jkarran
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| posted on 13/1/09 at 05:12 PM |
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Composite sandwich construction
I've had an idea buzzing around in my head for a while now to make a composite chassis. I know this has been discussed on here before and that
responses are generally negative. Has anyone actually tried and had success (or a failure)?
I'm thinking quick, unique roadcar. Construction along the lines of: Epoxy carbon/kevlar/glass over medium density styrofoam skins/beams for the
main tub and floor. Lost-foam hollow beams if/where required for pipes etc (Mostly tunnel). Bonded in aluminium tophat-bobbings for structural
attachment points. Lost foam (with foam filled crash protection structures) for the body and roof. Maybe steel rollover protection.
I'm aware it's hard to get optimal epoxy/fiber ratios doing wet layup and there's a cost in strength and weight. It's far from
impossible however to achieve a good wet layup without any fancy equipment.
I know steel is cheaper, more forgiving, and more readily repairable but I fancy exploring something different.
Would a structure like this, semi-monocoque with no steel chassis as such, pose a particular problem for SVA?
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tegwin
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| posted on 13/1/09 at 05:32 PM |
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No comment on using it in a car...
But the homebuilt hovercraft guys use that method.... CSM over PU foam..... Built in vacum bagged pannels and then bonded together...
Have alook at the sevtech hovercraft for ideas
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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twybrow
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| posted on 13/1/09 at 05:46 PM |
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For SVA (IVA) you may need to prove with calculations, that the chassis is up to the job. This wouldn't be difficult, and with some basic
materials knowledge, and modelling software, you could match and exceed the Locost chassis no problem. Yuo would also need to think about point loads,
like harness mountings, seats, etc, where spreader plates and clever design would be needed to distribute the stress.
It's good to hear people thinking about using composites. Personally, I wouldn't (and I do it for a job), but mostly because I am too lazy
to design/test/build the thing.... It can be done, and for someone brave, I'm sure it could be a stack load stiffer than a steel chassis. Not
sure it would weigh a lot less however.... Keep us postes with your thought process, I would love to hear more.
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JonBowden
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| posted on 13/1/09 at 06:48 PM |
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this guy did something a bit simiar using foam sandwich panels http://www.geocities.com/MotorCity/7630/index.html
Recently, the aluminium monocoque robin Hood cars could not pass the SVA mainly due to concerns over seat belt anchorage - I can see similar problems
for you.
Despite potential issues, I like the idea a lot - hope you post pictures and description on here
Jon
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Alan B
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| posted on 13/1/09 at 06:49 PM |
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quote:
Originally posted by jkarran
I've had an idea buzzing around in my head for a while now to make a composite chassis. I know this has been discussed on here before and that
responses are generally negative...........
I wouldn't say that "please don't even think about unless you really, really know what you are doing" kind of response was
negative...more careful and sensible more than anything.
I'm pretty sure anyone who really knows what they are doing with composite design and manfacture will go ahead and do it anyway with or without
the go ahead from the forum.
Not really trying to discourage or encourage anyone to try something different (I do enough different things myself...) just do your research and be
very, very careful.
Alan
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Volvorsport
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| posted on 13/1/09 at 06:58 PM |
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www.teklkam.com
mosler MT900 are made from it , it costs a cool £500 for 48x96 inch sheet .
weight/stiffness ratio is very god tho .
all you need is a router to make slots for it to assemble together then laminate/bond inside/outside for the perfect DIY job
you MUST have load bearing inserts bonded into the chassis tho .
www.dbsmotorsport.co.uk
getting dirty under a bus
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blakep82
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| posted on 13/1/09 at 06:59 PM |
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if its good enough for F1....
...but they also know what they're doing  and have all the ovens needed, and tools, and have been doing it for years... and the money...
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Alan B
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| posted on 13/1/09 at 07:06 PM |
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quote:
Originally posted by blakep82
if its good enough for F1....
...but they also know what they're doing and have all the ovens needed, and tools, and have been doing it for years... and the money...
Blake, exactly right....
Nobody doubts in can be done and be spectacular......whether we as amateurs have the knowledge, skills and money is of course another matter.....
But, to those who give it a go my hat is off to you and I truly wish you every success.
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iank
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| posted on 13/1/09 at 07:25 PM |
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There was an article in one of the kit car magazines about a guy who'd made a complete carbon monocoque. It had taken him a 11 years,
he'd built an autoclave in his garage and had more 5 cars worth of scrap panels when he'd finished.
Found it, he built two - green and red "Brabini GT".
http://www.completekitcar.co.uk/issueapril08.html
Worth getting the back issue just to get a feel for whether you've got the commitment to do it.
There are a bunch of fibreglass monocoques that go through SVA ok (GTM's), but as said they're not as easy for the testers to assess so
they might want to see some believable numbers and a comforting level of knowledge from the designer before waving the construction through as safe.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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twybrow
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| posted on 13/1/09 at 08:04 PM |
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jkarran - do you have access to a CAD and FEA package (maybe via work)?
What composites experience do you have?
What facilites do you have (garage space, or fully kitted out commercial premises etc)?
I think as a minimum, you would want to wet lay, and then vacuum bag to give a more consistant product. Ideally, I would use either room/low
temperature cure prepregs, or resin infusion. Leave wet layup to boats!
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Volvorsport
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| posted on 13/1/09 at 08:14 PM |
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mosler use wet lay up carbon/kevlar .
darrian use wet lay up , with some rules of thumb , its perfectly acceptable to build from it .
bagging would be better , but unless you have the facilities to vacuum bag a chassis and keep the vacuum on it while it cures it may well be past a
DIY solution .
www.dbsmotorsport.co.uk
getting dirty under a bus
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smart51
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| posted on 13/1/09 at 08:32 PM |
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I'm making GRP / polyurethane foam sandwich bodywork. Once the GRP has hardened, it is surprisingly stiff.
The recipie is 2x 300g woven rovings on either side of 50mm PU foam sanded to shape. I bet I could put a long piece between two trestles and stand on
the middle without it bending much.
I have a steel space frame chassis underneath though.
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twybrow
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| posted on 13/1/09 at 08:35 PM |
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quote:
Originally posted by Volvorsport
mosler use wet lay up carbon/kevlar .
darrian use wet lay up , with some rules of thumb , its perfectly acceptable to build from it .
bagging would be better , but unless you have the facilities to vacuum bag a chassis and keep the vacuum on it while it cures it may well be past a
DIY solution .
So do/did Lotus, but it doesn't mean it is desirable...!
Oh and Mosler say something rather different on their website!
A 2nd hand vaccum pump can be bought from ebay for £50. Alternatively, you can make one from an old fridge (don't try using a vacuum cleaner, it
doesn't work!).
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Volvorsport
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| posted on 13/1/09 at 08:43 PM |
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having worked for mosler , the bodywork is carbon pre preg , but the chassis , is a different kettle of fish , teh roof section you see bonded on to
the composite honeycomb section chassis is hand lay up .
www.dbsmotorsport.co.uk
getting dirty under a bus
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jkarran
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| posted on 13/1/09 at 08:45 PM |
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Some interesting information cropping up here, thanks. That German thermoforming core material (name escapes me but there's a link in one of the
links) sounds like an interesting product.
I have very little composites experience, I've made some bits for my Striker and model aircraft parts. All layed up wet without bagging.
Obviously it'd be foolish go straight in and start a chassis with my limited experience, there's books to be read and experiments to be
performed first were I to go on with this. At the moment, I'm just trying to get a feel for what competent home builders have achieved and what
materials are available.
I don't currently have any serious CAD but I'd almost certainly design in Solidworks first.
Those suggesting vacuum bagging make a good point regarding quality and repeatability of results. A diy vacuum setup is probably a requirement.
I'm not certain why people are suggesting autoclaving is a necessity, there's plenty of good resins that cure at room temperature and
pressure. I think as a diy builder you have to accept you wont get 100% from the material, there will always be compromises on weight and strength.
Resin infusion sounds like a real headache. I'm sure the results are great when it works but my understanding is that without some serious
computer modeling it's pretty hard to get the resin to flow out evenly first time.
Cheers for the info and comments so far, please keep it coming 
jk
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twybrow
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| posted on 13/1/09 at 11:13 PM |
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Infusion is not rocket science. Simple parts, done with the right materials will be a doddle. I have infused a 60' yacht hull, with no modelling
whatsoever, and after the infusion was done, my prediction was 7 minutes out on a 3.5 hour infusion... Read up some more info on it, as it really is a
viable technology for the serious DIY builder to make high quality parts.
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jkarran
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| posted on 13/1/09 at 11:41 PM |
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Ok, I'll look into it. I'd only ever read bad things about it with respect to one off jobs. One of the perils of the interweb I guess!
I'm warming to this idea more the more I read. There's a lot of interesting products out there. Time to get a couple of good books on
composite structure design and mechanical engineering I think.
jk
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