Designation:E1457−15StandardTestMethodforMeasurementofCreepCrackGrowthTimesinMetals1ThisstandardisissuedunderthefixeddesignationE1457;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthedeterminationofcreepcrackinitiation(CCI)andcreepcrackgrowth(CCG)inmetalsatelevatedtemperaturesusingpre-crackedspecimenssubjectedtostaticorquasi-staticloadingconditions.Thesolutionspresentedinthistestmethodarevalidatedforbasematerial(i.e.homogenousproperties)andmixedbase/weldmaterialwithinhomogeneousmicrostructuresandcreepproperties.TheCCItime,t0.2,whichisthetimerequiredtoreachaninitialcrackextensionofδai=0.2mmtooccurfromtheonsetoffirstappliedforce,andCCGrate,a˙orda/dtareexpressedintermsofthemagnitudeofcreepcrackgrowthcorrelatedbyfracturemechanicsparameters,C*orK,withC*definedasthesteadystatedeterminationofthecracktipstressesderivedinprincipalfromC*(t)andCt(1-17).2Thecrackgrowthderivedinthismannerisidentifiedasamaterialpropertywhichcanbeusedinmodelingandlifeassessmentmethods(17-28).1.1.1ThechoiceofthecrackgrowthcorrelatingparameterC*,C*(t),Ct,orKdependsonthematerialcreepproperties,geometryandsizeofthespecimen.Twotypesofmaterialbehavioraregenerallyobservedduringcreepcrackgrowthtests;creep-ductile(1-17)andcreep-brittle(29-44).Increepductilematerials,wherecreepstrainsdominateandcreepcrackgrowthisaccompaniedbysubstantialtime-dependentcreepstrainsatthecracktip,thecrackgrowthrateiscorrelatedbythesteadystatedefinitionsofCtorC*(t),definedasC*(see1.1.4).Increep-brittlematerials,creepcrackgrowthoccursatlowcreepductility.Consequently,thetime-dependentcreepstrainsarecomparabletoordominatedbyaccompanyingelasticstrainslocaltothecracktip.Undersuchsteadystatecreep-brittleconditions,CtorKcouldbechosenasthecorrelatingparameter(8-14).1.1.2Inanyonetest,tworegionsof...
