Piezoelectric monitoring of the reliability of adhesive joints

Abstract

Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. In order to validate the method, the piezoelectric properties of the adhesive were measured during the fatigue test. Electrically conducting adherends were used as electrodes without embedded sensors, and the adhesively bonded joint was modeled as the equivalent parallel circuit composed of electric charge and capacitance. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally. a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.