ASTM G49-85(2019)
(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 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.
1.5 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.
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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.
Designation: G49 − 85 (Reapproved 2019)
Standard Practice for
Preparation and Use of Direct Tension Stress-Corrosion
Test Specimens
ThisstandardisissuedunderthefixeddesignationG49;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G35 Practice for Determining the Susceptibility of Stainless
Steels and Related Nickel-Chromium-Iron Alloys to
1.1 This practice covers procedures for designing,
Stress-Corrosion Cracking in Polythionic Acids
preparing,andusingASTMstandardtensiontestspecimensfor
G36 Practice for Evaluating Stress-Corrosion-Cracking Re-
investigating susceptibility to stress-corrosion cracking. Axi-
sistance of Metals and Alloys in a Boiling Magnesium
ally loaded specimens may be stressed quantitatively with
Chloride Solution
equipment for application of either a constant load, constant
G37 Practice for Use of Mattsson’s Solution of pH 7.2 to
strain, or with a continuously increasing strain.
Evaluate the Stress-Corrosion Cracking Susceptibility of
1.2 Tension test specimens are adaptable for testing a wide
Copper-Zinc Alloys
variety of product forms as well as parts joined by welding,
G44 PracticeforExposureofMetalsandAlloysbyAlternate
riveting, or various other methods.
Immersion in Neutral 3.5 % Sodium Chloride Solution
1.3 The exposure of specimens in a corrosive environment
3. Summary of Practice
is treated only briefly because other standards are being
prepared to deal with this aspect. Meanwhile, the investigator 3.1 This practice covers the use of axially loaded, quantita-
is referred to Practices G35, G36, G37, and G44, and toASTM
tively stressed ASTM standard tension test specimens for
Special Technical Publication 425 (1). investigating the resistance to stress-corrosion cracking of
metallic materials in all types of product forms. Consideration
1.4 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.
1.5 This international standard was developed in accor-
4. Significance and Use
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 4.1 Axially loaded tension specimens provide one of the
most versatile methods of performing a stress-corrosion test
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical because of the flexibility permitted in the choice of type and
size of test specimen, stressing procedures, and range of stress
Barriers to Trade (TBT) Committee.
levels.
2. Referenced Documents
4.2 The uniaxial stress system is simple; hence, this test
2.1 ASTM Standards:
method is often used for studies of stress-corrosion mecha-
E8/E8M Test Methods for Tension Testing of Metallic Ma-
nisms. This type of test is amenable to the simultaneous
terials
exposure of unstressed specimens (no applied load) with
stressed specimens and subsequent tension testing to distin-
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
guish between the effects of true stress corrosion and mechani-
of Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-
cal overload (2). Additional considerations in regard to the
tally Assisted Cracking.
significance of the test results and their interpretation are given
Current edition approved Nov. 1, 2019. Published November 2019. Originally
approved in 1976. Last previous edition approved in 2011 as G49–85 (2011). DOI:
in Sections 6 and 10.
10.1520/G0049–85R19.
4.3 Wide variations in test results may be obtained for a
The boldface numbers in parentheses refer to a list of references at the end of
this standard.
given material and specimen orientation with different speci-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
men sizes and stressing procedures. This consideration is
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
significant especially in the standardization of a test procedure
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. for interlaboratory comparisons or quality control.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G49 − 85 (2019)
5. Test Specimens desired stress. Tests should be made on specimens with strain
gages affixed to the specimen surface (around the circumfer-
5.1 Whenever possible, tension test specimens used in
ence in 90° or 120° intervals) to verify strain and stress
evaluating susceptibility to stress-corrosion cracking should
uniformity and determine if machining practices and stressing
conform to the dimensions of standard tension test specimens
jigs are of adequate tolerance and quality.
specified in Test Methods E8/E8M, which contain details for
specimens machined from various product forms. 6.2 Another consideration is the possible increase in net
section stress that will occur when corrosion develops during
5.2 A wide range of sizes for tension test specimens is
the environmental exposure (1, 5). As shown schematically in
possible, depending primarily upon the dimensions of the
Fig. 1, there are two limiting curves: one for zero stiffness
product to be tested. Because the stress-corrosion test results
(dead weight) and the other for infinite stiffness (ideal constant
can be markedly influenced by the cross section of the test
strain). In actual testing with various types of stressing frames,
specimen, this factor should be given careful consideration
such as those shown in Figs. 2-4, the increase in net section
with regard to the object of the investigation. Although larger
stress will be somewhere in between. When the net section
specimens may be more representative of most actual
stress becomes greater than the nominal gross section stress
structures, they often cannot be machined from product forms
and increases to the point of fracture, either of two events can
to be evaluated; and they present more difficulties in stressing
occur: (1) fracture by mechanical overload of a material that is
and handling in the laboratory.Also, larger specimens of some
not susceptible to stress-corrosion cracking, or (2) stress-
materials may require longer exposure periods than smaller
corrosion cracking of a material at an unknown stress higher
specimens.
than the intended nominal test stress. The occurrence of either
5.3 Smaller cross-section specimens are widely used be-
of these phenomena would interfere with a valid evaluation of
cause they (1) have a greater sensitivity to the initiation of
materials with a relatively high resistance to stress corrosion.
stress-corrosion cracking, (2) usually give test results more
These considerations must be taken into account in experi-
quickly, and (3) permit greater convenience in testing. On the
ments undertaken to determine “threshold” stresses. The sig-
other hand, the smaller specimens are more difficult to
nificance of these factors is discussed further in Section 10.
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
stressstateattherootofthenotchwhereintheactualstresswill
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
crack) has been started will be the subject of another ASTM
standard. Various types of precracked specimens are discussed
in other publications (2, 4).
6. Stress Considerations
6.1 There are several factors that may introduce bending
moments on specimens, such as a longitudinal curvature,
misalignmentofthreadsonthreaded-endroundspecimens,and
the corners of sheet-type specimens. The significance of these
factors is greater for specimens with smaller cross sections.
Even though eccentricity in loading can be minimized to equal
the same standards accepted for tension testing machines,
NOTE 1—The behavior shown is generally representative, but the
inevitably, there is some variation in the tensile stress around
curves will vary with specific alloys and tempers.
the circumference of the test specimen which can be of such
FIG. 1 Effect of Loading Method and Extent of Cracking or Corro-
magnitude that it will introduce considerable error in the sion Pattern on Average Net Section Stress
G49 − 85 (2019)
FIG. 2 Spring-Loaded Stressing Frame (6)
loading is seldom achieved because a stressing frame with
infinitestiffnesswouldberequired.Stress-corrosiontestresults
can be influenced by the type of loading in combination with
the design of the test specimen; therefore, the investigator
shouldselectloadingconditionsmostapplicabletothepurpose
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.
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
to stress-corrosion testing to provide a simple, compact, and
easily operated device to apply axial load (7); see Fig. 3(a).
The load is applied by tightening a nut on one of the bolts and
is determined by carefully measuring the change in ring
diameter.Anothersimilarbutlesssophisticatedringdevicecan
also be used, the difference being that the load is applied with
a hydraulic jig (7) as shown in Fig. 3(b). In either ring device,
FIG. 3 Sustained Load Devices Using Ring Frames (7)
the bolt contains a keyway to prevent a torsional stress from
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-
strain type. The specimen is loaded to the required stress level
7.1 General Considerations:
7.1.1 Tension specimens may be subjected to a wide range and the moving beam then locked in position. Other laboratory
stressing frames have also been used, generally in testing
of stress levels associated with either elastic or elastic and
plastic strain. Because the stress system is intended to be specimens of lower strength of smaller cross section (8). Fig.
4(a) shows an exploded view of such a stressing frame, and
essentially uniaxial (except in the case of notched specimens),
great care must be exercised in the construction of stressing Fig. 4(b) shows a special loading device developed to ensure
axial loading with a minimum of torsion and bending of the
frames so that bending stresses are avoided or minimized.
7.1.2 Although a number of different stressing frames have specimen.
been used with tension specimens, three basic types are 7.2.2.1 For stressing frames that do not contain any mecha-
considered herein: constant (sustained) load, constant strain nism for the measurement of load, it is desirable to determine
(deformation), and continuously increasing strain. A constant the stress levels from measurement of the strain. It must be
loadcanbeobtainedwithdeadweight,buttrulyconstantstrain noted,however,thatonlywhentheintendedstressisbelowthe
G49 − 85 (2019)
FIG. 4 Constant-Strain Type of Stressing Frame (8)
elastic limit of the test material is the average linear stress (σ) environment and strain rate is slow enough, stress-corrosion
proportional to the average linear strain (e), σ/e =E, where the cracking may occur during the test. This can result in shorter
constant E is the modulus of elasticity. times to fracture or in lower values of elongation or reduction
7.2.2.2 When tests are conducted at elevated temperatures of area, or both, than obtained for a specimen strained at the
with constant-strain loaded specimens, consideration should be same rate in air or in an inert environment at the same
given to the possibility of stress relaxation. temperature as the corrodent. Appropriate combinations of
7.2.3 Continuously Increasing Strain—A tension testing specimen cross section and corrosive environment must be
machine may be used to load the test specimen at a constant determined, as well as the range of critical strain rate for
rate to failure (10). If the specimen is surrounded by a test specific alloy systems.
G49 − 85 (2019)
8. Preparation of Specimens the presence of cracks due, for example, to the presence of
corrosion products on the specimen surface, it may be
8.1 The pronounced effect of surface conditions on the time
necessary, at the conclusion of the test, to chemically clean the
required to initiate stress-corrosion cracking in test specimens
specimen to facilitate adequate inspection.
is well-known. Unless it is desired to evaluate the as-fabricated
surface, the final surface preparation generally preferred is a 10.2 It must be emphasized
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G49 − 85 (Reapproved 2019)
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.
1. Scope G35 Practice for Determining the Susceptibility of Stainless
Steels and Related Nickel-Chromium-Iron Alloys to
1.1 This practice covers procedures for designing,
Stress-Corrosion Cracking in Polythionic Acids
preparing, and using ASTM standard tension test specimens for
G36 Practice for Evaluating Stress-Corrosion-Cracking Re-
investigating susceptibility to stress-corrosion cracking. Axi-
sistance of Metals and Alloys in a Boiling Magnesium
ally loaded specimens may be stressed quantitatively with
Chloride Solution
equipment for application of either a constant load, constant
G37 Practice for Use of Mattsson’s Solution of pH 7.2 to
strain, or with a continuously increasing strain.
Evaluate the Stress-Corrosion Cracking Susceptibility of
1.2 Tension test specimens are adaptable for testing a wide
Copper-Zinc Alloys
variety of product forms as well as parts joined by welding,
G44 Practice for Exposure of Metals and Alloys by Alternate
riveting, or various other methods.
Immersion in Neutral 3.5 % Sodium Chloride Solution
1.3 The exposure of specimens in a corrosive environment
3. Summary of Practice
is treated only briefly because other standards are being
prepared to deal with this aspect. Meanwhile, the investigator
3.1 This practice covers the use of axially loaded, quantita-
is referred to Practices G35, G36, G37, and G44, and to ASTM tively stressed ASTM standard tension test specimens for
Special Technical Publication 425 (1).
investigating the resistance to stress-corrosion cracking of
metallic materials in all types of product forms. Consideration
1.4 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.
1.5 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
Development of International Standards, Guides and Recom- most versatile methods of performing a stress-corrosion test
because of the flexibility permitted in the choice of type and
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. size of test specimen, stressing procedures, and range of stress
levels.
2. Referenced Documents
4.2 The uniaxial stress system is simple; hence, this test
2.1 ASTM Standards:
method is often used for studies of stress-corrosion mecha-
E8/E8M Test Methods for Tension Testing of Metallic Ma-
nisms. This type of test is amenable to the simultaneous
terials
exposure of unstressed specimens (no applied load) with
stressed specimens and subsequent tension testing to distin-
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
guish between the effects of true stress corrosion and mechani-
of Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-
cal overload (2). Additional considerations in regard to the
tally Assisted Cracking.
significance of the test results and their interpretation are given
Current edition approved Nov. 1, 2019. Published November 2019. Originally
approved in 1976. Last previous edition approved in 2011 as G49–85 (2011). DOI:
in Sections 6 and 10.
10.1520/G0049–85R19.
4.3 Wide variations in test results may be obtained for a
The boldface numbers in parentheses refer to a list of references at the end of
this standard.
given material and specimen orientation with different speci-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
men sizes and stressing procedures. This consideration is
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
significant especially in the standardization of a test procedure
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. for interlaboratory comparisons or quality control.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G49 − 85 (2019)
5. Test Specimens desired stress. Tests should be made on specimens with strain
gages affixed to the specimen surface (around the circumfer-
5.1 Whenever possible, tension test specimens used in
ence in 90° or 120° intervals) to verify strain and stress
evaluating susceptibility to stress-corrosion cracking should
uniformity and determine if machining practices and stressing
conform to the dimensions of standard tension test specimens
jigs are of adequate tolerance and quality.
specified in Test Methods E8/E8M, which contain details for
specimens machined from various product forms. 6.2 Another consideration is the possible increase in net
section stress that will occur when corrosion develops during
5.2 A wide range of sizes for tension test specimens is
the environmental exposure (1, 5). As shown schematically in
possible, depending primarily upon the dimensions of the
Fig. 1, there are two limiting curves: one for zero stiffness
product to be tested. Because the stress-corrosion test results
(dead weight) and the other for infinite stiffness (ideal constant
can be markedly influenced by the cross section of the test
strain). In actual testing with various types of stressing frames,
specimen, this factor should be given careful consideration
such as those shown in Figs. 2-4, the increase in net section
with regard to the object of the investigation. Although larger
stress will be somewhere in between. When the net section
specimens may be more representative of most actual
stress becomes greater than the nominal gross section stress
structures, they often cannot be machined from product forms
and increases to the point of fracture, either of two events can
to be evaluated; and they present more difficulties in stressing
occur: (1) fracture by mechanical overload of a material that is
and handling in the laboratory. Also, larger specimens of some
not susceptible to stress-corrosion cracking, or (2) stress-
materials may require longer exposure periods than smaller
corrosion cracking of a material at an unknown stress higher
specimens.
than the intended nominal test stress. The occurrence of either
5.3 Smaller cross-section specimens are widely used be-
of these phenomena would interfere with a valid evaluation of
cause they (1) have a greater sensitivity to the initiation of
materials with a relatively high resistance to stress corrosion.
stress-corrosion cracking, (2) usually give test results more
These considerations must be taken into account in experi-
quickly, and (3) permit greater convenience in testing. On the
ments undertaken to determine “threshold” stresses. The sig-
other hand, the smaller specimens are more difficult to
nificance of these factors is discussed further in Section 10.
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
crack) has been started will be the subject of another ASTM
standard. Various types of precracked specimens are discussed
in other publications (2, 4).
6. Stress Considerations
6.1 There are several factors that may introduce bending
moments on specimens, such as a longitudinal curvature,
misalignment of threads on threaded-end round specimens, and
the corners of sheet-type specimens. The significance of these
factors is greater for specimens with smaller cross sections.
Even though eccentricity in loading can be minimized to equal
the same standards accepted for tension testing machines,
NOTE 1—The behavior shown is generally representative, but the
inevitably, there is some variation in the tensile stress around
curves will vary with specific alloys and tempers.
the circumference of the test specimen which can be of such
FIG. 1 Effect of Loading Method and Extent of Cracking or Corro-
magnitude that it will introduce considerable error in the sion Pattern on Average Net Section Stress
G49 − 85 (2019)
FIG. 2 Spring-Loaded Stressing Frame (6)
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.
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
to stress-corrosion testing to provide a simple, compact, and
easily operated device to apply axial load (7); see Fig. 3(a).
The load is applied by tightening a nut on one of the bolts and
is determined by carefully measuring the change in ring
diameter. Another similar but less sophisticated ring device can
also be used, the difference being that the load is applied with
a hydraulic jig (7) as shown in Fig. 3(b). In either ring device,
FIG. 3 Sustained Load Devices Using Ring Frames (7)
the bolt contains a keyway to prevent a torsional stress from
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
and the moving beam then locked in position. Other laboratory
7.1.1 Tension specimens may be subjected to a wide range
of stress levels associated with either elastic or elastic and stressing frames have also been used, generally in testing
specimens of lower strength of smaller cross section (8). Fig.
plastic strain. Because the stress system is intended to be
essentially uniaxial (except in the case of notched specimens), 4(a) shows an exploded view of such a stressing frame, and
Fig. 4(b) shows a special loading device developed to ensure
great care must be exercised in the construction of stressing
frames so that bending stresses are avoided or minimized. axial loading with a minimum of torsion and bending of the
specimen.
7.1.2 Although a number of different stressing frames have
been used with tension specimens, three basic types are 7.2.2.1 For stressing frames that do not contain any mecha-
considered herein: constant (sustained) load, constant strain nism for the measurement of load, it is desirable to determine
(deformation), and continuously increasing strain. A constant the stress levels from measurement of the strain. It must be
load can be obtained with dead weight, but truly constant strain noted, however, that only when the intended stress is below the
G49 − 85 (2019)
FIG. 4 Constant-Strain Type of Stressing Frame (8)
elastic limit of the test material is the average linear stress (σ) environment and strain rate is slow enough, stress-corrosion
proportional to the average linear strain (e), σ/e = E, where the cracking may occur during the test. This can result in shorter
constant E is the modulus of elasticity. times to fracture or in lower values of elongation or reduction
7.2.2.2 When tests are conducted at elevated temperatures of area, or both, than obtained for a specimen strained at the
with constant-strain loaded specimens, consideration should be same rate in air or in an inert environment at the same
given to the possibility of stress relaxation. temperature as the corrodent. Appropriate combinations of
7.2.3 Continuously Increasing Strain—A tension testing specimen cross section and corrosive environment must be
machine may be used to load the test specimen at a constant determined, as well as the range of critical strain rate for
rate to failure (10). If the specimen is surrounded by a test specific alloy systems.
G49 − 85 (2019)
8. Preparation of Specimens the presence of cracks due, for example, to the presence of
corrosion products on the specimen surface, it may be
8.1 The pronounced effect of surface conditions on the time
necessary, at the conclusion of the test, to chemically clean the
required to initiate stress-corrosion cracking in test specimens
specimen to facilitate adequate inspection.
is well-known. Unless it is desired to evaluate the as-fabricated
surface, the final surface preparation generally preferred is a 10.2 It must be emphasized that fracture of the test speci-
m
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM 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.
Designation: G49 − 85 (Reapproved 2011) G49 − 85 (Reapproved 2019)
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.
1. 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).
1.4 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.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E8E8/E8M Test Methods for Tension Testing of Metallic Materials [Metric] E0008_E0008M
G35 Practice for Determining the Susceptibility of Stainless Steels and Related Nickel-Chromium-Iron Alloys to Stress-
Corrosion Cracking in Polythionic Acids
G36 Practice for Evaluating Stress-Corrosion-Cracking Resistance of Metals and Alloys in a Boiling Magnesium Chloride
Solution
G37 Practice for Use of Mattsson’s Solution of pH 7.2 to Evaluate the Stress-Corrosion Cracking Susceptibility of Copper-Zinc
Alloys
G44 Practice for Exposure of Metals and Alloys by Alternate Immersion in Neutral 3.5 % Sodium Chloride Solution
3. Summary of Practice
3.1 This practice covers the use of axially loaded, quantitatively stressed ASTM standard tension test specimens for
investigating the resistance to stress-corrosion cracking of metallic materials in all types of product forms. Consideration is given
to important factors in the selection of appropriate specimens, the design of loading equipment, and the effects of these factors on
the state of stress in the specimen as corrosion occurs.
4. 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.
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.06 on Environmentally
Assisted Cracking.
Current edition approved March 1, 2011Nov. 1, 2019. Published April 2011November 2019. Originally approved in 1976. Last previous edition approved in 20052011
as G49–85(2005).G49–85 (2011). DOI: 10.1520/G0049-85R11.10.1520/G0049–85R19.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
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’sstandard’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
G49 − 85 (2019)
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.
5. Test Specimens
5.1 Whenever possible, tension test specimens used in evaluating susceptibility to stress-corrosion cracking should conform to
the dimensions of standard tension test specimens specified in Test Methods E8E8/E8M, which contain details for specimens
machined from various product forms.
5.2 A wide range of sizes for tension test specimens is possible, depending primarily upon the dimensions of the product to be
tested. Because the stress-corrosion test results can be markedly influenced by the cross section of the test specimen, this factor
should be given careful consideration with regard to the object of the investigation. Although larger 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 because 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 crack)
has been started will be the subject of another ASTM standard. Various types of precracked specimens are discussed in other
publications (2, 4).
6. Stress Considerations
6.1 There are several factors that may introduce bending moments on specimens, such as a longitudinal curvature, misalignment
of threads on threaded-end round specimens, and the corners of sheet-type specimens. The significance of these factors is greater
for specimens with smaller cross sections. Even though eccentricity in loading can be minimized to equal the same standards
accepted for tension testing machines, inevitably, there is some variation in the tensile stress around the circumference of the test
specimen which can be of such magnitude that it will introduce considerable error in the desired stress. Tests should be made on
specimens with strain gages affixed to the specimen surface (around the circumference in 90° or 120° intervals) to verify strain
and stress uniformity and determine if machining practices and stressing jigs are of adequate tolerance and quality.
6.2 Another consideration is the possible increase in net section stress that will occur when corrosion develops during the
environmental exposure (1, 5). As shown schematically in Fig. 1, there are two limiting curves: one for zero stiffness (dead weight)
and the other for infinite stiffness (ideal constant strain). In actual testing with various types of stressing frames, such as those
shown in Figs. 2-4, the increase in net section stress will be somewhere in between. When the net section stress becomes greater
than the nominal gross section stress and increases to the point of fracture, either of two events can occur: (1) fracture by
mechanical overload of a material that is not susceptible to stress-corrosion cracking, or (2) stress-corrosion cracking of a material
at an unknown stress higher than the intended nominal test stress. The occurrence of either of these phenomena would interfere
with a valid evaluation of materials with a relatively high resistance to stress corrosion. These considerations must be taken into
account in experiments undertaken to determine “threshold” stresses. The significance of these factors is discussed further in
Section 10.
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NOTE 1—The behavior shown is generally representative, but the curves will vary with specific alloys and tempers.
FIG. 1 Effect of Loading Method and Extent of Cracking or Corrosion Pattern on Average Net Section Stress
7. Stressing Methods
7.1 General Considerations:
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.
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 to
stress-corrosion testing to provide a simple, compact, and easily operated device to apply axial load (7); see Fig. 3(a). The load
is applied by tightening a nut on one of the bolts and is determined by carefully measuring the change in ring diameter. Another
similar but less sophisticated ring device can also be used, the difference being that the load is applied with a hydraulic jig (7) as
shown in Fig. 3(b). In either ring device, the bolt contains a keyway to prevent a torsional stress from being applied to the specimen
while tightening the nut.
7.2.2 Constant Strain—Stress-corrosion tests performed in low-compliance tension testing machines are of the constant-strain
type. The specimen is loaded to the required stress level and the moving beam then locked in position. Other laboratory stressing
frames have also been used, generally in testing specimens of lower strength of smaller cross section (8).Fig. 4(a) shows an
exploded view of such a stressing frame, and Fig. 4(b) shows a special loading device developed to ensure axial loading with a
minimum of torsion and bending of the specimen.
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FIG. 2 Spring-Loaded Stressing Frame (6)
FIG. 3 Sustained Load Devices Using Ring Frames (7)
7.2.2.1 For stressing frames that do not contain any mechanism for the measurement of load, it is desirable to determine the
stress levels from measurement of the strain. It must be noted, however, that only when the intended stress is below the elastic limit
of the test material is the average linear stress (σ) proportional to the average linear strain (e), σ/e = E, where the constant E is the
modulus of elasticity.
7.2.2.2 When tests are conducted at elevated temperatures with constant-strain loaded specimens, consideration should be given
to the possibility of stress relaxation.
7.2.3 Continuously Increasing Strain—A tension testing machine may be used to load the test specimen at a constant rate to
failure (10). If the specimen is surrounded by a test environment and strain rate is slow enough, stress-corrosion cracking may
occur during the test. This can result in shorter times to fracture or in lower values of elongation or reduction of area, or both, than
obtained for a specimen strained at the same rate in air or in an inert environment at the same temperature as the corrodent.
Appropriate combinations of specimen cross section and corrosive environment must be determined, as well as the range of critical
strain rate for specific alloy systems.
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FIG. 4 Constant-Strain Type of Stressing Frame (8)
8. Preparation of Specimens
8.1 The pronounced effect of surface conditions on the time required to initiate stress-corrosion cracking in test specimens is
well-known. Unless it is desired to evaluate the as-fabricated surfa
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