1、Designation: E1681 03 (Reapproved 2008)2Standard Test Method forDetermining Threshold Stress Intensity Factor forEnvironment-Assisted Cracking of Metallic Materials1This standard is issued under the fixed designation E1681; the number immediately following the designation indicates the year oforigin
2、al adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEA1.5.1.1 was editorially corrected in May 2010.2NOTEFigures 5 and 6 were
3、 made more legible in September 2011.1. Scope1.1 This test method covers the determination of theenvironment-assisted cracking threshold stress intensity factorparameters, KIEACand KEAC, for metallic materials fromconstant-force testing of fatigue precracked beam or compactfracture specimens and fro
4、m constant-displacement testing offatigue precracked bolt-load compact fracture specimens.1.2 This test method is applicable to environment-assistedcracking in aqueous or other aggressive environments.1.3 Materials that can be tested by this test method are notlimited by thickness or by strength as
5、long as specimens are ofsufficient thickness and planar size to meet the size require-ments of this test method.1.4 A range of specimen sizes with proportional planardimensions is provided, but size may be variable and adjustedfor yield strength and applied force. Specimen thickness is avariable ind
6、ependent of planar size.1.5 Specimen configurations other than those contained inthis test method may be used, provided that well-establishedstress intensity calibrations are available and that specimendimensions are of sufficient size to meet the size requirementsof this test method during testing.
7、1.6 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 practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced D
8、ocuments2.1 ASTM Standards:2D1141 Practice for the Preparation of Substitute OceanWaterE8/E8M Test Methods for Tension Testing of MetallicMaterialsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE647 Test Method for Measurement of Fatigue CrackGrowth RatesE
9、1823 Terminology Relating to Fatigue and Fracture Test-ingG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTesting33. T
10、erminology3.1 Definitions:3.1.1 For definitions of terms relating to fracture testingused in this test method, refer to Terminology E1823.3.1.2 For definitions of terms relating to corrosion testingused in this test method, refer to Terminology G15.3.1.3 stress-corrosion cracking (SCC)a cracking pro
11、cessthat requires the simultaneous action of a corrodent andsustained tensile stress.3.1.4 stress intensity factor threshold for plane strainenvironment-assisted cracking (KIEACFL3/2)the highestvalue of the stress intensity factor (K) at which crack growth isnot observed for a specified combination
12、of material andenvironment and where the specimen size is sufficient to meetrequirements for plane strain as described in Test MethodE399.3.1.5 stress intensity factor threshold for environment-assisted cracking (KEACFL3/2)the highest value of thestress intensity factor (K) at which crack growth is
13、not1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.06 on CrackGrowth Behavior.Current edition approved Nov. 1, 2008. Published February 2009. Originallyapproved in 1995. Last previous edition approved in 20
14、03 as E1681 - 03. DOI:10.1520/E1681-03R08E02.2For 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.3Withdrawn. The
15、last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.observed for a specified combination of material and environ-ment and where the measured value may depend
16、on specimenthickness.3.1.6 physical crack size (apL)the distance from areference plane to the observed crack front. This distance mayrepresent an average of several measurements along the crackfront. The reference plane depends on the specimen form, andit is normally taken to be either the boundary
17、or a planecontaining either the loadline or the centerline of a specimen orplate. The reference plane is defined prior to specimen defor-mation.3.1.7 original crack size (aoL)the physical crack size atthe start of testing.3.1.8 original uncracked ligament (boL)distance fromthe original crack front t
18、o the back edge of the specimen (bo=Wao).3.1.9 specimen thickness (BL)the side-to-side dimen-sion of the specimen being tested.3.1.10 tensile strength (sTSFL2)the maximum tensilestress that a material is capable of sustaining. Tensile strengthis calculated from the maximum force during a tension tes
19、tcarried to rupture and the original cross-section area of thespecimen.3.2 Definitions of Terms Specific to This Standard:3.2.1 environment-assisted cracking (EAC)a crackingprocess in which the environment promotes crack growth orhigher crack growth rates than would occur without thepresence of the
20、environment.3.2.2 normalized crack size (a/W)the ratio of crack size,a, to specimen width, W. Specimen width is measured from areference position such as the front edge in a bend specimen orthe loadline in the compact specimen to the back edge of thespecimen.3.2.3 yield strength (sYSFL2)the stress a
21、t which amaterial exhibits a specific limiting deviation from the propor-tionality of stress to strain. This deviation is expressed in termsof strain.NOTE 1In this test method, the yield strength determined by the 0.2 %offset method is used.3.2.4 effective yield strength (sYFL2)an assumed valueof un
22、iaxial yield strength that represents the influences ofplastic yielding upon fracture test parameters. For use in thismethod, it is calculated as the average of the 0.2 % offset yieldstrength sYS, and the ultimate tensile strength, sTS,orsY5 sYS1sTS! / 2 (1)3.2.5 notch length (an(L)the distance from
23、 a referenceplane to the front of the machined notch. The reference planedepends on the specimen form and normally is taken to beeither the boundary or a plane containing either the loadline orthe centerline of a specimen or plate. The reference plane isdefined prior to specimen deformation.4. Summa
24、ry of Test Method4.1 This test method involves testing of single-edge notchedSE(B) specimens, compact C(T) specimens, or bolt-loadcompact MC(W) specimens, precracked in fatigue. Thesingle-edge notched beam specimen is tested by dead weightloading. An environmental chamber is either attached to thesp
25、ecimen, or the specimen is contained within the chamber.The chamber must enclose the portion of the specimen wherethe crack tip is located. Prescribed environmental conditionsmust be established and maintained within the chamber at alltimes during the test.4.1.1 Specimens shall be deadweight loaded
26、or otherwiseheld under constant force or held under constant displacement(defined in 6.2) for a prescribed length of time, during whichfailure by crack growth leading to fracture may or may notoccur. KIEACand KEACare defined as the highest value of stressintensity factor at which neither failure nor
27、 crack growthoccurs. The stress intensity factor (K) is calculated from anexpression based on linear elastic stress analysis. To establisha suitable crack-tip condition for constant force tests, thestress-intensity level at which the fatigue precracking of thespecimen is conducted is limited to a va
28、lue substantially lessthan the measured KIEACor KEACvalues. For constant dis-placement tests, the stress-intensity level at which the fatigueprecracking of the specimen is conducted is limited to therequirements of Test Method E399. The validity of the KIEACvalue determined by this test method depen
29、ds on meeting thesize requirements to ensure plane strain conditions, as stated inTest Method E399. The validity of the KEACvalue depends onmeeting the size requirements for linear elastic behavior, asstated in the Test Method E647.4.1.2 This test method can produce information on the onsetof enviro
30、nment-assisted crack growth. Crack growth rateinformation can be obtained after crack nucleation, but themethod for obtaining this information is not part of this testmethod (1).44.2 The mechanisms of environment-assisted cracking arevaried and complex. Measurement of a KEACor KIEACvaluefor a given
31、combination of material and environmental pro-vides no insight into the particular cracking mechanism thatwas either operative or dominant. Two prominent theories ofenvironment-assisted cracking are anodic reaction and hydro-gen embrittlement (2). The data obtained from this test methodmay be interp
32、reted by either theory of environment-assistedcracking.4.3 Specimen thickness governs the proportions of planestrain and plane stress deformation local to the crack tip, alongwith the environmental contribution to cracking. Since thesechemical and mechanical influences cannot be separated insome mat
33、erial/environment combinations, thickness must betreated as a variable. In this test method, however, the stress inthe specimen must remain elastic. For these reasons, twothreshold values of EAC are defined by this test method. Themeasurement of KIEACrequires that the thickness requirementsof plane
34、strain constraint are met. The less restrictive require-ments of KEACare intended for those conditions in which theresults are a strong function of the thickness of the specimenand the application requires the testing of specimens withthickness representative of the application.4The boldface numbers
35、 in parentheses refer to the list of references at the end ofthis standard.E1681 03 (2008)224.4 A variety of environmental (temperature, environmentcomposition, and electrode potential, for example) and metal-lurgical (yield strength, alloy composition, and specimenorientation) variables affect KEAC
36、and KIEAC.5. Significance and Use5.1 The parameters KEACor KIEACdetermined by this testmethod characterize the resistance to crack growth of amaterial with a sharp crack in specific environments underloading conditions in which the crack-tip plastic region is smallcompared with the crack depth and t
37、he uncracked ligament.The less restrictive thickness requirements of KEACare in-tended for those conditions in which the results are a strongfunction of the thickness of the specimen and the applicationrequires the testing of specimens with thickness representativeof the application. Since the chemi
38、cal and mechanical influ-ences cannot be separated, in some material/environmentcombinations, the thickness must be treated as a variable. AKEACor KIEACvalue is believed to represent a characteristicmeasurement of environment-assisted cracking resistance in aprecracked specimen exposed to an environ
39、ment under sus-tained tensile loading. A KEACor KIEACvalue may be used toestimate the relationship between failure stress and defect sizefor a material under any service condition, where the combi-nation of crack-like defects, sustained tensile loading and thesame specific environment would be expec
40、ted to occur. (Back-ground information concerning the development of this testmethod can be found in Refs (3-18).5.1.1 The apparent KEACor KIEACof a material under agiven set of chemical and electrochemical environmentalconditions is a function of the test duration. It is difficult tofurnish a rigor
41、ous and scientific proof for the existence of athreshold (4, 5). Therefore, application of KEACor KIEACdatain the design of service components should be made withawareness of the uncertainty inherent in the concept of a truethreshold for environment-assisted cracking in metallic mate-rials (6, 18).
42、A measured KEACor KIEACvalue for a particularcombination of material and environment may, in fact, repre-sent an acceptably low rate of crack growth rather than anabsolute upper limit for crack stability. Care should be exer-cised when service times are substantially longer than testtimes.5.1.2 The
43、degree to which force deviations from statictensile stress will influence the apparent KEACor KIEACof amaterial is largely unknown. Small-amplitude cyclic loading,well below that needed to produce fatigue crack growth,superimposed on sustained tensile loading was observed tosignificantly lower the a
44、pparent threshold for stress corrosioncracking in certain instances (7, 8). Therefore, caution shouldbe used in applying KEACor KIEACdata to service situationsinvolving cyclic loading. In addition, since this standard is forstatic loading, small-amplitude cyclic loading should beavoided during testi
45、ng.5.1.3 In some material/environment combinations, thesmaller the specimen, the lower the measured KEACvalue,while in other material/environment combinations the mea-sured KIEACvalue will be the lowest value (5, 9, 10, 11, 12). If,for the material/environment combination of interest, it is notknown
46、 which specimen size will result in the lower measuredvalue, then it is suggested that the use of both specimen sizesshould be considered; that is, specimens with thicknessesrepresentative of the application and specimens in which thethickness meets the requirements (see 7.2.1)ofaKIEACvalue.5.1.3.1
47、The user may optionally determine and report aKEACvalue or a KIEACvalue. The specimen size validityrequirements for a KEACvalue meet the size requirementsdeveloped for Test Method E647 to achieve predominatelyelastic behavior in the specimen. Test Method E647 sizerequirements for compact specimens s
48、hould be applied to boththe compact specimen and the beam specimen. The specimensize validity requirements for a KIEACvalue meet the sizerequirements developed for plane strain conditions for TestMethod E399.5.1.4 Evidence of environment-assisted crack growth underconditions that do not meet the val
49、idity requirements of 7.2may provide an important indication of susceptibility toenvironmental cracking but cannot be used to determine a validKEACvalue (14).5.1.5 Environment-assisted cracking is influenced by bothmechanical and electrochemical driving forces. The latter canvary with crack depth, opening, or shape and may not beuniquely described by the fracture mechanics stress intensityfactor. As an illustrative example, note the strong decreasereported in KISCC5with decreasing crack size below 5 mm forsteels in 3 % NaCl in water
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