Automatic Non-Contact Defect Inspection of Cylindrical Shell Using a Laser-Ultrasonic Technique

摘要

Ultrasonic guided wave has been widely used for tube inspection. The conventional method is to use piezoelectric transducers that should be contacted to the target surface. However, in order to inspect tubes used in high temperature in-service, non-contact inspections are necessary. In this paper, we have proposed a non-contact inspection method generating the ultrasonic guided wave by laser and receiving by air-coupled transducer. This method can generate and receive the guided wave of a specific mode, which makes the interpretation of received signal clearer and resultantly improve the accuracy of inspection. Also the detected signal was analyzed by using the wavelet transform that was useful for the mode identification. The proposed method was applied to the real tube specimen with artificial defects and its inspection performance was verified. Finally we have developed a practical automatic inspection system, in which the inspection result is shown as a 2-D image.