Carbon fiber, vacuum bagging technique?

Ant · #1 (**permalink**) 10-06-2003, 07:48 PM

Would love to hear of others experience with laying up Carbon fiber, and "VACUUM BAGGING" for a stronger result! Incidently I have done a bit of normal fiberglass work over the years, but still learning!

About to cover my transmission tunnel with uni-directional carbon lengthways on the corners and 2-3 layers of double biased carbon, completely over the tunnel with a flange enabling it to be bolted to the chassis, tubing at each end of tunnel to crossmembers etc - to provide a hopefully effective backbone with some additional torsional rigidity. Reason is my Cobra, has a ladder platform chassis, which is limiting by its own nature, thought of adding a tubular backbone but the main rails are about 26.5" apart.
"THIS GUY WONT ACCEPT HE CANT ENHANCE IT, FOR THE VERY LITTLE TIME IT WILL BE ON THE RACE TRACK!

Any info gratefully appreciated

Bumpster · #2 (**permalink**) 10-06-2003, 10:32 PM

On the television show Dream Car Garage on speedchannel a few months ago they made a hood for a Chevelle, I believe it was, using a vaccum method with fiberglass. They went through it step by step and it was very interesting and well done. If you can get a tape of the show, it may be what you are looking for.

Bumpster

Ant · #3 (**permalink**) 10-07-2003, 12:21 AM

Thanks Bumpster,

I have emailed them to see if I can get the video!

Bob Putnam · #4 (**permalink**) 10-07-2003, 04:48 AM

Lots of information available from Fibreglast Developments .

Ant · #5 (**permalink**) 10-07-2003, 07:20 PM

Thanks Bob!

mikeinatlanta · #6 (**permalink**) 11-01-2003, 08:35 PM

are you bonding it to the current tunnel or as a separate piece? what it the tunnel made of?
Mike

Ant · #7 (**permalink**) 11-02-2003, 12:41 AM

Mike,

I am intending to bond over the existing fibreglass tunnel, which is part of the car body attached to front and rear firewalls!

Not sure whether I will continue this idea, because I was going to run tubing to the suspension pick up points from the carbon fibre tunnel.
It would be better to run a backbone attached to the chassis and keep the body separate?

mikeinatlanta · #8 (**permalink**) 11-02-2003, 06:38 PM

You will gain very little stiffness by bonding the carbon to the fiberglass tunnel. Composites gain stiffness relative to the distance between the face sheets. This requires making the part very thick to achieve the desired results which would normally be accomplished with honeycomb core. Unless you wanted to replace the entire tunnel with a honeycomb sandwich piece, you won't be doing much other than adding weight. To achieve maximim stiffness, you also need to box in the structure. Unless the bottom of the tunnel is closed in, you will have very little structural integrity.
Try this:
Take a paper towel roll and try to twist it like a torsion bar. You will notice that is is very stiff. Cut a slit along its' length and you will see that it loses all of its' stiffness in torsion. This is what you have when the bottom of the tunnel is open.

IMHO, you are better off installing a roll cage or investing in a new chasis.

Ant · #9 (**permalink**) 11-02-2003, 09:53 PM

Mike,

You make very good sense about just covering the tunnel with carbon, will achieve a minimal result!

I had a guy look at the car, from a composite supplyer, he suggested that it would make a big difference, but in the last few weeks I have gone off the idea, and you have 'hit the nail on the head' on how it should be constructed. It is not going to be practical, especially with the open bottom, even though I was going to secure that every 12".

I have a Homologated rollbar for racing, with diagonal forward bracing to main chassis rail, and back to rear of chassis. Regarding fabricating a tubular backbone section, that is reasonably easy to do as per the Cobra Coupe, which added a claimed 50% to that. I am still quite happy with the conventional ladder platform chassis, as its a bit heavier than original (4X3) and I would say quite a bit more rigid than original, plus I am going to run a small block 347with alloy heads, I am sure with the right selection of springs shocks etc, and the wee bit of track experience I have had over the years may help in setting it up! ALL THAT IS WISHFULL THINKING AND A BIT OF GUESS WORK!

I did contemplate building a space frame or backbone style chassis, then thought the devil I know, plus in NZ the motorsport clubs are going away from non original style concepts, so to keep it a bit period!