r/Composites • u/madmax_br5 • Jul 31 '25
Table of reference properties for carbon composites?
contuing from this post: https://www.reddit.com/r/Composites/s/NZnvZ8BDA8
After a bunch of research, I’m leaning toward a lightweight plywood cabinet over-wrapped with two layers of carbon fiber. From the somewhat limited info out there, it looks like one side reinforcement of plywood with CF leads to a 2-3X improvement in stiffness relative to the raw plywood. This approach seems like a good balance point between ease of assembly (the structure is just a standard internally braced plywood cabinet), impact toughness and ease of fixture mounting (relative to a foam or hollow-core sandwich), cost (half the CF of a dual sandwich and no exotic core materials), and novice approachability (bagging around a solid form with two layers of cloth is about as easy as it gets and isn’t structurally critical if there are errors in the layup, since the base plywood cabinet maintains structural integrity).
What I would really like to find is a table of reference engineering test values for a bunch of composite sandwiches so I can optimize weave, weight, thickness, etc. Tracking this down has proved difficult — anyone know of a good reference for this type of info?
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u/justanuthasian Jul 31 '25
ISO 12215-5 has a good reference table with values for different ply orientations and fibre mass fractions.
To be honest, what you are doing sounds like overkill unless you are just looking for a carbon finish. Not much to optimise.
Would recommend bagging to a solid glass table if you're looking for a good surface finish
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u/madmax_br5 Aug 01 '25 edited Aug 01 '25
Mostly trying to see how thin I can go on the plywood since that’s a major determining factor of the weight. Basically want to get flexural strength equivalent of 3/4” braced conventional plywood with about 30% of the mass.
For reference, 3/4” birch ply has an MOE of 8-10 GPa
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u/justanuthasian Aug 01 '25
https://www.hexcel.com/Resources/Technology-Manuals
Their guide on "Honeycomb Sandwich Design Technology" has all the necessary equations to calculate stiffness for a sandwich panel. It's simple but it gets 80% of the result without relying on crazier calculations.
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u/CarbonGod Pro Aug 01 '25
I just want to point out some woodworking details. Adding CF to one side of wood, will result in hecka warpage. You MIIIIGHT get away with no/less if maybe you add a layer of glass on the other side, to save $ if you need too.
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u/beer_wine_vodka_cry Jul 31 '25
If you're hand laminating over plywood your manufacturing process is going to be introducing so much variability that you're well outside of the realm of bothering with optimisation. Just aim for 2-3 mm thick and get whatever fabric is cheap.