Bearing Life Estimation Formulas


Fatigue (L10) Life

The following formulas permit the calculation of the fatigue life of bearings subjected to radial loads or combined radial and axial loads. Some of the formulas include approximations. Contact the PACAMOR KUBAR BEARINGS’ Engineering Department, if the calculated life is borderline in comparison to the desired life, or if the loading conditions differ from those presented.

The Fatigue Life (synonymous with L10 and Rating Life) of the bearings is the number of hours or revolutions reached by 90% of a group of bearings subjected to the same loads before the onset of fatigue. Conversely, 10% of the same group of bearings can be expected to show evidence of fatigue before the L10 Life is reached.

Bearing life is defined as the length of time (number of revolutions) until a specific failure occurs. Predicting the life of a ball bearing is a statistical calculation of the fatigue properties of the various bearing components. “Life” is the number of hours that a percentage of similar bearings have survived under an essentially identical set of operating conditions and loads. Life can be affected by a number of factors including loads, speed, lubrication, fit, maintenance, temperature, contamination, and others. Because of the diverse variety of contributing factors, it is extremely difficult to predict life precisely. Because handling and contamination damage can dramatically reduce bearing life, bearings should be properly stored, mounted, dismounted, and inspected. Optimized performance and life is also contingent on appropriate lubrication and sufficient protection form foreign matter. Bearings should be stored in a cool, clean, low humidity environment free of dust, shocks and vibrations. Proper fitting, using specialized tools and techniques, will also help maximize bearing life. Further information is available under the Installation Guide section of this website.

The Average Life of this same group of bearings will be approximately 5 times the L10 Life.


Fatigue Life Calculation

LR = (C/P)3 LR is in millions of revolutions
LH = (C/P)3 X (16,667 / RPM). LH is in hours
C = Basic Dynamic Rating. Ratings for each bearing are included in this catalog
P = Radial Equivalent Load Calculated as indicated below


Radial Equivalent Load Calculation

Load Condition Inner Ring Rotating in Relation to Load Direction Inner Ring Stationary in Relation to Load Direction
Radial Load (T=0) P = R P = 1.2 R
T/R < .17 P = R P = 1.2 R
T/R > .17 P = .56 R + 2.1 T P = .67 R + 2.1 T


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