ASTM E1304-97(2014)
(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
5.1 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 (6-15).
5.1.1 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.
5.1.2 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.
5.2 This test method can serve the following purposes:
5.2.1 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.
5.2.2 For specifications of acceptance and manufacturing quality control, but only when there is a sound basis for specification of minimum ...
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. (A) See Fig. 6. (A) See Fig. 6.(B) See Note 1. (A) Compiled from Refs (1), (2), (3), and (4), and using the polynomials in Table 5.(B) Minimum value of Y*. (A) Compiled from Refs (1), (2), (3), and (4).(B) Y* = exp[C0 + C1 r + C2 r2 + C3 r3 + C4 r4 ], accuracy ±0.5 %.(C) Estimated from finite element analysis (3), and extrapolated equation from Ref (4). Accuracy for 0.3 ≤ r ≤ 0.85 is ±0.5 %.(D) Extrapolated from equations in Ref (4). Accuracy estimated to be ±0.5 % for 0.2 ≤ r ≤ 0.85.(E) Equation from Ref (4). Accuracy estimated to be± 0.5 % for 0.15 ≤ r ≤ 0.6.
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Designation: E1304 − 97 (Reapproved 2014)
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.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method covers the determination of plane-
strain (chevron-notch) fracture toughnesses, K or K ,of
Iv IvM
2. Referenced Documents
metallic materials. Fracture toughness by this method is
2.1 ASTM Standards:
relative to a slowly advancing steady state crack initiated at a
E4Practices for Force Verification of Testing Machines
chevron-shaped notch, and propagating in a chevron-shaped
E8/E8MTest Methods for Tension Testing of Metallic Ma-
ligament (Fig. 1). Some metallic materials, when tested by this
terials
method, exhibit a sporadic crack growth in which the crack
E399Test Method for Linear-Elastic Plane-Strain Fracture
front remains nearly stationary until a critical load is reached.
Toughness K of Metallic Materials
Ic
The crack then becomes unstable and suddenly advances at
E1823TerminologyRelatingtoFatigueandFractureTesting
highspeedtothenextarrestpoint.Forthesematerials,thistest
method covers the determination of the plane-strain fracture
3. Terminology
toughness, K or K , relative to the crack at the points of
Ivj IvM
3.1 Definitions:
instability.
3.1.1 The terms described in Terminology E1823 are appli-
NOTE 1—One difference between this test method and Test Method
cable to this test method.
E399 (which measures K ) is that Test Method E399 centers attention on
Ic −3/2
3.1.2 stress-intensity factor, K [FL ]—the magnitude of
I
the start of crack extension from a fatigue precrack. This test method
the mathematically ideal crack-tip stress field (stress-field
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
singularity) for mode I in a homogeneous linear-elastic body.
principles of linear elastic fracture mechanics, this difference, plus other
3.1.2.1 Discussion—Valuesof Kformode Iaregivenbythe
differences in test procedure, may cause the values from this test method
following equation:
tobelargerthan K valuesinsomematerials.Therefore,toughnessvalues
Ic
½
determined by this test method cannot be used interchangeably with K .
K 5 limit σ 2πr
Ic @ #
I y x
1.2 This test method uses either chevron-notched rod speci-
r →0
x
mens of circular cross section, or chevron-notched bar speci-
where:
mens of square or rectangular cross section (Figs. 1-10). The
r = distance from the crack tip to a location where the
x
terms “short rod” and “short bar” are used commonly for these
stress is calculated and
types of chevron-notched specimens.
σ = the principal stress r normal to the crack plane.
y x
1.3 The values stated in inch-pound units are to be regarded
3.2 Definitions of Terms Specific to This Standard:
as standard. The values given in parentheses are mathematical
3.2.1 plane-strain (chevron-notch) fracture toughness, K
Iv
conversions to SI units that are provided for information only
−3/2
or K [FL ]—under conditions of crack-tip plane strain in a
Ivj
and are not considered standard.
chevron-notched specimen: K relates to extension resistance
Iv
1.4 This standard does not purport to address all of the
with respect to a slowly advancing steady-state crack. K
Ivj
safety concerns, if any, associated with its use. It is the
relates to crack extension resistance with respect to a crack
responsibility of the user of this standard to establish appro-
which advances sporadically.
3.2.1.1 Discussion—For slow rates of loading the fracture
toughness, K or K , is the value of stress-intensity factor as
Iv Ivj
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 July 1, 2014. Published September 2014. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ε1
approved in 1989. Last previous edition approved in 2009 as E1304–97(2009) . Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E1304-97R14. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1304 − 97 (2014)
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
o
length “a” shown. (Not to scale.)
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.
Theeffectiveunloadinglineisdefinedashavinganoriginat
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
the high point.
IvM
−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
c
3.2.4 crack jump behavior—in tests of chevron-notch
the critical crack length.
specimens, that type of sporadic crack growth which is
3.2.8 critical crack length—the crack length in a chevron-
characterizedprimarilybyperiodsduringwhichthecrackfront
notch specimen at which the specimen’s stress-intensity factor
is nearly stationary until a critical force is reached, whereupon
coefficient, Y* (see 3.2.11 and Table 3), is a minimum, or
the crack becomes unstable and suddenly advances at high
equivalently, the crack length at which the maximum force
speed to the next arrest point, where it remains nearly station-
would occur in a purely linear elastic fracture mechanics test.
ary until the force again reaches a critical value, etc. (see Fig.
At the critical crack length, the width of the crack front is
5).
approximately one third the dimension B (Figs. 2 and 3).
3.2.4.1 Discussion—A chevron-notch specimen is said to
3.2.9 high point, High—the point on a force-displacement
have a crack jump behavior when crack jumps account for
plot, at the start of an unloading-reloading cycle, at which the
more than one half of the change in unloading slope ratio (see
displacement reverses direction, that is, the point at which the
3.2.6) as the unloading slope ratio passes through the range
specimen mouth begins closing due to unloading (see points
from0.8r to1.2r (see3.2.6and3.2.7,and8.3.5.2).Onlythose
c c
labeled High in Figs. 4 and 5).
sudden crack advances that result in more than a 5% decrease
3.2.10 low point, Low—thepointonthereloadingportionof
inforceduringtheadvancearecountedascrackjumps(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.
E1304 − 97 (2014)
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
Fig.10,orfromthetabulationsinTable4orfromthe
graphsin 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).
4.1.1 In metals that exhibit smooth crack behavior (3.2.3),
4. Summary of Test Method
thecrackinitiatesatalowforceatthetipofasufficientlysharp
chevron, and each incremental increase in its length corre-
4.1 Thistestmethodinvolvestheapplicationofaloadtothe
sponds to an increase in crack front width and requires further
mouth of a chevron-notched specimen to induce an opening
increase in force. This force increase continues until a point is
displacement of the specimen mouth.An autographic record 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
forcepointcorrespondstoawidthofcrackfrontapproximately
calculate the crack length based on compliance techniques.
These crack lengths are expressed indirectly as slope ratios. one third the specimen diameter or thickness. If the loading
E1304 − 97 (2014)
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.
FIG. 7 Suggested Loading Grip Design
systemissufficientlystiff,thecrackcanbemadetocontinueits
smooth crack growth under decreasing force. Two unloading- use of the maximum force. Values of K versus K are
Iv IvM
reloadingcyclesareperformedtodeterminethelocationofthe discussed in Annex A1.
crack, the force used to calculate K , and to provide validity 4.1.2 A modified procedure is used to determine K when
Iv Ivj
checks on the test. The fracture toughness is calculated from crack jump behavior is encountered. In this procedure,
theforcerequiredtoadvancethecrackwhenthecrackisatthe unloading-reloading cycles are used to determine the crack
critical crack length (see 3.2.8). The plane-strain fracture location at which the next jump will begin. The K values are
Ivj
toughness determined by this procedure is termed K .An calculated from the forces that produce crack jumps when the
Iv
alternative procedure, described in Annex A1, omits the crack front is in a defined region near the center of the
unloading cycles and uses the maximum test force to calculate specimen. The K values so determined have the same
Ivj
a plane-strain fracture toughness K , where M signifies the significance as K .
IvM Iv
E1304 − 97 (2014)
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
different values of φ and a (5), so that the crack front has the same width
o
as with straight cuts, at the critical
...
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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E1304 − 97 (Reapproved 2008) E1304 − 97 (Reapproved 2014)
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. A number 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
1.1 This test method covers the determination of plane-strain (chevron-notch) fracture toughnesses, K or K , of metallic
Iv IvM
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, K or K , relative to the crack at the points of instability.
Ivj IvM
NOTE 1—One difference between this test method and Test Method E399 (which measures K ) is that Test Method E399 centers attention on the start
Ic
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 K values in some materials. Therefore, toughness values determined by this
Ic
test method cannot be used interchangeably with K .
Ic
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 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.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines
E8/E8M Test Methods for Tension Testing of Metallic Materials
E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness K of Metallic Materials
Ic
E1823 Terminology Relating to Fatigue and Fracture Testing
3. Terminology
3.1 Definitions:
3.1.1 The terms described in Terminology E1823 are applicable to this test method.
−3/2
3.1.2 stress-intensity factor, K [FL ]—the magnitude of the mathematically ideal crack-tip stress field (stress-field singularity)
I
for mode I in a homogeneous linear-elastic body.
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.02 on Standards and
Terminology.
Current edition approved Nov. 1, 2008July 1, 2014. Published February 2009September 2014. Originally approved in 1989. Last previous edition approved in 20022009
ε1
as E1304 – 97(2002).(2009) . DOI: 10.1520/E1304-97R08E01.10.1520/E1304-97R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3.1.2.1 Discussion—
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1304 − 97 (2014)
NOTE 1—The crack commences at the tip of the chevron-shaped ligament and propagates (shaded area) along the ligament, and has the length “a”
shown. (Not to scale.)
FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a) and Short Bar (b) Specimens
Values of K for mode I are given by the following equation:
½
K 5 limit σ @2πr #
I y x
r →0
x
where:
r = distance from the crack tip to a location where the stress is calculated and
x
σ = the principal stress r normal to the crack plane.
y x
3.2 Definitions of Terms Specific to This Standard:
−3/2
3.2.1 plane-strain (chevron-notch) fracture toughness, K or K [FL ]—under conditions of crack-tip plane strain in a
Iv Ivj
chevron-notched specimen: K relates to extension resistance with respect to a slowly advancing steady-state crack. K relates
Iv Ivj
to crack extension resistance with respect to a crack which advances sporadically.
3.2.1.1 Discussion—
For slow rates of loading the fracture toughness, K or K , is the value of stress-intensity factor as measured using the operational
Iv Ivj
procedure (and satisfying all of the validity requirements) specified in this test method.
−3/2
3.2.2 plane-strain (chevron-notch) fracture toughness, K [FL ]—determined similarly to K or K (see 3.2.1) using the
IvM Iv Ivj
same specimen, or specimen geometries, but using a simpler analysis based on the maximum test force. The analysis is described
in Annex A1. Unloading-reloading cycles as described in 3.2.6 are not required in a test to determine K .
IvM
3.2.3 smooth crack growth behavior—generally, that type of crack extension behavior in chevron-notch specimens that is
characterized primarily by slow, continuously advancing crack growth, and a relatively smooth force displacement record (Fig. 4).
However, any test behavior not satisfying the conditions for crack jump behavior is automatically characterized as smooth crack
growth behavior.
3.2.4 crack jump behavior—in tests of chevron-notch specimens, that type of sporadic crack growth which is characterized
primarily by periods during which the crack front is nearly stationary until a critical force is reached, whereupon the crack becomes
unstable and suddenly advances at high speed to the next arrest point, where it remains nearly stationary until the force again
reaches a critical value, etc. (see Fig. 5).
3.2.4.1 Discussion—
A chevron-notch specimen is said to have a crack jump behavior when crack jumps account for more than one half of the change
in unloading slope ratio (see 3.2.6) as the unloading slope ratio passes through the range from 0.8r to 1.2r (see 3.2.6 and 3.2.7,
c c
and 8.3.5.2). Only those sudden crack advances that result in more than a 5 % decrease in force during the advance are counted
as crack jumps (Fig. 5).
3.2.5 steady-state crack—a crack that has advanced slowly until the crack-tip plastic zone size and crack-tip sharpness no longer
change with further crack extension. Although crack-tip conditions can be a function of crack velocity, the steady-state crack-tip
conditions for metals have appeared to be independent of the crack velocity within the range attained by the loading rates specified
in this test method.
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.
E1304 − 97 (2014)
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
3.2.6.1 Discussion—
This unloading slope ratio provides a method of determining the crack length at various points on the 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 the test as indicated schematically in Fig. 4 and Fig. 5. For each unloading-reloading trace, the
effective unloading slope ratio, r, is defined in terms of the tangents of two angles:
r 5 tan θ/tanθ
o
where:
tan θ = the slope of the initial elastic line, and
o
tan θ = the slope of an effective unloading line.
The effective unloading line is defined as having an origin at the high point where the displacement reverses direction on
unloading (slot mouth begins to close) and joining the low point on the reloading line where the force is one half that at the high
point.
3.2.6.2 Discussion—
E1304 − 97 (2014)
FIG. 4 Schematic of a Load-Displacement Test Record for Smooth Crack Growth Behavior, with Unloading/Reloading Cycles, Data Re-
duction Constructions, and Definitions of Terms
FIG. 5 Schematic of a Load-Displacement Test Record for Crack Jump Behavior, with Unloading/Reloading Cycles, Data Reduction
Constructions, and Definitions of Terms
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
For a brittle material with linear elastic behavior the unloading-reloading lines of an unloading-reloading cycle would be linear
and coincident. For many engineering materials, deviations from linear elastic behavior and hysteresis are commonly observed to
a varying degree. These effects require an unambiguous method of obtaining an effective unloading slope from the test record
(6-5).
The boldface numbers in parentheses refer to the list of references at the end of this standard.
3.2.6.3 Discussion—
E1304 − 97 (2014)
NOTE 1—Machine finish all over equal to or better than 64 μin.
NOTE 2—Unless otherwise specified, dimensions 60.010B; angles 62°.
NOTE 3—Grip hardness should be RC = 45 or greater.
FIG. 7 Suggested Loading Grip Design
NOTE 1—To assist alignment, shims may be placed at these locations and removed before the load is applied, as described in 8.3.2.
FIG. 8 Recommended Tensile Test Machine Test Configuration
Although r is measured only at those crack positions where unloading-reloading cycles are performed, r is nevertheless defined
at all points during a chevron-notch specimen test. For any particular point it is the value that would be measured for r if an
unloading-reloading cycle were performed at that point.
3.2.7 critical slope ratio, r —the unloading slope ratio at the critical crack length.
c
3.2.8 critical crack length—the crack length in a chevron-notch specimen at which the specimen’s stress-intensity factor
coefficient, Y* (see 3.2.11 and Table 3), is a minimum, or equivalently, the crack length at which the maximum force would occur
in a purely linear elastic fracture mechanics test. At the critical crack length, the width of the crack front is approximately one third
the dimension B (Figs. 2 and 3).
3.2.9 high point, High—the point on a force-displacement plot, at the start of an unloading-reloading cycle, at which the
displacement reverses direction, that is, the point at which the specimen mouth begins closing due to unloading (see points labeled
High in Figs. 4 and 5).
3.2.10 low point, Low—the point on the reloading portion of an unloading-reloading cycle where the force is one half the high
point force (see points labeled Low in Figs. 4 and 5).
3.2.11 stress-intensity factor coeffıcient, Y*—a dimensionless parameter that relates the applied force and specimen geometry
to the resulting crack-tip stress-intensity factor in a chevron-notch specimen test (see 9.6.3).
3.2.11.1 Discussion—
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FIG. 9 Suggested Design for the Specimen Mouth Opening Gage
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
between the chords spanning the plunge cut arcs, and it is necessary to use
different values of φ and a (5), so that the crack front has the same width
o
as with straight cuts, at the critical crack length.
NOTE 3—The dimension a must be achieved when forming the side
o
grooves. A separate cut that blunts the apex of the chevron ligament is not
permissible.
NOTE 4—Grip groove surfaces are to be flat and parallel to chevron
notch within± 2°.
NOTE 5—Notch on centerline within ±0.005B and perpendicular or
parallel to surfaces as applicable within 0.005B (TIR).
NOTE 6—The imaginary line joining the conical gage seats must be
perpendicular (±2°) to the plane of the specimen slot.
Value
Sym-
Name Tolerance
bol
W/B = 1.45 W/B = 2.0
B Diameter B B .
W Length 1.450B 2.000B ±0.010B
a Distance to chevron tip 0.481B 0.400B ±0.005B
o
S Grip groove depth 0.150B 0.150B ±0.010B
alternate groove 0.130B 0.130B ±0.010B
X Distance to load line 0.100B 0.100B ±0.003B
alternate groove 0.050B 0.050B ±0.003B
T Grip groove width 0.350B 0.350B ±0.005B
alternate groove 0.313B 0.313B ±0.005B
A A
t Slot thickness #0.030B #0.030B .
φ Slot angle 54.6° 34.7° ±0.5°
A
See Fig. 6.
Values of Y* can be found from the graphs in Fig. 10, or from the tabulations in Table 4 or from the polynominal expressions in
Table 5.
3.2.12 minimum stress-intensity factor coeffıcient, Y* —the minimum value of Y* (Table 3).
m
4. Summary of Test Method
4.1 This test method involves the application of a load to the mouth of a chevron-notched specimen to induce an opening
displacement of the specimen mouth. An autographic record is made of the load versus mouth opening displacement and the slopes
of periodic unloading-reloading cycles are used to calculate the crack length based on compliance techniques. These crack lengths
E1304 − 97 (2014)
TABLE 2 Bar 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
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