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Aluminium spar attach in carbon fiber (avoiding galvanic corrosion)

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billy

Member
Joined
Mar 25, 2010
Messages
7
Location
Spain
Hello everyone

I am building a spar attach arrangement "similar" to that in the Dr-107 One Design, that I put a copy on the plans. There is the AN bolt that will go through aluminium bushings that will be held by the carbon fiber spar attach points. Since I am making a big chunck of carbon to hold the aluminium bushing I am looking for the max strength of the carbon be retained. Problem is the galvanic corrosion if aluminium gets in contact with carbon. In other parts, I have avoided by (as per recomended in this forun and aparently by Locked Martin) using the last layer of the layup with fiberglass. Here I can't since the carbon will be "machined" to recive the aluminium bushing.

I would love to ear what would be my best option to retain the maximun strength provided to the structere once mated with this options:

-one design plans. Machine the carbon with some tolerance and insert the aluminum and fill the gap with epoxy. Weakest part would be the epoxy lining....

-one design plus using flox (epoxy plus choped glass fiber). Here weakest part would be the flox and as you can see in the attached study can be 175% of what epoxy is.

-put primer on the part of the aluminium that would contact the carbon, then cover it with a thin layer of epoxy and machine tight the carbon. Sand a little the epoxy for good adhesion and insert it in the carbon using epoxy to permanently join the part. This would mantain max strength of the carbon (holding the aluminum part wich is weaker) and if there is a thin layer of primer and other of epoxy, in theory no contact in between carbon and aluminium.

Please let me know what you thing or if there is other way to bond aluminium to a machined part of carbon.

Thanks

Jorge
 

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