ASTM E1681-03(2008)e2
(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
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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´2
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 2. Referenced Documents
1.1 This test method covers the determination of the 2.1 ASTM Standards:
environment-assisted cracking threshold stress intensity factor D1141Practice for the Preparation of Substitute Ocean
parameters, K and K , for metallic materials from Water
IEAC EAC
constant-force testing of fatigue precracked beam or compact E8/E8MTest Methods for Tension Testing of Metallic Ma-
fracture specimens and from constant-displacement testing of terials
fatigue precracked bolt-load compact fracture specimens. E399Test Method for Linear-Elastic Plane-Strain Fracture
Toughness K of Metallic Materials
Ic
1.2 This test method is applicable to environment-assisted
E647 Test Method for Measurement of Fatigue Crack
cracking in aqueous or other aggressive environments.
Growth Rates
1.3 Materials that can be tested by this test method are not
E1823TerminologyRelatingtoFatigueandFractureTesting
limited by thickness or by strength as long as specimens are of
G1Practice for Preparing, Cleaning, and Evaluating Corro-
sufficient thickness and planar size to meet the size require-
sion Test Specimens
ments of this test method.
G5Reference Test Method for Making Potentiostatic and
1.4 A range of specimen sizes with proportional planar Potentiodynamic Anodic Polarization Measurements
G15TerminologyRelatingtoCorrosionandCorrosionTest-
dimensions is provided, but size may be variable and adjusted
ing (Withdrawn 2010)
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
1 2
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Growth Behavior. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2008. Published February 2009. Originally the ASTM website.
approved in 1995. Last previous edition approved in 2003 as E1681-03. DOI: The last approved version of this historical standard is referenced on
10.1520/E1681-03R08E02. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´2
E1681 − 03 (2008)
valueofthestressintensityfactor(K)atwhichcrackgrowthis depends on the specimen form and normally is taken to be
not observed for a specified combination of material and either the boundary or a plane containing either the loadline or
environment and where the specimen size is sufficient to meet the centerline of a specimen or plate. The reference plane is
requirements for plane strain as described in Test Method defined prior to specimen deformation.
E399.
4. Summary of Test Method
3.1.5 stress intensity factor threshold for environment-
–3/2
4.1 Thistestmethodinvolvestestingofsingle-edgenotched
assisted cracking (K [FL ])—the highest value of the
EAC
stress intensity factor (K) at which crack growth is not [SE(B)] specimens, compact [C(T)] specimens, or bolt-load
compact [MC(W)] specimens, precracked in fatigue. The
observed for a specified combination of material and environ-
ment and where the measured value may depend on specimen single-edge notched beam specimen is tested by dead weight
thickness. loading. An environmental chamber is either attached to the
specimen, or the specimen is contained within the chamber.
3.1.6 physical crack size (a [L])—the distance from a ref-
p
The chamber must enclose the portion of the specimen where
erence plane to the observed crack front. This distance may
the crack tip is located. Prescribed environmental conditions
represent an average of several measurements along the crack
must be established and maintained within the chamber at all
front. The reference plane depends on the specimen form, and
times during the test.
it is normally taken to be either the boundary or a plane
4.1.1 Specimens shall be deadweight loaded or otherwise
containingeithertheloadlineorthecenterlineofaspecimenor
held under constant force or held under constant displacement
plate. The reference plane is defined prior to specimen defor-
(defined in 6.2) for a prescribed length of time, during which
mation.
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
occurs. The stress intensity factor (K ) is calculated from an
o
the original crack front to the back edge of the specimen (b =
expression based on linear elastic stress analysis. To establish
o
W–a ).
a suitable crack-tip condition for constant force tests, the
o
stress-intensity level at which the fatigue precracking of the
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-
–2
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
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
information can be obtained after crack nucleation, but the
3.2.2 normalizedcracksize(a/W)—theratioofcracksize,a,
method for obtaining this information is not part of this test
to specimen width, W. Specimen width is measured from a
method (1).
referencepositionsuchasthefrontedgeinabendspecimenor
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
for a given combination of material and environmental pro-
3.2.3 yield strength (σ [FL ])—the stress at which a
YS
vides no insight into the particular cracking mechanism that
material exhibits a specific limiting deviation from the propor-
was either operative or dominant. Two prominent theories of
tionalityofstresstostrain.Thisdeviationisexpressedinterms
environment-assisted cracking are anodic reaction and hydro-
of strain.
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
σ 5 σ 1σ /2 (1)
~ !
Y YS TS
3.2.5 notch length (a (L))—the distance from a reference
n Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
plane to the front of the machined notch. The reference plane this standard.
´2
E1681 − 03 (2008)
some material/environment combinations, thickness must be cracking in certain instances (7, 8). Therefore, caution should
treated as a variable. In this test method, however, the stress in be used in applying K or K data to service situations
EAC IEAC
the specimen must remain elastic. For these reasons, two involving cyclic loading. In addition, since this standard is for
threshold values of EAC are defined by this test method. The static loading, small-amplitude cyclic loading should be
measurementofK requiresthatthethicknessrequirements avoided during testing.
IEAC
of plane strain constraint are met. The less restrictive require-
5.1.3 In some material/environment combinations, the
ments of K are intended for those conditions in which the
EAC smaller the specimen, the lower the measured K value,
EAC
results are a strong function of the thickness of the specimen
while in other material/environment combinations the mea-
and the application requires the testing of specimens with
suredK valuewillbethelowestvalue (5, 9, 10, 11, 12).If,
IEAC
thickness representative of the application.
for the material/environment combination of interest, it is not
known which specimen size will result in the lower measured
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 .
EAC IEAC
thickness meets the requirements (see 7.2.1)ofaK value.
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
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
same specific environment would be expected to occur. (Back- ISCC
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
given set of chemical and electrochemical environmental EAC
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
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1 ´1
Designation: E1681 – 03 (Reapproved 2008) E1681 – 03 (2008) ´2
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.
was editorially corrected in May 2010.
´ NOTE—Figures 5 and 6 were made more legible in September 2011.
1. Scope
1.1 Thistestmethodcoversthedeterminationoftheenvironment-assistedcrackingthresholdstressintensityfactorparameters,
K andK ,formetallicmaterialsfromconstant-forcetestingoffatigueprecrackedbeamorcompactfracturespecimensand
IEAC EAC
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 Arange 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.
2. Referenced Documents
2.1 ASTM Standards:
D1141 Practice for the Preparation of Substitute Ocean Water
E8/E8M Test Methods for Tension Testing of Metallic Materials
E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness K of Metallic Materials
Ic
E647 Test Method for Measurement of Fatigue Crack Growth Rates
E1823 Terminology Relating to Fatigue and Fracture Testing
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G5 Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements
G15 Terminology Relating to Corrosion and Corrosion Testing
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms relating to fracture testing used in this test method, refer to Terminology E1823.
3.1.2 For definitions of terms relating to corrosion testing used in this test method, refer to Terminology G15.
3.1.3 stress-corrosion cracking (SCC)—a cracking process that requires the simultaneous action of a corrodent and sustained
tensile stress.
–3/2
3.1.4 stress intensity factor threshold for plane strain environment-assisted cracking (K [FL ])—the highest value of the
IEAC
stressintensityfactor(K)atwhichcrackgrowthisnotobservedforaspecifiedcombinationofmaterialandenvironmentandwhere
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 Growth
Behavior.
Current edition approved Nov. 1, 2008. Published February 2009. Originally approved in 1995. Last previous edition approved in 2003 as E1681-03. DOI:
10.1520/E1681-03R08E012.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.ForAnnualBookofASTMStandards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
´2
the specimen size is sufficient to meet requirements for plane strain as described in Test Method E399.
–3/2
3.1.5 stress intensity factor threshold for environment-assisted cracking (K [FL ])—the highest value of the stress
EAC
intensity factor (K) at which crack growth is not observed for a specified combination of material and environment and where the
measured value may depend on specimen thickness.
3.1.6 physical crack size (a [L])—the distance from a reference plane to the observed crack front.This distance may represent
p
an average of several measurements along the crack front. The reference plane depends on the specimen form, and it is normally
taken to be either the boundary or a plane containing either the loadline or the centerline of a specimen or plate. The reference
plane is defined prior to specimen deformation.
3.1.7 original crack size (a [L])—the physical crack size at the start of testing.
o
3.1.8 original uncracked ligament (b [L])—distance from the original crack front to the back edge of the specimen (b =W–
o o
a ).
o
3.1.9 specimen thickness (B[L])—the side-to-side dimension of the specimen being tested.
–2
3.1.10 tensile strength (s [FL ])—the maximum tensile stress that a material is capable of sustaining. Tensile strength is
TS
calculated from the maximum force during a tension test carried to rupture and the original cross-section area of the specimen.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 environment-assisted cracking (EAC)—a cracking process in which the environment promotes crack growth or higher
crack growth rates than would occur without the presence of the environment.
3.2.2 normalized crack size (a/W)—the ratio of crack size, a, to specimen width, W. Specimen width is measured from a
reference position such as the front edge in a bend specimen or the loadline in the compact specimen to the back edge of the
specimen.
–2
3.2.3 yield strength (s [FL ])—the stress at which a material exhibits a specific limiting deviation from the proportionality
YS
of stress to strain. This deviation is expressed in terms of strain.
NOTE 1—In this test method, the yield strength determined by the 0.2% offset method is used.
–2
3.2.4 effective yield strength (s [FL ])—an assumed value of uniaxial yield strength that represents the influences of plastic
Y
yieldinguponfracturetestparameters.Foruseinthismethod,itiscalculatedastheaverageofthe0.2%offsetyieldstrength s ,
YS
and the ultimate tensile strength, s ,or
TS
s 5 s 1s /2 (1)
~ !
Y YS TS
E1681-03R08E02_1
3.2.5 notchlength(a (L))—thedistancefromareferenceplanetothefrontofthemachinednotch.Thereferenceplanedepends
n
on the specimen form and normally is taken to be either the boundary or a plane containing either the loadline or the centerline
of a specimen or plate. The reference plane is defined prior to specimen deformation.
4. Summary of Test Method
4.1 This test method involves testing of single-edge notched [SE(B)] specimens, compact [C(T)] specimens, or bolt-load
compact [MC(W)] specimens, precracked in fatigue. The single-edge notched beam specimen is tested by dead weight loading.
Anenvironmentalchamberiseitherattachedtothespecimen,orthespecimeniscontainedwithinthechamber.Thechambermust
enclose the portion of the specimen where the crack tip is located. Prescribed environmental conditions must be established and
maintained within the chamber at all times during the test.
4.1.1 Specimens shall be deadweight loaded or otherwise held under constant force or held under constant displacement
(defined in 6.2) for a prescribed length of time, during which failure by crack growth leading to fracture may or may not occur.
K and K are defined as the highest value of stress intensity factor at which neither failure nor crack growth occurs. The
IEAC EAC
stress intensity factor (K ) is calculated from an expression based on linear elastic stress analysis. To establish a suitable crack-tip
conditionforconstantforcetests,thestress-intensitylevelatwhichthefatigueprecrackingofthespecimenisconductedislimited
to a value substantially less than the measured K or K values. For constant displacement tests, the stress-intensity level at
IEAC EAC
which the fatigue precracking of the specimen is conducted is limited to the requirements of Test Method E399. The validity of
the K value determined by this test method depends on meeting the size requirements to ensure plane strain conditions, as
IEAC
stated in Test Method E399. The validity of the K value depends on meeting the size requirements for linear elastic behavior,
EAC
as stated in the Test Method E647.
4.1.2 This test method can produce information on the onset of environment-assisted crack growth. Crack growth rate
information can be obtained after crack nucleation, but the method for obtaining this information is not part of this test method
(1).
4.2 The mechanisms of environment-assisted cracking are varied and complex. Measurement of a K or K value for a
EAC IEAC
given combination of material and environmental provides no insight into the particular cracking mechanism that was either
operative or dominant. Two prominent theories of environment-assisted cracking are anodic reaction and hydrogen embrittlement
(2). The data obtained from this test method may be interpreted by either theory of environment-assisted cracking.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
´2
4.3 Specimen thickness governs the proportions of plane strain and plane stress deformation local to the crack tip, along with
the environmental contribution to cracking. Since these chemical and mechanical influences cannot be separated in some
material/environmentcombinations,thicknessmustbetreatedasavariable.Inthistestmethod,however,thestressinthespecimen
must remain elastic. For these reasons, two threshold values of EAC are defined by this test method. The measurement of K
IEAC
requires that the thickness requirements of plane strain constraint are met. The less restrictive requirements of K are intended
EAC
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.
4.4 Avariety of environmental (temperature, environment composition, and electrode potential, for example) and metallurgical
(yield strength, alloy composition, and specimen orientation) variables affect K and K .
EAC IEAC
5. Significance and Use
5.1 TheparametersK orK determinedbythistestmethodcharacterizetheresistancetocrackgrowthofamaterialwith
EAC IEAC
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 K are intended for those conditions in
EAC
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.AK or K value is believed to represent a
EAC IEAC
characteristicmeasurementofenvironment-assistedcrackingresistanceinaprecrackedspecimenexposedtoanenvironmentunder
sustained tensile loading.AK or K value may be used to estimate the relationship between failure stress and defect size
EAC IEAC
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 K or K of a material under a given set of chemical and electrochemical environmental conditions
EAC IEAC
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 K or K data in the design of service components should be made with awareness of the
EAC IEAC
uncertainty inherent in the concept of a true threshold for environment-assisted cracking in metallic materials (6, 18).Ameasured
K or K value for a particular combination of material and environment may, in fact, represent an acceptably low rate of
EAC IEAC
crack growth rather than an absolute upper limit for crack stability. Care should be exercised when service times are substantially
longer than test times.
5.1.2 The degree to which force deviations from static tensile stress will influence the apparent K or K of a material is
EAC IEAC
largely unknown. Small-amplitude cyclic loading, well below that needed to produce fatigue crack growth, superimposed on
sustained tensile loading was observed to significantly lower the apparent threshold for stress corrosion cracking in certain
instances (7, 8). Therefore, caution should be used in applying K or K data to service situations involving cyclic loading.
EAC IEAC
In addition, since this standard is for static loading, small-amplitude cyclic loading should be avoided during testing.
5.1.3 Insomematerial/environmentcombinations,thesmallerthespecimen,thelowerthemeasuredK value,whileinother
EAC
material/environment combinations the measured K value will be the lowest value (5, 9, 10, 11, 12). If, for the
IEAC
material/environment combination of interest, it is not known which specimen size will result in the lower measured value, then
it is suggested that the use of both specimen sizes should be considered; that is, specimens with thicknesses representative of the
application and specimens in which the thickness meets the requirements (see 7.2.1) of a K value.
IEAC
5.1.3.1 The user may optionally determine and report a K value or a K value. The specimen size validity requirements
EAC IEAC
foraK value meet the size requirements developed for Test Method E647 to achieve predominately elastic behavior in the
EAC
specimen. Test Method E647 size requirements for compact specimens should be applied to both the compact specimen and the
beam specimen. The specimen size validity requirements for a K value meet the size requirements developed for plane strain
IEAC
conditions for Test Method E399.
...
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