A in ship construction, building, bridges, trains, car doors,

A sandwich  composite is fabricated by binding two thin stiff skins to a lightweight thick core. The core material is a low strength material, but due to high thickness of the sandwich composite yields with high bending stiffness with overall low density. balsa wood, syntactic foam Open cell and closed cell structured foam and composite honeycomb are mainly used core materials. Glass or carbon fiber reinforced laminates are widely used as skin materials. Sheet metal is also used as skin materials in some cases. They are commonly being used in ship construction, building, bridges, trains, car doors, panels etc. In construction new green sandwich structures are also being introduced where the core is usually made from the natural materials (wood) and the skin is made from earth (clay) instead of cement. Thus making it more environment friendly.                                                                              Generally, the sandwich composites are symmetric, the core configuration plays major role in variations of sandwich component construction The core of a sandwich structure can be any material, but in general they are classified into four different types; honeycomb core, foam or solid core, web core and corrugated or truss core. For the functioning of the sandwich structure as a whole the binding of core and face sheets is another important criterion.                       The basic concept of a sandwich structure is that the face sheets carry the bending loads while the core carries the shear loads. The face sheets are strong and stiff in tension and compression compared to the low density core material and the  primary purpose of core material is to keep the face sheets separated in order to maintain a high section modulus (a high “moment of inertia” or “second moment of the area”) .The core material has relatively low density (e.g., honeycomb or foam), so that it  results in high flexural strength and stiffness properties relative to the overall density of panel. Therefore, sandwich panels are efficient in carrying bending loads. Also, they provide increase in buckling resistance to shear panels and compression members. Sandwich construction results in lower lateral deformations, higher buckling resistance and higher natural frequencies than monocoque constructions. A sandwich composite operates in the same way with the traditional I-beam structure, which will be having two flanges and a web connecting the flanges. The connecting web makes it possible for the flanges to act together and resist shear stresses. Sandwich structure and an I-beam differ from each other that, in a sandwich composite the core and laminates are different materials and the core provides continuous support for the laminates rather than being concentrated in a narrow web. When the structure is subjected to bending, the laminates act together, resisting the external bending moment so that one laminate is loaded in compression and the other in tension. The core will resist transverse forces and , supports the laminates and stabilizes them against buckling and wrinkling at the same time.