ASTM_E_2899_-_15.pdf

Designation:E289915Standard 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,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 cracks 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,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 details 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 this 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 and 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.NOTE1Constraint-based framework.In the context of this testmethod,constraint is used 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 Use.)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.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 micromechanicalfailure 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 method 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-cable 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 testspecimen 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,the 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.These 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 fracture 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.1T