ISO 7438:2020

Overview

ISO 7438:2020 - "Metallic materials - Bend test" specifies a standardized method to determine the ability of metallic materials to undergo plastic deformation by bending. The fourth edition (2020) describes test piece types, test equipment, test procedures and interpretation rules for bend tests on metallic products. It applies to test pieces taken from products as defined by the relevant product standard, but is not applicable to certain items (for example full-section tubes or welded joints) for which separate standards exist.

Key topics and technical requirements

• Test principle: Plastic bending of round, square, rectangular or polygonal cross-section test pieces until a specified bend angle or condition (parallel legs or contact) is reached.
• Test equipment: Three common setups are covered - bending device with two supports and a former, V-block and former, and clamp with former. Supports, formers and V-block edges must be of sufficient hardness and sized relative to the test piece.
• Test-piece dimensions:
  • Width and thickness limits and guidance: e.g., sheet thickness normally equals product thickness; pieces >25 mm may be reduced to ≥25 mm by machining (tension side left unmachined).
  • Round/polygonal cross-sections: full cross-section up to 30 mm permitted; guidance provided for up to 50 mm and above (minimum retained cross-section ≥25 mm).
  • Edge radii for rectangular pieces specified by thickness class (3 mm, 1.5 mm, 1 mm).
• Procedure and conditions:
  • Ambient testing between 10 °C and 35 °C; controlled tests at (23 ± 5) °C.
  • Bending force applied slowly to permit free plastic flow; dispute rate of former displacement = (1 ± 0.2) mm/s.
  • Methods: bend to a specified angle, make legs parallel at a specified distance, or bring legs into direct contact.
  • Annex A provides angle calculation from former displacement; Annex B (new in 2020) covers bend testing under plane-strain conditions.
• Safety and reporting: Adequate guarding required; test report content and interpretation rules are specified (absence of visible cracks when no product standard criteria exist).

Applications

• Quality control and acceptance testing of metallic products (sheets, strips, sections, forgings, castings, semi-finished products).
• Characterizing ductility, formability and bending performance of metals for design, production and inspection.
• Verifying compliance with product standards that reference ISO 7438 test methods.

Who uses this standard

• Materials testing laboratories, metal fabricators, product manufacturers, quality assurance engineers, metallurgists, and standards authors specifying mechanical testing requirements.

Related standards

• ISO 7438:2020 was prepared by ISO/TC 164 (Mechanical testing of metals) in collaboration with CEN. Other ISO or national standards address bend testing variants for welded joints, tubes and specialized product types - refer to the relevant product or welding standards when applicable.

Keywords: ISO 7438:2020, bend test, metallic materials, bending test, plastic deformation, plane strain, test piece, V-block, former, test procedure.