1、Designation: E1457 072Standard Test Method forMeasurement of Creep Crack Growth Times in Metals1This standard is issued under the fixed designation E1457; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEEquation 6 was editorially corrected in August 2008.2NOTEEquation A2.3 was editorially corrected in October 2009.1. Scope1.1 This test method
3、 covers the determination of creep crackgrowth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loadingconditions. The time (CCI), t0.2to an initial crack extensiondai= 0.2 mm from the onset of first applied force and creepcrack growth rate, a
4、or da/dt is expressed in terms of themagnitude of creep crack growth relating parameters, C*orK.With C* defined as the steady state determination of the cracktip stresses derived in principal from C*(t) and Ct(1-14).2Thecrack growth derived in this manner is identified as a materialproperty which ca
5、n be used in modeling and life assessmentmethods (15-25).1.1.1 The choice of the crack growth correlating parameterC*, C*(t), Ct,orK depends on the material creep properties,geometry and size of the specimen. Two types of materialbehavior are generally observed during creep crack growthtests; creep-
6、ductile (1-14) and creep-brittle (26-37). In creepductile materials, where creep strains dominate and creep crackgrowth is accompanied by substantial time-dependent creepstrains at the crack tip, the crack growth rate is correlated bythe steady state definitions of Ctor C*(t), defined as C* (see1.1.
7、4). In creep-brittle materials, creep crack growth occurs atlow creep ductility. Consequently, the time-dependent creepstrains are comparable to or dominated by accompanyingelastic strains local to the crack tip. Under such steady statecreep-brittle conditions, Ctor K could be chosen as thecorrelati
8、ng parameter (8-14).1.1.2 In any one test, two regions of crack growth behaviormay be present (9, 10). The initial transient region whereelastic strains dominate and creep damage develops and in thesteady state region where crack grows proportionally to time.Steady-state creep crack growth rate beha
9、vior is covered bythis standard. In addition specific recommendations are madein 11.7 as to how the transient region should be treated in termsof an initial crack growth period. During steady state, a uniquecorrelation exists between da/dt and the appropriate crackgrowth rate relating parameter.1.1.
10、3 In creep ductile materials, extensive creep occurswhen the entire uncracked ligament undergoes creep deforma-tion. Such conditions are distinct from the conditions ofsmall-scale creep and transition creep (1-7). In the case ofextensive creep, the region dominated by creep deformation issignificant
11、 in size in comparison to both the crack length andthe uncracked ligament sizes. In small-scale-creep only a smallregion of the uncracked ligament local to the crack tipexperiences creep deformation.1.1.4 The creep crack growth rate in the extensive creepregion is correlated by the C*(t)-integral. T
12、he Ctparametercorrelates the creep crack growth rate in the small-scale creepand the transition creep regions and reduces, by definition, toC*(t) in the extensive creep region (5). Hence in this documentthe definition C* is used as the relevant parameter in the steadystate extensive creep regime whe
13、reas C*(t) and/or Ctare theparameters which describe the instantaneous stress state fromthe small scale creep, transient and the steady state regimes increep. The recommended functions to derive C* for thedifferent geometries is shown in Annex A1 is described inAnnex A2.1.1.5 An engineering definiti
14、on of an initial crack extensionsize daiis used in order to quantify the initial period of crackdevelopment. This distance is given as 0.2 mm. It has beenshown (38-40) that this period which exists at the start of thetest could be a substantial period of the test time. During thisearly period the cr
15、ack tip undergoes damage development aswell as redistribution of stresses prior reaching steady state.Recommendation is made to correlate this initial crack growthperiod defined as t0.2at dai= 0.2 mm with the steady state C*when the crack tip is under extensive creep and with K forcreep brittle cond
16、itions. The values for C* and K should becalculated at the final specified crack size defined as ao+ daiwhere aoinitial size of the starter crack.1.1.6 The recommended specimens for CCI and CCG test-ing is the standard compact tension specimen C(T) (see Fig.A1.1) which is pin-loaded in tension under
17、 constant loading1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.06 on CrackGrowth Behavior.Current edition approved March 15, 2007. Published April 2007. Originallyapproved in 1992. Last previous edition a
18、pproved in 2000 as E1457 00. DOI:10.1520/E1457-07E01.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.conditions. The clevis setup is show
19、n in Fig.A1.2 (see 7.2.1 fordetails). Additional geometries which are valid for testing inthis procedure are shown in Fig. A1.3. These are the C-ring intension CS(T), middle tension M(T), single notch tensionSEN(T), single notch bend SEN(B), and double edge notchbend tension DEN(T). In Fig. A1.3, th
20、e specimens side-grooving position for measuring displacement at the force-line(FLD) crack mouth opening displacement (CMOD) and alsoand positions for the potential drop (PD) input and output leadsare shown. Recommended loading for the tension specimens ispin-loading. The configurations, size range
21、and initial cracksize and their extent of side-grooving are given in Table A1.1of Annex A1, (40-44). Specimen selection will be discussed in5.9.1.1.7 The state-of-stress at the crack tip may have aninfluence on the creep crack growth behavior and can causecrack-front tunneling in plane-sided specime
22、ns. Specimen size,geometry, crack length, test duration and creep properties willaffect the state-of-stress at the crack tip and are importantfactors in determining crack growth rate. A recommended sizerange of test specimens and their side-grooving are given inTable A1.1 in Annex A1. It has been sh
23、own that for this rangethe cracking rates do not vary for a range of materials andloading conditions (40-44). Suggesting that the level of con-straint, for the relatively short term test durations (less than oneyear), does not vary within the range of normal data scatterobserved in tests of these ge
24、ometries. However it is recom-mended that, within the limitations imposed on the laboratory,that tests are performed on different geometries, specimen size,dimensions and crack size starters. In all cases a comparison ofthe data from the above should be made by testing the standardC(T) specimen wher
25、e possible. It is clear that increasedconfidence in the materials crack growth data can be producedby testing a wider range of specimen types and conditions asdescribed above.1.1.8 Material inhomogenities, residual stresses and mate-rial degradation at temperature, specimen geometry and low-force lo
26、ng duration tests (mainly greater that one year) caninfluence the rate of crack growth properties (39-47). In caseswhere residual stresses exist, the effect can be significant whentest specimens are taken from material that characteristicallyembodies residual stress fields or the damaged material. F
27、orexample weldments, and/or thick cast, forged, extruded, com-ponents, plastically bent components and complex componentshapes where full stress relief is impractical. Specimens takenfrom such component that contain residual stresses will like-wise contain residual stresses which may have altered is
28、 theirextent and distribution due to specimen fabrication. Extractionof specimens in itself partially relieves and redistributes theresidual stress pattern; however, the remaining magnitude canstill cause significant effects in the ensuing test. Residual stressis superimposed on applied stress and r
29、esults in crack-tip stressintensity that is different from that based solely on externallyapplied forces or displacements. Distortion during specimenmachining can also indicate the presence of residual stresses.1.1.9 Stress relaxation of the residual stresses due to creepand crack extension should a
30、lso be taken into consideration.No specific allowance is included in this standard for dealingwith these variations. However the method of calculating C*presented in this document which used the specimens creepdisplacement rate to estimate C* inherently takes into accountthe effects described above
31、as reflected by the instantaneouscreep strains that have been measured. However extra cautionshould still be observed with the analysis of these types of testsas the correlating parameters K and C* shown in Annex A2even though it is expected that stress relaxation at hightemperatures could in part n
32、egate the effects due to residualstresses.1.1.10 Specimen configurations and sizes other than thoselisted in Table A1.1 which are tested under constant force willinvolve further validity requirements. This is done by compar-ing data from recommended test configurations. Nevertheless,use of other geo
33、metries are applicable by this method provideddata are compared to data obtained from standard specimens(as identified in Table A1.1) and the appropriate correlatingparameters have been validated.1.2 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in paren
34、theses are forinformation only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitatio
35、ns prior to use.2. Scope of Material Properties Data Resulting from ThisStandard2.1 This test method covers the determination of initialcreep crack extension (CCI) times and growth (CCG) in metalsat elevated temperature using pre-cracked specimens subjectedto static or quasi-static loading condition
36、s. The metallic mate-rials investigated range from creep-ductile to creep-brittleconditions.2.2 The crack growth rate a or da/dt is expressed in terms ofthe magnitude of CCG rate relating parameters, C*(t), Ctor K.The resulting output derived as avC* (as the steady stateformulation of C*(t), Ctfor c
37、reep-ductile materials or as avK(for creep-brittle materials) is deemed as material property forCCG.2.3 In addition for CCI derivation of crack extension timet0.2vC* (for creep-ductile materials) or t0.2vK(for creep-brittle materials) can also be used as a material property for thepurpose of modelin
38、g and remaining life assessment.2.4 The output from these results can be used as Bench-markmaterial properties data which can subsequently be usedin crack growth numerical modeling, in component design andremaining life assessment methods.3. Referenced Documents3.1 ASTM Standards:3E4 Practices for F
39、orce Verification of Testing Machines3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.E1457 0722E74 Practice o
40、f Calibration of Force-Measuring Instru-ments for Verifying the Force Indication of Testing Ma-chinesE83 Practice for Verification and Classification of Exten-someter SystemsE139 Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic MaterialsE220 Test Method for Calib
41、ration of Thermocouples ByComparison TechniquesE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE647 Test Method for Measurement of Fatigue CrackGrowth RatesE813 Test Method for JIc,AMeasure of FractureToughnessE1152 Test Method for Determining-J-R-CurvesE18
42、20 Test Method for Measurement of Fracture Tough-nessE1823 Terminology Relating to Fatigue and Fracture Test-ing4. Terminology4.1 Terminology related to fracture testing contained inTerminology E1823 is applicable to this test method. Addi-tional terminology specific to this standard is detailed in
43、4.2.For clarity and easier access within this document some of theterminology in E1823 relevant to this standard is repeatedbelow (see Terminology E1823, for further discussion anddetails).4.1.1 crack-plane orientationan identification of theplane and direction of fracture test specimen in relation
44、toproduct configuration. This identification is designated by ahyphenated code with the first letter(s) representing the direc-tion normal to the crack plane and the second letter(s)designating the expected direction of crack propagation.4.1.2 J-integral, J FL-1a mathematical expression, aline or su
45、rface integral that encloses the crack front from onecrack surface to the other, used to characterize the localstress-strain field around the crack front.4.1.3 net thickness, BNLdistance between the roots ofthe side grooves in side-grooved specimens.4.1.4 original crack size, aoLthe physical crack s
46、ize atthe start of testing.4.1.5 specimen thickness, B Ldistance between the par-allel sides of the specimen.4.1.6 specimen width, W Lthe distance from a referenceposition (for example, the front edge of a bend specimen or theforce line of a compact specimen) to the rear surface of thespecimen.4.1.7
47、 stress intensity factor, K FL-3/2the magnitude ofthe ideal crack tip stress field (a stress-field singularity) forMode 1 in a homogeneous, linear-elastic body.4.1.8 yield strength, sYSFL-2the stress at which thematerial exhibits a deviation equal to a strain of 0.02 % offsetfrom the proportionality
48、 of stress to strain.4.2 Definitions of Terms Specific to This Standard:4.2.1 C*(t)-integral, C*(t) FL-1T-1a mathematical ex-pression a line or surface integral that encloses the crack frontfrom one crack surface to the other, used to characterize thelocal stress-strain rate fields at any instant ar
49、ound the crackfront in a body subjected to extensive creep conditions.4.2.1.1 DiscussionThe C*(t) expression for a two-dimensional crack, in the x-z plane with the crack front parallelto the z-axis, is the line integral:C*t! 5*GSW*t!dy T uxdsD(1)where:W*(t) = instantaneous stress-power or energy rate per unitvolume,G = path of the integral, that encloses (that is, contains)the crack tip contour,ds = increment in the contour path,T = outward traction vector on ds,u = displacement rate vector at ds,x, y, z = rectangular coordinate syst
