COMPUTATIONAL
INVERSE TECHNIQUES
in
NONDESTRUCTIVE
EVALUATION
© 2003 by CRC Press LLC
CRC PRESS
Boca Raton London New York Washington, D.C.
COMPUTATIONAL
INVERSE TECHNIQUES
in
NONDESTRUCTIVE
EVALUATION
G. R. Liu
X. Han
© 2003 by CRC Press LLC
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International Standard Book Number 0-8493-1523-9
Library of Congress Card Number 2003043554
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
Printed on acid-free paper
Library of Congress Cataloging-in-Publication Data
Liu, G.R.
Computational inverse techniques in nondestructive evaluation / G.R., Liu, X. Han,
p. cm.
Includes bibliographical references and index.
ISBN 0-8493-1523-9 (alk. paper)
1. Non-destructive testing—Mathematics. I. Han, X. II. Title.
TA417.2.L58 2003
620.1′127—dc21 2003043554
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© 2003 by CRC Press LLC
Dedication
To Zuona
Yun, Kun, Run,
and my family
for the time they gave to me
G. R. Liu
To Zhenglin, Weiqi
and my family for their support
To my mentor, Dr. Liu
for his guidance
X. Han
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© 2003 by CRC Press LLC
Preface
In the past 2 decades, inverse problems have been one of the most important
focal areas of research in engineering. Advances in computational numerical
methods and techniques in computer hardware and software in so-called soft
computing have enabled inverse techniques to become a powerful tool for
practical engineering problems. However, for many researchers and engi
-
neers, inverse analysis is still a distant topic because of a frightening and
mysterious image of the difficulty of grasping and dealing with its concepts.
In the early 1980s, G. R. Liu encountered the first inverse problem in his
years of postgraduate study for the characterization of composite laminates.
Dr. Liu was alarmed and confused by the flood of unfamiliar terminologies
related to inverse problems, such as ill-posedness, regularization, stability,
uniqueness, etc. In fact, he worried so much about the possibility of doing
things improperly that he finally gave up pursuing the problem in the context
of inverse analysis. He solved the problem by cutting the composite laminates
into pieces and measuring the mechanical and thermal properties using
traditional tensile machines and thermal measurement equipment — a
destructive, time consuming, problematic, but conventionally accepted
approach. Back then, he wished for a book like this one to guide his research
work so that he could conduct it in a more advanced manner.
The next time Dr. Liu got the courage to face the same inverse problem
was in 1997, when he had a set of good forward solvers for waves in
composite laminates. This time he decided to put these terminologies aside
and go straight ahead to formulate and use the optimization tools to solve
the problem. He managed to obtain the solution without too much difficulty,
but with many mistakes. Based on confidence built upon the first trial study,
he then turned to look at these terminologies, and found that they were, in
fact, walls that scared people away.
The best way to break open these walls is to solve an inverse problem first
following general knowledge, and then dealing with the issues as they occur.
Slowly, experience will accumulate and tricks and techniques will be learned
so that increasing numbers of inverse problems can be solved. This means
learning or training was difficult before, but much easier and particularly
useful now because these practices can be performed in a PC environment,
to which almost everyone has access.
The authors have learned some inverse techniques through the aforemen-
tioned hard way; they decided to put their experiences in this book on how
inverse problems of mechanics can be formulated and solved and the possible
issues important for successful inverse analysis. They are committed to put
-
ting all these materials in a very simple and easy-to-understand form, as well
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© 2003 by CRC Press LLC
