Onthe repeatability of electromechanical impedance for monitoring of bonded joints

Abstract

The repeatability and sensitivity of the electromechanical impedance (EMI) method when employed for the structural health monitoring of bonded joints were investigated. A simple joint was assembled by bonding an aluminum strip to a square aluminum plate. Two rounds of experiments were performed. The first set aimed at verifying the repeatability of the method. The joint was monitored by using one piezoelectric sensor. The PZT was glued to the plate and never removed, whereas a poorly bonded joint was assembled and disassembled three times. For each case, the electromechanical signature was measured during the curing of the adhesive. After the three tests, the same joint was built with a different adhesive to analyze the differences with the previous ones. The first set demonstrated the repeatability and sensitivity of the EMI for the monitoring of the adhesive in bonded elements, whereas the latter measurement served to capture the response of the conductance signatures to a bond of different quality. The second round of experiments was performed by building three specimens, geometrically identical, but with three different bond qualities. Three piezoelectric sensors provided by the same manufacturer and with identical specifications were glued on each plate. The electromechanical response of the PZTs was related to the quality of the adhesive mix. For both rounds of experiments, the statistical index of the root mean square deviation (RMSD) was used, and in both rounds, it was found that the final value and the gradient of the RMSD are repeatable and are able to discriminate weak joints from sound joints.