Optimized rib-stiffened composite structure

1. A rib-stiffened composite structure, comprising:

a composite face sheet having a continuous reinforcing fiber in a polymer matrix;

a polymer core in a grid pattern directly disposed on the composite face sheet, the grid pattern comprising a first series of paths crossing over a second series of paths wherein material voids are formed in the spaces between the first and second series of paths; and

a composite rib-cap directly disposed upon an upper surface of the polymer core, the composite rib-cap comprising a continuous reinforcing fiber in a polymer matrix, wherein fibers of the continuous reinforcing fiber in the polymer matrix of the composite rib-cap are oriented in a direction along the first and second series of paths of the grid pattern of the polymer core.

2. The rib-stiffened composite structure of claim 1 , wherein the polymer used in the polymer matrix of the composite face sheet and the composite rib-cap is the same polymer used in the polymer core.

3. The rib-stiffened composite structure of claim 1 , wherein a side wall of the polymer core is not covered by either the composite face sheet or the composite rib-cap.

4. The rib-stiffened composite structure of claim 1 , wherein the core material is a polymer foam, a syntactic foam, a closed cell foam, an unfilled polymer, or a filled polymer comprising a filler, wherein the filler is a chopped fiber, a nanotube or graphene.

5. The rib-stiffened composite structure of claim 1 , wherein the continuous reinforcing fiber of the composite face sheet and/or the continuous reinforcing fiber of the composite rib-cap comprises carbon fiber and/or glass fiber.

6. The rib-stiffened composite structure of claim 1 , wherein the composite face sheet is planar and/or the composite rib-cap is planar.

7. The rib-stiffened composite structure of claim 1 , wherein the composite face sheet comprises at least one curve.

8. The rib-stiffened composite structure of claim 7 , wherein the composite rib-cap comprises a second curve, wherein a shape of the second curve is the same as a shape of the at least one curve of the composite face sheet.

9. The rib-stiffened composite structure of claim 1 , wherein the polymer core does not comprise a plurality of material voids disposed within the first and the second series of paths.

10. The rib-stiffened composite structure of claim 1 , wherein the composite face sheet does not have material voids matching the material voids formed in the grid pattern of the polymer core.

11. The rib-stiffened composite structure of claim 10 , wherein the composite rib-cap does have material voids matching the material voids formed in the grid pattern of the polymer core.

12. The rib-stiffened composite structure of claim 1 , where the rib-stiffened composite structure is made by a method comprising the following steps:

forming the composite face sheet;

forming the composite rib cap;

wherein fibers of the continuous reinforcing fiber of the polymer matrix of the composite rib cap are oriented in a direction along the first and second series of paths;

providing a first mold securing the composite rib cap a distance from the composite face sheet, the first mold extending through the material voids of the composite rib cap and engaging with the composite face sheet forming a hollow space between the composite face sheet and composite rib cap;

injecting a core material into the hollow space delimited by the composite face sheet, the composite rib cap and the first mold; and

removing the first mold from the composite face sheet, composite rib cap and core material thereby resulting in the rib-stiffened composite structure.

13. The rib-stiffened composite structure of claim 12 , wherein the injection of the core material into the hollow space delimited by the composite face sheet, the composite rib cap and the first mold comprises injection molding, compression molding, transfer molding or resin transfer molding.

14. The rib-stiffened composite structure of claim 1 , where the rib- stiffened composite structure is made by a method comprising the following steps:

forming the composite face sheet;

depositing the extruded polymer core in the grid pattern on the composite face sheet, wherein the extruded polymer core is deposited using a plurality of layers by a material extrusion process; and

depositing the composite rib-cap upon an upper surface of the extruded polymer core, wherein fibers of the continuous reinforcing fiber of the polymer matrix of the composite rib cap are oriented in a direction along the first and second series of paths of the grid pattern of the extruded polymer core.

15. The rib-stiffened composite structure of claim 14 , wherein the first series of paths crossing over the second series of paths define junctions, where each junction has alternating continuous prepreg layers of the first series and second series of paths forming a junction of similar thickness to the rest of the first and second series of paths.