What is ISO 13939 - Performance testing of foil journal bearings about?  
ISO 13939 is an International Standard that discusses performance testing of foil bearings. It provides best practices to ensure stability and load capacity of foil journal bearings can be optimized.
ISO 13939 describes a method for comparing the performance test results of foil journal bearings, which are lubricated by air (gas) and supported by the gas-dynamic force generated via the rotations of the rotating shaft. The test method described in ISO 13939 has the following application coverage.
- The criterion for evaluating the static load capacity is the steady-state condition; i.e. the method is applicable under limited operating conditions with uniform magnitude, load direction, and rotational speed
- The evaluation procedure can be applied only if the foil journal bearing is under uniform rotating inertia at an arbitrary rotational speed
- The dynamic load with time-variant magnitude and direction is not considered
Who is ISO 13939 - Performance testing of foil journal bearings for? 
ISO 13939 on performance testing of foil journal bearings is relevant to: 
- Manufacturers of foil bearings
- High-speed and high-temperature applications
- Manufacturers of turbo machinery
- Industrial machinery manufacturers
- Aeronautics and power industry
- Fabricators and mechanical engineers
Why should you use ISO 13939 - Performance testing of foil journal bearings?  
Foil bearings operate without oil because they are lubricated by a gas film. A thin top foil is supported by a corrugated bump foil in a basic foil bearing. The basic function of these components is to support a rotating shaft. 
The test procedure proposed in ISO 13939 aims to predict and evaluate the static load capacity, friction coefficient, and lifetime of foil journal bearings and compare the results of these parameters under different test conditions, i.e. at varying dimensions of foil bearing, rotational speed of a shaft, pressure, and humidity of the surroundings. 
By providing indications on static load capacity, friction coefficient, and lifetime of foil journal bearings, ISO 13939 helps you manufacture foil journal bearings that meet requirements of stability and load capacity, while avoid misalignment and power loss, for the efficient functioning of the end-use application.
What’s changed since the last update?
BS ISO 13939:2019 supersedes ISO 13939:2012, which is withdrawn. BS ISO 13939:2019 includes some technical changes with respect to ISO 13939:2012. These include: 
- The content of Scope has been changed to a clearer expression
- Table 1, Table 2, all figures, and all formulae have been reviewed
- The wording of definitions has been reviewed for consistency with ISO rules
