Experimental investigation of modulation effects for contact-type interfaces in vibro-acoustic modulation tests

Abstract

This study is an experimental research on non-linear effects occurring in vibro-acoustic modulation tests. The work focuses on the analysis of the modulation type. The modulation of the response signal is due to interaction between low- and high-frequency excitation and damage surfaces, which results in the formation of higher harmonics and sidebands. The analysis of the sidebands is an extremely important issue. Their presence may indicate damage in structure. In many cases, the sidebands can be used to determine the damage index. However, not always, the distribution of the sidebands and their evaluation with excitation amplitude allow for an unambiguous interpretation. This may be the result of various damage-related non-linearity sources, which depend on the amplitude of the excitation. Because different types of non-linearities are manifested in different ways, the change in non-linearity type can cause, for example, the disappearance of odd sidebands and/or even harmonics or change in modulation type. To analyse the indicated issues, the sample with prepared contact surfaces was tested in experimental works. Two excitation types, low and high frequencies, are introduced into the structure via electromagnetic shaker and piezoelectric transducer, respectively, to produce contact-related non-linear effects. The contact surfaces are driven to move relative to each other. For a given scenario, the analysis of modulation sidebands is performed based on signal response. The instantaneous frequency approach is used to evaluate modulation type. The results show that the changes in the amplitude of the excitation change the modulation type of response signal. The probable causes of this phenomenon are given.

A novel method for improving damage detectability in nonlinear wave modulation: Modeling and design of a driving system

“…After this, the equations of motion are solved by following a time stepping procedure. Since the slip is tiny, only normal contact is introduced [50].…”

Theoretical and experimental investigations on control parameters of piezo-based vibro-acoustic modulation health monitoring of contact acoustic nonlinearity in a sandwich beam

“…The Hilbert transform (HT), which belongs to the latter group, is a common signal processing tool for demodulating the received signal and extracting amplitude and phase modulation DIs [8,32,33]. According to some studies, demodulating the sensory signal in VAM can reveal small sidebands buried beneath the background noise or carrier frequency sidelobes in the case of very lowfrequency pump actuation [34], as well as provide information on the type of damage [30,35], or damage growth stage [36].…”