Vibro-Acoustic Modulation Utilizing a Swept Probing Signal for Robust Crack Detection

Abstract

One practical issue that must be addressed prior to the implementation of a vibration-based structural health monitoring system is the influence that variations in the structure's environmental and boundary conditions can have on the vibration response of the structure. This issue is especially prominent in the structural health monitoring of aircraft, which operate in a wide variety of different environmental conditions and possess complex structural components connected through various boundary conditions. However, many types of damage introduce nonlinear stiffness and damping restoring forces, which may be used to detect damage even in the midst of these varying conditions. Vibro-acoustic modulation is a nondestructive evaluation technique that is highly sensitivity to the presence of nonlinearities. One factor that complicates the use of vibro-acoustic modulation as a structural health monitoring technique is that the amount of measured modulation has been shown to be dependent on the frequency of the probing signal. The frequency dependence of the modulation was investigated and the magnitude of modulation was found to be correlated with the underlying vibration characteristics of the structure, which are influenced by environmental and boundary condition variations. To facilitate the use of nonlinear vibro-acoustics for the health monitoring of complex aerospace components in varying environments, a vibro-acoustic modulation technique utilizing a swept probing signal has been developed. The developed method was demonstrated on a steel beam in varying operational conditions. The presence of a crack in the beam was detected both through an increase in the amount of normalized modulation and without the use of historical data by utilizing generalized extreme value statistics.

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

“…One of the parameters to vary is the carrier frequency, both in amplitude and in frequency. Yoder et al [10] found a strong correlation between the amplitude of the carrier sidebands and the magnitude of the underlying spectral response of the damaged structure. This is supported by the theoretical single degree of freedom model (see section 1.…”

“…Traditional vibration based methods, relatively easy to implement, but suffering from a limited sensitivity [3,4], often rely on a linear system description, while more recent work also features nonlinear dynamic effects introduced by local defects [5,6]. Potential benefits are reported in terms of sensitivity [7][8][9] and environmental robustness [10,11].…”

Fatigue Crack Localization Using Laser Nonlinear Wave Modulation Spectroscopy (LNWMS)

“…Normally, a lowfrequency pumping input and a high-frequency probing input are used in NWMS for creating modulation. Here, the amplitude of modulation heavily depends on the choice of the probing and pumping frequencies, and the optimal combination of these two input frequencies is also affected by environmental and operational conditions (e.g., temperature and loading) of the target structure and even by defect configurtions [7,[9][10][11]. Therefore, finding the optimal combination of the probing and pumping frequencies, which can maximize the modulation level, becomes a moving target.…”

“…Therefore, finding the optimal combination of the probing and pumping frequencies, which can maximize the modulation level, becomes a moving target. To find an optimal combination of the probing and pumping frequencies that can maximize the modulation level, frequency-swept probing signals and a frequency-fixed pumping signal are used [11].…”

Bayesian model updating approach for experimental identification of damage in beams using guided waves

“…They demonstrated that the resulting modulated signal contains new frequency components, which are can be used to detect the defect in the structures. Yoder and Adams 20 proposed a swept probing signal to increase the applicability and robustness of the vibro-acoustic modulation technique in damage detection with experimental verification. Klepka et al 21 carried out an experimental investigation of the low-frequency vibration excitation on modulation intensity and associated nonlinear wave interaction mechanisms, which further enhanced the understanding of using the vibro-acoustic modulation technique in damage detection.…”