ASTM G39-99(2011)

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

SIGNIFICANCE AND USE
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 designed for testing at stress levels below the elastic limit of the alloy. For testing in the plastic range, U-bend specimens should 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 plastic range is not recommended for general use.
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 (see Note 1). Stress calculations by this practice are not applicable to plastically stressed specimens.
Note 1—It is the nature of these practices 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 loaded 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 practices deal with this aspect, for example, Specification D1141, and Practices G30, G36, G44, G50, and G85. The experimenter is referred to ASTM Special Technical Publication 425 (2).  
1.6 The bent-beam practice 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 practice 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 values 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 7 and 12.1.)

General Information

• Status: Historical
• Publication Date: 28-Feb-2011
• 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

• Replaces: ASTM G39-99(2005) - Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens
• Effective Date: 01-Mar-2011
• Referred By: ASTM G41-90(2018) - Standard Practice for Determining Cracking Susceptibility of Metals Exposed Under Stress to a Hot Salt Environment
• Effective Date: 01-Mar-2011
• Referred By: ASTM G111-21a - Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or Both
• Effective Date: 01-Mar-2011
• Referred By: ASTM G30-22 - Standard Practice for Making and Using U-Bend Stress-Corrosion Test Specimens
• Effective Date: 01-Mar-2011
• Referred By: ASTM G52-20 - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• Effective Date: 01-Mar-2011
• 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: 01-Mar-2011
• Referred By: ASTM G58-85(2015) - Standard Practice for Preparation of Stress-Corrosion Test Specimens for Weldments
• Effective Date: 01-Mar-2011

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:G39 −99(Reapproved 2011)
Standard Practice for
Preparation and Use of Bent-Beam Stress-Corrosion Test
Specimens
ThisstandardisissuedunderthefixeddesignationG39;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope valuesdiscussedinthispracticeapplyonlytothestateofstress
existing before initiation of cracks.
1.1 This practice covers procedures for designing,
preparing, and using bent-beam stress-corrosion specimens. 1.7 The values stated in SI units are to be regarded as
standard. The inch-pound values in parentheses are provided
1.2 Differentspecimenconfigurationsaregivenforusewith
for information.
different product forms, such as sheet or plate. This practice
1.8 This standard does not purport to address all of the
applicable to specimens of any metal that are stressed to levels
safety concerns, if any, associated with its use. It is the
less than the elastic limit of the material, and therefore, the
responsibility of the user of this standard to establish appro-
applied stress can be accurately calculated or measured (see
priate safety and health practices and determine the applica-
Note 1). Stress calculations by this practice are not applicable
bility of regulatory limitations prior to use. (For more specific
to plastically stressed specimens.
safety hazard information see Section 7 and 12.1.)
NOTE 1—It is the nature of these practices that only the applied stress
canbecalculated.Sincestress-corrosioncrackingisafunctionofthetotal
2. Referenced Documents
stress, for critical applications and proper interpretation of results, the
residual stress (before applying external stress) or the total elastic stress
2.1 ASTM Standards:
(after applying external stress) should be determined by appropriate
D1141Practice for the Preparation of Substitute Ocean
nondestructive methods, such as X-ray diffraction (1).
Water
1.3 Test procedures are given for stress-corrosion testing by
G30 Practice for Making and Using U-Bend Stress-
exposure to gaseous and liquid environments.
Corrosion Test Specimens
G36Practice for Evaluating Stress-Corrosion-Cracking Re-
1.4 The bent-beam test is best suited for flat product forms,
sistance of Metals and Alloys in a Boiling Magnesium
suchassheet,strip,andplate.Forplatematerialthebent-beam
specimen is more difficult to use because more rugged speci- Chloride Solution
G44PracticeforExposureofMetalsandAlloysbyAlternate
men holders must be built to accommodate the specimens. A
double-beam modification of a four-point loaded specimen to Immersion in Neutral 3.5 % Sodium Chloride Solution
G50Practice for Conducting Atmospheric Corrosion Tests
utilize heavier materials is described in 10.5.
on Metals
1.5 The exposure of specimens in a corrosive environment
G85Practice for Modified Salt Spray (Fog) Testing
is treated only briefly since other practices deal with this
2.2 NACE Documents:
aspect, for example, Specification D1141, and Practices G30,
NACE TM0177-96Laboratory Testing of Metals for Resis-
G36, G44, G50, and G85. The experimenter is referred to
tancetoSpecificFormsofEnvironmentalCrackinginH S
ASTM Special Technical Publication 425 (2). 2
Environments
1.6 The bent-beam practice generally constitutes a constant
strain (deflection) test. Once cracking has initiated, the state of
3. Terminology
stress at the tip of the crack as well as in uncracked areas has
3.1 Definitions of Terms Specific to This Standard:
changed,andtherefore,theknownorcalculatedstressorstrain
3.1.1 cracking time—the time elapsed from the inception of
test until the appearance of cracking.
This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-
tally Assisted Cracking. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2011. Published April 2011. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1973. Last previous edition approved in 2005 as G39–99(2005). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0039-99R11. the ASTM website.
2 4
The boldface numbers in parentheses refer to a list of references at the end of Available from NACE International (NACE), 1440 South Creek Dr., Houston,
this standard. TX 77084-4906, http://www.nace.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G39−99 (2011)
3.1.1.1 Discussion—The test begins when the stress is
applied and the stressed specimen is exposed to the corrosive
environment, whichever occurs later.
3.1.1.2 Discussion—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.
3.1.2 stress-corrosion cracking—a cracking process requir-
ingthesimultaneousactionofacorrodentandsustainedtensile
stress. This excludes corrosion-reduced sections that fail by
fastfracture.Italsoexcludesintercrystallineortranscrystalline
corrosion which can disintegrate an alloy without either
applied or residual stress.
4. Summary of Practice
4.1 This practice involves the quantitative stressing of a
beamspecimenbyapplication of a bending stress.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-
FIG. 1 Schematic Specimen and Holder Configurations
signed for testing at stress levels below the elastic limit of the
alloy.Fortestingintheplasticrange,U-bendspecimensshould
be employed (see Practice G30). Although it is possible to
6.1.2 Whenthestress-corrosiontestisconductedbyimmer-
stress bent-beam specimens into the plastic range, the stress
sion in an electrolyte, galvanic action between specimen and
level cannot be calculated for plastically-stressed three- and
holder (or spacer) shall be prevented (see Note 5). This is
four-point loaded specimens as well as the double-beam
accomplishedby(1)makingtheholderofthesamematerialas
specimens. Therefore, the use of bent-beam specimens in the
the individual specimens, (2) inserting electrically insulating
plastic range is not recommended for general use.
materials between specimen and holder at all points of contact
(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
hydrophobic filler (such as grease or wax).
self-contained and does not require a holder.
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 deadweight
experienced in outdoor exposure tests.
arrangement to change the mode of loading.
6.2 StressingJigs—Three-pointandfour-pointloadedspeci-
6.1.1 The holder shall be made of a material that would
men holders, Fig. 1(b and c), contain a stressing feature in the
withstand the influence of the environment without deteriora-
form of a loading screw.To stress two-point loaded specimens
tion or change in shape.
(Fig. 1(a)), a separate stressing jig shall be used.Aconvenient
NOTE4—Itshouldberecognizedthatmanyplasticstendtocreepwhen
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.
G39−99 (2011)
8. Sampling
8.1 Test specimens shall be selected so that they represent
the material to be tested. In simulating a service condition, the
directionofloadapplicationinthespecimenshallrepresentthe
anticipatedloadingdirectioninservicewithrespecttoprocess-
ing conditions, for example, rolling direction.
8.2 Paragraphs 9.4 and 9.5 deal specifically with specimen
selection as related to the original material surface.
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
FIG. 2 Stressing Jig and Two-Point Loaded Specimen with
stenciled area. Care must be taken to prevent the identification
Holder (approximately ⁄4 actual size)
from being obliterated by corrosion.
9.3 Mechanical properties should be determined on the
sameheat-treatmentlotfromwhichstress-corrosionspecimens
6.3 Deflection Gauges—Deflection of specimens is deter-
are obtained.
mined by separate gages or by gages incorporated in a loading
9.4 The specimens can be cut from sheet or plate in such a
apparatus as shown in Fig. 3. In designing a deflection gage to
fashion that the original material surface is retained. This
suit individual circumstances care must be taken to reference
procedure is recommended when it is desired to include the
the deflection to the proper support distance as defined in 10.2
effect of surface condition in the test.
– 10.5.
9.5 If, however, it is desired that surface conditions should
7. Hazards
not influence the test results of several materials with different
surface conditions, the surfaces of all specimens must be
7.1 Bent-beam specimens made from high-strength materi-
prepared in the same way. It is recommended that grinding or
alsmayexhibithighratesofcrackpropagationandaspecimen
machiningtoasurfacefinishofatleast0.7µm(30µin.)andto
may splinter into several pieces. Due to high stresses in a
a depth of at least 0.25 mm (0.01 in.) be utilized for surface
specimen,thesepiecesmayleavethespecimenathighvelocity
preparation. It is desirable to remove the required amount of
and can be dangerous. Personnel installing and examining
metalinseveralstepsbyalternatelygrindingoppositesurfaces.
specimens should be cognizant of this possibility and be
This practice minimizes warpage due to residual stresses
protected against injury.
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
thegivenmetaloralloyshouldbeused.Caremustbeexercised
nottocontaminatecleanedspecimens.Also,itissuggestedthat
specimens be examined for cracks before exposure to the test
environment.
10. Stress Calculations
10.1 The equations given in this section are valid only for
stresses below the elastic limit of the material. At stresses
abovetheelasticlimit,butbelowtheengineeringyieldstrength
FIG. 3 Specimen Loading Apparatus for Three-Point Loaded
Beam Specimens with Integral Deflection Gage (0.2% offset) only a small error results from use of the
G39−99 (2011)
equations (see Note 1). The equations must not be used above 10.2.2 The mathematical analysis establishes that Eq 1 and
the yield strength of the material. The following paragraphs Eq2definetherelationshipbetweenthestrainεand(L−H)⁄H
give relationships used to calculate the maximum longitudinal in parameter form. The common parameter in these equations
stress in the outer fibers of the specimen convex surface. is the modulus k of the elliptic integrals. Thus, the following
Calculations for transverse stress or edge-to-edge variation of procedure can be used to determine the specimen length L that
longitudinal stress are not given; the specimen dimensions are is required to produce a given maximum stress σ:
chosen to minimize these stresses consistent with convenient
10.2.2.1 Divide the stress σ by the modulus of elasticity E
m
useofthespecimens.Thespecimendimensionsgivenherecan to determine the strain ε.
bemodifiedtosuitspecificneeds.However,ifthisisdone,the
ε 5 σ/E
m
approximatespecimenproportionsshouldbepreservedtogive
a similar stress distribution (for instance, if the length is 10.2.2.2 From Eq 1 determine the value of k corresponding
doubled the width should be doubled also). to the required value of ε.
10.1.1 When specimens are tested at elevated temperatures,
10.2.2.3 By using appropriate values of k, evaluate Eq 2 for
the possibility of stress relaxation should be investigated.
L.Tofacilitatecalculations,acomputercanbeusedtogenerate
Relaxation can be estimated from known creep data for the
a table for a range of strain ε and H/t with resultant values of
specimen, holder, and insulating materials. Differences in
(L−H)⁄H.
thermal expansion also should be considered.
10.2.3 Cal
...