ASTM E1221-96(2002)
(Test Method)Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, KIa, of Ferritic Steels
Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, K<sub>Ia</sub>, of Ferritic Steels
SCOPE
1.1 This test method employs a side-grooved, crack-line-wedge-loaded specimen to obtain a rapid run-arrest segment of flat-tensile separation with a nearly straight crack front. This test method provides a static analysis determination of the stress intensity factor at a short time after crack arrest. The estimate is denoted K a. When certain size requirements are met, the test result provides an estimate, termed KIa, of the plane-strain crack-arrest toughness of the material.
1.2 The specimen size requirements, discussed later, provide for in-plane dimensions large enough to allow the specimen to be modeled by linear elastic analysis. For conditions of plane-strain, a minimum specimen thickness is also required. Both requirements depend upon the crack arrest toughness and the yield strength of the material. A range of specimen sizes may therefore be needed, as specified in this test method.
1.3 If the specimen does not exhibit rapid crack propagation and arrest, Ka cannot be determined.
1.4 Values stated in inch-pound units are to be regarded as the standards. SI units are provided for information only.
1.5 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.
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Designation:E1221–96 (Reapproved 2002)
Standard Test Method for
Determining Plane-Strain Crack-Arrest Fracture Toughness,
K , of Ferritic Steels
Ia
This standard is issued under the fixed designation E1221; 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 E616 Terminology Relating to Fracture Testing
E1304 Test Method for Plane-Strain (Chevron Notch)
1.1 This test method employs a side-grooved, crack-line-
Fracture Toughness of Metallic Materials
wedge-loadedspecimentoobtainarapidrun-arrestsegmentof
flat-tensile separation with a nearly straight crack front. This
3. Terminology
test method provides a static analysis determination of the
3.1 Definitions:
stress intensity factor at a short time after crack arrest. The
3.1.1 Definitions in Terminology E616 are applicable to
estimate is denoted K . When certain size requirements are
a
this test method.
met, the test result provides an estimate, termed K ,ofthe
Ia
3.2 Definitions of Terms Specific to This Standard:
plane-strain crack-arrest toughness of the material.
3.2.1 conditional value of the plane-strain crack-arrest
1.2 The specimen size requirements, discussed later, pro-
−3/2
fracture toughness, K (FL )—the conditional value of K
Qa Ia
vide for in-plane dimensions large enough to allow the speci-
calculated from the test results and subject to the validity
men to be modeled by linear elastic analysis. For conditions of
criteria specified in this test method.
plane-strain, a minimum specimen thickness is also required.
3.2.1.1 Discussion—In this test method, side-grooved
Both requirements depend upon the crack arrest toughness and
specimens are used. The calculation of K is based upon
Qa
the yield strength of the material. A range of specimen sizes
measurements of both the arrested crack length and of the
may therefore be needed, as specified in this test method.
crack-mouth opening displacement prior to initiation of a
1.3 Ifthespecimendoesnotexhibitrapidcrackpropagation
fast-running crack and shortly after crack arrest.
and arrest, K cannot be determined.
a
−3/2
3.2.2 crack-arrest fracture toughness, K (FL )—the
a
1.4 Values stated in inch-pound units are to be regarded as
value of the stress intensity factor shortly after crack arrest.
the standards. SI units are provided for information only.
3.2.2.1 Discussion—The in-plane specimen dimensions
1.5 This standard does not purport to address all of the
must be large enough for adequate enclosure of the crack-tip
safety concerns, if any, associated with its use. It is the
plastic zone by a linear-elastic stress field.
responsibility of the user of this standard to establish appro-
3.2.3 plane-strain crack-arrest fracture toughness, K
Ia
priate safety and health practices and determine the applica-
−3/2
(FL )—the value of crack-arrest fracture toughness, K , for
a
bility of regulatory limitations prior to use.
acrackthatarrestsunderconditionsofcrack-frontplane-strain.
2. Referenced Documents 3.2.3.1 Discussion—The requirements for attaining condi-
tions of crack-front plane-strain are specified in the procedures
2.1 ASTM Standards:
of this test method.
E8 TestMethodsforTensionTestingofMetallicMaterials
−3/2
3.2.4 stressintensityfactoratcrackinitiation,K (FL )—
o
E23 Test Methods for Notched Bar Impact Testing of
the value of K at the onset of rapid fracturing.
Metallic Materials
3.2.4.1 Discussion—In this test method, only a nominal
E208 Test Method for Conducting Drop-Weight Test to
estimate of the initial driving force is needed. For this reason,
Determine Nil-DuctilityTransitionTemperature of Ferritic
K is calculated on the basis of the original (machined) crack
o
Steels
(ornotch)lengthandthecrack-mouthopeningdisplacementat
E399 Test Method for Plane-Strain Fracture Toughness of
the initiation of a fast-running crack.
Metallic Materials
4. Summary of Test Method
ThistestmethodisunderthejurisdictionofASTMCommitteeE08onFracture 4.1 This test method estimates the value of the stress
Testing and is the direct responsibility of Subcommittee E08.07 on Linear-Elastic
intensity factor, K, at which a fast running crack will arrest.
Fracture.
This test method is made by forcing a wedge into a split-pin,
Current edition approved June 10, 1996. Published August 1996. Originally
whichappliesanopeningforceacrossthecrackstarternotchin
published as E1221–88. Last previous edition E1221–88.
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.
E1221–96 (2002)
a modified compact specimen, causing a run-arrest segment of the introduction of additional energy into the specimen during
crack extension.The rapid run-arrest event suggests need for a the run-arrest event, the loading system must have a low
dynamic analysis of test results. However, experimental obser- compliance compared with the test specimen. For this reason a
vations (1, 2) indicate that, for this test method, an adjusted wedge and split-pin assembly is used to apply a load on the
static analysis of test results provides a useful estimate of the crack line. This loading arrangement does not permit easy
value of the stress intensity factor at the time of crack arrest. measurement of opening loads. Consequently, opening dis-
4.2 Calculationofanominalstressintensityatinitiation,K , placement measurements in conjunction with crack size and
o
isbasedonmeasurementsofthemachinednotchlengthandthe compliance calibrations are used for calculating K and K .
o a
crack-mouth opening displacement at initiation. The value of 6.2 Loading Arrangement:
K is based on measurements of the arrested crack length and 6.2.1 Atypical loading arrangement is shown in Fig. 1.The
a
the crack-mouth opening displacements prior to initiation and specimen is placed on a support block whose thickness should
shortly after crack arrest. be adequate to allow completion of the test without interfer-
ence between the wedge and the lower crosshead of the testing
5. Significance and Use
machine. The support block should contain a hole that is
5.1 In structures containing gradients in either toughness or
aligned with the specimen hole, and whose diameter should be
stress, a crack may initiate in a region of either low toughness
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
specimen. The load that forces the wedge into the split-pin is
higher toughness or lower stress, or both. The value of the
transmitted through a load cell.
stress intensity factor during the short time interval in which a
6.2.1.1 The surfaces of the wedge, split-pin, support block,
fast-running crack arrests is a measure of the ability of the
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
preferred. Molybdenum disulfide (both dry and in a grease
methods of analysis, provide a value for the crack-arrest
vehicle) and high-temperature lubricants can also be used.
fracture toughness which will be termed K in this discussion.
6.2.1.2 A low-taper-angle wedge and split-pin arrangement
A
Static methods of analysis, which are much less complex, can
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
crackarrest.Theestimateofthecrack-arrestfracturetoughness
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
dynamiceffectsarealsoknowntobesmall, K determinations
Ia
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
Ia
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
FIG. 1 Schematic Pictorial and Sectional Views Showing the
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standard Arrangement of the Wedge and Split-Pin Assembly, the
this test method. Test Specimen, and the Support Block
E1221–96 (2002)
blasted) on the sliding surfaces may be helpful in avoiding
galling. The split-pin must be long enough to contact the full
specimen thickness, and the radius must be large enough to
avoid plastic indentationsofthetestspecimen.Inallcasesitis
recommendedthatthediameterofthesplit-pinshouldbe0.005
in. (0.13 mm) less than the diameter of the specimen hole.The
wedgemustbelongenoughtodevelopthemaximumexpected
opening displacement. Any air or oil hardening tool steel is
suitableformakingthewedgeandsplit-pins.Ahardnessinthe
rangefromR 45toR 55hasbeenusedsuccessfully.Withthe
C C
recommended wedge angle and proper lubrication, a loading
FIG. 3 Sectional View of a Loading Arrangement That May Be
1 1
machine producing ⁄5 to ⁄10 the expected maximum opening Helpful When Testing Specimens at Higher Temperatures
load is adequate. The dimensions of a wedge and split-pin
assembly suitable for use with a 1.0-in. (25.4-mm) diameter
that seating contact with the specimen is not altered by the
loading hole are shown in Fig. 2. The dimensions should be
jump of the crack. Two methods that have proven satisfactory
scaled when other hole diameters are used.Ahole diameter of
for doing this are shown in Fig. 4. Other gages can be used so
1.0in.hasbeenfoundsatisfactoryforspecimenshaving5< W
long as their accuracy is within 2%.
< 6.7 in. (125 < W < 170 mm).
NOTE 1—Specimens tested with the arrangement shown in Fig. 1 may
7. Specimen Configuration, Dimensions, and Preparation
not exhibit an adequate segment of run-arrest fracturing, for example, at
7.1 Standard Specimen:
testing temperatures well above the NDT temperature. In these circum-
7.1.1 The configuration of a compact-crack-arrest (CCA)
stances,theuseoftheloadingarrangementshowninFig.3hasbeenfound
specimen that is satisfactory for low- and intermediatestrength
to be helpful (2, 7) and may be employed.
steels is shown in Fig. 5. (In this context, an intermediate-
6.3 Displacement Gages—Displacement gages are used to
strength steel is considered to be one whose static yield stress,
measure the crack-mouth opening displacement at 0.25W from
s , is of the order of 100 ksi (700 MPa) or less.)
YS
the load-line. Accuracy within 2% over the working range is
7.1.1.1 The thickness, B, shall be either full product plate
required. Either the gage recommended in Test Method E399
thickness or a thickness sufficient to produce a condition of
or a similar gage modified to accommodate conical seats is
plane-strain, as specified in 9.3.3.
satisfactory. It is necessary to attach the gage in a fashion such
7.1.1.2 Sidegroovesofdepth B/8persideshallbeused.For
alloys that require notch-tip embrittlement (see 7.1.3.2) the
sidegroovesshouldbeintroducedafterdepositionofthebrittle
weld.
7.1.1.3 Thespecimenwidth, W,shallbewithintherange2B
# W# 8B.
7.1.1.4 The displacement gage shall measure opening dis-
placementsatanoffsetfromtheloadlineof0.25W,awayfrom
the crack tip.
7.1.2 Specimen Dimensions:
7.1.2.1 In order to limit the extent of plastic deformation in
thespecimenpriortocrackinitiation,certainsizerequirements
must be met. These requirements depend upon the material
yieldstrength.Theyalsodependupon K ,andthereforethe K
a o
needed to achieve an appropriate run-arrest event.
7.1.2.2 The in-plane specimen dimensions must be large
enoughtoallowforthelinearelasticanalysisemployedbythis
testmethod.Theserequirementsaregivenin9.3.2and9.3.4,in
in. mm
terms of allowable crack jump lengths.
A 8.00 203
7.1.2.3 For a test result to be termed plane-strain (K )by
B 0.33 8.4 Ia
D 0.99 25.1 this test method, the specimen thickness, B, should meet the
E 1.00 25.4
requirement given in 9.3.3.
F 2.25 57.2
7.1.3 Starting Notch:
G 2.00 50.8
H 1.50 38.1 7.1.3.1 Thefunctionofthestartingnotchistoproducecrack
initiation at an opening displacement (or wedging force) that
NOTE 1—The dimensions given are suitable for use with a 1.0 in. (25.4
will permit an appropriate length of crack extension prior to
mm) diameter loading hole in a 2.0 in. (50.8 mm) thick test specimen.
crack arrest. Different materials require different starter notch
These dimensions should be scaled appropriately when other hole
preparation procedures.
diameters and specimen thicknesses are used.
7.1.3.2 The recommended starter notch for low- and
FIG. 2 Suggested Geometry and Dimensions of a Wedge and
Split-Pin Assembly intermediate-strength steels is a notched brittle weld, as shown
E1221–96 (2002)
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 clip gage is installed by sliding it into the gap.
FIG. 4 Two Alternative Clip Gage Seating Arrangements Using Knife Edges and Using Conical Mounts
H=0.6 W 6 0.005 W
S=(B−B )/2 6 0.01 B
N
N# W/10
0.15 W# L# 0.25 W
0.20 W# a # 0.40 W
o
0.125 W 6 0.005 W# D# 0.250 W 6 0.005 W
FIG. 5 Geometry and Dimensions of a Crack-Line-Wedge-Loaded Compact-Crack-Arrest (CCA) Test Specimen that is Satisfactory for
Low and Medium Strength Steels
in Fig
...
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