ASTM E1921-18
(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, <emph type="bdit">T<inf >o</inf></emph>, for Ferritic Steels in the Transition Range
SIGNIFICANCE AND USE
5.1 Fracture toughness is expressed in terms of an elastic-plastic stress intensity factor, KJc, that is derived from the J-integral calculated at fracture.
5.2 Ferritic steels are microscopically 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 (16). This results in a distribution of fracture toughness values that is amenable to characterization using the statistical methods in this test method.
5.3 The statistical methods in this test method presume that the test materials are macroscopically homogeneous such that both the tensile and toughness properties are uniform. The fracture toughness evaluation of nonuniform materials is not amenable to the statistical analysis methods employed in the main body of this test method. For example, multipass weldments can create heat-affected and brittle zones with localized properties that are quite different from either the bulk material or weld. Thick section steel also often exhibits some variation in properties near the surfaces. An appendix to analyze the cleavage toughness properties of nonuniform or inhomogeneous materials is currently being prepared. In the interim, users are referred to (6-8) for procedures to analyze inhomogeneous materials. Metallographic analysis can be used to identify possible nonuniform regions in a material. These regions can then be evaluated through mechanical testing such as hardness, microhardness, and tensile testing to compare with the bulk material. It is also advisable to measure the toughness properties of these nonuniform regions distinctly from the bulk material.
5.4 Distributions of KJc data from replicate tests can b...
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)2 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 recomme...
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Designation: E1921 − 18
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. Scope recommended that the specimen type be reported along with
thederivedT valueinallreporting,analysis,anddiscussionof
o
1.1 Thistestmethodcoversthedeterminationofareference
results. This recommended reporting is in addition to the
temperature, T , which characterizes the fracture toughness of
o
requirements in 11.1.1.
ferritic steels that experience onset of cleavage cracking at
elastic, or elastic-plastic K instabilities, or both. The specific 1.4 Requirements are set on specimen size and the number
Jc
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 < 2 MPa√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) in Annex A1. Note that this threshold loading rate
The dimension on which the proportionality is based is
for application of AnnexA1 is a much lower threshold than is
specimen thickness. required in other fracture toughness test methods such as E399
and E1820.
1.3 Median K values tend to vary with the specimen type
Jc
at a given test temperature, presumably due to constraint
1.6 The statistical effects of specimen size on K in the
Jc
differences among the allowable test specimens in 1.2. The
transition range are treated using the weakest-link theory (4)
degree of K variability among specimen types is analytically
applied to a three-parameter Weibull distribution of fracture
Jc
2
predicted to be a function of the material flow properties (1)
toughness values. A limit on K values, relative to the
Jc
and decreases with increasing strain hardening capacity for a
specimen size, is specified to ensure high constraint conditions
given yield strength material. This K dependency ultimately
along the crack front at fracture. For some materials, particu-
Jc
leads to discrepancies in calculated T values as a function of
larly those with low strain hardening, this limit may not be
o
specimen type for the same material. T values obtained from
sufficient to ensure that a single-parameter (K ) adequately
o
Jc
C(T) specimens are expected to be higher than T values
describes the crack-front deformation state (5).
o
obtained from SE(B) specimens. Best estimate comparisons of
1.7 Statistical methods are employed to predict the transi-
several materials indicate that the average difference between
tion toughness curve and specified tolerance bounds for 1T
C(T) and SE(B)-derived T values is approximately 10°C (2).
o
specimens of the material tested.The standard deviation of the
C(T) and SE(B) T differences up to 15°C have also been
o
datadistributionisafunctionofWeibullslopeandmedianK .
Jc
recorded (3). However, comparisons of individual, small data-
The procedure for applying this information to the establish-
sets may not necessarily reveal this average trend. Datasets
ment of transition temperature shift determinations and the
which contain both C(T) and SE(B) specimens may generate
establishment of tolerance limits is prescribed.
T results which fall between the T values calculated using
o o
1.8 This test method assumes that the test material is
solely C(T) or SE(B) specimens. It is therefore strongly
macroscopically homogeneous such that the materials have
uniform tensile and toughness properties. The fracture tough-
nessevaluationofnonuniformmaterialsisnotamenabletothe
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
statistical analysis methods employed in the main body of this
and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.
Current edition approved Jan. 15, 2018. Published March 2018. Originally
test method. Application of the analysis of this test method to
...
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.
Designation: E1921 − 17a E1921 − 18
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of a reference temperature, T , which characterizes the fracture toughness of
o
ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic K instabilities, or both. The specific types
Jc
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 K values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences
Jc
among the allowable test specimens in 1.2. The degree of K variability among specimen types is analytically predicted to be a
Jc
2
function of the material flow properties (1) and decreases with increasing strain hardening capacity for a given yield strength
material. This K dependency ultimately leads to discrepancies in calculated T values as a function of specimen type for the same
Jc o
material. T values obtained from C(T) specimens are expected to be higher than T values obtained from SE(B) specimens. Best
o o
estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived T values is
o
approximately 10°C (2). C(T) and SE(B) T differences up to 15°C have also been recorded (3). However, comparisons of
o
individual, small datasets may not necessarily reveal this average trend. Datasets which contain both C(T) and SE(B) specimens
may generate T results which fall between the T values calculated using solely C(T) or SE(B) specimens. It is therefore strongly
o o
recommended that the specimen type be reported along with the derived T value in all reporting, analysis, and discussion of
o
results. This recommended reporting is in addition to the requirements in 11.1.1.
1.4 Requirements are set on specimen size and the number of replicate tests that are needed to establish acceptable
characterization of K data populations.
Jc
1.5 T is dependent on loading rate. T is evaluated for a quasi-static loading rate range with 0.1< dK/dt < 2 MPa√m/s. Slowly
o o
loaded specimens (dK/dt < 0.1 MPa√m) can be analyzed if environmental effects are known to be negligible. Provision is also
made for higher loading rates (dK/dt > 2 MPa√m/s) in Annex A1. Note that this threshold loading rate for application of Annex
A1 is a much lower threshold than is required in other fracture toughness test methods such as E399 and E1820.
1.6 The statistical effects of specimen size on K in the transition range are treated using the weakest-link theory (4) applied
Jc
to a three-parameter Weibull distribution of fracture toughness values. A limit on K values, relative to the specimen size, is
Jc
specified to ensure high constraint conditions along the crack front at fracture. For some materials, particularly those with low
strain hardening, this limit may not be sufficient to ensure that a single-parameter (K ) adequately describes the crack-front
Jc
deformation state (5).
1.7 Statistical methods are employed to predict the transition toughness curve and specified tolerance bounds for 1T specimens
of the material tested. The standard deviation of the data distribution is a function of Weibull slope and median K . The procedure
Jc
for applying this information to the establishment of transition temperature shift determinations and the establishment of tolerance
limits is prescribed.
1.8 This test method assumes that the test material is macroscopically homogeneous such that the materials have uniform tensile
and toughness properties. The fracture toughness evaluation of nonuniform materials is not amenable to the statistical analysis
1
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