Interesting reading about foam core panels.

[loaderman]

"It is estimated that by increasing the sandwich thickness by two, the panel will become 12 times as stiff and six times as strong. The advantage of a sandwich is that little weight is added when increasing the thickness." http://www.sandwichpanels.org/articles/article_sandwichoanelcores.html


"Based on my spreadsheet, a 4’x8’ panel comprised of a ½” BC plywood (5-ply) top and bottom lid and a 2” extruded polystyrene core (i.e., pink or blue rigid foam insulation board) can carry a load of 41 pounds per square foot,"
http://theatreface.ning.com/profiles/blog/show?id=2529492%3ABlogPost%3A147917&commentId=2529492%3AComment%3A148435&xg_source=activity

[GPW]

We’ve been saying all along , when in doubt make the foam thicker ...

[pete42]

Interesting confirmation to what Glenn has been saying.

Double the thickness six times as strong........let's see; at 16 I was this thick, at 70 I'm now this thick................hummmm

nope I don't feel six times as strong must not work in all cases.

oh well........lets have another beer...........

[eaglesdare]

how about wine instead of beer

[GPW]

Think about it ... how secure would feel with a 4” thick wall , or a 6” thick wall ? ... As L' has confirmed . thicker IS stronger , and my Little foamie is stronger because the 2” material is “relatively” thicker than it would be on a larger Foamie ... Does that make sense ? Think of the Insulation factor of a thicker material too ... Foam is still the lightest part of the equation , so you can use a LOT of it without much weight penalty ...

[GPW]

For those that would feel even more secure with a thicker skin , but prefer the ease of using canvas for the panel skin ... we have seen and painted on some extremely Heavy (thick) canvas in the past .. Incredibly Strong , a Bit heavier too ... obviously more expensive ... but if you want strength .. It’s out there... just have to look around the industrial sites ... Ever see a canvas fire hose ... TOUGH stuff ... !

[loaderman]

Yep, makes sense, just real good to have numbers to back it up.

[atahoekid]

Facts like these might even convince the naysayers. I never thought of it as a core panel when I started my build but when you stop, step back and take a look, that's exactly what we're building. If I had thought about it as core panels originally, I might have gone about my build a bit differently. Vacuum bagging even starts making sense...

[GPW]

QUOTE: “ Facts like these might even convince the naysayers. “ .... Not likely ... unless they’ve actually Built one ...

[atahoekid]

Sorry, the optimist in me got carried away....

[angib]

"Based on my spreadsheet, a 4’x8’ panel comprised of a ½” BC plywood (5-ply) top and bottom lid and a 2” extruded polystyrene core (i.e., pink or blue rigid foam insulation board) can carry a load of 41 pounds per square foot,"

Two half-inch ply skins on 2" foam core is hardly lightweight material is it? And I wonder if the guy has actually done all the stress calcs and not just the bending one - I would expect the insulation foam to fail in shear long before the ply skins failed. Real foam-core structures are made with structural foam that is slightly less expensive than gold, but only slightly.

We don;t seem to be seeing forum members posting a flood of finished foam teardrops, which may be because it's easy to start a foamie but not so easy to finish it?

[GPW]

See what I mean !!! Guess they told the Wright Bros. that too ... we know how that turned out ...

[linuxmanxxx]

With the display of how simple paper and elmer's glue can more than triple the load on the foam, why does everyone get their head wrapped around using heavy materials on the skin such as 1/4 plywood? I've used 1/8" luan on all mine and can walk on it at almost 200 pounds so I'm just confused why people keep using 1/4 and 1/2 in their torsion box builds.

[eamarquardt]

As it has been explained to me an "I" beam gets stronger proportional to the Cube (3rd power) of the distance between the horizontal elements. So a beam 2" high is 8 times stronger than a beam 1" high.

Here's the formula (but it's in "Greek")

In reality I think the foam/skin bond would break down prior to reaching this predicted strength but it supports the notion espoused earlier.

I'm not sure why the formula won't show but it's in my album: gallery/image_page.php?album_id=1588&image_id=87997

Cheers,

Gus

[loaderman]

the link says I am not authorized.