Vibro-acoustic modulation–based damage identification in a composite skin–stiffener structure

Abstract

The vibro-acoustic modulation method is applied to a composite skin-stiffener structure to investigate the possibilities to utilise this method for damage identification in terms of detection, localisation and damage quantification. The research comprises a theoretical part and an experimental part. An impact load is applied to the skin-stiffener structure, resulting in a delamination underneath the stiffener. The structure is interrogated with a low frequency pump excitation and a high frequency carrier excitation. The analysis of the response in a frequency band around the carrier frequency is employed to assess the damage identification capabilities and to gain a better understanding of the modulations occurring and the underlying physical phenomena. Though vibro-acoustic is shown to be a sensitive method for damage identification, the complexity of the damage, combined with a high modal density, complicate the understanding of the relation between the physical phenomena and the modulations occurring.

Nonlinear vibroacoustic wave modulations for structural damage detection: an overview

“…A similar result was obtained in Ref. 70 showing that increased amplitude modulation effects are measured at the damaged area, whereas there is no direct relation between the location of the damage and the frequency modulation. The authors in Ref.…”

Nonlinear modulation with low-power sensor networks using undersampling

“…Recent studies assumed that AM and PM/FM are caused by different physical effects. 1–3 Donskoy and Ramezani 2 suggest that FM may better indicate early fatigue damage, while Hu et al 1 found that AM correlates better with the size of large, visible cracks. In our experiments, we cannot confirm that either AM or PM/FM is a reliable indicator on its own.…”

“…The standard approach for splitting a signal into instantaneous amplitude (IA) and IP is the HT, which has been used in some recent work on VAM. 1,3 The STFT is not equivalent to HT, but it is an approximation that is sufficient for VAM, where the pumping frequency is much smaller than the probing frequency, that is, the modulation happening within a single chunk during STFT is negligible.…”

“…Since the 1990s, several research groups have exploited VAM to detect fatigue damage before visible cracks appeared. 1–4…”

“…Recent research suggests that splitting the VAM signals into amplitude modulation (AM) and frequency modulation (FM) might increase sensitivity to damage. Different techniques have been used to achieve the separation of both modulation types: the Hilbert transform (HT), 3 the Hilbert–Huang transform, 1 and the in-phase/quadrature homodyne separation (IQHS) algorithm. 2 However, all three methods require even higher computational power than the conventional MI.…”