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Source mechanisms of acoustic emissions as an indicator of injury during a full scale fatigue test of a wind turbine rotor blade

: Schubert, L.; Schulze, E.; Frankenstein, B.

Roeck, G. de:
8th International Conference on Structural Dynamics, EURODYN 2011. Proceedings : Leuven, Belgium, 4 - 6 July 2011
Leuven, 2011
ISBN: 978-90-76019-31-4
European Conference on Structural Dynamics (EURODYN) <8, 2011, Leuven>
Conference Paper
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()

To operate wind turbines safely and efficiently, condition monitoring for the main components are of increasing importance. Especially, the lack of access of offshore installations increases inspection and maintenance costs. The installation of a condition monitoring system will cause a decisive impact on reliability and maintenance and considerably reduce down times by condition dependent inspections. So far, such systems are installed only in a low percentage of the wind turbines. Furthermore, there is a limitation on monitoring of changes in Eigen frequencies. Usually, this type of information does not provide a spatial resolution necessary for damage detection and localization of structural changes. The current work at Fraunhofer IZFP Dresden in the field of monitoring of wind turbines is focused on the development of a condition monitoring systems for rotor blades. The monitoring concept is based on a combination of low frequency integral vibration monitoring and a coustic monitoring techniques in the frequency range between 10 kHz and 100 kHz using guided waves. The paper is focused on the results of the acoustic emission measurements that were used in a full-scale fatigue test at a rotor blade made from carbon- and glass fiber reinforced plastics (CFRP, GFRP) with an overall length of 40 meters. The spatial and temporal development of the acoustic emissions and their signal parameters can be used as damage indicator. Moreover, the test instrumentation and results of acoustic emission measurements on a rotating rotor blade are shown. When using acoustic emission on such a field installation one has to overcome additional parameters caused by environmental influences like rain and wind speed to name a few of them. It can be shown, that the acoustic emission hit rate correlates with wind speed.