Impedance-based structural health monitoring for temperature varying applications

A new structural health monitoring technique capable of in-service, on-line incipient damage detection has been proposed by the Center for Intelligent Material Systems and Structures, Physical changes in a structure cause cha nges in the mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change causes a change in the electrical impe dance of the piezoelectric sensor. Hence, by monitoring the electrical impe dance and comparing this to a baseline measurement, we can determine when s tructural damage has either occurred or is imminent. However, in almost all practical health monitoring applications, the structure being monitored is constantly undergoing change due to the effect of external boundary condit ions. One of the important factors that leads to this change is the tempera ture variations. In this paper, temperature effects on the electrical imped ance of piezoelectric materials and the structures have been investigated. A computer algorithm was developed which incorporates temperature compensat ion into our health monitoring applications. Three experimental investigati ons were performed successfully under the temperature varying condition, in the range of 25 to 75 degrees C, including a bolted pipe structure, compos ite reinforced aluminum and precision part such as gears. It was found that , by this compensation procedure, the impedance based health monitoring teh cnique is able to detect damage in the incipient stage, even with the prese nce of significant temperature variation.