Investigation of Alternative Electromechanical Impedance Method for Condition Monitoring

Abstract

This research investigates the use of the electromechanical impedance (EMI) method for condition monitoring of structures. Condition monitoring is the continuous observation of a particular parameter in an engineering structure in order to predict changes leading to failure. The EMI method is a damage detection technique that utilizes a single piezoelectric transducer as an actuator and a sensor simultaneously. The piezoelectric transducer induces mechanical vibration that interrogates the structure, and when some mechanical aspect of the structure changes, the electrical impedance spectrum of the piezoelectric transducer changes as well. Specific types of structural damage correspond to specific frequency ranges, which vary by structure. Hence, damage can be detected by comparing the impedance spectrum of a structure in an unknown state to a known “healthy” state. Any difference in the impedance spectrum of the measurement compared to the healthy state can be interpreted as damage. Traditionally, impedance analyzers are used for making impedance measurements. However, as they are large, heavy, expensive, and slow, an alternative measurement technique employing general-purpose data acquisition hardware paired with a custom-written LabVIEW program for data collection and processing is used in this work. Some of the advantages of this alternative measurement method include allowing the use of various types of excitation signals, having no limits on the number of sampling points, and being compatible with a wide range of data acquisition hardware. A set of aluminum beams with various damage states are experimentally tested to confirm the system’s ability to detect damage.