Structural health monitoring method for wind turbine trailing edge: Crack growth detection using Fibre Bragg Grating sensor embedded in composite materials

In this article a novel method to assess a crack growing/damage event in composite material using Fibre Bragg Grating (FBG) sensors embedded in a host material and its application into a composite material structure, Wind Turbine Trailing Edge, is presented. A Structure-Material-FBG model was developed, which simulates the FBG sensor output response, when embedded in a host material, during a crack growing/damage event.

This Structure-Material-FBG model provides a tool to analyse the application of this monitoring technique in other locations/structures, by predicting the sensor output and deciding, based on this, the optimal sensor distribution/configuration. All the different features in the fracture (cracking) mechanism that can induce a change in the FBG response were identified.

With this, it was possible to identify specific phenomenon that will only happen in the proximity of a crack, such as compression fields ahead the crack or non-uniform strain fields, and then identify the presence of such damage in the structure. Experimental tests were conducted to fully characterize this concept and support the model.

Double Cantilever Beams (DCB), made with two glass fibre beams glued with structural adhesive, were instrumented with one array of FBG sensors embedded into the host material, and digital image correlation technique was used to determine the presence of the specific phenomena caused by the crack, and to correlate with the FBG sensor.