| 摘要 |
PROBLEM TO BE SOLVED: To detect a defect sufficiently even when the intensity of generated plate- wave ultrasonic waves is comparatively small by using a laser ultrasonic inspection apparatus which can change a position in which the plate-wave ultrasonic waves are generated on a steel product comparatively easily. SOLUTION: A common irradiation position 19 on a steel product 1 is irradiated with a laser beam 17 and a laser beam 18 by a proper optical system, their interference is generated, and plate-wave ultrasonic waves are generated. The irradiation position 19 is situated in the central part in the width direction of the steel product 1. The optical frequency difference between the laser beam 17 and the laser beam 18 is changed over at a prescribed timing in such a way that the plate-wave ultrasonic waves advancing to the right side from the irradiation position 19 and the plate-wave ultrasonic waves advancing to the left side are generated alternately. The propagation distance of the plate-wave ultrasonic waves reflected by the end part of the steel product 1 so as to be returned again to the irradiation position 19 becomes nearly equal to the width of the steel product 1, Thereby, the propagation distance is shortened to about 1/2 as compared with a case in which the end part on one side of the steel product 1 is irradiated with a laser beam so as to generate plate-wave ultrasonic waves. |
