Factor of Safety

Definition

The Factor of Safety (FoS) is the ratio of ultimate strength to the working stress of a material.

Purpose

The purpose of the Factor of Safety is to ensure the reliability and safety of structures and components by providing a margin of error between the expected maximum load and the load that would cause failure. This accounts for uncertainties in material properties, load estimations, and potential flaws.

Examples of Use

• Structural Engineering: Designing beams and columns with a factor of safety to prevent collapse under load.
• Mechanical Design: Specifying the factor of safety for gears and shafts in machinery to ensure long-term performance.
• Aerospace Engineering: Applying higher factors of safety to critical components to account for the extreme conditions experienced in flight.

Related Terms

• Ultimate Strength: The maximum stress a material can withstand before failure.
• Working Stress: The stress expected to be experienced under normal operating conditions.
• Load Factor: A multiplier applied to the expected loads to determine design loads.

Notes

• The appropriate factor of safety varies depending on the application, material, and potential risks.
• Overly conservative factors of safety can lead to increased costs and material usage.