ASTM E1221-96

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Designation: E 1221 – 96
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Determining Plane-Strain Crack-Arrest Fracture Toughness,
K , of Ferritic Steels
Ia
This standard is issued under the fixed designation E 1221; 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.
1. Scope E 1304 Test Method for Plane-Strain (Chevron Notch)
Fracture Toughness of Metallic Materials
1.1 This test method employs a side-grooved, crack-line-
wedge-loaded specimen to obtain a rapid run-arrest segment of
3. Terminology
flat-tensile separation with a nearly straight crack front. This
3.1 Definitions:
test method provides a static analysis determination of the
3.1.1 Definitions in Terminology E 616 are applicable to
stress intensity factor at a short time after crack arrest. The
this test method.
estimate is denoted K . When certain size requirements are
a
3.2 Definitions of Terms Specific to This Standard:
met, the test result provides an estimate, termed K ,ofthe
Ia
3.2.1 conditional value of the plane-strain crack-arrest
plane-strain crack-arrest toughness of the material.
−3/2
fracture toughness, K (FL )—the conditional value of K
Qa Ia
1.2 The specimen size requirements, discussed later, pro-
calculated from the test results and subject to the validity
vide for in-plane dimensions large enough to allow the speci-
criteria specified in this test method.
men to be modeled by linear elastic analysis. For conditions of
3.2.1.1 Discussion—In this test method, side-grooved
plane-strain, a minimum specimen thickness is also required.
specimens are used. The calculation of K is based upon
Qa
Both requirements depend upon the crack arrest toughness and
measurements of both the arrested crack length and of the
the yield strength of the material. A range of specimen sizes
crack-mouth opening displacement prior to initiation of a
may therefore be needed, as specified in this test method.
fast-running crack and shortly after crack arrest.
1.3 If the specimen does not exhibit rapid crack propagation
−3/2
3.2.2 crack-arrest fracture toughness, K (FL )—the
a
and arrest, K cannot be determined.
a
value of the stress intensity factor shortly after crack arrest.
1.4 Values stated in inch-pound units are to be regarded as
3.2.2.1 Discussion—The in-plane specimen dimensions
the standards. SI units are provided for information only.
must be large enough for adequate enclosure of the crack-tip
1.5 This standard does not purport to address all of the
plastic zone by a linear-elastic stress field.
safety concerns, if any, associated with its use. It is the
3.2.3 plane-strain crack-arrest fracture toughness, K
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responsibility of the user of this standard to establish appro-
−3/2
(FL )—the value of crack-arrest fracture toughness, K , for
a
priate safety and health practices and determine the applica-
a crack that arrests under conditions of crack-front plane-strain.
bility of regulatory limitations prior to use.
3.2.3.1 Discussion—The requirements for attaining condi-
2. Referenced Documents tions of crack-front plane-strain are specified in the procedures
of this test method.
2.1 ASTM Standards:
−3/2
3.2.4 stress intensity factor at crack initiation, K (FL )—
o
E 8 Test Methods for Tension Testing of Metallic Materials
the value of K at the onset of rapid fracturing.
E 23 Test Methods for Notched Bar Impact Testing of
3.2.4.1 Discussion—In this test method, only a nominal
Metallic Materials
estimate of the initial driving force is needed. For this reason,
E 208 Test Method for Conducting Drop-Weight Test to
K is calculated on the basis of the original (machined) crack
o
Determine Nil-Ductility Transition Temperature of Ferritic
2 (or notch) length and the crack-mouth opening displacement at
Steels
the initiation of a fast-running crack.
E 399 Test Method for Plane-Strain Fracture Toughness of
Metallic Materials
4. Summary of Test Method
E 616 Terminology Relating to Fracture Testing
4.1 This test method estimates the value of the stress
intensity factor, K, at which a fast running crack will arrest.
This test method is under the jurisdiction of ASTM Committee E-8 on Fracture
This test method is made by forcing a wedge into a split-pin,
Testing and is the direct responsibility of Subcommittee E08.07 on Linear-Elastic
which applies an opening force across the crack starter notch in
Fracture.
Current edition approved June 10, 1996. Published August 1996. Originally a modified compact specimen, causing a run-arrest segment of
published as E 1221 – 88. Last previous edition E 1221 – 88.
crack extension. The rapid run-arrest event suggests need for a
Annual Book of ASTM Standards, Vol 03.01.
E 1221
dynamic analysis of test results. However, experimental obser- the run-arrest event, the loading system must have a low
vations (1, 2) indicate that, for this test method, an adjusted compliance compared with the test specimen. For this reason a
static analysis of test results provides a useful estimate of the wedge and split-pin assembly is used to apply a load on the
value of the stress intensity factor at the time of crack arrest. crack line. This loading arrangement does not permit easy
4.2 Calculation of a nominal stress intensity at initiation, K , measurement of opening loads. Consequently, opening dis-
o
is based on measurements of the machined notch length and the placement measurements in conjunction with crack size and
crack-mouth opening displacement at initiation. The value of compliance calibrations are used for calculating K and K .
o a
K is based on measurements of the arrested crack length and 6.2 Loading Arrangement:
a
the crack-mouth opening displacements prior to initiation and 6.2.1 A typical loading arrangement is shown in Fig. 1. The
shortly after crack arrest. specimen is placed on a support block whose thickness should
be adequate to allow completion of the test without interfer-
5. Significance and Use
ence between the wedge and the lower crosshead of the testing
machine. The support block should contain a hole that is
5.1 In structures containing gradients in either toughness or
stress, a crack may initiate in a region of either low toughness aligned with the specimen hole, and whose diameter should be
between 1.05 and 1.15 times the diameter of the hole in the
or high stress, or both, and arrest in another region of either
higher toughness or lower stress, or both. The value of the specimen. The load that forces the wedge into the split-pin is
transmitted through a load cell.
stress intensity factor during the short time interval in which a
fast-running crack arrests is a measure of the ability of the 6.2.1.1 The surfaces of the wedge, split-pin, support block,
and specimen hole should be lubricated. Lubricant in the form
material to arrest such a crack. Values of the stress intensity
of thin (0.005 in. or 0.13 mm) strips of TFE-fluorocarbon is
factor of this kind, which are determined using dynamic
methods of analysis, provide a value for the crack-arrest preferred. Molybdenum disulfide (both dry and in a grease
vehicle) and high-temperature lubricants can also be used.
fracture toughness which will be termed K in this discussion.
A
Static methods of analysis, which are much less complex, can 6.2.1.2 A low-taper-angle wedge and split-pin arrangement
is used. If grease or dry lubricants are used, a matte finish (grit
often be used to determine K at a short time (1 to 2 ms) after
crack arrest. The estimate of the crack-arrest fracture toughness blasted) on the sliding surfaces may be helpful in avoiding
galling. The split-pin must be long enough to contact the full
obtained in this fashion is termed K . When macroscopic
a
dynamic effects are relatively small, the difference between K
A
and K is also small (1-4). For cracks propagating under
a
conditions of crack-front plane-strain, in situations where the
dynamic effects are also known to be small, K determinations
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using laboratory-sized specimens have been used successfully
to estimate whether, and at what point, a crack will arrest in a
structure (5, 6). Depending upon component design, loading
compliance, and the crack jump length, a dynamic analysis of
a fast-running crack propagation event may be necessary in
order to predict whether crack arrest will occur and the arrest
position. In such cases, values of K determined by this test
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method can be used to identify those values of K below which
the crack speed is zero. More details on the use of dynamic
analyses can be found in Ref (4).
5.2 This test method can serve at least the following
additional purposes:
5.2.1 In materials research and development, to establish in
quantitative terms significant to service performance, the
effects of metallurgical variables (such as composition or heat
treatment) or fabrication operations (such as welding or form-
ing) on the ability of a new or existing material to arrest
running cracks.
5.2.2 In design, to assist in selection of materials for, and
determine locations and sizes of, stiffeners and arrestor plates.
6. Apparatus
6.1 The procedure involves testing of modified compact
specimens that have been notched by machining. To minimize
the introduction of additional energy into the specimen during
FIG. 1 Schematic Pictorial and Sectional Views Showing the
The boldface numbers in parentheses refer to the list of references at the end of Standard Arrangement of the Wedge and Split-Pin Assembly, the
this test method. Test Specimen, and the Support Block
E 1221
specimen thickness, and the radius must be large enough to
avoid plastic indentations of the test specimen. In all cases it is
recommended that the diameter of the split-pin should be 0.005
in. (0.13 mm) less than the diameter of the specimen hole. The
wedge must be long enough to develop the maximum expected
opening displacement. Any air or oil hardening tool steel is
suitable for making the wedge and split-pins. A hardness in the
range from R 45 to R 55 has been used successfully. With the
C C
recommended wedge angle and proper lubrication, a loading
1 1
machine producing ⁄5 to ⁄10 the expected maximum opening
load is adequate. The dimensions of a wedge and split-pin
FIG. 3 Sectional View of a Loading Arrangement That May Be
assembly suitable for use with a 1.0-in. (25.4-mm) diameter Helpful When Testing Specimens at Higher Temperatures
loading hole are shown in Fig. 2. The dimensions should be
for doing this are shown in Fig. 4. Other gages can be used so
scaled when other hole diameters are used. A hole diameter of
1.0 in. has been found satisfactory for specimens having 5 < W long as their accuracy is within 2 %.
< 6.7 in. (125 < W < 170 mm).
7. Specimen Configuration, Dimensions, and Preparation
NOTE 1—Specimens tested with the arrangement shown in Fig. 1 may
7.1 Standard Specimen:
not exhibit an adequate segment of run-arrest fracturing, for example, at
7.1.1 The configuration of a compact-crack-arrest (CCA)
testing temperatures well above the NDT temperature. In these circum-
specimen that is satisfactory for low- and intermediatestrength
stances, the use of the loading arrangement shown in Fig. 3 has been found
steels is shown in Fig. 5. (In this context, an intermediate-
to be helpful (2, 7) and may be employed.
strength steel is considered to be one whose static yield stress,
6.3 Displacement Gages—Displacement gages are used to
s , is of the order of 100 ksi (700 MPa) or less.)
YS
measure the crack-mouth opening displacement at 0.25W from
7.1.1.1 The thickness, B, shall be either full product plate
the load-line. Accuracy within 2 % over the working range is
thickness or a thickness sufficient to produce a condition of
required. Either the gage recommended in Test Method E 399
plane-strain, as specified in 9.3.3.
or a similar gage modified to accommodate conical seats is
7.1.1.2 Side grooves of depth B/8 per side shall be used. For
satisfactory. It is necessary to attach the gage in a fashion such
alloys that require notch-tip embrittlement (see 7.1.3.2) the
that seating contact with the specimen is not altered by the
side grooves should be introduced after deposition of the brittle
jump of the crack. Two methods that have proven satisfactory
weld.
7.1.1.3 The specimen width, W, shall be within the range 2B
# W # 8B.
7.1.1.4 The displacement gage shall measure opening dis-
placements at an offset from the load line of 0.25W, away from
the crack tip.
7.1.2 Specimen Dimensions:
7.1.2.1 In order to limit the extent of plastic deformation in
the specimen prior to crack initiation, certain size requirements
must be met. These requirements depend upon the material
yield strength. They also depend upon K , and therefore the K
a o
needed to achieve an appropriate run-arrest event.
7.1.2.2 The in-plane specimen dimensions must be large
enough to allow for the linear elastic analysis employed by this
test method. These requirements are given in 9.3.2 and 9.3.4, in
terms of allowable crack jump lengths.
7.1.2.3 For a test result to be termed plane-strain (K )by
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this test method, the specimen thickness, B, should meet the
in. mm
requirement given in 9.3.3.
A 8.00 203
7.1.3 Starting Notch:
B 0.33 8.4
D 0.99 25.1 7.1.3.1 The function of the starting notch is to produce crack
E 1.00 25.4
initiation at an opening displacement (or wedging force) that
F 2.25 57.2
will permit an appropriate length of crack extension prior to
G 2.00 50.8
H 1.50 38.1
crack arrest. Different materials require different starter notch
preparation procedures.
NOTE 1—The dimensions given are suitable for use with a 1.0 in. (25.4
7.1.3.2 The recommended starter notch for low- and
mm) diameter loading hole in a 2.0 in. (50.8 mm) thick test specimen.
intermediate-strength steels is a notched brittle weld, as shown
These dimensions should be scaled appropriately when other hole
in Fig. 6. It is produced by depositing a weld across the
diameters and specimen thicknesses are used.
specimen thickness. Guidelines on welding procedures are
FIG. 2 Suggested Geometry and Dimensions of a Wedge and
Split-Pin Assembly given in Appendix X1.
E 1221
NOTE 1— Dimension A should be 0.002–0.010 in. (0.05–0.25 mm) less than the thickness of the clip gage arm.
NOTE 2—The knife edge can be attached to the specimen with mechanical fasteners or adhesives.
NOTE 3—The cli
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