Carbon fiber thickness vs strength

[joeybutts]

So I’ve had/have a lot of time to plan a lot of projects and am ready to finally get my subwoofer in my car. I want to go pretty far out with this project and was going to use a pre made sheet of carbon fiber. I thought I read 2mm would be thick enough, but I just can’t believe it would handle it.

The entire perimeter of the panel will be slid into a “frame”, and essentially the panel will be 20”x40” and will hold an Aurasound MR18.4 (ns18) running “IB”.

Anybody have some knowledge on how thick a piece I would need?

Otherwise I’ll just get the thinnest sheet and adhere it to a piece of Baltic birch.

Thanks!

[djg]

I have some experience making carbon and carbon kevlar motorcycle fairings. I say just do an overlay on wood. Carbon is very strong and stiff, but brittle. I can see your carbon panel failing at the speaker mounting holes as you hit a big bump. Just my opinion.

[guitar maestro]

Are you talking about making a carbon fibre panel that will actually support that massive Aura on it's own? or just an overlay on an MDF or wood panel? We've been making sub-panel practice pieces for the Solar Car at my school, and it's quite interesting to test it out in various ways.

[gregrueff]

I have experience doing wet-layup over MDF for speaker enclosures.
The epoxy or polyester resin (whatever is compatible with the mat or weave you choose) ends up sealing the MDF better than anything I've experienced and laying it up wet is going to bond the carbon to the MDF better than anything else.

While the modulus of carbon fiber, depending on the weave, can rival 36 ksi steel, that's not to say you should forgo the MDF. It'd be the same as building an enclosure out of thin steel plate.

By overlaying the carbon sheet over MDF you are actually creating a composite material that is going to have properties that are superior to either material by itself. The MDF gives you mass and compressive strength. Mass is especially important to subwoofers with a lot of energy. The carbon, applied to the outside provides the stiffness. It's like steel reinforced concrete.

In my past I used one layer of a 3K twill weave over 3/4 MDF.
I was shocked at how well it worked even before I had added the cabinet bracing.
My unscientific "knock-test" sounded very good.

Hope this helps.
Greg

[joeybutts]

Thanks djg. I was concerned about the same and would hate to spend $2-$300 on a piece and ruin it.

Yes maestro, I wanted to suspend the driver from it. But my back up plan is a veneer sheet of cf over a board of Baltic birch, which I think will be the smarter and stronger choice.

[joeybutts]

Hmm Greg, I’ve done some fiberglass work in the past but never carbon fiber. And I was trying to steer clear of working with resins and epoxies but didn’t think about the effects if I bonded them together.

Shoot. Something to consider.

[killa]

If I remember the properties are different depending on the resin used. It is strong in thin layers but is very resonant. I have an acoustic guitar that is made out of it. http://www.rainsong.com/ If you are just going for the look a cheaper option might be a layer of carbon fiber over fiberglass.

[zomby woof]

Hmm Greg, I’ve done some fiberglass work in the past but never carbon fiber. And I was trying to steer clear of working with resins and epoxies but didn’t think about the effects if I bonded them together..

How have you done fiberglass without using a resin?

[joeybutts]

Thanks Killa!

Sorry zw, what I was saying was that I didn’t want to have to deal with the fumes of resin and epoxy in this project. I didn’t think about how binding the cf and wooden substrate would work together to benefit the project. Sorry I was unclear. 😬

[Squidspeak]

Epoxy resin will definitely be stronger over polyester (fiberglass) resin in almost every situation when laminating cloth onto a substrate.

[joeybutts]

Starting to think I may be doing some carbon fiber laying!!

[Squidspeak]

Starting to think I may be doing some carbon fiber laying!!

Joey were you going for the strength of CF or do you want the look of CF. There are some products that you laminate like formica using contact cement that
are made from Carbon Fiber, that may be an easier process.

[joeybutts]

First and foremost the aesthetics of CF, but if strength comes with the territory and I’m only spending a little more money I’d do solely CF. A sheet of 5x5 13mm birch is 50-60 and the veneer CF will run me about 100. A 2-3mm sheet of CF is 2-250. 150ish vs 250 for a lot less work and beautiful CF is worth it to me.

All in all I want real CF as the finish in some facet, not vinyl for this project.

[djg]

Starting to think I may be doing some carbon fiber laying!!

A wet layup of carbon fiber cloth will never look as uniform as pre preg professionally done work. Also, the surface will not be glass smooth unless it is layed up on a sheet of glass. Sanding will totally destroy the beautiful cloth weave look you want. Believe me, using a manufactured sheet over wood is the way to go.

There are low odor epoxies available. I would consider using contact adhesive.

[joeybutts]

Djg- I was gonna pick up three pieces of this-
And you can order it with adhesive applied. The cuts would end up basically hidden due to where they would land. I may be able to get away with two pieces.