ASTM E1921-09ce2
(Test Method)Standard Test Method for Determination of Reference Temperature, To, for Ferritic Steels in the Transition Range
Standard Test Method for Determination of Reference Temperature, <span class="bdit">T<sub>o</sub></span>, for Ferritic Steels in the Transition Range
SIGNIFICANCE AND USE
Fracture toughness is expressed in terms of an elastic-plastic stress intensity factor, KJc, that is derived from the J-integral calculated at fracture.
Ferritic steels are inhomogeneous with respect to the orientation of individual grains. Also, grain boundaries have properties distinct from those of the grains. Both contain carbides or nonmetallic inclusions that can act as nucleation sites for cleavage microcracks. The random location of such nucleation sites with respect to the position of the crack front manifests itself as variability of the associated fracture toughness (13). This results in a distribution of fracture toughness values that is amenable to characterization using statistical methods.
Distributions of KJc data from replicate tests can be used to predict distributions of KJc for different specimen sizes. Theoretical reasoning (9), confirmed by experimental data, suggests that a fixed Weibull slope of 4 applies to all data distributions and, as a consequence, standard deviation on data scatter can be calculated. Data distribution and specimen size effects are characterized using a Weibull function that is coupled with weakest-link statistics (14). An upper limit on constraint loss and a lower limit on test temperature are defined between which weakest-link statistics can be used.
The experimental results can be used to define a master curve that describes the shape and location of median KJc transition temperature fracture toughness for 1T specimens (15). The curve is positioned on the abscissa (temperature coordinate) by an experimentally determined reference temperature, To. Shifts in reference temperature are a measure of transition temperature change caused, for example, by metallurgical damage mechanisms.
Tolerance bounds on KJc can be calculated based on theory and generic data. For added conservatism, an offset can be added to tolerance bounds to cover the uncertainty associated with estimating the reference temperature, To, fr...
SCOPE
1.1 This test method covers the determination of a reference temperature, To, which characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic KJc instabilities, or both. The specific types of ferritic steels (3.2.1) covered are those with yield strengths ranging from 275 to 825 MPa (40 to 120 ksi) and weld metals, after stress-relief annealing, that have 10 % or less strength mismatch relative to that of the base metal.
1.2 The specimens covered are fatigue precracked single-edge notched bend bars, SE(B), and standard or disk-shaped compact tension specimens, C(T) or DC(T). A range of specimen sizes with proportional dimensions is recommended. The dimension on which the proportionality is based is specimen thickness.
1.3 Median KJc values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences among the allowable test specimens in 1.2. The degree of KJc variability among specimen types is analytically predicted to be a function of the material flow properties (1) and decreases with increasing strain hardening capacity for a given yield strength material. This KJc dependency ultimately leads to discrepancies in calculated To values as a function of specimen type for the same material. To values obtained from C(T) specimens are expected to be higher than To values obtained from SE(B) specimens. Best estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived To values is approximately 10°C (2). C(T) and SE(B) To differences up to 15°C have also been recorded (3). However, comparisons of individual, small datasets may not necessarily reveal this average trend. Datasets which contain both C(T) and SE(B) specimens may generate To results which fall between the To values calculated using solely C(T) or SE(B) specimens. It is therefore strongly recommend...
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´2
Designation: E1921 – 09c
Standard Test Method for
Determination of Reference Temperature, T , for Ferritic
o
1
Steels in the Transition Range
This standard is issued under the fixed designation E1921; 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—9.3 and 8.7.2 were editorially corrected in December 2009.
2
´ NOTE—Equation references were editorially updated in March 2010.
1. Scope solely C(T) or SE(B) specimens. It is therefore strongly
recommended that the specimen type be reported along with
1.1 Thistestmethodcoversthedeterminationofareference
thederivedT valueinallreporting,analysis,anddiscussionof
o
temperature, T , which characterizes the fracture toughness of
o
results. This recommended reporting is in addition to the
ferritic steels that experience onset of cleavage cracking at
requirements in 11.1.1.
elastic, or elastic-plastic K instabilities, or both. The specific
Jc
1.4 Requirements are set on specimen size and the number
types of ferritic steels (3.2.1) covered are those with yield
of replicate tests that are needed to establish acceptable
strengths ranging from 275 to 825 MPa (40 to 120 ksi) and
characterization of K data populations.
Jc
weld metals, after stress-relief annealing, that have 10% or
1.5 T is dependent on loading rate. T is evaluated for a
o o
less strength mismatch relative to that of the base metal.
quasi-static loading rate range with 0.1< dK/dt<2MPa=m/s.
1.2 The specimens covered are fatigue precracked single-
Slowly loaded specimens (dK/dt < 0.1 MPa=m) can be
edge notched bend bars, SE(B), and standard or disk-shaped
analyzed if environmental effects are known to be negligible.
compact tension specimens, C(T) or DC(T). A range of
Provision is also made for higher loading rates (dK/dt > 2
specimen sizes with proportional dimensions is recommended.
MPa=m/s).
The dimension on which the proportionality is based is
1.6 The statistical effects of specimen size on K in the
Jc
specimen thickness.
transition range are treated using weakest-link theory (4)
1.3 Median K values tend to vary with the specimen type
Jc
applied to a three-parameter Weibull distribution of fracture
at a given test temperature, presumably due to constraint
toughness values. A limit on K values, relative to the
Jc
differences among the allowable test specimens in 1.2. The
specimen size, is specified to ensure high constraint conditions
degree of K variability among specimen types is analytically
Jc
2
along the crack front at fracture. For some materials, particu-
predicted to be a function of the material flow properties (1)
larly those with low strain hardening, this limit may not be
and decreases with increasing strain hardening capacity for a
sufficient to ensure that a single-parameter (K ) adequately
Jc
given yield strength material. This K dependency ultimately
Jc
describes the crack-front deformation state (5).
leads to discrepancies in calculated T values as a function of
o
1.7 Statistical methods are employed to predict the transi-
specimen type for the same material. T values obtained from
o
tion toughness curve and specified tolerance bounds for 1T
C(T) specimens are expected to be higher than T values
o
specimens of the material tested.The standard deviation of the
obtained from SE(B) specimens. Best estimate comparisons of
datadistributionisafunctionofWeibullslopeandmedianK .
several materials indicate that the average difference between Jc
The procedure for applying this information to the establish-
C(T) and SE(B)-derived T values is approximately 10°C (2).
o
ment of transition temperature shift determinations and the
C(T) and SE(B) T differences up to 15°C have also been
o
establishment of tolerance limits is prescribed.
recorded (3). However, comparisons of individual, small
1.8 The fracture toughness evaluation of nonuniform mate-
datasetsmaynotnecessarilyrevealthisaveragetrend.Datasets
rial is not amenable to the statistical analysis methods em-
which contain both C(T) and SE(B) specimens may generate
ployed in this standard. Materials must have macroscopically
T results which fall between the T values calculated using
o o
uniform tensile and toughness properties. For example, multi-
pass weldments can create heat-affected and brittle zones with
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
localizedpropertiesthatarequitedifferentfromeitherthebulk
and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.
material or weld. Thick section steel also often exhibits some
Current edition approved June 15, 2009. Published August 20
...
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