use of carbon fiber for auto parts 1

[willjessup]

I'm wondering about the practicality (costs aside) and reliability that stressed carbon fiber auto parts have. For example, I drive a 1991 toyota MR2. It's a mid engined sports car but suffers from too much weight in the rear. The rear cross member weights something like 80 lbs. Fashioning that peice out of carbon fiber would help almost every handling characteristic of the car.

so, any insights would be appreciated , thanks!

 

[patprimmer]

Carbon fibre has very high strength and rigidity, but very low elongation at break. Also it is really only strong in the direction of the lay of the fibre.

This means that you need to be aware of this in the design stage, and specify the fabric structure or lay of the fibres. Also, the design will be more sensitive to stress concentrations, as the low elongation may cause cracks to start before the material can yield sufficiently at the most stressed points.

So long as these points are considered, and cost is no object, carbon fibre can be used, and in fact is on top end race cars like F1. I think from memory, that some model Corvettes have some carbon fibre components in their suspension, although I expect the real advantage in that case lies with marketing and the "high tech aerospace" image.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[Dave K]

The only production street car Corvette, that I am aware of, that uses any carbon fibre is the special Lemans edition (blue w/red and white stripes), and that was only the hood.

The new Porsche GT has some really nice carbon work for its subframes.

-Dave
"Everything should be designed as simple as possible, but not simpler"

 

[Tmoose]

I was stunned to read Corvettes went to transverse leafs front and rear a while ago. The spring material is usually described as fiberglass or epoxy glass. I would have figured they might try some thing more exotic there, like carbon.

 

[Rob45]

Corvettes have had transverse leaf springs in the rear suspension as long back as the '60's, and have been using "plastic" (composite) transverse leaf springs front and rear since at least '84.

Rob

 

[patprimmer]

Guys, I know I mentioned the Corvette, but we are a long way from the question of carbon fibre sub-frame components.

One problem that I might expect with a carbon fibre cross-member in a spot welded steel chassis, is that the elongation of carbon is a lot lower than that of steel, therefore, the carbon component will bear a disproportional large portion of the load as the chassis is flexed.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.