Astm stp 1461 2005

STP 1461 Fatigue and Fracture Mechanics, 34 th Volume Steven R Daniewicz, James C Newman, and Karl-Heinz Schwalbe, Editors ASTM Stock Number: STP1461 ASTM International 100 Barr Harbor Drive PO Box C700 West Conshohocken, PA 19428-2959 INTERNATIONAL Printed in the U S A Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized ISBN: - - - ISSN: - Copyright @2005 ASTM International, West Conshohocken, PA All rights reserved This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher Photocopy Rights Authorization to photocopy items for internal, personal, or educational classroom use, or the internal, personal, or educational classroom use of specific clients, is granted by ASTM International (ASTM) provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923; Tel: 978-750-8400; online: http:llwww.copyright.coml Peer Review Policy Each paper published in this volume was evaluated by two peer reviewers and at least one editor The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM International Committee on Publications To make technical information available as quickly as possible, the peer-reviewed papers in this publication were prepared "camera-ready" as submitted by the authors The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of the peer reviewers In keeping with long-standing publication practices, ASTM International maintains the anonymity of the peer reviewers The ASTM International Committee on Publications acknowledges with appreciation their dedication and contribution of time and effort on behalf of ASTM International Printed in Lancaster, PA September 2005 Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Foreword The Second International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (34th National Symposium on Fatigue and Fracture Mechanics) was held in Tampa, Florida on 19-21 November 2003 ASTM International Committee E08 on Fatigue and Fracture and the European Structural Integrity Society (ESIS) served as sponsors Symposium chairmen and co-editors of this publication were Steven R Daniewicz, Mississippi State University, Mississippi State, MS; James C Newman, Mississippi State University, Mississippi State, MS; and Karl-Heinz Schwalbe, GKSS Forschungszentrum, Geesthact, Germany Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Contents Overview ix SESSION : SWEDLOWLECTURE AND KEYNOTE ADDRESSES M o d e l i n g of T h r e e - D i m e n s i o n a l Effects o n F a t i g u e C r a c k C l o s u r e P r o c e s s e s in Small-Scale Y i e l d i n g - - R H DODOS, JR AND S ROYCHOWDHURY F r a c t o g r a p h i c R e a s s e s s m e n t of t h e Significance of F a t i g u e C r a c k Closure -R SUNDER 22 SESSION 2A: FATIGUECRACK GROWTH THRESHOLDS I L o a d H i s t o r y Effects R e s u l t i n g f r o m C o m p r e s s i o n P r e c r a c k i n g - - M A JAMES, S C FORTH, AND J A NEWMAN 43 Use of A C R M e t h o d to E s t i m a t e C l o s u r e a n d R e s i d u a l S t r e s s F r e e Small C r a c k G r o w t h D a t a - - H R ZONKER,G U BRAY, K GEORGE, AND M D GARRATT 60 I n f l u e n c e of T e m p e r a t u r e a n d M i c r o s t r u c t u r e o n the F a t i g u e B e h a v i o u r in t h e T h r e s h o l d R e g i m e for a S u p e r D u p l e x Stainless Steel -c CrtAI AND S HANSSON 73 SESSION 2B: FRACTUREFUNDAMENTALS E v a l u a t i o n of t h e Effect of C r a c k Tip C o n s t r a i n t on F a t i g u e C r a c k G r o w t h R a t e in Ineonel 718 J A JOYCE 87 V Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized vi CONTENTS SESSION 3A: F A T I G U E C R A C K G R O W T H THRESHOLDS I I T h e Effect of Negative Stress Ratio L o a d H i s t o r y on High Cycle Fatigue T h r e s h o l d - - P J GOLDEN AND T NICHOLAS 107 F a t i g u e C r a c k G r o w t h R a t e a n d Stress-Intensity F a c t o r C o r r e c t i o n s for Out-of-Plane C r a c k G r o w t h - - s c FORTH, D J HERMAN, M A JAMES, AND W M JOHNSTON 124 A s s e s s m e n t for Decrease in T h r e s h o l d Stress Intensity F a c t o r (SIF) R a n g e Due to High M a x i m u m SIF T MESHU, K iSHIHARA, AND K WATANABE 138 E n v i r o n m e n t a l l y Influenced Fatigue in H i g h S t r e n g t h Steels E U LEE AND 151 A K VASUDEVAN SESSION 3B: INTEGRITY ASSESSMENT I Selection of M a t e r i a l for W e l d e d Steel S t r u c t u r e s Based o n F r a c t u r e Mechanics-ms HOHLER AND G SEDLACEK 167 Assessment of P l a n e Stress T e a r i n g in T e r m s of V a r i o u s C r a c k Driving P a r a m e t e r s - - - v P NAUMENKO AND G S VOLKOV 182 E v a l u a t i o n of Fatigue C r a c k T h r e s h o l d s Using Various E x p e r i m e n t a l M e t h o d s - - s c FORTH, J C NEWMAN, JR., AND R G FORMAN 203 SESSION 4A: SMALL CRACKS I M i c r o s t r u c t n r a i Influences on the D e v e l o p m e n t a n d G r o w t h of Small Fatigue C r a c k s in the Near T h r e s h o l d Regime -J A SCHNEIDERAND E KEN1K 221 Size Effect of M i c r o d a m a g e G r o w t h a n d Its Relation to M a c r o Fatigue Life -E ALTUS 232 SESSION 4B: INTEGRITY ASSESSMENT II O n the C o n s t r a i n t - B a s e d F a i l u r e A s s e s s m e n t of Surface C r a c k e d Plates u n d e r Biaxial L o a d i n g - - x WANG AND X YU 245 A n E x p e r i m e n t a l S t u d y o n Surface C r a c k G r o w t h u n d e r M o d e - I Load Y KIM, Y J CHAO, S LIU, AND S-K JANG 260 SESSION 5A: FATIGUE I Effect of Residual Stresses o n the Fatigue C r a c k P r o p a g a t i o n in W e l d e d Joiuts N GUBELJAK, J PREDAN, R PIPPAN, AND M OBLAK 281 U l t r a s o n i c Fatigue Testing of Ti-6AI-4V R J MORR[SSEYAND P J GOLDEN 299 F a t i g u e E n d u r a n c e D i a g r a m for M a t e r i a l s with Defects B-J I~IMAND t~ KUJAWS~:I 309 Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorize CONTENTS vii SESSION 5B: EXPERIMENTALMETHODS I C o n s t r u c t i o n of J - R C u r v e s U s i n g the C o m m o n a n d C o n c i s e F o r m a t s - - J R DONOSO, J ZAHR, AND J D LANDES 323 T e m p e r a t u r e D e p e n d e n t F r a c t u r e T o u g h n e s s of a Single C r y s t a l Nickel S u p e r a l l o y - - D M BAHRAND W S JOHNSON 340 SESSION 6A: FATIGUECRACK GROWTH IN THE RAILROADINDUSTRY S t r u c t u r a l Reliability A n a l y s i s of R a i l r o a d T a n k C a r s S u b j e c t e d to F a t i g u e a n d Corrosion w ZHAO AND M A SUTTON 355 S i m u l a t i o n of F a t i g u e C r a c k P r o p a g a t i o n in R a i l w a y A x l e s - - s BERETTAAND M CARBON] 368 SESSION 6B: EXPERIMENTALMETHODS II E v a l u a t i o n of the Effect o f Biaxial L o a d i n g o n t h e To R e f e r e n c e T e m p e r a t u r e U s i n g a C r u c i f o r m S p e c i m e n G e o m e t r y - - J A JOYCE, R E LINK, AND J GAIES 385 SESSION 7A: SMALL CRACKS II T h e Effect of L o a d R e d u c t i o n S c h e m e o n C r a c k C l o s u r e in t h e N e a r - T h r e s h o l d R e g i m e - - s R DANIZWICZ 405 I n t e r p r e t a t i o n of M a t e r i a l H a r d n e s s , S t r e s s Ratio, a n d C r a c k Size Effects on t h e ~r~m of Small C r a c k s B a s e d o n C r a c k C l o s u r e M e a s u r e m e n t - - Y RONDO, C SAKAE, M KUBOTA,AND M KASHIWAGI 415 SESSION 7B: DUCTILE-TO-BRITTLETRANSITION Critical A s s e s s m e n t of t h e S t a n d a r d A S T M E 399 K R W WALLIN 433 SESSION 8A: FATIGUEII Sensitivity of C r e e p C r a c k Initiation a n d G r o w t h in Plates to M a t e r i a l P r o p e r t i e s V a r i a t i o n s - - n WASMER,K M NIKBIN, AND G A WEBSTER 457 F r e t t i n g F a t i g u e a n d S t r e s s R e l a x a t i o n B e h a v i o r s of S h o t - P e e n e d Ti-6AI-4V H LEE AND S MALL 472 SESSION 8B: ADDITIONALFRACTURETOPICS A n a l y s i s of R o u g h n e s s - I n d u c e d C r a c k - T i p S h i e l d i n g in T e r m s of Size Ratio Effect J POKLUDA,P SANDERA,AND J HORN[KOVA 491 C h a r a c t e r i z a t i o n of C r a c k L e n g t h M e a s u r e m e n t M e t h o d s f o r F l a t F r a c t u r e with T u n n e l i n g - - M A JAMES AND J C NEWMAN,JR 506 Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions au viii CONTENTS SESSION 9: CRACK CLOSURE A New Method for Opening Load Determination from Compliance M e a s u r e m e n t s - - D KUJAWSKI AND S STOYCHEV 525 SESSION 10: FATIGUE I I I Crack Initiation, Propagation, and Arrest i n L M o d e l P i p e C o m p o n e n t s u n d e r Thermal F a t i g u e - - E PAFFUMI, K-F NILSSON, N TAYLOR, R HURST, AND M BACHE 539 Effect of Periodic Overloads on Threshold Fatigue Crack Growth in A I - A l l o y s - - m SUNDER 557 Notch-Root Elastic-Plastic Strain-Stress in Particulate Metal Matrix Composites S u b j e c t e d to General L o a d i n g C o n d i t i o n s - - - G M OWOLABI AND M N K SINGH 573 Influence of Crack-Surface Oxidation on Creep-Fatigue Crack Behavior of 1Cr-and C r - S t e e l s - - F MUELLER, A SCHOLZ, AND C BERGER Index 589 605 Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproducti Overview ASTM InternationalCommittee E08 on Fatigue and Fracture and the European Structural Integrity Society (ESIS) jointly sponsored the second International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (34th ASTM National Symposium on Fatigue and Fracture Mechanics) which was held November 19-21, 2003 in Tampa, Florida This book represents the proceedings of that important event The symposium was co-chaired by S R Daniewicz and J C Newman, Jr of Mississippi State University, USA and K.-H Schwalbe of GKSS Research Center, Geesthacht, Germany The 37 papers which comprise the symposium proceedings are roughly focused on two significant topics within damage tolerance: Structural Assessment and Fatigue Behavior in the Threshold Regime Approximately 50 % of these papers were presented by researchers from outside the United States, making the symposium truly an international event It is noteworthy that this ASTM Special Technical Publication (STP) is the last proceedings to be published by ASTM as STP 1461, with papers from future ASTM/ESIS Symposia on Fatigue and Fracture Mechanics to be archived within the Journal of ASTM International This marks the end of a tradition, in which the proceedings of each ASTM National Symposium on Fatigue and Fracture Mechanics were published as an STP This long and proud tradition began with the publication of STP 381 in 1965, which featured papers by numerous pioneering researchers such as W F Brown, G R Irwin, F A McClintock, P C Paris, R Pelloux, J E Srawley, G Sih, and R P Wei Some 40 years later, the contents of STP 1461 reveal that ASTM and ESIS symposium participants continue to perform research of superior quality and sustaining technical importance S R Daniewicz Mississippi State University April 2005 ix Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized SESSION 1: S W E D L O W L E C T U R E AND K E Y N O T E ADDRESSES Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further MUELLER ETAL ON CRACK SURFACE OXIDATION 595 One distinguishes different kinds of the cr ack closure, which are based on different mechanisms The three essential crack closure mechanisms for metals [8] are: 9 plastically-induced crack closing oxide-layer-induced crack closing roughness-induced crack closing In practice, it is impossible to separate the individual influence of each mechanism on the fatigue crack growth Through crack closure, only a part o f the applied load contributes to the crack growth The stress intensity factor AKI is introduced by a correction as effective stress intensity factor AKer~ [9] in the following form: AKeff = U AK1 (8) where U is the crack opening factor There are different procedures proposed for the calculation of U One of them is given as [9]: U = 0.5 + 0.4 R (9) Shielded gas tests are conducted without oxidation; therefore factor U is smaller than for air tests The statement: "fatigue crack growth rate under shielded gas is lower than in air" is still valid A quantitative determination of the crack closure factor U for fatigue crack tests in air and under shielded gas is still under investigation Crack Growth under Pure Creep The parameter C* has been chosen for the presentation of the creep crack growth rate The above-mentioned correction for the determination o f the parameter C* for creep crack tests in air was considered The creep crack growth rate for tests in air and under shielded gas of 1CrMo(Ni)V-steel is plotted in Fig and for 10CrMoWVNbNsteel in Fig 10 In both cases there is no difference between forged steel and cast steel The results under shielded gas are within the scatter band of the results from air tests This result is not surprising if the creep crack damage mechanism is considered The formation of pores and microcracks occurs in front of the crack-tip in the ligament of the material, irrespective of the kind of surrounding medium used FIG Creep crack growth rate versus parameter C* 1CrMo(Ni)V-steel, 530 and 550~ Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 596 FATIGUE AND FRACTURE MECHANICS FIG l O Creep crack growth rate versus parameter C*, l OCrMoWVNbN-steel, 550 and 600~ Crack Growth under Creep-Fatigue Conditions The creep-fatigue crack growth rate can be compared with the pure creep crack growth rate, as well as with the pure fatigue crack propagation rate In Fig 11 some results for 1CrMo(Ni)V-steels are compared with the results of the fatigue crack test With increasing hold time, an increase of the creep crack propagation per cycle can be observed As a result, there is no significant influence of air and shielded gas on creep-fatigue crack propagation rate However, this crack propagation rate is achieved with a lower cyclical stress intensity factor This is an acceleration of the creep-fatigue crack propagation rate under shielded gas At creep-fatigue crack experiments, crack closure effects must be considered The oxide layer has a great influence (Fig 3) as indicated by the assumed load process in Fig 12 The crack will be closed earlier during the creep-fatigue crack test in air than under shielded gas The effective load at the crack-tip under shielded gas is greater than in air The creep-fatigue crack closure in air cannot be taken as a constant crack opening factor U, like in the fatigue crack test The influence of the oxidation on crack closure is a function of time (Fig 4) Future investigations are planned FIG l Creep-fatigue crack growth rate versus parameter and 550~ Z1KI, ICrMo(Ni)V-steel, 530 Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized MUELLER ET AL ON CRACK SURFACE OXIDATION 597 - - - growing up oxide layer between the crack tip surfaces - "supposed" load cycle "true" load cycle for tests in "Air" time t FIG 12 Load distribution during the creep fatigue crack test in "Air, "schematically Crack Initiation Behavior A technical crack initiation length has been defined to determine the crack initiation behavior under creep and creep-fatigue conditions for tests in air and under shielded gas This paper deals with a technical crack initiation length of A a i = a i - a = 0.5 ram Crack Initiation under Pure Creep The creep crack initiation time ti c against the parameter C* is shown in Fig 13 for the 1CrMo(Ni)V-steel and in Fig 14 for the 10CrMoWVNbN-steel No significant difference between forged and cast steel can be observed Furthermore, there is no difference between creep crack initiation in air and under shielded gas The solid lines correspond to the lower boundary of the scatter band, which is the worst case The creep crack initiation time t i c is shown as a function of Kx0 in Figs 15 and 16 for 1CrMo(Ni)V- and 10CrMoWVNbN-steels, respectively For the forged and cast 10CrMoWVNbN-steels (Fig 16), a common creep crack initiation function can be reproduced This is not valid for the 1CrMo(Ni)V-steels There is a difference between forged and cast steel However, the respective shielded gas results overlapped the air results Using the so-called "Two-Criteria-Method" [10], it is possible to determine analytically the crack initiation of components under creep conditions The nominal stress Crnpl considers the stress situation in the ligament, and the fictitious elastic parameter KI id characterizes the cracktip situation These loading parameters are normalized in a "Two-Criteria-Diagram" ("2CD") by the creep rupture strength R~evT and the parameter Kilo, which characterized the creep crack initiation of the material The normalized parameters are the stress ratio R~ = ~n pl/R,/vT for the far-field and the stress intensity ratio RK = K~ia/K~i ~ for the crack-tip The "2CD" distinguishes three fields of damage modes Above R~/RK=2, ligament damage is expected, below P~/RK = 0.5, crack-tip damage is expected, and between these two lines a mixed damage mode is observed Crack initiation is only expected above the boundary line The "2CDs" are shown in Figs 17 and 18 for 1CrMo(Ni)V- and 10CrMoWVNbN-steel, respectively This shows that the "2CD" can also be used for creep crack initiation under shielded gas without any changes Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 598 FATIGUE AND FRACTURE MECHANICS 10~ ~ i C* (N/rnmh) i 10 ~ [] L ] T = 530 and 550 I ~ Cs25-specimens aoNV = 0.55 Aa i = 0.5 mm T *) creep crack initiation in "Ar + 3% H2" 10-~ 104 ii ~ (> G17CrMoV5-11/BA._ R 10' 10 10 10 t i (h) 10 s FIG 13 Creep crack initiation time versus parameter C*, lCrMo(Ni)V-steel, 530 and 550 ~ 101 10CrMoWVNbN-steel T = 550 and 600 ~ Cs25-specirnens ae/W = 0.55 ~xai = 0.5 mm C'* (I mh) 10 "~ I *} creep crack initiation in "Ar + 3% H2" 10 104 J 10-s 10' - - " i = ' " ( t , ) -1"09 ~ II ! II E1 XI2CrMoWVNbN10-1-1/1A *y1~R'~~ 102 103 10' t I (h) 10 ~ FIG ]4 Creep crack initiation time versus parameter C*, lOCrMoWVNbN-steeI, 550 and 600~ 8O 70 CrMo(Ni)V-steel T : 530 and 550 *C Cs25-specimens ao/W = 0.55 z~ai = O.5 mm 40 i 30 ") creep crack initiation in "At + 3% H2" [] %,~-~[] ~,~ , 20 I [3 30CrMoNiV4-11 lAMA Kli c = 105.0.(ti)-022 T I ~ G17CrMoV5-11/BAR -Kli c = 236.0.(tl) 0"35 J , , 10 10 ~ 102 - - , 103 % , ' t04 tlc(h ) 102 FIG 15 Creep crack initiation time versus parameter K z, lCrMo(Ni)V-steel, 530 and 550~ Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized MUELLER ET AL ON CRACK SURFACE OXIDATION 599 ?oI ~om = | ~] p 0.55 Aa i = 0.5 rnm | I- I*) creep crack initiation / L_ in "Ar + 3% H2" I-i 30 C~ 10 101 # T = 600 ~ Cs25-specimens KIO (MPa m /2) 40 X12CrMoWVNbN 10-1~1/IA GX 12CrMoWVNbN 10-1-1/2A i 102 103 104 , _tic (h) 105 FIG 16 Creep crack initiation time versus parameter K~, 10CrMo WVNbN-steel, 600~ 1.4 I Re= I I ~ ~ ~ ~n pl/Ru/t/T 1.0 ' ~ 0.6 [][3 [3 i I " ' , ' ? tCrMo(Ni)V-steel T = 530 and 550 ~ Cs25-specimens ao/W = 0.55 &ai = 0'5 rnm mixed damage I r~ m i ~ ' ~ ,,I 0.8 ' CRACK ! e / @~ [] - D * ~/ i ~ / , I *) creep crack initiation ~t~i,~;p I in"Ar + 3~176 H2" 0.4 r lin 0.2 / 30CrMoNiV4-11/AMA G17CrMoV5-1 l/BAR 0.0 0.0 I 0.5 1.0 1.5 2.0 RK = KI id/Kli c 3.0 FIG 17 Presentation of 2CD for creep crack initiation, 1CrMo(Ni)V-steel, 530 and 550~ 1.4 I Ra = ,IR ,np, wE, r 1.0 ~ ' 0.8 ~ ' ' tt I' ' ' r ' ~ ~ / " ?>~v - NO CRACK / / I / / I , J 0.5 , ' , ,, ~ I n in "At + 3% H," damage border line "2 - t / / / "RJRK oJK = 0.5 " o.o L:~ 0.0 , 10CrMoWVNbN-steel I T = 600 ~ Cs25-specimens J a _ / W = 0.55 ~ A~i ~-'0.5 mm mixed damage *) i CRACK " 0.4 L [ = '~ ~, I ~ ~ 'l ~ ~ i -,, -O[3 - - - X12CrMoWVNbN10*1-1/1AG ] 1.0 , , 1.5 , , 2.0 , , , RK = KI id/Kli c 3.0 FIG 18 Presentation of 2CD for creep crack initiation, l OCrMo WVNbN-steel, 600~ Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 600 FATIGUE AND FRACTURE MECHANICS Crack Initiation under Creep-Fatigue Conditions The crack initiation under creep-fatigue conditions is shown in Fig 19 for the 1CrMo(Ni)V-steel and for the 10CrMoWVNbN-steel in Fig 20 in a respective K10-ti crdiagram A reduction in time for crack initiation time t i cf at decreasing holding times tn could be determined The results under shielded gas are clearly below the respective air results in some cases The solid and dash-dotted lines are the creep crack initiation curves taken from Figs 15 and 16 The dashed and dotted lines represent the reduced creep crack initiation curve for the modified "2CD" by the factor L i ~ = ti cf/ti ~ (10) for creep-fatigue experiments in air for hold times of 0.3 < tH < 3.0 h, as assumed in [11] and [12] In Fig 21, the ratio Lic is represented against hold time for 1CrMo(Ni)V-steel and in Fig 22 for 10CrMoWVNbN-steel The line Lic = 1.0 reflects the correlation for creep crack initiation, and the line L i c = 0.6 gives the above described reduction for the creep-fatigue crack behavior in air For hold times of 0.3 h, in order to stay on the conservative side, an L i c reduction to 0.25 would be necessary The use of the engineering factor of 0.6 will result in a certain increase of the crack initiation length, but it will still be tolerable within the values of A(Aai) < 0.5 mm That means that the predicted creep-fatigue crack initiation time by "2CD" is longer than the real one For creep-fatigue crack tests with hold times of 3.0 h, a reduction is not necessary [11,12] The modified "2CD" of 1CrMo(Ni)V-steel is shown in Fig 23 and for 10CrMoWVNbNsteel in Fig 24 The validity of the boundary line is confirmed by the results of creep-fatigue crack initiation tests in air and under shielded gas No data points were found within the NOCRACK area 80 [ ~ 1CrMo(Ni)V-stee, I T = 530 and 550 ~ 1/2, - ] Cs25-speci (MPa m " ' ) ~ ao/W = 0.55 Aa i = 0.5 mrn ,ot I i / t: 30h 20 ~'~ H *)creep-fat~ k I ] II initiation in "At + 3% H2" I I [1 I ] I 30CrMoNiV4-1 llAMA [] t = 0.3 h K G17CrMoV5-11/BAR ' I = 105.0" t-0.22 II l[ K,,o =230.o.(t,)-~ II K,,c, ~ 10 I 101 [ '- , | I 102 103 104 tic, tier (h) 102 FIG 19 Creep-fatigue crack initiation time versus parameter K I, 1CrMo(Ni) V-steel, 530 and 550~ Copyright by ASTM Int'l (all rights reserved); Sun Dec 13 19:13:07 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized MUELLER ET AU ON CRACK SURFACE OXIDATION 80 70 KI 0n1/2 ) _ 40 i 10CrMoWVNbN-steel T = 600 ~ Cs25-specimens a0/W = 0.55 Aa i = 0.5 mm - - | crack initiation ") creep-fatigue in "At + 3% H2" / Klic = 151"5"(ti)-0'27 Kucf = 132 0.( i)-0"27 -.,.% 30 20 601 \ X12CrMoWVNbN10-1-1/1A~,[] tH = 0"3 3'0 h ~ ~ , ~ , GX12CrMoWVNbN10-1-1/2A ~> tH = 0,3 h tH=3.0h J 10 10~ " 10~ 10~ 104 tic, ticf (h) 10~ FIG 20 Creep-fatigue crack initiation time versus parameter K I, tOCrMoWVNbNsteel, 600~ 2.00 L,o= I ticl/tic f 1.50~ I 1CrMo(Ni)V-steel T = 530 and 550 ~ Cs25-specimens aoAN = 0.55 Aa i = 0.5 mm 1.25 100 El 0.75 050 0.25 0.00 0.01 (*~ 30CrMoNiV4-1llAMA B tH = 0.3 h BI ta = 3.0 h G17CrMoV5-11/BAR