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Previsão do tempo de vida de fadiga da aeronave Epsilon TB-30 baseada em ensaios experimentais representativos da operação da aeronave em provetes que simulam as zonas críticas
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Abstract(s)
Os objetivos do presente trabalho são a caracterização do regime de operação e a previsão do tempo de vida de fadiga da frota Epsilon TB-30 da Força Aérea Portuguesa, através da implementação de um sistema de Structural Health Monitoring na referida aeronave. A implementação deste sistema consistiu na instrumentação de uma das aeronaves da frota, através da instalação de um acelerómetro perto do centro de gravidade da aeronave, de cinco extensómetros em localizações críticas da mesma e de um sistema de aquisição de dados.
Esta instrumentação possibilitou a recolha de dados de voo que permitiram a definição de funções transferência, correlacionando a aceleração da aeronave com a extensão nas localizações críticas da mesma. A análise de dados de voo de aceleração provenientes de uma anterior instrumentação permitiu a obtenção do espetro de carga acumulado para 1000HV , na qual se utilizaram filtros de sinal e o método de contagem de ciclos level cross counting.
Com o objetivo de caracterizar o regime de operação da frota, estabeleceu-se uma comparação de severidade com o regime de operação de referência considerado pelo fabricante da aeronave. A metodologia utilizada consistiu no cálculo do dano acumulado e no estudo da propagação de fissuras, para a qual se geraram sequências de carga aleatórias a partir dos espetros de carga acumulados para 1000HV .
O estudo da propagação de fissuras incluiu uma componente numérica, através dos modelos de propagação de Walker e NASGRO implementados no software AFGROW © e de um modelo de elementos finitos desenvolvido no software ABAQUS©.
Adicionalmente, incluiu uma componente experimental, através de ensaios de fadiga com amplitude variável realizados no Instituto Superior Técnico. No âmbito da propagação de fissuras, projetou-se um provete representativo de uma das localizações críticas da aeronave numa liga de alumínio 2024-T351, no qual se inseriu um entalhe de canto por eletroerosão.
Os resultados do presente estudo poderão contribuir para um ajuste do programa de manutenção da aeronave e fornecer, ao fabricante, informação quantitativa dos esforços existentes nas localizações críticas da mesma.
The objectives of this work are the characterization of the Portuguese Air Force Epsilon TB-30 fleet operation and the fatigue lifetime predicition with the implementation of a Structural Health Monitoring system in this aircraft. The implementation of this system comprised the installation of one accelerometer near the aircraft center of gravity, five strain sensors in five critical locations and a data acquisition unit. Flight data was recorded with this system, allowing the definition of transfer functions that correlate the aircraft acceleration with the strain in the critical locations. The analysis of acceleration flight data from a previous instrumentation, using signal filters and the level cross counting method, allowed the definition of the 1000 flight hours accumulated load spectrum. The objective of characterizing the fleet operation led to the need of establishing a severity comparison with the reference operation considered by the aircraft manufacturer. The methodology used in this work consisted of the accumulated damage calculation and a crack propagation study, for which random load sequences were generated based on the 1000 flight hours accumulated load spectra. The crack propagation study included a numerical approach with the Walker and NASGRO crack propagation models in the AFGROW© software and a finite element model developed in the ABAQUS© software. Additionally, it included an experimental approach with variable amplitude fatigue tests performed in Instituto Superior Técnico. In the scope of the crack propagation study, a 2024-T351 aluminium alloy representative specimen of one of the aircraft critical locations was designed, in which a corner notch was inserted by electrical discharge machining. The results of the present study may contribute to a possible change of the aircraft maintenance program and provide quantitative information about the stresses in the aircraft critical locations to the manufacturer.
The objectives of this work are the characterization of the Portuguese Air Force Epsilon TB-30 fleet operation and the fatigue lifetime predicition with the implementation of a Structural Health Monitoring system in this aircraft. The implementation of this system comprised the installation of one accelerometer near the aircraft center of gravity, five strain sensors in five critical locations and a data acquisition unit. Flight data was recorded with this system, allowing the definition of transfer functions that correlate the aircraft acceleration with the strain in the critical locations. The analysis of acceleration flight data from a previous instrumentation, using signal filters and the level cross counting method, allowed the definition of the 1000 flight hours accumulated load spectrum. The objective of characterizing the fleet operation led to the need of establishing a severity comparison with the reference operation considered by the aircraft manufacturer. The methodology used in this work consisted of the accumulated damage calculation and a crack propagation study, for which random load sequences were generated based on the 1000 flight hours accumulated load spectra. The crack propagation study included a numerical approach with the Walker and NASGRO crack propagation models in the AFGROW© software and a finite element model developed in the ABAQUS© software. Additionally, it included an experimental approach with variable amplitude fatigue tests performed in Instituto Superior Técnico. In the scope of the crack propagation study, a 2024-T351 aluminium alloy representative specimen of one of the aircraft critical locations was designed, in which a corner notch was inserted by electrical discharge machining. The results of the present study may contribute to a possible change of the aircraft maintenance program and provide quantitative information about the stresses in the aircraft critical locations to the manufacturer.
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Keywords
Epsilon TB-30 Fadiga Structural Health Monitoring Espetro de carga Dano acumulado Propagação de fissur