Cellular Structures model parameters

Cellular Structures are hybrids of a solid and a gas. The Cellular Structures model predicts the performance of three main types of cellular solid: foams (open-cell and closed-cell), honeycombs (extruded and expanded), and triangulated lattices. These can either be used on their own or integrated into sandwich panels as a core material, where they are frequently used to reduce weight or increase thermal insulation characteristics.

Foams are made by expanding polymers, metals, ceramics or glasses with a foaming agent - a generic term for introducing a gas. An idealized unit cell for an open-celled low-density foam is shown below. It has solid cell edges surrounding a void containing a gas or fluid. In closed-cell foams, continuous cell walls form between the cell edges. When a load is applied to a foam, the cell walls bend.

When a load is applied to a triangulated lattice structure, the cell edges stretch instead of bend, resulting in a stiffer and stronger structure than equivalent foams of the same density. A triangulated lattice structure and its unit cell are shown below. Lattice structures are generally more difficult to manufacture than foams. On a large scale (strut length = meters) they are manufactured by assembling individual struts. On a smaller scale, they can be produced by casting or additive manufacturing.

Honeycombs are anisotropic and therefore the properties are dependent on the direction, generally either through-thickness or in-plane. For expanded honeycombs (where a third of the cell faces have double thickness), there is an additional degree of anisotropy within the plane. The through-thickness properties are generally of more interest as they are the important ones when honeycombs are used as core material for a sandwich panel. The in-plane mechanical properties tend to be bending-dominated while the through-thickness properties are stretch-dominated.