Vibro-acoustic modulation technique comparison with conventional nondestructive evaluation methods

In the last two decades, nonlinear ultrasonic testing is getting more attention due to their sensitivity to microcracks among a variety of NDT techniques used in infrastructure. Vibro-Acoustic Modulation (VAM) technique is one of the practical methods, that does not need the expensive hardware components required for the conventional nonlinear methods. This method is capable of identifying damage growth using the correlation of the level of nonlinearity to the severity or density of the damage. To be able to determine the sensitivity of VAM technique in comparison with other conventional nondestructive testing methods, Acoustic Emission (AE) technique as a global method and Ultrasonic Testing (UT) and Eddy current Testing (ET) techniques as local methods are investigated in an identical testing condition for similar specimens. The comparison has been conducted by testing a typical steel material used in the steel bridges under cyclic tension load. All these methods have some features in common and some differences. A comprehensive comparison study of these techniques sheds light on their practicality for various applications. Unlike the AE technique that listens to the structure for the received signal of the released elastic energy from the defects, VAM introduces the signals to the specimen and monitors the signal that was modulated by the vibration to get information about the crack. VAM and AE have some similarities such as no need for positioning sensors on the cracks and capability of detecting the crack in the early stages. On the other hand, local techniques such as UT and ET are more accurate than the VAM technique in terms of localization but less sensitive in terms of how soon they detect cracks.