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
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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.
Contents Page
European foreword . 3
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.
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
ISO 7539-9:2021(E)
© 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
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
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
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.
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
2 © ISO 2021 – All rights reserved
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
K
Ic
25,
R
p02,
and that, where possible, larger specimens where both a and B are at least
K
Ic
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
K
I
25,
R
p02,
and preferably should be not less than
K
I
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
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].
4 © ISO 2021 – All rights reserved
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
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
6 © ISO 2021 – All rights reserved
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
r external radius
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°.
ISO 7539-9:2021(E)
Dimensions in millimetres
Key
a
Mill with a 60° cutter; notch root radius 0,3 mm maximum for all test piece sizes.
Figure 4 — Chevron notch
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 5 a). Alternatively,
separate knife edges can either be screwed or glued onto the specimen at opposite sides of the notch, as
shown in Figure 5 b). Details of a suitable tapered beam displacement gauge are given in Figure 6.
8 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
a) Integral type
b) Screw-on type
NOTE Provided adequate strength can be ensured, the above knife edges can be fixed using adhesive.
Figure 5 — Knife edges for location of displacement gauges
ISO 7539-9:2021(E)
a) Displacement gauge mounted on a test piece
b) Dimensions of beams
10 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
c) Bridge measurement circuit
Key
A, B terminals
V voltage
T , T strain gauges under tension
1 2
C , C strain gauges under compression
1 2
a
This dimension should be 3,8 × the minimum initial gauge length.
b
Beam thickness taper: 0,5 to 0,8.
Strain gauges and materials should be selected to suit the test environment.
Figure 6 — Details of tapered beam displacement gauge
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 crack in
I
specimens or structures of various geometries can be expressed by formulae of the form
Ka =×Q σ ×
I
where
Q is the geometrical constant;
σ is the applied stress;
a is the crack length.
5.3.2 The solutions for K for specimens of particular geometry and loading method can be established
I
by means of finite element stress analysis, or by either experimental or theoretical determinations of
specimen compliance.
5.3.3 K values can be calculated by means of a dimensionless stress intensity coefficient, Y, related
I
to crack length expressed in terms of a/W through relationship of the form, for compact tension and
C-shaped specimens, as shown in:
YP
K =
I
BW
where
ISO 7539-9:2021(E)
P is the width of the specimen;
W is the width of the specimen.
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
n
on the stress intensity can be taken into account by replacing B in the formula above by:
BB ×
n
However, the 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 12135 and Reference [7] provide information for other
geometries.
12 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
YP
K =
I
BW
where
S
is the distance from centre of notch to loading point
Y
1 a
=62, 1 −−1 in the case where S = 1,5W.
()
W
a
1 −
()
W
This formula was originally derived from the combined techniques of stress analysis and compliance
and, although its inaccuracy and validity limits are not well-defined, it has been used over the range
a
02,,≤≤06 . For greater confidence, it is recommended that an empirical compliance be used.
W
NOTE Formulae for other bend specimens can be found in Reference [7].
Figure 7 — Stress intfensity factor solution for cantilever bend specimen
ISO 7539-9:2021(E)
YP
K =
I
BW
a
2+
2 3 4
a a a a
W
where Y = 0,,886+−464133,,2 +1472 −56, .
W W W W
a
1−
W
a
NOTE The inaccuracy of this formula is considered to be no greater than ±0,5 % over the range 02,,≤≤10
W
.
Figure 8 — Stress intensity factor solution for compact tension specimen
14 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
P X a a r a
K = 31++,,9111+−02, 51 1− f
W W W r W
BW√
2
a
√
2 3
a a a a
W
where f = 37,,46−+30 63, 22− ,,43 .
W W W W
a
1−
W
a r
NOTE The accuracy of this formula for for all values of is considered to be as follows: within 1,0 %
W r
a X a X
over the range 04,,50≤≤ 55 and of 0 or 0,5; within 1,5 % for 02,≤≤1 and of 0 or 0,5; within
W W W W
a X
3,0 % for 02, ≤≤1 and 01≤≤ .
W W
Figure 9 — Stress intensity factor solution for C-shaped specimen
5.4 Specimen preparation
5.4.1 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 localized 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.
ISO 7539-9:2021(E)
5.4.2 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.
a) Basic fracture plane identification: Rectangular section
16 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
b) Basic fracture plane identification: c) Basic fracture plane identification:
Cylindrical section with radial grain flow Cylindrical section with axial grain flow
— Axial working direction — Radial working direction
d) Non-basic fracture plane identification
Key
a
Grain flow.
Figure 10 — Fracture plane identification
5.4.3 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.
ISO 7539-9:2021(E)
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,
ISCC
unless facilities are available 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 % of 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 of crack extension, the fatigue
I
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 can be helpful when the K values are
ISCC
expected to be low.
6.4 The final length of the fatigue crack should be such that the requirement for plane strain
predominance is satisfied, i.e.
K
I
a ≥ 25,
R
p02,
This condition is optimized when the final a/W ratio is in the range 0,45 to 0,55.
NOTE Crack size can 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.
a) Bend test piece
18 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
b) Tensile test piece
c) Bend or tensile test piece
a
Edge of test piece.
b
Loading line of test piece.
Figure 11 — Envelope limiting size and form of notch and fatigue crack
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 W = 5 %.
6.7 Additional guidance on fatigue pre-cracking procedures is available in ISO 11782-2, while
ISO 15653 provides guidance for welds.
7 Procedure
7.1 General
Before testing, the thickness B and width W shall be measured to ±0,1 % on a line not further than 10 %
of 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 7.5).
I
ISO 7539-9:2021(E)
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).
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-crack and anticipated crack growth region of the specimen. Crevice problems may also arise where
the specimen emerges from the test cell and these should be avoided by appropriate design of the cell or
by the use of protective coatings at such locations. If total immersion in the corrodent is contemplated,
20 © ISO 2021 – All rights reserved
ISO 7539-9:2021(E)
the loading points should be protected against corrosion. If this is not possible, appropriate measures
shall be taken through,
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...