Three-dimensional curved surface concave hexagonal negative Poisson's ratio lattice structure

Abstract

The invention discloses a three-dimensional curved surface concave hexagonal negative Poisson's ratio lattice structure which comprises a plurality of basic cell elements, each basic cell element comprises two concave hexagonal units which are orthogonalized along a central axis, and each concave hexagonal unit comprises two spaced horizontal supports and two side supports. The two ends of the two horizontal supports are connected through the side face supports so that a cavity can be defined in the inwards-concave hexagonal unit, the two horizontal supports located at the same end of the basic cell element are arranged in a crossed mode, the two horizontal supports are arranged in a coplanar mode, and the middles of the two side face supports are sunken towards the direction of the cavity. And a bending line is formed on the side bracket and is parallel to the horizontal bracket. The lattice structure is arranged through mutual connection of the basic cell elements, and when the lattice structure is axially compressed, the lattice structure can be integrally and transversely shrunk, so that the lattice structure is more and more compact, and the lattice structure has better capacity of resisting compression bearing.

Description

Technical Field

[0001] This invention relates to the field of metamaterial structure technology, specifically a three-dimensional concave negative Poisson's ratio lattice structure. Background Technology

[0002] Mechanical / metamaterial structures refer to artificial materials with extraordinary mechanical properties, such as low density and high modulus, negative Poisson's ratio, and modulated elastic waves. Typical structures include two-dimensional honeycomb structures, three-dimensional lattice structures, and origami structures. In particular, lattice metamaterial structures with lightweight, high stiffness, and high strength have been widely used, providing important structural design solutions for industrial systems such as aerospace, shipbuilding, high-speed rail, and automobiles.

[0003] Energy-absorbing materials, as a new type of material with broad application prospects, have high strength, deformability and energy absorption capacity. When subjected to external forces such as collision, impact and vibration, they can convert external energy into heat energy or other forms of energy through internal plastic deformation, fracture and friction mechanisms, thereby reducing the degree of damage to the structure caused by external forces and protecting the safety of people and engineering equipment.

[0004] Generally, materials exhibit lateral contraction and expansion under tension and compression, while negative Poisson's ratio materials show the opposite behavior: they undergo lateral collision under tension and lateral contraction under compression. Meanwhile, novel artificial negative Poisson's ratio materials are emerging, such as rhombic honeycomb, chiral structures, and rotated polygonal structures. Most of these are based on two-dimensional planes, while the latter utilizes various transformations to extend to three-dimensional space, forming lattice structures. However, these negative Poisson's ratio materials exhibit low modulus and low strength. Summary of the Invention

[0005] The purpose of this invention is to provide a three-dimensional concave hexagonal negative Poisson's ratio lattice structure. When subjected to axial compression, the lattice structure contracts laterally, making it increasingly dense and thus exhibiting better resistance to compressive loads.

[0006] To achieve the above objective, a three-dimensional curved surface concave hexagonal negative Poisson's ratio lattice structure is provided, comprising: a plurality of basic cells, each basic cell including two concave hexagonal units orthogonalized along a central axis; each concave hexagonal unit including two spaced-apart horizontal supports and two side supports; the two ends of the two horizontal supports are connected by the side supports to form a cavity within the concave hexagonal unit; the two horizontal supports located at the same end of the basic cell are arranged in a cross shape and are coplanar; the middle portions of the two side supports are recessed towards the cavity to form a bending line on the side supports, the bending line being parallel to the horizontal supports.

[0007] As a further improvement of the present invention, the side support is curved into a curved support, the curved support including a first curved support and a second curved support located on both sides of the bending line, the centers of the first curved support and the second curved support are arranged in opposite directions.

[0008] As a further improvement of the present invention, both the horizontal support and the side support are plates, or both the horizontal support and the side support are elastic rods.

[0009] As a further improvement of the present invention, the basic cell has multiple layers, and the basic cells of two adjacent layers share a horizontal support.

[0010] As a further improvement of the present invention, the multi-layered basic cells form cell groups, and there are multiple cell groups arranged in a row and column manner. At least one basic cell is connected between two adjacent cell groups to form a lattice structure. The basic cell connected between the two adjacent cell groups is a first basic cell. The two ends of the two horizontal supports of the first basic cell are connected to the bending lines of the two cell groups. The side supports located on both sides of the bending lines in the vertical direction are the first side support and the second side support, respectively. The second side support of the cell group is the first side support of the first basic cell.

[0011] As a further improvement of the present invention, the concave hexagonal unit is formed by 3D printing and extrusion molding.

[0012] As a further improvement of the present invention, the relative density of the concave hexagonal unit is between 9% and 20%.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. This invention provides a lattice structure with a negative Poisson's ratio effect that has a curved surface that can resist impact and absorb high energy. When subjected to axial compression, the structure will also shrink laterally and become more and more compact. Due to the certain curvature of the sides, it has a good ability to resist compressive load.

[0015] 2. Compared with existing porous lattice materials, this negative Poisson's ratio lattice structure has a smaller relative density and is not fully covered (there will be gaps between cells), so the relative density of the overall lattice structure is smaller than that of a single cell, which further reduces the weight and increases the distance to achieve the densification of the structure.

[0016] 3. The elastic properties, compressive strength, and energy absorption characteristics of this negative Poisson's ratio lattice structure are all controllable. By adjusting the proportions of various geometric parameters (such as l1 and l2, b and t, etc.) or the angle between the horizontal wall and the side wall, the relative density of the entire structure can be changed, thus controlling its various mechanical properties over a wide range. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the concave hexagonal unit in this invention;

[0018] Figure 2 This is a schematic diagram of the structure of the concave hexagonal unit in another embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the orthogonalized basic cell structure in this invention;

[0020] Figure 4 This is a top view of the 3x3 region of the lattice structure in this invention;

[0021] Figure 5 This is an overall schematic diagram of the lattice structure in this invention;

[0022] Figure 6 for Figure 5 Enlarged view of point A in the middle;

[0023] Figure 7 This is a schematic diagram of the basic cell element in this invention, where the concave hexagonal unit is an elastic rod;

[0024] Figure 8 This is a schematic diagram illustrating the quasi-static compression simulation of the YZ surface of the three-dimensional curved surface with curvature K0 in this invention, showing the changes in the concave negative hexagonal Poisson's ratio lattice structure.

[0025] Figure 9 This is a schematic diagram illustrating the quasi-static compression simulation of the YZ surface change of the three-dimensional curved surface concave negative hexagonal Poisson's ratio lattice structure with curvature K0.0625 in this invention.

[0026] Figure 10 This is a schematic diagram illustrating the quasi-static compression simulation of the YZ surface change of the three-dimensional curved surface concave negative hexagonal Poisson's ratio lattice structure with curvature K0.125 in this invention.

[0027] Figure 11 This is a schematic diagram of the nominal stress-nominal strain curves of three three-dimensional curved concave negative hexagonal Poisson's ratio lattice structures in this invention under different curvatures (K0, K0.0625, K0.125);

[0028] Figure 12This is a schematic diagram of the quasi-static compression simulation specific energy absorption curves of the three-dimensional concave negative hexagonal Poisson's ratio lattice structure (3D-PLS) and the three-dimensional curved surface concave negative Poisson's ratio lattice structure (3D-CPLSⅠ,Ⅱ) in this invention.

[0029] In the figure: 1. Concave hexagonal unit; 11. Horizontal support; 12. Side support; 121. First side support; 122. Second side support; 13. Curved support; 131. First curved support; 132. Second curved support; 14. Bending line; 15. Cavity; 16. Elastic rod; 2. Basic cell; 3. Cell group; 4. First basic cell; 5. Lattice structure. Detailed Implementation

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] like Figures 1 to 12 As shown, to achieve the above objective, this invention proposes a three-dimensional curved surface concave hexagonal negative Poisson's ratio lattice structure, comprising multiple basic cells 2, which can be connected to form a lattice structure 5. Each basic cell 2 includes two concave hexagonal units 1 orthogonalized along a central axis. The central axis is the central axis of the basic cell 2. Each concave hexagonal unit 1 includes two spaced-apart horizontal supports 11 and two side supports 12. The two ends of the two horizontal supports 11 are connected by the side supports 12 to create a cavity 15 within the concave hexagonal unit 1. The two horizontal supports 11 located at the same end of the basic cell 2 are arranged in a cross shape, and the two horizontal supports 11 at the same end of the two concave hexagonal units 1 are coplanar.

[0032] Both side supports 12 are recessed in the middle towards the cavity 15. The concave hexagonal unit 1 is a hexagon that is recessed towards the cavity 15. After the two side supports 12 are recessed towards the cavity 15, a bending line 14 is formed on the side supports 12, which is parallel to the horizontal support 11. When the material is subjected to axial compression along the Z-axis, since the side supports 12 along the X and Y axes are pre-bent during the design process, after the elastic stage, they enter the plastic strengthening stage. The deformation of the side supports 12 will further deform towards the pre-bent shape, eliminating the process of the concave hexagonal side cell wall deforming from straight to curved in related technologies, thus having better compressive strength and energy absorption capacity.

[0033] Two identical concave hexagonal units 1 are orthogonalized along the central axis to form a basic cell 2. The upper and lower horizontal supports 11 of the two concave hexagonal units 1 are cross-shaped, and the entire basic cell 2 is a whole with a large reserved deformation space in the middle. Then, multiple basic cells 2 are connected to form a lattice structure 5. When the lattice structure 5 is subjected to axial compression, the two side supports 12 will shrink towards the cavity 15, that is, the whole will shrink laterally, making the lattice structure 5 more and more dense, thus having a better ability to resist compressive load.

[0034] Figure 2 As shown, the side support 12 is curved into a curved support 13. The curved support 13 includes a first curved support 131 and a second curved support 132 located on both sides of the bending line 14. The centers of the first curved support 131 and the second curved support 132 are arranged in opposite directions, that is, the center of the first curved support 131 is arranged towards the cavity 15, and the center of the second curved support 132 is arranged towards the outside of the cavity 15; or, the center of the first curved support 131 is arranged towards the outside of the cavity 15, and the center of the second curved support 132 is arranged towards the cavity 15.

[0035] The curvatures of the first curved support 131 and the second curved support 132 are equal. By changing the curvature of the side support 12 of the basic cell 2, the relative density of the basic cell 2 is affected, thereby changing the energy absorption effect of the energy-absorbing metamaterial.

[0036] The side support 12 is curved, and a new geometric parameter curvature is introduced to obtain the basic cell 2 that makes up the lattice structure 5. Two identical curved concave hexagonal units 1 are orthogonalized along the central axis to form the basic cell 2. Since the side of the basic cell 2 has a certain curvature, when the lattice structure 5 is subjected to axial compression, the side support 12 of the basic cell 2 can provide better support, so that the lattice structure 5 has a better ability to resist compressive load.

[0037] Figures 1-3 As shown, both the horizontal support 11 and the side support 12 are plates, which makes the processing of the basic cell 2 simpler.

[0038] Figure 7 As shown, or, the horizontal support 11 and the side support 12 are both elastic rods 16, serving as cylindrical structures capable of withstanding large deformations such as compression, bending, and torsion. These include, but are not limited to, soft rubber rods, helical springs, carbon nanotubes, and fiber-reinforced rods. Compared to a plate, this design results in a smaller volume for the basic cell 2 and a larger deformation space for the material. In situations where the material needs to resist large deformations, it can withstand greater compression, and in cases of small deformations, the elastic rods 16 can return to their original state when unloaded.

[0039] By changing the shape of the basic cell 2 (plate, elastic rod 16), the overall energy absorption capacity of the energy-absorbing metamaterial can be changed.

[0040] like Figures 4-6 The diagram shows a metamaterial lattice structure 5 of the present invention, which is composed of a three-dimensional curved surface concave hexagonal negative Poisson's ratio lattice structure. The side supports 12 located on both sides of the bending line 14 in the vertical direction are respectively the first side support 121 and the second side support 122, which are composed of two horizontal supports 11, two first side supports 121 and two second side supports 122. Figure 3 As shown, the lengths of the two horizontal supports 11 are l1 = 20 mm, the lengths of the first side support 121 and the second side support 122 are both l2 = 8 mm, the thickness of the basic cell 2 is t = 1 mm, when the horizontal supports 11 and the side supports 12 are plates, the width of the basic cell 2 is b = 6 mm, when the horizontal supports 11 and the side supports 12 are elastic rods 16, the diameter of the elastic rods 16 is D = 1 mm, the angle between the first side support 121 and the horizontal support 11 is θ, the angle between the second side support 122 and the horizontal support 11 is also θ, θ = 60°, and the curvature of the side plate support is K = 0.125.

[0041] The basic cell 2 has multiple layers. The basic cells 2 of adjacent layers share a horizontal support 11. They are orthogonalized by two concave hexagonal units 1, and each orthogonalized concave hexagonal unit 1 is connected by the shared horizontal support 11, so that each face forms a stable local resonance cell body connected with other faces. All cells form a whole, which not only improves the compressive, tensile and shear strength of the whole structure, but also increases the vibration reduction and energy absorption effect.

[0042] For example, both the horizontal support 11 and the side support 12 are plates, and two adjacent basic cells 2 share a horizontal plate.

[0043] For example, both the horizontal support 11 and the side support 12 are elastic rods 16, and two adjacent basic cells 2 share an elastic horizontal rod.

[0044] Multiple basic cells 2 form cell groups 3. These cell groups 3 are arranged in a row-and-column pattern. At least one basic cell 2 connects two adjacent cell groups 3. This connection can be either one basic cell 2 or two basic cells 2 connected between adjacent cell groups 3. The two basic cells 2 are stacked vertically and share a horizontal support 11. These multiple cell groups 3 arranged in a row-and-column pattern form a lattice structure 5. The basic cell 2 connecting two adjacent cell groups 3 is the first basic cell 4. The two ends of the two horizontal supports 11 of the first basic cell 4 are connected to the bending lines 14 of the two cell groups 3. The side supports 12 located on both sides of the bending lines 14 in the vertical direction are the first side support 121 and the second side support 122, respectively. The second side support 122 of the cell group 3 is the first side support 121 of the first basic cell 4.

[0045] In the lattice structure 5, two adjacent basic cells 2 share the upper and lower horizontal supports 11, and two adjacent basic cells 2 share the side supports 12. They present a dense pattern on the plane. From the top view, the entire structure can be seen to be arranged in a mesh, so that each face of the basic cell 2 forms a stable local resonant cell body connected with other faces. All basic cells 2 form a whole, which not only improves the compressive, tensile, and shear strength of the entire lattice structure 5, but also increases the vibration reduction and energy absorption effect.

[0046] The concave hexagonal unit 1 is formed using 3D printing and extrusion molding processes. These processes include FDM (Fused Deposition Modeling), EBM (Electron Beam Molding), SLM (Selective Laser Melting), SLA (Stereolithography), and SLS (Selective Laser Sintering). To ensure compatibility with these manufacturing methods, the selected aluminum alloy must possess good laser absorption or hot workability, avoiding the risk of cracking due to excessive amounts of high-alloying elements such as zinc and chromium. Compared to other alloys like titanium alloys, using aluminum alloys significantly reduces costs. Furthermore, the processing equipment is more versatile, suitable for mass production to meet the needs of various consumer scenarios.

[0047] Based on the above principles, 6061 aluminum alloy from the 6-series was selected. It uses magnesium and silicon as the main alloying elements, possessing both strength and ductility. Its main parameters are as follows: density (2700 kg / m³). 3 The core manufacturing processes for aluminum alloy plate-shaped cells are 3D printing (SLM selective laser melting, suitable for complex concave structures) and extrusion + bending forming. The parameters are: elastic modulus (70 GPa), yield strength (276 MPa), Poisson's ratio (0.3), and hardness (≥95 HB).

[0048] Figures 8-10As shown, Ls-Dyna was used to perform a quasi-static compression simulation of the arrayed 3×3×5 lattice structure 5 along the negative Z-axis. The size of the basic cell 2 is similar to... Figure 1 The same applies in the middle. It can be seen that on the sides (ZX and ZY planes) of the overall lattice structure 5, the lattice structure 5 contracts inward after being compressed, maintaining good negative Poisson's ratio characteristics, and the compression deformation mode in both directions is the same (structural symmetry).

[0049] Figure 11 As shown, the nominal stress and nominal strain curves of the structure under different conditions were obtained through quasi-static compression simulation. It can be seen from the curves that as K gradually increases from 0, the bearing capacity becomes stronger and stronger. The lattice structure 5 has a longer densification strain and absorbs more energy.

[0050] Figure 12 As shown, the specific energy absorption diagrams of three structures, 3D-PLS (K0), 3D-CPLSⅠ (K0.0625), and 3D-CPLSⅡ (K0.125), are presented. It can be seen that the specific energy absorption increases with the increase of K.

[0051] Under several major curvature K values, other geometric parameters and their ratios can be further adjusted to form concave negative Poisson's ratio lattice structures with various relative densities, so as to control and find the optimal geometric numerical distribution to improve the mechanical properties of the corresponding structure, such as strength, energy absorption efficiency and specific energy absorption.

[0052] The relative density of the concave hexagonal unit 1 is between 9% and 20%. The lattice structure 5 has a very low relative density, which can be maintained at around 10% within the allowable range of various parameters (l1, l2, t, b, θ, K). However, for the sake of overall material lightweighting and compressibility, the maximum relative density should not exceed 20%. The basic cell 2 of the lattice structure 5 has a relatively low relative density, and there are gaps between the basic cells 2, making the relative density of the overall lattice structure 5 even lower than that of a single basic cell 2, further reducing weight and increasing the range for achieving structural compaction.

[0053] In some implementations, different materials can be selected depending on the specific application scenario. For example, aluminum alloy can be used as the base material for plate-shaped basic cells to meet the "synergistic requirements of structure for strength, lightweight, and forming process." The density of aluminum alloy is 2600–2800 kg / m³. 3 With a weight lower than most alloy materials, metamaterials can further reduce their overall weight, making them suitable for applications requiring lightweighting, such as automotive and aerospace. Furthermore, metamaterials need to balance both compressive strength and plastic deformation capacity. They must meet the requirements for buckling resistance to prevent premature structural fracture or breakage, while also possessing a certain elongation to ensure energy absorption through plastic deformation during impact.

[0054] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A three-dimensional curved in-plane concave hexagonal negative Poisson's ratio lattice knot characterized in that, The application relates to a kind of lattice structures, comprising: A plurality of basic cells (2), the basic cell (2) includes two inner recessed hexagonal units (1) along the central axis orthogonalization, the inner recessed hexagonal unit (1) includes two spaced apart horizontal supports (11) and two side supports (12), two ends of two horizontal supports (11) are connected by side support (12) respectively, to form a cavity (15) in the inner recessed hexagonal unit (1), two horizontal supports (11) at the same end of the basic cell (2) are arranged in a cross, and two horizontal supports (11) are arranged in a plane, the middle part of two side supports (12) is recessed towards the direction of the cavity (15), to form a bending line (14) on the side support (12), the bending line (14) is parallel to the horizontal support (11).

2. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure of claim 1, wherein, The side support (12) is curved into a curved support (13), the curved support (13) includes a first curved support (131) and a second curved support (132) on both sides of the bending line (14), the centers of the first curved support (131) and the second curved support (132) are arranged in opposite directions.

3. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure of claim 2, wherein, The horizontal support (11) and the side support (12) are both plate bodies, or the horizontal support (11) and the side support (12) are both elastic rods (16).

4. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure according to claim 1 or 2, characterized in that, The basic cell (2) is provided with multiple layers, and the basic cell (2) of adjacent two layers shares a horizontal support (11).

5. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure of claim 4, wherein, A plurality of basic cells (2) form a cell group (3), the cell group (3) is provided with a plurality of cell groups (3) and is arranged in a matrix, and at least one basic cell (2) is connected between adjacent two cell groups (3) to form a lattice structure (5), the basic cell (2) connected between the adjacent two cell groups (3) is a first basic cell (4), two ends of two horizontal supports (11) of the first basic cell (4) are connected to the bending line (14) of two cell groups (3), the side support (12) on the upper and lower sides of the bending line (14) is a first side support (121) and a second side support (122) respectively, and the second side support (122) of the cell group (3) is the first side support (121) of the first basic cell (4).

6. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure of claim 1 or 2, wherein, The inner recessed hexagonal unit (1) is processed by 3D printing and extrusion molding process.

7. The three-dimensional curved in-plane concave hexagonal negative Poisson’s ratio lattice structure according to claim 1 or 2, characterized in that, The relative density of the inner recessed hexagonal unit (1) is between 9% and 20%.

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