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  FATIGUE LIFE  

BASIC BEARING FATIGUE LIFE

The basic fatigue life of a rotating deep-groove ball bearing is given as:
 
C
P

3

.
106 revolutions

L10= 

 

where:   
L10
=
rated fatigue life with a statistical reliability of 90%
  P
=
bearing equivalent load
  C
=
basic radial dynamic load rating (see individual bearing selection charts)


TEMPERATURE CORRECTION FACTOR

If rolling bearings are used at high temperature, the hardness of the bearing steel decreases. Consequently the basic radial dynamic load rating C must be corrected:

          Ct = ft • C

Bearing temperature oC
< 150
175
200
250
Temperature factor ft
1.00
0.95
0.9
0.75

Note: The temperature correction factor assumes that a lubricant is used that is suitable for given temperature.


GENERAL FATIGUE LIFE CORRECTION FACTORS

The L10 preload life of a bearing is normally adjusted as follows, according to real-world operating conditions:

Lna 

=
a1a2 L10
where:
Lna = adjusted bearing fatigue life


a1 =
Life correction factor for material and desired statistical reliability, the values for a1 being given below:

       Values for Life Correction Factor a1
MATERIAL
STATISTICAL RELIABLITY (%)
90
95
96
97
98
99
52100
1.00
.62
.53
.44
.33
.21
440C
.50
.31
.27
.22
.17
.11
DR/ES1
.8
.49
.42
.35
.27
.17


a2 = Life correction factor for operating conditions. It has been empirically determined to have a value between 2.0 under ideal operating conditions and 0.2 where one or more of the following conditions may apply:
  • The lubricant film thickness between the raceways and the rolling elements is low
  • Bearing raceways are excessively misaligned
  • Oscillatory motion
  • Rotation speed of the bearing elements is very low
  • Contamination or water is present in the bearing
Since there are many factors that determine observed bearing life, the above figures should be used conservatively.

Useful link: Bearing failure





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