Bonding Carbon Fiber Sheet to Aluminum Plate? 1

[bradler]

Got a few ?'s about bonding carbon fiber sheets to an aluminum plate. This is a structural drive train part subject to high loads and vibration. The idea is to reinforce or stiffen a 6061 aluminum torque plate by bonding a carbon fiber laminate onto one or both sides. Im looking at pre made solid carbon quasi laminates without any core material that have a texture finish on one side for a bonding surface.

First question, is the textured epoxy bonding surface on the laminate sufficient to isolate the carbon and aluminum so there is no concern of galvanic corrosion (will be in a wet environment) or should I still consider a thin fiberglass layer between?

Second, any comments on the 3m DP-460, Hysol 9394, or E120HP for this purpose? My oven is too small to fit this part but I might be able to cure at elevated temps. Was also planning on a chromic acid ether to prep the Al and my buddy from Boeing suggested a BR-127 primer for the Al, any other prep concerns?

Thanks Much!
Ryan

 

[bradler]

Also, the carbon reinforcements will be ~6in x 18in, is there concern from thermal expansion/contraction issues stressing the bond on a part this size? It will be subject to below freezing temps on a regular basis.

 

[MikeHalloran]

Is there some reason you can't just buy thicker aluminum plate?


Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

In a wet enviroment you are building a battery,
If you are hell bent on doing it, put a layer of fiberglass between the
aluminum and the carbon fiber.
You may be better off looking at a rubber modified epoxy like Hysol EA9309 NA, the tensile will be lower , but the peel strength will be higher.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[TVP]

Surface prep is always critical for this type of application. I concur with berkshire that you may need to investigate a toughened adhesive. Hysol EA 9309NA is a good option. Here is a link to some of the various products from 3M.

http://solutions.3m.com/wps/portal/...ECIE20SOG5000000_nid=GGT0WP8F36be1K3HXBTMF8gl

 

[btrueblood]

You might also discuss with Lord Aerospace (Lord Chemicals) suitable bonding primers for the aluminum.

 

[bradler]

Thanks Guys!

The reason for using a carbon laminate to stiffen the plate is mainly for weight (must be as light weight as possible) and there are clearance issues to moving drivetrain parts that limit how thick the plate can be. Basically, an Al plate that is thick enough wont fit and this plate must be very stiff. The tight fit also makes mechanical fastners a real problem.

Is the rubber modified epoxy like Hysol EA9309 NA to allow some give in the bond for expansion/contraction concerns? Would the fiberglass in between also help with this since its kind of a middle ground between the carbon and AL in terms of CLTE? I will have to double check with my buddy but I thought he said the BR-127 primer would also isolate the Al from the carbon to prevent corrosion...

Thanks again!

 

[berkshire]

If this is a drive train part and you have penetrations with shafts and bearings you are still going to have an electrical path.
If you are going to the trouble of adding carbon fiber. with the constraints you have mentioned, you may be better off constructing the whole plate from carbon fiber and getting rid of the aluminum. You could also look at Titanium.

Yes the reason for suggesting rubber modified epoxy was to help your bond line and to up the peel strength, because of your expansion rate differences.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[cloa]

Or reinforce it with ceramics such as alumina depending on what direction that stiffness is required- could be fibers.

 

[bradler]

There are penetrations for shafts but the bearings dont press into the plate. So there is 1/8in gap around the shafts and the penetrations so no contact between the carbon and any bearings/shafts. I would love to make the entire plate out of carbon but there are several interference fit motor mounts that get pressed into the alum plate as well as counterbores for the mounting hardware that create a bunch of other issues with all carbon. That and the area I want to stiffen with the carbon is only 1/2 the size of the alum plate footprint. Looked at titanium but too expensive!

Thanks again berk!