KR101682992B1 - Auxetic structure based on wire-woven metal and fabrication method and appratus of the same - Google Patents
Auxetic structure based on wire-woven metal and fabrication method and appratus of the same Download PDFInfo
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- KR101682992B1 KR101682992B1 KR1020150154675A KR20150154675A KR101682992B1 KR 101682992 B1 KR101682992 B1 KR 101682992B1 KR 1020150154675 A KR1020150154675 A KR 1020150154675A KR 20150154675 A KR20150154675 A KR 20150154675A KR 101682992 B1 KR101682992 B1 KR 101682992B1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F27/00—Making wire network, i.e. wire nets
- B21F27/12—Making special types or portions of network by methods or means specially adapted therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F27/00—Making wire network, i.e. wire nets
- B21F27/12—Making special types or portions of network by methods or means specially adapted therefor
- B21F27/128—Making special types or portions of network by methods or means specially adapted therefor of three-dimensional form by connecting wire networks, e.g. by projecting wires through an insulating layer
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C2/00—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels
- E04C2/30—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure
- E04C2/34—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure composed of two or more spaced sheet-like parts
- E04C2/36—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure composed of two or more spaced sheet-like parts spaced apart by transversely-placed strip material, e.g. honeycomb panels
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
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Abstract
Description
BACKGROUND OF THE
Generally, when a material is stretched, it contracts in a direction perpendicular thereto, and conversely, when a material is compressed, it is stretched in a direction perpendicular thereto. In other words, the deformation (transverse deformation) in the direction perpendicular to the load application direction with respect to the deformation (longitudinal deformation) in the load application direction is opposite to that of the normal material. (Poisson's ratio) defined by giving a value of " Poisson's ratio " has a positive value. On the other hand, for a material having a specific structure, it has a negative Poisson's ratio, which is called an Auxetic material. These intumescent materials are found in a wide range from microscopic levels such as molecular structures to macroscopic levels in the order of a few centimeters.
1 to 4 show a typical structure of a conventionally known intumescent material (Reference: Yanping Liu and Hong Hu, Scientific Research and Essays Vol. 5 (10), pp. 1052-1063, May 18, 2010. A. Alderson , Chemistry & Industry, pp. 384-391, 17 May 1999. A. Al-derson and KL Alderson Proc. IMechE Part G: J. Aerospace Engineering, Vol.221, pp. 565-575. Fig. 1 shows a re-rentrant structure, which shows a two-dimensional honeycomb structure (Figs. 1 (a) to (f)) and a three-dimensional structure unit cell. Fig. 2 shows a chiral structure, in which the linear elements are spirally arranged on the outer periphery of a circular or polygonal rigid body. 3 shows a rotating structure, in which the rigid bodies of polygons are connected to each other at apexes. Fig. 4 shows an angle-ply laminates structure, which is applied to a fiber-reinforced composite material composed of a matrix having a high rigidity and a relatively low rigidity. FIG. 4 (a) is an example of a negative Poisson's ratio in a vertical direction when a force is applied in an acute angle direction of 10 to 40 degrees when a fiber layer (layer or ply) arranged unidirectionally is laminated in two directions , And Fig. 4 (b) shows a more complicated example. On the other hand, in the case of an open-type foam material having a three-dimensional network structure in which the rod-shaped elements are connected to each other in an irregular shape, when compressed in three mutually perpendicular directions, the foam material is deformed into the re- (RS Lakes, Science, Vol. 235, pp. 1038-1040, 1987). Fig. 5 (a) shows the microstructure of the general foamed material, and Fig. 5 (b) shows the microstructure of the foamed material modified to have the characteristics of the inflatable material.
Except for the angle-ply laminates structure shown in FIG. 4 among the structures of the conventional inflatable materials according to the prior art, the remaining three structures are porous structures having a very high porosity, The strength as a structural material is very low.
Further, it is known that, in the case of a porous material having a porosity of 40% or less, the constituent material itself can not have an expanding property over the entire material unless it is auxetic (Haeri AY, Weidner DJ, Parise JB (1992), Science, 257: 650-652.). In addition, there has been reported in the literature an α-phase cristobalite which is one of silicon dioxide (SiO 2 ) homogeneous forms as such an expansive substance. Figure 6 (a) shows the molecular structure of this cristobalite in alpha phase. When the α-phase cristobalite is loaded, the tetrahedral molecular structure of SiO 4 , consisting of the central silicon atom and the oxygen atom at the four vertexes, is hardly deformed and is located at the vertex, It has been reported that deformation due to rotation at the oxygen (O) atom position serving as a connecting part occurs (H. Kimizukal, S. Ogata, Y. Shibutani, Materials Transactions, Vol. 46, pp. 1161-11166, 2005). Therefore, the cristobalite on the? -Phase is composed of a rigid tetrahedron and has a three-dimensional deformation characteristic similar to that of the rotating structure of the intumescent material according to FIG. 6 (b) shows an auxetic deformation pattern according to a compressive load when the molecular structure of the cristobalite of the alpha phase is simulated as a rotating structure composed of tetrahedra.
Expandable (auxetic) As another example of materials, LaNiO 3 / SrTiO 3 has disclosed a super lattice (superlattices) bar (J. Hwang, J. Son, JY Zhang, A. Janotti, CG Van de Walle, S. 5 Stemmer, Structural origins of the properties of rare earth nickelate superlatives, PHYSICAL REVIEW B 87, 060101 (R), 2013). FIG. 7 (a) shows a shape in which the octahedral molecular structure of NiO 3 in the crystal structure is tilted in three directions perpendicular to each other. When the lanthanum (La) is omitted from the crystal structure of Fig. 7 (a) to show a deformation pattern of the structure composed of only the octahedron of NiO 3 , as shown on the right side of Fig. 7 (b) It is expected to have a three-dimensional denaturing characteristic similar to a rotating structure.
On the other hand, a material having a regular truss structure as a porous material having a high porosity is known to have a very high strength (Haydn NG Wadley, Phil. Trans. R. Soc. ). 8 (a) and 8 (b) show truss structures of tetrahedron and octahedron, respectively. The present inventors have proposed a method for manufacturing a porous material having a truss structure in Korean Patent Nos. 10-1029183 and 10-1155267, in which a metal wire formed by spirally preliminarily spinning is inserted and then the intersections of the wires are joined There is one. Figs. 9 (a) and 9 (b) show a porous material assembled with a helical wire having a truss structure of a tetrahedron and an octahedron proposed in Korean Patent Nos. 10-1029183 and 10-1155267. The structures according to Figs. 9 (a) and 9 (b) have structures similar to those of Figs. 6 (b) and 7 (b) I have. The present inventors have also found that the Korean Patent No. 10-1057946 discloses a wire porous material as shown in Fig. 9 (a) by filling a small tetrahedron portion with a solid material, and as shown in Figs. 10 and 11, And a method of manufacturing the material has been proposed. In addition, the present inventors have confirmed through experimentation that buckling of a truss element is suppressed by filling a small tetrahedron portion of a wire porous material made of a steel wire with brass (Ki-Ju Kang, A Wire- Woven Cellular Metal of Ultra-High Strength, Acta Mateialia, Vol. 57, pp. 1865-1874, 2009).
As described above, conventional porous auxetic materials are known to be inadequate for use in engineering applications due to their low strength.
It is an object of the present invention to provide a porous new inflatable structure made of a regular truss structure based on the prior art related to such a porous material and having a high strength and an Auxetic characteristic, and a method of manufacturing the same. .
Another object of the present invention is to provide an apparatus for manufacturing an inflatable structure which can be applied to the manufacturing method.
In the process of researching and developing a new porous inflatable structure by using a truss structure having a high strength in connection with the above-mentioned problem, the inventors of the present invention have found that a truss structure having a unit cell of a tetrahedron or an octahedron, It has been found that an expandable characteristic can be imparted by initially plastic-deforming the truss structure after filling the inside with a separate solid, leading to the present invention. The gist of the present invention related to the above problem is as follows.
(1) forming a wire into a spiral shape; Weaving the helical wire to provide a truss structure having a tetrahedral or octahedral unit cell; Filling the inside of the unit cell with a solid material; And performing an initial plastic deformation to induce rotational deformation of a connection portion between unit cells of the truss structure.
(2) The method according to the above (1), wherein the initial plastic deformation is performed in at least one of x, y and z with respect to a truss structure having a macroscopic rectangular parallelepiped shape.
(3) The method of manufacturing an inflatable structure according to (1) or (2), wherein the initial plastic deformation is performed by compressing the truss structure.
(4) the initial plastic deformation is arranged such that a pair of dies having irregularities of pitch intervals corresponding to twice the lattice size of the unit cell are disposed so as to be opposed to any one of xy, yz and zx of the truss structure , And the pair of dies facing each other are matched with each other in the opposite direction to each other. The method of manufacturing the inflatable structure according to the above (3).
(5) The method of manufacturing an inflatable structure according to (3), wherein the initial plastic deformation is performed in a state in which a rod having a smaller diameter is inserted into an empty space between the unit cells.
(6) The initial plastic deformation is performed by forcibly inserting a rod having a predetermined cross-sectional shape into the void space between the unit cells to deform the void space between the unit cells viewed in a specific direction into the shape of the rod (1) or (2).
(7) The method of manufacturing an inflatable structure according to (6), wherein the initial plastic deformation is performed stepwise using a plurality of rods having different sectional shapes.
(8) A truss structure having a unit cell of a tetrahedron or an octahedron woven with a helical wire and filled with a solid material, wherein a connection portion between the unit cells of the truss structure is rotationally deformed.
(9) The inflatable structure of (8), wherein the wire is a metal.
(10) The inflatable structure according to (8), wherein the solid matter is any one of soldering, brazing paste, synthetic resin, and metal.
(11) The inflatable structure according to (8), wherein the rotational deformation of the truss structure with respect to the connection portion between the unit cells is made in any one of x, y and z directions.
(12) An apparatus for manufacturing an inflatable structure by compressing a truss structure to induce an initial plastic deformation, the apparatus comprising: a pair of first die assemblies disposed opposite each other; A pair of second die assemblies disposed inside the first die assembly opposite the first die assembly in a direction perpendicular to the opposite direction; And a plurality of connecting members hinged to each of the pair of second die assemblies, wherein each of the pair of first die assemblies and the pair of second die assemblies And a plurality of connecting members symmetrically connect the pair of first die assemblies and the pair of second die assemblies toward the accommodation space, characterized in that the plurality of connecting members symmetrically connect the pair of first die assemblies and the pair of second die assemblies Of the inflatable structure.
(13) Each of the pair of first die assemblies and the pair of second assemblies includes a pair of dies having pitch irregularities corresponding to twice the lattice size of the truss structure unit cell, The apparatus for manufacturing inflatable structure according to (12), wherein the pair of dies facing each other are matched with the recessed portion and the convex portion in the opposite direction.
A method for manufacturing an inflatable structure according to the present invention is a method for manufacturing an inflatable structure, comprising the steps of: weaving a truss structure having a unit cell of a tetrahedral or octahedral shape by metal wires, filling the inside with a separate solid, Can be deformed into a slightly rotated shape to provide a new porous inflatable structure. This manufacturing method is advantageous for mass production of a large-sized inflatable structure in a simple manner. In addition, the inflatable structure according to the present invention is a regular truss structure of a metal wire. Since the interior is filled and fixed by a solid body, buckling of the truss elements does not occur at a source, The momentum is generated only at the portions where the grids of the lattices are connected to each other and has a swelling characteristic that is deformed by rotation, so that it can be used in various engineering applications such as a core material of a sandwich plate subjected to a high load such as mechanical, It can be used as absorbent material.
Figs. 1 to 4 are structural diagrams of conventional representative inflatable materials. Fig.
5 is a structural view of a conventional open type foam member.
FIG. 6 is a schematic diagram of a molecular structure and a deformation pattern of a conventional α-cristobalite. FIG.
7 is a conventional LaNiO 3 / SrTiO 3 a schematic view of the molecular structure, and deformation pattern of a super lattice (superlattices).
8 is a geometrical view of a truss structure having a conventional tetrahedral or octahedral unit cell.
9 is a structural view of a truss structure having a tetrahedral or octahedral unit cell woven with a conventional helical wire.
10 is a structural view of a truss structure having a tetrahedron unit cell filled with a conventional solid material.
11 is a photograph of a truss structure having a tetrahedron unit cell filled with a conventional solid material.
12 is a process diagram of a method of manufacturing an inflatable structure according to an embodiment of the present invention;
13 is a schematic view showing an initial plastic deformation at a unit cell connection portion of a truss structure according to an embodiment of the present invention.
FIG. 14 is a structural view of a truss structure in which a tetrahedron unit cell filled with a solid is simplified in accordance with an embodiment of the present invention. FIG.
15 is a perspective view of an arrangement and a shape of a die according to an embodiment of the present invention;
16 is a layout diagram of a die according to an embodiment of the present invention.
17 is a structural view of an apparatus for manufacturing an inflatable structure according to an embodiment of the present invention.
18 is a schematic diagram of an initial plastic deformation by die compression with the rod inserted in accordance with an embodiment of the present invention.
19 is a structural view of a truss structure having an initially plastic-deformed tetrahedral unit cell according to an embodiment of the present invention.
20 is a photograph before and after deformation of a truss water tank having unit cells of an initially plastic-deformed tetrahedral body according to an embodiment of the present invention.
21 is a structural view of a truss structure in which an octahedral unit cell filled with a solid is simplified in accordance with an embodiment of the present invention.
22 is a structural view of a truss structure having an initially plastic-deformed octahedral unit cell according to an embodiment of the present invention.
23 is a graph showing the results of finite analysis for a truss structure having an initially plastic-deformed tetrahedral unit cell.
24 is a photograph of an initial plastic deformation method using a rod according to an embodiment of the present invention.
FIG. 25 is a structural view of a truss structure having an initially plastic-deformed tetrahedral unit cell according to the embodiment of FIG. 24 before and after the transformation; FIG.
Hereinafter, the present invention will be described in detail with reference to examples. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the configuration of the embodiment described in the present specification is merely the most preferred embodiment of the present invention, and does not represent all the technical ideas of the present invention, so that various equivalents And variations may be made. On the other hand, in the drawings, the same or similar reference numerals are given to the same or equivalent elements in the drawings, and, in the entire specification, when a component is referred to as being "comprising" But may include other components.
12 shows a process diagram for a method of manufacturing an inflatable structure according to an embodiment of the present invention. A method of manufacturing an inflatable structure according to an embodiment of the present invention includes the steps of: (a) forming a wire into a spiral shape (S10); (b) weaving the helical wire to provide a truss structure having unit cells (S20); (c) filling the inside of the unit cell with a solid material (S30); And (d) initial plastic deformation in a direction perpendicular to the truss structure (S40). In this case, the above steps (a) to (c) can be performed by the method disclosed in the patents filed by the inventors of the present invention, the contents of which are incorporated herein by reference.
First, the wire is formed into a spiral shape. Step S10 of forming the wire into a spiral is necessary in order to assemble the structure by rotationally inserting the wire in the subsequent weaving step. In this case, the helix radius and pitch of the wire are determined according to the thickness of the wire and the size of the tetrahedral or octahedral unit cell, so that the wires intersect with each other with the minimum gap. A method of forming the wire into a spiral shape can be performed, for example, by the method disclosed in Korean Patent No. 10-1498777.
Next, step S20 of weaving the helical wire to provide a truss structure is performed in a manner of rotationally inserting the spirally shaped wire. The weaving of such a truss structure can be carried out, for example, by the method disclosed in Korean Patent No. 10-1029183 and Japanese Patent No. 10-1155267. In this case, the truss structure has a particularly tetrahedral or octahedral unit cell as shown in Figs. 9 (a) and 9 (b).
Next, the tetrahedron or octahedral unit cell of the truss structure is filled with a separate solid material (S30). The filling of the solids into the unit cell can be carried out, for example, by the method disclosed in Korean Patent No. 10-1298812. As the additional solid matter, it is possible to select a solidified solder or brazing paste melt or a liquid synthetic resin or a metal solidified. When the tetrahedral or octahedral unit cell has a small internal space, some of the cells may be filled with a liquid synthetic resin or metal by dipping the truss structure in liquid synthetic resin or metal. In the filling process of the solid material with respect to the unit cell, the viscosity, density, surface tension of the liquid synthetic resin or metal, affinity with the material constituting the truss element, capillary phenomenon, It can be induced to be filled, and after filling, it can be solidified by natural cooling or forced cooling or other heating. If the internal space of the tetrahedron or octahedral cell is not sufficiently small, or the conditions such as viscosity, density, surface tension, affinity with the material forming the truss element, and capillary phenomenon are inadequate, a tetrahedron or octahedral unit cell It is also possible to introduce a separate solid into the interior of the unit cell so that the remaining space in the unit cell is minimized to induce the liquid synthetic resin or metal to be filled. FIG. 10 shows a photograph of a truss structure in which a metal bead is inserted into a tetrahedral unit cell, and the remaining space is filled with an epoxy resin. FIG.
Finally, an 'initial plastic deformation' is performed on the truss structure to have an auxetic property (S40). In this case, the 'initial plastic deformation' refers to inducing rotational deformation of a connecting portion between tetrahedrons or octahedral unit cells of the truss structure. Such rotational deformation is accompanied by 'bending' and 'twisting'. Referring to FIG. 13, when the 'initial plastic deformation' is performed on the tetrahedron unit cell, the unit cells rotate with the arrows as the rotation axis. On the other hand, the swell characteristic can be controlled according to the extent of the rotational deformation. In the case of the tetrahedron unit cell, the angle at which the unit cell rotates while contacting each adjacent cell is no longer rotated is about 60 degrees.
The direction of this initial plastic deformation can be performed in more than one direction, targeting a truss structure provided macroscopically in the shape of a rectangular parallelepiped. When the unit cells are octahedrons, the directions of x, y, and z are perpendicular to each other and have the same shape, so that the initial plastic deformation may be any direction. In contrast, when the unit cell is a tetrahedron, the cell itself is not symmetrical with respect to the vertical axis, but has symmetry with respect to three directions having intervals of 120 degrees. Therefore, the initial plastic deformation varies depending on which direction x, y, .
On the other hand, with respect to the method of the initial plastic deformation, as an example thereof, the truss structure having a macroscopically rectangular shape can be compressed.
FIGS. 14 to 20 illustrate examples of initial plastic deformation of a truss structure having a tetrahedral unit cell by this compression, and are performed in such a manner that they are compressed in directions perpendicular to each other with respect to the truss structure. FIG. 14 shows a structural view of a truss structure in which a unit cell filled with a solid in FIG. 9 (a) is simplified by a tetrahedron. Fig. 15 (a) is a view in which a pair of dies having surface irregularities are arranged to induce compression plastic deformation in the x and y directions perpendicular to each other with respect to the rectangular parallelepiped truss structure shown in Fig. 14 And Fig. 15 (b) shows the surface relief shape of the die. Figs. 16 (a) and 16 (b) show a state in which the die of Fig. 15 is opposed to each of the zx plane and the yz plane of the truss structure.
15, the irregularities of the die serve to press one edge of the tetrahedral or octahedral unit cell to rotate the unit cell, so that the pitch interval of the concavo-convex pitch is set so that only one corner contacts each cell as shown in FIG. And preferably has a pitch interval corresponding to twice the unit cell lattice size. In addition, the depth of the concavity and convexity of the die is such that the outermost unit cell, whose edge is not in direct contact with the concave portion, protrudes outward in the case of rotational deformation for initial plastic deformation, and a depth sufficient to accommodate the protruding unit cell Should have. In addition, referring to Fig. 16, a pair of dies opposed to each other are alternately arranged such that a concave portion and a convex portion correspond to each other in the opposite direction.
17 is a structural view of an apparatus for manufacturing an inflatable structure according to an embodiment of the present invention. 15 and 16, the
The
In this case, as shown in FIGS. 15 and 16, the
The plurality of connecting
The
Although not shown in the drawings, the displacement for any one of the
On the other hand, as shown in Figs. 15 and 16, in the case of the initial plastic deformation using the die, only the outermost unit cells are intensively deformed and the internal unit cells are not deformed. In order to compensate for this, as shown in FIG. 18, initial plastic deformation using a die can be performed in a state in which a rod having a predetermined diameter passing through an empty space between unit cells is inserted in advance. In this case, since the degree of deformation of the unit cell is limited by the inserted rod, a uniform initial plastic deformation can be induced to the entire unit cell. The rod is circular in section and its diameter is smaller than the empty space between unit cells.
Fig. 19 is a structural view of the truss structure of Fig. 14 showing a state of compression plastic deformation using the dies of Figs. 15 and 15. Fig. The truss structure shows that the tetrahedron unit cell is plastically deformed to rotate regularly around the vertex of the connecting part, and is transformed into a structure similar to the cristobalite of the alpha phase in Fig. 6 (b). 20 shows comparative photographs in which truss structures having tetrahedron unit cells are photographed in the same viewing direction before and after the initial plastic deformation.
FIGS. 21 and 22 show examples of plastic deformation of a truss structure having octahedral unit cells by compression. FIG. 21 shows a structural view of a truss structure in which unit cells filled with solids in FIG. 9 (b) are simplified by an octahedron. In this embodiment as well, as in Figs. 15 and 16, compression plastic deformation is induced in the x and y directions perpendicular to each other by using a pair of dies having irregularities. Fig. Fig. Also, as shown in FIG. 18, the initial plastic deformation can be performed using a die in a state where a circular rod is inserted between empty spaces between unit cells.
The truss structure of Figure 22 is the plastic strain in the form of regularly rotate about an octahedral unit cell corners, Fig 7 (b) of LaNi? Z 3 / SrTi? Z 3 super-lattice (super lattices) Ni0 in the crystal structure 3 octahedron is converted to a tilted structure. Fig. 23 shows a finite analysis result of the truss structure of Fig. 19 having the initially plastically deformed tetrahedral unit cell. Specifically, Fig. 23 (a) is a result of predicting a stress-strain curve in the z-axis direction that occurs when a compression or tensile load is applied in the z-axis direction, and Fig. 25 (b) The Poisson's ratio is calculated from the strain predicted to occur in the x or y direction. It can be seen that not only the elastic deformation observed at the initial stage of the load but also the stable Poisson's ratio even after plastic deformation after yielding.
As another method of the initial plastic deformation, the rod may be forcibly inserted so that the void space between the unit cells viewed in a specific direction is deformed into a sectional shape of the rod.
24 is a photograph showing an initial plastic deformation method using a rod according to an embodiment of the present invention. In FIG. 24, the hole shape of the truss structure expected after the initial plastic deformation using the rod on the upper left side, the sectional shape of the different rods used for the initial plastic deformation on the upper center and the sectional shape of the rod used for the initial plastic deformation on the upper right side A sample photograph is shown. 24 shows a photograph of a state in which a plurality of rods are inserted in the lateral direction on the specimen of the truss structure.
Referring to the upper center of Fig. 24, in this case, a rod having a plurality of sectional shapes can be used. When the stiffness of the truss element is large, a middle rod having a small aspect ratio of the cross section is used as in the embodiment, and after the first deformation, a final rod having a large aspect ratio of the cross section is used, And can be sequentially deformed into a shape. Needless to say, the intermediate rods can be deformed into a plurality of stages by a plurality of types, if necessary.
If the initial plastic deformation is performed by forcibly inserting such a rod, a uniform initial plastic deformation can be induced irrespective of its position with respect to the entire unit cell in the truss structure rather than the simple die compression described above, which is advantageous. As described above, in the case of die compression, the deformation of the unit cell located outside the inner side of the truss structure may become large. Such a nonuniform deformation may be intensified as the total size of the truss structure becomes larger. However, These restrictions can be overcome.
FIG. 25 shows a structural view of a truss structure having an initially plastic-deformed tetrahedral unit cell according to the embodiment of FIG. 24, before and after the transformation. FIG. That is, if an ideally uniform deformation occurs, the structure as shown in the upper part of FIG. 25 shows a perspective view on the upper and lower left sides, and a projection view seen from the directions (a), (b), and (c) respectively on the right side. The projection shows that the circular hole before the deformation was deformed into an elliptical shape after the initial deformation. In order to induce deformation in the form of a hole, a method of forcibly inserting a rod having an elliptical cross section may be used.
As described above, a truss structure having a unit cell of a tetrahedron or an octahedron is woven by a metal wire, the inside is filled with a separate solid, and an initial plastic deformation is applied to form a tetrahedron or an octahedron And the Poisson 's ratio of the negative shrinkage or tension is generated in the remaining two vertical directions when the compression or the tensile is applied in one direction from the outside.
The foregoing is a description of specific embodiments of the present invention. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. It should be understood that this is possible. For example, as described above, in the present invention, if the initial plastic deformation inducing the rotational deformation accompanied by bending and twisting at the unit cell connection portion of the truss structure is satisfied so as to have an expanding characteristic, It is also possible to use other methods other than the fitting method, and all such modifications and alterations can be understood as falling within the scope of the invention disclosed in the claims or their equivalents.
100: Expansive structure manufacturing apparatus
110: first die assembly
112: first base
114: first die
120: second die assembly
112: second base
114: second die
130:
Claims (13)
Wherein the pair of first die assemblies and the pair of second die assemblies form a receiving space of a rectangular parallelepiped that accommodates the truss structure and the plurality of connecting members are connected to the pair of first die And the pair of second die assemblies symmetrically connect the assembly and the pair of second die assemblies.
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| CN110553135A (en) * | 2019-09-18 | 2019-12-10 | 汕头大学 | Truss structure with adjustable mechanical property and manufacturing method thereof |
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| CN113333750A (en) * | 2021-05-31 | 2021-09-03 | 西北有色金属研究院 | Preparation process of metal fiber porous material with three-dimensional negative Poisson's ratio |
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| CN114151489B (en) * | 2021-12-14 | 2024-04-05 | 长沙理工大学 | Multi-cell energy absorber and design method thereof |
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