[VAC] Re: Aluminum Honeycomb

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

Basically aluminum honeycomb is a structural assembly of two fairly thin
sheets of aluminum separated by an aluminum or paper hex celled
honeycomb. The sheets are generally attached with epoxy, the axis of the
cells is perpendicular to the surface of the sheets. This principle can
be applied to wood to make a strong lightweight structure (ala hollow
core doors). It can also be applied to some types of foam as the
spreader. 

There was an article in Ham Radio magazine back about 1970 or before
(the magazine began in 1968) on using thin aluminum sheets, aluminum
honeycomb and epoxy to build parabolic reflectors.

The Aircraft Spruce Company sells structural foam and honeycomb and
describes its use for aircraft. Their catalog is free and has a lot of
useful information including fancy structural grade wood pieces. They
have a good web page. No doubt other companies that cater to the home
built aircraft trade have similar information and materials.

There was an article in Fine Woodworking perhaps ten years ago about
making cantilevered tables using thin wood with a multitude of maybe
3/16" strips of wood on edge for spacers. The top was probably 1-1/2 or
2" thick.

The fundamental of all of these is that the bending concentrates most of
the stresses near the skins, even in a solid block of wood, the stress
in the middle is zero (except for some shear) and is maximum at the
surfaces. The bending strength of any beam is dependent on the spacing
of those skins. The composite skin/foam or honeycomb/skin structure
depends on the foam or honeycomb to keep the skins separated. The
bending strength is proportional to the spacing to the fourth power so
spacing is extremely important.

Using such a composite for a floor means the upper surface material
needs to be selected to spread the point loads of spike heel shoes out
over several of the interior spans (if a relatively large celled grid)
and then it works well. Takes a lot of glue and details to create. Its
much quicker to start with a closed cell foam and glue plywood to its
surface, as in some modern house panel constructions. Some use a
urethane foam that they foam in place, some start with standard Dow blue
board and glue plywood or oriented strand board to the surfaces. Such
construction can result in lightweight, strong, and well insulated walls
and floors. Its stronger and better insulated the thicker it is.

Gerald J.