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Damage Detection in Wind Turbine Blades using two
Different Acoustic Techniques
Abstract
Facing the climate change the use of renewable energies gains in importance. Especially the wind
energy branch grows very fast. Bigger and more powerful wind mills will be built in the next
decades and the safety of the mills will play a major role. Wind turbines are treated as buildings
and therefore have to be inspected at regular intervals. Especially the turbine blades are highly
stressed during operation and a blade breakdown can cause a big economic damage.
The turbine blades consist of glass fiber reinforced plastics (GFRP) and sandwich areas
containing wood or plastic foam. The blades are manufactured as two halves and glued together
afterwards. Typical damages are delaminations within the GFRP or the sandwich and missing
adhesive or deficient bond at the bonding surfaces.
The regular inspections of wind turbine blades are done manually by experts and are limited
to visual appraisals and simple tapping tests. To improve the safety of wind turbine blades nondestructive
testing techniques using acoustic waves are being developed.
To detect delaminations within the laminates of the turbine blade a local resonance
spectroscopy is used. A small hammer is used to tap onto the blade and the excited sound is
recorded using a microphone. A structural change within the material is displayed in a change of
the frequency content. Furthermore the exciting signal is recorded and gives additional
information about the structural health of the wind turbine blade.
To detect missing or kissing bond areas from the outside of the blade the impulse-echotechnique
is used. An ultrasonic pulse is sent into the material and is reflected at flaws or material
boundaries. This pulse has to be strong because the GFRP are highly damping. It is difficult to
see through several centimeters of GFRP and the choice of the ideal transducer is very important.
To inspect bonding areas from outside the blade will be a great advance in wind turbine safety. |
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发表于 2009-4-27 21:32:21
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