Nondestructive characterization of texture and plastic strain ratio of metal sheets with electromagnetic acoustic transducers

Abstract

All the lowest-order independent CODF (crystallite orientation distribution function) coefficients W400, W420, and W440 of rolled steel sheets, with thickness less than 1 mm, have been obtained nondestructively by using the known single-crystal elastic constants and the relative ultrasonic velocities measured with EMATs (electromagnetic acoustic transducers). The ultrasonic velocities of all the waves, longitudinal waves, shear waves propagating in the through thickness direction, and SH0 (shear horizontal) plate waves, were measured by the EMATs. No acoustic coupling medium was necessary, making possible quick, accurate, and reproducible measurements. It is shown that the CODF coefficients can be obtained as the solutions of three linear equations in which the measured relative ultrasonic velocities are included. There was an overall correspondence between the ultrasonic pole figures drawn using the obtained CODF coefficients and x-ray pole figures. All nine elastic constants of a steel sheet were also calculated. Average Young’s modulus Ē and planar variation in Young’s modulus dE calculated using the nine elastic constants were consistent with average plastic strain ratio r̄ and planar variation in plastic strain ratio dr, respectively, showing that the ultrasonic method here is well adapted for practical use.