1、Designation: B 646 06aStandard Practice forFracture Toughness Testing of Aluminum Alloys1This standard is issued under the fixed designation B 646; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 Fracture toughness is a key property for a number ofalumin
3、um alloys utilized in aerospace and process industries.Fracture toughness testing is often required for supplier quali-fication, quality control, and material release purposes. Thepurpose of this practice is to provide uniform test proceduresfor the industry, pointing out which current standards are
4、utilized in specific cases, and providing guidelines where nostandards exist. This practice provides guidance for testing (a)sheet and other products having a specified thickness less than6.35 mm (0.250 in.), (b) intermediate thicknesses of plate,forgings, and extrusions that are too thin for valid
5、plane-strainfracture toughness testing but too thick for treatment as sheet,such as products having a specified thickness greater than orequal to 6.35 mm (0.250 in.) but less than 25 to 50 mm (1 to2 in.), depending on toughness level, and (c) relatively thickproducts where Test Method E 399 is appli
6、cable.1.2 This practice addresses both direct measurements offracture toughness and screening tests, the latter recognizingthe complexity and expense of making formal fracture tough-ness measurements on great quantities of production lots.1.3 The values stated in SI units are to be regarded as thest
7、andard. The values in inch-pound units given in parenthesisare provided for information 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-priate safety and he
8、alth practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 557 Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy ProductsB 645 Practice for PlaneStrain Fracture Toughness Testingof Aluminum AlloysE
9、338 Test Method of Sharp-Notch Tension Testing ofHigh-Strength Sheet MaterialsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 561 Test Method for K-R Curve DeterminationE 602 Test Method for Sharp-Notch Tension Testing withCylindrical SpecimensE 1304 Tes
10、t Method for Plane-Strain (Chevron-Notch)Fracture Toughness of Metallic MaterialsE 1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 The terminology and definitions in the referenced docu-ments, especially E 1823, are applicable to this practice.3.2 Definitions of Terms Spe
11、cific to This Standard:3.2.1 For purposes of this practice, the following descrip-tions of terms are applicable in conjunction with Test MethodE 561:3.2.2 CMODcrack mouth opening displacement; themeasurement of specimen displacement between two pointsspanning the machined notch at locations specific
12、 to thespecimen being tested.3.2.3 KR25a value of KRon the K-R curve based on a 25 %secant intercept of the force-CMOD test record from a C(T)specimen and the effective crack length aeat that point thatotherwise satisfies the remaining-ligament criterion of TestMethod E 561. If the maximum force is
13、reached prior to the25 % secant intercept point, the maximum force point shall beused instead to determine the KR25value.3.2.4 Kcfor the purpose of this practice, Kcis the criticalstress intensity factor based on the maximum force value of theforce-CMOD test record from an M(T) specimen and theeffec
14、tive crack length, ae, at that point that otherwise satisfiesthe remaining-ligament criterion of Test Method E 561.3.2.5 Kapp(also commonly designated Kco)the apparentplane stress fracture toughness based on the original cracklength, ao, and the maximum force value of the force-CMOD1This practice is
15、 under the jurisdiction of ASTM Committee B07 on LightMetals and Alloys, and is the direct responsibility of Subcommittee B07.05 onTesting.Current edition approved Sept. 1, 2006. Published September 2006. Originallyapproved in 1978. Last previous edition approved in 2006 as B 646 06.2For referenced
16、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 Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright
17、ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.test record from an M(T) specimen that otherwise satisfies theremaining-ligament criterion of Test Method E 561.4. Summary of Practice4.1 This practice provides guidelines for the selection oftest
18、s to evaluate the fracture toughness properties of aluminumalloys, particularly for quality assurance and material releasepurposes. It also provides supplemental information regardingspecimen size selection, analysis, and interpretation of resultsfor the following products and test methods:4.2 Fract
19、ure Toughness Testing of Thin Products:4.2.1 K-R curve testing of middle-crack tension M(T) speci-mens in accordance with Test Method E 561.4.2.2 Kcand Kapp(Kco) testing of M(T) specimens ingeneral accordance with Test Method E 561.4.3 Fracture Toughness Testing of Intermediate ThicknessProducts:4.3
20、.1 Testing of compact-tension C(T) specimens in accor-dance with Test Method E 399 supplemented with PracticeB 645.4.3.2 Tests on C(T) specimens in accordance with TestMethod E 561 using the toughness parameter, KR25.4.4 Fracture Toughness Testing of Thick Products:4.4.1 Linear-elastic plane-strain
21、fracture testing in accor-dance with Test Method E 399 supplemented with PracticeB 645.4.5 Screening Tests:4.5.1 Screening tests of thin products using sharply-edge-notched, sheet-type specimens in accordance with Test MethodE 338.4.5.2 Screening tests of both intermediate and relativelythick produc
22、ts using the chevron notch (short-rod or short-bar)in accordance with Test Method E 1304.4.5.3 Screening tests of thick products using sharply-notched cylindrical specimens in accordance with Test MethodE 602.5. Significance and Use5.1 This practice is provided to develop and maintainuniformity in p
23、ractices for the evaluation of the toughness ofaluminum alloys, particularly with regard to supplier qualifi-cation, quality assurance, and material release to specifications.5.2 It is emphasized that the use of these procedures will notalter the validity of data determined with specific test method
24、s,but provides guidance in the interpretation of test results (validor invalid) and guidance in the selection of a reasonable testprocedure in those instances where no standard exists today.6. Selection of Fracture Toughness Test Methods forSpecific Products6.1 Direct measures of fracture toughness
25、are preferred overscreening test methods and are highly recommended forsupplier qualification and periodic quality control testing. Thefollowing measures of fracture toughness and test methods arerecommended for these products:6.2 Thin ProductsFor sheet and other products havingspecified thicknesses
26、 less than 6.35 mm (0.250 in.):6.2.1 The critical stress intensity factor (Kc) or the apparentfracture toughness (Kapp) from an M(T) specimen and tested ingeneral accordance with Test Method E 561 as supplementedby this practice in 8.1.6.2.2 The K-R curve measured from an M(T) specimentested in acco
27、rdance with Test Method E 561 as supplementedby this practice in 8.2.6.3 Thick ProductsFor products sufficiently thick to ob-tain a valid linear-elastic plane-strain fracture toughness mea-surement, KIc, from C(T) specimens measured in accordancewith Test Method E 399 supplemented by Practice B 645
28、andby this practice in 8.3.6.4 Intermediate Thickness ProductsFor products havingthicknesses greater than or equal to 6.35 mm (0.250 in.), buttoo thin for valid linear-elastic plane-strain fracture toughnesstesting:6.4.1 KQfrom C(T) specimens tested in accordance withTest Method E 399 supplemented w
29、ith Practice B 645 and thispractice in 8.3;or6.4.2 KR25from C(T) specimens tested in accordance withTest Method E 561 as supplemented by this practice in 8.4.6.5 Thin Specimens from Thicker ProductsThe methodsof 6.2 may also be utilized on thin specimens machined fromintermediate thickness or thick
30、products for the purpose ofevaluating their fracture toughness under plane stress condi-tions. These methods may be particularly desirable for prod-ucts which will be subsequently thinned by machining or othermeans. Typically, the specimen is machined from the productto a thickness representative of
31、 that used in the final applica-tion.6.6 Low Strength Alloy ProductsThere are no currentstandard recommendations for toughness testing of relativelylow-strength aluminum alloys which display large-scale yield-ing even in the presence of extremely large cracks in very thicksections. Such cases must b
32、e dealt with individually on aresearch basis using tests selected from program needs andanticipated design criteria. A typical case for general guidanceis given in the literature.37. Selection of Screening Test Methods for SpecificProducts7.1 Screening tests are permitted for high volume, materialre
33、lease testing provided they are allowed by the materialspecification or by agreement between the purchaser andsupplier. The following screening test methods are recom-mended for these products:7.2 Thin ProductsFor sheet and other products having aspecified thickness less than 6.35 mm (0.250 in.):7.2
34、.1 Tension tests of sharply-edge-notched, sheet-typespecimens in accordance with Test Method E 338 as supple-mented by this practice in 9.1 and 9.2, and the correspondingcorrelations of such data with the critical stress-intensityfactors (Kc) determined in accordance with this practice arerecommende
35、d.3Kaufman, J. G., and Kelsey, R.A., “Fracture Toughness and Fatigue Propertiesof 5083-0 Plate and 5183 Welds for Liquefied Natural GasApplications,” Propertiesof Materials for Liquefied Natural Gas Tankage, ASTM STP 579, ASTM, 1975, pp.138158.B 646 06a27.3 Thick ProductsFor products sufficiently th
36、ick to ob-tain a valid linear-elastic plane-strain fracture toughness mea-surement:7.3.1 Tension tests of sharply-notched, cylindrical speci-mens in accordance with Test Method E 602 as supplementedby this practice in 9.1 and 9.3 and the associated correlationwith linear-elastic plane-strain fractur
37、e toughness, KIc,asdetermined in accordance with Test Method E 399 and PracticeB 645 are recommended. In addition, the following recom-mended alternative screening tests may be applied:7.3.2 The chevron notch (short-rod and short-bar) testdescribed in Test Method E 1304 as supplemented by thispracti
38、ce in 9.1 and 9.4.7.4 Intermediate Thickness ProductsFor products havingspecified thicknesses greater than or equal to 6.35 mm (0.250in.), but too thin for valid plane-strain fracture toughnesstesting, there is insufficient data to justify strong recommenda-tions for screening test procedures. Presu
39、mably, correlationwith fracture toughness indices could be made with the resultsof tests using either chevron-notch (short-rod or short-bar)specimens, sharp-edge-notched, sheet-type specimens,sharply-notched, cylindrical specimens or sharp-notch Charpyspecimens.8. Fracture Toughness Testing Methods
40、andInterpretation8.1 Kcand Kapp(Kco) TestingFracture toughness testing toobtain either the critical stress intensity (Kc) or the apparentfracture toughness (Kapp) shall be performed on M(T) speci-mens in accordance with Test Method E 561 and the followingsupplemental requirements. Kcois another comm
41、only useddesignation for the apparent fracture toughness, so all require-ments for Kapptesting are also applicable to Kco.NOTE 1Kc, Kapp, and the K-R curve may all be obtained from thesame test record and specimen. Kcor Kappare often preferred for qualityassurance or material release purposes becaus
42、e they provide a single valuemeasure of material fracture toughness that can be compared against aminimum specification value. For higher strength, lower toughness alloyswhere the maximum force is preceded by one or more unstable extensionsof the crack, Kappis recommended for material release purpos
43、es.8.1.1 The M(T) specimen width W and original crack lengthaoshall be in accordance with the material specification. Thespecimen thickness shall be the full thickness of the product forthin products less than or equal to 6.35 mm (0.250 in.) inthickness. The specimen shall be machined to a thickness
44、 of6.35 mm (0.250 in.) by removing equal amounts from the topand bottom surfaces for thicker products, unless otherwisestated in the material specification. Recommended widths areW = 406 mm (16 in.) for medium strength, higher toughnessproducts and W = 160 mm (6.3 in.) for high strength, lowertoughn
45、ess products. For very high toughness sheet alloys, W =760 mm (30 in.) are also sometimes used for supplier qualifi-cation. The recommended original crack size is 2ao/W = 0.25.In all cases the original crack size 2aoshould be within therange of 0.25 to 0.40 W, inclusive, as allowed in Test MethodE 5
46、61. If no dimensional requirements are given in the materialspecification, the nominal specimen size shall be 406 mm (16in.) wide, with 380 mm (15 in.) being an acceptable minimumwidth and the original crack size shall be 2ao/W = 0.25. For allspecimen widths and original crack sizes, the tolerance f
47、or theoriginal crack size shall be +0.0125W/- 0W or +2.5/-0 mm(+0.1/-0 in.), whichever is greater.8.1.1.1 Tests for qualification and lot release testing shall beperformed on specimens having the same width, or less, thanspecimens used for determining specification values.NOTE 2The values of Kcand K
48、appare dependent upon the interactionof the crack driving force, which is a function of specimen width, W, andthe crack resistance curve (K-R curve). Thus, these values are dependenton specimen width (as well as thickness) and their values will typicallydecrease with decreasing specimen width, all o
49、ther factors being equal.They also depend to a lesser extent on the original crack length, ao.8.1.2 The M(T) specimen shall be machined and precrackedin accordance with Test Method E 561. The value of Kfmaxinthe fatigue precracking shall not exceed 16.5 MPa=m (15ksi=in.). Fatigue precracking may be omitted only if it can beshown that doing so does not increase the measured value of Kcor Kapp.8.1.3 Except when specifically stated in the material speci-fication, testing shall be performed with face stiffeners on thespecimen to prevent buckling above or below the center
