1、Designation: E2899 15Standard Test Method forMeasurement of Initiation Toughness in Surface CracksUnder Tension and Bending1This standard is issued under the fixed designation E2899; 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 describes the method for testingfatigue-sharpened, semi-elliptically shaped surface crack
3、s inrectangular flat panels subjected to monotonically increasingtension or bending. Tests quantify the crack-tip conditions atinitiation of stable crack extension or immediate unstable crackextension.1.2 This test method applies to the testing of metallicmaterials not limited by strength, thickness
4、, or toughness.Materials are assumed to be essentially homogeneous and freeof residual stress. Tests may be conducted at any appropriatetemperature.The effects of environmental factors and sustainedor cyclic loads are not addressed in this test method.1.3 This test method describes all necessary det
5、ails for theuser to test for the initiation of crack extension in surface cracktest specimens. Specific requirements and recommendationsare provided for test equipment, instrumentation, test specimendesign, and test procedures.1.4 Tests of surface cracked, laboratory-scale specimens asdescribed in t
6、his test method may provide a more accurateunderstanding of full-scale structural performance in the pres-ence of surface cracks. The provided recommendations help toassure test methods and data are applicable to the intendedpurpose.1.5 This test method prescribes a consistent methodologyfor test an
7、d analysis of surface cracks for research purposes andto assist in structural assessments. The methods described hereutilize a constraint-based framework (1, 2)2to evaluate thefracture behavior of surface cracks.NOTE 1Constraint-based framework. In the context of this testmethod, constraint is used
8、as a descriptor of the three-dimensional stressand strain fields in the near vicinity of the crack tip, where materialcontractions due to the Poisson effect may be suppressed and thereforeproduce an elevated, tensile stress state (3, 4). (See further discussions inTerminology and Significance and Us
9、e.) When a parameter describing thisstress state, or constraint, is used with the standard measure of crack-tipstress amplitude (K or J), the resulting two-parameter characterizationbroadens the ability of fracture mechanics to accurately predict theresponse of a crack under a wider range of loading
10、. The two-parametermethodology produces a more complete description of the crack-tipconditions at the initiation of crack extension. The effects of constraint onmeasured fracture toughness are material dependent and are governed bythe effects of the crack-tip stress-strain state on the micromechanic
11、alfailure processes specific to the material. Surface crack tests conductedwith this test method can help to quantify the material sensitivity toconstraint effects and to establish the degree to which the materialtoughness correlates with a constraint-based fracture characterization.1.6 This test me
12、thod provides a quantitative framework tocategorize test specimen conditions into one of three regimes:(I) a linear-elastic regime, (II) an elastic-plastic regime, or (III)a field-collapse regime. Based on this categorization, analysistechniques and guidelines are provided to determine an appli-cabl
13、e crack-tip parameter for the linear-elastic regime (K or J)or the elastic-plastic regime (J), and an associated constraintparameter. Recommendations are provided to assess the testdata in the context of a toughness-constraint locus (2). The useris directed to other resources for evaluation of the t
14、estspecimen in the field-collapse regime when extensive plasticdeformation in the specimen eliminates the identifiable crack-front fields of fracture mechanics.1.7 The specimen design and test procedures described inthis test method may be applied to evaluation of surface cracksin welds; however, th
15、e methods described in this test method toanalyze test measurements may not be applicable. Weld frac-ture tests generally have complicating features beyond thescope of data analysis in this test method, including the effectsof residual stress, microstructural variability, and non-uniformstrength. Th
16、ese effects will influence test results and must beconsidered in the interpretation of measured quantities.1.8 This test method is not intended for testing surfacecracks in steel in the cleavage regime. Such tests are outsidethe scope of this test method. A methodology for evaluation ofcleavage frac
17、ture toughness in ferritic steels over the ductile-to-brittle region using C(T) and SE(B) specimens can be foundin Test Method E1921.1.9 UnitsThe values stated in SI units are to be regardedas the standard. The values given in parentheses are forinformation only.1This test method is under the jurisd
18、iction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.07 on FractureMechanics.Current edition approved June 1, 2015. Published August 2015. Last previousedition approved in 2013 as E2899 13. DOI: 10.1520/E2899-15.2The boldface numbers in parentheses
19、 refer to the list of references at the end ofthis test method.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.10 This practice may involve hazardous materials,operations, and equipment. This standard does not purport toaddress all
20、of the safety problems associated with its use. It isthe responsibility of the users of this standard to establishappropriate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1421 Test Methods for Determi
21、nation of Fracture Tough-ness of Advanced Ceramics at Ambient TemperatureE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE111 Test Method for Youngs Modulus, Tangent Modulus,a
22、nd Chord ModulusE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE647 Test Method for Measurement of Fatigue CrackGrowth RatesE740 Practice for Fracture Testing with Surface-Crack Ten-sion SpecimensE1012 Practice for Verification of Testing Frame and Speci-m
23、en Alignment Under Tensile and Compressive AxialForce ApplicationE1820 Test Method for Measurement of Fracture ToughnessE1823 Terminology Relating to Fatigue and Fracture TestingE1921 Test Method for Determination of ReferenceTemperature, To, for Ferritic Steels in the TransitionRange3. Terminology3
24、.1 For definitions of terms used in this Test Method,Terminologies E6 and E1823 apply.3.2 Symbols:3.2.1 crack depth, a Lsee Terminology E1823 and Fig.1 in this test method.3.2.1.1 DiscussionIn this test method, the term aois theoriginal surface crack depth, as determined in subsection 8.4,used in th
25、e evaluation of the test.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 onthe ASTM website.FIG. 1 Test Specimen and Crack Confi
26、gurationsE2899 1523.2.2 crack-mouth opening displacement, CMOD LseeTerminology E1823 and Fig. 1 in this test method.3.2.3 force, P Fsee Terminology E1823.3.2.4 J-integral, J FL-1or FLL-2see TerminologyE1823.3.2.5 modulus of elasticity, E FL-2see TerminologyE1823.3.2.6 net section area, ANL2see Termi
27、nology E1823.For surface cracks AN= WB a0c0/2.3.2.7 plane-strain fracture toughness, KIcFL-3/2see Ter-minology E1823.3.2.8 Poissons ratio, see Terminology E6.3.2.9 specimen thickness, B Lsee Terminology E1823and Fig. 1 from this test method.FIG. 2 Toughness-Constraint Locus with Example Trajectories
28、FIG. 3 Recommended Configuration of Tension Testing ClevisNOTE 1Flat bottomed holes are not required, but may be used in configurations found in Test Methods E399 or E1820.E2899 1533.2.10 specimen width, W Lsee Terminology E1823 andFig. 1 from this test method.3.2.11 stable crack extension, Lsee Ter
29、minology E1823.3.2.12 stress ratio, Rsee Terminology E1823.3.2.13 surface crack length, 2c Lsee TerminologyE1823 and Fig. 1 in this test method.FIG. 4 Specimen Design PrinciplesFIG. 5 Recommended Configuration of Bend Testing ApparatusE2899 1543.2.13.1 DiscussionIn this test method, the term 2c0is t
30、heoriginal surface crack length, as determined in subsection 8.4,used in the evaluation of the test.3.2.14 yield strength, YSFL-2see Terminology E1823,as determined by 0.2% offset strain method.3.3 Definitions of Terms Specific to This Standard:3.3.1 characteristic length, ra,rbLa physical lengthmea
31、sured post-test on the specimen fracture surface andcompared to the length scale provided by the deformationlimit. rais the distance measured on the crack plane normal tothe crack front at the parametric angle ito the front face(cracked face) of the specimen. rbis the distance measured onthe crack p
32、lane normal to the crack front at the parametricangle ito the back face (uncracked face) or side of thespecimen (Fig. A3.1).3.3.2 constraint, in the context of this test method,constraint is a descriptor of the three dimensional stress andstrain fields in the near vicinity of the crack tip where mat
33、erialcontractions due to the Poisson effect may be suppressed andtherefore produce an elevated, three-dimensional tensile (hy-drostatic) stress state. An elevated hydrostatic stress statesuppresses material yielding and permits larger stresses todevelop. The material, geometry, and externally applie
34、d loadsinfluence the development of the elevated hydrostatic stressstate.3.3.3 elastic-plastic regimeconditions in a test specimenwhere crack-tip deformations exceed limits of the linear-elasticregime defined in this test method, but J alone or J and aconstraint term still characterize the crack-tip
35、 stress and strainfields.The non-dimensional parameters, CJaand CJb, define thedeformation limits for validity of the elastic-plastic regime inthis test method.3.3.3.1 DiscussionNon-dimensional deformation limitssuch as CK, CJaand CJbare commonly designated by the letter“M” in the literature (5).3.3
36、.4 elastic-plastic regime crack size deformation limit,CJathe non-dimensional, upper limit of deformation for theelastic-plastic regime based on limiting the crack-tip openingdisplacement relative to the crack size.3.3.5 elastic-plastic regime ligament deformation limit,CJbthe non-dimensional, upper
37、 limit of deformation for theelastic-plastic regime based on limiting plasticity in the re-maining ligament.3.3.6 far field stress, FL-2stress far removed from thecrack plane resulting from applied forces or moments.3.3.6.1 DiscussionFor applied tensile forces, the far fieldstress is the average str
38、ess over the gross area, that is = P/WB.For applied bending moments, the far field stress is themaximum tensile outer fiber stress across the gross area, that is =6M/(WB2).3.3.7 fatigue crack starter notch height, N Lthe heightof the fatigue crack starter notch measured on the front face ofthe speci
39、men prior to testing (Fig. 6).3.3.8 field-collapse regimeconditions in a test specimenwhere crack-tip deformations exceed the limit of the elastic-plastic regime defined in this test method. Extensive plasticFIG. 6 Fatigue Crack Starter Notch ConfigurationE2899 155deformation in the specimen elimina
40、tes the identifiable crack-front fields of fracture mechanics, which precludes analysis oftest conditions in this test method.3.3.9 initiation angle, ithe parametric angle determinedin accordance with Annex A5 that identifies the location alongthe crack perimeter where the test result is evaluated.3
41、.3.10 initiation of surface crack extensionin the contextof this test method, the point during the test when, undermonotonically increasing force or moment, the precrack ex-tends a small but consistently measurable amount by stable,ductile tearing, or when the precrack extends in an immediate,unstab
42、le ductile mode, failing the specimen.3.3.10.1 DiscussionParameters associated with the initia-tion of surface crack extension are designated herein with asubscript i (for example, Pi) and define the state at which thecrack front fields are characterized to render the toughness testresult. The initi
43、ation of surface crack extension will generallybe a local occurrence along the perimeter of a surface crack.Due to this localization, defining and experimentally quantify-ing a universal measure of relative or absolute crack extensionfor the surface crack geometry is not practical with commonlyavail
44、able laboratory equipment. Therefore, if identifiable, theextent and location of stable crack extension is recorded as anintegral part of the test result. See subsection 8.3.4. In thiscontext, the surface crack toughness result identifies a point onthe materials tearing resistance curve as influence
45、d by thelocal crack tip constraint conditions. See J-R curve and K-Rcurve definitions in Terminology E1823.3.3.11 initiation crack mouth opening displacement,CMODiLthe CMOD at which initiation of surface crackextension occurs.3.3.12 initiation force, PiFthe force at which initiationof surface crack
46、extension occurs.3.3.13 initiation moment MiFLthe applied moment atwhich initiation of surface crack extension occurs.3.3.14 J-dominancecrack-tip conditions where the elastic-plastic stress and strain fields are quantified by the value of theJ-integral without constraint adjustment.3.3.14.1 Discussi
47、onCrack-tip fields described asJ-dominant in this test method exist when elastic-plasticconditions develop at the crack front and high crack-tipconstraint conditions prevail (for example, T-stress 0).J-dominant fields permit the use of a single parameter charac-terization of fracture toughness in te
48、rms of a critical J-value. Inthis test method, J-dominant conditions prevail to higher levelsof crack-tip deformation than do K-dominant conditions.3.3.15 JKFL-1or FLL-2a value of the J-integral calcu-lated from KIusing the equation:JK5KI21 2 2!E(1)that is valid for linear-elastic, plane-strain cond
49、itions.3.3.16 JpFL-1or FLL-2the peak value of the J-integralaround the perimeter of the surface crack during monotonicloading.3.3.17 JFL-1or FLL-2the J-integral value at theinitiation angle (i) when the specimen reaches the initiationcrack mouth opening displacement (CMODi).3.3.18 K-dominancecrack-tip conditions where the stressand strain fields immediately surrounding the crack-tip plasticzone are quantified by the stress intensity factor, KI, withoutconstraint adjust
