Standard Test Method for Creep-Fatigue Crack Growth Testing

SIGNIFICANCE AND USE
Creep-fatigue crack growth testing is typically performed at elevated temperatures over a range of frequencies and hold-times and involves the sequential or simultaneous application of the loading conditions necessary to generate crack tip cyclic deformation/damage enhanced by creep deformation/damage or vice versa. Unless such tests are performed in vacuum or an inert environment, oxidation can also be responsible for important interaction effects relating to damage accumulation. The purpose of creep-fatigue crack growth tests can be to determine material property data for (a) assessment input data for the damage condition analysis of engineering structures operating at elevated temperatures, (b) material characterization, or (c) development and verification of rules for design and life assessment of high-temperature components subject to cyclic service with low frequencies or with periods of steady operation, or a combination thereof.
In every case, it is advisable to have complementary continuous cycling fatigue data (gathered at the same loading/unloading rate), creep crack growth data for the same material and test temperature(s) as per Test Method E1457, and creep-fatigue crack formation data as per Test Method E2714. Aggressive environments at high temperatures can significantly affect the creep-fatigue crack growth behavior. Attention must be given to the proper selection and control of temperature and environment in research studies and in generation of design data.
Results from this test method can be used as follows:
Establish material selection criteria and inspection requirements for damage tolerant applications where cyclic loading at elevated temperature is present.
Establish, in quantitative terms, the individual and combined effects of metallurgical, fabrication, operating temperature, and loading variables on creep-fatigue crack growth life.
The results obtained from this test method are designed for crack dominant regimes of creep-fatigu...
SCOPE
1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneous materials by use of pre-cracked compact type, C(T), test specimens subjected to uniaxial cyclic forces. It concerns fatigue cycling with sufficiently long loading/unloading rates or hold-times, or both, to cause creep deformation at the crack tip and the creep deformation be responsible for enhanced crack growth per loading cycle. It is intended as a guide for creep-fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. Therefore, this method requires testing of at least two specimens that yield overlapping crack growth rate data. The cyclic conditions responsible for creep-fatigue deformation and enhanced crack growth vary with material and with temperature for a given material. The effects of environment such as time-dependent oxidation in enhancing the crack growth rates are assumed to be included in the test results; it is thus essential to conduct testing in an environment that is representative of the intended application.
1.2 Two types of crack growth mechanisms are observed during creep/fatigue tests: (1) time-dependent intergranular creep and (2) cycle dependent transgranular fatigue. The interaction between the two cracking mechanisms is complex and depends on the material, frequency of applied force cycles and the shape of the force cycle. When tests are planned, the loading frequency and waveform that simulate or replicate service loading must be selected.
1.3 Two types of creep behavior are generally observed in materials during creep-fatigue crack growth tests: creep-ductile and creep-brittle (1). In creep-ductile materials, creep strains dominate and creep-fatigue crack growth is accompanied by substantial time-dependent creep strains near the crack tip. In creep-...

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ASTM E2760-10e1 - Standard Test Method for Creep-Fatigue Crack Growth Testing
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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´1
Designation: E2760 − 10
StandardTest Method for
1
Creep-Fatigue Crack Growth Testing
This standard is issued under the fixed designation E2760; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1
´ NOTE—3.2.19 was editorially revised in December 2011.
1. Scope creep-brittle materials, creep-fatigue crack growth occurs at
low creep ductility. Consequently, the time-dependent creep
1.1 This test method covers the determination of creep-
strainsarecomparabletoorlessthantheaccompanyingelastic
fatigue crack growth properties of nominally homogeneous
strains near the crack tip.
materials by use of pre-cracked compact type, C(T), test
1.3.1 In creep-brittle materials, creep-fatigue crack growth
specimens subjected to uniaxial cyclic forces. It concerns
rates per cycle or da/dN, are expressed in terms of the
fatigue cycling with sufficiently long loading/unloading rates
magnitude of the cyclic stress intensity parameter, ∆K. These
or hold-times, or both, to cause creep deformation at the crack
crack growth rates depend on the loading/unloading rates and
tip and the creep deformation be responsible for enhanced
hold-time at maximum load, the force ratio, R, and the test
crack growth per loading cycle. It is intended as a guide for
temperature (see Annex A1 for additional details).
creep-fatigue testing performed in support of such activities as
1.3.2 In creep-ductile materials, the average time rates of
materials research and development, mechanical design, pro-
cess and quality control, product performance, and failure crack growth during a loading cycle, (da/dt) , are expressed
avg
as a function of the average magnitude of the C parameter,
analysis.Therefore, this method requires testing of at least two
t
(C) (2).
specimens that yield overlapping crack growth rate data. The
t avg
cyclicconditionsresponsibleforcreep-fatiguedeformationand
NOTE 1—The correlations between (da/dt) and (C) have been
avg t avg
enhanced crack growth vary with material and with tempera-
shown to be independent of hold-times (2, 3).
ture for a given material. The effects of environment such as
1.4 The crack growth rates derived in this manner and
time-dependent oxidation in enhancing the crack growth rates
expressed as a function of the relevant crack tip parameter(s)
areassumedtobeincludedinthetestresults;itisthusessential
are identified as a material property which can be used in
to conduct testing in an environment that is representative of
integrity assessment of structural components subjected to
the intended application.
similar loading conditions during service and life assessment
1.2 Two types of crack growth mechanisms are observed
methods.
during creep/fatigue tests: (1) time-dependent intergranular
1.5 Theuseofthispracticeislimitedtospecimensanddoes
creep and (2) cycle dependent transgranular fatigue. The
not cover testing of full-scale components, structures, or
interaction between the two cracking mechanisms is complex
consumer products.
and depends on the material, frequency of applied force cycles
and the shape of the force cycle. When tests are planned, the
1.6 This practice is primarily aimed at providing the mate-
loading frequency and waveform that simulate or replicate
rial properties required for assessment of crack-like defects in
service loading must be selected.
engineeringstructuresoperatedatelevatedtemperatureswhere
1.3 Two types of creep behavior are generally observed in creep deformation and damage is a design concern and are
materialsduringcreep-fatiguecrackgrowthtests:creep-ductile
subjected to cyclic loading involving slow loading/unloading
2
and creep-brittle (1). In creep-ductile materials, creep strains rates or hold-times, or both, at maximum loads.
dominate and creep-fatigue crack growth is accompanied by
1.7 This practice is applicable to the determination of crack
substantial time-dependent creep strains near the crack tip. In
growth rate properties as a consequence of constant-amplitude
load-controlledtestswithcontrolledloading/unloadingratesor
hold-times at the maximum load, or both. It is primarily
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
concerned with the testing of C(T) specimens subjected to
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
Growth Behavior.
uniaxial loading in load control mode. The focus of the
Current edition approved May 1, 2010. Published July 2010. DOI: 10.1520/
procedure is on tests in which creep and fatigue deformation
E2760-10E01.
2
and damage is generated simultaneously within a given cycle.
The bold
...

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