G. A. Alers
NIST, MS 853, 325 Broadway, Boulder, CO 80303
Several applications have been explored for ultrasonic resonance measurements using electromagnetic-acoustic transduction on cylinders and spheres. Since the transduction is noncontacting, acoustic velocities and damping can be determined with great accuracy, and small changes in related material properties or the sample environment can be detected. The resonant frequencies of certain ``axial-shear'' modes in induction-hardened steel rods have been found to be highly correlated with case depth, providing a nondestructive measure of depth comparable in accuracy to destructive tests. Applied stress on an aluminum cylinder has been measured with automatic temperature compensation using the resonant frequencies of an axial-shear mode and a torsional mode, thus demonstrating the basis for an acoustic load cell. Elastic anisotropy in aluminum has been measured from the relative frequency splitting of axial-shear modes that would be degenerate in isotropic material. Also, electromagnetic-acoustic transduction has been incorporated in a system used to obtain basic data on the elastic constants and damping of metallic spheres at elevated temperatures.