Desenvolvimento de modelos de previsão da vida à fadiga de ligações rebitadas
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Data
2008
Autores
Correia, José António Fonseca de Oliveira
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Resumo
A presente dissertação tem como tema principal o desenvolvimento de modelos de previsão da vida à fadiga de ligações rebitadas. Este estudo visa, essencialmente, a apresentação de resultados do modelo de previsão baseado em duas fases de crescimento de fendas, para efeitos de apresentação de previsões da vida à fadiga de ligações rebitadas e de demonstração dos efeitos benéficos na resistência à fadiga do pré-esforço nos rebites.
Para a modelação da resistência à fadiga de ligações rebitadas através de modelos de elementos finitos de ligações rebitadas assumiu-se a existência de fendas a emanar dos furos dos rebites, determinando-se, desta forma, factores de intensidade de tensões através da técnica modificada do fecho de fenda virtual. Com base nos valores numéricos dos factores de intensidade de tensões, foram realizadas previsões de propagação das fendas de fadiga até à rotura final das ligações, sendo estas previsões comparadas com os resultados experimentais.
Também se propõem modelos de elementos finitos paramétricos de ligações rebitadas que permitem a avaliação das localizações críticas das ligações rebitadas e a determinação das histórias das deformações e tensões elastoplásticas nesses pontos críticos, utilizadas para a determinação do número de ciclos necessário à iniciação de fendas de fadiga.
Este trabalho também serviu para gerar informação experimental relativa à resistência à fadiga de ligações rebitadas e à caracterização do comportamento à fadiga de um material usado em pontes metálicas rebitadas. Este comportamento à fadiga inclui as respostas elastoplásticas cíclicas, as relações deformação-vida e a resistência à propagação de fendas de fadiga.
The main theme of this thesis is the development of procedures for fatigue life prediction of riveted connections. The proposed procedures are based on a two-phase fatigue model that assesses the crack initiation and propagation according to distinct approaches. The proposed procedures area able to demonstrate the beneficial effects on fatigue strength or fatigue life of the clamping force of the rivets. While the crack initiation was modeled using local approaches, such as the strain-life approach, the crack propagation was based on the Linear Elastic Fracture Mechanics. Both analyses were supported by 3D finite element calculations. Two types of finite element models were built, namely models without cracks, to derive the critical locations and the respective elastic stress concentration factors, and models with cracks to derive the stress intensity factors according to the virtual crack closure technique. The proposed procedures were applied to a riveted shear splice from the Portuguese railway Trezói bridge. An experimental program was conducted to derive the required experimental data of the material (ex: strain-life curves, crack growth curves), as well as the fatigue strength of the connection. The performance of the proposed procedures was assessed through comparisons between predictions and experimental data available for the riveted connection. The comparisons revealed very consistent predictions, which are justified by the separate assessment of both crack initiation and propagation phases. The proposed model requires the support of a 3D finite element model able to account the local geometric features as well as the rivet clamping effects.
The main theme of this thesis is the development of procedures for fatigue life prediction of riveted connections. The proposed procedures are based on a two-phase fatigue model that assesses the crack initiation and propagation according to distinct approaches. The proposed procedures area able to demonstrate the beneficial effects on fatigue strength or fatigue life of the clamping force of the rivets. While the crack initiation was modeled using local approaches, such as the strain-life approach, the crack propagation was based on the Linear Elastic Fracture Mechanics. Both analyses were supported by 3D finite element calculations. Two types of finite element models were built, namely models without cracks, to derive the critical locations and the respective elastic stress concentration factors, and models with cracks to derive the stress intensity factors according to the virtual crack closure technique. The proposed procedures were applied to a riveted shear splice from the Portuguese railway Trezói bridge. An experimental program was conducted to derive the required experimental data of the material (ex: strain-life curves, crack growth curves), as well as the fatigue strength of the connection. The performance of the proposed procedures was assessed through comparisons between predictions and experimental data available for the riveted connection. The comparisons revealed very consistent predictions, which are justified by the separate assessment of both crack initiation and propagation phases. The proposed model requires the support of a 3D finite element model able to account the local geometric features as well as the rivet clamping effects.
Descrição
Dissertação de Mestrado em Engenharia Civil, domínio científico da Engenharia Estrutural
Palavras-chave
Resistência dos materiais , Fadiga dos materiais , Fractura dos materiais , Tensão dos materiais