ASTM E1304-97(2002)
(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
SCOPE
1.1 This test method covers the determination of plane-strain (chevron-notch) fracture toughnesses, KIv or K IvM, 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 K Ic) 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 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 1304 – 97 (Reapproved 2002)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the determination of plane- 2.1 ASTM Standards:
strain (chevron-notch) fracture toughnesses, K or K ,of E4 Practices for Force Verification of Testing Machines
Iv IvM
metallic materials. Fracture toughness by this method is E8 Test Methods for Tension Testing of Metallic Materials
relative to a slowly advancing steady state crack initiated at a E399 Test Method for Linear-Elastic Plane-Strain Fracture
chevron-shaped notch, and propagating in a chevron-shaped Toughness K of Metallic Materials
Ic
ligament (Fig. 1). Some metallic materials, when tested by this E1823 Terminology Relating to Fatigue and Fracture Test-
method, exhibit a sporadic crack growth in which the crack ing
front remains nearly stationary until a critical load is reached.
3. Terminology
The crack then becomes unstable and suddenly advances at
3.1 Definitions:
highspeedtothenextarrestpoint.Forthesematerials,thistest
method covers the determination of the plane-strain fracture 3.1.1 The terms described in Terminology E1823 are ap-
plicable to this test method.
toughness, K or K , relative to the crack at the points of
Ivj IvM
−3/2
instability. 3.1.2 stress-intensity factor, K (dimensionalunitsFL )—
I
the magnitude of the ideal crack-tip stress field singularity for
NOTE 1—One difference between this test method and Test Method
mode I in a homogeneous linear-elastic body.
E399(whichmeasures K )isthatTestMethodE399centersattentionon
Ic
3.1.2.1 Discussion—Values of K for mode I are given by:
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 ½
K 5limit s [2pr
#
I y x
the initiation of a crack jump. Although both methods are based on the
principles of linear elastic fracture mechanics, this difference, plus other
r→0
differences in test procedure, may cause the values from this test method x
tobelargerthan K valuesinsomematerials.Therefore,toughnessvalues
Ic
where:
determined by this test method cannot be used interchangeably with K .
Ic
r = a distance directly forward from the crack tip to a
x
1.2 This test method uses either chevron-notched rod speci-
locationwherethesignificantstressiscalculatedand
mens of circular cross section, or chevron-notched bar speci-
s = the principal stress r normal to the crack plane.
y x
mens of square or rectangular cross section (Figs. 1-10). The
3.2 Definitions of Terms Specific to This Standard:
terms“shortrod”and“shortbar”areusedcommonlyforthese
3.2.1 plane-strain (chevron-notch) fracture toughness, K
Iv
types of chevron-notched specimens. −3/2
orK (FL )—underconditionsofcrack-tipplanestrainina
Ivj
1.3 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
responsibility of the user of this standard to establish appro-
relates to crack extension resistance with respect to a crack
priate safety and health practices and determine the applica-
which advances sporadically.
bility of regulatory limitations prior to use.
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
measuredusingtheoperationalprocedure(andsatisfyingallof
the validity requirements) specified in this test method.
ThistestmethodisunderthejurisdictionofASTMCommitteeE08onFracture
Fatigue and is the direct responsibility of Subcommittee E08.02 on Standards and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Terminology. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved April 10, 1997. Published June 1997. Originally Standards volume information, refer to the standard’s Document Summary page on
published as E1304–89. Last previous edition E1304–89. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1304 – 97 (2002)
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,
r, is defined in terms of the tangents of two angles:
r 5tan u/tan u
o
where:
tan u = the slope of the initial elastic line, and
o
tan u = the slope of an effective unloading line.
Theeffectiveunloadinglineisdefinedashavinganoriginat
NOTE 1—The crack commences at the tip of the chevron-shaped
the high point where the displacement reverses direction on
ligament and propagates (shaded area) along the ligament, and has the
unloading (slot mouth begins to close) and joining the low
length “a” shown. (Not to scale.)
point on the reloading line where the force is one half that at
FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a)
and Short Bar (b) Specimens the high point.
3.2.6.2 Discussion—Forabrittlematerialwithlinearelastic
behavior the unloading-reloading lines of an unloading-
3.2.2 plane-strain (chevron-notch) fracture toughness, K reloading cycle would be linear and coincident. For many
IvM
−3/2
engineering materials, deviations from linear elastic behavior
(FL )—determined similarly to K or K (see 3.2.1) using
Iv Ivj
the same specimen, or specimen geometries, but using a and hysteresis are commonly observed to a varying degree.
These effects require an unambiguous method of obtaining an
simpler analysis based on the maximum test force. The
analysis is described inAnnexA1. Unloading-reloading cycles effective unloading slope from the test record (1-4).
3.2.6.3 Discussion—Although r is measured only at those
as described in 3.2.6 are not required in a test to determine
crack positions where unloading-reloading cycles are per-
K .
IvM
3.2.3 smoothcrackgrowthbehavior—generally,thattypeof formed, r is nevertheless defined at all points during a
chevron-notch specimen test. For any particular point it is the
crack extension behavior in chevron-notch specimens that is
characterized primarily by slow, continuously advancing crack value that would be measured for r if an unloading-reloading
cycle were performed at that point.
growth, and a relatively smooth force displacement record
(Fig. 4). However, any test behavior not satisfying the condi- 3.2.7 critical slope ratio, r —the unloading slope ratio at
c
the critical crack length.
tions for crack jump behavior is automatically characterized as
smooth crack growth behavior. 3.2.8 critical crack length—the crack length in a chevron-
notch specimen at which the specimen’s stress-intensity factor
3.2.4 crack jump behavior—intestsofchevron-notchspeci-
mens, that type of sporadic crack growth which is character- coefficient, Y* (see 3.2.11 and Table 3), is a minimum, or
equivalently, the crack length at which the maximum force
izedprimarilybyperiodsduringwhichthecrackfrontisnearly
stationaryuntilacriticalforceisreached,whereuponthecrack would occur in a purely linear elastic fracture mechanics test.
At the critical crack length, the width of the crack front is
becomes unstable and suddenly advances at high speed to the
next arrest point, where it remains nearly stationary until the approximately one third the dimension B (Figs. 2 and 3).
3.2.9 high point, High—the point on a force-displacement
force again reaches a critical value, etc. (see Fig. 5).
3.2.4.1 Discussion—A chevron-notch specimen is said to plot, at the start of an unloading-reloading cycle, at which the
displacement reverses direction, that is, the point at which the
have a crack jump behavior when crack jumps account for
more than one half of the change in unloading slope ratio (see specimen mouth begins closing due to unloading (see points
labeled High in Figs. 4 and 5).
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 3.2.10 lowpoint,Low—thepointonthereloadingportionof
c c
sudden crack advances that result in more than a 5% decrease an unloading-reloading cycle where the force is one half the
high point force (see points labeled Low in Figs. 4 and 5).
inforceduringtheadvancearecountedascrackjumps(Fig.5).
3.2.5 steady-state crack—a crack that has advanced slowly 3.2.11 stress-intensity factor coeffıcient, Y*—a dimension-
less parameter that relates the applied force and specimen
until the crack-tip plastic zone size and crack-tip sharpness no
longerchangewithfurthercrackextension.Althoughcrack-tip geometry to the resulting crack-tip stress-intensity factor in a
chevron-notch specimen test (see 9.6.3).
conditions can be a function of crack velocity, the steady-state
crack-tip conditions for metals have appeared to be indepen- 3.2.11.1 Discussion—Values of Y* can be found from the
graphsinFig.10,orfromthetabulationsinTable4orfromthe
dent of the crack velocity within the range attained by the
loading rates specified in this test method. polynominal expressions in Table 5.
3.2.12 minimum stress-intensity factor coeffıcient, Y*
3.2.6 effective unloading slope ratio, r—the ratio of an
m
effective unloading slope to that of the initial elastic loading —the minimum value of Y*(Table 3).
slope on a test record of force versus specimen mouth opening
displacement.
3.2.6.1 Discussion—This unloading slope ratio provides a
The boldface numbers in parentheses refer to the list of references at the end
methodofdeterminingthecracklengthatvariouspointsonthe of this standard.
E 1304 – 97 (2002)
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
4. Summary of Test Method 4.1.1 In metals that exhibit smooth crack behavior (3.2.3),
thecrackinitiatesatalowforceatthetipofasufficientlysharp
4.1 Thistestmethodinvolvestheapplicationofaloadtothe
chevron, and each incremental increase in its length corre-
mouth of a chevron-notched specimen to induce an opening
sponds to an increase in crack front width and requires further
displacement of the specimen mouth.An autographic record is
increase in force. This force increase continues until a point is
made of the load versus mouth opening displacement and the
reached where further increases in force provide energy in
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
Thecharacteristicsoftheforceversusmouthopeningdisplace-
systemissufficientlystiff,thecrackcanbemadetocontinueits
ment trace depend on the geometry of the specimen, the
smooth crack growth under decreasing force. Two unloading-
specimen plasticity during the test, any residual stresses in the
reloadingcyclesareperformedtodeterminethelocationofthe
specimen, and the crack growth characteristics of the material
crack, the force used to calculate K , and to provide validity
beingtested.Ingeneral,twotypesofforceversusdisplacement
Iv
tracesarerecognized,namely,smoothbehavior(see3.2.3)and checks on the test. The fracture toughness is calculated from
crack jump behavior (see 3.2.4). theforcerequiredtoadvancethecrackwhenthecrackisatthe
E 1304 – 97 (2002)
R# 0.010B
f # 60°
s
t# 0.03B
NOTE 1—Theserequirementsaresatisfiedbyslotswitharoundbottom
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
Jump Behavior, with Unloading/Reloading Cycles, Data
Reduction Constructions, and Definitions of Terms
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.
critical crack length (see 3.2.8). The plane-strain fracture
FIG. 7 Suggested Loading Grip Design
toughness determined by this procedure is termed K .An
Iv
alternative procedure, described in Annex A1, omits 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
significance as K .
discussed in Annex A1. Iv
4.1.3 Theequationsforcalculatingthetoughnesshavebeen
4.1.2 A modified procedure is used to determine K when
Ivj
established on the basis of elastic stress analyses of the
crack jump behavior is encountered. In this procedure,
specimen types described in this test method.
unloading-reloading cycles are used to determine the crack
location at which the next jump will begin.The K values are 4.2 The specimen size required for testing purposes in-
Ivj
calculated from the forces that produce crack jumps when the creases as the square of the ratio of fracture toughness to yield
E 1304 – 97 (2002)
NOTE 1—Compiled from Refs (8), (10), (11), and (13).
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, f is the angle
betweenthechordsspanningtheplungecutarcs,anditisnecessarytouse
differentvaluesof fand a (4),sothatthecrackfronthasthesamewidth
o
as with straight cuts, at the critical crack length.
NOTE 3—The dimension a must be achieved when forming the side
o
...
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