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What is a sandwich structure?


Sandwich structures can be classed as composite materials in that they consist of two or more individual components of differing properties which when combined result in a high performance material. In contrast to monolithic composites - which consist of an intimate mixture of fibres (glass, kevlar, carbon, metal, etc) supported within a continuous matrix (e.g. thermoplastic or thermoset resin) - sandwich structures have a discrete structure in which a core material is bonded to, and faced with, a skin material. The skin material usually has a high stiffness, whereas the core typically has high compressive and shear strength. When these are bonded together, this combination gives the sandwich structure a high flexural modulus.

Skin material can vary but common forms include:

  • FRP (fibre reinforced polymer - thermoplastic and thermoset)
  • Polymer
  • Wood
  • Aramid sheet
  • Metals (aluminium, titanium, steel, etc)
  • Ceramic
  • Stone

The core can exist in a number of structures and materials:

  • Expanded/extruded foam (polymer - polyurethane, epoxy; metal - aluminium)
  • Honeycomb structure (metal - aluminium, steel; Nomex - aramid fibre dipped in resin (epoxy, phenolic or polyamide) to form a paper-like material)
  • Solid (wood - balsa; polymer - epoxy)

The skins are bonded to the core with film, liquid or paste adhesives and normally cured using heat and pressure, although some adhesives can cure at room temperature. It is important to note that the chosen adhesive needs to have the appropriate mechanical and thermal properties to achieve compatibility between the skin and core materials, especially with respect to thermal expansion differences.

Sandwich panels are used in preference to conventional composites where the characteristics of low weight and high resistance to bending are required.

Further information

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