Attaching metal brackets to carbon fibre layup 1

[berkshire]

I am being asked to attach by riveting, a hinge bracket to a carbon fibre panel which is going to get wet.The hinge is SAE 4130 painted
I have been asked to use something other than titanium
I think stainless steel may work. Everything else I have looked at so far screams "battery" when put aroung carbon fibre. Any suggestions?
B.E.

 

[rnd2]

It will be a "battery" only if it gets wet. Even if you use ss, if does get wet, it won't help if salt is present and can accumulate. Isolate the two materials with a creep resisting electrical insulator such as epoxy grp, heavy film Mylar from Dupont. Electrical insulation specialist suppliers will be able to help with material in sheet/film/tube form. You have to isolate the rivets as well. If there is load DO NOT USE regular thermo plastics to isolate the two parts as they thin out with creep.

 

[berkshire]

So you would reccommend pre drilling the holes and painting them with epoxy,then allowing that to harden prior to riveting? I can also add an additional layer of glass between the carbon fibre and the hinge.
B.E.

 

[rnd2]

As long as carbon fibers are prevented from being in electrical contact with the metal part it should be OK. Longer term chafing might be worth considering.

 

[minchungli]

It's not a bad idea to consider Composi-Lok by Fairchild in addition to the glass ply. And, avoid if you can flush head at the composite side.

 

[berkshire]

Minchungli
That the one thing I cannot avoid.
The countersunk head has to be on the Composite side, also since I can get at both sides it does not have to be a blind fastener. The customer has specified riveting But I could talk him into bolting the assembly.
B.E.

 

[ewh]

When we have a situation where the c'sink is in the composite, we use a bonded grommet to prevent hole failure. Unfortuately, you still have to isolate the grommet from the carbon.

 

[minchungli]

Flush head does not mean "won't work". It's just not as strong as protruded ones. You probably can do some test to get the pull-through strength and compare with your predicted fastener loads. For the concern of direct contact between carbon and metals. Generally, we put a glass if it's Al. For Ti and CRS, which most likely your fastener is made of, we don't usually put a glass in between. Maybe ewh can clarify what material his grommet is made of.

 

[ewh]

The grommets we use are 304 CRES. As minchungli mentioned, anytime we have contact with AL, we use a glass barrier ply.

 

[berkshire]

Gentlemen,
What I am getting from all of this is that I really do not want the metal of the fastener touching the carbon.
But that if I have to, CRES will work, which is what I suspected in the first place.
B.E.