On the repeatability of the EMI for the Monitoring of Bonded Joints

Abstract

We study the feasibility and the repeatability of the electromechanical impedance (EMI) method for the health monitoring of lightweight bonded joints. The EMI technique exploits the coupling between the displacement field and the potential field of a piezoelectric material, by attaching or embedding a piezoelectric transducer to the structure to be monitored. The sensor is excited by an external voltage and the electrical admittance which is the ratio between the electric current and the applied voltage is measured as it depends on the mechanical coupling between the transducer and the host structure. Owing to this interaction, the admittance may represent a signature for the health of the host structure. In this study the EMI method is applied to aluminum joints adhesively bonded. We investigate the repeatability of the proposed method by monitoring the same aluminum components bonded many times using the same adhesive mix, and then by monitoring the same two components bonded several times by means of different adhesive qualities. The results demonstrate that the EMI is repeatable and variations in the admittance signatures are related to the quality (health) of the bond.