Hi DF,
1) I cant find anywhere that explains how to create an Aluminium core composite and how to bond the core to the fabric and if it can be infusion formed.
BUT I still dont get how to do it - I mean do I create a skin then spread the epoxy all over it - if so how thick - on both surfaces ? (like I was sticking ceramic tiles on a wall) then do I vac-bag it to get a good bond or do I need to heat the work-piece up.
You need to make the contituent sheets first (so if you want skins of fibreglass on the panel you would need to make the fibreglass first) ideally with a peel-ply finish on the inside. You then apply
honeycomb bonding adhesive to the peel-ply side of the first panel, lower the honeycomb onto it, do the same with the other face and then lower that face onto the other side of the honeycomb before weighting them down (or pulling a light vacuum) whilst the adhesive cures. Aim to apply the adhesive about 0.3mm thick. the adhesive cures at room temperature, no need to heat it up.
2) If I am going to construct a big 3D construction, how do I choose the right sandwich components for a good combination of rigidity and flexibility and ease of production - I am thinking about silver glass (or 2x2 CF) on the outside with 2x kevlar layers around aluminium or foam core ?
Choosing the right materials depends so much on your design and how it all comes together that it's impossible for anyone to tell you, in a generic sense, what would be right. Your laminate of 2 layers of fabric will give you about 0.5mm of thickness on the inside and outside. That is a very very thin laminate; it's possible that it's right but unlikely. I think my suggestion would be to make up some sample panels using the skins that you think will be right and bonding them to some honeycomb in the way that you will do on the full scale part. You can then do some stress and destruction testing on those panels so that you've got a really good idea of what construction will be right for your full scale part.
3) If I find the right combination of sandwich materials and create a side panel and a roof panel how do I join the two - I understand the different techniques but just want to choose the right combination of epoxy, bolts, extrusion etc. - I don't want to just bond the two together and find the roof peels off on the motorway! What particularly concerns me
That's a really complicated subject and again is all down to your design. Sandwich panels (particularly those using honeycomb) are vulnerable at the edges and so generally you would want to have some solid sections forming a frame around the edge of your panels (which you laminate in at the time you construct the panel. This will give you a lot more options when it comes to fixing them together.
4) It occurred to me that I could build a box-ally frame and then I would have a solid base, for example to bolt a spare wheel to. Then I thought should I try and build a frame into the composite shell or just both the sell to the frame or is having a frame overkill.
This is a really wide subject and we can't design your vehicle for you. What I can say is that most modern composite vehicle bodies (generally refrigerated vehicles) use a frameless design these days. The panels are joggled and fixed together to leverage the stiffness of the panels rather than to 'hang off' a heavy and not particularly sound steel frame. A process invented by Truck Panels Ltd in the 80's and now used the world over.
I hope this helps,
--Matt
Matt StathamEasy Composites / Carbon Mods - Technical Sales