A novel composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio and its design method

Abstract

The present invention discloses a novel composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio, which includes a frame structure in the shape of an inwardly concave hexagon. On both sides of the frame structure, there are outwardly protruding corner structures, and a quadrilateral material is arranged between the frame structure and the corner structures. The quadrilateral material is made of a high-molecular material that resists tension but not compression. The present invention combines the positive Poisson's ratio of traditional materials with the negative Poisson's ratio of metamaterials. The designed novel composite metamaterial can exhibit both the properties of positive Poisson's ratio and negative Poisson's ratio. When it is longitudinally compressed or stretched, the transverse deformation always shrinks inward. The present invention enriches the functions of metamaterials and expands the practical application scope of metamaterials.

Description

Technical Field

[0001] The present invention relates to the field of metamaterial design, and more particularly to a novel composite metamaterial capable of realizing positive-negative Poisson's ratio conversion and its design method. Background Art

[0002] Poisson's ratio is an elastic constant reflecting the transverse deformation of a material, which refers to the ratio of the absolute value of the transverse normal strain to the axial normal strain when the material is uniaxially tensioned or compressed. Currently, there are traditional materials with positive Poisson's ratio and metamaterials with negative Poisson's ratio. They can only exhibit a single Poisson's ratio under uniaxial loading. For example: when a traditional material with positive Poisson's ratio is longitudinally uniaxially compressed, its transverse direction expands; while when it is longitudinally uniaxially tensioned, its transverse direction contracts. The negative Poisson's ratio metamaterial is exactly the opposite. When it is longitudinally uniaxially compressed, its transverse direction contracts; while when it is longitudinally uniaxially tensioned, its transverse direction expands. Summary of the Invention

[0003] The purpose of the present invention is to provide a novel composite metamaterial capable of realizing positive-negative Poisson's ratio conversion, and the transverse deformation of this metamaterial always contracts inward regardless of whether it is compressed or tensioned longitudinally.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A novel composite metamaterial capable of realizing positive-negative Poisson's ratio conversion, including a frame structure in the shape of an inwardly concave hexagon, with outwardly protruding corner structures arranged on both sides of the frame structure, and a quadrilateral material arranged between the frame structure and the corner structures.

[0006] Preferably, the quadrilateral material is made of a high molecular material that resists tension but not compression.

[0007] Preferably, the quadrilateral material is made of glass fiber; the frame structure is made of steel material, and the corner structure is made of aluminum material.

[0008] Preferably, the frame structure is formed by sequentially connecting a first horizontal section, a first inwardly concave bending section, a second horizontal section, and a second inwardly concave bending section end to end;

[0009] The first horizontal section and the second horizontal section are arranged in parallel and have equal lengths; the first inwardly concave bending section and the second inwardly concave bending section are symmetrically distributed;

[0010] Both between the first horizontal section and the first inwardly concave bending section, the second inwardly concave bending section, and between the second horizontal section and the first inwardly concave bending section, the second inwardly concave bending section are movably connected;

[0011] Both the first concave bending section and the second concave bending section are composed of two first straight sections. The two first straight sections have equal lengths and are movably connected at the endpoints.

[0012] Preferably, the angles between the first horizontal section and the first concave bending section, and between the first horizontal section and the second concave bending section, as well as the angles between the second horizontal section and the first concave bending section, and between the second horizontal section and the second concave bending section are equal, all being 50° to 60°.

[0013] Preferably, the ratio of the length of the first horizontal section to the length of the first straight section is 2:1.

[0014] Preferably, the folding angle structure is formed by connecting two second straight sections. The two ends of the folding angle structure are respectively movably connected to the ends of the first horizontal section and the second horizontal section; the two second straight sections are also movably connected, and the included angle is 160° to 180°.

[0015] Preferably, the thickness of the frame structure is equal to the thickness of the folding angle structure. The thickness of the quadrilateral material is less than or equal to 1 / 10 of the thickness of the frame structure, and the quadrilateral material is located at the middle cross-section position of the frame structure and the folding angle structure.

[0016] Preferably, as a structural unit, the composite metamaterial is arranged periodically in the X-axis direction and the Y-axis direction.

[0017] Preferably, two composite metamaterial structural units as described above are cross-crossed, that is, they are arranged vertically (one composite metamaterial structural unit is in the horizontal plane, and the other composite metamaterial structural unit is in the vertical plane, and the corresponding first horizontal sections and second horizontal sections of the two composite metamaterial structural units are fixedly connected in a cross manner), so that the effects of both positive Poisson's ratio and negative Poisson's ratio can also be achieved.

[0018] The present invention also provides a design method for a novel composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio as described above, including the following steps:

[0019] (1) Process the first horizontal section, the first concave bending section, the second horizontal section, and the second concave bending section from steel material, and then connect them end to end in sequence to obtain a frame structure in the shape of an inner concave hexagon, which is a negative Poisson's ratio metamaterial;

[0020] (2) Process the folding angle structure from aluminum material, and then connect a folding angle structure on each side of the frame structure. The folding angle structure is a positive Poisson's ratio material;

[0021] (3) A quadrilateral material is provided between the first concave bending section and the second concave bending section of the folding angle structure and the frame structure. The quadrilateral material is in the form of a thin film and is made of glass fiber. The quadrilateral material is a material with a positive Poisson's ratio, thus forming a composite metamaterial structural unit as a whole.

[0022] When a pressure in the Y direction is applied to the unit, the first concave bending section and the second concave bending section of the frame structure contract inward after being stressed, causing the quadrilateral material to be under tension, thereby driving the folding angle structure to contract inward, presenting a negative Poisson's ratio effect.

[0023] When a tensile force in the Y direction is applied to the unit, the folding angle shows a positive Poisson's ratio and contracts inward. The first concave bending section and the second concave bending section of the frame structure expand outward. However, due to the low compressive resistance of the quadrilateral material, the force transmission between the folding angle and the frame structure is not sufficient to cause the folding angle to expand outward, and the unit presents a positive Poisson's ratio.

[0024] (4) The composite metamaterial structural units are arranged periodically in the X-axis direction and the Y-axis direction to obtain a new composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio.

[0025] The beneficial technical effects of the present invention are as follows:

[0026] The present invention combines the positive Poisson's ratio of traditional materials with the negative Poisson's ratio of metamaterials. The designed new composite metamaterial can exhibit both the properties of positive Poisson's ratio and negative Poisson's ratio. When it is compressed or stretched longitudinally, the transverse deformation always contracts inward. The present invention enriches the functions of metamaterials and expands the practical application scope of metamaterials. Brief Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the structural principle of a single composite metamaterial structural unit in the present invention;

[0028] Figure 2 It is a schematic diagram of the deformation of the composite metamaterial structural unit in the present invention when compressed in the Y direction;

[0029] Figure 3 It is a schematic diagram of the deformation of the composite metamaterial structural unit in the present invention when stretched in the Y direction;

[0030] Figure 4 It is a schematic diagram of the structure of the overall new composite metamaterial formed by arranging the composite metamaterial structural units of the present invention in a 3×3 period, and the figure shows the deformation diagram of the metamaterial when stretched in the Y direction;

[0031] Figure 5 It is a schematic diagram of the structure of the overall new composite metamaterial formed by arranging the composite metamaterial structural units of the present invention in a 3×3 period, and the figure shows the deformation diagram of the metamaterial when compressed in the Y direction;

[0032] Figure 6 Shows the strain relationship between the Y - direction and the X - direction when the overall new composite metamaterial formed by arranging the composite metamaterial structural units of the present invention in a 3×3 period is stressed in the Y - direction.

[0033] Figure 7 This is another embodiment of a single composite metamaterial structural unit in the present invention. The figure shows a three - dimensional structural unit connected orthogonally. Detailed implementation mode

[0034] Existing traditional materials and negative Poisson's ratio metamaterials can only exhibit a single positive or negative Poisson's ratio when uniaxially compressed or stretched. And currently, in the combination of negative Poisson's ratio metamaterials and positive Poisson's ratio traditional materials, there is no property that can make it exhibit both positive and negative Poisson's ratios. However, through the design and combination of negative Poisson's ratio metamaterials and traditional positive Poisson's ratio materials, the present invention obtains a new composite metamaterial. When it is uniaxially compressed, the internal negative Poisson's ratio metamaterial drives the external positive Poisson's ratio traditional material to contract inward, making it exhibit a negative Poisson's ratio; when it is uniaxially stretched, the external positive Poisson's ratio traditional material contracts inward. Although the internal negative Poisson's ratio metamaterial expands outward, the force between the traditional material and the negative Poisson's ratio metamaterial is less than the force of the positive Poisson's ratio contracting inward. Therefore, the overall new composite metamaterial still contracts inward, and at this time it exhibits a positive Poisson's ratio. This design method of the new metamaterial enables the positive Poisson's ratio traditional material and the negative Poisson's ratio metamaterial to work together, making it have both positive and negative Poisson's ratio properties, expanding the properties of the material, and providing more choices for the practical application of metamaterials.

[0035] The following further explains the present invention in combination with the accompanying drawings and specific implementation modes.

[0036] As shown in Figure 1 A new composite metamaterial capable of realizing the positive - negative conversion of Poisson's ratio includes a frame structure 11 in the shape of an inward - concave hexagon. On the left and right sides of the frame structure 11, there are respectively arranged a first angled structure 12 and a second angled structure 13 protruding outward. Between the left side of the frame structure and the first angled structure 12, there is a first quadrilateral material 14, and between the right side of the frame structure and the second angled structure 13, there is a second quadrilateral material 15. The overall structural unit of the composite metamaterial is symmetric up - down, left - right.

[0037] As a further design of the present invention, the frame structure 11 in the shape of an inward - concave hexagon is made of steel material, and both the first angled structure 12 and the second angled structure 13 are made of aluminum material. The first quadrilateral material 14 and the second quadrilateral material 15 are both made of high - molecular materials or high - strength film materials that are tensile but not compressive. For example, the quadrilateral material can be made of glass fiber. The specific material properties are shown in Table 1.

[0038] Table 1

[0039]

[0040] That is to say, the frame structure 11 of the concave hexagon is a negative Poisson's ratio metamaterial, while the first folding angle structure 12, the second folding angle structure 13, the first quadrilateral material 14, and the second quadrilateral material 15 are all positive Poisson's ratio materials. Figure 2 and Figure 3 respectively show two states of the composite metamaterial structural unit when compressed and stretched in the Y direction. As Figure 2 shown, when a pressure in the Y direction is applied to the overall structural unit of the composite metamaterial, the unit exhibits a negative Poisson's ratio effect. This is because the concave hexagon negative Poisson's ratio metamaterial contracts inward after being stressed, causing the two-sided quadrilateral materials to be subjected to tensile forces, thereby driving the two-sided folding angle structures to contract inward. As Figure 3 shown, when a tensile force in the Y direction is applied to the unit, the unit exhibits a positive Poisson's ratio. This is because when subjected to the tensile force, the folding angle exhibits a positive Poisson's ratio and contracts inward, and the concave hexagon negative Poisson's ratio metamaterial expands outward. However, since the extrusion force borne by the quadrilateral material is very small, or rather, although the concave hexagon negative Poisson's ratio metamaterial expands outward, the quadrilateral material will contract and deform appropriately and still only has a very small outward expansion force. Therefore, the force transmission between the folding angle and the concave hexagon negative Poisson's ratio metamaterial is not sufficient to cause the folding angle to expand outward. Therefore, overall, the folding angle exhibits a positive Poisson's ratio and contracts inward.

[0041] Furthermore, the frame structure 11 is formed by sequentially connecting the first horizontal section 101, the first concave bending section 102, the second horizontal section 103, and the second concave bending section 104 end to end. The first horizontal section 101 and the second horizontal section 103 are arranged in parallel and have equal lengths; the first concave bending section 102 and the second concave bending section 104 are symmetrically distributed. The first horizontal section 101 is respectively movably connected to the first concave bending section 102 and the second concave bending section 104, and the second horizontal section 103 is respectively movably connected to the first concave bending section 102 and the second concave bending section 104. The first concave bending section 102 and the second concave bending section 104 are each composed of two first straight section bodies 105. The two first straight section bodies have equal lengths and are movably connected at the endpoints.

[0042] Even further, the angles between the first horizontal section 101 and the first concave bending section 102, the second concave bending section 104, and the angles between the second horizontal section 103 and the first concave bending section 102, the second concave bending section 104 are equal. As Figure 1 shown, the angle 16 is 50° to 60°. The ratio of the length of the first horizontal section 101 to the first straight section body 105 is 2:1.

[0043] Further, both the first folding angle structure 12 and the second folding angle structure 13 are formed by connecting two second straight sections 106. The two ends of the first folding angle structure 12 and the second folding angle structure 13 are respectively movably connected to the ends of the first horizontal section 101 and the second horizontal section 103. The two second straight sections 106 are also movably connected, and the included angle is 160° to 180°, that is, the included angle 17 between the second straight section 106 and the transverse center line of the composite metamaterial structure unit is 80° to 90°.

[0044] Furthermore, the thickness of the frame structure 11 is equal to the thickness of the first folding angle structure 12 and the second folding angle structure 13. The sections of the frame structure and the folding angle structure, such as the first horizontal section and the second straight section, can be in the shape of a strip-shaped cuboid or a slender cylindrical rod. The first quadrilateral material 14 and the second quadrilateral material 15 are both in the shape of a planar thin film. The thickness of the first quadrilateral material 14 and the second quadrilateral material 15 is less than or equal to 1 / 10 of the thickness of the frame structure, and the quadrilateral material is at the middle cross-section position of the frame structure and the folding angle structure, that is, the plane where the quadrilateral material is located is also the central cross-section of the frame structure and the folding angle structure. When assembling the composite metamaterial structure unit, a certain prestress can be applied to the quadrilateral material, and the deformation generated by the prestress on the concave hexagon negative Poisson's ratio metamaterial and the folding angle structure is less than the proportional limit.

[0045] The above composite metamaterial can be used as a structural unit and arranged periodically in the X-axis direction and the Y-axis direction. That is, when manufacturing the overall new composite metamaterial, the designed new composite metamaterial units are fixedly connected in a periodic arrangement in the Y direction and the X direction. The adjacent new composite metamaterial structure units in the Y direction can share a bottom edge to be connected end to end, and the adjacent new composite metamaterial structure units are symmetric about their common bottom edge, and this bottom edge is the above-mentioned first horizontal section or the second horizontal section. As Figure 4 and Figure 5 shown in the deformation diagrams of the 3×3 overall new composite metamaterial under tension and compression in the Y direction. It can be seen from the figure that the overall new composite metamaterial exhibits negative Poisson's ratio properties when compressed in the Y direction and positive Poisson's ratio properties when stretched.

[0046] Figure 6 shows the strain relationship between the Y direction and the X direction when the 3×3 overall new composite metamaterial is stressed in the Y direction. Since the transverse strain in the X direction of the overall new composite metamaterial is inconsistent, the average value of the total X displacements between the sites 51 and 51', between the sites 52 and 52', and between the sites 53 and 53' in Figure 5 is taken and divided by the X distance between the sites 51 and 51' before deformation as the X direction strain. Tensile strain is regarded as positive strain, and compressive strain is regarded as negative strain. From Figure 6It can be seen that regardless of whether the strain in the Y direction is positive or negative, the strain in the X direction is always negative. That is to say, when the proposed new composite metamaterial generates tensile strain or compressive strain in the Y direction, a contraction strain is generated in the X direction, which also verifies Figure 4 and Figure 5 deformation. In addition, it can also be seen from Figure 6 that when the tensile strain and compressive strain generated in the Y direction are the same, the magnitudes of the contraction deformations generated in the X direction are different.

[0047] The above composite metamaterial structural units can also be arranged and combined in other different ways, and still be able to achieve the effect of positive and negative Poisson's ratio conversion. As Figure 7 shown, two composite metamaterial structural units as Figure 1 [[ID= / / ID=13]]shown are cross-crossed, that is, they are arranged vertically (one composite metamaterial structural unit is in the horizontal plane, and the other composite metamaterial structural unit is in the vertical plane, and the corresponding first horizontal section and the second horizontal section of the two composite metamaterial structural units are fixedly connected in a cross manner), so that the effects of both positive Poisson's ratio and negative Poisson's ratio can also be achieved.

[0048] The present invention also provides a design method for a new composite metamaterial capable of realizing positive and negative Poisson's ratio conversion, including the following steps:

[0049] (1) The first horizontal section 101, the first concave bending section 102, the second horizontal section 103 and the second concave bending section 104 are processed and made of steel material, and then connected end to end in sequence to obtain a frame structure 11 in the shape of a concave hexagon, and this frame structure 11 is a negative Poisson's ratio metamaterial.

[0050] (2) A corner structure is processed and made of aluminum material, and then a corner structure is connected to each side of the frame structure, that is, the first corner structure 12 and the second corner structure 13, and this corner structure is a positive Poisson's ratio material.

[0051] (3) A quadrilateral material is arranged between the first corner structure 12, the second corner structure 13 and the first concave bending section 102, the second concave bending section 104 of the frame structure respectively. The quadrilateral material is in the shape of a thin film and is processed and made of glass fiber. This quadrilateral material is a positive Poisson's ratio material, so as to form a composite metamaterial structural unit as a whole.

[0052] During the design, a certain prestress is also applied to the quadrilateral material, and the deformation generated by the prestress on the concave hexagon negative Poisson's ratio metamaterial and the corner structure is less than the proportional limit. The purpose of applying prestress to the quadrilateral material is, generally speaking, to eliminate wrinkles and make it initially in a tensioned state.

[0053] When a pressure in the Y direction is applied to the unit, the first concave bending section 102 and the second concave bending section 104 of the frame structure contract inward after being stressed, causing the quadrilateral material to be subjected to tensile force, thereby driving the corner structure to contract inward and presenting a negative Poisson's ratio effect.

[0054] When a tensile force in the Y direction is applied to the unit, the corner presents a positive Poisson's ratio and contracts inward. The first concave bending section 102 and the second concave bending section 104 of the frame structure expand outward. However, since the quadrilateral material has low compressive resistance, the force transmission between the corner and the frame structure is not sufficient to cause the corner to expand outward, and the unit presents a positive Poisson's ratio.

[0055] (4) Periodically arrange the composite metamaterial structure unit in the X-axis direction and the Y-axis direction to obtain a new composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio.

[0056] For the parts not described in the above manner, the existing technology can be adopted or borrowed to achieve.

[0057] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A novel composite metamaterial capable of achieving positive-negative conversion of Poisson's ratio, characterized in that: It includes a frame structure in the shape of an inward concave hexagon, with outward protruding angled structures provided on both sides of the frame structure, and a quadrilateral material is provided between the frame structure and the angled structures; The quadrilateral material is made of a polymer material that is tensile but not compressive; The frame structure is formed by sequentially connecting a first horizontal section, a first inward concave bending section, a second horizontal section, and a second inward concave bending section end to end; The first horizontal section and the second horizontal section are arranged in parallel and have equal lengths; the first inward concave bending section and the second inward concave bending section are symmetrically distributed; Between the first horizontal section and the first inward concave bending section and the second inward concave bending section respectively, and between the second horizontal section and the first inward concave bending section and the second inward concave bending section respectively, they are all connected movably; Both the first inward concave bending section and the second inward concave bending section are composed of two first straight sections, the two first straight sections have equal lengths, and are connected movably at the endpoints; The included angles between the first horizontal section and the first inward concave bending section and the second inward concave bending section respectively, and between the second horizontal section and the first inward concave bending section and the second inward concave bending section respectively are equal, all being 50° to 60°; The angled structure is formed by connecting two second straight sections, and the two ends of the angled structure are respectively connected movably to the ends of the first horizontal section and the second horizontal section; the two second straight sections are also connected movably, and the included angle is 160° to 180°.

2. A novel composite metamaterial capable of realizing positive-negative conversion of Poisson's ratio according to claim 1, characterized in that: The quadrilateral material is made of glass fiber; the frame structure is made of steel material, and the angled structure is made of aluminum material.

3. A novel composite metamaterial capable of realizing positive-negative conversion of Poisson's ratio according to claim 1, characterized in that: The ratio of the length of the first horizontal section to the first straight section is 2:

1.

4. A novel composite metamaterial capable of achieving positive and negative Poisson's ratio conversion according to claim 1, characterized in that: The thickness of the frame structure is equal to the thickness of the angled structure, the thickness of the quadrilateral material is less than or equal to 1 / 10 of the thickness of the frame structure, and the quadrilateral material is at the middle cross-section position between the frame structure and the angled structure.

5. A novel composite metamaterial capable of realizing positive-negative conversion of Poisson's ratio according to claim 1, characterized in that: As a structural unit, this composite metamaterial is arranged periodically in the X-axis direction and the Y-axis direction.

6. The design method of a novel composite metamaterial capable of realizing positive-negative conversion of Poisson's ratio according to any one of claims 1-5, characterized in that It includes the following steps: (1) Use steel material to process the first horizontal section, the first inward concave bending section, the second horizontal section, and the second inward concave bending section, and then connect them end to end in sequence to obtain a frame structure in the shape of an inward concave hexagon, and this frame structure is a negative Poisson's ratio metamaterial; (2) Use aluminum material to process the angled structure, and then connect an angled structure to both sides of the frame structure respectively, and this angled structure is a positive Poisson's ratio material; (3) A quadrilateral material is provided between the angled structure and the first inward concave bending section and the second inward concave bending section of the frame structure. The quadrilateral material is in the shape of a thin film and is made of glass fiber. This quadrilateral material is a positive Poisson's ratio material, thus forming a composite metamaterial structural unit as a whole; When a pressure in the Y direction is applied to the unit, the first inward concave bending section and the second inward concave bending section of the frame structure contract inward after being stressed, causing the quadrilateral material to be subjected to tensile force, thereby driving the angled structure to contract inward, presenting a negative Poisson's ratio effect; When a tensile force in the Y direction is applied to the unit, the fold angle shows a positive Poisson's ratio and contracts inward, while the first and second concave bending segments of the frame structure expand outward. However, due to the low compressive resistance of the quadrilateral material, the force transmission between the fold angle and the frame structure is not sufficient to expand the fold angle outward, and the unit shows a positive Poisson's ratio; (4) Periodically arrange the composite metamaterial structural unit in the X-axis and Y-axis directions to obtain a new composite metamaterial capable of realizing the positive-negative conversion of Poisson's ratio.

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