PSI - Issue 82

Valentyn Uchanin et al. / Procedia Structural Integrity 82 (2026) 281–287 Valentyn Uchanin et al. / Structural Integrity Procedia 00 (2026) 000–000

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Fig. 2. (a) Multilayer aircraft structure: 1 , 2 – skins; 3 – reinforcing belt; 4 – stringer; 5 – crack; 6 – EC probe; 7 – scan trajectory. EC probe signals obtained from the crack and the reinforcing belt edge for different vertical amplifications: (b) K Y = K Х ; (c) K Y > K Х .

2.3. Detection of the local corrosion damage on the side surface of the multilayer aircraft structure The AA double-layer AS of a fuselage and wings are highly susceptible to corrosion-induced metal loss during in-service life. Detection of local CD, such as pitting on the internal surfaces of multilayer AS, using traditional EC probes, does not provide sufficient sensitivity due to the limited penetration depth of eddy currents. Improved sensitivity to such defects can be achieved by using the double-differential EC probes described above. A double-differential EC probe with an operational diameter of 8 mm was developed to detect hidden local CD from the back, undamaged surface (Uchanin, 2024). Local CDs were simulated using flat-bottomed drilled holes of varying diameters and depths (diameters: 2.0, 3.0, 5.0 mm; depths: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 mm) in a 4 mm thick AA plate. The specimen with simulated local CD was scanned from the undamaged side, and the EC signals generated by a 2.0 mm diameter local CD on the reverse (undamaged) side of the skin were analyzed in the complex plane at an operating frequency of 2.5 kHz. Both through defects ( h r = 0, Fig. 3a) and CD of varying sizes (Fig. 3b–f) were included in the analysis.

Fig. 3. (a) EC signal in the complex plane for 2.0 mm diameter local drillings, representing surface corrosion damage; and EC signals for residual thicknesses of (b) 0.5 mm, (c) 1.0 mm, (d) 2.0 mm, and (e) 2.5 mm. The flaw detector sensitivity increased relative to surface drillings by 6 dB (b), 16 dB (c), and 26 dB (d, e). So, the obtained EC probe signals are dependent on the diameter and the residual thicknesses of the local CD. To estimate the residual thicknesses h r the phase of the EC signal or inclination in the complex plane can be applied.