Thick sandwiches designed for infusion

Tom Shelley investigates a new type of sandwich material that could replace aluminium honeycomb in defence and aerospace applications

A sandwich material has been developed that combines a polypropylene honeycomb, polypropylene film on both faces, and a non-woven polyester fabric.
Available in standard thicknesses of from 5 to 90mm, it is seen as being particularly suitable for making floors for niche vehicles, wind turbine nacelles and superstructures for leisure craft.

It is made by the French company, Nidaplast, and has been designated 8RI. The panel can, if necessary, be perforated, in which case it is designated 8RI P, this is available in thicknesses from 5 to 50mm. Panel sizes are 1200 x 2500mm or 2134 x 1219mm.

The non-woven polyester is intended to facilitate the infusion of polyester and other resins, or to facilitate adhesive bonding. Infusion is normally with resins with a viscosity of less than 300 centipoises, and under a pressure of between 0.85 and 0.95bar. The membrane is there to prevent penetration into and therefore any loss of resin through the honeycomb.

Because of the air gap, thermal insulation properties are good, with an R value, which measures thermal resistance, of 0.3m2.°C/W for 20mm thick or 0.6 m2.°C/W for 90mm thick.

Standard quality material is flammable, but it has very good resistance of most acids, bases and salts. Shear modulus for 20mm thick material is 5MPa for Nidaplast 8 or 9MPa for Nidaplast 9. Shear strengths are 0.4 MPa and 0.6MPa respectively.

Tom Shelley

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