Disbond repair

[audacious1234]

Hello,

I have a composite panel (AL core 1.89" and AL face sheet 0.032" bonded with BMS 5-101, Type I, Grade 10) to be used on attendant partition with a 2 disbondings between core and face sheet. The disbonding size is 2” X 9” one away from edge and other disbonding of similar size near edge of the panel. I searched on Boeing SRM and chapter 51-70 gives me repair procedure for large damage but the problem is per this repair procedure I will have to replace skin with a gauge thicker doubler. But that will create an offset (0.08”) on panel surface which won’t allow me to install attendant seat on it. Supplier is claiming that we can use injection repair method for voids which will allow us to repair it. But the problem is there is no standard procedure (Boeing SRM or FAA approved) which will allow us to approve this repair. Can someone recommend/ guide me to a standard procedure which allows repair without adding gauge thicker doubler? I am doing the substantiation by testing so I have to make sure the production unit is stronger or equivalent to test article after void repairs. Or is there any analysis method by which I can show the repair is stronger or equivalent to test article. Test article didn’t have any voids in it.

Thanks

 

[SWComposites]

Are you just repairing a local area, or replacing the entire skin?

I have never heard of an injection method for repairing a core to facesheet bond. Such method can be used for repairing disbonds between the plies of a fiber reinforced composite laminate. Injecting resin into the core-facesheet interface is going to fill up the core cells.

If you are going to substantiate the repair by testing, seems like it would be less expensive to remove and replace the entire facesheet, or just make a new panel.

 

[der8110]

just shim the attendant seat out .08, if geometry allows. Use longer fasteners, check for bending. In other words, add non- functional doublers to provide a level surface. You probably do not want to mess with alternate repair schemes on something as critical as a seat.

 

[bf109g]

Hi guys. I have repaired honeycomb disbonds by drilling facesheets, "spoiling" the core and filling with resin. These are generally time limited repairs for secondary structures. I've even used them on control surfaces in conjunction with a Boecomm.

In the case of a partition supporting an attendant seat, I'd be a little cautious using that procedure since the partition is taking loads from an occupied seat. If you have somenting that allows you to use a doubler per an SRM repair, do it and shim as der8110 suggests. I can't imagine a .080 shim getting you into a fastener bending problem, but check it anyway.

 

[StressHack]

I have several years experience in composite and metal bonded repairs. In order to restore the load carrying capability of the face sheet and bond strength to the core, you must have an overlapped hot bonded repair. If you are outside the size limits of an injection repair per the SRM, you are unlikely to get OEM or DER approval for this method of repair.

In order to prevent a step at the location of a seat, you can replace the core and skin with the same type & gage an the original. Size the replacement skin larger than the seat landing area. Next, install a splice strap that overlaps the original skin & skin patch. The splice strap is typically one gage higher than the original face sheet.

BTW, I am a contract engineer with access to DER's for FAA approval. Let me know if you want me to author and obtain FAA approval for this repair.

 

[Hansmeister]

Injecting a foam or loaded epoxy into the debond zone of a damaged honeycomb sandwich panel is not an acceptable repair.

After the skin is removed from the panel in the damaged zone, one needs to determine if the debond is between the skin and core, or failure of the core itself. If the core is damaged, it will need replacement as well. The probability of getting a good, new bond between the replacement facesheet and the core (if it is not replaced) is also questionable.

In all cases, a doubler will be required, which apparently is causing seat fit-up problems.

The best recommendation is to replace the panel and re-use any hardware if possible.