ATTENUATION OF ULTRASONIC WAVES IN CUBIC METALS HAVING ELONGATED, ORIENTED GRAINS

Abstract The attcntuation of ultrasonic waves propagating in polycrystalline metals is a subject which has received considerable experimental and theoretical attention. Important recent contributions include the work of Hirsekorn and of Stanke and Kino. In this paper, we extend the approach of the latter authors to a particular problem motivated by the cast stainless steels that are utilized in the piping of nuclear reactors. In those materials, large columnar grains often are found as a result of the directional solidification occurring in the casting. To model the effects of these grains on the ultrasonic attenuation, we consider a medium consisting of ellipsoidal grains with the axes of revolution all parallel to a preferred direction and having an arbitrary aspect ratio. In each grain, one of the axes of the cubic lattice is assumed to lie parallel to the preferred direction while the rotation about this axis is random. The unified theory of Stanke and Kino, based on an anisotropic extension of the Keller approximation, is utilized to obtain numerical results for the velocity and attenuation of longitudinal and horizontally polarized shear waves as a function of the direction of propagation, grain size and aspect ratio and frequency. In this approach, an autocorrelation function is used to characterize the shapes of the grains and thereby avoid coherent artifacts.