Weight Reducing Structural System for Panels

There is far more to composite sandwich panel design and construction than can be covered in a post or two.

A very good yet very brief text that can get you started on the basics is this one by Hexcel:

http://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/Honeycomb_Sandwich_Design_Technology.pdf

Don't be thrown off by the "honeycomb" in the title. Any core material will have specified values for compressive strength and stiffness, shear strength and stiffness, etc, etc, etc. (So plastic foams can replace honeycomb as a core in many panels with some sacrifice in weight but a reduction in cost.) Honeycombs are a little more challenging to bond to skins, because the bond area is very small and because care must be taken to avoid filling the cells with excess adhesive. With foam cores, it is often possible to laminate the cores and skins all at once, using the laminating resin as the adhesive between core and skin. (However, in very light panels the amount of resin that fills the surface can be an issue that must be controlled, even with foams.)

If you look around the world of cored panels, you will see skins of aluminum (and other metals), wood, solid plastics, fiber-reinforced plastics (with 6 or 8 common fiber types and 4 or 5 common resin classes) and various (typically resin infused) paper products. Cores can be numerous types of foams, kraft paper honeycomb, aluminum honeycomb, aramid honeycombs, etc., all available in a wide range of material properties (including stiffness and strength in various directions, corrosion resistance water intrusion resistance, fire resistance, electrical resistance, etc).

The fundamental design principle of a cored panel is that of the I beam: under load, one skin is in tension, the other in compression, and the core is in shear. But in practice, the core will be subjected to high point loadings (compressive) that can destroy the structure if not correctly planned for. You need to understand exactly how the panel will function as a beam early in the design process. Given a particular beam loading, then an optimized panel will have a particular total thicknesses and ratio of core thickness to skin thickness, depending upon the properties of the materials used.

All that can be said at this point regarding your application is that the core material must have a compressive strength of greater than 100N/cm2 at very least. But it is a very rare sandwich panel that need only resist a compressive load normal to its surface. There is usually a reason that a sandwich panel is chosen over a simpler construction, such as its stiffness in bending. If you are using a sandwich to resist bending, then the first thing is to find out is the magnitude of the bending load. That will, of course, vary dramatically with the spacing of supports.

The Hexcel document will get you started at looking at the basic design issues. At its end, it provides a couple further references.