Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and use of pre-cracked specimens (ISO 7539-6:1989)

Korrosion der Metalle und Legierungen - Prüfung der Spannungsrißkorrosion - Teil 6: Vorbereitung und Anwendung von angerissenen Proben (ISO 7539-6:1989)

Der vorliegende Teil von ISO 7539 behandelt Verfahren für die Gestaltung, Vorbereitung und Anwendung von angerissenen Proben zur Untersuchung der Anfälligkeit von Metallen für Spannungsrißkorrosion. Empfehlungen in Bezug auf gekerbte Proben werden im Anhang A gegeben. In diesem Teil von ISO 7539 werden mit der Benennung "Metall" auch Legierungen erfaßt.

Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 6: Préparation et utilisation des éprouvettes préfissurées (ISO 7539-6:1989)

Korozija kovin in zlitin - Ugotavljanje pokanja zaradi napetostne korozije - 6. del: Priprava in uporaba preskušancev z umetno razpoko (ISO 7539-6:1989)

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SIST EN ISO 7539-6:1999

Korozija kovin in zlitin - Ugotavljanje pokanja zaradi napetostne korozije - 6. del:

Priprava in uporaba preskušancev z umetno razpoko (ISO 7539-6:1989)

Corrosion of metals and alloys - Stress corrosion testing - Part 6: Preparation and use of

pre-cracked specimens (ISO 7539-6:1989)

Korrosion der Metalle und Legierungen - Prüfung der Spannungsrißkorrosion - Teil 6:

Vorbereitung und Anwendung von angerissenen Proben (ISO 7539-6:1989)

Corrosion des métaux et alliages - Essais de corrosion sous contrainte - Partie 6:

Préparation et utilisation des éprouvettes préfissurées (ISO 7539-6:1989)
Ta slovenski standard je istoveten z: EN ISO 7539-6:1995
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 7539-6:1999 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 7539-6:1999
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SIST EN ISO 7539-6:1999
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SIST EN ISO 7539-6:1999
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SIST EN ISO 7539-6:1999
First edition
Corrosion of metals and alloys - Stress
corrosion testing -
Part 6:
Preparation and use of pre-cracked specimens
Essais de corrosion sous contrainte -
Corrosion des mhtaux et alliages -
Partie 6: Prbparation et utilisation des kprouvettes prkfissurkes
Reference number
ISO 7539-6 : 1989 (E)
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (E)

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. Esch 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, govern-

mental 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.

Draft International Standards adopted by the technical committees are circulated to

the member bodies for approval before their acceptance as International Standards by

the ISO Council. They are approved in accordance with ISO procedures requiring at

least 75 % approval by the member bodies voting.

International Standard ISO 7539-6 was prepared by Technical Committee ISO/TC 156,

Corrosion of metals and alloys.

ISO 7539 consists of the following Parts, under the general title Corrosion of metals

and alloys - S tress corrosion testing :
Part 1: General guidance on testing procedures
Part 2: Preparation and use of bent-beam specimens
Part 3: Preparation and use of U-bend specimens
Part 4: Preparation and use of uniaxially loaded tension specimens
Part 5: Preparation and use of C-ring specimens
Part 6: Preparation and use of pre-cracked specimens
- Part 7: Slow strain rate testing
Part 8: Preparation and use of welded specimens
Annex A forms an integral part of this part of ISO 7599.
0 ISO 1989

All rights reserved. No part of this publication may be reproduced or utilized in any form or by any

means, electronie or mechanical, including photocopying and microfilm, without Permission in

writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-121 1 Geneve 20 l Switzerland
Printed in Switzerland
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (El

This part of ISO 7539 is one of a series giving procedures for designing, preparing and

using various forms of test specimen to carry out tests to establish a metals resistance

to stress corrosion.

Esch of the Standards in the series needs to be read in association with ISO 7539-1.

This helps in the choice of an appropriate test procedure to suit particular

circumstances as well as giving guidance towards assessing the significance of the

results of the tests.
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SIST EN ISO 7539-6:1999
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (E)
Corrosion of metals and alloys - Stress corrosion
testing -
Part 6:
Preparation and use of pre-cracked specimens
3 Definitions
1 Scope
For the purposes of this part of ISO 7539, the following
1.1 This part of ISO 7539 covers procedures for designing,
definitions and those given in ISO 7539-1 apply.
preparing and using pre-cracked specimens for investigating
susceptibility to stress corrosion. Recommendations concern-
31 Crack length, a : The effective Crack length measured
ing notched specimens are given in annex A.
from the Crack tip to either the mouth of the notch or the
loading Point axis depending on the specimen geometry.
The term “metal” as used in this part of ISO 7539 includes
3.2 specimen width, W : The effective width of the
specimen measured from the back face to either the face con-
1.2 Because of the need to maintain elastically constrained
taining the notch or the loading plane depending on the
conditions at the Crack tip, pre-cracked specimens are not
specimen geometry.
suitable for the evaluation of thin products such as sheet or
wire and are generally used for thicker products including plate,
33 . specimen thickness, B.
bar and forgings. They tan also be used for Parts joined by
Self-explanatory term.
1.3 Pre-cracked specimens may be stressed quantitatively
34 .
reduced thickness at side grooves, B,.
with equipment for application of a constant load or a
Self-explanatory term.
monotonically increasing load or tan incorporate a device to
produce a constant displacement at the loading Points.
3.5 specimen half-height, H.
1.4 A particular advantage of pre-cracked specimens is that
Self-explanatory term.
they allow data to be acquired from which critical defect sizes,
above which stress corrosion cracking may occur, tan be
3.6 applied load, P.
estimated for components of known geometry subjected to
known Stresses. They also enable rates of stress corrosion
Self-explanatory term.
Crack propagation to be determined.
3.7 deflection at loading Point axis, Vv.
2 Normative reference
Self-explanatory term.
The following Standard contains provisions which, through
3.8 deflection away from the loading line, V.
reference in this text, constitute provisions of this part of
Self-explanatory term.
ISO 7539. At the time of publication, the edition indicated was
valid. All Standards are subject to revision, and Parties to

agreements based on this patt of ISO 7539 are encouraged to 3.9 Modulus of elasticity, E.

investigate the possibility of applying the most recent edition of
Self-explanatory term.
the Standard indicated below. Members of IEC and ISO main-
tain registers of currently valid International Standards.
3.10 stress intensity factor coefficient, Y : A factor de-

ISO 7539-1 : 1987, Corrosion of metals and alo ys - Stress rived from the stress analysis for a particular specimen

geometry which relates the stress intensity factor for a given
corrosion testing - Part 7: General guidance on testing pro-
cedures. Crack length to the load and specimen dimensions.
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (E)

3.11 plane strain stress intensity factor, K, : A function of 3.25 specimen orientation : The fracture plane of the

specimen identified in terms of firstly the direction of stressing
applied load, Crack length and specimen geometry having

dimensions of stress x length which uniquely defines the and secondly the direction of Crack growth expressed with

elastic stress field intensification at the tip of a Crack subjected respect to three reference axes. These are identified by the

to opening mode displacements : letters X, Y and Z where : Z is coincident with the main working

forte employed during manufacture of the material (short-
K, = applied stress 9 &@%, in N 1 m -3~
transverse axis); X is coincident with the direction of grain flow
(longitudinal axis); and Y is normal to the X and Z axes (sec
figure 6).
3.12 initial stress intensity factor, K,i.
Self-explanatory term.
4 Principle
3.13 plane strain fracture toughness, K,,: The critical

value of K, at which the first significant environmentally 4.1 The use of pre-cracked specimens acknowledges the

independent extension of the Crack occurs under the influence
difficulty of ensuring that Crack-like defects introduced during
of rising stress intensity under conditions of high constraint to
either manufacture or subsequent Service are totally absent
plastic deformation.
from structures. Furthermore, the presence of such defects tan
Cause a susceptibility to stress corrosion cracking which in
some materials (e.g. titanium) may not be evident from tests
3.14 a provisional value of K,,. K,: K, = K,, when the
under constant load on smooth specimens. The principles of
validity criteria for plane strain predominance are satisfied.
linear elastic fracture mechanics tan be used to quantify the
stress Situation existing at the Crack tip in a pre-cracked
3.15 threshold stress intensity factor for susceptibility
specimen or structure in terms of the plane strain-stress inten-
to stress corrosion cracking, K,,,,: That stress intensity
factor above which stress corrosion cracking will initiate and
grow for the specified test conditions under conditions of high
4.2 The test involves subjecting a specimen in which a Crack
constraint to plastic deformation, i.e. under plane strain pre-
has been developed from a machined notch by fatigue to either
dominant conditions.
a constant load or displacement at the loading Points or to an
increasing load during exposure to a chemically aggressive
3.16 a provisional vaIue of K,,,,, KOSCC: K,,,, = K,,,,
environment. The objective is to quantify the conditions under
when the validity criteria for plane strain predominance are
which environmentally-assisted Crack extension tan occur in
terms of the threshold stress intensity for stress corrosion
cracking, K,,,,, and the kinetics of Crack propagation.
3.17 fatigue stress intensity, Kf: The plane strain stress
intensity corresponding to the maximum forte of the fatigue
4.3 The empirical data tan be used for design or life pre-
diction purposes in Order to ensure either that the Stresses
within large structures are insufficient to promote the initiation

3.18 fatigue stress intensity range, AK,. of environmentally-assisted cracking at whatever pre-existing

defects may be present or that the amount of Crack growth
Self-explanatory term.
which would occur within the design life or inspection periods
tan be tolerated without the risk of unstable failure.
3-W 0,2 % proof stress, RP0 2.
Self-explanatory term. 5 Spetimens
3.20 5.1 General
applied stress, 0.
Self-explanatory term.
5.1.1 A wide range of Standard specimen geometries of the
type employed in fracture toughness tests may be used. The

3.21 geometrical correction factor, Q. particular type of specimen used will be dependent upon the

form, the strength and the susceptibility to stress corrosion
Self-explanatory term.
cracking of the material to be tested and also on the objective
of the test.
3.22 fatigue forte ratio, R : The algebraic ratio of minimum

to maximum forte in the fatigu e cycle. 5.1.2 A basic requirement is that the dimensions shall be

sufficient to maintain predominantly triaxial (plane strain) con-
ditions in which plastic deformation is limited in the vicinity of
3.23 Crack velocity : The instantaneous rate of stress cor-
the Crack tip. Experience with fracture toughness testing has
rosion Crack propagation measured by a continuous Crack
shown that for a valid K,, measurement, both the Crack length,
monitoring technique.
a, and the thickness, B, should be not less than
3.24 average Crack velocity : The average rate of Crack
propagation calculated by dividing the Change in Crack length
due to stress corrosion by the test duration.
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (El
corrosion Cracks from the fatigue pre-Crack, in which case a
and that, where possible, larger specimens where both a and B
are at least series of specimens must be used to pin-Point the threshold
value, or by the arrest of a propagating Crack since under con-
stant displacement testing conditions the stress intensity
Klc 2
decreases progressively as Crack propagation occurs. In this
( PU )
case a Single specimen will suffice in principle, but in practice
the use of several specimens (not less than 3) is often recom-
should be used to ensure adequate constraint.
mended, taking into account the disadvantages described
in 5.1.6.
From the view of fracture mechanics, a minimum thickness
from which an invariant value of K,,,, is obtained cannot be
5.1.6 The disadvantages of constant displacement specimens
specified at this time. The presence of an aggressive environ-
ment during stress corrosion may reduce the extent of plasticity
associated with fracture and hence the specimen dimensions
a) applied loads tan only be measured indirectly by
needed to limit plastic deformation. However, in Order to
displacement changes;
minimize the risk of inadequate constraint, it is recommended
that similar criteria to those employed during fracture
b) Oxide formation or corrosion products tan either wedge
toughness testing should be employed regarding specimen
open the Crack surfaces, thus changing the applied dis-
dimensions, i.e. both a and B should be not less than
placement and load, or tan block the Crack mouth, thus
preventing the ingress sf corrodant and tan impair the
accuracy of Crack length measurements by electrical
z5 jj--
resistance methods;
( >
c) Crack branching, blunting or growth out of plane tan
and preferably should be not less than
invalidate Crack arrest data;
d) Crack arrest must be defined by Crack growth below
some arbitrary rate which tan be difficult to measure
( )
where K, is the stress intensity to be applied during testing.
e) elastic relaxation of the loading System during Crack
growth tan Cause increased displacement and higher loads
The threshold stress intensity value eventually determined
than expected;
should be substituted for K, in the first of these expressions as a
test for its validity.
fl plastic relaxation due to time-dependent processes
within the specimen tan Cause lower loads than expected;
5.1.3 If the specimens are to be used for the determination of
g) it is sometimes impossible to introduce the test environ-
KIScc, the initial specimen size should be based on an estimate
ment Prior to application of the load which tan retard Crack
of the K,scc of the material (in the first instance, it being better
value and therefore use a larger initiation during subsequent testing.
to over-estimate the K,,,,
specimen than may eventually be found necessary). Where the
Service application involves the use of material of insufficient
5.1.7 Constant load specimens have the advantage that stress
thickness to satisfy the conditions for validity, it is permissible
Parameters tan be quantified with confidence. Since Crack
to test specimens of similar thickness, provided that it is clearly
growth results in increasing Crack opening there is less
stated that the threshold intensity value obtained, K,,,,, is of
likelihood that Oxide films will either block the Crack or wedge it
relevante only to that specific application. Where it is required
open. Crack length measurements tan be made readily with a
to determine stress corrosion Crack growth behaviour as a
number of continuous monitoring methods. A wide choice of
function of stress intensity, the specimen size should be based
constant load specimen geometries is available to suit the form
on an estimate of the highest stress intensity at which Crack
of the test material, the experimental facilities available and the
growth rates are to be measured.
objectives of the test. This means that Crack growth tan be
studied under either bend or tension loading conditions. The
specimens tan be used for either the determination of K,,,, by
5.1.4 Two basic types of specimen tan be used
the initiation of a stress corrosion Crack from a pre-existing
fatigue Crack using a series of specimens or for measurements
a) those intended for testing under constant displace-
of Crack growth rates. Constant load specimens tan be loaded
ment, which are invariably self-loaded by means of built-in
during exposure to the test environment in Order to avoid the
loading bolts;
risk of unnecessary incubation periods.
b) those intended for testing under constant load, for
which an external means of load application is required.
5.1.8 The principal disadvantage of constant load specimens
is the expense and bulk associated with the need for an external
loading System. Bend specimens tan be tested in relatively
5.1.5 Constant displacement specimens, being self-loaded,
simple cantilever beam equipment but specimens subjected to
have the advantage of economy in use since no external stress-
tension loading require constant load creep rupture or similar
ing equipment is required. Their compact dimensions also
testing machines. In this case the expense tan be minimized by
facilitate exposure to operating Service environments. They tan
testing chains of specimens connected by loading links which
be used for the determination of K Iscc by the initiation of stress
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (E)

are designed to prevent unloading on the failure of specimens. b 1 compact tension (CTS) specimens which minimize the

The size of these loading Systems means that it is difficult to material requirement for constant load testing;

test constant load specimens under operating conditions but
c) self-loaded double cantilever beam (DCB) specimens
they tan be tested in environments bled off from operating
which are easy to test under constant displacement in ser-
vice situations;
5.2 Specimen design
d) T-type wedge opening loaded IT-WOL) specimens
which are also self-loaded and minimize the material require-
some of the pre-cracked specimen
Figure 1 Shows geometries
ment for constant displacement testing;
which are used for stress corrosion testing.
C-shaped specimens which tan be machined from thick
5.2.1 Constant load specimens tan be of two distinct types
walled cylinders in Order to study the radial propagation of
longitudinally oriented Cracks under constant load.
in which the stress intensity increases with
a) those
increasing Crack length;
Details of Standard specimen designs for each of these types of
specimen are given in figures 2a) to e).
b) those in which the stress intensity is eff ectively
independent of Crack
5.2.6 If required, for example if fatigue Crack initiation and/or
propagation is difficult to control satisfactorily, a chevron notch
Type a) is suitable for K,scc determinations and studies of
configuration as shown in figure 3 may be used. If uired, its
Crack propagation rates as a function of K,, while type b) is
increased from
included angle may be 9o” to 120°
useful for fundamental studies of stress corrosion mechanisms.
5.2.7 Where it is necessary to mesure Crack opening
5.2.2 Increasing K constant load specimens tan be subjected
displacements, as during the application of deflection to con-
to either tension or bend loading. Depending on the design,
stant displacement specimens, knife edges for the location of
tension loaded specimens tan experience Stresses at the Crack
displacement gauges tan be machined into the mouth of the
tip which are predominantly tensile (as in remote tension types
notch, as shown in figure 4a). Alternatively, separate knife
such as the centre-cracked plate) or contain a significant bend
edges tan either be screwed or glued onto the specimen at
component (as in crackline loaded types such as compact ten-
opposite sides of the notch, as shown in figure 4b). Details of a
sion specimens). The presence of significant bending stress at
are given in
suitable tapered displacement
the Crack tip tan adversely affect the Crack path stability during WKP
figure 4
stress corrosion testing and tan facilitate Crack branching in Cl.
certain materials. Bend specimens tan be loaded in 3-Point,
4-Point or cantilever bend fixtures.
5.3 Stress intensity factor considerations
5.2.3 Constant K constant load specimens tan be subjected
5.3.1 lt tan be shown using elastic theory that the stress
to either torsion loading, as in the case of the double torsion
intensity, K,, acting at the tip of a Crack in specimens or struc-
Single edge cracked plate specimen, or tension loading as in the
tures of various geometries tan be expressed by relationships
case of contoured double cantilever beam specimens. Al-
of the form
though loaded in tension, the design of the latter specimens
produces crackline bending with an associated tendency for
K, = Qa&-
Crack growth out of plane which tan be curbed by the use of
side grooves.
is the geometrical constant;
5.2.4 Constant displacement specimens are usually self-
loaded by means of a loading bolt in one arm which impinges
0 is the applied stress;
on either an anvil or a second loading bolt in the opposite arm.
is the Crack length.
Two types are available a
a) those which are (W-a) dominated, such as the T-type
5.3.2 The solutions for K, for specimens of particular
wedge opening loaded (T-WOL) specimen in which the
geometry and loading method tan be established by means of
proximity of the back face to the Crack tip influences the
finite element stress analysis, or by either experimental or
Crack tip stress field;
theoretical determinations of specimen compliance.
b) those which are (W-a) indifferent, such as the double
cantilever beam (DCB) specimen in which the back face is
5.3.3 K, values tan be calculated by means of a dimensionless

sufficiently remote from the Crack tip to ensure that its pos- stress intensity coefficient, Y, related to Crack length expressed

ition has a negligible effect on the Crack tip stress field.
in terms of al W, or alHfor 1 W-a) indifferent specimens, where
W is the width and H is the half-height of the specimen,
through relationship of the form
5.2.5 A number of the specimen geometries described above
have specific advantages which have caused them to be fre-
quently used for stress corrosion testing. These include
K, = ~
a) cantilever bend specimens which are easy to machine
for compact tension or C-shaped specimens
and inexpensive to test under constant load;
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SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (EI
or 6 Initiation and propagation of fatigue Cracks
K, = p
6.1 The machine used for fatigue cracking should have a
method of loading such that the stress distribution is sym-
metrical about the notch and the applied forte should be
for T-type wedge opening loaded specimens
known to an accuracy within + 2,5 %.
6.2 The environmental conditions employed during fatigue
pre-cracking, as well as the stressing conditions, tan influence
K, = p
BJN the subsequent behaviour of the specimen during stress cor-
rosion testing. In some materials the introduction of the stress
for double cantilever beam specimens.
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
5.3.4 Where it is necessary to use side-grooved specimens in
stress corrosion cracking. This may facilitate the subsequent
Order to curb Crack branching tendencies, etc., shallow side
initiation of stress corrosion cracking and lead to the determi-
grooves (usually 5 % of the specimen thickness on both sides)
nation of consecutive initiation values of Kl,,,. However,
tan be employed. Ether semi-circular or 60° V-grooves tan be
unless facilities are available to commence stress corrosion
used, but it should be noted that even with semi-circular side
testing immediately following the pre-cracking Operation, cor-
grooves of up to 50 % of the specimen thickness it is not
rodant remaining at the Crack tip may promote blunting due to
always possible to maintain the Crack in the desired plane of
corrosive attack. Furthermore, the reproducibility of results
extension. Where side grooves are employed, the effect of the
may suffer when pre-cracking is conducted in the presence of
reduced thickness, B,, due to the grooves on the stress inten-
an aggressive environment because of the greater sensitivity of
sity tan be taken into account by replacing B by dmin the
the corrosion fatigue fracture mode to the cyclic loading con-
above expressions. However, the influence of side grooving on
ditions. In addition, more elaborate facilities may be needed for
the stress intensity factor is far from established and correction
environmental control purposes during pre-cracking. For these
factors should be treated with caution, particularly if deep side
reasons, it is recommended that, unless agreed otherwise
grooves are used.
between the Parties, fatigue pre-cracking should be conducted
in the normal laboratory air environment.
5.3.5 Solutions for Y for specimens with geometries which
are often used for stress corrosion testing are given in
figures 5a) to e).
6.3 The specimens should be pre-cracked by fatigue loading
with an R value in the range 0 to 0,l until the Crack extends at
least 2,5 % W or 1,25 mm beyond the notch at the side sur-
5.4 Specimen preparation
faces, whichever is greater. The Crack may be started at higher
K, values but, during the final 0,5 mm of Crack extension, the
5.4.1 Spetimens of the required orientation (see figure 6)
fatigue pre-cracking should be completed at as low a maximum
should, where possible, be machined in the fully heat-treated
stress intensity as possible (below the expected Kl,,,, if poss-
condition. For specimens in material that cannot easily be com-
pletely 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
6.4 The final length of the fatigue Crack should be such that
from the thickness at this finish machining Stage. However,
the requirement for plane strain predominance is satisfied, i.e.
heat treatment may be carried out on fully machined specimens
in cases in which heat treatment will not result in detri-
mental surface conditions, residual stress, quench cracking or
This condition is optimized when the final al W ratio is in the
5.4.2 After machining, the specimens should be fully
range 0,45 to 0,55 [except in the case of (W-a) indifferent
degreased in Order to ensure that no contamination of the Crack
tip occurs during subsequent fatigue pre-cracking or stress cor-
rosion testing. In cases where it is necessary to attach elec-
trodes to the specimen by soldering or brazing for Crack
6.5 In Order to avoid the interaction of the stress field
monitoring by means of electrical resistance measurements,
associated with the Crack with that due to the notch, the Crack
the specimens should be degreased following this Operation
should lie within the limiting envelope as shown in figure 7.
Prior to pre-cracking in Order to remove traces of remnant flux.

5.5 Specimen identification 6.6 In Order to ensure the validity of the stress intensity

analysis, the fatigue Crack should be inspected on each side of
Specimen identification marks may be stamped or scribed on
the specimen to ensure that no part of it lies in a plane the slope

either the face of the specimen bearing the notch or on the end of which exceeds an angle of IO0 from the plane of the notch

faces parallel to the notch.
and that the differente in lengths does not exceed 5 % W.
---------------------- Page: 13 ----------------------
SIST EN ISO 7539-6:1999
ISO 7539-6 : 1989 (El
7.2.2 For the determination of K,,cc by Crack arrest, the pre-
7 Procedure
cracked specimen should be fixed in a holding device and, if
practical, the environment should be applied to the region of
7.1 General
the notch root.
7.1.1 Before testing, the thickness B and either width u/’ or
half-height 1c-I [in the case of (W-a) indifferent specimens] shall
7.2.3 The arms of the specimen should then be deflected by
be measured to within 0,l % u/ (or H) on a line not further
turning a bolt to give a pre-determined Kl, value in excess of the
than 10 % UI’ (or H) from the Crack plane. The average length
anticipated K,,,, value. Over-deflection must be avoided. The
of the fatigue pre-Crack on both sides of the specimen shall also
deflection, Vy, at the loading line tan be related to the deflec-
be determined and this value is used in assessing the load re-
tion, V, measured by displacement gauge at knife edges
quired to produce the desired ini

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