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Mechanics of Nondestructive Testing Mechanics of Nondestructive Testing Edited by W. W. Stinchcomb Virginia Polytechnic Institute and State University Blacksburg, Virginia Associate Editors: J. C. Duke, Jr. E. G. Henneke, II K. L. Reifsnider Virginia Polytechnic Institute and State University Blacksburg, Virginia Plenum Press . New York and London Library of Congress Cataloging in Publication Data Conference on the Mechanics of Nondestructive Testing, Virginia Tech, 1980. Mechanics of nondestructive testing. Papers from a conference held Sept. 10-12, 1980, sponsored by the Materials Response Group, Engineering Science and Mechanics Dept., Virginia Polytechnic Institute and State University. Includes index. 1. Non-destructive testing-Congresses. I. Stinchcomb, W. W. II. Virginia Poly technic Institute and State University. Engineering Science and Mechanics Dept. Materials Response Group. III. Title. TA417.2.C661980 620.1'127 80-23808 ISBN-13 978-1-4684-3859-8 e-ISBN-13: 978-1-4684-3857-4 001: 10.1007/978-1-4684-3857-4 Proceedings of the Conference on the Mechanics of Nondestructive Testing, held at Virginia Polytechnic Institute and State University, Blacksburg, Virginia, September 10-12, 1980. © 1980 Plenum Press, New York Softcover reprint of the hardcover 15t edition 1980 A Division of Plenum Publishing Corporation 227 West 17th Street, New York, N. Y. 10011 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the publisher PREFACE The synergism of the mechanics of nondestructive testing and the mechanics of materials response has great potential value in an era of rapid development of new materials and new applications for con ventional materials. The two areas are closely related and an advance in one area often leads to an advance in the other. As our understanding of basic principles increases, nondestructive testing is outgrowing the image of "black box techniques" and is rapidly becoming a legitimate technical area of science and engineering. At the present time, however, an understanding of the mechanics of nondestructive testing is lagging behind other advances in the field. The key to further development in the mechanics of nondestructive testing lies in the mechanics of the phenomena or response being investigated - a better understanding of materials response suggests better nondestructive test methods to investigate the response which, in turn, advances our understanding of materials response, and so on. With this approach in mind, the Materials Response Group of the Engineering Science and Mechanics Department at Virginia Polytechnic Institute and State University hosted a Conference on the Mechanics of Nondestructive Testing on September 10 through 12, 1980. Sponsors of the conference were the Army Research Office, the National Science Foundation, and the Engineering Science and Mechanics Department. The objective of the conference was to promote an understanding of the mechanics of nondestructive testing as related to the evaluation of materials response. The papers in this volume cover many of the frequently used NDT methods and introduce several new and innovative ideas in the field. Five overview papers present the general phi losophy of optical techniques, analysis of acoustic emission, electro magnetic methods, stiffness measurements, and ultrasonic techniques. Collectively, the papers seek to develop relationships between non destructive methods of investigation and the response of materials. Our sincere appreciation is extended to all who worked so hard and contributed to the success of the conference: the authors and participants, Dr. Daniel Frederick, Head of the Engineering Science v PREFACE and Mechanics Department, Dean Paul Torgersen, Dean of the College of Engineering, Dr. Clifford Astill, the National Science Foundation, Dr. Fred Schmiedeshoff, the Army Research Office, Dr. Ralph Siu, and Dr. Richard Harshberger and the staff of the Donaldson Brown Con tinuing Education Center at Virginia Tech. A very special recog nition and note of gratitude is expressed to Mrs. Phyllis Schmidt and Mrs. Betty Eaton who worked with patience and dedication in preparing the manuscripts for publication. Wayne W. Stinchcomb, Editor and John C. Duke, Edmund G. Henneke, II, Kenneth L. Reifsnider, Associate Editors September, 1980 Virginia Polytechnic Institute and State University Blacksburg, Virginia CONTENTS SESSION I Mechanics of Nondestructive Testing: Overview 1. Optical Interference for Deformation Measurements-- Classical, Holographic and Moire Interferometry. . . 1 Daniel Post 2. Basic Wave Analysis of Acoustic Emission. . • . • . . .• 55 Robert E. Green, Jr. 3. A Survey of Electromagnetic Methods of Nondestructive Testing. • . . . . . . . . . . . . . . . . . . . 77 W. Lord 4. Stiffness Change as a Nondestructive Damage Measurement.. 101 T. Kevin O'Brien 5. Concepts and Techniques for Ultrasonic Evaluation of Material Mechanical Properties . . . . . . . . . • . 123 Alex Vary SESSION II Material Property Determination Harold Burger, Chairman 1. Neutron Diffraction and Small-Angle Scattering as Nondestructive Probes of the Microstructure of Ma terials . . . . . . . • . . . . . . . . . . . 143 C. J. Glinka, H. J. Prask and C. S. Choi 2. Determination of Fundamental Acoustic Emission Signal Characteristics . 165 Richard Weisinger vii viii CONTENTS 3. A Simple Determination of Von Karman Critical Velocities • • . . . . • • . . . . • • . . . 187 R. B. Pond, Sr. and J. M. Winter, Jr. 4. Fracture Prediction by Rayleigh Wave Scattering Measuremen t • . • • . . . • . • . . . • . • • • 197 M. T. Resch, J. Tien, B. T. Khuri-Yakub, G. S. Kino, and J. C. Shyne 5. Anisotropic Elastic Constants of a Fiber Reinforced Boron-Aluminum Composite. • 215 S. K. Datta and H. M. Ledbetter 6. Nondestructive Evaluation of the Effects of Dynamic Stress Produced by High-Power Ultrasound in Materials ...... . 231 Richard B. Mignogna and Robert E. Green, Jr. SESSION III Defect and Flaw Characterization Robert Crane, Chairman 1. The Mechanics of Vibrothermography . . 249 K. L. Reifsnider, E. G. Henneke, and W. W. Stinchcomb 2. Dynamic Photoelasticity as an Aid to Sizing Surface Cracks by Frequency Analysis . . • . 277 A. Singh, C. P. Burger, L. W. Schmerr and L. W. Zachary 3. Ultrasonic and X-Ray Radiographic Inspection and Characterization of Defects in Gr/Al Composites. 293 T. Romano, L. Raymond, and L. Davis 4. Evaluation of Sensitivity of Ultrasonic Detection of Delaminations in Graphite/Epoxy Laminates . . . 309 S. W. Schramm, I. M. Daniel and W. G. Hamilton SESSION IV Material Damage-Initiation and Growth: Life Prediction Francis Chang, Chairman 1. Influence of Initial Defect Distribution on the Life of the Cold Leg Piping System . . . 325 B. N. Leis, M. E. Mayfield, T. P. Forte, and R. J. Eiber CONTENTS ix 2. In-Flight Acoustic Emission Monitoring. . • . . • • . . .• 343 Gary G. Martin 3. On Interrelation of Fracture Mechanisms of Metals and Acoustic Emission. . . . . . 367 G. S. Pisarenko, S. I. Likhatsky, and Yu. V. Dobrovolsky 4. Fatigue Delamination in CFRP Composites: Study with Acoustic Emission and Ultrasonic Testing • . . . . • . . . . 391 F. X. De Charentenay, K. Kamimura and A. Lemascon Index . . . . . . . . . • 403 OPTICAL INTERFERENCE FOR DEFORMATION MEASUREMENTS- CLASSICAL, HOLOGRAPHIC AND MOIRE INTERFEROMETRY Daniel Post Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061 INTRODUCTION Interferometry is a powerful tool. It enables measurements of surface topography, dimensional changes and deformations of solid bodies, all in the sub-wavelength sensitivity range. This article is a tutorial treatment of the subject. Its purpose is to introduce modern interferometric techniques of engineering measurements; and to explain them in sufficient detail to gener ate a comfortable association with the subject. Ultimately, the mission is to foster understanding and appreciation in order to inspire increased utilization and further development. The fundamentals of interferometry are easy to understand. The rather diverse implementations, including holographic and moire interferometry, fit under a common umbrella. Only a few basic concepts and a few equations are involved and these will be reviewed in sufficient depth for practical usefulness. Inter ferometry is easy to apply to many important measurements problems. The name has long been associated with delicate instrumentation and masterful laboratory technique. These images no longer represent many applications, and they are grossly relaxed in most others. More than anything else, the substitution of lasers in place of classical light sources has simplified the technology. The fundamental ideas and relationships will be reviewed first. Classical interferometry will be described, but with the admission of lasers to the classical technology. Then, holography and holographic interferometry will be explained. These techni ques are especially useful for out-of-plane measurements, e.g., surface topography, change of specimen length, and displacements 2 DANIEL POST normal to the specimen surface. Moire interferometry will be presented last. This is an emerging technology to measure in-plane displacements, i.e., displacements in the plane of the specimen surface, with high sensitivity and accuracy. While placed last by historical chronology, it holds the promise of a powerful NDT technique for observation and measurement of material integrity and structural performance. Familiar codes will be used in the diagrams. It is es pecially important to remember that a sketch of an eye (as in Fig. 9) represents any observing system, such as a human eye, a camera or a video receiver. In addition, a ray of light in a diagram (as in Fig. 2) represents the beam of light that contains the ray; when a reader sees a simple ray, he/she should always picture the full beam and the wave trains and wavefronts traveling in the beam. Always. FUNDAMENTALS Our Model of Light The wave theory of light is sufficient to explain all the characteristics we use. A parallel beam of light emitted in the z-direction is depicted (at a given instant) as a train of re gularly spaced disturbances that vary with z as A a cos 2n ~ (1) A Symbol A describes the amplitude or strength of the disturbance, which is usually viewed as the strength of an electro-magnetic field at a point in space. Coefficient a is a constant. The field strength varies harmonically along z, where the distance between neighboring maxima is A, called the wavelength. Length z is not endless--for that would represent an eternal light- but it is very long compared to A; in the case of laser light, length z of the wave train may be a million wavelengths or more. Many such wave trains exist simultaneously in a beam of light. However, the wave train is not stationary. It travels or propagates through space with a very high constant velocity C. At any fixed point along the path of the wave train, the disturb ance is a periodic variation of field strength. Field strength varies through one full cycle in the brief time interval A/C (seconds/cycle); its frequency w is CiA (cycles/second). During the passage of the wave train through any fixed point z = zo' the light disturbance varies with time t as
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