In the design of machine members, it is necessary to understand the Safety factor (SF). It is also known as Factor of safety (FoS). It describes that the load carrying capacity of any designed member. This can be defined by the ratio of capacity to the duty. Make sense? Let’s get into the topic thoroughly.
The Safety Factor
It is defined as the ratio of the Design capacity to the applicable Duty.
Safety Factor(SF) = Design capacity/Duty
Let’s take an example of a bearing needed to be designed for a shaft that is operating at 3600 RPM. We have a bearing in the market that is capable to run at 10000 RPM. Then the factor of safety is defined as
The factor of safety (FoS) = Capacity/ Duty
The factor of safety (FoS) = 10000/3600 = 2.7778
2.78 is the safety factor.
And not only with the speed, there are so many other factors like stress, torque, etc that we can calculate the factor of safety.
The factor of Safety is also defined as the ratio of the Maximum stress to the working stress.
The factor of safety (FoS) = Maximum stress/Working stress
Further, we can describe the factor of safety between the ductile materials and the brittle materials.
The safety Factor based on material property
For Ductile materials, the yield point is defined so the factor of safety can be defined as the ratio of the Yield point stress to the Working stress.
The factor of safety (FoS) = Yield point stress/ Working stress.
The factor of safety (FoS) = Ultimate stress/ Working stress.
The safety factor for any machine or machine part can be defined as the Capacity divided by the Duty or operating condition of the machine part.