PSI - Issue 52

Sidney Goossens et al. / Procedia Structural Integrity 52 (2024) 647–654 Sidney Goossens / Structural Integrity Procedia 00 (2023) 000 – 000

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3.2. BVID detection An impact of 35 J was performed on the outside (concave) side of the panel under the stringer foot, between the locations of sensors 23 and 24 of fibre 2. The baseline and inspection measurements were acquired before and after the BVID respectively, and the wavelength shifts Δλ B,i were computed for all sensors, as explained in section 2.3. From the figure, it is clear that the temperature compensated wavelength shifts exceeded the threshold of τ = 8.07 pm, with the maximum recorded wavelength shift Δλ B,max = 379.63 pm. We conclude that the FBG sensors have successfully detected the presence and the location of the BVID under the damage-prone stringer foot, due to the residual strain change with respect to the pristine state of the panel.

Fig. 4. Wavelength shift of the fibre under which a BVID was created between sensors 23 and 24.

4. Conclusion In this work we reported for the first time to the best of our knowledge, the ability to detect and locate a BVID of calibrated size on a damage-prone region of an industrial large scale composite curved panel of 5 x 3 m² using FBG sensors mounted using an aerospace-grade installation method. We used a total of 120 FBG sensors distributed over 4 optical fibres to instrument 4 feet of two stringers of said panel. We first carried out a temperature calibration of the sensors, which allows defining a BVID-detection threshold and for performing temperature compensation between the baseline and the inspection measurement. We then created calibrated BVIDs and compared the residual strain before and after the impact by means of the optical measurements, and we were able to detect the presence and to locate the BVID, as the sensor wavelength shifts exceeded the preestablished damage threshold. This work indicates the potential of using optical fibre-based sensor networks in composite aerospace applications for condition-based structural health monitoring in view of avoiding the incurrence of excessive downtime costs associated with time-based maintenance. Acknowledgements This work was partially supported by the Joint Technology Initiative Cleansky 2 project SHERLOC, funded by the European Union’ s Horizon 2020 research and innovation programme under grant agreement n° 314768. Interreg North West Europe (NWE758, Fotonica pilootlijnen), Industrial Research Fund (IOF), OZR of Vrije Universiteit Brussel, Methusalem Foundation and the FWO Research Infrastructure program are acknowledged as well.