Ultrasonic Measurement of Sheet Anisotrophy and Formability

The anisotropy of Young's modulus in steel sheet is closely related to the r-value. Commercially available instrumentation is often used to predict formability by measuring the resonant frequencies of coupons cut at 0°, 45°, and 90° to the rolling direction. This paper describes recent advances in instrumentation to acquire equivalent information nondestructively, with the possibility of on-line process control. The technique uses electromagnetic-acoustic transducers (EMAT's) to excite and detect ultrasonic guided waves propagating in the plane of the sheet. Theories of wave propagation relate the velocities of these waves to Young's modulus anisotropy or to the orientation distribution coefficients (ODC's) describing the texture. The paper reviews the principles of the measurement and then presents correlations of the elastic anisotropy, as deduced by the ultrasonic instrumentation, with tensile measurements of r. Measurements of Young's modulus anisotropy and neutron diffraction measurements of ODC's are also included.