Orientador: Fernando de Azevedo Silva / Banca: José Elias Tomazini / Banca: Silvana Aparecida Barbosa / Resumo: Juntas rebitadas sobrepostas representam elementos críticos na construção de estruturas aeronáuticas quando projetadas à fadiga. Por serem elementos de fixação largamente utilizados na indústria aeronáutica, o estudo de suas propriedades e variáveis à fadiga tem sido cada vez mais amplo. A variável que tem mostrado possuir alta influência na resistência à fadiga de juntas rebitadas é a força de aperto aplicada no processo de rebitagem. A vida da peça tende a ser maior quando o valor dessa força é aumentado. O método dos elementos finitos, que é uma ferramenta de cálculo aplicada nos mais diversos campos de atuação e tem se tornado parte indispensável de projetos mecânicos, é utilizado nesta dissertação para a análise de uma junta rebitada sobreposta de uso aeronáutico. A junta é simulada levando em conta as etapas do processo de fabricação e aplicação, a fim de realizar a análise de seu comportamento mecânico e calcular sua vida em fadiga. Através de um teste experimental de tração monotônica foram obtidos valores de deformação com extensômetros, e é feita a correlação desses dados com o modelo numérico a fim de validar a modelagem. Em seguida são feitas mais duas análises com diferentes forças de aperto, com o objetivo de verificar a influência dessa variação na vida em fadiga da peça. / Abstract: Riveted lap joints represent a critical element in metallic airframe construction when designing against fatigue. These elements are widely used in the aerospace industry, so the study of the fatigue's properties and variables has been increasingly broad. The variable that has shown to have a high influence on the fatigue strength of riveted joints is the clamping force applied to the riveting process. The life of the part tends to be higher when the clamping force applied is increased. The finite element method, which is a calculation tool applied in various fields of activity and has become an indispensable step of mechanical design, is used in this dissertation for the analysis of a riveted lap joint of aeronautic use. The joint is simulated considering the stages of the manufacturing process and application, in order to perform analysis of mechanical behavior and calculate the fatigue life. Through an experimental test of monotonic tensile, strain values were obtained with strain-gauges, and is made the correlation of these data with the numerical model to validate the modeling. Finally two more tests are made with different clamping forces, in order to check the influence of this variation in fatigue life of the joint. / Mestre

The overall aim of the project is to examine the rivetability of new steels and to investigate the mechanical behaviour of self-piercing riveted (SPR) aluminium-steel hybrid structures for automotive applications. Interstitial Free Steel (I.F.) of 1.2 mm thickness was joined to Aluminium 5754 of 2 mm thickness and Aluminium 5182 (coated and uncoated) of 1.5 mm thickness. The work began by initially conducting a quality assessment of the various joints that were produced in order to establish the optimum conditions for joining the various sample combinations to be investigated. A relationship was established between the head height and the interlock distance on the one hand and between the interlock distance and the lap shear strength of samples. It was also established that for higher lap shear strength, it is preferable to use the stronger material (I.F. steel) as the pierced sheet and the weaker material (5182) as the locked sheet. However, the results showed that this rule could not be applied for predicting the fatigue behaviour of SPR joints between I.F. steel and 5182. An investigation of the fatigue failure mechanisms was undertaken and possible reasons for this behaviour are discussed. The influence of fretting was also investigated by using scanning electron microscopy and reported. The fatigue behaviour of Dual Phase (DP600 + 5182) SPR joints was investigated. It was observed that the position of fatigue crack initiation differed with the maximum applied load. An explanation for this observation was provided by considering the failure mechanism of the samples under different load levels. The study also showed how fretting led to the initiation of fatigue cracks. The corrosion behaviour of (I.F. steel + 5182) samples was investigated by conducting tests in a salt spray according to the ASTM B117-97 standard. Three types of corrosion were observed; galvanic corrosion, differential aeration corrosion, uniform corrosion and are discussed. The weight change with time was monitored and was used to describe the corrosion behaviour. The lap shear strength was measured as a function of corrosion time. The presence of the corrosion product within the overlap was observed to greatly influence the lap shear strength behaviour. A further study was carried out in order to examine the influence of the individual alloys on the corrosion of the SPR samples. In this part the potential influence of pulse current treatment on corrosion was also investigated and was observed to increase greatly the corrosion resistance of the I.F. steel. Principal findings for this observation are also provided.

Thesis (Ph. D.)--Technische Universiteit Delft, 1997. / Cover title. Summary in Dutch. Includes bibliographical references.

Thesis (Ph. D.)--Technische Universiteit Delft, 1997. / Cover title. Summary in Dutch. Includes bibliographical references.

No description available.

La fatigue représente la deuxième cause d’endommagement des structures métalliques anciennes après la corrosion. Celle-ci se manifeste par l’apparition de fissures, dans les zones fortement sollicitées présentant des concentrations de contraintes importantes, et peut mener à terme à la ruine de l’ouvrage. Dans le cas des structures métalliques anciennes, les fissures de fatigue s’amorcent généralement au droit des trous de rivets rendant difficile leur détection par les techniques de contrôle non destructif conventionnelles. De même, les matériaux métalliques anciens de la construction, et notamment le fer puddlé, limitent l’utilisation de certaines techniques. Dans le cadre de ce travail de thèse, l’objectif principal est d’étudier l’efficacité d’un renforcement par composites collés dans le cas de fissures de fatigue émanant de trous de rivets. Pour cela, des éprouvettes de petites dimensions, présentant un perçage central et une unique fissure de fatigue en bord de perçage, ont été considérées. De même, deux matériaux métalliques, acier doux et fer puddlé, ainsi que deux procédés de renforcement PRFC (polymères renforcés de fibres de carbone), à Module Normal et à Ultra Haut Module, sont étudiés. Pour chaque procédé de renforcement, différentes configurations de renforcement ont été testées et notamment la mise en précontrainte du plat composite MN avant collage. Cela a permis de mettre en évidence l’efficacité de la technique de collage de plats PRFC pour un renforcement à la fatigue de matériaux métalliques anciens. Par ailleurs, les expressions analytiques simples proposées pour le facteur d’intensité de contraintes pourront par la suite être utilisés pour une application aux structures rivetées en tenant compte de la présence du rivet ainsi que celle des plaques assemblées. / After corrosion, fatigue phenomenon is the main cause of damage in old metallic structures. Fatigue cracks appear in stress concentration area subject to high stresses, and can lead to the ruin of the bridge. In old metallic structures, fatigue cracks mainly occur at the edge of the rivet hole and are thus difficult to detect with the common non-destructive inspection technique (NDI). Moreover, due to the poor quality of the old metallic materials, particularly puddled iron, some of the NDI techniques cannot be used. The main objective of the present work is to study the effectiveness of carbon fibre reinforced polymer (CFRP) laminates in reinforcing fatigue crack emanating from the rivet hole. Thus, investigations on small-scale specimens were done. These specimens consist of metallic plates with center hole from which one single crack emanates. Two metallic materials, puddled iron and mild steel, and two reinforcement processes were used. These reinforcement processes consist of Normal Modulus (NM) and Ultra High Modulus (HHM) CFRP laminates. Furthermore, symmetrical and un-symmetrical reinforcement configurations are considered as well as pre-stressing NM laminates before application. The experimental results showed firstly the efficiency of the different studied reinforcement configurations in slowing down crack propagation. In conclusion of this work, the achieved results, particularly those in terms of Stress Intensity Factor, could be used for reinforcement of riveted structures by CFRP bonding, taking into account the presence of rivets as well as the presence of the others elements of the assembly.

Uniões por prendedores são elementos amplamente utilizados na indústria aeronáutica para a união de partes constituintes da aeronave. Contudo, devido à sua geometria e aos carregamentos sofridos, estes elementos estão frequentemente sujeitos a falhas por fadiga. Assim, para um projeto e dimensionamento bem executado dessas juntas, é necessário conhecer seu comportamento mecânico e o campo de tensões ao qual estão sujeitas. O método dos elementos finitos certamente atende a estas necessidades; porém, o uso de elementos sólidos tridimensionais para a representação destas uniões pode levar a análises demasiadamente demoradas e custosas, sendo desejável o uso de modelos mais simplificados. Nesse trabalho, juntas de topo assimétricas são modeladas pelo método dos elementos finitos, utilizando tanto elementos sólidos tridimensionais quanto elementos de casca, com o objetivo de encontrar um modelo relativamente simples que apresente resultados satisfatórios e requeira um menor tempo de solução. Os resultados numéricos obtidos são comparados com resultados experimentais, que utilizam extensômetros e fotoelasticidade. / Riveted joints are structural elements widely used in the aeronautic industry to connect different parts of the aircraft. However, due to their geometry and working load, they are frequently subjected to fatigue failure. Therefore, to a well executed project of this type of joint, it is necessary to understand the mechanical behavior and the stress field to which they are subjected. The finite element method can certainly answer those needs; however, the use of tridimensional elements to represent this type of joint can lead to time consuming and expensive analysis, being desirable the use of simpler models. In this work, asymmetric butt joints are modeled using the finite element method using both, tridimensional and shell elements, with the objective of finding a model that provides satisfactory results at smaller solution time. The numerical results obtained are compared with experimental results using strain gage and photoelastic procedures.

Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-15Bitstream added on 2014-06-13T18:57:54Z : No. of bitstreams: 1 arbex_aa_me_guara.pdf: 3130393 bytes, checksum: e1c62358ab112fd781ed4b9dfabf900d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Juntas rebitadas sobrepostas representam elementos críticos na construção de estruturas aeronáuticas quando projetadas à fadiga. Por serem elementos de fixação largamente utilizados na indústria aeronáutica, o estudo de suas propriedades e variáveis à fadiga tem sido cada vez mais amplo. A variável que tem mostrado possuir alta influência na resistência à fadiga de juntas rebitadas é a força de aperto aplicada no processo de rebitagem. A vida da peça tende a ser maior quando o valor dessa força é aumentado. O método dos elementos finitos, que é uma ferramenta de cálculo aplicada nos mais diversos campos de atuação e tem se tornado parte indispensável de projetos mecânicos, é utilizado nesta dissertação para a análise de uma junta rebitada sobreposta de uso aeronáutico. A junta é simulada levando em conta as etapas do processo de fabricação e aplicação, a fim de realizar a análise de seu comportamento mecânico e calcular sua vida em fadiga. Através de um teste experimental de tração monotônica foram obtidos valores de deformação com extensômetros, e é feita a correlação desses dados com o modelo numérico a fim de validar a modelagem. Em seguida são feitas mais duas análises com diferentes forças de aperto, com o objetivo de verificar a influência dessa variação na vida em fadiga da peça. / Riveted lap joints represent a critical element in metallic airframe construction when designing against fatigue. These elements are widely used in the aerospace industry, so the study of the fatigue’s properties and variables has been increasingly broad. The variable that has shown to have a high influence on the fatigue strength of riveted joints is the clamping force applied to the riveting process. The life of the part tends to be higher when the clamping force applied is increased. The finite element method, which is a calculation tool applied in various fields of activity and has become an indispensable step of mechanical design, is used in this dissertation for the analysis of a riveted lap joint of aeronautic use. The joint is simulated considering the stages of the manufacturing process and application, in order to perform analysis of mechanical behavior and calculate the fatigue life. Through an experimental test of monotonic tensile, strain values were obtained with strain-gauges, and is made the correlation of these data with the numerical model to validate the modeling. Finally two more tests are made with different clamping forces, in order to check the influence of this variation in fatigue life of the joint.

Uniões por prendedores são elementos amplamente utilizados na indústria aeronáutica para a união de partes constituintes da aeronave. Contudo, devido à sua geometria e aos carregamentos sofridos, estes elementos estão frequentemente sujeitos a falhas por fadiga. Assim, para um projeto e dimensionamento bem executado dessas juntas, é necessário conhecer seu comportamento mecânico e o campo de tensões ao qual estão sujeitas. O método dos elementos finitos certamente atende a estas necessidades; porém, o uso de elementos sólidos tridimensionais para a representação destas uniões pode levar a análises demasiadamente demoradas e custosas, sendo desejável o uso de modelos mais simplificados. Nesse trabalho, juntas de topo assimétricas são modeladas pelo método dos elementos finitos, utilizando tanto elementos sólidos tridimensionais quanto elementos de casca, com o objetivo de encontrar um modelo relativamente simples que apresente resultados satisfatórios e requeira um menor tempo de solução. Os resultados numéricos obtidos são comparados com resultados experimentais, que utilizam extensômetros e fotoelasticidade. / Riveted joints are structural elements widely used in the aeronautic industry to connect different parts of the aircraft. However, due to their geometry and working load, they are frequently subjected to fatigue failure. Therefore, to a well executed project of this type of joint, it is necessary to understand the mechanical behavior and the stress field to which they are subjected. The finite element method can certainly answer those needs; however, the use of tridimensional elements to represent this type of joint can lead to time consuming and expensive analysis, being desirable the use of simpler models. In this work, asymmetric butt joints are modeled using the finite element method using both, tridimensional and shell elements, with the objective of finding a model that provides satisfactory results at smaller solution time. The numerical results obtained are compared with experimental results using strain gage and photoelastic procedures.

No description available.