Measurements of the weak bonding interfacial stiffness by using air-coupled ultrasound

Abstract

An air-coupled ultrasonic method, focusing on the problem that weak bonding interface is difficult to accurately measure using conventional nondestructive testing technique, is proposed to evaluate the bond integrity. Based on the spring model and the potential function theory, a theoretical model is established to predict the through-transmission spectrum in double-layer adhesive structure. The result of a theoretical algorithm shows that all the resonant transmission peaks move towards higher frequency with the increase of the interfacial stiffness. The reason for these movements is related to either the normal stiffness (KN) or the transverse stiffness (KT). A method to optimize the measurement parameters (i.e. the incident angle and testing frequency) is put forward through analyzing the relationship between the resonant transmission peaks and the interfacial spring stiffness at the frequency below 1MHz. The air-coupled ultrasonic testing experiments at the normal and oblique incident angle respectively are carried out to verify the theoretical analysis and to accurately measure the interfacial stiffness of double-layer adhesive composite plate. The experimental results are good agreement with the results from the theoretical algorithm, and the relationship between bonding time and interfacial stiffness is presented at the end of this paper.

Measurement Interface Stiffness of Bonded Structures Using Air-Coupled Ultrasonic Transmission Technology

“…It is 6 × 6 matrix in above formula, the odd rows are derived from the sound pressure, while the even rows are obtained from the particle velocity. The transmission coefficient T from ultrasonic waves in the measured medium can be calculated by solving the formula (7).…”

“…Therefore, it is necessary to measure and evaluate the interfacial bonding quality of laminated composite structures to reveal the hidden dangers in time and avoid serious consequences [6]. There are many ways to distinguish the quality of the interface bonding, one of which is ultrasonic techniques that have always been favored by inspectors [7,8]. Ultrasonic technology has no obvious effect on the bonding rigidity of the structure, although it is recognized as an effective defect detection method.…”

Comparison of different non-destructive testing techniques for bonding quality evaluation

“…Not only conventional longitudinal pulse-echo ultrasonic inspection, but also advanced measurement techniques such as acoustic microscopy, air-coupled ultrasound, and guided waves have been used to evaluate bonding quality [19]- [26]. Moreover, the nonlinear behaviour has been related to bonding quality with nonlinear ultrasonic NDT [27], [28].…”

Study on the Viscoelasticity Measurement of Materials Based on Surface Reflected Waves

“…According to the research of material properties such as the storage modulus L′ and loss modulus L″, the value of tansans-serifδ, which has a great relationship with friction, was used in the viscoelastic index, and following simulation and experiment, the SRM was shown to be feasible. Typically, the SRM and BRM ignore the thickness of the coupling layer; however, it was found that adding the influence of coupling layer thickness to the calculation can greatly reduce the error [16,17]. The density measurement must be performed by the Archimedes’ principle in these measurements, which is complicated.…”