Stack up repair

[emgo]

Hi everybody,

I´m new in eng-tips.com and it´s my first thread.
I´m looking for a long time for investigations/studies about 'stack up doublers'.

I know the small threshold from the 1st repair is a reason of the eccentricity.

My investigations shows a acceptable threshold for 3rd repair but I need also good represent argumentations.

Mainly about load transfers, inspection possibilities...

Where should I look for suitable sources deals with "stack up"

best regards

 

[rb1957]

i'm confused ... you're asking about references for load transfer (Michael Niu is pretty good), but you've already investigated the 3rd repair design and determined an acceptable thresold (which i don't think you can do without detailing the load transfer) ? i wouldn't have thought that option 1 was so significantly different to option 3, though setpping the dblr is always a good idea. i'd've thought that the key problem with the repair is the single row joining thedblr to the RH skin.

can you add more rivet rows between the 1.6mm skin and the 2mm dblr ? ... right now there are 3 rivets tking the load out of the LH skin and only 1 returning it into the RH skin. I assume internal dblrs (like option 2) are unacceptable ... they often are.

what about CSK depths (you don't want knife-edging) ? what about support against secondary bending (which is the problem created by stack up)?

 

[SWComposites]

1) as rb mentioned, the single row on the right skin looks very, very bad.

2) what do you mean by "investigations"? Have you done a load transfer analysis? a full static stress analysis? a full damage tolerance analysis including crack growth and residual strength?

3) do you work for an airline or OEM or ? What data are you using for your DT analysis?

 

[emgo]

Forgive me please,

I have started a discussion before the thinking.

I am young and inexperienced.

They both showed me that I am not ready for the discussion and I should sort my thoughts.

Still Thanks for the quick answer and I hope that I am ready for a discussion in an early future.


I´m so sorry to have wasted your time.
best regards!!!

 

[ESPcomposites]

Emgo,

No problem, I think you have the right approach by taking some time out and better understanding the problem.

More comments:

One of the reasons to stack the doublers is to "smooth" out the load transfer in the fasteners. For 2-3 rows, you won't see much benefit. The benefit usually comes after more rows than that.

The solution approach is to set up a system of simultaneous equations that represent the fastener flexibility and member flexibility. I am working on some software that calculates this, but it is not currently ready. You could also use FEM if you don't have software at your company or don't want to build it manually.

In the end, what you are after is reducing the bearing load for increased static and fatigue performance. As noted, a single row is going to have high bearing loads and you will have relatively poor performance.

The other thing to consider is joint optimization, though I don't know material systems you are working with. The number of rows and the fastener spacing go together in an optimized joint.

That being said, without getting too carried away, you want at least 2 rows (preferably 3) and 4D spacing is a good place to start. A tripler may help the bearing loads, but is also good for producibility as 2 thinner sheets are easier to form than 1 thick sheet. The downside is that if damage tolerance is required in the repair, you could have a hidden crack in the doubler which reduces your inspectibility.


Brian

http://www.espcomposites.com