Evaluating interfacial bonding characteristics of the composite material thin layer by ultrasound delay time spectrum

Abstract In response to the difficulties in evaluating the thin layer interface bonding of composite materials accurately, an ultrasound delay time spectrum method is proposed. A mathematical model, with spring model simulates the stiffness coefficient of interfacial bonding, is established based on the ultrasound delay time spectrum evaluation of interfacial stiffness coefficient by the rule of the acoustic wave vertical incident to double-layer medium. Numerical simulation results show that with the increase of stiffness coefficient, the delay time peak becomes smaller, and the resonant frequency is independent of the interfacial stiffness coefficient but related to the thickness of the thin layer. The period of resonant frequency has a great positive correlation with the thickness of the thin layer. Finally, a series of experiments are carried out for the 1 mm thickness rubber thin layers with different bonded interfaces. Prepared the weakly bonded interface and the perfect interface compared with the infinite stiffness coefficient, respectively. The results show that the delay time peak of the weak bonding interface is much greater than that of the perfect interface. The delay time peak of the perfect interface is slightly larger than that of the infinite stiffness coefficient interface. Therefore, the experimental results illustrate that it is feasible to apply the ultrasound delay time spectrum method in evaluating the interfacial bonding.