Uncovering the Fatigue Degradation Mechanisms in Composite Materials Used in Wind Turbine Blades

Being able to observe and understand fatigue damage in the load carrying laminates of wind turbine blade plays an important role designing longer and lighter turbine blades and thereby making it possible to increase the size of wind turbines or to upgrade existing turbines for lower wind classes’. Thereby it will be possible to lower the cost of energy for wind energy based electricity.

In the presented study, the governing fatigue failure mechanism is uncovered in a typical non-crimp quasi-unidirectional glass fiber fabric reinforced polymer matrix composites used in conventional wind turbine blades. The study utilize two non-destructive experimental techniques (in-situ trans-illuminated white light imagining and ex-situ 3D x-ray tomography) used to uncover the interaction between the fatigue damage initiation in the backing bundles and the fatigue failure in the load carrying fibers.

The study show that both tension/tension and tension/compression fatigue damage of the investigated composites is govern by the architecture of the backing bundles leading to a fatigue damage very different from the compression/compression fatigue damage mechanism. For the tension/tension fatigue, a modified cure profile of an epoxy-based composite is used in order to delay those failure mechanisms and thereby raising the fatigue resistance of the composites.