Laser Ultrasonic Technique for Visualizing Ultrasonic Waves Propagating on 3-D Object

If it were possible to perform ultrasonic inspections while observing the propagation of ultrasonic waves as dynamic images, the identification of defect echoes would become easier, and inspection, quicker. Furthermore, fewer defects would be overlooked or improperly identified, leading to higher-reliability inspections. For visualizing ultrasonic propagation, we have developed a generation laser scanning method with a pulsed laser. This method has the following features that make it superior to the conventional visualization methods such as the photo-elasticity method and the reception probe scanning method. (1) It enables us to visualize ultrasonic waves propagating on a complexly shaped object. (2) It makes high-speed imaging possible and enables us to remotely measure images of ultrasonic waves. Using this laser ultrasonic imaging technique, we tried to visualize ultrasonic waves scattered from artificial defects such as corrosion on an inner surface of a pipe elbow and cracks on the backside surface in metal plates. From the measured dynamic images, we could observe the defect echoes as they scatter radially, like water rings, on the surface of the specimen. These results indicate that this method can be utilized for nondestructive inspection of materials.