Experimental Investigation of Bonding Quality for CFRP Bonded Structures with Thick Adhesive Layers Based on Ultrasonic Transmission Coefficient Spectrums

The experimental study of ultrasonic transmission coefficient measurement method was carried out for the problem of bonding quality inspection of bonded structures of composites with thick adhesive layer. For the uniaxial CFRP bonded specimens, the ultrasonic waves’ phase velocity distribution and the ultrasonic transmission coefficient spectrums were measured by the water-immersion ultrasonic transmission method. Then their complex elastic constants were inversed by the particle swarm optimization algorithm based on simulated annealing. Based on this, CFRP bonded specimens in perfect bonding status and having single weak bonding interface, dual weak bonding interfaces were manufactured. Then the ultrasonic transmission coefficient spectrums were measured, and the distinction of bonding quality between different bonding specimens was predicted. At the same time, according to the shift characteristics of the measured ultrasonic transmission coefficient spectra, the influence of the symmetry of the CFRP bonded structures with thick adhesive layers on the ultrasonic transmission coefficient spectrums was investigated experimentally. In addition, by comparing the time-domain and coefficient spectra characteristics of transmitted waves, the advantage of using the coefficient spectrum measurement method in bonding quality detection was expounded.