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Fatigue performance of adhesively bonded spars of wind turbine rotor blades

: Nagel, C.

Adhesion Society -AS-, Bethesda/Md.:
37th Annual meeting of the Adhesion Society 2014. Proceedings : San Diego, California, USA, 23 - 26 February 2014
Red Hook, NY: Curran, 2014
ISBN: 978-1-63266-320-7
Adhesion Society (Annual Meeting) <37, 2014, San Diego/Calif.>
Fraunhofer IFAM ()

The beam tests have shown that normal stress cracks in the bond line already appear after a relatively short time period, with crack tips penetrating into the laminate. This is very similar to the situation in real rotor blades, so there seems to be a potential risk of crack propagation from the bond line crack tips. Beam tests have further shown that cracks grow near the interface within the laminate, starting at the tips of the normal stress cracks, and finally leading to the de-bonding of the spar caps. Because this explains the fracture surface appearance of broken blades, it is considered to be a likely scenario of failure in rotor blades. Simulations of the beam test have shown that the critical state is reached by the coagulation of several subcritical, near-interface cracks rather than by exceeding Gc within a single crack. This clearly shows that knowing the critical, static Gc value is not sufficient. The propagation rate for near-interface cracks, as a function of the local strain energy release rate, should be considered instead. Simulations of the beam tests have further shown that bond line crack initiation and near-interface crack growth as measured in the test beam could be modeled with relatively high accuracy at fully reversed, cyclic fatigue loading. This indicates that the risk of failure in rotor blades may be reduced by considering crack initiation and growth using the suggested methods.