Static structures (e.g. – buildings) – Facers; e.g. – modules – mutually bonded by internal settable... – Retaining feature on module exterior
Reexamination Certificate
1998-01-09
2001-03-20
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Facers; e.g., modules, mutually bonded by internal settable...
Retaining feature on module exterior
C052S440000, C052S441000
Reexamination Certificate
active
06202376
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a sandwich structure having a pair of substantially parallel walls and a core arranged between said walls.
BACKGROUND
Sandwich structures of this type are known, for example, from French patent specifications No. 2.038.668 and 2.325.503, Swiss patent specification No. 394,566 European patent specification No. 281689 and from UK patent specifications No. 2138551 and 2263164.
The latter prior art reference discloses, inter alia, that the core may comprise an array of core units which are arranged in a staggered pattern such that in a first direction between said walls adjacent core units are substantially aligned and in a second direction between said walls which is transversal to said first direction at least some adjacent core units partly face each other.
Although the known core is suitable for many applications it has the drawback that its ability to conform to curvative in the said first direction is limited, and elongate gaps are present between adjacent rows of core units in order to create a drapeable core. These gaps form elongate zones where the walls are not supported. It has been found that in such elongate zones the walls may become subject to high stresses such that cracks in the walls or between walls and core may develop if the structure is heavily loaded in service. The risk of cracking appeared to be particularly high in areas where the gaps are relatively wide as may be the case if the structure comprises regions of compound curvature.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sandwich structure having a core which can be easily produced and which is strong even if the structure has a complex shape.
It is a further object of the present invention to provide a sandwich structure having a core which is structural yet drapeable and which does not form through-gaps in the core web, thus retaining its structural integrity.
It is yet a further object of the present invention to provide a sandwich structure which is hardly prone to air entrapment between the core and walls of the structure during the manufacturing process of the structure.
It is also an object of the invention to provide a large core-to-face skin bond area, symmetrically balanced about the core webs, to minimize peel initiation points.
Another object of the invention is to provide an integral means of arresting the propagation of any debond between the core and the face skin, which could occur following impact loading in service.
The sandwich structure according to the invention thereto comprises a core comprising an array of core units which are arranged in said first direction at generally larger mutual spacings than in said second direction.
DETAILED DESCRIPTION
The structure according to the invention is based upon the insight that it is possible to create relatively wide gaps between adjacent core units in said first direction to provide a drapeable core, but which gaps do, because they are staggered, not form elongate zones where the walls are not supported by the core units, so that the risk of crack propagation in the walls or between walls and core is minimized.
Preferably the core units consist of rectangular or trapezoidal tubular sections which are staggered such that the openings of adjacent tubular sections are oriented in the direction of said first direction and are substantially aligned. In this way a permeable core is created through which a cooling and/or heating fluid may be circulated. Alternatively the core units may be oriented with the openings at top and bottom so that the openings face the walls of the structure. This provides greater through-thickness compression and shear strength but reduced core-to-face skin bond area, and fluid flow between the sandwich walls is prevented (or restricted if core unit webs are pierced).
It is also preferred that the core units are each at one side thereof bonded to a carrier cloth or fabric which is later laminated or bonded to one of the walls of the sandwich structure.
Furthermore, it is preferred that the core units are bonded to the carrier cloth such that when the carrier cloth is in a substantially flat position adjacent core units touch each other in said second direction and are spaced apart in said first direction such that gaps are present between adjacent aligned core units and that these gaps have a width between 0.04 and 0.4 times the core height.
If in such case the core units are rectangular tubular sections of which the openings are substantially aligned the side walls of these sections will generally be bonded to the side walls of adjacent sections by resin that will flow into the narrow gaps, if any, between these side walls so that the thus fused side walls will form drapeable I-beams which provide significant reinforcement of the structure once the resin is hardened. Even if no resin would flow into the narrow gaps the side walls of adjacent core units will support each other and reduce the risk of buckling and create a drapeable I-beam configuration.
If the carrier cloth is laminated to a curved inner surface of a wall of the sandwich structure then the core can be laid over areas where the wall has a large curvature in different directions, i.e. it is a drapeable core.
The core units and/or the walls of the sandwich structure may be made of a fibre reinforced plastic material.
If the core units are laminated or bonded to the walls of the sandwich structure and/or the carrier cloth by a compliant resin then the structure is suitable to form part of a containing means for a cryogenic fluid, such as a liquefied natural gas storage tank or pipeline. Such laminating of the core units to the wall(s) and/or carrier cloth is also useful if the sandwich structure is subject to repeated impact.
If the sandwich structure is a tubular, flat or curved component of a ship, such as a hull, bulkhead, bow, deck, walkway or storage tank then the ability of the structure to withstand repeated impacts without the risk of delamination is of significance.
If the sandwich structure according to the invention is used for the manufacture of a pipe then a core may be arranged between the inner and outer pipe walls in short staggered lengths circumferentially, in longer lengths axially or, for ease of application, by winding a fabric carrier tape carrying staggered open box core units helically around the inner pipe wall.
Preferably, when seen in longitudinal direction of the carrier tape, the core units are arranged in alternating rows of two elongate open box core units and three short open box core units.
It is also preferred that in each row the openings of adjacent open box core units face each other and a gap is present between adjacent openings, while the carrier tape is wound around the inner pipe wall at such a pitch angle that adjacent edges of the tape are contiguous.
These and other features, objects and advantages of the sandwich structure according to the invention will become apparent from the accompanying claims, abstract and drawings, in which:
REFERENCES:
patent: 394566 (1965-11-01), None
patent: 281689 (1988-09-01), None
patent: 2038668 (1970-12-01), None
patent: 2325503 (1977-04-01), None
patent: 2138551A (1984-10-01), None
patent: 2263164A (1993-07-01), None
Shell Research Limited
Stephan Beth A.
LandOfFree
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