1、Designation: E 1290 07e1Standard Test Method forCrack-Tip Opening Displacement (CTOD) FractureToughness Measurement1This standard is issued under the fixed designation E 1290; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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.e1NOTEEditorial changes made throughout in November 2007.1. Scope1.1 This test method covers the determination of criticalcr
3、ack-tip opening displacement (CTOD) values at one or moreof several crack extension events. These CTOD values can beused as measures of fracture toughness for metallic materials,and are especially appropriate to materials that exhibit a changefrom ductile to brittle behavior with decreasing temperat
4、ure.This test method applies specifically to notched specimenssharpened by fatigue cracking. The recommended specimensare three-point bend SE(B) compact C(T), or arc-shapedbend A(B) specimens. The loading rate is slow and influencesof environment (other than temperature) are not covered. Thespecimen
5、s are tested under crosshead or clip gage displacementcontrolled loading.1.1.1 The recommended specimen thickness, B, for theSE(B) and C(T) specimens is that of the material in thicknessesintended for an application. For the A(B) specimen, therecommended depth, W, is the wall thickness of the tube o
6、rpipe from which the specimen is obtained. Superficial surfacemachining may be used when desired.1.1.2 For the recommended three-point bend specimensSE(B), width, W, is either equal to, or twice, the specimenthickness, B, depending upon the application of the test. (See4.3 for applications of the re
7、commended specimens.) ForSE(B) specimens the recommended initial normalized cracksize is 0.45 # ao/W # 0.70. The span-to-width ratio (S/W)isspecified as 4.1.1.3 For the recommended compact specimen C(T) theinitial normalized crack size is 0.45 # ao/W # 0.70. Thehalf-height-to-width ratio (H/W) equal
8、s 0.6 and the width tothickness ratio W/B is specified to be 2.1.1.4 For the recommended arc-shaped bend A(B) speci-men, B is one-half the specimen depth, W. The initial normal-ized crack size is 0.45 0.6 to 1.0, a span to width ratio, S/W, of 4 may beused. For r1/r2ratios from 0.4 to 0.6, an S/W of
9、 3 may be used.1.2 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.
10、2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE8 Test Methods for Tension Testing of Metallic MaterialsE 399 Test Method for Plane-Strain Fracture Toughness ofMetallic MaterialsE 1820 Test Method for Measurement of Fracture Tough-nessE 1823 Termino
11、logy Relating to Fatigue and FractureTesting3. Terminology3.1 Terminology E 1823 is applicable to this test method.3.2 Definitions:3.2.1 crack tip opening displacement, (CTOD), dLthecrack displacement due to elastic and plastic deformation atvariously defined locations near the original (prior to an
12、application of force) crack tip.3.2.1.1 DiscussionIn this test method, CTOD is the dis-placement of the crack surfaces normal to the original (un-loaded) crack plane at the tip of the fatigue precrack, ao.In CTOD testing, dcL is the value of CTOD at the onset of unstablebrittle crack extension (see
13、3.2.13) or pop-in (see 3.2.7) when Dap0.2 mm (0.008 in.). The force Puand the clip gage1This test method 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 July 15, 2007. Publish
14、ed August 2007. Originallypublished in 1989. Last previous edition published in 2002 as E 1290 02e1.2For 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 Do
15、cument Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.displacement vu, for duare indicated in Fig. 1.3.2.2 effective yield strength, sYFL2an assumed valueof uniaxial yield strength that represents the
16、 influence of plasticyielding upon fracture test parameters.3.2.2.1 DiscussionThe calculation of sYis the average ofthe 0.2 % offset yield strength (sYS), and the tensile strength(sTS), that is (sYS+ sTS)/2. Both sYSand sTSare determined inaccordance with Test Methods E8.3.2.3 original crack size, a
17、oLsee Terminology E 1823.3.2.4 original uncracked ligament, boLthe distancefrom the original crack front to the back surface of thespecimen at the start of testing, bo= W ao.3.2.5 physical crack extension, DapLan increase inphysical crack size, Dap= ap ao.3.2.6 physical crack size, apLsee Terminolog
18、y E 1823.3.2.6.1 DiscussionIn CTOD testing, ap= ao+ Dap.3.2.7 pop-ina discontinuity in the force versus clip gagedisplacement record. The record of a pop-in shows a suddenincrease in displacement and, generally, a decrease in force.Subsequently, the displacement and force increase to abovetheir resp
19、ective values at pop-in.3.2.8 slow stable crack extension La displacement con-trolled crack extension beyond the stretch zone width (see3.2.12). The extension stops when the applied displacement isheld constant.3.2.9 specimen span, S Lthe distance between specimensupports in a bend specimen.3.2.10 s
20、pecimen thickness, BLsee Terminology E 1823.3.2.11 specimen width, W Lsee Terminology E 1823.3.2.12 stretch zone width, SZW Lthe length of crackextension that occurs during crack-tip blunting, for example,prior to the onset of unstable brittle crack extension, pop-in, orslow stable crack extension.
21、The SZW is in the same plane asthe original (unloaded) fatigue precrack and refers to anextension beyond the original crack size.3.2.13 unstable brittle crack extension Lan abrupt crackextension that occurs with or without prior stable crackextension in a standard test specimen under crosshead or cl
22、ipgage displacement control.4. Summary of Test Method4.1 The objective of the test is to determine the value ofCTOD at one of the following crack extension events. Thevalues of CTOD may correspond to: dc, the onset of unstablebrittle crack extension with no significant prior slow stablecrack extensi
23、on (see 3.2.1), or du, the onset of unstable brittlecrack extension following prior slow stable crack extension.4.2 The test method involves crosshead or clip gage dis-placement controlled three-point bend loading or pin loading offatigue precracked specimens. Force versus clip gage crackopening dis
24、placement is recorded, for example, Fig. 1. Theforces and displacements corresponding to the specific eventsin the crack initiation and extension process are used todetermine the corresponding CTOD values. For values of dcand du, the corresponding force and clip gage displacementsare obtained direct
25、ly from the test records.4.3 The rectangular section bend specimen and the compactspecimen are intended to maximize constraint and these aregenerally recommended for those through-thickness cracktypes and orientations for which such geometries are feasible.For the evaluation of surface cracks in str
26、uctural applicationsfor example, orientationsT-S or L-S (Terminology E 1823), thesquare section bend specimen is recommended. Also forcertain situations in curved geometry source material or weldedjoints, the square section bend specimen may be preferred.Square section bend specimens may be necessar
27、y in order tosample an acceptable volume of a discrete microstructure.4.4 The arc-shaped bend specimen permits toughness test-ing in the C-R orientation (Terminology E 1823), for pipe ortube. This orientation is of interest since pipes and tubes underpressure often fail with longitudinal cracks. The
28、 specimengeometry is convenient for obtaining samples with minimal useof material.NOTE 1Construction lines drawn parallel to the elastic loading slope to give vp, the plastic component of total displacement, vg.NOTE 2In curves b and d, the behavior after pop-in is a function of machine/specimen comp
29、liance, instrument response, etc.FIG. 1 Types of Force Versus Clip Gage Displacement RecordsE129007e125. Significance and Use5.1 This test method characterizes the fracture toughness ofmaterials through the determination of crack-tip opening dis-placement (CTOD) at one of two events: (a) onset of un
30、stablecrack extension without significant prior stable crack exten-sion, or (b) onset of unstable crack extension with significantprior stable crack extension. This test method may also be usedto characterize the toughness of materials for which theproperties and thickness of interest preclude the d
31、eterminationof Klcfracture toughness in accordance with Test MethodE 399.5.2 The different values of CTOD determined by this testmethod characterize the resistance of a material to crackinitiation and early crack extension at a given temperature.5.3 The values of CTOD may be affected by specimendime
32、nsions. It has been shown that values of CTOD deter-mined on SE(B) specimens using the square section geometrymay not be the same as those using the rectangular sectiongeometry, and may differ from those obtained with either the(C)T or (A)B specimens.5.4 The values of CTOD determined by this test me
33、thodmay serve the following purposes:5.4.1 In research and development, CTOD testing can showthe effects of certain parameters on the fracture toughness ofmetallic materials significant to service performance. Theseparameters include material composition, thermo-mechanicalprocessing, welding, and th
34、ermal stress relief.5.4.2 For specifications of acceptance and manufacturingquality control of base materials, weld metals, and weld heataffected zones.5.4.3 For inspection and flaw assessment criteria, when usedin conjunction with fracture mechanics analyses. Awareness ofdifferences that may exist
35、between laboratory test and fieldconditions is required to make proper flaw assessment (see 4.3and 4.4).6. Apparatus6.1 This procedure involves measurement of applied force,P, and clip gage crack opening displacement, v. Force versusdisplacement is autographically recorded on an x-y plotter forvisua
36、l display, or converted to and recorded in digital form forsubsequent processing. Testing is performed under crossheador clip gage displacement control in a compression or tensiontesting machine, or both, that conforms to the requirements ofPractices E4.6.2 Fixturing for Three-Point Bend SpecimensA
37、recom-mended SE(B) or A(B) specimen fixture is shown in Fig. 2.Friction effects between the support rollers and specimen arereduced by allowing the rollers to rotate during the test. Theuse of high hardness steel of the order of 40 HRC or more isrecommended for the fixture and rollers to prevent ind
38、entationof the platen surfaces.6.3 Tension Testing ClevisA loading clevis suitable fortesting C(T) specimens is shown in Fig. 3. Each leg of thespecimen is held by such a clevis and loaded through pins, inorder to allow rotation of the specimen during testing. Toprovide rolling contact between the l
39、oading pins and the clevisholes, these holes are produced with small flats on the loadingsurfaces. Other clevis designs may be used if it can bedemonstrated that they will accomplish the same result as thedesign shown. Clevises and pins should be fabricated fromsteels of sufficient strength and hard
40、ness (greater than 40 HRC)to elastically resist indentation forces. The critical tolerancesand suggested proportions of the clevis and pins are given inFig. 3. These proportions are based on specimens having W/B= 2 for B 12.7 mm (0.5 in.) and W/B = 4 for B #12.7 mm(0.5 in.). If a 1930-MPa (280 000-p
41、si) yield strength maragingsteel is used for the clevis and pins, adequate strength will beobtained. If lower strength grip material is used, or if substan-tially larger specimens are required at a given sYS/E ratio, thenheavier grips will be required.As indicated in Fig. 3, the clevisNOTE 1Roller p
42、ins and specimen contact surface of loading ram must be parallel to each other within 0.002W.NOTE 2 0.10 in. = 2.54 mm; 0.15 in. = 3.81 mm.FIG. 2 SE(B) Test Fixture DesignE129007e13corners may be cut off sufficiently to accommodate seating ofthe clip gage in specimens less than 9.5 mm (0.375 in.) th
43、ick.Attention should be given to achieving good alignment throughcareful machining of all auxiliary gripping fixtures.6.4 Displacement Measuring Devices:6.4.1 Displacement measuring gages are used to measureopening displacements on SE(B) specimens at either knifeedges a distance z beyond the crack m
44、outh, Fig. 4a, or at thecrack mouth (z = 0) in the case of integral knife edges, Fig. 4b.For C(T) specimens, where the opening displacement is notmeasured on the load line, the difference between the load lineand the displacement measuring point shall constitute thedimension z (see 9.2). Alternative
45、ly, when the opening dis-placements on C(T) specimens are made on or within 60.002W of the load line, it may be assumed that z = 0. For A(B)specimens, special measurements must be taken to establishlocation of the clip gage knife edges with respect to the crackplane. Paragaphs 8.9.4 and 8.9.5 provid
46、e more detail onrequired measurements.6.4.2 The clip gage recommended in Test Method E 399may be used in cases where the total expected displacement is2.5 mm (0.1 in.) or less. Sensitivity and linearity requirementsspecified in Test Method E 399, shall be met over the fullworking range of the gage.
47、In addition, the gage is to becalibrated to within6 1 % of the working range.6.4.3 For cases where a linear working range of up to 8 mm(0.3 in.) or more is needed, an enlarged gage such as thatshown in Fig. 5 can be used. Both linearity and accuracy of theequipment or system used shall be demonstrat
48、ed to be within61 % of the working range of the equipment.6.4.4 The seating between the clip gage and knife edgesshall be firm and free from friction drag.6.5 Force MeasurementThe sensitivity of the force sens-ing device shall be sufficient to avoid distortion caused by overamplification and the dev
49、ice shall have linearity identical tothat for the displacement signal. The combination of forcesensing device and recording system shall permit the force P tobe determined from the test record within an accuracy of61%.7. Specimen Configurations, Dimensions, andPreparation7.1 The SE(B) specimens, shown in Fig. 6 and Fig. 7, aretested with a span to width ratio, S/W, of 4. Therefore, it issuggested that overall specimen length should be at least 4.5 W.7.1.1 The standard bend specimens shall be of thickness, B,at least eq
