Composite flange element

1. A composite flange element, the flange element comprising a portion of a gas turbine engine casing and an adjoining flange portion, the flange element having a ply layup defining the portion of the gas turbine engine casing and defining the adjoining flange portion, the ply layup comprising:

a plurality of first plies forming part of both the portion of the gas turbine engine casing and the flange portion;

a plurality of second plies forming part of the flange portion, one or more of the second plies forming part of the flange portion only; and

a plurality of third plies forming part of the portion of the gas turbine engine casing, one or more of the third plies forming part of the gas turbine engine casing only;

wherein the first, second and third plies are selected to provide desirable properties for the portions which they form part of, each of the first, second, and third plies having a different construction;

the flange element further comprising:

one or more load spreading features associated with the flange portion; and

one or more stress reduction features associated with the region where the portion of the gas turbine engine casing meets the flange portion, and wherein the second plies that form part of the flange portion only are next to the first plies and at least one of the second plies extends to the gas turbine casing and at least two of the first plies are adjacent to both of the at least one of the second plies and one of the second plies that form part of the flange portion only.

2. A composite flange element as claimed in claim 1 , wherein one or more of the second plies also form a portion of the gas turbine engine casing, to a lesser extent than the first plies.

3. A composite flange element as claimed in claim 1 , wherein one or more of the third plies also form part of the flange portion, to a lesser extent than the first plies.

4. A composite flange element as claimed in claim 1 , wherein the first plies are formed by weaving, braiding, interleaving, felting knitting or tatting.

5. A composite flange element as claimed in claim 1 , further comprising a layer of glass fibre material and/or a layer of a polymer outward of the composite plies.

6. A composite flange element as claimed in claim 5 , wherein the polymer is an aromatic polyimide or PTFE.

7. A composite flange element as claimed in claim 1 , wherein the second plies are formed by layering several layers of fabric, each layer of fabric having orthogonal fibres, wherein the flange portion is curved and the layers are placed in different orientations such that there are radially and circumferentially oriented fibres around the flange.

8. A composite flange element as claimed in claim 1 , wherein the first plies comprise helical fibres.

9. A composite flange element as claimed in claim 1 , wherein the third plies are a woven fabric.

10. A composite flange element as claimed in claim 9 , wherein the third plies are a 5 harness satin weave.

11. A composite flange element as claimed in claim 9 , wherein the third plies are a multiple ply non crimp fabric.

12. A composite flange element as claimed in claim 9 , wherein the woven fabric is one or more of: an angle interlock weave, a layer-to-layer weave or an orthogonal weave.

13. A composite flange element as claimed in claim 1 , wherein the third plies are formed by 2½ D braiding or interleaving.

14. A composite flange element as claimed in claim 1 , wherein the third plies are formed by filament winding.

15. A composite flange element as claimed in claim 1 , in which the load spreading feature comprises an annular washer.

16. A composite flange element as claimed in claim 1 , wherein the portion of the gas turbine engine casing and the adjoining flange portion are arranged in a non-parallel manner with respect to each other.

17. A composite flange element as claimed in claim 1 , wherein the portion of the gas turbine engine casing and the adjoining flange portion are arranged substantially perpendicular with respect to each other.

18. A composite flange element as claimed in claim 1 , wherein the one or more stress reduction features are discontinuous fibres.

19. A composite flange element as claimed in claim 1 , wherein one of the stress reduction features is arranged proximate to an inner corner formed at the region where the portion of the gas turbine engine casing meets the flange portion and another of the stress reduction features is arranged proximate to an outer corner formed at the region where the portion of the gas turbine engine casing meets the flange portion.

20. A composite flange element as claimed in claim 1 , wherein:

the second plies provide resistance to asymmetric loading;

the first plies provide torsional stiffness to the flange element; and

the third plies provide radial and/or axial stiffness.

21. A composite flange element as claimed in claim 1 , wherein

two or more first plies each form both (i) part of the portion of the gas turbine engine casing and (ii) part of the flange portion.

22. A composite flange element as claimed in claim 21 , wherein:

the ply layup bends between the flange portion and the portion of the gas turbine engine; and

one of the first plies is formed along a radially outer region of the bend and the other of the first plies is formed along a radially inner region of the bend.