Multi-level combined star arrow negative Poisson's ratio structure

Abstract

The invention discloses a multi-level combined star arrow negative Poisson's ratio structure. The structure is formed by combining a plurality of periodic unit cells in an array mode in the horizontal direction and the vertical direction, and each periodic unit cell is composed of a centrosymmetric star-shaped structure, 4n arrowhead sub-cells located at the concave position of the centrosymmetric line of the star-shaped structure and four overhanging ligaments of the arrowhead sub-cells. Geometric parameters of the center star-shaped structure include the side length L0, the included angle theta 0 and the width t0. The arrowhead subcell is formed by connecting 4n arrowheads and four overhanging ligaments along the center line. The ith arrow sub-cell structure consists of a long bevel edge Li, a tip included angle 2 alpha i, a short bevel edge included angle beta i and a width ti, and the number i of the arrow sub-cells is equal to 1,..., n. And the ligament at the concave part of the arrow at the tail end is S in length and tn in width. The multi-level combined star arrow negative Poisson's ratio structure shows good negative Poisson's ratio characteristics and energy absorption capability, and multi-level parameter changes of the unit cells and the subcells can influence the mechanical property of the whole structure.

Description

A multi-level combined star-shaped arrow negative Poisson's ratio structure Technical Field

[0001] This invention relates to the fields of multilevel structures and metamaterials / metastructures, and particularly to a multilevel structure with a negative Poisson's ratio effect. Background Technology

[0002] The concept of "metamaterials," proposed in 21st-century physics, defines a category of materials that achieve extraordinary physical properties unattainable by natural materials through artificially designed composite structures. Their applications are wide-ranging, encompassing acoustics, optics, thermodynamics, mechanics, and electromagnetism. In mechanics, negative Poisson's ratio materials / structures (i.e., tensile materials / structures) are typical mechanical metamaterials, exhibiting behavior significantly different from the positive Poisson's ratio materials / structures commonly found in nature. The characteristic of this structure—lateral expansion during stretching and lateral contraction during compression—is powerful evidence of how metamaterials endow materials with novel properties through structural design.

[0003] Most materials in nature have a positive Poisson's ratio, meaning they undergo lateral contraction (or vice versa) under axial tensile loads. Conversely, metamaterials / metastructures with negative Poisson's ratios exhibit unconventional mechanical responses of axial tension-lateral expansion and axial compression-lateral contraction. These materials / structures have significant advantages in shear resistance (resistance to interlaminar slip), fracture toughness (inhibition of crack propagation), and energy absorption efficiency (impact dissipation), ultimately resulting in improved overall performance such as lightweighting, high damping, sound absorption and energy absorption, vibration reduction, and thermal insulation.

[0004] Multilevel materials / structures refer to meticulously designed structural hierarchies across multiple scales (from nanoscale to macroscale), where the structural units at each level work synergistically to achieve comprehensive performance far exceeding that of materials at a single scale. The core lies in achieving breakthrough improvements in strength, toughness, and functionality through cross-scale structural coupling. These materials exhibit ultra-lightweight properties, excellent specific stiffness and strength, efficient energy absorption (impact dissipation), superior acoustic attenuation, and thermal insulation properties, making them highly valuable for applications in biomedicine, defense engineering, aerospace, and civil engineering.

[0005] Negative Poisson's ratio materials / structures have shown great potential in the biomedical field. For example, negative Poisson's ratio functional medical bandages can intelligently control the amount of drug released based on the severity of the wound. Due to their unique unidirectional curvature, negative Poisson's ratio medical bandages provide better wound conformity, reduce tissue pressure, and effectively relieve pressure in swollen areas.

[0006] The superior energy absorption properties of negative Poisson's ratio materials / structures also have broad prospects and applications in aerospace, shipbuilding, and other fields. Examples include spacecraft protective honeycomb shields or impact-resistant structures for energy absorption, deformable aircraft wing sandwich core materials, smart deformable antennas or solar panel support structures, and negative Poisson's ratio honeycomb core layer ship side protection structures and vibration isolation bases.

[0007] Depending on the deformation mechanism, negative Poisson's ratio materials / structures can be classified into two-dimensional or three-dimensional honeycomb structures such as concave, chiral, rotational rigid bodies, and arrowhead structures. The cell walls of these structures are all solid continuous bodies, which hinders the structures from achieving higher lightweighting, specific strength, energy absorption efficiency, shear toughness, and fracture toughness. Therefore, this invention proposes a star-shaped arrowhead negative Poisson's ratio structure with multi-level combinations. Variations in the cell size at different levels can affect the overall mechanical properties and energy absorption efficiency of the structure. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to propose a multi-level combined star-shaped arrow negative Poisson's ratio structure. This structure is composed of multi-level arrow sub-cell structures and exhibits a good negative Poisson's ratio effect. Changes in cell size at different levels can affect the overall mechanical properties and energy absorption efficiency of the structure.

[0009] To achieve the objectives of this invention, the invention is implemented through the following technical solutions:

[0010] A further improvement is that the multi-level combined star-shaped arrow negative Poisson's ratio structure is made of materials such as shape memory alloy, thermoplastic polyurethane (TPU), and alloy steel, which can be prepared by 3D printing technology.

[0011] A further improvement is that each of the periodic unit cells comprises a centrally symmetric star-shaped structure and 4n arrow-shaped daughter cells located at the four concave points (top, bottom, left, and right) along the central symmetry line of the star, along with their four outward-extending ligaments. The periodic unit cell and the arrow-shaped daughter cells have a parent-child relationship. The multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure is arrayed in the horizontal and vertical directions along the central lines of the arrow-shaped daughter cells and their four outward-extending ligaments, forming m×m multi-level combined star-shaped arrow negative Poisson's ratio structures.

[0012] Further improvements are made in that: the centrally symmetric star structure is composed of equal side length L0, equal included angle θ0 and equal width t0. The arrow sub-cells and four outward ligaments located at the four concave points on the top, bottom, left and right of the star structure are combined as follows: (1) The arrow sub-cell is composed of 4n arrows and four outward ligaments connected along the central line. The number of arrows, the length of the arrows, the angle of the arrows and the width of the arrows all affect the geometric dimensions of the structure. The arrow sub-cells, the outward ligaments and the centrally symmetric star structure together form a single-cell structure. (2) Along the horizontal or vertical direction, the i-th arrow sub-cell structure is composed of the long hypotenuse L i , the included angle of the tip is 2α i The angle β between the shorter hypotenuse and the center line i and width t i Composition, the number of arrow subcells is i = 1, ..., n. (3) The length of the horizontal (or vertical) ligament at the concave part of the nth arrow (i.e. the last arrow) is S, and its geometric relationship satisfies S > x. A x A This represents the horizontal coordinate value at point A, the tail end of the last arrow. The ligament width is the same as the width of the nth arrow cell, both being t. n (4) Due to symmetry, the length and width of the multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure are both H.

[0013] Further improvements are made in the ABAQUS finite element software preprocessing module, where material properties, analysis steps, contact properties, boundary conditions, and load conditions are first set for the structure, and the finite element mesh of the structure is generated, thereby performing quasi-static compression simulation calculations on the structure.

[0014] Further improvements are made by using the finite element ABAQUS simulation software to perform quasi-static compression simulation on three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures, and obtaining the deformation process, stress-strain curves, Poisson's ratio-strain curves, and specific energy absorption-strain curves of the three sets of structures under in-plane quasi-static compressive loads.

[0015] The beneficial effects of this invention are as follows: Changes in the macroscopic and microscopic geometric parameters of the multi-level combined star-shaped arrow negative Poisson's ratio structure have a significant impact on the overall mechanical properties and energy absorption of the structure. In the biomedical field, the multi-level combined star-shaped arrow negative Poisson's ratio structure of this invention possesses multi-scale structural characteristics and the ability to vary between zero and negative Poisson's ratios. This makes it suitable for developing multifunctional medical drug bandages with good wound adhesion and automatic release based on different drug sizes. Furthermore, the multi-level combined star-shaped arrow negative Poisson's ratio structure of this invention exhibits good energy absorption efficiency and can be applied to vibration damping and energy absorption devices in aerospace, machinery, and shipbuilding. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the multi-level combined star-shaped arrow unit cell structure of Embodiment 1 of the present invention (other parameters remain unchanged, only the number of arrows changes).

[0017] Figure 2 is a schematic diagram of the multi-level combined star-shaped arrow structure of Embodiment 1 of the present invention (other parameters remain unchanged, only the number of arrows changes).

[0018] Figure 3 shows the deformation process of the multi-level combined star-shaped arrow negative Poisson's ratio structure of Embodiment 2 of the present invention under quasi-static compressive load.

[0019] Figure 4 shows the stress-strain curve of the multi-level combined star-shaped arrow negative Poisson's ratio structure of Embodiment 2 of the present invention under quasi-static compressive load.

[0020] Figure 5 shows the Poisson's ratio-strain curve of the multi-level combined star-shaped arrow negative Poisson's ratio structure of Embodiment 2 of the present invention under quasi-static compressive load.

[0021] Figure 6 shows the specific energy absorption-strain curve of the multi-level combined star-shaped arrow negative Poisson's ratio structure of Embodiment 2 of the present invention under quasi-static compressive load. Detailed Implementation

[0022] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0023] Example 1

[0024] As shown in Figure 1, this embodiment provides a multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure. Each of the periodic unit cells comprises a centrally symmetric star-shaped structure and 4n arrow daughter cells located at the four concave points (top, bottom, left, and right) along the central symmetry line of the star, along with four outward-extending ligaments. The periodic unit cell and the arrow daughter cells have a parent-child relationship.

[0025] As shown in Figure 1, this embodiment provides a multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure. The centrally symmetric star structure is composed of equal side length L0, equal included angle θ0, and equal width t0. The arrow sub-cells and four outward ligament structures located at the four concave points on the top, bottom, left, and right of the star structure are combined as follows: (1) The arrow sub-cell is composed of 4n arrows and four outward ligaments connected along the center line. The number of arrows, arrow length, arrow angle, and arrow width all affect the geometric dimensions of the structure. The arrow sub-cells, outward ligaments, and centrally symmetric star structure together form a unit cell structure. (2) Along the horizontal or vertical direction, the i-th arrow sub-cell structure is composed of the long hypotenuse L i , the included angle of the tip is 2α i The angle β between the shorter hypotenuse and the center line i and width t iComposition, the number of arrow subcells is i = 1, ..., n. (3) The length of the horizontal (or vertical) ligament at the concave part of the nth arrow (i.e. the last arrow) is S, and its geometric relationship satisfies S > x. A x A This represents the horizontal coordinate value at point A, the tail end of the last arrow. The ligament width is the same as the width of the nth arrow cell, both being t. n (4) Due to symmetry, the length and width of the multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure are both H.

[0026] As shown in Figure 2, this embodiment provides a multi-level combined star-shaped arrow negative Poisson's ratio structure. The multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure is arrayed in the horizontal and vertical directions along the center lines of the arrow sub-cells and their four outward-extending ligaments, forming 4×4 multi-level combined star-shaped arrow negative Poisson's ratio structures.

[0027] The materials used to fabricate the multi-level combined star-shaped unit cells and daughter cells are 3D printed shape memory alloy materials, thermoplastic polyurethane (TPU) materials, and alloy steel, etc.

[0028] Example 2

[0029] In the preprocessing module of the ABAQUS finite element software, the material properties of the structure are first set, the analysis step and contact properties are set, the boundary conditions and load conditions are set, and the finite element mesh of the structure is generated, so as to perform quasi-static compression simulation calculations on the structure.

[0030] In the ABAQUS finite element simulation software, material parameters were set, and aluminum alloy was selected as the research object. The material elastic modulus E = 69 GPa, the material Poisson's ratio μ = 0.33, and the yield stress σ = 76 MPa.

[0031] As shown in Figure 3, this embodiment provides a deformation contour map of a multi-level combined star-shaped arrowhead structure with negative Poisson's ratio under quasi-static compressive load. The figure shows that at ε = 0.2, the arrowhead sub-cells and ligaments at the upper and lower edges of the three sets of multi-level star-shaped arrowhead structures contract vertically, while the structure remains essentially unchanged horizontally, exhibiting zero Poisson's ratio performance initially. At ε = 0.4, the three sets of multi-level structures contract both vertically and horizontally, contacting the central star-shaped structure, exhibiting negative Poisson's ratio performance. With increasing strain, the three sets of multi-level arrowhead sub-cells and ligaments further contact the central star-shaped structure. When the strain ε = 0.6, the structure exhibits significant plasticity and a stress plateau. When the strain reaches ε = 0.8, the three sets of structures further contract and contact each other, showing a more pronounced compaction.

[0032] As shown in Figure 4, this example provides the stress-strain curves of three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures under quasi-static compressive loading. The figure shows that the stress-strain response of the multi-level combined star-shaped arrow negative Poisson's ratio structures can be divided into three stages. First, within the linear elastic range, the stress of all three multi-level structures increases linearly with strain until reaching peak stress, with the first-level structure exhibiting the highest peak stress. Subsequently, the three structures enter the stress plateau plastic region. At strains of approximately 0.3, 0.4, and 0.55, the stresses of the first, second, and third-level structures rise rapidly, reaching the densification region. Figure 4 demonstrates that the three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures exhibit a relatively long stress plateau period, effectively increasing the structure's energy absorption.

[0033] As shown in Figure 5, this embodiment provides the Poisson's ratio-strain curves of three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures under quasi-static compressive loading. The figure shows that the three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures exhibit a good zero Poisson's ratio effect in the linear elastic stage. From the plateau period onwards, the Poisson's ratio gradually increases with increasing strain, reaching a peak negative Poisson's ratio before its absolute value gradually decreases to zero. Figure 5 also shows that the absolute value of the negative Poisson's ratio reaches its maximum in a single-level structure.

[0034] As shown in Figure 6, this embodiment provides the specific energy absorption-strain curves of three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures under quasi-static compressive load. As can be seen from the figure, the specific energy absorption of all three sets of multi-level combined star-shaped arrow negative Poisson's ratio structures increases with increasing strain. The specific energy absorption of the single-level structure is greater than that of the two- and three-level structures, and all three structures exhibit good energy absorption performance.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-level combined star-shaped arrow negative Poisson's ratio structure, characterized in that: The structure is composed of multiple periodic unit cells arranged in a horizontal and vertical array. Each periodic unit cell includes a centrally symmetric star-shaped structure and 4n arrow-shaped daughter cells located at the four concave points on the central symmetry line of the star, along with its four outward-extending ligaments. The periodic unit cell and the arrow-shaped daughter cells have a parent-child relationship.

2. The multi-level combined star-shaped arrowhead negative Poisson's ratio unit cell structure according to claim 1, characterized in that: The centrally symmetric star structure is composed of equal side length L0, equal included angle θ0 and equal width t0. The arrow sub-cells and four outward ligaments located at the four concave points on the top, bottom, left and right of the star structure are combined as follows: (1) The arrow sub-cell is composed of 4n arrows and four outward ligaments connected along the central line. The number of arrows, arrow length, arrow angle and arrow width all affect the geometric dimensions of the structure. The arrow sub-cells, outward ligaments and the centrally symmetric star structure together form a single cell structure; (2) Along the horizontal or vertical direction, the i-th arrow sub-cell structure is composed of the long hypotenuse L i , the included angle of the tip is 2α i The angle β between the shorter hypotenuse and the center line i and width t i Composition, the number of arrow subcells is i = 1, ..., n; (3) the length of the horizontal (or vertical) ligament at the concave part of the nth arrow (i.e. the last arrow) is S, and its geometric relationship satisfies S > x A x A This represents the horizontal coordinate value at point A, the tail end of the last arrow. The ligament width is the same as the width of the nth arrow cell, both being t. n (4) Due to symmetry, the length and width of the multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure are both H.

3. The multi-level combined star-shaped arrow negative Poisson's ratio structure according to claim 1, characterized in that: The multi-level combined star-shaped arrow negative Poisson's ratio unit cell structure is arrayed along the center lines of the arrow sub-cells and their four outward ligaments in both horizontal and vertical directions to form m×m multi-level combined star-shaped arrow negative Poisson's ratio structures.

4. The multi-level combined star-shaped arrow negative Poisson's ratio structure according to claim 1, characterized in that: It was prepared using 3D printing technology.

5. The multi-level combined star-shaped arrow negative Poisson's ratio structure according to claim 1, characterized in that: The materials used to manufacture the unit cell and daughter cells are one of the following: shape memory alloy, thermoplastic polyurethane (TPU), and alloy steel.

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