I have a glass fibre car with a rotten mild steel space frame chassis. Is it feasible to replace (partially replace) with your carbon fibre tubes and sections? I mean would they be strong enough. The main rust is in the main backbone chassis and the sections that come out along the sills. If i have a 1inch mild steel tube section what would i replace that with for same strength?

I would replace complete section for instance the whole backbone not just patch up the rusty bit.

Graham

Hi Graham,

It's feasable but there would be lots of considerations specific to working with composite tubes compared to more conventional steel tubes (which the chassis was designed for).

One example would be to consider how the tubes would behave in a crash situation; composites, and particularly carbon fibre, are very strong until the break but once they do they tend to break completely. The spaceframe of your car creates important protection for the driver and will have been designed with some knowledge of how the frame would crumple in the event of different impacts. Simply swapping metal tubes for carbon tubes would change the crumple characteristics of the chassis considerably which could have major consequences in terms of safety.

Another consideration is the type of forces that will go through the tubes and whether they will be sympathetic with the fibre orientation of the tubes (composite tubes are stronger in some directions than others). Our roll wrapped tubes have a good spread of strength but it's still worth thinking about. Their 0,90 fibre orientation means they're not very strong in torsion (twist).

Another consideration is how you will connect between the carbon fibre tubes and the exisiting tubes; you'll need to make special metal fabrications which the carbon tubes can be bonded into but which can then be bolted up to the metal tubes. This alone would be quite a bit of work.

I hope this helps. You might conclude that in this case you'd be better sticking with metal tubes in which case I think I would agree with you but like I said at the top of the post, it would be possible.

Kind regards, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Thank you for coming back to me. I used to own a lotus elan +2 which had a steel backbone chassis  - after an accident i replaced the chassis with an aftermarket Spyder spaceframe chassis. My current car which i have had from new is a 1998 5.0l Chimaera but after about 10 years the chassis has rotted through. I live on Anglesey exposed to the sea air all year round. I can buy a new chassis but i am more than annoyed that when you buy a car with extensive corrosion protection on the chassis i need to buy a new one. The problem being the new chassis is exactly the same as the old one. Powercoated - which falls off.

All the above not your problem but it was to give you an idea why i was considering it.

thanks anyway.

Graham

simpler solution might be to repair the old chasis then get it hot dip galvanised. Then powder coat/paint it then fill all the voids with a good corrosion inhibitor.

If you had the time, money, space and engineering knowledge, you could build a carbon chassis.   However, if you do a bit of research into carbon chassis technology you will find most are either a complete carbon monococque or a central carbon tub with bolt on front/rear subframes.

F1 cars are an obvious example but there are quite a lot of sports/race/supercars knocking about with carbon monococques/centre tubs.

As Matt eludes to, using just a tubular carbon copy of the steel spaceframe would be difficult and leave issues surrounding crash design.  Hence why most carbon cars are a monocoque design which best utilises the strengths of the carbon/composite material.

Also in terms of failure modes, a conventional steel structure it is allowable in the design to have crumple zones and an element of deformation to absorb the energy. With the failure of carbon structures generally being a total failure of the part, it means you need to make the part stronger so that the essential central tub does not fail and hence protects the occupants.

I find myself considering doing this as well  for the areas of the chassis that hold the body on, the biggest issue will be that the tow points are in this area so need to take loads of car being towed.... I'm thinking of using tube or rod bonded into carbon sheets that I make myself, might even incorporate the rods or tube in the actual infusion process of making the panels.

You are mad - as in carbon mad but that's no bad thing.

I see no reason why it won't work for bodywork supports.

You could use a small metal tube to take the load back to the main chassis with the carbon sheeting replacing the rest of the structure.  Shouldnt need to be too big when you look and see the actual size of the FIA spec mounting points and eyes etc on some cars!

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

No in one word

If I am out out of line, let me know, this is my first post.  This topic touched on the reason I started reading up on CF and composites.  Background, I am 54, repair equipment as full time job, can fix or build almost anything, except I have NOT done auto body work.  I would like to build a car, originally was thinking of making it traditional style with sheet metal, but have been interested in CF light weight and strength. 

Is it possible for a newbie to learn enough about the engineering qualities mentioned in this thread to make a reasonable safe car?  Either by using a donar car/truck frame or by making a unibody or monocoque? What sources or books or websites might I go to?  I know and respect the years of university training engineers must learn. 

Thanks!

With the help of EC advice over the last 1.5years I have learnt how to make moulds and composite parts and have effectively made all the body panels for my car out of carbon/Kevlar.

If you dont have the engineering know how/experience to design a chassis and measure it to be safe, then you need to use either other designs you know to be sound structurally as the basis for your car or pay someone to do the design for you.

In most cases its easy to overengineer such things with some simple knowledge and experience, and with lightweight composites that is usually fine and still achieves what the guy wants.

The hard part is cutting things down to a minimum and designing your chassis to have the least weight and least material in certain places etc.  Get it wrong even a tiny bit and your chassis could fail at the worst moment.

But generally most of us arent in the game of getting 110% out of the materials.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant