ASTM E740/E740M-03(2010)e2
(Practice)Standard Practice for Fracture Testing with Surface-Crack Tension Specimens
Standard Practice for Fracture Testing with Surface-Crack Tension Specimens
SIGNIFICANCE AND USE
4.1 The surface-crack tension (SCT) test is used to estimate the load-carrying capacity of simple sheet- or plate-like structural components having a type of flaw likely to occur in service. The test is also used for research purposes to investigate failure mechanisms of cracks under service conditions.
4.2 The residual strength of an SCT specimen is a function of the crack depth and length and the specimen thickness as well as the characteristics of the material. This relationship is extremely complex and cannot be completely described or characterized at present.
4.2.1 The results of the SCT test are suitable for direct application to design only when the service conditions exactly parallel the test conditions. Some methods for further analysis are suggested in Appendix X1.
4.3 In order that SCT test data can be comparable and reproducible and can be correlated among laboratories, it is essential that uniform SCT testing practices be established.
4.4 The specimen configuration, preparation, and instrumentation described in this practice are generally suitable for cyclic- or sustained-force testing as well. However, certain constraints are peculiar to each of these tests. These are beyond the scope of this practice but are discussed in Ref. (1).
SCOPE
1.1 This practice covers the design, preparation, and testing of surface-crack tension (SCT) specimens. It relates specifically to testing under continuously increasing force and excludes cyclic and sustained loadings. The quantity determined is the residual strength of a specimen having a semielliptical or circular-segment fatigue crack in one surface. This value depends on the crack dimensions and the specimen thickness as well as the characteristics of the material.
1.2 Metallic materials that can be tested are not limited by strength, thickness, or toughness. However, tests of thick specimens of tough materials may require a tension test machine of extremely high capacity. The applicability of this practice to nonmetallic materials has not been determined.
1.3 This practice is limited to specimens having a uniform rectangular cross section in the test section. The test section width and length must be large with respect to the crack length. Crack depth and length should be chosen to suit the ultimate purpose of the test.
1.4 Residual strength may depend strongly upon temperature within a certain range depending upon the characteristics of the material. This practice is suitable for tests at any appropriate temperature.
1.5 Residual strength is believed to be relatively insensitive to loading rate within the range normally used in conventional tension tests. When very low or very high rates of loading are expected in service, the effect of loading rate should be investigated using special procedures that are beyond the scope of this practice. Note 1—Further information on background and need for this type of test is given in the report of ASTM Task Group E24.01.05 on Part-Through-Crack Testing (1).2
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.7 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: E740/E740M − 03(Reapproved 2010)
Standard Practice for
Fracture Testing with Surface-Crack Tension Specimens
This standard is issued under the fixed designation E740/E740M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The units statement (1.6) and the designation were editorially revised in January 2011.
ε NOTE—3.1.2 was editorially revised in May 2013.
1. Scope 1.6 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in
1.1 This practice covers the design, preparation, and testing
each system may not be exact equivalents; therefore, each
of surface-crack tension (SCT) specimens. It relates specifi-
system shall be used independently of the other. Combining
cally to testing under continuously increasing force and ex-
values from the two systems may result in non-conformance
cludes cyclic and sustained loadings. The quantity determined
with the standard.
istheresidualstrengthofaspecimenhavingasemiellipticalor
1.7 This standard does not purport to address all of the
circular-segment fatigue crack in one surface. This value
safety concerns, if any, associated with its use. It is the
dependsonthecrackdimensionsandthespecimenthicknessas
responsibility of the user of this standard to establish appro-
well as the characteristics of the material.
priate safety and health practices and determine the applica-
1.2 Metallic materials that can be tested are not limited by
bility of regulatory limitations prior to use.
strength, thickness, or toughness. However, tests of thick
specimens of tough materials may require a tension test
2. Referenced Documents
machine of extremely high capacity. The applicability of this
2.1 ASTM Standards:
practice to nonmetallic materials has not been determined.
E4Practices for Force Verification of Testing Machines
1.3 This practice is limited to specimens having a uniform
E8Test Methods for Tension Testing of Metallic Materials
rectangular cross section in the test section. The test section
E338Test Method of Sharp-Notch Tension Testing of High-
widthandlengthmustbelargewithrespecttothecracklength.
Strength Sheet Materials (Withdrawn 2010)
Crack depth and length should be chosen to suit the ultimate
E399Test Method for Linear-Elastic Plane-Strain Fracture
purpose of the test.
Toughness K of Metallic Materials
Ic
1.4 Residual strength may depend strongly upon tempera-
E466Practice for Conducting Force Controlled Constant
ture within a certain range depending upon the characteristics
Amplitude Axial Fatigue Tests of Metallic Materials
of the material. This practice is suitable for tests at any
E561Test Method forK-R Curve Determination
appropriate temperature.
E1823TerminologyRelatingtoFatigueandFractureTesting
1.5 Residual strength is believed to be relatively insensitive
3. Terminology
to loading rate within the range normally used in conventional
tension tests. When very low or very high rates of loading are
3.1 Definitions:
expected in service, the effect of loading rate should be
3.1.1 Definitions given in Terminology E1823 are appli-
investigatedusingspecialproceduresthatarebeyondthescope
cable to this practice.
of this practice.
3.1.2 crack mouth opening displacement (CMOD), 2v
m
(L)—crack—opening displacement resulting from the total
NOTE 1—Further information on background and need for this type of
deformation (elastic plus plastic) measured under force at the
test is given in the report of ASTM Task Group E24.01.05 on Part-
Through-Crack Testing (1). location on the crack surface that has the largest displacement
per unit force.
ThispracticeisunderthejurisdictionofASTMCommitteeE08onFatigueand
Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture
Mechanics. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2010. Published January 2011. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2003 as E740–03. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0740-03R10E02. the ASTM website.
2 4
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof The last approved version of this historical standard is referenced on
this standard. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E740/E740M − 03 (2010)
NOTE 2—In surface-crack tension (SCT) specimens, CMOD is mea-
5.2 FatiguePrecrackingApparatus—Axialtensionorthree-
sured on the specimen surface along the normal bisector of the crack
point, four-point, or cantilever bending are all acceptable
length.
modes for fatigue precracking. Fixture design is not critical as
3.1.3 fracture toughness—a generic term for measures of
long as the crack growth is symmetrical and the plane of the
resistance to extension of a crack. E616
crack remains perpendicular to the specimen face and the
3.1.4 original crack size, a [L]—the physical crack size at tensileforcevector.Theeffectofcyclicfrequencyisthoughtto
o
be negligible below 100 Hz in a nonaggressive environment.
the start of testing. (E616)
3.2 Definitions of Terms Specific to This Standard:
NOTE 4—Certain crack shapes are more readily produced in axial
tension, others in bending (see Annex A1).
3.2.1 crack depth, a [L]—in surface-crack tension (SCT)
specimens, the normal distance from the cracked plate surface
5.2.1 Devices and fixtures for cantilever bending of sheet
tothepointofmaximumpenetrationofthecrackfrontintothe
and plate specimens are described in Refs. (2) and (3),
material. Crack depth is a fraction of the specimen thickness.
respectively. Others may be equally suitable. The axial fatigue
3.2.1.1 Discussion—In this practice, crack depth is the
machines described in Practice E466 are suitable for precrack-
original depth a and the subscript o is everywhere implied.
ing in tension; however, since the precracking operation is
o
terminated prior to specimen failure, one should ensure that
3.2.2 crack length, 2c [L]—in surface-crack tension
load variations during slowdown or shutdown do not exceed
specimens, a distance measured on the specimen surface
those desired.
between the two points at which the crack front intersects the
5.2.2 A magnifier of about 20 power should be used to
specimensurface.Cracklengthisafractionofspecimenwidth.
monitor the fatigue precracking process. Ease of observation
3.2.2.1 Discussion—In this practice, crack length is the
willbeenhancedifthecyclicratecanbereducedtoabout1Hz
original length 2c and the subscript o is everywhere implied.
o
when desired.Alternatively, a stroboscopic light synchronized
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3.2.3 residual strength, σ (FL )—the maximum value of
r
with the maximum application of tensile force may serve as
the nominal stress, neglecting the area of the crack, that a
well.
cracked specimen is capable of sustaining.
5.3 Testing Machine—The test should be conducted with a
NOTE3—Insurface-cracktension(SCT)specimens,residualstrengthis
tension testing machine that conforms to the requirements of
the ratio of the maximum load (P ) to the product of test section width
max
Practices E4.
(W) times thickness (B), P /(BW). It represents the stress at fracture
max
5.3.1 The devices for transmitting force to the specimen
normal to and remote from the plane of the crack.
shallbesuchthatthemajoraxisofthespecimencoincideswith
4. Significance and Use theloadaxis.Thepin-and-clevisarrangementdescribedinTest
Method E338 should be suitable for specimens whose width is
4.1 The surface-crack tension (SCT) test is used to estimate
less than about 4 in. [100 mm]. An arrangement such as that
the load-carrying capacity of simple sheet- or plate-like struc-
shown in Fig. 2 of Practice E561 should be suitable for wider
tural components having a type of flaw likely to occur in
specimens.
service. The test is also used for research purposes to investi-
5.3.2 For tests at other than room temperature, the tempera-
gate failure mechanisms of cracks under service conditions.
turecontrolandtemperaturemeasurementrequirementsofTest
4.2 The residual strength of an SCT specimen is a function
Method E338 are appropriate.
of the crack depth and length and the specimen thickness as
5.4 Displacement Gage (Optional)—If used to measure
well as the characteristics of the material. This relationship is
CMOD, the displacement gage output should accurately indi-
extremely complex and cannot be completely described or
cate the relative displacement of two gage points on the
characterized at present.
cracked surface, spanning the crack at the midpoint of its
4.2.1 The results of the SCT test are suitable for direct
length. Further information on displacement gages appears in
application to design only when the service conditions exactly
Appendix X2.
parallel the test conditions. Some methods for further analysis
5.5 For some combinations of material and crack geometry,
are suggested in Appendix X1.
thecrackmaypropagateentirelythroughthethicknesspriorto
4.3 In order that SCT test data can be comparable and
totalfailure.Methodsofdetectingthisoccurrence,shoulditbe
reproducible and can be correlated among laboratories, it is
of interest, are discussed briefly in Ref. (1).
essential that uniform SCT testing practices be established.
6. Test Specimen
4.4 The specimen configuration, preparation, and instru-
mentation described in this practice are generally suitable for 6.1 Configuration and Notation—The SCT test specimen
cyclic- or sustained-force testing as well. However, certain
and the notation used herein are shown in Fig. 1. Grip details
constraintsarepeculiartoeachofthesetests.Thesearebeyond
have been omitted, since grip design may depend on specimen
the scope of this practice but are discussed in Ref. (1).
size (5.3.1) and material toughness. In general, the only
gripping requirements are that the arrangement be strong
5. Apparatus
enough to carry the maximum expected force and that it allow
uniform distribution of force over the specimen cross section.
5.1 The procedure involves testing of specimens that have
been precracked in fatigue. force versus CMOD, if CMOD is 6.2 Dimensions—The crack depth and length and specimen
measured, is recorded autographically or digitally. thickness should be chosen according to the ultimate purpose
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E740/E740M − 03 (2010)
depth and length are close to predetermined target values, and
whose subsequent fracture behavior will not be influenced by
any detail of the preparation process. A small slit or crack
starter is machined into the specimen surface at the center of
the test section (Fig. 2) to locate and help initiate the fatigue
crack.Regularityofcrackconfigurationisinfluencedprimarily
by fatigue force uniformity, which can be maximized by
careful alignment of force train and fixtures. Material
inhomogeneity, residual stresses, and starter notch root radius
variation can produce irregularities which may be beyond
control. Fatigue crack size and shape control are discussed in
Annex A1.
6.3.1 Crack starters have been produced by a variety of
methods. The following procedures are known to produce
acceptable results.
6.3.1.1 The crack starter should be machined, either by
slittingwithathinjeweler’scircularsaworsimilarcutterorby
electrical discharge machining (EDM) with a thin, shaped
electrode.
6.3.1.2 The crack starter plane should be perpendicular to
the specimen face and the tensile force vector within 10°.
6.3.1.3 The starter notch root radius should be less than
0.010 in. [0.25 mm].
FIG. 1 Typical Surface-Crack Specimen (Grip Details Omitted)
6.3.1.4 The crack starter length and depth should be chosen
and Nomenclature
with the desired crack dimensions and the requirements of
6.3.2.2 in mind.
of the test. Further discussion of this subject may be found in 6.3.2 The following procedures should ensure the produc-
AppendixX3.ThespecimenwidthWshouldbeatleast5times tion of an effective sharp fatigue crack.
the crack length 2c and the specimen test section length L
6.3.2.1 Fatigue crack with the specimen in the heat treat-
should be at least twice the width W. Should these width and
ment condition in which it is to be tested, if at all possible.
length dimensions exceed actual service dimensions, the ser-
6.3.2.2 Whenever it is physically possible, the crack should
vice dimensions should be used but one should not then
be extended at least 0.05 in. [1.3 mm]; in any event the fatigue
attempt to generalize data from such tests.
crack extension must not be less than 5% of the final crack
6.3 Fatigue Precracking—The object is to produce at a depth, and the crack and its starter must lie entirely within an
prescribed location a fatigue crack whose configuration is imaginary 30° wedge whose apex is at the crack tip. These
regular (that is, a half-ellipse or a segment of a circle), whose two-dimensional descriptions shall apply around the entire
NOTE 1—Section A-A refers to the plane normal to any tangent to the crack periphery and containing the point of tangency.
FIG. 2 Fatigue Crack and Starter Details
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E740/E740M − 03 (2010)
crackfront,thatis,inallplanesnormaltotangentstoallpoints traveling microscope is usually satisfactory. Observe the crack
on the crack periphery (Fig. 2). shape;itshouldcloselyapproximateasemiellipseorasegment
6.3.2.3 The ratio of minimum to maximum cyclic stress, R, of a circle. If the crack shape is irregular or unsymmetric the
should not be greater than 0.1. test should be discarded. Using the actual crack dimensions,
6.3.2.4 For at least the final 2.5% of the total crack depth, verify that the requirement 6.3.2.4 was indeed met.
1/2 1/2
theratioK /Eshouldnotexceed0.002in. [0.00032m ],
max
7.6 Residual Strength—Calculate the residual strength as σ
r
where K is the maximum stress intensity factor during
max
=P /(BW).
max
fatigue cracking and E is the material’s elastic modulus. An
8. Report
estimate of K can be computed based on the cyclic stress
max
and the target crack dimensions using the appropriate equation
8.1 The report should include the following for each speci-
from AnnexA2. Compute K at the surface or at the deepest
max men tested:
point, whichever is greater.
8.1.1 Test section width, W, and thickness, B.
8.1.2 Maximum stress intensity factor during fatigue
7. Procedure
precracking,
...
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