ASTM E1681-99e1
(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
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-load testing of fatigue precracked beam or 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 load. 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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e1
Designation: E 1681 – 99
Standard Test Method for
Determining Threshold Stress Intensity Factor for
Environment-Assisted Cracking of Metallic Materials
This standard is issued under the fixed designation E 1681; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Committee and Subcommittee jurisdictions were editorially revised in April 2000.
1. Scope E 399 Test Method for Plane-Strain Fracture Toughness of
Metallic Materials
1.1 This test method covers the determination of the
E 647 Test Method for Measurement of Fatigue Crack
environment-assisted cracking threshold stress intensity factor
Growth Rates
parameters, K and K , for metallic materials from
IEAC EAC
E 1823 Terminology Relating to Fatigue and Fracture Test-
constant-force testing of fatigue precracked beam or compact
ing
fracture specimens and from constant-displacement testing of
G 1 Practice for Preparing, Cleaning, and Evaluating Cor-
fatigue precracked bolt-load compact fracture specimens.
rosion Test Specimens
1.2 This test method is applicable to environment-assisted
G 5 Standard Reference Method for Making Potentiostatic
cracking in aqueous or other aggressive environments.
and Potentiodynamic Anodic Polarization Measurements
1.3 Materials that can be tested by this test method are not
G 15 Terminology Relating to Corrosion and Corrosion
limited by thickness or by strength as long as specimens are of
Testing
sufficient thickness and planar size to meet the size require-
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 E 1823.
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 G 15.
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
value of the stress intensity factor (K) at which crack growth is
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 E 399.
3.1.5 stress intensity factor threshold for environment-
2.1 ASTM Standards:
–3/2
assisted cracking (K [FL ])—the highest value of the
EAC
D 1141 Specification for Substitute Ocean Water
3 stress intensity factor (K) at which crack growth is not
E 8 Methods for Tension Testing of Metallic Materials
observed for a specified combination of material and environ-
ment and where the measured value may depend on specimen
thickness.
This test method is under the jurisdiction of ASTM Committee E-8 on Fatigue 3.1.6 physical crack size (a [L])—the distance from a
p
and Fracture and is the direct responsibility of Subcommittee E08.06 on Crack
reference plane to the observed crack front. This distance may
Growth Behavior.
represent an average of several measurements along the crack
Current edition approved April 10, 1999. Published August 1999. Originally
published as E 1681 - 95. Last previous edition E 1681 - 95.
Annual Book of ASTM Standards, Vol 11.02.
3 4
Annual Book of ASTM Standards, Vol 03.01. Annual Book of ASTM Standards, Vol 03.02.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1681
front. The reference plane depends on the specimen form, and held under constant force or held under constant displacement
it is normally taken to be either the boundary or a plane (defined in 6.2) for a prescribed length of time, during which
containing either the loadline or the centerline of a specimen or failure by crack growth leading to fracture may or may not
plate. The reference plane is defined prior to specimen defor- occur. K and K are defined as the highest value of stress
IEAC EAC
mation. intensity factor at which neither failure nor crack growth
3.1.7 original crack size (a [L])—the physical crack size at occurs. The stress intensity factor (K) is calculated from an
o
the start of testing. expression based on linear elastic stress analysis. To establish
3.1.8 original uncracked ligament (b [L])—distance from a suitable crack-tip condition for constant force tests, the
o
the original crack front to the back edge of the specimen (b 5 stress-intensity level at which the fatigue precracking of the
o
W– a ). specimen is conducted is limited to a value substantially less
o
3.1.9 specimen thickness (B[L])—the side-to-side dimen- than the measured K or K values. For constant dis-
IEAC EAC
sion of the specimen being tested. placement tests, the stress-intensity level at which the fatigue
–2
3.1.10 tensile strength (s [FL ])—the maximum tensile precracking of the specimen is conducted is limited to the
TS
stress that a material is capable of sustaining. Tensile strength requirements of Test Method E 399. The validity of the K
IEAC
is calculated from the maximum force during a tension test value determined by this test method depends on meeting the
carried to rupture and the original cross-section area of the size requirements to ensure plane strain conditions, as stated in
specimen. Test Method E 399. The validity of the K value depends on
EAC
3.2 Definitions of Terms Specific to This Standard: meeting the size requirements for linear elastic behavior, as
3.2.1 environment-assisted cracking (EAC)—a cracking stated in the Test Method E 647.
process in which the environment promotes crack growth or 4.1.2 This test method can produce information on the onset
higher crack growth rates than would occur without the of environment-assisted crack growth. Crack growth rate
presence of the environment. information can be obtained after crack nucleation, but the
3.2.2 normalized crack size (a/W)—the ratio of crack size, method for obtaining this information is not part of this test
a, to specimen width, W. Specimen width is measured from a method (1).
reference position such as the front edge in a bend specimen or 4.2 The mechanisms of environment-assisted cracking are
the loadline in the compact specimen to the back edge of the varied and complex. Measurement of a K or K value
EAC IEAC
specimen. for a given combination of material and environmental pro-
–2
3.2.3 yield strength (s [FL ])—the stress at which a vides no insight into the particular cracking mechanism that
YS
material exhibits a specific limiting deviation from the propor- was either operative or dominant. Two prominent theories of
tionality of stress to strain. This deviation is expressed in terms environment-assisted cracking are anodic reaction and hydro-
of strain. gen embrittlement (2). The data obtained from this test method
may be interpreted by either theory of environment-assisted
NOTE 1—In this test method, the yield strength determined by the 0.2 %
cracking.
offset method is used.
4.3 Specimen thickness governs the proportions of plane
–2
3.2.4 effective yield strength (s [FL ])—an assumed value
Y
strain and plane stress deformation local to the crack tip, along
of uniaxial yield strength that represents the influences of
with the environmental contribution to cracking. Since these
plastic yielding upon fracture test parameters. For use in this
chemical and mechanical influences cannot be separated in
method, it is calculated as the average of the 0.2 % offset yield
some material/environment combinations, thickness must be
strength s , and the ultimate tensile strength, s ,or
YS TS
treated as a variable. In this test method, however, the stress in
s 5 ~s 1s ! / 2 (1)
the specimen must remain elastic. For these reasons, two
Y YS TS
threshold values of EAC are defined by this test method. The
3.2.5 notch length (a (L))—the distance from a reference
n
measurement of K requires that the thickness requirements
plane to the front of the machined notch. The reference plane IEAC
of plane strain constraint are met. The less restrictive require-
depends on the specimen form and normally is taken to be
ments of K are intended for those conditions in which the
either the boundary or a plane containing either the loadline or EAC
results are a strong function of the thickness of the specimen
the centerline of a specimen or plate. The reference plane is
and the application requires the testing of specimens with
defined prior to specimen deformation.
thickness representative of the application.
4. Summary of Test Method
4.4 A variety of environmental (temperature, environment
4.1 This test method involves testing of single-edge notched
composition, and electrode potential, for example) and metal-
[SE(B)] specimens, compact [C(T)] specimens, or bolt-load
lurgical (yield strength, alloy composition, and specimen
compact [MC(W)] specimens, precracked in fatigue. The
orientation) variables affect K and K .
EAC IEAC
single-edge notched beam specimen is tested by dead weight
loading. An environmental chamber is either attached to the 5. Significance and Use
specimen, or the specimen is contained within the chamber.
5.1 The parameters K or K determined by this test
EAC IEAC
The chamber must enclose the portion of the specimen where
method characterize the resistance to crack growth of a
the crack tip is located. Prescribed environmental conditions
must be established and maintained within the chamber at all
times during the test.
The boldface numbers in parentheses refer to the list of references at the end of
4.1.1 Specimens shall be deadweight loaded or otherwise this standard.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1681
material with a sharp crack in specific environments under developed for Test Method E 647 to achieve predominately
loading conditions in which the crack-tip plastic region is small elastic behavior in the specimen. Test Method E 647 size
requirements for compact specimens should be applied to both
compared with the crack depth and the uncracked ligament.
The less restrictive thickness requirements of K are in- the compact specimen and the beam specimen. The specimen
EAC
size validity requirements for a K value meet the size
tended for those conditions in which the results are a strong
IEAC
function of the thickness of the specimen and the application requirements developed for plane strain conditions for Test
Method E 399.
requires the testing of specimens with thickness representative
of the application. Since the chemical and mechanical influ- 5.1.4 Evidence of environment-assisted crack growth under
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
environmental cracking but cannot be used to determine a valid
K or K value is believed to represent a characteristic
IEAC
EAC
K value (14).
measurement of environment-assisted cracking resistance in a
EAC
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. A K 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
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 Not all combinations of material and environment will
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
decreasing material strength level. When a material in a certain
threshold for environment-assisted cracking in metallic mate-
environment is not susceptible to environment-assisted crack-
rials (6, 18). A measured K or K value for a particular
EAC IEAC
ing, it will not be possible to measure K or K . This
EAC IEAC
combination of material and environment may, in fact, repre-
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-
data can quantitati
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