1、Designation: E1681 03 (Reapproved 2008)1Standard 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 2010.1. Scope1.1 This test met
3、hod 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 from constant-displacement testing offatigue precracked bolt-load
4、 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 long as specimens are ofsufficient thickness and planar size t
5、o 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 independent of planar size.1.5 Specimen configurations other than
6、 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.1.6 This standard does not purport to address all of thesafety
7、 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 Documents2.1 ASTM Standards:2D1141 Practice for the Preparation
8、 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 RatesE1823 Terminology Relating to Fatigue and Fracture Test-ingG1 P
9、ractice 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. Terminology3.1 Definitions:3.1.1 For definitions of terms relat
10、ing 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 processthat requires the simultaneous action of a corrodent andsu
11、stained 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 of material andenvironment and where the specimen size is suff
12、icient 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 not1This test method is under the jurisdiction of ASTM Committ
13、ee 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 2003 as E1681 - 03. DOI:10.1520/E1681-03R08.2For referenced ASTM
14、 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 last approved version of this historical standard is referencedon
15、 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 on specimenthickness.3.1.6 physical crack size (apL)the distance
16、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 or a planecontaining either the loadline or the centerline of a s
17、pecimen 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 to the back edge of the specimen (bo=Wao).3.1.9 specimen thickness
18、 (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 testcarried to rupture and the original cross-section area of thespe
19、cimen.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 environment.3.2.2 normalized crack size (a/W)the ratio of crack s
20、ize,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 at which amaterial exhibits a specific limiting deviation from the
21、 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 uniaxial yield strength that represents the influences ofplastic yi
22、elding 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 a referenceplane to the front of the machined notch. The referen
23、ce 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. Summary of Test Method4.1 This test method involves testing of single-
24、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 thespecimen, or the specimen is contained within the chamber.The chamb
25、er 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 or otherwiseheld under constant force or held under constant disp
26、lacement(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 crack growthoccurs. The stress intensity factor (K) is calculate
27、d 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 value substantially lessthan the measured KIEACor KEACvalues. For c
28、onstant 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 depends on meeting thesize requirements to ensure plane strain conditi
29、ons, 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 environment-assisted crack growth. Crack growth rateinformation can be
30、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 combination of material and environmental pro-vides no insight in
31、to 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 interpreted by either theory of environment-assistedcracking.4.3 Specim
32、en 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 material/environment combinations, thickness must betreated as a var
33、iable. 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 strain constraint are met. The less restrictive require-ments of
34、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 in parentheses refer to the list of references at the end ofthis
35、 standard.E1681 03 (2008)124.4 A variety of environmental (temperature, environmentcomposition, and electrode potential, for example) and metal-lurgical (yield strength, alloy composition, and specimenorientation) variables affect KEACand KIEAC.5. Significance and Use5.1 The parameters KEACor KIEACd
36、etermined 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 the uncracked ligament.The less restrictive thickness requirements
37、 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 chemical and mechanical influ-ences cannot be separated, in some mater
38、ial/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 environment under sus-tained tensile loading. A KEACor KIEACvalue may be
39、 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 expected to occur. (Back-ground information concerning the development
40、 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 rigorous and scientific proof for the existence of athreshold (4, 5).
41、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). A measured KEACor KIEACvalue for a particularcombination of mater
42、ial 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 degree to which force deviations from statictensile stress will i
43、nfluence 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 apparent threshold for stress corrosioncracking in certain instanc
44、es (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 testing.5.1.3 In some material/environment combinations, thesmaller th
45、e 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 which specimen size will result in the lower measuredvalue, then
46、 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 The user may optionally determine and report aKEACvalue or a KIEA
47、Cvalue. 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 should be applied to boththe compact specimen and the beam specime
48、n. 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 validity requirements of 7.2may provide an important indication of s
49、usceptibility 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 solution (15). Geometry effects onK similitude should be experiment
