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Visual Analysis for PCA-based Skin-stringer Debonding of Composite Stiffened Panels



The debonding between the skin and the stringer flange in composite aircraft wing panels is a critical aspect in terms of the resulting load-carrying capability of the full panel, and selection of reliable NDI inspection techniques. Usually, the run-out of the stringer is the point of the onset of the debonding under the in-service loads. The detection of the debonding onset and the measurement of the debonding length stringer/skin, has been object of this work by applying a SHM system. It consists of Fiber-Optic sensors in the frequency range 1 Hz to 250 Hz. In this work, the Principal Component Analysis (PCA) technique has been combined with Visual Analytics methods to identify and localize possible damage over aeronautical composite structures, so that skin-stringer debonding detection is made easier and friendly through visual exploration of real structure images. The PCA-based algorithm, looking for significant deviations between a baseline set of strain measurements and the current structural response, has been improved for more efficient damage identification. The “normal behavior” strain range, based on projections on the principal components, has been automatically tuned to the specific distribution of deviations themselves. In this way, an increased number of possible damage is detected. In addition, to exploit at best the obtained results, a Visual Analytics application has been designed and implemented, letting domain experts to navigate an image of the structural component under test, collecting information about: occurrence of possible damage, location of possible damage, strain measurement index position-based (maximum, minimum, mean), strain deviation between healthy and current states; all in an integrated way. The proposed combination of PCA and Visual Analytics has been applied and verified on a small stiffened panel. The debonding between the skin and the stringers has been provoked by a low energy impact, induced in the center of the skin, between the two stringers, with an energy level of 15 J.


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