peelply left in a layup 1

[berkshire]

I have a conundrum, I discovered a layer of peel-ply in a finished installation. This is tabbing a bulkhead into a hull configuration. The peel-ply is on the bulkhead.
Logic says rip out the tabbing, take off the peel-ply and redo the layup.
The other voice says The item has been in service for three years, the other side of the bulkhead is properly tabbed in and the loading is in shear and nothing is loose. Why not leave it there? The peel ply was discovered when a hole was drilled through the bulkhead for an electrical cable.
Does anybody have any data on the shear strength of a layer of polyester cloth in the center of a glass layup.
I am presuming that if the polyester is not bonded then the joint is relying on the shear or tensile strength of the un-reinforced epoxy resin.
Any thoughts on this? I do not know if am making myself clear.
B.E.

 

[RPstress]

Never seen any strength data for embedded peel plies.

I'm somwhat unclear about what the tabbing arrangement is.

Is the peel ply somehow embedded in the bulkhead layup, or is it perhaps between a bonded on tab and the bulkhead?

 

[MechanicalChef]

If the piece failed, does the possibility exist that someone could get hurt? That would be #1.

 

[Compositepro]

As noted by others the first question is what are the consequences of a bond failure?
I don't have any hard numbers on peel-ply adhesion but will say that while some nylon peel plies have a release agent applied polyester generally does not. Also, peeling is the weakest failure mode in composites and carbon and fiberglass will often peel easier than peel-ply itself. The reason for using polyester or nylon for peel-ply are the weave texture and the toughness of the polymer which resists tearing while peeling. My opinion is that your question is a very valid one. The layer of peel-ply is not necessarilly a structural flaw. I would contact the peel-ply manufacturer with your question.

 

[berkshire]

RP stress,
The tabbing is a 1"x 1" angle made from two layers of 300gm twill weave, between the hull and the bulkhead on each side. The bulkhead is a 3/8 foam core with two layers of 220gm unidirectional glass 90 degrees to each other on each side. The peel ply is of course on the surface of the 220 gm unidirectional so it is between the the tab and the bulkhead on one side only.
MechanicalChef
If the piece failed the only consequence would be some loss of stiffness in the hull. For it to do that the tabbing would have to fail on both sides
Composite pro.
I feel your comment is echoing my thoughts. if the peel-ply is well encapsulated which it is, it was on the tool side of the layup. It should have sufficient strength for this function. I will have to go back to the manufacturer to find out where he got the peel-ply, then find out if the peel-ply maker has any data.
It may be quicker and easier just to rip out the tabbing and re do it.
B.E.

 

[SWComposites]

Why not just remove the peel ply from the exposed area of the bulkhead and overlay the existing tab with a larger tab?

 

[berkshire]

SWComposites (Aerospace)
I can do that, that may be the simplest solution.
Thank you.
B.E.

 

[MNLiaison]

You could perform a wet lay-up repair that starts on the bulkhead and spans over the tab. Size the repair such that the repair laminate shear strength is equal to or greater then the original bulkhead to tab joint shear strength. The repair laminate will transfer the shear loading between the two members if the original tab to bulkhead joint fails due to the peel ply inclusion.


Regards.

 

[berkshire]

MNLiaison (Aerospace)
That is what I am doing. This is essentially what SWComposites said. This also seals in the peel-ply and prevents the edge from delaminating later.
B.E.

 

[Compositepro]

Be careful about adding reinforcement. That will add stiffness to the area and may therefore increase stresses which can create a new problem. You don't want to waste effort on something that will only make the problem worse. Right now you don't have a structural problem but only a concern.

 

[berkshire]

I am only adding one layer of glass to the tabbing.
The idea being to seal down the area where the peel-ply was so it cannot peel up later.
I feel if I have the edge encapsulated it will be fine in shear. The load here is shared by the tabbing on the other side of the bulkhead,Most of the load on this bulkhead is a compressive load.
B.E.

 

[RPstress]

Sounds a sound approach. While there are many repairs out there that actually make a structure worse off, I'd be leery of leaving a potential delamination starter be without doing anything. Three years of service is not thirty...