Full-Scale Blade Testing Enhanced By Acoustic Emission Monitoring


To appear in the proceedings of European Wind Energy Conference - EWEC 2003

D. J. Lekou, P. Vionis, P. A. Joosse, D. R. V. van Delft, D. Kouroussis, A. Anastasopoulos, M. J. Blanch, A. G. Dutton, A. Proust


Current wind turbine blade certification procedure requires static and fatigue tests on the full-scale blade, to ensure that the blade can sustain design loads and to assess its behavior during service life. During these tests sudden audible cracking sounds from somewhere within the blade are often generated, without the operators being able to locate the noise source or to evaluate the existence or the extent of any damage. As blade structures continue to grow in size the detection of any damage, whether through visible inspection or through the location of the sound source becomes an indomitable task for the test engineer. Moreover, since applied loading increases along with the size growth of the blade, it is also important to have a forewarning of any impending failure, since the energy released by such an event becomes enormous due to the high forces. Both these issues can be improved by the use of acoustic emission (AE) monitoring methodology in parallel with standard testing procedures. Within the framework of an EU-funded project named AEGIS (JOR3-CT98-0283), a comprehensive assessment of the application of AE monitoring complementing structural testing of composite material blades was conducted and respective methodologies were developed.

A previously developed testing procedure for small blades incorporating AE monitoring was applied to full-scale static and fatigue tests of commercial quality and size blades. Two 16m blades were driven to failure following current certification testing procedures, enhanced, however, through the quasi on-line analysis of the AE data. On-line analysis of AE data included damage location and criticality assessment by use of pattern recognition software previously calibrated through tests on small blades. The methodology was assessed investigating the possibility of including AE monitoring during standard blade certification tests.

Results from a static and a fatigue test of the 16m blades following the developed methodology, which were carried out within AEGIS project, are presented revealing that the applied methodology can be successfully applied to large commercial blades. Although some size and material related issues might need some refinement, when passing the pattern recognition software from smaller to larger blades, results from both tests show that critical areas can be effectively identified and assessed with respect to the blade's structural integrity. Especially when combining standard measuring methods during blade testing, e.g. strain reading, with AE monitoring, the test operator is fortified against untraceable damage.