1、Designation: G 129 00 (Reapproved 2006)Standard Practice forSlow Strain Rate Testing to Evaluate the Susceptibility ofMetallic Materials to Environmentally Assisted Cracking1This standard is issued under the fixed designation G 129; the number immediately following the designation indicates the year
2、 oforiginal adoption or, in 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 practice covers procedures for the design, prepara
3、-tion, and use of axially loaded, tension test specimens andfatigue pre-cracked (fracture mechanics) specimens for use inslow strain rate (SSR) tests to investigate the resistance ofmetallic materials to environmentally assisted cracking (EAC).While some investigators utilize SSR test techniques in
4、com-bination with cyclic or fatigue loading, no attempt has beenmade to incorporate such techniques into this practice.1.2 Slow strain rate testing is applicable to the evaluation ofa wide variety of metallic materials in test environments whichsimulate aqueous, nonaqueous, and gaseous service envir
5、on-ments over a wide range of temperatures and pressures thatmay cause EAC of susceptible materials.1.3 The primary use of this practice is to furnish acceptedprocedures for the accelerated testing of the resistance ofmetallic materials to EAC under various environmental condi-tions. In many cases,
6、the initiation of EAC is acceleratedthrough the application of a dynamic strain in the gauge sectionor at a notch tip or crack tip, or both, of a specimen. Due to theaccelerated nature of this test, the results are not intended tonecessarily represent service performance, but rather to pro-vide a ba
7、sis for screening, for detection of an environmentalinteraction with a material, and for comparative evaluation ofthe effects of metallurgical and environmental variables onsensitivity to known environmental cracking problems.1.4 Further information on SSR test methods is available inISO 7539 and in
8、 the references provided with this practice(1-6).21.5 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibi
9、lity 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. Furthermore, insome cases, special facilities will be required to isolate thesetests from laboratory personnel if high pressures or toxicch
10、emical environments, or both, are utilized in SSR testing.2. Referenced Documents2.1 ASTM Standards:3A 370 Test Methods and Definitions for Mechanical Testingof Steel ProductsB 557 Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy ProductsD 1193 Specification for Reagent
11、 WaterE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE8 Test Methods for Tension Testing of Metallic MaterialsE 399 Standard Test Method for Linear-Elastic Plane-StrainFracture Toughness KIcof Metallic MaterialsE 602 Test Method for Sh
12、arp-Notch Tension Testing withCylindrical SpecimensE 616 Terminology Relating to Fracture Testing4E 647 Test Method for Measurement of Fatigue CrackGrowth RatesE 1681 Test Method for Determining Threshold Stress In-tensity Factor for Environment-Assisted Cracking of Me-tallic MaterialsG15 Terminolog
13、y Relating to Corrosion and CorrosionTestingG49 Practice for Preparation and Use of Direct TensionStress-Corrosion Test SpecimensG 111 Guide for Corrosion Tests in High Temperature orHigh Pressure Environment, or BothG 142 Test Method for Determination of Susceptibility of1This practice is under the
14、 jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-tally Assisted Cracking.Current edition approved Nov. 1, 2006. Published December 2006. Originallyapproved in 1995. Last previous edition approved in 2000 as G 129 00.2The
15、boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For 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 Summ
16、ary page onthe ASTM website.4Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Metals to Embrittlement in Hydrogen Containing Environ-ments at High Pressure, High Temperature, or Both2.2 ISO Standard:5ISO 7539 Part 7, Slow St
17、rain Rate Testing3. Terminology3.1 For purposes of this practice the following terms aredefined:3.2 control environmentan environment in which SSRspecimens are tested that has been shown not to cause EAC orexcessive corrosion of the material. The results of testsconducted in this environment may be
18、used as a basis forcomparison with corresponding tests conducted in the testenvironment(s), usually at the same temperature as the testenvironment.3.3 environmentally assisted cracking (EAC) cracking ofa material caused by the combined effects of stress and thesurrounding environment, for example, s
19、tress corrosion crack-ing, hydrogen embrittlement cracking, sulfide stress crackingand liquid metal embrittlement.3.4 slow strain rate (SSR)a dynamic slowly increasingstrain imposed by an external means on the gauge section ornotch tip of a uniaxial tension specimen or crack tip of a fatiguepre-crac
20、ked specimen for purposes of materials evaluation.The strain rate for a plain or smooth specimen (given in unitsof extension divided by the gage length per unit time) or thestrain rate at a notch tip of a notched tension specimen or cracktip of a fatigue pre-cracked specimen is applied through theap
21、plication of a slow constant extension rate (given in units ofextension per unit time). The slow constant extension rateproduces a gauge section strain rate, which is usually in therange from 104to 107/s1. Rigorous analytical solutions ofthe local strain rate at a notch tip of a tension specimen or
22、at acrack tip of a fatigue pre-cracked specimen are not available.The average or local strain rate should be slow enough to allowtime for certain corrosion processes to take place, but fastenough to produce failure or cracking of the specimen in areasonable period of time for evaluation purposes. In
23、 caseswhere extremely slow strain rates are being utilized (that is,107to 108/s1for smooth tension specimens), an interruptedSSR test can be employed whereby the specimen is strainedinto the plastic range at the intended strain rate followed bymore rapid straining to failure.3.5 The terminology foun
24、d in Test Methods and DefinitionsA 370, Test Method B 557, and Test Method E 602 along withthe definitions given in Terminologies E6, E 616, and G15shall apply to the terms used in this practice.4. Summary of Practice4.1 This practice describes the use of tension and fatiguepre-cracked specimens for
25、 the determination of resistance toEAC of metallic materials. The procedure involves the appli-cation of very slow strain rates, which are achieved by aconstant extension rate on the specimen while monitoring loadand extension of the specimen. The SSR test always producesfracture of the test specime
26、n. Typically, the results from testsconducted in the test environment are compared to correspond-ing test results for the same material in a control environment.The degree of susceptibility to EAC is generally assessedthrough observation of the differences in the behavior of thematerial in tests con
27、ducted in a test environment from thatobtained from tests conducted in the control environment. Forsmooth tension specimens, either changes in time-to-failure, orspecimen ductility, or visual indications of EAC, or often somecombination of these methods, are utilized in determiningsusceptibility to
28、EAC. For notched tension specimens, changesin the notch tensile strength and visual indications of EAC onthe primary fracture surface are used in determining suscepti-bility to EAC. For fatigue pre-cracked specimens, changes inthe threshold stress intensity factor and visual indications ofEAC on the
29、 primary fracture surface are used in determiningsusceptibility to EAC.5. Significance and Use5.1 The slow strain rate test is used for relatively rapidscreening or comparative evaluation, or both, of environmen-tal, processing or metallurgical variables, or both, that canaffect the resistance of a
30、material to EAC. For example, thistesting technique has been used to evaluate materials, heattreatments, chemical constituents in the environment, andtemperature and chemical inhibitors.5.2 Where possible, the application of the SSR test and dataderived from its use should be used in combination wit
31、hservice experience or long-term EAC data, or both, obtainedthrough literature sources or additional testing using othertesting techniques. In applications where there has been little orno prior experience with SSR testing or little EAC data on theparticular material/environment combination of inter
32、est, thefollowing steps are recommended:5.2.1 The SSR tests should be conducted over a range ofapplied extension rates (that is, usually at least one order ofmagnitude in applied extension rate above and below 106in/s(2.54 3 105mm/s) to determine the effect of strain rate or rateof increase of the s
33、tress or stress intensity factor on suscepti-bility to EAC.5.2.2 Constant load or strain EAC tests should also beconducted in simulated service environments, and serviceexperience should be obtained so that a correlation betweenSSR test results and anticipated service performance can bedeveloped.5.3
34、 In many cases the SSR test has been found to be aconservative test for EAC. Therefore, it may produce failuresin the laboratory under conditions which do not necessarilycause EAC under service application. Additionally, in somelimited cases, EAC indications are not found in smooth tensionSSR tests
35、even when service failures have been observed. Thiseffect usually occurs when there is a delay in the initiation oflocalized corrosion processes. Therefore, the suggestions givenin 5.2 are strongly encouraged.5.4 In some cases, EAC will only occur in a specific rangeof strain rates. Therefore, where
36、 there is little prior informationavailable, tests should be conducted over a range of strain ratesas discussed in 5.2.5Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.G 129 00 (2006)26. Apparatus6.1 Testing Machines:6.1.1
37、 Tension testing machines used for SSR testing shallconform to the requirements of Practices E4.6.1.2 The loads used in SSR testing shall be within thecalibrated load ranges of the testing machine in accordancewith Practices E4.6.1.3 The testing machines used for SSR testing shall becapable of accur
38、ate application of extension rates in the rangeof interest for evaluation of EAC. These extension rates areusually between 104and 107in/s (2.54 3 103and 2.54 3106mm/s).6.1.4 An example of a SSR testing machine setup includingthe load frame, instrumentation, and local test cell is shown inFig. 1. Ano
39、ther example of a SSR machine setup with a metaltest cell or autoclave can be found in Test Method G 142. Thetest specimen is loaded with a grip assembly and load frameinside the autoclave. The autoclave is equipped with a tensileloading feed-through to provide transmission of loads from thetensile
40、machine to the specimen using a pull rod in combina-tion with the feed-through. Some SSR testing machines may beable to test more than one specimen at a time in a particularenvironment. However, this type of machine should only beused if it can be shown that failure of one or multiplespecimens does
41、not influence the behavior of the other speci-mens.6.2 Gripping DevicesThe types of gripping devices thatmay be used to transmit the applied load from the testingmachine to the tension specimen conform to those described inTest Methods E8. Alignment procedures are provided in TestMethod E8.6.3 Clevi
42、ces and FixturesA loading clevis that is suitablefor loading pre-cracked compact specimens should conformwith clevices described in Test Method E 399. A bend testfixture for loading pre-cracked bend specimens should conformwith bend fixtures described in Test Method E 399.Itisimportant that attentio
43、n be given to achieving good load trainalignment through careful machining of all clevices andfixtures.6.4 Displacement GaugesAn electronic crack mouthopening displacement (CMOD) gauge attached to the frontface of pre-cracked specimens and spanning the crack starternotch to detect crack growth durin
44、g testing should be inaccordance with displacement gauges described in TestMethod E 399. Alternatively, the displacements can be trans-ferred outside the environmental test cell in the case of testsconducted in high temperature or severely corrosive environ-ments.An extensometer placed outside the t
45、est cell can be usedto detect the crack growth. A displacement gauge can beattached to the specimen at alternative locations to detect crackgrowth if the proper compliance-crack length relationship hasbeen determined for the measurement location on the speci-men.6.5 Environmental Test CellsTest cell
46、s shall be con-structed in a manner to facilitate handling and monitoring ofthe test environment while allowing testing of the tensionspecimen. This will require the incorporation of a suitablelow-friction feed-through in the vessel for application of loadto the test specimen. Additionally, the test
47、 cell shall be able tosafely contain the test environment with adequate accommo-dation for the temperature and pressure under which the SSRtests will be conducted.6.5.1 Test cells shall be effectively inert (that is, have a lowcorrosion rate and not susceptible to EAC in the test environ-ment so tha
48、t they do not react with or contaminate theenvironment).6.5.2 The test cell size should be such that a solutionvolume-to-exposed specimen surface area is not less than 30mL/cm2.6.6 Galvanic EffectsEliminate galvanic effects betweenthe test specimen and various metallic components of thegripping fixt
49、ures and test cell by electrically insulating orisolating these components unless it is specifically desired tosimulate galvanic interactions found in service conditions andtheir effects on EAC. Check electrical isolation with anohmmeter, if required, prior to testing. It should be noted that,in some cases, electrical insulation may be bridged by depositsFIG. 1 An Example of a SSR Testing Machine.G 129 00 (2006)3of conductive or semiconductive solid corrosion productsduring the test, thereby introducing galvanic effects into theSSR test.7. Reagents7.1 As is the
