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Comportamento Monotónico e Cíclico de Diferentes Tipos de Ligações Coladas
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As técnicas que utilizam colagem têm vindo a ser desenvolvidas em várias indústrias com o principal objetivo de obter estruturas leves e duradouras. Dependendo do tipo de estrutura e dos materiais que se pretendem colar, poderão ser necessárias diversas geometrias de ligações coladas, que podem ter melhor ou pior comportamento, conforme o caso prático em que sejam aplicadas. O comportamento de uma ligação colada é de conhecimento limitado, pois apenas é bem conhecido para os principais tipos de geometria, como é o caso das ligações de sobreposição simples. A falta de conhecimento, por exemplo, sobre o processo de descolamento de ligações coladas em degraus é elevada.
Assim, o presente trabalho pretende colmatar esta lacuna através do estudo dos processos de descolamento de ligações coladas com degrau simples e com degrau duplo cujos aderentes são os compósitos reforçados com polímeros de fibras de carbono (CFRP) e o alumínio. Para este fim, foi aplicada uma abordagem numérica descontínua, nomeadamente o método dos elementos discretos (MED), para estudar diferentes geometrias da ligação e identificar qual delas apresenta o melhor desempenho quando sujeita a carregamentos impostos monotónicos e cíclicos, consistentes com o modo II de rotura pura. A imposição de dois tipos de carregamento às ligações coladas permitiu fazer uma análise paramétrica e perceber quais as diferenças no comportamento de uma ligação quando esta é sujeita a um carregamento usual de referência, contínuo e monotónico até à rotura ou quando é sujeita a um carregamento com várias amplitudes cíclicas.
O processo de descolamento foi analisado com base nas tensões de aderência desenvolvidas na interface das ligações coladas. Os resultados demonstraram que quando o rácio de rigidez axial entre os aderentes é r=1,00, a capacidade de carga é maximizada para os casos de ligação com degrau simples. Nos casos de ligação com degrau duplo a capacidade de carga é bastante sensível ao rácio de rigidez axial do lado esquerdo (ra) e do lado direito (rb).
A identificação das ligações com melhor desempenho das duas configurações geométricas teve em conta, não só a maior capacidade de carga, como também a evolução menos acentuada do dano global.
Bonding techniques have been developed in various industries with the main aim of obtaining light-weight and durable structures. Depending on the type of structure and materials to be bonded, various geometries of bonded joints may be required, which may have better or worse behaviour depending on the practical case in which they are applied. The behaviour of a bonded joint is of limited knowledge, as it is only well known for the main types of geometry, such as simple overlap joints. There is a lack of knowledge, for example, about the debonded process of stepped-lap joints. This work therefore aims to fill this gap by studying the debonding processes of single and double step bonded joints which adherents are carbon fiber reinforced polymer (CFRP) composites and aluminum. For this purpose, a discontinuous numerical approach was applied, specifically the discrete element method (DEM), to study different bond geometries and identify which one performs best when sub-jected to monotonic and cyclic imposed loads, consistent with pure mode II failure. The imposition of two types of loading on the bonded joints made it possible to carry out a parametric analysis and understand the differences in the behaviour of a connection when it is subjected to the usual reference loading, which is continuous and monotonic until failure or when it is subjected to loading with various cyclic amplitudes. The debonding process was analyzed based on the bond stresses developed at the interface of the bonded joints. The results showed that, when the axial stiffness ratio between the adherends is r=1.00, the load-bearing capacity is maximized for cases of single-step joints. In the case of double-steps joints, the load capacity is very sensitive to the axial stiffness ratio of the left side (ra) and the right side (rb). The identification of the best performing joints of the two geometric configurations took into account not only the greater load capacity, but also the less pronounced way evolution of global damage.
Bonding techniques have been developed in various industries with the main aim of obtaining light-weight and durable structures. Depending on the type of structure and materials to be bonded, various geometries of bonded joints may be required, which may have better or worse behaviour depending on the practical case in which they are applied. The behaviour of a bonded joint is of limited knowledge, as it is only well known for the main types of geometry, such as simple overlap joints. There is a lack of knowledge, for example, about the debonded process of stepped-lap joints. This work therefore aims to fill this gap by studying the debonding processes of single and double step bonded joints which adherents are carbon fiber reinforced polymer (CFRP) composites and aluminum. For this purpose, a discontinuous numerical approach was applied, specifically the discrete element method (DEM), to study different bond geometries and identify which one performs best when sub-jected to monotonic and cyclic imposed loads, consistent with pure mode II failure. The imposition of two types of loading on the bonded joints made it possible to carry out a parametric analysis and understand the differences in the behaviour of a connection when it is subjected to the usual reference loading, which is continuous and monotonic until failure or when it is subjected to loading with various cyclic amplitudes. The debonding process was analyzed based on the bond stresses developed at the interface of the bonded joints. The results showed that, when the axial stiffness ratio between the adherends is r=1.00, the load-bearing capacity is maximized for cases of single-step joints. In the case of double-steps joints, the load capacity is very sensitive to the axial stiffness ratio of the left side (ra) and the right side (rb). The identification of the best performing joints of the two geometric configurations took into account not only the greater load capacity, but also the less pronounced way evolution of global damage.
Descrição
Palavras-chave
Ligação colada Método dos elementos discretos CFRP Alumínio Rácio de rigidez axial Deslizamento