ASTM E1304-97(2014)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
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.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 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.
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´1
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.
ε NOTE—Editorial changes were made throughout in May 2020.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This test method covers the determination of plane-
mine the applicability of regulatory limitations prior to use.
strain (chevron-notch) fracture toughnesses, K or K ,of
Iv IvM
1.5 This international standard was developed in accor-
metallic materials. Fracture toughness by this method is
dance with internationally recognized principles on standard-
relative to a slowly advancing steady state crack initiated at a
ization established in the Decision on Principles for the
chevron-shaped notch, and propagating in a chevron-shaped
Development of International Standards, Guides and Recom-
ligament (Fig. 1). Some metallic materials, when tested by this
mendations issued by the World Trade Organization Technical
method, exhibit a sporadic crack growth in which the crack
Barriers to Trade (TBT) Committee.
front remains nearly stationary until a critical load is reached.
The crack then becomes unstable and suddenly advances at
2. Referenced Documents
highspeedtothenextarrestpoint.Forthesematerials,thistest
2.1 ASTM Standards:
method covers the determination of the plane-strain fracture
E4Practices for Force Verification of Testing Machines
toughness, K or K , relative to the crack at the points of
Ivj IvM
E8/E8MTest Methods for Tension Testing of Metallic Ma-
instability.
terials
NOTE 1—One difference between this test method and Test Method
E399Test Method for Linear-Elastic Plane-Strain Fracture
E399 (which measures K ) is that Test Method E399 centers attention on
Ic
Toughness of Metallic Materials
the start of crack extension from a fatigue precrack. This test method
E1823TerminologyRelatingtoFatigueandFractureTesting
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
3. Terminology
principles of linear elastic fracture mechanics, this difference, plus other
differences in test procedure, may cause the values from this test method
3.1 Definitions:
tobelargerthan K valuesinsomematerials.Therefore,toughnessvalues
Ic
3.1.1 The terms described in Terminology E1823 are appli-
determined by this test method cannot be used interchangeably with K .
Ic
cable to this test method.
1.2 This test method uses either chevron-notched rod speci-
−3/2
3.1.2 stress-intensity factor, K [FL ]—the magnitude of
I
mens of circular cross section, or chevron-notched bar speci-
the mathematically ideal crack-tip stress field (stress-field
mens of square or rectangular cross section (Figs. 1-10). The
singularity) for mode I in a homogeneous linear-elastic body.
terms “short rod” and “short bar” are used commonly for these
3.1.2.1 Discussion—Valuesof Kformode Iaregivenbythe
types of chevron-notched specimens.
following equation:
1.3 The values stated in inch-pound units are to be regarded
½
K 5 limit σ @2πr #
I y x
as standard. The values given in parentheses are mathematical
r →0
conversions to SI units that are provided for information only x
and are not considered standard.
where:
1.4 This standard does not purport to address all of the
r = distance from the crack tip to a location where the
x
safety concerns, if any, associated with its use. It is the
stress is calculated and
σ = the principal stress r normal to the crack plane.
y x
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/E1304-97R14E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
ϵ1
E1304 − 97 (2014)
3.2.5 steady-state crack—a crack that has advanced slowly
until the crack-tip plastic zone size and crack-tip sharpness no
longerchangewithfurthercrackextension.Althoughcrack-tip
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
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.
NOTE 1—The crack commences at the tip of the chevron-shaped
3.2.6.1 Discussion—This unloading slope ratio provides a
ligament and propagates (shaded area) along the ligament, and has the
methodofdeterminingthecracklengthatvariouspointsonthe
length “a” shown. (Not to scale.)
test record and therefore allows evaluation of stress intensity
FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a)
coefficient Y* (see 3.2.11). The effective unloading slope ratio
and Short Bar (b) Specimens
is measured by performing unloading-reloading cycles during
thetestasindicatedschematicallyinFig.4andFig.5.Foreach
unloading-reloading trace, the effective unloading slope ratio,
3.2 Definitions of Terms Specific to This Standard:
r, is defined in terms of the tangents of two angles:
3.2.1 plane-strain (chevron-notch) fracture toughness, K
Iv
r 5 tan θ/tanθ
−3/2
o
or K [FL ]—under conditions of crack-tip plane strain in a
Ivj
chevron-notched specimen: K relates to extension resistance where:
Iv
with respect to a slowly advancing steady-state crack. K
Ivj tan θ = the slope of the initial elastic line, and
o
relates to crack extension resistance with respect to a crack
tan θ = the slope of an effective unloading line.
which advances sporadically.
Theeffectiveunloadinglineisdefinedashavinganoriginat
3.2.1.1 Discussion—For slow rates of loading the fracture
the high point where the displacement reverses direction on
toughness, K or K , is the value of stress-intensity factor as
Iv Ivj
unloading (slot mouth begins to close) and joining the low
measuredusingtheoperationalprocedure(andsatisfyingallof
point on the reloading line where the force is one half that at
the validity requirements) specified in this test method.
the high point.
3.2.2 plane-strain (chevron-notch) fracture toughness, K
3.2.6.2 Discussion—For a brittle material with linear elastic
IvM
−3/2
[FL ]—determined similarly to K or K (see 3.2.1) using
behavior the unloading-reloading lines of an unloading-
Iv Ivj
the same specimen, or specimen geometries, but using a
reloading cycle would be linear and coincident. For many
simpler analysis based on the maximum test force. The
engineering materials, deviations from linear elastic behavior
analysisisdescribedinAnnexA1.Unloading-reloadingcycles
and hysteresis are commonly observed to a varying degree.
as described in 3.2.6 are not required in a test to determine
These effects require an unambiguous method of obtaining an
K .
effective unloading slope from the test record (6-5).
IvM
3.2.6.3 Discussion—Although r is measured only at those
3.2.3 smooth crack growth behavior—generally,thattypeof
crack positions where unloading-reloading cycles are
crack extension behavior in chevron-notch specimens that is
performed, r is nevertheless defined at all points during a
characterized primarily by slow, continuously advancing crack
chevron-notch specimen test. For any particular point it is the
growth, and a relatively smooth force displacement record
value that would be measured for r if an unloading-reloading
(Fig. 4). However, any test behavior not satisfying the condi-
cycle were performed at that point.
tions for crack jump behavior is automatically characterized as
smooth crack growth behavior.
3.2.7 critical slope ratio, r —the unloading slope ratio at
c
the critical crack length.
3.2.4 crack jump behavior—in tests of chevron-notch
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
from0.8r to1.2r (see3.2.6and3.2.7,and8.3.5.2).Onlythose
c c
sudden crack advances that result in more than a 5% decrease
The boldface numbers in parentheses refer to the list of references at the end
inforceduringtheadvancearecountedascrackjumps(Fig.5). of this standard.
ϵ1
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
specimen mouth begins closing due to unloading (see points 4. Summary of Test Method
labeled High in Figs. 4 and 5).
4.1 Thistestmethodinvolvestheapplicationofaloadtothe
3.2.10 low point, Low—thepointonthereloadingportionof
mouth of a chevron-notched specimen to induce an opening
an unloading-reloading cycle where the force is one half the
displacement of the specimen mouth.An autographic record is
high point force (see points labeled Low in Figs. 4 and 5).
made of the load versus mouth opening displacement and the
3.2.11 stress-intensity factor coeffıcient, Y*—a dimension-
slopes of periodic unloading-reloading cycles are used to
less parameter that relates the applied force and specimen
calculate the crack length based on compliance techniques.
geometry to the resulting crack-tip stress-intensity factor in a
These crack lengths are expressed indirectly as slope ratios.
chevron-notch specimen test (see 9.6.3).
Thecharacteristicsoftheforceversusmouthopeningdisplace-
3.2.11.1 Discussion—Values of Y* can be found from the
ment trace depend on the geometry of the specimen, the
graphsinFig.10,orfromthetabulationsinTable4orfromthe
specimen plasticity during the test, any residual stresses in the
polynominal expressions in Table 5.
specimen, and the crack growth characteristics of the material
3.2.12 minimum stress-intensity factor coeffıcient, Y* —the
m beingtested.Ingeneral,twotypesofforceversusdisplacement
minimum value of Y*(Table 3).
ϵ1
E1304 − 97 (2014)
R# 0.010B
φ # 60°
s
h# 0.03B
NOTE 1—These requirements are satisfied by slots with a round bottom
whenever h ≤ 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-
NOTE 2—Unless otherwise specified, dimensions 60.010B; angles
tion Constructions, and Definitions of Terms
62°.
NOTE 3—Grip hardness should be RC=45 or greater.
FIG. 7 Suggested Loading Grip Design
traces are recognized, namely, smooth behavior (see3.2.3) and
crack jump behavior (see 3.2.4).
4.1.1 In metals that exhibit smooth crack behavior (3.2.3), smooth crack growth under decreasing force. Two unloading-
thecrackinitiatesatalowforceatthetipofasufficientlysharp reloadingcyclesareperformedtodeterminethelocationofthe
chevron, and each incremental increase in its length corre- crack, the force used to calculate K , and to provide validity
Iv
sponds to an increase in crack front width and requires further checks on the test. The fracture toughness is calculated from
increase in force. This force increase continues until a point is theforcerequiredtoadvancethecrackwhenthecrackisatthe
reached where further increases in force provide energy in critical crack length (see 3.2.8). The plane-strain fracture
excess of that required to advance the crack. This maximum toughness determined by this procedure is termed K .An
Iv
forcepointcorrespondstoawidthofcrackfrontapproximately alternative procedure, described in Annex A1, omits the
one third the specimen diameter or thickness. If the loading unloading cycles and uses the maximum test force to calculate
systemissufficientlystiff,thecrackcanbemadetocontinueits a plane-strain fracture toughness K , where M signifies the
IvM
ϵ1
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 crack length.
NOTE 3—The dimension a must be achieved when forming the side
o
grooves.Aseparate
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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 2014) 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—Editorial changes were made throughout in May 2020.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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.
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 of Metallic Materials
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.
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.
ε1
Current edition approved July 1, 2014. Published September 2014. Originally approved in 1989. Last previous edition approved in 2009 as E1304 – 97(2009) . DOI:
10.1520/E1304-97R14.10.1520/E1304-97R14E01.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
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
−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.
3.1.2.1 Discussion—
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).
´1
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
3.2.5 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.
3.2.6.1 Discussion—
´1
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
th # 0.03B
NOTE 1—These requirements are satisfied by slots with a round bottom whenever th ≤ 0.020B.
FIG. 6 Slot Bottom Configuration
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—
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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
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).
3.2.6.3 Discussion—
The boldface numbers in parentheses refer to the list of references at the end of this standard.
´1
E1304 − 97 (2014)
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 .
A A
h Notch height #0.030B #0.030B .
φ Slot angle 54.6° 34.7° ±0.5°
A
See Fig. 6.
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
´1
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 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 Thickness 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 .
A A
h Notch height #0.030B #0.030B .
φ Slot angle 54.6° 34.7° ±0.5°
H Half-height
(square specimen) 0.500B 0.500B ±0.005B
B
(rectangular spec- 0
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