ISO 7905-1:2021

Overview

ISO 7905-1:2021 - "Plain bearings - Bearing fatigue - Part 1" specifies how to evaluate and report bearing fatigue for oil‑lubricated plain cylindrical bearings operating under full hydrodynamic lubrication. The standard aims to improve comparability of test‑rig results and to ensure fatigue assessments in real applications are based on fully defined hydrodynamic conditions. It covers dynamic loading of bi‑metal and multilayer bearings and requires evaluation of the oil‑film pressure and the resulting stresses in bearing layers (see Annex A).

Key topics and requirements

• Fatigue objective: Measure dynamic load‑carrying capacity (endurance limit) as stress amplitude versus number of cycles (σ–N) or as an endurance stress for a specified cycle count; endurance is defined when surface cracks > 5 mm appear.
• Hydrodynamic focus: Restricted to conditions with full film separation - excludes mixed lubrication, wear‑induced or tribochemical effects.
• Test rig characteristics:
  • Simple, clear mechanical construction and easy dismantling (in‑situ inspection preferred)
  • Dimensional stability and resistance to housing/shaft deformation
  • Adequate lubricant supply without impairing oil‑film pressure
  • Capability to cover practical ranges of load, stress, and temperature
• Test method requirements:
  • Ability to measure oil film thickness, lubricant temperature, pressure distribution and wear/crack debris
  • Verified hydrodynamic behaviour (viscosity and operating parameters)
  • Clear distinction between running‑in (possible mixed lubrication) and fatigue testing (full hydrodynamic)
  • Use of rotating/uniform stress traversal to reveal material irregularities
• Essential test procedures:
  • Controlled running‑in to avoid overheating and asperity damage; initial minimum film thickness (h0) related to surface profile heights (Rz)
  • Monitoring options: temperature, electrical contact resistance, radiotracer wear or impedance
  • Control of geometry to avoid housing distortion or shaft misalignment
  • Record dynamic load amplitude/direction, film thickness and pressure distributions as functions of time and location
• Stress evaluation: Calculation/measurement of pressure distribution and resulting time‑dependent stresses in bearing layers, with emphasis on the maximum alternating stress (Annex A provides guidance).

Applications and users

ISO 7905-1 is used by:

• Bearing designers and material engineers evaluating fatigue endurance
• Test‑rig manufacturers and laboratories standardizing fatigue tests
• Tribologists and R&D teams comparing bearing materials and coatings
• Maintenance and reliability engineers specifying qualification tests for plain bearings in engines, turbines, compressors and industrial machinery

Practical uses include establishing comparable σ–N data, validating test rigs, and ensuring test conditions match real application hydrodynamic regimes.

Related standards

• ISO 7902‑1 / ISO 7902‑2 / ISO 7902‑3 (hydrodynamic plain journal bearing calculations and parameters)
• ISO 4287 (surface texture/profile parameters)
• Other parts of ISO 7905 series (ISO 7905‑2 to ‑4) for alternate fatigue testing methods

Keywords: ISO 7905‑1, plain bearings, bearing fatigue, hydrodynamic lubrication, test rigs, oil film thickness, pressure distribution, endurance limit, σ–N curve.