Overview
ISO 3327:2009 specifies a standardized method for determining the transverse rupture (bend) strength of hardmetals using a three-point bending arrangement. It is intended for hardmetals of negligible ductility; when specimens show significant plastic deformation before fracture, results can be misleading and the method should then be used only for comparative purposes. The standard defines specimen geometries, apparatus, test procedure, calculation methods and reporting requirements to ensure reproducible bend-strength data for quality control and materials evaluation.
Key topics and technical requirements
- Scope and limitation: Applicable to hardmetals with negligible plasticity; caution advised if plastic deformation occurs.
- Specimen types & dimensions: Three standard specimen types:
- Type A (rectangular) - 35 × 5 × 5 mm
- Type B (rectangular) - 20 × 6.5 × 5.25 mm
- Type C (cylindrical) - nominal 25 mm length, diameter ~3.3 mm
- Test fixture: Three rollers (supports and loading roller) of tungsten carbide, same diameter (3.2–6 mm); a 10 mm ball may be used for flat specimens only. Support spans: 30 mm ±0.5 mm (Type A) and 14.5 mm ±0.5 mm (Types B/C).
- Surface and machining: Strict surface preparation required - machined specimens: surface roughness R ≤ 0.4 µm; chamfers 0.15–0.2 mm at 45°. Green (as-sintered) specimens may be used but typically give lower bend-strength values.
- Loading rate: Force must increase uniformly at ≤ 200 N/(mm·s) (limits expressed as maximum N/s for each specimen type in the standard).
- Calculations: Bend strength is calculated using the standard three-point bend formulae provided for rectangular and cylindrical specimens (correction factor k applied for chamfers). Mean of at least five tests is reported and rounded per the standard.
- Reporting: Mandatory details include specimen type, surface preparation (S = sintered, G = ground), loading method, test geometry and any deviations or incidents.
Applications and users
- Quality control in hardmetal and cemented carbide manufacturing
- Materials testing laboratories assessing bend (transverse rupture) strength for production lots or R&D
- Powder metallurgy and tooling manufacturers who need standardized strength data for design and warranty claims
- Metallurgists and engineers comparing processing routes (sintered vs machined) or different compositions
Keywords: ISO 3327:2009, hardmetals testing, transverse rupture strength, three-point bend test, bend strength, specimen preparation, cemented carbide.
Related standards and references
- Developed by ISO/TC 119 (Powder metallurgy); third edition replaces ISO 3327:1982.
- Bibliography includes VAMAS reports on bend-strength measurement and effect of specimen geometry for further context.
