Quality assessment of adhesive joints using third harmonics of fundamental shear horizontal wave mode

Abstract

This study aims to investigate the bond quality of aluminum–epoxy–aluminum tri-layer bonds using nonlinear ultrasonics. An experimental methodology was developed in which the tri-layer bonds with different interface qualities were inspected using the fundamental shear horizontal guided wave mode (SH0). An in-house developed magnetostrictive transducer assembly was used to excite the SH0 wave mode in the bonded samples. The harmonic generation of the SH0 wave mode was confirmed using dispersion curves overlaid on short-time Fourier transform (STFT) and frequency–wavenumber plots. The sensitivity of the third harmonics to the interface quality of the bonds was estimated using a relative nonlinearity parameter (δ*). In this work, the mean δ* for the non-sandblasted bond is found to be 70% more than that of the sandblasted sample, which shows the sensitivity of the third-harmonic generation to the interfacial degradation. The analysis shows that the technique can be implemented for a quick and early inspection of the bonded samples for their bond quality.