Composite toughening using three dimensional printed thermoplastic pins

1. A composite article, comprising:

fiber tows, each comprising a bundle of fibers;

pins, passing through spaces that are bounded by the fiber tows; and

a resin that surrounds the fiber tows and the pins;

wherein:

the fiber rows are located in plies;

at least two of adjacent ones of the fiber tows are in different ones of the plies;

each of the spaces extends through the plies and is bounded by the adjacent ones of the fiber tows;

each of the pins extends into only one of the spaces;

at least one of the pins extends through only some of the plies;

each of the pins is bonded to a surface of at least one of the fiber tows; and

the pins form physical barriers that reduce propagation of cracks in the composite article.

2. The composite article of claim 1 , wherein:

each of the pins has a length from 1 mm to 3 mm.

3. The composite article of claim 1 , wherein the pins have different mechanical properties from one another.

4. The composite article of claim 1 , wherein each of the pins fills at least 90% of a volume of each of the spaces, bounded by fiber tows.

5. The composite article-of claim 1 , wherein:

at least one of the fiber tows comprises an undistorted fiber tow that is not distorted by insertion of the pins into the plies; and

at least one of the pins is bonded to, and is in contact with, the surface of the undistorted fiber tow.

6. The composite article of claim 1 , wherein:

at least one of the fiber tows comprises an unfrayed fiber, and

at least one of the pins is bonded to the surface of the unfrayed fiber.

7. A composite article, comprising:

fiber tows, each comprising a bundle of fibers;

pins, passing through spaces that are bounded by the fiber tows; and

a resin that surrounds the fiber tows and the pins;

wherein:

at least one of the pins has a corrugated surface along its length L;

each of the pins is bonded to a surface of at least one of the fiber tows; and

the pins form physical barriers that reduce propagation of the cracks in the composite article.

8. The composite article of claim 1 , wherein at least one of the pins has a cross-section, varying along its length so that the at least one of the pins is wider between the plies than in the plies.

9. The composite article of claim 1 , wherein the pins bond to the resin and the fiber tows.

10. The composite article of claim 1 , further comprising a base layer and a plurality of anchors on the base layer, wherein each of the pins is drawn between the spaces from a different one of the anchors.

11. The composite article of claim 1 , wherein at least one of the pins extends through all of the plies.

12. The composite article of claim 1 , wherein:

the composite article further comprises a layer of material, deposited on either side of each of the plies;

the pins couple to the layer of material on either side of each of the plies; and

the plies comprise a fabric.

13. An integrated aircraft structure, comprising:

a skin, comprising the composite article of claim 1 ;

a stiffener; and

an interface between the skin and the stiffener,

wherein the composite article of the skin is located adjacent the interface.

14. A method of manufacturing a composite article, the method comprising steps of:

(a) depositing material in spaces, bounded by fibers tows, each comprising a bundle of fibers, so as to form pins, each passing through a different one of the spaces, wherein the step (a) comprises steps of:

(i) depositing the material from an outlet onto a base layer and into one of the spaces while moving the outlet and the base layer relative to one another, first in an x-y plane and then in a z-direction, so as to form an anchor on the base layer;

(ii) moving the outlet and the base layer relative to one another with no feed of the material from the outlet, so that a portion of the anchor is drawn to create each of the pins;

(iii) releasing each of the pins from the outlet and moving the outlet and the base layer relative to one another so that the outlet is positioned above a next one of the spaces; and

(iv) repeating the steps (i)-(iii) so as to create the pins.

15. The method of claim 14 , wherein the fiber tows are located in plies, the method further comprising,

repeating the step (a) so that the material is deposited in the spaces after each one of the plies is deposited, wherein at least some of the material deposited in the spaces in a next one of the plies is aligned with and connects to the material deposited in the spaces in a previous one of the plies so as to form the pins, extending through the plies.

16. The method of claim 14 , further comprising:

depositing a stack of plies, comprising the fiber tows; and

performing the step (a) so as to form the pins, extending through at least some of the plies.

17. The method of claim 14 , further comprising heating the pins and the fiber tows in a post-processing step after the pins have been formed, so as to increase bonding of the pins to the fiber tows.

18. The method of claim 14 , further comprising depositing the material using an additive manufacturing technique comprising three dimensional printing, wherein the pins bond to the fiber tows during the deposition of the material using the additive manufacturing technique.

19. The method of claim 14 , wherein:

the fiber tows are located in plies;

each of the fiber tows has a diameter of at least 2 mm and comprises at least 1000 fibers, each comprising at least one material, chosen from thermoplastic, fiberglass, Kevlar, and carbon;

each of the spaces has a diameter of at least 2 mm;

each of the plies has a thickness from 2 to 10 mm;

each of the pins has a thickness from 2 to 5 mm and comprises at least one thermoplastic, selected from polyamide, polyetherketone, polyetheretherketone, polyetherketoneketone, polyimide, polyetherimide, and polyphenylsulphone, and hybrids thereof;

each of the pins has a length from 1 to 3 mm; and

the composite article has a total thickness from 10 mm to 1 meter.

20. The method of claim 14 , wherein at least one of the pins has a corrugated surface along its length L.

21. An integrated aircraft structure, comprising-:

a skin;

a stiffener, comprising the composite article of claim 1 ; and

an interface between the skin and the stiffener,

wherein the composite article of the stiffener is located adjacent the interface.

22. An integrated aircraft structure, comprising:

a skin;

a stiffener; and

an interface between the skin and the stiffener,

wherein the interface comprises the composite article of claim 1 .