ASTM E1304-97(2008)e1
(Test Method)Standard Test Method for Plane-Strain (Chevron-Notch) Fracture Toughness of Metallic Materials
Standard Test Method for Plane-Strain (Chevron-Notch) Fracture Toughness of Metallic Materials
SIGNIFICANCE AND USE
The fracture toughness determined by this test method characterizes the resistance of a material to fracture by a slowly advancing steady-state crack (see 3.2.5) in a neutral environment under severe tensile constraint. The state of stress near the crack front approaches plane strain, and the crack-tip plastic region is small compared with the crack size and specimen dimensions in the constraint direction. A KIv or KIvj value may be used to estimate the relation between failure stress and defect size when the conditions described above would be expected, although the relationship may differ from that obtained from a KIc value (see Note 1). Background information concerning the basis for development of this test method in terms of linear elastic fracture mechanics may be found in Refs (1-15).
The KIv, KIvj, or KIvM value of a given material can be a function of testing speed (strain rate) and temperature. Furthermore, cyclic forces can cause crack extension at KI values less than KIv, and crack extension can be increased by the presence of an aggressive environment. Therefore, application of KIv in the design of service components should be made with an awareness of differences that may exist between the laboratory tests and field conditions.
Plane-strain fracture toughness testing is unusual in that there can be no advance assurance that a valid KIv, KIvj, or KIvM will be determined in a particular test. Therefore, it is essential that all the criteria concerning the validity of results be carefully considered as described herein.
This test method can serve the following purposes:
To establish the effects of metallurgical variables such as composition or heat treatment, or of fabricating operations such as welding or forming, on the fracture toughness of new or existing materials.
For specifications of acceptance and manufacturing quality control, but only when there is a sound basis for specification of minimum KIv, KIvj, or KIvM values, and then ...
SCOPE
1.1 This test method covers the determination of plane-strain (chevron-notch) fracture toughnesses, KIv or KIvM, of metallic materials. Fracture toughness by this method is relative to a slowly advancing steady state crack initiated at a chevron-shaped notch, and propagating in a chevron-shaped ligament (Fig. 1). Some metallic materials, when tested by this method, exhibit a sporadic crack growth in which the crack front remains nearly stationary until a critical load is reached. The crack then becomes unstable and suddenly advances at high speed to the next arrest point. For these materials, this test method covers the determination of the plane-strain fracture toughness, KIvj or KIvM, relative to the crack at the points of instability.
Note 1—One difference between this test method and Test Method E 399 (which measures KIc) is that Test Method E 399 centers attention on the start of crack extension from a fatigue precrack. This test method makes use of either a steady state slowly propagating crack, or a crack at the initiation of a crack jump. Although both methods are based on the principles of linear elastic fracture mechanics, this difference, plus other differences in test procedure, may cause the values from this test method to be larger than KIc values in some materials. Therefore, toughness values determined by this test method cannot be used interchangeably with KIc.
1.2 This test method uses either chevron-notched rod specimens of circular cross section, or chevron-notched bar specimens of square or rectangular cross section (Figs. 1-10). The terms “short rod” and “short bar” are used commonly for these types of chevron-notched specimens.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.4 This standard does not purport to addre...
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Designation: E1304 − 97(Reapproved 2008)
Standard Test Method for
Plane-Strain (Chevron-Notch) Fracture Toughness of
Metallic Materials
This standard is issued under the fixed designation E1304; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The term stress-intensity factor was editorially updated in March 2009.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method covers the determination of plane-
bility of regulatory limitations prior to use.
strain (chevron-notch) fracture toughnesses, K or K ,of
Iv IvM
metallic materials. Fracture toughness by this method is
2. Referenced Documents
relative to a slowly advancing steady state crack initiated at a
2.1 ASTM Standards:
chevron-shaped notch, and propagating in a chevron-shaped
E4Practices for Force Verification of Testing Machines
ligament (Fig. 1). Some metallic materials, when tested by this
E8/E8MTest Methods for Tension Testing of Metallic Ma-
method, exhibit a sporadic crack growth in which the crack
terials
front remains nearly stationary until a critical load is reached.
E399Test Method for Linear-Elastic Plane-Strain Fracture
The crack then becomes unstable and suddenly advances at
Toughness K of Metallic Materials
Ic
highspeedtothenextarrestpoint.Forthesematerials,thistest
E1823TerminologyRelatingtoFatigueandFractureTesting
method covers the determination of the plane-strain fracture
toughness, K or K , relative to the crack at the points of
Ivj IvM
3. Terminology
instability.
3.1 Definitions:
NOTE 1—One difference between this test method and Test Method
3.1.1 The terms described in Terminology E1823 are appli-
E399 (which measures K ) is that Test Method E399 centers attention on
Ic
cable to this test method.
the start of crack extension from a fatigue precrack. This test method
−3/2
3.1.2 stress-intensity factor, K [FL ]—the magnitude of
I
makes use of either a steady state slowly propagating crack, or a crack at
the mathematically ideal crack-tip stress field (stress-field
the initiation of a crack jump. Although both methods are based on the
principles of linear elastic fracture mechanics, this difference, plus other
singularity) for mode I in a homogeneous linear-elastic body.
differences in test procedure, may cause the values from this test method
3.1.2.1 Discussion—Valuesof Kformode Iaregivenbythe
tobelargerthan K valuesinsomematerials.Therefore,toughnessvalues
Ic
following equation:
determined by this test method cannot be used interchangeably with K .
Ic
½
K 5 limit σ 2πr
@ #
I y x
1.2 This test method uses either chevron-notched rod speci-
mens of circular cross section, or chevron-notched bar speci- r →0
x
mens of square or rectangular cross section (Figs. 1-10). The
where:
terms “short rod” and “short bar” are used commonly for these
r = distance from the crack tip to a location where the
x
types of chevron-notched specimens.
stress is calculated and
1.3 The values stated in inch-pound units are to be regarded
σ = the principal stress r normal to the crack plane.
y x
as standard. The values given in parentheses are mathematical
3.2 Definitions of Terms Specific to This Standard:
conversions to SI units that are provided for information only
3.2.1 plane-strain (chevron-notch) fracture toughness, K
Iv
and are not considered standard.
−3/2
or K [FL ]—under conditions of crack-tip plane strain in a
Ivj
1.4 This standard does not purport to address all of the
chevron-notched specimen: K relates to extension resistance
Iv
safety concerns, if any, associated with its use. It is the
with respect to a slowly advancing steady-state crack. K
Ivj
relates to crack extension resistance with respect to a crack
which advances sporadically.
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
and Fracture and is the direct responsibility of Subcommittee E08.02 on Standards
and Terminology. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2008. Published February 2009. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1989. Last previous edition approved in 2002 as E1304–97(2002). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1304-97R08E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E1304 − 97 (2008)
3.2.6 effective unloading slope ratio, r—the ratio of an
effective unloading slope to that of the initial elastic loading
slope on a test record of force versus specimen mouth opening
displacement.
3.2.6.1 Discussion—This unloading slope ratio provides a
methodofdeterminingthecracklengthatvariouspointsonthe
test record and therefore allows evaluation of stress intensity
coefficient Y* (see 3.2.11). The effective unloading slope ratio
is measured by performing unloading-reloading cycles during
thetestasindicatedschematicallyinFig.4andFig.5.Foreach
unloading-reloading trace, the effective unloading slope ratio,
NOTE 1—The crack commences at the tip of the chevron-shaped
r, is defined in terms of the tangents of two angles:
ligament and propagates (shaded area) along the ligament, and has the
r 5 tan θ/tanθ
length “a” shown. (Not to scale.)
o
FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a)
where:
and Short Bar (b) Specimens
tan θ = the slope of the initial elastic line, and
o
tan θ = the slope of an effective unloading line.
3.2.1.1 Discussion—For slow rates of loading the fracture
Theeffectiveunloadinglineisdefinedashavinganoriginat
toughness, K or K , is the value of stress-intensity factor as
Iv Ivj
the high point where the displacement reverses direction on
measuredusingtheoperationalprocedure(andsatisfyingallof
unloading (slot mouth begins to close) and joining the low
the validity requirements) specified in this test method.
point on the reloading line where the force is one half that at
3.2.2 plane-strain (chevron-notch) fracture toughness, K
IvM the high point.
−3/2
[FL ]—determined similarly to K or K (see 3.2.1) using
3.2.6.2 Discussion—For a brittle material with linear elastic
Iv Ivj
the same specimen, or specimen geometries, but using a
behavior the unloading-reloading lines of an unloading-
simpler analysis based on the maximum test force. The
reloading cycle would be linear and coincident. For many
analysisisdescribedinAnnexA1.Unloading-reloadingcycles
engineering materials, deviations from linear elastic behavior
as described in 3.2.6 are not required in a test to determine
and hysteresis are commonly observed to a varying degree.
K .
These effects require an unambiguous method of obtaining an
IvM
effective unloading slope from the test record (6-5).
3.2.3 smooth crack growth behavior—generally,thattypeof
3.2.6.3 Discussion—Although r is measured only at those
crack extension behavior in chevron-notch specimens that is
crack positions where unloading-reloading cycles are
characterized primarily by slow, continuously advancing crack
performed, r is nevertheless defined at all points during a
growth, and a relatively smooth force displacement record
chevron-notch specimen test. For any particular point it is the
(Fig. 4). However, any test behavior not satisfying the condi-
value that would be measured for r if an unloading-reloading
tions for crack jump behavior is automatically characterized as
cycle were performed at that point.
smooth crack growth behavior.
3.2.7 critical slope ratio, r —the unloading slope ratio at
3.2.4 crack jump behavior—in tests of chevron-notch c
the critical crack length.
specimens, that type of sporadic crack growth which is
characterizedprimarilybyperiodsduringwhichthecrackfront
3.2.8 critical crack length—the crack length in a chevron-
is nearly stationary until a critical force is reached, whereupon
notch specimen at which the specimen’s stress-intensity factor
the crack becomes unstable and suddenly advances at high
coefficient, Y* (see 3.2.11 and Table 3), is a minimum, or
speed to the next arrest point, where it remains nearly station-
equivalently, the crack length at which the maximum force
ary until the force again reaches a critical value, etc. (see Fig.
would occur in a purely linear elastic fracture mechanics test.
5).
At the critical crack length, the width of the crack front is
3.2.4.1 Discussion—A chevron-notch specimen is said to
approximately one third the dimension B (Figs. 2 and 3).
have a crack jump behavior when crack jumps account for
3.2.9 high point, High—the point on a force-displacement
more than one half of the change in unloading slope ratio (see
plot, at the start of an unloading-reloading cycle, at which the
3.2.6) as the unloading slope ratio passes through the range
displacement reverses direction, that is, the point at which the
from 0.8r to 1.2r (see 3.2.6 and 3.2.7, and 8.3.5.2). Only
c c
specimen mouth begins closing due to unloading (see points
those sudden crack advances that result in more than a 5%
labeled High in Figs. 4 and 5).
decrease in force during the advance are counted as crack
3.2.10 low point, Low—thepointonthereloadingportionof
jumps (Fig. 5).
an unloading-reloading cycle where the force is one half the
3.2.5 steady-state crack—a crack that has advanced slowly
high point force (see points labeled Low in Figs. 4 and 5).
until the crack-tip plastic zone size and crack-tip sharpness no
3.2.11 stress-intensity factor coeffıcient, Y*—a dimension-
longerchangewithfurthercrackextension.Althoughcrack-tip
less parameter that relates the applied force and specimen
conditions can be a function of crack velocity, the steady-state
crack-tip conditions for metals have appeared to be indepen-
dent of the crack velocity within the range attained by the
The boldface numbers in parentheses refer to the list of references at the end
loading rates specified in this test method. of this standard.
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E1304 − 97 (2008)
NOTE 1—See Table 1 for tolerances and other details.
FIG. 2 Rod Specimens Standard Proportions
NOTE 1—See Table 2 for tolerances and other details.
FIG. 3 Bar Specimens Standard Proportions
geometry to the resulting crack-tip stress-intensity factor in a Thecharacteristicsoftheforceversusmouthopeningdisplace-
chevron-notch specimen test (see 9.6.3). ment trace depend on the geometry of the specimen, the
3.2.11.1 Discussion—Values of Y* can be found from the specimen plasticity during the test, any residual stresses in the
graphsinFig.10,orfromthetabulationsinTable4orfromthe
specimen, and the crack growth characteristics of the material
polynominal expressions in Table 5. beingtested.Ingeneral,twotypesofforceversusdisplacement
traces are recognized, namely, smooth behavior (see3.2.3) and
3.2.12 minimum stress-intensity factor coeffıcient, Y* —the
m
crack jump behavior (see 3.2.4).
minimum value of Y*(Table 3).
3.2.3),
4.1.1 In metals that exhibit smooth crack behavior (
4. Summary of Test Method
thecrackinitiatesatalowforceatthetipofasufficientlysharp
4.1 Thistestmethodinvolvestheapplicationofaloadtothe chevron, and each incremental increase in its length corre-
sponds to an increase in crack front width and requires further
mouth of a chevron-notched specimen to induce an opening
displacement of the specimen mouth.An autographic record is increase in force. This force increase continues until a point is
reached where further increases in force provide energy in
made of the load versus mouth opening displacement and the
slopes of periodic unloading-reloading cycles are used to excess of that required to advance the crack. This maximum
calculate the crack length based on compliance techniques. forcepointcorrespondstoawidthofcrackfrontapproximately
These crack lengths are expressed indirectly as slope ratios. one third the specimen diameter or thickness. If the loading
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E1304 − 97 (2008)
R# 0.010B
φ # 60°
s
t# 0.03B
NOTE 1—These requirements are satisfied by slots with a round bottom
whenever t ≤ 0.020B.
FIG. 6 Slot Bottom Configuration
FIG. 4 Schematic of a Load-Displacement Test Record for
Smooth Crack Growth Behavior, with Unloading/Reloading
Cycles, Data Reduction Constructions, and Definitions of Terms
FIG. 5 Schematic of a Load-Displacement Test Record for Crack
NOTE 1—Machine finish all over equal to or better than 64 µin.
Jump Behavior, with Unloading/Reloading Cycles, Data Reduc-
tion Constructions, and Definitions of Terms
NOTE 2—Unless otherwise specified, dimensions 60.010B; angles
62°.
NOTE 3—Grip hardness should be RC=45 or greater.
systemissufficientlystiff,thecrackcanbemadetocontinueits
FIG. 7 Suggested Loading Grip Design
smooth crack growth under decreasing force. Two unloading-
reloadingcyclesareperformedtodeterminethelocationofthe
crack, the force used to calculate K , and to provide validity
Iv
checks on the test. The fracture toughness is calculated from
4.1.2 A modified procedure is used to determine K when
Ivj
theforcerequiredtoadvancethecrackwhenthecrackisatthe
crack jump behavior is encountered. In this procedure,
critical crack length (see 3.2.8). The plane-strain fracture
unloading-reloading cycles are used to determine the crack
toughness determined by this procedure is termed K .An
Iv
location at which the next jump will begin. The K values are
alternative procedure, described in Annex A1, omits the
Ivj
calculated from the forces that produce crack jumps when the
unloading cycles and uses the maximum test force to calculate
crack front is in a defined region near the center of the
a plane-strain fracture toughness K , where M signifies the
IvM
specimen. The K values so determined have the same
use of the maximum force. Values of K versus K are
Ivj
Iv IvM
discussed in Annex A1. significance as K .
Iv
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E1304 − 97 (2008)
NOTE 1—Compiled from Refs (1), (2), (3), and (4).
FIG. 10 Normalized Stress-Intensity Factor Coefficients as a
Function of Slope Ratio (r) for Chevron-Notch Specimens
TABLE 1 Rod Dimensions
NOTE 1—All surfaces to be 64-µin. finish or better.
NOTE 2—Side grooves may be made with a plunge cut with a circular
blade, such that the sides of the chevron ligament have curved profiles,
provided that the blade diameter exceeds 5.0B. In this case, φ is the angle
betweenthechordsspanningtheplungecutarcs,anditisnecessarytouse
dif
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