WO2008082093A1

WO2008082093A1 - Light weight sandwich panels manufactured by using expanded metal process and bending process and manufacturing method thereof

Info

Publication number: WO2008082093A1
Application number: PCT/KR2007/006414
Authority: WO
Inventors: Ki Ju Kang; Chang Jun Lee; Dong Seok Lee; Byung Cheol Lee
Original assignee: Industry Foundation Of Chonnam National University
Priority date: 2006-12-28
Filing date: 2007-12-10
Publication date: 2008-07-10

Abstract

Disclosed are a lightweight sandwich panel and a method for manufacturing the same. The lightweight sandwich panel includes upper and lower face sheets, and a truss core. The truss core is formed by an expanded metal process and a bending process. That is, a thin flat plate is expanded into the shape of a metal mesh having hexagonal holes through the expanded metal process, and the truss core is formed by bending the expanded metal mesh along I ines connecting ones of apexes of the hexagonal holes, which are located at the corresponding positions so as to produce a V-shaped uneven surface. Then, the sandwich panel is formed by respectively attaching thin face sheets to the upper and lower surfaces of the truss core. The sandwich panel has a desired mechanical performance by adjusting the thickness of the flat panel, the thickness of a lattice forming the expanded metal mesh, the bending angle, and the shape of the hexagonal holes. The core has the ideal tetrahedral truss structure and thus has excellent mechanical strength and hardness, and is manufactured only by the well established conventional expanded metal process and the bending process and thus reduces production costs.

Description

[DESCRIPTION] [Invention Title]

LIGHT WEIGHT SANDWICH PANELS MANUFACTURED BY USING EXPANDED METAL PROCESS AND BENDING PROCESS AND MANUFACTURING METHOD THEREOF

[Technical Field]

The present invention relates to a lightweight sandwich panel manufactured by an expanded metal process and a bending process and a manufacturing method thereof.

[Background Art]

Generally, sandwich panel structures include upper and lower face sheets made of a material having a high strength/density and a core made of a porous material having a low density, such as Styrofoam, or a lattice-shaped material .

FIG.1 is a perspective view i 1 lustrat ing several conventional sandwich panel structures, each of which has a lattice-shaped core.

Most lattice-shaped cores or porous materials include several closed chambers formed therein, and thus cause a difficulty in space utilization.

Recently, a periodic truss structure as a novel material for a core has been introduced (H.N.G. Wadley, N.A. Fleck, A.G. Evans, 2003, Composite Science and Technology, Vo1.63, pp.2331-2343). A truss structure designed to have the optimum strength through precise calculation is advantageous in that the truss structure has mechanical properties almost similar to those of a honeycomb lattice structure, and the inside of the truss structure is opened and thus the internal space of the truss structure can be used.

The most general truss structure is a pyramid truss. The pyramid truss is configured such that four regular triangular lattices form inclined planes and a regular tetragonal lattice forms a lower (or upper) plane, and thus has an advantage in forming a rectangular plate structure.

Further, there is another truss structure, i.e., an Octet truss, in which regular tetrahedrons and regular octahedrons are mixed, (R. Buckminster Fuller, 1961, US Patent 2,986,241). In this structure, respective elements of the truss structure form an equi lateral triangle. In the twenty first century, a Kagome truss, which is transformed from the Octet truss, has been developed (S. Hyun, A.M. Karlsson, S. Torquato, A.G. Evans, 2003, Int J. of Solids and structures, Vol.40, pp.6989-6998). FIGs. 2, 3, and 4 illustrate sandwich panels obtained by attaching face sheets to upper and lower surfaces of cores respectively having a pyramid, Octet, and Kagome truss structures. It was known that the Octet and Kagome truss structures are superior in compressive strength to weight to the pyramid truss structure. In order to manufacture a sandwich panel having a truss core, several methods can be used, as follows. (H.H.G. Wadley, etc., 2003,

"Fabrication and structural performance of periodic cellular metal sandwich structure" , Composite Science Technology, Vol.63, pp.2331-2343). The first method is that an entire structure including a truss core is made of a resin and then a metal is cast using the structure as a mold. The first method is disadvantageous in that this method requires high production costs, is limited to a metal having an excellent castability, and easily causes defects.

The second method is that a truss core is made by forming periodic hexagonal holes through a thin plate so as to produce the plate in a mesh shape and bending the plate in a V shape along lines connecting ones, out of apexes of the hexagonal holes of the plate, which are located at the corresponding positions, and then face sheets are respectively attached to the upper and lower surface of the core. This method produces a core having the ideal Octet truss structure, but generates a material loss during a process for punching the plate. In order to remove the material loss of the second method, the third method is that a metal plate in a mesh shape is made by an expanded metal process instead of punching. A metal mesh provided with rectangular holes is made by the conventional expanded metal process, and is then bent along diagonal lines so as to form V-shaped prominences and depressions, thereby producing a core having a pyramid truss structure.

The fourth method is that a core having a pyramid truss structure is formed by bending a wire mesh, obtained by interweaving wires in orthogonal two directions, along diagonal lines of crossing points so as to form V-shaped prominences and depressions, and face sheets are respectively attached to the upper and lower surfaces of the core.

The third and fourth methods are basically the same in that a mesh having rectangular holes is made and then is bent into a V shape. FIGs. 5 and 6 respectively illustrate the second and third methods. The third method uses the conventional expanded metal process, which was well established, and thus does not cause a material loss and has a simple manufacturing process, compared with the second method, but produces a pyramid truss structure having a relatively poor compressive strength.

[Disclosure] [Technical Problem]

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a lightweight sandwich panel, in which a core is formed only by an expanded metal process and a bending process so as to reduce production cots and easily mass produce the panel, and the core has a tetrahedral truss structure similar to an Octet truss structure having an excellent compressive strength, and a manufacturing method thereof.

[Technical Solution]

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for manufacturing a lightweight sandwich panel having upper and lower face sheets and a truss core, comprising expanding a thin flat plate into the shape of a metal mesh having hexagonal holes with nearly the same length of respective sides through an expanded metal process; forming the truss core by bending the expanded metal mesh along 1 ines connecting ones, out of apexes of the hexagonal holes, which are located at the corresponding positions so as to produce a V-shaped uneven surface; and forming the sandwich panel by respectively attaching thin face sheets to the upper and lower surfaces of the truss core. The method may further comprise, after the formation of the sandwich panel, filling the vacant space in the truss core with one selected from the group consisting of a porous material , fluid, resin, metal , and ceramic, on purpose to add or improve the performances of the panel .

In accordance with another aspect of the present invention, there is provided a lightweight sandwich panel manufactured by the above method, wherein the core is made by forming periodic tetrahedral unit structures, each provided with three truss elements, and the cross-sectional area of one element out of the three elements is equal to the total sum of the cross-sectional areas of other two elements.

The cross-sectional area of one element out of the three elements may be two times the cross-sectional area of each of other two elements.

[Advantageous Effects]

As described above, the lightweight sandwich panel of the present invention has advantages, as follows.

First, the lightweight sandwich panel has a core formed only by an expanded metal process, which is simple and well established, and a bending process, thus reducing product ion costs and being easi Iy mass-produced.

Second, the lightweight sandwich panel includes the core having a tetrahedral truss structure, which is superior in compressive strength to weight to a pyramid truss structure, thus being capable of achieving a high strength.

Third, the lightweight sandwich panel obtains a desired mechanical performance by adjusting the ratio of the lengths of truss elements of a tetrahedral truss structure and the angles between the neighboring truss elements, thus having a high flexibility indesign.

[Description of Drawings]

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view i 1 lustrat ing various conventional sandwich panel structures;

FIGs.2 to 4 are perspect ive views illustrating sandwich panels, each of which is obtained by attaching face sheets to upper and lower surfaces of a core composed of a pyramid, Octet, or Kagome truss structure; FIG. 5 is a schematic view illustrating a conventional method for manufacturing a truss core by forming hexagonal holes through a thin plate and then bending the plate;

FIG. 6 is a schematic view illustrating a conventional method for manufacturing a truss core by forming an expanded metal mesh and then bending the metal mesh;

FIG.7 is a schematic view i 1 lustrat ing a conventional process for manufacturing an expanded metal mesh by shearing and expanding;

FIG.8 is a schematic view illustrating a conventional process for manufacturing a metal mesh by forming regular slits on a thin flat plate and then expanding the plate!

FIG.9 is a perspective view of a typical conventional expanded metal mesh;

FIG. 10 is a perspective view of an expanded metal mesh used in the present invention!

FIG. 11 is a view illustrating a process for forming a truss core by bending the expanded metal mesh of FIG. 10;

FIG.12 is a perspective view of a unit structure of the truss core of FIG. 11;

FIG. 13 shows plan, front, and right side views of the unit structure of FIG. 12; and

FIG.14 is a perspective view of a sandwich panel manufactured in accordance with the present invention.

[Mode for Invention]

Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings.

FIG.7 is a schematic view i llustrating the most general process for forming a metal mesh, i.e., an expanded metal process. In this process, a step of feeding a thin metal plate on a platform towards the edge of the platform bit by bit and a step of expanding the metal plate to a metal mesh by shearing and expanding a narrow band-shaped portion of the metal plate, exposed to the outside from the edge of the platform, between a saw-toothed cutting blade and a straight cutting blade, are repeated. Thus, the process is simple and effective.

After the process, a process for flattening the expanded metal mesh through rolling may be additionally performed.

FIG.8 illustrates a process for manufacturing a metal mesh by forming regular slits on a thin flat plate using laser cutting, electric-discharge wire cutting, or other methods, and then expanding the panel to both sides.

FIG. 9 illustrates a typical shape of an expanded metal mesh 1 manufactured by the process of FIG.7 or FIG.8. Holes forming the expanded metal mesh 1 have the shape similar to a lozenge. In the drawing, a region connecting the holes to each other in the direction of a short diagonal line is referred to as a bond 2. The size of the bond 2 is changed by adjusting the length of an upper/lower horizontal portion of the saw-toothed cutting blade of FIG.7 and the length of a region connecting the slits of FIG.8 in their lengthwise direction.

FIG. 10 illustrates an expanded metal mesh 3, in which bonds

2 of holes are intentionally lengthened and thus the holes have a hexagonal shape on purpose to be used as a material for a core of a lightweight sandwich panel in accordance with the present invention.

FIG. 11 illustrates a process for forming a truss core by bending the expanded metal mesh 3 in a V shape along dotted lines connecting ones, out of apexes of the hexagonal holes of the expanded metal mesh 3, which are located at the corresponding positions.

FIG.12 and FIG.13 illustrate a unit truss 4 of the truss core of FIG. 11. In FIG. 10, the bond 2 of the expanded metal mesh 3 has a width twice that of other sides of the hexagonal hole, a truss element corresponding to the bond 2, i.e., a strut, has a cross-sectional area twice that of other two truss elements. The truss 4 is a kind of tetrahedral truss simi lar to an Octet truss, but sectional areas of the respective truss elements of the truss 4 are not regular. Thus, in order to have a desired mechanical performance, it is necessary to adjust the lengths of the respective truss elements and the angles between the neighboring truss elements. For example, when the angles of inclination of the truss elements of FIG. 12 are 55° and 71° (α=55° , β =71° ), the compressive strength to weight of the truss 4 is the same as that of the Octet truss. When bending load is applied to the sandwich panel of the present invention, the truss core is mainly subjected to shear load (N. Wicks and J.W. Hutchinson, 2001, "Optimal Truss Plates" , Int. J. Solids and Structures, Vol.38, pp.5165-5183). Accordingly, the lengths of the truss elements and the angles between the neighboring truss elements are designed in consideration of the strength of the truss against the shearing load and the dependency of its strength on the shearing direction.

A sandwich panel is manufactured by respectively attaching thin face sheets 5 to the upper and lower surfaces of the truss core obtained by the above process. Here, the thin face sheets 5 are respectively attached to the upper and lower surfaces of the truss core by welding, brazing, or resin-bonding. FIG. 14 illustrates the shape of the sandwich panel manufactured in accordance with the present invention.

After the above manufacturing process has been completed, a step of filling the vacant space in the truss core with one selected from the group consisting of a porous material , fluid, resin, metal, and ceramic, may be added on purpose to improve the insulating capacity, noise and vibration suppression performance, and other mechanical properties of the panel and provide other functions to the panel. Thereby, a high-performance lightweight sandwich panel can be manufactured.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible.

For example, modifications, in which the widths or the ratio of the cross-sectional areas of two truss elements branched off from a truss element corresponding to the bond in consideration of the orientation of the shearing load, or a sandwich panel having a multi-layer structure including at least two cores is manufactured, are possible. Thus, these modifications, additions and substitutions do not depart from the scope and spirit of the invention as described in the accompanying claims or its equivalents.

Claims

[CLAIMS] [Claim 1]

A method for manufacturing a lightweight sandwich panel having upper and lower face sheets and a truss core, comprising: expanding a thin flat plate into the shape of a metal mesh having hexagonal holes with nearly the same length of respective sides through an expanded metal process! forming the truss core by bending the expanded metal mesh along lines connecting ones, out of apexes of the hexagonal holes, which are located at the corresponding positions so as to produce a V-shaped uneven surface; and forming the sandwich panel by respectively attaching thin face sheets to the upper and lower surfaces of the truss core.

[Claim 2]

The method according to claim 1, further comprising, after the format ion of the sandwich panel , fi 11 ing the vacant space in the truss core with one selected from the group consisting of a porous material , fluid, resin, metal, and ceramic, on purpose to add or improve the performances of the panel.

[Claim 3]

A lightweight sandwich panel manufactured by the method according to claim 1 or 2, wherein the core is made by forming periodic tetrahedral unit structures, each provided with three truss elements, and the cross-sectional area of one element out of the three elements is equal to the total sum of the cross-sectional areas of other two e1ements.

[Claim 4]

The lightweight sandwich panel according to claim 3, wherein the cross-sectional area of one element out of the three elements is two times the cross-sectional area of each of other two elements.