Casing having a non-axisymmetric composite wall

1. A wall of a gas turbine engine casing, comprising:

a plurality of composite plies arranged in a ply layup,

wherein the wall is annular and is circumferentially segmented into a plurality of regions, the plurality of regions including at least a first region and a second region,

wherein the ply layup has a thickness along a radial direction,

wherein the ply layup in the first region extends along the radial direction over the thickness and is formed from only a first plurality of plies, the first plurality of plies comprising first fibers oriented in a first direction and second fibers oriented in a second direction,

wherein the ply layup in the second region is formed from the first plurality of plies and a second plurality of plies, the second plurality of plies comprising third fibers oriented in a third direction and fourth fibers oriented in a fourth direction, each of the third direction and the fourth direction being different from each of the first direction and the second direction, and

wherein the ply layup in the first region is different from the ply layup in the second region such that the ply layup is non-axisymmetric.

2. The wall of claim 1 , wherein the first direction is orthogonal to the second direction.

3. The wall of claim 1 , wherein the third direction is orthogonal to the fourth direction.

4. The wall of claim 1 ,

wherein the ply layup in the second region is radially unsymmetrical about a radial center of the thickness.

5. The wall of claim 1 , wherein the plurality of regions includes two first regions and two second regions, where the two first regions includes the first region and the two second regions includes the second region.

6. The wall of claim 5 , wherein each of the two first regions and the two second regions comprise an equal angular portion of the wall.

7. The wall of claim 1 , wherein the wall is a fan casing back sheet.

8. The wall of claim 1 , wherein the ply layup in the first region is formed from a first plurality of plies,

wherein the first plurality of plies comprises first fibers oriented in a 0° orientation with respect to a reference axis and second fibers oriented in a 90° orientation with respect to the reference axis.

9. The wall of claim 8 , wherein the ply layup in the second region is formed from the first plurality of plies and a second plurality of plies,

wherein the second plurality of plies comprises third fibers oriented in a +45° orientation with respect to the reference axis and fourth fibers oriented in a −45° orientation with respect to the reference axis.

10. The wall of claim 9 , wherein the second plurality of plies are laid up between layers of the first plurality of plies.

11. The wall of claim 1 , wherein the plurality of regions includes two first regions and two second regions, where the two first regions includes the first region and the two second regions includes the second region, and wherein each first region comprises a different angular portion of the wall than each second region such that each first region is unequal in size to each second region.

12. The wall of claim 1 , wherein the ply layup in the first region is formed from a first plurality of plies,

wherein the ply layup in the second region is formed from the first plurality of plies and a second plurality of plies, and

wherein non-staggered butt splices are formed between the first plurality of plies and the second plurality of plies in a transition zone between the first region and the second region.

13. The wall of claim 1 , wherein staggered butt splices are formed between the first plurality of plies and the second plurality of plies in a transition zone between the first region and the second region.

14. The wall of claim 1 , wherein overlap splices are formed between the first plurality of plies and the second plurality of plies in a transition zone between the first region and the second region.

15. The wall of claim 1 , wherein the first region has a first thickness along a radial direction and the second region has a second thickness along the radial direction, and

wherein the second thickness is equal to or greater than the first thickness.

16. A fan case, comprising:

an annular inner shell;

a filler layer;

an annular back sheet; and

an annular outer layer,

wherein the annular back sheet is the wall of claim 1 .

17. A method for forming a wall of a fan case, the method comprising:

laying up a first plurality of first plies to form a first region of the fan case; and

laying up a second plurality of first plies and a plurality of second plies to form a second region of the fan case, the second region adjoining the first region,

wherein the first plurality of first plies, the second plurality of first plies, and the plurality of second plies form a ply layup, the ply layup having a thickness along a radial direction,

wherein the ply layup in the first region extends along the radial direction over the thickness and is formed from only a first plurality of plies, the first plurality of plies comprising first fibers oriented in a first direction and second fibers oriented in a second direction,

wherein the ply layup in the second region is formed from the first plurality of plies and a second plurality of plies, the second plurality of plies comprising third fibers oriented in a third direction and fourth fibers oriented in a fourth direction, each of the third direction and the fourth direction being different from each of the first direction and the second direction, and

wherein the second plies are oriented differently than the first plies such that the ply layup is non-axisymmetric.

18. The method of claim 17 , wherein the ply layup in the second region is radially unsymmetrical along the thickness.

19. The method of claim 17 , wherein overlap splices are formed between the first plurality of first plies and the plurality of second plies in a transition zone between the first region and the second region.