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)

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

Status
Published
Public Enquiry End Date
14-Oct-2020
Publication Date
21-Sep-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
15-Sep-2021
Due Date
20-Nov-2021
Completion Date
22-Sep-2021

RELATIONS

Buy Standard

Standard
SIST EN ISO 7539-9:2021
English language
39 pages
sale 10% off
Preview
sale 10% off
Preview
e-Library read for
1 day
Draft
oSIST prEN ISO 7539-9:2020
English language
36 pages
sale 10% off
Preview
sale 10% off
Preview
e-Library read for
1 day

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.

---------------------- Page: 1 ----------------------
SIST EN ISO 7539-9:2021
---------------------- Page: 2 ----------------------
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.
---------------------- Page: 3 ----------------------
SIST EN ISO 7539-9:2021
EN ISO 7539-9:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
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.
---------------------- Page: 5 ----------------------
SIST EN ISO 7539-9:2021
---------------------- Page: 6 ----------------------
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
---------------------- Page: 7 ----------------------
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
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
---------------------- Page: 8 ----------------------
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

© ISO 2021 – All rights reserved iii
---------------------- Page: 9 ----------------------
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
---------------------- Page: 10 ----------------------
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.
© ISO 2021 – All rights reserved 1
---------------------- Page: 11 ----------------------
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
deflection at the loading point access measured over a fixed period
3.2
stress intensity factor at crack initiation
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
---------------------- Page: 12 ----------------------
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

the thickness, B, should be not less than
 
25,
 
 
p02,
 
and that, where possible, larger specimens where both a and B are at least
 
 
 
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

 
25,
 
 
p02,
 
and preferably should be not less than
 
 
 
p,02
 
where K is the stress intensity to be applied during testing.

As a test for its validity, the threshold stress intensity value eventually determined shall be substituted

for K in the first of these formulae.

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 2021 – All rights reserved 3
---------------------- Page: 13 ----------------------
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].

4 © ISO 2021 – All rights reserved
---------------------- Page: 14 ----------------------
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
© ISO 2021 – All rights reserved 5
---------------------- Page: 15 ----------------------
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

6 © ISO 2021 – All rights reserved
---------------------- Page: 16 ----------------------
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
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 2021 – All rights reserved 7
---------------------- Page: 17 ----------------------
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.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 7539-9:2020
---------------------- Page: 2 ----------------------
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
---------------------- Page: 3 ----------------------
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

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 2020 – All rights reserved
---------------------- Page: 4 ----------------------
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

© ISO 2020 – All rights reserved iii
---------------------- Page: 5 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
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
---------------------- Page: 6 ----------------------
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.
© ISO 2020 – All rights reserved 1
---------------------- Page: 7 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)

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

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
2 © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)

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,

both the crack length, a, and the thickness, B, should be not less than
 
2,5 
 
p0,2
and that, where possible, larger specimens where both a and B are at least
 
4 
 p0,2
should be used to ensure adequate constraint.
© ISO 2020 – All rights reserved 3
---------------------- Page: 9 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)

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
 
2,5 
 
p0,2
and preferably should be not less than
 
4 
 
p0,2
where K is the stress intensity to be applied during testing.

As a test for its validity, the threshold stress intensity value eventually determined shall be

substituted for K in the first of these expressions.

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.

4 © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
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

crack in specimens or structures of various geometries can be expressed by relationships of

the form
K = Q a
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

established by means of finite element stress analysis, or by either experimental or theoretical

determinations of specimen compliance.
© ISO 2020 – All rights reserved 5
---------------------- Page: 11 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)

5.3.3 K values can be calculated by means of a dimensionless stress intensity coefficient, Y,

related to crack length expressed in terms of a/W through relationship of the form

K =
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

can be taken into account by replacing B by B B in the above expression. 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 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.
6 © ISO 2020 – All rights reserved
---------------------- Page: 12 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(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, 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

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.
 
a  2,5  
 
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.
© ISO 2020 – All rights reserved 7
---------------------- Page: 13 ----------------------
oSIST prEN ISO 7539-9:2020
ISO/DIS 7539-9:2020(E)
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).
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
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.