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An innovative wide-ranging analytical approach for modelling the bond behaviour of frp-to-substrate joints with an elastic end anchorage
Publication . Biscaia, Hugo C.; Dai, Jian Guo; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Faculdade de Ciências e Tecnologia (FCT); Elsevier Science B.V., Amsterdam.
Fibre-reinforced polymers (FRP) are often externally bonded (EB) to concrete, steel or timber structures for structural strengthening purposes. In the EB reinforcement system, the bond between materials is critical for the success of such a bonding system. However, the system is prone to debond at an FRP strain level much lower than its rupture value. For this reason, it is often necessary to use end anchorages in FRP-strengthened beams to delay or avoid this premature debonding of FRP from the beams. To better understand the debonding process of mechanically anchored FRP-to-substrate joints, the present work proposes a new analytical approach that considers an elastic end anchorage, which can simulate, through a spring, the slips developed in an end anchorage such as an FRP U-wrap jacket, FRP spike anchor, steel plate anchorage, among others. This new approach can also simulate the bond performance of FRP-to-substrate joints with no end anchorages by assuming that the stiffness of the end anchorage is zero. Expressions for defining the load-slip curves, FRP strains, interfacial slips, and bond stresses developed throughout the bonded length are derived and validated against the results from the Finite Element Analysis (FEA). In the end, the model was used to simulate several experimental tests on mechanically anchored FRP-to-substrate joints available in the literature. Despite its simplicity, the proposed analytical approach covers wider situations that no other known similar approach can deal with.
Influence of uniform temperature variations on hybrid bonded joints with a circular or tubular cross-sectional area
Publication . Biscaia, Hugo C.; Martins, Ana P.; Gao, Wan Yang; Carvalho, Marta S.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Springer Science Business Media
The use of lightweight structures is a current concern in several engineering domains. To obtain such types of structures, the bonding technique using Carbon Fibre-Reinforced Polymers (CFRP) has been most recently considered a primary option. If CFRP is known to have a high strength-to-weight ratio or high corrosion resistance, the bonding technique does not need to add other fixation components and it also prevents stress concentrations. However, when combined with, e.g. a metallic surface, the high difference between the thermal expansion coefficient of the CFRP composite and the metallic material may raise some issues when the adhesively bonded structure is subjected to thermal loading. Therefore, the present work presents an analytical model that facilitates the comprehension of the impact of temperature on a hybrid bonded joint with a circular or tubular cross-sectional area. The full debonding process of a double but bonded joint with a regular curvature is discussed thoroughly. Due to the susceptibility of current adhesives to lose their mechanical properties for relatively high temperatures, the vitreous transition temperature of the adhesives and their influence on the local adhesive model is considered in a deeper analysis. The Finite Element Method (FEM) was used to validate all the derived analytical equations, which were achieved due to the close predictions obtained from both ways, i.e. from the numerical simulations and the proposed closed-form solutions.
Numerical bond assessment of carbon-epoxy stepped-lap joints
Publication . Biscaia, Hugo C.; Micaelo, Rui; Cornetti, Pietro; Almeida, Raquel; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; CERIS - Polo NOVA; DEC - Departamento de Engenharia Civil; Elsevier Science B.V., Amsterdam.
With the main purpose of obtaining lightweight and durable structures, bonding techniques have improved significantly in several industries. Depending on the type of structure, joining different components with different materials may require different joint geometries, which may perform better or worse. Still, only the bond performance of a very limited number of joint geometries is well known. A lack of knowledge, for instance, about the debonding process of one and two-step joints persists, especially for the latter. The present work intends to mitigate this gap by studying the debonding processes of one and two-step joints made with CFRP and aluminium adherends. To that end, implicit and explicit numerical methods (finite and distinct element methods, respectively), were applied to study different joint geometries and identify which one shows the best bond performance when subjected to a monotonic load consistent with pure fracture mode II. Based on the bond stresses obtained within the interface of the joints, the debonding propagations of the one and two-step joints are analyzed thoroughly. In the case of the one-step bonded joints, the results revealed that when the ratio between the axial stiffness of the adherends is r = 1.0 the load capacity of these joint configurations is maximized. With two-step joints, the load capacity is very sensitive to the relationship between the axial stiffness on the left (ra) and right-hand side (rb). Based on 162 different numerical simulations, the results also suggest that the load capacities of the two-step joint configurations can be maximized when the axial stiffness ra and rb of the joint are equal to 1/3 and 3.0, respectively.
Modelação e Simulação Numérica da União por Adesivo de Componentes Estruturais Sujeitos a Cargas Monotónicas e Temperatura Criogénica
Publication . Monteiro, Yuri Flávio Silva; Carvalho, Marta; Biscaia, Hugo
A ligação adesiva vem ganhando protagonismo nos processos de ligação de materiais
estruturais, incluindo a união de materiais dissimilares. Com a evolução tecnológica a
ligação adesiva vem substituindo os métodos tradicionais como a soldadura, brasagem, e
ligações mecânicas como aparafusamentos e rebitagens. Esta tendência deve-se a diversas
vantagens que a ligação adesiva oferece, dos quais se destacam a obtenção de estruturas
leves, com bom comportamento à fadiga, e sem esquecer que estas permitem ligações de
materiais dissimilares e com menores concentrações de tensões quando comparado com
os outros métodos de ligação.
A crescente utilização da ligação adesiva torna vantajosa a existência de ferramentas
que auxiliem o seu projeto. O Método de Elementos Finitos, combinado com critérios
ou modelos de dano, tem-se revelado eficaz na simulação e previsão do comportamento
de juntas adesivas, possibilitando assim a redução do tempo de projeto e dos custos.
Entre os critérios ou modelos de dano associados ao Método de Elementos Finitos, os
modelos de dano coesivo revelam bastante eficácia, combinando parâmetros de resistência
e tenacidade para prever o desempenho de juntas adesivas.
Com o objetivo de obter a melhor configuração de junta adesiva quando os aderentes
são materiais dissimilares, especificamente Polímeros Reforçados com Fibra de Carbono
(PRFC) e liga de alumínio, quando sujeita a temperaturas criogénicas e carga monotónica
de tração uniaxial, na presente dissertação foi modelada em LS-Dyna uma junta adesiva
tubular, tendo sido simuladas e analisadas cinco configurações com o mesmo compri-
mento colado e lei coesiva do adesivo. A análise da resposta decorrente da simulação dos
fenómenos físicos presentes no complexo processo de descolagem da junta foi realizada
quantificando os valores de deslizamento interfacial e as tensões de aderência do adesivo
e as extensões desenvolvidas nos aderentes ao longo do comprimento colado.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
EXPL/EME-APL/0994/2021