SIST EN ISO 12004-2:2021

SLOVENSKI STANDARD
oSIST prEN ISO 12004-2:2019
01-julij-2019
Kovinski materiali - Pločevina in trakovi - Določevanje krivulj preoblikovalnosti - 2.
del: Določevanje krivulj preoblikovalnosti v laboratoriju (ISO/DIS 12004-2:2019)
Metallic materials - Sheet and strip - Determination of forming-limit curves - Part 2:
Determination of forming-limit curves in the laboratory (ISO/DIS 12004-2:2019)
Metallische Werkstoffe - Bleche und Bänder - Bestimmung von
Grenzformänderungskurven - Teil 2: Bestimmung von Grenzformänderungskurven im
Labor (ISO/DIS 12004-2:2019)
Matériaux métalliques - Tôles et bandes - Détermination des courbes limites de formage
- Partie 2: Détermination des courbes limites de formage en laboratoire (ISO/DIS 12004-
2:2019)
Ta slovenski standard je istoveten z: prEN ISO 12004-2
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
oSIST prEN ISO 12004-2:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 12004-2:2019

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oSIST prEN ISO 12004-2:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 12004-2
ISO/TC 164/SC 2 Secretariat: JISC
Voting begins on: Voting terminates on:
2019-05-29 2019-08-21
Metallic materials — Sheet and strip — Determination of
forming-limit curves —
Part 2:
Determination of forming-limit curves in the laboratory
Matériaux métalliques — Tôles et bandes — Détermination des courbes limites de formage —
Partie 2: Détermination des courbes limites de formage en laboratoire
ICS: 77.040.10
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
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BEING ACCEPTABLE FOR INDUSTRIAL,
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STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
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WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 12004-2:2019(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 2019

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COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Contents Page
Foreword .iv
Introduction .vi
1 Scope (mandatory) . 1
2 Normative references (mandatory) . 1
3 Terms and definitions (mandatory) . 1
4 Symbols and abbreviated terms . 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 measurement. 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 introduction .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
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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.
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:
— Clause 2 and Clause 3 were added from the previous edition, and the subsequent sections were
renumbered.
— The descriptions of when to use part 1 or part 2 of this standard was revised in the Introduction.
— Permissions and requirements were clarified in Clauses 6.1.3, 6.1.5, 6.2.2, 6.2.3, 6.3.2, 6.3.4.3,
and 7.2.2.
— Permission for exceptional cases in Aluminium, as well as Steel, was added in Clause 6.3.1.
— Clarification was added that although the Nakajima method is known to have non-linear strain
paths (Clause 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 Clause 6.3.3.3. In Clause 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 Clause 6.3.4.4. In Clauses 6.3.3.3 and 6.3.4.4, a statement regarding rejection of specimens not
meeting the valid test requirements was added.
— The “Measuring Instrument” clause (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.
— The requirement on the second derivative range was clarified in Clause 7.2.3(c), and the requirements
in the Keys of Figures 8 and 9 were changed to match Clause 7.2.3(c).
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— The permission to use other methods of measurement was moved from Clause 7.2.1 to Clause 7.1,
and was clarified.
— The statement regarding the “time-dependent method” in Clause 7.1 was removed, but still appears
in the Note in Clause 5. The Note in Clause 5 now mentions “time and position dependent methods”.
— In Clause 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.
— 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.
— In normative Annex A, the method was changed to be required rather than proposed. Normative
Annex C was clarified to show that the procedure is required. Clarification to the text of normative
Annex D was added, and it’s 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 is
reported.
— Editorial changes and clarifications were made to Clauses 4, 5, 6.3.1, 6.3.3.2, 6.3.3.3, 6.3.4.3, 7.1,
7.2.1, 7.2.2, 7.2.3, 7.2.4, 8, 9, Annexes B, F, G, and H, and Figures 2, 5, 6, 8, 9, and C.1.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.
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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 is necessary.
The determination of the FLC has to be specific, and it is necessary to use different linear strain
paths. The ISO 12004-2 method should be used for this type of material characterization.
For this part of ISO 12004 (concerning determination of forming-limit curves in laboratory), the
following conditions are also valid.
— 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 fracture and/or localized necking. Many methods exist to
determine the forming limit of a material; however, it should be noted that 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 not only to judge 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.
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oSIST prEN ISO 12004-2:2019
DRAFT INTERNATIONAL STANDARD ISO/DIS 12004-2:2019(E)
Metallic materials — Sheet and strip — Determination of
forming-limit curves —
Part 2:
Determination of forming-limit curves in the laboratory
1 Scope (mandatory)
This part of ISO 12004 specifies the testing conditions to be used 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.
For steel sheet, a maximum thickness of 2,5 mm is recommended.
2 Normative references (mandatory)
There are no normative references in this document.
3 Terms and definitions (mandatory)
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 and abbreviated terms
For the purposes of this document, the symbols and terms given in Table 1 apply.
Table 1 — Symbols and abbreviated terms
Symbol English French German Unit
e Engineering strain Déformation conventionnelle Technische Dehnung %
True strain Déformation vraie Wahre Dehnung (Um-
ε —
(logarithmic strain) (déformation logarithmique) formgrad, Formänderung)
ε Major true strain Déformation majeure vraie Grössere Formänderung —
1
ε Minor true strain Déformation mineure vraie Kleinere Formänderung —
2
ε True thickness strain Déformation vraie en épaisseur Dickenformänderung —
3
σ Standard deviation Ecart-type Standardabweichung —
D Punch diameter Diamètre du poinçon Stempeldurchmesser mm
Carrier blank hole Lochdurchmesser des Trä-
D Diamètre du trou du contre-flan mm
bh
diameter gerblechs
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Table 1 (continued)
Symbol English French German Unit
X(0), X(1) X(m)
X-position Position en X X-Position mm
....X(n)
f(x) =
Best-fit parabola Parabole de meilleur fit Best-Fit-Parabel —
2
ax + bx + c
f(x) = 1/
Best-fit inverse parabola Parabole inverse de meilleur fit Inverse Best-Fit-Parabel —
2
(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 corre- Nummer der X-Position am
m tion at the failure/crack —
spondant 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
0
Coefficient d'anisotropie plas-
r Plastic strain ratio Senkrechte Anisotropie —
tique
Table 2 gives a comparison of the symbols used in different countries.
Table 2 — Comparison of symbols used in different countries
English French German German Anglo-Ameri- Format Unit
symbol can
symbol
Déformation con- Technische Deh-
Engineering strain ε e — %
ventionelle nung
True strain Déformation vraie Wahre Dehnung
(logarithmic (Déformation loga- (Umformgrad, φ ε Decimal —
strain) rithmique) Formänderung)
ε = ln(1 + e) ε = ln(1 + e) φ = ln(1 + ε) — — — —
The symbol used for true strain in Anglo-American-speaking countries is “ε ”; in German-speaking
countries, the symbol “φ” is used for true strain.
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 Anglo-American 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.
NOTE “Time-dependent” methods and combined “time and position dependent” methods are under
development, and may be added in later versions of this standard.
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
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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.
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
2
principal true strains ε on the Y-axis (see Figure 1).
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
2
Y major true strain, ε
1
F FLC
1 uniaxial tension, ε = −[r/(r + 1)] ε
2 1
2 intermediate tensile strain
3 plane strain
4 intermediate stretching strain state
5 intermediate stretching strain state
6 equi-biaxial tension (= stretching strain state) ε = ε
2 1
Figure 1 — Illustration of 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 thickness between 0,3 mm and 4 mm.
6.1.2 Test piece geometry
The following geometries are recommended.
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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).
Key
1 shaft length
2 remaining blank width
3 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.
2
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 or spark-erosion or other methods that do not cause cracks, work hardening or microstructure
changes may be used ensuring that fracture never initiates from the edges of test pieces.
6.1.4 Number of different test piece geometries
At least five geometries for the description of a complete FLC are necessary. (A uniform allocation of the
FLC from uniaxial to equi-biaxial tension is recommended.)
If the description of a complete FLC is not necessary, then a lower number of geometries is allowed, but
this shall be mentioned in the test report.
6.1.5 Number of tests for each geometry
As many test pieces as are necessary shall be tested to achieve at least three valid samples for each test
piece geometry.
6.2 Application of grid
6.2.1 Type of grid
The recommended grid size is approximately one times the material thickness (grid size is related to
the material thickness due to necking width), a maximum grid size of 2,5 times the material thickness
is allowed and the largest grid dimension allowed for a 100 mm punch is 2,54 mm (0,1 in). In general,
grid sizes of 1 mm or 2 mm are used. Small grid sizes are often limited because of their lack of accuracy
(if the undeformed grid is not measured before beginning of test).
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For a stochastic pattern, the “virtual” grid size should correspond to the recommended grid size. A
smaller “virtual” grid size may be used.
6.2.2 Grid application
Deterministic grids (e.g. squares, circles, dots) should have a rich contrast and shall be applied
without any notch effect and/or change in microstructure. Some common application techniques are
electrochemical, photochemical, offset print and grid transfer.
Stochastic (speckle) patterns can be applied by spraying paint onto the test piece surfaces. It is possible
to spray a thin, matt, white base layer to reduce back reflections from the test piece surfaces. Following
this, a cloud of randomly distributed black spots can be sprayed (e.g. black spray paint or graphite).
Grid/pattern adherence to the surface should be checked after deformation for both the deterministic
grids and stochastic patterns.
6.2.3 Accuracy of the undeformed grid
To achieve the required total system accuracy of 2 % (see 6.3.2), the initial grid accuracy should be
better than 1 % based on one times the standard deviation (1σ). This recommendation only applies for
systems where the local undeformed condition is not measured as part of the evaluation.
6.3 Test equipment
6.3.1 General
The following parameters are valid for both Nakajima and Marciniak tests.
Punch velocity: (1,5 ± 0,5) mm/s
Prevention of material’s draw-in: Draw-in shall be prevented as much as possible to ensure near-
ly linear strain paths. Possible methods of mitigation are: using
draw beads, suitable blank holder forces, serrated or knurled tools
(providing that the two last methods do not involve risk of strain
localization or fracture).
Blank holder force, in kN: Draw-in shall be prevented as much as possible.
Test temperature: (23 ± 5) °C
Test direction: For a given FLC, the main orientation of all test pieces shall be the
direction of lowest limit strain e and the same orientation rela-
1
tive to the rolling direction, see Figure 3.
Aluminium: Longitudinal (shaft orientation parallel to rolling direction); ex-
ceptional cases are allowed, but shall be repo
...