DAMAGE DETECTION IN SMART STRUCTURES THROUGH SENSITIVITY ENHANCING FEEDBACK CONTROL

Abstract

Non-destructive damage detection and isolation in structures using modal information is hindered by the sensitivity of modal frequencies to small changes in mass, stiffness, and damping parameters induced by damage. Here, a method of enhancing modal frequency sensitivity to damage using feedback control is introduced. Using state feedback, closed-loop modal frequencies are placed at locations in the complex plane that enhance sensitivity to particular types of damage. The method is intended for smart structures, which embody self-actuation and self-sensing capabilities. A simple example introduces the principle of sensitivity enhancing control for a single-degree-of-freedom structure. Then, the method is applied to finite-element models of a cantilevered beam to demonstrate the magnitude of sensitivity enhancement achievable for modest, local damage. Methods of implementing sensitivity enhancing full state or output feedback using point measurements of strain along the beam are described. Simulation results show that significant enhancement in sensitivity of modal frequencies of vibration to damage can be achieved using a single actuator and multiple strain sensors along the beam. The methodology enables a “dual use” smart structure—one that can be used for both vibration suppression and damage detection.