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

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Metallic materials — Determination of forming-limit curves for sheet and strip —Part 2: Determination of forming-limit curves in the laboratory由国际标准化组织(International Organization for Standardization，简称ISO)于2021-02发布，适用于全球范围。

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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 a nd definiti ons

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 —

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 D mm

bh

diameter des Trägerblechs

X(0), X(1) X-position Position en X X-Position mm

X(m) ....X(n)

Table 1 (continued)

Symbol English French German Unit

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

—

2

ax + bx + c

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

—

2

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

0

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.

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