A review on nondestructive testing of bonding interface using nonlinear ultrasonic technique

Abstract

<p indent="0mm">As an important complement to traditional mechanical connections, bonded structures are widely used in industry. Under the combined effect of external loads and environmental factors, the performance of the bonding interface will deteriorate, which seriously affects the safe use of bonding structures. Therefore, the performance evaluation of bonding interfaces has always been a hot and difficult issue in the field of non-destructive testing. Traditional linear ultrasonic technology can effectively detect damage such as delamination and debonding in the bonding interface, but it is difficult to detect and quantitatively evaluate the early degradation of the bonding interface (such as closed defects and weak bonding). However, the nonlinear ultrasonic technology can overcome the low sensitivity of the traditional linear ultrasonic technology and is expected to be an effective means for nondestructive testing of early deterioration of bonding interface performance. In this paper, we review the recent development of nonlinear ultrasonic technology for bonding interface detection from theoretical models and testing experiments. From the perspectives of contact nonlinearity of the interface and material nonlinearity of the interlayer, we introduce relevant theoretical models for nonlinear ultrasonic inspection of bonded interfaces, such as nonlinear spring model, interface contact model and contact model considering the thickness of the interlayer. These models can be used for the description of various acoustic nonlinear effects (such as second harmonic generation, wave mixing and nonlinear resonance) generated by ultrasonic waves at weak bonding interfaces, but the ability of different models to characterize the nonlinear propagation behavior of ultrasonic waves at weak bonding interfaces needs to be further investigated. Meanwhile, we review the progress of three nonlinear techniques of nonlinear ultrasonic resonance, wave mixing and second harmonic generation in the experimental testing of bonding interface properties. The nondestructive testing of bonding interface using nonlinear ultrasonic resonance technique remains relatively limited. Mixing technology is of great interest because of its flexibility and selectability of excitation frequency, mode and area of action, and its ability to effectively avoid the effects of system nonlinearity. Among the nonlinear ultrasonic methods, harmonic techniques are the most widely used, and have been used for damage detection and performance evaluation of bonding interfaces, such as bonding thickness measurement, debonding detection, bond strength and fatigue life evaluation. The harmonic technique is considered as a possible solution for the quantitative detection of the interface properties of multilayer bonded structures. However, how to distinguish the harmonics generated by weakly bonded interfaces from those generated by detection systems has been a challenge for its application. Finally, we provide an outlook for the development of nonlinear ultrasonic detection technology for early degradation of bonding interfaces.