Star-shaped chiral negative Poisson's ratio structure

Abstract

The present invention provides a star-shaped chiral negative Poisson's ratio structure, which is formed by connecting a plurality of periodic units in an array arrangement in the horizontal and vertical directions; each of the periodic units includes a star-shaped structure and a four-chiral structure; the star-shaped structure includes four concave arrows; the four concave arrows are symmetrically arranged circumferentially and are connected in sequence to form a ring; the four-chiral structure is embedded and connected in the star-shaped structure; the four-chiral structure includes a ring and four inclined cell walls, one end of the inclined cell walls is tangent and connected to the ring, and the other end of the inclined cell walls is respectively connected to the vertexes of the concave arrows; the included angle between adjacent inclined cell walls is 90°. For the star-shaped chiral negative Poisson's ratio structure of the present invention, compared with the traditional structure, the mutual cancellation effect generated by the internal star-shaped structure and chiral structure during deformation endows the structure with stronger ability to resist external impacts.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and particularly to a star-shaped chiral negative Poisson's ratio structure. Background Art

[0002] With the continuous development of engineering technologies, traditional materials and structures are increasingly unable to meet the requirements of actual engineering applications. Traditional materials and structures usually have a positive Poisson's ratio. When compressed, their cross-sections increase, and when stretched, their cross-sections decrease. Lakes first manufactured auxetic materials through the heat treatment of polyurethane foam in 1987. Later, Evans et al. achieved the negative Poisson's ratio effect in the study of tetrafluoroethylene and named it auxetic materials. Compared with traditional positive Poisson's ratio structures, negative Poisson's ratio structures are a special type of metamaterial. When compressed, their cross-sections will shrink, which means that such structures have higher shear resistance, impact resistance, indentation resistance, and energy absorption capabilities. Currently, common negative Poisson's ratio structures include star-shaped honeycombs, chiral honeycombs, arrow-shaped honeycombs, and concave hexagonal honeycombs, etc.

[0003] Poisson's ratio refers to the ratio of the transverse strain to the longitudinal strain of a material when it is stretched or compressed, and can be expressed as ν=-ε x / ε y .

[0004] Traditional single concave structures such as star-shaped structures, etc., have a short stress plateau region, the honeycombs enter the densification stage prematurely, and their deformation stability is poor, resulting in poor performance of the structures in terms of compressive strength, specific energy absorption, etc.

[0005] The development of additive manufacturing technology has made it possible to manufacture honeycombs with complex topological structures. This has also promoted the research on the basic deformation mechanisms of honeycomb structures by researchers.

[0006] Common deformation mechanisms of negative Poisson's ratio structures: concave mechanism and curling mechanism. In order to overcome the shortcomings of traditional single negative Poisson's ratio structures, their deformation mechanisms can be combined and some design ideas such as mixing, overlapping, and hierarchical ideas can be used to design innovative structures with novel deformation mechanisms. The research in this field has important research significance for expanding the application scope of negative Poisson's ratio structures. Summary of the Invention

[0007] Aiming at the deficiencies in the above-mentioned prior art, the present invention provides a star-shaped chiral negative Poisson's ratio structure. Compared with traditional structures, the mutual cancellation effect generated by the internal star-shaped structure and chiral structure during deformation of this structure enables the structure to have stronger resistance to external impacts.

[0008] To achieve the above object, the present invention provides a star-shaped chiral negative Poisson's ratio structure, which is formed by connecting a plurality of periodic units in an array arrangement in the horizontal and vertical directions; each of the periodic units includes a star-shaped structure and a four-chiral structure; the star-shaped structure includes four concave arrows; the four concave arrows are symmetrically arranged circumferentially and are connected in sequence to form a ring; the four-chiral structure is embedded and connected within the star-shaped structure; the four-chiral structure includes a ring and four inclined cell walls, one end of the inclined cell walls is tangent and connected to the ring, and the other end of the inclined cell walls is respectively connected to the vertices of the concave arrows;

[0009] The included angle between adjacent inclined cell walls is 90°; the structures and sizes of the concave arrows are the same; the included angle θ between the inclined cell walls and the vertical direction is less than 45°; the diameter of the ring is less than the distance between the vertices of two relatively concave arrows in the star-shaped structure.

[0010] Preferably, the periodic units are periodically arranged in a two-dimensional plane to form a novel two-dimensional negative Poisson's ratio structure.

[0011] Preferably, the thickness t of all cell walls of the star-shaped chiral negative Poisson's ratio structure is the same.

[0012] Preferably, the cross-sections of all cell walls of the star-shaped chiral negative Poisson's ratio structure are T-shaped, I-shaped, groove-shaped, box-shaped or polygonal, where the polygon includes a rectangle, triangle, rhombus, circle, ellipse or trapezoid.

[0013] Preferably, it is prepared by 3D printing technology.

[0014] Preferably, the material is metal or plastic.

[0015] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0016] The present invention is formed by connecting a plurality of periodic units in an array arrangement in the horizontal and vertical directions, and each periodic unit includes a star-shaped structure and a four-chiral structure; this structure has better energy absorption ability compared with the traditional structure. When the structure is subjected to in-plane quasi-static compression, the stress-strain curve presents two different plateau stages: in the first plateau stage, the vertical cell walls first undergo bending deformation. Until the vertical cell walls and the inclined cell walls come into contact, the thickness of some cell walls of the structure becomes 2t, and the stress value in this stage is relatively low; in the second plateau stage, it is mainly the bending deformation of the cell walls of the star-shaped structure and the rotational contraction deformation of the chiral structure. The stress value in this stage increases significantly, which can greatly increase the energy absorption ability of the structure; finally, the structure is crushed.

[0017] The impact energy absorption characteristics of this structure are controllable. Different impact energy absorption characteristics can be obtained by adjusting the slenderness ratio of the cell wall, the angle between the inclined side of the star structure and the vertical direction, and the radius of the circular ring. In addition, the impact energy absorption characteristics are also related to the impact velocity. Description of the Drawings

[0018] Figure 1 Schematic diagram of the star-shaped chiral negative Poisson's ratio structure according to an embodiment of the present invention;

[0019] Figure 2 Schematic diagram of the structure of the periodic unit according to an embodiment of the present invention;

[0020] Figures 3 to 8 Schematic diagram of the deformation process of the star-shaped chiral negative Poisson's ratio structure according to an embodiment of the present invention during in-plane quasi-static compression;

[0021] Figure 9 Comparison diagram of stress-strain curves of the two-dimensional structure according to an embodiment of the present invention, the classical four-chiral structure and the star structure under quasi-static compression under the condition of the same relative density;

[0022] Figure 10 Comparison diagram of specific energy absorption of the two-dimensional structure according to an embodiment of the present invention and the classical four-chiral honeycomb structure under quasi-static compression under the condition of the same relative density;

[0023] Figure 11 Comparison diagram of the absorbed energy of the two-dimensional structure according to an embodiment of the present invention and the classical four-chiral honeycomb structure under quasi-static compression under the condition of the same relative density;

[0024] Figure 12 Poisson's ratio-strain diagram of the star-shaped chiral negative Poisson's ratio structure according to an embodiment of the present invention. Detailed Embodiments

[0025] The following is based on the drawings Figures 1 to 12 , and the preferred embodiments of the present invention are given and described in detail to better understand the functions and features of the present invention.

[0026] Please refer to Figures 1 to 2 , a star-shaped chiral negative Poisson's ratio structure according to an embodiment of the present invention is formed by arranging and connecting a plurality of periodic units 1 in an array in the horizontal and vertical directions; each periodic unit 1 includes a star structure 2 and a four-chiral structure 3; the star structure 2 includes four concave arrows 21; the four concave arrows 21 are symmetrically arranged circumferentially and are connected in sequence to form a ring; the four-chiral structure 3 is embedded and connected in the star structure 2; the four-chiral structure 3 includes a circular ring 31 and four inclined cell walls 32, one end of the inclined cell wall 32 is tangent to and connected to the circular ring 31, and the other end of the inclined cell wall 32 is respectively connected to the vertex of the concave arrow 21;

[0027] The included angle between adjacent inclined cell walls 32 is 90°; the structures and dimensions of the concave arrows 21 are consistent; the included angle θ between the inclined cell wall 32 and the vertical direction is less than 45°; the diameter of the ring 31 is less than the distance between the vertices of two opposite concave arrows 21 in the star structure 2.

[0028] The periodic units 1 are periodically arranged in a two-dimensional plane to form a novel two-dimensional negative Poisson's ratio structure.

[0029] The slenderness ratio of the inclined cell wall 32, the included angle between the inclined cell wall 32 of the star structure 2 and the vertical direction, and the radius of the ring 31 can change the energy absorption characteristics of the structure. The thickness t of all cell walls of the star chiral negative Poisson's ratio structure is consistent.

[0030] The cross-sections of all cell walls of the star chiral negative Poisson's ratio structure are in the shape of T, I, groove, box or polygon, where the polygon includes rectangle, triangle, rhombus, circle, ellipse or trapezoid.

[0031] It is prepared by 3D printing technology.

[0032] The material is metal or plastic.

[0033] Please refer to Figures 2 to 12 , and quasi-static compression simulations of chiral, star and star chiral negative Poisson's ratio structures are carried out along the y direction. The dimensions of the periodic unit 1 are: L1 = L2 = 4 mm, L = 5 mm, R = 1 mm, θ = 30°. The out-of-plane thickness of the structure is the length of one grid unit and is set to 0.5 mm, and the cross-section is rectangular. The relative densities of the three structures are all 0.1. The periodic unit 1 of the present invention is arranged in parallel arrays in the x and y directions. The overall dimensions of these three structures are equal in the x and y directions and are both 117 mm. The stress-strain curve, specific energy absorption-strain curve, absorbed energy-strain curve, Poisson's ratio-strain curve after compression are shown in Figure 9 , 10 , 11, 12 respectively. It can be seen that the structure of the present invention has two platform stages during quasi-static compression in the y direction. The stress in the second platform stage is about 8 times that in the first platform stage, and compared with the other two negative Poisson's ratio structures, this structure has a longer densification strain, a higher platform stress, and absorbs more energy.

[0034] Specifically, when performing in-plane quasi-static compression on the structure, the stress-strain curve presents two different platform stages: in the first platform stage, the vertical cell wall first undergoes bending deformation until the vertical cell wall contacts the inclined cell wall 32 of the concave arrow 21, and the thickness of part of the cell wall of the structure becomes 2t. The stress value in this stage is relatively low, as shown in Figure 3 and Figure 4As shown; in the second platform stage, it is mainly the bending deformation of the star-shaped structure's two-cell wall and the rotational contraction deformation of the chiral structure. In this stage, the stress value increases significantly, which can greatly increase the energy absorption capacity of the structure, such as Figure 5 , 6 and as shown in 7; finally, the structure is crushed as Figure 8 shown.

[0035] The present invention has been described in detail above in combination with the embodiments in the drawings. Those of ordinary skill in the art can make various variations to the present invention according to the above description. Therefore, certain details in the embodiments should not constitute a limitation to the present invention, and the protection scope of the present invention will be defined by the scope defined in the appended claims.

Claims

1. A star-shaped chiral negative Poisson's ratio structure, characterized in that, It is formed by connecting a plurality of periodic units (1) in an array arrangement in the horizontal and vertical directions; each of the periodic units (1) includes a star structure (2) and a four-chiral structure (3); the star structure (2) includes four concave arrows (21); the four concave arrows (21) are symmetrically arranged circumferentially and are connected in sequence to form a ring; the four-chiral structure (3) is embedded and connected within the star structure (2); the four-chiral structure (3) includes a ring (31) and four inclined cell walls (32), one end of the inclined cell wall (32) is tangent to and connected to the ring (31), and the other end of the inclined cell wall (32) is respectively connected to the vertex of the concave arrow (21); the included angle between adjacent inclined cell walls (32) is 90°; the structures and sizes of the concave arrows (21) are the same; the included angle between the inclined cell wall of the concave arrow (21) and the vertical direction is less than 45°; the diameter of the ring (31) is less than the distance between the vertices of two opposite concave arrows (21) in the star structure (2).

2. The star-shaped chiral negative Poisson's ratio structure according to claim 1, characterized in that, The periodic unit (1) is arranged periodically in a two-dimensional plane to form a novel two-dimensional structure with negative Poisson's ratio.

3. The star-shaped chiral negative Poisson's ratio structure according to claim 1 or 2, characterized in that, All the cell wall thicknesses t of the star-shaped chiral structure with negative Poisson's ratio are consistent.

4. The star-shaped chiral negative Poisson's ratio structure according to claim 1 or 2, characterized in that, The cross-sections of all the cell walls of the star-shaped chiral structure with negative Poisson's ratio are in the shape of T, I, groove, box, circle, ellipse or polygon, where the polygon includes rectangle, triangle, rhombus or trapezoid.

5. The star-shaped chiral negative Poisson's ratio structure according to claim 1 or 2, characterized in that, It is prepared by 3D printing technology.

6. The star-shaped chiral negative Poisson's ratio structure according to claim 1 or 2, characterized in that, The material is metal or plastic.

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