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Detection of damages in beams and composite plates by harmonic excitation and time- frequency analysis
In structural health monitoring, multiple non destructive techniques such as thermography, eddy current and/or vibration monitoring may be used for detecting at early stage structural changes produced by corrosion, rivet damages or structural cracks. The aim of this study is to investigate an effective monitoring technique for detecting structural damage when it occurs. To answer to this problem, many studies have been based on the fact that the natural frequencies must decrease when the structure presents a weakening. The modal approach may work when the crack remains open. However, the natural frequency monitoring has been usually proved not very sensitive at the early stage of crack occurrence. In this study, there exists especial interest in fatigue breathing cracks. A breathing crack opens and closes periodically under an external excitation. It results in a periodically structural stiffness variation. It is a non-linear vibration problem. Consequently, the natural frequencies are periodically moving. This stiffness variation induces a variation of the critical damping and damping rate. It results in a response amplitude variation during one cycle that produces modulation frequencies and harmonics in the frequency domain. Consequently, method has been based on an external input to the structure that produces an harmonic excitation at a specific frequency which is equal to half of its first natural frequency. When there is no crack, the structure answers with a pure harmonic signal at this excitation frequency while when a crack appears, a second harmonic of the excitation frequency occurs with its amplitude amplified by the coincidence with the natural frequency. As the natural frequency is moving at each half cycle, the amplitude at the second harmonic is modulated and a time frequency analysis is required. The theoretical and experimental approach of this new method has been developed for cracked beams and theoretically applied to composite plates with delamination.
Detection of damages in beams and composite plates by harmonic excitation and time- frequency analysis
In structural health monitoring, multiple non destructive techniques such as thermography, eddy current and/or vibration monitoring may be used for detecting at early stage structural changes produced by corrosion, rivet damages or structural cracks. The aim of this study is to investigate an effective monitoring technique for detecting structural damage when it occurs. To answer to this problem, many studies have been based on the fact that the natural frequencies must decrease when the structure presents a weakening. The modal approach may work when the crack remains open. However, the natural frequency monitoring has been usually proved not very sensitive at the early stage of crack occurrence. In this study, there exists especial interest in fatigue breathing cracks. A breathing crack opens and closes periodically under an external excitation. It results in a periodically structural stiffness variation. It is a non-linear vibration problem. Consequently, the natural frequencies are periodically moving. This stiffness variation induces a variation of the critical damping and damping rate. It results in a response amplitude variation during one cycle that produces modulation frequencies and harmonics in the frequency domain. Consequently, method has been based on an external input to the structure that produces an harmonic excitation at a specific frequency which is equal to half of its first natural frequency. When there is no crack, the structure answers with a pure harmonic signal at this excitation frequency while when a crack appears, a second harmonic of the excitation frequency occurs with its amplitude amplified by the coincidence with the natural frequency. As the natural frequency is moving at each half cycle, the amplitude at the second harmonic is modulated and a time frequency analysis is required. The theoretical and experimental approach of this new method has been developed for cracked beams and theoretically applied to composite plates with delamination.
Detection of damages in beams and composite plates by harmonic excitation and time- frequency analysis
Schadensnachweis in Trägern und Verbundplatten durch Oberwellenerregung und Zeit-Frequenz-Analyse
Ouahabi, A. (author) / Thomas, M. (author) / Lakis, A.A. (author)
2006
8 Seiten, 8 Bilder, 8 Quellen
Conference paper
English
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