1、Designation: E1457 074E1457 13Standard Test Method forMeasurement of Creep Crack Growth Times and Rates inMetals1This 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
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTEEquation 6 was editorially corrected in August 2008.2 NOTEEquation A2.3 was editorially corrected in October 2009.3 NOTE4.2
3、.1 and Eq 8 were editorially revised in May 2011.4 NOTE4.2.2, 4.3.1 and 4.2.5 were editorially updated in December 2011.1. Scope1.1 This test method covers the determination of creep crack growth (CCG) time for a creep crack to grow on initial load (CCI)and its subsequent creep crack growth (CCG) ra
4、tes in metals at elevated temperatures using pre-cracked specimens subjected toelevated temperatures under static or quasi-static loading conditions. The tests are validated for either base material (homogenousproperties) or mixed base/weld material with inhomogeneous microstructures and creep prope
5、rties. For CCI the time (CCI), t0.2to an initial crack extension ai = 0.2 mm from the onset of first applied force and creep crack growth CCG rate, a or da/dt isareexpressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady statedetermination
6、 of the crack tip stresses derived in principal from C*(t) and Ct(1-14).2 The crack growth derived in this manner isidentified as a material property which can be used in modeling and life assessment methods (15-25).1.1.1 The choice of the crack growth correlating parameter C*, C*(t),Ct, or K depend
7、s on the material creep properties,geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests;creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where creep strains dominate and creep crack growth isaccompanied by
8、 substantial time-dependent creep strains at the crack tip, the crack growth rate is correlated by the steady statedefinitions of Ct or C*(t), defined as C* (see 1.1.4). In creep-brittle materials, creep crack growth occurs at low creep ductility.Consequently, the time-dependent creep strains are co
9、mparable to or dominated by accompanying elastic strains local to the cracktip. Under such steady state creep-brittle conditions, Ct or K could be chosen as the correlating parameter (8-14).1.1.2 In any one test, two regions of crack growth behavior may be present (9, 10). The initial transient regi
10、on where elasticstrains dominate and creep damage develops and in the steady state region where crack grows proportionally to time. Steady-statecreep crack growth rate behavior is covered by this standard. In addition specific recommendations are made in 11.7 as to howthe transient region should be
11、treated in terms of an initial crack growth period. During steady state, a unique correlation existsbetween da/dt and the appropriate crack growth rate relating parameter.1.1.3 In creep ductile materials, extensive creep occurs when the entire uncrackedun-cracked ligament undergoes creepdeformation.
12、 Such conditions are distinct from the conditions of small-scale creep and transition creep (1-7). In the case ofextensive creep, the region dominated by creep deformation is significant in size in comparison to both the crack length and theuncracked ligament sizes. In small-scale-creep only a small
13、 region of the uncrackedun-cracked ligament local to the crack tipexperiences creep deformation.1.1.4 The creep crack growth rate in the extensive creep region is correlated by the C*(t)-integral. The Ct parameter correlatesthe creep crack growth rate in the small-scale creep and the transition cree
14、p regions and reduces, by definition, to C*(t) in theextensive creep region (5). Hence in this document the definition C* is used as the relevant parameter in the steady state extensivecreep regime whereas C*(t) and/or Ct are the parameters which describe the instantaneous stress state from the smal
15、l scale creep,transient and the steady state regimes in creep. The recommended functions to derive C* for the different geometries is shown inAnnex A1 is described in Annex A2.1.1.5 An engineering definition of an initial crack extension size ai is used in order to quantify the initial period of cra
16、ckdevelopment. This distance is given as 0.2 mm. It has been shown (38-40) that this initial period which exists at the start of the1 This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack GrowthBehavi
17、or.Current edition approved March 15, 2007Feb. 1, 2013. Published April 2007May 2013. Originally approved in 1992. Last previous edition approved in 2000 asE1457 00.E1457 074. DOI: 10.1520/E1457-07E04.10.1520/E1457-13.2 The boldface numbers in parentheses refer to the list of references at the end o
18、f this standard.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users c
19、onsult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1test could be a substantial peri
20、od of the test time. During this early period the crack tip undergoes damage development as wellas redistribution of stresses prior reaching steady state. Recommendation is made to correlate this initial crack growth perioddefined as t0.2 at ai = 0.2 mm with the steady state C* when the crack tip is
21、 under extensive creep and with K for creep brittleconditions. The values for C* and K should be calculated at the final specified crack size defined as ao + ai where ao initial sizeof the starter crack.1.1.6 The recommended specimens for CCI and CCG testing is the standard compact tension specimen
22、C(T) (see Fig. A1.1)which is pin-loaded in tension under constant loading conditions. The clevis setup is shown in Fig. A1.2 (see 7.2.1 for details).Additional geometries which are valid for testing in this procedure are shown in Fig. A1.3. These are the C-ring in tension CS(T),middle tension M(T),
23、single notch tension SEN(T), single notch bend SEN(B), and double edge notch bend tension DEN(T). InFig. A1.3, the specimensside-grooving position side-grooving-position for measuring displacement at the force-line (FLD) crackmouth opening displacement (CMOD) and also and positions for the potential
24、 drop (PD) input and output leads are shown.Recommended loading for the tension specimens is pin-loading. The configurations, size range and initial crack size and theirextent of side-grooving are given in Table A1.1 of Annex A1, (40-44). Specimen selection will be discussed in 5.9.1.1.7 The state-o
25、f-stress at the crack tip may have an influence on the creep crack growth behavior and can cause crack-fronttunneling in plane-sided specimens. Specimen size, geometry, crack length, test duration and creep properties will affect thestate-of-stress at the crack tip and are important factors in deter
26、mining crack growth rate. A recommended size range of testspecimens and their side-grooving are given in Table A1.1 in Annex A1. It has been shown that for this range the cracking ratesdo not vary for a range of materials and loading conditions (40-44). Suggesting that the level of constraint, for t
27、he relatively shortterm test durations (less than one year), does not vary within the range of normal data scatter observed in tests of these geometries.However it is recommended that, within the limitations imposed on the laboratory, that tests are performed on different geometries,specimen size, d
28、imensions and crack size starters. In all cases a comparison of the data from the above should be made by testingthe standard C(T) specimen where possible. It is clear that increased confidence in the materials crack growth data can be producedby testing a wider range of specimen types and condition
29、s as described above.1.1.8 Material inhomogenities,inhomogeneities, residual stresses and material degradation at temperature, specimen geometryand low-force long duration tests (mainly greater that one year) can influence the rate of crack initiation and growth properties(39-47). In cases where res
30、idual stresses exist, the effect can be significant when test specimens are taken from material thatcharacteristically embodies residual stress fields or the damaged material. material, or both. For example weldments, and/oror thickcast, forged, extruded, components, plastically bent components and
31、complex component shapes shapes, or a combination thereof,where full stress relief is impractical. Specimens taken from such component that contain residual stresses willmay likewisecontain residual stresses which may have altered isin their extent and distribution due to specimen fabrication. Extra
32、ction ofspecimens in itself partially relieves and redistributes the residual stress pattern; however, the remaining magnitude cancould stillcause significant effects in the ensuing test. Residual stress is test unless post-weld heat treatment (PWHT) is performed. Otherwiseresidual stresses are supe
33、rimposed on applied stress and results in crack-tip stress intensity that is different from that based solelyon externally applied forces or displacements. Distortion Not taking the tensile residual stress effect into account will produce C*values lower than expected effectively producing a faster c
34、racking rate with respect to a constant C*. This would produceconservative estimates for life assessment and non-conservative calculations for design purposes. It should also be noted thatdistortion during specimen machining can also indicate the presence of residual stresses.1.1.9 Stress relaxation
35、 of the residual stresses due to creep and crack extension should also be taken into consideration. Nospecific allowance is included in this standard for dealing with these variations. However the method of calculating C* presentedin this document which used the specimens creep displacement rate to
36、estimate C* inherently takes into account the effectsdescribed above as reflected by the instantaneous creep strains that have been measured. However extra caution should still beobserved with the analysis of these types of tests as the correlating parameters K and C* shown in Annex A2 even though i
37、t isexpected that stress relaxation at high temperatures could in part negate the effects due to residual stresses. Annex A4 presents thecorrect calculations needed to derive J and C* for weldment tests where a miss-match factor needs to be taken into account.1.1.10 Specimen configurations and sizes
38、 other than those listed in TableA1.1 which are tested under constant force will involvefurther validity requirements. This is done by comparing data from recommended test configurations. Nevertheless, use of othergeometries are applicable by this method provided data are compared to data obtained f
39、rom standard specimens (as identified inTable A1.1) and the appropriate correlating parameters have been validated.1.2 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are forinformation only.1.3 This standard does not purport to address all
40、 of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.E1457 1322. Referenced Documents2.1 ASTM Standards:3E4 Practices f
41、or Force Verification of Testing MachinesE74 Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing MachinesE83 Practice for Verification and Classification of Extensometer SystemsE139 Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture
42、Tests of Metallic MaterialsE220 Test Method for Calibration of Thermocouples By Comparison TechniquesE399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE647 Test Method for Measurement of Fatigue Crack Growth RatesE813 Test Method for JIc, A Measure of Fract
43、ure ToughnessE1152 Test Method for Determining-J-R-CurvesE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture Testing3. Scope of Material Properties Data Resulting from This Standard3.1 This test method covers the determination of initial creep cr
44、ack extension (CCI) times and growth (CCG) in metals atelevated temperature using pre-cracked specimens subjected to static or quasi-static loading conditions. The metallic materialsinvestigated range from creep-ductile to creep-brittle conditions.3.2 The crack growth rate a or da/dt is expressed in
45、 terms of the magnitude of CCG rate relating parameters, C*(t),Ct or K.The resulting output derived as a vC* (as the steady state formulation of C*(t), Ct for creep-ductile materials or as avK (forcreep-brittle materials) is deemed as material property for CCG.3.3 In addition for CCI derivation of c
46、rack extension time t0.2 vC* (for creep-ductile materials) or t0.2 vK (for creep-brittlematerials) can also be used as a material property for the purpose of modeling and remaining life assessment.3.4 The output from these results can be used as Benchmarkmaterial properties data which can subsequent
47、ly be used in crackgrowth numerical modeling, in component design and remaining life assessment methods.3. Referenced Documents3.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE74 Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of T
48、esting MachinesE83 Practice for Verification and Classification of Extensometer SystemsE139 Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic MaterialsE220 Test Method for Calibration of Thermocouples By Comparison TechniquesE399 Test Method for Linear-Elastic Pl
49、ane-Strain Fracture Toughness KIc of Metallic MaterialsE647 Test Method for Measurement of Fatigue Crack Growth RatesE813 Test Method for JIc, A Measure of Fracture ToughnessE1152 Test Method for Determining-J-R-CurvesE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture Testing4. Terminology4.1 Terminology related to fracture testing contained in Terminology E1823 is applicable to this test method. Additionalterminology specific to this standard is detailed in 4.3. For clarity and easier access within this
