Published online by Cambridge University Press: 25 February 2011
Understanding the propagation of ultrasonic waves in polycrystals is important in nondestructive evaluation, both for the purpose of properly detecting or interpreting signals scattered from discrete flaws and for characterizing the microstructure itself. In this paper, the use of the unified theory for elastic wave propagation, developed by Stanke and Kino and based on the second order Keller approximation, is first discussed. After a brief review of the general formalism, recent extensions to the case of polycrystals with preferred grain orientation and elongation are presented. Particular attention is placed on a case commonly found in stainless steels in which the [001] crystallographic axes are aligned and the grains are elongated in the same direction. Techniques to predict the backscattered noise, based on single scattering approximation are then discussed and data motivating the need for extension to include multiple scattering is described. Finally, ways in which these theories can be used to provide improved characterizations of microstructures is indicated.