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.
Highlights
Bonding is increasingly used in automotive and aerospace industries, as it has reliably sealing performance and excellent shock absorption capacity compared with welding and bolting.[1,2] manufacturing imperfections viz., weak bonding, micro-porosity and micro-cracks, etc. cause some serious accidences frequently
Yang Zhengwei, et al proposed that the infrared thermography method can be employed to estimate the defect of adhesive structure,[12] whereas this method is not suitable for weak bonding structures
Based on the model of above researches, the change rule of transmission peaks can be analyzed by comparing Fig. 2(a), Fig. 2(d) and Fig. 2(e), when the value of KT remains constant and the value of KN varies from 1×1020 N·m-3 to 0. (note: the boundary conditions in Fig. 2(d) and Fig. 2(e) are extremely rare in reality
Summary
Bonding is increasingly used in automotive and aerospace industries, as it has reliably sealing performance and excellent shock absorption capacity compared with welding and bolting.[1,2] manufacturing imperfections viz., weak bonding, micro-porosity and micro-cracks, etc. cause some serious accidences frequently. These imperfections, especially for weak bonding interface, are complicated to implement using conventional non-destructive testing (NDT) techniques, and restrict the application of bonding technology to some extent.[3,4,5] A large amount of NDT methods have been proposed on inspection of bond interfacial integrity for decades.[6,7,8,9]. Compared with traditional ultrasonic techniques (i.e. contact and immersion ultrasonic technique), an air-coupled ultrasonic technique does not pollute the material surface and is appropriate for the materials which could be damaged by immersing the liquid This technique has the potentiality for detecting the bonded quality of the producing line due to convenient installation and high testing efficiency. Normal and transverse interfacial stiffness have been measured using the method of combining normal and oblique incidence
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