The objective of this study is to model and analyze a three dimensional single riveted lap joint (with and without a crack). By using finite element method, stress and fracture analyses are carried out under both the residual stress field and external tensile loading. Using a two step simulation, riveting process and subsequent tensile loading of the lap joint are simulated to determine the residual and overall stress state. Residual stress state due to riveting is obtained by interference and clamping misfit method. By employing different interference and clamping misfit values, the effects of riveting process parameters on stress state are examined. Two cracks namely the semi elliptical surface crack at faying surfaces of plates and the quarter elliptical corner crack at rivet hole are the most widely observed crack types in riveted joints. Fracture analysis of cracked riveted joints is carried out by introducing these two crack types to the outer plate at a plane perpendicular to the loading. The mixed mode stress intensity factors (SIFs) and energy release rates (G) around the crack front are obtained by using displacement correlation technique (DCT). Effects riveting process parameters (interference and clamping ratios) and geometrical parameters (crack shape and size) on fracture parameters are studied. The stress intensity factor solutions presented herein could be useful for correlating fatigue crack growth rates, fracture toughness computation, and multiple site damage (MSD) analysis in aircraft bodies.

La thèse s’inscrit dans un axe de recherche visant à améliorer l’analyse par éléments finis (EF) des structures aéronautiques soumises au crash et à l’impact. L’étude s’intéresse, en particulier, à la modélisation des assemblages rivetés dans les calculs de structures, qui sont des zones de concentrations de contraintes propices à l’initiation de ruptures. Si la rupture de la fixation est maîtrisée, les modes de rupture dus aux perforations sont, quant à eux, difficiles à simuler dans un calcul sur structure complète. Afin de prendre en compte avec précision l’influence des perforations sur la réponse mécanique de telles structures, un super-élément perforé à 8 nœuds a été formulé lors d’une précédente thèse. Cependant, sa frontière interne est analytique et libre de chargement, ce qui rend difficile la connexion avec un élément rivet, et donc la modélisation de l’assemblage. L’étude proposée ici consiste donc à développer un super-élément perforé qui soit capable de tenir compte de l’influence de la perforation sur les champs mécaniques, d’une part, et qui soit formulé de façon à rendre possible l’interaction avec un macro-élément rivet, d’autre part. / The thesis is made in a context which consists in improving the finite element (FE) analysis of full-scale aircraft structures subjected to crash and impact loadings. The study is focused, in particular, on the rivetedassemblies modeling in structural computations, which are stress concentrations areas where ruptures initiation can occur. If the fastener rupture is mastered, the rupture modes due to perforations are, however, difficult to simulate in a complete structure computation. In order to accurately take into account the perforations influence on the mechanical response of such structures, a perforated super-element featuring 8 nodes have been formulated in a previous thesis. Nevertheless, its internal boundary is analytic and free of loads, which makes difficult the connection with a rivet element, and consequently the assembly modeling. The study proposed here consists in the developement of a perforated super-element which is, on the one hand, able to take into account the perforation influence on the mechanical fields, and which is, on the other hand, formulated such as the interaction with a rivet macro-element is possible.

<p>Pack-rust corrosion is a type of corrosion that affects steel built-up members especially old  bridges. It is a localized corrosion that happens in the crevice between two mating surfaces. Pack-rust corrosion does not only cause section loss like other types of corrosions, but also induces local distortion in the structural members that are not the intention of the original designs. This corrosion can change the behavior of the connection fixity and could also cause instability in the overall  built-up members. The size of distortion and section loss were observed to behave linearly between  the free edge and the first line of fasteners. As the distance is moving toward the free edge, the  distortion in the members and section loss in the base material were observed to be maximum. Another important observation was that pack-rust corrosion does not grow beyond the fastener at the fastener’s line. </p> <p>The literature revealed that there are no comprehensive experimental and analytical studies focused on the behavior and effect of pack-rust corrosion on the overall performance of built-up members and connections in compression. Therefore, this research studies the effects of pack-rust corrosion on the capacity of built-up compression members including but not limited to stiffness, yield strength, maximum capacity, and change in fastener force under applied load. This research was studied by performing large-scale experimental testing of flexural members with simulated pack rust. Pack-rust distortion was simulated by placing washers in the crevice between two plates and then the two plates were drawn together using high-strength fasteners. There were also members with real pack-rust corrosion damage from bridge components that used to be in service, and were tested in axial compression tests. </p> <p>The experimental results were compared with hand calculation using conventional design  equations. Finite element analysis was also studied to compare with the experimental results in  order to calibrate future models, but it is not presented in this report. The findings of the  experimental results of all the specimens show that pack-rust corrosion affects yield strength and  maximum capacity of the member and minimally affects the member’s stiffness. Maximum load  of the member affected by pack-rust corrosion can still be estimated conservatively using the  conventional design equations with some modifications. There was no indication of significant  increase in fastener force under applied load, so the likelihood of fastener failing in tension was  very small as observed from this study.   </p>

No description available.

L'accroissement des performances des équipements de Traction ferroviaire, reposait essentiellement jusqu'à maintenant, sur l'intégration des innovations dans le domaine des composants électriques et des matériaux diélectriques mais la standardisation de sous-ensembles réutilisables nous conduit à reconsidérer les assemblages structuraux des coffres de traction (convertisseurs de puissance). Ces coffres de traction sont assemblés actuellement avec des éléments de fixation mécanique (boulon, rivet), le but est donc d'améliorer la connaissance des comportements mécaniques de ces types d'assemblages à travers d'une étude expérimentale basée sur des essais statiques et dynamiques sur des joints boulonnés et rivetés. Ces essais nous ont permis de valider des modèles numériques par des éléments finis en utilisant les codes de calcul ABAQUS et ANSYS. La deuxième partie de la thèse concerne les assemblages par collage structural. Nous avons étudié la possibilité de remplacer les assemblages mécaniques classiques par l'assemblage par collage structural. La première phase de notre travail a été de recenser et sélectionner des adhésifs structuraux susceptibles de répondre à notre cahier de charge. Dans cette partie les travaux suivants ont été réalisés : - Etude des comportements des adhésifs en tant que matériau, ce qui a nécessité de réaliser des éprouvettes massiques. - Réalisation d'essais expérimentaux en statique et en dynamique sur des joints collés avec l'adhésif sélectionné. - Création des modèles numériques non linéaires en 3D sur ABAQUS pour les joints collés. - Etude hygrothermique accélérée afin d'étudier l'effet du vieillissement sur les assemblages collés en fonction de l'humidité et de la température. / Increased performance of railway traction equipment, until now relied primarily on the integration of innovations in the field of electrical and dielectric materials, but the standardization of subassemblies reusable us to reconsider the structural assemblies of the traction cubicles (power converters). These cubicles are assembled now with mechanical fasteners (bolts, rivets), the first goal is to improve knowledge of the mechanical behaviour of these types of joints through an experimental study based on statics and dynamics tests of bolted and riveted joints. These tests have allowed us to validate numerical models of finite elements by using the computer codes ABAQUS® and ANSYS®. The second part of the thesis deals with the structural adhesive joints. We studied the possibility of replacing conventional mechanical assembly structural bonding. The first phase of our work was to identify and select structural adhesives that could meet our specifications. In this section the following work has been made: - Study of thermo-mechanical behaviour of the adhesive with the bulk Adhesive Test Specimens. - Statics and dynamics test in the bonded joint. - Non-linear 3D finite elements models. - Hygrothermal accelerated to study the effect of aging on the adhesive according to the humidity and temperature.

Foi realizado um estudo comparativo da capacidade de duas variantes do método de radiografia por raios- X em detectar trincas de fadiga em juntas sobrepostas rebitadas de laminado híbrido metal-fibra Glare&reg; de uso aeronáutico. Durante os ensaios mecânicos de fadiga sob amplitude constante de tensão, diversos corpos de prova rebitados foram periodicamente inspecionados por raios-X, em ambas as modalidades convencional e digital. Raios-X em filmes convencionais digital. Raios-X em filmes convencionais proporcionaram ótimo detalhamento de trincas nas juntas mecânicas, enquanto que as imagens geradas pela modalidade digital apresentaram qualidade muito inferior, prejudicando ou até mesmo impedindo a avaliação do grau de integridade estrutural das juntas rebitadas. / A comparison is performed on the ability of two modalities of nondestructive X-ray radiography method in detecting fatigue cracks in riveted lap joints of aeronautical grade fiber-metal laminate Glare&trade;. During constant amplitude loading in fatigue testing riveted specimens were periodically inspected using both the conventional and digital X-ray methodology. Conventional film X-ray modality provided high quality images of growing cracks in the mechanical joints, whereas digital radiography generated faulty images, which impaired or even prevented the structural integrity assessment of the riveted joints.

O processo de fadiga em pontes metálicas ferroviárias é um relevante problema de infraestrutura, largamente reconhecido como uma questão de segurança estrutural que precisa ser melhor compreendida. Apesar dos recentes avanços no campo da modelagem computacional, a aplicação de abordagens modernas para avaliação do comportamento à fadiga de ligações rebitadas típicas de pontes ainda é pouco explorada e impõe desafios. Nesse contexto, esta tese visa implementar metodologias de análise global-local para avaliação de detalhes rebitados de pontes ferroviárias, empregando ferramentas avançadas de análise em elementos finitos para investigação pormenorizada do processo de fadiga. Com o objetivo de contextualizar o comportamento à fadiga de ligações rebitadas, apresentam-se inicialmente as principais metodologias convencionais de avaliação, destacando as limitações dos métodos. Apresentam-se também os principais aspectos da modelagem local em elementos finitos e das metodologias de análise local, enquadrando os regimes de comportamento onde cada abordagem pode ser aplicada. Exemplos em pequena escala são desenvolvidos para testar procedimentos numéricos e investigar a influência dos principais parâmetros que podem influenciar no comportamento local de ligações rebitadas, tais como modelos interfaciais de contato, fricção, pré-esforço nos rebites e distribuição interna de cargas. Análises de sensibilidade são realizadas tomando como referência uma ligação rebitada com uma trinca inicial pré-existente, onde tais efeitos são investigados. São descritos os procedimentos gerais de uma metodologia de modelagem desenvolvida para resolução de problemas que envolvem a integração contínua entre modelos globais e locais e um conjunto de ferramentas criadas para possibilitar o acoplamento entre o programa de simulação em elementos finitos e sub-rotinas customizadas programadas para processamento recursivo dos modelos e análise local da fadiga. A metodologia é então aplicada ao estudo dos detalhes rebitados de uma ponte real. A caracterização do comportamento global da ponte é realizada recorrendo-se aos resultados de simulações estáticas e dinâmicas e do monitoramento de curto prazo da estrutura. Também são apresentados resultados de estudos de sensibilidade e de previsão da vida à fadiga de detalhes críticos da ponte usando o método das tensões nominais e curvas SN baseadas em classes de detalhes. Diferentes aspectos são abordados, tais como a consideração dos efeitos secundários de flexão nas ligações e a influência do tipo de veículo e da configuração do trem. Por último, é realizada uma análise local das ligações rebitadas da ponte ferroviária tomada como estudo de caso. Modelos tridimensionais detalhados das conexões são desenvolvidos em duas etapas. Na primeira são aplicadas técnicas de modelagem hierárquica para avaliar de forma pormenorizada os mecanismos de transferência de cargas entre os membros envolvidos, os efeitos secundários de flexão e a influência de diferentes hipóteses de modelagem. Na segunda etapa, são desenvolvidos submodelos com elementos sólidos e altas densidades de malhas para investigação dos campos de deformações e tensões locais nas regiões apontadas como críticas durante a modelagem hierárquica. As geometrias dos rebites são representadas explicitamente e todas as interações de contato são modeladas. A influência do pré-esforço nos rebites é avaliada. As abordagens ?N e SN são aplicadas para enquadrar o regime de fadiga das ligações, verificar critérios de falha incluindo tensões multiaxiais e fazer previsões da vida de iniciação da trinca. São apresentados os principais resultados das análises bem como as conclusões que corroboram a metodologia empregada. / The fatigue process in steel railway bridges is an important problem of infrastructure, widely recognized as an issue of structural safety that needs to be better understood. Despite the recent advances in computational modeling, application of modern approaches to fatigue assessment of typical riveted bridges is still little investigated and poses challenges. In this context, this thesis aims to implement some methodologies for global-local analyses in riveted details of steel railway bridges using advanced finite element analysis tools for a deep investigation of the fatigue process. In order to contextualize the fatigue behavior of riveted connections, the conventional assessment procedures are initially presented, highlighting the limitations of the methods. The main points of the local finite element modeling and of the local analysis methods are also described, defining the regimes where each approach can be applied. Examples on a small scale to test numerical procedures are developed and the influence of the main parameters that can influence the local behavior of riveted connections is investigated, such as contact interfacial models, friction, clamping force in rivets and internal load distribution. Sensitivity analyses with reference to a riveted connection with a pre-existing initial crack are performed, where such effects are investigated. The general procedures of a modeling methodology developed for problem solving that involves the seamless integration between global and local models and a set of tools created to enable coupling between the finite element simulation program and customized subroutines to recursive processing and fatigue local analysis of the models are described. Then, the methodology is applied to the study of riveted details of a railway bridge. The global behavior of the bridge is performed based on the results of static and dynamic simulations and from short-term monitoring data. The results of sensitivity studies and fatigue life predictions using the nominal stress method and detail class SN curves for critical details of the bridge are also presented. Different aspects, such as the consideration of bending secondary effects at connections and the influence of the vehicle types and train configurations are addressed. Finally, a local analysis is carried out in the riveted railway bridge taken as a case study. Three-dimensional models, detailing the connections in two stages are developed. The first hierarchical modeling techniques are applied to assess the load distribution mechanisms between the members involved, the bending secondary effects and the influence of different modeling assumptions. In the second stage, sub-models with solid elements and high mesh densities for investigation of strain and stress fields in the regions identified as critical by the hierarchical model are developed. The geometries of the rivets are explicitly represented and all contact interactions are modeled. The influence of rivet clamping forces is evaluated. The ?N and SN local approaches are applied to define the fatigue regime in critical points, check failure criteria in multi-axial stresses and to predict the crack initiation life. The main results of the analyses and the conclusions that support the methodology are presented.

O processo de fadiga em pontes metálicas ferroviárias é um relevante problema de infraestrutura, largamente reconhecido como uma questão de segurança estrutural que precisa ser melhor compreendida. Apesar dos recentes avanços no campo da modelagem computacional, a aplicação de abordagens modernas para avaliação do comportamento à fadiga de ligações rebitadas típicas de pontes ainda é pouco explorada e impõe desafios. Nesse contexto, esta tese visa implementar metodologias de análise global-local para avaliação de detalhes rebitados de pontes ferroviárias, empregando ferramentas avançadas de análise em elementos finitos para investigação pormenorizada do processo de fadiga. Com o objetivo de contextualizar o comportamento à fadiga de ligações rebitadas, apresentam-se inicialmente as principais metodologias convencionais de avaliação, destacando as limitações dos métodos. Apresentam-se também os principais aspectos da modelagem local em elementos finitos e das metodologias de análise local, enquadrando os regimes de comportamento onde cada abordagem pode ser aplicada. Exemplos em pequena escala são desenvolvidos para testar procedimentos numéricos e investigar a influência dos principais parâmetros que podem influenciar no comportamento local de ligações rebitadas, tais como modelos interfaciais de contato, fricção, pré-esforço nos rebites e distribuição interna de cargas. Análises de sensibilidade são realizadas tomando como referência uma ligação rebitada com uma trinca inicial pré-existente, onde tais efeitos são investigados. São descritos os procedimentos gerais de uma metodologia de modelagem desenvolvida para resolução de problemas que envolvem a integração contínua entre modelos globais e locais e um conjunto de ferramentas criadas para possibilitar o acoplamento entre o programa de simulação em elementos finitos e sub-rotinas customizadas programadas para processamento recursivo dos modelos e análise local da fadiga. A metodologia é então aplicada ao estudo dos detalhes rebitados de uma ponte real. A caracterização do comportamento global da ponte é realizada recorrendo-se aos resultados de simulações estáticas e dinâmicas e do monitoramento de curto prazo da estrutura. Também são apresentados resultados de estudos de sensibilidade e de previsão da vida à fadiga de detalhes críticos da ponte usando o método das tensões nominais e curvas SN baseadas em classes de detalhes. Diferentes aspectos são abordados, tais como a consideração dos efeitos secundários de flexão nas ligações e a influência do tipo de veículo e da configuração do trem. Por último, é realizada uma análise local das ligações rebitadas da ponte ferroviária tomada como estudo de caso. Modelos tridimensionais detalhados das conexões são desenvolvidos em duas etapas. Na primeira são aplicadas técnicas de modelagem hierárquica para avaliar de forma pormenorizada os mecanismos de transferência de cargas entre os membros envolvidos, os efeitos secundários de flexão e a influência de diferentes hipóteses de modelagem. Na segunda etapa, são desenvolvidos submodelos com elementos sólidos e altas densidades de malhas para investigação dos campos de deformações e tensões locais nas regiões apontadas como críticas durante a modelagem hierárquica. As geometrias dos rebites são representadas explicitamente e todas as interações de contato são modeladas. A influência do pré-esforço nos rebites é avaliada. As abordagens ?N e SN são aplicadas para enquadrar o regime de fadiga das ligações, verificar critérios de falha incluindo tensões multiaxiais e fazer previsões da vida de iniciação da trinca. São apresentados os principais resultados das análises bem como as conclusões que corroboram a metodologia empregada. / The fatigue process in steel railway bridges is an important problem of infrastructure, widely recognized as an issue of structural safety that needs to be better understood. Despite the recent advances in computational modeling, application of modern approaches to fatigue assessment of typical riveted bridges is still little investigated and poses challenges. In this context, this thesis aims to implement some methodologies for global-local analyses in riveted details of steel railway bridges using advanced finite element analysis tools for a deep investigation of the fatigue process. In order to contextualize the fatigue behavior of riveted connections, the conventional assessment procedures are initially presented, highlighting the limitations of the methods. The main points of the local finite element modeling and of the local analysis methods are also described, defining the regimes where each approach can be applied. Examples on a small scale to test numerical procedures are developed and the influence of the main parameters that can influence the local behavior of riveted connections is investigated, such as contact interfacial models, friction, clamping force in rivets and internal load distribution. Sensitivity analyses with reference to a riveted connection with a pre-existing initial crack are performed, where such effects are investigated. The general procedures of a modeling methodology developed for problem solving that involves the seamless integration between global and local models and a set of tools created to enable coupling between the finite element simulation program and customized subroutines to recursive processing and fatigue local analysis of the models are described. Then, the methodology is applied to the study of riveted details of a railway bridge. The global behavior of the bridge is performed based on the results of static and dynamic simulations and from short-term monitoring data. The results of sensitivity studies and fatigue life predictions using the nominal stress method and detail class SN curves for critical details of the bridge are also presented. Different aspects, such as the consideration of bending secondary effects at connections and the influence of the vehicle types and train configurations are addressed. Finally, a local analysis is carried out in the riveted railway bridge taken as a case study. Three-dimensional models, detailing the connections in two stages are developed. The first hierarchical modeling techniques are applied to assess the load distribution mechanisms between the members involved, the bending secondary effects and the influence of different modeling assumptions. In the second stage, sub-models with solid elements and high mesh densities for investigation of strain and stress fields in the regions identified as critical by the hierarchical model are developed. The geometries of the rivets are explicitly represented and all contact interactions are modeled. The influence of rivet clamping forces is evaluated. The ?N and SN local approaches are applied to define the fatigue regime in critical points, check failure criteria in multi-axial stresses and to predict the crack initiation life. The main results of the analyses and the conclusions that support the methodology are presented.

Foi realizado um estudo comparativo da capacidade de duas variantes do método de radiografia por raios- X em detectar trincas de fadiga em juntas sobrepostas rebitadas de laminado híbrido metal-fibra Glare&reg; de uso aeronáutico. Durante os ensaios mecânicos de fadiga sob amplitude constante de tensão, diversos corpos de prova rebitados foram periodicamente inspecionados por raios-X, em ambas as modalidades convencional e digital. Raios-X em filmes convencionais digital. Raios-X em filmes convencionais proporcionaram ótimo detalhamento de trincas nas juntas mecânicas, enquanto que as imagens geradas pela modalidade digital apresentaram qualidade muito inferior, prejudicando ou até mesmo impedindo a avaliação do grau de integridade estrutural das juntas rebitadas. / A comparison is performed on the ability of two modalities of nondestructive X-ray radiography method in detecting fatigue cracks in riveted lap joints of aeronautical grade fiber-metal laminate Glare&trade;. During constant amplitude loading in fatigue testing riveted specimens were periodically inspected using both the conventional and digital X-ray methodology. Conventional film X-ray modality provided high quality images of growing cracks in the mechanical joints, whereas digital radiography generated faulty images, which impaired or even prevented the structural integrity assessment of the riveted joints.

This thesis describes proposal of a methodology for evaluating fatigue life of riveted joints. The first section summarizes the theory used to evaluate fatigue life, description of the structure of operation load spectra and construction principles for the design joints for optimum durability. The second part of the thesis focuses on the proposal of a methodology enabling analytical solutions in closed form suitable for the initial structural design and also numerical solutions for use in detailed analyzes of the structure. The applicability of the methodology is demonstrated on an example of analysis of a real structural detail and subsequent comparison of the analysis with available test results.