ISO 3325:1996

Overview

ISO 3325:1996 specifies a standardized three-point bending test for determining the transverse rupture strength of sintered metal materials (excluding hardmetals). The method is primarily intended for comparative evaluation - for example, comparing the sintered strength of a production batch with a reference powder or reference strength. It applies to sintered parts whether or not they have been heat-treated, sized or coined after sintering, and to machined specimens when care is taken to avoid introducing stress raisers.

Key topics and technical requirements

• Test principle: A bar-shaped test piece is supported on two rollers and loaded at mid-span until fracture (transverse rupture / bend test).
• Specimen geometry: Nominal test-piece produced from a 30 mm × 12 mm die cavity, nominal thickness 6 mm; thickness must be uniform within specified tolerances and cut with faces perpendicular to compaction axis.
• Apparatus (rollers):
  • Support and loading cylinders diameter: 32 mm ± 0.1 mm
  • Support center distance: 25.0 mm ± 0.2 mm or 25.4 mm ± 0.2 mm
  • Cylinder material: hardened steel (≥700 HV) or hardmetal
  • Test machine: static loading with accuracy of ±1%
  • Load-applier mounted midway between supports; support mounting may be adjustable to compensate for non-parallel specimen faces
• Procedure highlights:
  • Position specimen symmetrically on supports with longitudinal axis at 90° ± 30° to cylinder axes
  • Increase load slowly so time to fracture is not less than 10 s
  • Record load at first sudden drop (first crack)
• Result expression: Transverse rupture strength Rtr calculated using the standard formula:
  • Rtr = 3 F L / (2 b h^2)
  • where F = fracture load, L = support span, b = specimen width, h = specimen thickness
• Uncertainty: Method absolute uncertainty is specified (ISO gives example AR = 0.02 R, i.e., about 2%).
• Reporting: Include reference to ISO 3325, specimen identification, support span used, test results (mean), and any non-standard operations or incidents.

Applications and who uses it

• Quality control and acceptance testing for sintered metal components
• Comparative evaluation of metal powders and sintering cycles in powder metallurgy
• Materials and mechanical engineers assessing bending strength for design, process optimization, or supplier qualification
• Research labs and certification bodies tracking batch-to-batch variability of sintered strength

Related standards

• Prepared by ISO/TC 119 (Powder metallurgy), Subcommittee SC 3 (sampling and testing). ISO 3325:1996 is the second edition and supersedes the 1975 edition.
• Refer to other ISO powder metallurgy test standards for complementary mechanical-property and dimensional-control methods.

Keywords: ISO 3325:1996, transverse rupture strength, sintered metal materials, powder metallurgy, three-point bending test, sintered strength, test specimen, test equipment.