Research On Ultrasonic Imaging And Testing Technologies For Fasteners

As the basic means of manufacturing assembly, fastening techniques are widely used in national economy, aerospace and related areas and have huge influence on work performance, service life and safe operation of the device and equipment. Due to stress concentration and machining defects, flaws tend to emerge on fastener hole surface. However, it is very hard to detect the flaws directly with the rivets or screws installed, that can lead to failure of equipment, even catastrophic accidents. Hence scholars and engineers have been looking for nondestructive testing techniques for fastener holes without the removal of fasteners. In this dissertation, On the base of understanding the acoustic mechanism how ultrasonic creeping wave propagates and interacts with flaws, circumferential and spiral creeping wave inspection technique were introduced respectively for fastener holes crack detection, Bscan imageing technique was used to visualized the fastener holes, and Bregman algorithm was applied to improve the vertical resolution of the images, a potable ultrasonic non-destructive testing system was developed and achieved purpose of fastener hole crack detection, The details of this dissertation were presented as follows:Chapter1, the important role of fastener assembly technique and the significance of nondestructive testing technology for fastener holes were introduced. Ultrasonic nondestructive testing techniques for fastener holes research status and development trend was summarized, and the research direction of this dissertation was indicated.Chapter2, the propagation properties of creeping wave on curved surface were systematically discussed. The goals and the diagram of the characterization and detecting system were also proposed.Chapter3, Research on creeping wave detection mechanism was carried on, and finite element technique was applied to verify the creeping wave theory. Circumferential and spiral creeping wave inspection technique for fastener holes were introduced and verified by the experiments.Chapter4, Bscan imageing technique was used to visualized the fastener holes, and Bregman algorithm was applied to improve the vertical resolution of the images.Chapter5, a potable ultrasonic non-destructive testing system was developed and he system was verified effective for the fastener hole crack detection.Chapter6, the main work and conclusions were summarized and the prospect for further research objects was put forward.