Application of Lamb wave scattering for grain size analysis in thin copper sheets: Results from laboratory and industrial trials

It is well established that attenuation of ultrasonic bulk waves may be used as a measure of grain size in polycrystalline materials. However, thinner samples usually do not allow for attenuation measurements with through-thickness ultrasonic bulk waves, and in order to overcome this obstacle, the present study was made to see whether attenuation of guided Lamb waves may be used instead. The analysis method, which employs Fourier analysis to reveal the frequency components in the ultrasonic Lamb traces, is tested on thin copper sheets of varying grain sizes. In addition, some of the tests have been carried out on-line at a continuously annealing line during production of copper sheets. The experimental data indicate that the estimation of attenuation from these measurements could be used as a measure of grain size. In addition, the experimental data have been compared to attenuation calculated from the grain scattering theory of Lamb waves and show reasonably good agreement.