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Carbon fiber + nomex honeycomb sandwich DML panel construction project
Carbon fiber + nomex honeycomb sandwich DML panel construction project
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Old 12th December 2016, 05:59 AM   #11
altie is offline altie
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Quote:
Originally Posted by DAMIC View Post
Unable to open any of pic's, posts 5-9.
Straight link to album: Carbon fiber + nomex honeycomb sandwich DML panel construction - Album on Imgur. They're not all annotated. I hope it's easy enough to track which ones go with which parts of the posts. Does right click -> "Open in new tab" work?

Last edited by altie; 12th December 2016 at 06:04 AM.
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Old 13th December 2016, 02:07 AM   #12
bentoronto is offline bentoronto  Canada
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Carbon fiber + nomex honeycomb sandwich DML panel construction project
Did I miss seeing weight per square foot?

Possible to use electrostatic drive?

B.
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Old 28th December 2016, 04:59 AM   #13
altie is offline altie
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I doubt electrostatic drive would work. If you're going for the DML principle, which will presumably vibrate the panel in a different pattern than ESL drive, you're probably going to need a driver capable of moving some mass. At reasonable playback volume for just me sitting in my living room, I can lightly grasp them between thumb and forefinger and feel a fair amount of vibration 6 inches or more away from where the exciter is placed.

Weight per square foot is going to be in the ballpark of https://dragonplate.com/ecart/categories.asp?cID=111, probably with a gram or two extra for our less than precision epoxying process. Someone on the diysound subreddit pointed out that using a vacuum chamber can improve the quality of carbon fiber epoxy jobs. That might be a good addition to the process I've described here for people who could swing it. They certainly work and from what my ears can tell work well without it though.
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Old 28th December 2016, 09:22 AM   #14
TBTL is offline TBTL  Germany
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Electrostatic drive doesn't require a membrane with a high bending stiffness, as the force can be applied over the whole membrane. A mylar film (which is lighter) will probably work better.
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Old 28th December 2016, 07:57 PM   #15
altie is offline altie
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After digging around more, it's hard to find the density from that page, but ~1/2" thick honeycomb with carbon fiber facing is going to be around half a pound per square foot.

For comparison, Gatorfoam Technical Bulletin gives Gatorboard's density as 15 lb/ft^3, so maybe just a hair more. On that measure, these panels may not perform substantially better than various stiff foam boards for applications like ESL.

The honeycomb sandwiches ought to perform way better in terms of stiffness, though. https://www.lairdplastics.com/produc...ical-datasheet reports Gatorboard's elastic modulus as between 5 and 15 N/mm^2 while Young's Modulus is a Measure of Stiffness in Carbon Fibre reports carbon fiber reinforced plastic - which I would guess is weaker than carbon + honeycomb - as 181 N/mm^2, more than 10 times as stiff, if my math is right.
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Old 28th December 2016, 07:59 PM   #16
altie is offline altie
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Anecdotally, these things feel strong as hell. I don't think I can bend them by hand - at all. Even though individually, both the honeycomb and the carbon fiber facings are very flexible. The panels feel like I could stand straight on them without damaging them, although I like the sound too much to risk trying it
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Old 29th December 2016, 11:41 PM   #17
fortitudine is offline fortitudine  United States
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For hobbyists, like us, the best source for great carbon fiber, IMO, is Soller Composites--
http://www.sollercomposites.com,carbon fiber,carbon fiber sleeve,Kevlar sleeve, fiberglass sleeves,carbon fiber fabric,epoxy,west system epoxy,nitrile,gloves,nitrile gloves,aramid,fiberglass,kevlar,tape,biaxial tape, biaxial sleeve
I built my own bicycle frame using their CF. Highest quality for great prices. They also sell epoxy suitable for laminating (that's what its called in the industry). Helpful tutorials, etc.

If you do not want to vacuum bag, then clamping is essential for a lightweight finished product.
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Old 30th December 2016, 04:12 AM   #18
altie is offline altie
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Yeah, that looks like a pretty killer deal. I went with Pro Tech for the simplicity of pre-stiffened sheets, but having slapped them together it doesn't seem like it would be a huge amount more work to use tape or fabric and paint some epoxy over it. Was it?

Also, got some documentation about that bike project? I thought about doing something like that a long time ago and never quite found the right path into it. Might be fun to get back to some day.
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Old 30th December 2016, 10:24 AM   #19
bentoronto is offline bentoronto  Canada
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Carbon fiber + nomex honeycomb sandwich DML panel construction project
Quote:
Originally Posted by TBTL View Post
Electrostatic drive doesn't require a membrane with a high bending stiffness, as the force can be applied over the whole membrane. A mylar film (which is lighter) will probably work better.
Without grasping all the implications, it just seems to me that ESL motivation is better off with a stiff radiating surface than a piece of Saran-wrap (allowing for differences in weight, thickness, etc.)???

With a film membrane, you do need to manage the location of the charge on the film, for example, and that wouldn't be much concern with a stiff surface that would average irregularities. On the other hand, not much attention needed to resonances with a film but could be troublesome with a stiff panel.

Still wondering....

BTW, I still don't have a good sense of how the stiff board compares in weight to Saran-wrap.

Ben
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Old 30th December 2016, 05:45 PM   #20
Discopete is offline Discopete  Canada
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Carbon fiber + nomex honeycomb sandwich DML panel construction project
So what's new? circa 1961?
Attached Images
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Last edited by Discopete; 30th December 2016 at 05:47 PM.
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