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