Factor of Safety on Ultimate Strength
Factor of Safety on Ultimate Strength
For brittle materials or where fracture (not yield) governs, the factor of safety is taken on the ultimate strength.
The factor of safety is n = S_ut/σ. where S_ut is the ultimate strength and σ the working stress.
Inputs
S_ut := 500 MPa=500 MPa
sigma := 125 MPa=125 MPa
Divide ultimate strength by working stress.
n := S_ut/sigma=4
Results
A larger factor gives more margin against fracture. Brittle materials use higher factors (3–4+) because they fail with little warning.
Assumptions & limitations
- Brittle/ultimate failure governs.
- Static load.
- Uniaxial stress.