Metallic materials - Determination of forming-limit curves for sheet and strip - Part 2: Determination of forming-limit curves in the laboratory (ISO 12004-2:2021)

This document specifies testing conditions for use when constructing a forming-limit curve (FLC) at
ambient temperature and using linear strain paths. The material considered is flat, metallic and of
thickness between 0,3 mm and 4 mm.
NOTE The limitation in thickness of up to 4 mm is proposed, giving a maximum allowable thickness to the
punch diameter ratio.

Metallische Werkstoffe - Bestimmung der Grenzformänderungskurve für Bleche und Bänder - Teil 2: Bestimmung von Grenzformänderungskurven im Labor (ISO 12004-2:2021)

Dieses Dokument legt Prüfbedingungen für die Verwendung bei der Erstellung einer für den betreffenden Werkstoff bei Umgebungstemperatur geltenden Grenzformänderungskurve (FLC) unter Verwendung von linearen Formänderungsverläufen fest. Der betrachtete Werkstoff ist eben, metallisch und hat eine Dicke von 0,3 mm bis 4 mm.
ANMERKUNG Die Begrenzung der Dicke auf bis zu 4 mm wird vorgeschlagen, wodurch sich ein maximal zulässiges Verhältnis von Dicke zu Stempeldurchmesser ergibt.

Matériaux métalliques - Détermination des courbes limites de formage pour les tôles et bandes - Partie 2: Détermination des courbes limites de formage en laboratoire (ISO 12004-2:2021)

Kovinski materiali - Določevanje krivulj preoblikovalnosti za pločevino in trakove - 2. del: Določevanje krivulj preoblikovalnosti v laboratoriju (ISO 12004-2:2021)

General Information

Status
Published
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
03-Mar-2021
Completion Date
03-Mar-2021

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SLOVENSKI STANDARD
SIST EN ISO 12004-2:2021
01-junij-2021
Nadomešča:
SIST EN ISO 12004-2:2009

Kovinski materiali - Določevanje krivulj preoblikovalnosti za pločevino in trakove -

2. del: Določevanje krivulj preoblikovalnosti v laboratoriju (ISO 12004-2:2021)

Metallic materials - Determination of forming-limit curves for sheet and strip - Part 2:

Determination of forming-limit curves in the laboratory (ISO 12004-2:2021)
Metallische Werkstoffe - Bestimmung der Grenzformänderungskurve für Bleche und
Bänder - Teil 2: Bestimmung von Grenzformänderungskurven im Labor (ISO 12004
2:2021)

Matériaux métalliques - Détermination des courbes limites de formage pour les tôles et

bandes - Partie 2: Détermination des courbes limites de formage en laboratoire (ISO

12004-2:2021)
Ta slovenski standard je istoveten z: EN ISO 12004-2:2021
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
77.140.50 Ploščati jekleni izdelki in Flat steel products and semi-
polizdelki products
SIST EN ISO 12004-2:2021 en,fr,de

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

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SIST EN ISO 12004-2:2021
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SIST EN ISO 12004-2:2021
EN ISO 12004-2
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2021
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 12004-2:2008
English Version
Metallic materials - Determination of forming-limit curves
for sheet and strip - Part 2: Determination of forming-limit
curves in the laboratory (ISO 12004-2:2021)

Matériaux métalliques - Détermination des courbes Metallische Werkstoffe - Bestimmung der

limites de formage pour les tôles et bandes - Partie 2: Grenzformänderungskurve für Bleche und Bänder -

Détermination des courbes limites de formage en Teil 2: Bestimmung von Grenzformänderungskurven

laboratoire (ISO 12004-2:2021) im Labor (ISO 12004 2:2021)
This European Standard was approved by CEN on 15 January 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 12004-2:2021 E

worldwide for CEN national Members.
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SIST EN ISO 12004-2:2021
EN ISO 12004-2:2021 (E)
Contents Page

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

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SIST EN ISO 12004-2:2021
EN ISO 12004-2:2021 (E)
European foreword

This document (EN ISO 12004-2:2021) has been prepared by Technical Committee ISO/TC 164

"Mechanical testing of metals" in collaboration with Technical Committee CEN/TC 459/SC 1 “Test

methods for steel (other than chemical analysis)” the secretariat of which is held by AFNOR.

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 September 2021, and conflicting national standards

shall be withdrawn at the latest by September 2021.

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 12004-2:2008.

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 12004-2:2021 has been approved by CEN as EN ISO 12004-2:2021 without any

modification.
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SIST EN ISO 12004-2:2021
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SIST EN ISO 12004-2:2021
INTERNATIONAL ISO
STANDARD 12004-2
Second edition
2021-02
Metallic materials — Determination
of forming-limit curves for sheet and
strip —
Part 2:
Determination of forming-limit curves
in the laboratory
Matériaux métalliques — Détermination des courbes limites de
formage pour les tôles et bandes —
Partie 2: Détermination des courbes limites de formage en laboratoire
Reference number
ISO 12004-2:2021(E)
ISO 2021
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
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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
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols ......................................................................................................................................................................................................................... 1

5 Principle ........................................................................................................................................................................................................................ 2

6 Test pieces and equipment ........................................................................................................................................................................ 3

6.1 Test pieces ................................................................................................................................................................................................... 3

6.1.1 Thickness of test pieces ............................................................................................................................................. 3

6.1.2 Test piece geometry ...................................................................................................................................................... 3

6.1.3 Test piece preparation in test area ................................................................................................................... 4

6.1.4 Number of different test piece geometries ............................................................................................... 4

6.1.5 Number of tests for each geometry ................................................................................................................. 4

6.2 Application of grid ............................................................................................................................................................................... 4

6.2.1 Type of grid ........................................................................................................................................................................... 4

6.2.2 Grid application ................................................................................................................................................................ 5

6.2.3 Accuracy of the undeformed grid ...................................................................................................................... 5

6.3 Test equipment ....................................................................................................................................................................................... 5

6.3.1 General...................................................................................................................................................................................... 5

6.3.2 Strain determination .................................................................................................................................................... 7

6.3.3 Nakajima test ...................................................................................................................................................................... 7

6.3.4 Marciniak test ..................................................................................................................................................................... 9

7 Analysis of strain profile and measurement of ε – ε pairs .................................................................................11

1 2

7.1 General ........................................................................................................................................................................................................11

7.2 Evaluation using section lines (position-dependent measurement) ....................................................11

7.2.1 General...................................................................................................................................................................................11

7.2.2 Position and processing of measurements ............................................................................................12

7.2.3 Extraction of the “bell-shaped curve” and determination of the inner

limits for the best-fit curve through experimental points ........................................................13

7.2.4 Definition of outer limits for best-fit windows and evaluation of the

inverse best-fit parabola on the “bell-shaped curve” ....................................................................14

8 Documentation ....................................................................................................................................................................................................15

9 Test report ................................................................................................................................................................................................................16

Annex A (normative) Second derivative and “filtered” second derivative .................................................................17

Annex B (normative) Calculation of the width of the fit window.........................................................................................18

Annex C (normative) Evaluation of the inverse best-fit parabola on the “bell-shaped curve” ..............19

Annex D (normative) Application/Measurement of grid —

Evaluation with magnifying glass or microscope ............................................................................................................21

Annex E (informative) Tables of experimental data for validation of calculation programme ............22

Annex F (normative) Representation and mathematical description of FLC ..........................................................23

Annex G (informative) Examples of critical section line data ..................................................................................................24

Annex H (normative) Flowchart from measured strain distributions to FLC values ......................................25

Bibliography .............................................................................................................................................................................................................................27

© ISO 2021 – All rights reserved iii
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(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 164, Mechanical testing of metals,

Subcommittee SC 2, Ductility testing, in collaboration with the European Committee for Standardization

(CEN) Technical Committee CEN/TC 459/SC 1, Test methods for steel (other than chemical analysis), in

accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 12004-2:2008), which has been

technically revised.
The main changes compared to the previous edition are as follows:
1) The title was changed to have three elements.

2) Clause 2 and Clause 3 were added from the previous edition, and the subsequent clauses were

renumbered.

3) The descriptions of when to use ISO 12004-1 or ISO 12004-2 (this document) was revised in the

Introduction.

4) Permissions and requirements were clarified in 6.1.3, 6.1.5, 6.2.2, 6.2.3, 6.3.2, 6.3.3.3, 6.3.4.3, 7.2.2,

and 7.2.3.

5) In 6.3.1, the punch velocity range was expanded and permission for exceptional cases in aluminium

alloys, as well as steel, was added.

6) Clarification was added that although the Nakajima method is known to have non-linear strain

paths (6.3.3.1), it is still acceptable. Clarification as to why the failure is required to be near the

apex of the dome was added to 6.3.3.3. In 6.3.3.3, the “validity of test” requirement for the Nakajima

test was made explicit in a similar format to that shown for the Marciniak test in 6.3.4.4. In 6.3.3.3

and 6.3.4.4, a statement regarding rejection of specimens not meeting the valid test requirements

was added.
iv © ISO 2021 – All rights reserved
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)

7) The “Measuring instrument” clause (4.3.5 in the previous edition) was removed since it is

a repetition of the “Measurement instrument” section of 6.3.2 but had a different accuracy

requirement. The required accuracy is now shown as originally described in 6.3.2.

8) The requirement on the second derivative range was clarified in 7.2.3(c), and the requirements in

the keys of Figures 8 and 9 were changed to match 7.2.3(c).

9) The permission to use other methods of measurement was moved from 7.2.1 to 7.1 and was

clarified.

10) The statement regarding the “time-dependent method” was removed from 7.1 but now a statement

admitting the use of other methods including both the “time-dependent method” or “time and

position dependent methods” appears in Clause 5.

11) In 7.2.2, the method of selecting the section line locations based on the crack position was clarified,

and permission was added to use the maximum strain location, as long as the test validity

requirements are still met.

12) The use of the procedure in 7.2.3 when extracting the “bell-shaped curve” for use in evaluating the

section lines using the position-dependent method has been changed to being required rather than

just suggested. This seems to be consistent with the original intent.

13) In Annex A, the method was changed to be required rather than proposed. Annex C was clarified

to show that the procedure is required. Clarification to the text of Annex D was added, and its use

is explicitly permitted. In Annex F, explicit permission to use a regression using in-house functions

was added, as well as the requirement that the function be reported.
14) Editorial changes and clarifications were made throughout the document.
A list of all parts in the ISO 12004 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.
© ISO 2021 – All rights reserved v
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)
Introduction
A forming-limit diagram (FLD) is a diagram containing major/minor strain points.

An FLD can distinguish between safe points and necked or failed points. The transition from safe to

failed points is defined by the forming-limit curve (FLC).
To determine the forming limit of materials, two different methods are possible.

1) Strain analysis on failed press shop components to determine component and process

dependent FLCs.

In the press shop, the strain paths followed to reach these points are generally not known. Such an

FLC depends on the material, the component, and the chosen forming conditions. This method is

described in ISO 12004-1 and is not intended to determine one unique FLC for each material.

2) Determination of FLCs under well-defined laboratory conditions.

For evaluating formability, one unique FLC for each material in several strain states can be

measured. The determination of the FLC must be specific and uses multiple linear strain paths.

This document, i.e. ISO 12004-2, is intended for this type of material characterization.

For this document (concerning determination of forming-limit curves in laboratory), the following

conditions are also of note.

— Forming-limit curves (FLCs) are determined for specific materials to define the extent to which

they can be deformed by drawing, stretching or any combination of drawing and stretching. This

capability is limited by the occurrence of localized necking and/or fracture. Many methods exist to

determine the forming limit of a material; but results obtained using different methods cannot be

used for comparison purposes.

— The FLC characterizes the deformation limit of a material in the condition after a defined thermo-

mechanical treatment and in the analysed thickness. For a judgement of formability, the additional

knowledge of mechanical properties and the material’s history prior to the FLC-test are important.

To compare the formability of different materials, it is important to judge not only the FLC but also the

following parameters:
a) mechanical properties at least in the main direction;
b) percentage plastic extension at maximum force, according to ISO 6892-1;
c) r-value with given deformation range, according to ISO 10113;
d) n-value with given deformation range, according to ISO 10275.
vi © ISO 2021 – All rights reserved
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SIST EN ISO 12004-2:2021
INTERNATIONAL STANDARD ISO 12004-2:2021(E)
Metallic materials — Determination of forming-limit
curves for sheet and strip —
Part 2:
Determination of forming-limit curves in the laboratory
1 Scope

This document specifies testing conditions for use when constructing a forming-limit curve (FLC) at

ambient temperature and using linear strain paths. The material considered is flat, metallic and of

thickness between 0,3 mm and 4 mm.

NOTE The limitation in thickness of up to 4 mm is proposed, giving a maximum allowable thickness to the

punch diameter ratio.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Symbols
For the purposes of this document, the symbols given in Table 1 apply.
Table 1 — Symbols
Symbol English French German Unit
e Engineering strain Déformation conventionnelle Technische Dehnung %
True strain Déformation vraie Wahre Dehnung
ε (logarithmic strain) (déformation logarithmique) (Umformgrad, —
Formänderung)
ε Major true strain Déformation majeure vraie Grössere Formänderung —
ε Minor true strain Déformation mineure vraie Kleinere Formänderung —
ε True thickness strain Déformation vraie en épaisseur Dickenformänderung —
σ Standard deviation Ecart-type Standardabweichung —
D Punch diameter Diamètre du poinçon Stempeldurchmesser mm
Carrier blank hole Diamètre du trou du contre-flan Lochdurchmesser
D mm
diameter des Trägerblechs
X(0), X(1)
X-position Position en X X-Position mm
X(m) ....X(n)
© ISO 2021 – All rights reserved 1
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)
Table 1 (continued)
Symbol English French German Unit
f(x) = Best-fit parabola Parabole de meilleur fit Best-Fit-Parabel
ax + bx + c

f(x) = Best-fit inverse parabola Parabole inverse de meilleur fit Inverse Best-Fit-Parabel

1/(ax + bx + c)
S(0), S(1)...S(5) Section Section Schnitt —
n Number of X-positions Nombre de points en X Nummer der X-Positionen —
Number of the X-posi- Numéro du point en X Nummer der X-Position am
m tion at the failure/crack correspondant à la rupture Riss —
position

w Width of the fit window Largeur de la fenêtre de fit Breite des Fit-Fensters mm

t Initial sheet thickness Épaisseur initiale de la tôle Ausgangsblechdicke mm
Plastic strain ratio Coefficient d'anisotropie Senkrechte Anisotropie
r —
plastique
Table 2 gives a comparison of the symbols used in different countries.
Table 2 — Comparison of symbols used in different countries
English International German Format Unit
symbol symbol
Engineering strain e ε — %
True strain
ε φ Decimal —
(logarithmic strain)
ε = ln(1 + e) — — — —

The symbol typically used for true strain is “ε”, but in German-speaking countries the symbol “φ” is used

for true strain. Additionally, in German-speaking countries the symbol “ε” is used to define engineering

strains.

The notation for true strain used in this text is “ε” following the typical international definition.

5 Principle

The FLC is intended to represent the almost intrinsic limit of a material in deformation assuming a

linear strain path. To determine the FLC accurately, it is necessary to have as nearly linear a strain path

as possible.

A deterministic grid of precise dimensions or a stochastic pattern is applied to the flat and undeformed

surface of a blank. This blank is then deformed using either the Nakajima or the Marciniak procedure

until failure, at which point the test is stopped.

The FLC determination from the measurements should be performed using the “position-dependent”

method described in 7.2.

Other methods (e.g. “time-dependent” or “time and position dependent” methods) of FLC determination

from the measurements exist. If agreed to by the interested parties, one of the other methods may be

used and, if used, shall be indicated in the test report.

The deformation (strain) across the deformed test piece is determined and the measured strains are

processed in such a way that the necked or failed area is eliminated from the results. The maximum

strain that can be imposed on the material without failing is then determined through interpolation.

This maximum of the interpolated curve is defined as the forming limit.
2 © ISO 2021 – All rights reserved
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)

The forming limits are determined for several strain paths (different ratios between ε and ε ). The

1 2

determined strain paths range from uniaxial tension to biaxial tension (stretch drawing). The collection

of the individual forming limits in different strain states is plotted as the forming-limit curve. The

curve is expressed as a function of the two true strains ε and ε on the sheet surface and plotted in a

1 2

diagram, the forming-limit diagram. The minor true strains ε are plotted on the X-axis and the major

principal true strains ε on the Y-axis (see Figure 1).

Standard conversion formulae permit the calculation of major (ε ) and minor true strains (ε ) from

1 2

measured length changes or engineering strains. In the following, the word "strain" implies the true

strain, which is also called logarithmic strain.
Key
X minor true strain, ε
Y major true strain, ε
F FLC
Uniaxial tension, ε = −[r/(r + 1)] ε .
2 1
Intermediate tensile strain.
Plane strain.
Intermediate stretching strain state.
Intermediate stretching strain state.
Equi-biaxial tension (= stretching strain state) ε = ε .
2 1
Figure 1 — Six different strain paths
6 Test pieces and equipment
6.1 Test pieces
6.1.1 Thickness of test pieces

This procedure is intended for flat, metallic sheets with a thickness between 0,3 mm and 4 mm.

For steel sheets a maximum thickness of 2,5 mm is recommended.
6.1.2 Test piece geometry

The following geometries are recommended: waisted blanks with a central, parallel shaft longer than

25 % of the punch diameter (for a 100 mm punch: preferable shaft length 25 mm to 50 mm; fillet radius

20 mm to 30 mm) (see Figure 2).
© ISO 2021 – All rights reserved 3
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SIST EN ISO 12004-2:2021
ISO 12004-2:2021(E)
Shaft length.
Remaining blank width.
Fillet radius.

Figure 2 — Waisted test piece geometry with parallel shaft length (dog bone shape)

For ε > 0, blanks with semi-circular cut-outs with different radii are possible.

For steel (mainly soft steel grades), rectangular strips with different widths are sufficient if test pieces

do not fail at the die radius; otherwise use the test piece geometry as described above.

With an outer circular shape of the blanks, a more uniform distribution of the experimental forming-

limit points is attainable than when rectangular strips are used.
6.1.3 Test piece preparation in test area

Milling, spark-erosion or other methods that do not cause cracks, work hardening or microstructure

changes may be used ensuring that fracture n
...

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