SIST EN ISO 8401:2017

SLOVENSKI STANDARD
01-maj-2017
1DGRPHãþD
SIST EN ISO 8401:1999
Kovinske prevleke - Pregled metod za merjenje duktilnosti (ISO 8401:2017)
Metallic coatings - Review of methods of measurement of ductility (ISO 8401:2017)
Metallische Schutzschichten - Überblick über Verfahren zur Messung der Duktilität (ISO
8401:2017)
Revêtements métalliques - Vue d'ensemble sur les méthodes de mesurage de la ductilité
(ISO 8401:2017)
Ta slovenski standard je istoveten z: EN ISO 8401:2017
ICS:
25.220.40 Kovinske prevleke Metallic coatings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 8401
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2017
EUROPÄISCHE NORM
ICS 17.040.20 Supersedes EN ISO 8401:1994
English Version
Metallic coatings - Review of methods of measurement of
ductility (ISO 8401:2017)
Revêtements métalliques - Vue d'ensemble sur les Metallische Schutzschichten - Überblick über
méthodes de mesurage de la ductilité (ISO 8401:2017) Verfahren zur Messung der Duktilität (ISO 8401:2017)
This European Standard was approved by CEN on 8 February 2017.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8401:2017 E
worldwide for CEN national Members.

Contents Page
European Foreword . 3

European Foreword
This document (EN ISO 8401:2017) has been prepared by Technical Committee ISO/TC 107 "Metallic
and other inorganic coatings" in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings” 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 August 2017 and conflicting national standards shall
be withdrawn at the latest by August 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document supersedes EN ISO 8401:1994.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 8401:2017 has been approved by CEN as EN ISO 8401:2017 without any modification.
INTERNATIONAL ISO
STANDARD 8401
Second edition
2017-02
Metallic coatings — Review of
methods of measurement of ductility
Revêtements métalliques — Vue d’ensemble sur les méthodes de
mesurage de la ductilité
Reference number
ISO 8401:2017(E)
©
ISO 2017
ISO 8401:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
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the requester.
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 8401:2017(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Tests on unsupported foils . 3
5.1 General . 3
5.2 Tensile testing . 4
5.2.1 Principle . 4
5.2.2 Apparatus . 4
5.2.3 Preparation of test pieces. 4
5.2.4 Procedure . 6
5.2.5 Expression of results . 6
5.2.6 Notes on procedure . 6
5.3 Bending (micrometer bend test) . 7
5.3.1 General. 7
5.3.2 Apparatus . 7
5.3.3 Preparation of test pieces. 7
5.3.4 Procedure . 7
5.3.5 Expression of results . 8
5.4 Folding (vice-bend test) .10
5.4.1 General.10
5.4.2 Apparatus .10
5.4.3 Preparation of test pieces.10
5.4.4 Procedure .10
5.4.5 Results .10
5.5 Hydraulic bulging .11
5.5.1 General.11
5.5.2 Principle .11
5.5.3 Apparatus .11
5.5.4 Procedure .12
5.5.5 Expression of results .13
5.5.6 Notes on procedure .13
5.6 Mechanical bulging .13
5.6.1 General.13
5.6.2 Apparatus .14
5.6.3 Procedure .14
5.6.4 Expression of results .15
5.6.5 Special cases .15
6 Tests on coatings on substrates .17
6.1 General .17
6.2 Tensile testing .18
6.2.1 Apparatus .18
6.2.2 Preparation of test pieces.18
6.2.3 Procedure .18
[10] 19
6.3 Three-point bending .
6.3.1 Principle .19
6.3.2 Apparatus .19
6.3.3 Procedure .19
6.3.4 Expression of results .20
[11] 21
6.4 Four-point bending .
6.4.1 General.21
ISO 8401:2017(E)
6.4.2 Expression of results .21
6.5 Cylindrical mandrel bending . .22
6.5.1 Principle .22
6.5.2 Apparatus .22
6.5.3 Preparation of test pieces.23
6.5.4 Procedure .23
6.5.5 Expression of results .23
6.5.6 Notes on procedure .23
6.6 Spiral mandrel bending .23
6.6.1 Principle .23
6.6.2 Apparatus .24
6.6.3 Procedure .24
6.6.4 Expression of results .24
6.7 Conical mandrel bending .25
6.7.1 Principle .25
6.7.2 Apparatus .25
6.7.3 Procedure .25
6.7.4 Expression of results .25
6.7.5 Special cases .26
6.8 Mechanical bulging .26
6.8.1 Apparatus .26
6.8.2 Preparation of test pieces.26
6.8.3 Procedure .26
6.8.4 Expression of results .26
7 Selection of test method .27
8 Test report .28
Annex A (informative) Methods of producing foils .29
Annex B (informative) Calculation of ductility when increasing the surface area of a
foil (bulging) .31
Annex C (informative) Calculation of ductility and tensile strength in the hydraulic bulge test .34
Annex D (informative) Calculation of ductility in the mechanical bulge test .37
Bibliography .38
iv © ISO 2017 – All rights reserved

ISO 8401:2017(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 on 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 the following URL: www . i so .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
This second edition cancels and replaces the first edition (ISO 8401:1986), of which it constitutes a
minor revision. The following changes have been made:
— Formula (C.10) has been corrected;
— changes have been made in line with the 2016 edition of the ISO/IEC Directives, Part 2.
INTERNATIONAL STANDARD ISO 8401:2017(E)
Metallic coatings — Review of methods of measurement of
ductility
1 Scope
This document specifies general methods for measuring the ductility of metallic coatings of thickness
below 200 μm prepared by electroplating, autocatalytic deposition or other processes.
It is applicable to the following methods:
— tests on unsupported foils (separated from the substrate);
— tests of coatings on substrates.
It does not apply to International Standards that include specific methods of testing for individual
coatings. In these cases, the methods specified are used in preference to the methods described in this
document and are agreed upon beforehand by the supplier and the purchaser.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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 http:// www .iso .org/ obp
3.1
ductility
ability of a metallic or other coating to undergo plastic or elastic deformation, or both, without fracture
or cracking
3.2
linear elongation
ratio of the elongation, Δl, to a definite initial length, l , of the test piece
Note 1 to entry: This is taken as a measure of ductility.
Note 2 to entry: Often, this ratio is expressed as a percentage.
Note 3 to entry: Normally, the test pieces are elongated [see Figure 1 a)]. With some bending tests, the outer layer
of the test piece, i.e. the plating, is elongated. In bulge tests, however, the surface of the foil is enlarged, requiring
calculation of linear elongation from the reduction in the thickness. Using the component of deformation
(stretching) in only one axis would give false information about the ductility of the material [see Figure 1 b)]. In
those cases, the thinning of the foil, as calculated from the increase in the surface area, is a better measure of the
ductility of the material (see Annex B).
ISO 8401:2017(E)
xyzx=− ddxy − yz + dz
()()()
xyzx=+yz xyddzx−−zy yzdx
ddz y dx
=+
z y x
ddz y
>
z y
dl
dz
t
=
l z
t
a) Tensile test   b) Cupping test
Figure 1 — Tensile and cupping tests
4 Principle
4.1 In the testing of unsupported foils separated from the substrate (see Figure 2), the foils may consist
of one or more metallic layers. Therefore, it is possible to measure the ductility of composites and to
determine the influence of individual layers on overall ductility. Methods of testing of unsupported foils
are described in Clause 5. Methods of producing foils for testing are discussed in Annex A.
4.2 In the testing of coatings on substrates (see Figure 3), it is especially important to determine the
exact point of crack initiation of the top layer. Attention is drawn to different methods of discerning this
point, by normal or corrected-to-normal vision or with a lens. See the guidance in the individual methods.
2 © ISO 2017 – All rights reserved

ISO 8401:2017(E)
These methods can also be used to detect embrittlement of the substrate that may have resulted from the
coating process. Methods of testing of coatings on substrates are described in Clause 6.
Key
1 metal foil
2 substrate
Figure 2 — Foil, which can be separated from the substrate
Key
1 coating
2 substrate
Figure 3 — Coating on the substrate
4.3 Although ductility is a property of the material and independent of the dimensions of the test piece,
thickness of the coating may have an influence on the value of linear elongation (Δl/l ).
4.3.1 Very thin layers have different properties as the build-up of the initial layers will be influenced
by the properties of the substrate (epitaxy). High internal stresses may be incorporated into the initial
layers and these may affect ductility.
4.3.2 It is essential that the test piece has uniform thickness, as thinner spots will give rise to premature
cracking. Also, the current density is lower at thinner parts and higher at thicker parts of electroplated
test pieces; in this way, current density differences may result in different ductilities. The current density
applied should be maintained as uniform as possible over the test piece, and its value reported.
5 Tests on unsupported foils
5.1 General
These techniques involve measurement of a foil which has been separated from the substrate (see
Figure 2). In this case, the foil to be tested can also consist of several layers so as to allow measurement
of the influence of undercoats on the ductility of the foil sandwich. Examples are gold flash on
gold/copper alloys and chromium-plated nickel deposits. Methods of producing unsupported foils are
given in Annex A.
Five methods are described: tensile testing (5.2), bending (micrometer bend test) (5.3), folding (vice-
bend test) (5.4), hydraulic bulging (5.5) and mechanical bulging (5.6).
ISO 8401:2017(E)
5.2 Tensile testing
5.2.1 Principle
Determination of the linear elongation of a foil, which is clamped into the jaws of a tensile testing
machine. In this type of stressing, the foil is lengthened, but both the width and the thickness of the foil
diminish.
5.2.2 Apparatus
This method may utilize conventional mechanical testing equipment, available commercially and
[1]
in many metallurgical laboratories . For some applications, tensile testing equipment adapted to
microscopic inspection during the test may be used.
5.2.3 Preparation of test pieces
Test pieces may be machined, chipped, punched or cut from the metallic foil or prepared by
photoprinting with the help of light-sensitive lacquers or light-sensitive foils which are pressed onto
a suitable substrate. After developing the pattern of the test piece, it is plated into the final form. A
similar method uses chemical or electrochemical milling of the desired shape from a foil on which has
been applied a suitable resist by silk screen printing or by applying a photosensitive resist. These last
methods are widely used in the printed circuit industry. The test pieces are usually rectangular in
shape (see Table 1 for recommended dimensions), but can be widened at both ends to avoid breaking in
the clamping jaws (see Figure 4).
[1]
Table 1 — Possible dimensions of tensile test pieces
Gauge length (mm) 200 50 25
Width (mm) 40 12,5 6,25
Some methods of preparing the test pieces may cause microcracking at the edges that results in
premature failure and erratic results. Test piece preparation involving photoprinting or electroforming
is preferred to avoid edge defects.
Test pieces plated into the final form may have thicker edges unless shielding and other techniques are
used to ensure uniform current distribution (see Figure 5).
Make equidistant marks on the surface of the test piece as illustrated in Figure 4 a). Determine the
distance between the marks before testing.
4 © ISO 2017 – All rights reserved

ISO 8401:2017(E)
a) Before testing b) After testing
ll+Δl =+ l
01 2
ll+− l
Δl
12 0
=
l l
0 0
Key
1 microcracks
Figure 4 — Tensile testing specimen before and after testing
Figure 5 — Plated test pieces with thicker edges
ISO 8401:2017(E)
5.2.4 Procedure
Clamp the test piece between the jaws of the tensile test equipment and apply strain using a selected
cross-head speed. Determine the distance between the marks on the test pieces after testing [see
Figure 4 b)].
5.2.5 Expression of results
5.2.5.1 Calculation
The ductility, D, expressed as a percentage, is given by Formula (1):
ll+− l
12 0
D = ×100 (1)
l
where
is the distance between the marks before testing;
l
is the distance between the marks after testing.
ll+
5.2.5.2 Coefficient of variation
Mechanically prepared test pieces can have coefficients of variation, sD/ (where s is the standard
deviation and D the mean ductility), as high as 20 %.
By plating into the final form using shields to ensure uniform current distribution, test pieces can be
produced which have lower coefficients of variation.
5.2.6 Notes on procedure
5.2.6.1 Necking of the test piece [see Figure 4 b)] may require measurement of very small changes in
length and the use of a microscope that has a Vernier scale.
5.2.6.2 Mounting fragile thin test pieces into the jaws of a tensile testing machine may give rise to
prestressed test pieces which thereby diminish the real value of elongation.
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ISO 8401:2017(E)
5.2.6.3 Care shall be taken to avoid twisting of the test piece (see Figure 6).
Key
1 microcracks
Figure 6 — Twisted test piece
5.2.6.4 When these sources of error (5.2.6.1 to 5.2.6.3) cannot be eliminated, other methods of
measuring ductility should be used.
5.3 Bending (micrometer bend test)
5.3.1 General
[2]
This method is suitable only for the evaluation of metallic foils having low ductility . The values
obtained have no simple relation to values obtained by other methods. This method is useful for brittle
metals such as bright nickel.
5.3.2 Apparatus
5.3.2.1 Micrometer.
5.3.3 Preparation of test pieces
Cut strips of 0,5 cm × 7,5 cm from the foil under test. The foils are usually 25 µm to 40 μm thick.
The difficulties described in 5.2.3 and 5.2.6 apply likewise to this test. Measure the thickness of the
test piece at the point of bending, using an instrument or method which enables the thickness to be
determined with maximum 5 % uncertainty.
5.3.4 Procedure
Bend the test piece into a U-shape and place it between the jaws of the micrometer (5.3.2.1) so that as the
jaws are closed, the bend remains between the jaws. Close the micrometer jaws slowly until the foil cracks.
Record the micrometer reading and the thickness of the foil (see Figure 7).
Carry out the test at least in duplicate.
ISO 8401:2017(E)
Key
1 test piece
2 micrometer
Figure 7 — Micrometer bend test
5.3.5 Expression of results
5.3.5.1 Calculation
Calculate the average of the micrometer readings (see 5.3.4).
The ductility, D, expressed as a percentage, is given by Formula (2) (see Figure 8):
δ
D = ×100 (2)
2r −δ
where
δ is the thickness of the test pieces;
is the average of the micrometer readings.
2r
8 © ISO 2017 – All rights reserved

ISO 8401:2017(E)
Δll
=
1 1
δδr
+
2 2
Δl δ
=
lr2 +δ
if δ ≪ 2r
Δl δ
=
lr2
Figure 8 — Bending of a test piece
5.3.5.2 Precision
As the value of D rises more rapidly than δ, it is essential that the value of δ be measured with high
precision. If a foil of 20 μm is read as 25 μm, the following difference, supposing 20r = ,5cm , will
be found:
−4
20×10
D = ×=100 04, %
−4
05, −×20 10
−4
25×10
D = ×=100 05, %
−4
05, −×25 10
i.e. a difference of 05,,%%−=04 01, % .
A thickness of 25 µm will give results that are 25 % higher than for a 20 µm thickness.
It is obvious that this method will give reproducible results only when δ is measured to within 1 μm
and 2r to within 0,01 cm.
ISO 8401:2017(E)
5.4 Folding (vice-bend test)
5.4.1 General
Although this test is simple and may have some utility, the nature of the test, the cold working that
occurs as a result of bending, and other factors may lead to incorrect measures of ductility. The
thickness of the test piece affects the results, but the influence of thickness cannot be calculated.
5.4.2 Apparatus
5.4.2.1 Machinist’s vice, equipped with two small machined jaws to hold the test piece (see Figure 9).
Key
1 bending lever
2 jaws
3 vice
Figure 9 — Vice-bend test apparatus
5.4.3 Preparation of test pieces
Cut rectangular strips, 1 cm wide by 5 cm long, from the metal foil.
5.4.4 Procedure
Grip the test piece between the jaws of the vice. Bend the test piece sharply through 90°, then bend it
successively in opposite directions through 180° until fracture occurs.
5.4.5 Results
The number of bends is taken as a measure of ductility.
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ISO 8401:2017(E)
5.5 Hydraulic bulging
5.5.1 General
Hydraulic bulge-testing can be used to measure the ductility of thin sheet materials accurately. No
machining of the test piece is required, there are no problems of achieving axial alignment as in tensile
[3][4][5]
testing, and the test is especially useful for measuring the ductility of ductile materials .
5.5.2 Principle
Clamping of a test piece between a bottom cylinder and an upper platen. The upper platen has a circular
opening of the same diameter as the cylinder. Increasing the water pressure slowly and steadily to
deform the test piece into a bulge or dome until the foil bursts. See Figure 10.
Dimension in millimetres
Key
1 test piece
2 water
Figure 10 — Principle of hydraulic bulging
5.5.3 Apparatus
For an example, see Figure 11; versions with mechanical sensor to measure the bulge height are also
possible.
ISO 8401:2017(E)
Dimension in millimetres
Key
1 test piece 6 nylon
2 water 7 glass gauge
3 pressure-sensitive module 8 digital 1 mV ≙ 0,01 cm
4 motor 9 measuring the heights of the meniscus with a light-sensor
5 potentiometer
Figure 11 — Apparatus for hydraulic bulging
5.5.4 Procedure
With the equipment shown schematically in Figure 11, fill the bottom cylinder with water to the rim.
Place the test piece on the surface of the water. Use the upper platen, in the shape of a hollow cone, to
clamp the test piece firmly in position.
Fill the hollow cone with water from the reservoir that is provided. The excess water will rise in the
glass gauge. When the level of the water is above the light-sensing device, close the valve that controls
the flow of water from the reservoir. Turn the motor on and slowly raise the light-sensing device. When
the device is aligned with the meniscus, the beam of light within the device will be deflected; the drop
in voltage that occurs as a result of this shuts off the motor.
The pressure under the test piece is increased by means of the plunger. When the meniscus in the glass
gauge begins to rise, the motor will automatically begin to operate and the light-sensing device will
track the rise in the level of water. By means of the potentiometer, record the increase in volume on an
x-y recorder.
A pressure sensor in the cylinder simultaneously records the pressure beneath the test piece. In a
commercial version of the equipment, a pressure-sensitive switch is used to shut the motor off at the
moment of bursting so that the total volume of displaced water can be read directly from the digital
display on the potentiometer.
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ISO 8401:2017(E)
5.5.5 Expression of results
5.5.5.1 Calculation
The ductility of the metal specimen may be calculated from the volume of the displaced water, which
equals the volume inside the dome. The ductility, expressed as a percentage, is given by the formulae
derived and discussed in Annex C. The tensile strength of the metal foil may also be determined from
the value of the pressure at bursting (see Annex C).
5.5.5.2 Coefficient of variation
Because only the centre of the foil (∅ 3 cm) is tested, the current density and the thickness in this region
are probably more constant than in the case of tensile tests. Values of sD/,= 005 , i.e. 5 %, are easily
arrived at.
5.5.6 Notes on procedure
Pinholes in the test piece are one possible source of error. Pinholes can be detected prior to testing by
“candling”. A 100 W light bulb in a box with a hole slightly smaller in diameter than the opening in the
top plate or cone is satisfactory.
When pinholes are present, it is possible to underlay the test piece with a very thin plastic foil which
will stop the water from passing through the pinholes.
By visual observation, it is possible to note the moment of cracking.
Stopping the motor of the light-sensing device at this moment will give fair indication of the ductility of
the porous foil.
5.6 Mechanical bulging
5.6.1 General
Mechanical bulge tests are similar to hydraulic bulge tests. The dome, however, is formed mechanically
as indicated schematically in Figure 12.
Dimensions in millimetres
Key
1 foil
2 mandrel
Figure 12 — Principle of mechanical bulging
ISO 8401:2017(E)
5.6.2 Apparatus
Equipment for measuring the ductility of thin metal foils is not readily available, but can be easily
assembled.
Two types of apparatus are used. The simplest one consists of a micrometer, a spindle extension with a
[6][7]
steel ball and a pair of circular plates each with a round opening at the centre (see Figure 13) .
Dimensions in millimetres
Key
1 test piece 5 epoxy insulation
2 O-ring 6 micrometer
3 steel ball 7 groove
4 spindle extension
Figure 13 — Apparatus for mechanical bulging
5.6.3 Procedure
Place a foil test piece between the circular plates. Clamp the upper and lower plates together firmly by
means of two screws. Then slowly push the test piece upward by turning the micrometer. Read from
the micrometer the distance travelled by the steel ball from the initial contact with the metal film to
the point of crack initiation.
The initial contact point between the steel ball and the test piece is detected electrically. A battery-
operated lamp is fitted into the upper brass plate in such a way that the lamp lights at the instant the
steel ball touches the test piece. The lamp stays lit throughout the test.
14 © ISO 2017 – All rights reserved

ISO 8401:2017(E)
The visual detection of the initiation of rupture is accomplished with the aid of a magnifier (15×)
attached to the upper plate (but not shown in Figure 13).
5.6.4 Expression of results
It is possible to calculate the ductility from the height of the cone by calculating the loss of thickness of
the foil (see Annex D).
5.6.5 Special cases
It may be preferable to use a slightly altered procedure. In the apparatus shown schematically in
Figures 14, 15 and 16, the steel ball remains stationary, but the two plates and the sample are moved
downward with a motor until the test piece cracks.
Key
1 metal microscope 4 gearing
2 threaded spindle 5 motor
3 potentiometer 6 isolating foil
Figure 14 — Alternative apparatus for mechanical bulging
ISO 8401:2017(E)
Dimensions in millimetres
Key
1 metal microscope
2 test piece
Figure 15 — Detail from Figure 14
Dimensions in millimetres
Figure 16 — Top view of Figure 15
16 © ISO 2017 – All rights reserved

ISO 8401:2017(E)
The instrument is placed under a microscope which enables use of 70× magnification when looking for
the first cracks. At the start of the test, the motor stops when electrical contact between the steel ball
and the test piece is made. At the moment of cracking, the motor is stopped by hand. The height of the
cone is measured by the displacement of a linear potentiometer with a resolution of 5 μm.
With the motor-driven apparatus
...