Functional gradient star-shaped inverse four-chiral negative Poisson's ratio structure

Abstract

A unit cell of the structure is formed by combining an axisymmetric star-shaped structure and four ligaments extending outwards along the star-shaped tip in a mirror image mode in the horizontal direction and the vertical direction, and the geometric dimensions of the unit cell are the length L1 and L2, the width t1 and t2 and the included angle theta 1 respectively. Firstly, unit cells are transversely arrayed along the horizontal center line of the structure to form a 1 * n substructure. And then, carrying out longitudinal array on the 1 * n substructures along the vertical center line of the structure, and carrying out gradient change (increasing or decreasing) on the thickness (or angle) of the 1 * n substructures, so that the 1 * n substructures are arrayed into the functionally gradient star-shaped inverse four-chiral negative Poisson's ratio structure with m * n gradient unit cells. According to the functionally gradient star-shaped anti-tetrachiral negative Poisson's ratio structure, the thickness (or angle) of the 1 * n substructure can be changed by changing the geometric dimension of a unit cell and changing the gradient, so that the structure has excellent mechanical property and energy absorption capacity.

Description

Technical Field

[0001] The invention belongs to the field of metamaterials, and in particular relates to a functionally gradient star-shaped anti-four-chirality negative Poisson's ratio structure. Background Art

[0002] Since the beginning of the 21st century, metamaterials have gradually developed into an indispensable part of the field of new material technology. Mechanical metamaterials are new materials that do not exist in nature by artificially changing the internal structure of the material. Such materials can generally achieve different mechanical properties. Mechanical metamaterials play a vital role in aerospace, biomedicine, energy power, transportation and other fields because of their outstanding advantages in acoustics, optics, heat conduction, energy absorption and consumption.

[0003] Negative Poisson's ratio metamaterial is a special mechanical metamaterial that has the opposite performance to the positive Poisson's ratio metamaterial. At present, most of the materials commonly found in nature are positive Poisson's ratio materials, that is, when the material (or structure) is subjected to axial tension (or compression), it has the mechanical property of contraction (or expansion) in the vertical direction, such as Figure 1 (a) shows. When a negative Poisson's ratio material (or structure) is subjected to axial tension (or compression), it has the mechanical property of expansion (or contraction) in the vertical direction. It is also called tensile material. Figure 1 (b) as shown.

[0004] Negative Poisson's ratio metamaterials show superiority in different aspects, including impact resistance, fracture resistance, energy absorption and vibration isolation, variable permeability, surface isotropy, etc. Negative Poisson's ratio metamaterials are increasingly widely used in aerospace, shipbuilding, biomedicine and other fields.

[0005] According to the different deformation mechanisms, negative Poisson's ratio metamaterials can be divided into: chiral structure, concave (star-shaped) honeycomb structure, double-arrow structure, rotating rigid body structure, etc.

[0006] If an object cannot be reconstructed with its mirror image through rotation and translation alone, it is called a chiral structure. Many chiral structural features are often found in natural materials and plants and animals in nature, such as shells, spiral goat horns, vines entwined in the forest, spiral tendrils of loofahs, etc.

[0007] The chiral structure is a honeycomb topology composed of rigid circular rotating bodies and tangential connecting ligaments. If the two circular rings connected by the tangential ligaments are located on both sides of the ligament, it is called a chiral structure. If the two circular rings connected by the tangential ligaments are located on the same side of the ligament, it is called an anti-chiral structure. According to the number of ligaments connected to each circular ring, it can be divided into five types: chiral / anti-chiral three-ligament (anti-trichirality), chiral / anti-chiral four-ligament (anti-tetrachirality), and chiral six-ligament superstructure. Summary of the invention

[0008] The present invention combines the traditional star-shaped honeycomb structure and the anti-quadrichirality structure, and proposes a star-shaped anti-quadrichirality negative Poisson's ratio structure with a functional gradient, which has excellent energy absorption capacity and negative Poisson's ratio effect. The unit cell geometric parameters and the gradient change of the thickness (or angle) of each row (or column) of the structure have an important influence on the mechanical properties of the overall structure.

[0009] The present invention is achieved through the following technical solutions:

[0010] A further improvement is that the functionally gradient star-shaped anti-quadrucilar negative Poisson's ratio structure is made of metal, nylon, polylactic acid, thermoplastic polyurethane, high elastic material or carbon fiber composite material, and can be prepared by 3D printing technology.

[0011] A further improvement is that the functional gradient star-shaped anti-quadruple-chirality negative Poisson's ratio structure is formed by a plurality of periodic unit cells arranged in a horizontal direction, and then the thickness (or angle) is changed gradiently in a vertical direction and connected in an array. Each of the periodic unit cells is a star-shaped anti-quadruple-chirality structure, and a quarter structure thereof is composed of an axisymmetric star-shaped structure and four ligaments extending outward from the tip of the star-shaped structure, and the unit cell of the functional gradient star-shaped anti-quadruple-chirality negative Poisson's ratio structure is composed of the above quarter structures mirrored in the horizontal and vertical directions.

[0012] A further improvement is that the combination process of the functional gradient star-shaped anti-four-chirality negative Poisson's ratio structure is as follows. First, a star-shaped anti-four-chirality negative Poisson's ratio unit cell is arrayed horizontally along the horizontal center line of the structure to form a 1×n partial substructure. Secondly, the above 1×n partial substructure is arrayed vertically along the vertical center line of the structure, and the thickness (or angle) of the 1×n star-shaped anti-four-chirality negative Poisson's ratio unit cells is gradiently changed (increased or decreased) to form a functional gradient star-shaped anti-four-chirality negative Poisson's ratio structure with m×n unit cells.

[0013] The further improvement is that the geometric dimensions of the functional gradient star-shaped anti-quadruple-chiral negative Poisson's ratio structure are: the axisymmetric star-shaped structure is composed of a side length L 1 , angle θ 1 and width t 1 The four external extension ligaments are composed of the same geometric dimensions and the length is L. 2 , width t 2 .

[0014] Further improvements are as follows: In the ABAQUS software pre-processing module, firstly, material parameters are set for the structure, the finite element mesh of the structure is divided, the analysis steps are set, the boundary conditions and load conditions are set, and the contact properties are set, so as to perform out-of-plane quasi-static compression simulation on the structure.

[0015] Further improvements are: using finite element ABAQUS simulation software to simulate the out-of-plane quasi-static compression of the functionally gradient star-shaped anti-quadrichiral negative Poisson's ratio structure, and obtaining the deformation process, stress-strain curve and specific energy absorption-strain curve of the functionally gradient star-shaped anti-quadrichiral negative Poisson's ratio structure under the action of in-plane quasi-static compression load.

[0016] A further improvement is that the mechanical properties and energy absorption of the functionally gradient star-shaped anti-quadrucilar negative Poisson's ratio structure under quasi-static compression load can be determined by adjusting the geometric dimensions of the unit cell and the gradient change of the thickness (or angle) of each row (or column).

[0017] The beneficial effects of the present invention are as follows: the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure of the present invention has good resistance to external impact and energy absorption capabilities, and the gradient changes in its structural geometric parameters and the thickness (or angle) of each row (or column) have an important influence on the overall mechanical properties of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the deformation mechanism of positive and negative Poisson's ratio materials under uniaxial tension.

[0019] Figure 2 This is a schematic diagram of the unit cell geometry of the functionally gradient star-shaped anti-quadrucilar negative Poisson's ratio structure in Example 1 of the present invention.

[0020] Figure 3 This is a schematic diagram of the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure according to Example 1 of the present invention changing with the thickness gradient.

[0021] Figure 4 This is a schematic diagram of the change of the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure with the angle gradient in Example 1 of the present invention.

[0022] Figure 5 This is the deformation process of the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure of Example 2 of the present invention when the structure changes with thickness under the action of a quasi-static compression load.

[0023] Figure 6 This is the deformation process of the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure of Example 2 of the present invention when the structure changes with the angle under the action of a quasi-static compression load.

[0024] Figure 7 This is the stress-strain curve of the functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure of Example 2 of the present invention when the structure changes with thickness and angle under quasi-static compression load.

[0025] Figure 8This is the specific energy absorption-strain curve of the functionally gradient star-shaped anti-quadrucilar negative Poisson's ratio structure of Example 2 of the present invention when the structure changes with thickness and angle under quasi-static compression load. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0027] Example 1

[0028] according to Figure 2 As shown, this embodiment provides a functional gradient star-shaped anti-four-chirality negative Poisson's ratio structure, wherein a quarter structure is composed of an axially symmetrical star-shaped structure and four ligaments extending outward from the tip of the star, and a unit cell of the functional gradient star-shaped anti-four-chirality negative Poisson's ratio structure is composed of the above-mentioned quarter structure mirrored in the horizontal and vertical directions.

[0029] according to Figure 3 As shown, this embodiment provides a star-shaped anti-four-chirality negative Poisson's ratio structure with a thickness gradient change. First, a star-shaped anti-four-chirality negative Poisson's ratio unit cell is arranged horizontally along the horizontal center line of the structure to form a 1×4 partial substructure. Secondly, the thickness of 1×4 star-shaped anti-four-chirality negative Poisson's ratio unit cells is gradiently changed so that the structural thickness of each column increases monotonically from 2mm to 5mm. Finally, the above-mentioned 4 rows of 1×4 partial substructures are longitudinally connected along the vertical center line of the structure to form a 4×4 star-shaped anti-four-chirality negative Poisson's ratio structure with an increasing thickness gradient.

[0030] according to Figure 4 As shown, this embodiment provides a star-shaped anti-four-chirality negative Poisson's ratio structure with angle gradient variation. First, a star-shaped anti-four-chirality negative Poisson's ratio unit cell is arranged horizontally along the horizontal center line of the structure to form a 1×4 partial substructure. Secondly, the angles of 1×4 star-shaped anti-four-chirality negative Poisson's ratio unit cells are gradient-changed so that the structural angle of each column increases monotonically from 20° to 50°. Finally, the above-mentioned 4 rows of 1×4 partial substructures are longitudinally connected along the vertical center line of the structure to form a 4×4 star-shaped anti-four-chirality negative Poisson's ratio structure with increasing angle gradient.

[0031] In one embodiment of the present invention, the base material of the functionally gradient star-shaped anti-quadrucistatic negative Poisson's ratio structure can be selected from metal, nylon, polylactic acid, thermoplastic polyurethane, high elastic material or carbon fiber composite material according to different functional requirements.

[0032] In one embodiment of the present invention, the functionally gradient star-shaped anti-quadrucilar negative Poisson's ratio structure is prepared by additive manufacturing technology (such as 3D printing).

[0033] Example 2

[0034] In the pre-processing module of ABAQUS finite element software, firstly, the material parameters of the structure are set, the structural finite element mesh is divided, the analysis step is set, the boundary conditions and load conditions are set, and the contact properties are set, so as to perform out-of-plane quasi-static compression simulation calculation on the structure.

[0035] The material parameters were set in the ABAQUS finite element simulation software, and nylon PA3300 was selected as the research object, with elastic modulus E = 830 MPa, Poisson's ratio μ = 0.33, and yield stress σ = 13 MPa.

[0036] according to Figure 5 As shown, this embodiment provides a deformation process of a functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure under a quasi-static compression load, in which the structure increases monotonically with the thickness. It can be seen that the deformation of the structure can be divided into three stages. In the initial stage, due to the small wall thickness of the upper structure (thickness 2mm), its star-shaped structure first rotates around the center and drives the cells as a whole to shrink toward the center, and the honeycomb exhibits a negative Poisson's ratio effect. As the strain increases, the upper star-shaped structure further rotates and contacts each other, and the lower star-shaped structure with a thicker wall (thickness 5mm) also begins to rotate, and the overall structure collapses layer by layer. Finally, the structure is densified, and the lower star-shaped structures further contact each other until the cell walls of the overall structure are completely compressed.

[0037] according to Figure 6 As shown, this embodiment provides a deformation process of a functionally gradient star-shaped anti-quadruciality negative Poisson's ratio structure under a quasi-static compression load, in which the structure monotonically increases with the angle. It can be seen that the deformation of the structure can be divided into three stages. In the initial stage, all the star-shaped structures in the structure rotate around the center, among which the rotation of the star-shaped structure at an angle of 20° in the upper part is more obvious, driving the overall structure to shrink toward the center, and the structure exhibits an obvious negative Poisson's ratio effect. With the increase of strain, all the star-shaped structures in the structure further rotate around the center, the peripheral ligaments of the star-shaped structures contact each other, and the overall structure collapses layer by layer. When the structure reaches the densification stage, the cell walls of the overall structure are completely compressed.

[0038] according to Figure 7As shown, this embodiment provides a stress-strain curve of a functionally gradient star-shaped anti-quadrichiral negative Poisson's ratio structure under a quasi-static compression load, when the structure changes with thickness and angle. It can be seen that the stress and elastic modulus of the functionally gradient star-shaped anti-quadrichiral negative Poisson's ratio structure (including thickness and angle changes) are higher than those of the traditional non-gradient star-shaped anti-quadrichiral negative Poisson's ratio structure, and the mechanical properties of the structure are significantly improved. In addition, by comparing the two star-shaped anti-quadrichiral negative Poisson's ratio structures with thickness and angle gradient changes, it can be seen that within the linear elastic range, the structure with angle changes has a higher elastic modulus than the structure with thickness changes; with the increase of strain, the structure with angle changes presents two platform stresses, and the second stage of platform stress is much higher than the platform stress of the structure with thickness changes; the structure with angle changes has a longer platform stress area and densification strain, and enters the densification stage later than the structure with thickness changes, and absorbs more energy.

[0039] according to Figure 8 As shown, this embodiment provides a functional gradient star-shaped anti-quadrichiral negative Poisson's ratio structure under a quasi-static compression load, and the specific energy absorption-strain curve when the structure changes with thickness and angle. It can be seen that the specific energy absorption of the three structures increases with the increase of strain, among which the specific energy absorption of the functional gradient star-shaped anti-quadrichiral negative Poisson's ratio structure (including thickness and angle changes) is higher than that of the traditional non-gradient star-shaped anti-quadrichiral negative Poisson's ratio structure, showing a better energy absorption effect. In addition, by comparing the two star-shaped anti-quadrichiral negative Poisson's ratio structures containing thickness and angle gradient changes, it can be seen that the specific energy absorption of the angle change structure is much higher than that of the thickness change structure. When the strain is equal to 0.6, the specific energy absorption of the angle change structure is about 1.5 times higher than that of the thickness change structure. The structural deformation of the present invention is more stable than the traditional star-shaped and anti-chiral negative Poisson's ratio structures, and has more excellent impact resistance and energy absorption capacity.

[0040] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It will also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0041] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A functionally gradient star-shaped anti-quadruple-chiral negative Poisson's ratio structure, characterized by: The structure is formed by multiple periodic unit cells arranged in a horizontal direction, and then changing the thickness (or angle) in a gradient manner in the vertical direction and connecting them in an array. Each of the periodic unit cells is a star-shaped anti-quadruciality structure, and its quarter structure is composed of an axisymmetric star-shaped structure and four ligaments extending outward from the tip of the star. The unit cell of the functional gradient star-shaped anti-quadruciality negative Poisson's ratio structure is composed of the above quarter structures mirrored in the horizontal and vertical directions.

2. The functionally gradient star-shaped anti-quadruple-chiral negative Poisson's ratio structure according to claim 1, characterized in that: First, a star-shaped anti-quadruple-chiral negative Poisson's ratio unit cell is arrayed horizontally along the horizontal center line of the structure to form a 1×n partial substructure. Secondly, the above 1×n partial substructure is arrayed vertically along the vertical center line of the structure, and the thickness (or angle) of 1×n star-shaped anti-quadruple-chiral negative Poisson's ratio unit cells is gradiently changed (increased or decreased) to form a functional gradient star-shaped anti-quadruple-chiral negative Poisson's ratio structure with m×n unit cells.

3. The quarter unit cell structure according to claim 1, characterized in that: The axisymmetric star-shaped structure is composed of the side length L1, the angle θ1 and the width t1. The geometric dimensions of the four extended ligaments are completely equal, with a length of L2 and a width of t2.

4. The functionally gradient star-shaped anti-quadruple chiral negative Poisson's ratio structure according to claim 1, characterized in that: The height of the structure is H, the width is W, and the out-of-plane thickness is H z Not shown in the floor plan.

5. The functionally gradient star-shaped anti-quadruple chiral negative Poisson's ratio structure according to claim 1, characterized in that: Prepared using 3D printing technology.

6. The functionally gradient star-shaped anti-quadruple-chiral negative Poisson's ratio structure according to claim 1, characterized in that: The manufacturing materials are metal, nylon, polylactic acid, thermoplastic polyurethane, high elastic material or carbon fiber composite material.

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