A three-dimensional chiral negative Poisson's ratio material structure

Abstract

The present invention discloses a three-dimensional chiral negative Poisson's ratio material structure, comprising a plurality of sequentially connected basic unit cells, wherein the basic unit cell comprises a central sphere and first to sixth connecting rods, wherein one end of the first to sixth connecting rods is connected to the outer wall of the central sphere but is not tangent thereto, and the other ends of the first to sixth connecting rods extend outwards, and the projections of the basic unit cell on the three coordinate planes of the spatial rectangular coordinate system each have four connecting rods forming a counterclockwise or clockwise rotation around the central circle and uniformly distributed along the circumference of the central circle, and adjacent basic unit cells are interconnected by any of the first to sixth connecting rods to form an array arrangement. By designing connecting rods connected at special node positions of the sphere, a three-dimensional basic unit cell is formed, which greatly reduces the number of connecting rods required for the structure compared to a three-dimensional negative Poisson's ratio structure connected by stacking two-dimensional chiral structures. Due to the small number of connecting rods, the negative Poisson's ratio structure can withstand a large load and can achieve negative Poisson performance in a relatively wide strain range.

Description

Technical Field

[0001] The present invention relates to the manufacture of negative Poisson's ratio materials, and in particular to a three-dimensional chiral negative Poisson's ratio material structure. Background Art

[0002] Negative Poisson's ratio materials, also known as tensile materials, expand laterally under axial tensile loads (or contract laterally under axial compressive loads). This property enables negative Poisson's ratio metamaterials to possess properties superior to other materials in physics and mechanics, such as high shear stiffness, excellent impact resistance, high fracture resistance, indentation resistance, sound absorption, and variable permeability. These advantages hold great potential for applications in aerospace, architecture, biomedicine, textiles, and sound absorption and vibration reduction.

[0003] Due to the limitations of 2D cellular structures, researchers have focused on the study of three-dimensional negative Poisson's ratio units. For example, in the prior art "Predictions of Young's modulus and negative Poisson's ratio of auxetic foams." Physica Status Solidi (b) 248.1 (2011).", a calculation model for 3D negative Poisson's ratio was proposed. With the development of 3D printing technology, some metamaterial models can be produced through 3D printing, which has greatly promoted the development of 3D. Several 3D models based on 2D cellular structures have been proposed. For example, in the prior art "Mechanical properties of 3D re-entrant honeycomb auxetic structures realized via additive manufacturing." International Journal of Solids and Structures 69-70. (2015).", a 3D reentrant hexagonal cellular structure was proposed. These structures all use a large number of connecting rods, and multiple connecting rods share a single node, which results in limited connecting rod size, easy breakage, and limited load bearing capacity. Summary of the Invention

[0004] Purpose of the invention: In view of the above shortcomings, the present invention provides a three-dimensional chiral negative Poisson's ratio material structure that can withstand a large load.

[0005] Technical solution: To solve the above problems, the present invention adopts a three-dimensional chiral negative Poisson's ratio material structure, comprising a number of basic unit cells connected in sequence, wherein the basic unit cell comprises a central sphere and first to sixth connecting rods, wherein one end of the first to sixth connecting rods is connected to the outer wall of the central sphere but is not tangent to the outer wall, and the other ends of the first to sixth connecting rods extend outward. The projections of the basic unit cell on the three coordinate planes of the spatial rectangular coordinate system all have four connecting rods forming a counterclockwise or clockwise rotation around the central circle and are evenly distributed along the circumference of the central circle. Adjacent basic unit cells are connected to each other through any first to sixth connecting rods to form an array arrangement.

[0006] Furthermore, the cross-sectional shapes of the first to sixth connecting rods are any one of circular, rectangular, or variable cross-sections. Of the four connecting rods projected from the basic unit cell onto a coordinate plane in a rectangular coordinate system, two opposing connecting rods are parallel to each other, and the vertical distance between the two connecting rods is equal to the radius of the sphere. The basic unit cell is 3D-printed. The central sphere is a hollow sphere.

[0007] Beneficial effect: Compared with the prior art, the significant advantage of the present invention is that it forms a three-dimensional basic unit cell through the design of connecting rods connected at special node positions of the sphere. Compared with the three-dimensional negative Poisson's ratio structure connected by stacking two-dimensional chiral structures, the number of connecting rods required for the structure is greatly reduced. Due to the smaller number of connecting rods and the fact that the connecting rods do not share common nodes, the connecting rods can be set thicker and less likely to break. They can withstand larger loads and can achieve negative Poisson performance within a wider strain range. Since the overall structural components are composed of basic square connecting rods and spherical cross-section connecting rods, the surface accuracy of the 3D printed model is higher. Since there are fewer connecting rods, it is more convenient to remove the printing support structure of the 3D printed model, making the preparation of the 3D model simpler and the yield rate higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Shown is a schematic structural diagram of a three-dimensional basic unit cell in the present invention;

[0009] Figure 2 FIG. 1 is a schematic diagram of a two-dimensional plane projection structure of a three-dimensional basic unit cell in the present invention;

[0010] Figure 3 The figure shows a schematic diagram of the 2*2*2 three-dimensional orthochiral material structure of the present invention;

[0011] Figure 4 Shown is a schematic diagram of the structure of a three-dimensional basic unit cell with different rod lengths in the present invention;

[0012] Figure 5 Shown is a schematic diagram of the three-dimensional basic unit cell structure of connecting rods of different thicknesses in the present invention;

[0013] Figure 6Shown is the three-dimensional chiral negative Poisson's ratio material structure obtained by 3D printing. DETAILED DESCRIPTION

[0014] like Figure 3 As shown, a three-dimensional chiral negative Poisson's ratio material structure in this embodiment includes a number of basic unit cells connected in sequence, such as Figure 1 As shown, the basic unit cell includes a sphere and the first to sixth connecting rods. The basic unit cell arranges the nodes connected to the connecting rods at specific positions (not end points) of the central sphere, and makes the connecting rods face the axial direction of stretching (not tangential). One end of the first to sixth connecting rods is connected to the outer wall of the hollow sphere but not tangentially, and the other ends of the first to sixth connecting rods extend outward, as shown in FIG. Figure 2 As shown, the projections of the basic unit cell onto the three coordinate planes of the spatial rectangular coordinate system each have four connecting rods arranged in a counterclockwise or clockwise direction around the central circle and evenly distributed along the circumference of the central circle. Adjacent basic unit cells are interconnected by any of the first through sixth connecting rods, forming an array arrangement. The tendency of the rigid nodes on the central sphere to move toward their right endpoints after being subjected to a tensile load drives the sphere to rotate. This rotation of each node produces a negative Poisson's ratio effect. Due to the unique node arrangement and minimal number of connecting rods, the negative Poisson's ratio structure in this embodiment can withstand significant loads.

[0015] The three-dimensional chiral structure in this embodiment is based on the 2D four-bar chiral structure, and is converted into a sphere through a central circle. Connecting rods are inserted at six nodes on the surface of the central body of the sphere that are not intersections of the coordinate axes along the six directions of the coordinate axes, and the vertical distances between the connecting rods and the coordinate axes are equal. That is, among the four connecting rods projected on a coordinate plane of the spatial rectangular coordinate system, the two opposite connecting rods are parallel to each other, and the vertical distance between the two connecting rods is equal to the radius of the sphere, thereby obtaining a basic three-dimensional chiral structure, the basic geometric shape of which is determined by five basic parameters: the inner diameter r and outer diameter R of the hollow sphere, the length l of the connecting rod, and the width b and thickness t of the connecting rod. The cross-sectional shape of the first to sixth connecting rods is any one of circular, rectangular, and variable cross-sections. In this embodiment, the connecting rod cross-section is set to be square, so b=t.

[0016] like Figure 3 As shown in Figure 1, by arranging the basic cell structure in an array and connecting two of them through the connecting rod cross-section of the basic unit cells, a chiral model can be obtained. Assuming that the number of unit cells on each side of the model is n, m, and k, respectively, this model is defined as a chiral model of n*m*k cells. The minimum repeating unit of the chiral model is a basic unit cell.

[0017] 3D chiral negative Poisson's ratio metamaterials exhibit different negative Poisson's ratio effects when subjected to tensile and compressive loads at different geometric sizes. For the negative Poisson's ratio chiral cell structure with a square cross-section connecting rod in this embodiment, there are three geometric parameters that determine the magnitude of the negative Poisson's ratio: the connecting rod length L, the spherical central body radius R, and the connecting rod cross-sectional width W. The spherical central body radius R is set to a constant value, such as Figure 4 As shown in , by changing the value of the connecting rod length L, the basic cell model with different L / R can be obtained, as Figure 5 As shown in the figure, by changing the value of the connecting rod cross-section width, basic cell models with different W / R can be obtained. The basic cell models with different size parameters are arranged in an array to obtain positive chirality models with different load bearing capacities.

[0018] The three-dimensional negative Poisson's ratio structure in this embodiment can be prepared by photosensitive resin laser 3D printing and obtained by removing the support.

Claims

1. A three-dimensional chiral negative Poisson's ratio material structure, characterized in that: The invention comprises a plurality of basic unit cells connected in sequence, wherein the basic unit cell comprises a central sphere and first to sixth connecting rods, wherein one end of the first to sixth connecting rods is connected to the outer wall of the central sphere but is not tangent thereto, and the other ends of the first to sixth connecting rods extend outward, and the projections of the basic unit cell on the three coordinate planes of the spatial rectangular coordinate system each have four connecting rods that rotate counterclockwise or clockwise around the central circle and are evenly distributed along the circumference of the central circle, and adjacent basic unit cells are connected to each other through any first to sixth connecting rods to form an array arrangement; among the four connecting rods projected on one coordinate plane of the spatial rectangular coordinate system, two opposite connecting rods are parallel to each other, and the vertical distance between the two connecting rods is equal to the radius of the sphere.

2. The three-dimensional chiral negative Poisson's ratio material structure according to claim 1, characterized in that: The cross-sectional shapes of the first to sixth connecting rods are any one of circular, rectangular, and variable cross-sectional shapes.

3. The three-dimensional chiral negative Poisson's ratio material structure according to claim 1, characterized in that: The basic unit cell adopts a 3D printing structure.

4. The three-dimensional chiral negative Poisson's ratio material structure according to claim 1, characterized in that: The central sphere is a hollow sphere.

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