An integrated health monitoring technique using structural impedance sensors

This paper presents an integrated methodology to detect and locate structur al damage. Two different damage detection schemes are combined in this meth odology, which involves utilizing the electromechanical coupling property o f piezoelectric materials and tracking the changes in the frequency respons e function data, respectively. Physical changes in the structure cause chan ges in mechanical impedance. Due to the electromechanical coupling in piezo electric materials, this change in structural mechanical impedance causes a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance one can qualitatively determine when st ructural damage has occurred or is imminent. Based on the fact that damage produces local dynamic changes, this technique utilizes a high frequency st ructural excitation (typically greater than 30 kHz) through the surface-bon ded piezoelectric sensor/actuators. As a second step, a newly developed mod el-based technique, using a wave propagation approach, has been used to qua ntitatively assess the state of structures. Direct frequency response funct ion data, as opposed to modal data, are utilized to characterize the damage in the structures. A numerical example and an experimental investigation o f one-dimensional structures are presented to illustrate the performance of this technique.