Metamaterial cell based on independent chiral distortion unit and metamaterial structure

Abstract

The invention discloses a metamaterial cell based on independent chiral distortion units and a metamaterial structure. The metamaterial cell comprises two chiral units in mirror symmetry; the chiral unit comprises two ring surfaces and a plurality of elastic rods, the two ring surfaces are coaxially arranged at intervals, and the elastic rods are periodically connected between the two ring surfaces in the circumferential direction of the ring surfaces; in the same chiral unit, when the chiral unit has no external load, the elastic rods are in an inclined state, and the inclined directions and the inclined angles of the elastic rods are the same; the two chiral units in mirror symmetry share one ring surface, or a pair of ring surfaces in the two chiral units in mirror symmetry are coaxially and fixedly connected. The lattice structure is applied to the field of metamaterial structures and has high static rigidity, high bearing buckling strength, large limit strain and high elastic strain energy density, and compared with an existing lattice structure composed of the same elements, under the constraint of the same base material strength, the equivalent modulus within a small deformation range is equivalent, and the lattice structure has the advantages that the lattice structure is simple in structure and low in cost. And the bearing buckling strength and the elastic strain energy density are obviously improved.

Description

Technical Field

[0001] The present invention relates to the fields of mechanical engineering, shipbuilding and ocean, vibration and noise control, structural impact resistance, and metamaterial structure technology. Specifically, it relates to a metamaterial cell and a metamaterial structure based on independent chiral distortion units, which can provide high static stiffness, high load-bearing buckling strength and high elastic strain energy density, and can be widely used in structural bearing, impact resistance, energy absorption, elastic energy storage, and vibration control of mechanical structures. Background Art

[0002] Materials and structures with high elastic energy storage density have broad application prospects in many fields, including energy storage, high load-bearing capacity, high impact resistance, and sensitive movement. However, achieving this goal requires that the material or structure has high modulus, high strength, and the ability to withstand large deformations. At the microscale, this can be achieved through high-strength materials such as carbon nanotubes, but achieving this goal at the macroscale faces great challenges and is currently difficult to achieve.

[0003] Mechanical / mechanical metamaterial structures refer to artificial materials with extraordinary mechanical properties, which can produce low-density high modulus, negative Poisson's ratio, elastic wave control and other characteristics. Typical structures include two-dimensional honeycomb structures, three-dimensional lattice structures, and folded structures. In particular, lattice metamaterial structures with light weight, high stiffness, and high strength have been widely used, providing important structural design solutions for industrial systems such as aviation, aerospace, ships, high-speed rail, and automobiles. However, the buckling of existing metamaterial structures under compressive load is dominated by the bending buckling of the elementary rod structure. Under the limited material strength limit, its buckling platform stress is contrary to its overall limit strain, which limits the ultimate elastic energy storage capacity. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a metamaterial cell and a metamaterial structure based on independent chiral twist units, which have high static stiffness, high load-bearing flexural strength, large ultimate strain and high elastic strain energy density. Compared with the existing lattice structure composed of the same primitives, under the same substrate strength constraint, the equivalent modulus within a small deformation range is equivalent, the load-bearing flexural strength is increased by 5-10 times, and the elastic strain energy density is increased by more than 5-20 times.

[0005] To achieve the above-mentioned object, the present invention provides a metamaterial cell based on an independent chiral twist unit, comprising two mirror-symmetric chiral units; The chiral unit comprises two annular surfaces and a plurality of elastic rods, the two annular surfaces are coaxially arranged at intervals, and the elastic rods are periodically distributed between the two annular surfaces along the circumferential direction of the annular surfaces; In the same chiral unit, when the chiral unit has no external load, the elastic rods are in an inclined state, and the inclination direction and inclination angle of each elastic rod are the same; The two mirror-symmetrical chiral units share one annular surface, or a pair of annular surfaces in the two mirror-symmetrical chiral units are coaxially fixedly connected.

[0006] In one embodiment, in the same chiral unit: The first end of the elastic rod is fixedly connected to one of the annular surfaces, and the distance between the center of the first end of the elastic rod and the center of the corresponding annular surface is a first pitch circle radius R1; The second end of the elastic rod is fixedly connected to another annular surface, and the distance between the center of the second end of the elastic rod and the center of the corresponding annular surface is the second pitch circle radius R2; Wherein, R1=R2=R, and R is the installation pitch radius of the elastic rod between the two annular surfaces.

[0007] In one embodiment, in the same chiral unit, the distance between two ring surfaces is h0, and h0≈4R~6R.

[0008] In one embodiment, the elastic rod is a cylindrical structure that can withstand large deformations such as compression, bending and torsion, including but not limited to soft rubber rods, spiral springs, steel wire ropes, carbon nanotubes, and fiber-reinforced rods.

[0009] In one embodiment, in the same chiral unit, the distance between two adjacent elastic rods is greater than or equal to the diameter of the elastic rod.

[0010] To achieve the above object, the present invention also provides a metamaterial structure based on independent chiral twisting units, comprising a plurality of the above metamaterial cells; Each of the metamaterial cells is distributed in a two-dimensional planar array, a three-dimensional multilayer array or a three-dimensional skeleton configuration.

[0011] In one embodiment, when the metamaterial cells are distributed in a two-dimensional planar array: The metamaterial cells are arrayed into a single-layer metamaterial structure on a two-dimensional plane, and the ring surfaces at the top and bottom layers of the single-layer metamaterial structure are respectively fixed or integrally formed on the same flat plate, but the central ring surfaces of the metamaterial cells are independent of each other.

[0012] In one embodiment, when the metamaterial cells are distributed in a three-dimensional multi-layer array, the metamaterial structure is composed of a plurality of single-layer metamaterial structures stacked in a vertical direction.

[0013] In one embodiment, when the metamaterial cells are distributed in a three-dimensional skeleton configuration, the metamaterial cells are connected to form a spatial skeleton of a polyhedral structure, and the nodes of the spatial skeleton are block structures.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: 1. The present invention forms metamaterial cells by layering chiral units. In the metamaterial structure composed of metamaterial cell arrays, the existing high-rigidity metamaterial structures such as rhombus and octahedral lattices with the same equivalent density can not only maintain the same stiffness (i.e., equivalent modulus) within a small deformation range, but also significantly outperform the existing high-rigidity metamaterial structures in terms of overall buckling bearing strength and elastic energy storage density of the metamaterial structure, and has the advantages of high static stiffness, high bearing buckling strength, large ultimate strain and high elastic strain energy density; 2. The elastic rod in the present invention can be directly prepared from materials or structures that can withstand large deformation, such as metal springs. It not only has high environmental adaptability and mature preparation technology, but also can maintain excellent elastic deformation recovery under large deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0016] Figure 1 Schematic diagram of the structure of the metamaterial cell in Example 1 of the present invention; Figure 2 Schematic diagram of the structure of the chiral unit in Example 1 of the present invention; Figure 3 Schematic diagram of the torsional buckling deformation mode of the metamaterial cell under axial compression in Example 1 of the present invention; Figure 4 This is a schematic diagram of the structure of a two-dimensional single-layer chiral metamaterial structure array in Example 2 of the present invention; Figure 5 This is a schematic diagram of the structure of a three-dimensional multilayer chiral metamaterial structure array in Example 2 of the present invention; Figure 6 This is a schematic diagram of the structure of the three-dimensional skeleton chiral metamaterial structure array in Example 2 of the present invention; Figure 7 Schematic diagram of metamaterial structures of different configurations made of the same elastic rods in an embodiment of the present invention, wherein: Figure 7 (a) is a simplified schematic diagram of the chiral lattice. Figure 7 (b) is a simplified schematic diagram of the octahedral lattice. Figure 7 (c) is a simple schematic diagram of the diamond lattice. Figure 7 (d) is a brief schematic diagram of the overall tensile lattice; Figure 8Graphs showing equivalent stress-strain curves of metamaterial structures of different configurations made of the same elastic rod in an example of an embodiment of the present invention; Fig. 9 The performance curves of different metamaterial arrays composed of uniform solid elastic rods in the embodiment of the present invention are shown in FIG. Fig. 9 (a) is the normalized mass density-Young's modulus curve. Fig. 9 (b) is the equivalent ultimate strain and normalized equivalent buckling strength curve for a given elastic rod strength. Fig. 9 (c) is the equivalent limit strain and normalized elastic strain energy density curve for a given elastic rod strength; Fig.10 It is a performance curve diagram of the diamond lattice composed of metal springs and the chiral metamaterial array in the example of the embodiment of the present invention, wherein: Fig.10 (a) is the curve of equivalent ultimate strain and equivalent buckling strength. Fig.10 (b) is the curve of equivalent limit strain and elastic strain energy density.

[0017] Figure numerals: torus 1, elastic rod 2.

[0018] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0021] Example 1 like Figure 1 The figure shows a metamaterial cell based on independent chiral twisting units disclosed in this embodiment (hereinafter referred to as "metamaterial cell"), where the metamaterial cell includes chiral units with the same structure, and the two chiral units are distributed in a mirror-symmetrical manner.

[0022] refer to Figure 2The chiral unit is cylindrical in shape as a whole, and is composed of two ring surfaces 1 and a plurality of elastic rods. The ring surface 1 can be a circular plate or an annular plate. The two ring surfaces 1 are arranged coaxially and spaced vertically, and the minimum distance between the two ring surfaces 1 is maintained at h0. Each elastic rod 2 is periodically connected between the two ring surfaces 1 along the circumferential direction of the ring surface 1. The upper and lower ring surfaces 1 of the chiral unit have an initial relative helical angle α0 that is not equal to 0 when there is no external load on the chiral unit. That is, in the same chiral unit, when there is no external load on the chiral unit, the elastic rod 2 is in a tilted state, and the tilt direction and tilt angle of each elastic rod 2 are the same, thereby forming chiral characteristics.

[0023] In the same metamaterial cell, the two mirror-symmetric groups of chiral units can share a torus 1, or a pair of torus 1 close to each other in the two groups of chiral units can be coaxially fixed together by gluing, snap connection, screw fixation, welding, etc. Under the action of external compressive load, the two torus 1 at both ends of the metamaterial cell remain fixed, while the middle torus 1 rotates and drives the internal elastic rod 2 to twist. When the compressive load is large, the elastic rod 2 will bend, forming a chiral distortion deformation as a whole, while the free chiral distortion deformation will not produce torque at the boundaries at both ends, that is, Figure 3 shown.

[0024] In the same chiral unit, the first end of the elastic rod 2 is fixedly connected to one of the torus 1 by gluing, riveting, welding, etc. or is integrally formed by 3D printing, and the distance between the center of the first end of the elastic rod 2 and the center of the corresponding torus 1 is the first pitch circle radius R1. The second end of the elastic rod 2 is fixedly connected to the other torus 1 by gluing, riveting, welding, etc. or is integrally formed by 3D printing, and the distance between the center of the second end of the elastic rod 2 and the center of the corresponding torus 1 is the second pitch circle radius R2. The performance of the metamaterial with parameter R1≠R2 is lower than that of the metamaterial with R1=R2, so in this embodiment, it is preferred that R1=R2=R, R is the installation pitch circle radius of the elastic rod 2 between the two torus 1, that is, the periodically distributed elastic rods 2 in the same chiral unit will not form a conical platform as a whole, but a cylinder.

[0025] In the specific application process, for a given annular surface spacing h0 and overall buckling strain, reducing the installation pitch radius R of the elastic rod 2 between the two annular surfaces 1 and the initial relative helical angle α0 of the annular surface 1 can improve the elastic energy storage density and bearing strength of the chiral metamaterial structure, and the performance improvement effect brought by reducing R is more significant. Therefore, in order to ensure the stability of the overall structure, in this embodiment, the spacing of the annular surfaces 1 is preferably set to h0≈4R~6R, for example, h0=30mm, R=7.5mm.

[0026] In this embodiment, the elastic rod 2 is a cylindrical structure that can withstand bending and torsion deformation, such as a rubber round rod, a metal spring, a steel wire rope, a carbon nanotube, a fiber-reinforced rod, etc. At the same time, in order to ensure that the elastic rods 2 after the chiral unit deformation do not contact each other before the structure collapses, in the same chiral unit, the spacing between two adjacent elastic rods 2 is set to be greater than or equal to the diameter of the elastic rod 2.

[0027] Example 2 This embodiment discloses a metamaterial structure based on independent chiral twisted units (hereinafter referred to as "metamaterial structure"), which mainly includes the metamaterial cells of embodiment 1, each metamaterial cell is distributed in a two-dimensional planar array, a three-dimensional multilayer array or a three-dimensional skeleton structure. Among them, the two-dimensional single-layer array and the three-dimensional multilayer array can provide higher energy storage density and higher buckling bearing strength.

[0028] refer to Figure 4 When each metamaterial cell is distributed in a two-dimensional planar array, each metamaterial cell is arrayed in a single-layer metamaterial structure on the two-dimensional plane, and the ring surfaces at the top and bottom of the single-layer metamaterial structure are respectively fixed or integrally formed on the same flat plate, but the central ring surfaces of each metamaterial cell are independent of each other. Preferably, in the single-layer metamaterial structure, the lattice of the two-dimensional array is square or rhombus, and the distance between the metamaterial cells is as small as possible without mutual interference.

[0029] refer to Figure 5 When the metamaterial cells are distributed in a three-dimensional multilayer array, the metamaterial structure consists of multiple Figure 4 The single-layer metamaterial structure shown is stacked in a vertical direction, and two adjacent single-layer metamaterial structures are fixed by gluing.

[0030] refer to Figure 6 When each metamaterial cell is distributed in a three-dimensional skeleton configuration, each metamaterial cell is connected to form a spatial skeleton of a polyhedral structure. The spatial skeleton can be a cube, a rhombus, an octahedron, a dodecahedron, etc., and the preferred configuration in this embodiment is a cube. Among them, the nodes of the spatial skeleton are block-shaped skeleton node blocks, and their size is equivalent to the torus at both ends of the chiral unit. The chiral cells are fixedly connected to the skeleton node blocks at the head and tail.

[0031] The metamaterial structure based on the independent chiral twisting unit in this embodiment is further described below in conjunction with two groups of specific performance comparison examples with existing metamaterial structures.

[0032] In Example 1, all metamaterial structures are composed of uniform elastic rods with a radius of r = 1.5 mm and a length of L. 0 =30mm, the Young's modulus of the elastic rod is E s , assuming its strength is σ v=0.2Es, the example uses dimensionless normalized performance indicators for comparison. refer to Figure 7 , the existing octahedral lattice, rhombus lattice, stretched integral lattice and the chiral lattice in this embodiment (specifically Figure 4 The single-layer metamaterial structure shown in the figure is used for simulation performance comparison. The tensile overall lattice is composed of tensile and compressive rods added inside the regular tetradecahedron. The initial parameters of the chiral lattice are h 0 =30mm, R=7.5mm, α0=5°. The equivalent compressive stress-strain curves of different metamaterial structures prepared from the same hard rubber are shown in Figure 8 As shown. Nonlinear finite element method is used to carry out numerical calculations on different metamaterial models. In the calculation, compressive loads are applied to different models to make the metamaterial structure produce the compressive buckling deformation required by theory. limit The maximum Mises stress in the rod of the metamaterial reaches the strength σ v The global equivalent compressive strain of σ is larger, indicating higher anti-deformation ability. bk for Figure 8 In the compression buckling curve of the metamaterial structure shown in the figure, the global equivalent stress at the buckling platform stage is larger, indicating that the buckling bearing strength of the metamaterial structure is higher. ɸ is the stress of the metamaterial structure when the local stress reaches σ v (corresponding to global strain reaching ɛ limit ). E is the equivalent Young's modulus of the metamaterial under small strain.

[0033] like Fig. 9 As shown in Example 1, the properties of chiral metamaterials with different parameters are calculated, and experimental tests are completed under typical parameters, such as Figure 8 Both simulation and experimental test results show that: 1. Compared with existing high-rigidity metamaterial structures such as rhombus and octahedral lattices with the same equivalent density, the layered array chiral metamaterial structure proposed in this embodiment has a stiffness (i.e., equivalent modulus) comparable to that of existing metamaterials within a small deformation range, i.e., has a high-rigidity characteristic; 2. Under the strength constraint of the matrix elastic rod material, compared with the high-rigidity rhombus lattice metamaterial structure, the overall buckling bearing strength of the layered array chiral metamaterial structure proposed in this embodiment is increased by 3 times, and the elastic energy storage density is increased by 5 times; compared with the high-rigidity octahedral lattice metamaterial structure, the overall buckling bearing strength of the layered array chiral metamaterial structure proposed in this embodiment is increased by more than 15 times, and the elastic energy storage density is increased by more than 20 times; compared with the tensile overall structure, the performance proposed in this embodiment is increased by more than 100 times.

[0034] According to the analysis of Example 1, the diamond lattice configuration has excellent performance. Therefore, in Example 2, this embodiment designs a diamond lattice metamaterial structure composed of steel springs and a two-dimensional single-layer chiral metamaterial structure for comparison. Among them, the spring is a mold spring with a rectangular cross-section. The steel spring has high environmental adaptability and mature preparation technology, and can maintain excellent elastic deformation recovery under large deformation.

[0035] In Example 2, the spring has an outer diameter of 6 mm, an inner diameter of 3.2 mm, and a length of 30 mm. The performance comparison method is the same as in Example 1. The performance curve calculated using the nonlinear finite element method is as follows: Fig.10 The strength of the spring material is σ v =2.75GPa. The simulation results show that, compared with the high-density diamond lattice structure, the chiral superstructure proposed in this embodiment can increase the overall buckling bearing strength by more than 3 times and the energy storage density by more than 5 times.

[0036] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A metamaterial cell based on independent chiral twist units, characterized in that: It includes two mirror-symmetric chiral units; The chiral unit comprises two annular surfaces and a plurality of elastic rods, the two annular surfaces are coaxially arranged at intervals, and the elastic rods are periodically distributed between the two annular surfaces along the circumferential direction of the annular surfaces; In the same chiral unit, when the chiral unit has no external load, the elastic rods are in an inclined state, and the inclination direction and inclination angle of each elastic rod are the same; The two mirror-symmetrical chiral units share one annular surface, or a pair of annular surfaces in the two mirror-symmetrical chiral units are coaxially fixedly connected.

2. The metamaterial cell based on independent chiral twisting units according to claim 1, characterized in that: In the same chiral unit: The first end of the elastic rod is fixedly connected to one of the annular surfaces, and the distance between the center of the first end of the elastic rod and the center of the corresponding annular surface is a first pitch circle radius R1; The second end of the elastic rod is fixedly connected to another annular surface, and the distance between the center of the second end of the elastic rod and the center of the corresponding annular surface is the second pitch circle radius R2; Wherein, R1=R2=R, and R is the installation pitch radius of the elastic rod between the two annular surfaces.

3. The metamaterial cell based on independent chiral distortion unit according to claim 2, characterized in that: In the same chiral unit, the distance between the two ring surfaces is h0, and h0≈4R~6R.

4. The metamaterial cell based on independent chiral distortion units according to claim 1, 2 or 3, characterized in that: The elastic rod is a cylindrical structure that can withstand large deformations such as compression, bending and torsion, including but not limited to soft rubber rods, spiral springs, steel wire ropes, carbon nanotubes, and fiber-reinforced rods.

5. The metamaterial cell based on independent chiral distortion units according to claim 1, 2 or 3, characterized in that: In the same chiral unit, the distance between two adjacent elastic rods is greater than or equal to the diameter of the elastic rod.

6. A metamaterial structure based on independent chiral twisting units, characterized in that: A metamaterial cell comprising a plurality of metamaterial cells according to any one of claims 1 to 5; Each of the metamaterial cells is distributed in a two-dimensional planar array, a three-dimensional multilayer array or a three-dimensional skeleton configuration.

7. The metamaterial structure based on independent chiral twisting units according to claim 6, characterized in that: When the metamaterial cells are distributed in a two-dimensional planar array: The metamaterial cells are arrayed into a single-layer metamaterial structure on a two-dimensional plane, and the ring surfaces at the top and bottom layers of the single-layer metamaterial structure are respectively fixed or integrally formed on the same flat plate, but the central ring surfaces of the metamaterial cells are independent of each other.

8. The metamaterial structure based on independent chiral twisting units according to claim 7, characterized in that: When the metamaterial cells are distributed in a three-dimensional multilayer array, the metamaterial structure is formed by stacking a plurality of single-layer metamaterial structures in a vertical direction.

9. The metamaterial structure based on independent chiral twisting units according to claim 6, 7 or 8, characterized in that: When the metamaterial cells are distributed in a three-dimensional skeleton configuration, the metamaterial cells are connected to form a spatial skeleton of a polyhedral structure, and the nodes of the spatial skeleton are block structures.

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