Fail-Safe Approach

[lLouie]

A fail safe strength investigation in which it is shown by analysis, tests, or both, that catastrophic failure of the structure is not probable after fatigue failure, or obvious partial failure, of a principal structural element, and that the remaining structure is able to withstand a static ultimate load factor of 75 percent of the critical limit load at Vc.

What should I understand exactly? The part is subject to fatigue, and it should not cause damage to other structures after it has fatigued. Am I right?
What should I do an analysis for this?

 

[rb1957]

I assume your wing construction is like traditional wings .. upper and lower skins, front spar, rear spar, ribs A/R ?

Some key questions that I can't answer as I'm not a composite specialist ...
1) the size of damage depends on what is detectable with your inspection technique. Either this is a "rule of thumb" (like a tap test will detect a 2" diameter void) or a test.
2) by removing the elements you're failing the entire lay-up, rather than failing one inter-laminar adhesive layer (if that's a thing). It goes to your definition of failure ... a single ply or all of them (obviously conservative) and failing all of them conservatively convers failing any of them (the plies).
3) I would've thought that the key question is how does the damage respond to the fatigue loads ? does it grow ? (that would be "bad", but not fatal). I don't know how to determine this.
4) Another thing ... only 1 damage location on the wing ? one in each "PSE" zone ? How do you know if the damages are affecting each other ?? Is one detectable damage so unlikely that you don't need to consider this ??

Why not a fail-life design, for a UAV ?

We've barely talked about load spectra, critical to both fatigue and DTA.

I assume you're doing a bird strike test on this wing ? Or designed the L/E D-nose to account for this ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[lLouie]

I'm not doing a bird strike test on wing which is tradional wing as you said. After a structure receives damage from fatigue, I just want to see whether other structures receive damage or not.