12.19 Life

A gearset’s design life L is determined by the particular application. Some gears such as hand tools are considered expendable, and a short life is acceptable, while others such as marine gears must be designed for long life. Some applications have variable loads where the maximum loads occur for only a fraction of the total duty cycle. In these cases, the maximum load usually does the most fatigue damage, and the gearset can be designed for the number of hours at which the maximum load occurs.

Typical design lives:
Application No. CyclesDesign Life, L(hr)

Vehicle 107 - 108 3000
Aerospace 106 - 109 4000
Industrial 1010 50000
Marine 1010 150000
Petrochemical1010 - 1011 200000

The number of load cycles per gear is calculated from the required life (L), the speed (n) and the number of contacts per revolution (q):

N  = 60 ⋅ L ⋅ n ⋅ q

The sizing button PIC can be used to calculate the lifetime where the required safety factors (see 11.3) are reached.