ISO 12004-2:2021

Overview

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" - defines laboratory procedures for constructing a reproducible forming-limit curve (FLC) at ambient temperature using linear strain paths. It applies to flat metallic sheets and strips with thickness from 0.3 mm to 4 mm and gives test conditions, measurement procedures and evaluation methods required to obtain material-specific FLCs for formability characterization.

Key topics and requirements

• Scope & purpose: Specifies controlled laboratory testing to determine a unique FLC for a material, distinct from process- or component-dependent FLCs obtained in production (ISO 12004-1).
• Test pieces & geometry: Requirements for specimen thickness, geometry, preparation and the number of tests and geometries to be used.
• Grid application & strain measurement: Use of grids (type, application, accuracy) to determine major/minor true strains (ε1, ε2) and thickness strain; permission for alternate measurement methods is addressed.
• Test equipment & methods: Procedures for common laboratory forming tests such as the Nakajima and Marciniak methods; criteria for valid tests (e.g., failure location relative to dome apex) and strain-determination instruments.
• Strain analysis & evaluation: Position-dependent measurement using section lines, extraction of the characteristic “bell-shaped curve”, use of best-fit parabola and inverse best-fit parabola, second-derivative filtering and windows for reliable ε1–ε2 pair extraction.
• Documentation & reporting: Required documentation and test-report content to ensure repeatability and traceability of the FLC.
• Annexed methods: Normative and informative annexes cover computation of fit-window widths, mathematical representation of FLCs, flowcharts from measured distributions to reported FLC values, and validation data.

Applications and who uses it

ISO 12004-2:2021 is intended for:

• Materials and metallurgical engineers characterizing sheet formability
• Stampings/forming process designers validating simulation inputs
• R&D laboratories developing new alloys or heat treatments
• Quality and certification labs producing material data sheets
• Automotive, aerospace and metal-supplier organizations comparing material performance

Practical uses include producing laboratory-derived FLCs for process design, validating finite-element forming simulations, comparing materials for selection, and establishing formability limits for product development.

Related standards

• ISO 12004-1 (component/press-shop based FLC determination)
• Mechanical-property standards referenced for complementary data: ISO 6892-1, ISO 10113, ISO 10275

Keywords: ISO 12004-2:2021, forming-limit curve, FLC, forming-limit diagram (FLD), Nakajima test, Marciniak test, sheet metal formability, strain measurement, laboratory FLC.