Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Engineering Science and Mechanics

First Advisor

Lester W. Schmerr

Abstract

In the field of ultrasonic Nondestructive Evaluation (NDE), it is important to be able to classify a flaw as cracklike or volumetric, based on features contained in an ultrasonic scattering response. In the present work, it demonstrated, based on model studies, that three fundamental features, obtained from the early time response of a flaw are in principle useful for classification purposes. These features are based on the Kirchhoff approximation for cracks and a new subtracted surface integral formulation of the Born approximation for volumetric flaws. To reliably extract such features from an experimental response, however, it is important to perform both deconvolution and low frequency extrapolation procedures. Here, we show that a new flaw-derived reference deconvolution method and a low frequency extrapolation technique, using the Gerchberg-Papoulis algorithm, can be effective for these purposes. Once these fundamental features are extracted, a simple adaptive learning procedure has been successfully applied for performing the classification.

DOI

https://doi.org/10.31274/rtd-180813-8676

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Lat Sang Koo

Language

en

Proquest ID

AAI8805097

File Format

application/pdf

File Size

199 pages

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