The electro-mechanical (E/M) impedance-based method is one important and effective method in damage detection. The basic concept is to monitor the variations in the structural mechanical impedance spectrum caused by damage in the structure. Comparing the impedance spectrum to a baseline measurement of the undamaged structure, the real part of the E/M impedance reflects the state of structural health in the local area. The structural damage can be localized and a local-area self-sensing method is implemented. In this paper, an aluminium plate mounted on an electromagnetic shaker is used to detect growing fatigue damage. For the case of a static artificial damage the concept is also demonstrated to an Airbus A320 fuselage part using 9 self-sensing elements on the stringers. The sensitivity of the damage indicator decreases as the distance between actuator and damage crack increases. For the E/M impedance method to choose an appropriate frequency range is a vital step which also determines the detectable size of the cracks. A frequency range of 10-20kHz was used in this study. The impedance test can be performed on-line during the running operational load which was demonstrated by the shaker at a frequency of 18 Hz and this dynamical form of testing worked much better than the off-line test, where the very sharp fatigue crack was closed again. For practical applications the PZT material data like ultimate strength or fatigue strength have to be known in order to place the actuators in a well-suited position. The dilemma is how to be close to the critical place without damaging also the actuator material. An effective method should be developed to detect the health of the piezo actutors on the host structure.
Monitoring of growing fatigue damage using the E/M impedance method
Überwachung von Risswachstum und Materialermüdung anhand der elektromechanischen Impedanz
2007
6 Seiten, 12 Bilder, 6 Quellen
Conference paper
English
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