Wolfgang Sachse Richard Weaver
Theor. and Appl. Mech., Cornell Univ., Ithaca, NY 14853-1503
The essential elements of a point--source/point--receiver ultrasonic system include a broad bandwidth, small-aperture source generating elastic waves with a broad angular spectrum and a receiver with similar characteristics to detect them. By moving the source or receiver and stacking the received waveforms, one generates a scan image that provides a view of the complete elastic wave field in a test specimen. Wave arrivals are related to the speeds of propagation of various wave modes in various directions and the signal amplitudes reflect the propagational characteristics of the material. An interpretation of the scan images requires an understanding of the propagation of transient elastic waves in a bounded structure. Recent developments on both the forward and inverse problems are summarized and the full solution of the forward problem for the response of a general axisymmetric anisotropic viscoelastic plate is reported. The computed results are compared to measured waveforms in viscoelastic and transversely isotropic materials. Also reviewed are the approaches for processing single wave forms and scan images to recover the elastic and viscoelastic properties of a test specimen. Extensions of this approach to materials of arbitrary anisotropy and layered microstructures are also considered. [Work supported by Cornell's Materials Science Center (NSF) and the Office of Naval Research (Physical Acoustics and Solid Mechanics Programs).]