Aircraft floor panels using edge coated honeycomb

#1. Field of the Invention

#The present invention relates generally to sandwich panels and other related structural composite materials. Sandwich panels are typically made up of face sheets (also referred to as “skins”) that are adhesively bonded to opposite sides of a core material, such as honeycomb, to form the sandwich panel. In particular, the present invention relates to treating honeycomb in order to improve the bond between the honeycomb and face sheets. The invention is particularly applicable to aircraft floor panels, which are composed of composite honeycomb and composite face sheets.

#2. Description of Related Art

#FIG. 1 is a perspective view of a preferred exemplary honeycomb core and two composite face sheets prior to bonding of the honeycomb to the face sheets using a nylon adhesive (polyamide or modified polyamide) in accordance with the present invention.

#FIG. 2 is a perspective view of a preferred exemplary sandwich panel where the components shown in FIG. 1 have been bonded together and cured to form the final honeycomb sandwich panel.

#FIG. 3 is a partially diagrammatic representation of an exemplary method in accordance with the present invention showing a single edge-coated honeycomb wall being bonded to a face sheet.

#It is preferred that the nylon (polyamide) adhesives in accordance with the present invention be used to improve the bonding of composite face sheets (particularly self-adhesive prepregs) to honeycomb cores to form light-weight structural panels for use in aerospace applications where light weight and structural strength are especially important design criteria. However, those of ordinary skill will recognize that the present invention is not limited to aerospace applications, but may also be used in any situation where there is a need for honeycomb sandwich panels that have face sheets, which are made from composite materials.

#The three basic components of a preferred exemplary honeycomb sandwich panel for use in aerospace applications are shown in FIG. 1 prior to formation of the panel. The components include a honeycomb core 12 that has walls 11 which form a plurality of honeycomb cells 13. The walls have edges that form the faces or edges of the honeycomb as shown at 14 and 16. The other two components are prepreg face sheets 17 and 19. The face sheets 17 and 19 include interior surfaces 21 and 23, respectively, for bonding to the honeycomb edges. The face sheets 17 and 19 also include exterior surfaces 25 and 27, respectively. In accordance with the present invention, the edges 14 and 16 of honeycomb 12 are coated with an adhesive (not visible in FIG. 1) that includes polyamide as an essential ingredient to form an edge-coated honeycomb. The use of a polyamide adhesive (polyamide coating) improves the bonding of face sheets 17 and 19 to the honeycomb 12, while adding very little to the weight of the resultant panel. The uncured prepreg face sheets or skins 17 and 19 are applied to the edge-coated honeycomb 12 and then cured to form face sheets 18 and 20 of the finished panel 10 as shown in FIG. 2.

#FIG. 3 is a partially diagrammatic representation showing the method for bonding the honeycomb to one of the face sheets 19 in accordance with the present invention. For simplicity, FIG. 3 shows the bonding of a single wall 11 with it being understood that the entire edge 16 of the honeycomb is coated with the polyamide-based adhesive (coating). As shown in FIG. 3, the lower edge of honeycomb wall 11 is coated with a polyamide adhesive (polyamide coating) 15 prior to bonding to the lower uncured prepreg face sheet 19. As represented by arrow 30, the edge-coated honeycomb is located against the face sheet 19 such that the polyamide adhesive (polyamide coating) flows partially onto the prepreg 19 to form fillets 28 and 29. Then, as represented by arrow 40, the prepreg is cured to form the final sandwich panel 10 that includes the cured face sheet 20.