Accurate Determination of Elastic Anisotropy to Detect Internal Microstructures Using Resonant Ultrasound Spectroscopy

Elastic constants are of great significance, because they are fundamental thermodynamic susceptibilities that connect directly to thermodynamics and electronic structure, as well as to mechanical properties. Resonant ultrasound spectroscopy (RUS) measures non-destructively all fundamental elastic properties by determining the natural frequencies at which a 3D object resonates when is mechanically excited (normal modes). By using an inversion scheme, it is possible to extract the entire elastic tensor of a material with extreme sensitivity in a single frequency sweep using only one, small sample. This makes RUS particularly advantageous to study physical properties of low-symmetry single crystals and textured bulk materials. I will present recent RUS measurement examples of its applications to thermodynamic and materials science problems. I will focus on the effect of texture in elastic constants as a result of mechanical or growth processes and the robustness of results obtained by RUS. In materials such as aluminum that is often considered isotropic but shows clear anisotropy when it is extruded, or 3D printed. Similar but much larger effect is found in additive manufactured stainless steel where the growth process leads to a large anisotropy with a softening of 40%–50% along the build direction.