Composite stiffeners for aerospace vehicles

1. An aerospace vehicle comprising a plurality of composite stiffeners, each stiffener of the plurality having a stack of plies of reinforcing fibers; at least some of the plies in the stack having reinforcing fibers oriented at ±α with respect to an axis of primary loading, where α is between 2 and 12 degrees; at least some of the plies having reinforcing fibers oriented at ±β with respect to the axis of primary loading, where β is between 50 and 85 degrees.

2. The vehicle of claim 1 , further comprising a plurality of skin panels stiffened by the stiffeners, wherein the stiffeners include bases fastened to the skin panels by fasteners, whereby the fibers oriented at ±α suppress or delay ply splitting in the bases.

3. The vehicle of claim 1 , wherein α is between 2 and 8 degrees.

4. The vehicle of claim 1 , wherein α is between 3 and 5 degrees.

5. The vehicle of claim 1 , wherein the reinforcing fibers oriented at ±α constitute at least 50% of the total number of fibers in each stiffener.

6. The vehicle of claim 1 , wherein the stiffeners include webs, and wherein the fibers oriented at ±β are biased towards outer surfaces of the webs to increase stiffness in buckling and transverse bending.

7. The vehicle of claim 1 , wherein the skin panels and the stiffeners include carbon fibers in a polymer matrix.

8. The vehicle of claim 1 , wherein the vehicle includes a fuselage, wing assemblies and empennage; and wherein the plurality of stiffeners are included in at least one of the fuselage, the wing assemblies and the empennage.

9. The vehicle of claim 1 , wherein all fibers in the stack consist of the fibers oriented at ±α and ±β; and wherein 20-30% of the total fibers are oriented at ±β to reach bearing strength levels similar to traditional 0/+45/−45/90 degree hard laminates.

10. An article comprising an aerospace vehicle stiffener, the stiffener including a base and a web, at least one of the base and web including a stack of plies of reinforcing fibers, at least 50% of the reinforcing fibers oriented at ±α with respect to an axis of primary loading, where α is between 2 and 12 degrees.

11. The article of claim 10 , wherein the base has fastener apertures, whereby the reinforcing fibers in the base are oriented at ±α degrees to suppress or delay splitting caused by the fastener apertures.

12. The article of claim 10 , wherein α is between 2 and 8 degrees.

13. The article of claim 10 , wherein α is between 3 and 5 degrees.

14. The article of claim 10 , wherein the reinforcing fibers oriented at ±α constitute 100% of the total number of fibers in the stack.

15. The article of claim 10 , wherein the stack further includes plies of reinforcing fibers oriented at ±β degrees with respect to the axis of primary loading, where β is between 50 and 85 degrees.

16. The article of claim 15 , wherein the fibers oriented at ±β are biased towards outer surfaces of the webs to increase stiffness in buckling and transverse bending.

17. The article of claim 10 , wherein the reinforcing fibers in the stack include carbon fibers embedded in a polymer matrix.

18. An article comprising an aerospace vehicle stiffener, the stiffener including a base and a web, the web including plies of reinforcing fibers for providing strength in tension and compression along an axis of primary loading, the web also including plies of reinforcing fibers oriented at ±β degrees with respect to the axis of primary loading, where β is between 50 and 85 degrees, wherein the fibers oriented at ±β degrees are biased towards outer surfaces of the web to increase stiffness in buckling and transverse loading.

19. The article of claim 18 , wherein the reinforcing fibers for providing strength in tension and compression are oriented at ±α with respect to the axis of primary loading, where α is between 2 and 12 degrees.

20. The article of claim 18 , wherein the reinforcing fibers are carbon fibers embedded in a polymer matrix.