Results on Broadband Scattering and Diffraction Suggest Methods to Classify and Reconstruct Defects in QNDE

Summary

Key goals of nondestructive testing, after a flaw is discovered, are its identification and the determination of its size, shape and orientation. Considerable progress has been made in understanding the scattered radiation pattern in the time domain, where the flaw signature is represented by a series of echoes in the form of impulses. Several specific conclusions have been drawn and key features such as the time of arrival of the impulses, their relative intensity, and their polarity have been identified. Our findings have been applied by Chou et al. in experiments [1–3] on specific (frequency encountered) inclusions in ceramics in a joint program. This work has successfully identified features in the time-domain in terms of elementary propagation processes and used them to identify inclusions and estimate their size. A measurement model which assumes a flaw is representable by a finite sum of d-functions has been developed and shown to give good results. The problem of a crack emanating from a void has been examined experimentally and theoretically in the time and frequency domain.

An inversion transformation has been developed which when used on back scattering data produces a function A(t) in the time domain and allows the extraction of geometrical parameters of a scatterer imbedded in a solid. For acoustic waves backscattered from a fixed, rigid sphere the function A(t) was derived explicitly and compared with the inversion of theoretical scattering data for a spherical void in titanium [4–6].