ASTM E2472-2006e1 Standard Test Method for Determination of Resistance to Stable Crack Extension under Low-Constraint Conditions.pdf

1、Designation: E2472 061Standard 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.1NOTE3.2.16 was editorially revised in May 2010.1. Scope1.1 This standard covers the determination of the resis

3、tanceto stable crack extension in metallic materials in terms of thecritical crack-tip-opening angle (CTOAc), ccand/or the crack-opening displacement (COD), d5resistance curve (1).2Thismethod applies specifically to fatigue pre-cracked specimensthat exhibit low constraint (crack-length-to-thickness

4、and un-cracked ligament-to-thickness ratios greater than or equal to 4)and that are tested under slowly increasing remote applieddisplacement. The recommended specimens are the compact-tension, C(T), and middle-crack-tension, M(T), specimens.The fracture resistance determined in accordance with this

5、standard is measured as cc(critical CTOA value) and/ord5(critical COD resistance curve) as a function of crackextension. Both fracture resistance parameters are character-ized using either a single-specimen or multiple-specimenprocedures. These fracture quantities are determined under theopening mod

6、e (Mode I) of loading. Influences of environmentand rapid loading rates are not covered in this standard, but theuser must be aware of the effects that the loading rate andlaboratory environment may have on the fracture behavior ofthe material.1.2 Materials that are evaluated by this standard are no

7、tlimited by strength, thickness, or toughness, if the crack-length-to-thickness (a/B) ratio and the ligament-to-thickness(b/B) ratio are greater than or equal to 4, which ensuresrelatively low and similar global crack-front constraint for boththe C(T) and M(T) specimens (2, 3).1.3 The values stated

8、in SI units are to be regarded as thestandard. The values given in parentheses (English) are forinformation purposes only.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-

9、priate safety and health practices 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 Test Methods for Tension Testing of Metallic MaterialsE399 Test Method for Linear-Elastic Pl

10、ane-Strain FractureToughness KIcof Metallic MaterialsE561 Test Method for K-R Curve DeterminationE647 Test Method for Measurement of Fatigue CrackGrowth RatesE1290 Test Method for Crack-Tip Opening Displacement(CTOD) Fracture Toughness MeasurementE1820 Test Method for Measurement of Fracture Tough-n

11、essE1823 Terminology Relating to Fatigue and Fracture Test-ingE2309 Practices for Verification of Displacement Measur-ing Systems and Devices Used in Material Testing Ma-chines2.2 ISO Standards:ISO/TC164/SC4-N413.4 Metallic MaterialsMethod ofTest for the Determination of Resistance to Stable CrackEx

12、tension Using Specimens of Low Constraint4ISO 12135 Metallic MaterialsUnified Method of Test forthe Determination of Quasistatic Fracture Toughness43. Terminology3.1 Terminology E1823 is applicable to this test standard.3.2 Definitions:3.2.1 crack extension, Da L, nan increase in cracklength.3.2.1.1

13、 DiscussionIt should be noted that in thin-sheetand thick-plate materials under low constraint conditions, the1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved

14、 June 15, 2006. Published August 2006. DOI: 10.1520/E2472-06E01.2The 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

15、 ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428

16、-2959, United States.crack extension observed on the surface of the specimen maybe significantly less than that in the interior of the specimendue to the effects of crack tunneling. This must be consideredif direct optical techniques are used to monitor and measurefree-surface crack extension. Indir

17、ect crack extension measure-ment techniques such as unloading compliance and electric-potential drop method may be used in place of (or to augment)the direct optical techniques to provide a measure of averagecrack extension. (See Test Method E647 for compliancemethods for C(T) and M(T) specimens; an

18、d ISO 12135 forelectric potential-drop methods for C(T) specimens.)3.2.2 crack length, a L, na linear measure of a principalplanar dimension of a crack. This measure is commonly usedin the calculation of quantities descriptive of the stress anddisplacement fields of cracked specimens.3.2.2.1 Discuss

19、ionA measure of the crack length after thefatigue pre-cracking stage is denoted as the original cracklength, ao. The value for aomay be obtained using surfacemeasurement, unloading compliance, electric-potential drop orother methods where validation procedures for the measure-ments are available.3.2

20、.3 crack-tip-opening angle (CTOA), c deg, nrelativeangle of the crack surfaces measured (or calculated) at 1-mmbehind current crack tip, where c = 2 tan-1(CTOD/2).3.2.4 critical crack-tip-opening angle (CTOAc), ccdeg,nsteady-state value of CTOA measured (or calculated) at1-mm behind the current crac

21、k tip, where CTOAc=2tan1(CTODc/2).3.2.4.1 DiscussionThe critical CTOA value tends to ap-proach a constant, steady-state value after a small amount ofcrack extension (associated with crack tunneling and transitionfrom flat-to-slant crack extension).3.2.5 crack-opening displacement, d5L, nrelative dis

22、-placement of the crack surfaces normal to the original (un-deformed) crack plane at the tip of the fatigue pre-crack length,ao. In this standard, d5is measured at the original crack lengthlocation over a gage length of 5-mm as the crack stably tears.3.2.6 crack-tip-opening displacement (CTOD), d L,

23、nrelative displacement resulting from the total deformation(elastic plus plastic) at variously defined locations near theoriginal (prior to force application) crack tip.3.2.7 critical crack-tip-opening displacement (CTODc),dcL, nsteady-state value of CTOD resulting from the totaldeformation (elastic

24、 plus plastic) measured (or calculated) at1-mm behind current crack-tip location.3.2.8 crack extension resistance curve (R curve),nvariation of d5with crack extension, Da.3.2.9 effective yield strength, sYFL-2, nan assumedvalue of uniaxial yield strength that represents the influence ofplastic yield

25、ing upon fracture test parameters.3.2.9.1 DiscussionEffective yield strength is calculated asthe average of the 0.2 % offset yield strength sYS, and theultimate tensile strength, sTSas follows:sY5 sYS1sTS! / 2 (1)NOTE 1The yield and ultimate tensile strength are determined fromTest Methods E8.3.2.9.

26、2 DiscussionIn estimating sY, influences of testingconditions, such as loading rate and temperature, should beconsidered.3.2.10 final crack length, afL, ncrack extension at endof stable tearing (af= ao+ Daf).3.2.11 final remaining ligament, bfL, ndistance fromthe tip of the final crack length to the

27、 back edge of thespecimen, that is bf= W af.3.2.12 force, P F, nforce applied to specimen.3.2.13 minimum crack extension, DaminL, ncrack ex-tension beyond which ccis nearly constant.3.2.14 maximum crack extension, DamaxL, ncrack ex-tension limit for ccand d5controlled crack extension.3.2.15 maximum

28、fatigue force, PfF, nmaximum fatigueforce applied to specimen during pre-cracking stage.3.2.16 modulus of elasticity, E FL-2, nthe ration ofstress to corresponding strain below the proportional limit.3.2.17 notch length, anL, nthe distance from a refer-ence plane to the tip of the machined notch, su

29、ch as the loadline in the compact-tension specimen to the notch tip or fromthe center line in the middle-crack tension specimen to thenotch tip.3.2.18 original crack length, aoL, nthe physical cracklength at the start of testing.3.2.19 original remaining ligament, boL, ndistancefrom the original cra

30、ck front to the back edge of the specimen,that is bo= W ao.3.2.20 remaining ligament, b L, ndistance from thecrack front to the back edge of the specimen, that is b = W a.3.2.21 specimen thickness, B L, nthe side-to-side di-mension of the specimen being tested (side grooving is notallowed).3.2.22 sp

31、ecimen width, W L, na physical dimension ona test specimen measured from a reference position, such as theload line in the compact-tension specimen or the center line inthe middle-crack tension specimen to the edge of the specimen.(Note that the total width of the M(T) specimen is defined as2W.)4. S

32、ummary 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 location (4, 5) or the CTOA (or CTOD) at1-mm behind the stably tearing crack

33、tip (6, 7), or both. Theresistance curve associated with the d5measurements and thecritical limiting value of the CTOA measurements are used tocharacterize the corresponding resistance to stable crack ex-tension. In contrast, the CTOD values determined from TestMethod E1290 (high-constraint bend spe

34、cimens) 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 configurations specified in this standard (C(T) orM(T) may be used to measure

35、or calculate either of thefracture resistance parameters considered. The fracture resis-tance parameters, CTOA (or CTOD) and d5, may be charac-terized using either a single-specimen or multiple-specimenE2472 0612procedure. In all cases, tests are performed by applying slowlyincreasing displacements

36、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 to determine the materials resistance to stablecrack extension.4.

37、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 correlation(DIC) (9).4.5 Three techniques are presented for measurin

38、g COD: d5clip 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 dimensions and specimen type (tensionor bending forces), but are

39、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), c and/or crack-opening displacement(COD), d5under the laboratory or application environment ofinterest

40、. 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 rate and laboratory environmentmay have on the fracture para

41、meters. 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 pertaining to their material,loading rates, temperature, and envi

42、ronment (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 (cc)oraresistance curve of d5, a measure of crack-opening displace-ment against crack extension, or both.5.4 The recommended specimens are the c

43、ompact-tension,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-length-to-thickness (a/B) ratio or ligament-to-thickness (b/B)ratio are equal to or greater than 4, which ensures rela

44、tivelylow and similar global crack-front constraint for both the C(T)and M(T) specimens (2, 3).5.6 The values of CTOA (and COD (d5) determined by thistest method may serve the following purposes:5.6.1 In research and development, CTOAc(cc)orCOD(d5), or both, testing can show the effects of certain p

45、arameterson 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 stressrelief.5.6.2 For specifications of acceptan

46、ce 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 make proper flaw assessment.5.6.4 The c

47、ritical CTOA (cc) 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 d5parameter has been related to the J-integral bymeans of the Engineering T

48、reatment 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 d5-resistance curve, in that, the concept has been applied toboth C(T) and M(T) spec

49、imens (under low-constraint condi-tions) and the K-R curve concept has been used successfully inindustry (11). However, the d5parameter has been related tothe J-integral and the parameter incorporates the materialnon-linear effects in its measurement. Comparisons have alsobeen made among various fracture criteria on fracture of C(T),M(T) and a structurally configured crack configuration (12)that were made of several different materials (two aluminumalloys and a very ductile steel), and the K-R curve