ASTM G49-85(2023)e1
(Practice)Standard Practice for Preparation and Use of Direct Tension Stress-Corrosion Test Specimens
Standard Practice for Preparation and Use of Direct Tension Stress-Corrosion Test Specimens
SIGNIFICANCE AND USE
4.1 Axially loaded tension specimens provide one of the most versatile methods of performing a stress-corrosion test because of the flexibility permitted in the choice of type and size of test specimen, stressing procedures, and range of stress levels.
4.2 The uniaxial stress system is simple; hence, this test method is often used for studies of stress-corrosion mechanisms. This type of test is amenable to the simultaneous exposure of unstressed specimens (no applied load) with stressed specimens and subsequent tension testing to distinguish between the effects of true stress corrosion and mechanical overload (2). Additional considerations in regard to the significance of the test results and their interpretation are given in Sections 6 and 10.
4.3 Wide variations in test results may be obtained for a given material and specimen orientation with different specimen sizes and stressing procedures. This consideration is significant especially in the standardization of a test procedure for interlaboratory comparisons or quality control.
SCOPE
1.1 This practice covers procedures for designing, preparing, and using ASTM standard tension test specimens for investigating susceptibility to stress-corrosion cracking. Axially loaded specimens may be stressed quantitatively with equipment for application of either a constant load, constant strain, or with a continuously increasing strain.
1.2 Tension test specimens are adaptable for testing a wide variety of product forms as well as parts joined by welding, riveting, or various other methods.
1.3 The exposure of specimens in a corrosive environment is treated only briefly because other standards are being prepared to deal with this aspect. Meanwhile, the investigator is referred to Practices G35, G36, G37, and G44, and to ASTM Special Technical Publication 425 (1).2
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
´1
Designation: G49 − 85 (Reapproved 2023)
Standard Practice for
Preparation and Use of Direct Tension Stress-Corrosion
Test Specimens
This standard is issued under the fixed designation G49; 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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorially updated units in November 2023.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers procedures for designing,
E8/E8M Test Methods for Tension Testing of Metallic Ma-
preparing, and using ASTM standard tension test specimens for
terials
investigating susceptibility to stress-corrosion cracking. Axi-
G35 Practice for Determining the Susceptibility of Stainless
ally loaded specimens may be stressed quantitatively with
Steels and Related Nickel-Chromium-Iron Alloys to
equipment for application of either a constant load, constant
Stress-Corrosion Cracking in Polythionic Acids
strain, or with a continuously increasing strain.
G36 Practice for Evaluating Stress-Corrosion-Cracking Re-
1.2 Tension test specimens are adaptable for testing a wide
sistance of Metals and Alloys in a Boiling Magnesium
variety of product forms as well as parts joined by welding,
Chloride Solution
riveting, or various other methods.
G37 Practice for Use of Mattsson’s Solution of pH 7.2 to
Evaluate the Stress-Corrosion Cracking Susceptibility of
1.3 The exposure of specimens in a corrosive environment
Copper-Zinc Alloys
is treated only briefly because other standards are being
G44 Practice for Exposure of Metals and Alloys by Alternate
prepared to deal with this aspect. Meanwhile, the investigator
Immersion in Neutral 3.5 % Sodium Chloride Solution
is referred to Practices G35, G36, G37, and G44, and to ASTM
Special Technical Publication 425 (1).
3. Summary of Practice
1.4 The values stated in SI units are to be regarded as
3.1 This practice covers the use of axially loaded, quantita-
standard. The values given in parentheses after SI units are
tively stressed ASTM standard tension test specimens for
provided for information only and are not considered standard. investigating the resistance to stress-corrosion cracking of
metallic materials in all types of product forms. Consideration
1.5 This standard does not purport to address all of the
is given to important factors in the selection of appropriate
safety concerns, if any, associated with its use. It is the
specimens, the design of loading equipment, and the effects of
responsibility of the user of this standard to establish appro-
these factors on the state of stress in the specimen as corrosion
priate safety, health, and environmental practices and deter-
occurs.
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
4. Significance and Use
dance with internationally recognized principles on standard-
4.1 Axially loaded tension specimens provide one of the
ization established in the Decision on Principles for the
most versatile methods of performing a stress-corrosion test
Development of International Standards, Guides and Recom-
because of the flexibility permitted in the choice of type and
mendations issued by the World Trade Organization Technical
size of test specimen, stressing procedures, and range of stress
Barriers to Trade (TBT) Committee.
levels.
4.2 The uniaxial stress system is simple; hence, this test
method is often used for studies of stress-corrosion mecha-
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
nisms. This type of test is amenable to the simultaneous
of Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-
tally Assisted Cracking.
Current edition approved Nov. 1, 2023. Published November 2023. Originally
approved in 1976. Last previous edition approved in 2019 as G49 – 85 (2019). DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/G0049-85R23E01. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
G49 − 85 (2023)
exposure of unstressed specimens (no applied load) with 6. Stress Considerations
stressed specimens and subsequent tension testing to distin-
6.1 There are several factors that may introduce bending
guish between the effects of true stress corrosion and mechani-
moments on specimens, such as a longitudinal curvature,
cal overload (2). Additional considerations in regard to the
misalignment of threads on threaded-end round specimens, and
significance of the test results and their interpretation are given
the corners of sheet-type specimens. The significance of these
in Sections 6 and 10.
factors is greater for specimens with smaller cross sections.
Even though eccentricity in loading can be minimized to equal
4.3 Wide variations in test results may be obtained for a
the same standards accepted for tension testing machines,
given material and specimen orientation with different speci-
inevitably, there is some variation in the tensile stress around
men sizes and stressing procedures. This consideration is
the circumference of the test specimen which can be of such
significant especially in the standardization of a test procedure
magnitude that it will introduce considerable error in the
for interlaboratory comparisons or quality control.
desired stress. Tests should be made on specimens with strain
gauges affixed to the specimen surface (around the circumfer-
5. Test Specimens
ence in 90° or 120° intervals) to verify strain and stress
uniformity and determine if machining practices and stressing
5.1 Whenever possible, tension test specimens used in
jigs are of adequate tolerance and quality.
evaluating susceptibility to stress-corrosion cracking should
conform to the dimensions of standard tension test specimens
6.2 Another consideration is the possible increase in net
specified in Test Methods E8/E8M, which contain details for
section stress that will occur when corrosion develops during
specimens machined from various product forms.
the environmental exposure (1, 5). As shown schematically in
Fig. 1, there are two limiting curves: one for zero stiffness
5.2 A wide range of sizes for tension test specimens is
(dead weight) and the other for infinite stiffness (ideal constant
possible, depending primarily upon the dimensions of the
strain). In actual testing with various types of stressing frames,
product to be tested. Because the stress-corrosion test results
such as those shown in Figs. 2-4, the increase in net section
can be markedly influenced by the cross section of the test
stress will be somewhere in between. When the net section
specimen, this factor should be given careful consideration
stress becomes greater than the nominal gross section stress
with regard to the object of the investigation. Although larger
and increases to the point of fracture, either of two events can
specimens may be more representative of most actual
structures, they often cannot be machined from product forms
to be evaluated; and they present more difficulties in stressing
and handling in the laboratory. Also, larger specimens of some
materials may require longer exposure periods than smaller
specimens.
5.3 Smaller cross-section specimens are widely used be-
cause they (1) have a greater sensitivity to the initiation of
stress-corrosion cracking, (2) usually give test results more
quickly, and (3) permit greater convenience in testing. On the
other hand, the smaller specimens are more difficult to
machine, and their performance is more likely to be influenced
by extraneous stress concentrations resulting from non-axial
loading, corrosion pits, etc. Therefore, specimens less than
about 10 mm (0.4 in.) in gauge length or 3.0 mm (0.12 in.) in
diameter are not recommended for general use.
5.4 Tension specimens containing machined notches have
been used in studies of stress-corrosion cracking and hydrogen
embrittlement (3). The presence of a notch induces a triaxial
stress state at the root of the notch wherein the actual stress will
be greater by a concentration factor dependent on the notch
geometry. Advantages of such specimens include the probable
localization of cracking to the notch region and acceleration of
failure. However, unless directly related to practical conditions
of usage, spurious results may ensue.
5.5 Tension specimens containing a machined notch in
which a mechanical precrack (for example, a fatigue or tension
NOTE 1—The behavior shown is generally representative, but the
crack) has been started will be the subject of another ASTM
curves will vary with specific alloys and tempers.
standard. Various types of precracked specimens are discussed
FIG. 1 Effect of Loading Method and Extent of Cracking or Corro-
in other publications (2, 4). sion Pattern on Average Net Section Stress
´1
G49 − 85 (2023)
FIG. 2 Spring-Loaded Stressing Frame (6)
7.1.1 Tension specimens may be subjected to a wide range
of stress levels associated with either elastic or elastic and
plastic strain. Because the stress system is intended to be
essentially uniaxial (except in the case of notched specimens),
great care must be exercised in the construction of stressing
frames so that bending stresses are avoided or minimized.
7.1.2 Although a number of different stressing frames have
been used with tension specimens, three basic types are
considered herein: constant (sustained) load, constant strain
(deformation), and continuously increasing strain. A constant
load can be obtained with dead weight, but truly constant strain
loading is seldom achieved because a stressing frame with
infinite stiffness would be required. Stress-corrosion test results
can be influenced by the type of loading in combination with
the design of the test specimen; therefore, the investigator
should select loading conditions most applicable to the purpose
of the investigation. Further information in regard to the type
of loading most applicable to various types of structures is
given in Ref (2).
7.2 Stressing Frames:
7.2.1 Constant Load:
7.2.1.1 The simplest method is a dead weight hung on one
end of the specimen, and it is particularly useful for wire
specimens (9). For specimens of larger cross section, however,
lever systems such as are used in creep testing machines are
more practical. The advantage of any dead-weight loading
device is the constancy of the applied load.
FIG. 3 Sustained Load Devices Using Ring Frames (7)
7.2.1.2 An approximation of a constant-load system can be
attained by the use of springs with a ring such as that shown in
Fig. 2 (6). The principle of the proving ring, as used in the
calibration of tension testing machines, has also been adapted
occur: (1) fracture by mechanical overload of a material that is
to stress-corrosion testing to provide a simple, compact, and
not susceptible to stress-corrosion cracking, or (2) stress-
easily operated device to apply axial load (7); see Fig. 3(a).
corrosion cracking of a material at an unknown stress higher
The load is applied by tightening a nut on one of the bolts and
than the intended nominal test stress. The occurrence of either
is determined by carefully measuring the change in ring
of these phenomena would interfere with a valid evaluation of
diameter. Another similar but less sophisticated ring device can
materials with a relatively high resistance to stress corrosion.
also be used, the difference being that the load is applied with
These considerations must be taken into account in experi-
a hydraulic jig (7) as shown in Fig. 3(b). In either ring device,
ments undertaken to determine “threshold” stresses. The sig-
the bolt contains a keyway to prevent a torsional stress from
nificance of these factors is discussed further in Section 10.
being applied to the specimen while tightening the nut.
7.2.2 Constant Strain—Stress-corrosion tests performed in
7. Stressing Methods
low-compliance tension testing machines are of the constant-
7.1 General Considerations: strain type. The specimen is loaded to the required stress level
´1
G49 − 85 (2023)
FIG. 4 Constant-Strain Type of Stressing Frame (8)
and the moving beam then locked in position. Other laboratory noted, however, that only when the intended stress is below the
stressing frames have also been used, generally in testing elastic limit of the test material is the average linear stress (σ)
specimens of lower strength of smaller cross section (8). Fig. proportional to the average linear strain (e), σ/e = E, where the
4(a) shows an exploded view of such a stressing frame, and constant E is the modulus of elasticity.
Fig. 4(b) shows a special loading device developed to ensure 7.2.2.2 When tests are conducted at elevated temperatures
axial loading with a minimum of torsion and bending of the with constant-strain loaded specimens, consideration should be
specimen. given to the possibility of stress relaxation.
7.2.2.1 For stressing frames that do not contain any mecha- 7.2.3 Continuously Increasing Strain—A tension testing
nism for the measurement of load, it is desirable to determine machine may be used to load the test specimen at a constant
the stress levels from measurement of the strain. It must be rate to failure (10). If the specimen is surrounded by a test
´1
G49 − 85 (2023)
environment and strain rate is slow enough, stress-corrosion 10. Inspection
cracking may occur during the test. This can result in shorter
10.1 One of the advantages of the direct-tension type of
times to fracture or in lower values of elongation or reduction
specimen is that when stress-corrosion cracking occurs, it
of area, or both, than obtained for a specimen strained at the
generally results in complete fracture of the specimen, which is
same rate in air or in an inert environment at the same
easy to detect. However, when there is some uncertainty as to
temperature as the corrodent. Appropriate combinations of
the presence of cracks due, for example, to the presence
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.