Missing rivet with crack rivet hole 2

[a5130]

We found missing rivet and a crack of 6 mm found on the rivet hole. These is located in a pressurized fuselage skin. Can I do a stopped drill crack or have to carry out an external doubler repair?

 

[CoffinsCorner]

Do you want a leaking fuselage?? Do not experiment, repair per SRM!!

 

[rb1957]

nah, just fill it with PRC ... ...

no, wait, some serious advice ...
stop drill AND exernal dblr ! as above, refer to SRM.

what a/c ?

Quando Omni Flunkus Moritati

 

[blakmax]

You should firstly check the SRM for allowable defect limits, but I would be surprised if any OEM would accept a 6mm crack in a pressurised fuselage.

In my experience, stop drilling is one of the best ways to record crack growth rates, because you can record when each stop drill was implemented and correlate that against service life. Understand that what I am saying is that I have no confidence in stop drilling to actually "stop" a crack. I have seen far to many examples where it hasn't.

The frustrating thing is that the SRM will call for crack removal, maybe fabricating an insert, and the addition of a huge number of fasteners to attach a doubler, with the result that the nett section is reduced more than the crack size. Why? because mechanical repairs are so inefficient. A decent well designed and well installed bonded repair would fix your problem and not require any access to the back face to fit fasteners and would produce a far better result from a fatigue and damage tolerance perspective. You could leave the crack alone and monitor it using NDI, whereas you can't for a mechanical repair. For bonded repairs, crack removal by routing to an "acceptable" shape provides the worst fatigue result. Stop drilling will at best produce the same fatigue result (or worse) than leaving the crack alone. This is because stop drilling removes the plastic zone at the crack tip which provides crack closure effects which provide beneficial compressive stresses when a bonded repair is installed over the region.

Regards

Blakmax

 

[rb1957]

i guess we have a difference of opinion.

sure you "can" leave a crack in the skin and monitor it, but (if this is a transport (FAR25) aircraft) that requires a lot of engineering justification (see other threads about flying with known cracks).

sure a badly stop drilled crack is worse than nothing, most of the time they're too small and often do't take out the crack tip. the stop drill has to take out the yield zone to be effective. with this size of crack (assuming it's on a rivet line and not an isolated rivet) i'd suggest cutting out the adjacent rivets (a hole diameter = 2 rivet pitches) and a two row dblr over that. and now there'll need to be continuing inspections of this dblr. you'll need a RDC/RDA for this, including DTA ... i'm assuming this is a part 23 or 25 aircraft. what's the rivet doing there ? joining two pieces of skin together ? frame flange ??

yes, mechanically attached dblrs are inefficient, but they're the best thing we have for Al skins. yes, you can design a bonded repair, but that is a certification, engineering, and manufacturing nightmare (unless you're experienced with them).

there is very little retardation effect in a pressure cabin.

Quando Omni Flunkus Moritati

 

[a5130]

Many thanks for all your input...i checked the SRM and found the repair..the repair will be carried out by cutting out the damage and installing an external doubler repair with a filler on the frame because the missing rivet runs through a frame and stringer.
Cheers,

 

[Sparweb]

Some searching for the cause is also in order.

And a brief hunt for similar or incipient loss of nearby fasteners...

Some problems "come in threes" as they say.

STF