ASTM E1457-07e2
(Test Method)Standard Test Method for Measurement of Creep Crack Growth Times in Metals
Standard Test Method for Measurement of Creep Crack Growth Times in Metals
SIGNIFICANCE AND USE
Creep crack growth rate expressed as a function of the steady state C* or K characterizes the resistance of a material to crack growth under conditions of extensive creep deformation or under brittle creep conditions. Background information on the rationale for employing the fracture mechanics approach in the analyses of creep crack growth data is given in (8, 10, 27-32).
Aggressive environments at high temperatures can significantly affect the creep 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.
Expressing CCI time, t0.2 and CCG rate, da/dt as a function of an appropriate fracture mechanics related parameter, as discussed in 11.8 generally provides results that are independent of specimen size and planar geometry for the same stress state at the crack tip for the range of geometries and sizes presented in this document (see Annex A1). Thus, the appropriate correlation will enable exchange and comparison of data obtained from a variety of specimen configurations and loading conditions. Moreover, this feature enables creep crack growth data to be utilized in the design and evaluation of engineering structures operated at elevated temperatures where creep deformation is a concern. The concept of similitude is assumed, implying that cracks of differing sizes subjected to the same nominal C*(t), Ct, or K will advance by equal increments of crack extension per unit time, provided the conditions for the validity for the specific crack growth rate relating parameter are met. See 11.7 for details.
The effects of crack tip constraint arising from variations in specimen size, geometry and material ductility can influence t0.2 and da/dt. For example, crack growth rates at the same value of C*(t), Ct in creep-ductile materials generally increases with increasing thickness. It is therefore necessary to keep the component dimensions in mind when selecting...
SCOPE
1.1 This test method covers the determination of creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and creep crack growth rate, ˙a or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and Ct (1-14). The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (15-25).
1.1.1 The choice of the crack growth correlating parameter C*, C*(t), Ct, or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where creep strains dominate and creep crack growth is accompanied by substantial time-dependent creep strains at the crack tip, the crack growth rate is correlated by the steady state definitions of Ct or C*(t), defined as C* (see 1.1.4). In creep-brittle materials, creep crack growth occurs at low creep ductility. Consequently, the time-dependent creep strains are comparable to or dominated by accompanying elastic strains local to the crack tip. Under such steady state creep-brittle conditions, Ct or K could be chosen as the correlating parameter (8-14).
1.1.2 In any one test, two regions of crack growth behavior may be present (9, 10). The initial transient region where elastic strains dominate and creep damage develops and in the steady state region where crack grows proportionally to time. Steady-state creep crack growth rate behavior is covered by this standard. In addition specific recommendations are made in 11.7 a...
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´2
Designation: E1457 – 07
Standard Test Method for
1
Measurement of Creep Crack Growth Times in Metals
This standard is issued under the fixed designation E1457; 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—Equation 6 was editorially corrected in August 2008.
2
´ NOTE—Equation A2.3 was editorially corrected in October 2009.
1. Scope in11.7astohowthetransientregionshouldbetreatedinterms
of an initial crack growth period. During steady state, a unique
1.1 Thistestmethodcoversthedeterminationofcreepcrack
correlation exists between da/dt and the appropriate crack
growth (CCG) in metals at elevated temperatures using pre-
growth rate relating parameter.
cracked specimens subjected to static or quasi-static loading
1.1.3 In creep ductile materials, extensive creep occurs
conditions. The time (CCI), t to an initial crack extension
0.2
when the entire uncracked ligament undergoes creep deforma-
da =0.2 mm from the onset of first applied force and creep
i
tion. Such conditions are distinct from the conditions of
crack growth rate, a˙ or da/dt is expressed in terms of the
small-scale creep and transition creep (1-7). In the case of
magnitude of creep crack growth relating parameters, C*or K.
extensive creep, the region dominated by creep deformation is
With C* defined as the steady state determination of the crack
2
significant in size in comparison to both the crack length and
tip stresses derived in principal from C*(t) and C (1-14). The
t
theuncrackedligamentsizes.Insmall-scale-creeponlyasmall
crack growth derived in this manner is identified as a material
region of the uncracked ligament local to the crack tip
property which can be used in modeling and life assessment
experiences creep deformation.
methods (15-25).
1.1.4 The creep crack growth rate in the extensive creep
1.1.1 The choice of the crack growth correlating parameter
region is correlated by the C*(t)-integral. The C parameter
C*, C*(t), C,or K depends on the material creep properties, t
t
correlates the creep crack growth rate in the small-scale creep
geometry and size of the specimen. Two types of material
and the transition creep regions and reduces, by definition, to
behavior are generally observed during creep crack growth
C*(t)intheextensivecreepregion (5).Henceinthisdocument
tests; creep-ductile (1-14) and creep-brittle (26-37). In creep
thedefinitionC*isusedastherelevantparameterinthesteady
ductilematerials,wherecreepstrainsdominateandcreepcrack
state extensive creep regime whereas C*(t) and/or C are the
t
growth is accompanied by substantial time-dependent creep
parameters which describe the instantaneous stress state from
strains at the crack tip, the crack growth rate is correlated by
the small scale creep, transient and the steady state regimes in
the steady state definitions of C or C*(t), defined as C* (see
t
creep. The recommended functions to derive C* for the
1.1.4). In creep-brittle materials, creep crack growth occurs at
different geometries is shown in Annex A1 is described in
low creep ductility. Consequently, the time-dependent creep
Annex A2.
strains are comparable to or dominated by accompanying
1.1.5 An engineering definition of an initial crack extension
elastic strains local to the crack tip. Under such steady state
size da is used in order to quantify the initial period of crack
i
creep-brittle conditions, C or K could be chosen as the
t
development. This distance is given as 0.2 mm. It has been
correlating parameter (8-14).
shown (38-40) that this period which exists at the start of the
1.1.2 In any one test, two regions of crack growth behavior
test could be a substantial period of the test time. During this
may be present (9, 10). The initial transient region where
early period the crack tip undergoes damage development as
elastic strains dominate and creep damage develops and in the
well as redistribution of stresses prior reaching steady state.
steady state region where crack grows proportionally to time.
Recommendation is made to correlate this initial crack growth
Steady-state creep crack growth rate behavior is covered by
period defined as t at da = 0.2 mm with the steady state C*
this standard. In addition specific recommendations are made 0.2 i
when the crack tip is under extensive creep and with K for
creep brittle conditions. The values for C* and K should be
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
calculated at the final specified crack size defined as a + da
o i
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
where a initial size of the sta
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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.
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Designation:E 1457–00 Designation: E1457 – 07
Standard Test Method for
1
Measurement of Creep Crack Growth RatesTimes in Metals
This standard is issued under the fixed designation E 1457; 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.
This standard is issued under the fixed designation E1457; 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—Equation 6 was editorially corrected in August 2008.
2
´ NOTE—Equation A2.3 was editorially corrected in October 2009.
1. Scope
1.1This test method covers the determination of creep crack growth rates in metals at elevated temperature using compact type,
C(T), (see Fig. 1) specimens subjected to static or quasi-static loading conditions. The time rate of crack growth,
1.1 Thistestmethodcoversthedeterminationofcreepcrackgrowth(CCG)inmetalsatelevatedtemperaturesusingpre-cracked
specimenssubjectedtostaticorquasi-staticloadingconditions.Thetime(CCI),t toaninitialcrackextension da =0.2mmfrom
0.2 i
the onset of first applied force and creep crack growth rate, a˙ (t)or da/dt is expressed in terms of the magnitude of crack growth
rate relating parameters, C*(t), or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C*or
K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and C or K.
t
1.1.1The choice of the crack growth rate relating parameter, C*(t), C ,or K depends on the material behavior. Two types of
t
materialbehavioraregenerallyobservedduringcreepcrackgrowthtests;creep-ductileandcreep-brittle.Increepductilematerials,
creep crack growth is accompanied by substantial time-dependent creep strains at the crack tip and the crack growth rate is
2
correlated by C*(t) and/or C t (1-41-14). In creep-brittle materials, creep crack growth occurs at low creep ductility.
t
Consequently, the time-dependent creep strains are comparable to or dominated by accompanying elastic strains local to the crack
tip.Undersuchsteadystatecreep-brittleconditions, Kischosenasthecorrelatingparameter (5The crack growth derived in this
manner is identified as a material property which can be used in modeling and life assessment methods (15-25).
1.1.2In creep ductile materials, extensive creep occurs when the entire uncracked ligament undergoes creep deformation. Such
conditions are distinct from the conditions of small-scale creep and transition creep (4, 6
1.1.1 The choice of the crack growth correlating parameter C*, C*(t), C,or K depends on the material creep properties,
t
geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests;
creep-ductile(1-14).Inthecaseofextensivecreep,theregiondominatedbycreepdeformationissignificantinsizeincomparison
to the crack size and to the uncracked ligament size. In small-scale-creep only a small region of the uncracked ligament near the
crack tip experiences creep deformation. The creep crack growth rate in the extensive creep region is correlated by the C*(t)-
integral. The and creep-brittle (26-37). In creep ductile materials, where creep strains dominate and creep crack growth is
accompanied by substantial time-dependent creep strains at the crack tip, the crack growth rate is correlated by the steady state
definitions of C, parameter correlates the creep crack growth rate in the small-scale creep and the transition creep regions and
t
reduces,bydefinition,toC*(t)intheextensivecreepregion(4torC*(t),definedasC*(see1.1.4).Increep-brittlematerials,creep
crack growth occurs at low creep ductility. Consequently, the time-dependent creep strains are comparable to or dominated by
accompanying elastic strains local to the crack tip. Under such steady state creep-brittle conditions, C or K could be chosen as
t
the correlating parameter (8-14).
1.1.3Only steady-state creep crack growth rate behavior is covered by this method. During steady state, a unique correlation
exists between a˙ and the appropriate crack growth rate relating parameter. Transient crack growth conditions occur in the ea
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