Margin of safety for a failure load (measure of structural capacity)

Description

Many government agencies and industries (such as aerospace) require the use of a margin of safety (MoS or M.S.) to describe the ratio of the strength of the structure to the requirements. There are two separate definitions for the margin of safety so care is needed to determine which is being used for a given application. One usage of M.S. is as a measure of capacity like FoS. The other usage of M.S. is as a measure of satisfying design requirements (requirement verification). Margin of safety can be conceptualized (along with the reserve factor explained below) to represent how much of the structure’s total capacity is held “in reserve” during loading. M.S. as a measure of structural capacity basically says that if the part is loaded to the maximum load it should ever see in service, how many more loads of the same force can it withstand before failing. In effect, this is a measure of excess capacity. If the margin is 0, the part will not take any additional load before it fails, if it is negative the part will fail before reaching its design load in service. If the margin is 1, it can withstand one additional load of equal force to the maximum load it was designed to support.

M.S. can be calculated as a funcion of the failure load as shown.

Related formulas

Variables

MSmargine of safety (dimensionless)
FLfailure load (dimensionless)
DLdesign load (dimensionless)