Mechanical Design & Analysis

The ratio of a component's load-carrying or strength capacity to the actual applied load or stress, expressing margin against failure.

n = Sy / σ, where Sy is the yield strength and σ is the applied (working) stress.

To account for uncertainties in loads, material properties, manufacturing variation, analysis assumptions, and consequences of failure.

The design factor (nd) is the target chosen before design; the realized factor of safety (n) is computed from the final geometry and may differ from nd.

Predicting failure of brittle materials; failure occurs when the maximum principal stress reaches the material's ultimate strength.