Astm stp 591 1976

RESISTANCE TO PLANE-STRESS FRACTURE (R-CURVE BEHAVIOR) OF A572 STRUCTURALSTEEL Presented at Eighth National Symposium on Fracture Mechanics, Brown University, Providence, R I., 26-28 Aug 1974 ASTM SPECIAL TECHNICAL PUBLICATION 591 So R Novak U S Steel Corporation Research Laboratory List price $5.25 04-591000-30 itTi AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 BY AMERICAN SOCIETY FOR TESTING AND MATERIALS 1976 Library of Congress Catalog Card Number: 75-18414 NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication Printed m New Carlisle, Ohio February 1976 Foreword This publication, Resistance to Plane-Stress Fracture (R-Curve Behavior) of A572 Structural Steel, is one of the papers presented at the Eighth National Symposium on Fracture Mechanics which was held at Brown University, Providence, R I., 26-28 Aug 1974 A summary only appears in the proceedings of this symposium (Mechanics of Crack Growth, ASTM STP 590) The symposium was sponsored by Committee E-24 on Fracture Testing of Metals of the American Society for Testing and Materials J R Rice and P C Paris, Brown University, presided as symposium co-chairmen Related ASTM Publications Mechanics of Crack Growth, STP 590 (1976), $45.25,04-590000-30 Fracture Analysis, STP 560 (1974), $22.75,04-560000-30 Fracture Toughness and Slow-Stable Cracking, STP 559 (1974), $25.25,04-559000-30 Fatigue and Fracture Toughness Cryogenic Behavior, STP 556 (1974), $20.25, 04556000-30 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 A S T M Committee on Publications Editorial Staff Jane B Wheeler, Managing Editor Helen M Hoersch, Associate Editor Charlotte E Wilson, Senior Assistant Editor Ellen J McGlinchey, Assistant Editor Table of Contents Page ABSTRACT INTRODUCTION BASIC ELEMENTS OF R-CURVES MATERIALS, EXPERIMENTAL WORK, AND ANALYSIS Materials Test Specimens and Conditions Analytical Techniques LEFM Technique COS Technique 6 i0 Ii ii RESULTS AND DISCUSSION i R-Curve Results IA Summary of Basic Behavior lB Effects of Temperature for B = 1.5-Inch 12 12 12 12 2E 2F 2G 18 19 22 23 Method Load-Control vs Displacement-Control Test Methods Effect of Thickness (B = I n c h v s B = I n c h ) for the Load-Control Test Method Local Variation in Fracture Toughness Comparison of K c and Kic Behaviors Reservations Concerning Present R-Curve Results 24 26 Significance of Present R-Curve Results 3A Critical-Flaw-Size Calculations 3B Application of Results to Structures SUMMARY AND CONCLUSIONS GLOSSARY TABLES FIGURES OF 29 30 33 40 41 41 44 47 52 53 ACKNOWLEDGMENT REFERENCES IC Effects of Temperature for B = 0.5-Inch Specimens ID Nature of Fracture-Instability Event General Discussion 2A Overall Scatter Observed in K c Results 2B~ Repeatability of K c Results for a Specific Test 2C 2D Specimens SYMBOLS 56 STP591-EB/Feb 1976 RESISTANCE TO P L A N E - S T R E S S FRACTURE (R-CURVE BEHAVIOR) OF A572 S T R U C T U R A L STEEL By S R Novak Abstract The R-curve b e h a v i o r of A572 Grade 50 steel was e s t a b l i s h e d over the t e m p e r a t u r e range -40 to +72 F by using s t a t e - o f - t h e - a r t procedures Both l i n e a r - e l a s t i c - f r a c t u r e - m e c h a n i c s (LEFM) and cracko p e n i n g - s t r e t c h (COS) analytical techniques were used in assessing e x p e r i m e n t a l results o b t a i n e d under load-control and d i s p l a c e m e n t control testing conditions This study represents a pioneer effort in that it is the first known attempt to e v a l u a t e the R-curve behavior of a l o w - s t r e n g t h structural steel in some depth Results showed a steep K c t r a n s i t i o n b e h a v i o r for 1.5-inchthick (38 mm) plate, with m i n i m u m K c values of 57, 155, and 318 ksi /inch (63, 171, and 350 MNm -3/2) o b t a i n e d at -40, +40 and +72 F (-40, +4.5, and +22 C), respectively A similar behavior was observed for - i n c h - t h i c k (12.7 mm) plate, with m i n i m u m K~ values of 150, 273, and >380 ksi /inch (165, 300, and >418 MNm-372) o b t a i n e d at the c o r r e s p o n d i n g test temperatures The results are d i s c u s s e d in relation to the influence of m a t e r i a l and testing method, as well as in relation to earlier Kic results o b t a i n e d at cryogenic temperatures The m i n i m u m K c values m e a s u r e d d e m o n s t r a t e extensive crack tolerance for A572 Grade 50 steel under all combinations of the test conditions studied With one exception, these m i n i m u m behaviors can be t r a n s l a t e d into total critical flaw lengths that are at least times the plate thickness (2acr ~ 7B) for cracks embedded in large planar structures and subjected to t e n s i l e - s t r e s s levels equal to 3/4 the y i e l d strength The a p p l i c a b i l i t y of acr c a l c u l a t i o n s o b t a i n e d from R-curve m e a s u r e m e n t s generally, and on the A572 Grade 50 steel specifically, is d i s c u s s e d in relation to typical structural members such as H-beams Copyright 1976 by ASTM International www.astm.org -2- Introduction The ability of linear-elastic fracture mechanics to successfully predict the onset of catastrophic is well known The success of this approach tative and accurate manner (o) and flaw size intensity characterize attendant fracture resulting fracture crack-tip plasticity by K c is the opposite negligible (stress) conditions at fracture than KIc and varies The K c for fixed conditions thickness crack length, service temperature thickness to characterize represented by K i c o t h a t elastic (T) and strain (B) as well strain rate, is, constraint to times larger rate Furtherand plate value will also vary with temperatures, steel p l a t e ~ used plane-stress c = 0) with zz initial a o- The operating of most is generally of temperature, (T, ~, and B), the K (e the behavior through-thickness not only wis c are KIc to (Ozz = 0) with attendant Thus, value (~), as does Kic, but with plate more, and K extreme of that represented rather than complete of stress The critical-stress- conditions plasticity, in metals from the quanti- from the LEFM approach crack-tip under plane-stress large-scale derives is predicted under plane-strain small-scale fracture in which the interchangeability (a) at fracture parameters (LEFM)* rather structures than plane-strain Consequently, * The nomenclature in the Glossary in actual rate of loadings, are.generally conditions actually the present work was conducted for the various terms used and thickness such that exist in to study the in this paper is given I I I I I I I 7C @ - F 5OO l 400 - Kc = 386 ks~ ~ @ RT 17C) # / 200 - - t I CONVERSION FACTORS: ; kst - ~ MN/m k~ ~ - I.Ce8 MNm -312 l ir~h - 26.4 mm C - ~F - 32) Ki - 121 lad ~ @ -.40 F i7C) I 1.2 I 1.4 I 1.6 FIG 7~R-curve and K, results for full-thickness (B = 1.5 in.) specimens ofA572 steel processed to 62-ksi strength level at two different temperatures _ I I I I I I ' ' 2T 5OO 400 / kli I " 6.896 MN/m ~V///////'y/~F //////////./ ' I00 % I I -20 I I - - I +20 +40 TEMPERATURE F ~ I ~ I I +100 ~" FIG Summary of K~ results for full-thickness (B = 1.5 in.) specimens ofA572 grade 50 steel and A572 steel processed to 62-ksi strength level FIG -Fracture surfaces of full-thickness (B = 1.5 in.) 2T CT specimens ofA572 grade 50 steel tested under load-control conditions using an essentially monotonic loading sequence (Armco procedure) FIG lO -Fracture surfaces offull-thickness (B = 1.5 in.) 4T CT specimens ofA572 Grade50 steel tested under load-control conditions using a total unload]reload loading sequence (U S Steel procedure) FIG 11 -R-curve specimens ofA572 Grade 50 steel tested at ambient temperature (.~ 72~ The 2T and 4T specimens were tested to fracture under load-control conditions, and the 7C specimen was tested to the limit of available capacity uader displacement-control conditions Note: Aa = as - ao "~0.50 in on the specimen surface for the 7C specimen at the end of the test I I I I I I I I 500 I CONVERSION FM~TORS~ ! Iwi~a'= 1.01D MN~ -312 I ind~ - 25.4 mm C = S ~ F - 32) _ Kc " 316 ksi ~ (21") Kc " 150 ksi ~ / i r ~ (4T) I 0.2 I 0.4 I I Q.6 0.8 I 1.0 I 1.2 I 1,4 I 1.6 FIG 12 -R-curve and K, results for subthickness (B = 0.5 in ) specimens ofA572 Grade 50 steel tested at -40~ I I I I I I I 5OO CONVtCRSION FACTORS: k s i ~ r ~ - 1,OgO MNm -3/2 inch - 25.4 mm C - s/gIF - 321 40O Kc " 313 k*; ~ ~aoo (2T) (4T) 20O 100 I G2 I 0.4 I ~6 ~ I I 1.6 I 1~ I 1.4 I 1.6 FIG 13 R-curve and K~ results for subthickness (B = 0.5 in.) specimens ofA572 Grade 50 steel tested at +40~ I I I i I I I / / I!t/,.F _ l,~ i ~ ~4 ~ ~ , ,~: 1~ ~,,_-, ~" I 1~ tA i 1~ ~.ind~ FIG 14 R-curve and Kc results for subthickness (B = 0.5 in.) specimens ofA572 Grade 50 steel tested at +72~ I _ 31~ I I I I I I / / / / / tO0 o I -~ I -~ I I +~ I +40 I +60 I +~ I +1~ TEMPERATURE F FIG 15 -Summary of K, results for subthickness (B = 0.5 in.) specimens ofA572 Grade 50 steel FIG 16 -Fracture surfaces of subthickness (B = 0.5 in.) 2T CT specimens ofA572 Grade 50 steel tested under load-control conditions using an essentially monotonic loading sequence (Armco procedure) FIG 17~Fracture surfaces of subthickness (B = 0.5 in.) 4T CT specimens of A 572 Grade steel tested under load-control conditions using a total unload/reload loading sequence (U S Steel procedure) F|G 18 Subthickness (B = 0.5 in.) T C T specimen 7-2 tested at + 72~ Photograph was taken alter unload 33 and j u s t prior to complete fracture (intentional) Note the extent o(stable crack extension visib)e on the specimen surface (Ata = ar - a ,, ~ 1.60 in.) I ! I I I ! "I 'I I bl IlL " li " ~ J - - -.~*" p-~b K I r,~k - 2$.4 m l I I , ~" ~ , ' ~ = I ", _ I i - ~ ~ , ".s " "~._"'~ ~.I ] p - ~.seo ,,- , swo~ _ I p,.= - ao 4,~ 0.2 0.40.II o ~T~mom~ ~ OCCURREO AV ] OI l.O ,, 3.47 I n d i I [ 1.2 ~t~.ktdm FIG 19 Superposition of ~Bs and P in the development for the 4T subthickness (B = 0.5 in.) specimen ofA572 Grade 50 steel tested at +72~ t T4 TEMPERATURE, F b FIG 20 Combined CVN energy-absorption behavior ofA572 Grade 50 steel as determined from the broken halves of 11 CT specimens used to establish R-curve behavior I T II I I I I go 8O - 70 r 60 5O r /1 liZC /~'~ ~f~e'/ ~ ft-lb = 1.36 J 2O ~ J / 7, % ' 10 i 20 , 3O i 4O - - i 50 go i i 70 8O LE, LATERAL EXPANSION, mils FIG l Correlation between CVN energy absorption and lateral expansion (LE) for A572 Grade 50 steel at all temperatures ( - to +72~ as determined from the broken halves of 11 CT specimens used to establish R-curve behavior [] l 10( KIC KQ(KLsI I'1 KLrnax / I J /~ = 04 ~,O z = f [] / ~ w f ( " I ~ ~ ~ ~ ~ , ., / o I- 4c CONVERSION FACTORS: kli = 6.8115 MN/m ksi ~ = 1009 MNm -3/2 c = s/S(E - J = 2( NDT - - TEMPERATURE, F FIG 22 Results of static J~acture-toughness tests of A572 Grade steel (cru = 50 ksi) FIG 23—Results o f static fracture-toughness tests o f A572 Grade 50 steel (σm = 62 ksi) FIG 24— Summary comparisons o f Kc and Klc behavior obtained from 1.5-in.-thick plates o f A572 steel FIG 25— Schem atics o f relationships betw een K c a nd K lc FIG 26— L ongitudinal C harpy V-notch energy absorption fo r im pact and slow -bend tests o f standard C V N sp ecim en s I 5( T I I I I A572 GRADE 50 STEE~'-~ (ay = ksi) /- SLOW BEND/ IMPACT [ I o E / o /0 / ~~.o'/~ 9 A A / 0 ~ &* 52( I 9& / i A & ,/AA / -2~ ~o~ ,- CDI^O/U A o ,~A