SIST EN ISO 7539-9:2021
(Main)Corrosion of metals and alloys - Stress corrosion testing - Part 9: Preparation and use of pre-cracked specimens for tests under rising load or rising displacement (ISO 7539-9:2021)
Corrosion of metals and alloys - Stress corrosion testing - Part 9: Preparation and use of pre-cracked specimens for tests under rising load or rising displacement (ISO 7539-9:2021)
1.1 This document specifies procedures for designing, preparing and using pre-cracked specimens for
investigating the susceptibility of metal to stress corrosion cracking (SCC) by means of tests conducted
under rising load or rising displacement. Tests conducted under constant load or constant displacement
are dealt with in ISO 7539-6.
The term “metal” as used in this document includes alloys.
1.2 Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable
for the evaluation of thin products such as sheet or wire and are generally used for thicker products
including plate, bar, and forgings. They can also be used for parts joined by welding.
1.3 Pre-cracked specimens can be stressed quantitatively with equipment for application of a
monotonically increasing load or displacement at the loading points.
1.4 A particular advantage of pre-cracked specimens is that they allow data to be acquired from which
critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components
of known geometry subjected to known stresses. They also enable rates of stress corrosion crack
propagation to be determined.
1.5 A principal advantage of the test is that it takes account of the potential impact of dynamic straining
on the threshold for stress corrosion cracking.
1.6 At sufficiently low loading rates, the threshold stress intensity factor for susceptibility to stress
corrosion cracking, KISCC, determined by this method can be less than or equal to that obtained by
constant load or displacement methods and can be determined more rapidly.
Korrosion von Metallen und Legierungen - Prüfung der Spannungsrisskorrosion - Teil 9: Vorbereitung und Anwendung von angerissenen Proben für die Prüfung mit zunehmender Kraft oder zunehmender Verformung (ISO 7539-9:2021)
1.1 Dieses Dokument legt Verfahren für die Gestaltung, Vorbereitung und Anwendung von angerissenen Proben zur Untersuchung der Beständigkeit von Metallen gegen Spannungsrisskorrosion (SCC, en: stress corrosion cracking) mithilfe von Prüfungen, die mit zunehmender Kraft oder zunehmender Verformung durchgeführt werden, fest. Prüfungen mit konstanter Kraft oder konstanter Verformung werden in ISO 7539 6 behandelt.
In diesem Dokument werden mit der Benennung „Metall“ auch Legierungen erfasst.
1.2 Für die Bewertung dünner Produkte, z. B. Feinbleche oder Drähte, sind angerissene Proben nicht geeignet, weil die Notwendigkeit besteht, die Plastizität an der Rissspitze zu beschränken; sie werden im Allgemeinen zur Bewertung dickerer Produkte angewendet, zu denen Grobbleche, Stangen und Schmiedestücke gehören. Sie können auch zur Bewertung von Schweißverbindungen angewendet werden.
1.3 Zur quantitativen Beanspruchung der angerissenen Proben kann eine Prüfeinrichtung verwendet werden, die an den Kraftangriffspunkten eine monoton zunehmende Kraft oder Verformung aufbringt.
1.4 Ein besonderer Vorteil angerissener Proben ist die Möglichkeit zur Ermittlung von Daten zur Abschätzung kritischer Fehlergrößen, bei deren Überschreitung Spannungsrisse auftreten können, für Komponenten mit bekannter Geometrie, die bekannten Spannungen ausgesetzt werden. Mithilfe von angerissenen Proben ist es ferner möglich, die Ausbreitungsgeschwindigkeit von Spannungskorrosionsrissen zu bestimmen.
1.5 Der wichtigste Vorteil dieser Prüfung ist, dass der potentielle Einfluss einer dynamischen Verformung auf den Wert zur Auslösung von durch Spannungskorrosion erzeugten Rissen berücksichtigt wird.
1.6 Nach diesem Verfahren kann bei einer ausreichend niedrigen Beanspruchungsgeschwindigkeit ein kleinerer oder gleich großer KISCC Wert (kritischer Spannungsintensitätsfaktor für die Beständigkeit gegen Spannungsrisskorrosion) als nach dem Verfahren mit konstanter Kraft oder Verformung ermittelt werden und kann schneller bestimmt werden.
Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 9: Préparation et utilisation des éprouvettes préfissurées pour essais sous charge croissante ou sous déplacement croissant (ISO 7539-9:2021)
1.1 Le présent document spécifie les modes opératoires de conception, de préparation et d’utilisation d’éprouvettes préfissurées servant à évaluer la sensibilité d’un métal à la fissuration par corrosion sous contrainte à l’aide d’essais sous charge croissante ou sous déplacement croissant. Les essais effectués sous charge constante ou sous déplacement constant font l’objet de l’ISO 7539‑6.
Pour les besoins du présent document, le terme « métal » inclut également les alliages.
1.2 Comme il est nécessaire de maintenir la plasticité en fond de fissure, les éprouvettes préfissurées ne se prêtent pas à l’évaluation des produits minces tels que les tôles minces et les fils, et sont généralement utilisées pour des produits plus épais tels que les tôles fortes, les barres et les pièces forgées. Elles peuvent aussi être utilisées pour des pièces assemblées par soudage.
1.3 Les éprouvettes préfissurées peuvent être soumises à une contrainte à l’aide d’appareils exerçant une charge ou un déplacement en croissance constante aux points d’application de charge.
1.4 Les éprouvettes préfissurées présentent l’avantage de permettre l’acquisition de données dont il est possible de déduire les tailles critiques de défaut au‑delà desquelles une fissuration par corrosion sous contrainte peut se produire au niveau de pièces de géométrie connue soumises à des efforts connus. Ces éprouvettes permettent également de déterminer la vitesse de propagation des fissures de corrosion sous contrainte.
1.5 L’essai a pour principal avantage de prendre en compte l’effet potentiel de la déformation dynamique sur la limite de fissuration par corrosion sous contrainte.
1.6 À des taux de charge suffisamment faibles, le facteur d’intensité de contrainte limite pour la fissuration par corrosion sous contrainte KISCC déterminé par cette méthode peut être inférieur ou égal à celui obtenu par des méthodes d’essai sous charge constante ou sous déplacement constant et peut être déterminé plus rapidement.
Korozija kovin in zlitin - Preskušanje napetostne korozije - 9. del: Priprava in uporaba preskušancev z umetno razpoko za preskuse pri naraščajoči obremenitvi ali naraščajoči deformaciji (ISO 7539-9:2021)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 7539-9:2021
01-november-2021
Nadomešča:
SIST EN ISO 7539-9:2008
Korozija kovin in zlitin - Preskušanje napetostne korozije - 9. del: Priprava in
uporaba preskušancev z umetno razpoko za preskuse pri naraščajoči obremenitvi
ali naraščajoči deformaciji (ISO 7539-9:2021)
Corrosion of metals and alloys - Stress corrosion testing - Part 9: Preparation and use of
pre-cracked specimens for tests under rising load or rising displacement (ISO 7539-
9:2021)
Korrosion von Metallen und Legierungen - Prüfung der Spannungsrisskorrosion - Teil 9:
Vorbereitung und Anwendung von angerissenen Proben für die Prüfung mit
zunehmender Kraft oder zunehmender Verformung (ISO 7539-9:2021)
Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 9:
Préparation et utilisation des éprouvettes préfissurées pour essais sous charge
croissante ou sous déplacement croissant (ISO 7539-9:2021)
Ta slovenski standard je istoveten z: EN ISO 7539-9:2021
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 7539-9:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 7539-9:2021
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SIST EN ISO 7539-9:2021
EN ISO 7539-9
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2021
EUROPÄISCHE NORM
ICS 77.060 Supersedes EN ISO 7539-9:2008
English Version
Corrosion of metals and alloys - Stress corrosion testing -
Part 9: Preparation and use of pre-cracked specimens for
tests under rising load or rising displacement (ISO 7539-
9:2021)
Corrosion des métaux et alliages - Essais de corrosion Korrosion von Metallen und Legierungen - Prüfung der
sous contrainte - Partie 9: Préparation et utilisation des Spannungsrisskorrosion - Teil 9: Vorbereitung und
éprouvettes préfissurées pour essais sous charge Anwendung von angerissenen Proben für die Prüfung
croissante ou sous déplacement croissant (ISO 7539- mit zunehmender Kraft oder zunehmender
9:2021) Verformung (ISO 7539-9:2021)
This European Standard was approved by CEN on 24 July 2021.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7539-9:2021 E
worldwide for CEN national Members.
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SIST EN ISO 7539-9:2021
EN ISO 7539-9:2021 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 7539-9:2021
EN ISO 7539-9:2021 (E)
European foreword
This document (EN ISO 7539-9:2021) has been prepared by Technical Committee ISO/TC 156
"Corrosion of metals and alloys" in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys”
the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2022, and conflicting national standards
shall be withdrawn at the latest by February 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 7539-9:2008.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN websites.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 7539-9:2021 has been approved by CEN as EN ISO 7539-9:2021 without any
modification.
3
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SIST EN ISO 7539-9:2021
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SIST EN ISO 7539-9:2021
INTERNATIONAL ISO
STANDARD 7539-9
Second edition
2021-08
Corrosion of metals and alloys —
Stress corrosion testing —
Part 9:
Preparation and use of pre-cracked
specimens for tests under rising load
or rising displacement
Corrosion des métaux et alliages — Essais de corrosion sous
contrainte —
Partie 9: Préparation et utilisation des éprouvettes préfissurées pour
essais sous charge croissante ou sous déplacement croissant
Reference number
ISO 7539-9:2021(E)
©
ISO 2021
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Specimens . 3
5.1 General . 3
5.2 Specimen design . 4
5.3 Stress intensity factor considerations . .11
5.4 Specimen preparation .15
5.5 Specimen identification .17
6 Initiation and propagation of fatigue cracks .18
7 Procedure.19
7.1 General .19
7.2 Environmental considerations .20
7.3 Environmental chamber .20
7.4 Environmental control and monitoring .21
7.5 Selection of initial K value prior to dynamic loading .22
7.6 Determination of K .
ISCC 22
7.6.1 General.22
7.6.2 Determination schedule .22
7.6.3 Validation of test results .24
7.7 Determination of crack velocity .25
8 Test report .25
Annex A (informative) Determination of a suitable displacement rate for determining K
ISCC
from constant displacement rate tests .27
Annex B (informative) Determination of crack growth velocity.29
Annex C (informative) Information on indirect methods for measuring crack length (see
also ISO 21153) .30
Bibliography .32
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
262, Metallic and other inorganic coatings, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 7539-9:2003), which has been technically
revised.
The main change compared to the previous edition is as follows: the formula for K in Figure 9 has been
corrected.
A list of all parts in the ISO 7539 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
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SIST EN ISO 7539-9:2021
INTERNATIONAL STANDARD ISO 7539-9:2021(E)
Corrosion of metals and alloys — Stress corrosion
testing —
Part 9:
Preparation and use of pre-cracked specimens for tests
under rising load or rising displacement
1 Scope
1.1 This document specifies procedures for designing, preparing and using pre-cracked specimens for
investigating the susceptibility of metal to stress corrosion cracking (SCC) by means of tests conducted
under rising load or rising displacement. Tests conducted under constant load or constant displacement
are dealt with in ISO 7539-6.
The term “metal” as used in this document includes alloys.
1.2 Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable
for the evaluation of thin products such as sheet or wire and are generally used for thicker products
including plate, bar, and forgings. They can also be used for parts joined by welding.
1.3 Pre-cracked specimens can be stressed quantitatively with equipment for application of a
monotonically increasing load or displacement at the loading points.
1.4 A particular advantage of pre-cracked specimens is that they allow data to be acquired from which
critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components
of known geometry subjected to known stresses. They also enable rates of stress corrosion crack
propagation to be determined.
1.5 A principal advantage of the test is that it takes account of the potential impact of dynamic straining
on the threshold for stress corrosion cracking.
1.6 At sufficiently low loading rates, the threshold stress intensity factor for susceptibility to stress
corrosion cracking, K , determined by this method can be less than or equal to that obtained by
ISCC
constant load or displacement methods and can be determined more rapidly.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7539-6, Corrosion of metals and alloys — Stress corrosion testing — Part 6: Preparation and use of
precracked specimens for tests under constant load or constant displacement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7539-6 as well as the following
apply.
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp.
3.1
rate of change of crack opening displacement at loading plane
V
LL
deflection at the loading point access measured over a fixed period
3.2
stress intensity factor at crack initiation
K
I-init
stress intensity applied at the commencement of measurable crack growth
3.3
displacement rate
dq/dt
rate of increase of the deflection either measured at the loading point axis or away from the loading line
4 Principle
4.1 The use of pre-cracked specimens acknowledges the difficulty of ensuring that crack-like defects
introduced during either manufacture or subsequent service are totally absent from structures.
Furthermore, the presence of such defects can cause a susceptibility to stress corrosion cracking which in
some materials (e.g. titanium) may not be evident from tests under constant load on smooth specimens.
The principles of linear elastic fracture mechanics can be used to quantify the stress situation existing at
the crack tip in a pre-cracked specimen or structure in terms of the plane strain-stress intensity.
4.2 The test involves subjecting a specimen in which a crack has been developed from a machined notch
by fatigue to an increasing load or displacement during exposure to a chemically agressive environment.
The objective is to quantify the conditions under which environmentally-assisted crack extension can
occur in terms of the threshold stress intensity for stress corrosion cracking, K , and the kinetics of
ISCC
crack propagation.
4.3 Tests may be conducted in tension or in bending. The most important characteristic of the test is
the low loading/displacement rate which is applied.
4.4 Because of the dynamic straining which is associated with this method the data obtained may
differ from those obtained for pre-cracked specimens with the same combination of environment and
material when the specimens are subjected to static loading only.
4.5 The empirical data can be used for design or life prediction purposes in order to ensure either that
the stresses within large structures are insufficient to promote the initiation of environmentally-assisted
cracking at whatever pre-existing defects may be present or that the amount of crack growth which
would occur within the design life or inspection periods can be tolerated without the risk of unstable
failure.
4.6 Stress corrosion cracking is influenced by both mechanical and electrochemical driving forces.
The latter can vary with crack depth, opening or shape because of variations in crack-tip chemistry and
electrode potential and may not be uniquely described by the fracture mechanics stress intensity factor.
4.7 The mechanical driving force includes both applied and residual stresses. The possible influence
of the latter should be considered in both laboratory testing and the application to more complex
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
geometries. Gradients in residual stress in a specimen may result in non-uniform crack growth along the
crack front.
4.8 K is a function of the environment, which should simulate that in service, and of the conditions
ISCC
of loading.
5 Specimens
5.1 General
5.1.1 A wide range of standard specimen geometries of the type employed in fracture toughness
tests may be used, those most commonly employed are described in ISO 7539-6. The particular type of
specimen used will be dependent upon the form, the strength and the susceptibility to stress corrosion
cracking of the material to be tested and also on the objective of the test.
5.1.2 A basic requirement is that the dimensions shall be sufficient to maintain predominantly triaxial
(plane strain) conditions in which plastic deformation is limited in the vicinity of the crack tip. Experience
with fracture toughness testing has shown that for a valid K measurement, both the crack length, a, and
Ic
the thickness, B, should be not less than
2
K
Ic
25,
R
p02,
and that, where possible, larger specimens where both a and B are at least
2
K
Ic
4
R
p,02
should be used to ensure adequate constraint.
From the view of fracture mechanics, a minimum thickness from which an invariant value of K
ISCC
is obtained cannot currently be specified. The presence of an aggressive environment during stress
corrosion may reduce the extent of plasticity associated with fracture and hence the specimen
dimensions needed to limit plastic deformation. However, in order to minimize the risk of inadequate
constraint, it is recommended that similar criteria to those employed during fracture toughness testing
should be employed regarding specimen dimensions, i.e. both a and B should be not less than
2
K
I
25,
R
p02,
and preferably should be not less than
2
K
I
4
R
p,02
where K is the stress intensity to be applied during testing.
I
As a test for its validity, the threshold stress intensity value eventually determined shall be substituted
for K in the first of these formulae.
I
5.1.3 If the specimens are to be used for the determination of K , the initial specimen size should be
ISCC
based on an estimate of the K of the material. In the first instance, it is better to over-estimate the K
ISCC ISCC
value and therefore use a larger specimen than that which may eventually be found necessary. Where
the service application involves the use of material of insufficient thickness to satisfy the conditions for
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
validity, it is permissible to test specimens of similar thickness, provided that it is clearly stated that
the provisional value of K obtained, K , is of relevance only to that specific application. Where it
ISCC QSCC
is required to determine stress corrosion crack growth behaviour as a function of stress intensity, the
specimen size should be based on an estimate of the highest stress intensity at which crack growth rates
are to be measured.
5.1.4 A wide choice of specimen geometries is available to suit the form of the test material, the
experimental facilities available and the objectives of the test. Two basic types of specimen can be used:
a) those intended for being loaded by means of a tensile force;
b) those intended for being loaded by means of a bending force.
This means that crack growth can be studied under either bend or tension loading conditions. The
specimens can be used for either the determination of K by the initiation of a stress corrosion crack
ISCC
from a pre-existing fatigue crack using a series of specimens and for measurements of crack growth
rates. Since the specimens are loaded during exposure to the test environment the risk of unnecessary
incubation periods is avoided.
5.1.5 Crack length measurements can be made readily with a number of continuous monitoring
methods such as the electrical resistance technique (see Annex C).
5.1.6 Bend specimens can in principle be tested in relatively simple cantilever beam equipment but
specimens subjected to tension loading require a tensile test machine.
5.2 Specimen design
5.2.1 The specimens can be subjected to either tension or bend loading. Depending on the design,
tension loaded specimens can experience stresses at the crack tip which are predominantly tensile, as
in remote tension types such as the centre-cracked plate, or contain a significant bend component, as in
crack-line loaded types such as compact tension specimens. The presence of significant bending stress at
the crack tip can adversely affect the crack path stability during stress corrosion testing and can facilitate
crack branching in certain materials. Bend specimens can be loaded in 3-point, 4-point or cantilever
bend fixtures.
5.2.2 The occurrence of crack-line bending with an associated tendency for crack growth out of plane
can be curbed by the use of side grooves.
5.2.3 A number of specimen geometries have specific advantages which have caused them to be
frequently used for rising load/displacement stress corrosion testing. These include
a) compact tension (CTS) specimens which minimize the material requirement;
b) cantilever, three-point, and four-point bend specimens which are easy to machine and inexpensive
to test;
c) C-shaped specimens which can be machined from thick walled cylinders in order to study the radial
propagation of longitudinally oriented cracks.
Details of standard specimen designs for several of these types of specimen are given in Figures 1 to 3.
Further examples for other geomteries including three-point bend can be found in Reference [7].
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Dimensions in millimetres, surface roughness values in micrometres
Key
a effective crack length, a = 0,45W to 0,55W
B thickness, B = 0,5W
l effective notch length, l = 0,25W to 0,45W
N notch width, N = 0,065W maximum (if W > 25 mm) or 1,5 mm maximum (if W ≤ 25 mm)
W width
Figure 1 — Proportional dimensions and tolerances for cantilever, three-point and four-point
bend test pieces
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Dimensions in millimetres, surface roughness values in micrometres
Key
a effective crack length, a = 0,45W to 0,55W
B thickness, B = 0,5W
C total width, C = 1,25W minimum
D hole diameter, D = 0,25W
F half-distance between hole outer edges, F = 1,6D
H half-height, H = 0,6W
l effective notch length, l = 0,25W to 0,40W
N notch width, N = 0,065W maximum
W net width
Figure 2 — Proportional dimensions and tolerances for compact tension test pieces
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Dimensions in millimetres, surface roughness values in micrometres
Key
B thickness, B = 0,50W ± 0,01W
D diameter of holes, D = 0,25W ± 0,005W
l effective notch length, l = 0,3W
N notch width, N = 1,5 mm minimum (0,1W maximum)
r internal radius
1
r external radius
2
T Distance from the hole axis to outer surface, T = 0,25W ± 0,01W
W net width
X distance from the hole axis to a tangent with the inner surface, X = 0,50W ± 0,005W
Z distance from the hole axis to face of specimen, Z = 0,25W ± 0,01W
All surfaces should be perpendicular and parallel, as applicable, to within 0,002W total indicator reading (TIR) and
“E” surfaces should be perpendicular to “Y” surfaces to within 0,02W TIR.
Figure 3 — Proportional dimensions and tolerances for C-shaped test pieces
5.2.4 If required, for example if either fatigue crack initiation or propagation, or both, are difficult to
control satisfactorily, a chevron notch configuration as shown in Figure 4 may be used. If required, its
included angle may be increased from 90° to 120°.
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SIST EN ISO 7539-9:2021
ISO 7539-9:2021(E)
Dimensions in millimetres
Key
...
SLOVENSKI STANDARD
oSIST prEN ISO 7539-9:2020
01-oktober-2020
Korozija kovin in zlitin - Preskušanje napetostne korozije - 9. del: Priprava in
uporaba preskušancev z umetno razpoko za preskuse pri naraščajoči obremenitvi
ali naraščajoči deformaciji (ISO/DIS 7539-9:2020)
Corrosion of metals and alloys - Stress corrosion testing - Part 9: Preparation and use of
pre-cracked specimens for tests under rising load or rising displacement (ISO/DIS 7539-
9:2020)
Korrosion von Metallen und Legierungen - Prüfung der Spannungsrisskorrosion - Teil 9:
Vorbereitung und Anwendung von angerissenen Proben für die Prüfung mit
zunehmender Kraft oder zunehmender Verformung (ISO/DIS 7539 9:2020)
Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 9:
Préparation et utilisation des éprouvettes préfissurées pour essais sous charge
croissante ou sous déplacement croissant (ISO/DIS 7539-9:2020)
Ta slovenski standard je istoveten z: prEN ISO 7539-9
ICS:
77.060 Korozija kovin Corrosion of metals
oSIST prEN ISO 7539-9:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 7539-9:2020
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oSIST prEN ISO 7539-9:2020
DRAFT INTERNATIONAL STANDARD
ISO/DIS 7539-9
ISO/TC 156 Secretariat: SAC
Voting begins on: Voting terminates on:
2020-07-28 2020-10-20
Corrosion of metals and alloys — Stress corrosion
testing —
Part 9:
Preparation and use of pre-cracked specimens for tests
under rising load or rising displacement
Corrosion des métaux et alliages — Essais de corrosion sous contrainte —
Partie 9: Préparation et utilisation des éprouvettes préfissurées pour essais sous charge croissante ou sous
déplacement croissant
ICS: 77.060
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 7539-9:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
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Published in Switzerland
ii © ISO 2020 – All rights reserved
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oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
Contents
1 Scope . 1
2 Normative references . 1
3 Terms and Definitions . 2
4 Principle . 2
5 Specimens . 3
6 Initiation and propagation of fatigue cracks . 7
7 Procedure . 8
8 Test report . 12
9 References . 13
Annex A(Informative)Determination of a suitable displacement rate for determining KISCC
from constant displacement rate tests . 14
Annex B(Informative)Determination of Crack Growth Velocity . 16
Annex C(Informative)Information on indirect methods for measuring crack length (see also ISO
21153). 17
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Foreword
ISO (the International Organisation for Standardisation) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organisations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardisation.
International Standards are drafted in accordance with the rules given in the Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies
for voting. Publication as an International Standard requires approval by at least 75 % of the member
bodies casting a vote.
International Standard ISO 7539-9 was prepared by Technical Committee ISO/TC 156, Corrosion of
metals and alloys, in collaboration with GKSS (Germany).
A list of all parts in the ISO 7539 series can be found on the ISO website.
iv © ISO 2020 – All rights reserved
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oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
Corrosion of metals and alloys - Stress corrosion testing -
Part 9:
Preparation and use of pre-cracked specimens for tests under rising load
or rising displacement
1 Scope
1.1 This part of ISO 7539 covers procedures for designing, preparing and using pre-cracked
specimens for investigating the susceptibility of metal to stress corrosion cracking by means
of tests conducted under rising load or rising displacement. Tests conducted under constant
load or constant displacement are dealt with in ISO 7539-6.
The term "metal" as used in this part of ISO 7539 includes alloys.
1.2 Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not
suitable for the evaluation of thin products such as sheet or wire and are generally used for
thicker products including plate, bar, and forgings. They can also be used for parts joined by
welding.
1.3 Pre-cracked specimens may be stressed quantitatively with equipment for application of
a monotonically increasing load or displacement at the loading points.
1.4 A particular advantage of pre-cracked specimens is that they allow data to be acquired
from which critical defect sizes, above which stress corrosion cracking may occur, can be
estimated for components of known geometry subjected to known stresses. They also enable
rates of stress corrosion crack propagation to be determined.
1.5 A principal advantage of the test is that it takes account of the potential impact of dynamic
straining on the threshold for stress corrosion cracking.
1.6 At sufficiently low loading rates, the K determined by this method can be less than
ISCC
or equal to that obtained by constant load or displacemenet methods and can be determined
more rapidly.
2 Normative references
The following referenced documents are indispensable for the application of this document.T
the latest edition of the referenced document (including any amendments) applies.
ISO 7539-1: Corrosion of metals and alloys - Stress corrosion testing - Part 1: General
guidance on testing procedures.
ISO 7539-6: Corrosion of metals and alloys - Stress corrosion testing—Part 6: Preparation
and use of pre-cracked specimens for tests under constant load or constant displacement.
ISO 7539-7: Corrosion of metals and alloys - Stress corrosion testing—Part 7: Slow strain rate
stress corrosion tests.
ISO 7539-8: Corrosion of metals and alloys - Stress corrosion testing—Part 8:
Preparation and use of specimens to evaluate weldments.
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ISO 11782-2: Corrosion of metals and alloys - Corrosion fatigue testing – Crack propagation
testing using precracked specimens
ISO 12135: Metallic materials -- Unified method of test for the determination of quasistatic
fracture toughness
ISO 15653: Metallic materials — Method of test for the determination of quasistatic fracture
toughness of welds
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in ISO 7539-6 as well as
the following apply.
3.1 rate of change of crack opening displacement at loading plane
𝑉̇
𝐿𝐿
deflection at the loading point access measured over a fixed period
3.2 stress intensity factor at crack
initiation
KI-init
stress intensity applied at the commencement of measurable crack growth
3.3
range of stress intensity factor
∆K , in fatigue
f
algebraic difference between the maximum and minimum stress intensity factors in a
cycle
3.4
displacement
rate dq/dt
rate of increase of the deflection either measured at the loading point axis or away from the loading line
4 Principle
4.1 The use of pre-cracked specimens acknowledges the difficulty of ensuring that crack-
like defects introduced during either manufacture or subsequent service are totally absent from
structures. Furthermore, the presence of such defects can cause a susceptibility to stress
corrosion cracking which in some materials (e.g. titanium) may not be evident from tests under
constant load on smooth specimens. The principles of linear elastic fracture mechanics can be
used to quantify the stress situation existing at the crack tip in a pre-cracked specimen or
structure in terms of the plane strain-stress intensity.
4.2 The test involves subjecting a specimen in which a crack has been developed from a
machined notch by fatigue to an increasing load or displacement during exposure to a
chemically agressive environment. The objective is to quantify the conditions under which
environmentally-assisted crack extension can occur in terms of the threshold stress intensity
for stress corrosion cracking, K , and the kinetics of crack propagation.
ISCC
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4.3 Tests may be conducted in tension or in bending. The most important characteristic of
the test is the low loading/displacement rate which is applied.
4.4 Because of the dynamic straining which is associated with this method the data obtained
may differ from those obtained for pre-cracked specimens with the same combination of
environment and material when the specimens are subjected to static loading only.
4.5 The empirical data can be used for design or life prediction purposes in order to ensure
either that the stresses within large structures are insufficient to promote the initiation of
environmentally-assisted cracking at whatever pre-existing defects may be present or that the
amount of crack growth which would occur within the design life or inspection periods can be
tolerated without the risk of unstable failure.
4.6 Stress corrosion cracking is influenced by both mechanical and electrochemical driving
forces. The latter can vary with crack depth, opening or shape because of variations in crack-
tip chemistry and electrode potential and may not be uniquely described by the fracture
mechanics stress intensity factor.
4.7 The mechanical driving force includes both applied and residual stresses. The possible
influence of the latter should be considered in both laboratory testing and the application to
more complex geometries. Gradients in residual stress in a specimen may result in non-
uniform crack growth along the crack front.
4.8 K is a function of the environment, which should simulate that in service, and of the
ISCC
conditions of loading.
5 Specimens
5.1 General
5.1.1 A wide range of standard specimen geometries of the type employed in fracture
toughness tests may be used, those most commonly employed are described in ISO 7539-6.
The particular type of specimen used will be dependent upon the form, the strength and the
susceptibility to stress corrosion cracking of the material to be tested and also on the objective
of the test.
5.1.2 A basic requirement is that the dimensions shall be sufficient to maintain predominantiy
triaxial (plane strain) conditions in which plastic deformation is limited in the vicinity of the crack
tip. Experience with fracture toughness testing has shown that for a valid K measurement,
lc
both the crack length, a, and the thickness, B, should be not less than
2
K
Ic
2,5
R
p0,2
and that, where possible, larger specimens where both a and B are at least
2
K
Ic
4
R
p0,2
should be used to ensure adequate constraint.
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From the view of fracture mechanics, a minimum thickness from which an invariant value of
K is obtained cannot cuurently be specified. The presence of an aggressive environment
ISCC
during stress corrosion may reduce the extent of plasticity associated with fracture and hence
the specimen dimensions needed to limit plastic deformation. However, in order to minimize
the risk of inadequate constraint, it is recommended that similar criteria to those employed
during fracture toughness testing should be employed regarding specimen dimensions, i.e.
both a and B should be not less than
2
K
I
2,5
R
p0,2
and preferably should be not less than
2
K
I
4
R
p0,2
where K is the stress intensity to be applied during testing.
I
As a test for its validity, the threshold stress intensity value eventually determined shall be
substituted for K in the first of these expressions.
I
5.1.3 If the specimens are to be used for the determination of K , the initial specimen size
ISCC
should be based on an estimate of the K of the material (in the first instance, it being better
ISCC
to over-estimate the K value and therefore use a larger specimen than may eventually be
ISCC
found necessary). Where the service application involves the use of material of insufficient
thickness to satisfy the conditions for validity, it is permissible to test specimens of similar
thickness, provided that it is clearly stated that the threshold intensity value obtained, K ,
QSCC
is of relevance only to that specific application. Where it is required to determine stress
corrosion crack growth behaviour as a function of stress intensity, the specimen size should
be based on an estimate of the highest stress intensity at which crack growth rates are to be
measured.
5.1.4 A wide choice of specimen geometries is available to suit the form of the test material,
the experimental facilities available and the objectives of the test. Two basic types of specimen
can be used
a) those intended for being loaded by means of a tensile force;
b) those intended for being loaded by means of a bending force.
This means that crack growth can be studied under either bend or tension loading conditions.
The specimens can be used for either the determination of K by the initiation of a stress
ISCC
corrosion crack from a pre-existing fatigue crack using a series of specimens and for
measurements of crack growth rates. Since the specimens are loaded during exposure to the
test environment the risk of unnecessary incubation periods is avoided.
5.1.5 Crack length measurements can be made readily with a number of continuous
monitoring methods such as the electrical resistance technique (Appendix C).
5.1.6 Bend specimens can in principle be tested in relatively simple cantilever beam
equipment but specimens subjected to tension loading require a tensile test machine.
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5.2 Specimen design
5.2.1 The specimens can be subjected to either tension or bend loading. Depending on the
design, tension loaded specimens can experience stresses at the crack tip which are
predominantly tensile (as in remote tension types such as the centre-cracked plate) or contain
a significant bend component (as in crack-line loaded types such as compact tension
specimens). The presence of significant bending stress at the crack tip can adversely affect
the crack path stability during stress corrosion testing and can facilitate crack branching in
certain materials. Bend specimens can be loaded in 3-point, 4-point or cantilever bend fixtures.
5.2.2 The occurrence of crack-line bending with an associated tendency for crack growth out
of plane can be curbed by the use of side grooves.
5.2.3 A number of specimen geometries have specific advantages which have caused them
to be frequently used for rising load/displacement stress corrosion testing. These include
a) compact tension (CTS) specimens which minimize the material requirement;
b) cantilever, three-point, and four-point bend specimens which are easy to machine and
inexpensive to test;
c) C-shaped specimens which can be machined from thick walled cylinders in order to study
the radial propagation of longitudinally oriented cracks.
Details of standard specimen designs for several of these types of specimen are given in
Figures 1 to 3. Further examples for other geomteries including three-point bend can be found
in Reference 1.
5.2.4 If required, for example if fatigue crack initiation and/or propagation is difficult to control
satisfactorily, a chevron notch configuration as shown in Figure 4 may be used. If required, its
included angle may be increased from 90° to 120°.
5.2.5 Where it is necessary to measure crack opening displacements knife edges for the
location of displacement gauges can be machined into the mouth of the notch, as shown in
Figure 5a). Alternatively, separate knife edges can either be screwed or glued onto the
specimen at opposite sides of the notch, as shown in Figure 3b) Details of a suitable tapered
beam displacement gauge are given in Figure 3c).
5.3 Stress intensity factor considerations
5.3.1 It can be shown using elastic theory that the stress intensity, K , acting at the tip of a
I
crack in specimens or structures of various geometries can be expressed by relationships of
the form
K = Q a
I
where
Q is the geometrical constant,
is the applied stress in MPa,
a is the crack length in metres.
5.3.2 The solutions for K for specimens of particular geometry and loading method can be
I
established by means of finite element stress analysis, or by either experimental or theoretical
determinations of specimen compliance.
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5.3.3 K values can be calculated by means of a dimensionless stress intensity coefficient, Y,
l
related to crack length expressed in terms of a/W through relationship of the form
YP
K =
I
B W
for compact tension and C-shaped specimens, where W is the width of the specimen in
metres and P is the applied load.
5.3.4 Where it is necessary to use side-grooved specimens in order to curb crack branching
tendencies, etc., shallow side grooves (usually 5 % of the specimen thickness on both sides)
can be used. Either semi-circular or 60° V-grooves can be used, but it should be noted that
even with semi-circular side grooves of up to 50 % of the specimen thickness it is not always
possible to maintain the crack in the desired plane of extension. Where side grooves are
employed, the effect of the reduced thickness, B , due to the grooves on the stress intensity
n
can be taken into account by replacing B by B B in the above expression. However, the
n
influence of side grooving on the stress intensity factor is far from established and correction
factors should be treated with caution, particularly if deep side grooves are used.
5.3.5 Solutions for Y for specimens with geometries which are often used for stress corrosion
testing are given in Figures 7 to 9. ISO 11782-2, ISO 13235 and Reference 1 provide
information for other geometries.
5.4 Specimen preparation
Residual stresses can have an influence on stress corrosion cracking. The effect can be
significant when test specimens are removed from material in which complete stress relief is
impractical, such as weldments, as-quenched materials and complex forged or extruded
shapes. Residual stresses superimposed on the applied stress can cause the localised crack-
tip stress intensity factor to be different from that computed solely from externally applied loads.
The presence of significant residual stress often manifests itself in the form of irregular crack
growth, namely excessive crack front curvature or out-of-plane crack growth, Measurement of
residual stress is desirable.
5.4.1 Specimens of the required orientation (see Figure 10) shall, where possible, be
machined in the fully heat-treated condition. For specimens in material that cannot easily be
completely machined in the fully heat-treated condition, the final heat treatment may be given
prior to the notching and finishing operations provided that at least 0.5 mm per face is removed
from the thickness at this finish machining stage. However, heat treatment may be carried out
on fully machined specimens in cases in which heat treatment will not result in detrimental
surface conditions, residual stress, quench cracking or distortion.
5.4.2 After machining, the specimens shall be fully degreased in order to ensure that no
contamination of the crack tip occurs during subsequent fatigue pre-cracking or stress
corrosion testing. In cases where it is necessary to attach electrodes to the specimen by
soldering or brazing for crack monitoring by means of electrical resistance measurements, the
specimens shall be fully degreased following this operation prior to pre-cracking in order to
remove traces of remnant flux.
5.5 Specimen identification
Specimen identification marks may be stamped or scribed on either the face of the specimen
bearing the notch or on the end faces parallel to the notch.
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6 Initiation and propagation of fatigue cracks
6.1 The machine used for fatigue cracking shall have a method of loading such that the
stress distribution is symmetrical about the notch and the inaccuracy in measurement of
applied load is not greater than 2.5 %.
6.2 The environmental conditions employed during fatigue pre-cracking, as well as the
stressing conditions, can influence the subsequent behaviour of the specimen during stress
corrosion testing. In some materials the introduction of the stress corrosion test environment
during the pre-cracking operation will promote a change from the normal ductile transgranular
mode of fatigue cracking to one which more closely resembles stress corrosion cracking. This
may facilitate the subsequent initiation of stress corrosion cracking and lead to the
determination of conservative initiation values of K . However, unless facilities are available
ISCC
to commence stress corrosion testing immediately following the pre-cracking operation,
corrodant remaining at the crack tip may promote blunting due to corrosive attack.
Furthermore, the repeatability of results may suffer when pre-cracking is conducted in the
presence of an aggressive environment because of the greater sensitivity of the corrosion
fatigue fracture mode to the cyclic loading conditions. In addition, more elaborate facilities may
be needed for environmental control purposes during pre-cracking. For these reasons, it is
recommended that, unless agreed otherwise between the parties, fatigue pre-cracking should
be conducted in the normal laboratory air environment.
6.3 The specimens shall be pre-cracked by fatigue loading with an R value in the range 0 to
0.1 until the crack extends at least 2.5 % W or 1.3 mm beyond the notch at the side surfaces,
whichever is greater. The crack may be started at higher K values but, during the final 0.5 mm
I
of crack extension, the fatigue pre-cracking shall be completed at as low a maximum stress
intensity as possible (below the expected K ).
ISCC
NOTE Load shedding procedures as described in ISO 11782-2 may be helpful when the
K values are expected to be low.
ISCC
6.4 The final length of the fatigue crack should be such that the requirement for plane strain
predominance is satisfied, i.e.
2
K
I
a 2,5
R
p0,2
This condition is optimized when the final a/W ratio is in the range 0,45 to 0,55.
NOTE Crack size may be important in relation to SCC.
6.5 In order to avoid the interaction of the stress field associated with the crack with that due
to the notch, the crack should lie within the limiting envelope as shown in Figure 11.
6.6 In order to ensure the validity of the stress intensity analysis, the fatigue crack should be
inspected on each side of the specimen to ensure that no part of it lies in a plane the slope of
which exceeds an angle of 10° from the plane of the notch and that the difference in lengths
does not exceed 5 % W.
6.7 Additional guidance on fatigue pre-cracking procedures is available in ISO 11782-2,
while ISO 15653 provides guidance for welds.
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7 Procedure
7.1 General
7.1.3 Before testing, the thickness B and width W shall be measured to within 0.1 % W on a
line not further than 10 % W from the crack plane. The average length of the fatigue pre-crack
on both sides of the specimen shall also be determined and this value is used in assessing the
pre-load required to produce the desired initial stress intensity, K (see 7.6).
I
7.2 Environmental considerations
7.2.1 Because of the specificity of metal-environment interactions, it is essential that stress
corrosion crack propagation tests are conducted under environmental conditions which are
closely controlled (see 7.2.3 and 7.2.4 below).
7.2.2 The environmental testing conditions will depend upon the intent of the test but, ideally,
should be the same as those prevailing for the intended use of the alloy or comparable to the
anticipated service condition.
7.2.3 Environmental factors of importance are electrode potential, temperature, solution
composition, pH, concentration of dissolved gases, flowrate and pressure. ISO 7539-1
provides useful background information. In relation to gaseous environments a critical factor
is purity of the gas.
7.2.4 Tests may be conducted under open circuit conditions in which the electrode potential of
the metal is dependent on the specific environmental conditions of the test, of which the degree
of aeration is an important factor. Alternatively, the electrode potential may be displaced from
the open circuit value by potentiostatic or galvanostatic methods.
7.2.5 Auxiliary electrodes to apply external current should be designed to produce uniform
current distribution on the specimen, i.e. the electrode potential should be constant.
7.2.6 When practical, it is recommended that the specimens be stressed after being brought
into contact with the test environment. Otherwise, the stressed specimens should be exposed
to the test environment as soon as possible after stressing.
7.3 Environmental chamber
7.3.1 The environmental chamber shall completely enclose the test section of the specimen.
Wherever possible, the gripped portions shall be excluded from contact with the solution
environment to prevent galvanic effects and crevice corrosion. These problems can be
overcome by the use of a local environmental cell of the type shown in Figure 12 in which the
environment is circulated around the vicinity of the notch, pre-cr
...
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