1、Designation: E1221 12Standard Test Method forDetermining Plane-Strain Crack-Arrest Fracture Toughness,KIa, of Ferritic Steels1This standard is issued under the fixed designation E1221; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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.1. Scope1.1 This test method employs a side-grooved, crack-line-wedge-loaded specimen to obtain a rapid run-arrest s
3、egment offlat-tensile separation with a nearly straight crack front. Thistest method provides a static analysis determination of thestress intensity factor at a short time after crack arrest. Theestimate is denoted Ka. When certain size requirements aremet, the test result provides an estimate, term
4、ed KIa,oftheplane-strain crack-arrest toughness of the material.1.2 The specimen size requirements, discussed later, pro-vide for in-plane dimensions large enough to allow the speci-men to be modeled by linear elastic analysis. For conditions ofplane-strain, a minimum specimen thickness is also requ
5、ired.Both requirements depend upon the crack arrest toughness andthe yield strength of the material. A range of specimen sizesmay therefore be needed, as specified in this test method.1.3 If the specimen does not exhibit rapid crack propagationand arrest, Kacannot be determined.1.4 The values stated
6、 in SI units are to be regarded as thestandards. The values given in parentheses are provided forinformation only.1.5 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 s
7、afety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E8 Test Methods for Tension Testing of Metallic MaterialsE23 Test Methods for Notched Bar Impact Testing ofMetallic MaterialsE208 Test Method for Conducting D
8、rop-Weight Test toDetermine Nil-Ductility Transition Temperature of FerriticSteelsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE616 Terminology Relating to Fracture Testing3E1304 Test Method for Plane-Strain (Chevron-Notch) Frac-ture Toughness of Metalli
9、c MaterialsE1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Definitions:3.1.1 Definitions in Terminology E1823 are applicable tothis test method.3.2 Definitions of Terms Specific to This Standard:3.2.1 conditional value of the plane-strain crack-arrestfracture toughness,
10、KQa(FL3/2)the conditional value of KIacalculated from the test results and subject to the validitycriteria specified in this test method.3.2.1.1 DiscussionIn this test method, side-groovedspecimens are used. The calculation of KQais based uponmeasurements of both the arrested crack size and of thecr
11、ack-mouth opening displacement prior to initiation of afast-running crack and shortly after crack arrest.3.2.2 crack-arrest fracture toughness, KA(FL3/2)thevalue of the stress intensity factor shortly after crack arrest asdetermined from dynamic methods of analysis.3.2.2.1 DiscussionThe in-plane spe
12、cimen dimensionsmust be large enough for adequate enclosure of the crack-tipplastic zone by a linear-elastic stress field.3.2.3 crack-arrest fracture toughness, Ka(FL3/2)thevalue of the stress intensity factor shortly after crack arrest, asdetermined from static methods of analysis.1This test method
13、 is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved May 1, 2012. Published July 2012. Originally approvedin 1988. Last previous edition approved in 2010 as E1221 10. DOI: 10.1520
14、/E1221-12.2For 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.3Withdrawn. The last approved version of this histo
15、rical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.3.1 DiscussionThe in-plane specimen dimensionsmust be large enough for adequate enclosure of the crack-tipplastic zone by a linear-elasti
16、c stress field.3.2.4 plane-strain crack-arrest fracture toughness, KIa(FL3/2)the value of crack-arrest fracture toughness, Ka, fora crack that arrests under conditions of crack-front plane-strain.3.2.4.1 DiscussionThe requirements for attaining condi-tions of crack-front plane-strain are specified i
17、n the proceduresof this test method.3.2.5 stress intensity factor at crack initiation, Ko(FL3/2)the value of K at the onset of rapid fracturing.3.2.5.1 DiscussionIn this test method, only a nominalestimate of the initial driving force is needed. For this reason,Kois calculated on the basis of the or
18、iginal (machined) crack(or notch) size and the crack-mouth opening displacement atthe initiation of a fast-running crack.4. Summary of Test Method4.1 This test method estimates the value of the stressintensity factor, K, at which a fast running crack will arrest.This test method is made by forcing a
19、 wedge into a split-pin,which applies an opening force across the crack starter notch ina modified compact specimen, causing a run-arrest segment ofcrack extension. The rapid run-arrest event suggests need for adynamic analysis of test results. However, experimental obser-vations (1, 2)4indicate tha
20、t, for this test method, an adjustedstatic analysis of test results provides a useful estimate of thevalue of the stress intensity factor at the time of crack arrest.4.2 Calculation of a nominal stress intensity at initiation, Ko,is based on measurements of the machined notch size and thecrack-mouth
21、 opening displacement at initiation. The value ofKais based on measurements of the arrested crack size and thecrack-mouth opening displacements prior to initiation andshortly after crack arrest.5. Significance and Use5.1 In structures containing gradients in either toughness orstress, a crack may in
22、itiate in a region of either low toughnessor high stress, or both, and arrest in another region of eitherhigher toughness or lower stress, or both. The value of thestress intensity factor during the short time interval in which afast-running crack arrests is a measure of the ability of thematerial t
23、o arrest such a crack. Values of the stress intensityfactor of this kind, which are determined using dynamicmethods of analysis, provide a value for the crack-arrestfracture toughness which will be termed KAin this discussion.Static methods of analysis, which are much less complex, canoften be used
24、to determine K at a short time (1 to 2 ms) aftercrack arrest. The estimate of the crack-arrest fracture toughnessobtained in this fashion is termed Ka. When macroscopicdynamic effects are relatively small, the difference between KAand Kais also small (1-4). For cracks propagating underconditions of
25、crack-front plane-strain, in situations where thedynamic effects are also known to be small, KIadeterminationsusing laboratory-sized specimens have been used successfullyto estimate whether, and at what point, a crack will arrest in astructure (5, 6). Depending upon component design, loadingcomplian
26、ce, and the crack jump length, a dynamic analysis ofa fast-running crack propagation event may be necessary inorder to predict whether crack arrest will occur and the arrestposition. In such cases, values of KIadetermined by this testmethod can be used to identify those values of K below whichthe cr
27、ack speed is zero. More details on the use of dynamicanalyses can be found in Ref (4).5.2 This test method can serve at least the followingadditional purposes:5.2.1 In materials research and development, to establish inquantitative terms significant to service performance, theeffects of metallurgica
28、l variables (such as composition or heattreatment) or fabrication operations (such as welding or form-ing) on the ability of a new or existing material to arrestrunning cracks.5.2.2 In design, to assist in selection of materials for, anddetermine locations and sizes of, stiffeners and arrestor plate
29、s.6. Apparatus6.1 The procedure involves testing of modified compactspecimens that have been notched by machining. To minimizethe introduction of additional energy into the specimen duringthe run-arrest event, the loading system must have a lowcompliance compared with the test specimen. For this rea
30、son awedge and split-pin assembly is used to apply a force on thecrack line. This loading arrangement does not permit easymeasurement of opening forces. Consequently, opening dis-placement measurements in conjunction with crack size andcompliance calibrations are used for calculating Koand Ka.6.2 Lo
31、ading Arrangement:6.2.1 A typical loading arrangement is shown in Fig. 1. Thespecimen is placed on a support block whose thickness shouldbe adequate to allow completion of the test without interfer-ence between the wedge and the lower crosshead of the testingmachine. The support block should contain
32、 a hole that isaligned with the specimen hole, and whose diameter should bebetween 1.05 and 1.15 times the diameter of the hole in thespecimen. The force that pushes the wedge into the split-pin istransmitted through a force transducer.6.2.1.1 The surfaces of the wedge, split-pin, support block,and
33、specimen hole should be lubricated. Lubricant in the formof thin (0.13 mm or 0.005 in.) strips of TFE-fluorocarbon ispreferred. Molybdenum disulfide (both dry and in a greasevehicle) and high-temperature lubricants can also be used.6.2.1.2 A low-taper-angle wedge and split-pin arrangementis used. If
34、 grease or dry lubricants are used, a matte finish (gritblasted) on the sliding surfaces may be helpful in avoidinggalling. The split-pin must be long enough to contact the fullspecimen thickness, and the radius must be large enough toavoid plastic indentations of the test specimen. In all cases it
35、isrecommended that the diameter of the split-pin should be 0.13mm (0.005in.) less than the diameter of the specimen hole. Thewedge must be long enough to develop the maximum expectedopening displacement. Any air or oil hardening tool steel issuitable for making the wedge and split-pins.Ahardness in
36、therange from RC45 to RC55 has been used successfully. With therecommended wedge angle and proper lubrication, a loading4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.E1221 122machine producing15 to110 the expected maximum openingforce is adequate.
37、 The dimensions of a wedge and split-pinassembly suitable for use with a 25.4-mm (1.0-in.) diameterloading hole are shown in Fig. 2. The dimensions should bescaled when other hole diameters are used. A hole diameter of1.0 in. has been found satisfactory for specimens having 125 W 170 mm (5 W 6.7 in.
38、).NOTE 1Specimens tested with the arrangement shown in Fig. 1 maynot exhibit an adequate segment of run-arrest fracturing, for example, attesting temperatures well above the NDT temperature. In these circum-stances, the use of the loading arrangement shown in Fig. 3 has been foundto be helpful (2, 7
39、) and may be employed.6.3 Displacement GagesDisplacement gages are used tomeasure the crack-mouth opening displacement at 0.25W fromthe load-line. Accuracy within 2 % over the working range isrequired. Either the gage recommended in Test Method E399or a similar gage modified to accommodate conical s
40、eats issatisfactory. It is necessary to attach the gage in a fashion suchthat seating contact with the specimen is not altered by thejump of the crack. Two methods that have proven satisfactoryfor doing this are shown in Fig. 4. Other gages can be used solong as their accuracy is within 2 %.7. Speci
41、men Configuration, Dimensions, and Preparation7.1 Standard Specimen:7.1.1 The configuration of a compact-crack-arrest (CCA)specimen that is satisfactory for low- and intermediatestrengthsteels is shown in Fig. 5. (In this context, an intermediate-strength steel is considered to be one whose static y
42、ield stress,sYS, is of the order of 700 MPa (100 ksi) or less.)7.1.1.1 The thickness, B, shall be either full product platethickness or a thickness sufficient to produce a condition ofplane-strain, as specified in 9.3.3.7.1.1.2 Side grooves of depth B/8 per side shall be used. Foralloys that require
43、 notch-tip embrittlement (see 7.1.3.2) theside grooves should be introduced after deposition of the brittleweld.7.1.1.3 The specimen width, W, shall be within the range 2B# W # 8B.7.1.1.4 The displacement gage shall measure opening dis-placements at an offset from the load line of 0.25W, away fromth
44、e crack tip.7.1.2 Specimen Dimensions:7.1.2.1 In order to limit the extent of plastic deformation inthe specimen prior to crack initiation, certain size requirementsmust be met. These requirements depend upon the materialyield strength. They also depend upon Ka, and therefore the Koneeded to achieve
45、 an appropriate run-arrest event.7.1.2.2 The in-plane specimen dimensions must be largeenough to allow for the linear elastic analysis employed by thistest method. These requirements are given in 9.3.2 and 9.3.4,interms of allowable crack jump lengths.7.1.2.3 For a test result to be termed plane-str
46、ain (KIa)bythis test method, the specimen thickness, B, should meet therequirement given in 9.3.3.7.1.3 Starting Notch:7.1.3.1 The function of the starting notch is to produce crackinitiation at an opening displacement (or wedging force) thatwill permit an appropriate length of crack extension prior
47、 tocrack arrest. Different materials require different starter notchpreparation procedures.7.1.3.2 The recommended starter notch for low- andintermediate-strength steels is a notched brittle weld, as shownin Fig. 6. It is produced by depositing a weld across thespecimen thickness. Guidelines on weld
48、ing procedures aregiven in Appendix X1.7.1.3.3 Alternative crack starter configurations (8) and em-brittlement methods may also be used. Examples of bothalternative configurations and alternative test methods are alsodescribed in Appendix X1.7.1.3.4 While it is expected that aovalues for the startin
49、gnotch will typically lie in the range 0.30 W # ao# 0.40 W, itis sometimes useful to utilize values as low as 0.20 W. Thelower initial value of ao/Wresults in a greater and quicker dropin the crack driving force as the crack extends. This may aid inarresting the running crack at a shorter final crack length andcould be useful for conditions where the crack extension is toogreat with larger initial ao/W values.8. Procedure8.1 Number of TestsIt is recommended that at least threevalid test results be obtained at a single test temperature.FIG. 1 Schematic Pictorial a
