ASTM E1304-97(2008)
(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...
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 1304 – 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.
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/E8M Test Methods for Tension Testing of Metallic
relative to a slowly advancing steady state crack initiated at a Materials
chevron-shaped notch, and propagating in a chevron-shaped E399 Test Method for Linear-Elastic Plane-Strain Fracture
ligament (Fig. 1). Some metallic materials, when tested by this Toughness K of Metallic Materials
Ic
method, exhibit a sporadic crack growth in which the crack E1823 Terminology Relating to Fatigue and Fracture Test-
front remains nearly stationary until a critical load is reached. ing
The crack then becomes unstable and suddenly advances at
3. Terminology
highspeedtothenextarrestpoint.Forthesematerials,thistest
method covers the determination of the plane-strain fracture 3.1 Definitions:
3.1.1 The terms described in Terminology E1823 are ap-
toughness, K or K , relative to the crack at the points of
Ivj IvM
instability. plicable to this test method.
−3/2
3.1.2 stress-intensity factor, K (dimensional units FL )—
I
NOTE 1—One difference between this test method and Test Method
the magnitude of the ideal crack-tip stress field singularity for
E399(whichmeasures K )isthatTestMethodE399centersattentionon
Ic
mode I in a homogeneous linear-elastic body.
the start of crack extension from a fatigue precrack. This test method
3.1.2.1 Discussion—Values of K for mode I are given by:
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
½
K 5limit s [2pr #
I y x
principles of linear elastic fracture mechanics, this difference, plus other
differences in test procedure, may cause the values from this test method
tobelargerthan K valuesinsomematerials.Therefore,toughnessvalues r→0
Ic x
determined by this test method cannot be used interchangeably with K .
Ic
where:
1.2 This test method uses either chevron-notched rod speci-
r = a distance directly forward from the crack tip to a
x
mens of circular cross section, or chevron-notched bar speci-
location where the significant stress is calculated and
mens of square or rectangular cross section (Figs. 1-10). The
s = the principal stress r normal to the crack plane.
y x
terms “short rod” and “short bar” are used commonly for these
3.2 Definitions of Terms Specific to This Standard:
types of chevron-notched specimens.
3.2.1 plane-strain (chevron-notch) fracture toughness, K
Iv
−3/2
1.3 The values stated in inch-pound units are to be regarded
orK [FL ]—underconditionsofcrack-tipplanestrainina
Ivj
as standard. The values given in parentheses are mathematical
chevron-notched specimen: K relates to extension resistance
Iv
conversions to SI units that are provided for information only
with respect to a slowly advancing steady-state crack. K
Ivj
and are not considered standard.
relates to crack extension resistance with respect to a crack
1.4 This standard does not purport to address all of the
which advances sporadically.
safety concerns, if any, associated with its use. It is the
3.2.1.1 Discussion—For slow rates of loading the fracture
responsibility of the user of this standard to establish appro-
toughness, K or K , is the value of stress-intensity factor as
Iv Ivj
priate safety and health practices and determine the applica-
measuredusingtheoperationalprocedure(andsatisfyingallof
bility of regulatory limitations prior to use.
the validity requirements) specified in this test method.
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 For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Terminology. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2008. Published March 2009. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1989. Last previous edition approved in 2002 as E1304–97(2002). the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1304 – 97 (2008)
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 (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
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 (2008)
R# 0.010B
f # 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
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 The equations for calculating the toughness have been
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 (2008)
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 diame
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.