Interfacial adhesion (kissing bond) detection using shear horizontal (SH) waves

Horizontally polarized shear (SH) ultrasonic guided wave modes are considered to infer adhesion changes at different interfaces. In this study, the SH0 interaction with different lap joints are investigated. Experiments were performed on aluminium lap joint samples. Aluminium surfaces were prepared in a specific way to vary the adhesion. SH modes are generated and received using periodic permanent magnet (PPM) electromagnetic acoustic transducers (EMATs), the periodicity of which is equal to the wavelength of the transducer. SH0 is generated in the plate that comprises the lap joint and received in transmission mode. Distinct signatures were observed for different samples. To investigate the physics of interaction with tri-layer and to corroborate the experiment results, three dimensional finite element (FE) models were developed. Different cases of interfacial adhesion were simulated by changing the boundary condition at both aluminium-epoxy-aluminium interfaces. This work shows the potential of SH modes for quantifying properties at adhesive interfaces.