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Abstract(s)
As ligações adesivas têm vindo a desempenhar um papel bastante importante na ligação de diferentes estruturas. Existem indústrias que estão cada vez mais a apostar neste tipo de ligações, como é o caso da indústria aeronáutica, aeroespacial e automóvel. As ligações adesivas são frequentemente utilizadas na fabricação de estruturas com geometria complexa com a finalidade de proporcionar uma ligação estrutural que, em teoria deveria ter pelo menos a mesma resistência do que o material de base. Por outro lado, existem esforços que, quando aplicados em substratos de menor espessura, podem originar esforços prejudiciais à ligação, como por exemplo os esforços de arrancamento. No entanto, algumas geometrias podem melhorar a resistência da ligação ao arrancamento, como é o caso de juntas adesivas T de reforço. As principais vantagens destas juntas são o aumento de rigidez da estrutura de base e a minimização dos picos de tensão de arrancamento. O objetivo desta dissertação é estudar numericamente juntas adesivas em T, com diferentes geometrias e sujeitas ao arrancamento, utilizando modelos de dano coesivo (MDC). Para isso foram utilizados três adesivos estruturais com diferentes propriedades e substratos em liga de alumínio. A espessura de adesivo (ta) foi considerada constante. As variáveis estudadas foram a espessura do substrato da base (a), a espessura do T (t), o comprimento de sobreposição (l) e o raio do T (r). Numa primeira fase, foi efetuada uma validação experimental da técnica usada nesta dissertação (MDC) através de um trabalho já realizado. O trabalho referido consitiu num estudo em juntas T, formadas por dois componentes em L aplicados simetricamente, solicitadas a esforços de arrancamento, com com diferentes espessuras de L (tP2) e com dois tipos de adesivos diferentes. De um modo geral, foi possível concluir que, para todos os valores de tP2, os resultados numéricos apresentaram bom acordo com os experimentais. O trabalho numérico realizado focou-se na análise de juntas em T, incluindo análises de tensões na junta, o estudo da variável de dano no adesivo, a previsão da resistência e a previsão da energia dissipada com recurso a um software que utiliza o Método dos Elementos Finitos (MEF) e MDC. Como conclusão, verificou-se que o adesivo com elevada ductilidade (Sikaforce® 7752) é recomendado para este tipo de solicitação, devido à capacidade de distribuir tensões sobre uma maior área, o que traduziu em valores mais elevados de força máxima. Por outro lado, foi possível compreender em detalhe o efeito de cada variável geométrica utilizada.
Adhesive joints have been playing a very important role to join different structures. There are industries that are increasingly betting on these types of joints, such as the aeronautical, aerospace and automotive industries. Adhesive joints are often used in the manufacture of structures with complex geometry in order to provide a structural bond that, in theory, should have at least the same strength as the base material. On the other hand, there are loads that, when applied to thinner substrates, can lead to damaging stresses on the bond, such as peel stresses. However, some geometries can improve the joint strength to peel, as is the case with T reinforcement adhesive joints. The main advantages of these joints are the increased stiffness of the base structure and the minimization of peak peel stresses. The objective of this dissertation is to numerically study T-adhesive joints, with different geometries and subjected to peel loads, using cohesive zone models (CZM). For this, three structural adhesives with different properties and adherends in aluminum alloy were used. The thickness of the adhesive (ta) was considered constant. The studied variables were the base adherend thickness (a), the T thickness (t), the overlap length (l) and the T radius (r). In a first phase, an experimental validation of the technique used in this dissertation (CZM) was undertaken through a previous work. The referred work consisted of a study in T joints, formed by two L-shaped components applied symmetrically, loaded in peel, with different L thicknesses (tP2) and with two different types of adhesives. In general, it was possible to conclude that, for all tP2 values, the numerical results showed good agreement with the experimental ones. The numerical work carried out focused on the analysis of T-joints, including joint stress analysis, study of the damage variable in the adhesive, strength prediction and dissipated energy prediction using software that uses the Finite Element Method (FEM) and CZM. In conclusion, it was found that the adhesive with high ductility (Sikaforce® 7752) is recommended for this type of application, due to the ability to distribute stresses over a larger area, which translated into higher values of maximum load. On the other hand, it was possible to understand in detail the effect of each geometric variable used.
Adhesive joints have been playing a very important role to join different structures. There are industries that are increasingly betting on these types of joints, such as the aeronautical, aerospace and automotive industries. Adhesive joints are often used in the manufacture of structures with complex geometry in order to provide a structural bond that, in theory, should have at least the same strength as the base material. On the other hand, there are loads that, when applied to thinner substrates, can lead to damaging stresses on the bond, such as peel stresses. However, some geometries can improve the joint strength to peel, as is the case with T reinforcement adhesive joints. The main advantages of these joints are the increased stiffness of the base structure and the minimization of peak peel stresses. The objective of this dissertation is to numerically study T-adhesive joints, with different geometries and subjected to peel loads, using cohesive zone models (CZM). For this, three structural adhesives with different properties and adherends in aluminum alloy were used. The thickness of the adhesive (ta) was considered constant. The studied variables were the base adherend thickness (a), the T thickness (t), the overlap length (l) and the T radius (r). In a first phase, an experimental validation of the technique used in this dissertation (CZM) was undertaken through a previous work. The referred work consisted of a study in T joints, formed by two L-shaped components applied symmetrically, loaded in peel, with different L thicknesses (tP2) and with two different types of adhesives. In general, it was possible to conclude that, for all tP2 values, the numerical results showed good agreement with the experimental ones. The numerical work carried out focused on the analysis of T-joints, including joint stress analysis, study of the damage variable in the adhesive, strength prediction and dissipated energy prediction using software that uses the Finite Element Method (FEM) and CZM. In conclusion, it was found that the adhesive with high ductility (Sikaforce® 7752) is recommended for this type of application, due to the ability to distribute stresses over a larger area, which translated into higher values of maximum load. On the other hand, it was possible to understand in detail the effect of each geometric variable used.
Description
Keywords
Adesivo estrutural Juntas adesivas Juntas em T Método de Elementos Finitos Modelos de dano coesivo Structural adhesive Adhesive joints T joints Finite Element Method Cohesive zone models