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A composite structure fabricated by thermoplastic welding, and a method for producing such structures. First and second composite parts are provided, having first and second surfaces, respectively, that define an interface where the parts are to be joined. The parts include a thermoplastic matrix. A

A composite structure fabricated by thermoplastic welding, and a method for producing such structures. First and second composite parts are provided, having first and second surfaces, respectively, that define an interface where the parts are to be joined. The parts include a thermoplastic matrix. An insert is provided, which includes a film portion, which may include the same thermoplastic matrix. The insert is provided with an electric resistance heating element. The first and second parts are urged together using low fusion pressure while the insert is heated using the electric resistance heating element. After a selected period of time, the electrical supply to the resistance heating element is turned off. A high fusion pressure is then applied to urge the parts together. The weldment joint is allowed to cool. After cooling, excess material may be removed, to form a composite structure.

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1. A method for fabrication of a composite structure, comprising: (a) providing a first composite part having a first surface and a second composite part having a second surface, said first composite part and said second composite part having a common thermoplastic matrix component;(b) juxtaposing t

1. A method for fabrication of a composite structure, comprising: (a) providing a first composite part having a first surface and a second composite part having a second surface, said first composite part and said second composite part having a common thermoplastic matrix component;(b) juxtaposing the first surface and the second surface to define a weldment area therebetween, at which the first composite part and the second composite part are to be joined;(c) providing an insert, the insert comprising (1) a film portion having a thickness T of about zero point zero three zero (0.030) inches, said film portion comprising said common thermoplastic matrix component, and (2) a resistance heating element;(d) placing the insert between the first surface and the second surface;(e) applying a selected electric current for a first selected time to said resistance heating element, to preheat said insert to at least a glass transition temperature, and then applying a selected electric current in a pulsating on-off manner to said resistance heating element, to further heat said insert and said first surface and said second surface;(f) during at least a portion of said selected time, applying a low fusion pressure to the first composite part and the second composite part to urge said first surface toward said second surface, and wherein said thermoplastic matrix in said film portion bonds with a thermoplastic matrix in or adjacent said first surface and in or adjacent said second surface to form said composite structure;(g) terminating application of said electric current;(h) applying a high fusion pressure between the first composite part and the second composite part while allowing the composite structure to cool. 2. The method as set forth in claim 1, wherein applying a selected electric current in a pulsating on-off manner to said resistance heating element comprises a pulse-on cycle and a pulse-off cycle, wherein the time for said pulse-on cycle is longer than the time of said pulse-off cycle. 3. The method as set forth in claim 2, wherein applying a selected electric current in a pulsating on-off manner to said resistance heating element is conducted over a time of about two minutes. 4. The method as set forth in claim 3, wherein said pulse-off cycle time is about five seconds. 5. The method as set forth in claim 2, wherein said pulse-on cycle time is about fifteen seconds. 6. The method as set forth in claim 1, wherein said insert further comprises Z-pins. 7. The method as set forth in claim 6, wherein said Z-pins comprise carbon fiber. 8. The method as set forth in claim 1, wherein said low fusion pressure between the first composite part and the second composite part is about one pound per square inch. 9. The method as set forth in claim 1, wherein said high fusion pressure between the first composite part and the second composite part is about one hundred pounds per square inch. 10. The method as set forth in claim 1, wherein said first composite part comprises extra material adjacent said first surface, said extra material comprising material not needed for structural integrity of said finished composite structure. 11. The method as set forth in claim 1, wherein said second composite part comprises extra material adjacent said second surface, said extra material comprising material not needed for structural integrity of said finished composite structure. 12. The method as set forth in claim 1, wherein applying said high fusion pressure to urge the first composite part and the second composite part together results in emergence of residual material along a joint between the first surface and the second surface, and where the method further comprises removal of the residual material from the composite structure. 13. The method as set forth in claim 1, wherein the film portion is provided in a shape and size at least as large as said weldment area. 14. The method as set forth in claim 1, wherein the film portion is provided in a shape and size conforming to said weldment area. 15. The method as set forth in claim 1, wherein the film portion has a variation V in the thickness T of about two thousandths of an inch (0.002 inches), or less. 16. The method as set forth in claim 1, wherein the resistance heating element is wrapped around the film portion. 17. The method as set forth in claim 1, wherein the resistance heating element is embedded in the film portion. 18. The method as set forth in claim 1, wherein the resistance heating element comprises a wire. 19. The method as set forth in claim 1, wherein the first composite part comprises polyetheretherketone. 20. The method as set forth in claim 1, wherein the film portion comprises polyetheretherketone. 21. The method as set forth in claim 1, wherein method comprises application of a patch to a composite structure. 22. The method as set forth in claim 1, wherein said first surface is set out in said first part at an angle alpha (α), wherein the angle alpha (α) is not ninety degrees (90°) as compared to a longitudinal axis of the first part, and wherein said second surface is set out in said second part at an angle beta (β), wherein the angle beta (β) is not ninety degrees (90°) as compared to a longitudinal axis of the second part, thereby providing an angled joint between said first part and said second part. 23. A method for fabrication of a composite structure, comprising: (a) providing a first composite part having a first surface and a second composite part having a second surface, said first composite part and said second composite part having a common thermoplastic matrix component, said common thermoplastic matrix component comprising polyetheretherketone;(b) juxtaposing the first surface and the second surface to define a weldment area therebetween, at which the first composite part and the second composite part are to be joined;(c) providing an insert, the insert comprising (1) a film portion having a thickness T of about zero point zero three zero (0.030) inches, said film portion comprising polyetheretherketone, and (2) a resistance heating element;(d) placing the insert between the first surface and the second surface;(e) applying a selected electric current for a first selected time to said resistance heating element, to preheat said insert to at least a glass transition temperature, and then applying a selected electric current in a pulsating on-off manner to said resistance heating element, to further heat said insert and said first surface and said second surface;(f) during at least a portion of said selected time, applying a low fusion pressure to the first composite part and the second composite part to urge said first surface toward said second surface, and wherein said thermoplastic matrix in said film portion bonds with a thermoplastic matrix in or adjacent said first surface and in or adjacent said second surface to form said composite structure;(g) terminating application of said electric current;(h) applying a high fusion pressure between the first composite part and the second composite part while allowing the composite structure to cool. 24. The method as set forth in claim 23, wherein applying a selected electric current in a pulsating on-off manner to said resistance heating element comprises a pulse-on cycle and a pulse-off cycle, wherein the time for said pulse-on cycle is longer than the time of said pulse-off cycle. 25. The method as set forth in claim 24, wherein applying a selected electric current in a pulsating on-off manner to said resistance heating element is conducted over a time of about two minutes. 26. The method as set forth in claim 24, wherein said pulse-on cycle time is about fifteen seconds. 27. The method as set forth in claim 24, wherein said pulse-off cycle time is about five seconds. 28. The method as set forth in claim 23, wherein said low fusion pressure between the first composite part and the second composite part is about one pound per square inch. 29. The method as set forth in claim 23, wherein said high fusion pressure between the first composite part and the second composite part is about one hundred pounds per square inch. 30. The method as set forth in claim 23, wherein said first composite part comprises extra material adjacent said first surface, and said second composite part comprises extra material adjacent said second surface, said extra material comprising material not needed for structural integrity of said finished composite structure.