AutoSpeed: lightweight, simple composite construction technique (monocoque + body)

[MetroMPG]

Julian at AutoSpeed has started what looks like another really interesting series:

Building an Ultra Light-Weight Car, Part 1
An incredible way of producing your own vehicle

If you follow the green car blogs, you probably saw the University of South Australia's tandem tadpole trike EV in 2008:



Part 1 of this series shows how the students laid out that design and made its monocoque tub out of honeycomb sandwich fiberglass panels:

The beauty of this technique is the ease with which a one-off monocoque tub can be constructed. Such an approach can result in a very stiff, ultra light-weight foundation for a vehicle – all without the need for welding or metal-working!

AutoSpeed: Building an Ultra Light-Weight Car, Part 1

[Compaq888]

I've seen a lot of new research places build carbon fiber cars that weigh less than 2000lbs. The auto manufacturers refuse to do that. At least BMW started putting in CF roofs, got to start somewhere.

[tasdrouille]

Very interesting article indeed!

Compaq, it's all about the money. I bet material and manufacturing costs for CF are prohibitive compared to pressed steel panels.

[bikin' Ed]

The expense of CF is one thing, but the safety is another. Carbon fiber in the passenger compartment can become lethal in a crash. During a crash it turns into sharp strong shards capable of ripping a person apart.

That being said, I like the idea of CF for fenders, hoods, trunk lids, and the entire trunk if it's not a part of the passenger compartment.

[wilky]

Originally Posted by bikin' Ed

Carbon fiber in the passenger compartment can become lethal in a crash. During a crash it turns into sharp strong shards capable of ripping a person apart.

And sheet metal doesn't? If this were true to the degree you say, it would not be used in racing applications as much as it is. F1 makes their "tubs" out of the stuff - completely encasing their drivers. If it was as you say, that would be like an iron maiden. No way any sanctioning body would put drivers in such a death trap. Passengers in a road car would be a significantly greater distance away from said shards in a crash as opposed to a driver of an open-wheel racer, further absurdifying (yes, I made that up) the "flying shards" theory.

[instarx]

I used to work in the health and safety area of the advanced composite industry and here are my thought as to why composites are not used much in cars.

1. Expense. The materials are expensive on their own, but the biggest expense is labor to make them. These parts have to be made by hand, alternating sheets of partially cured composite materials at different angles. Body parts would have to be hand-made. Roofs are easy because they are essentially flat, but fenders etc, would be extremely expensive to make. Anything with an internal structure like a door would be outrageously expensive.
2. Environmental. Although fairly inert after they are made, composite parts are not environmentally friendly to make. Just the resins alone are hazardous when liquid, and the amount of hazardous vapor produced during curing is considerable. Each part has to be cured under heat and vacuum for DAYS, so it is very energy intensive.
3. On severe impact these materials can fracture into some long, thin fragments about pencil length, but they are light-weight and bendy so would be unlikely to cause injury. Composite panels are actually quite strong when impacted and are not likely to shatter into large pieces that fly around. Helicopters use composite armor, so it's not like it shatters easily.
4. In case of a fire, everything electric in the immediate area might be shorted out by the smoke (composites will burn). The smoke has fine carbon fibers in it which short out electronics. When I was doing that work about 20 years ago investigators had to enclose their radios in plastic bags to keep them from shorting out when they investigated military plane crashes involving composites. Don't know if they have worked that problem out yet or not. There may even have been an electrical sub-station that was shorted out by smoke from a composite fire, but that was just a story that was making its rounds in the industry and I did not see anything published about it (not surprisingly).
5. Health concerns. When sanded, very small fibers are released into the air that may be a serious health risk, like asbestos. That's something of an unknown, so it is probably best not to put too many composite cars in the hands of local body-shops.

[blueflame]

Balsa or plywood framing? Hemp fibre and corn resins for panels? Alloy subframe with polystyrene hand carved shell?

Some design principles could be sooo easy like pressing an alloy sheet into a big 1 piece skirt that is essentially the whole body shell, on top a little jetsons clear bubble, hinged on one side that flips open to get in and out off. 2 piece's period! over an alloy subframe with a ply and carpet lined cockpit, that seals against the bubble.

[cfg83]

Hello -

In terms of the CF price issues. the Rocky Mountain Institute Hypercar venture spinned off into this :

Fiberforge: Lightweighting Your World With Thermoplastic Advanced Composite Parts

Fiberforge is a technology company that has developed a breakthrough process to enable the high volume, low cost production of thermoplastic advanced composite parts for a broad range of applications.

Improve system and product performance
by "lightweighting your world" with Fiberforge technology.

Thermoplastic advanced composites compared to other materials:
60% lighter and 600% stiffer than steel
30% lighter than aluminum
200% tougher than thermoset composites
500% stiffer than injection molded plastics
60% less scrap during production than sheet goods

It is not pure CF per se, but it is intended to be used as same. Here is more meat and potatoes :

Fiberforge: Resource Library, Thermoplastic Advanced Composite Technology

Question: I heard that CF was *not* recyclable in the way that steel and other metals are. Is this true?

CarloSW2

[MazdaMatt]

I wondered that as well... then i found out that this laptop that i'm typing on is made of a plastic containing shredded recycled carbon fiber - as are most laptops. Strong, light, cheap.

[dcb]

Originally Posted by cfg83

Question: I heard that CF was *not* recyclable in the way that steel and other metals are. Is this true?

It stands to reason. You can rather simply extract the steel from a car and make another car. Separating the carbon from the polymers takes some interesting chemicals and/or mechanical shredding (which shortens the fibers and weakens the result) Carbon fiber reinforced polymer - Wikipedia, the free encyclopedia