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  • 1
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3091-3093 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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 (1–10 μm) 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.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1815-1817 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ceramic materials, such as silicon nitride and silicon carbide, are important because of their high mechanical strength at high temperature and in nonlubricative environments. The weakness of these materials lies in their brittleness. Stress concentration caused by the existence of surface or subsurface cracks can lead to the total mechanical failure of parts. In this letter, we describe the application of the resonant-sphere technique to perform nondestructive evaluation of ceramic bearing balls. The technique had been shown to be capable of measuring various material properties, such as Vs (shear wave velocity) and ν (Poisson's ratio). We use phase and amplitude measurements to simplify the evaluation of various resonance quality factors (Q), and we present, for the first time, the use of a resonance technique to propagate and detect surface waves on a sphere. We also show a decrease in Q for surface-wave modes due to the existence of surface cracks.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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