ASTM G39-99

Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens

SCOPE
1.1 This practice covers procedures for designing, preparing, and using bent-beam stress-corrosion specimens.  
1.2 Different specimen configurations are given for use with different product forms, such as sheet or plate. This practice applicable to specimens of any metal that are stressed to levels less than the elastic limit of the material, and therefore the applied stress can be accurately calculated or measured (Note 1). Stress calculations by this practice are not applicable to plastically stressed specimens.  Note 1-It is the nature of these methods that only the applied stress can be calculated. Since stress-corrosion cracking is a function of the total stress, for critical applications and proper interpretation of results, the residual stress (before applying external stress) or the total elastic stress (after applying external stress) should be determined by appropriate nondestructive methods, such as X-ray diffraction (1).  
1.3 Test procedures are given for stress-corrosion testing by exposure to gaseous and liquid environments.  
1.4 The bent-beam test is best suited for flat product forms such as sheet, strip, and plate. For plate material the bent-beam specimen is more difficult to use, because more rugged specimen holders must be built to accommodate the specimens. A double-beam modification of a four-point specimen to utilize heavier materials is described in 10.5.  
1.5 The exposure of specimens in a corrosive environment is treated only briefly, since other methods deal with this aspect, for example, Specification D1141, Practices G30, G36, G44, and G50, and Method G43. The experimenter is referred to ASTM Special Technical Publication 425 (2).  
1.6 The bent-beam method generally constitutes a constant strain (deflection) test. Once cracking has initiated, the state of stress at the tip of the crack as well as in uncracked areas has changed, and therefore the known or calculated stress or strain values discussed in this method apply only to the state of stress existing before initiation of cracks.  
1.7 The values stated in SI units are to be regarded as standard. The inch-pound equivalents in parentheses are provided for information.  
1.8 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. (For more specific safety hazard information see Section 8 and 12.1.)

General Information

• Status: Historical
• Publication Date: 09-Jan-1999
• ICS: 77.040.10 - Mechanical testing of metals
• ICS: 77.060 - Corrosion of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.06 - Environmentally Assisted Cracking

Relations

• Replaced By: ASTM G39-99(2005) - Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens
• Effective Date: 01-May-2005
• Referred By: ASTM G41-90(2018) - Standard Practice for Determining Cracking Susceptibility of Metals Exposed Under Stress to a Hot Salt Environment
• Effective Date: 10-Jan-1999
• Referred By: ASTM G30-22 - Standard Practice for Making and Using U-Bend Stress-Corrosion Test Specimens
• Effective Date: 10-Jan-1999
• Referred By: ASTM G111-21a - Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or Both
• Effective Date: 10-Jan-1999
• Referred By: ASTM G58-85(2015) - Standard Practice for Preparation of Stress-Corrosion Test Specimens for Weldments
• Effective Date: 10-Jan-1999
• Referred By: ASTM G52-20 - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• Effective Date: 10-Jan-1999
• Referred By: ASTM G103-97(2023)e1 - Standard Practice for Evaluating Stress-Corrosion Cracking Resistance of Low Copper 7XXX Series Al-Zn-Mg-Cu Alloys in Boiling 6 % Sodium Chloride Solution
• Effective Date: 10-Jan-1999

Standards Content (Sample)

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: G 39 – 99
Standard Practice for
Preparation and Use of Bent-Beam Stress-Corrosion Test
Specimens
ThisstandardisissuedunderthefixeddesignationG39;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.7 The values stated in SI units are to be regarded as
standard. The inch-pound equivalents in parentheses are pro-
1.1 This practice covers procedures for designing, prepar-
vided for information.
ing, and using bent-beam stress-corrosion specimens.
1.8 This standard does not purport to address all of the
1.2 Differentspecimenconfigurationsaregivenforusewith
safety concerns, if any, associated with its use. It is the
different product forms, such as sheet or plate. This practice
responsibility of the user of this standard to establish appro-
applicable to specimens of any metal that are stressed to levels
priate safety and health practices and determine the applica-
less than the elastic limit of the material, and therefore, the
bility of regulatory limitations prior to use. (For more specific
applied stress can be accurately calculated or measured (see
safety hazard information see Section 7 and 12.1.)
Note 1). Stress calculations by this practice are not applicable
to plastically stressed specimens.
2. Referenced Documents
NOTE 1—It is the nature of these practices that only the applied stress
2.1 ASTM Standards:
canbecalculated.Sincestress-corrosioncrackingisafunctionofthetotal
D1141 Specification for Substitute Ocean Water
stress, for critical applications and proper interpretation of results, the
G30 Practice for Making and Using U-Bend Stress Corro-
residual stress (before applying external stress) or the total elastic stress
sion Test Specimens
(after applying external stress) should be determined by appropriate
G36 Practice for Performing Stress-Corrosion Cracking
nondestructive methods, such as X ray diffraction (1).
Tests in a Boiling Magnesium Chloride Solution
1.3 Test procedures are given for stress-corrosion testing by
G44 Practice for Evaluating Stress Corrosion Cracking
exposure to gaseous and liquid environments.
ResistanceofMetalsandAlloysbyAlternateImmersionin
1.4 The bent-beam test is best suited for flat product forms,
3.5% Sodium Chloride Solution
suchassheet,strip,andplate.Forplatematerialthebent-beam
G50 Practice for ConductingAtmospheric Corrosion Tests
specimen is more difficult to use because more rugged speci-
on Metals
men holders must be built to accommodate the specimens. A
G85 Practice for Modified Salt Spray (Fog) Testing
double-beam modification of a four-point loaded specimen to
2.2 NACE Documents:
utilize heavier materials is described in 10.5.
NACETM0177-96 LaboratoryTesting of Metals for Resis-
1.5 The exposure of specimens in a corrosive environment
tancetoSpecificFormsofEnvironmentalCrackinginH S
is treated only briefly since other practices deal with this
Environments
aspect, for example, Specification D1141, and Practices G30,
G36, G44, G50, and G85. The experimenter is referred to
3. Terminology
ASTM Special Technical Publication 425 (2).
3.1 Definitions of Terms Specific to This Standard:
1.6 The bent-beam practice generally constitutes a constant
3.1.1 stress-corrosion cracking—a cracking process requir-
strain (deflection) test. Once cracking has initiated, the state of
ingthesimultaneousactionofacorrodentandsustainedtensile
stress at the tip of the crack as well as in uncracked areas has
stress. This excludes corrosion-reduced sections that fail by
changed,andtherefore,theknownorcalculatedstressorstrain
fastfracture.Italsoexcludesintercrystallineortranscrystalline
valuesdiscussedinthispracticeapplyonlytothestateofstress
corrosion which can disintegrate an alloy without either
existing before initiation of cracks.
applied or residual stress.
3.1.2 cracking time—thetimeelapsedfromtheinceptionof
test until the appearance of cracking.
This practice is under the jurisdiction ofASTM Committee G-1 on Corrosion
of Metals, and is the direct responsibility of Subcommittee G01.06 on Stress
Corrosion Cracking and Corrosion Fatigue.
Current edition approved Jan. 10, 1999. Published April 1999. Originally Annual Book of ASTM Standards, Vol 11.02.
e1 4
published as G39–73. Last previous edition G39–90 (1994) . Annual Book of ASTM Standards, Vol 03.02.
2 5
The boldface numbers in parentheses refer to the list of references appended to Available from National Association of Corrosion Engineers, Int., P. O. Box
this practice. 218340, Houston, TX 77218–8340.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G39
3.1.2.1 Discussion—1 The test begins when the stress is
applied and the stressed specimen is exposed to the corrosive
environment, whichever occurs later.
3.1.2.2 Discussion—2 The specimen is considered to have
failed when cracks are detected. Presence of cracks can be
determined with or without optical, mechanical, or electronic
aids. However, for meaningful interpretation, comparisons
should be made only among tests employing crack detection
methods of equivalent sensitivity.
4. Summary of Practice
4.1 This practice involves the quantitative stressing of a
beamspecimenbyapplicationofabendingstress.Theapplied
stress is determined from the size of the specimen and the
bendingdeflection.Thestressedspecimensthenareexposedto
the test environment and the time required for cracks to
developisdetermined.Thiscrackingtimeisusedasameasure
of the stress-corrosion resistance of the material in the test
environment at the stress level utilized.
5. Significance and Use
5.1 The bent-beam specimen is designed for determining
the stress-corrosion behavior of alloy sheets and plates in a
variety of environments. The bent-beam specimens are de-
signed for testing at stress levels below the elastic limit of the
alloy.FortestingintheplasticrangeU-bendspecimensshould
be employed (see Practice G30). Although it is possible to
stress bent-beam specimens into the plastic range, the stress
level cannot be calculated for plastically stressed three- and
four-point loaded specimens as well as the double-beam
specimens. Therefore, the use of bent-beam specimens in the FIG. 1 Schematic Specimen and Holder Configurations
plastic range is not recommended for general use.
(see Note 4), (3) making the entire holder out of a nonmetallic
6. Apparatus
material (see Note 4), or ( 4) coating the holder with an
6.1 Specimen Holders—Bent-beam specimens require a
electrically nonconducting coating that effectively prevents
specimen holder for each specimen, designed to retain the
contact between holder and electrolyte.
applied stress on the specimen. Typical specimen holder
6.1.3 Crevice corrosion may occur in an electrolyte at
configurations are shown schematically in Fig. 1.
contact points between specimen and holder (or spacer). In
these instances the critical areas should be packed with a
NOTE 2—The double-beam specimen, more fully described in 10.5, is
self-contained and does not require a holder.
hydrophobic filler (such as grease or wax).
NOTE 3—Specimen holders can be modified from the constant defor-
NOTE 5—In atmospheres (gas) galvanic action between specimen and
mation type shown in Fig. 1 to give a constant-load type of stressing. For
holder either does not exist or is confined to a very small area as
instance, the loading bolt can be supplanted by a spring or dead-weight
experienced in outdoor exposure tests.
arrangement to change the mode of loading.
6.2 Stressing Jigs—Three-point and four-point loaded
6.1.1 The holder shall be made of a material that would
specimen holders, Fig. 1 ( b and c), contain a stressing feature
withstand the influence of the environment without deteriora-
in the form of a loading screw. To stress two-point loaded
tion or change in shape.
specimens (Fig. 1(a)), a separate stressing jig shall be used.A
NOTE 4—Itshouldberecognizedthatmanyplasticstendtocreepwhen
convenient stressing jig is shown in Fig. 2.
subjectedtosustainedloads.Ifspecimenholdersorinsulatorsaremadeof
suchmaterials,theappliedstressonthespecimenmaychangeappreciably NOTE 6—The double-beam specimen, described in 10.5, requires a
with time. By proper choice of holder and insulator materials, however, mechanical or hydraulic stressing frame (a universal tension testing
many plastics can be used, especially in short-time tests. machine can also be used) as well as welding equipment.
6.1.2 Whenthestress-corrosiontestisconductedbyimmer- 6.3 Deflection Gages—Deflection of specimens is deter-
sion in an electrolyte, galvanic action between specimen and mined by separate gages or by gages incorporated in a loading
holder (or spacer) shall be prevented (see Note 5). This is apparatus as shown in Fig. 3. In designing a deflection gage to
accomplishedby(1)makingtheholderofthesamematerialas suit individual circumstances care must be taken to reference
the individual specimens, (2) inserting electrically insulating the deflection to the proper support distance as defined in
materials between specimen and holder at all points of contact 10.2-10.5.
G39
9. Test Specimen
9.1 The bent-beam stress-corrosion specimens shall be flat
strips of metal of uniform, rectangular cross section, and
uniform thickness.
9.2 The identification of individual specimens should be
permanentlyinscribedateachendofthespecimenbecausethis
is the area of lowest stress and cracking is not expected to be
initiatedbytheidentificationmarkings.Ifstencilingisusedfor
identification, this shall be done only on softened material
beforeanyhardeningheattreatmentstopreventcrackinginthe
stenciled area. Care must be taken to prevent the identification
from being obliterated by corrosion.
9.3 Mechanical properties should be determined on the
sameheat-treatmentlotfromwhichstress-corrosionspecimens
are obtained.
9.4 The specimens can be cut from sheet or plate in such a
fashion that the original material surface is retained. This
procedure is recommended when it is desired to include the
effect of surface condition in the test.
FIG. 2 Stressing Jig and Two-Point Loaded Specimen with Holder 9.5 If, however, it is desired that surface conditions should
(approximately ⁄4 actual size)
not influence the test results of several materials with different
surface conditions, the surfaces of all specimens must be
prepared in the same way. It is recommended that grinding or
machiningtoasurfacefinishofatleast0.7µm(30µin.)andto
a depth of at least 0.25 mm (0.01 in.) be utilized for surface
preparation. It is desirable to remove the required amount of
metalinseveralstepsbyalternatelygrindingoppositesurfaces.
This practice minimizes warpage due to residual stresses
caused by machining.All edges should be similarly ground or
machined to remove cold-worked material from previous
shearing. Chemical or electrochemical treatments that produce
hydrogen on the specimen surface must not be used on
materials that may be subject to embrittlement by hydrogen or
that react with hydrogen to form a hydride.
9.6 Immediately before stressing, the specimens should be
degreased and cleaned to remove contamination that occurred
during specimen preparation. Only chemicals appropriate for
FIG. 3 Specimen Loading Apparatus for Three-Point Loaded
thegivenmetaloralloyshouldbeused.Caremustbeexercised
Beam Specimens with Integral Deflection Gage
nottocontaminatecleanedspecimens.Also,itissuggestedthat
specimens be examined for cracks before exposure to the test
environment.
7. Hazards
7.1 Bent-beam specimens made from high-strength materi-
10. Stress Calculations
alsmayexhibithighratesofcrackpropagationandaspecimen
may splinter into several pieces. Due to high stresses in a
10.1 The equations given in this section are valid only for
specimen,thesepiecesmayleavethespecimenathighvelocity
stresses below the elastic limit of the material. At stresses
and can be dangerous. Personnel installing and examining
abovetheelasticlimitbutbelowtheengineeringyieldstrength
specimens should be cognizant of this possibility and be
(0.2% offset) only a small error results from use of the
protected against injury.
equations (see Note 1). The equations must not be used above
the yield strength of the material. The following paragraphs
8. Sampling
give relationships used to calculate the maximum longitudinal
8.1 Test specimens shall be selected so that they represent stress in the outer fibers of the specimen convex surface.
the material to be tested. In simulating a service condition, the Calculations for transverse stress or edge-to-edge variation of
directionofloadapplicationinthespecimenshallrepresentthe longitudinal stress are not given; the specimen dimensions are
anticipatedloadingdirectioninservicewithrespecttoprocess- chosen to minimize these stresses consistent with convenient
ing conditions, for example, rolling direction. useofthespecimens.Thespecimendimensionsgivenherecan
8.2 Paragraphs 7.4 and 7.5 deal specifically with specimen be modified to suit specific needs. However, if this is done the
selection as related to the original material surface. approximatespecimenproportionsshouldbepreservedtogive
G39
a similar stress distribution (for instance, if the length is 10.2.2.3 By using appropriate values of k evaluate Eq 2 for
doubled the width should be doubled also). L.Tofacilitatecalculationsacomputercanbeusedtogenerate
a table for a range of strain e and H/t with resultant values of
10.1.1 When specimens are tested at elevated temperatures,
(L − H)/H.
the possibility of stress relaxation should be investigated.
10.2.3 Calculate the deflection of the specimen as follows:
Relaxation can be estimated from known creep data for the
specimen, holder, and insulating materials. Differences in
y/H 5 k/~2E 2 K! (3)
thermal expansion also should be considered.
where:
10.1.2 Theappliedstressisdeterminedbyspecimendimen-
y 5 maximum deflection.
sions and the amount of bending deflection.Thus, the errors in
The other quantities are given in 10.2.1.
the applied stress are related to those inherent in the use of
Thisrelationshipcanbeusedasasimplechecktoensurethat
measuring instruments (micrometers, deflection gages, strain
the maximum stress does not exceed the proportional limit. If
gages,andsoforth).Forthetwo-pointloadedspecimens,most
itshouldexceedtheproportionallimit,themeasureddeflection
measured values lie within 5% of the values calculated in
will be greater than that calculated from Eq 3.
accordance with the procedur
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