As bonded structures are widely used in modern manufacturing, their quality and safety have received much attention. Scientists all over the world propose many techniques to describe the relationship between acoustic wave propagation characteristics and the status of the bonding interface.

A research group led by WANG Xiaomin from the Institute of Acoustics, Chinese Academy of Sciences also carried out a series of studies on this hot issue and investigated the propagation of a longitudinal ultrasonic wave normally incident upon an adhesively bonded structure. The structure based on consists of adherend and adhesive layers with finite thickness. Interfaces between adherend and adhesive are regarded as distributed springs.

In the studies, they find that resonant frequencies of the bonded structure vary sensitively with the interface stiffness constants and adhesive thickness, and these interface characteristics could be inversed by the simulation annealing (SA) method. Furthermore, they compare the distribution image of interface stiffnesses with the state of fracture interface, and achieve the quantitative prediction of shear strength based on the distribution of interface stiffnesses and adhesive thicknesses by using a back-propagation (BP) neutral network. The practical experiment result shows that the average relative error of the shear strength from prediction to real value is 10.7%.