Ultrasonic imaging of material condition using advanced simplified ultrasonic CT

In this research, as a new measurement method to estimate the infinitesimal change of material condition, the simplified ultrasonic CT system, which uses the information of three directions, that is, 90degrees, +45degrees and -45degrees direction about inspection plane is proposed. Use of simplified ultrasonic CT system has two merits: Firstly, the measurement time is very short comparing with general CT. Secondly, it can detect sensitively very infinitesimal defect in vertical or slant direction about inspection plane because the obtained image is not C scan image but CT image calculated from, three directions. From these merits, this method can be considered as a very effective method for the evaluation of material condition. In order to know the applicability of actual NDT, several kinds of welded specimens are investigated. The result showed that the CT images obtained were very similar to actual defect of specimens. Also, in order to confirm the performance of simplified ultrasonic CT, the D scan image by TOFD method was obtained for the same specimen. The C scan or CT image gave better information than the D scan image obtained from TOFD method. Frequency analysis method for enhancing the C scan or CT image is developed. This frequency analysis method is based on the frequency response property of the material. By comparing the magnitude at frequency domain, the special frequency which shows the big difference between welded joint and base material was searched for and used to get C scan or CT image.