Bondline Degradation Monitoring and Remaining Strength Estimation via an Electromechanical Impedance-Based Method

Abstract

Bondline integrity monitoring and assessment is one of the most critical concerns for mechanical and aerospace structures, such as aircraft or high-speed trains, up to date. Due to the lack of confidence on the integrity of the bondline both during fabrication and service, the industry standards and regulations require assembling the composites using the inefficient “black-aluminum†approach, i.e., drill holes and use fasteners. Current state-of-the-art non-destructive evaluation (NDE) and structural health monitoring (SHM) techniques do not provide mature solutions on the issue of bondline integrity monitoring. Therefore, the objective of this work is to investigate the feasibility of a novel monitoring approach that is based on (i) embedded piezoelectric sensors into adhesively bonded joints and (ii) appropriate diagnostic and prognostic techniques for determining the bondline integrity and estimating the remaining strength of the bondline. The proposed method makes use of an electromechanical-impedance (EMI) based method, which is a rapidly evolving “local†approach within the SHM family of methods. By embedding piezoelectric micro-sensors into adhesive bondlines, measuring the EMI spectrum of the sensors, and employing diagnostic/prognostic algorithms the strength of the adhesive joints may be estimated. The obtained results demonstrate the potential of the approach in providing increased confidence on the use of bonded joints for mechanical and aerospace structures.