Fracture Resistance of Aluminum Alloys Notch Toughness, Tear Resistance, and Fracture Toughness J. Gilbert Kaufman The Aluminum Association Incorporated 900 19th Street,N.W.,Washington,D.C.20006 Materials Park,Ohio 44073-0002 www.asminternational.org Copyright ©2001 by ASM International® 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, recording, or otherwise, without the written permission of the copyright owner. First printing,September 2001 Great care is taken in the compilation and production of this book, but it should be made clear that NO WAR- RANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF MER- CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE GIVEN IN CONNECTION WITH THIS PUBLICATION. 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ASM International staff who worked on this project included Veronica Flint, Manager of Book Acquisitions; Bonnie Sanders,Manager of Production; Nancy Hrivnak,Copy Editor; Kathleen Dragolich,Production Editor; and Scott Henry,Assistant Director of Reference Publications. Library of Congress Cataloging-in-Publication Data Kaufman,J.G. (John Gilbert),1931- Fracture resistance of aluminum alloys/J. Gilbert Kaufman. p.cm. 1. Aluminum alloys—Mechanical properties. 2. Fracture mechanics I. Title. TA480.A6 K355 2000 620.1’866—dc21 2001022228 ISBN:0-87170-732-2 SAN:204-7586 ASM International® Materials Park,OH 44073-0002 www.asminternational.org Printed in the United States of America Preface On behalf of the Aluminum Association, Inc., Alcoa, Inc., and ASM International,we are pleased to provide this summary of data on the fracture char- acteristics of aluminum alloys. It is broadly based on a publication produced by Alcoa in 1964,called Fracture Characteristics of Aluminum Alloys,and we want to acknowledge the support of Alcoa, Inc., notably Dr. Robert J. Bucci and Dr. William G. Truckner, in arranging to have the copyright to that publication transferred to the Aluminum Association, Inc. Further, we acknowledge the sup- port of Dr. John A.S. Green of the Aluminum Association,Inc. in making it avail- able for a joint publication with ASM International. In particular, we note the contributions of the members of the Aluminum Association Engineering and Design Task Force, Dr. Andrew J. Hinkle, Chair, through their review of and input to the organization and content of the book. This book is unique in the degree to which it presents individual test results for many individual lots of a wide range of aluminum alloys,tempers,and products, rather than simply broad summaries of data; it is also unique for the breadth of types of fracture parameters presented. This combination provides not only the ability to dig out specific data needed to evaluate alloy and temper selections for individual applications, but also the ability to check the degree to which the var- ious fracture parameters provide consistent relative ratings for specific alloys and tempers. We believe these capabilities will benefit a wide range of needs, from alloy evaluation and selections to design. A word is needed about the inclusion in the book of data for a number of alloys and tempers that are considered obsolete today. Such alloys are included because they may have been used in fracture-critical structures in years past,and special- ists dealing with maintenance and retrofit of those structures may be looking for data on the old alloys,even though it is unlikely that new structures will be made of them. An explanation is also needed about the treatment of units in this book. Because all of these data were generated in an environment of the usage of English/engineering units, and because of the mass of data involved, almost the entire book is presented in those units. While this is contrary to the normal ASM International and Aluminum Association,Inc. policies to present engineering and scientific data in both Standard International (SI) and English/engineering units, it saves a prodigious amount of expense related to both time for conversion and to the space required for dual presentation. Further, it avoids the inevitable com- promises surrounding rounding techniques for such conversions in a multitude of units. Additional help for those interested in SI conversion is provided in Appendix 2. J. Gilbert Kaufman iii ASM International Technical Books Committee (2000–2001) Sunniva R. Collins (Chair) James F.R. Grochmal Swagelok/Nupro Company Metallurgical Perspectives Charles A. Parker (Vice Chair) Nguyen P. Hung Allied Signal Aircraft Landing Nanyang Technological University Systems Serope Kalpakjian Eugen Abramovici Illinois Institute of Technology Gordon Lippa Bombardier Aerospace (Canadair) North Star Casteel A.S. Brar Jacques Masounave Seagate Technology Université du Québec Ngai Mun Chow K. Bhanu Sankara Rao Det Norske Veritas Pte Ltd. Indira Gandhi Centre for Atomic Seetharama C. Deevi Research Philip Morris, USA Mel M. Schwartz Bradley J. Diak Sikorsky Aircraft Corporation Queen’s University (Retired) James C. Foley Peter F. Timmins Ames Laboratory Risk Based Inspection, Inc. Dov B. Goldman George F. Vander Voort Precision World Products Buehler Ltd. iv Contents CHAPTER 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 CHAPTER 2: Definition of Terms Related to Fracture Behavior . . 5 CHAPTER 3: Tensile Properties as Indicators of Fracture Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 CHAPTER 4: Notched-Bar Impact and Related Tests for Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 CHAPTER 5: Notch Toughness and Notch Sensitivity . . . . . . . . 15 Wrought Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Cast Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 ASTM Standard Notch-Tensile Test Methods . . . . . . . . . . . . . . . 22 CHAPTER 6: Tear Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Wrought Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Cast Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 CHAPTER 7: Fracture Toughness . . . . . . . . . . . . . . . . . . . . . . . 75 Theory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Test Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 K and K Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Ic c Discussion of K and K Data. . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Ic c Industry K Database,ALFRAC . . . . . . . . . . . . . . . . . . . . . . . . . 87 Ic Typical and Specified Minimum Values of K and K Fracture Toughness. . . . . . . . . . . . . . . . . . . . . . . 88 Ic c Crack-Resistance Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Use of Fracture-Toughness Data . . . . . . . . . . . . . . . . . . . . . . . . . 90 Discussions of Individual Alloys . . . . . . . . . . . . . . . . . . . . . . . . . 96 v Understanding the Effect of Residual Stresses on Fracture-Toughness Values. . . . . . . . . . . . . . . . . . . . . . . . . . 96 CHAPTER 8: Interrelation of Fracture Characteristics . . . . . . . 105 CHAPTER 9: Toughness at Subzero and Elevated Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Wrought Alloys at Subzero Temperatures . . . . . . . . . . . . . . . . . 118 Wrought Alloys at Elevated Temperatures . . . . . . . . . . . . . . . . . 122 Cast Alloys at Subzero Temperatures. . . . . . . . . . . . . . . . . . . . . 123 Welds at Subzero Temperatures. . . . . . . . . . . . . . . . . . . . . . . . . 123 CHAPTER 10: Subcritical Crack Growth . . . . . . . . . . . . . . . . . 147 Fatigue Crack Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Creep Crack Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Stress-Corrosion Cracking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 CHAPTER 11: Metallurgical Considerations in Fracture Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Alloy Enhancement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Enhancing Toughness with Laminates . . . . . . . . . . . . . . . . . . . . 162 CHAPTER 12: Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 CHAPTER 13: References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 APPENDIX 1: Notch-Tensile, Tear, and Fracture Toughness Specimen Drawings . . . . . . . . . . . . . . 175 APPENDIX 2: Metric (SI) Conversion Guidelines . . . . . . . . . . 183 ALLOY INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 vi Figures Fig. 4.1 Notched bar impact data for aluminum alloys, transverse direction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Fig. 5.1 Similarity of ratings of alloys with respect to notch sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Fig. 5.2 Notch-yield ratios versus tensile yield strength of 0.250 in. plate. Transverse direction . . . . . . . . . . . . . . . . . . 18 Fig. 5.3 Notch-yield ratios versus tensile yield strength for wrought aluminum alloys. Transverse direction (Table 5.5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Fig. 5.4 Notch-yield ratios (notch tensile strength/tensile yield strength) for cast slabs and separately cast tensile bars of aluminum sand and permanent mold cast slabs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Fig. 5.5 Notch-yield ratio versus tensile yield strength for aluminum alloy castings from notched round specimens (Fig. A1.7a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Fig. 5.6 Ratings of aluminum alloy welds based on notch- yield ratios from sheet-type specimens (Fig. A1.4b) . . . . . . 21 Fig. 5.7 Notch-yield ratio versus tensile yield strength for welds in wrought and cast alloys (Tables 5.8 and 5.9). Specimens per Fig. A1.7(b). . . . . . . . . . . . . . . . . . . . . 21 Fig. 6.1 Tear-test specimen and representation of load- deformation curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Fig. 6.2 Ratings of 0.063 in. aluminum alloy sheet based upon unit propagation energy . . . . . . . . . . . . . . . . . . . . . . . 40 Fig. 6.3 Ratings of aluminum alloy plate, extruded shapes, and forgings based on unit propagation energy . . . . . . . . . . 41 Fig. 6.4 Ratings of aluminum alloy sand and permanent- mold cast slabs based on unit propagation energy . . . . . . . . 42 Fig. 6.5 Ratings of welds based on unit propagation energy. . . . . . . 42 Fig. 6.6 Unit propagation energy vs. tensile yield strength of 0.063 in. aluminum alloy sheet . . . . . . . . . . . . . . . . . . . . . . 44 Fig. 6.7 Unit propagation energy vs. elongation of 0.063 in. aluminum alloy sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Fig. 6.8 Unit propagation energy vs. tensile yield strength for aluminum alloy castings . . . . . . . . . . . . . . . . . . . . . . . . 45 Fig. 6.9 Unit propagation energy vs. tensile yield strength for welds in wrought aluminum alloys . . . . . . . . . . . . . . . . 46 vii Fig. 7.1 Schematic drawing of large, elastically stressed panel containing a crack . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Fig. 7.2 Schematic representation of influence of thickness on strain-energy release rate . . . . . . . . . . . . . . . . . . . . . . . . 78 Fig. 7.3 Fracture-toughness specimen in 3 million lb testing machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Fig. 7.4 Typical autographic load-deformation curves from fracture toughness tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Fig. 7.5 Schematic of typical R curves. . . . . . . . . . . . . . . . . . . . . . . 84 Fig. 7.6 R-curves for 2024-T3 and 2524-T3 clad sheet. . . . . . . . . . . 89 Fig. 7.7 R-curves for 7475-T7351, 7475-T7651, 7475-T651, and 7075-T7351, 7075-T651 plate . . . . . . . . . . . . . . . . . . . 90 Fig. 7.8 Gross-section stress at onset of rapid fracture vs. crack length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Fig. 7.9 Gross-section stress at initiation of slow crack growth or rapid crack propagation under plane- strain conditions versus crack length. . . . . . . . . . . . . . . . . . 92 Fig. 7.10 Illustrations of potential residual stresses in fracture toughness specimens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Fig. 8.1 Notch-yield ratio in relation to elongation and reduction of area for aluminum alloy plate . . . . . . . . . . . . 105 Fig. 8.2 Critical stress-intensity factor, K , versus notch- c yield ratio (edge-notched specimen) for aluminum alloy and plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Fig. 8.3 K and K for 1 in. thick panels (Fig. A1.9b) versus Ic c unit propagation energy from tear tests for aluminum alloy plates. . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Fig. 8.4 Relationship between plane-strain fracture toughness and unit propagation energy from tear tests for aluminum alloy products . . . . . . . . . . . . . . . . . . . 107 Fig. 8.5 Correlation of plane-strain fracture toughness and notch-yield ratio (specimens per Fig. A1.7a) for 2024 and 2124 plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Fig. 8.6 Correlation of plane-strain fracture toughness with notch-yield ratio (specimens per Fig. A1.7a) for 7075 and 7475 plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Fig. 8.7 Relationship between ratio of fatigue strength of notched specimens to tensile yield strength and notch-yield ratio for aluminum alloy plate. . . . . . . . . . . . . 109 Fig. 8.8 Relationship between unit propagation energy and fatigue-crack growth rate. . . . . . . . . . . . . . . . . . . . . . . . . . 109 Fig. 8.9 Comparison of fracture toughness and stress- corrosion resistance for some aluminum alloys . . . . . . . . . 110 Fig. 9.1 Notch-yield ratios for 1⁄8 in. aluminum alloy sheet at various temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 viii Fig. 9.2 Notch-yield ratios for plate at various temperatures. . . . . . 114 Fig. 9.3 Notch-yield ratios for welds in 1⁄8 in. aluminum alloy sheet at various temperatures. . . . . . . . . . . . . . . . . . . . . . . 114 Fig. 9.4(a) Notch-yield ratio versus temperature for sand cast aluminum alloy slabs. . . . . . . . . . . . . . . . . . . . . . . 115 Fig. 9.4(b) Notch-yield ratio versus temperature for permanent mold cast aluminum alloy slabs. . . . . . . . . . 115 Fig. 9.4(c) Notch-yield ratio versus temperature for premium strength cast aluminum alloy slabs . . . . . . . . . . . . . . . . 116 Fig. 9.5 Notch-yield ratio versus temperature for groove welds in wrought and casting alloys . . . . . . . . . . . . . . . . . 116 Fig. 9.6 Tear resistance versus temperature for aluminum alloy sheet and plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Fig. 9.7 Unit propagation energy versus temperature for welds in wrought aluminum alloy plate . . . . . . . . . . . . . . 118 Fig. 9.8 Plane-strain fracture toughness versus temperature for aluminum alloy plate. . . . . . . . . . . . . . . . . . . . . . . . . . 119 Fig. 9.9 Notch-yield ratio versus tensile yield strength for 1⁄8 in. aluminum alloy sheet at –423 ºF . . . . . . . . . . . . . . . 120 Fig. 9.10 Notch-yield ratio versus tensile yield strength for aluminum alloys at –452 ºF. . . . . . . . . . . . . . . . . . . . . . . 121 Fig. 9.11 Estimated (conservative) fracture stress versus flaw size relationship for 5083-O plate and 5183 welds . . . . . . 121 Fig. 9.12 Cross section of 125 ft diam tank for shipboard transportation of liquefied natural gas . . . . . . . . . . . . . . . 122 Fig. 9.13 Notch-yield ratio versus tensile yield strength for cast aluminum alloys at –320 and –423 ºF. . . . . . . . . . . . 124 Fig. 9.14 Joint yield strength versus notch-yield ratios for groove welds in wrought and cast aluminum alloys at –452 ºF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Fig. 10.1 Fatigue crack growth rate data for 2124-T851 plate and comparison to data for 2024-T851 plate . . . . . . . . . . 148 Fig. 10.2 Fatigue crack growth rates for 7050-T7451 plate (5.67 and 5.90 in. thick) . . . . . . . . . . . . . . . . . . . . . . . . . 149 Fig. 10.3 Crack growth rates (da/dt) for 2124-T851 and 2219-T851 plate at 300 ºF. . . . . . . . . . . . . . . . . . . . . . . . 150 Fig. 10.4 K versus temperature for 2124-T851 and 2219- Ic T851 plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Fig. 10.5 Effects of notches on stress-rupture strengths of 2219-T851 plate (1 in. thick) at 300 ºF . . . . . . . . . . . . . . 151 Fig. 10.6 Effects of notches on stress-rupture strengths of 5454-O and 5454-H32 plate (0.750 in.) at 300 ºF . . . . . . 152 Fig. 10.7 Crack propagation rates in stress-corrosion tests using precracked specimens of 2xxx and 7xxx series aluminum alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 ix Fig. 10.8 Stress-corrosion safe-zone plot . . . . . . . . . . . . . . . . . . . . 154 Fig. 10.9 Composite stress-stress intensity-SCC threshold safe-zone plot for two aluminum alloys exposed in a salt-dichromate-acetate solution . . . . . . . . . . . . . . . . . . 155 Fig. 11.1 Average plane-strain fracture toughness data for production lots of 4 to 5.5 in. thick 2024 plate . . . . . . . . 158 Fig. 11.2 Comparisons of K values for commercial Ic production lots of 2419-T851 and 2219-T851 plate. . . . . 158 Fig. 11.3 Plane-strain fracture toughness, K , for production Ic lots of 7075-T73651 plate in L-T orientation. . . . . . . . . . 159 Fig. 11.4 Plane-strain fracture toughness of 7075 and 7175 die forgings of the same configuration. . . . . . . . . . . . . . . 159 Fig. 11.5 Plane-strain fracture toughness, K , of 7475 plate Ic compared to band of data for conventional high- strength aluminum alloys . . . . . . . . . . . . . . . . . . . . . . . . 160 Fig. 11.6 Critical stress-intensity factor, K , versus tensile c yield strength for 0.040 to 0.188 in. aluminum alloy sheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Fig. 11.7 Gross section stress at initiation of unstable crack propagation versus crack length for wide sheet panels of four aluminum alloy/temper combinations . . . . . 161 Fig. 11.8 Crack resistance curves for 7475 sheet . . . . . . . . . . . . . . 162 Fig. 11.9 Results of fracture-toughness tests of plain and laminated panels of 7075-T6 and 7075-T651 sheet and plate (transverse) . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Fig. A1.1 Orientations of tear specimens in aluminum alloy products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Fig. A1.2(a) Crack plane orientation code for fracture toughness specimens from rectangular sections . . . . . 176 Fig. A1.2(b) Crack plane orientation code for fracture toughness specimens from welded plate. . . . . . . . . . . 176 Fig. A1.3 Sheet-type notch-tensile specimen, 1⁄2 in. wide test section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Fig. A1.4(a) Sheet-type notch-tensile specimen, 1 in. wide test section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Fig. A1.4(b) Sheet-type notch-tensile specimen, 1 in. wide test section, from welded panels. . . . . . . . . . . . . . . . . 177 Fig. A1.5 Sheet-type notch-tensile specimen, 3 in. wide test section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Fig. A1.6 Center-slotted sheet-type notch-tensile specimen, 3 in. test section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Fig. A1.7(a) Cylindrical notch-tensile specimen, 1⁄2 in. test section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Fig. A1.7(b) Cylindrical notch-tensile specimen, 1⁄2 in. test section, from welded panels. . . . . . . . . . . . . . . . . . . . 179 x