ASTM B646-2017 Standard Practice for Fracture Toughness Testing of Aluminum Alloys《铝合金断裂强度试验的标准实施规程》.pdf

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1、Designation: B646 12B646 17Standard Practice forFracture Toughness Testing of Aluminum Alloys1This standard is issued under the fixed designation B646; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu

2、mber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 Fracture toughness is a key property for a number

3、of aluminum alloys utilized in aerospace and process industries. Fracturetoughness testing is often required for supplier qualification, quality control, and material release purposes. The purpose of thispractice is to provide uniform test procedures for the industry, pointing out which current stan

4、dards are utilized in specific cases,and providing guidelines where no standards exist. This practice provides guidance for testing (a) sheet and other products havinga specified thickness less than 6.35 mm (0.250 in.), (b) intermediate thicknesses of plate, forgings, and extrusions that are too thi

5、nfor valid plane-strain fracture toughness testing but too thick for treatment as sheet, such as products having a specified thicknessgreater than or equal to 6.35 mm (0.250 in.) but less than 25 to 50 mm (1 to 2 in.), depending on toughness level, and (c) relativelythick products where Test Method

6、E399 is applicable.1.2 This practice addresses both direct measurements of fracture toughness and screening tests, the latter recognizing thecomplexity and expense of making formal fracture toughness measurements on great quantities of production lots.1.3 The values stated in SI units are to be rega

7、rded as the standard. The values in inch-pound units given in parenthesis areprovided for information purposes only.1.4 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

8、 safety and health practices and determine the applicability of regulatorylimitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International S

9、tandards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B557 Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy ProductsB557M Test Methods for Tension Testing Wrough

10、t and Cast Aluminum- and Magnesium-Alloy Products (Metric)B645 Practice for Linear-Elastic PlaneStrain Fracture Toughness Testing of Aluminum AlloysE399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic MaterialsE561 Test Method forKR Curve DeterminationE1304 Test Method

11、 for Plane-Strain (Chevron-Notch) Fracture Toughness of Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 The terminology and definitions in the referenced documents, especially E1823, are applicable to this practice.3.2 Definitions of Terms Specific to Th

12、is Standard:3.2.1 For purposes of this practice, the following descriptions of terms are applicable in conjunction with Test Method E561:3.2.2 CMODcrack mouth opening displacement; the measurement of specimen displacement between two points spanning themachined notch at locations specific to the spe

13、cimen being tested.1 This practice is under the jurisdiction of ASTM Committee B07 on Light Metals and Alloys and is the direct responsibility of Subcommittee B07.05 on Testing.Current edition approved May 1, 2012Aug. 1, 2017. Published June 2012August 2017. Originally approved in 1978. Last previou

14、s edition approved in 20062012 asB646 06a.B646 12. DOI: 10.1520/B0646-12.10.1520/B0646-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summ

15、ary page on the ASTM website.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

16、 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 C700, We

17、st Conshohocken, PA 19428-2959. United States13.2.3 KR25a value of KR on the K-RKR curve based on a 25 % secant intercept of the force-CMOD test record from a C(T)specimen and the effective crack lengthsize ae at that point that otherwise satisfies the remaining-ligament criterion of Test MethodE561

18、. If the maximum force is reached prior to the 25 % secant intercept point, the maximum force point shall be used insteadto determine the KR25 value.3.2.4 Kcfor the purpose of this practice, Kc is the critical stress intensity factor based on the maximum force value of theforce-CMOD test record from

19、 an M(T) specimen and the effective crack length,size, ae, at that point that otherwise satisfies theremaining-ligament criterion of Test Method E561.3.2.5 Kapp (also commonly designatedKco)the apparent plane stress fracture toughness based on the originalinitial cracklength,size, ao, and the maximu

20、m force value of the force-CMOD test record from an M(T) specimen that otherwise satisfies theremaining-ligament criterion of Test Method E561.4. Summary of Practice4.1 This practice provides guidelines for the selection of tests to evaluate the fracture toughness properties of aluminum alloys,parti

21、cularly for quality assurance and material release purposes. It also provides supplemental information regarding specimen size,analysis, and interpretation of results for the following products and test methods:4.2 Fracture Toughness Testing of Thin Products:4.2.1 K-R KR curve testing of M(T) middle

22、-crack tension specimens in accordance with Test Method E561.4.2.2 KcKc and Kapp (Kco) testing of M(T) specimens in general accordance with Test Method E561.4.3 Fracture Toughness Testing of Intermediate Thickness Products:4.3.1 Testing of C(T) compact-tension specimens in accordance with Test Metho

23、d E399 supplemented with Practice B645.4.3.2 Tests on C(T) specimens in accordance with Test Method E561 using the toughness parameter, KRKR25.4.4 Fracture Toughness Testing of Thick Products:4.4.1 Linear-elastic plane-strain fracture testing in accordance with Test Method E399 supplemented with Pra

24、ctice B645.5. Significance and Use5.1 This practice is provided to develop and maintain uniformity in practices for the evaluation of the toughness of aluminumalloys, particularly with regard to supplier qualification, quality assurance, and material release to specifications.5.2 It is emphasized th

25、at the use of these procedures will not alter the validity of data determined with specific test methods,but provides guidance in the interpretation of test results (valid or invalid) and guidance in the selection of a reasonable testprocedure in those instances where no standard exists today.6. Sel

26、ection of Fracture Toughness Test Methods for Specific Products6.1 Product size dictates the appropriate fracture toughness test method to be used for supplier qualification and periodic qualitycontrol testing. The fracture toughness measures and test methods are given below for the following produc

27、t sizes:6.2 Thin ProductsFor sheet and other products having specified thicknesses less than 6.35 mm (0.250 in.):6.2.1 Determine the critical stress intensity factor (Kc) or the apparent fracture toughness (Kapp) from M(T) specimens testedin general accordance with Test Method E561 as supplemented b

28、y this practice in 7.1; or6.2.2 Determine the K-RKR curve measured from M(T) specimens tested in accordance withTest Method E561 as supplementedby this practice in 7.2.6.3 Thick ProductsFor products sufficiently thick to obtain a valid linear-elastic plane-strain fracture toughness measurement,deter

29、mine KIc, from C(T) specimens measured in accordance with Test Method E399 and supplemented by Practice B645 and bythis practice in 7.3.NOTE 1The plane-strain chevron notch toughness KIvM may be used as a direct quantitative measure of fracture toughness3 when permitted by thematerial specification

30、or by agreement between the purchaser and supplier. Testing and analysis of short-rod or short-bar specimens to obtain KIvM shallbe performed in accordance with Test Method E1304. Fracture toughness minimums for KIvM should be established using the specimens and proceduresof Test Method E1304 becaus

31、e those minimums may differ significantly from KIc minimums established using Test Method E399. The standard chevronnotch specimens (short-rod or short-bar specimens 25.4 mm (1.00 in.) in diameter or width) are recommended. Two attractive features of the chevronnotch test method are a) fatigue precr

32、acking is not required, and b) the specimen is small.6.4 Intermediate Thickness ProductsFor products having thicknesses greater than or equal to 6.35 mm (0.250 in.), but too thinfor valid linear-elastic plane-strain fracture toughness testing:6.4.1 Determine KQ from C(T) specimens tested in accordan

33、ce with Test Method E399 supplemented with Practice B645 andthis practice in 7.3; or6.4.2 Determine KR2525 from C(T) specimens tested in accordance with Test Method E561 as supplemented by this practice in7.4.3 Rolfe, S. T. and Novak, S. R., “Review of Developments in Plane Strain Fracture Toughness

34、 Testing,” ASTM STP 463, ASTM, Sept. 1970, pp. 124159.B646 1726.5 Thin Specimens from Thicker ProductsThe methods of 6.2 may also be utilized on thin specimens machined fromintermediate thickness or thick products for the purpose of evaluating their fracture toughness under plane stress conditions.

35、Thesemethods may be particularly desirable for products that will be machined into a thinner structural member. Typically, the specimenis machined from the product to a thickness representative of that used in the final application.6.6 Low Strength Alloy ProductsThere are no current standard recomme

36、ndations for toughness testing of relativelylow-strength aluminum alloys which display large-scale yielding even in the presence of extremely large cracks in very thicksections. Such cases must be dealt with individually on a research basis using tests selected from program needs and anticipateddesi

37、gn criteria. A typical case for general guidance is given in the literature.47. Fracture Toughness Testing Methods and Interpretation7.1 Kc and Kapp (Kco) TestingFracture toughness testing to obtain either the critical stress intensity (Kc) or the apparentfracture toughness (Kapp) shall be performed

38、 on M(T) specimens in accordance with Test Method E561 and the followingsupplemental requirements. Kco is another commonly used designation for the apparent fracture toughness, so all requirements forKapp testing are also applicable to Kco.NOTE 2Kc,Kapp, and the K-RKR curve may all be obtained from

39、the same test record and specimen. Kc or Kapp are often preferred for quality assuranceor material release purposes because they provide a single value measure of material fracture toughness that can be compared against a minimumspecification value. For higher strength, lower toughness alloys where

40、the maximum force is preceded by one or more unstable extensions of the crack,Kapp is recommended for material release purposes.7.1.1 The M(T) specimen width W and originalinitial crack lengthsize ao shall be in accordance with the material specification.The specimen thickness shall be the full thic

41、kness of the product for thin products less than or equal to 6.35 mm (0.250 in.) inthickness. The specimen shall be machined to a thickness of 6.35 mm (0.250 in.) by removing equal amounts from the top andbottom surfaces for thicker products, unless otherwise stated in the material specification. Re

42、commended widths are W = 406 mm(16 in.) for medium strength, higher toughness products and W = 160 mm (6.3 in.) for high strength, lower toughness products.For very high toughness sheet alloys, W = 760 mm (30 in.) are also sometimes used for supplier qualification. The recommendedoriginalinitial cra

43、ck size is 2ao/W = 0.25. In all cases the originalinitial crack size 2ao should be within the range of 0.25 to 0.40W, inclusive, as allowed in Test Method E561. If no dimensional requirements are given in the material specification, the nominalspecimen size shall be 406 mm (16 in.) (16 in.) wide, wi

44、th 380 mm (15 in.) being an acceptable minimum width and theoriginalinitial crack size shall be 2ao/W = 0.25. For all specimen widths and originalinitial crack sizes, the tolerance for theoriginalinitial crack size shall be +0.0125 W/- 0W or +2.5/-0 mm (+0.1/-0 in.), whichever is greater.7.1.1.1 Tes

45、ts for qualification and lot release testing shall be performed on specimens having the same width, or less, thanspecimens used for determining specification values.NOTE 3The values of Kc and Kapp are dependent upon the interaction of the crack driving force, which is a function of specimen width, W

46、, and thecrack resistance curve (K-RKR curve). Thus, these values are dependent on specimen width (as well as thickness) and their values will typically decreasewith decreasing specimen width, all other factors being equal. They also depend to a lesser extent on the originalinitial crack length,size

47、, ao.7.1.2 The M(T) specimen shall be machined and precracked in accordance with Test Method E561. The value of Kfmaxmax inthe fatigue precracking shall not exceed 16.5 MPam (15 ksiin.). Fatigue precracking may be omitted only if it can be shownthat doing so does not increase the measured value of K

48、c or Kapp.7.1.3 Except when specifically stated in the material specification, testing shall be performed with face stiffeners on thespecimen to prevent buckling above or below the center slot.7.1.4 The Kc value shall be calculated at the maximum force by the use of the secant equation for the M(T)

49、specimen givenin Test Method E561. The half crack lengthsize used in the K-expression shall be the effective half crack length,size, ae, at themaximum force point calculated using the compliance expression for the M(T) specimens in Test Method E561. If, as sometimeshappens, there is considerable crack extension at maximum force, the point at which the force first reaches the maximum shall beused in the crack lengthsize calculations.7.1.5 The Kapp value shall be calculated at the maximum force by the use of the secant equation for the M(T) specimen givenin Test M