ASTM G39-99(2005)

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 G 30). 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 0). Stress calculations by this practice are not applicable to plastically stressed specimens. 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 ().
1.3 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 .
1.5 The exposure of specimens in a corrosive environment is treated only briefly since other practices deal with this aspect, for example, Specification D 1141, and Practices G 30, G 36, G 44, G 50, and G 85. The experimenter is referred to ASTM Special Technical Publication 425 ().
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 equivalents in parentheses are provided for information.
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 and .)

General Information

• Status: Historical
• Publication Date: 30-Apr-2005
• 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 - Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens
• Effective Date: 01-May-2005
• Replaced By: ASTM G39-99(2011) - Standard Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens
• 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-May-2005
• Referred By: ASTM G52-20 - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• 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: 01-May-2005
• Referred By: ASTM G30-22 - Standard Practice for Making and Using U-Bend Stress-Corrosion Test Specimens
• Effective Date: 01-May-2005
• 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-May-2005
• Referred By: ASTM G111-21a - Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or Both
• Effective Date: 01-May-2005

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 2005)
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 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 Practice for the Preparation of Substitute Ocean
stress, for critical applications and proper interpretation of results, the
Water
residual stress (before applying external stress) or the total elastic stress
G30 Practice for Making and Using U-Bend Stress-
(after applying external stress) should be determined by appropriate
Corrosion Test Specimens
nondestructive methods, such as X-ray diffraction (1).
G36 Practice for Evaluating Stress-Corrosion-Cracking Re-
1.3 Test procedures are given for stress-corrosion testing by
sistance of Metals and Alloys in a Boiling Magnesium
exposure to gaseous and liquid environments.
Chloride Solution
1.4 The bent-beam test is best suited for flat product forms,
G44 Practice for Exposure of Metals and Alloys by Alter-
suchassheet,strip,andplate.Forplatematerialthebent-beam
nate Immersion in Neutral 3.5 % Sodium Chloride Solu-
specimen is more difficult to use because more rugged speci-
tion
men holders must be built to accommodate the specimens. A
G50 Practice for Conducting Atmospheric Corrosion Tests
double-beam modification of a four-point loaded specimen to
on Metals
utilize heavier materials is described in 10.5.
G85 Practice for Modified Salt Spray (Fog) Testing
1.5 The exposure of specimens in a corrosive environment
2.2 NACE Documents:
is treated only briefly since other practices deal with this
NACETM0177-96 LaboratoryTesting of Metals for Resis-
aspect, for example, Specification D1141, and Practices G30,
tancetoSpecificFormsofEnvironmentalCrackinginH S
G36, G44, G50, and G85. The experimenter is referred to
Environments
ASTM Special Technical Publication 425 (2).
1.6 The bent-beam practice generally constitutes a constant
3. Terminology
strain (deflection) test. Once cracking has initiated, the state of
3.1 Definitions of Terms Specific to This Standard:
stress at the tip of the crack as well as in uncracked areas has
3.1.1 cracking time—thetimeelapsedfromtheinceptionof
changed,andtherefore,theknownorcalculatedstressorstrain
test until the appearance of cracking.
valuesdiscussedinthispracticeapplyonlytothestateofstress
3.1.1.1 Discussion—The test begins when the stress is
existing before initiation of cracks.
applied and the stressed specimen is exposed to the corrosive
environment, whichever occurs later.
This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
ofMetals,andisthedirectresponsibilityofSubcommitteeG01.06onEnvironmen-
tally Assisted Cracking. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2005. Published May 2005. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1973. Last previous edition approved in 1999 as G39–99. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0039-99R05. the ASTM website.
2 4
The boldface numbers in parentheses refer to the list of references appended to Available from National Association of Corrosion Engineers (NACE), 1440
this practice. South Creek Dr., Houston, TX 77084-4906.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G39 – 99 (2005)
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
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.Fortestingintheplasticrange,U-bendspecimensshould
be employed (see Practice G30). Although it is possible to
stress bent-beam specimens into the plastic range, the stress FIG. 1 Schematic Specimen and Holder Configurations
level cannot be calculated for plastically-stressed three- and
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
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
G39 – 99 (2005)
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
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
FIG. 2 Stressing Jig and Two-Point Loaded Specimen with Holder
(approximately ⁄4 actual size) 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.
9.5 If, however, it is desired that surface conditions should
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.
FIG. 3 Specimen Loading Apparatus for Three-Point Loaded
Beam Specimens with Integral Deflection Gage 9.6 Immediately before stressing, the specimens should be
degreased and cleaned to remove contamination that occurred
during specimen preparation. Only chemicals appropriate for
suit individual circumstances care must be taken to reference
thegivenmetaloralloyshouldbeused.Caremustbeexercised
the deflection to the proper support distance as defined in
nottocontaminatecleanedspecimens.Also,itissuggestedthat
10.2-10.5.
specimens be examined for cracks before exposure to the test
environment.
7. Hazards
10. Stress Calculations
7.1 Bent-beam specimens made from high-strength materi-
alsmayexhibithighratesofcrackpropagationandaspecimen
10.1 The equations given in this section are valid only for
may splinter into several pieces. Due to high stresses in a
stresses below the elastic limit of the material. At stresses
specimen,thesepiecesmayleavethespecimenathighvelocity
abovetheelasticlimit,butbelowtheengineeringyieldstrength
and can be dangerous. Personnel installing and examining
(0.2% offset) only a small error results from use of the
specimens should be cognizant of this possibility and be
equations (see Note 1). The equations must not be used above
protected against injury.
the yield strength of the material. The following paragraphs
give relationships used to calculate the maximum longitudinal
8. Sampling
stress in the outer fibers of the specimen convex surface.
8.1 Test specimens shall be selected so that they represent Calculations for transverse stress or edge-to-edge variation of
the material to be tested. In simulating a service condition, the longitudinal stress are not given; the specimen dimensions are
directionofloadapplicationinthespecimenshallrepresentthe chosen to minimize these stresses consistent with convenient
G39 – 99 (2005)
´5s/E
useofthespecimens.Thespecimendimensionsgivenherecan
m
bemodifiedtosuitspecificneeds.However,ifthisisdone,the
approximatespecimenproportionsshouldbepreservedtogive 10.2.2.2 From Eq 1 determine the value of k corresponding
a similar stress distribution (for instance, if the length is to the required value of ´.
doubled the width should be doubled also). 10.2.2.3 By using appropriate values of k, evaluate Eq 2 for
L.Tofacilitatecalculations,acomputercanbeusedtogenerate
10.1.1 When specimens are tested at elevated temperatures,
a table for a range of strain ´ and H/t with resultant values of
the possibility of stress relaxation should be investigated.
(L − H)/H.
Relaxation can be estimated from known creep data for the
10.2.3 Calculate the deflection of the specimen as follows:
specimen, holder, and insulating materials. Differences in
thermal expansion also should be considered. y/H 5 k/~2E 2 K! (3)
10.1.2 Theappliedstressisdeterminedbyspecimendimen-
where:
sions and the amount of bending deflection.Thus, the errors in
y = maximum deflection.
the applied stress are related to those inherent in the use of
The other quantities are given in 10.2.1.
measuring instruments (micrometers, deflection gages, strain
Thisrelationshipcanbeusedasasimplecheck
...