ASTM_E_2760_-_10e2.pdf

Designation:E2760102Standard Test Method forCreep-Fatigue Crack Growth Testing1This standard is issued under the fixed designation E2760;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.1NOTE3.2.19 was editorially revised in December 2011.2NOTESections 3.2.20 and 3.3.3 were editorially revised in March 2013.1.Scope1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneousmaterials by use of pre-cracked compact type,C(T),testspecimens subjected to uniaxial cyclic forces.It concernsfatigue cycling with sufficiently long loading/unloading ratesor hold-times,or both,to cause creep deformation at the cracktip and the creep deformation be responsible for enhancedcrack growth per loading cycle.It is intended as a guide forcreep-fatigue testing performed in support of such activities asmaterials research and development,mechanical design,pro-cess and quality control,product performance,and failureanalysis.Therefore,this method requires testing of at least twospecimens that yield overlapping crack growth rate data.Thecyclic conditions responsible for creep-fatigue deformation andenhanced crack growth vary with material and with tempera-ture for a given material.The effects of environment such astime-dependent oxidation in enhancing the crack growth ratesare assumed to be included in the test results;it is thus essentialto conduct testing in an environment that is representative ofthe intended application.1.2 Two types of crack growth mechanisms are observedduring creep/fatigue tests:(1)time-dependent intergranularcreep and(2)cycle dependent transgranular fatigue.Theinteraction between the two cracking mechanisms is complexand depends on the material,frequency of applied force cyclesand the shape of the force cycle.When tests are planned,theloading frequency and waveform that simulate or replicateservice loading must be selected.1.3 Two types of creep behavior are generally observed inmaterials during creep-fatigue crack growth tests:creep-ductileand creep-brittle(1).2In creep-ductile materials,creep strainsdominate and creep-fatigue crack growth is accompanied bysubstantial time-dependent creep strains near the crack tip.Increep-brittle materials,creep-fatigue crack growth occurs atlow creep ductility.Consequently,the time-dependent creepstrains are comparable to or less than the accompanying elasticstrains near the crack tip.1.3.1 In creep-brittle materials,creep-fatigue crack growthrates per cycle or da/dN,are expressed in terms of themagnitude of the cyclic stress intensity parameter,K.Thesecrack growth rates depend on the loading/unloading rates andhold-time at maximum load,the force ratio,R,and the testtemperature(see Annex A1 for additional details).1.3.2 In creep-ductile materials,the average time rates ofcrack growth during a loading cycle,(da/dt)avg,are expressedas a function of the average magnitude of the Ctparameter,(Ct)avg(2).NOTE1The correlations between(da/dt)avgand(Ct)avghave beenshown to be independent of hold-times(2,3).1.4 The crack growth rates derived in this manner andexpressed as a function of the relevant crack tip parameter(s)are identified as a material property which can be used inintegrity assessment of structural components subjected tosimilar loading conditions during service and life assessmentmethods.1.5 The use of this practice is limited to specimens and doesnot cover testing of full-scale components,structures,orconsumer products.1.6 This practice is primarily aimed at providing the mate-rial properties required for assessment of crack-like defects inengineering structures operated at elevated temperatures wherecreep deformation and damage is a design concern and aresubjected to cyclic loading involving slow loading/unloadingrates or hold-times,or both,at maximum loads.1.7 This practice is applicable to the determination of crackgrowth rate properties as a consequence of constant-amplitudeload-controlled tests with controlled loading/unloading rates orhold-times at the maximum load,or both.It is primarilyconcerned with the testing of C(T)specimens subjected touniaxial loading in load control mode.The focus of theprocedure is on tests in which creep and fatigue deformationand damage is generated simultaneously within a given cycle.1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.06 on CrackGrowth Behavior.Current edition approved May 1,2010.Published July 2010.DOI:10.1520/E2760-10E02.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 It does not co