1、Designation: E 1457 071Standard Test Method forMeasurement of Creep Crack Growth Times in Metals1This standard is issued under the fixed designation E 1457; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 A 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 2008.1. Scope1.1 This test method covers the determination of creep crackgrowth (CCG) in met
3、als 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 or da/dt is expressed in terms of themagnitude of creep cra
4、ck 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 can be used in modeling and life assessmentmethods (15-25).1.
5、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-ductile (1-14) and creep-brittle (26-37). In creepductile m
6、aterials, 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* (see1.1.4). In creep-brittle materials, creep crack growth occurs a
7、tlow 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 thecorrelating parameter (8-14).1.1.2 In any one test, two regions of c
8、rack 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 behavior is covered bythis standard. In addition specific recom
9、mendations 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.1.1.3 In creep ductile materials, extensive creep occurswhen th
10、e 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 in size in comparison to both the crack length andthe uncr
11、acked 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. The Ctparametercorrelates the creep crack growth rate in the
12、 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 whereas C*(t) and/or Ctare theparameters which describe the in
13、stantaneous 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 definition of an initial crack extensionsize daiis used in order to
14、 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 crack tip undergoes damage development aswell as redistributi
15、on 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 conditions. The values for C* and K should becalculated at the
16、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 constant loadingconditions. The clevis setup is shown in F
17、ig.A1.2 (see 7.2.1 fordetails). Additional geometries which are valid for testing in1This 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. Publis
18、hed April 2007. Originallyapproved in 1992. Last previous edition approved in 2000 as E 1457 00.2The 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
19、States.this 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, the specimens side-grooving position for measuring displacement at the force-line(FLD
20、) 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 and initial cracksize and their extent of side-grooving are given in Table A1.1of A
21、nnex 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 specimens. Specimen size,geometry, crack length, test duration and creep properties willaf
22、fect 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 shown that for this rangethe cracking rates do not vary for a range of materials andl
23、oading 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 geometries. However it is recom-mended that, within the limitations imposed on the la
24、boratory,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 where possible. It is clear that increasedconfidence in the materials crack growth data
25、 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 long duration tests (mainly greater that one year) caninfluence the rate of crack gro
26、wth 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. Forexample weldments, and/or thick cast, forged, extruded, com-ponents, plastically
27、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 theirextent and distribution due to specimen fabrication. Extractionof specimens i
28、n 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 results in crack-tip stressintensity that is different from that based solely on ext
29、ernallyapplied 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 also be taken into consideration.No specific allowance is included in this standard
30、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 as reflected by the instantaneouscreep strains that have been measured. However ext
31、ra 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 negate the effects due to residualstresses.1.1.10 Specimen configurations and sizes
32、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 geometries are applicable by this method provideddata are compared to data obtained fr
33、om 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 parentheses are forinformation only.1.3 This standard does not purport to address all of
34、 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 limitations prior to use.2. Scope of Material Properties Data Resulting from ThisStandard2.1
35、 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 conditions. The metallic mate-rials investigated range from creep-ductile to creep-brittleco
36、nditions.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 creep-ductile materials or as avK(for creep-brittle materials) is deemed as material
37、 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 modeling and remaining life assessment.2.4 The output from these results can be used as Be
38、nch-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 Force Verification of Testing MachinesE74 Practice of Calibration of Force-Measuring
39、 Instru-ments for Verifying the Force Indication of Testing Ma-chines3For 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
40、website.E14570712E83 Practice for Verification and Classification of Exten-someter SystemsE 139 Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic MaterialsE 220 Test Method for Calibration of Thermocouples ByComparison TechniquesE 399 Test Method for Linear-Elasti
41、c Plane-Strain FractureToughness KIcof Metallic MaterialsE 647 Test Method for Measurement of Fatigue CrackGrowth RatesE 813 Test Method for JIc, A Measure of Fracture Tough-nessE 1152 Test Method for Determining-J-R-CurvesE 1820 Test Method for Measurement of Fracture Tough-nessE 1823 Terminology R
42、elating to Fatigue and Fracture Test-ing4. Terminology4.1 Terminology related to fracture testing contained inTerminology E 1823 is applicable to this test method. Addi-tional terminology specific to this standard is detailed in 4.2.For clarity and easier access within this document some of thetermi
43、nology in E 1823 relevant to this standard is repeatedbelow (see Terminology E 1823, for further discussion anddetails).4.1.1 crack-plane orientationan identification of theplane and direction of fracture test specimen in relation toproduct configuration. This identification is designated by ahyphen
44、ated 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 surface integral that encloses the crack front from onecrack surface to
45、 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 size atthe start of testing.4.1.5 specimen thickness, B Ldistance betw
46、een 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 stress intensity factor, K FL-3/2the magnitude ofthe ideal crack tip
47、 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 of stress to strain.4.2 Definitions of Terms Specific to This Standa
48、rd: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 around the crackfront in a body subjected to extensive creep conditions
49、.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 system, andT uxs (2)is the rate of stress-power input into the area en
