Closed-loop based detection of debonding of piezoelectric actuator patches in controlled beams

A practical closed loop control based damage detection scheme is presented aiming at detecting small damage in controlled structures. In this detection method, a deliberately designed sensitive control system is used to augment small frequency shifts caused by small structural damage. Since a small frequency change can destabilize such a sensitive control system, it can be easily observed and thus the small damage can be detected. To perform active control of structures, a modal velocity observer (MVO) is designed by combining two observers, which can be used for multi-mode control. By properly choosing the parameters in the MVO, it can be made very sensitive to the frequency shift suitable for small damage detection. To demonstrate this method in detecting small debonding of piezoelectric patches on a smart beam, a detailed model of beam with partly debonded piezoelectric patches is established based on the Timoshenko’s beam theory, in which both transverse and longitudinal vibrations are modeled, and a characteristic equation is also derived to examine the effect of the debonding on the control performance. Both the model and the control law are validated by an active vibration control experiment. Finally, an example is given to illustrate application of the method in piezoelectric actuator debonding detection. The results show that even a small edge debonding in a piezoelectric actuator patch can make the sensitive control system unstable, and therefore can be detected.