ASTM E1681-03(2008)e1
(Test Method)Standard Test Method for Determining a Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
Standard Test Method for Determining a Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
SIGNIFICANCE AND USE
The parameters KEAC or KIEAC determined by this test method characterize the resistance to crack growth of a material with a sharp crack in specific environments under loading conditions in which the crack-tip plastic region is small compared with the crack depth and the uncracked ligament. The less restrictive thickness requirements of KEAC are intended for those conditions in which the results are a strong function of the thickness of the specimen and the application requires the testing of specimens with thickness representative of the application. Since the chemical and mechanical influences cannot be separated, in some material/environment combinations, the thickness must be treated as a variable. A KEAC or KIEAC value is believed to represent a characteristic measurement of environment-assisted cracking resistance in a precracked specimen exposed to an environment under sustained tensile loading. A KEAC or KIEAC value may be used to estimate the relationship between failure stress and defect size for a material under any service condition, where the combination of crack-like defects, sustained tensile loading and the same specific environment would be expected to occur. (Background information concerning the development of this test method can be found in Refs (3-18).
SCOPE
1.1 This test method covers the determination of the environment-assisted cracking threshold stress intensity factor parameters, KIEAC and KEAC, for metallic materials from constant-force testing of fatigue precracked beam or compact fracture specimens and from constant-displacement testing of fatigue precracked bolt-load compact fracture specimens.
1.2 This test method is applicable to environment-assisted cracking in aqueous or other aggressive environments.
1.3 Materials that can be tested by this test method are not limited by thickness or by strength as long as specimens are of sufficient thickness and planar size to meet the size requirements of this test method.
1.4 A range of specimen sizes with proportional planar dimensions is provided, but size may be variable and adjusted for yield strength and applied force. Specimen thickness is a variable independent of planar size.
1.5 Specimen configurations other than those contained in this test method may be used, provided that well-established stress intensity calibrations are available and that specimen dimensions are of sufficient size to meet the size requirements of this test method during testing.
1.6 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: E1681 – 03 (Reapproved 2008)
Standard Test Method for
Determining Threshold Stress Intensity Factor for
Environment-Assisted Cracking of Metallic Materials
This standard is issued under the fixed designation E1681; 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.
´ NOTE—A1.5.1.1 was editorially corrected in May 2010.
´ NOTE—Figures 5 and 6 were made more legible in September 2011.
1. Scope D1141 Practice for the Preparation of Substitute Ocean
Water
1.1 This test method covers the determination of the
E8/E8M Test Methods for Tension Testing of Metallic
environment-assisted cracking threshold stress intensity factor
Materials
parameters, K and K , for metallic materials from
IEAC EAC
E399 Test Method for Linear-Elastic Plane-Strain Fracture
constant-force testing of fatigue precracked beam or compact
Toughness K of Metallic Materials
fracture specimens and from constant-displacement testing of Ic
E647 Test Method for Measurement of Fatigue Crack
fatigue precracked bolt-load compact fracture specimens.
Growth Rates
1.2 This test method is applicable to environment-assisted
E1823 Terminology Relating to Fatigue and Fracture Test-
cracking in aqueous or other aggressive environments.
ing
1.3 Materials that can be tested by this test method are not
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
limited by thickness or by strength as long as specimens are of
sion Test Specimens
sufficient thickness and planar size to meet the size require-
G5 Reference Test Method for Making Potentiostatic and
ments of this test method.
Potentiodynamic Anodic Polarization Measurements
1.4 A range of specimen sizes with proportional planar
G15 Terminology Relating to Corrosion and Corrosion
dimensions is provided, but size may be variable and adjusted
Testing
for yield strength and applied force. Specimen thickness is a
variable independent of planar size.
3. Terminology
1.5 Specimen configurations other than those contained in
3.1 Definitions:
this test method may be used, provided that well-established
3.1.1 For definitions of terms relating to fracture testing
stress intensity calibrations are available and that specimen
used in this test method, refer to Terminology E1823.
dimensions are of sufficient size to meet the size requirements
3.1.2 For definitions of terms relating to corrosion testing
of this test method during testing.
used in this test method, refer to Terminology G15.
1.6 This standard does not purport to address all of the
3.1.3 stress-corrosion cracking (SCC)—a cracking process
safety concerns, if any, associated with its use. It is the
that requires the simultaneous action of a corrodent and
responsibility of the user of this standard to establish appro-
sustained tensile stress.
priate safety and health practices and determine the applica-
3.1.4 stress intensity factor threshold for plane strain
bility of regulatory limitations prior to use.
–3/2
environment-assisted cracking (K [FL ])—the highest
IEAC
2. Referenced Documents valueofthestressintensityfactor(K)atwhichcrackgrowthis
not observed for a specified combination of material and
2.1 ASTM Standards:
environment and where the specimen size is sufficient to meet
requirements for plane strain as described in Test Method
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
E399.
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
3.1.5 stress intensity factor threshold for environment-
Growth Behavior.
–3/2
assisted cracking (K [FL ])—the highest value of the
Current edition approved Nov. 1, 2008. Published February 2009. Originally
EAC
approved in 1995. Last previous edition approved in 2003 as E1681-03. DOI:
stress intensity factor (K) at which crack growth is not
10.1520/E1681-03R08E01.
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 Withdrawn. The last approved version of this historical standard is referenced
the ASTM website. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E1681 – 03 (2008)
observed for a specified combination of material and environ- loading. An environmental chamber is either attached to the
ment and where the measured value may depend on specimen specimen, or the specimen is contained within the chamber.
thickness. The chamber must enclose the portion of the specimen where
3.1.6 physical crack size (a [L])—the distance from a the crack tip is located. Prescribed environmental conditions
p
reference plane to the observed crack front. This distance may must be established and maintained within the chamber at all
represent an average of several measurements along the crack times during the test.
front. The reference plane depends on the specimen form, and
4.1.1 Specimens shall be deadweight loaded or otherwise
it is normally taken to be either the boundary or a plane
held under constant force or held under constant displacement
containingeithertheloadlineorthecenterlineofaspecimenor
(defined in 6.2) for a prescribed length of time, during which
plate. The reference plane is defined prior to specimen defor-
failure by crack growth leading to fracture may or may not
mation.
occur. K and K are defined as the highest value of stress
EAC
IEAC
3.1.7 original crack size (a [L])—the physical crack size at
intensity factor at which neither failure nor crack growth
o
the start of testing.
occurs. The stress intensity factor (K) is calculated from an
3.1.8 original uncracked ligament (b [L])—distance from
expression based on linear elastic stress analysis. To establish
o
the original crack front to the back edge of the specimen (b =
a suitable crack-tip condition for constant force tests, the
o
W–a ).
stress-intensity level at which the fatigue precracking of the
o
3.1.9 specimen thickness (B[L])—the side-to-side dimen-
specimen is conducted is limited to a value substantially less
sion of the specimen being tested.
than the measured K or K values. For constant dis-
IEAC EAC
–2
3.1.10 tensile strength (s [FL ])—the maximum tensile
placement tests, the stress-intensity level at which the fatigue
TS
stress that a material is capable of sustaining. Tensile strength
precracking of the specimen is conducted is limited to the
is calculated from the maximum force during a tension test
requirements of Test Method E399. The validity of the K
IEAC
carried to rupture and the original cross-section area of the
value determined by this test method depends on meeting the
specimen.
sizerequirementstoensureplanestrainconditions,asstatedin
3.2 Definitions of Terms Specific to This Standard:
Test Method E399.The validity of the K value depends on
EAC
3.2.1 environment-assisted cracking (EAC)—a cracking meeting the size requirements for linear elastic behavior, as
process in which the environment promotes crack growth or
stated in the Test Method E647.
higher crack growth rates than would occur without the
4.1.2 Thistestmethodcanproduceinformationontheonset
presence of the environment.
of environment-assisted crack growth. Crack growth rate
3.2.2 normalized crack size (a/W)—the ratio of crack size,
information can be obtained after crack nucleation, but the
a, to specimen width, W. Specimen width is measured from a
method for obtaining this information is not part of this test
referencepositionsuchasthefrontedgeinabendspecimenor
method (1).
the loadline in the compact specimen to the back edge of the
4.2 The mechanisms of environment-assisted cracking are
specimen.
varied and complex. Measurement of a K or K value
EAC IEAC
–2
3.2.3 yield strength (s [FL ])—the stress at which a
YS for a given combination of material and environmental pro-
material exhibits a specific limiting deviation from the propor-
vides no insight into the particular cracking mechanism that
tionalityofstresstostrain.Thisdeviationisexpressedinterms
was either operative or dominant. Two prominent theories of
of strain.
environment-assisted cracking are anodic reaction and hydro-
genembrittlement (2).Thedataobtainedfromthistestmethod
NOTE 1—Inthistestmethod,theyieldstrengthdeterminedbythe0.2%
offset method is used. may be interpreted by either theory of environment-assisted
cracking.
–2
3.2.4 effective yield strength (s [FL ])—an assumed value
Y
4.3 Specimen thickness governs the proportions of plane
of uniaxial yield strength that represents the influences of
strain and plane stress deformation local to the crack tip, along
plastic yielding upon fracture test parameters. For use in this
with the environmental contribution to cracking. Since these
method, it is calculated as the average of the 0.2% offset yield
chemical and mechanical influences cannot be separated in
strength s , and the ultimate tensile strength, s ,or
YS TS
some material/environment combinations, thickness must be
s 5 ~s 1s !/2 (1)
Y YS TS
treated as a variable. In this test method, however, the stress in
3.2.5 notch length (a (L))—the distance from a reference the specimen must remain elastic. For these reasons, two
n
threshold values of EAC are defined by this test method. The
plane to the front of the machined notch. The reference plane
depends on the specimen form and normally is taken to be measurementofK requiresthatthethicknessrequirements
IEAC
of plane strain constraint are met. The less restrictive require-
either the boundary or a plane containing either the loadline or
the centerline of a specimen or plate. The reference plane is ments of K are intended for those conditions in which the
EAC
results are a strong function of the thickness of the specimen
defined prior to specimen deformation.
and the application requires the testing of specimens with
thickness representative of the application.
4. Summary of Test Method
4.1 Thistestmethodinvolvestestingofsingle-edgenotched
[SE(B)] specimens, compact [C(T)] specimens, or bolt-load
compact [MC(W)] specimens, precracked in fatigue. The
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
single-edge notched beam specimen is tested by dead weight this standard.
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E1681 – 03 (2008)
4.4 A variety of environmental (temperature, environment value, then it is suggested that the use of both specimen sizes
composition, and electrode potential, for example) and metal- should be considered; that is, specimens with thicknesses
lurgical (yield strength, alloy composition, and specimen representative of the application and specimens in which the
orientation) variables affect K and K . thickness meets the requirements (see 7.2.1)ofaK value.
EAC IEAC IEAC
5.1.3.1 The user may optionally determine and report a
5. Significance and Use
K value or a K value. The specimen size validity
IEAC
EAC
5.1 The parameters K or K determined by this test
requirements for a K value meet the size requirements
EAC IEAC
EAC
method characterize the resistance to crack growth of a
developed for Test Method E647 to achieve predominately
material with a sharp crack in specific environments under
elastic behavior in the specimen. Test Method E647 size
loadingconditionsinwhichthecrack-tipplasticregionissmall
requirements for compact specimens should be applied to both
compared with the crack depth and the uncracked ligament.
the compact specimen and the beam specimen. The specimen
The less restrictive thickness requirements of K are in-
EAC size validity requirements for a K value meet the size
IEAC
tended for those conditions in which the results are a strong
requirements developed for plane strain conditions for Test
function of the thickness of the specimen and the application
Method E399.
requires the testing of specimens with thickness representative
5.1.4 Evidence of environment-assisted crack growth under
of the application. Since the chemical and mechanical influ-
conditions that do not meet the validity requirements of 7.2
ences cannot be separated, in some material/environment
may provide an important indication of susceptibility to
combinations, the thickness must be treated as a variable. A
environmentalcrackingbutcannotbeusedtodetermineavalid
K or K value is believed to represent a characteristic
IEAC K value (14).
EAC EAC
measurement of environment-assisted cracking resistance in a
5.1.5 Environment-assisted cracking is influenced by both
precracked specimen exposed to an environment under sus-
mechanical and electrochemical driving forces. The latter can
tained tensile loading.AK or K value may be used to
vary with crack depth, opening, or shape and may not be
EAC IEAC
estimate the relationship between failure stress and defect size
uniquely described by the fracture mechanics stress intensity
for a material under any service condition, where the combi-
factor. As an illustrative example, note the strong decrease
nation of crack-like defects, sustained tensile loading and the
reported in K with decreasing crack size below 5 mm for
ISCC
same specific environment would be expected to occur. (Back-
steels in 3% NaCl in water solution (15). Geometry effects on
ground information concerning the development of this test
K similitude should be experimentally assessed for specific
method can be found in Refs (3-18).
material/environment systems.Application modeling based on
5.1.1 The apparent K or K of a material under a
EAC IEAC K similitude should be conducted with caution when
EAC
given set of chemical and electrochemical environmental
substantial differences in crack and specimen geometry exist
conditions is a function of the test duration. It is difficult to
between the specimen and the component.
furnish a rigorous and scientific proof for the existence of a
5.1.6 Notallcombinationsofmaterialandenvironmentwill
threshold (4, 5). Therefore, application of K or K data
EAC IEAC result in environment-assisted cracking. In general, suscepti-
in the design of service components should be made with
bility to aqueous stress-corrosion cracking decreases with
awareness of the uncertainty inherent in the concept of a true
decreasingmaterialstrengthlevel.Whenamaterialinacertain
threshold for environment-assisted cracking in metallic mate-
environment is not susceptible to environment-assisted crack-
rials (6, 18).Ameasured K or K value for a particular
ing, it will not be possible to measure K or K . This
EAC IEAC
EAC IEAC
combination of ma
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