1. Field of the Invention
The present invention relates to a method for manufacturing an elongate structural element configured for stiffening a shell structure, and to a method for manufacturing a rigid shell structure integrated with at least one elongate stiffening element. Preferably, such methods are related to use of curable composite materials, such as fiber-reinforced composite materials, carbon fiber epoxies, etc.
2. Related Art
The manufacturing of structural elements used for the construction of vehicles, vessels and aircraft often requires high strength, light-weight composite materials containing a plurality of curable layers of fibers and metal joined by adhesive thermoset and thermoplastics. Conventionally, structural elements of composite materials are manufactured by arranging a former made of metal on a base plate and laying up laminate layers of so-called “prepeg” on the former. Then, the base plate, former and laminate material are encapsulated in one or more vacuum bags before inserting the assembly into a pressure tank in order to increase the pressure acting on the composite material in the tank and to cure the structural element. The curing of the structural element may also take place in a so-called autoclave, or possibly in an oven.
Previously known methods of manufacturing structural elements of more complex shapes, for example curved elongate hat profiles configured for stiffening a shell structure, often require destructible formers (e.g. so-called “Stabilam”) in order to be able to remove the finished element therefrom.
For example, the EP application No. 05002075.9, not published before the present application, describes use of a water-soluble former when manufacturing an elongate hat or omega-profiled structural elements, such as stiffeners, spars, fittings or the like. This involves further manufacturing steps. Also, in such elongate hat or omega-shaped profiles high shearing and splitting stresses are often exerted on the outwardly directed flanges of the finished structural element which calls for a more rigid structure.
U.S. Pat. No. 6,458,309 B1 discloses a method for fabrication of composite aerostructure articles wherein an elongated hollow mandrel made of a pre-stiffened, flexible, spirally arranged tape is used as a former for hat-profiled reinforcement sections of a shell structure. However, although the former may remain in the finished article as a “fly-away tool”, a spring-like flexibility of the hollow mandrel makes it not able to take up any greater loads, especially not in the longitudinal direction of the hat profile.
It is an object of the present invention to present a method which makes it possible to manufacture elongate structural elements of complex configurations configured for stiffening a shell structure, which elements have improved strength to withstand high stresses and loads acting on the flange joints between the profiles and the shell structure, both in a longitudinal and a transverse direction of the profiles.
Another object of the invention is to suggest a method which makes it possible to manufacture such elongate structural elements of complex configurations without using a destructible former.
To this end, according to one aspect of the invention, in order to form a preformed, cured, integrated stiffening element for attachment to a predetermined surface of a shell structure the method comprises the steps of:
By using a preformed form-stable elongate reinforcement member having two flange portions directed inwardly to oppose each other while engaging an opposite surface of the base-forming body, and applying an elongate hat profile of uncured composite material over the preformed reinforcement member, so that a web portion of the hat profile covers the web portion of the reinforcement member, and two outwardly directed flange portions of the hat profile engage the opposite surface of the base-forming body, it is possible to integrate the form-stable reinforcement member, as a load-carrying element within the assembled structure and to obtain, after curing the entire structure assembly, an elongate structural element having both outwardly and inwardly directed flanges with thus a doubled ability of taking up stresses tending to split or tear apart the structural element from a shell structure to which it is adapted to be attached, as well as taking up greater loads in the longitudinal direction of the assembly. Preferably, the form-stable reinforcement member is preformed of a multilayer composite sheet material and precured.
The present invention also relates to the manufacturing of a rigid shell structure integrated with at least one elongate stiffening element produced in accordance with the method set forth above. In order to obtain such a stiffened integral shell structure one, or preferably a plurality of mutually spaced, preformed elongate stiffening elements are either placed on an uncured shell structure of a composite material and cured together therewith, or placed on a preformed shell and bonded thereto in a suitable manner.
Further features of the invention will be described more in detail below and defined in the appended claims with reference to the accompanying drawings.
In
As seen in
Several layers of uncured composite material 24, e.g. “prepeg”, are then laid over the elongate hat-shaped reinforcement member 16 to form an external hat profile having two outwardly directed flanges 26. Furthermore, when more than one structural profile element 12 are to be applied to the shell structure 10, such as shown in
Thus, according to the method of the present invention, a preformed form-stable, load-carrying reinforcement member 16 also serves as a form tool (a so-called “fly-away-tool”) which may remain in the finished product as a rigid load-carrying component thereof. This will result in an elongate structural element having both outwardly and inwardly directed flanges 26 and 20, respectively, which, in comparison with a hat profile lacking inwardly directed flanges, will offer a doubled ability of taking up stresses tending to split or tear apart the structural element from a shell structure to which it is adapted to be attached, as well as taking up greater loads in the longitudinal direction of the hat profiled stiffening element. Elongate hat profile elements to be integrated with a shell structure and having curved or other complex shapes may here be produced without using destructible formers, such as “Stabilam” or “Flexact”.
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Number | Date | Country | Kind |
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05112448 | Dec 2005 | EP | regional |
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20070176327 A1 | Aug 2007 | US |