Open Access

ARTICLE

Electromechanical Impedance Method for the Health Monitoring of Bonded Joints: Numerical Modelling and Experimental Validation

by Vincenzo Gulizzi¹, Piervincenzo Rizzo², Alberto Milazzo⁴

1 PhD Student, Department of Civil, Environmental, Aerospace, and Materials Engineering. Uni-versity of Palermo, Viale delle Scienze, Ed. 8, Palermo, 90128, Italy.
2 Associate Professor, Laboratory for nondestructive evaluation and structural health monitoring studies, Department of Civil and Environmental Engineering. University of Pittsburgh, 3700 O’Hara Street, Pittsburgh, PA, 15261, USA.
3 Corresponding author: Tel. +1-412-624-9575; Fax: +1-412-624-0135; E-mail: pir3@pitt.edu
4 Associate Professor, Department of Civil, Environmental, Aerospace, and Materials Engineering. University of Palermo, Viale delle Scienze, Ed. 8, Palermo, 90128, Italy.

Structural Durability & Health Monitoring 2014, 10(1), 19-54. https://doi.org/10.3970/sdhm.2014.010.019

Abstract

The electromechanical impedance (EMI) method is one of the many nondestructive evaluation approaches proposed for the health monitoring of aerospace, civil, and mechanical structures. The method consists of attaching or embedding one or more wafer-type piezoelectric transducers (PZTs) to the system of interest, the host structure, and measuring certain electrical characteristics of the transducers. As these characteristics are also related to the impedance of the host structure, they can be used to infer the mechanical properties of the monitored structure. In the study presented in this paper, we utilize the EMI to monitor the quality of adhesively bonded joints. A finite element formulation was implemented to predict the electromechanical response of PZT attached to simple adhesivelybonded joints. The model was coded in Matlab and its results were validated by comparing them with the results associated with a few case studies implemented using commercial software. The finite element code was used to model the EMI measurement of a simple adhesively bonded joint subjected to adhesive layers of different qualities. Finally, the EMI was validated experimentally. A low cost circuit was designed and assembled to measure the electromechanical characteristics of a PZT glued to the structure of interest. We monitored the curing process of the adhesive forming the joint. This simulates at large the inverse of the degradation that may occur in bonded joints. The experimental results show that the EMI technique is able to capture variations of the stiffness of the adhesive layer.

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