Lightweight structure having a honeycomb interior

1,070,927. Laminates. BRISTOL AEROPLANE PLASTICS Ltd. June 26, 1964 [June 28, 1963], No. 25838/63. Heading B5N. A laminated structural unit comprises outer skins 18 and 20 of sheet material and a cellular interlayer formed from a plurality of individual rectangular, hexagonal or other cell units 15, each cell unit comprising a corrugated wall of closed perimeter perpendicular to the sheets and secured thereto over an area which is several times greater than the cross-sectional area of the cell unit wall taken through an imaginary plane between the sheets. The cell unit may comprise a moulded or extruded outer member 2 comprising a wall provided with flat-crested corrugations 4 and an integral base 10 and an inner member 14 comprising a wall 13 and an integral base 10, fitting within the outer member and adhered thereto, the bases 10 and 19 being at opposite ends of the cell unit and forming the loading surfaces between the cell and outer skins. Alternatively the outer wall of the cell unit may be provided with alternating interfitting tongues and grooves which may constitute the corrugations in a cylindrical cell wall. The cell unit may comprise a hollow block of integral cells. In another construction it is formed as a single wall of closed perimeter either closed at both ends by a lid, with or without a depending flange, or provided at each end with flanges to provide the necessary bonding area. To form the laminate, as shown, a sheet 18 of felted glass fibres impregnated with epoxy resin is laid on a concrete support 16 and cell units 15 coated with epoxy resin assembled thereon with the crests 6 of neighbouring cells abutting. A top sheet 20 of felted glass fibre impregnated with epoxy resin is pressed thereon using a roller and the structure cured under heat or at room temperature whereby the sheets become bonded to each cell unit over the area of the surfaces 10 and 19. A second layer of cells and top sheet may be provided. The support 16 may be singly or doubly curved to permit curved structures to be made by using flexible sheets and tapered cell units or corrugated cell units with partially interfitting tongues and slots whereby the cells are connected at an angle to one another. For a structure of double curvature the sheet material is also stretchable. Alternatively preformed rigid curved outer sheets can be used. Tapered cells may be used in flat structures by inverting alternate cells. Suitable sheet materials are: fibrous material impregnated