ISO/TC 4/SC 8/WG 9 - Rolling bearings — Methods for calculating the modified reference rating life for universally loaded bearings

This document contains information on the reliability analysis for rolling bearings. The method described only pertains to the fatigue life per ISO 281 or ISO 16281 of rolling bearings. Other mechanisms of failure, like wear, microspalling (gray-staining) or white etching cracks (WEC), lie outside the scope of this document. A multi-row rolling bearing is considered as a single rolling bearing in the context of this document. The method is based on the life analysis per ISO 281 or ISO 16281, thus the general directions and limitations given in these documents apply. The calculated theoretical reliability is not suitable as the only criterion to select or optimize a rolling bearing or rolling bearing arrangements in powertrains, because the actual bearing reliability in service is also dependent on minimum load, rolling element slip, lubricant and lubricant supply, and heat dissipation. The calculated theoretical reliability does not replace or substitute any safety factors used for consideration of uncertainties in load assumptions, e.g. operation factors for shock loads.

This document defines the calculation of the modified reference rating life taking into consideration lubrication, contamination, and fatigue load limit of the bearing material, as well as tilting or misalignment, operating clearance of the bearing and internal load distribution on rolling elements. The calculation method provided in this document covers influencing parameters additional to those described in ISO 281. The general directions and limitations given in ISO 281 apply to this document. The calculation methods pertain to the fatigue life of the bearings. Other mechanisms of failure, like wear or microspalling (gray-staining), lie outside the scope of this document. This document applies to single- and multi-row radial and thrust ball bearings, subjected to radial and axial load and with radial clearance and tilt taken into account. It also applies to single- and multi-row radial and thrust roller bearings, subjected to radial and axial load and with radial clearance, edge stress and tilt taken into account. References to methods for the analysis of the internal load distribution under general load are given. The calculation of load distribution and basic reference rating life is also applicable to hybrid bearings, using the dynamic load ratings per ISO 20056-1[2]. The calculation of the modified reference rating life is not applicable to hybrid bearings.