ASTM E1457-07
(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
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 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 uncracked 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 uncracked 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 Ct parameter correlates 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 Ct are the parameters which describe the instantaneous stress state from the small scale creep, 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 δai is used in order to quantify the initial period of crack development. This distance is given as 0.2 mm. It has been shown (38-40) that this period which exists at the start of 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. Recommendation is made to correlate this initial crack growth period defined as t0.2 at δai = 0.2 mm with the steady state C* when the crack tip is under extensive creep and with K for...
General Information
Relations
Standards Content (Sample)
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
Designation: E 1457 – 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope correlation exists between da/dt and the appropriate crack
growth rate relating parameter.
1.1 Thistestmethodcoversthedeterminationofcreepcrack
1.1.3 In creep ductile materials, extensive creep occurs
growth (CCG) in metals at elevated temperatures using pre-
when the entire uncracked ligament undergoes creep deforma-
cracked specimens subjected to static or quasi-static loading
tion. Such conditions are distinct from the conditions of
conditions. The time (CCI), t to an initial crack extension
0.2
small-scale creep and transition creep (1-7). In the case of
da =0.2 mm from the onset of first applied force and creep
i
extensive creep, the region dominated by creep deformation is
crack growth rate, a˙ or da/dt is expressed in terms of the
significant in size in comparison to both the crack length and
magnitude of creep crack growth relating parameters, C*or K.
theuncrackedligamentsizes.Insmall-scale-creeponlyasmall
With C* defined as the steady state determination of the crack
2 region of the uncracked ligament local to the crack tip
tip stresses derived in principal from C*(t) and C (1-14). The
t
experiences creep deformation.
crack growth derived in this manner is identified as a material
1.1.4 The creep crack growth rate in the extensive creep
property which can be used in modeling and life assessment
region is correlated by the C*(t)-integral. The C parameter
t
methods (15-25).
correlates the creep crack growth rate in the small-scale creep
1.1.1 The choice of the crack growth correlating parameter
and the transition creep regions and reduces, by definition, to
C*, C*(t), C,or K depends on the material creep properties,
t
C*(t)intheextensivecreepregion (5).Henceinthisdocument
geometry and size of the specimen. Two types of material
thedefinitionC*isusedastherelevantparameterinthesteady
behavior are generally observed during creep crack growth
state extensive creep regime whereas C*(t) and/or C are the
t
tests; creep-ductile (1-14) and creep-brittle (26-37). In creep
parameters which describe the instantaneous stress state from
ductilematerials,wherecreepstrainsdominateandcreepcrack
the small scale creep, transient and the steady state regimes in
growth is accompanied by substantial time-dependent creep
creep. The recommended functions to derive C* for the
strains at the crack tip, the crack growth rate is correlated by
different geometries is shown in Annex A1 is described in
the steady state definitions of C or C*(t), defined as C* (see
t
Annex A2.
1.1.4). In creep-brittle materials, creep crack growth occurs at
1.1.5 An engineering definition of an initial crack extension
low creep ductility. Consequently, the time-dependent creep
size da is used in order to quantify the initial period of crack
strains are comparable to or dominated by accompanying i
development. This distance is given as 0.2 mm. It has been
elastic strains local to the crack tip. Under such steady state
shown (38-40) that this period which exists at the start of the
creep-brittle conditions, C or K could be chosen as the
t
test could be a substantial period of the test time. During this
correlating parameter (8-14).
early period the crack tip undergoes damage development as
1.1.2 In any one test, two regions of crack growth behavior
well as redistribution of stresses prior reaching steady state.
may be present (9, 10). The initial transient region where
Recommendation is made to correlate this initial crack growth
elastic strains dominate and creep damage develops and in the
period defined as t at da = 0.2 mm with the steady state C*
0.2 i
steady state region where crack grows proportionally to time.
when the crack tip is under extensive creep and with K for
Steady-state creep crack growth rate behavior is covered by
creep brittle conditions. The values for C* and K should be
this standard. In addition specific recommendations are made
calculated at the final specified crack size defined as a + da
o i
in11.7astohowthetransientregionshouldbetreatedinterms
where a initial size of the starter crack.
o
of an initial crack growth period. During steady state, a unique
1.1.6 The recommended specimens for CCI and CCG test-
ing is the standard compact tension specimen C(T) (see Fig.
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
A1.1) which is pin-loaded in tension under constant loading
and Fracture and is
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.