Single Point Contact Measurements of Mechanical Resonances

In this paper we present a novel technique for measuring the material properties of spherical objects. The technique is also capable of detecting the presence of surface defects in these objects. We excite resonances of spheres at both low and high frequencies. Resonances are generated by forming a one-point Hertzian contact between the sphere and a spherical depression in a buffer rod with a transducer. The resonance specuum is detected from the opposite pole of excitation using a Heterodyne interferometer. At low frequencies, bulk resonances of the sphere are excited and material properties are determined. At high frequencies, surface wave resonances of the sphere are excited and the dispersion relation of the waves is measured. The measured dispersion relation of the sphere is correlated to the surface wave velocity on the sphere and to the presence of surface defects.