Detection of Internal Cracks in Square Billets Using Time of Flight of Longitudinal Waves

Abstract

We propose a method for the reconstruction of internal cracks using time of flight (TOF) of longitudinal waves. Since the longitudinal wave is the fastest elastic wave, it is possible to reconstruct cracks using a matrix method with apparent sound velocities calculated from the TOF. This method can neglect mode transformation and other waves because the first wave received is always the longitudinal wave. In addition, this method has the potential to be free from a blind sector and to detect the cracks precisely, because it is a transmission method and uses time domain analysis. We simulate crack detection using the transmission-line matrix (TLM) method. This proposed method detects cracks regardless of their location, direction, and number. It was also possible to detect the cracks when their length was smaller than the wavelength or when the billet had some error in its shape. This technique is expected to be useful for ultrasonic testing.