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
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