kaizokuace
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| posted on 22/11/05 at 07:30 AM |
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body paneling
does the aluminum paneling offer more rigidity? or can other materials be used to save weight such as carbon fiber? what would be a good way to
attach CF paneling if so?
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Hammerhead
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| posted on 22/11/05 at 10:23 AM |
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I'm also thinking of using CF paneling on the underside of my MK (when its ready to pick up) I dont have much experience with it but I am
thinking of the following:
layer 1 - 300gsm plain weave CF
layer 2 - Kevlar
layer 3 - 300gsm plain weave CF
bonded and riveted to chassis just like ally panels. anyone think this wont work?
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oliwb
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| posted on 22/11/05 at 10:39 AM |
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Was thinking of doing the same after SVA on my Tiger CAT. Was also thinking of a 3 layer weave with Kevlar sandwiched between to layers of CF. My
only concern was with the riveting of the panels to the chassis. My plan was to mould in metal sleeves of some sort to aid with some rigidity where
the pop rivets go through. Oli.
If your not living life on the edge you're taking up too much room!
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kaizokuace
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| posted on 22/11/05 at 11:31 AM |
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so i'm not alone then : )
yea i am wondering how to attach the CF panels to the chassis. riviting might crack the CF. I am wondering if it doesnt need to be attached so well
to the chassis. Drilling holes and just bolting it to brackets seems to be the best way in my mind. Glue is out of the question because i want to be
able to take it off easily. but i want to use CF panels so i can mould it to any shape i want to get some better aero on the body and ofcourse weight
reduction. I just want to know if the chassis will lose substantial rigidity if its not aluminum panels rivited on.
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Hammerhead
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| posted on 22/11/05 at 03:29 PM |
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I dont think the carbon would split if rivets were used as long as you had a sandwich of kevlar. Kevlar doesnt seem to 'explode' so to
speak like CF does.
However, you stated that you would like to be able to take the panels off - how about using Dzus clips like on motorcycles? In terms of rigidity you
could do what I am going to do and weld in extra crossmembers in the chassis under where the seats go. This should compensate for any loss in rigidity
from not permanantly attaching aluminium panels.
The above is all theory that I will apply to my MK Indy, but I am no expert on any of it. I would be interested to see what you do in the end.
Phew!!
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caber
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| posted on 22/11/05 at 09:10 PM |
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Erm, if anyone sees the Carbon Fibre underneath you will be in serious trouble! Weight at the bottom of the car is better than higher up, I would keep
ally or steel for the floor and put the carbon fibre/kevlar higher up, bonnets, side panels back panel etc.
No chips, beer, chocolate etc for a year or two would also help power to weight ratio, (certainly would mine:-)
Caber
Or have I got it wrong and you are going to put lot of Kevlar in to make the ultimate bulletproof drive by shooting vehicle!
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caber
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| posted on 22/11/05 at 09:18 PM |
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How about making up panels and glassing them on to the chassis and to each other this would certainly increase structural rigidity giving a composite
frame / monocoque construction. If you completely glass in the tubes you could probably use smaller size or wall thickness. This would also be
interesting to see where stress cracking happens in the gelcoat first as these would be the areas of maximum flex or stress.
I would deffinitely look at bonding rather than mechanical fixings as these will always be stress points in the composite and it really doesn't
like point stresses.
Caber
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Hugh Paterson
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| posted on 22/11/05 at 10:14 PM |
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 Waste of time fellas if you wanna get exotic just build the fecking car in CF. If you hand lay up the resin/kevlar/CF for a floor undertray to
save weight, and at the same time expect to match the stiffness achieved by welding or riviting the panels to the chassis tubes by dzus fastners or
some other temporary mechanical fixing you need to take yer head out that pot of glue and plastic bag Try going on a diet before you climb in it,
trust me it works better
Shug.
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kaizokuace
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| posted on 23/11/05 at 12:21 AM |
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well i was planing to make the bottom steel like in the book and weld that on, but i want to do like the side panels and bonnet in CF so i can do some
aero moulding. i was also wondering, would doing something like filling all the chassis tubes with an expanding foam help with rigidity?
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Hammerhead
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| posted on 23/11/05 at 09:58 AM |
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not sure about filling the chassis tubes with foam - if you have seen this done in industries such as aerospace or motor racing then it might be worth
trying, but I dont recall ever seeing anything like that.
I included the kevlar layer in the floor pan because if when driving along something flicks up from the road, it wont puncture.
I am also looking at making all the panels from CF, and possibly the floor with rear airsplitter. I am not that interested in saving weight in the
car, as I am adding extra structural bracing, using CF will allow me to sculpt bodywork that is quite different to the Lotus 7 style. I dont see the
point building a car that looks like everyone elses.
I wont be using much glassfibre because I want to see the CF weave on the finished panels.
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flak monkey
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| posted on 23/11/05 at 10:09 AM |
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quote:
Originally posted by kaizokuace
i was also wondering, would doing something like filling all the chassis tubes with an expanding foam help with rigidity?
Put simply....No..
The resistance of a beam to bending comes about through its second moment of inertia. This relies on how the material is distributed around the
neutral axis. The further the material is from the neutral axis the more rigid the beam. This is why if you want a stiffer beam you do not increase
its wall thickness, you increase is diameter.
Composite panels and structures that use a foam or paper core only use the core to hold the sheets of composite together, the core carries no load,
and would be useless if it did! (They can carry some, but it depends how the panel is used. If used correctly the load in the core should tend to
zero...)
My research project is on composite panels...you would never guess 
Regards to your other questions...
If you bond the panels to the chassis it will help with rigidity, but only if you get a perfect joint. Otherwise you are wasting your time.
A good rule with composites used in structures.....
If you dont know what you are doing, dont bother.
The design rules for composites are horrendous, and in a lot of cases rules don't really exist. To model the behaviour of a metal under load you
need only 3 constants, for a composite you need 32, all of which need to be determined... Composites fail catastrophically as well.
However if you want to just use the panels as panels, i.e. not structural, its easy.
David
[Edited on 23/11/05 by flak monkey]
Sera
http://www.motosera.com
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kb58
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| posted on 23/11/05 at 02:50 PM |
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There's another aspect of composite not mentioned.
When a metal panel bends in a crash, the sheet just bends. A composite panel will, depending on the amound of bend, break and splinter, like a thin
sheet of wood, leaving VERY sharp splinters. Simply handling my carbon chassis was always a test to keep from bleeding by catching my hand on a
hardened threads of carbon.
I can see in an accident being shreaded alived by a broken composite panel.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Avoneer
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| posted on 23/11/05 at 03:20 PM |
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Won't all this be irrelevant unless you use pre-preg and baking it under pressure?
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Hammerhead
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| posted on 23/11/05 at 05:25 PM |
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hi Pat,
you can do a wet lay-up with a hard roller then vacuum bag (so yes pressure is good) this gives a nice even distribution of resin and minimises air
bubbles. You need a breather layer too.
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kaizokuace
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| posted on 23/11/05 at 06:43 PM |
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thanx guys, i decided to do the aluminum paneling for the sides and around the tranny tunnel and make the nose cone, bonnet, dash and fenders from
CF. Has anyone made like a removable hard top? that might be a fun CF project. Or would a hard top just look funny? It would be cool just for the
sake of being cool to have a roof that slides forward like the batmobile.
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stevec
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| posted on 23/11/05 at 07:09 PM |
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Hammerhead, you said in a earlier post (when its ready to pick up) The Indy that is.
Does that mean you have been waiting long?
Its just that I have just put the deposit for mine in the post.How long have you waited?
Cheers.
Steve.
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Hammerhead
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| posted on 23/11/05 at 07:26 PM |
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hi stevec. Only been waiting 4 weeks, so not too long. I've made some special requests' so now they are waiting for me to take the elise
engine to them so they can make engine mounts. Its just that i didnt realise that they were waiting for me!
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stevec
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| posted on 23/11/05 at 07:49 PM |
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Thanks for that. I was hoping to get mine for Christmas, Give me something to do on christmas day,( fat chance) Not sure what engine yet, we have a
couple of brand new Rover 1.8 K16 turbo engines at work but I fancy a Bike engine.
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Avoneer
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| posted on 23/11/05 at 09:42 PM |
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quote:
Originally posted by Hammerhead
hi Pat,
you can do a wet lay-up with a hard roller then vacuum bag (so yes pressure is good) this gives a nice even distribution of resin and minimises air
bubbles. You need a breather layer too.
Doesn't this end up not as stong structurarly and very brittle - not so good in a floor?
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Hammerhead
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| posted on 23/11/05 at 11:44 PM |
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it works fine in racing rowing boats, so is very strong
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