SIST EN ISO 12004-2:2009
(Main)Metallic materials - Sheet and strip - Determination of forming-limit curves - Part 2: Determination of forming-limit curves in the laboratory (ISO 12004-2:2008)
Metallic materials - Sheet and strip - Determination of forming-limit curves - Part 2: Determination of forming-limit curves in the laboratory (ISO 12004-2:2008)
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.
Metallische Werkstoffe - Bleche und Bänder - Bestimmung der Grenzformänderungskurve - Teil 2: Bestimmung von Grenzformänderungskurven im Labor (ISO 12004-2:2008)
Dieser Teil von ISO 12004 legt Prüfbedingungen fest, die bei der Erstellung einer für den betreffenden Werkstoff bei Umgebungstemperatur geltenden Grenzformänderungskurve (FLC) mit Hilfe von linearen Form-ände¬rungsverläufen anzuwenden sind. Das Prüfmaterial ist eben, metallisch und von einer Dicke zwischen 0,3 mm und 4 mm.
ANMERKUNG Die Begrenzung der Dicke auf bis zu 4 mm wird vorgeschlagen, um das zulässige Verhältnis Dicke/
Stempeldurchmesser maximal werden zu lassen. Für größere Dicken liegen nicht genügend Erfahrungen vor, und daher kann die Zuverlässigkeit der entsprechenden Grenzdehnungen nicht garantiert werden.
Für Stahlbleche wird eine Maximaldicke von 2,5 mm empfohlen.
Matériaux métalliques - Tôles et bandes - Détermination des courbes limites de formage - Partie 2: Determination des courbes limites de formage en laboratoire (ISO 12004-2:2008)
L'ISO 12004-2:2008 spécifie les conditions d'essai à utiliser pour la construction d'une courbe limite de formage (CLF) à la température ambiante et au moyen de chemins linéaires de déformation. Le matériau considéré est plat, métallique et d'épaisseur comprise entre 0,3 mm et 4 mm.
Kovinski materiali - Pločevina in trakovi - Določevanje krivulj preoblikovalnosti - 2. del: Določevanje krivulj preoblikovalnosti v laboratoriju (ISO 12004-2:2008)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 12004-2:2009
01-april-2009
.RYLQVNLPDWHULDOL3ORþHYLQDLQWUDNRYL'RORþHYDQMHNULYXOMSUHREOLNRYDOQRVWL
GHO 'RORþHYDQMHNULYXOMSUHREOLNRYDOQRVWLYODERUDWRULMX ,62
Metallic materials - Sheet and strip - Determination of forming-limit curves - Part 2:
Determination of forming-limit curves in the laboratory (ISO 12004-2:2008)
Metallische Werkstoffe - Bleche und Bänder - Bestimmung der
Grenzformänderungskurve - Teil 2: Bestimmung von Grenzformänderungskurven im
Labor (ISO 12004-2:2008)
Matériaux métalliques - Tôles et bandes - Détermination des courbes limites de formage
- Partie 2: Determination des courbes limites de formage en laboratoire (ISO 12004-
2:2008)
Ta slovenski standard je istoveten z: EN ISO 12004-2:2008
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
SIST EN ISO 12004-2:2009 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST EN ISO 12004-2:2009
---------------------- Page: 2 ----------------------
SIST EN ISO 12004-2:2009
EUROPEAN STANDARD
EN ISO 12004-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2008
ICS 77.040.10
English Version
Metallic materials - Sheet and strip - Determination of forming-
limit curves - Part 2: Determination of forming-limit curves in the
laboratory (ISO 12004-2:2008)
Matériaux métalliques - Tôles et bandes - Détermination Metallische Werkstoffe - Bleche und Bänder - Bestimmung
des courbes limites de formage - Partie 2: Détermination der Grenzformänderungskurve - Teil 2: Bestimmung von
des courbes limites de formage en laboratoire (ISO 12004- Grenzformänderungskurven im Labor (ISO 12004-2:2008)
2:2008)
This European Standard was approved by CEN on 12 October 2008.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12004-2:2008: E
worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 12004-2:2009
EN ISO 12004-2:2008 (E)
Contents Page
Foreword.3
2
---------------------- Page: 4 ----------------------
SIST EN ISO 12004-2:2009
EN ISO 12004-2:2008 (E)
Foreword
This document (EN ISO 12004-2:2008) has been prepared by Technical Committee ISO/TC 164 "Mechanical
testing of metals" in collaboration with Technical Committee ECISS/TC 1 “Steel - Mechanical testing” 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 April 2009, and conflicting national standards shall be withdrawn at the
latest by April 2009.
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.
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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 12004-2:2008 has been approved by CEN as a EN ISO 12004-2:2008 without any
modification.
3
---------------------- Page: 5 ----------------------
SIST EN ISO 12004-2:2009
---------------------- Page: 6 ----------------------
SIST EN ISO 12004-2:2009
INTERNATIONAL ISO
STANDARD 12004-2
First edition
2008-10-15
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
Reference number
ISO 12004-2:2008(E)
©
ISO 2008
---------------------- Page: 7 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Symbols and abbreviated terms . 1
3 Principle. 2
4 Test pieces and equipment. 3
5 Analysis of strain profile and measurement of ε - ε pairs . 10
1 2
6 Documentation. 15
7 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 cross-sectional data . 24
Annex H (normative) Flowchart from measured strain distributions to FLC values . 25
Bibliography . 27
© ISO 2008 – All rights reserved iii
---------------------- Page: 9 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 12004-2 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 2, Ductility testing.
This first edition of ISO 12004-2, together with ISO 12004-1, cancels and replaces ISO 12004:1997 which has
been technically revised.
ISO 12004 consists of the following parts, under the general title Metallic materials — Sheet and strip —
Determination of forming-limit curves:
⎯ Part 1: Measurement and application of forming-limit diagrams in the press shop
⎯ Part 2: Determination of forming-limit curves in the laboratory
iv © ISO 2008 – All rights reserved
---------------------- Page: 10 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(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.
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.
This method should be used for material characterization as described in ISO 12004-2.
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, 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.
© ISO 2008 – All rights reserved v
---------------------- Page: 11 ----------------------
SIST EN ISO 12004-2:2009
---------------------- Page: 12 ----------------------
SIST EN ISO 12004-2:2009
INTERNATIONAL STANDARD ISO 12004-2:2008(E)
Metallic materials — Sheet and strip — Determination of
forming-limit curves —
Part 2:
Determination of forming-limit curves in the laboratory
1 Scope
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 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
ε —
(logarithmic strain) (déformation logarithmique) (Umformgrad, 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 Diamètre du trou du contre-flan Lochdurchmesser des
D mm
bh
diameter Trägerblechs
X(0), X(1)
X-position Position en X X-Position mm
X(m) .X(n)
2
f(x) = ax + bx + c Best-fit parabola Parabole de meilleur fit Best-Fit-Parabel —
f(x) = Best-fit inverse parabola Parabole inverse de meilleur fit Inverse Best-Fit-Parabel
2 —
1/(ax + bx + c)
© ISO 2008 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
Table 1 (continued)
Symbol English French German Unit
S(0), S(1).S(5) Section Section Schnitt —
n Number of X-positions Nombre de points en X Nummer der X-Positionen —
Section number of the Numéro de la section Nummer des Schnittes zum
m —
failure position correspondant à la rupture Riss
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
r Plastic strain ratio Coefficient d'anisotropie plastique Senkrechte Anisotropie —
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-American Format Unit
symbol symbol
Déformation Technische
Engineering strain e — %
ε
conventionelle Dehnung
True strain Déformation vraie Wahre Dehnung
(logarithmic strain) (Déformation (Umformgrad, Decimal —
ϕ ε
logarithmique) 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.
3 Principle
The FLC is intended to represent the almost intrinsic limit of a material in deformation assuming a proportional
strain path. To determine the FLC accurately, it is necessary to have a nearly frictionless state in the zone of
evaluation.
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 measurement should be performed using a “position-dependent” method (see 5.2).
NOTE A “time-dependent” method is under development.
The deformation (strain) across the deformed test piece is determined and the measured strains are
processed in such 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 2008 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
The forming limits are determined for several strain paths (different ratios between ε and ε ). The determined
1 2
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 diagram, the forming-limit
1 2
diagram. The minor true strains ε are plotted on the X-axis and the major principal true strains ε on the
2 1
Y-axis (see Figure 1).
Standard conversion formulae permit the calculation of major (ε ) and minor true strains (ε ). In the following,
1 2
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
4 Test pieces and equipment
4.1 Test pieces
4.1.1 Thickness of test pieces
This procedure is intended for flat, metallic sheets with thickness between 0,3 mm and 4 mm.
4.1.2 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 2008 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
Key
1 shaft length
2 remaining blank width
3 fillet radius = R = 20 mm to 30 mm
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 outer circular shape of the blanks, a more uniform distribution of the experimental forming-limit points is
attainable than when rectangular strips are used.
4.1.3 Test piece preparation in test area
Milling or spark-erosion or other methods that do not cause cracks, work hardening or microstructure changes
can be used ensuring that fracture never initiates from the edges of test pieces.
4.1.4 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.
4.1.5 Number of tests for each geometry
As many test pieces as are necessary to achieve at least three valid samples.
4 © ISO 2008 – All rights reserved
---------------------- Page: 16 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
4.2 Application of grid
4.2.1 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).
For a stochastic pattern, the “virtual” grid size should correspond to the recommended grid size. A smaller
“virtual” grid size may be used.
4.2.2 Grid application
Deterministic grids (e.g. squares, circles, dots) should have a rich contrast and have to 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. Paint adherence
to the surface should be checked after deformation. 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).
4.2.3 Accuracy of the undeformed grid
To achieve the required system accuracy of 2 %, the initial grid accuracy should be better than 1 % based on
one times the standard deviation (1σ). This is only required for systems where the undeformed condition is not
considered for evaluation.
4.3 Test equipment
4.3.1 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 nearly linear
strain paths. Possible measures 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 direction of all test pieces shall be the direction
of lowest limit strain e or e and same relative to the rolling direction,
1 2
see Figure 3.
Aluminium: Longitudinal (shaft parallel to rolling direction).
Steel: Transverse (shaft perpendicular to rolling direction); exceptional cases
are allowed, but have to be reported.
In the case that the preferred failure direction is not known, it should be checked using a biaxial strain test or
any other suitable method
© ISO 2008 – All rights reserved 5
---------------------- Page: 17 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
a) Steel b) Aluminium
a
Rolling direction (RD).
Figure 3 — Shaft orientation with respect to the rolling direction (RD)
Surface roughness of punch: The contacting area of the punch surface should be polished.
Die material and hardness: Hardened steel.
Blank holder shape: Full circular blank holder, see Figure 4.
Key
D cut-out width, equal to punch diameter
1 serrated blank holder with cut-out
2 blank
3 punch
NOTE To come closer to ideal linear strain paths and to reach a more uniform distribution of true strain values, a
circular blank holder with a cut-out might be useful (recommended width of cut-out = punch diameter).
Figure 4 — Blank holder with cut-out
Test stop criterion: Crack occurrence.
Crack detection: Visual or force drop.
4.3.2 Strain measurement
Total system accuracy:
The total accuracy of the measurement system should be better than 2 % based on one times the
standard deviation (1σ) (accuracy depends on grid accuracy/resolution, camera resolution, measuring
field, calculation algorithm.).
6 © ISO 2008 – All rights reserved
---------------------- Page: 18 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
Accuracy of the undeformed grid:
Initial grid accuracy should be better than 1 % based on one times the standard deviation (1 σ) (only
required for systems where the undeformed condition is not used in evaluation).
Measurement instrument:
Any convenient grid-measuring device is accepted; the uncertainty of the measurement device shall be
less than 1 % of the measured length. Cameras and software allowing total measuring accuracy better
than 2 % based on one times the standard deviation (1 σ) are recommended.
Strain measurement:
Strain measurement can be performed either by measurement of only the final grid dimension, where the
precision of the initial grid is known (< 1 %), or by comparison of the final grid dimension relative to the
initial one, or using an incremental method, which refers to the initial grid size for the strain calculation.
4.3.3 Nakajima test
4.3.3.1 General
The Nakajima forming method uses a hemispherical punch, see Figure 5.
Dimensions in millimetres
Key
1 lubrication layer
Figure 5 — Illustration of the cross section of the tool used for Nakajima testing
4.3.3.2 Tool
Punch diameter: (100 ± 2) mm
Die diameter: Preferably 105 mm and W punch diameter plus 2,5 times the material thickness
Die radius: Preferably 8 mm with a minimum of either 5 mm or 2 times the material thickness,
whichever is the greater value.
© ISO 2008 – All rights reserved 7
---------------------- Page: 19 ----------------------
SIST EN ISO 12004-2:2009
ISO 12004-2:2008(E)
4.3.3.3 Test conditions
Type of lubricant:
The tribo-system should be adjusted so that fracture occurs within a distance less than 15 % of the punch
diameter away from the apex of the dome. The test is only valid in this case. With an optimal tribo-system,
it is possible to induce fracturing very near to the apex of the dome. In this case, the problem of
pronounced double necking symmetrical to the apex of the dome (where afterwards one of the two
necked zones is fractured) is drastically reduced. The strong double peaks in the strain profile cross
section are reduced. This makes automatic evaluation of ε - ε pairs more accurate. The tribo-system
1 2
may not be changed during the measurement of one specific FLC.
Recommended lubricant systems are:
a) for low punch forces (thinner sheets or materials with relative low tensile strength, e.g. for Al-sheets
< 2 mm):
1) oil or grease (e.g. lanolin);
2) circular blanks of PE or PTFE foil (e.g. 0,05 mm thick);
3) oil or grease.
b) for high punch forces (thicker sheets or materials with higher tensile strength):
1) simple:
as a) but with soft PVC instead of PTFE.
2) complex:
i) oil or grease (e.g. lanolin);
ii) circular blanks of PE or PTFE foil (0,05 mm to 0,1 mm thick);
iii) oil or grease;
iv) soft PVC sheet (3 mm thick);
v) oil or grease;
vi) circular blanks of PE or PTFE foil (0,05 mm to 0,1 mm thick );
vii) oil or grease.
Layers i and vii are optional.
With these two lubrication systems, most of the tests meet the condition of a fracture on the top of the dome.
From previous testing experience on different material types, no general tribo-system (suitable for all materials
and all thickness ranges) could be recommended. The most difficult conditions are encountered during the
testing of high strength materials of large thickness. Alternative lubrication systems can be used based on
personal practice and experience. In such cases, it is recommended that the lubrication systems be tested in
advance during hemispherical punch stretching. The tribo-system providing the largest limiting dome height,
and meeting the condition of a fracture on the top of the dome, is considered to be the most suitable.
The diameter of the foil blank should be smaller than the punch diameter to prevent the foil wrinkling.
8 © ISO 2008 – All
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.