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Deteção de dano em estruturas tubulares utilizando Funções de Resposta em Frequência
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Estruturas tubulares de paredes finas, de secção circular ou prismática são amplamente
utilizadas na indústria. A grande maioria são fabricadas em material metálico, no entanto, com
o aparecimento dos materiais compósitos e impressão 3D, novas oportunidades de utilização
têm vindo a surgir.
Ao longo do seu tempo de vida estas estruturas estão sujeitas a vários tipos de esforços e
expostas a ambientes que podem levar ao surgimento de dano estrutural. Os tipos de defeitos
verificados em materiais compósitos costumam ser diferentes dos encontrados em metais e os
mecanismos de falha são mais complexos. Torna-se então importante estudar métodos eficazes
de deteção de dano que permitam uma monotorização contínua e a identificação do dano
precocemente, nestas estruturas, de modo a evitar a ocorrência de falhas catastróficas.
Neste trabalho, pretende-se estudar a utilização das Funções de Resposta em Frequência (FRFs)
na deteção e localização de danos em estruturas tubulares de parede fina feitas em material
compósito. As FRFs descrevem a resposta dinâmica do sistema quando é aplicada uma força
excitadora, dentro de uma gama de frequência previamente definida. A sua utilização apresenta
várias vantagens, destacando-se a facilidade de obtenção.
Para testar a sua aplicabilidade, foi realizado um estudo numérico. Começou por ser realizada
uma simulação numérica de uma estrutura tubular de apoio livre-livre, na qual foram
introduzidos danos por redução de massa. Este processo foi repetido utilizando o elemento
finito de viga e utilizando o elemento finito de casca com o objetivo de perceber se ambos os
elementos eram adequados para a simulação da estrutura.
As simulações numéricas para obtenção de resultados são realizadas com o auxílio do programa
Ansys APDL. São criados nove casos de dano ao longo do comprimento da estrutura, variando
os mesmos de localização e severidade e obtidas as FRFs em termos de translação em nove
pontos de medição distribuídos ao longo da superfície da estrutura.
Posteriormente, para a utilização e gestão dos dados das FRFs, foi aplicada uma metodologia,
através do programa MATLAB, que considera como input as FRFs e recorre a indicadores que
permite relacionar as curvas obtidas com e sem dano, possibilitando assim a identificação do
dano.Adicionalmente, é estudada a influência que alguns fatores têm na correta localização do dano,
nomeadamente, a severidade do dano, a quantidade e posição das forças a aplicar para a
localização do dano e a presença de ruído nas respostas obtidas.
Thin-walled, circular or prismatic tubular structures are widely used in industry. The majority are made of metallic material, however, with the advent of composite materials and 3D printing, new opportunities have arisen. Throughout their lifetime, these structures are subjected to various types of stress and exposed to environments that can lead to structural damage. The types of defects found in composite materials are often different from those found in metals and the failure mechanisms are more complex. Therefore, is important to study effective damage detection methods that allow continuous monitoring and identification of early damage in these structures to prevent failures or catastrophes. This work aims to study the use of Frequency Response Functions (FRFs) in the detection and localization of damage in thin-walled tubular structures made of composite materials. FRFs describe the dynamic response of the system when an exciting force is applied within a previously defined frequency range. Their use has several advantages, the biggest being the ease with which they can be obtained. To test their applicability, a numerical study was carried out. First, a numerical simulation of a free-standing tubular structure was carried out, in which mass reduction damage was introduced. This process was repeated using a beam finite element and a shell finite element to determine whether both elements were suitable for simulating the structure. Numerical simulations are carried out using the Ansys APDL program to obtain the results. Nine damage cases were created along the length of the structure, changing their location and severity, and the FRFs were obtained in terms of translation at nine measurement points distributed along the surface of the structure. Subsequently, to use and manage the FRF data, a methodology was applied using the MATLAB program, which takes the FRFs as input and uses indicators to relate the curves obtained with and without damage, thus making it possible to identify the damage. In addition, the influence that certain factors have on the correct location of the damage is studied, namely the severity of the damage, the amount and position of the forces to be applied to locate the damage and the presence of noise in the responses obtained.
Thin-walled, circular or prismatic tubular structures are widely used in industry. The majority are made of metallic material, however, with the advent of composite materials and 3D printing, new opportunities have arisen. Throughout their lifetime, these structures are subjected to various types of stress and exposed to environments that can lead to structural damage. The types of defects found in composite materials are often different from those found in metals and the failure mechanisms are more complex. Therefore, is important to study effective damage detection methods that allow continuous monitoring and identification of early damage in these structures to prevent failures or catastrophes. This work aims to study the use of Frequency Response Functions (FRFs) in the detection and localization of damage in thin-walled tubular structures made of composite materials. FRFs describe the dynamic response of the system when an exciting force is applied within a previously defined frequency range. Their use has several advantages, the biggest being the ease with which they can be obtained. To test their applicability, a numerical study was carried out. First, a numerical simulation of a free-standing tubular structure was carried out, in which mass reduction damage was introduced. This process was repeated using a beam finite element and a shell finite element to determine whether both elements were suitable for simulating the structure. Numerical simulations are carried out using the Ansys APDL program to obtain the results. Nine damage cases were created along the length of the structure, changing their location and severity, and the FRFs were obtained in terms of translation at nine measurement points distributed along the surface of the structure. Subsequently, to use and manage the FRF data, a methodology was applied using the MATLAB program, which takes the FRFs as input and uses indicators to relate the curves obtained with and without damage, thus making it possible to identify the damage. In addition, the influence that certain factors have on the correct location of the damage is studied, namely the severity of the damage, the amount and position of the forces to be applied to locate the damage and the presence of noise in the responses obtained.
Descrição
Palavras-chave
Deteção e localização de dano Funções de Resposta em Frequência Estrutura tubular de parede fina