1、Designation: E 1221 06Standard Test Method forDetermining Plane-Strain Crack-Arrest Fracture Toughness,KIa, of Ferritic Steels1This standard is issued under the fixed designation E 1221; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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 employs a side-grooved, crack-line-wedge-loaded specimen to obtain a rapid run-arres
3、t segment 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, t
4、ermed 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 r
5、equired.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 sta
6、ted 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-priat
7、e safety 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 MaterialsE 208 Test Method for Conducti
8、ng Drop-Weight Test toDetermine Nil-Ductility Transition Temperature of FerriticSteelsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 616 Terminology Relating to Fracture Testing (Discontin-ued 1996)3E 1304 Test Method for Plane-Strain (Chevron-Notch)Fra
9、cture Toughness of Metallic MaterialsE 1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Definitions:3.1.1 Definitions in Terminology E 1823 are applicable tothis test method.3.2 Definitions of Terms Specific to This Standard:3.2.1 conditional value of the plane-strain crac
10、k-arrestfracture toughness, 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 arre
11、sted crack size and of thecrack-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.
12、1 DiscussionThe in-plane specimen 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 o
13、f analysis.3.2.3.1 DiscussionThe in-plane specimen dimensionsmust be large enough for adequate enclosure of the crack-tipplastic zone by a linear-elastic 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 arres
14、ts under conditions of crack-front plane-strain.1This test method is under the jurisdiction ofASTM Committee E08 on FractureTesting and is the direct responsibility of Subcommittee E08.07 on Linear-ElasticFracture.Current edition approved Jan. 15, 2006. Published February 2006. Originallyapproved in
15、 1988. Last previous edition approved in 2002 as E 1221 96 (2002).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 web
16、site.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4.1 DiscussionThe requirements for attaining condi-tions of crack-front plane-strain are specified in the proceduresof this test method.3.2.5 stress intensity factor
17、 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 original (machined) crack(or notch) size and the crack-mouth openin
18、g 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 wedge into a split-pin,which applies an opening force across the
19、 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 that, for this test method, an adjustedstatic analysis of test resul
20、ts 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 opening displacement at initiation. The value ofKais based on me
21、asurements 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 initiate in a region of either low toughnessor high stress, or both
22、, 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 to arrest such a crack. Values of the stress intensityfactor of th
23、is 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 to determine K at a short time (1 to 2 ms) aftercrack arrest. The
24、 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 crack-front plane-strain, in situations where thedynamic effects
25、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, loadingcompliance, and the crack jump length, a dynamic analysis ofa fast-runnin
26、g 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 crack speed is zero. More details on the use of dynamicanalyses can
27、 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 metallurgical variables (such as composition or heattreatment) or fabrication
28、 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 plates.6. Apparatus6.1 The procedure involves testing of modified comp
29、actspecimens 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 reason awedge and split-pin assembly is used to apply a force on the
30、crack 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 Loading Arrangement:6.2.1 A typical loading arrangement is shown in
31、 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 a hole that isaligned with the specimen hole, and whose diameter
32、 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 specimen hole should be lubricated. Lubricant in the formof thin
33、(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 grease or dry lubricants are used, a matte finish (gritblasted)
34、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 isrecommended that the diameter of the split-pin should be 0.13mm
35、 (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 therange from RC45 to RC55 has been used successfully. With there
36、commended wedge angle and proper lubrication, a loadingmachine producing15 to110 the expected maximum openingforce is adequate. 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 othe
37、r hole diameters are used. A hole diameter of4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.E12210621.0 in. has been found satisfactory for specimens having 125 W 170 mm (5 W 6.7 in.).NOTE 1Specimens tested with the arrangement shown in Fig. 1 mayn
38、ot 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) and may be employed.6.3 Displacement GagesDisplacement gages are
39、 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 E 399or a similar gage modified to accommodate conical seats issatisfactory. It is necessary to attach the gage in a fash
40、ion 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. Specimen Configuration, Dimensions, and Preparation7.1 Standard Specim
41、en: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 yield stress,sYS, is of the order of 700 MPa (100 ksi) or less.)7.
42、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 notch-tip embrittlement (see 7.1.3.2) theside grooves should be
43、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 fromthe crack tip.7.1.2 Specimen Dimensions:7.1.2.1 In order to limit t
44、he 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 an appropriate run-arrest event.7.1.2.2 The in-plane specimen di
45、mensions 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-strain (KIa)bythis test method, the specimen thickness, B, should me
46、et 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 tocrack arrest. Different materials require different starter no
47、tchpreparation 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 welding procedures aregiven in Appendix X1.7.1.3.3 Alternative crack
48、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 startingnotch will typically lie in the range 0.30 W # ao# 0.40 W, itis
49、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.8.2 Specimen MeasurementMeasure the specimen thick-ness, B, and the crack plane thickness, BN,
