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

Abstract

In this study, both linear and nonlinear vibrational defect imaging is performed for a cross-ply carbon fiber-reinforced polymer (CFRP) plate with artificial delaminations and for a quasi-isotropic CFRP with delaminations at the edge. The measured broadband chirp vibrational response is decomposed into different components: the linear response and the nonlinear response in terms of the higher harmonics. This decomposition is performed using the short-time Fourier transformation combined with bandpass filtering in the time-frequency domain. The linear and nonlinear vibrational response of the defect is analyzed by calculation of the defect-to-background ratio. Damage maps are created using band power calculation, which does not require any user-input nor prior information about the inspected sample. It is shown that the damage map resulting from the linear band power shows high sensitivity to shallow defects, while the damage map associated to the nonlinear band power shows a high sensitivity to both shallow and deep defects. Finally, a baseline-free framework is proposed for the detection and localization of out-of-sight damage. The damage is localized by source localization of the observed nonlinear wave components in the wavenumber domain.

Nonlinear local wave-direction estimation for in-sight and out-of-sight damage localization in composite plates

“…In addition, the plate with BVID is covered with removable reflective tape (3M™ Scotchlite™ 680CRE10). This was required to be able to detect the nonlinear vibrational components which are of low J o u r n a l P r e -p r o o f amplitude [23,37,38]. In both cases, the propagation of the fundamental anti-symmetric Lamb mode (A 0 ), which has a dominant out-of-plane surface velocity response, is investigated.…”

“…One speaks about nonlinear elastic wave spectroscopy (NEWS) [24][25][26][27][28][29][30] or nonlinear elastic wave modulation spectroscopy (NEWMS) [31][32][33][34][35][36], when there is a single excitation or when there are multiple excitation signals, respectively. Very recently, the current authors used J o u r n a l P r e -p r o o f (numerical as well as experimental) NEWS to show that the nonlinear response at the defect can be used for the detection of shallow damages and, more important, deep backside delaminations [37,38]. It was observed that defects act as secondary sources of higher harmonic vibrational components which can be measured at a distance from the defect's location.…”

Broadband nonlinear elastic wave modulation spectroscopy for damage detection in composites

“…In a previous study of the current authors [38], it was illustrated how the short-time Fourier transform (STFT) and specific bandpass windows in the time-frequency domain can be used to extract higher harmonic components from broadband measurement data. Here, the same technique is used with the difference that there is a second sine excitation source present.…”

“…As such, it is beneficial to match the excitation frequency with a frequency for which efficient energy trapping, or better LDR, occurs [11]. When a single source of vibrations is employed, the nonlinear elastic wave spectroscopy (NEWS) shows promising results in revealing the defect as a source of higher harmonic components [31][32][33][34][35][36][37][38][39]. Current authors showed that a backside delamination (i.e.…”

Nonlinear elastic wave propagation and breathing-debond identification in a smart composite structure

“…Nonlinear analysis methods have gained popularity in the theoretical and applied research focusing on nonclassical nonlinear behaviour of interfaces (referred to as local nonlinearities) [33][34]. Recent studies have primarily focused on the investigation of higher harmonic generation due to the J o u r n a l P r e -p r o o f presence of nonlinear-elasticity [28,35] and contact-nonlinearity [36][37] phenomena. A contact acoustic nonlinearity model of a closed crack in an aluminium plate was developed for the analysis of nonlinear characteristics of the crack induced elastic waves in the structure [38].…”