John in CR wrote: Hillhater wrote:
Unless each layer of foil is bonded to its partner layers with something that has the same properties as aluminium, the end "sandwich" will have only the strength of the bonding agent.
Aluminium foil has zero strength, other than in pure tension, and only then if you can avoid any / all minor imperfections.
.. Acid etching 0.024 mm foil would be an interesting project !
Not true. It will be like 20 perfectly fitting very thin aluminum tubes one slid over the next one and end up quite similar to a .5mm tube of AL over a 3.5" solid core. Now if you guys think .5mm isn't enough, then I'm listening.
A tube under a bending load has a spectrum of forces on it. There is a line of pure tension on the outside of the bend, a line of pure compression on the inside of the bend, and a gradient of tension, compression, and shearing forces everywhere between the extremes.
The only part of this spectrum in which a bunch of layers has the same integrity as a single thickness is along the narrow line of pure tension. It should be obvious that layers of foil have no structural value in compression, but I'm saying it. Compressive strength is basically tensile strength perpendicular to the direction of compression, and a stack of foil sheets loaded against its edge doesn't have that.
It should also go without saying, but I'm saying it, that a stack of foil sheets puts up minimal resistance to shearing forces, compared to an equal single thickness.
I ask you to assess the difference in bending stiffness between a book and an equivalent thickness of wood or MDF fiberboard, which are basically the same material.
I suggest that a narrow .5mm thick strip of solid aluminum bonded or riveted to the top and bottom of your monocoque would be of more structural value than a cumulative .5mm of layered aluminum foil around the whole thing. Ribs and stringers, inside or out, would be of much more value yet.