Surface Acoustic Wave Probing of Ceramic Bearing Balls
This work is a continuation of our effort to develop a nondestructive technique for the detection and characterization of surface and near surface defects in ceramic bearing balls. We reported earlier on a method for detecting and sizing submicron surface depressions using a scanning acoustic microscope. Our present work deals with the detection and sizing of surface cracks in the ceramic bearing balls, a problem which requires knowledge of the surface wave reflection coefficient of the crack, either at a single frequency in the long wavelength regime or as a function of frequency in the short wavelength regime. For this purpose, we need to learn the characteristics of surface wave propagation on spherical surfaces, the scattering of the surface waves from the cracks, and we need to develop a method for exciting the surface wave. We present a detailed theory of surface wave propagation on spheres. The results indicate that an arc source focuses the surface acoustic waved in a manner similar to bulk acoustic waves focusing by spherical transducers. We will present the details of this self focusing behavior. A spherical cap transducer structure similar to a planar wedge transducer is proposed to excite the spherical surface waves. We will present the details of the design of the spherical cap transducer for efficient surface wave excitation.
KeywordsSurface Wave Surface Acoustic Wave Spherical Surface Acoustic Field Bearing Ball
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