PSI - Issue 77

João Queirós et al. / Procedia Structural Integrity 77 (2026) 475–483

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(a) (b) Fig. 6. CFRP plate inspection results: (a) PT phase; (b) sum of filtered phase maps.

Among the remaining thermography results, the PT phase image exhibited better contrast between the damage signatures and the background than the PCA-filtered images. Both damages were also identifiable in the LT images, but with difficulty due to lower contrast. This limitation arises because LT applies only a single excitation frequency, making the simultaneous observation of both damages more challenging. The image results consistently revealed anomalies that clearly correlated with the two distinct impacts in terms of both location and energy. Specifically, a larger region was found in the lower right quadrant, corresponding to the higher energy impact, and a smaller region was located in the upper-left quadrant, correlating with the lower energy impact. The PT phase image successfully identified both anomalies based on their contrast with the background. While the damage from the higher-energy impact was easily discernible, the anomaly associated with the lower-energy impact was notably more difficult to distinguish from the surrounding background. In contrast, the sum of the filtered phase maps offered superior clarity. This method clearly exhibited distinct gradient peaks for both impact locations and sharply defined the contour region for the highest energy impact, which is likely a strong indicator of the extent of its internal damage. 6. Conclusions The results demonstrate the comparative performance of DS and AT in identifying multi-damage on the laminated plate. The findings indicate that DS is a more suitable method than AT for identifying internal damage in thin laminated plates due to its higher sensitivity. Specifically, the results from the DS method successfully revealed the locations of the two impacts and the full extent of the internal damage. The sum of the filtered phase maps offered superior clarity. This image clearly exhibited distinct gradient peaks for both impact locations and sharply defined the contour region for the highest energy impact, which is likely a strong indicator of the extent of its internal damage. While the PT phase image allowed a clear identification of the damage from the higher-energy impact, the anomaly associated with the lower-energy impact was notably more difficult to distinguish from the surrounding background. Acknowledgements This research was funded by Fundação para a Ciência e a Tecnologia (FCT), LAETA Base 681 Funding (DOI: 10.54499/UIDB/50022/2020). References

Aebischer, H.A., Waldner, S., 1999. Simple and effective method for filtering speckle-interferometric phase fringe patterns. Optics Communications 162(4), 205–210.