joints are an increasingly used method in the design and manufacture of mechanical structures, because of the significant advantages of this technique compared to traditional bonds. Benefits include weight reduction and the ability to join different materials, including composites, without damaging the structures to be bonded. Commercial adhesives range from strong and brittle (e.g. Araldite® AV138) to less strong and ductile (e.g. Araldite® 2015). A new family of polyurethane adhesives combines strength and ductility (e.g. SikaForce® 7752). This dissertation compares the tensile performance of the three abovementioned adhesives in aluminum tubular joints (AW6082-T651), considering the variation of the overlap length (Cs). This comparison involves elaborating a numerical analysis and a physical model created and tested in the laboratory. Numerical analysis of cohesive zone models (CZM) was performed to analyze peel (y) and shear stresses (xy) in the adhesive layer and to evaluate the CZM ability to predict joint strength. In the end, it appears that, although there is a considerable dispersion of maximum failure values of the tested specimens, it can be proved that the numerically calculated values accurately describe reality. It should also be noted that the experimentally obtained failure strengths for the joints with the SikaForce® 7752 are higher than those calculated numerically, because a triangular cohesive law was used to model a markedly ductile adhesive. Therefore, it can be said that CZM is a good tool for design and predicting the behavior of adhesive joints.
Description
Keywords
Epóxido Poliuretano Juntas adesivas tubulares Método de Elementos Finitos Modelos de Dano Coesivo Epoxy Polyurethane Tubular adhesive joints Finite Element Method Cohesive Zone Models