Defect Detection in Square Billet Using Time-of-Flight of Longitudinal Waves

Abstract

We investigate defect detection using the time-of-flight (TOF) of longitudinal waves in an experiment. The apparent sound velocity is reconstructed using the TOF measured by the transmission method. The defects are visualized as a decrease in apparent sound velocity because the TOF increases owing to diffraction at the defects. In addition, the effects caused by the frequency of the input signal and the transducer size are evaluated by calculation prior to the experiment. Wave propagation is calculated by the transmission-line matrix method. As a result, the proposed method could detect defects of 2.8 mm when the frequency was 2.0 MHz and transducer diameter was 5 mm by calculation. The defect detection was evaluated in an experiment using a transducer whose diameter was 5 mm. The defects could be identified and their location conformed to the setup. Therefore, the proposed method could detect defects by experiment as well as calculation.