ACOUSTIC EMISSION & NDT SCIENTIFIC PUBLICATIONS

 

Acoustic Emission Monitoring from Wind Turbine Blades Undergoing Static and Dynamic Fatigue Testing

 

British Journal of NDT Insight, Vol. 42, No. 12, p. 805-808, December 2000

(Originally published at the proceedings of 15^th World Conference on NDT, Rome, Italy, 15-21 October, 2000)

A. G. Dutton, M. Blanch, P. Vionis, V. Kolovos, D. R. Van Delft, P. Joosse, A. Anastasopoulos, D. Kouroussis, T. Kossivas, J. ter Laak, T. Philippidis, Y. Kolaxis, G. Fernando, G. Zheng, T. Liu, A. Proust

 

The ever increasing size (and hence cost) of wind turbine blades and the desire of developers to start siting their machines offshore place an ever higher premium on the need for effective condition monitoring of the blades.

A current EC-funded research project is looking at the possibility of using acoustic emission (AE) monitoring for proof-testing of the fibre composite blades. Results will be presented from two static blade tests and one dynamic fatigue test conducted to failure in the laboratory.

The test methodology will be presented and discussed in the context of the blade certification procedure followed by the manufacturers. In order to be acceptable, the test procedure must enable maximum benefit to be gained from the AE readings, but at the same time not inflict additional damage to the blade than occurs during the normal certification test.

For static testing a series of load-hold steps were applied to the blades and acoustic emission recorded continuously. Results using zonal and linear location techniques will be presented progressively through the tests until the final failure of the blades. The location of this failure is clearly indicated by the AE emissions during the last load step.

For fatigue testing, only periodic monitoring of hit data was possible in order to avoid hard disk saturation. Only the absolute signal level and absolute energy were recorded on a continuous basis. Periodic measurement of hit data was made during the regular slower load cycles which are a normal part of the test to evaluate stiffness degradation.

Inferences will be drawn about small differences in the manufacture of the nominally identical blades and conclusions presented for the further development of the methodology during the remainder of the project.