EFFECT OF LOAD SPECTRUM VARIABLES ON FATIGUE CRACK INITIATION AND PROPAGATION A symposium sponsored by ASTM Committee E-9 on Fatigue AMERICAN SOCIETY FOR TESTING AND MATERIALS San Francisco, Calif., 21 May 1979 ASTM SPECIAL TECHNICAL PUBLICATION 714 D F Bryan, The Boeing Wichita Co., and J M Potter, Air Force Flight Dynamics Laboratory, editors 04-714000-30 AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 # Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Copyright © by AMERICAN SOCIETY FOR TESTING AND MATERIALS 1980 Library of Congress Catalog Card Number: 80-66078 NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication Printed in Baltimore, Md October 1980 Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Foreword The symposium on Effect of Load Spectrum Variables on Fatigue Crack Initiation and Propagation was presented at San Francisco, Calif., 21 May 1979 The symposium was sponsored by the American Society for Testing and Materials through its Committee E-9 on Fatigue D F Bryan, The Boeing Wichita Co., and J M Potter, Air Force Flight Dynamics Laboratory, presided as symposium chairmen and editors of this publication Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Related ASTM Publications Part-Through Crack Fatigue Life Predictions, STP 687 (1979), $26.65, 04-687000-30 Service Fatigue Loads Monitoring, Simulation, and Analysis, STP 671 (1979), $29.50, 04-671000-30 Fatigue Crack Growth under Spectrum Loads, STP 595 (1976), $34.50, 04-595000-30 Manual on Statistical Planning and Analysis for Fatigue Experiments, STP 588 (1975), $15.00, 04-588000-30 Handbook of Fatigue Testing, STP 566 (1974), $17.25, 04-566000-30 Damage Tolerance in Aircraft Structures, STP 486 (1971), $19.50, 04-486000-30 Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized A Note of Appreciation to Reviewers This publication is made possible by the authors and, also, the unheralded efforts of the reviewers This body of technical experts whose dedication, sacrifice of time and effort, and collective wisdom in reviewing the papers must be acknowledged The quality level of ASTM publications is a direct function of their respected opinions On behalf of ASTM we acknowledge with appreciation their contribution ASTM Committee on Publications Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authoriz Editorial Staff Jane B Wheeler, Managing Editor Helen M Hoersch, Associate Editor Helen Mahy, Senior Assistant Editor Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Contents Introduction Effect of Spectrum Editing on Fatigue Crack Initiation and Propagation in a Notclied Menit)er—D F SOCIE AND P I ARTWOHL Discussion 23 Time Dependent Clianges in Notcli Stress/Notcli Strain and Tlieir Effects on Crack Initiation—j R CARROLL, JR 24 Ranking 7XXX Aluminum Alloy Fatigue Crack Growth Resistance Under Constant Amplitude and Spectrum Loading— R J B U C C I , A B T H A K K E R , T H SANDERS, R R SAWTELL, AND J T STALEY 41 Effects of Compressive Loads on Spectrum Fatigue Crack Growth R a t e — T M HSU A N D W M M C G E E 79 Observation of Crack Retardation Resulting from Load Sequencing Characteristic of Military Gas Turbine Operation— J M LARSEN AND C G ANNIS, JR 91 Effects of Gas Turbine Engine Load Spectrum Variables on Crack Propagation—D E MACHA, A F GRANDT, JR., AND B J WICKS 108 An Engineering Model for Assessing Load Sequencing Effects— I T WOZUMI, T SPAMER, AND G E LAMBERT 128 Effect of Transport Aircraft Wing Loads Spectrum Variation on Crack G r o w t h — p R ABELKIS 143 Effect of Gust Load Alleviation on Fatigue and Crack Growth in ALCLAD 2024-T3—J B DE IONGE AND A NEDERVEEN 170 Prediction Model for Fatigue Crack Growth in Windmill Structures— R W FINGER 185 Discussion Copyright Downloaded/printed University 199 by by of Effects of Fighter Attack Spectrum on Crack Growth—H D DILL, C R SAFF, AND J M POTTER 205 Evaluating Spectrum Effects in U.S Air Force Attack/Fighter/ Trainer Individual Aircraft Tracking—c E LARSON, D J WHITE, AND T D GRAY 218 Summary 228 Index 231 Copyright Downloaded/printed University by by of STP714-EB/Oct 1980 Introduction The effects of variations in the parameters that characterize in-service loading on the Hfe of engineering structures has received ever-increasing attention in recent years Many investigators have shown fatigue crack initiation and growth to be sensitive to loading variables such as load sequence, frequency and magnitude of peak overloads and underloads, load spectrum truncation, compression hold times, and others The ability of the stress analyst to predict the useful life of a particular structure depends not only on having a truly representative loading spectrum, but also on knowing the effects of variations in the load history parameters This symposium is a timely and logical follow-on to the American Society for Testing and Materials (ASTM) sponsored symposium on Service Fatigue Loads Monitoring, Simulation, and Analysis presented in Atlanta, Ga., 14-15 Nov 1977 The objective of the present symposium was to bring together engineers, scientists, and academicians to exchange ideas and present state-of-the-art papers on the analytical and experimental evaluation of various load spectrum effects on crack initiation and propagation The papers in this publication cover a wide range of subjects from various engineering fields Load spectra representative of aircraft structures, gas turbines, and windmill structures are presented along with analytical and experimental fatigue and fracture results The effects of spectrum editing, time dependent changes in material characteristics, compression loads, and gust alleviation are discussed A crack growth model incorporating both retardation and acceleration effects and a unique approach to ranking 7000 series aluminum alloys are included The state-of-the-art information in this publication should be helpful to those engineers responsible for life predictions of structures subjected to repetitive loads Scientists and educators in the field of engineering structures should likewise find this publication of great interest The symposium organizing committee wishes to express sincere appreciation to the authors, reviewers, and ASTM staff for their efforts in making this publication possible D F Bryan J M Potter The Boeing Wichita Company, Wichita, Kans 67210; symposium cochairman and coeditor AFFDL/FBE Wright-Patterson Air Force Base, Ohio 45433; symposium cochairman and coeditor Copyright by ASTM Int'l (all rights Downloaded/printed Copyright® 1980 b y by A S I M International www.astm.org University of Washington (University of reserved); Washington) Sun pursuant Dec 27 to 13:3 License LARSON ET AL ON INDIVIDUAL AIRCRAFT TRACKING 223 each curve notes fracture It is seen that the content of the different spectra impact the crack growth rates as well as the critical crack lengths Dividing the (spectrum) time to failure for each of the spectra by the time to failure under the baseline spectrum results in the normalized crack growth life data of Table The variations in life range from a —88 percent in the case of the horizontal tail under Spectrum to +800 percent for the same location under Spectrum Variations of this magnitude are difficult to explain physically and likely point out that the analysis is method limited in the case of the horizontal tail That is, the method of predicting the horizontal tail stresses possibly fails for variations of this magnitude in the spectrum parameters It is judged that trends in the results are preserved, however The significance of the data of Table is that large changes in life are apparent under the influence of relatively small changes in Mach number and weight The counting accelerometer is blind to both these variables The counting accelerometer is at least partially blind to the mission variations represented by Spectra 8, 9, and 10 The Mach number and weight experience effective variations by shifting the time spent in the subject missions The MSR has an obvious advantage in these cases, since it reflects the actual load experienced at the location Figures through address the remaining question with respect to lAT—that of being able to track the damage state at locations remote to the reference location In these figures, the crack growth curve data is normalized to give an indication of the rate of damage at the stations remote to wing station (WS) 32, the reference for the A-7D The data is normalized as follows For a given location, the minimum failure crack length was read for each spectrum Each of the spectrum times corresponding to these lengths were divided by the time it took to reach the minimum length for the baseline spectrum The normalized values of each of the locations are plotted against the values of the reference station, WS 32 Note that the 45-deg line on the graphs represents perfect correlation of the damage at the various locations with the damage at the reference Note also that the lower half of the divided quadrant represents conservative comparisons while the upper half is nonconservative An examination of the data in Fig through reveals that the error in the damage rates of WS 53, pylon stub hole, and the outer wing panel, relative to the reference is especially good The average of the variations in damage rate for these locations is percent For the wing attach lug, the variation from perfect correlation is about 10 percent and for the longeron, about 18 percent These variations are considered moderate when taken as an average, but the maximum variations for particular spectra are 27 and 48 percent, respectively These large variations make the usefulness of such damage transfer somewhat tenuous for these stations The variations in the damage rate correlations for the two tail stations are considered completely out of order Copyright by ASTM Int'l (all rights reserved); Sun Dec 27 13:33:51 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 224 EFFECT OF LOAD SPECTRUM VARIABLES o "? o O O O O O O V O O u^ o "? o "? o o o o o o o o o "^ ? o "7 o t^ rtrtrt«00 — O in vo VI c^oooc^oCT^-< N ^ t N :?; ao ^ ^ in — O O - H O O O O O -I H U < •a lO ^ a S g Z S -^H^