Platypusimon
Aerospace
- Jan 20, 2023
- 11
Hello everyone,
I would like some advice, clarity and guidance on something that I have been debating with my self for a while in regards to Factor of Safety/Safety Factor and Margins of Safety in aerospace structures design.
It's generally recommended to design parts in aerospace with a FoS of 1.25. However, what is bugging me is the way in which one would like to apply this FoS to their design. I feel like there is two methods, but not standardised choice in which method to use.
Method 1:
Let's say for a metal, you would have Yield Load/Applied Load,
Yield = 500MPa So : Yield/Applied = 2.5
Applied = 200 MPa Given we have a ratio of 2.5, we could say the FoS is 2.5, thus a Safety Factor of 1.25 is well in place in our design.
Method 2 :
Again, let's say a metal and we want a FoS of 1.25, there is the option of doing:
Yield/(Applied*FoS) ---> 500/(200*1.25)= 2
MoS = 2 - 1 = 1 --> MoS = 100%
Which method would you say is the most appropriate? I feel like the 2nd method is safer, however you would lead to design a structure with a higher weight, which is not preferable at all in aerospace applications.
I would strongly like more expert and experiences engineers input on this.
Also, would you say an eigenvalue factor could be considered as an FoS in the case of buckling?
Many thanks in advance.
I would like some advice, clarity and guidance on something that I have been debating with my self for a while in regards to Factor of Safety/Safety Factor and Margins of Safety in aerospace structures design.
It's generally recommended to design parts in aerospace with a FoS of 1.25. However, what is bugging me is the way in which one would like to apply this FoS to their design. I feel like there is two methods, but not standardised choice in which method to use.
Method 1:
Let's say for a metal, you would have Yield Load/Applied Load,
Yield = 500MPa So : Yield/Applied = 2.5
Applied = 200 MPa Given we have a ratio of 2.5, we could say the FoS is 2.5, thus a Safety Factor of 1.25 is well in place in our design.
Method 2 :
Again, let's say a metal and we want a FoS of 1.25, there is the option of doing:
Yield/(Applied*FoS) ---> 500/(200*1.25)= 2
MoS = 2 - 1 = 1 --> MoS = 100%
Which method would you say is the most appropriate? I feel like the 2nd method is safer, however you would lead to design a structure with a higher weight, which is not preferable at all in aerospace applications.
I would strongly like more expert and experiences engineers input on this.
Also, would you say an eigenvalue factor could be considered as an FoS in the case of buckling?
Many thanks in advance.