ASTM E2760-16
(Test Method)Standard Test Method for Creep-Fatigue Crack Growth Testing
Standard Test Method for Creep-Fatigue Crack Growth Testing
SIGNIFICANCE AND USE
4.1 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.
4.2 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.
4.3 Results from this test method can be used as follows:
4.3.1 Establish material selection criteria and inspection requirements for damage tolerant applications where cyclic loading at elevated temperature is present.
4.3.2 Establish, in quantitative terms, the individual and combined effects of metallurgical, fabrication, operating temperature, and loading variables on creep-fatigue crack growth life.
4.4 The results obtained from this test method are designed for crac...
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)2. For highly creep-ductile materials that have rupture ductility of 10 % or higher, creep strains dominate and creep-fatigue crack growth is accompanied by substantial t...
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Designation: E2760 − 16
Standard Test 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. Scope materials, creep-fatigue crack growth occurs at low creep
ductility. Consequently, the time-dependent creep strains are
1.1 This test method covers the determination of creep-
comparable to or less than the accompanying elastic strains
fatigue crack growth properties of nominally homogeneous
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
fatigue cycling with sufficiently long loading/unloading rates rates per cycle or da/dN, are expressed in terms of the
magnitude of the cyclic stress intensity parameter, ∆K. These
or hold-times, or both, to cause creep deformation at the crack
tip and the creep deformation be responsible for enhanced crack growth rates depend on the loading/unloading rates and
crack growth per loading cycle. It is intended as a guide for hold-time at maximum load, the force ratio, R, and the test
creep-fatigue testing performed in support of such activities as temperature (see Annex A1 for additional details).
materials research and development, mechanical design, pro-
1.3.2 In creep-ductile materials, the average time rates of
cess and quality control, product performance, and failure
crack growth during a loading cycle, (da/dt) , are expressed
avg
analysis.Therefore, this method requires testing of at least two
as a function of the average magnitude of the C parameter,
t
specimens that yield overlapping crack growth rate data. The
(C) (2).
t avg
cyclicconditionsresponsibleforcreep-fatiguedeformationand
NOTE 1—The correlations between (da/dt) and (C) have been
enhanced crack growth vary with material and with tempera-
avg t avg
shown to be independent of hold-times (2, 3) for highly creep-ductile
ture for a given material. The effects of environment such as
materials that have rupture ductility of 10 percent or higher.
time-dependent oxidation in enhancing the crack growth rates
areassumedtobeincludedinthetestresults;itisthusessential 1.4 The crack growth rates derived in this manner and
to conduct testing in an environment that is representative of expressed as a function of the relevant crack tip parameter(s)
the intended application. are identified as a material property which can be used in
integrity assessment of structural components subjected to
1.2 Two types of crack growth mechanisms are observed
similar loading conditions during service and life assessment
during creep/fatigue tests: (1) time-dependent intergranular
methods.
creep and (2) cycle dependent transgranular fatigue. The
interaction between the two cracking mechanisms is complex
1.5 Theuseofthispracticeislimitedtospecimensanddoes
and depends on the material, frequency of applied force cycles
not cover testing of full-scale components, structures, or
and the shape of the force cycle. When tests are planned, the
consumer products.
loading frequency and waveform that simulate or replicate
1.6 This practice is primarily aimed at providing the mate-
service loading must be selected.
rial properties required for assessment of crack-like defects in
1.3 Two types of creep behavior are generally observed in
engineeringstructuresoperatedatelevatedtemperatureswhere
materialsduringcreep-fatiguecrackgrowthtests:creep-ductile
2 creep deformation and damage is a design concern and are
and creep-brittle (1) . For highly creep-ductile materials that
subjected to cyclic loading involving slow loading/unloading
haveruptureductilityof10%orhigher,creepstrainsdominate
rates or hold-times, or both, at maximum loads.
and creep-fatigue crack growth is accompanied by substantial
time-dependent creep strains near the crack tip. In creep-brittle
1.7 This practice is applicable to the determination of crack
growth rate properties as a consequence of constant-amplitude
load-controlledtestswithcontrolledloading/unloadingratesor
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
hold-times at the maximum load, or both. It is primarily
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
concerned with the testing of C(T) specimens subjected to
Growth Behavior.
Current edition approved Nov. 1, 2016. Published January 2017. Originally
uniaxial loading in load control mode. The focus of the
ɛ2
approved in 2010. Last previous edition approved in 2010 as
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´2
Designation: E2760 − 10 E2760 − 16
Standard Test 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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1
ε NOTE—3.2.19 was editorially revised in December 2011.
2
ε NOTE—Sections 3.2.20 and 3.3.3 were editorially revised in March 2013.
1. 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
2
creep-brittle (1).) In creep-ductile materials, . For highly creep-ductile materials that have rupture ductility of 10 % or higher,
creep strains dominate and creep-fatigue crack growth is accompanied by substantial time-dependent creep strains near the crack
tip. In creep-brittle materials, creep-fatigue crack growth occurs at low creep ductility. Consequently, the time-dependent creep
strains are comparable to or less than the accompanying elastic strains near the crack tip.
1.3.1 In creep-brittle materials, creep-fatigue crack growth rates per cycle or da/dN, are expressed in terms of the magnitude
of the cyclic stress intensity parameter, ΔK. These crack growth rates depend on the loading/unloading rates and hold-time at
maximum load, the force ratio, R, and the test temperature (see Annex A1 for additional details).
1.3.2 In creep-ductile materials, the average time rates of crack growth during a loading cycle, (da/dt) , are expressed as a
avg
function of the average magnitude of the C parameter, (C ) (2).
t t avg
NOTE 1—The correlations between (da/dt) and (C ) have been shown to be independent of hold-times (2, 3).) for highly creep-ductile materials
avg t avg
that have rupture ductility of 10 percent or higher.
1.4 The crack growth rates derived in this manner and expressed as a function of the relevant crack tip parameter(s) are
identified as a material property which can be used in integrity assessment of structural components subjected to similar loading
conditions during service and life assessment methods.
1.5 The use of this practice is limited to specimens and does not cover testing of full-scale components, structures, or consumer
products.
1.6 This practice is primarily aimed at providing the material properties required for assessment of crack-like defects in
engineering structures operated at elevated temperatures where creep deformation and damage is a design concern and are
subjected to cyclic loading involving slow loading/unloading rates or hold-times, or both, at maximum loads.
1
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
...
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