Detection of an axial surface microcrack in steel wire rods with noncontact ultrasonic reverberation spectroscopy

In the manufacturing process of steel rod, a number of micro-scale defects occur along the axial direction on the surface of the rods. To prevent failures in advance, a method to detect the micro-scale cracks remaining on the surface of rod is required. This work employs an Electromagnetic acoustic transducer (EMAT) to evaluate the cracks of the wire rods with the noncontact Ultrasonic reverberation spectroscopy (URS). The resonance at the cross section of the cylindrical rods is generated by horizontally polarized shear waves driven in the circumferential direction. Through a series of URS experiments, changes in the resonant frequency, the amplitude of the resonant peak, and the attenuation of the ultrasonic reverberation were observed at intact and defected parts of specimens. The results showed that the URS technique may be one of the effective tools to detect the axial surface microcrack with its depth of a few tens of micrometers.