ASTM E1457-13
(Test Method)Standard Test Method for Measurement of Creep Crack Growth Times and Rates in Metals
Standard Test Method for Measurement of Creep Crack Growth Times and Rates in Metals
SIGNIFICANCE AND USE
6.1 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).
6.2 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.
6.2.1 Expressing CCI time, t0.2 and CCG rate, da/dt as a function of an appropriate fracture mechanics related parameter 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.
6.2.2 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 selectin...
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1.1 This test method covers the determination of time for a creep crack to grow on initial load (CCI) and its subsequent creep crack growth (CCG) rates in metals at elevated temperatures using pre-cracked specimens subjected to elevated temperatures under static or quasi-static loading conditions. The tests are validated for either base material (homogenous properties) or mixed base/weld material with inhomogeneous microstructures and creep properties. For CCI the time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and CCG rate, a˙ or da/dt are 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).2 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 reg...
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Designation: E1457 − 13
StandardTest Method for
Measurement of Creep Crack Growth Times and Rates in
1
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. Scope elastic strains dominate and creep damage develops and in the
steady state region where crack grows proportionally to time.
1.1 This test method covers the determination of time for a
Steady-state creep crack growth rate behavior is covered by
creep crack to grow on initial load (CCI) and its subsequent
this standard. In addition specific recommendations are made
creep crack growth (CCG) rates in metals at elevated tempera-
in11.7astohowthetransientregionshouldbetreatedinterms
tures using pre-cracked specimens subjected to elevated tem-
of an initial crack growth period. During steady state, a unique
peratures under static or quasi-static loading conditions. The
correlation exists between da/dt and the appropriate crack
tests are validated for either base material (homogenous
growth rate relating parameter.
properties) or mixed base/weld material with inhomogeneous
1.1.3 In creep ductile materials, extensive creep occurs
microstructures and creep properties. For CCI the time (CCI),
t toaninitialcrackextensionδa =0.2mmfromtheonsetof when the entire un-cracked ligament undergoes creep defor-
0.2 i
mation. Such conditions are distinct from the conditions of
first applied force and CCG rate, a˙ or da/dt are expressed in
terms of the magnitude of creep crack growth relating small-scale creep and transition creep (1-7). In the case of
parameters, C*or K. With C* defined as the steady state extensive creep, the region dominated by creep deformation is
determinationofthecracktipstressesderivedinprincipalfrom significant in size in comparison to both the crack length and
2
C*(t) and C (1-14). The crack growth derived in this manner theuncrackedligamentsizes.Insmall-scale-creeponlyasmall
t
is identified as a material property which can be used in region of the un-cracked ligament local to the crack tip
modeling and life assessment methods (15-25). experiences creep deformation.
1.1.1 The choice of the crack growth correlating parameter
1.1.4 The creep crack growth rate in the extensive creep
C*, C*(t), C,or K depends on the material creep properties,
t region is correlated by the C*(t)-integral. The C parameter
t
geometry and size of the specimen. Two types of material
correlates the creep crack growth rate in the small-scale creep
behavior are generally observed during creep crack growth
and the transition creep regions and reduces, by definition, to
tests; creep-ductile (1-14) and creep-brittle (26-37). In creep
C*(t)intheextensivecreepregion (5).Henceinthisdocument
ductilematerials,wherecreepstrainsdominateandcreepcrack
thedefinitionC*isusedastherelevantparameterinthesteady
growth is accompanied by substantial time-dependent creep
state extensive creep regime whereas C*(t) and/or C are the
t
strains at the crack tip, the crack growth rate is correlated by
parameters which describe the instantaneous stress state from
the steady state definitions of C or C*(t), defined as C* (see
t
the small scale creep, transient and the steady state regimes in
1.1.4). In creep-brittle materials, creep crack growth occurs at
creep. The recommended functions to derive C* for the
low creep ductility. Consequently, the time-dependent creep
different geometries is shown in Annex A1 is described in
strains are comparable to or dominated by accompanying
Annex A2.
elastic strains local to the crack tip. Under such steady state
1.1.5 An engineering definition of an initial crack extension
creep-brittle conditions, C or K could be chosen as the
t
size δa is used in order to quantify the initial period of crack
i
correlating parameter (8-14).
development. This distance is given as 0.2 mm. It has been
1.1.2 In any one test, two regions of crack growth behavior
shown (38-40)thatthisinitialperiodwhichexistsatthestartof
may be present (9, 10). The initial transient region where
the test could be a substantial period of the test time. During
this early period the crack tip undergoes damage development
as well as redistribution of stresses prior reaching steady state.
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
Recommendation is made to correlate this initial crack growth
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
period defined as t at δa = 0.2 mm with the steady state C*
Growth Behavior.
0.2 i
Current edition approved Feb. 1, 2013. Published May 2013. Originally
...
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.
´4
Designation: E1457 − 07 E1457 − 13
Standard Test Method for
Measurement of Creep Crack Growth Times and Rates in
1
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. 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—Equation 6 was editorially corrected in August 2008.
2
ε NOTE—Equation A2.3 was editorially corrected in October 2009.
3
ε NOTE—4.2.1 and Eq 8 were editorially revised in May 2011.
4
ε NOTE—4.2.2, 4.3.1 and 4.2.5 were editorially updated in December 2011.
1. Scope
1.1 This test method covers the determination of creep crack growth (CCG) time for a creep crack to grow on initial load (CCI)
and its subsequent creep crack growth (CCG) rates in metals at elevated temperatures using pre-cracked specimens subjected to
elevated temperatures under static or quasi-static loading conditions. The tests are validated for either base material (homogenous
properties) or mixed base/weld material with inhomogeneous microstructures and creep properties. For CCI the time (CCI), t
0.2
to an initial crack extension δa = 0.2 mm from the onset of first applied force and creep crack growth CCG rate, a˙ or da/dt isare
i
expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state
2
determination of the crack tip stresses derived in principal from C*(t) and C (1-14). The crack growth derived in this manner is
t
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),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) 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 or C*(t), defined as C* (see 1.1.4). 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. Under such steady state creep-brittle conditions, C or K could be chosen as the correlating parameter (8-14).
t
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 as to how
the transient region should be treated in terms of an initial crack growth period. During steady state, a unique correlation exists
between da/dt and the appropriate crack growth rate relating parameter.
1.1.3 In creep ductile materials, extensive creep occurs when the entire uncrackedun-cracked ligament undergoes creep
deformation. Such conditions are distinct from the conditions of small-scale creep and transition creep (1-7). In the case of
extensive creep, the region dominated by creep deformation is significant in size in comparison to both the crack length and the
uncracked ligament sizes. In small-scale-creep only a small region of the uncrackedun-cracked ligament local to the crack tip
experiences creep deformation.
1.1.4 The creep crack growth rate in the extensive creep region is correlated by the C*(t)-integral. The C parameter correlates
t
the creep crack growth rate in the small-scale creep and the transition creep regions and reduces, by definition, to C*(t) in the
extensive creep region (5). Hence in this document the definition C* is used as the relevant parameter in the steady state extensive
creep regime whereas C*(t) and/or C are the parameters which describe the instantaneous stress state from the small scale creep,
t
transient and the steady state regimes in creep. The recommended functions to derive C* for the different geometries is shown in
Annex A1 is described in Annex A2.
1.1.5 An engineering definition of an initial crack extension size δa is used in order to quantify the initial perio
...
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