Bondline Integrity Monitoring of Adhesively Bonded Structures via an Electromechanical Impedance Based Approach

Abstract

Bondline integrity is still one of the most critical concerns in the design of aircraft structures 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. Furthermore, current state-of-the-art non-destructive evaluation (NDE) and structural health monitoring (SHM) techniques are incapable of offering mature solutions on the issue of bondline integrity monitoring. Therefore, the objective of this work is to investigate the feasibility to embed piezoelectric sensors into the adhesively bonded joints in order to detect bondlines degradation. The proposed method makes use of an electromechanical-impedance (EMI) based method, which is a rapidly evolving approach within the SHM family. This approach is based on the use of (i) micro-sensors integrated into adhesive leaving a minimal footprint on the material, (ii) numerical and analytical modeling of the EMI spectrum of the adhesive bondline, (iii) EMI based diagnostic algorithms for monitoring the bondline integrity, and (iv) the experimental assessment via prototype adhesively bonded structures in static (varying loads) environment. The obtained results demonstrate the potential of the approach in providing increased confidence on the use of bonded joints for aerospace structures.

In situ spatial strain monitoring of a single-lap joint using inkjet-printed carbon nanotube embedded thin films

“…where I l is the current injected into the l th electrode, V l is the boundary voltage collected while I l is being injected, and z l is the contact impedance of the lth electrode. Equations (11), (13), and (14) constitute the equations to be solved via FE analysis. Instead of solving for the actual conductivity, a one-step inverse calculation was adopted from Alder and Guardo 36 to estimate the change in conductivity before and after the load.…”

A stochastic global identification framework for aerospace structures operating under varying flight states

“…[1,2], (ii) sense their flight and aeroelastic state (airspeed, angle of attack, flutter, stall, aerodynamic loads, etc.) and internal structural condition (stresses, strains, damage) [3,4], and (iii) effectively interpret the sensing data to achieve real-time state awareness and health monitoring [5][6][7][8][9][10][11][12]. Towards this end, novel data-driven approaches are needed for the accurate interpretation of sensory data collected under varying flight states, structural conditions, and uncertainty in complex dynamic environments.…”

Integrity monitoring of adhesively bonded joints via an electromechanical impedance-based approach

“…In recent studies, 31–33 the authors and co-workers addressed the problem of bondline integrity monitoring via the use of piezoelectric transducers embedded inside adhesively bonded lap joints and monitoring the EMI signatures. The problem was tackled via an EMI-based cross-correlation approach 31 and a preliminary approach based on the use of EMI-based damage indices.…”

“…The problem was tackled via an EMI-based cross-correlation approach 31 and a preliminary approach based on the use of EMI-based damage indices. 32,33 In these studies, the changes in the EMI with respect to static loading conditions showed significant potential in successfully diagnosing the degradation of the bondline. Therefore, this study aims at the postulation and extended experimental assessment and evaluation of an EMI-based method for monitoring the integrity of adhesively bonded structures.…”