One-point contact measurement of spherical resonances

Ceramic bearing balls are desirable for use in high-temperature and nonlubricative environments because of their ability to retain high mechanical strength and reduced wear. However, because ceramics are brittle, it is very important to inspect ceramic parts for the existence of small (l-10 pm) surface defects. The contact-contact resonant sphere technique has been shown to be able to detect the presence of surface defects in spherical objects. This technique, however, has certain limitations that are especially important when inspecting small spheres. In this letter we present a true one-point-contact technique to circumvent these limitations. 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 spectrum is detected from the opposite pole of excitation using an optical 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.