ASTM E561-2015 red 9591 Standard Test Method for KR Curve Determination.pdf

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1、Designation: E561 102E561 15Standard Test Method forK-RKR 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 parenthe

2、ses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTE3.2.2 was editorially updated in December 2011.2 NOTE3.2.2 was editorially updated in March 2013.1. Scope*1.1 This test method covers the determination of the

3、resistance to fracture of metallic materials under Mode I loading at staticrates using either of the following notched and precracked specimens: the middle-cracked tension M(T) specimen or the compacttension C(T) specimen. A K-RKR curve is a continuous record of toughness development (resistance to

4、crack extension) in termsof KR plotted against crack extension in the specimen as a crack is driven under an increasing stress intensity factor, K.1.2 Materials that can be tested for K-RKR curve development are not limited by strength, thickness, or toughness, so long asspecimens are of sufficient

5、size to remain predominantly elastic to the effective crack extension value of interest.1.3 Specimens of standard 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 dev

6、elop K-RKR curves are covered in this method.1.5 The test is applicable to conditions where a material exhibits 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 ar

7、e to be regarded as the standard. The values given in parentheses are for information only.1.7 This standard does 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 practi

8、ces and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE1823 Terminology Relating to Fatig

9、ue and Fracture Testing2.2 Other Document:AISC Steel Construction Manual33. Terminology3.1 DefinitionsTerminology 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 original cra

10、ck size and the maximumforce achieved during the test. Kapp is an engineering estimate of toughness that can be used to calculate residual strength. Kappdepends 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

11、modulus that allows a theoretical (modulus normalized) compliance to match anexperimentally measured compliance 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 Fr

12、actureMechanics.Current edition approved Nov. 1, 2010Oct. 15, 2015. Published November 2010December 2015. Originally approved in 1974. Last previous edition approved in 20082010as E561 08E561 10 12. DOI: 10.1520/E0561-10E02.10.1520/E0561-15.2 For referencedASTM standards, visit theASTM website, www.

13、astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American Institute of Steel Construction (AISC), One E. Wacker Dr., Suite 3100,700, Chicago, IL 60601-2

14、001.60601-1802, http:/www.aisc.org.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 reco

15、mmends that users consult prior editions 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 C7

16、00, West Conshohocken, PA 19428-2959. 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 materialp

17、roperty.3.2.3.1 DiscussionSee the discussion 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

18、or incrementally increasing force or displacement. Measurements are madeperiodically for determination of the effective crack size and for calculation of K values, which are individual data points that definethe K-RKR curve for the material under those test conditions.4.2 The crack starter is a low-

19、stress-level fatigue crack.4.3 The method 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 direct

20、ly. Methods of measuring crack extension 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 a

21、nd Use5.1 The K-RKR curve characterizes the resistance to fracture of materials during slow, stable crack extension and results fromthe growth 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 d

22、riven stably under increasing applied stress intensity factor K. For a given material, K-RKRcurves are dependent upon specimen thickness, temperature, and strain rate. The amount of valid K-RKR data generated in the testdepends on the specimen type, size, method of loading, and, to a lesser extent,

23、testing machine characteristics.5.2 For an untested geometry, the K-RKR 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 (1).4 In making this estimate, K-RKRcurves are regar

24、ded as being independent of original crack size ao and the specimen configuration in which they are developed.For a given material, material thickness, and test temperature, K-RKRcurves appear to be a function of only the effective crackextension ae(2).4 The boldface numbers in parentheses refer to

25、the list of references at the end of this standard.FIG. 1 Schematic Representation of K-RKR curve and Applied K Curves to Predict Instability; Kc,P3, ac, Corresponding to an OriginalCrack Size, aoE561 1525.2.1 To predict crack behavior and instability in a component, a family of crack driving curves

26、 is generated by calculating Kas a function of crack size for the component using a series of force, displacement, or combined loading conditions. The K-RKRcurve may be superimposed on the family of crack driving curves as shown in Fig. 1, with the origin of the K-RKR curve coincidingwith the assume

27、d original crack size ao. The intersection of the crack driving curves with the K-RKR curve shows the expectedeffective stable crack extension for each loading condition. The crack driving curve that develops tangency with the K-RKR curvedefines the critical loading condition that will cause the ons

28、et of unstable fracture under the loading conditions used to developthe crack driving curves.5.2.2 Conversely, the K-RKR curve can be shifted left or right in Fig. 1 to bring it into tangency with a crack driving curve todetermine the original crack size that would cause crack instability under that

29、 loading condition.5.3 If the K-gradient (slope of the crack driving curve) of the specimen chosen to develop the K-RKR curve has negativecharacteristics (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 r

30、eached (3, 4, 5). When a specimen with positive K-gradient characteristics (see Note 2) is used, theextent of the K-RKR curve which can be developed is terminated when the crack becomes unstable.NOTE 1Fixed displacement in crack-line-loaded specimens results in a decrease of K with crack extension.N

31、OTE 2With force control, K usually increases with crack extension, and instability will occur at maximum force.6. Apparatus6.1 Testing MachineMachines used for K-RKR curve testing shall conform to the requirements of Practices E4. The forcesused in determining KR values shall be within the verified

32、force application range of the testing machine as defined in PracticesE4.6.2 Grips and Fixtures for Middle-Cracked Tension (M(T) SpecimensIn middle-cracked tension specimens, the grip fixturesare designed to develop uniform stress distribution in the central region of the specimen. Single pin grips

33、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 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

34、 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 gripping arrangements can be used if the appropriate stress intensity factor and complianceFIG. 2 Middle-Cracked Tension (M(T) Panel Test SetupE561 153relati

35、onships 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 to aid the symmetry of loading. Ifextra-heavy-gauge, high-toughness materials are to be tes

36、ted, the suitability of the grip arrangement may be checked using theAISC Steel Construction Manual.6.3 Grips and Fixtures for Compact Tension (C(T) SpecimensThe grips and fixtures described in Test Method E399 arerecommended for K-RKR curve testing where C(T)-type specimens are loaded in tension.6.

37、4 Buckling ConstraintsBuckling may develop in unsupported specimens depending upon the specimen thickness, materialtoughness, crack size, and specimen size (6). Buckling seriously affects the validity of a K analysis and is particularly troublesomewhen using compliance techniques to determine crack

38、size (7). It is therefore required that buckling constraints be affixed to theM(T) and C(T) specimens in critical regions when conditions for buckling 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 th

39、e 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 ratios increase and as the forceincreases. Unless it can be shown by measurement or analysis that buckling will not occur during a test, buckling constraint

40、s shallbe attached to the central portion of the specimen. The guides shall be so designed to prevent sheet kinking about the crack planeand sheet wrinkling along the specimen width. Buckling constraints should provide a high stiffness constraint against out-of-planesheet displacements while minimiz

41、ing friction. Buckling constraints with additional pressure adjustment capability near the centerof the specimen are recommended (6). Friction between the specimen and the buckling constraints shall not interfere with thein-plane stress distribution in the specimen. Friction can be minimized by usin

42、g a low-friction coating (such as thinTFE-fluorocarbon sheet) on the contact surfaces of the constraints and by using just enough clamping force to prevent bucklingwhile allowing free movement of the guides along the length of the specimen. A suspension system to prevent the bucklingconstraint from

43、sliding down the specimen is recommended. Several buckling constraint configurations for M(T) specimens areshown in (7) and (8).6.4.2 For C(T) specimens, the portion of the specimen arms and back edge which are in compression may need to be restrainedfrom buckling in thinner specimens of high toughn

44、ess alloys. It is convenient to use a base plate and cover plate with ports cutat appropriate locations for attaching clip gages and for crack size observations. Friction between buckling restraints and specimenfaces is detrimental and should be minimized as much as possible.6.4.3 Lubrication shall

45、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 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 di

46、stribution in the region of the crack tip at any time duringthe test.6.5 Displacement GagesDisplacement gages are used to accurately measure the 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 E39

47、9 may havea sufficient linear working range to be used. However, testing specimens with W greater than 127 mm (5 in.) may require gageswith a larger working range, such as the gage shown in Fig. 3.6.5.1 Arecommended gage for use in M(T) specimens is shown in Fig. 4 (9). This gage is inserted into a

48、machined hole havinga circular knife edge. The diameter di, is the gage span 2Y used in the calibration. Detail drawings of the gage are given in Fig.5. Radius of the attachment tip should be less than the radius of the circular knife edge in the specimen.6.5.2 The gage recommended in 6.5.1 is prefe

49、rred 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 calibration curve given in Eq 5, the proper 2Y value