Foam Stiffened Structure and Method of Making the Same
A structure includes a skin and a foam member. The foam member has a molded contour, the mold contour being configured to provide tooled surface for the skin. When the skin is a composite skin, the foam member provides support for the skin so that the skin can be cured under heat and pressure. A method of making the foam member for a foam stiffened structure includes creating a mold having an interior cavity which resembles a desired shape the foam member. A subsequent step involves introducing a foam mixture into the mold. Next, the foam mixture is allowed to polymerize so as to expand and distribute within the cavity of the mold. The method further includes selectively controlling a density of the foam member in the mold. The foam member is at least partially cured. The foam member is assembled with a skin to produce the foam stiffened structure.
1. Field of the Invention
The system of the present application relates to a structure for a vehicle, such as a rotorcraft. In particular, the system of the present application relates to a foam stiffened structure and method of making the foam stiffened structure. The system of the present application can be applied to many different structures, both static and mobile. Furthermore, the system of the present application is described herein with regard to a rotorcraft structure for exemplary purposes.
2. Description of Related Art
One typical aerospace structural assembly includes an exterior aerodynamic skin with a plurality of internal structural members. Referring to
Although the developments in aerospace structures have produced significant improvements, considerable shortcomings remain.
The novel features believed characteristic of the system of the present application are set forth in the appended claims. However, the system itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein:
While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the method to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTIllustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.
Referring to
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Further, elevator 301 may include an inboard rib 303, an outboard rib 305, and a trailing edge member 309. Inboard rib 303, outboard rib 305, and trailing edge member 309 are exemplary of members that may be formed integrally with foam member 311, or assembled to foam member 311 in an assembly operation subsequent to the formation of foam member 311. Inboard rib 303, outboard rib 305, and trailing edge member 311 can be formed from any conventional manufacturing operation, such as machining, molding, casting, injection molding, compression molding, to name a few. Further, an adhesive can be used to promote a bond between any of the skin 307, foam member 311, inboard rib 303, outboard rib 305, and trailing edge member 309.
Foam member 311 provides structural stiffness to elevator 301. Skin 307 preferably comprise a plurality of reinforcing fibers disposed in a polymeric matrix. As discussed further herein, skin 307 is preferably placed onto foam member 311 as a plurality of uncured composite plies, and then later cured to form a rigid composite laminate. It should be appreciated that skin 307 can be formed from a variety of fiber and resin systems. It should also be appreciated that the specific composite material, or sheet metal, is implementation specific. For example, carbon fiber may be desirable in one application, while fiberglass fiber may be desirable in another application.
The molded foam member 311 is preferably formed with a pourable and expandable structural foam in a mold, as discussed further herein. The molded foam member 311 is configured to provide the structural integrity to elevator 301 in a wide variety of geometries and contours. Curing of skin 307 may require pressure, such as autoclave curing pressure, for proper curing. As such, foam member 311 is configured to provide structural resistance to the pressure so as to preserve the desired surface geometry of skin 307. Foam member 311 is configured to be isotropic, thus the isotropic properties of foam member 311 allow it to retain structural integrity in a wide variety of geometries and contours.
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A process 605 of method 601 includes fabricating foam member 311. Referring now also to
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A step 615 of process 605 includes creating a foam mixture 807. Referring now also to
The total weight amount of mixture 807 is at least partially dependent upon the desired density and the volume of foam member 311. For example, because density is the relationship of mass per unit volume, the desired density of foam member 311 at least partially dictates the weight amount of mixture 807. However, a portion of the mixture 807 may escape from within cavity 707, which may affect the final density determination of foam member 311.
A step 617 of process 605 includes pouring foam mixture 807 into cavity 707. Once the mixing in step 615 is complete, it is preferred that mixture 807 is poured into cavity 707 mold 701 as quickly as possible.
A step 619 includes controlling expansion of foam mixture 807 in cavity 707. Referring to
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In one embodiment of elevator 301, a structural bond exists between skin 307 and foam member 311 such that shearing loads are transferred between skin 307 and foam member 311 through the structural bond. In such an embodiment, the bond can be formed from the resin in the composite skin. The structural bonding can also be created or supplemented with an adhesive layer located between foam member 311 and skin 307. In an alternative embodiment, a release material may be applied to prevent a structural bond between skin 307 and foam member 311.
In the preferred embodiment, step 607 includes applying uncured composite material onto foam member 311. It should be appreciated that the composite manufacturing process may take on a wide variety of processes because skin 307 may be formed from a wide variety of composite fiber/resin systems, or from metallic materials. Referring now also to
A step 611 of method 601 includes final assembly elevator 301. If inboard rib 303, outboard rib 305, and trailing edge member 309 are not already integrated with foam member 311, then step 611 includes assembling these parts with foam member 311 and skin 307. Step 611 can include assembling any other parts and performing final finish to elevator 301.
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The system of the present application provides significant advantages, including: (1) providing a stiffness producing foam member in a composite structure that can be molded in a variety of geometries and contours; (2) providing a stiffness producing foam member in a composite structure that can withstand autoclave curing pressure; (3) providing a stiffness producing foam member in a composite structure, the density of the foam member being selectively tailored; (4) providing a stiffness producing foam member in a composite structure that provides tooled support for a skin, such that the foam member not only provides structural stiffness, but also a tooling surface for the skin; and (5) providing a stiffness producing foam member in a structure, the foam member having a plurality of volumes of varying densities so that the strength/weight of the foam member is optimized for the predicted loading.
The particular embodiments disclosed above are illustrative only, as the application may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that a system with significant advantages has been described and illustrated. Although the system of the present application is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.
Claims
1. A structure, comprising:
- a foam member, the foam member having an outer molded surface; and
- a skin member located at least partially around the outer molded surface of the foam member;
- wherein the outer molded surface of the foam member is configured to provide a tooling surface for the skin member during assembly of the structure.
2. The structure according to claim 1, wherein the skin is a composite material.
3. The structure according to claim 1, wherein the skin is a metallic material.
4. The structure according to claim 1, wherein the foam member has a side portion left exposed such that the skin member only partially envelopes the foam member.
5. The structure according to claim 1, wherein the foam member is adhesively bonded to the skin member with an adhesive layer, so that the foam member is capable of carrying a shear load upon the skin member.
6. The structure according to claim 1, wherein a release agent is used to prevent the foam member from being in bonding contact with the skin member, so as to substantially prevent a shear load from the skin member from being carried through the foam member.
7. The structure according to claim 1, wherein a density of the foam member is tailored so that the foam member is able to withstand a predicted pressure load that the foam member will experience during a curing cycle.
8. The structure according to claim 1, wherein a density of the foam member is tailored so that a strength of the foam member is tailored to withstand a predicted load that the foam member will experience during the lifetime of the structure.
9. The structure according to claim 1, wherein the skin is an airfoil shape.
10. The structure according to claim 1, wherein the structure is an airfoil member for an aircraft.
11. A method of making a foam member for a structure, comprising:
- creating a mold having an interior cavity which resembles a desired shape of the foam member;
- introducing a foam mixture into the mold;
- allowing the foam mixture to polymerize so as to expand and distribute within the cavity of the mold;
- selectively controlling a density of the foam member in the mold; and
- curing the foam member.
12. The method according to claim 11, wherein the step of selectively controlling a density of the foam member involves allowing the foam mixture to free rise by not constricting a pressure within the cavity.
13. The method according to claim 11, wherein the step of selectively controlling a density of the foam member involves using a lid member to restrict the expansion of the foam mixture.
14. The method according to claim 13, wherein a vent opening is located in the lid member.
15. The method according to claim 11, further comprising:
- applying a release agent in the cavity of the mold prior to pouring the liquid mixture into the pour opening.
16. The method according to claim 11, wherein the step of selectively controlling a density of the foam member in the mold includes selectively sizing a vent opening in a lid member.
17. A method of making a composite structure, comprising:
- manufacturing an at least partially cured foam member;
- laying up an uncured composite skin onto an outer surface of the foam member such that the foam member acts as a tool for the uncured composite skin;
- curing the composite skin while foam member supports the portion of the composite skin.
18. The method according to claim 17, wherein the step of manufacturing an at least partially cured foam member comprises:
- creating a mold having an interior cavity which resembles a desired shape of the foam member;
- introducing a foam mixture into the mold;
- allowing the foam mixture to polymerize so as to expand and distribute within the cavity of the mold;
- selectively controlling a density of the foam member in the mold; and
- at least partially curing the foam member.
19. The method according to claim 17, further comprising:
- applying an adhesive layer between the foam member and the uncured composite skin.
20. The method according to claim 17, wherein the step of laying up an uncured composite skin onto an outer surface of the foam member is achieved with a fiber placement machine.
21. The method according to claim 18, wherein the step of manufacturing an at least partially cured foam member further comprises:
- locating a rib within the mold.
Type: Application
Filed: Sep 2, 2011
Publication Date: May 10, 2012
Inventors: Ramesh Thiagarajan (Plano, TX), Suvankar Mishra (Carrollton, TX), Mark Chris (Dallas, TX), William Evans, III (Hurst, TX), Mike Mikel (Fort Worth, TX)
Application Number: 13/224,532
International Classification: B32B 3/26 (20060101); B32B 38/00 (20060101); B29C 44/02 (20060101); B32B 37/00 (20060101); B32B 1/06 (20060101); B32B 7/12 (20060101);