1、Designation: E2472 121Standard Test Method forDetermination of Resistance to Stable Crack Extensionunder Low-Constraint Conditions1This standard is issued under the fixed designation E2472; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTE3.2.5 and 3.2.6 were editorially revised in March 2013.1. Scope1.1 This standard covers the determination
3、of the resistanceto stable crack extension in metallic materials in terms of thecritical crack-tip-opening angle (CTOA), cand/or the crack-opening displacement (COD), 5resistance curve (1).2Thismethod applies specifically to fatigue pre-cracked specimensthat exhibit low constraint (crack-size-to-thi
4、ckness and un-cracked ligament-to-thickness ratios greater than or equal to 4)and that are tested under slowly increasing remote applieddisplacement. The test specimens are the compact, C(T), andmiddle-crack-tension, M(T), specimens. The fracture resis-tance determined in accordance with this standa
5、rd is measuredas c(critical CTOA value) and/or 5(critical COD resistancecurve) as a function of crack extension. Both fracture resis-tance parameters are characterized using either a single-specimen or multiple-specimen procedures. These fracturequantities are determined under the opening mode (Mode
6、 I) ofloading. Influences of environment and rapid loading rates arenot covered in this standard, but the user must be aware of theeffects that the loading rate and laboratory environment mayhave on the fracture behavior of the material.1.2 Materials that are evaluated by this standard are notlimite
7、d by strength, thickness, or toughness, if the crack-size-to-thickness (a/B) ratio and the ligament-to-thickness (b/B)ratio are greater than or equal to 4, which ensures relativelylow and similar global crack-front constraint for both the C(T)and M(T) specimens (2, 3).1.3 The values stated in SI uni
8、ts are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 prac
9、tices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE399 Test Method for Linear-Elastic Plane-Strain FractureTough
10、ness KIcof Metallic MaterialsE561 Test Method forK-R Curve DeterminationE647 Test Method for Measurement of Fatigue CrackGrowth RatesE1290 Test Method for Crack-Tip Opening Displacement(CTOD) Fracture Toughness Measurement (Withdrawn2013)4E1820 Test Method for Measurement of Fracture ToughnessE1823
11、Terminology Relating to Fatigue and Fracture TestingE2309 Practices for Verification of Displacement MeasuringSystems and Devices Used in Material Testing Machines2.2 ISO Standards:5ISO 22889:2007 Metallic MaterialsMethod ofTest for theDetermination of Resistance to Stable Crack ExtensionUsing Speci
12、mens of Low ConstraintISO 12135 Metallic MaterialsUnified Method of Test forthe Determination of Quasistatic Fracture Toughness3. Terminology3.1 Terminology E1823 is applicable to this test standard.3.2 Definitions:3.2.1 crack extension, a L, nan increase in crack size.1This test method is under the
13、 jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved July 1, 2012. Published January 2013. Originallyapproved in 2006. Last previous edition approved in 2006 as E2472061. DOI:10.1520/E2472-12E
14、01.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For 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 Doc
15、ument Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.5Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.Copyright ASTM I
16、nternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1.1 DiscussionIt should be noted that in thin-sheet andthick-plate materials under low constraint conditions, the crackextension observed on the surface of the specimen may besignificantly less than
17、 that in the interior of the specimen dueto the effects of crack tunneling. This must be considered ifdirect optical techniques are used to monitor and measurefree-surface crack extension. Indirect crack extension measure-ment techniques such as unloading compliance and electric-potential drop metho
18、d may be used in place of (or to comple-ment) the direct optical techniques to provide a measure ofaverage crack extension. (See Test Method E647 for compli-ance methods for C(T) and M(T) specimens; and ISO 12135and Test Method E647 for electric potential-drop methods forC(T) specimens.)3.2.2 crack
19、size, a L, nprincipal linear dimension usedin the calculation of fracture mechanics parameters for throughthickness cracks.3.2.2.1 DiscussionA measure of the crack size after thefatigue pre-cracking stage is denoted as the original crack size,ao. The value for aomay be obtained using surfacemeasurem
20、ent, unloading compliance, electric-potential drop orother methods where validation procedures for the measure-ments are available.3.2.3 crack-tip-opening angle (CTOA), deg, nrelativeangle of crack surfaces resulting from the total deformation(elastic plus plastic) measured (or calculated) at 1-mm b
21、ehindthe current crack tip as the crack stably tears, where = 2 tan1(1/2).3.2.4 critical crack-tip-opening angle (CTOAc), cdeg,nsteady-state relative angle of crack surfaces resulting fromthe total deformation (elastic plus plastic) measured (or calcu-lated) at 1-mm behind the current crack tip as t
22、he crack stablytears, where c= 2 tan1(1c/2).3.2.4.1 DiscussionCritical CTOA value tends to approacha constant, steady-state value after a small amount of crackextension (associated with crack tunneling and transition fromflat-to-slant crack extension).3.2.5 crack-opening displacement, (COD) 5Lforce-
23、induced separation vector between two points. The direction ofthe vector is normal to the crack plane (normal to the facingsurfaces of a crack) at a specified gage length. In this standard,5is measured at the fatigue precrack tip location over a gagelength of 5-mm as the crack stably tears.3.2.6 cra
24、ck-tip-opening displacement (CTOD), 1L,nrelative displacement of crack surfaces resulting from thetotal deformation (elastic plus plastic) measured (or calculated)at 1- mm behind the current crack tip as the crack stably tears.3.2.7 critical crack-tip-opening displacement (CTODc), 1cL, nsteady-state
25、 relative displacement of crack surfacesresulting from the total deformation (elastic plus plastic)measured (or calculated) at 1-mm behind the current crack tipas the crack stably tears.3.2.8 crack extension resistance curve (R curve),nvariation of 5with crack extension, a.3.2.9 effective yield stre
26、ngth, YFL-2, nan assumedvalue of uniaxial yield strength that represents the influence ofplastic yielding upon fracture test parameters.3.2.9.1 DiscussionEffective yield strength is calculated asthe average of the 0.2 % offset yield strength YS, and theultimate tensile strength, TSas follows:Y5 YS1T
27、S!/2 (1)NOTE 1The yield and ultimate tensile strength are determined fromTest Methods E8/E8M.3.2.9.2 DiscussionIn estimating Y, influences of testingconditions, such as loading rate and temperature, should beconsidered.3.2.10 final crack size, afL, ncrack extension at end ofstable tearing (af= ao+ a
28、f).3.2.11 final remaining ligament, bfL, ndistance fromthe tip of the final crack size to the back edge of the specimen,that is bf= W af.3.2.12 force, P F, nforce applied to a test specimen or toa component.3.2.13 minimum crack extension, aminL, ncrack exten-sion beyond which cis nearly constant.3.2
29、.14 maximum crack extension, amaxL, ncrack ex-tension limit for cand 5controlled crack extension.3.2.15 maximum fatigue force, PfF,nmaximum fatigueforce applied to specimen during pre-cracking stage.3.2.16 modulus of elasticity, E FL-2, nthe ratio of stressto corresponding strain below the proportio
30、nal limit.3.2.17 notch size, anL, ndistance from a reference planeto the front of the machined notch, such as the force line in thecompact specimen to the notch front or from the center line inthe middle-crack-tension specimen to the notch front.3.2.18 original crack size, aoL, nthe physical crack s
31、izeat the start of testing.3.2.19 original ligament, boL, ndistance from the origi-nal crack front to the back edge of the specimen, that is bo= W ao.3.2.20 remaining ligament, b L, ndistance from thephysical crack front to the back edge of the specimen, that is b= W a.3.2.21 specimen thickness, B L
32、, ndistance between theparallel sides of a test specimen or component. Side groovingis not allowed.3.2.22 specimen width, W L, ndistance from a referenceposition (for example, the force line of a compact specimen orcenter line in the middle-crack-tension specimen) to the rearsurface of the specimen.
33、 (Note that the total width of the M(T)specimen is defined as 2W.)4. Summary of Test Method4.1 The objective of this standard is to induce stable crackextension in a fatigue pre-cracked, low-constraint test speci-men while monitoring and measuring the COD at the originalfatigue pre-crack-tip locatio
34、n (4, 5) or the CTOA(or CTOD) at1-mm behind the stably tearing crack tip (6, 7), or both. Theresistance curve associated with the 5measurements and thecritical limiting value of the CTOA measurements are used tocharacterize the corresponding resistance to stable crack ex-tension. In contrast, the CT
35、OD values determined from TestE2472 1212Method E1290 (high-constraint bend specimens) are values atone or more crack extension events, such as the CTOD at theonset of brittle crack extension with no significant stable crackextension.4.2 Either of the fatigue pre-cracked, low-constraint testspecimen
36、configurations specified in this standard C(T) orM(T) may be used to measure or calculate either of thefracture resistance parameters considered. The fracture resis-tance parameters, CTOA (or CTOD) and 5, may be charac-terized using either a single-specimen or multiple-specimenprocedure. In all case
37、s, tests are performed by applying slowlyincreasing displacements to the test specimen and measuringthe forces, displacements, crack extension and angles realizedduring the test. The forces, displacements and angles are thenused in conjunction with certain pre-test and post-test specimenmeasurements
38、 to determine the materials resistance to stablecrack extension.4.3 Four procedures for measuring crack extension are:surface visual, unloading compliance, electrical potential, andmultiple specimens.4.4 Two techniques are presented for measuring CTOA:optical microscopy (OM) (8) and digital image co
39、rrelation(DIC) (9).4.5 Three techniques are presented for measuring COD: 5clip gage (5), optical microscopy (OM) (8), and digital imagecorrelation (DIC) (9).4.6 Data generated following the procedures and guidelinescontained in this standard are labeled qualified data and areinsensitive to in-plane
40、dimensions and specimen type (tensionor bending forces), but are dependent upon sheet or platethickness.5. Significance and Use5.1 This test method characterizes a metallic materialsresistance to stable crack extension in terms of crack-tip-opening angle (CTOA), and/or crack-opening displacement(COD
41、), 5under the laboratory or application environment ofinterest.This method applies specifically to fatigue pre-crackedspecimens that exhibit low constraint and that are tested underslowly increasing displacement.5.2 When conducting fracture tests, the user must considerthe influence that the loading
42、 rate and laboratory environmentmay have on the fracture parameters. The user should performa literature review to determine if loading rate effects havebeen observed previously in the material at the specifictemperature and environment being tested. The user shoulddocument specific information pert
43、aining to their material,loading rates, temperature, and environment (relative humid-ity) for each test.5.3 The results of this characterization include the determi-nation of a critical, lower-limiting value, of CTOA (c)oraresistance curve of 5, a measure of crack-opening displace-ment against crack
44、 extension, or both.5.4 The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens.5.5 Materials that can be evaluated by this standard are notlimited by strength, thickness, or toughness, if the crack-size-to-thickness (a/B) ratio or ligament-to-thickness (b/B) ratio areequ
45、al to or greater than 4, which ensures relatively low andsimilar global crack-front constraint for both the C(T) andM(T) specimens (2, 3).5.6 The values of CTOA and COD (5) determined by thistest method may serve the following purposes:5.6.1 In research and development, CTOA (c)orCOD(5), or both, te
46、sting can show the effects of certain parameterson the resistance to stable crack extension of metallic materialssignificant to service performance. These parameters include,but are not limited to, material thickness, material composition,thermo-mechanical processing, welding, and thermal stressreli
47、ef.5.6.2 For specifications of acceptance and manufacturingquality control of base materials.5.6.3 For inspection and flaw assessment criteria, when usedin conjunction with fracture mechanics analyses. Awareness ofdifferences that may exist between laboratory test and fieldconditions is required to
48、make proper flaw assessment.5.6.4 The critical CTOA (c) has been used with theelastic-plastic finite-element method to accurately predictstructural response and force carrying capacity of simple andcomplex cracked structural components, see Appendix X1.5.6.5 The 5parameter has been related to the J-
49、integral bymeans of the Engineering Treatment Model (ETM) (10) andprovides an engineering approach to predict the structuralresponse and force carrying capacity of cracked structuralcomponents.5.6.6 The K-R curve method (Practice E561) is similar tothe 5-resistance curve, in that, the concept has been applied toboth C(T) and M(T) specimens (under low-constraint condi-tions) and the K-R curve concept has been used successfully inindustry (11). However
