VISUALIZATION OF ULTRASONIC WAVES SCATTERED FROM REAR DEFECTS BY USING A LASER‐BASED IMAGING TECHNIQUE

We proposed a method for visualizing wave propagation in ultrasonic fields. This method generates thermal‐excitation ultrasonic waves on a specimen through pulsed laser scanning and detects the propagating signals via a reception transducer mounted on a fixed point. Dynamic images of ultrasonic waves propagated from a fixed point are created using the reciprocity principle of wave propagation. This method has the excellent feature that enables a visible and quick flaw inspection for actual objects. However, since this method visualizes all waves propagating on an object, it is disadvantageous in that defect echoes are often hidden in the forward traveling wave. In this research, we developed a data processing method for image enhancement of defect echoes. In the ultrasonic tests with aluminum plates or pipes with rear defects, we could visualize the defect echoes as they scatter in a radial manner, like water rings, on the surface of the specimen, which proved the validity of this data processing method. ...