Abstract
Ultrasonic flaw detection and sizing is an important issue for ensuring structural reliability of industrial plants. The ultrasonic phased array technique is one of the most effective tools for visualizing the flaws in structural components. It is important to enhance the spatial resolution of phased array images to clearly visualize flaws; however, the spatial resolution of phased array images needs more research. A high spatial resolution phased array probe was designed as the first stage of this study. To investigate the spatial resolution of the phased array probe, acoustic analysis was conducted utilizing the Rayleigh-Sommerfeld Integral. The spatial resolution was investigated by changing the total aperture of the probe. As a result, the large-aperture phased array probe achieved high spatial resolution. Next, ultrasonic testing was simulated by the finite differential method using conventional and specially designed phased array probes. For the conventional probe, the flaw could be visualized but the shape was not clear enough. On the other hand, for the specially designed large-aperture probe, extensive noise appeared in the image and the flaws could not be visualized. Because of mode conversion, Rayleigh waves are generated at the contact surface between the transducer and testing material. The amplitude of Rayleigh waves are much higher than the diffraction echoes, hence the Rayleigh waves disturb the visualized image at the near field of the probe. Consequently a new technique for flaw visualization at the near field of the phased array probe was developed by eliminating detrimental waves. As a result the flaws could be clearly visualized using this technique.
