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

An improvement of the detection efficiency for cracks is essential for a laser ultrasonic inspection system because it provides a relatively low signal-to-noise ratio when compared with conventional transducers. In this paper, a nondestructive inspection system using accumulated line profiles and multiple laser surface waves is configured to detect surface cracks. An optical line profile is used to detect a crack’s position, and multiple laser surface waves are adopted to accurately extract information on the crack’s depth. During a scanning test, multiple surface waves provide precise crack-depth information after a crack’s position is detected from an image of accumulated line profiles when a crack is positioned in the middle of multiple pulse laser beams. Multiple laser surface waves are composed of two parts, a reference part and a data part when a surface crack is positioned in the middle of these multiple pulse laser beams. Detailed crack-depth information can be extracted from the normalized multiple surface waves by referencing the reference part. The crack depth is proportional to the difference between the two peak frequencies of the reference and the data signals. With visual detection using an image of the accumulated line profiles, a nondestructive inspection system using multiple surface waves provides reliable surface-crack information. KCI Citation Count: 3