Overview
ISO/TR 25269:2026, Rolling bearings - Calculation of theoretical reliability, is an ISO technical report that provides a standardized method for analyzing the theoretical reliability of rolling bearings, specifically in terms of fatigue life. This standard is built on the principles established in ISO 281 and ISO 16281, focusing exclusively on failure mechanisms associated with rolling contact fatigue. Other bearing failure modes such as wear, microspalling (gray-staining), or white etching cracks (WEC) are excluded from its scope.
The method outlined in ISO/TR 25269:2026 utilizes statistical distributions, primarily the Weibull distribution, to estimate the probability that a rolling bearing or a system of bearings will perform without fatigue-related failure under specified operating conditions and for a defined period or number of revolutions. It is important to note that the calculated theoretical reliability is not intended as the sole criterion for bearing selection or optimization, as real-world reliability depends on additional operational factors.
Key Topics
- Reliability Analysis Focus: The standard details the procedures for calculating the theoretical reliability of rolling bearings using fatigue life data as per ISO 281 and ISO 16281.
- Statistical Methods: The Weibull distribution (both two-parameter and three-parameter forms) is used for modeling the variability of bearing life and failure probability.
- System Reliability: Provides a method to calculate the combined theoretical reliability of arrangements containing multiple individual rolling bearings.
- Exclusions and Limitations:
- Only fatigue life failure mode is covered.
- Does not address failure due to wear, microspalling, or WEC.
- Theoretical reliability calculations do not substitute for operational safety factors or compensate for uncertainties in load assumptions.
- Multi-row rolling bearings are treated as single entities in reliability analysis.
- Practical Examples and Graphical Representations: Includes demonstrative calculation examples and diagrams to clarify reliability computations.
Applications
The guidance provided by ISO/TR 25269:2026 is highly valuable across industries where rolling bearings are essential components, such as automotive, industrial machinery, wind energy, and power transmissions. Key applications include:
- Engineering Design: Supports engineers in conducting comparative assessments of rolling bearings based on standardized fatigue life reliability calculations.
- System Analysis: Enables the assessment of total reliability for systems with multiple bearings, such as gearboxes and drivetrains.
- Predictive Maintenance Planning: Assists in estimating bearing longevity for maintenance scheduling and risk management.
- Quality Control: Facilitates a uniform approach to evaluating bearing reliability for product development and validation.
- Education and Training: Provides a technical foundation for teaching and understanding statistical methods in bearing reliability assessment.
While ISO/TR 25269:2026 is a crucial tool for theoretical calculations, users should always integrate operational realities, including minimum load, lubrication, rolling element slip, and thermal conditions, when selecting bearings or planning maintenance.
Related Standards
Understanding and using ISO/TR 25269:2026 often requires familiarity with several closely related international standards:
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ISO 281:2007 – Rolling bearings - Dynamic load ratings and rating life
Defines basic dynamic load ratings and the method for calculating bearing life.
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ISO 16281:2025 – Rolling bearings - Methods for calculating the modified reference rating life for universally loaded rolling bearings
Addresses life calculation methods considering actual operating conditions.
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ISO/TR 1281-1 and ISO/TR 1281-2 – Explanatory notes on ISO 281
Provide background, explanations, and guidance related to ISO 281 and bearing life calculation.
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VDMA 23904
Focuses on reliability assessment for wind energy gearboxes.
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IEC/TS 61400-4-1
Addresses reliability assessment of drivetrain components in wind turbines.
Leveraging ISO/TR 25269:2026 in combination with these standards enables a holistic approach to rolling bearing reliability analysis and supports the engineering of safer, more dependable mechanical systems.