In order to improve the safety, reliability and operational life of structures, it is an urgent task to monitor the integrity of structures. Generally, the availability of some efficient techniques for non-destructive detection is essential. However, many existing nondestructive inspections such as ultrasonic wave, X ray and thermography need to suspend the operation of structure, and have possibilities of human carelessness. Therefore, it is difficult to guarantee the integrity of structures with high reliability in aspect of real-time. Accordingly, in recent years, the concept called as structural health monitoring is a technology that automatically monitors structural conditions from sensor information in real-time, by equipping sensor network and diagnosis algorithms into structures. Lamb wave can propagate by a long distance in plate-like and shell-like structures, by virtue of this advantage, many researchers build up structural health-monitoring systems using Lamb wave. Generally, Lamb wave has two fundamental modes, i.e., symmetric mode (S wave), and anti-symmetric mode (A wave). Most of researches use S0 wave for damage detection. The propagating velocity of S0 wave is higher than that of A0 and other lamb wave mode so that it is comparatively easy to pick up the damage information from experimental data of S0 wave. On the other hand, the wavelength of S0 wave is larger than that of A0 wave so that it is insensitive to some small damages.
In this study, we attach two PZT actuators with opposite applied voltages on both sides of aluminum plates or beams to amplify the component of A0 wave and to reduce the component of S0 wave. The objective of the present thesis is to detect damage in aluminum plates and beams using A0 wave.
edited by Hideaki EBINA