WIKI STRESS|February 25, 2013 1:31 pm

Factor of Safety


Factor of safety

Main article: Factor of safety

The factor of safety (also “margin of safety” or “design factor”) is a design requirement for the structure based on the uncertainty in loads, material strength, and consequences of failure. In design of structures, calculated stresses are restricted to be less than a specified allowable stress, also known as working, designed or limit stresses, that is chosen as some fraction of the yield strength or of the ultimate strength of the material which the structure is made of. The ratio of the ultimate stress to the allowable stress is defined as the factor of safety.

Laboratory test are usually performed on material samples in order to determine the yield strength and the ultimate strength that the material can withstand before failure. Often a separate factor of safety is applied to the yield strength and to the ultimate strength. The factor of safety on yield strength is to prevent detrimental deformations and the factor of safety on ultimate strength is to prevent collapse.

The factor of safety is used to calculate a maximum allowable stress:

\text{Factor of safety} = \frac{\text{Ultimate tensile strength}}{\text{Maximum allowable stress}}
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