IABG has developed a new, considerably improved method for dynamic fatigue testing rotor blades over the prior art that offers significant advantages on existing test methods.
The fatigue strength of rotor blades must be proven to certify wind energy plants. As a rule, this verification comprises over several million load cycles; i.e. by vibration testing rotor blades subject to the resonance principle.
The test frequency is hereby limited by the test item’s natural initial bending frequency, which – for current blades – is well under one Hertz, causing long test durations and high costs. In addition to that, the blade’s bend line that occurs from areodynamic loads in real operation often deviates from the bend line of its initial natural mode during resonance testing. This can lead to local hypo or hyper loads and thus considerably influences the test quality.
The standard to avoid this is to approximate the bend line to real operating conditions by attaching auxiliary masses during testing. However, this decreases the natural frequency and leads to even longer test durations. Due the systemic setup, the test is furthermore carried out in a consistent central position and thus cannot reproduce the variable wind-depended mean loads occurring in real operation.
The improved test method developed by IABG allows for significantly reducing or avoiding these disadvantages. The method facilitates an increase of the natural bend mode, optimising the bend line, as well as adapting the mean load during testing.
The patent for the testing method has in the meantime been granted by the German Patent and Trade Mark Office. In the context of an application example using a real rotor blade it could be shown that IABG’s new method is suited to double the testing frequency while reproducing the desired bend line occurring in real operation at the same time.
As early as in the nineteen-eighties, IABG was able to successfully test the rotor blade of the GROWIAN wind energy plant based on its many years of experience in testing aircraft wings. Thanks to its expertise from various high technology markets, IABG supports leading manufacturers of wind energy plants in terms of method development, as well as in verification by calculation and testing.
