Building with Carbon fiber and nomex honeycomb

[Fgayford]

Hello
I am new to this group and have a very simple question for someone who knows the answer.
I have tried in vain to get an answer from anyone or any site on the net so far.(a year plus and boy have I tried)
The question. To make a part out of nomex honey comb (say 1/4 inch thick overexpanded cells for drapability)with carbon fiber skins sandwitched inside and out using epoxy. Is this the proper procedure.(this comes from what I have gathered so far)
1.Layup the carbon fiber in the mold and cure this outer layer. (whether wet layup, vacuum bagged or infused shouldn't matter)
2. Apply structural adhesive to this cured layer and nest the nomex honeycomb and vacuum bag this until cured. (other say just use epoxy, the adhesive camp says don't ever use just epoxy laminating resin)
3. Now pre wet out the final carbon fiber layers and drap over the honeycomb core and vacuum bag this for the completed part. (some say only prepreg should be used, others say an adhesive film should be used between the core and the final carbon fiber layers)
Advise welcomed from your experiences.(I am aviation oriented)
Thanks
Fred

[thedutchtouch]

i have built things using exactly that method in non-boating worlds, but dont know how well this practice transfers over to boat hulls. we used only epoxy/ epoxy thickened with microballoons, we did NOT use "structural adhesive"

[Fgayford]

Originally Posted by thedutchtouch

i have built things using exactly that method in non-boating worlds, but dont know how well this practice transfers over to boat hulls. we used only epoxy/ epoxy thickened with microballoons, we did NOT use "structural adhesive"

Thank you sir! I am only using this on aircraft and not boat hulls.
Could you explain how you did the final layer over the honeycomb in detail please. That is where I am not sure how it goes.
Thanks
Fred

[susho]

As far as I know glue films aren't used with wet resins, only prepregs.
core-skin bond is done with a silica thickened epoxy. Apply with a roller, press the honeycomb in, cure under vacuüm(this way you'll create small fillets on the bonding area). I'm planning on using this method for both skins, as I only need (some sort of) panels, with both sides for visual application.
Pre wet fabrics laid on top of the honeycomb should have the same strenght as glueing, but you have to be carefull not to suck too much resin out of the laminate.

[Fgayford]

When you vacuum bag the final layers over the honeycomb does the vacuum not drag the cloth into the honeycomb cells leaving a dimpled surface. I haven't tried it yet so I don't know. Should you use less vacuum for the final layer?
Thanks
Fred

[Herman]

Use only moderate vacuum. And try a piece first!

[thedutchtouch]

sorry for the delay, as the previous few posters relayed, we used moderate bagging and multiple layers of carbon, in addition the outer two were faired before and after with microbaloons/epoxy. i do need to stress that i'm no expert so take my advice at face value. it did work just fine for our needs however, and no delamination or structural issues on projects 10-15 years old built with similar methods.

[latman]

i did it years ago with wet epoxy resin and no adhesive layer for a K1 kayak, i think it was about 200gsm Carbon/Kevlar fibre on the outside (with polyester gelcoat and Duratec coupling agent) that was vacuum bagged with the Nomex core in one hit , after that cured the inner layer of 200GSM Carbon and ultra fine 60GSM Kevlar was wet out on plastic and placed over the nomex , then Vacuumed in place . I think I turned the mould upside down so any excess resin sat against the inner fabric and would form fillets with the Nomex core . I was worried about water penetrating the air gaps of the core through a Porous inner skin as well as fibre bond to the core failing but it all worked great.