Sandwich construction is a composite material structure combining low weight, high strength and good dynamic properties. Typically a sandwich composite consists of three main parts: two thin, stiff and strong facing layers separated by a thick, light and weaker inner core. The faces are adhesively bonded to the core to obtain a load transfer between the components. This way the properties of each separate component is utilized to the structural advantage of the whole assembly leading to a very high stiffness-to-weight and high bending strength-to-weight ratio. As a result sandwich components achieve the same structural performance as conventional materials with less weight.

Figure 1: Honeycomb sandwich composite

Source: http://www.eng.uab.edu/compositesLab/F_sandwch3.htm (University of Alabama)

Sandwich constructions can be realised with a great variety of materials both for facing layers and inner core.

The facing layers are typically realised by aluminium plates, high presure laminates, glass fibre reinforced plastics etc.

For the core material quite different realisations exist. The two most common ones are honeycombs (cf. Figure 1) and foams. Honeycombs have been used successfully for decades in airplanes. They are made from aluminium and more recently from glass or aramid fibre reinforced plastics. Typical foams used for sandwich cores are: chlorofluorocarbons (CFCs), halonfluorocarbons (HFCs) and CO₂-foamed materials (the latter being the present lane of development).

Manufacurers

• M/s. Hexcel Corporation Inc., USA (leading international composites manufacturer for railways),
• Kansas Structural Composites Inc., USA,
• Nida Core, Finland
• Fiberline Composites A/S, Denmark
• Concargo Composites, UK