ISO 7905:2021

Description

This document specifies a method of improving test result comparability by evaluating the stresses in the bearing layers leading to fatigue (see Annex A). A similar evaluation is required in practical applications. Because the stresses are the result of pressure build-up in the hydrodynamic film, it is essential to fully state the conditions of operation and lubrication. In addition to dynamic loading, dimensional and running characteristics, the inclusion of the following adequately defines the fatigue system:

a)    under conditions of dynamic loading the minimum bearing oil film thickness as a function of time and location to ensure no excessive local  overheating or shearing as a result of mixed lubrication when running in;

b)    the distribution of pressure circumferentially and axially with time under dynamic loading;

c)    from this the resulting stresses in the bearing layers as a function of time and location, especially the maximum alternating stress.

Furthermore, bearing fatigue can be affected by mixed lubrication, wear, dirt, tribochemical reactions and other effects encountered in use thus complicating the fatigue problem. This document is therefore restricted to fatigue under full hydrodynamic separation of the bearing surfaces by a lubricant film.

This document applies to oil-lubricated plain cylindrical bearings, in test rigs and application running in conditions of full hydrodynamic lubrication. It comprises dynamic loading in bi-metal and multilayer bearings.

NOTE      The number of practical applications with different requirements has led to the development of many bearing test rigs. If the conditions of lubrication employed on these test rigs are not defined in detail, test results from different rigs are generally neither comparable nor applicable in practice. Different test rigs can yield inconsistent ranking among equal materials.