In machine design, while designing the component, it is necessary to provide sufficient reserve strength in case of an accident so this is achieved by taking a suitable factor of safety.
fs = Failure stress / Allowable stress
fs = Failure load / Working load
The magnitude of the factor of safety depends upon the following factors:
- Effect of failure
- Types of load
- A degree of accuracy in force analysis
- Material of component
- Reliability of component
- Cost of component
- Testing of the machine element
- Service conditions
- Quality of manufacture
Points mention below the following condition where a higher factor of safety is chosen :
- Magnitude and nature of external forces acting on the machine component cannot be precisely estimated.
- The material of the machine component has a non-homogeneous structure.
- The component of the machine is subject to the force of impact in service.
- There is a possibility of residual stresses in a machine component.
- The machine part is subjected to a high temperature during operation.
- In applications such as aircraft components, higher reliability is required.
- There is a possibility if abnormal variation in external load on some occasions.
- The machine part's manufacturing quality is poor.
- There is stress concentration in a machine component.
A higher factor of safety increases the component's reliability.