ISO 7905-2:2021

Overview

ISO 7905-2:2021 specifies a laboratory method to determine the endurance limit in fatigue of metallic plain bearing materials tested as standalone specimens (i.e., not bonded to steel backing). The method uses a polished, cylindrical specimen and an axial oscillating load to reproduce the cyclic stresses that cause bearing fatigue. Results are presented as stress–number (S–N or Wöhler) curves and evaluated statistically to define endurance limits under controlled test conditions.

Key topics and requirements

• Specimen geometry and surface finish: Cylindrical specimens manufactured in accordance with the standard’s figure and polished to be representative of production bearing surfaces. Surface roughness is specified as R < 6 µm (per ISO 4287).
• Test rig and loading: Specimens are axially clamped and subjected to an oscillating compressive/tensile load. The rig must record load and displacement; an example configuration is provided in the standard.
• Test parameters: The standard defines the test cycle range, test frequency range (document specifies 50–80 Hz) and the approach for finite-life and endurance (infinite-life) determination.
• Data presentation and evaluation:
  • S–N (Wöhler) curves at a specified temperature (±2 °C).
  • Statistical evaluation is recommended because of fatigue scatter.
  • Alternative representations such as Gerber or Goodman–Haigh diagrams may be used to show stress amplitude vs mean stress.
  • Metallographic examination of failed specimens to identify damage mechanisms, corrosion or thermal diffusion effects.
• Limitations noted: Results apply to bulk material specimens; they do not capture residual stresses or metallurgical conditions that may exist in thin bearing layers bonded to backing materials.

Applications and users

ISO 7905-2 is practical for:

• Bearing manufacturers validating material fatigue endurance of plain bearing alloys
• Materials and tribology engineers conducting R&D on bearing materials
• Independent test laboratories performing fatigue characterization or quality assurance
• Design engineers needing S–N data to inform bearing life predictions and safety factors

Use cases include material selection, comparative fatigue performance testing, and supporting specifications for plain bearings where the bearing material behaviour (not the bonded assembly) must be quantified.

Related standards

• ISO 4287 - Surface texture: profile method (referenced for roughness)
• Other parts of the ISO 7905 series (plain bearing test methods)
• ISO 3548-1 and ISO 4378-1 (related bearing design, materials and terminology)

Keywords: ISO 7905-2, plain bearings, bearing fatigue testing, endurance limit, cylindrical specimen, S–N curve, Wöhler curve, metallic bearing material.