WO2010016637A1

WO2010016637A1 - Truss type periodic cellular materials having polyhedrons or spheres in their internal vacancies and a manufacturing method of the same

Info

Publication number: WO2010016637A1
Application number: PCT/KR2008/005674
Authority: WO
Inventors: Ki Ju Kang; Hae Kyu Hur; Byung Cheol Lee
Original assignee: Industry Foundation Of Chonnam National University
Priority date: 2008-08-08
Filing date: 2008-09-24
Publication date: 2010-02-11
Also published as: KR101029170B1; KR20100019041A

Abstract

The present invention provides a truss type periodic cellular material, in which internal vacancies are filled with polyhedral or spherical fillers, and a method for manufacturing the same. In the present invention, the internal vacancies of the truss structure are filled with fillers, such as metal, ceramic or synthetic resin, which have high strength but are difficult to form in a large volume inherently. Accordingly, the buckling of the truss elements, which might easily occur when they are exposed to external compression or shear load, can be effectively prevented, so that the periodic cellular material has high strength and strain energy absorption.

Description

[DESCRIPTION] [Invention Title]

TRUSS TYPE PERIODIC CELLULAR MATERIALS HAVING POLYHEDRONS OR SPHERES IN THEIR INTERNAL VACANCIES AND A MANUFACTURING METHOD OF THE SAME

[Technical Field]

The present invention relates to a cellular material and a method for manufacturing the same, and more particularly, to a truss type periodic cellular material of which internal vacancies are fi lied with polyhedral or spherical fillers, and a method for manufacturing the same.

[Background Art] Cellular materials are materials that are light and have a relatively high strength because of a plurality of internal vacancies.

Among such cellular materials, a material which is regular in size, shape and arrangement of internal vacancies is called a periodic cellular material. In recent years, a truss type periodic cellular material is introduced as a new intermediate mater ial (H. N. G. Wadley, N. A. Fleck, A. G. Evans, 2003, Composite Science and Technology, Vol. 63, pp. 2331-2343) .

A truss structure is designed to have an optimal strength through a precise calculation so that it has mechanical properties comparable to honeycomb lattice structures, and it is also advantageous in utilizing its inside space which is opened.

FIG. 1 illustrates a single layer structure of a pyramid truss, an Octet truss, and a Kagome truss. Hereinafter, the kinds of the truss structures will be described with reference to FIG. 1.

The most general truss structure is the pyramid truss. Specifically, the pyramid truss is configured such that four regular triangular lattices form inclined planes around one apex and a regular tetragonal lattice forms a lower or upper plane, and thus has an advantage in forming a square plate structure.

Furthermore, the Octet truss has a structure in which regular tetrahedrons and regular octahedrons are combined alternately, and respect ive truss elements form an equi lateral triangle (R. Buckminster Fuller, 1961, U.S. patent No. 2,986,241).

In the twenty first century, the Kagome truss has been developed by transforming the Octet truss (S. Hyun, A.M. Karlsson, S. Torquato, A.G. Evans, 2003, Int J. of Solids and structures, Vol. 40, pp. 6989-6998). It is known that the Kagome truss has less anisotropy of strength, compared to the pyramid truss and the Octet truss and, in part icular , it is superior in resistance to buckl ing, stabi 1 ity against deformation after buckling, and energy absorption capability.

Meanwhi Ie, in recent years, there have been proposed methods for manufacturing a truss type cellular material by using wires such as piano wire, which is advantageous in realizing mass production, easy fabrication, and high strength. Those methods are disclosed indetai led in Korean Registered Patent Nos.566729, 633657, 700212 and 767186 and

Korean Patent Application No. 2006-0119233. FIGS. 2 to 6 illustrate periodic cellular materials manufactured by the above-listed patents and patent application. In this case, lighter truss type periodic cellular materials can be manufactured by using wires formed of fiber reinforced plastic composite material. If loads such as compression or shear are applied to the truss type periodic cellular material, the cellular materials are occasionally damaged by the buckling of the truss elements. In part icular , elast ic buckl ing easi Iy occurs when the slenderness rat io of the truss elements is large or when the wire materials are high-strength metals, such as piano wires, or high-strength fibers or fiber reinforced plastic used in composite materials. If such an elastic buckling occurs, the strength of the periodic cellular materials tends to be rapidly reduced so that stability required as the structural materials and strain energy absorption capacity may be severely reduced.

In addition, ceramic or some high-strength metals have limitation in use as the structural material because they are difficult to manufacture and fabricate in a large volume. Therefore, such materials must be used in a relatively small size through sintering.

For example, when relatively large structures such as structural plates are needed, those ceramic or high-strength metallic materials are reinforced to use by being attached with adhesive or being stacked just 1 ike in bricks or mortar , or by attaching fiber reinforced plastic (FRP), composite plates and metal plates on the surfaces thereof.

However, the structures manufactured in those manners are susceptible to impact load and, once damage begins, they reach a final rupture at a fast speed.

Furthermore, in recent years, there was developed a method which manufactures a metal hollow sphere (MHS) by spray-coating metal powder on the surface of Styrofoam sphere, heating it, and firing the Styrofoam sphere. A kind of a cellular metal can be manufactured by attaching a plural ity of MHSs by using resins or applying heat and pressure (K.M. Hurysz, J.L. Clark, A. R. Nagle, CU. Hardwicke, K.J. Lee, J. K. Cochran et al . , Steel and titanium hollow sphere foams. In: A. Evans, D. Schwartz, D. ShihandH. Wadley, Editors, Porous and cellular materials for structural applications MRS Proceedings vol. 521, Materials Research Society, Pittsburgh, PA (1998), pp. 191203). The cellular metals made by MHSs are superior to the typical metal foam in view of strength and strain energy absorption, but there are limitations in their utilization because the internal vacancies are closed.

[Disclosure]

[Technical Problem]

In order to solve the above-mentioned problem, the present invention provides a truss type cellular material, which has a structural stability and an increased energy absorption capability against strain.

[Technical Solution]

In order to solve the above-mentioned problem of the prior arts, the present invention provides a truss type periodic cellular material in which a plurality of internal vacancies are formed, characterized in that at least a part of the plural ity of internal vacancies are f i 1 led with polyhedral or spherical fillers.

According to the second aspect of the present invention, the polyhedral or spherical fillers may be formed of a material selected from the group consisting of metal, ceramic, and synthetic resin.

According to third aspect of the present invention, there is provided a method for manufacturing a truss type periodic cellular material of claim 1 or 2, and the method includes following steps: weaving or crossing wires to form a mesh-shaped two-dimensional plane having a plurality of holes; arranging polyhedral or spherical fillers in at least a part of the plurality of holes formed in the two-dimensional plane! stacking the two-dimensional plane, where the polyhedral or spherical fillers are arranged, in multiple layers; and forming a three-dimensional truss structure by weaving the multi-layer two-dimensional planes with wires inserted in an out-of-plane direction.

According to the fourth aspect of the present invention, the method may further include attaching the polyhedral or spherical fillers to the wires.

According to the fifth aspect of the present invention regarding the method, the spherical fillers may be metal hollow spheres (MHS) formed by spray-coat ing metal powder on the surface of Styrofoam sphere, heating the metal powder, and firing the Styrofoam sphere.

[Advantageous Effects]

According to the truss type periodic eel lular materials, in which the internal vacancies are filled with the polyhedral or spherical materials, and the methods for manufacturing the same of the present invention, it is possible to suppress the buckl ing of the truss elements during the compression or shear loads, and it is possible to prevent the strength from being rapidly reduced even after the buckling, thereby improving the stability of the structural material and increasing the strain energy absorption. Furthermore, since the truss type periodic cellular materials can be made lightweight, they can be used as the structural materials such as plates. Since the truss type periodic cellular materials are manufactured by using the known attaching technologies, the production cost is reduced and the mass production is facilitated.

[Description of Drawings] FIG. 1 illustrates a single layer structure of a pyramid truss, an Octet truss, and a Kagome truss.

FIGS.2 through 6 illustrate exemplary kinds of truss structure made of wires, which are processed to form truss type periodic eel lular materials according to embodiments of the present invention. FIGS. 7 through 10 illustrate structures of the truss type periodic cellular materials according to various embodiments of the present invention.

FIGS. 11 through 14 illustrate methods for manufacturing the periodic cellular materials according to the embodiments of FIGS. 7 through 10, respectively.

[Mode for Invention]

Hereinafter, preferred embodiments of a truss type periodic cellular material, which is filled with a polyhedral or spherical material in its inside, and a method for manufacturing the same will be described in detail with reference to the accompanying drawings.

Like reference numerals denote like elements throughout the drawings.

First , a truss type periodic eel lular material wi 11 be described hereinafter.

FIG.7 illustrates a structure of a truss type periodic material according to an embodiment of the present invention. Referring to FIG. 7, the truss type periodic cellular material according to an embodiment of the present invention includes a truss structure 10 and fillers 30.

The truss structure 10 is formed in a method of crossing and weaving wires 20, and the fillers 30 are filled into a plurality of vacancies formed inside the truss structure 10.

The wires 20 restrict the fillers 30 so that the fillers 30 may not deviate from specific positions.

The fillers 30 may be formed of metals, ceramics, synthetic resins, considering impact loads to be applied thereto. In addition, the fillers 30 are formed in a spherical shape corresponding to the vacancies formed in the truss structure 10. In this case, although the spherical fillers are exemplified in this embodiment, the shape of the fillers is not limited to the sphere. The fillers may be formed in a polyhedral shape according to the shape of the vacancies. This will be described later.

The fillers 30 formed of the above-described material in the above-described shape may be filled into the parts or entire of the plurality of vacancies formed in the truss structure 10 with the consideration of the required strength.

Various embodiments of the truss type periodic eel lular material according to the embodiment of the present invention will be described hereinafter.

FIGS. 8 and 10 illustrate structures of truss type cellular materials according to other embodiments of the present invention.

FIG. 8 illustrates a structure of a periodic cellular material in which case hexahedral fillers 31 are filled in hexahedral truss structures 11 formed of straight wires 21 of three directions perpendicular to one another. When the fillers filled in the truss structure are polyhedrons, the edge of the fillers 31 is processed to have grooves 34 corresponding to the outer surfaces of the wires 21 at the edges of the fillers 31 as illustrated in the right side of FIG. 8, so that each filler 31 can be maximally closely attached to the adjacent filler 31 without interference with the wires 21.

As another embodiment of the present invention, FIG. 9 i 1 lustrates a structure of a periodic eel lular material where spherical fillers 32 are filled in a pseudo Octet truss structure 12 composed of continuous straight wires 22.

As another embodiment of the present invention, FIG. 10 illustrates a structure of a periodic cellular material where pyramid fillers 33 and tetrahedral fillers 33' are filled in a pyramid truss structure. For convenience of explanation, only a 1-layer structure is illustrated in this embodiment. Like the embodiment of FIG.8, since this embodiment uses polyhedral fillers 33 and 33', not spherical fillers, it is preferable that grooves 34 corresponding to the shape of the wires 23 are formed at edges of the fillers 33 and 33' so that the fillers 33 and 33' are closely attached together. As described above, the truss type periodic cellular materials according to various embodiments of the present invent ion are comprised of the truss structure and the filler members, so that they may hold all merits of both members. For example, when the truss structure is formed using carbon fibers or wires such as piano wire, it is possible to form a cellular material which has ideal physical properties, i.e. has both strong tensile strength of the wires and compressive strength of the fillers filled within the vacancies of the truss structure at the same time. The above description has been made on the truss type periodic cellular material whose internal vacancies are filled with the polyhedral or spherical filler materials.

Hereinafter, a method for manufacturing the truss type periodic cellular material according to an embodiment of the present invention will be described in detail.

The method for manufacturing a truss type periodic cellular material includes: weaving or alternately arranging wires to form a mesh-shaped two-dimensional plane having a plurality of holes; arranging polyhedral or spherical fillers in at least a part of the plurality of holes formed in the two-dimensional plane; stacking the two-dimensional plane, where the polyhedral or spherical fillers are arranged, in multiple layers; and forming a three-dimensional truss structure by weaving the multi-layer two-dimensional planes with wires.

After forming the truss structure, the method may further include the step of attaching the polyhedral or spherical f i 1 lers to the wires by resin bonding, brazing, soldering, or brazing method.

If the metal hollow sphere (MHS) is used as the filler, it is possible to obtain the truss type periodic cellular material which is lighter and has an improved strength and strain energy absorption. The method for manufacturing the truss type periodic cellular material according to the present invention can be carried out in various manners, and specif ic embodiments of the present invention wi 11 be described hereinafter with reference to the attached drawings.

FIGS. 11 through 14 illustrate methods for manufacturing the periodic cellular materials according to the embodiments of FIGS. 7 through 10, respectively. Referring to FIG. 11, spiral wires 20 of three directions are woven in-plane to form a two-dimensional Kagome truss structure, and spherical f i 1 lers 30 are placed in a plural ity of hexagonal holes formed in the two-dimensional Kagome truss structure, and then, the resulting two-dimensional Kagome truss structures provided with hexagonal holes are stacked in multiple layers, and then, spiral wires 20 are rotational Iy inserted in three directions of out-of-plane to form a structure 10 similar to a three-dimensional Kagome truss structure.

Referring to another embodiment of FIG. 12, parallel wires 21 of two directions are vertically arranged in-plane, and a plurality of hexahedral fillers 31 are arranged thereon. Then, third wires 21' are inserted in a vertical direction of out-of-plane to form a cellular structure 11. In this case, since the wires 21 and 21' do not constrain each other, the positions of the wires 21 and 21' need to be fixed by using a separate support frame (not shown) disposed in the outside of the cellular structure 11.

Another embodiment of the present invention is illustrated in FIG. 13.

Specifically, referring to FIG. 13, straight wires 22 of three directions in-plane are intersected and overlapped to have azimuth angles of 60 degrees or 120 degrees, and then, spherical fillers 32 are arranged in a plurality of triangular holes, and the resulting structures are stacked in multiple layers. Continuously, straight wires 22 of three directions out-of-plane are inserted to form a structure 12 similar to a three-dimensional Octet truss.

When the spherical fillers 32 are arranged in the plurality of triangular holes in this case, it is preferable that they are not arranged in all holes, considering the volume of the fillers 32, but holes adjacent to the holes filled with the fillers 32 are left as vacancies.

As another embodiment of the present invention, FIG. 14 illustrates a method for manufacturing a cellular structure by using pyramid filler and tetrahedral filler. First, a plurality of pyramid fillers 33 are arranged on a flat panel 40 while maintaining predetermined distance, and tetrahedral fillers 33' are arranged in the plural ity of vacancies formed between adjacent pyramid f i 1 lers 33.

Then, a pyramid truss structure is placed on the flat panel where the fillers 33 and 33' are arranged, and the tetrahedral fillers 33' and the pyramid fillers 33 are arranged in sequence, thereby a separate flat panel 41 is arranged to form a cellular structure 13.

After forming the cellular structure according to the embodiments of FIGS. 11 through 14, as described above, the wires, the truss structure, the fillers, and the flat panels may be attached and fixed one another. Specifically, braze may be used as adhesive means when the fillers are ceramic having high melt ing point, or metal having higher melting point than metal constituting the wires or the truss structure. In addition to brazing, resin bonding, soldering and the like may also be used depending on the kind of materials or usage of the wires, the truss structure, and the fillers.

Whi Ie the truss type periodic eel lular materials, whose internal vacancies are filled with the polyhedral or spherical materials, and the methods for manufacturing the same has been described in detail with reference to the accompanying drawings, the scope of the present invention is not limited to the above-described embodiments. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

[CLAIMS] [Claim 1]

A truss type periodic cellular material in which a plurality of internal vacancies are formed, characterized in that at least a part of the plurality of internal vacancies are filled with polyhedral or spherical fillers. [Claim 2]

The truss type periodic cellular material of claim 1, wherein the polyhedral or spherical fillers are formed of a material selected from the group consisting of metal, ceramic, and synthetic resin. [Claim 3]

A method for manufacturing a truss type periodic cellular material of claim 1 or 2, the method comprising: weaving or crossing wires to form a mesh-shaped two-dimensional plane having a plurality of holes; arranging polyhedral or spherical fillers in at least a part of the plurality of holes formed in the two-dimensional plane; stacking the two-dimensional plane, where the polyhedral or spherical fillers are arranged, in multiple layers! and forming a three-dimensional truss structure by weaving the multi-layer two-dimensional planes with wires inserted in an out-of-plane direction. [Claim 4]

The method of claim 3, further comprising the step of attaching the polyhedral or spherical fillers to the wires. [Claim 5]

The method of claim 3, wherein the spherical fillers are metal hollow spheres (MHS) formed by spray-coating metal powder on the surface of Styrofoam sphere, heating the metal powder, and firing the Styrofoam sphere.