“Expanded calculation of the adjusted rating life”
Schaeffler introduced the “Expanded calculation of the adjusted rating life” in 1997. This method was standardised for the first time in DIN ISO 281 Appendix 1 and has been a constituent part of the international standard ISO 281 since 2007. As part of the international standardisation work, the life adjustment factor a_{DIN} was renamed as a_{ISO} but without any change to the calculation method.
The basis of the rating life calculation in accordance with ISO 281 is Lundberg and Palmgren's fatigue theory which always gives a final rating life.
However, modern, high quality bearings can exceed by a considerable margin the values calculated for the basic rating life under favourable operating conditions. Ioannides and Harris have developed a further model for fatigue in rolling contact that expands on the Lundberg and Palmgren theory and gives a better description of the performance capability of modern bearings.
Values which must be taken into account in the “Expanded calculation of the adjusted rating life”
The method “Expanded calculation of the adjusted rating life” takes account of the following influences:
 the bearing load
 the fatigue limit of the material
 the extent to which the surfaces are separated by the lubricant
 the cleanliness in the lubrication gap
 additives in the lubricant
 the internal load distribution and frictional conditions in the bearing
The influencing factors, especially those relating to contamination, are extremely complex. A great deal of experience is essential for an accurate assessment. As a result, please consult Schaeffler for further advice.
The tables and diagrams in this chapter can only give guide values.
The required size of a rolling bearing is dependent on the demands made on its:
 rating life
 load carrying capacity
 operational reliability
Basic dynamic load ratings
The dynamic load carrying capacity is described in terms of the basic dynamic load ratings. The basic dynamic load ratings are based on DIN ISO 281.
The basic dynamic load ratings for rolling bearings are matched to empirically proven performance standards published in previous FAG and INA catalogues.
The fatigue behaviour of the material determines the dynamic load carrying capacity of the rolling bearing.
Dynamic load carrying capacity
The dynamic load carrying capacity is described in terms of the basic dynamic load rating and the basic rating life.
Factors influencing the fatigue life
The fatigue life is dependent on:
 the load
 the operating speed
 the statistical probability of the first appearance of failure
Basic dynamic load rating C
The basic dynamic load rating C applies to rotating rolling bearings. It is:
 a constant radial load C_{r} for radial bearings
 a constant, concentrically acting axial load C_{a} for axial bearings
The basic dynamic load rating C is that load of constant magnitude and direction which a sufficiently large number of apparently identical bearings can endure for a basic rating life of one million revolutions.
Calculation methods
The methods for calculating the rating life are:
L_{10} or L_{10h}
The basic rating life in millions of revolutions (L_{10}) is determined in accordance with ➤ Equation, the basic rating life in operating hours (L_{10h}) is determined in accordance with ➤ Equation.
Rating life in revolutions
Rating life in operating hours
Legend
L_{10} 
10^{6} 
The basic rating life in millions of revolutions, that is reached or exceeded by 90% of a sufficiently large number of apparently identical bearings before the first indications of material fatigue appear

L_{10h} 
h 
The basic rating life in operating hours, that is reached or exceeded by 90% of a sufficiently large number of apparently identical bearings before the first indications of material fatigue appear

C 
N 
Basic dynamic load rating, see product tables

P 
N 
Equivalent dynamic bearing load

p 
 
Life exponent; for roller bearings: p = ^{10}/_{3} for ball bearings: p = 3

n 
min^{1} 
Operating speed (nominal speed)

The basic rating life L_{10} in accordance with ➤ Equation is defined for a load of constant magnitude acting in a constant direction. In the case of radial bearings, this is a purely radial load, while in the case of axial bearings it is a purely axial load.
Equivalent dynamic load P is identical to the combined load occurring in practice
If the load and speed are not constant, equivalent operating values can be determined that induce the same fatigue as the actual loading conditions.
Equivalent operating values for variable load and speed ➤ section.
Equivalent dynamic radial bearing load
The equivalent dynamic load P on a bearing subjected to combined load (with a radial and axial load) is calculated in accordance with ➤ Equation.
Equivalent dynamic radial bearing load
Legend
P 
N 
Equivalent dynamic radial bearing load

X 
 
Radial load factor; see product tables

F_{r} 
N 
Radial load

Y 
 
Axial load factor; see product tables

F_{a} 
N 
Axial load

The calculation in accordance with ➤ Equation cannot be applied to radial needle roller bearings, axial needle roller bearings and axial cylindrical roller bearings. Combined loads are not permissible with these bearings.
For radial needle roller bearings ➤ Equation, for axial bearings ➤ Equation.
Equivalent dynamic radial bearing load
Legend
P 
N 
Equivalent dynamic radial bearing load

F_{r} 
N 
Radial load

Equivalent dynamic axial bearing load
In axial bearings with α = 90°, only axial loads are possible
Axial deep groove ball bearings, axial cylindrical roller bearings, axial needle roller bearings and axial tapered roller bearings with the nominal contact angle α = 90° can only support purely axial forces. For concentric axial load ➤ Equation.
Equivalent dynamic axial bearing load
Legend
P_{a} 
N 
Equivalent dynamic axial bearing load

F_{a} 
N 
Axial load

In axial bearings with α ≠ 90°, axial and radial loads are possible
Axial angular contact ball bearings, axial spherical roller bearings and axial tapered roller bearings with the nominal contact angle α ≠ 90° can support not only an axial force F_{a} but also a radial force F_{r}. The equivalent dynamic axial load P_{a} is thus determined in accordance with ➤ Equation.
Equivalent dynamic axial bearing load
Legend
P_{a} 
N 
Equivalent dynamic axial bearing load

X 
 
Radial load factor; see product tables

F_{r} 
N 
Radial load

Y 
 
Axial load factor; see product tables

F_{a} 
N 
Axial load

The calculation of the expanded adjusted rating life L_{nm} was standardised for the first time in DIN ISO 281 Appendix 1 and included in the global standard ISO 281 in 2007. It replaces the previously used adjusted rating life L_{na}. Computeraided calculation to DIN ISO 281 Appendix 4 has been specified since 2008 in ISO/TS 16281 and standardised in DIN 26281 since 2010.
The expanded adjusted rating life L_{nm} is calculated in accordance with ➤ Equation.
Expanded adjusted rating life
Legend
L_{nm} 
10^{6} 
Expanded adjusted rating life in millions of revolutions in accordance with ISO 281:2007

a_{1} 
 
Life adjustment factor for a requisite reliability other than 90% ➤ Table

a_{ISO} 
 
Life adjustment factor for operating conditions

κ 
 
Viscosity ratio

e_{C} 
 
Life adjustment factor for contamination

C_{u} 
kN 
Fatigue limit load; see product tables

C 
kN 
Basic dynamic load rating; see product tables

P 
kN 
Equivalent dynamic bearing load

p 
 
Life exponent

Fatigue limit load C_{u}
The fatigue limit load C_{u} in accordance with ISO 281 is defined as the load below which, under laboratory conditions, no fatigue occurs in the material. The fatigue limit load C_{u} serves as a calculation value for determining the life adjustment factor a_{ISO} and not as a design criterion. With poor lubrication or contamination of the lubricant in particular, it is also possible for the material to undergo fatigue at loads which are significantly below the fatigue limit load C_{u}.
Life adjustment factor a_{1}
The values for the life adjustment factor a_{1} were redefined in ISO 281:2007 and differ from the previous data ➤ Table.