Application of a non-contact laser ultrasonic imaging technique in surface defect detection

A technique of completely non-contact laser ultrasonic imaging was proposed to detect austenitic stainless steel with an artificial defect. Austenitic stainless steel was scanned by using the pulse of Nd:YAG laser, and the ultrasonic wave was received by the interferometer. The ultrasonic vibrations image at different locations away from the damages was analyzed in detail, and then taking discrete sine/cosine transform (DST/DCT) method, which transforms ultrasonic time-domain signals into similar frequency domain signals, which helps to improve the effects of detection the flaw or damage. The experimental results show that the proposed full-noncontact laser ultrasonic imaging technique using the DST/DCT method can directly and efficiently detect the location, the size of the damages. Hence, the discrete sine/cosine transform ultrasonic imaging technology provides an method for quantitative detection of defects in manufacturing.