Assessment of structural deterioration due to in-service and environmental loads is an essential element in ensuring safety, operability and long life of civilian and military aircrafts. Even for relatively new structures early signs material deterioration can be observed at the micro-scale. Material degradation often progresses further leading to coalescence of micro-failures and formation of one or several macro-cracks. Although the onset of the macro-scale cracking can be reliably detected by modern SHM methods, there is an increasing need for inspection technologies that may allow for assessing structural damage at a wide range of material scales, i.e. from micro to macro. This contribution presents a nonlinear acoustic vibro-acoustic modulation technique (VAMT) that is sensitive to micro and macro scale material imperfections ranging from dislocations conglomerations to delaminations and cracks. VMT utilizes a combined excitation comprising of a high frequency ultrasonic wave and low frequency vibrations that interact at the damage interface producing distinctive sideband components at the spectrum of the received signal. Assessment of material nonlinearity, and thus damage severity, is achieved by measuring the modulation index defined as a ratio of amplitudes of the sideband and the fundamental frequencies. Practical examples of the micro scale nonlinear acoustic damage detection in aerospace materials are provided and damage prediction methodologies are discussed. Experimental studies suggest that VAMT is a valuable tool for continuous structural health monitoring of aging aircraft components before and after the macro-scale fracture.
Nonlinear vibro-acoustic modulation technique for life prediction of aging aircraft components
Nichtlineares vibro-akustisches Modulationsverfahren für die Lebensdauervorhersage von alternden Flugzeugkomponenten
2006
8 Seiten, 5 Bilder, 23 Quellen
Conference paper
English
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