1、Designation: E 1681 03Standard Test Method forDetermining Threshold Stress Intensity Factor forEnvironment-Assisted Cracking of Metallic Materials1This standard is issued under the fixed designation E 1681; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of theenvironment-assisted cracking thr
3、eshold 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 compact fracture specimens.1.2 This test method is applicable to en
4、vironment-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 to meet the size require-ments of this test method.1.4 A range of spe
5、cimen 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 those contained inthis test method may be used, provided that well-
6、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 concerns, if any, associated with its use. It is theresponsibility
7、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:D 1141 Specification for Substitute Ocean Water2E8 Methods for Tension Testing of Metallic Materials3E
8、399 Test Method for Plane-Strain Fracture Toughness ofMetallic Materials3E 647 Test Method for Measurement of Fatigue CrackGrowth Rates3E 1823 Terminology Relating to Fatigue and Fracture Test-ing3G1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test Specimens4G5 Standard Reference Met
9、hod for Making Potentiostaticand Potentiodynamic Anodic Polarization Measurements4G15 Terminology Relating to Corrosion and CorrosionTesting43. Terminology3.1 Definitions:3.1.1 For definitions of terms relating to fracture testingused in this test method, refer to Terminology E 1823.3.1.2 For defini
10、tions 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 andsustained tensile stress.3.1.4 stress intensity factor threshold for plane strainenvironment-a
11、ssisted 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 sufficient to meetrequirements for plane strain as described in Test MethodE 399.3.1.5 stress in
12、tensity factor threshold for environment-assisted cracking (KEACFL3/2)the highest value of thestress intensity factor (K) at which crack growth is notobserved for a specified combination of material and environ-ment and where the measured value may depend on specimenthickness.3.1.6 physical crack si
13、ze (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 or a planecontaining either the loadline or
14、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.1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility
15、of Subcommittee E08.06 on CrackGrowth Behavior.Current edition approved Sept. 10, 2003. Published November 2003. Originallyapproved in 1995. Last previous edition approved in 1999 as E 1681 - 99e1.2Annual Book of ASTM Standards, Vol 11.02.3Annual Book of ASTM Standards, Vol 03.01.4Annual Book of AST
16、M Standards, Vol 03.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 (BL)the side-to-si
17、de 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 thespecimen.3.2 Definitio
18、ns 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 size,a, to specimen
19、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 propor-tionality o
20、f 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 yielding upon fractur
21、e 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 reference planedepends on
22、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-edge notchedSE(B) s
23、pecimens, 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 chamber must enclose the
24、 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 displacement(defined in
25、 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 calculated from anexpression
26、 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 constant dis-placeme
27、nt tests, the stress-intensity level at which the fatigueprecracking of the specimen is conducted is limited to therequirements of Test Method E 399. The validity of the KIEACvalue determined by this test method depends on meeting thesize requirements to ensure plane strain conditions, as stated inT
28、est Method E 399. The validity of the KEACvalue depends onmeeting the size requirements for linear elastic behavior, asstated in the Test Method E 647.4.1.2 This test method can produce information on the onsetof environment-assisted crack growth. Crack growth rateinformation can be obtained after c
29、rack nucleation, but themethod for obtaining this information is not part of this testmethod (1).54.2 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 into the particula
30、r 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 Specimen thickness gov
31、erns 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 variable. In this t
32、est 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 KEACare intended
33、 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.4.4 A variety of environmental (temperature, environmentcomposition, and electrode potential, for exam
34、ple) and metal-lurgical (yield strength, alloy composition, and specimenorientation) variables affect KEACand 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
35、 underloading conditions in which the crack-tip plastic region is smallcompared with the crack depth and the 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 app
36、lication5The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E1681032requires the testing of specimens with thickness representativeof the application. Since the chemical and mechanical influ-ences cannot be separated, in some material/environmentcombinatio
37、ns, 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 used toestimate the rela
38、tionship 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 of this testmethod can b
39、e 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). Therefore, application of
40、 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 material and environment may,
41、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 influence the apparent KEA
42、Cor 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 instances (7, 8). Therefore, cau
43、tion 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 the specimen, the lower the
44、 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 it is suggested that the
45、 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 KIEACvalue. The specimen size
46、 validityrequirements for a KEACvalue meet the size requirementsdeveloped for Test Method E 647 to achieve predominatelyelastic behavior in the specimen. Test Method E 647 sizerequirements for compact specimens should be applied to boththe compact specimen and the beam specimen. The specimensize val
47、idity requirements for a KIEACvalue meet the sizerequirements developed for plane strain conditions for TestMethod E 399.5.1.4 Evidence of environment-assisted crack growth underconditions that do not meet the validity requirements of 7.2may provide an important indication of susceptibility toenviro
48、nmental 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 inte
49、nsityfactor. As an illustrative example, note the strong decreasereported in KISCC6with decreasing crack size below 5 mm forsteels in 3 % NaCl in water solution (15). Geometry effects onK similitude should be experimentally assessed for specificmaterial/environment systems. Application modeling based onKEACsimilitude should be conducted with caution whensubstantial differences in crack and specimen geometry existbetween the specimen and the component.5.1.6 Not all combinations of material and environment willresult in environment-assisted crac
