ASTM E2760-10e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´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
...