Development of Diagnosing Method for Health Condition of a Joint Based on Piezo-electric Impedance Measurement

Abstract

Infrastructures dealing with social activities and providing services to the daily life of people are almost impossible to be shut down for the regular damage detection procedures. However, according to the standards and codes for infrastructures, both early detections of the damage and continuous monitoring are necessary. In order to prevent unexpected accidents, numerous health monitoring techniques were developed to examine or monitor the damage or physical changes in the structures. This paper presents the development of Structural Health Monitoring based on Piezo-ceramic Embedded Impedance Measuring Technique. In order to automatically detect the abnormalities of structure due to damages, the diagnosis method is proposed. The loosening state of one bolt on one joint in the prototype structure is taken as the example of abnormality state. Since the fastening state of bolts affects the mechanical impedance in the structure, PZT patches were embedded on the structure so that the mechanical impedance change can be measured precisely by the variation of the electric impedance in PZT patches. An unusual fastening torque is recognized by the behaviour of impedance waveform obtained from a series of repeated tests. Then this torque is used as the threshold and based on it the diagnosing method, introducing the damage index ΔS, is proposed. The experimental results show that this method has successfully detected all unusual states during the experiments.