Practical issues related to the application of the electromechanical impedance technique inthe structural health monitoring of civil structures: I. Experiment

Abstract

The advent of smart materials such as the piezo-impedance transducer (lead zirconatetitanate, PZT) and optical fiber (FBG) has ushered in a new era in the field ofstructural health monitoring (SHM) based on non-destructive evaluation (NDE). Sofar, successful research and investigations conducted on the electromechanicalimpedance (EMI) technique employing a piezo-impedance transducer are oftenlaboratory based and mainly theoretical. Real-life application of the technique,especially under harsh environments, has frequently been questioned. In this researchproject, investigative studies were conducted to evaluate the problems involved inreal-life applications of the EMI technique, attempting to reduce the gap betweentheory and application. This two-part paper presents a series of experimentation(part I) and numerical verification (part II) on various issues related to real-lifeapplication, including the durability of PZT transducers, and the effects of bonding andtemperature under conceivable nominal construction site conditions. The repeatability ofelectrical admittance signatures acquired from the PZT patches surface bonded onaluminum structures was found to be excellent up to a period of one and a half years.Experimental investigations revealed that the bonding thickness should preferably bethinner than one-third of the patch to avoid any adverse effect caused by the PZTpatch’s resonance on the admittance signatures which reflect the host structuralbehavior. On the other hand, the effect of temperature on the admittance signatureswas found to be closely related to the thickness of bonding, as an increase intemperature would reduce the stiffness of the bonding layer, thus affecting straintransfer. It was concluded that PZT patches with thick bonding thickness andhigh frequency of excitation are undesirable, especially at elevated temperatures.