ASTM E561-2015a red 0894 Standard Test Method for KR Curve Determination《K-R曲线测定的标准试验方法》.pdf

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1、Designation: E561 15E561 15aStandard Test Method forKR Curve Determination1This standard is issued under the fixed designation E561; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses

2、 indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the resistance to fracture of metallic materials under Mode I loading at staticrates using either of the follo

3、wing notched and precracked specimens: the middle-cracked tension M(T) specimen or the compacttension C(T) specimen. A KR curve is a continuous record of toughness development (resistance to crack extension) in terms ofKR plotted against crack extension in the specimen as a crack is driven under an

4、increasing stress intensity factor, K.(1)21.2 Materials that can be tested for KR curve development are not limited by strength, thickness, or toughness, so long asspecimens are of sufficient size to remain predominantly elastic to the effective crack extension value of interest.1.3 Specimens of sta

5、ndard proportions are required, but size is variable, to be adjusted for yield strength and toughness of thematerials.1.4 Only two of the many possible specimen types that could be used to develop KR curves are covered in this method.1.5 The test is applicable to conditions where a material exhibits

6、 slow, stable crack extension under increasing crack drivingforce, which may exist in relatively tough materials under plane stress crack tip conditions.1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.7 This standard do

7、es not purport to address all 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.2. Referenced Documents2.1 ASTM Stand

8、ards:3E4 Practices for Force Verification of Testing MachinesE399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture Testing2.2 Other Document:AISC Steel Construction Manual43. Terminology3.1 DefinitionsTerminolo

9、gy E1823 is applicable to this method.3.2 Definitions of Terms Specific to This Standard:3.2.1 apparent plane-stress fracture toughness, KappThe value of K calculated using the originalinitial crack size and themaximum force achieved during the test. Kapp is an engineering estimate of toughness that

10、 can be used to calculate residualstrength. Kapp depends on the material, specimen size, and specimen thickness and as such is not a material property.3.2.2 effective modulus, Eeff FL-2an elastic modulus that allows a theoretical (modulus normalized) compliance to match anexperimentally measured com

11、pliance for an actual initial crack size ao.1 This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved Oct. 15, 2015Dec. 1, 2015. Published December 2015. Originally

12、approved in 1974. Last previous edition approved in 20102015 asE561 10E561 15.2. DOI: 10.1520/E0561-15.10.1520/E0561-15A.2 The boldface numbers in parentheses refer to the list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactAS

13、TM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4 Available from American Institute of Steel Construction (AISC), One E. Wacker Dr., Suite 700, Chicago, IL 60601-1802, http:/www.aisc.org.Thi

14、s 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 consult prior editio

15、ns as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.

16、United States13.2.3 plane-stress fracture toughness, KcThe value of KR at instability in a force-controlled test corresponding to themaximum force point in the test. Kc depends on the material, specimen size, and specimen thickness and as such is not a materialproperty.3.2.3.1 DiscussionSee the disc

17、ussion of plane-strain fracture toughness in Terminology E1823.4. Summary of Test Method4.1 During slow-stable fracturing, the developing crack extension resistance KR is equal to the applied stress intensity factor K.The crack is driven forward by continuously or incrementally increasing force or d

18、isplacement. Measurements are madeperiodically for determination of the effective crack size and for calculation of K values, which are individual data points that definethe KR curve for the material under those test conditions.4.2 The crack starter is a low-stress-level fatigue crack.4.3 The method

19、 covers two techniques for determination of effective crack size: (1) direct measurement of the physical cracksize which is then adjusted for the developing plastic zone size, and (2) compliance measurement techniques that yield the effectivecrack size directly. Methods of measuring crack extension

20、and of making plastic-zone corrections to the physical crack size areprescribed. Expressions for the calculation of crack-extension force KR are given. Criteria for determining if the specimenconditions are predominantly elastic are provided.5. Significance and Use5.1 The KR curve characterizes the

21、resistance to fracture of materials during slow, stable crack extension and results from thegrowth of the plastic zone ahead of the crack as it extends from a fatigue precrack or sharp notch. It provides a record of thetoughness development as a crack is driven stably under increasing applied stress

22、 intensity factor K. For a given material, KR curvesare dependent upon specimen thickness, temperature, and strain rate. The amount of valid KR data generated in the test dependson the specimen type, size, method of loading, and, to a lesser extent, testing machine characteristics.5.2 For an unteste

23、d geometry, the KR curve can be matched with the crack driving (applied K) curves to estimate the degreeof stable crack extension and the conditions necessary to cause unstable crack propagation (12). In making this estimate, KR curvesare regarded as being independent of originalinitial crack size a

24、o and the specimen configuration in which they are developed. Fora given material, material thickness, and test temperature, KR curves appear to be a function of only the effective crack extensionae(23).5.2.1 To predict crack behavior and instability in a component, a family of crack driving curves

25、is generated by calculating Kas a function of crack size for the component using a series of force, displacement, or combined loading conditions. The KR curvemay be superimposed on the family of crack driving curves as shown in Fig. 1, with the origin of the KR curve coinciding withthe assumed origi

26、nalinitial crack size aao. The intersection of the crack driving curves with the KR curve shows the expectedFIG. 1 Schematic Representation of KR curve and Applied K Curves to Predict Instability; Kc,P3, ac, Corresponding to anOriginalInitial Crack Size, aoE561 15a2effective stable crack extension f

27、or each loading condition. The crack driving curve that develops tangency with the KR curvedefines the critical loading condition that will cause the onset of unstable fracture under the loading conditions used to developthe crack driving curves.5.2.2 Conversely, the KR curve can be shifted left or

28、right in Fig. 1 to bring it into tangency with a crack driving curve todetermine the originalinitial crack size that would cause crack instability under that loading condition.5.3 If the K-gradient (slope of the crack driving curve) of the specimen chosen to develop the KR curve has negativecharacte

29、ristics (see Note 1), as in a displacement-controlled test condition, it may be possible to drive the crack until a maximumor plateau toughness level is reached (34, 45, 56). When a specimen with positive K-gradient characteristics (see Note 2) is used,the extent of the KR curve which can be develop

30、ed is terminated when the crack becomes unstable.NOTE 1Fixed displacement in crack-line-loaded specimens results in a decrease of K with crack extension.NOTE 2With force control, K usually increases with crack extension, and instability will occur at maximum force.6. Apparatus6.1 Testing MachineMach

31、ines used for KR curve testing shall conform to the requirements of Practices E4. The forces usedin determining KR values shall be within the verified force application range of the testing machine as defined in Practices E4.6.2 Grips and Fixtures for Middle-Cracked Tension (M(T) SpecimensIn middle-

32、cracked tension specimens, the grip fixturesare designed to develop uniform stress distribution in the central region of the specimen. Single pin grips can be used on specimensless than 305 mm (12 in.) wide if the specimen is long enough to ensure uniform stress distribution in the crack plane (see

33、8.5.3.)For specimens wider than 305 mm (12 in.), multiple-bolt grips such as those shown in Fig. 2 or wedge grips that apply a uniformdisplacement along the entire width of the specimen end shall be used if the stress intensity factor and compliance equations inSection 11 are to be used. Other gripp

34、ing arrangements can be used if the appropriate stress intensity factor and compliancerelationships are verified and used. Grips should be carefully aligned to minimize the introduction of bending strain into thespecimen. Pin or gimbal connections can be located between the grips and testing machine

35、 to aid the symmetry of loading. Ifextra-heavy-gauge, high-toughness materials are to be tested, the suitability of the grip arrangement may be checked using theAISC Steel Construction Manual.FIG. 2 Middle-Cracked Tension (M(T) Panel Test SetupE561 15a36.3 Grips and Fixtures for Compact Tension (C(T

36、) SpecimensThe grips and fixtures described in Test Method E399 arerecommended for KR curve testing where C(T)-type specimens are loaded in tension.6.4 Buckling ConstraintsBuckling may develop in unsupported specimens depending upon the specimen thickness, materialtoughness, crack size, and specimen

37、 size (67). Buckling seriously affects the validity of a K analysis and is particularly troublesomewhen using compliance techniques to determine crack size (78). It is therefore required that buckling constraints be affixed to theM(T) and C(T) specimens in critical regions when conditions for buckli

38、ng are anticipated. A procedure for the detection ofbuckling is described in 9.8.3.6.4.1 For an M(T) specimen in tension, the regions above and below the notch are in transverse compression which can causethe specimen to buckle out of plane. The propensity for buckling increases as W/B and 2a/W rati

39、os increase and as the forceincreases. Unless it can be shown by measurement or analysis that buckling will not occur during a test, buckling constraints shallbe attached to the central portion of the specimen. The guides shall be so designed to prevent sheet kinking about the crack planeand sheet w

40、rinkling along the specimen width. Buckling constraints should provide a high stiffness constraint against out-of-planesheet displacements while minimizing friction. Buckling constraints with additional pressure adjustment capability near the centerof the specimen are recommended (67). Friction betw

41、een the specimen and the buckling constraints shall not interfere with thein-plane stress distribution in the specimen. Friction can be minimized by using a low-friction coating (such as thinTFE-fluorocarbon sheet) on the contact surfaces of the constraints and by using just enough clamping force to

42、 prevent bucklingwhile allowing free movement of the guides along the length of the specimen. A suspension system to prevent the bucklingconstraint from sliding down the specimen is recommended. Several buckling constraint configurations for M(T) specimens areshown in (78) and (89).6.4.2 For C(T) sp

43、ecimens, the portion of the specimen arms and back edge which are in compression may need to be restrainedfrom buckling in thinner specimens of high toughness alloys. It is convenient to use a base plate and cover plate with ports cutat appropriate locations for attaching clip gages and for crack si

44、ze observations. Friction between buckling restraints and specimenfaces is detrimental and should be minimized as much as possible.6.4.3 Lubrication shall be provided between the face plates and specimen. Care shall be taken to keep lubricants out of the crack.Sheet TFE-fluorocarbon or heavy oils or

45、 both can be used. The initial clamping forces between opposing plates should be highenough to prevent buckling but not high enough to change the stress distribution in the region of the crack tip at any time duringthe test.6.5 Displacement GagesDisplacement gages are used to accurately measure the

46、crack-mouth opening displacement (CMOD)across the crack at a specified location and span. For small C(T) specimens, the gage recommended in Test Method E399 may havea sufficient linear working range to be used. However, testing specimens with W greater than 127 mm (5 in.) may require gageswith a lar

47、ger working range, such as the gage shown in Fig. 3.6.5.1 A recommended gage for use in M(T) specimens is shown in Fig. 4 (910). This gage is inserted into a machined holehaving a circular knife edge. The diameter di, is the gage span 2Y used in the calibration. Detail drawings of the gage are given

48、in Fig. 5. Radius of the attachment tip should be less than the radius of the circular knife edge in the specimen.Dimensionsgmm (in.)dmm (in.)tmm (in.)hmm (in.)wmm (in.)23.3 (0.918) 12.7 (0.500) 1.6 (0.062) 86.4 (3.400) 7.6 (0.300)FIG. 3 Enlarged Clip Gage for Compliance Measurements on Large Specim

49、ensE561 15a46.5.2 The gage recommended in 6.5.1 is preferred because of its excellent linearity characteristics and ease of attachment.However, other types of gages used over different span lengths are equally acceptable provided the precision and accuracyrequirements are retained. For example, the conventional clip gage of Test Method E399 may be used with screw attached knifeedges spanning the crack at a chosen span 2Y. In M(T) tests, the proper compliance calibration curve must be used becausecompliance is a function of Y/W. When using the compliance c