Structural element of high unidirectional rigidity

• US 6,355,337 B1
• Filed: 10/05/1999
• Issued: 03/12/2002
• Est. Priority Date: 10/05/1998
• Status: Expired due to Fees

• Current Assignee: Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
• Original Assignee: Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
• Inventors: Piening, Matthias, Sigle, Christof, Pabsch, Arno
• Primary Examiner(s): Weisbergen, Rich
• Application Number:
  US09/412,656
• Time in Patent Office: 889 Days
• Field of Search: 498/292.1, 428/223, 428/293.7
• US Class Current: 428/223
• CPC Class Codes: B29C 70/48 and impregnating the reinforcements in the closed mould, e.g. resin transfer moulding [RTM] , e.g. by vacuum
• CPC Class Codes: B64C 1/06 Frames; Stringers; Longerons ; Fuselage sections
• CPC Class Codes: B64C 1/12 Construction or attachment of skin panels
• CPC Class Codes: B64C 2001/0072 from composite materials
• CPC Class Codes: B64C 3/20 Integral or sandwich constructions
• CPC Class Codes: Y02T 50/40 Weight reduction
• CPC Class Codes: Y10T 428/249923 Including interlaminar mechanical fastener
• CPC Class Codes: Y10T 428/249924 Noninterengaged fiber-containing paper-free web or sheet which is not of specified porosity
• CPC Class Codes: Y10T 428/249929 Fibers are aligned substantially parallel

Abstract

In a structural element of high unidirectional rigidity, in which unidirectional fiber strands are completely embedded in sheaths and said sheaths are connected to a shell skin and wherein part of the shell skin is in the form of stringers, there is provided an inner division of the cross-section of the shell skin thereby providing the strength of the fibers and the stiffness of the fibers in a direction perpendicular to the skin plane for every direction of loading.

Claims

1. A structural element of high unidirectional rigidity, in which unidirectional fibre strands are completely embedded in sheaths and said sheaths are connected to a laminate shell skin and wherein part of the shell skin is in the form of stringers whereby the shell skin has a skin plane and comprises a skin thickness, wherein the cross-section of the shell skin is arranged to provide the strength of the fibers and the stiffness of the fibers in a direction perpendicular to the skin plane for every direction of loading, and in that one or more parting layers are provided in an upstanding skin fold of a stringer.

2. The structural element in accordance with claim 1, wherein the orientation of the fibers in the laminates of the shell skin is substantially ±

45°

with angular variations of ±

10°

.

3. The structural element according to claim 1, wherein for sections in the shell skin subject to a load, longitudinal force flows are guided around these sections.

4. The structural element according to claim 1, wherein the shell skin thickness is selected to be so great that the shape of the cross-section is adapted to be independently and continuously varied.

5. The structural element according to claim 1, wherein there are provided a supporting layer for accommodating longitudinal elongations and a supporting layer for accommodating shear deformations of up to predeterminable magnitudes.

6. The structural element in accordance with claim 5, wherein the longitudinal supporting layer and the shear supporting layer of the shell skin are connected together and a boundary layer is provided between the longitudinal supporting layer and the shear supporting layer for accommodating the forces arising from their combined deformation.

7. The structural element in accordance with claim 1, wherein the cross-section and the orientation of the fibers of the encased fibre strands are adaptable to the specific application of use and in dependence on the load.

8. The structural element in accordance with claim 1, wherein a fibre stiffener is arranged in the region of the fibre strands in the sheath.

9. The structural element in accordance with claim 1, wherein a fibre stiffener is provided in the folds of the shell skin or the stringers.

10. The structural element in accordance with claim 1, wherein a fibre stiffener is provided in the region of the shear resistant laminate of the shell skin.

11. The structural element in accordance with claim 10, wherein the fibre stiffener in the region of the shear resistant laminate is provided in the form of a sewn reinforcement.

12. The structural element in accordance with claim 1, wherein the fibre stiffener is aligned in the direction of the cross-sectional parameters caused by an external load (P).

13. The structural element in accordance with claim 1, wherein there is provided a unidirectionally aligned fibre strand whose orientations and/or preferred directions of the material properties are in conformity with the state of stress.

14. The structural element in accordance with claim 1, wherein an anisotropic material is used to form the fibre strand.

15. The structural element in accordance with claim 14, wherein the fibre strands consist of a fibre material.

16. The structural element in accordance with claim 1, wherein the dimensions of the fiber strands, the shear resistant shell skin, or both the fiber strands and the shear resistant shell, are independent of each other and are adaptable to the requirements appropriate to the application.

17. A method of producing dimensioned amounts of fibre stiffness perpendicular to the skin plane of the shell skin in the case of large structural elements in accordance with claim 1, wherein a differential pressure resin transfer molding injection process is used to produce uniaxial stresses in layers formed by the unidirectional fiber strands and in which the stresses are in conformity with the directional properties of the fibers.

18. The method in accordance with claim 17, wherein a dry, semi-finished layered product is positioned and fixed in a molding cavity of the autoclave by stitching, and that the dry, semi-finished layered product is moistened with resin at a controlled flow speed.

19. The structural element of claim 1, wherein the partition is provided adjacent the upstanding skin fold.

20. The structural element of claim 1, wherein parting layer is provided within the shear resistant sheath of a fibre strand.

21. The structural element of claim 1, wherein the orientation of the fibers in the laminates of the shell skin is substantially 0°

to 25°

with variations of ±

10°

.

22. A structural element of high unidirectional rigidity, in which unidirectional fibre strands are completely embedded in sheaths and said sheaths are connected to a laminate shell skin and wherein part of the shell skin is in the form of stringers whereby the shell skin has a skin plane and comprises a skin thickness, wherein the cross-section of the shell skin is arranged to provide the strength of the fibers and the stiffness of the fibers in a direction perpendicular to the skin plane for every direction of loading, and in that one or more joints are provided in the upstanding skin fold of a stringer.