Applications of scanning laser source technique for detection of surface-breaking defects

摘要

A new laser ultrasonic approach, the Scanning Laser Source (SLS) technique, is presented for detection of small surface-breaking defects. In this approach, we do not monitor the interaction of a generated ultrasonic wave with a flaw, as in the case of traditional pitch-catchor pulse-echo methods, but rather monitor the changes in the laser generated ultrasonic signal as the source is scanned over a defect. Changes in the amplitude and frequency content of the laser-generated ultrasound are observed resulting from the changed conditions under which the ultrasound is generated over areas without and with a surface-breaking crack. These changes are quite readily detectable using existing ultrasonic detectors. The SLS system includes a fiberized portable Q-switched YAG:Nd laser, which can be combined either with conventional PZT transducers or laser interferometers.