Structural health monitoring of adhesive joints under pure mode I loading using the electrical impedance measurement

•Preparation of MWCNT-Epoxy or GNP-Epoxy adhesives with proper sensory capability.•SHM of adhesive joint carried out using the GNP-epoxy and CNT-epoxy materials.•Correlation between the crack extension and electrical impedance response of the DCB specimens. The addition of Multi-wall carbon nanotubes (MWCNTs) or functionalized-graphene nanoplatelets (f-GNPs) into the epoxy resin create an electrical conductive networks which can be employed for structural health monitoring (SHM) in sensitive adhesive joints. The opening fracture mode (Mode I) loading condition, as one of the important fracture modes in adhesive joints was precisely evaluated in this study. The study aims to investigate the crack extension in the adhesive joint (Fracture mechanics) under mode I loading by both smart adhesives and proper measurement technique. In order to provide high sensing capability in the adhesive joint, several aluminum to aluminum adhesive joints were prepared by dispersion of 2.5 wt% MWCNTs or 12 wt% f-GNPs into the epoxy adhesive, respectively. Considering the electrical impedance changes simultaneously with the mechanical response of the adhesive joints, novel outcomes were obtained. Almost linear trend has been observed in the impedance curve for the strain value of 0.57. During crack growth, the conductive network in epoxy matrix near the crack tip would be break and thus the electrical impedance would be increased. In addition, the electrical impedance curve has exhibited several sharp increases, which are attributed to the rapid crack growth.