Design Factor and Safety Factor


The design factor and safety factor are two separate things.

The symbol used to denote the design factor is nd
The symbol used to denote the safety factor is n

nd =
loss-of-function parameter
maximum allowable parameter

The parameter, for example, can be load or torque.
When trying to determine the design factor, all loss-of-function modes must be analyzed. A loss-of-function mode may be something that causes some kind of wear on the component in question. The mode that leads to the smallest design factor governs. After the design is completed, the design factor may become the safety factor as a result of changes such as rounding up to a standard size for a cross section or using off-the-shelf components. Technically, the factor of safety has the same definition as the design factor, but it generally differs numerically.