ASTM E1457-23e1
(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
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 (11, 13, 30-35).
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 selecti...
SCOPE
1.1 This test method covers the determination of creep crack initiation (CCI) and creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The solutions presented in this test method are validated for base material (that is, homogenous properties) and mixed base/weld material with inhomogeneous microstructures and creep properties. The CCI time, t0.2, which is the time required to reach an initial crack extension of δai = 0.2 mm to occur 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 correlated by fracture mechanics 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 (1-17).2 The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (17-28).
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 (1-17) and creep-brittle (29-44). 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 (12, 13)....
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E1457 − 23
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. 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—Section 4.2.11 was editorially corrected in April 2024.
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 creep crack
Steady-state creep crack growth rate behavior is covered by
initiation (CCI) and creep crack growth (CCG) in metals at
this standard. In addition, specific recommendations are made
elevated temperatures using pre-cracked specimens subjected
in 11.7 as to how the transient region should be treated in terms
to static or quasi-static loading conditions. The solutions
of an initial crack growth period. During steady state, a unique
presented in this test method are validated for base material
correlation exists between da/dt and the appropriate crack
(that is, homogenous properties) and mixed base/weld material
growth rate relating parameter.
with inhomogeneous microstructures and creep properties. The
1.1.3 In creep ductile materials, extensive creep occurs
CCI time, t , which is the time required to reach an initial
0.2
when the entire un-cracked ligament undergoes creep defor-
crack extension of δa = 0.2 mm to occur from the onset of first
i
mation. Such conditions are distinct from the conditions of
applied force, and CCG rate, a˙ or da/dt are expressed in terms
small-scale creep and transition creep (1-10). In the case of
of the magnitude of creep crack growth correlated by fracture
extensive creep, the region dominated by creep deformation is
mechanics parameters, C* or K, with C* defined as the steady
significant in size in comparison to both the crack length and
state determination of the crack tip stresses derived in principal
2
the uncracked ligament sizes. In small-scale-creep only a small
from C*(t) and C (1-17). The crack growth derived in this
t
region of the un-cracked ligament local to the crack tip
manner is identified as a material property which can be used
experiences creep deformation.
in modeling and life assessment methods (17-28).
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, region is correlated by the C*(t)-integral. The C parameter
t 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 (1-17) and creep-brittle (29-44). In creep
C*(t) in the extensive creep region (5). Hence in this document
ductile materials, where creep strains dominate and creep crack
the definition C* is used as the relevant parameter in the steady
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
the small scale creep, transient and the steady state regimes in
t
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 shown in Annex A1 is described in Annex
strains are comparable to or dominated by accompanying
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 (41-44) that this initial period which exists at the start of
may be present (12, 13). 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.
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This test method is under the jurisdiction o
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