ASTM E1681-03(2013)
(Test Method)Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials
SIGNIFICANCE AND USE
5.1 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).
5.1.1 The apparent KEAC or KIEAC of a material under a given set of chemical and electrochemical environmental conditions is a function of the test duration. It is difficult to furnish a rigorous and scientific proof for the existence of a threshold (4, 5). Therefore, application of KEAC or KIEAC data in the design of service components should be made with awareness of the uncertainty inherent in the concept of a true threshold for environment-assisted cracking in metallic materials (6, 18). A measured KEAC or KIEAC value for a particular combination of material and environment may, in fact, represent an acceptably low rate of crack growth rather than an absolute upper limit f...
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 2013)
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.
1. Scope E8/E8MTest Methods for Tension Testing of Metallic Ma-
terials
1.1 This test method covers the determination of the
E399Test Method for Linear-Elastic Plane-Strain Fracture
environment-assisted cracking threshold stress intensity factor
Toughness K of Metallic Materials
Ic
parameters, K and K , for metallic materials from
IEAC EAC
E647 Test Method for Measurement of Fatigue Crack
constant-force testing of fatigue precracked beam or compact
Growth Rates
fracture specimens and from constant-displacement testing of
E1823TerminologyRelatingtoFatigueandFractureTesting
fatigue precracked bolt-load compact fracture specimens.
G1Practice for Preparing, Cleaning, and Evaluating Corro-
1.2 This test method is applicable to environment-assisted
sion Test Specimens
cracking in aqueous or other aggressive environments.
G5Reference Test Method for Making Potentiodynamic
1.3 Materials that can be tested by this test method are not Anodic Polarization Measurements
G15TerminologyRelatingtoCorrosionandCorrosionTest-
limited by thickness or by strength as long as specimens are of
sufficient thickness and planar size to meet the size require- ing (Withdrawn 2010)
ments of this test method.
3. Terminology
1.4 A range of specimen sizes with proportional planar
3.1 Definitions:
dimensions is provided, but size may be variable and adjusted
3.1.1 For definitions of terms relating to fracture testing
for yield strength and applied force. Specimen thickness is a
used in this test method, refer to Terminology E1823.
variable independent of planar size.
3.1.2 For definitions of terms relating to corrosion testing
1.5 Specimen configurations other than those contained in
used in this test method, refer to Terminology G15.
this test method may be used, provided that well-established
3.1.3 stress-corrosion cracking (SCC)—a cracking process
stress intensity calibrations are available and that specimen
that requires the simultaneous action of a corrodent and
dimensions are of sufficient size to meet the size requirements
sustained tensile stress.
of this test method during testing.
3.1.4 stress intensity factor threshold for plane strain
1.6 This standard does not purport to address all of the
–3/2
environment-assisted cracking (K [FL ])—the highest
IEAC
safety concerns, if any, associated with its use. It is the
valueofthestressintensityfactor(K)atwhichcrackgrowthis
responsibility of the user of this standard to establish appro-
not observed for a specified combination of material and
priate safety and health practices and determine the applica-
environment and where the specimen size is sufficient to meet
bility of regulatory limitations prior to use.
requirements for plane strain as described in Test Method
2. Referenced Documents E399.
2.1 ASTM Standards: 3.1.5 stress intensity factor threshold for environment-
–3/2
assisted cracking (K [FL ])—the highest value of the
D1141Practice for the Preparation of Substitute Ocean
EAC
stress intensity factor (K) at which crack growth is not
Water
observed for a specified combination of material and environ-
ment and where the measured value may depend on specimen
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
thickness.
Growth Behavior.
3.1.6 physical crack size (a [L])—the distance from a ref-
Current edition approved Oct. 15, 2013. Published March 2014. Originally
p
ε2
approved in 1995. Last previous edition approved in 2008 as E1681-03(2008) .
erence plane to the observed crack front. This distance may
DOI: 10.1520/E1681-03R14.
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1681 − 03 (2013)
represent an average of several measurements along the crack the crack tip is located. Prescribed environmental conditions
front. The reference plane depends on the specimen form, and must be established and maintained within the chamber at all
it is normally taken to be either the boundary or a plane times during the test.
containingeithertheloadlineorthecenterlineofaspecimenor 4.1.1 Specimens shall be deadweight loaded or otherwise
plate. The reference plane is defined prior to specimen defor- held under constant force or held under constant displacement
mation. (defined in 6.2) for a prescribed length of time, during which
failure by crack growth leading to fracture may or may not
3.1.7 original crack size (a [L])—the physical crack size at
o
occur.K andK aredefinedasthehighestvalueofstress
IEAC EAC
the start of testing.
intensity factor at which neither failure nor crack growth
3.1.8 original uncracked ligament (b [L])—distance from
o
occurs. The stress intensity factor (K ) is calculated from an
the original crack front to the back edge of the specimen (b =
o
expression based on linear elastic stress analysis. To establish
W–a ).
o
a suitable crack-tip condition for constant force tests, the
3.1.9 specimen thickness (B[L])—the side-to-side dimen-
stress-intensity level at which the fatigue precracking of the
sion of the specimen being tested.
specimen is conducted is limited to a value substantially less
–2
than the measured K or K values. For constant dis-
IEAC EAC
3.1.10 tensile strength (σ [FL ])—the maximum tensile
TS
placement tests, the stress-intensity level at which the fatigue
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
carried to rupture and the original cross-section area of the IEAC
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 normalizedcracksize(a/W)—theratioofcracksize,a, information can be obtained after crack nucleation, but the
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 (σ [FL ])—the stress at which a
for a given combination of material and environmental pro-
YS
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
NOTE1—Inthistestmethod,theyieldstrengthdeterminedbythe0.2%
may be interpreted by either theory of environment-assisted
offset method is used.
cracking.
–2
3.2.4 effective yield strength (σ [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 σ , and the ultimate tensile strength, σ ,or
YS TS
some material/environment combinations, thickness must be
σ 5 ~σ 1σ !/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
n
the specimen must remain elastic. For these reasons, two
plane to the front of the machined notch. The reference plane
threshold values of EAC are defined by this test method. The
depends on the specimen form and normally is taken to be
measurementofK requiresthatthethicknessrequirements
IEAC
either the boundary or a plane containing either the loadline or
of plane strain constraint are met. The less restrictive require-
the centerline of a specimen or plate. The reference plane is
ments of K are intended for those conditions in which the
EAC
defined prior to specimen deformation.
results are a strong function of the thickness of the specimen
and the application requires the testing of specimens with
4. Summary of Test Method
thickness representative of the application.
4.1 Thistestmethodinvolvestestingofsingle-edgenotched
4.4 A variety of environmental (temperature, environment
[SE(B)] specimens, compact [C(T)] specimens, or bolt-load
composition, and electrode potential, for example) and metal-
compact [MC(W)] specimens, precracked in fatigue. The
lurgical (yield strength, alloy composition, and specimen
single-edge notched beam specimen is tested by dead weight
orientation) variables affect K and K .
EAC IEAC
loading. An environmental chamber is either attached to the
specimen, or the specimen is contained within the chamber.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
The chamber must enclose the portion of the specimen where this standard.
E1681 − 03 (2013)
5. Significance and Use 5.1.3.1 The user may optionally determine and report a
K value or a K value. The specimen size validity
IEAC
EAC
5.1 The parameters K or K determined by this test
EAC IEAC
requirements for a K value meet the size requirements
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
EAC
K value (14).
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
EAC IEAC
vary with crack depth, opening, or shape and may not be
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
rials (6, 18).Ameasured K or K value for a particular
EAC IEAC
cracking, it will not be possible to measure K or K .
EAC IEAC
combination of material and environment may, in fact, repre-
This method can serve the following purposes:
sent an acceptably low rate of crack growth rather than an
5.1.6.1 In research and development, valid K or K
EAC IEAC
absolute upper limit for crack stability. Care should be exer-
datacanquantitativelyestablishtheeffectsofmetallurgicaland
cised when service times are substantially longer than test
environmental variables on the envi
...
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