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.