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Acoustic emission analysis in the dynamic fatigue testing of fiber composite components

: Weihnacht, Bianca

Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin; European Working Group on Acoustic Emission -EWGAE-:
31st Conference of the European Working Group on Acoustic Emission, EWGAE 2014. CD-ROM : September 3 - 5, 2014 in Dresden, Germany
Berlin: DGZfP, 2014 (DGZfP-Berichtsbände 149)
ISBN: 978-3-940283-63-4
8 S.
European Working Group on Acoustic Emission (EWGAE Conference) <31, 2014, Dresden>
Fraunhofer IKTS ()

The main objective of dynamic fatigue tests is the initiation of slowgrowing damages in composite structures. For this purpose, the load spectrum has to be adjusted accordingly when the first indications of damage occur. For damage detection, the acoustic emission analysis has been successfully used for small scale analyses of bonded joints applied for especially manufactured beam structures and dynamic tests of wind turbine rotor blades. The acoustic emission testing is well accepted for static testing of fiber composite components, since high energetic acoustic emissions are initiated in fiber composites by fiber breaks and delamination processes during damaging. The challenge lies in the application of the method during dynamic fatigue tests, in filtering influences from the strong noise environment and in the unfavorable acoustic properties of composite materials. These requirements are met by an acoustic measurement system with high measurement dynamics, the storage and the assessment of the complete waveforms and specific evaluation and tracking algorithms which is presented in this paper. The range of the detected acoustic waves is determined by the damping properties of the composite material. Therefore, a sensor network has been developed which monitors the highly stressed parts like the web connections of the blades. Depending on the blade type, 52 to 60 sensor nodes were installed for an array of 3 by 5 meters. During the dynamic fatigue testing of the rotor blades on test plants, the growing damage of specific leaf elements has manifested itself as a result of the acoustic emission testing. Areas of increased AE event density were correlated to a damage of the cap-web bonding and undulations in the fiberglass spar caps by other non-destructive testing methods. The structural components failed after a specific time evolution of the acoustic emissions events.