ASTM E1921-97

Standard Test Method for Determination of Reference Temperature, T_o, for Ferritic Steels in the Transition Range

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 Requirements are set on specimen size and the number of replicate tests that are needed to establish acceptable characterization of KJc data populations.
1.4 The statistical effects of specimen size on KJc in the transition range are treated using weakest-link theory (1) applied to a three-parameter Weibull distribution of fracture toughness values. A limit on KJc values, relative to the specimen size, is 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 (KJc) adequately describes the crack-front deformation state (2).
1.5 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 KJc. The procedure for applying this information to the establishment of transition temperature shift determinations and the establishment of tolerance limits is prescribed.
1.6 The fracture toughness evaluation of nonuniform material is not amenable to the statistical analysis methods employed in this standard. Materials must have macroscopically uniform tensile and toughness properties. 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. Metallography and initial screening may be necessary to verify the applicability of these and similarly graded materials. Data falling outside the 2 % or 98 % tolerance bounds may be indicative of a nonuniform material (see 9.3).
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Mar-2002
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: E08 - Fatigue and Fracture
• Drafting Committee: E08.07 - Fracture Mechanics

Relations

• Replaced By: ASTM E1921-02 - Standard Test Method for Determination of Reference Temperature, T_o, for Ferritic Steels in the Transition Range
• Effective Date: 10-Mar-2002
• Referred By: ASTM E1823-23 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 10-Mar-2002
• Referred By: ASTM E2215-19 - Standard Practice for Evaluation of Surveillance Capsules from Light-Water Moderated Nuclear Power Reactor Vessels
• Effective Date: 10-Mar-2002
• Referred By: ASTM E1820-23b - Standard Test Method for Measurement of Fracture Toughness
• Effective Date: 10-Mar-2002
• Referred By: ASTM E399-23 - Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials
• Effective Date: 10-Mar-2002
• Referred By: ASTM E1253-21 - Standard Guide for Reconstitution of Charpy-Sized Specimens
• Effective Date: 10-Mar-2002
• Referred By: ASTM E185-21 - Standard Practice for Design of Surveillance Programs for Light-Water Moderated Nuclear Power Reactor Vessels
• Effective Date: 10-Mar-2002
• Referred By: ASTM E509/E509M-21 - Standard Guide for In-Service Annealing of Light-Water Moderated Nuclear Reactor Vessels
• Effective Date: 10-Mar-2002
• Referred By: ASTM E636-20 - Standard Guide for Conducting Supplemental Surveillance Tests for Nuclear Power Reactor Vessels
• Effective Date: 10-Mar-2002
• Referred By: ASTM E2899-19e1 - Standard Test Method for Measurement of Initiation Toughness in Surface Cracks Under Tension and Bending
• Effective Date: 10-Mar-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: E 1921 – 97
Standard Test Method for
Determination of Reference Temperature, T , for Ferritic
o
Steels in the Transition Range
This standard is issued under the fixed designation E 1921; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorial changes were made through-out the standard in December 2001.
1. Scope that are located in heat-affected zones of multipass weldments
is not amenable to the statistical methods employed in the
1.1 This test method covers the determination of a reference
present test method.
temperature, T , which characterizes the fracture toughness of
o
1.7 This standard does not purport to address all of the
ferritic steels that experience onset of cleavage cracking at
safety concerns, if any, associated with its use. It is the
elastic, or elastic-plastic K instabilities, or both. The specific
Jc
responsibility of the user of this standard to establish appro-
types of ferritic steels (3.2.1) covered are those with yield
priate safety and health practices and determine the applica-
strengths ranging from 275 to 825 MPa (40 to 120 ksi) and
bility of regulatory limitations prior to use.
weld metals, after stress-relief annealing, that have 10 % or
less strength mismatch relative to that of the base metal.
2. Referenced Documents
1.2 The specimens covered are fatigue precracked single-
2.1 ASTM Standards:
edge notched bend bars, SE(B), and standard or disk-shaped
E 4 Practices for Force Verification of Testing Machines
compact tension specimens, C(T) or DC(T). A range of
E 8M Test Methods for Tension Testing of Metallic Mate-
specimen sizes with proportional dimensions is recommended.
rials (Metric)
The dimension on which the proportionality is based is
E 74 Practice for Calibration of Force Measuring Instru-
specimen thickness.
ments for Verifying the Force Indication of Testing Ma-
1.3 Requirements are set on specimen size and the number
chines
of replicate tests that are needed to establish acceptable
E 208 Test Method for Conducting Drop-Weight Test to
characterization of K data populations.
Jc
Determine Nil-Ductility Transition Temperature of Ferritic
1.4 The statistical effects of specimen size on K in the
Jc
2 Steels
transition range are treated using weakest-link theory (1)
E 399 Test Method for Plane-Strain Fracture Toughness of
applied to a three-parameter Weibull distribution of fracture
Metallic Materials
toughness values. A limit on K values, relative to the
Jc
E 436 Test Method for Drop-Weight Tear Tests of Ferritic
specimen size, is specified to ensure high constraint conditions
Steels
along the crack front at fracture. For some materials, particu-
E 561 Practice for R-Curve Determination
larly those with low strain hardening, this limit may not be
E 812 Test Method for Crack Strength of Slow-Bend, Pre-
sufficient to ensure that a single-parameter (K ) adequately
Jc
cracked Charpy Specimens of High-Strength Metallic
describes the crack-front deformation state (2).
Materials
1.5 Statistical methods are employed to predict the transi-
E 813 Test Method for J , A Measure of Fracture Tough-
lc
tion toughness curve and specified tolerance bounds for 1T
ness
specimens of the material tested. The standard deviation of the
E 1152 Test Method for Determining J-R Curves
data distribution is a function of Weibull slope and median K .
Jc
E 1823 Terminology Relating to Fatigue and Fracture Test-
The procedure for applying this information to the establish-
ing
ment of transition temperature shift determinations and the
establishment of tolerance limits is prescribed.
3. Terminology
1.6 The fracture toughness evaluation of local brittle zones
3.1 Terminology given in Terminology E 1823 is applicable
to this test method.
This test method is under the jurisdiction of ASTM Committee E-8 on Fatigue 3.2 Definitions:
and Fracture and is the direct responsibility of E08.08 on Elastic-Plastic Fracture
3.2.1 ferritic steel— carbon and low-alloy steels, and higher
Mechanics Technology.
Current edition approved Dec. 10, 1997. Published February 1998.
The boldface numbers in parentheses refer to the list of references at the end of
this standard. Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1921
alloy steels, with the exception of austenitic stainless, marten- 3.3.10.1 Discussion—A pop-in event is usually audible, and
sitic, and precipitation hardening steels. All ferritic steels have is a sudden cleavage crack initiation event followed by crack
body centered cubic crystal structures that display a ductile- arrest. A test record will show increased displacement and drop
to-cleavage transition temperature (see also Test Methods in applied load if the test frame is stiff. Subsequently, the test
E 208 and E 436). record may continue on to higher loads and increased displace-
ment.
NOTE 1—This definition is not intended to imply that all of the many
3.3.11 reference temperature, T [°C]—The test temperature
o
possible types of ferritic steels have been verified as being amenable to
at which the median of the K distribution from 1T size
analysis by this test method.
Jc
specimens will equal 100 MPa=m (90.9 ksi=in.).
–3/2
3.2.2 stress-intensity factor, K[FL ]—the magnitude of
3.3.12 SE(B) specimen span, S[L]—the distance between
the mathematically ideal crack-tip stress field coefficient (stress
specimen supports (see Test Method E 1152, Fig. 2).
field singularity) for a particular mode of crack-tip region
3.3.13 specimen thickness, B[L]—the distance between the
deformation in a homogeneous body.
sides of specimens.
3.2.3 Discussion—In this test method, Mode I is assumed.
3.3.13.1 Discussion—In the case of side-grooved speci-
See Terminology E 1823 for further discussion.
mens, thickness, B , is the distance between the roots of the
N
–1
3.2.4 J-integral, J[FL ]—a mathematical expression; a
side-groove notches.
line or surface integral that encloses the crack front from one
3.3.14 specimen size, nT—a code used to define specimen
crack surface to the other; used to characterize the local
dimensions, where n is expressed in multiples of 1 in.
stress-strain field around the crack front (3). See Terminology
3.3.14.1 Discussion—In this method, specimen proportion-
E 1823 for further discussion.
ality is required. For compact specimens and bend bars,
3.3 Definitions of Terms Specific to This Standard:
specimen thickness B=n in.
3.3.1 control load, P [F]—a calculated value of maximum
M
3.3.15 temperature, T [°C]—For K values that are devel-
Q Jc
load used in Test Method E 1152-87 (7.6.1) to stipulate
oped using specimens or test practices, or both, that do not
allowable precracking limits.
conform to the requirements of this test method, a temperature
3.3.1.1 Discussion—In this method, P is not used for
M
of 100 MPa=m fracture toughness is defined as T .T is not
Q Q
precracking, but is used as a minimum load above which
a provisional value of T .
o
partial unloading is started for crack growth measurement.
3.3.16 Weibull fitting parameter, K — a scale parameter
3.3.2 crack initiation—describes the onset of crack propa-
located at the 63.2 % cumulative failure probability level (6).
gation from a preexisting macroscopic crack created in the
K =K when p = 0.632.
Jc f
specimen by a stipulated procedure.
3.3.17 Weibull slope, b—with p and K data pairs plotted in
f Jc
–2
3.3.3 effective modulus, E [FL ]—an elastic modulus that
e
linearized Weibull coordinates (see Fig. X1.1), b is the slope of
can be used with experimentally determined elastic compliance
a line that defines the characteristics of the typical scatter of K
Jc
to effect an exact match to theoretical (modulus-normalized)
data.
compliance for the actual initial crack size, a .
o
3.3.17.1 Discussion—A Weibull slope of 4 is used exclu-
–2
3.3.4 elastic modulus, E8[FL ]—a linear-elastic factor re-
sively in this method.
–2
lating stress to strain, the value of which is dependent on the
3.3.18 yield strength, s [FL ]—a value of material
ys
degree of constraint. For plane strain, E8 = E/(1 – v ) is used,
strength at 0.2 % plastic strain as determined by tensile testing.
and for plane stress E8 = E.
4. Summary of Test Method
3.3.4.1 Discussion—In this test method, plane stress elastic
modulus is used.
4.1 This test method involves the testing of notched and
–3/2
3.3.5 elastic-plastic K [FL ]—An elastic-plastic equiva-
fatigue precracked bend or compact specimens in a tempera-
J
lent stress intensity factor derived from J-integral.
ture range where either cleavage cracking or crack pop-in
3.3.5.1 Discussion—In this test method, K also implies a
develop during the loading of specimens. Crack aspect ratio,
J
stress intensity factor determined at the test termination point
a/W, is nominally 0.5. Specimen width in compact specimens
under conditions determined to be invalid by 8.9.2.
is two times the thickness. In bend bars, specimen width can be
–3/2
3.3.6 elastic-plastic K [FL ]—an elastic-plastic equiva-
either one or two times the thickness.
Jc
lent stress intensity factor derived from the J-integral at the
4.2 Load versus displacement across the notch at a specified
point of onset of cleavage fracture, J .
location is recorded by autographic recorder or computer data
c
3.3.7 Eta (h)—a dimensionless parameter that relates plas-
acquisition, or both. Fracture toughness is calculated at a
tic work done on a specimen to crack growth resistance defined
defined condition of crack instability. The J-integral value at
in terms of deformation theory J-integral (4).
instability, J , is calculated and converted into its equivalent in
c
3.3.8 failure probability, p —the probability that a single units of stress intensity factor, K . Validity limits are set on the
f
Jc
selected specimen chosen at random from a population of
suitability of data for statistical analyses.
specimens will fail at or before reaching the K value of 4.3 Tests that are replicated at least six times can be used to
Jc
interest.
estimate the median K of the Weibull distribution for the data
Jc
3.3.9 initial ligament length, b [L]— the distance from the population (7). Extensive data scatter among replicate tests is
o
initial crack tip, a , to the back face of a specimen. expected. Statistical methods are used to characterize these
o
3.3.10 pop-in—a discontinuity in a load versus displace- data populations and to predict changes in data distributions
ment test record (5). with changed specimen size.
E 1921
4.4 The statistical relationship between specimen size and margin adjustment to T in the form of a reference temperature
o
K fracture toughness can be assessed using weakest-link shift.
Jc
theory, thereby providing a relationship between the specimen 5.6 For some materials, particularly those with low strain
size and K (1). Limits are placed on the fracture toughness hardening, the value of T may be influenced by specimen size
Jc o
range over which this model can be used. due to a partial loss of crack-tip constraint (2). When this
4.5 For definition of the toughness transition curve, a master occurs, the value of T may be lower than the value that would
o
curve concept is used (8, 9). The position of the curve on the be obtained from a data set of K values derived using larger
Jc
temperature coordinate is established from the experimental specimens.
determination of the temperature, designated T , at which the
o
6. Apparatus
median K for 1T size specimens is 100 MPa=m (90.9
Jc
6.1 Precision of Instrumentation—Measurements of applied
ksi=in.). Selection of a test temperature close to that at which
loads and load-line displacements are needed to obtain work
the median K value will be 100 MPa=m is encouraged and
Jc
done on the specimen. Load versus load-line displacements
a means of estimating this temperature is suggested. Small
may be recorded digitally on computers or autographically on
specimens such as precracked Charpy may have to be tested at
x-y plotters. For computers, digital signal resolution should be
temperatures below T where K is well below 100
o Jc(med)
1/32,000 of the displacement transducer signal range and
MPa=m. In such cases, additional specimens may be required
1/4000 of the load transducer signal range.
as stipulated in 8.5.
6.2 Grips for C(T) Specimens—A clevis with flat-bottom
4.6 Tolerance bounds can be determined that define the
holes is recommended. See Test Method E 399-90, Fig. A6.2,
range of scatter in fracture toughness throughout the transition
for a recommended design. Clevises and pins should be
range. The standard deviation of the fitted distribution is a
fabricated from steels of sufficient strength to elastically resist
function of Weibull slope and median K value, K .
Jc Jc(med)
indentation loads (greater than 40 Rockwell hardness C scale
5. Significance and Use
(HRC)).
5.1 Fracture toughness is expressed in terms of an elastic- 6.3 Bend Test Fixture—A suitable bend test fixture scheme
plastic stress intensity factor, K , that is derived from the is shown in Fig. A3.2 of Test Method E 399-90. It allows for
Jc
J-integral calculated at fracture. roller pin rotation and minimizes friction effects during the test.
5.2 Ferritic steels are inhomogeneous with respect to the Fixturing and rolls should be made of high-hardness steel
orientation of individual grains. Also, grain boundaries have (HRC greater than 40).
properties distinct from those of the grains. Both contain 6.4 Displacement Gage for Compact Specimens:
carbides or nonmetallic inclusions on the size scale of indi- 6.4.1 Displacement measurements are made so that J values
vidual grains that can act as nucleation sites for cleavage can be determined from area under load versus displacement
microcracks. The random location of such nucleation sites with test records (a measure of work done). If the test temperature
respect to the position of the crack front manifests itself as selection recommendations of this practice are followed, crack
variability of the associated fracture toughness (10). This growth measurement will probably prove to be unimportant.
results in a distribution of fracture toughness values that is Results that fall within the limits of uncertainty of the
amenable to characterization using statistical methods. recommended test temperature estimation scheme will prob-
5.3 Distributions of K data from replicate tests can be
...