1、Designation: E1457 073Standard 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 2009.3NOTE4.2.1 and Eq 8 were edi
3、torially revised in May 2011.1. Scope1.1 This test method 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 on
4、set of first applied force and creepcrack growth rate, a 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
5、 this manner is identified as a materialproperty which can 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
6、generally observed during creep crack growthtests; creep-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 stead
7、y state definitions of Ctor C*(t), defined as C* (see1.1.4). 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-b
8、rittle conditions, Ctor K could be chosen as thecorrelating 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 proport
9、ionally to time.Steady-state creep crack growth rate behavior 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
10、 the appropriate crackgrowth rate relating parameter.1.1.3 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
11、, the region dominated by creep deformation issignificant 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 ext
12、ensive creepregion is correlated by the C*(t)-integral. The 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 relevan
13、t parameter in the steadystate extensive creep regime whereas 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
14、 A1 is described inAnnex A2.1.1.5 An engineering definition 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 substantia
15、l period of the test time. During thisearly period the crack tip undergoes damage development as1This 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,
16、2007. Published April 2007. Originallyapproved in 1992. Last previous edition approved 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
17、Conshohocken, PA 19428-2959, United States.well 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
18、conditions. 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 u
19、nder constant loadingconditions. The clevis setup is shown 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), a
20、nd double edge notchbend tension DEN(T). In Fig. A1.3, the 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
21、 specimens ispin-loading. The configurations, size range 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
22、and can causecrack-front tunneling in plane-sided specimens. 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-gr
23、ooving are given inTable A1.1 in Annex A1. It has been shown 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
24、range of normal data scatterobserved in tests of these geometries. 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
25、 should be made by testing the standardC(T) specimen where 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 degra
26、dation at temperature, specimen geometry and low-force long 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 characteristicallye
27、mbodies residual stress fields or the damaged material. Forexample 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
28、-wise contain residual stresses which may have altered is 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 tes
29、t. Residual stressis superimposed on applied stress and results 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 r
30、esidual stresses due to creepand crack extension should also 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*
31、inherently takes into accountthe effects described above 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 t
32、hat stress relaxation at hightemperatures could in part negate 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 recom
33、mended test configurations. Nevertheless,use of other geometries 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 reg
34、arded as thestandard. The inch-pound units given in parentheses 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
35、 and determine the applica-bility of regulatory limitations 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 speci
36、mens subjectedto static or quasi-static loading conditions. 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
37、as avC* (as the steady stateformulation of C*(t), Ctfor creep-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
38、 be used as a material property for thepurpose of modeling 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.E145
39、7 07323. Referenced Documents3.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE74 Practice of Calibration of Force-Measuring Instru-ments for Verifying the Force Indication of Testing Ma-chinesE83 Practice for Verification and Classification of Exten-someter SystemsE139 Tes
40、t Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic MaterialsE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE647 Test Method for Measurement of Fatigue
41、CrackGrowth RatesE813 Test Method for JIc,AMeasure of FractureToughnessE1152 Test Method for Determining-J-R-CurvesE1820 Test Method for Measurement of Fracture Tough-nessE1823 Terminology Relating to Fatigue and Fracture Test-ing4. Terminology4.1 Terminology related to fracture testing contained in
42、Terminology E1823 is applicable to this test method. Addi-tional terminology specific to this standard is detailed in 4.4.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 andde
43、tails).4.2 Definitions:4.2.1 creep crack growth (CCG) rate, da/dt, Da/Dat L/tthe rate of crack extension caused by creep damage andexpressed in terms of average crack extension per unit time.E18234.3 Definitions of Terms Specific to This Standard:4.3.1 crack-plane orientationan identification of the
44、plane and direction of fracture test specimen in relation 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.4.3.
45、2 J-integral, J FL-1a mathematical expression, aline or surface integral that encloses the crack front from onecrack surface to the other, used to characterize the localstress-strain field around the crack front.4.3.3 net thickness, BNLdistance between the roots ofthe side grooves in side-grooved sp
46、ecimens.4.3.4 original crack size, aoLthe physical crack size atthe start of testing.4.3.5 specimen thickness, B Ldistance between the par-allel sides of the specimen.4.3.6 specimen width, W Lthe distance from a referenceposition (for example, the front edge of a bend specimen or theforce line of a
47、compact specimen) to the rear surface of thespecimen.4.3.7 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.4.3.8 yield strength, sYSFL-2the stress at which thematerial exhibits a deviation
48、equal to a strain of 0.02 % offsetfrom the proportionality of stress to strain.4.4 Definitions of Terms Specific to This Standard:4.4.1 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 charact
49、erize thelocal stress-strain rate fields at any instant around the crackfront in a body subjected to extensive creep conditions.4.4.1.1 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 = displac
