ABSTRACT
The inside (core) of a sandwich includes almost anything and can vary in thickness, density, and solidity. Occasionally, one can encounter a doubledecker sandwich as well, as in many box materials used for shipping. The core of a sandwich structure can be almost any material or architecture, but in general, cores fall into four types: foam or solid core, honeycomb core, web core, and a corrugated or truss core. Developments in new cores continue to be of primary interest, such as new cores developed by Christensen and Czaplicki. Foam or solid cores are relatively inexpensive and can consist of balsa wood and an almost infinite selection of foam/plastic materials with a wide variety of densities and shear moduli. In the web core and truss core constructions, the space in the core could be used for liquid storage or as a heat exchanger.
