1、Designation: E1457 074Standard 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 2011.4NOTE4.2.2, 4.3.1 and 4.2.4 were editorially updated in December 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. Th
4、e 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 crack growth relating parameters, C*orK.With C* defined as the steady state determination of the cracktip stresses de
5、rived 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).1.1.1 The choice of the crack growth correlating parameterC*, C*(t), Ct,orK depends on the material creep properties
6、,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 materials, where creep strains dominate and creep crackgrowth is accompanied by substantial time-dependent creepstr
7、ains 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 atlow creep ductility. Consequently, the time-dependent creepstrains are comparable to or dominated by accompanying
8、elastic 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 crack growth behaviormay be present (9, 10). The initial transient region whereelastic strains dominate and creep d
9、amage 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 recommendations are madein 11.7 as to how the transient region should be treated in termsof an initial crack growth per
10、iod. 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 the entire uncracked ligament undergoes creep deforma-tion. Such conditions are distinct from the conditions ofsmall
11、-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 uncracked ligament sizes. In small-scale-creep only a smallregion of the uncracked ligament local to the crack tipexpe
12、riences 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 small-scale creepand the transition creep regions and reduces, by definition, toC*(t) in the extensive creep regi
13、on (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 instantaneous stress state fromthe small scale creep, transient and the steady state regimes increep. The recommende
14、d 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 quantify the initial period of crackdevelopment. This distance is given as 0.2 mm. It has beenshown (38-40) that
15、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 as1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommit
16、tee E08.06 on CrackGrowth Behavior.Current edition approved March 15, 2007. Published April 2007. Originallyapproved in 1992. Last previous edition approved in 2000 as E1457 00. DOI:10.1520/E1457-07E04.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1C
17、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West 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*wh
18、en the crack tip is under extensive creep and with K forcreep brittle 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
19、 tension specimen C(T) (see Fig.A1.1) which is pin-loaded in tension under 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
20、 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) crack mouth opening displacement (CMOD) and alsoand positions for the potential drop (PD
21、) 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 Annex A1, (40-44). Specimen selection will be discussed in5.9.1.1.7 The state-of-stress at
22、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 willaffect the state-of-stress at the crack tip and are importantfactors in determining crack gr
23、owth 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 andloading conditions (40-44). Suggesting that the level of con-straint, for the relatively sh
24、ort 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 laboratory,that tests are performed on different geometries, specimen size,dimensions and cr
25、ack 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 can be producedby testing a wider range of specimen types and conditions asdescribed abov
26、e.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 growth properties (39-47). In caseswhere residual stresses exist, the effect can be significa
27、nt 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 bent components and complex componentshapes where full stress relief is impractical. Speci
28、mens 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 in itself partially relieves and redistributes theresidual stress pattern; however, the rem
29、aining 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 externallyapplied forces or displacements. Distortion during specimenmachining can also indic
30、ate 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 for dealingwith these variations. However the method of calculating C*presented in this do
31、cument 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 extra cautionshould still be observed with the analysis of these types of testsas the correla
32、ting 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 other than thoselisted in Table A1.1 which are tested under constant force willinvolve fur
33、ther 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 from standard specimens(as identified in Table A1.1) and the appropriate correlatingparamete
34、rs 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 thesafety concerns, if any, associated with its use. It is theresponsibility of the user
35、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 This test method covers the determination of initialcreep crack extension (CCI) times and
36、 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-brittleconditions.2.2 The crack growth rate a or da/dt is expressed in terms ofthe magnitude of CCG
37、 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 property forCCG.2.3 In addition for CCI derivation of crack extension timet0.2vC* (for cr
38、eep-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 Bench-markmaterial properties data which can subsequently be usedin crack growth numerical m
39、odeling, in component design andremaining life assessment methods.E1457 07423. 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 Practic
40、e 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 Calibration of Thermocouples ByComparison TechniquesE399 Test Method for Linear-Elastic Plane-Strain FractureToughnes
41、s KIcof Metallic MaterialsE647 Test Method for Measurement of Fatigue 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-ing
42、4. 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 4.3.For clarity and easier access within this document some of theterminology in E1823 relevant to this standard
43、 is repeatedbelow (see Terminology E1823, for further discussion anddetails).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.E18234.2.2 C*(t)-integral, C*(t) FL-1T-
44、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.4.2.2.1 DiscussionThe C*(t) expressi
45、on 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 = inc
46、rement in the contour path,T = outward traction vector on ds,u = displacement rate vector at ds,x, y, z = rectangular coordinate system, andTuxds is the rate of stress-power input into the area enclosedby G across the elemental length ds.4.2.2.2 DiscussionThe value of C*(t) from this equationis path
47、-independent for materials that deform according to thefollowing constitutive laws that may be separated into single-value time and stress functions or strain and stress functions ofthe forms: 5 f1t!f2s! (2) 5 f3!f4s! (3)where f1-f4represent functions of elapsed time, t, strain, andapplied stress, s
48、, respectively and is the strain rate.4.2.2.3 DiscussionFor materials exhibiting creep defor-mation for which the above equation is path-independent, theC*(t)-integral is equal to the value obtained from two, stressed,identical bodies with infinitesimally differing crack areas. Thisvalue is the diff
49、erence in the stress-power per unit difference incrack area at a fixed value of time and displacement rate, or ata fixed value of time and applied force.4.2.2.4 DiscussionThe value of C*(t) corresponding tothe steady-state conditions is called C*. Steady-state is said tohave been achieved when a fully developed creep stressdistribution has been produced around the crack tip. Thisoccurs when the secondary creep deformation characterized bythe following equation dominates the behavior of the speci-men.ss5 As” (4)4.2.2.5 Discussion
