Defect detection and size estimation in billet from profile of time-of-flight using ultrasonic transmission method with linear scanning

In this study, defect detection and size estimation in billet by transmission method with linear scanning were carried out and the validity of the method was evaluated by numerical simulation. In addition, the suitable signal frequency and aperture of transducers were clarified. As a result, the following were found: a defect can be detected, signals with frequencies lower than those generally used in conventional ultrasonic testing (i.e., 0.5–1.5 MHz) are desirable, and the time-of-flight (TOF) deviation Δτ becomes largest when the wavelength at center frequency and the aperture of transducers are comparable. Defect size can be estimated when a single defect exists alone and the defect is not near the surface of a billet. Although defect size estimation becomes difficult when the defect is near the surface of a billet, the defect can be detected by our proposed method.