Multi-layer Metal Bonding Structural Adhesive Quality Of Ultrasonic Testing

Adhesive structure is widely applied in aviation & aerospace, war industry and other important fields, because of its high specific strength and specific modulus characteristics. However, it is easy to appear defects during bonding process, such as weak bonding, air hole, local debonding and so on, to destroy the integrality of the adhesive structure. At present, ultrasonic testing has already become one of the most widely-applied techniques in NDT of adhesive structure. Researches on the ultrasonic testing of multi-layered metal-nonmetal adhesive structure begin earlier, and tend to be ripe, but those of multi-layered metal-metal adhesive structure are less. According to the actual production need, this paper researches on the bonding qualities of multi-layered metal-metal.This paper according to the actual need of production, designed different layered bonding samples of metal-metal plane, established respective acoustic models, and analysed the applicability of different testing methods. Then associated with transmission model of ultrasonic in multi-layered media, this paper analysed its sound pressure transmissivities and energy losses in above three-layered metal-metal adhesive structure by immersion testing under different frequencies. The analysis result showed that both multiple echo method with direct contact and immersion testing could detect the position of the artificial defect in two-layered adhesive structure; immersion focusing probes with frequencies of 5MHz, 2 MHz and 1 MHz all could detect the artificial defect on the second bonding interface of the three-layered adhesive structure; and in four-layered adhesive structure, immersion focusing probe with frequency of 5MHz was difficult to detect the defect because of the attenuation in media, but those of 2 MHz and 1 MHz could be used to detect.On the basis of analysis of the acoustic properties of the adhesive structure, this paper proposed the contrivance of low-frequency immersion focusing probe. According to the contrivance , it planed to design the probe from chips choice, backing design and optimization and acoustic lens design, and specific design index are also proposed.Finally, testing experiments of bonding samples were carried on by self-design immersion focusing probe and 5 MHz probe, the experiments result showed that multiple echo method with direct contact and immersion testing could detect the 06mm defect in two-layered adhesive structure; immersion testing could achieve better detection of 06mm defect on the second bonding interface of the three-layered adhesive structure, but the capacity of detection of 5MHz probe was obviously higher than 2MHz and 1MHz probes; and in four-layered adhesive structure, 2 MHz and 1 MHz probes could detect 06mm defect on the third bonding interface, but 5MHz probe could not complete the detection because of the large energy loss. This was basically consistent with the theoretical analysis result mentioned above, and provided certain available experience for ultrasonic testing of similar adhesive structure.