Non-destructive evaluation of formability in cold rolled steel sheets using the SH 0-mode plate wave by electromagnetic acoustic transducer

Abstract

We evaluated the relation between the Lankford value ( r-value) and the velocity of cold rolled steel sheets using the fundamental shear horizontal plate wave (SH 0-mode plate wave) and the fundamental symmetrical Lamb wave ( S 0-mode Lamb wave) as a function of the propagation angle. The SH 0-mode plate wave at the traveling angle of 45° showed the opposite tendency compared with that of other traveling angles or other ultrasonic modes. Using the velocity equations derived by accounting for texture and cubic crystal anisotropy, we found that the velocity at 45° was strongly influenced by the 1 0 0 crystallographic plane compared with that of other ultrasonic conditions. Next, the measurement accuracy for the formability of cold rolled steel sheets using the S 0-mode Lamb wave and the SH 0-mode plate wave was estimated to find that the evaluation accuracy using the SH 0-mode plate wave became poor as compared with the case of the S 0-mode Lamb wave. For this, the effect of the ultrasonic velocity anisotropy to the propagation direction was the main cause, because the anisotropy of the SH 0-mode plate wave was bigger than that of the S 0-mode Lamb wave. Finally, we confirmed that the evaluation precision could be improved by using the SH 0-mode EMAT with a narrow-width sensor coil to transmit and receive the sharp ultrasonic beam.