1. Factor of safety (N) = Load carrying capability
Applied load
N= y/ L or N = u/ L (1)
 where,
L - is the stress due to the applied load;
Y - is the yield strength of the material;
Ou is the ultimate strength of the material.
Figure 1. –
Cyclic nature of detail design

2. Occasional shock loads
For ductile materials (< 1500 MN/m2 tensile strength) typical factors of safety N
are shown in table 1.
Table 1
Steady loads
Occasional shock loads
Tension and, or beoding 3 6
Compression and/or contact prssure 6*
Torsion and /or shear
4,5 9
*This represents the crushing limit, You should also check buckling.
Figure 2. -
Load and strength distibutions
Figure Combined curve

4. Fig. 4 - Cost of reliability

5. Fig. 5 - Colour intensity philosophies