Assembly of a Carbon-Fiber frame/tub 1

[kittt]

Hello all,

Lexus and Lamborghini have both created supercars that have a carbon-fiber main frame/tub: Lamborghini Aventador and Lexus LFA.

Do you guys have an idea of what type of mechanical joining they use to put together that CFRP frame/tub? In pictures I've seen, the frame looks very smooth, and therefore I was wondering if everything was bonded with glue/adhesives.

Sub-question: if there is also bolting involved, do you know if the bolts/rivets are there only for assembly purposes, or if they play a fundamental role in ensuring resistance to peel of the joints?

Thanks a lot,
Christopher

 

[patprimmer]

They generally use a prepreg which is a fabric impregnated with a very accurately controlled amount of resin.

The prepreg is layed on the mould in the required shape with appropriate overlap at joints and extra layers applied where extra strength is required.

The complete unit is then cured ideally in an autoclave, but can be by various methods to instigate a cure in the resin.

After curing, additional parts can be attached by using a compatible resin (usually epoxy for CF) and fabric. Sanding and ore-treating the surface may be required to improve the bond. A better bond will result if the extra mat is applied before the original is 100% cured.

Regards
Pat
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[Tmoose]

Mil spex for "secondary" bonded components require mechanical attachment, too, I think.

 

[GregLocock]

They do, but the mechanical fasteners are a daft idea and any designer who has the freedom to do so and understands their materials omits them.

You might also bear in mind that a lot of the carbon in road cars is there for show, and is quite often the outer layer of a rather conventional multilayer prepreg. CF is not necessarily a particularly useful composite for a chassis, more than one F1 team has raced with steel suspension arms with a CF overlay. The CF would have done very little other than look expensive.





Cheers

Greg Locock


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[kittt]

Thank you for your answers. I didn't realize carbon fibre wasn't as ideal as one might think...

I have another question. In those supercars, do you know how they manage to attach the seats to the carbon fibre floor panel?
I figured that these joints probably bear the highest loads, so I was wondering what solutions had come up to avoid damaging or creeping the carbon fibre.

Cheers,
Christopher

 

[thruthefence]

Here is the most appropriate application of carbon fiber technology in the automotive world:

http://tinyurl.com/3cpoqkh

or

http://image.made-in-china.com/2f0j...uning-Real-Carbon-Fiber-Key-Chain-CBK009-.jpg

 

[TVP]

Connections in composite structures often use inserts. Here are some references:

http://www.shur-lok.com/product_dls/Design_Manual.pdf

http://eprints.soton.ac.uk/65075/1/CEAS_manuscript-414v2.pdf

http://www.speautomotive.com/SPEA_CD/SPEA2004/pdf/a/a7.pdf

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ada305407.pdf&Location=U2&doc=GetTRDoc.pdf

http://fire.nist.gov/bfrlpubs/build00/PDF/b00043.pdf

 

[GregLocock]

I'd bond the seat rail direct to the CF with a layer of 45/45 to distribute the load into the structure.

Seat loads are tiny compared with seat belt loads.

Cheers

Greg Locock


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