Toward Characterization of Single Crystal Elastic Properties in Polycrystalline Materials Using Resonant Ultrasound Spectroscopy

Resonance ultrasound spectroscopy (RUS) is a nondestructive technique that exploits the natural resonance behavior of a material to characterize its elastic properties. The traditional RUS approach utilizes an analytic approximation to determine resonance behavior given a guess set of elastic moduli. An optimization process is then used to fit elastic properties to experimentally measured resonance frequencies. This approach generally requires certain limiting assumptions to be made with respect to sample geometry, crystallographic orientation, and requires single crystal samples to obtain single crystal elastic properties. Toward the goal of developing a measurement process to obtain single crystal elastic properties on polycrystalline aerospace alloys without the aforementioned limitations, a framework has been developed to enable this process on samples with multiple grains, arbitrary sample shape, and without restrictions to crystallographic orientation. This framework utilizes off-the-shelf finite element method software and optimization routines, enabling rapid modeling and easy adaptation to different scenarios. Testing of this framework was performed on an amorphous specimen, a single crystal specimen, and preliminary results show promise on a nickel aluminide bicrystal, provided that the sample geometry, density, and crystallographic orientations are adequately characterized.