ASTM E399-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E399 − 23
Standard Test Method for
Linear-Elastic Plane-Strain Fracture Toughness of Metallic
Materials
This standard is issued under the fixed designation E399; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 1.2 This test method is divided into two parts. The first part
gives general recommendations and requirements for testing
1.1 This test method covers the determination of fracture
and includes specific requirements for the K test procedure.
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toughness (K and optionally K ) of metallic materials under
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The second part consists of Annexes that give specific infor-
predominantly linear-elastic, plane-strain conditions using fa-
mation on displacement gage and loading fixture design,
tigue precracked specimens having a thickness of 1.6 mm
special requirements for individual specimen configurations,
(0.063 in.) or greater subjected to slowly, or in special
and detailed procedures for fatigue precracking. Additional
(elective) cases rapidly, increasing crack-displacement force.
annexes are provided that give specific procedures for beryl-
Details of test apparatus, specimen configuration, and experi-
lium and rapid-force testing, and the K test procedure, which
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mental procedure are given in the annexes. Two procedures are
provides an optional additional analysis procedure for the test
outlined for using the experimental data to calculate fracture
data collected as part of the K test procedure.
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toughness values:
1.3 General information and requirements common to all
1.1.1 The K test procedure is described in the main body of
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specimen configurations:
this test standard and is a mandatory part of the testing and
Section
results reporting procedure for this test method. The K test
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Referenced Documents 2
procedure is based on crack growth of up to 2 % percent of the
Terminology 3
specimen width. This can lead to a specimen size dependent
Stress-Intensity Factor 3.1.1
Plane-Strain Fracture Toughness 3.1.2
rising fracture toughness resistance curve, with larger speci-
Crack Plane Orientation 3.1.4
mens producing higher fracture toughness results.
Summary of Test Method 4
1.1.2 The K test procedure is described in Appendix X1
Significance and Use 5
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Significance 5.1
and is an optional part of this test method. The K test
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Precautions 5.1.1 – 5.1.5
procedure is based on a fixed amount of crack extension of 0.5
Practical Applications 5.2
mm, and as a result, K is less sensitive to specimen size than Apparatus (see also 1.4) 6
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Tension Machine 6.1
K . This less size-sensitive fracture toughness, K , is called
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Fatigue Machine 6.2
size-insensitive throughout this test method. Appendix X1
Loading Fixtures 6.3
contains an optional procedure for reinterpreting the force-
Displacement Gage, Measurement 6.4
Specimen Size, Configurations, and Preparation (see 7
displacement test record recorded as part of this test method to
also 1.5)
calculate the additional fracture toughness value, K .
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Specimen Size Estimates 7.1
NOTE 1—Plane-strain fracture toughness tests of materials thinner than Standard and Alternative Specimen Configurations 7.2
Fatigue Crack Starter Notches 7.3.1
1.6 mm (0.063 in.) that are sufficiently brittle (see 7.1) can be made using
Fatigue Precracking (see also 1.6) 7.3.2
other types of specimens (1). There is no standard test method for such
Crack Extension Beyond Starter Notch 7.3.2.2
thin materials.
General Procedure 8
Specimen Measurements
Thickness 8.2.1
Width 8.2.2
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue
Crack Size 8.2.3
and Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture
Crack Plane Angle 8.2.4
Mechanics. Specimen Testing
Current edition approved June 1, 2023. Published July 2023. Originally approved Loading Methods 8.3
Loading Rate 8.4
in 1970. Last previous edition approved in 2022 as E399 – 22. DOI: 10.1520/
Test Record 8.5
E0399-23.
Calculation and Interpretation of Results 9
For additional information relating to the fracture toughness testing of
Test Record Analysis 9.1
aluminum alloys, see Practice B645.
P /P Validity Requirement 9.1.3
max Q
The boldface numbers in parentheses refer to the list of references at the end of
Specimen Size Validity Requirements 9.1.4
this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E399 − 23
Temperature, T , for Ferritic Steels in the Transition
Section
Reporting 10
Range
Precision and Bias 11
E1942 Guide for Evaluating Data Acquisition Systems Used
1.4 Specific requirements related to test apparatus:
in Cyclic Fatigue and Fracture Mechanics Testing
Double-Cantilever Displacement Gage Annex A1 E3076 Practice for Determination of the Slope in the Linear
Testing Fixtures Annex A2
Region of a Test Record
Bend Specimen Loading Fixture Annex A2.1
Compact Specimen Loading Clevis Annex A2.2
3. Terminology
1.5 Specific requirements related to individual specimen
3.1 Definitions: Terminology E1823 is applicable to this test
configurations:
method:
Bend Specimen SE(B) Annex A3
−3/2
3.1.1 stress-intensity factor, K, K , K , K [FL ]—
Compact Specimen C(T) Annex A4 I II III
Disk-Shaped Compact Specimen DC(T) Annex A5
magnitude of the ideal-crack-tip stress field (a stress-field
Arc-Shaped Tension Specimen A(T) Annex A6
singularity), for a particular mode of crack displacement, in a
Arc-Shaped Bend Specimen A(B) Annex A7
homogeneous, linear-elastic body.
1.6 Specific requirements related to special test procedures:
3.1.1.1 K is a function of applied force and test specimen
Fatigue Precracking K and K Specimens Annex A8
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size, geometry, and crack size, and has the dimensions of force
Hot-Pressed Beryllium Testing Annex A9
-3/2
times length .
Rapid-Force Testing Annex A10
Determination of K Appendix X1 3.1.1.2 Values of K for modes I, II, and III are given as:
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1.7 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information 1/2
lim
K 5 σ 2πr (1)
@ ~ ! #
I yy
only.
r→0
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1/2
lim
K 5 τ 2πr (2)
@ ~ ! #
II xy
responsibility of the user of this standard to establish appro-
r→0
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1/2
lim
K 5 τ 2πr (3)
@ ~ ! #
III yz
1.9 This international standard was developed in accor-
r→0
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
where r is the distance directly forward from the crack tip to
Development of International Standards, Guides and Recom-
the location where the significant stress is calculated.
-3/2
mendations issued by the World Trade Organization Technical
3.1.2 plane-strain fracture toughness, K [FL ]—the
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Barriers to Trade (TBT) Committee.
crack-extension resistance under conditions of crack-tip plane
strain in Mode I for slow rates of loading under predominantly
2. Referenced Documents
linear-elastic conditions and negligible plastic-zone adjust-
2.1 ASTM Standards:
ment. The stress intensity factor, K , is measured using the
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B909 Guide for Plane Strain Fracture Toughness Testing of
operational procedure (and satisfying all of the validity require-
Non-Stress Relieved Aluminum Products
ments) specified in Test Method E399, that provides for the
B645 Practice for Linear-Elastic Plane-Strain Fracture
measurement of crack-extension resistance at the onset (2% or
Toughness Testing of Aluminum Alloys
less) of crack extension and provides operational definitions of
E4 Practices for Force Calibration and Verification of Test-
crack-tip sharpness, onset of crack extension, and crack-tip
ing Machines
plane strain.
E8/E8M Test Methods for Tension Testing of Metallic Ma- 3.1.2.1 See also definitions of crack-extension resistance,
terials
crack-tip plane strain, and mode in Terminology E1823.
E177 Practice for Use of the Terms Precision and Bias in 3.1.3 crack mouth opening displacement (CMOD), V [L]—
m
ASTM Test Methods
crack opening displacement resulting from the total deforma-
E456 Terminology Relating to Quality and Statistics tion (elastic plus plastic), measured under force at the location
E647 Test Method for Measurement of Fatigue Crack
on a crack surface that has the largest displacement per unit
Growth Rates
force.
E691 Practice for Conducting an Interlaboratory Study to
3.1.4 crack plane orientation—identification of the plane
Determine the Precision of a Test Method
and direction of crack extension in relation to the characteristic
E1820 Test Method for Measurement of Fracture Toughness
directions of the product. A hyphenated code defined in
E1823 Terminology Relating to Fatigue and Fracture Testing
Terminology E1823 is used wherein the letter(s) preceding the
E1921 Test Method for Determination of Reference
hyphen represents the direction normal to the crack plane and
the letter(s) following the hyphen represents the anticipated
direction of crack extension (see Fig. 1).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.4.1 Wrought Products—the fracture toughness of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
wrought material depends on, among other factors, the orien-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. tation and propagation direction of the crack in relation to the
E399 − 23
(a) Rectangular Sections—Specimens Aligned with Reference Directions
(b) Rectangular Sections—Specimens Not Aligned with Reference Directions
(c) Cylindrical Bars and Tubes
L = direction of maximum grain flow
R = radial direction
C = circumferential or tangential direction
FIG. 1 Crack Plane Identification
E399 − 23
material’s anisotropy, which depends, in turn, on the principal 3.1.4.8 Discussion—when products are to be compared on
directions of mechanical working and grain flow. Orientation the basis of fracture toughness, it is essential that specimen
of the crack plane shall be identified wherever possible. In location and orientation with respect to product characteristic
addition, product form shall be identified (for example, directions be comparable and that the results not be generalized
beyond these limits.
straight-rolled plate, cross-rolled plate, pancake forging, and so
forth) along with material condition (for example, annealed,
3.2 Definitions of Terms Specific to This Standard:
solution treated plus aged, and so forth). The user shall be
3.2.1 lower bound force of linear region, P [F]—the lower
L
referred to product specifications for detailed processing infor-
bound force of the fitted range of the best-fit line to the initial
mation.
linear region of the force-displacement (CMOD) record.
3.1.4.2 For rectangular sections, the reference directions are
3.2.2 origin point of linear region, O [L]—the displacement
identified as in Fig. 1(a) and Fig. 1(b), which give examples for
at zero force of the best-fit line to the initial linear region of the
rolled plate. The same system is used for sheet, extrusions, and
force-displacement (CMOD) record
-3/2 -1
forgings with nonsymmetrical grain flow.
˙
3.2.3 stress-intensity factor rate, K (FL t )—change in
L = direction of principal deformation (maximum grain flow) stress-intensity factor, K, per unit time.
T = direction of least deformation
3.2.4 upper bound force of linear region, P [F]—the upper
U
S = third orthogonal direction
bound force of the fitted range of the best-fit line to the initial
3.1.4.3 Using the two-letter code, the first letter designates
linear region of the force-displacement (CMOD) record.
the direction normal to the crack plane, and the second letter
the expected direction of crack propagation. For example, in
4. Summary of Test Method
Fig. 1(a), the T-L specimen fracture plane normal is in the
4.1 This test method covers the determination of the plane-
width direction of a plate and the expected direction of crack
strain fracture toughness (K ) of metallic materials by
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propagation is coincident with the direction of maximum grain
increasing-force tests of fatigue precracked specimens. Force is
flow (or longitudinal) direction of the plate.
applied either in tension or three-point bending and force
3.1.4.4 For specimens tilted in respect to two of the refer-
versus crack mouth opening displacement (CMOD) is re-
ence axes as in Fig. 1(b), crack plane orientation is identified
corded. The force at a 5 % secant offset from the initial slope
by a three-letter code. The designation L-TS, for example,
(corresponding to about 2.0 % apparent crack extension) is
indicates the crack plane to be perpendicular to the principal
established by a specified deviation from the linear portion of
deformation (L) direction, and the expected fracture direction
the record (1). The value of K is calculated from this force
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to be intermediate between T and S. The designation TS-L
using equations that have been established by elastic stress
means that the crack plane is perpendicular to a direction
analysis of the specimen configurations specified in this test
intermediate between T and S, and the expected fracture
method. The validity of the K value determined by this test
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direction is in the L direction.
method depends upon the establishment of a sharp-crack
3.1.4.5 For cylindrical sections, where grain flow can be in
condition at the tip of the fatigue crack in a specimen having a
the longitudinal, radial or circumferential direction, specimen
size adequate to ensure predominantly linear-elastic, plane-
location and crack plane orientation shall reference original
strain conditions. To establish the suitable crack-tip condition,
cylindrical section geometry such that the L direction is always
the stress-intensity factor level at which specimen fatigue
the axial direction for the L-R-C system, as indicated in Fig.
precracking is conducted is limited to a relatively low value.
1(c), regardless of the maximum grain flow. Note that this is a
4.2 Details of the test specimens and experimental proce-
geometry based system. As such, the direction of maximum
dures are given in the Annexes. The specimen size required for
grain flow shall be reported when the direction is known.
test validity increases as the square of the material’s toughness-
to-yield strength ratio. Therefore a range of proportional
NOTE 2—The same system is useful for extruded or forged parts having
circular cross section. In most cases the L direction corresponds to the
specimens is provided.
direction of maximum grain flow, but some products such as pancake,
disk, or ring forgings can have the R or C directions correspond to the
5. Significance and Use
direction of maximum grain flow, depending on the manufacturing
method.
5.1 The property K determined by this test method char-
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L = axial direction acterizes the resistance of a material to fracture in a neutral
R = radial direction
environment in the presence of a sharp crack under essentially
C = circumferential or tangential direction
linear-elastic stress and severe tensile constraint, such that (1)
3.1.4.6 In the case of complex structural shapes, where the
the state of stress near the crack front approaches tritensile
grain flow is not uniform, specimen location and crack plane
plane strain, and (2) the crack-tip plastic zone is small
orientation shall reference host product form geometry and be
compared to the crack size, specimen thickness, and ligament
noted on component drawings.
ahead of the crack.
3.1.4.7 non-wrought products—for non-wrought products, 5.1.1 Variation in the value of K can be expected within
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specimen location and crack plane orientation shall be defined
the allowable range of specimen proportions, a/W and W/B. K
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on the part drawing. The result of a fracture toughness test from may also be expected to rise with increasing ligament size.
a non-wrought product shall not carry an orientation designa- Notwithstanding these variations, however, K is believed to
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tion. represent a lower limiting value of fracture toughness (for 2 %
E399 − 23
apparent crack extension) in the environment and at the speed when residual stresses may be significantly biasing test results,
and temperature of the test. and methods for minimizing the effects of residual stress
during testing.
5.1.2 Lower and more highly variable values of fracture
toughness can be obtained from specimens that fail by cleavage
5.2 This test method can serve the following purposes:
fracture; for example, specimens of ferritic steels tested at
5.2.1 In research and development, to establish in quantita-
temperatures in the ductile-to-brittle transition region or below.
tive terms significant to service performance, the effects of
Specimens failing by cleavage are also more likely to exhibit
metallurgical variables such as composition or heat treatment,
warm prestressing effects, where precracking at a temperature
or of fabricating operations such as welding or forming, on the
higher than the test temperature can artificially increase the
fracture toughness of new or existing materials.
fracture toughness measured (2). The present test method is not
5.2.2 In service evaluation, to establish the suitability of a
intended for cleavage fracture. Instead, the user is referred to
material for a specific application for which the stress condi-
Test Method E1921 and E1820 which are applicable to
tions are prescribed and for which maximum flaw sizes can be
cleavage fracture and contain safeguards against warm pre-
established with confidence.
stressing. Likewise this test method should not be used when
5.2.3 For specifications of acceptance and manufacturing
specimen failure is accompanied by appreciable plastic defor-
quality control, but only when there is a sound basis for
mation even after the specimen size has been maximized
specifying minimum K values, and then only if the dimen-
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within product dimensional constraints. Guidance on testing
sions of the product are sufficient to provide specimens of the
elastic-plastic materials is given in Test Method E1820.
size required for valid K determination. The specification of
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5.1.3 The value of K obtained by this test method may be
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K values in relation to a particular application should signify
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used to estimate the relation between failure stress and crack
that a fracture control study has been conducted for the
size for a material in service wherein the conditions of high
component in relation to the expected loading and
constraint described above would be expected. Background
environment, and in relation to the sensitivity and reliability of
information concerning the basis for development of this test
the crack detection procedures that are to be applied prior to
method in terms of linear elastic fracture mechanics may be
service and subsequently during the anticipated life.
found in Refs (1) and (3).
5.1.4 Cyclic forces can cause crack extension at K values
I
6. Apparatus
less than K . Crack extension under cyclic or sustained forces
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6.1 Testing Machine and Force Measurement—The calibra-
(as by stress corrosion cracking or creep crack growth) can be
tion of the testing machine shall be verified in accordance with
influenced by temperature and environment. Therefore, when
Practices E4. A data acquisition system shall be used to record
K is applied to the design of service components, differences
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force and CMOD for subsequent analysis. The user is referred
between laboratory test and field conditions shall be consid-
to Guide E1942 for a detailed discussion of requirements for
ered.
data acquisition systems.
5.1.5 Plane-strain fracture toughness testing is unusual in
that there can be no advance assurance that a valid K will be
Ic 6.2 Fatigue Precracking Machine—When possible, the cali-
determined in a particular test. Therefore, compliance with the
bration of the fatigue machine and force-indicating device shall
specified validity criteria of this test method is essential.
be verified statically in accordance with Practices E4. If the
5.1.6 Residual stresses can introduce bias into the indicated machine cannot be calibrated and verified statically, the applied
K and K value determinations. The effect can be especially force shall otherwise be known to 62.5 %. Careful alignment
Q Ic
significant for specimens removed from as-heat treated or of the specimen and fixturing is necessary to encourage straight
otherwise non-stress relieved stock, from weldments, from fatigue cracks. The fixturing shall be such that the stress
complex wrought products, rapidly-solidified castings, distribution is uniform across the specimen thickness and
additively-manufactured products or from products with inten- symmetrical about the plane of the prospective crack.
tionally induced residual stresses. In addition, residual stresses
6.3 Loading Fixtures—Fixtures suitable for loading the
will redistribute when the specimen is extracted from the host
specified specimen configurations are shown in the Annexes.
product and machined. The magnitude of residual stress
The fixtures are designed to minimize friction contributions to
influence on K and K in the test specimen may be quite
Q Ic
the measured force.
different from that in the original or finish machined product.
In addition, the behavior of cracks in the full-sized product 6.4 Displacement Gage—The displacement gage electrical
may not be predictable from the fracture toughness measured output represents relative displacement (V) of two precisely
on the specimen because of the influence of the different located gage positions spanning the crack starter notch mouth.
residual stresses in each. Indications of residual stress include Exact and positive positioning of the gage on the specimen is
distortion during specimen machining, results that are speci- essential, yet the gage must be released without damage when
men configuration dependent, and irregular fatigue precrack the specimen breaks. Displacement gage and knife-edge de-
growth (either excessive crack front curvature or out-of-plane signs shall provide for free rotation of the points of contact
growth). Guide B909 provides supplementary guidelines for between the gage and the specimen. A recommended design for
plane strain fracture toughness testing of aluminum alloy a self-supporting, releasable displacement gage is shown in
products for which complete stress relief is not practicable. Fig. 2 and described in Annex A1. The gage’s strain gage
Guide B909 includes additional guidelines for recognizing bridge arrangement is also shown in Fig. 2.
E399 − 23
FIG. 2 Double–Cantilever Clip-In Displacement Gage Showing Mounting by Means of Integral Knife Edges
(Gage Design Details are Given in Annex A1)
6.4.1 The specimen shall be provided with a pair of accu-
rately machined knife edges to support the gage arms and serve
as displacement reference points. The knife edges may be
machined integral with the specimen as shown in Figs. 2 and 3,
or they may be separate pieces affixed to the specimen. A
suggested design for attachable knife edges is shown in Fig. 4.
This design features a knife edge spacing of 5 mm (0.2 in.).
NOTE 1—Dimensions are in mm.
NOTE 2—Effective gage length = 2C + Screw Thread Diameter ≤ W/2.
(This will always be greater than the gage length specified in A1.1.)
NOTE 3—Dimension shown corresponds to clip gage spacer block
dimension in Annex A1.
Inch-Pound Units Equvalients
mm 0.81 1.5 1.8 2.54 3.18
in. 0.032 0.060 0.070 0.100 0.125
FIG. 4 Example of Attachable Knife Edge Design
NOTE 1—Dimensions in mm.
NOTE 2— Gage length shown corresponds to clip gage spacer block
dimensions shown in Annex A1, but other gage lengths may be used The effective gage length is established by the points of contact
provided they are appropriate to the specimen (see 6.4.3).
between the screw and the hole threads. For the design shown,
NOTE 3—For starter notch configurations see Fig. 5.
the major diameter of the screw is used in setting this gage
Inch-Pound Units Equivalents
length. A No. 2 screw will permit the use of attachable knife
mm 1.3 1.5 5.08 6.35
edges for specimens having W > 25 mm (1.0 in.).
in. 0.050 0.060 0.200 0.250
6.4.2 Each gage shall be verified for linearity using an
FIG. 3 Example of Integral Knife Edge Design extensometer calibrator or other suitable device. The resolution
E399 − 23
of the calibrator at each displacement interval shall be within When it has been established that 2.5(K /σ ) is substan-
Ic YS
0.0005 mm (0.00002 in.). Readings shall be taken at ten tially less than the minimum recommended ligament size given
in the preceding table, then a correspondingly smaller speci-
equally spaced intervals over the working range of the gage
(see Annex A1). The verification procedure shall be performed men can be used.
three times, removing and reinstalling the gage in the calibra-
7.2 Specimen Configurations—Recommended specimen
tion fixture after each run. The required linearity shall corre-
configurations are shown in Figs. A3.1-A6.1 and Fig. A7.1.
spond to a maximum deviation of 0.003 mm (0.0001 in.) of the
7.2.1 Specimen Proportions—Crack size, a, is nominally
individual displacement readings from a least-squares-best-fit
between 0.45 and 0.55 times the width, W. Bend specimens can
straight line through the data. The absolute accuracy, as such,
have a width to thickness, W/B, ratio of 1 ≤ W/B ≤ 4. Tension
is not important in this application, since the test method is
specimen configurations can be 2 ≤ W/B ≤ 4.
concerned with relative changes in displacement rather than
7.2.1.1 Recommended Proportions—It is recommended that
absolute values (see 9.1). Verification of gage calibration shall
the thickness, B, is nominally one-half the specimen width, W
be performed at the temperature of test 65.6 °C (10 °F). The
(that is, W/B = 2). Likewise, the crack size, a, should be
gage shall be verified during the time the gage is in use at time
nominally equal to one-half the width, W (that is a/W = 1/2).
intervals defined by established quality assurance practices.
Commercial gages are typically verified annually. NOTE 3—Alternative W/B ratios different from the recommended ratio
in 7.2.1.1 but still meeting the requirements in 7.2.1 are sometimes useful,
6.4.3 It is not the intent of this test method to exclude the
especially for quality control or lot releases purposes, because they allow
use of other types of gages or gage-fixing devices provided the
a continuous range of product thicknesses to be tested using a discrete
gage used meets the requirements listed above and provided number of specimen widths while still maintaining specimens of full
product thickness. However, because specimen width influences the
the gage length does not exceed those limits given in the Annex
amount of crack extension corresponding to the 95 % slope, K obtained
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appropriate to the specimen being tested.
with alternative W/B ratios may not agree with those obtained using the
recommended W/B ratio, particularly in products exhibiting a Type I
7. Specimen Size, Configurations, and Preparation
force-CMOD record (6). As an example, a specimen with the recom-
mended proportion W/B = 2 would tend to yield a lower K than a
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7.1 Specimen Size:
specimen with an alternative proportion W/B = 4. Also, because a shorter
ligament length may hinder resistance curve development, an alternative
7.1.1 In order for a result to be considered valid according
specimen with W/B < 2 (allowed only for bend specimens) may pass the
to this test method (see also 3.1.2.1), the specimen ligament
P /P requirement, while a specimen with the recommended W/B ratio
max Q
size (W – a) must be not less than 2.5(K /σ ) , where σ is
Ic YS YS
would fail. Conversely, an alternative specimen with W/B >2 (allowed in
the 0.2 % offset yield strength of the material in the environ-
both tension and bend specimens) may fail the P /P requirement,
max Q
ment and orientation, and at the temperature and loading rate of while a specimen with the recommended W/B would pass.
the test (1, 4, 5). For testing at rates other than quasi-static see
7.2.2 Alternative Specimens—In certain cases it may be
Annex A10, Rapid Force Testing. The specimen must also be
necessary or desirable to use specimens having W/B ratios
of sufficient thickness, B, to satisfy the specimen proportions in
other than that specified in 7.2.1. Alternative W/B ratios and
7.2.1 or 7.2.1.1 and meet the P /P requirement in 9.1.3.
max Q
side-grooved specimens are allowed as specified in 7.2.1.1 and
Meeting the ligament size and P /P requirements cannot be
max Q
7.2.2.1. These alternative specimens shall have the same crack
assured in advance. Thus, specimen dimensions shall be
length-to-specimen width ratio as the standard specimen.
conservatively selected for the first test in a series. If the form
7.2.2.1 Alternative Side-Grooved Specimens—For the com-
of the material available is such that it is not possible to obtain
pact C(T) and the bend SE(B) specimen configurations side-
a test specimen with ligament size equal to or greater than
grooving is allowed as an alternative to plain-sided specimens.
2.5(K /σ ) , then it is not possible to make a valid K
Ic YS Ic
The total thickness reduction shall not exceed 0.25 B. A total
measurement according to this test method.
reduction of 0.20 B has been found to work well (7) for many
7.1.2 The initial selection of specimen size for a valid K
Ic materials and is recommended (10% per side). Any included
measurement is often based on an estimated value of K for the
Ic angle less than 90° is allowed. The root radius shall be 0.5 6
material.
0.2 mm (0.02 6 0.01 in.). Precracking prior to the side-
7.1.3 Alternatively, the ratio of yield strength to elastic grooving operation is recommended to produce nearly straight
modulus may be used for selecting a specimen size that will be fatigue precrack fronts. B is the minimum thickness measured
N
adequate for all but the toughest materials: at the roots of the side grooves. The root of the side groove
shall be located along the specimen centerline. Fig. 6 is a
Minimum Recommended
σ /E Ligament Size
schematic showing an example cross section of an alternative
YS
mm in.
side grooved specimen.
0.0050 to 0.0057 76 3
NOTE 4— Side-grooves increase the level of constraint with respect to
0.0057 to 0.0062 64 2 ⁄2
the recommended specimen. The increased constraint promotes a more
0.0062 to 0.0065 51 2
uniform stress state along the crack front and inhibits shear lip develop-
0.0065 to 0.0068 44 1 ⁄4
ment. As a result, the K value from a side-grooved specimen is expected
0.0068 to 0.0071 38 1 ⁄2
Ic
to be lower than the K obtained from the recommended specimen,
0.0071 to 0.0075 32 1 ⁄4
Ic
0.0075 to 0.0080 25 1
particularly for thin products or products exhibiting Type I behavior. The
0.0080 to 0.0085 19 ⁄4
value of K from a side-grooved specimen may better represent the
Ic
0.0085 to 0.0100 13 ⁄2
fracture toughness of the material in structural situations where plasticity
0.0100 or greater 6.4 ⁄4
is more highly constrained by the crack front geometry such as may be the
E399 − 23
(a) Straight-Through Starter Notches and Fatigue Cracks (b) Chevron Notch and Detail
Note 1—Fatigue crack extension on each surface of the specimen con- Note 8—For a chevron crack starter notch the fatigue crack shall
taining a straight-through wide-notch shall be at least 0.025 W or 1.3 mm emerge on both surfaces of the specimen.
(0.050 in.), whichever is larger.
Note 2—Fatigue crack extension on each surface of the specimen con- Note 9—A = C within 0.010 W.
taining a straight-through narrow notch shall be at least 0.0125 W or 0.6
mm (0.024 in.), whichever is larger
Note 3—Fatigue crack extension on each surface of the specimen from Note 10—Cutter tip angle 90° max.
the stress raiser tipping the hole shall be at least 0.5 D or 1.3 mm (0.050
in.), whichever is larger.
Note 4—Crack starter notch shall be perpendicular to the specimen sur- Note 11—Radius at chevron notch root 0.25 mm
faces and parallel to the intended direction of crack propagation (0.010 in.) max.
within ±2°.
Note 5—Notch height h need not be less than 1.6 mm ( ⁄16 in.).
Note 6—Notch height h need not be less than 0.30 mm (0.012 in.)
Note 7—From notched edge or centerline of loading holes, as
appropriate.
FIG. 5 Crack Starter Notch and Fatigue Crack Configurations
FIG. 6 Schematic of Side Groove Configuration
case for a surface or corner crack, or by structural details such as keyways, requirement, enabling a valid K to be obtained in products for which it
Ic
radii, notches, etc. The value of K from the recommended specimen may would not be possible using the recommended specimen. Side grooving
Ic
better represent the fracture toughness of the material in structural after precracking beneficially removes a portion of the non-linear crack
situations where surface plasticity and shear lip development is not front at the ends of the crack front, thus increasing the likelihood of
constrained such as a through crack in a region of uniform thickness. meeting crack front straightness requirements. However, side grooving
Side-grooving increases the likelihood of meeting the P /P may also remove material that influences service performance. This is
max Q
E399 − 23
often true for cast parts and those for which thermo-mechanical working
in a hole (of diameter D < W/10), and need only emerge from
is part of the heat treating cycle. The increased constraint also can lead to
the chevron starter configuration.
increased likelihood of material delamination, for instance, in the plane of
the specimen, which could lead to test results different from those
8. General Procedure
obtained from plane-sided specimens.
NOTE 5—No interlaboratory ‘round robin’ test program has yet been
8.1 Number of Tests—It is recommended that triplicate tests,
conducted to compare the performance of plain-sided and side-grooved
minimum, be made for each material condition.
specimens. However, the results of several studies (7) indicate that K
Ic
from side-grooved specimens is zero to 10 % less than that of plain-sided
8.2 Specimen Measurement—Specimen dimensions shall
specimens, the difference increasing with increasing material toughness.
conform to the drawings of Figs. A3.1-A6.1 and Fig. A7.1.
The within-laboratory repeatability was determined according to the
Measurements essential to the calculation of K are specimen
Ic
conditions in Terminology E456 and the results are presented in 11.3.
thickness, B (and in the case of side-grooved alternative
7.2.2.2 For lot acceptance testing, side-grooved specimens
specimens, B ), crack size, a, and width, W.
N
shall not be used unless specifically allowed by the product
8.2.1 Specimen thickness, B (and in the case of side-
specification or by agreement between producer and user.
grooved alternative specimens, B ), shall be measured before
N
testing to a precision equal to or better than 0.03 mm (0.001
7.3 Specimen Preparation—All specimens shall be tested in
in.) or to 0.1 %, whichever is larger. For plain-sided specimens,
the finally heat-treated, mechanically-worked, and
B shall be measured adjacent the notch. For side-grooved
environmentally-conditioned state. Specimens shall normally
specimens, B shall be measured at the root of the notch and B
be machined in this final state. However, for material that N
adjacent the notch.
cannot be machined in the final condition, the final treatment
may be carried out after machining provided that the required
NOTE 6—For plane-sided specimens the value of B is equal to the
N
dimensions and tolerances on specimen size, shape, and overall
thickness B.
finish are met (see specimen drawings of Figs. A3.1-A6.1 and
8.2.2 Specimen width, W, shall be measured, in confor-
Fig. A7.1), and that full account is taken of the effects of
mance with the procedure of the annex appropriate to the
specimen size on metallurgical condition induced by certain
specimen configuration, to a precision equal to or better than
heat treatment procedures; for example, water quenching of
0.03 mm (0.001 in.) or 0.1 %, whichever is larger, at not less
steels.
than three positions near the notch location, and the average
7.3.1 Fatigue Crack Starter Notch—Four fatigue crack
value recorded.
starter notch configurations are shown in Fig. 5. To facilitate
8.2.3 Specimen crack size, a, shall be measured after
fatigue precracking at low stress intensity levels, the suggested
fracture to a precision equal to or better than 0.5 % at
root radius for a straight-through wide-slot terminating in a
mid-thickness and the two quarter-thickness points (based on B
V-notch is 0.08 mm (0.003 in.) or less. A straight-through
for plain-sided specimens and B for side-grooved specimens).
N
narrow notch (h < 0.01W) does not need a V-notch or
The average of these three measurements shall be taken as the
additional sharpening of the notch tip before precracking. For
crack size, a. The difference between any two of the three crack
the chevron form of notch, the suggested root radius is 0.25
size measurements shall not exceed 10 % of the average. The
mm (0.010 in.) or less. For the slot ending in a drilled hole, it
crack size shall be measured also at each surface. For the
is necessary to provide a sharp stress raiser at the end of the
straight-through wide-notch starter configuration, no part of the
hole. Care shall be taken to ensure that this stress raiser is so
crack front shall be closer to the machined starter notch than
located that the crack plane orientation requirements of 8.2.4
0.025W or 1.3 mm (0.050 in.), whichever is larger; and for the
can be met.
narrow-notch starter configuration, no part of the crack front
7.3.2 Fatigue Precracking—Fatigue precracking is per-
shall be closer to the machined starter notch than 0.0125 W or
formed by cyclically loading the notched specimen at a ratio of
0.6 mm (0.024 in.), whichever is larger; furthermore, neither
minimum-to-maximum force between -1 and +0.1 for a num-
surface crack size measurement shall differ from the average
4 6
ber of cycles, usually between about 10 and 10 depending on
crack size by more than 15 % and their difference shall not
specimen size, notch preparation, and cyclic stress intensity
exceed 10 % of the average crack size. For the chevron notch
factor level. Fatigue precracking procedures, limits on maxi-
starter configuration, the fatigue crack shall emerge from the
mum stress intensity factor and other requirements are de-
chevron on both surfaces; furthermore, neither surface crack
scribed in detail in Annex A8. Fatigue cycling is continued
size measurement shall differ from the average crack size by
until a crack is produced that satisfies the requirements of
more than 15 %, and their difference shall not exceed 10 % of
Annex A8, 7.3.2.1, and 7.3.2.2 that follow.
the average crack size. Measurement locations are schemati-
7.3.2.1 Crack size (total size of crack starter plus fatigue
cally illustrated in Fig. 7 for a plain-sided C(T) specimen.
crack) shall be between 0.45W and 0.55W.
8.2.4 The plane of the fatigue precrack and subsequent 2 %
crack extension (in the central flat fracture area; that is,
7.3.2.2 The size of the fatigue crack on each face of the
excluding surface shear lips) shall be parallel to the plane of the
specimen shall be greater than or equal to the larger of 0.025W
starter notch to 610°. For side-grooved specimens, the plane
or 1.3 mm (0.050 in.) for the straight-through, wide-notch
of the fatigue precrack and subsequent 2% crack extension
crack starter configuration, greater than or equal to the larger of
shall be within the root of the side-groove.
0.0125 W or 0.6 mm (0.024 in.) for the straight-through,
narrow-notch crack starter configuration, greater than or equal 8.2.5 There shall be no evidence of multiple cracking (that
to the larger of 0.5D or 1.3 mm (0.050 in.) for the slot ending is, more than one crack) (8).
E399 − 23
FIG. 7 Crack size measurement locations for plain-sided C(T) specimen.
8.3 Loading Methods—Test specimens may be loaded in 9.1.1 The conditional value P is determined by the secant
Q
servo-hydraulic or electro-mechanical test machines. The rec- line OP , (see Fig. 8) through the origin (point O) of the test
ommended method of specimen loading is machine crosshead record with slope (P/V) equal to 0.95(P/V) , where (P/V) is
5 o o
or actuator displacement control. Other displacement- the slope of the tangent OA to the initial linear portion of the
indicating devices, force control, or K-control may also be record between the lower bound force (P ) and the upper
L
used. Machine instability can occur at specimen pop-in or bound force (P ), inclusive (Note 7). In practice the origin
U
failure using some loading methods including force control and (point O) is not necessarily at the intersection of the displace-
crack mouth opening displacement (CMOD) gage control. For ment and force axes. The point O lies on the best fit line
these methods, setting appropriate machine control limits on through the initial linear portion of the record and at the
force or displacement can prevent potential injury to personnel intersection of the best fit line with the displacement axis.
or damage to the specimen, clevises or test machine. Thus, in calculating the secant line OP , the rotation point of
the slope adjustment should be at the intersection of the line
8.4 Loading Rate—For conventional (quasi-static) tests, the
OA with the displacement axis. The force P is then defined as
Q
specimen shall be loaded such that the stress-intensity factor
follows: if the force at every point on the record which
˙
rate K during the initial elastic displacement portion of the test
precedes P is lower than P (Fig. 8, Type I), then P is P ; if,
5 5 5 Q
is between 0.55 and 2.75 MPa√m/s (30 and 150 ksi√in./min).
however, there is a maximum force preceding P which
Loading rates corresponding to these stress-intensity factor
exceeds it (Fig. 8, Types II and III), then this maximum force
rates are given in the Annex appropriate to the specimen
is P .
Q
configuration being tested. If the initial rate is estimated by
loading and unloading the specimen prior to the test, K shall
NOTE 7—Slight initial nonlinearity of the test record is frequently
max
observed, and is to be ignored. However, it is important to establish the
not exceed 60 % of K or K determined in the subsequent
Q Qsi
initial slope of the record with high precision. Therefore it is advisable to
test. Loading and unloading shall be performed at the test
minimize this nonlinearity by preliminarily loading the specimen to a
temperature and using the same apparatus as the test. For
maximum force corresponding to a stress-intensity factor level not
rapid-force tests, loading rates are to be as specified in Annex
exceeding that during final crack extension of fatigue precracking, then
A10.
unloading.
8.5 Test Record—A record shall be made of the output of the
9.1.2 The algorithms for determining the lower bound force
force-sensing transducer versus the output of the displacement
(P ) and the upper bound force (P ) of the fitted range of the
L U
gage. The data acquisition system shall be set such that not less
best-fit line to the initial linear region and its slope (P/V) , the
o
than 50 % of full range is used for the test record. The data
origin point (O), P , P and P are discretionary. One
5 Q max
acquisition system shall capture enough data to permit the
recommended method for determining the initial linear region
calculations of Section 9.
is described in Practice E3076. For any method employed
...