PSI - Issue 28

Thomas Bergmayr et al. / Procedia Structural Integrity 28 (2020) 1473–1480

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C.V. Thomas Bergmayr et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 7. (a) One side ( x > 0) of the symmetric and idealized FE-spoiler model, with the calculated ZST (thick blue and green lines). The β 1 direction according to Fig.1 is marked blue, compared to the β 2 direction which is marked green. The areas where there is no zero-strain direction because the principal strains do not have opposite signs the minor α 1 and major α 2 principal strain directions are depicted instead. (b) Submodel area with the considered ZST. ZST numbered from 1 till 5 are vertically orientated, whereas the ZST numbered from 6 till 10 are horizontally orientated.

Fig. 8. Comparison of the strain profile along the ZST-5 β 1 and the strain profile along the ZST-9 β 1 at the di ff erent damage states.

layer debonding as damage clearly show the high sensitivity of the indirect damage monitoring by strain measurements along ZST. Strain sensors optimally placed along these ZST are used to detect and monitor debonding propagation. With this novel approach a damage is localized due to the fact that all measurement positions with a larger distance to the damage have a very little signal whereas the closer ones measure a significant strain amplitude. Because of the local strain increase close to the considered face layer debonding the method shows high potential for damage localization in sandwich panels but also in pure laminates. The presented numerical results successfully show that the novel approach has high potential for monitoring the structural integrity of an aircraft sandwich structure. Nevertheless, these results now have to be evaluated by experimental tests with distributed continuous FOS or FBG sensors placed on the surface in order to achieve higher accuracy for better comparison with the numerical results. Furthermore, the methods applicability for other damage types of sandwich and other composite structures needs to be investigated and evaluation issues with, e.g., scattered loading conditions have to be solved.