Bond stiffness estimation with shear horizontal guided waves generated using PPM-EMATs

This paper aims to develop a technique for estimating an aluminium/epoxy/aluminium lap shear joint stiffness. Shear horizontal guided waves are employed using periodic permanent magnet electromagnetic acoustic transducers (PPM EMATs). Based on the source influence of the EMATs and sensitivity of SH-like mode to adhesion, an appropriate transduction regime is selected. Different modality of inspection, such as reflection and transmission mode, is explored. The arrival time of the received signal in transmission mode depends on the adhesion level. A procedure for calculating the energy velocity in the bond and inverse calculation of bond stiffness is proposed. Experiments were performed on samples of different surface treatments. Based on the proposed method, the stiffness of the samples was estimated. Results show the technique's potential to quantify the adhesion level rather than merely classifying as good, weak, and bad bonds.