Non-Linear Vibro-Acoustic Wave Modulations - Analysis of Different Types of Low-Frequency Excitation

Abstract

Signal processing method based on wavelet transform used in non-linear acoustic test is presented in the paper. The method is applied for sidebands identification in response signal acquired during vibro-acoustic modulation test of impacted carbon fiber reinforced plate (CFRP). The plate was impacted with known energy using drop-weight testing machine. The modulation effect in investigated specimen results from the interaction of low and high frequency excitation with damage. The paper investigates different than mono-harmonic low-frequency excitation usually used in non-linear acoustics tests. Application of aperiodic low-frequency excitation signal allows to omit the modal test, where natural frequency of the structure are estimated. However, this requires the use of dedicated signal processing methods.

Efficient swept sine chirp excitation in the non-linear vibro-acoustic wave modulation technique used for damage detection

“…5,19 Different types of excitation can be used in practice, including single harmonic, 13–19 impact 35 and chirp excitations. 20,30–34 The former is the most commonly used method of excitation. The latter requires advanced signal processing to extract information about frequency modulations.…”

“…Damage is detected by the presence of modulation sidebands in analysed power spectra. In addition, instantaneous amplitudes/frequencies, 36 higher-order spectra 37 and wavelet analysis 31–33 can also be used to extract and analyse VAMs.…”

“…A linear frequency sweep has been used for the HF ultrasonic excitation in recent studies. 20,30–34 Data post-processing is then needed to extract information about the modulation intensity that relates to damage. The linear response subtraction procedure – combined with the signal demodulation technique – can be performed in the time domain.…”

“…20,34 The use of wavelet analysis to demodulate the frequency sideband components was also demonstrated in this context. 31–33 It is important to underline that the methods proposed to date require substantial signal processing effort and do not address the problem related to LF excitation, which is described above. The problem related to the selection of the LF excitation can be somehow avoided when transient (e.g.…”

Enhanced nonlinear crack-wave interactions for structural damage detection based on guided ultrasonic waves

“…The second problem relates to damage localization that is very difficult – and often not possible – to achieve. Although several attempts have been made to investigate the amplitude level of LF excitation – which inevitably decides about the level of nonlinearity – and to explain the physics behind various nonlinear phenomena , this problem still remains a major issue that needs to be solved. Several approaches have been reported to address the second problem .…”