Probing the limits of full-field linear local defect resonance identification for deep defect detection

Abstract

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Nonlinear Elastic Wave Energy Imaging for the Detection and Localization of In-Sight and Out-of-Sight Defects in Composites

“…For the deep delamination near the backside, no LDR behavior is observed in the linear response due to the limited reduction in local bending stiffness at the delamination [9]. Indeed, the DBR lin (f) curve (see blue curve in Figure 5e) is close to 1 at all frequencies and does not show any significant local maximum.…”

“…In order to improve the readability of the graphs, the frequency axis is scaled with the order of the higher harmonic. As an example, the red line in Figure 5a The shallow delamination shows pronounced LDR behavior due to the high reduction in local bending stiffness (see also [9]). This LDR behavior corresponds to the local maxima in the DBR lin (f) curve, for instance at 17.3 kHz.…”

“…The band power (BP * ) represents the broadband vibrational energy of the sample corresponding to velocity component V * Z . The BP * is defined as [9]:…”

Backside delamination detection in composites through local defect resonance induced nonlinear source behavior

“…As a proof of concept, an explicit finite element simulation (ABAQUS) is performed for a 180x165x2 mm 3 CFRP coupon, with layup [(0/90) 2 ] s , using 115736 linear hexahedral elements. Orthotropic material properties are used in accordance with the material properties of the experimentally investigated coupon (see Table 3 in Ref.…”

“…As the existence of LDR is linked to the difference in stiffness between the defect and the surrounding sound material, it is clear that the detection of defects, which are located deep inside the coupon, with LDR is problematic. A recent study of the current authors indicated that the classical LDR can detect defects up to a depth of 50% (relative to full thickness of the sample) [3]. Enhanced defect detection is possible using nonlinear defect imaging, exploiting the relatively high vibrational activity of the defect under LDR frequency excitation [4][5][6][7][8].…”