Nondestructive Inspection System Using Optical Profiles and Laser SurfaceWaves to Detect a Surface Crack

摘要

An improvement of the detection efficiency for cracks is essential for a laser ultrasonic inspectionsystem because it provides a relatively low signal-to-noise ratio when compared with conventionaltransducers. In this paper, a nondestructive inspection system using accumulated line profiles andmultiple laser surface waves is configured to detect surface cracks. An optical line profile is usedto detect a crack's position, and multiple laser surface waves are adopted to accurately extractinformation on the crack's depth. During a scanning test, multiple surface waves provide precisecrack-depth information after a crack's position is detected from an image of accumulated lineprofiles when a crack is positioned in the middle of multiple pulse laser beams. Multiple lasersurface waves are composed of two parts, a reference part and a data part when a surface crack ispositioned in the middle of these multiple pulse laser beams. Detailed crack-depth information canbe extracted from the normalized multiple surface waves by referencing the reference part. The crackdepth is proportional to the difference between the two peak frequencies of the reference and thedata signals. With visual detection using an image of the accumulated line profiles, a nondestructiveinspection system using multiple surface waves provides reliable surface-crack information.