Negative Poisson's ratio cell with embedded symmetrical broken subcell structure

Abstract

The invention relates to the technical field of mechanical metamaterials, in particular to a negative Poisson's ratio cell element with an embedded symmetrical broken subcell structure, which comprises a concave hexagonal main body, the concave hexagonal main body comprises two horizontal cell walls and inclined cell walls arranged at two ends of the two horizontal cell walls, and the central points of the two inclined cell walls are bent towards one side close to the central points of the horizontal cell walls; the number of the bent wall rods is two, and the two bent wall rods are symmetrically arranged in the inwards-concave hexagonal body. The inherent contradiction that the stretching performance must be sacrificed when the rigidity of a traditional concave honeycomb structure is improved is successfully solved, and the negative Poisson's ratio effect and the energy absorption capacity of the structure can be further improved while the structural rigidity is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical metamaterials, and in particular to a negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure. Background Art

[0002] With the rapid development of additive manufacturing technologies (such as 3D printing), the design and implementation of various negative Poisson's ratio structures have become increasingly popular. These structures include chiral structures, anti-tetrahedral chiral structures, rotationally rigid structures, origami structures, and concave hexagonal structures. Since its initial proposal by Gibson et al. in 1982, the concave hexagonal honeycomb structure has become a hot topic of research due to its simple geometry and low-cost manufacturing process. Traditional concave hexagonal honeycomb structures exhibit excellent negative Poisson's ratio effects and exhibit unique mechanical properties under external forces, particularly enhanced energy absorption capacity and strong shear stiffness. These structures hold significant potential for applications in protective materials, structural cushioning, and other fields. However, these traditional concave hexagonal honeycomb structures have inherent drawbacks. To achieve this excellent negative Poisson's ratio effect, they typically require large internal voids, resulting in high porosity and, consequently, low in-plane stiffness. Furthermore, due to their high porosity, they are susceptible to buckling under heavy loads, which in turn reduces their load-bearing capacity and energy absorption performance. Therefore, although the concave hexagonal honeycomb structure has many advantages, its performance still has certain limitations in high-strength and high-stiffness engineering applications.

[0003] To address the shortcomings of traditional indented hexagonal honeycomb structures in terms of stiffness and energy absorption capacity and enhance their potential for engineering applications, researchers have proposed various improvement strategies. These strategies fall into two main categories: component addition and partial replacement. The former enhances structural performance by adding components such as horizontal or vertical wall bars, diamond-shaped wall bars, and biomimetic lotus leaf vein wall bars to the traditional indented hexagonal honeycomb structure. The latter involves partial replacement, replacing the inclined concave cell walls of the indented hexagonal cells with curved walls or replacing horizontal cell walls with elliptical walls. While these improvements improve the overall stiffness of the honeycomb structure by enhancing the bending resistance of the inclined wall bars, they often come at the expense of weakening the negative Poisson's ratio effect. This weakening of the negative Poisson's ratio limits the structure's shrinkage and deformation capacity, thereby reducing its shear resistance. Maintaining or further enhancing the negative Poisson's ratio effect while improving stiffness and energy absorption has become a hot topic of research. Effectively resolving this contradiction would greatly promote the widespread application of indented hexagonal honeycomb structures in high-performance engineering and open up new development opportunities. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies in the prior art and proposes a negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure, aiming to solve at least one of the problems raised in the above-mentioned background technology.

[0005] In a first aspect, the present invention provides a negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure, comprising: a concave hexagonal body, comprising two horizontal cell walls and inclined cell walls provided at both ends of the two horizontal cell walls, wherein the center points of the two inclined cell walls are bent toward a side close to the center point of the horizontal cell wall;

[0006] There are two bent wall rods, and the two bent wall rods are symmetrically arranged inside the concave hexagonal body.

[0007] In some embodiments, each of the bent wall rods has two bending points, the upper bending points of the two bent wall rods are connected to each other through a horizontal wall rod, the lower bending point of the bent wall rod is connected to the inclined cell wall through the horizontal wall rod, and the two ends of the bent wall rod are respectively connected to the two horizontal cell walls.

[0008] In some embodiments, a uniaxial symmetry-breaking sub-cell structure and two biaxial symmetry-breaking sub-cell structures are formed inside the concave hexagonal body.

[0009] In some embodiments, the concave hexagonal body has 10 independent parameters set within it;

[0010] They are: a, b, c, d, θ0, θ1, h0, l0, t0, t1;

[0011] Wherein, a is the distance between the two connection points of the bending wall rod and the horizontal cell wall at the bottom, b is the straight-line distance from the lower bending point to the horizontal cell wall at the bottom, θ1 represents the angle between the bending wall rod and the horizontal cell wall, t1 is the thickness of the internal bending wall rod and the horizontal wall rod, t0 represents the thickness of the concave hexagonal body, c represents the distance between the upper symmetrical bending points; l0 represents the width of the concave hexagonal body, h0 represents the height of the concave hexagonal body, θ0 represents the angle between the horizontal cell wall and the inclined cell wall, and d is the distance between the horizontal cell wall and the upper bending point of the bending wall rod.

[0012] In some embodiments, wherein 0°<θ1≤90°;

[0013] a, b and θ1 satisfy: b

[0014] ​In a second aspect, a negative Poisson's ratio honeycomb structure according to an embodiment of the present application is provided, wherein the negative Poisson's ratio honeycomb structure is composed of a plurality of negative Poisson's ratio cells with embedded symmetry-breaking sub-cell structures that are staggered and connected.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the negative Poisson's ratio honeycomb structure with embedded symmetry-breaking sub-cell structure overcomes the unstable buckling problem of the traditional concave honeycomb structure, and while enhancing the rigidity of the honeycomb structure, further enhances the negative Poisson's ratio effect and energy absorption performance of the honeycomb structure. The honeycomb structure can also show stable compression deformation and excellent negative Poisson's ratio effect within a large deformation range, with large specific energy absorption and high energy absorption efficiency. By setting different geometric parameters, a variety of adjustable stress-strain curves and Poisson's ratio-strain curves can be achieved. In addition, the honeycomb structure of the present invention has the following significant advantages: (1) simple structure, convenient and quick in structural manufacturing; (2) customized property design can be achieved through reasonable parametric design; (3) spatially expandable to a three-dimensional structure, with greater design and application potential.

[0016] The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure.

[0017] Other features and aspects of the present disclosure will become more apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic diagram of a negative Poisson's ratio cell structure of an embedded symmetry-breaking subcell structure provided by an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of a negative Poisson's ratio cell structure of an embedded symmetry-breaking subcell structure provided by an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of a negative Poisson's ratio cell structure of an embedded symmetry-breaking subcell structure provided by an embodiment of the present invention;

[0022] Figure 4 A schematic diagram of a negative Poisson's ratio cell structure of an embedded symmetry-breaking subcell structure provided by an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of a negative Poisson's ratio cell honeycomb structure with an embedded symmetry-breaking subcell structure provided by an embodiment of the present invention;

[0024] Figure 6 A schematic diagram comparing deformation modes of a negative Poisson's ratio honeycomb structure of the present invention and a traditional negative Poisson's ratio structure under quasi-static compression provided by an embodiment of the present invention;

[0025] Figure 7 Poisson's ratio-strain curves of the negative Poisson's ratio honeycomb structure of the present invention and a traditional negative Poisson's ratio structure under quasi-static compression provided by an embodiment of the present invention;

[0026] Figure 8 A stress-strain curve diagram of a negative Poisson's ratio honeycomb structure of the present invention and a traditional negative Poisson's ratio structure under quasi-static compression provided by an embodiment of the present invention;

[0027] Figure 9 Specific energy absorption-strain curves of the negative Poisson's ratio honeycomb structure of the present invention and the traditional negative Poisson's ratio structure under quasi-static compression provided in an embodiment of the present invention.

[0028] Among them: 1. Concave hexagonal body; 2. Horizontal cell wall; 3. Inclined cell wall; 4. Bent wall rods; 5. Horizontal wall rods; 6. Uniaxial symmetry broken daughter cell structure; 7. Biaxial symmetry broken daughter cell structure. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0031] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0032] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0033] See Figure 1-5 As shown, the first embodiment:

[0034] A negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure according to an embodiment of the present application includes:

[0035] The concave hexagonal body 1 includes two horizontal cell walls 2 and inclined cell walls 3 provided at both ends of the two horizontal cell walls 2, wherein the center points of the two inclined cell walls 3 are bent toward a side close to the center point of the horizontal cell wall 2;

[0036] There are two bent wall rods 4 , and the two bent wall rods 4 are symmetrically arranged inside the concave hexagonal main body 1 .

[0037] In some specific embodiments, each of the bending wall rods 4 has two bending points, the upper bending points of the two bending wall rods 4 are connected to each other through a horizontal wall rod 5, the lower bending point of the bending wall rod 4 is connected to the inclined cell wall 3 through the horizontal wall rod 5, and the two ends of the bending wall rod 4 are respectively connected to the two horizontal cell walls 2.

[0038] In some specific embodiments, a uniaxial symmetry-breaking sub-cell structure 6 and two biaxial symmetry-breaking sub-cell structures 7 are formed inside the concave hexagonal body 1 .

[0039] In some specific embodiments, 10 independent parameters are set in the concave hexagonal body 1;

[0040] They are: a, b, c, d, θ0, θ1, h0, l0, t0, t1;

[0041] Wherein, a is the distance between the two connection points of the bending wall rod 4 and the horizontal cell wall 2 at the bottom, b is the straight-line distance from the lower bending point to the horizontal cell wall 2 at the bottom, θ1 represents the angle between the bending wall rod 4 and the horizontal cell wall 2, t1 is the thickness of the internal bending wall rod 4 and the horizontal wall rod 5, t0 represents the thickness of the concave hexagonal body 1, c represents the distance between the upper symmetrical bending points; l0 represents the width of the concave hexagonal body 1, h0 represents the height of the concave hexagonal body 1, θ0 represents the angle between the horizontal cell wall 2 and the inclined cell wall 3, and d is the distance between the horizontal cell wall 2 and the upper bending point of the bending wall rod 4.

[0042] In some specific embodiments, wherein 0°<θ1≤90°;

[0043] a, b and θ1 satisfy: b

[0044] It should be understood that, in addition, a may be equal to or not equal to c; b may be equal to or not equal to d; and t0 may be equal to or not equal to t1.

[0045] In this embodiment, a dimensionless parameter β = θ1 / θ0 is defined to further illustrate the diversity of the configurations of the present invention. Specifically, when the outer cell wall angle θ0 = 60°, the bending wall rod angle θ1 is set to 45°, 52.5°, 60°, 67.5°, and 75°, respectively.

[0046] Correspondingly, the values of the dimensionless parameter β are 0.75, 0.875, 1, 1.125 and 1.25.

[0047] Second embodiment:

[0048] According to an embodiment of the present application, a negative Poisson's ratio honeycomb structure is provided, wherein the negative Poisson's ratio honeycomb structure is composed of a plurality of negative Poisson's ratio cells with embedded symmetry-breaking sub-cell structures that are staggered and connected.

[0049] It should be understood that this structure is formed by staggering the negative Poisson's ratio cells of the first embodiment in a horizontal and vertical arrangement, with seven columns arranged in the horizontal direction and four rows in the vertical direction. During the assembly process, the cells are combined by replicating and moving them to ensure that each cell has the same structure and size.

[0050] Specifically, vertically, the upper and lower horizontal cell walls overlap (i.e., they share a common horizontal cell wall); horizontally, adjacent cells are staggered by a vertical distance of h0 / 2, while their opposing inclined cell walls overlap (i.e., they share a common inclined cell wall). The overall size of the honeycomb structure can be adjusted by adjusting the length and height of the cells, as well as the number of periodic arrangements, to meet the needs of different engineering applications. ​

[0051] Different β values correspond to the mechanical response of negative Poisson's ratio honeycomb structure SARH under quasi-static compression:

[0052] Table 1 of this example provides the configurations of the SARH and traditional negative Poisson's ratio cells corresponding to different β values in the present invention. To illustrate the advantages of the proposed structure in terms of deformation stability and negative Poisson's ratio effect, the deformation modes and Poisson's ratios of the SARH corresponding to different β values under quasi-static compression were studied, and the results were compared with those of the traditional concave hexagonal structure.

[0053] Table 1

[0054]

[0055] like Figure 6 Figure 2 shows a comparison of the crush deformation patterns of the negative Poisson's ratio honeycomb structure SARH-β and the conventional honeycomb structure ARH under quasi-static compression conditions for three different β values. It can be observed that the ARH first exhibits typical "X"-shaped diagonal plastic deformation during stable compression, which is one of the main reasons for its excellent negative Poisson's ratio effect. However, as the strain value increases, the deformation pattern of the ARH gradually transitions from asymmetric destruction to recovery of "I"-shaped symmetric deformation. In contrast, at a strain of 0.2, the SARH-β not only exhibits similar "X"-shaped diagonal plastic deformation, but also forms a double inverted "V"-shaped deformation band. This characteristic enables the SARH-β to exhibit stronger inward contraction and more stable compression deformation during compression, resulting in a more significant negative Poisson's ratio effect than the ARH.

[0056] Figure 7 The Poisson's ratio-nominal strain curves of SARH-β and ARH corresponding to different β values under quasi-static compression conditions are shown. It can be found that when the strain value is less than 0.1, due to the high in-plane stiffness of SARH-β, its deformation capacity is weaker than that of ARH, resulting in a negative Poisson's ratio effect that is not as good as that of ARH. However, it is worth noting that when 0.1<ε y Within the strain range of <0.5, the absolute values of the Poisson's ratios of all SARH-β structures were significantly higher than those of the ARH. Quantitative analysis revealed that the average Poisson's ratio (APR) of each SARH-β structure at the densification strain (-0.970) was 26% lower than that of the ARH (-0.771). This indicates that the negative Poisson's ratio effect of the SARH is significantly superior to that of the ARH. This phenomenon is primarily attributed to the more uniform deformation pattern of the SARH structure during quasi-static compression, as well as the coordinated deformation between its internal symmetry-breaking sub-cells and the external concave cells, which results in the SARH's tendency to deform inward during the plateau stress phase.

[0057] Effect of different β values on the platform stress of negative Poisson's ratio honeycomb structure under quasi-static compression:

[0058] like Figure 8 As shown in the figure, the stress-nominal strain curves of SARH-β and ARH corresponding to different β values are compared. It can be clearly found that the platform stress of SARH-β is significantly higher than that of traditional ARH, about 6.5 times, and it shows a double-platform stress stage characteristic (the dots in the figure represent the transition points between the first platform stress stage and the second platform stress stage, and the triangles represent the end of the second platform stress stage and the beginning of the densification stage). At the same time, as the β value increases, the initial peak stress of SARH-β also increases, which indicates that its in-plane stiffness is positively correlated with the β value. However, combined with Figure 7 It can also be seen that its negative Poisson's ratio effect also weakens slightly with the increase of β value.

[0059] Figure 9 The specific energy absorption-nominal strain curves of SARH-β and ARH for different β values are shown. Obviously, due to the increase in the number of wall rods participating in plastic deformation in the SARH structure, the specific energy absorption of SARH-β is much higher than that of the traditional ARH.

[0060] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure, characterized in that: include: The concave hexagonal body includes two horizontal cell walls and inclined cell walls provided at both ends of the two horizontal cell walls, wherein the center points of the two inclined cell walls are bent toward a side close to the center point of the horizontal cell wall; There are two bent wall rods, and the two bent wall rods are symmetrically arranged inside the concave hexagonal body.

2. The negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure according to claim 1, characterized in that: Each of the bent wall rods has two bending points, the upper bending points of the two bent wall rods are connected to each other through a horizontal wall rod, the lower bending point of the bent wall rod is connected to the inclined cell wall through the horizontal wall rod, and the two ends of the bent wall rod are respectively connected to the two horizontal cell walls.

3. The negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure according to claim 2, characterized in that: A uniaxial symmetry-breaking sub-cell structure and two biaxial symmetry-breaking sub-cell structures are formed inside the concave hexagonal body.

4. The negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure according to claim 3, characterized in that: There are 10 independent parameters set in the concave hexagonal body; They are: a, b, c, d, θ0, θ1, h0, l0, t0, t1; Wherein, a is the distance between the two connection points of the bending wall rod and the horizontal cell wall at the bottom, b is the straight-line distance from the lower bending point to the horizontal cell wall at the bottom, θ1 represents the angle between the bending wall rod and the horizontal cell wall, t1 is the thickness of the internal bending wall rod and the horizontal wall rod, t0 represents the thickness of the concave hexagonal body, c represents the distance between the upper symmetrical bending points; l0 represents the width of the concave hexagonal body, h0 represents the height of the concave hexagonal body, θ0 represents the angle between the horizontal cell wall and the inclined cell wall, and d is the distance between the horizontal cell wall and the upper bending point of the bending wall rod.

5. The negative Poisson's ratio cell with an embedded symmetry-breaking subcell structure according to claim 4, characterized in that: Where 0°<θ1≤90°; a, b and θ1 satisfy: b is applied to a negative Poisson's ratio cell of an embedded symmetry-breaking subcell structure as described in any one of claims 1 to 5, wherein the negative Poisson's ratio honeycomb structure is composed of a plurality of negative Poisson's ratio cells of an embedded symmetry-breaking subcell structure that are staggered and bonded together.

6. A negative Poisson's ratio honeycomb structure, characterized in that: ​

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