Shaft-loads

8.8 Factor of Safety

The factor of safety reflects the designer's confidence in the data used and the consequences of failure.

Use the factor of safety to reduce the predicted strength of the material. For ductile materials, apply it to both the yield strength and the fatigue strength.

Uncertainty exists in:

load magnitude
material properties
manufacturing quality
service conditions

A factor within the range 1.25 to 4.0, based on the material yield strength, normally suffices.

Equation 1 may now be written:

N.f_m/f_y + N.f_a/K.f_e'

(where K is the product of all the relevant fatigue and safety factors)