1、Designation: E740/E740M 03 (Reapproved 2016)Standard Practice forFracture Testing with Surface-Crack Tension Specimens1This standard is issued under the fixed designation E740/E740M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the design, preparation, and testingof surface-crack tension (SCT) specimens. It rela
3、tes specifi-cally to testing under continuously increasing force and ex-cludes cyclic and sustained loadings. The quantity determinedis the residual strength of a specimen having a semielliptical orcircular-segment fatigue crack in one surface. This valuedepends on the crack dimensions and the speci
4、men thickness aswell as the characteristics of the material.1.2 Metallic materials that can be tested are not limited bystrength, thickness, or toughness. However, tests of thickspecimens of tough materials may require a tension testmachine of extremely high capacity. The applicability of thispracti
5、ce to nonmetallic materials has not been determined.1.3 This practice is limited to specimens having a uniformrectangular cross section in the test section. The test sectionwidth and length must be large with respect to the crack length.Crack depth and length should be chosen to suit the ultimatepur
6、pose of the test.1.4 Residual strength may depend strongly upon tempera-ture within a certain range depending upon the characteristicsof the material. This practice is suitable for tests at anyappropriate temperature.1.5 Residual strength is believed to be relatively insensitiveto loading rate withi
7、n the range normally used in conventionaltension tests. When very low or very high rates of loading areexpected in service, the effect of loading rate should beinvestigated using special procedures that are beyond the scopeof this practice.NOTE 1Further information on background and need for this ty
8、pe oftest is given in the report of ASTM Task Group E24.01.05 on Part-Through-Crack Testing (1).21.6 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used in
9、dependently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.7 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 safet
10、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE338 Test Method of Sharp-Notch Tension Testi
11、ng of High-Strength Sheet Materials (Withdrawn 2010)4E399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE466 Practice for Conducting Force Controlled ConstantAmplitude Axial Fatigue Tests of Metallic MaterialsE561 Test Method forKRCurve DeterminationE1823 Term
12、inology Relating to Fatigue and Fracture Testing3. Terminology3.1 Definitions:3.1.1 Definitions given in Terminology E1823 are appli-cable to this practice.3.1.2 crack mouth opening displacement (CMOD), 2vm(L)crackopening displacement resulting from the totaldeformation (elastic plus plastic) measur
13、ed under force at thelocation on the crack surface that has the largest displacementper unit force.NOTE 2In surface-crack tension (SCT) specimens, CMOD is mea-sured on the specimen surface along the normal bisector of the cracklength.1This practice is under the jurisdiction ofASTM Committee E08 on F
14、atigue andFracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved Oct. 1, 2016. Published October 2016. Originallyapproved in 1988. Last previous edition approved in 2010 as E740/E740M 03(2010)2. DOI: 10.1520/E0740_E0740M-03R16.2The boldface num
15、bers in parentheses refer to the 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 Summary page o
16、nthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.3 fracture toughnessa generic term for measures ofresistance to extension of a c
17、rack. E6163.1.4 original crack size, aoLthe physical crack size atthe start of testing. (E616)3.2 Definitions of Terms Specific to This Standard:3.2.1 crack depth, a Lin surface-crack tension (SCT)specimens, the normal distance from the cracked plate surfaceto the point of maximum penetration of the
18、 crack front into thematerial. Crack depth is a fraction of the specimen thickness.3.2.1.1 DiscussionIn this practice, crack depth is theoriginal depth aoand the subscript o is everywhere implied.3.2.2 crack length, 2c Lin surface-crack tensionspecimens, a distance measured on the specimen surfacebe
19、tween the two points at which the crack front intersects thespecimen surface. Crack length is a fraction of specimen width.3.2.2.1 DiscussionIn this practice, crack length is theoriginal length 2coand the subscript o is everywhere implied.3.2.3 residual strength, r(FL2)the maximum value ofthe nomina
20、l stress, neglecting the area of the crack, that acracked specimen is capable of sustaining.NOTE 3In surface-crack tension (SCT) specimens, residual strength isthe ratio of the maximum load (Pmax) to the product of test section width(W) times thickness (B), Pmax/(BW). It represents the stress at fra
21、cturenormal to and remote from the plane of the crack.4. Significance and Use4.1 The surface-crack tension (SCT) test is used to estimatethe load-carrying capacity of simple sheet- or plate-like struc-tural components having a type of flaw likely to occur inservice. The test is also used for researc
22、h purposes to investi-gate failure mechanisms of cracks under service conditions.4.2 The residual strength of an SCT specimen is a functionof the crack depth and length and the specimen thickness aswell as the characteristics of the material. This relationship isextremely complex and cannot be compl
23、etely described orcharacterized at present.4.2.1 The results of the SCT test are suitable for directapplication to design only when the service conditions exactlyparallel the test conditions. Some methods for further analysisare suggested in Appendix X1.4.3 In order that SCT test data can be compara
24、ble andreproducible and can be correlated among laboratories, it isessential that uniform SCT testing practices be established.4.4 The specimen configuration, preparation, and instru-mentation described in this practice are generally suitable forcyclic- or sustained-force testing as well. However, c
25、ertainconstraints are peculiar to each of these tests. These are beyondthe scope of this practice but are discussed in Ref. (1).5. Apparatus5.1 The procedure involves testing of specimens that havebeen precracked in fatigue. force versus CMOD, if CMOD ismeasured, is recorded autographically or digit
26、ally.5.2 Fatigue Precracking ApparatusAxial tension or three-point, four-point, or cantilever bending are all acceptablemodes for fatigue precracking. Fixture design is not critical aslong as the crack growth is symmetrical and the plane of thecrack remains perpendicular to the specimen face and the
27、tensile force vector. The effect of cyclic frequency is thought tobe negligible below 100 Hz in a nonaggressive environment.NOTE 4Certain crack shapes are more readily produced in axialtension, others in bending (see Annex A1).5.2.1 Devices and fixtures for cantilever bending of sheetand plate speci
28、mens are described in Refs. (2) and (3),respectively. Others may be equally suitable. The axial fatiguemachines described in Practice E466 are suitable for precrack-ing in tension; however, since the precracking operation isterminated prior to specimen failure, one should ensure thatload variations
29、during slowdown or shutdown do not exceedthose desired.5.2.2 A magnifier of about 20 power should be used tomonitor the fatigue precracking process. Ease of observationwill be enhanced if the cyclic rate can be reduced to about 1 Hzwhen desired. Alternatively, a stroboscopic light synchronizedwith t
30、he maximum application of tensile force may serve aswell.5.3 Testing MachineThe test should be conducted with atension testing machine that conforms to the requirements ofPractices E4.5.3.1 The devices for transmitting force to the specimenshall be such that the major axis of the specimen coincides
31、withthe load axis. The pin-and-clevis arrangement described in TestMethod E338 should be suitable for specimens whose width isless than about 4 in. 100 mm. An arrangement such as thatshown in Fig. 2 of Practice E561 should be suitable for widerspecimens.5.3.2 For tests at other than room temperature
32、, the tempera-ture control and temperature measurement requirements of TestMethod E338 are appropriate.5.4 Displacement Gage (Optional)If used to measureCMOD, the displacement gage output should accurately indi-cate the relative displacement of two gage points on thecracked surface, spanning the cra
33、ck at the midpoint of itslength. Further information on displacement gages appears inAppendix X2.5.5 For some combinations of material and crack geometry,the crack may propagate entirely through the thickness prior tototal failure. Methods of detecting this occurrence, should it beof interest, are d
34、iscussed briefly in Ref. (1).6. Test Specimen6.1 Configuration and NotationThe SCT test specimenand the notation used herein are shown in Fig. 1. Grip detailshave been omitted, since grip design may depend on specimensize (5.3.1) and material toughness. In general, the onlygripping requirements are
35、that the arrangement be strongenough to carry the maximum expected force and that it allowuniform distribution of force over the specimen cross section.6.2 DimensionsThe crack depth and length and specimenthickness should be chosen according to the ultimate purposeof the test. Further discussion of
36、this subject may be found inAppendix X3. The specimen width W should be at least 5 timesthe crack length 2c and the specimen test section length LE740/E740M 03 (2016)2should be at least twice the width W. Should these width andlength dimensions exceed actual service dimensions, the ser-vice dimensio
37、ns should be used but one should not thenattempt to generalize data from such tests.6.3 Fatigue PrecrackingThe object is to produce at aprescribed location a fatigue crack whose configuration isregular (that is, a half-ellipse or a segment of a circle), whosedepth and length are close to predetermin
38、ed target values, andwhose subsequent fracture behavior will not be influenced byany detail of the preparation process. A small slit or crackstarter is machined into the specimen surface at the center ofthe test section (Fig. 2) to locate and help initiate the fatiguecrack. Regularity of crack confi
39、guration is influenced primarilyby fatigue force uniformity, which can be maximized bycareful alignment of force train and fixtures. Materialinhomogeneity, residual stresses, and starter notch root radiusvariation can produce irregularities which may be beyondcontrol. Fatigue crack size and shape co
40、ntrol are discussed inAnnex A1.6.3.1 Crack starters have been produced by a variety ofmethods. The following procedures are known to produceacceptable results.6.3.1.1 The crack starter should be machined, either byslitting with a thin jewelers circular saw or similar cutter or byelectrical discharge
41、 machining (EDM) with a thin, shapedelectrode.6.3.1.2 The crack starter plane should be perpendicular tothe specimen face and the tensile force vector within 10.6.3.1.3 The starter notch root radius should be less than0.010 in. 0.25 mm.6.3.1.4 The crack starter length and depth should be chosenwith
42、the desired crack dimensions and the requirements of6.3.2.2 in mind.6.3.2 The following procedures should ensure the produc-tion of an effective sharp fatigue crack.6.3.2.1 Fatigue crack with the specimen in the heat treat-ment condition in which it is to be tested, if at all possible.6.3.2.2 Whenev
43、er it is physically possible, the crack shouldbe extended at least 0.05 in. 1.3 mm; in any event the fatiguecrack extension must not be less than 5 % of the final crackdepth, and the crack and its starter must lie entirely within animaginary 30 wedge whose apex is at the crack tip. Thesetwo-dimensio
44、nal descriptions shall apply around the entirecrack front, that is, in all planes normal to tangents to all pointson the crack periphery (Fig. 2).6.3.2.3 The ratio of minimum to maximum cyclic stress, R,should not be greater than 0.1.FIG. 1 Typical Surface-Crack Specimen (Grip Details Omitted)and No
45、menclatureNOTE 1Section A-A refers to the plane normal to any tangent to the crack periphery and containing the point of tangency.FIG. 2 Fatigue Crack and Starter DetailsE740/E740M 03 (2016)36.3.2.4 For at least the final 2.5 % of the total crack depth,the ratio Kmax/E should not exceed 0.002 in.1/2
46、0.00032 m1/2,where Kmaxis the maximum stress intensity factor duringfatigue cracking and E is the materials elastic modulus. Anestimate of Kmaxcan be computed based on the cyclic stressand the target crack dimensions using the appropriate equationfrom Annex A2. Compute Kmaxat the surface or at the d
47、eepestpoint, whichever is greater.7. Procedure7.1 Number of TestsIf only one crack geometry (that is,fixed crack depth and length) is to be studied, at least threespecimens should be tested. If geometry is to be varied, at leasttwo specimens should be tested for each combination ofdepth-to-length (a
48、/2c) and depth-to-thickness (a/B) ratios.7.2 Specimen MeasurementsMeasure the specimen thick-ness B at the points midway between each crack tip and thenearest specimen edge, to the nearest 0.001 in. 0.025 mm or0.1 %, whichever is larger. If these measurements are notwithin 3 % of their average, the
49、specimen should be discardedor remachined as appropriate. Measure the specimen width Wat the crack plane to within 1 % of W.7.3 TestingConduct the test in a manner similar to that foran ordinary tension specimen. The test loading rate shall besuch that the rate of increase of the nominal stress P/BW is lessthan 100 000 psi 690 MPa/min. Record the maximum force,Pmax, reached during the test.7.4 Test RecordIf CMOD is measured, a test recordshould be made consisting of an autographic plot or digitalrecord of the output of a force-sensi
