1、Designation: B646 12Standard 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 number in
2、 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 Department of Defense.1. Scope*1.1 Fracture toughness is a key property for a number ofaluminum a
3、lloys 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 areutil
4、ized 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 plan
5、e-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 E399 is applicable
6、.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 thestandar
7、d. 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 health
8、practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B557 Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy ProductsB557M Test Methods forTensionTestingWrought and CastAluminum- and Magnesium-Alloy P
9、roducts (Metric)B645 Practice for Linear-Elastic PlaneStrain FractureToughness Testing of Aluminum AlloysE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE561 Test Method for K-R Curve DeterminationE1304 Test Method for Plane-Strain (Chevron-Notch) Frac-ture
10、 Toughness of Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 The terminology and definitions in the referenced docu-ments, especially E1823, are applicable to this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 For purposes of this p
11、ractice, the following descrip-tions of terms are applicable in conjunction with Test MethodE561:3.2.2 CMODcrack mouth opening displacement; themeasurement of specimen displacement between two pointsspanning the machined notch at locations specific to thespecimen being tested.3.2.3 KR25a value of KR
12、on 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 E561. If the maximum force is reached prior to the25 % secant intercept point, the
13、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 theeffective crack length, ae, at that point that otherwise s
14、atisfiesthe remaining-ligament criterion of Test Method E561.3.2.5 Kapp(also commonly designated Kco)the apparentplane stress fracture toughness based on the original cracklength, ao, and the maximum force value of the force-CMODtest record from an M(T) specimen that otherwise satisfies theremaining
15、-ligament criterion of Test Method E561.1This practice is under the jurisdiction of ASTM Committee B07 on LightMetals and Alloys and is the direct responsibility of Subcommittee B07.05 onTesting.Current edition approved May 1, 2012. Published June 2012. Originallyapproved in 1978. Last previous edit
16、ion approved in 2006 as B646 06a. DOI:10.1520/B0646-12.2For referenced 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 Su
17、mmary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Practice4.1 This practice provides guidelines for the selection oftests to evaluate the fracture toughness prop
18、erties of aluminumalloys, particularly for quality assurance and material releasepurposes. It also provides supplemental information regardingspecimen size, analysis, and interpretation of results for thefollowing products and test methods:4.2 Fracture Toughness Testing of Thin Products:4.2.1 K-R cu
19、rve testing of M(T) middle-crack tension speci-mens in accordance with Test Method E561.4.2.2 Kcand Kapp(Kco) testing of M(T) specimens ingeneral accordance with Test Method E561.4.3 Fracture Toughness Testing of Intermediate ThicknessProducts:4.3.1 Testing of C(T) compact-tension specimens in accor
20、-dance with Test Method E399 supplemented with PracticeB645.4.3.2 Tests on C(T) specimens in accordance with TestMethod E561 using the toughness parameter, KR25.4.4 Fracture Toughness Testing of Thick Products:4.4.1 Linear-elastic plane-strain fracture testing in accor-dance with Test Method E399 su
21、pplemented with PracticeB645.5. Significance and Use5.1 This practice is provided to develop and maintainuniformity in practices for the evaluation of the toughness ofaluminum alloys, particularly with regard to supplier qualifi-cation, quality assurance, and material release to specifications.5.2 I
22、t is emphasized that the use of these procedures will notalter the validity of data determined with specific test methods,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 exi
23、sts today.6. Selection of Fracture Toughness Test Methods forSpecific Products6.1 Product size dictates the appropriate fracture toughnesstest method to be used for supplier qualification and periodicquality control testing. The fracture toughness measures andtest methods are given below for the fol
24、lowing product sizes:6.2 Thin ProductsFor sheet and other products havingspecified thicknesses less than 6.35 mm (0.250 in.):6.2.1 Determine the critical stress intensity factor (Kc)ortheapparent fracture toughness (Kapp) from M(T) specimens testedin general accordance with Test Method E561 as suppl
25、ementedby this practice in 7.1;or6.2.2 Determine the K-R curve measured from M(T) speci-mens tested in accordance with Test Method E561 as supple-mented by this practice in 7.2.6.3 Thick ProductsFor products sufficiently thick to ob-tain a valid linear-elastic plane-strain fracture toughness mea-sur
26、ement, determine KIc, from C(T) specimens measured inaccordance with Test Method E399 and supplemented byPractice B645 and by this practice in 7.3.NOTE 1The plane-strain chevron notch toughness KIvMmay be usedas a direct quantitative measure of fracture toughness3when permitted bythe material specif
27、ication or by agreement between the purchaser andsupplier.Testing and analysis of short-rod or short-bar specimens to obtainKIvMshall be performed in accordance with Test Method E1304. Fracturetoughness minimums for KIvMshould be established using the specimensand procedures ofTest Method E1304 beca
28、use those minimums may differsignificantly from KIcminimums established using Test Method E399.The standard chevron notch specimens (short-rod or short-bar specimens25.4 mm (1.00 in.) in diameter or width) are recommended. Two attractivefeatures of the chevron notch test method are a) fatigue precra
29、cking is notrequired, and b) the specimen is small.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 Determine KQfrom C(T) specimens tested in accor-dance w
30、ith Test Method E399 supplemented with PracticeB645 and this practice in 7.3;or6.4.2 Determine KR25from C(T) specimens tested in accor-dance with Test Method E561 as supplemented by this practicein 7.4.6.5 Thin Specimens from Thicker ProductsThe methodsof 6.2 may also be utilized on thin specimens m
31、achined fromintermediate thickness or thick products for the purpose ofevaluating their fracture toughness under plane stress condi-tions. These methods may be particularly desirable for prod-ucts that will be machined into a thinner structural member.Typically, the specimen is machined from the pro
32、duct to athickness representative of that used in the final application.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 ve
33、ry thicksections. Such cases must be 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.47. Fracture Toughness Testing Methods andInterpretation7.1 Kcand Kapp(Kco) TestingFra
34、cture 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 E561 and the followingsupplemental requirements. Kcois another commonly useddesignation for the apparent fracture t
35、oughness, so all require-ments for Kapptesting are also applicable to Kco.NOTE 2Kc, 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 because they provide a single valuemeasure of material
36、 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 extensions3Rolfe, S. T. and Novak, S. R., “Review of Developments in Plane StrainFracture Toughness Testing,” ASTM STP
37、 463, ASTM, Sept. 1970, pp. 124159.4Kaufman, 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.B646 122of the crack, K
38、appis recommended for material release purposes.7.1.1 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.
39、The specimen shall be machined to a thickness 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 = 16
40、0 mm (6.3 in.) for high strength, lowertoughness 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.
41、40 W, inclusive, as allowed in Test MethodE561. 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 widt
42、hs and original crack sizes, the tolerance for theoriginal crack size shall be +0.0125W/- 0W or +2.5/-0 mm(+0.1/-0 in.), whichever is greater.7.1.1.1 Tests for qualification and lot release testing shall beperformed on specimens having the same width, or less, thanspecimens used for determining spec
43、ification values.NOTE 3The values of Kcand Kappare 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 typicallyde
44、crease with decreasing specimen width, all other factors being equal.They also depend to a lesser extent on the original crack length, ao.7.1.2 The M(T) specimen shall be machined and precrackedin accordance with Test Method E561. The value of Kfmaxinthe fatigue precracking shall not exceed 16.5 MPa
45、=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.7.1.3 Except when specifically stated in the material speci-fication, testing shall be performed with face stiffeners on thespecimen to prevent buckling above or
46、below the center slot.7.1.4 The Kcvalue shall be calculated at the maximum forceby the use of the secant equation for the M(T) specimen givenin Test Method E561. The half crack length used in theK-expression shall be the effective half crack length, ae,atthemaximum force point calculated using the c
47、ompliance expres-sion for the M(T) specimens in Test Method E561. If, assometimes happens, there is considerable crack extension atmaximum force, the point at which the force first reaches themaximum shall be used in the crack length calculations.7.1.5 The Kappvalue shall be calculated at the maximu
48、mforce by the use of the secant equation for the M(T) specimengiven in Test Method E561. The half crack length used in theK-expression shall be the original crack length, ao.7.1.6 The net section validity of Kcor Kappshall bedetermined at the maximum force in accordance with TestMethod E561.7.1.7 Va
49、lues of Kcor Kappcalculated under conditions inwhich the net section stress exceeds 100 % of the tensile yieldstrength of the material are not suitable for design purposes anddo not express the full toughness capability of the material, butthey are useful for quality control or lot release; and such valueof Kcor Kappthat equals or exceeds a specified minimum valueshall constitute evidence that the material passes the statedspecification if the latter is based upon tests of the same orlarger width of specimen.7.2 K-R curve TestingFracture toughness testing to obtaint
