The task of the core
In lightweight sandwich constructions the core is usually relatively thick and has a much lower density compared to the skins. The primary mechanical requirement for the core layer is to prevent the movement of the skins relative to each other (in-plane and out-of-plane). Sufficient out-of-plane compression properties of the sandwich core are required to support the skins to maintain their distance from the neutral axis, to prevent them from buckling and to restrict their deformations due to local out-of-plane loads. Furthermore, sufficient out-of-plane shear properties of the core are demanded to restrict in-plane displacement of the skins relative to each other due to bending moments and transverse loads. The core layer can furthermore have additional functions e.g. thermal and acoustic isolation or energy absorption during impact.
The task of the skins
The skin layers in sandwich constructions carry the in-plane tensile/compression stresses and in-plane shear stresses. They are usually relatively thin and have a high stiffness and strength. In addition to high mechanical in-plane properties per weight the skin material usually has to fulfill also other requirements like low costs, high surface quality and good impact performance.